Positive electrode active material and non-aqueous electrolyte secondary battery
By designing lithium transition metal composite oxide cathode active materials with different particle sizes and compositions, the problem of reduced thermal stability in existing secondary batteries has been solved, achieving a balance between high capacity and thermal stability.
Patent Information
- Application Number
- CN202510641117.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-05-21
- Filing Date
- 2025-05-19
- Publication Date
- 2025-11-21
AI Technical Summary
In the prior art, although adjusting the disorder of Ni in Ni-containing lithium composite oxides can improve the output characteristics and durability of secondary batteries, thermal stability often decreases.
A lithium transition metal composite oxide containing two different average particle sizes is used as the positive electrode active material. The first active material is a secondary particle formed by the aggregation of more than 50 primary particles, and the second active material is a secondary particle formed by the aggregation of a single particle or 2-10 primary particles. By controlling the content and disorder of Ni and Ti, the particle size distribution and mass ratio are optimized to form a high-capacity and thermally stable positive electrode active material.
High capacity and good thermal stability of rechargeable batteries have been achieved. By rationally designing the particle size and composition of active materials, the overall performance of the battery has been improved.
Smart Images
Figure BDA0005408239790000121
Abstract
Description
Technical Field
[0001] This invention relates to positive electrode active materials and non-aqueous electrolyte secondary batteries. Background Technology
[0002] To achieve high battery capacity, it is known to use two Ni-containing lithium composite oxides with high Ni content and different average particle sizes as positive electrode active materials. For example, International Patent Publication No. 2020 / 003642 discloses adjusting the disorder of Ni in Ni-containing lithium composite oxides to obtain good output characteristics and durability. Summary of the Invention
[0003] However, even when adjusting the disorder of Ni in Ni-containing lithium composite oxides, the thermal stability of secondary batteries can sometimes decrease.
[0004] The purpose of this disclosure is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can achieve high capacity and excellent thermal stability, and a non-aqueous electrolyte secondary battery using the same.
[0005] [1] A positive electrode active material comprising a first active material and a second active material, wherein the second active material has a smaller average particle size (D50) than the first active material.
[0006] The aforementioned first active substance is a secondary particle formed by the aggregation of more than 50 primary particles.
[0007] The aforementioned second active substance is at least one of a single particle and a secondary particle formed by the aggregation of 2 to 10 primary particles.
[0008] The first active material mentioned above is a lithium transition metal composite oxide containing more than 75 mol% Ni and 0.5 to 2.8 mol% Ti relative to the total molar amount of metal elements other than Li.
[0009] The second active material mentioned above is a lithium transition metal composite oxide containing more than 75 mol% Ni relative to the total molar percentage of metal elements other than Li.
[0010] The Ti content of the second active substance mentioned above is less than 0.1 mol% relative to the total molar percentage of metal elements other than Li.
[0011] The disorder degree of Ni in the first active material mentioned above is 2.1%–2.6%.
[0012] The disorder of Ni in the second active material mentioned above is less than 2.0%.
[0013] [2] According to the positive electrode active material described in [1], the content of Ti in the first active material is 1 to 2.5 mol relative to the total number of moles of metal elements other than Li.
[0014] [3] According to the positive electrode active material described in [1] or [2], wherein the mass ratio of the first active material to the second active material is, i.e., the first active material: the second active material = 7:3 to 5:5.
[0015] [4] The positive electrode active material according to any one of [1] to [3], wherein the average particle size (D50) of the first active material is 12 to 20 μm.
[0016] [5] The positive electrode active material according to any one of [1] to [4], wherein the average particle size (D50) of the second active material is 2 to 6 μm.
[0017] [6] The positive electrode active material according to any one of [1] to [5], wherein the particle size distribution ({average particle size (D90) - average particle size (D10)} / average particle size (D50)) of the first active material is 0.2 to 0.8.
[0018] [7] The positive electrode active material according to any one of [1] to [6], wherein the particle size distribution ({average particle size (D90) - average particle size (D10)} / average particle size (D50)) of the second active material is 0.7 to 1.5.
[0019] [8] The positive electrode active material according to any one of [1] to [7], wherein the content of Co in the first active material relative to the total number of moles of metal elements other than Li is less than the content of Co in the second active material relative to the total number of moles of metal elements other than Li.
[0020] [9] A non-aqueous electrolyte secondary battery, having a positive electrode plate,
[0021] The above-mentioned positive electrode plate has an active material layer comprising any one of the positive electrode active materials described in [1] to [8].
[0022] The above and other objects, features, aspects and advantages of the present invention will become clear from the following detailed description of the present invention. Detailed Implementation
[0023] Unless otherwise specified, the numerical ranges "x~y" in this specification include both upper and lower limits. That is, "x~y" represents a numerical range "above x and below y". Any value selected from this range can be used as a new upper or lower limit. For example, a new numerical range can be set by arbitrarily combining values within the range with values recorded in other parts of this specification or tables.
[0024] (Positive electrode active material)
[0025] The positive electrode active material of this embodiment (hereinafter also referred to as "this positive electrode active material") is used in the positive electrode plate of non-aqueous electrolyte secondary batteries such as lithium-ion batteries (hereinafter also referred to as "secondary batteries").
[0026] This positive electrode active material comprises a first active material and a second active material. The second active material has a smaller average particle size (D50) than the first active material. The first active material is a secondary particle (hereinafter also referred to as "first secondary particle") formed by the aggregation of 50 or more primary particles. The second active material is at least one of a single particle and a secondary particle (hereinafter also referred to as "second secondary particle") formed by the aggregation of 2 to 10 primary particles.
[0027] The first active material is a lithium transition metal composite oxide containing at least 75 mol% Ni and 0.5–2.8 mol% Ti relative to the total molar percentage of metal elements other than Li. The second active material is a lithium transition metal composite oxide containing at least 75 mol% Ni relative to the total molar percentage of metal elements other than Li. The Ti content of the second active material is less than 0.1 mol% relative to the total molar percentage of metal elements other than Li. The disorder degree of Ni in the first active material is 2.1–2.6%. The disorder degree of Ni in the second active material is less than 2.0%.
[0028] By using a positive electrode active material containing a first active material and a second active material with different average particle size (D50) and particle aggregation morphology within the aforementioned range of Ni content, it is easy to achieve high capacity in secondary batteries, but sometimes the thermal stability of the secondary battery decreases. In this positive electrode active material, since the first active material contains Ti in the aforementioned amount and the Ni disorder is within the aforementioned range, the thermal stability of the secondary battery can be improved. On the other hand, if the thermal stability of the secondary battery is improved using the aforementioned first active material, the capacity of the secondary battery sometimes decreases. However, in this positive electrode active material, since the second active material contains no Ti or only a trace amount of Ti, and the Ni disorder is within the aforementioned range, high capacity in the secondary battery can also be achieved. Based on this positive electrode active material, a secondary battery that achieves both high capacity and good thermal stability can be obtained.
[0029] The first active substance is a primary or secondary particle formed by the aggregation of more than 50 primary particles. The number of primary particles aggregated in the primary or secondary particles can be more than 100 or more than 1000, but is usually 5 × 10⁻⁶. 6 For numbers less than 1, it can be 5×10 5 The number of primary particles is less than 1. In this specification, the number of primary particles can be confirmed, for example, by using SEM images obtained using a scanning electron microscope (hereinafter also referred to as "SEM").
[0030] The first active material is a lithium transition metal composite oxide (hereinafter also referred to as "the first composite oxide") containing at least 75 mol% Ni and 0.5 to 2.8 mol% Ti relative to the total molar amount of metal elements other than Li. The Ni content of the first composite oxide relative to the total molar amount of metal elements other than Li is preferably at least 80 mol%, preferably at least 82 mol%, and can be 75 to 96 mol%, 80 to 93 mol%, or 82 to 90 mol%. The Ti content of the first composite oxide relative to the total molar amount of metal elements other than Li is preferably 0.8 to 2.8 mol%, preferably 1.0 to 2.5 mol%, or 1.3 to 2.2 mol%. The Ti contained in the first active material is preferably dissolved in solid solution in the entire first active material. The ranges of Ni content and Ti content of the first composite oxide can be arbitrarily combined from the above ranges.
[0031] The disorder of Ni in the first active material is 2.1–2.6%, specifically 2.2–2.6%, 2.3–2.6%, or 2.1–2.5%. The disorder of Ni in the first active material represents the incorporation rate (cation mixing amount) of Ni elements at lithium sites in the crystal structure of the first active material. The range of the disorder of Ni in the first active material can be arbitrarily combined with the above-mentioned ranges of the content of Ni and / or Ti in the first composite oxide, i.e., the first active material. By ensuring that the Ti content and Ni disorder of the first active material are within the above-mentioned ranges, the thermal stability of the secondary battery can be improved.
[0032] The first active material, i.e., the first composite oxide, preferably contains Co. The content of Co in the first active material relative to the total moles of metal elements other than Li (in mol%) is preferably less than the content of Co in the second active material relative to the total moles of metal elements other than Li (described later) (in mol%). This readily yields a secondary battery with high capacity and excellent thermal stability. The content of Co in the first active material relative to the total moles of metal elements other than Li can, for example, be 2–15 mol%, 2–10 mol%, or 3–7 mol%.
[0033] The first composite oxide can have a structure, for example, represented by formula (I).
[0034] Li x1 (Ni (1－y1－z1) Co y1 Me1 z1 O2 (I)
[0035] In formula (I),
[0036] 0.8≤x1≤1.3, 0.02≤y1≤0.15, and 0.01≤z1≤0.18,
[0037] Me1 contains Ti and may contain one or more elements selected from Mn, Al, Mg, Mo, Nb, W, B, and Zr.
[0038] In Equation (I), x1 can be 1.0 ≤ x1 ≤ 1.2, 1.0 ≤ x1 ≤ 1.1, or 1.01 ≤ x1 ≤ 1.08. In Equation (I), y1 can be 0.02 ≤ y1 ≤ 0.12, 0.03 ≤ y1 ≤ 0.10, or 0.04 ≤ y1 ≤ 0.08. In Equation (I), z1 can be 0.01 ≤ z1 ≤ 0.15, 0.02 ≤ z1 ≤ 0.12, or 0.03 ≤ z1 ≤ 0.10. In Equation (I), Me1 preferably includes Ti, and includes one or more selected from Mn and Al, more preferably including Ti and Mn. The ranges of x1, y1, z1, and M1 can be arbitrarily combined from the above ranges.
[0039] The second active substance is at least one of a single particle and a secondary particle formed by the aggregation of 2 to 10 primary particles. The second active substance can be a single particle, a secondary particle, or a mixture of a single particle and a secondary particle. The number of primary particles aggregated in the secondary particle can be 2 to 8, 2 to 5, or 3 to 5.
[0040] The second active material is a lithium transition metal composite oxide (hereinafter also referred to as "the second composite oxide") containing 75 mol% or more of Ni relative to the total molar percentage of metal elements other than Li. The second composite oxide may or may not contain Ti. The Ni content of the second composite oxide relative to the total molar percentage of metal elements other than Li is preferably 80 mol% or more, may be 82 mol% or more, may be 75–96 mol%, may be 80–93 mol%, or may be 82–90 mol%. The Ti content of the second composite oxide relative to the total molar percentage of metal elements other than Li is 0.10 mol% or less, may be 0.05 mol% or less, or may be 0.01 mol% or less. When the second active material contains Ti, it can be dissolved in the entire second active material. The ranges of Ni content and Ti content of the second composite oxide can be arbitrarily combined from the above ranges.
[0041] The disorder of Ni in the second active material is 2.0% or less, and can be 0.1% to 2.0%, 0.5% to 1.8%, or 0.8% to 1.7%. The disorder of Ni in the second active material represents the incorporation rate (cation mixing amount) of Ni element at lithium sites in the crystal structure of the second active material. The range of the disorder of Ni in the second active material can be arbitrarily combined with the above-mentioned range of the content of Ni and / or Ti in the second composite oxide, i.e., the second active material. By making the Ti content and Ni disorder of the second active material within the above-mentioned ranges, the secondary battery can be made to have a high capacity.
[0042] The second active material, i.e., the second composite oxide, preferably contains Co. The content of Co in the second active material relative to the total moles of metal elements other than Li (mol%) is preferably greater than the content of Co in the first active material relative to the total moles of metal elements other than Li (mol%). This readily yields a secondary battery with high capacity and excellent thermal stability. The content of Co in the second active material relative to the total moles of metal elements other than Li can, for example, be 2–20 mol%, 5–18 mol%, or 8–15 mol%.
[0043] The second composite oxide can have a structure, for example, represented by formula (II).
[0044] Li x2 (Ni (1－y2－z2) Co y2 Me2 z2 O2 (II)
[0045] In formula (II),
[0046] 0.8≤x²≤1.2, 0.02≤y²≤0.2, and 0.001≤z²≤0.15,
[0047] Me2 may contain one or more elements selected from Ti, Mn, Al, Mg, Mo, Nb, W, B, and Zr.
[0048] In Equation (II), x2 can be 1.0 ≤ x2 ≤ 1.1 or 1.01 ≤ x2 ≤ 1.08. In Equation (II), y2 can be 0.02 ≤ y2 ≤ 0.20, 0.02 ≤ y2 ≤ 0.12, 0.03 ≤ y2 ≤ 0.10, or 0.04 ≤ y2 ≤ 0.08. In Equation (II), z2 can be 0.005 ≤ z2 ≤ 0.12, 0.01 ≤ z2 ≤ 0.1, or 0.02 ≤ z2 ≤ 0.08. In Equation (II), Me2 preferably includes one or more elements selected from Mn and Al, and more preferably includes Mn. The ranges of x2, y2, z2, and M2 can be arbitrarily combined and set from the above ranges.
[0049] The Ni and Ti contents of the first and second composite oxides can be adjusted by the amount of Ni and Ti contained in the raw materials (Ni source and Ti source) used to manufacture them respectively. The composition of the first and second composite oxides can be determined by dissolving them in nitric acid or the like and then analyzing them using ICP (inductively coupled plasma) emission spectroscopy.
[0050] The disorder of Ni in the first and second active materials can be adjusted by the Ti content of the first and second active materials, the calcination temperature, number of calcinations, calcination time, and other calcination conditions during the manufacture of the first and second composite oxides. The disorder of Ni in the first and second active materials can be determined by Rietveld analysis of the measurement data obtained by X-ray diffraction.
[0051] The number of primary particles in the first secondary particles constituting the first active substance and the number of primary particles in the second secondary particles constituting the second active substance can be adjusted by the calcination conditions during the manufacture of the first composite oxide and the second composite oxide, respectively.
[0052] The average particle size (D50) of the first active substance is preferably 12–20 μm, but can be 14–18 μm or 15–17 μm. The particle size distribution of the first active substance is preferably 0.2–0.8, but can be 0.2–0.6 or 0.3–0.5. The particle size distribution in this specification is calculated using the following formula.
[0053] Particle size distribution
[0054] = {Average particle size (D90) - Average particle size (D10)} / Average particle size (D50)
[0055] In this specification, the average particle size (D10), average particle size (D50), and average particle size (D90) are the particle sizes at which the cumulative frequency of the smallest particle size in the volumetric particle size distribution reaches 10%, 50%, and 90%, respectively. The volumetric particle size distribution can be determined using a laser diffraction particle size distribution measuring device.
[0056] The average primary particle size of the first secondary particles constituting the first active substance is preferably 0.5 to 1.5 μm, and can be 0.7 to 1.2 μm. The average primary particle size of the first secondary particles is calculated as the average distance between the two furthest points on the contour lines of more than 10 primary particles randomly selected from the SEM image of the particle surface of the first active substance.
[0057] The average particle size (D50) of the second active substance is preferably 2–6 μm, but can be 2.5–5.0 μm or 3.0–4.5 μm. The particle size distribution of the second active substance is preferably 0.7–1.5, but can be 1.0–1.4 or 1.1–1.3.
[0058] For the individual particles of the second active material and the primary particles constituting the second secondary particles, the average particle size (hereinafter also referred to as "average particle size") is preferably 1 to 3 μm, and can be 1 to 2 μm. The average particle size of the second active material is calculated as the average distance between the two furthest points on the contour lines of a total of 10 or more individual particles and primary particles randomly selected from the SEM image of the particle surface of the second active material.
[0059] By setting the average particle size (D50) and particle distribution of the first and second active materials within the aforementioned ranges, it is easy to form an active material layer using this positive electrode active material at a high density (described later), thus facilitating the high capacity of the secondary battery. The ranges of the average particle size and particle size distribution of the first and second active materials can be arbitrarily combined and set from the aforementioned ranges.
[0060] For the first and second active materials, the above-mentioned aggregation morphology, the content of elements such as Ti, Ni, and Co, the disorder of Ni, the average particle size (D50), the particle size distribution, the average primary particle size, and the average particle size can be arbitrarily combined and set from the above ranges.
[0061] The first active material can be obtained, for example, by mixing and calcining a Ni-containing compound, a lithium compound, and a Ti-containing compound. The Ni-containing compound may contain metallic elements other than Ni, such as Co and Mn. The Ni-containing compound can be a hydroxide or an oxide. Examples of Ni-containing compounds include NiCoMn composite hydroxides. Examples of lithium compounds include lithium hydroxide or lithium carbonate. Examples of Ti-containing compounds include titanium oxide.
[0062] The second active material can be obtained, for example, by mixing a Ni-containing compound and a lithium compound and then calcining them. Examples of the Ni-containing compound and lithium compound mentioned above are examples of such substances.
[0063] The preferred mass ratio of the first active material to the second active material in this positive electrode active material is 7:3 to 5:5, and can be 6.5:3.5 to 5.5:4.5. By keeping the mass ratio within the above range, it is easy to form an active material layer (described later) using this positive electrode active material at a high density, and it is easy to achieve high capacity in the secondary battery.
[0064] This positive electrode active material may contain only the first active material and the second active material, or it may contain other active materials besides the first and second active materials. The total content of the first and second active materials in this positive electrode active material, relative to the total amount of this positive electrode active material, may be 85-100% by mass, 90-100% by mass, 92-99% by mass, or 95-98% by mass.
[0065] (Non-aqueous electrolyte secondary battery)
[0066] The non-aqueous electrolyte secondary battery of this embodiment (hereinafter also referred to as "this battery") includes a positive electrode plate having an active material layer (hereinafter also referred to as "positive electrode active material layer") containing the positive electrode active material. Because this battery has a positive electrode plate with a positive electrode active material layer, it can achieve both high capacity and good thermal stability.
[0067] This battery may include an electrode body containing a positive electrode plate and a non-aqueous electrolyte, and may include a battery casing that houses the electrode body and the non-aqueous electrolyte. The battery casing may include an outer body with an opening and a sealing plate that seals the opening. The outer body and the sealing plate are preferably made of metal, and may be formed using aluminum, aluminum alloy, iron, or iron alloy. A resin sheet serving as an electrode support may be disposed between the electrode body and the outer body. Alternatively, the battery casing may be formed of a composite film. The composite film, for example, has a laminated structure consisting of a metal layer and a resin layer. A pouch-shaped battery casing may be formed by overlapping and welding the edges of the composite film.
[0068] In addition to the positive electrode plate, the electrode body may also include a negative electrode plate and a spacer. In the electrode body, the positive active material layer of the positive electrode plate and the negative active material layer of the negative electrode plate are positioned opposite each other, separated by the spacer. The electrode body can be a stacked type, consisting of a positive electrode plate, a negative electrode plate, and a spacer, or a wound type, formed by winding a long strip of the stacked positive electrode plate, negative electrode plate, and spacer. The wound type electrode body can have a flat shape, formed by pressing the long strip of the stacked body after winding.
[0069] The positive electrode plate may have a positive electrode active material layer on one or both sides of the positive electrode current collector foil. The positive electrode current collector foil may be, for example, a metal foil made of aluminum materials such as aluminum and aluminum alloys. In addition to the positive electrode active material itself, the positive electrode active material layer may further contain at least one of a conductive additive and a binder material.
[0070] Examples of adhesive materials include resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE); polyacrylonitrile (PAN); polyimide; acrylic resin; polyolefin; cellulose-based resins such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and hydroxypropyl cellulose; and polyethylene oxide (POE). An adhesive material may contain one or more of the above-mentioned adhesive materials.
[0071] Examples of conductive additives include carbon materials. Examples of carbon materials include one or more selected from fibrous carbon, carbon black (acetylene black, Ketjen black, etc.), coke, and activated carbon. Examples of fibrous carbon include carbon nanotubes (CNTs). CNTs can be single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), or other multi-walled carbon nanotubes. The conductive additive may include one or more of the above-mentioned conductive additives.
[0072] A positive electrode plate can be obtained, for example, by forming a layer of positive electrode active material on a positive electrode current collector foil. For instance, a layer of positive electrode active material can be formed by coating a positive electrode slurry containing the present positive electrode active material onto the positive electrode current collector foil and then drying and compressing it, thereby obtaining a positive electrode plate. In addition to containing the present positive electrode active material, the positive electrode slurry may also contain binders, conductive additives, and solvents such as N-methyl-2-pyrrolidone (NMP).
[0073] A negative electrode plate typically has a negative electrode current collector foil and a negative electrode active material layer. The negative electrode plate may have the negative electrode active material layer on one or both sides of the negative electrode current collector foil. The negative electrode current collector foil is, for example, a metal foil made of copper materials such as copper and copper alloys. The negative electrode active material layer contains the negative electrode active material and may further contain conductive additives and adhesive materials.
[0074] Examples of anode active materials include, for example, carbon-based active material particles and metal-based active material particles. Examples of carbon-based active material particles include particles selected from one or more carbon materials such as graphite (natural graphite and artificial graphite), hard carbon, soft carbon, and amorphous coated graphite. Examples of metal-based active material particles include particles containing elemental metals or metal oxides selected from silicon (Si), tin (Sn), antimony (Sb), bismuth (Bi), titanium (Ti), and germanium (Ge). Examples of metal-based active material particles include one or more particles selected from Si, SiOx (x = 0.5–1.5), Si / C composites (hereinafter also referred to as "SiC composites"), and Sn.
[0075] Examples of adhesive materials include cellulose-based resins such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and hydroxypropyl cellulose; polyacrylic acid; and styrene-butadiene rubber (SBR). The adhesive material may contain one or more of these. Examples of conductive additives include the aforementioned conductive additives, and the material may contain one or more of the aforementioned conductive additives.
[0076] A negative electrode plate can be obtained, for example, by forming a layer of negative electrode active material on a negative electrode current collector foil. For instance, a layer of negative electrode active material can be formed by coating a negative electrode slurry containing a negative electrode active material onto the negative electrode current collector foil and then drying and compressing it, thereby obtaining a negative electrode plate. In addition to the negative electrode active material, the negative electrode slurry may also contain conductive additives, binders, and solvents such as water.
[0077] The spacer has a substrate, and may have a functional layer on at least one side of the substrate. The substrate may be a membrane made of polyolefins such as polyethylene and polypropylene, polyester, cellulose, polyamide, or a porous sheet such as nonwoven fabric. The substrate may be a single-layer structure or a multi-layer structure. Examples of functional layers include an adhesive layer and a heat-resistant layer; one or both of these layers may be present. The adhesive layer may be formed, for example, by an adhesive. The heat-resistant layer may include, for example, fillers and adhesives.
[0078] The non-aqueous electrolyte is preferably a solution containing an electrolyte in a non-aqueous solvent such as an organic solvent. Examples of electrolytes include LiPF6, LiBF4, LiClO4, LiFSO3, and LiBOB (lithium dioxolane-borate). The non-aqueous electrolyte may contain one or more of these electrolytes. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), butyl carbonate (BC), and diethyl carbonate (DEC). The non-aqueous electrolyte may contain one or more of these non-aqueous solvents. The non-aqueous electrolyte may further contain additives such as vinylene carbonate (VC), ethylene ethylene carbonate (VEC), and fluoroethylene carbonate.
[0079] Example
[0080] The following examples and comparative examples further illustrate this disclosure in detail.
[0081] [Examples 1-4, Comparative Examples 1-4]
[0082] (Preparation of positive electrode active material)
[0083] The first active material was obtained by mixing NiCoMn composite hydroxide, lithium compound, and titanium oxide and calcining the mixture in the temperature range of 700–900 °C. The first active material consisted of secondary particles formed by the aggregation of more than 50 primary particles. The first active material was dissolved in nitric acid, and its composition was determined by ICP (inductively coupled plasma) emission spectroscopy. The results showed that, relative to the total molar number of metal elements other than Li, it contained 83 mol% Ni, and Ti was also present, as shown in Table 1.
[0084] The second active material was obtained by mixing NiCoMn composite hydroxide and lithium compound and calcining it in the temperature range of 800-900℃. The second active material is at least one of single particles and secondary particles formed by the aggregation of 2 to 10 primary particles. The second active material was dissolved in nitric acid, and its composition was determined by ICP emission spectroscopy. The results showed that it contained 83 mol% Ni relative to the total moles of metal elements other than Li. The Ti content of the second active material was less than 0.1 mol%.
[0085] (Making the positive electrode plate)
[0086] The first active material, the second active material, carbon black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder were mixed in a mass ratio of 58.5:39:1.5:1.0 (first active material: second active material: conductive additive: binder). An appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added to prepare a positive electrode slurry. The positive electrode slurry was coated onto an aluminum foil (used as the positive electrode current collector) and dried. It was then compressed to a specified thickness using a calendering roller, cut to the specified size, and fitted with aluminum tabs to obtain the positive electrode plate.
[0087] (Preparation of the experimental battery)
[0088] Prepare a lithium foil metal foil and a spacer made of polyolefin as the counter electrode, which serves as the positive electrode plate. Stack the positive electrode plate, spacer, and lithium foil metal foil to obtain a stacked electrode body. Insert the electrode body into an outer casing of an aluminum composite membrane, inject a non-aqueous electrolyte, and seal the opening of the outer casing to obtain a test cell. The non-aqueous electrolyte is prepared as follows: Lithium hexafluorophosphate (LiPF6) as the electrolyte is dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of EC:EMC = 30:70, and ethylene carbonate (VC) is added as an additive at a concentration of 0.3% by mass relative to the total amount of the mixed solvent.
[0089] [Calculation of the disorder of Ni in the first and second active substances]
[0090] Using a fully automated multi-functional X-ray diffractometer (Rigaku, "SmartLab"), with Cu as the target element in the X-ray tube, a tube voltage of 45 kV, and a tube current of 200 mA, X-ray diffraction measurements were performed on the first and second active materials filled in a dedicated holder using the reflection method. The disorder of Ni in the first and second active materials was determined by Rietveld analysis of the measurement data. The results are shown in Table 1.
[0091] [Determination of the average particle size and particle size distribution of the first and second active substances]
[0092] The average particle size (D10), average particle size (D50), and average particle size (D90) of the first and second active substances were measured using a particle size distribution measuring device (Malvern Panalvtical, “Mastersizer-3000”). The particle size distribution was calculated using the following formula. The results are shown in Table 1.
[0093] Particle size distribution
[0094] = {Average particle size (D90) - Average particle size (D10)} / Average particle size (D50)
[0095] [Evaluation of thermal stability]
[0096] The test battery was charged at 0.2 mA / cm. 2 Constant current charging to 4.3V vs. Li / Li + Further, with 4.3V vs. Li / Li + Constant voltage charging was performed until the current density reached 0.04 mA / cm². 2 Next, the positive electrode mixture constituting the positive electrode active material layer was removed from the positive electrode plate. Using a differential thermal-thermogravimetric analyzer (Shimadzu, "DTG-60A"), the positive electrode mixture was heated to 300℃ at a rate of 5℃ / min, and the derivative curve of the resulting TG curve, i.e., the minimum value of the DTG curve, was determined. The results are shown in Table 1. The minimum value of the DTG curve represents the rate of weight loss of the positive electrode mixture; the larger the value, the better the thermal stability.
[0097] [Evaluation of discharge capacity]
[0098] At a temperature of 25℃, the test battery was subjected to an input current of 0.2 mA / cm. 2 Constant current charging to 4.3V vs. Li / Li + Further, with 4.3V vs. Li / Li + Constant voltage charging was performed until the current density reached 0.04 mA / cm². 2 The test battery was operated at 0.04 mA / cm. 2 Constant current discharge up to 3.0V vs. Li / Li + The discharge capacity was thus determined. The results are shown in Table 1.
[0099] [Table 1]
[0100]
[0101] *1: The proportion relative to the total number of moles of metallic elements other than Li.
[0102] *2: Minimum value of the DTG curve
[0103] Embodiments of the present invention have been described, and should be understood as illustrative rather than limiting. The scope of the invention is defined by the claims, which mean that all modifications of the same meaning and scope as the claims may be included.
Claims
1. A positive electrode active material comprising a first active material and a second active material, wherein the second active material has an average particle size D50 smaller than that of the first active material. The first active substance is a secondary particle formed by the aggregation of more than 50 primary particles. The second active substance is at least one of a single particle and a secondary particle formed by the aggregation of 2 to 10 primary particles. The first active material is a lithium transition metal composite oxide containing more than 75 mol% Ni and 0.5 to 2.8 mol% Ti relative to the total molar amount of metal elements other than Li. The second active material is a lithium transition metal composite oxide containing more than 75 mol% Ni relative to the total molar percentage of metal elements other than Li. The Ti content of the second active material is less than 0.1 mol% relative to the total molar percentage of metal elements other than Li. The disorder degree of Ni in the first active material is 2.1–2.6%. The disorder of Ni in the second active material is less than 2.0%.
2. The positive electrode active material according to claim 1, wherein, The Ti content of the first active material is 1 to 2.5 mol relative to the total number of moles of metal elements other than Li.
3. The positive electrode active material according to claim 1 or 2, wherein, The mass ratio of the first active substance to the second active substance is, i.e., the ratio of the first active substance to the second active substance is 7:3 to 5:
5.
4. The positive electrode active material according to claim 1 or 2, wherein, The average particle size D50 of the first active substance is 12–20 μm.
5. The positive electrode active material according to claim 4, wherein, The average particle size D50 of the second active substance is 2–6 μm.
6. The positive electrode active material according to claim 4, wherein, The particle size distribution ({average particle size D90 - average particle size D10} / average particle size D50) of the first active substance is 0.2 to 0.
8.
7. The positive electrode active material according to claim 5, wherein, The particle size distribution ({average particle size D90 - average particle size D10} / average particle size D50) of the second active substance is 0.7 to 1.
5.
8. The positive electrode active material according to claim 1 or 2, wherein, The content of Co in the first active substance relative to the total number of moles of metal elements other than Li is less than the content of Co in the second active substance relative to the total number of moles of metal elements other than Li.
9. A non-aqueous electrolyte secondary battery, having a positive electrode plate, The positive electrode plate has an active material layer comprising the positive electrode active material according to any one of claims 1 to 8.