A positive electrode active material, a method for preparing the same, and an application thereof

Abstract

This application discloses a positive electrode active material, its preparation method, and its application. The positive electrode active material includes a core and a shell, wherein the core comprises a material with the chemical formula LiFe. 1‑x‑y Ti x V y The material is PO4, wherein 0.003 ≤ x ≤ 0.01, 0.003 ≤ y ≤ 0.01, and the core contains Ti-O-V bridging bonds; the shell covers at least a portion of the outer surface of the core, and the shell includes a carbon layer. The positive electrode active material of this application includes a material with the chemical formula LiFe containing Ti-O-V bridging bonds. 1‑x‑y Ti x V y The core and carbon coating of PO4 materials can improve the overall electrochemical performance of materials, such as compaction density, discharge capacity, and energy efficiency.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a positive electrode active material, its preparation method, and its application. Background Technology

[0002] Lithium iron phosphate (LiFePO4) has become one of the mainstream cathode materials for power and energy storage lithium-ion battery cells due to its advantages such as high safety, long cycle life, and environmental friendliness. However, its polyanionic structure, characterized by alternating vertices and edges of Fe-O octahedra and PO tetrahedra, as well as the one-dimensional ion diffusion channels along the

[010] crystal plane, results in low intrinsic electronic conductivity and lithium-ion diffusion coefficient, ultimately leading to poor overall electrochemical performance and limiting its application in high-energy-density batteries.

[0003] To overcome this drawback, elemental doping strategies have been widely adopted in research and practical production. This involves introducing isovalent or heterovalent metal cations into the LiFePO4 lattice to alter the lattice parameters. Single-element doping can introduce lattice defects to some extent, improving the intrinsic conductivity and lithium-ion diffusion coefficient of the material, thereby enhancing its electrochemical performance. For example, titanium doping (Ti...) 4+ Doping vanadium (V) can stabilize crystal structure, inhibit grain growth, and broaden lithium-ion migration channels. The multiple valence states of vanadium (V) can effectively regulate the electronic structure of materials, improve electronic conductivity, and enhance rate performance and cycle life. However, the modification effect of single doping is limited, often only improving one aspect (such as electronic conductivity or ion diffusion rate), and it is difficult to achieve a significant improvement in the electrochemical performance of materials.

[0004] To address the aforementioned issues, there are reports of Ti and V co-doping. For example, some related technologies employ a process of primary milling, spraying, pulverizing, followed by secondary dry mixing and secondary sintering to prepare lithium iron phosphate. While this technology uses a two-stage dry mixing process to produce high-compact (>2.50 g / cc) lithium iron phosphate, it carries the risk of uneven secondary mixing leading to impurity phases. Other related technologies also exhibit varying degrees of problems, such as low doping efficiency and weak synergistic effects between the two elements.

[0005] Therefore, how to effectively dope lithium iron phosphate materials to improve their overall electrochemical performance remains a pressing technical problem to be solved. Summary of the Invention

[0006] The inventors discovered that in related technologies, the common methods for achieving Ti and V dual-element co-doping are simple physical mixing or stepwise doping. However, such technologies suffer from problems such as uneven element distribution, low doping efficiency, and easy formation of impurity phases, resulting in insignificant synergistic effects and a bottleneck in improving the overall electrochemical performance of finished lithium iron phosphate products.

[0007] To address the aforementioned problems, one objective of this application is to provide a positive electrode active material, which includes a chemical formula of LiFe containing Ti-OV bridging bonds. 1-x-y Ti x V y The core and carbon coating of PO4 materials can improve the overall electrochemical performance of materials, such as compaction density, discharge capacity, and energy efficiency.

[0008] Another objective of this application is to provide a method for preparing a positive electrode active material.

[0009] Another objective of this application is to provide a positive electrode sheet.

[0010] Another object of this application is to provide a battery.

[0011] To achieve the above objectives, the first aspect of this application provides a positive electrode active material, comprising: The core, comprising the chemical formula LiFe 1-x-y Ti x V y The material is PO4, wherein 0.003≤x≤0.01, 0.003≤y≤0.01, and the core contains Ti-OV bridging bonds; An outer shell, which covers at least a portion of the outer surface of the core, the outer shell comprising a carbon layer.

[0012] The positive electrode active material described in this application can bring at least the following beneficial effects: Because it contains a Ti-OV bridging bond, the chemical formula is LiFe. 1-x-y Ti x V y The core and carbon coating of PO4 materials can improve the overall electrochemical performance of materials, such as compaction density, discharge capacity, and energy efficiency.

[0013] In some embodiments, the Ti-OV bridging bond exists in the chemical formula LiFe 1-x-y Ti x V y The interior of PO4 material.

[0014] In some embodiments, the Ti-OV bridging bond is obtained by copolymerization of a first solution, a second solution, and a coupling agent, wherein the first solution contains -Ti-O- and the second solution contains metavanadate ions.

[0015] In some embodiments, the first solution is a solution formed by dissolving a titanium salt in a first solvent, wherein the titanium salt includes at least one of soluble titanium salts, and the first solvent includes at least one of an alcohol solvent and water.

[0016] In some embodiments, the second solution is a solution formed by dissolving metavanadate in a second solvent, wherein the metavanadate includes at least one of ammonium metavanadate (NH4VO3) and lithium metavanadate (LiVO3), and the second solvent includes at least one of water and 0.1-1 wt% ammonia water.

[0017] In some embodiments, the coupling agent includes at least one of an organic ligand containing -OH and an organic ligand containing -COOH.

[0018] Optionally, the coupling agent includes at least one of ethylene glycol, triethanolamine, glycerol, and terephthalic acid.

[0019] In some embodiments, the Ti and V doping is carried out in the chemical formula LiFe 1-x-y Ti x V y In the crystal lattice of PO4 material.

[0020] In some embodiments, the Dv50 of the positive electrode active material is 800-1800 nm, and can be selected as 1000-1500 nm.

[0021] The second aspect of this application discloses a method for preparing a positive electrode active material, comprising: The first solution and the second solution are copolymerized with a coupling agent to obtain a dopant, wherein the dopant includes the Ti-OV bridging bond; the first solution contains -Ti-O- and the second solution contains metavanadate ions.

[0022] The method for preparing the positive electrode active material described in this application, in addition to having the beneficial effects of the positive electrode active material described in this application, can also bring at least the following beneficial effects: A controlled copolymerization reaction involving a first solution containing -Ti-O-, a second solution containing metavanadate ions, and a coupling agent is conducted to generate a metal complex precursor rich in Ti-OV bridging bonds, thereby achieving pre-uniform bonding of dopant elements at the atomic scale. Using this precursor along with subsequent lithium sources as raw materials, a high-efficiency lithium iron phosphate composite material (i.e., the cathode active material) with atomically uniform doping and a unique microstructure can be obtained, effectively improving the overall electrochemical performance of the material.

[0023] In some embodiments, the first solution is a solution formed by dissolving a titanium salt in a first solvent, the titanium salt including at least one of soluble titanium salts, and the first solvent including an alcohol solvent or water.

[0024] In some embodiments, the second solution is a solution formed by dissolving metavanadate in a second solvent, wherein the metavanadate includes at least one of ammonium metavanadate (NH4VO3) and lithium metavanadate (LiVO3), and the second solvent includes water or 0.1-1 wt% ammonia.

[0025] In some embodiments, the coupling agent includes at least one of an organic ligand containing -OH and an organic ligand containing -COOH.

[0026] In some embodiments, the coupling agent includes at least one of ethylene glycol, triethanolamine, glycerol, and terephthalic acid.

[0027] In some embodiments, the reaction temperature of the copolymerization reaction is from room temperature to 80°C, and optionally from 50-70°C.

[0028] In some embodiments, the reaction time of the copolymerization reaction is 2-12 hours, optionally 2-6 hours.

[0029] In some embodiments, the pH of the copolymerization reaction is 4-7.

[0030] In some embodiments, the molar amount of the coupling agent participating in the copolymerization reaction is a mol, and the total molar amount of titanium and vanadium is b mol, wherein a and b satisfy: 1 ​​≤ a / b ≤ 5.

[0031] In some embodiments, the molar ratio of titanium in the first solution and vanadium in the second solution participating in the copolymerization reaction is x:y.

[0032] In some embodiments, the method for preparing the positive electrode active material further includes: The phosphorus source, iron source, lithium source, carbon source and the dopant are ground, spray-dried and sintered to obtain the positive electrode active material.

[0033] In some embodiments, the total mass content of titanium and vanadium in the dopant is 0.2-1% based on the mass of the iron source, and optionally 0.3-1%.

[0034] In some embodiments, the mass content of the carbon source is 5-15% of the mass of the iron source.

[0035] In some embodiments, the molar ratio of lithium in the lithium source to iron in the iron source is (1.01-1.10):1.

[0036] In some embodiments, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is (0.955-0.985):1.

[0037] In some embodiments, both the phosphorus source and the iron source include iron phosphate, and when both the phosphorus source and the iron source are iron phosphate, the material being ground also includes a supplementary phosphorus source.

[0038] In some embodiments, the supplementary phosphorus source accounts for 0.2-1% of the molar ratio of the iron phosphate.

[0039] In some embodiments, the sintering is carried out in a nitrogen or inert gas atmosphere.

[0040] In some embodiments, the sintering temperature is 720-820°C, and the sintering time is 5-10 hours.

[0041] The third aspect of this application proposes a positive electrode sheet, including the positive electrode active material described in the first aspect of this application, or a positive electrode active material prepared by the method for preparing the positive electrode active material described in the second aspect of this application.

[0042] The fourth aspect of this application discloses a battery comprising the positive electrode sheet described in the third aspect of this application.

[0043] Both the positive electrode sheet and the battery described in this application have at least the beneficial effects of the positive active material and the preparation method of the positive active material described in this application.

[0044] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0045] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings. in: Figure 1 This is a flowchart illustrating a method for preparing a positive electrode active material, as shown in an exemplary embodiment of this application.

[0046] Figure 2 The image shows a scanning electron microscope (SEM) image of the positive electrode active material prepared in Example 1.

[0047] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the positive electrode active material prepared in Example 1.

[0048] Figure 4 This is a particle size distribution diagram of the positive electrode active material prepared in Example 1. Detailed Implementation

[0049] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0050] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all raw materials and equipment involved in this application are self-made through commercial means or known methods; and all methods involved are conventional methods unless otherwise specified.

[0052] In this application, room temperature refers to 20-30℃, including but not limited to 22℃, 25℃ or 28℃.

[0053] In this application, Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50%, that is, the volume content of particles smaller than or equal to this particle size accounts for 50% of the total particle volume.

[0054] <Positive Electrode Active Materials> The positive electrode active material of this application includes a core and a shell. The core comprises a material with the chemical formula LiFe. 1-x-y Ti x V yThe material is PO4, wherein 0.003≤x≤0.01 and 0.003≤y≤0.01; the core has Ti-OV bridging bonds; the shell covers at least a portion of the outer surface of the core, and the shell includes a carbon layer.

[0055] It is understood that the core and shell of the positive electrode active material in the embodiments of this application constitute a core-shell structure, that is, the positive electrode active material has a core-shell structure. Furthermore, the chemical formula is LiFe. 1-x-y Ti x V y PO4 materials can be understood as having a lithium iron phosphate matrix. Based on this, when the core is LiFe... 1-x-y Ti x V y When the material and outer shell of PO4 are carbon layers, the chemical formula of the positive electrode active material in this application embodiment can be expressed as: LiFe 1-x-y Ti x V y PO4@C, where "@" represents coating, refers to the carbon layer coating LiFe. 1-x-y Ti x V y PO4 material.

[0056] The positive electrode active material in this application embodiment includes a chemical formula of LiFe containing Ti-OV bridging bonds. 1-x- y Ti x V y The core and carbon coating of PO4 materials can improve the overall electrochemical performance of materials, such as compaction density, discharge capacity, and energy efficiency.

[0057] For example, the chemical formula is LiFe 1-x-y Ti x V y In PO4 materials, the values ​​of x include, but are not limited to, 0.004, 0.005, 0.006, 0.007, 0.008, or 0.009, and the values ​​of y include, but are not limited to, 0.004, 0.005, 0.006, 0.007, 0.008, or 0.009. It should be noted that the values ​​of x and y can be the same or different.

[0058] In some embodiments, the Ti-OV bridging bond exists in the chemical formula LiFe 1-x-y Ti x V y The interior of PO4 material.

[0059] In some embodiments, the Ti-OV bridging bond is obtained by copolymerization of a first solution, a second solution, and a coupling agent, wherein the first solution contains -Ti-O- and the second solution contains metavanadate ions.

[0060] In some embodiments, the first solution is a solution formed by dissolving a titanium salt in a first solvent.

[0061] In some embodiments, the titanium salt includes at least one of the soluble titanium salts.

[0062] For example, the soluble titanium salt includes, but is not limited to, at least one of titanate esters, titanium sulfate (Ti(SO4)2), titanium nitrate (Ti(NO3)4), and titanium oxysulfate (TiOSO4). Among them, titanate esters include, but are not limited to, at least one of tetrabutyl titanate (Ti(OBu)4) and tetraisopropyl titanate.

[0063] As an optional example, the titanium salt is at least one of tetrabutyl titanate (Ti(OBu)4), tetraisopropyl titanate, and titanium oxysulfate (TiOSO4).

[0064] In some embodiments, the first solvent includes at least one of an alcohol solvent and water (e.g., deionized water, distilled water, etc.).

[0065] For example, the alcohol solvent includes, but is not limited to, at least one of anhydrous ethanol, isopropanol, etc.

[0066] It should be noted that in some cases, when the titanium salt is selected from titanium esters such as tetrabutyl titanate (Ti(OBu)4) and tetraisopropyl titanate, the first solvent is anhydrous ethanol, isopropanol, or other alcohol solvents; while when the titanium salt is selected from inorganic titanium salts such as titanium sulfate (Ti(SO4)2), titanium nitrate (Ti(NO3)4), and titanium oxysulfate (TiOSO4), the first solvent is water.

[0067] In some embodiments, the concentration of the first solution is 0.1-0.5 mol / L, including but not limited to 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, or 0.45 mol / L.

[0068] In some embodiments, the second solution is a solution formed by dissolving metavanadate in a second solvent.

[0069] For example, the metavanadate includes, but is not limited to, at least one of ammonium metavanadate (NH4VO3), lithium metavanadate (LiVO3), etc.

[0070] For example, the second solvent includes, but is not limited to, at least one of water (e.g., deionized water, distilled water, etc.) and dilute ammonia (e.g., 0.1-1 wt% ammonia).

[0071] Further optionally, the concentration of the second solution is 0.1-0.5 mol / L, including but not limited to 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L or 0.45 mol / L.

[0072] In some embodiments, the coupling agent includes at least one of an organic ligand containing -OH and an organic ligand containing -COOH. When an organic ligand containing -OH and / or -COOH is used as a coupling agent, its carboxyl and hydroxyl groups can coordinate with Ti and V ions, forming steric hindrance, promoting the formation of stable Ti-OV bridging bonds, controlling the copolymerization rate, and preventing the product from precipitating too quickly.

[0073] For example, organic ligands containing -OH include, but are not limited to, at least one of ethylene glycol, triethanolamine, glycerol, etc.

[0074] For example, organic ligands containing -COOH include, but are not limited to, at least one of terephthalic acid, biphenyl 4,4'-dicarboxylic acid (also known as biphenyl 4,4'-dicarboxylic acid), etc.

[0075] As an optional example, the coupling agent includes at least one of ethylene glycol, triethanolamine, glycerol, and terephthalic acid.

[0076] In some embodiments, the types of copolymerization reactions described above include, but are not limited to, hydrothermal reactions, coprecipitation reactions, etc.

[0077] It should be noted that in the embodiments of this application, the order of addition of each raw material is not restricted when carrying out the above copolymerization reaction.

[0078] As a possible example, a first solution (containing -Ti-O-) is slowly added dropwise to a second solution (containing metavanadate ions), and then a coupling agent is added to carry out a copolymerization reaction.

[0079] As another possible example, a coupling agent is added simultaneously to a first solution (containing -Ti-O-) and a second solution (containing metavanadate ions) to induce a copolymerization reaction.

[0080] As another possible example, a copolymerization reaction is carried out by simultaneously adding a first solution (containing -Ti-O-), a second solution (containing metavanadate ions), and a coupling agent to the reaction system.

[0081] As another possible example, a first solution (containing -Ti-O-) and a second solution (containing metavanadate ions) are simultaneously added to the reaction system, followed by the addition of a coupling agent to carry out a copolymerization reaction.

[0082] In some embodiments, the reaction temperature of the copolymerization reaction is from room temperature to 80°C, but is not limited to room temperature, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C or 75°C, etc., and can be selected as 50-70°C.

[0083] Controlling the reaction temperature of the copolymerization reaction within the above range can promote the controlled polymerization of Ti cations and V anions, form stable Ti-OV bridge bonds, and control the molecular weight and particle size of the product. If the reaction temperature is too low, the reaction kinetics will be slow, the polymerization efficiency will be low, and it will be difficult to effectively form Ti-OV bridge bonds. If the reaction temperature is too high, the reaction rate will be too fast, which may lead to uneven precipitation of the product or side reactions, destroying the formation of the bridged structure.

[0084] In some embodiments, the reaction time of the copolymerization reaction is 2-12 hours, including but not limited to 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours or 11 hours, and can be selected as 2-6 hours.

[0085] As an optional example, the copolymerization reaction is carried out under water bath heating conditions of 50-70°C for 2-6 hours. This ensures that the reaction proceeds fully.

[0086] In some embodiments, the pH of the copolymerization reaction is 4-7, including but not limited to 4.5, 5, 5.5, 6 or 6.5.

[0087] In the embodiments of this application, controlling the pH of the copolymerization reaction within the above-mentioned range can achieve the stable formation of dopants; if the pH is too low, the final copolymerization product may dissolve; if the pH is too high, metal hydroxide precipitates may form, and the bridging structure may not be formed.

[0088] In some embodiments, the pH is adjusted during the copolymerization process by adding ammonia (e.g., 0.1 mol / L ammonia) or acetic acid.

[0089] In some embodiments, the molar amount of the coupling agent participating in the copolymerization reaction is a mol, and the total molar amount of titanium and vanadium is b mol, wherein a and b satisfy: a / b≥1.

[0090] As an alternative example, 1 ≤ a / b ≤ 5.

[0091] For example, the values ​​of a / b mentioned above include, but are not limited to, 1.5, 2, 2.5, 3, 3.5, 4, or 4.5.

[0092] It can be understood that the value of a / b mentioned above is the molar ratio of the coupling agent participating in the copolymerization reaction, the total molar amounts of titanium and vanadium in the first and second solutions participating in the copolymerization reaction (that is, the total molar amounts of titanium in the titanium salt used to prepare the first solution and vanadium in the metavanadate used to prepare the second solution). Alternatively, it can be understood that, based on the total molar amounts of titanium and vanadium in the first and second solutions participating in the copolymerization reaction, the molar amount of the coupling agent participating in the copolymerization reaction is 1-5 times the total molar amounts of titanium and vanadium.

[0093] In some embodiments, the molar ratio of titanium in the first solution and vanadium in the second solution participating in the copolymerization reaction is x:y.

[0094] In some embodiments, the Ti and V doping is carried out in the chemical formula LiFe 1-x-y Ti x V y In the crystal lattice of PO4 material.

[0095] In some embodiments, the Dv50 of the positive electrode active material is 800-1800nm, including but not limited to 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1600nm or 1700nm, and can be selected as 1000-1500nm.

[0096] <Preparation Methods of Positive Electrode Active Materials> The method for preparing the positive electrode active material according to the embodiments of this application can be used to prepare the positive electrode active material according to the embodiments of this application. The method includes the step of preparing a dopant and the step of using the prepared dopant as a raw material together with a lithium source to prepare a lithium iron phosphate composite material (i.e., the positive electrode active material).

[0097] The following describes a method for preparing a positive electrode active material according to an embodiment of this application, with reference to the accompanying drawings.

[0098] Figure 1 This is a flowchart illustrating a method for preparing a positive electrode active material, as shown in an exemplary embodiment of this application.

[0099] like Figure 1 As shown, the preparation method includes the following steps: S101. Prepare a first solution containing -Ti-O-.

[0100] In some embodiments, the first solution is a solution formed by dissolving a titanium salt in a first solvent.

[0101] In some embodiments, preparing the first solution includes dissolving the titanium salt in a first solvent to form the first solution.

[0102] In some embodiments, the titanium salt includes at least one of the soluble titanium salts.

[0103] For example, the soluble titanium salt includes, but is not limited to, at least one of titanate esters, titanium sulfate (Ti(SO4)2), titanium nitrate (Ti(NO3)4), and titanium oxysulfate (TiOSO4). Among them, titanate esters include, but are not limited to, at least one of tetrabutyl titanate (Ti(OBu)4) and tetraisopropyl titanate.

[0104] As an optional example, the titanium salt is at least one of tetrabutyl titanate (Ti(OBu)4), tetraisopropyl titanate, and titanium oxysulfate (TiOSO4).

[0105] In some embodiments, the first solvent includes at least one of an alcohol solvent and water (e.g., deionized water, distilled water, etc.).

[0106] For example, the alcohol solvent includes, but is not limited to, at least one of anhydrous ethanol, isopropanol, etc.

[0107] It should be noted that in some cases, when the titanium salt is selected from titanium esters such as tetrabutyl titanate (Ti(OBu)4) and tetraisopropyl titanate, the first solvent is anhydrous ethanol, isopropanol, or other alcohol solvents; while when the titanium salt is selected from inorganic titanium salts such as titanium sulfate (Ti(SO4)2), titanium nitrate (Ti(NO3)4), and titanium oxysulfate (TiOSO4), the first solvent is water.

[0108] For example, the concentration of the first solution is 0.1-0.5 mol / L, including but not limited to 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L or 0.45 mol / L, etc.

[0109] S102. Prepare a second solution containing metavanadate ions.

[0110] In some embodiments, the second solution is a solution formed by dissolving metavanadate in a second solvent.

[0111] For example, the metavanadate includes, but is not limited to, at least one of ammonium metavanadate (NH4VO3), lithium metavanadate (LiVO3), etc.

[0112] For example, the second solvent includes, but is not limited to, at least one of water (e.g., deionized water, distilled water, etc.) and dilute ammonia (e.g., 0.1-1 wt% ammonia).

[0113] In some embodiments, preparing the second solution includes dissolving metavanadate in a second solvent to form the second solution.

[0114] For example, the concentration of the second solution is 0.1-0.5 mol / L, including but not limited to 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L or 0.45 mol / L, etc.

[0115] S103. The first solution, the second solution and the coupling agent are subjected to a copolymerization reaction to obtain a dopant, wherein the dopant includes the Ti-OV bridging bond.

[0116] In some embodiments, the coupling agent includes at least one of an organic ligand containing -OH and an organic ligand containing -COOH. When an organic ligand containing -OH and / or -COOH is used as a coupling agent, its carboxyl and hydroxyl groups can coordinate with Ti and V ions, forming steric hindrance, promoting the formation of stable Ti-OV bridging bonds, controlling the copolymerization rate, and preventing the product from precipitating too quickly.

[0117] For example, organic ligands containing -OH include, but are not limited to, at least one of ethylene glycol, triethanolamine, glycerol, etc.

[0118] For example, organic ligands containing -COOH include, but are not limited to, at least one of terephthalic acid, etc.

[0119] As an optional example, the coupling agent includes at least one of ethylene glycol, triethanolamine, glycerol, and terephthalic acid.

[0120] In some embodiments, the types of copolymerization reactions described above include, but are not limited to, hydrothermal reactions, coprecipitation reactions, etc.

[0121] It should be noted that in the embodiments of this application, the order of addition of each raw material is not restricted when carrying out the above copolymerization reaction.

[0122] As a possible example, a first solution (containing -Ti-O-) is slowly added dropwise to a second solution (containing metavanadate ions), and then a coupling agent is added to carry out a copolymerization reaction.

[0123] As another possible example, a coupling agent is added simultaneously to a first solution (containing -Ti-O-) and a second solution (containing metavanadate ions) to induce a copolymerization reaction.

[0124] As another possible example, a copolymerization reaction is carried out by simultaneously adding a first solution (containing -Ti-O-), a second solution (containing metavanadate ions), and a coupling agent to the reaction system.

[0125] As another possible example, a first solution (containing -Ti-O-) and a second solution (containing metavanadate ions) are simultaneously added to the reaction system, followed by the addition of a coupling agent to carry out a copolymerization reaction.

[0126] In some embodiments, the reaction temperature of the copolymerization reaction is from room temperature to 80°C, but is not limited to room temperature, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C or 75°C, etc., and can be selected as 50-70°C.

[0127] Controlling the reaction temperature of the copolymerization reaction within the above range can promote the controlled polymerization of Ti cations and V anions, form stable Ti-OV bridge bonds, and control the molecular weight and particle size of the product. If the reaction temperature is too low, the reaction kinetics will be slow, the polymerization efficiency will be low, and it will be difficult to effectively form Ti-OV bridge bonds. If the reaction temperature is too high, the reaction rate will be too fast, which may lead to uneven precipitation of the product or side reactions, destroying the formation of the bridged structure.

[0128] In some embodiments, the reaction time of the copolymerization reaction is 2-12 hours, including but not limited to 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours or 11 hours, and can be selected as 2-6 hours.

[0129] As an optional example, the copolymerization reaction is carried out under water bath heating conditions of 50-70°C for 2-6 hours. This ensures that the reaction proceeds fully.

[0130] In some embodiments, the pH of the copolymerization reaction is 4-7, including but not limited to 4.5, 5, 5.5, 6 or 6.5.

[0131] In the embodiments of this application, controlling the pH of the copolymerization reaction within the above-mentioned range can achieve the stable formation of dopants; if the pH is too low, the final copolymerization product may dissolve; if the pH is too high, metal hydroxide precipitates may form, and the bridging structure may not be formed.

[0132] In some embodiments, the pH is adjusted during the copolymerization process by adding ammonia (e.g., 0.1 mol / L ammonia) or acetic acid.

[0133] In some embodiments, the molar amount of the coupling agent participating in the copolymerization reaction is a mol, and the total molar amount of titanium and vanadium is b mol, wherein a and b satisfy: a / b≥1.

[0134] As an alternative example, 1 ≤ a / b ≤ 5.

[0135] For example, the values ​​of a / b mentioned above include, but are not limited to, 1.5, 2, 2.5, 3, 3.5, 4, or 4.5.

[0136] It can be understood that the value of a / b mentioned above is the molar ratio of the coupling agent participating in the copolymerization reaction, the total molar amounts of titanium and vanadium in the first and second solutions participating in the copolymerization reaction (that is, the total molar amounts of titanium in the titanium salt used to prepare the first solution and vanadium in the metavanadate used to prepare the second solution). Alternatively, it can be understood that, based on the total molar amounts of titanium and vanadium in the first and second solutions participating in the copolymerization reaction, the molar amount of the coupling agent participating in the copolymerization reaction is 1-5 times the total molar amounts of titanium and vanadium.

[0137] In the embodiments of this application, controlling the value of a / b within the above range can ensure that the coupling agent is fully coordinated with the metal ions to form a spatial network structure, stabilize the Ti-OV bridge bond, and avoid introducing too much organic residue. If the value of a / b is too low, the coupling agent is insufficient and cannot effectively stabilize the bridge bond, and the product is prone to agglomeration or precipitation. If the value of a / b is too high, there will be too much organic ligand residue, which may generate too much carbon or impurities in subsequent sintering, affecting the purity and electrochemical performance of the material.

[0138] In some embodiments, the molar ratio of titanium in the first solution and vanadium in the second solution participating in the copolymerization reaction is x:y.

[0139] As an alternative example, a copolymerization reaction is carried out with a coupling agent involving a first solution (containing -Ti-O-) and a second solution (containing metavanadate ions), comprising: The first solution is slowly added dropwise to the second solution, or vice versa, to carry out the copolymerization reaction between -Ti-O- and metavanadate ions. During the reaction, the pH and temperature of the reaction system are controlled; simultaneously, organic ligands containing -OH and / or -COOH are added as coupling agents.

[0140] In some embodiments, the method for preparing the positive electrode active material further includes a step of purifying the product obtained from the copolymerization reaction after the copolymerization reaction.

[0141] For example, the purification includes: solid-liquid separation (e.g., centrifugation) of the product obtained from the copolymerization reaction, washing, and drying.

[0142] S104. The phosphorus source, iron source, lithium source, carbon source and the dopant obtained in step S103 are ground, spray-dried and sintered to obtain the positive electrode active material.

[0143] In the embodiments of this application, there are no restrictions on the specific materials selected for the phosphorus source, iron source, lithium source and carbon source. They can be any phosphorus source, iron source, lithium source and carbon source known in the art for preparing lithium iron phosphate materials.

[0144] For example, the phosphorus source includes, but is not limited to, at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, lithium phosphate, and iron phosphate.

[0145] For example, the iron source includes, but is not limited to, at least one of ferric phosphate, ferrous sulfate, ferric chloride, and ferric oxide.

[0146] For example, the lithium source includes, but is not limited to, at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, and lithium acetate.

[0147] For example, the carbon source includes, but is not limited to, at least one of glucose, sucrose, polyethylene glycol, polyvinyl alcohol, etc.

[0148] In some embodiments, the total mass content of titanium and vanadium in the dopant is 0.2-1% based on the total mass of the iron source, including but not limited to 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 0.9%, and optionally 0.3-1%.

[0149] In the embodiments of this application, controlling the total mass content of titanium and vanadium elements in the dopant within the above-mentioned range can ensure a balance between the electrochemical performance and compaction density of the final product; if it is less than 0.2%, it is easy to lead to a low doping amount and weak electrochemical performance; if it is more than 1%, it will significantly hinder the particle fusion of the lithium iron phosphate material, resulting in a low compaction density.

[0150] In some embodiments, the mass content of the carbon source is 5-15% of the mass of the iron source, including but not limited to 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13% or 14%.

[0151] In some embodiments, the molar ratio of lithium in the lithium source to iron in the iron source is (1.01-1.10):1, including but not limited to 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1 or 1.09:1, etc.

[0152] In some embodiments, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is (0.955-0.985):1, including but not limited to 0.960:1, 0.965:1, 0.970:1, 0.975:1 or 0.980:1.

[0153] In some embodiments, both the phosphorus source and the iron source include iron phosphate.

[0154] In some embodiments, when both the phosphorus source and the iron source are iron phosphate, the material being ground also includes a supplementary phosphorus source.

[0155] In some embodiments, the supplementary phosphorus source includes, but is not limited to, at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate.

[0156] In some embodiments, when both the phosphorus source and the iron source are iron phosphate, the supplementary phosphorus source accounts for 0.2-1% of the molar ratio of the iron phosphate, including but not limited to 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 0.9%.

[0157] It should be noted that the above-mentioned amount of supplemental phosphorus source refers to the amount of pure phosphoric acid when the supplemental phosphorus source is phosphoric acid. When 85wt% phosphoric acid is used as the supplemental phosphoric acid source, the required amount needs to be the same as that of pure phosphoric acid, therefore a conversion is necessary.

[0158] In some embodiments, the sintering is carried out in a nitrogen or inert gas atmosphere.

[0159] For example, the inert gas includes, but is not limited to, at least one of helium, argon, or neon.

[0160] In some embodiments, the sintering temperature is 720-820°C, including but not limited to 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, or 810°C.

[0161] In some embodiments, the sintering time is 5-10 hours, including but not limited to 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, or 9.5 hours.

[0162] In some embodiments, the grinding includes at least one of wet sand milling and wet ball milling.

[0163] In some embodiments, the grinding speed is 500-1500 rpm, including but not limited to 500 rpm, 750 rpm, 1000 rpm, 1250 rpm or 1500 rpm.

[0164] In some embodiments, the grinding time is 0.5-2.5 hours, including but not limited to 0.5 hours, 1 hour, 1.5 hours, 2 hours or 2.5 hours.

[0165] In some embodiments, the spray drying process conditions include: atomizing disc rotation speed of 12000-16000 rpm, inlet air temperature of 220-280℃, and outlet air temperature of 80-130℃.

[0166] It should be noted that if the first solution containing -Ti-O- and the second solution containing metavanadate ions can be obtained commercially, the preparation method of the positive electrode active material in this application embodiment can omit steps S101 and S102.

[0167] Furthermore, it should be noted that step S104 is essentially a step for preparing lithium iron phosphate material. This application is not limited to the method of step S104; in addition to the method of this application, any method for preparing lithium iron phosphate material well known in the art can also be used. That is, after obtaining the dopant, except for step S104 of this application, it can be used as a dopant to prepare lithium iron phosphate material using any method for preparing lithium iron phosphate material well known in the art.

[0168] As an optional example, a method for preparing a positive electrode active material includes the following steps: (1) The first solution and the second solution are copolymerized with a coupling agent to obtain a dopant, wherein the dopant includes the Ti-OV bridge bond, the first solution contains -Ti-O-, and the second solution contains metavanadate ions; (2) The iron phosphate source, lithium source, carbon source, supplementary phosphorus source and dopant are subjected to wet sand milling or ball milling to obtain slurry; (3) The slurry is spray-dried to obtain a spray-dried material; (4) The spray material is sintered once under an inert atmosphere to obtain lithium iron phosphate composite material, which is the positive electrode active material of the present application embodiment.

[0169] The method for preparing the positive electrode active material in this application involves a controlled copolymerization reaction using a first solution containing -Ti-O-, a second solution containing metavanadate ions, and a coupling agent to generate a metal complex precursor rich in Ti-OV bridging bonds, thereby achieving pre-uniform bonding of dopant elements at the atomic scale. Using this precursor along with a lithium source as raw materials, a high-efficiency lithium iron phosphate composite material (i.e., the positive electrode active material) with atomically uniform doping and a unique microstructure can be obtained, effectively improving the overall electrochemical performance of the material.

[0170] <Positive Electrode> The positive electrode sheet of this application embodiment includes the positive electrode active material of this application embodiment, or the positive electrode active material prepared by the preparation method of the positive electrode active material of this application embodiment.

[0171] In some embodiments, the positive electrode sheet further includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the positive electrode active material of the embodiment of the present application, or includes the positive electrode active material prepared by the preparation method of the positive electrode active material of the embodiment of the present application.

[0172] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0173] The positive electrode film layer further includes other positive electrode active materials. The other positive electrode active materials can be selected from materials capable of absorbing and releasing lithium.

[0174] The specific types of the other positive electrode active materials are not specifically limited and can be selected according to requirements. As an example, the other positive electrode active materials can include, but are not limited to, lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium iron pyrophosphate (Li2FeP2O7), lithium cobalt oxide (LiCoO2), spinel-type lithium manganate (LiMn2O4), spinel-type lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), layered lithium manganate (LiMnO2), lithium nickel oxide (LiNiO2), lithium niobate (LiNbO2), lithium ferrite (LiFeO2), lithium manganate (LiMgO2), lithium calcium oxide (LiCaO2), lithium copper oxide (LiCuO2), lithium zinc oxide (LiZnO2), lithium molybdate (LiMoO2), lithium tantalate (LiTaO2), lithium tungstate (LiWO2), lithium nickel cobalt aluminum oxide (LiNi x Co y Al 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example LiNi 0.8 Co 0.15 Al 0.05 O2), lithium nickel cobalt manganese oxide (LiNi x Co y Mn 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi<​​​​​​​​​​At least one of the following: O2, lithium-rich materials (e.g., lithium-rich nickel-cobalt-manganese oxide), manganese oxide (MnO2), vanadium oxide, sulfur oxide, silicate oxide, and their respective modified compounds. These materials may be used alone or in combination of two or more.

[0175] The modified compounds for the other positive electrode active materials mentioned above can be modified by doping, surface coating, or simultaneous doping and coating of other positive electrode active materials.

[0176] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0177] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0178] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0179] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0180] <Battery> The battery of this application embodiment includes the positive electrode sheet of this application embodiment.

[0181] In some embodiments, the battery includes a secondary battery, which includes a lithium-ion battery, etc.

[0182] In some embodiments, the battery further includes a negative electrode, an electrolyte, and a separator.

[0183] [Negative electrode plate] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0184] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0185] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0186] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0187] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0188] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0189] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0190] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0191] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0192] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0193] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0194] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0195] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0196] [Isolation membrane] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0197] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0198] The positive electrode sheet and battery of the present application embodiments have at least the beneficial effects of the positive electrode active material and the preparation method of the positive electrode active material of the present application embodiments.

[0199] The following non-limiting embodiments further illustrate certain features of the present technology.

[0200] I. Examples and Comparative Examples The iron-to-phosphorus ratios mentioned in the following examples and comparative examples refer to the molar ratio of iron (Fe) to phosphorus (P).

[0201] The room temperature involved in the following examples and comparative examples is 25±1℃.

[0202] Example 1 This embodiment provides a positive electrode active material, and the preparation method of the positive electrode active material includes the following steps: Step 1: Preparation of dopant A method for preparing a dopant includes the following steps: (1) Weigh out tetrabutyl titanate and dissolve it in a mixed solvent of anhydrous ethanol and isopropanol in a volume ratio of anhydrous ethanol:isopropanol = 3:1 to form a first solution of 0.1 mol / L.

[0203] (2) Weigh out ammonium metavanadate and dissolve it in deionized water to form a second solution of 0.1 mol / L.

[0204] (3) Slowly add the second solution obtained in step (2) to the first solution obtained in step (1) while adding ethylene glycol, so that the ratio of the molar amount of ethylene glycol added to the system, the total molar amount of titanium and vanadium in the first and second solutions is 2:1, and the molar ratio of titanium in the first solution to vanadium in the second solution is 1:1; then, use 0.1 mol / L ammonia to adjust the pH of the system to 5.5 to form a mixed solution.

[0205] (4) Heat the mixed solution obtained in step (3) to 60°C and react for 6 hours. Then, centrifuge, wash with deionized water, filter and dry the product to obtain the dopant.

[0206] Step 2: Preparation of lithium iron phosphate materials A method for preparing lithium iron phosphate materials includes the following steps: 1) Weigh out iron phosphate, lithium carbonate, glucose, PEG2000, 85wt% phosphoric acid (molar ratio to iron phosphate), and dopant in sequence, add deionized water, homogenize, and then feed the slurry into a sand mill to obtain a slurry with a particle size Dv50 of 500nm.

[0207] The iron-to-phosphorus ratio of iron phosphate is 0.958, the molar ratio of Li in lithium carbonate to Fe in iron phosphate is 1.02:1, and the total mass content of titanium (Ti) and vanadium (V) in the dopant is 0.7% of the mass of iron phosphate. Glucose and PEG2000 are both carbon sources, with glucose added at 8% of the mass of iron phosphate, PEG2000 added at 4% of the mass of iron phosphate, and 85wt% phosphoric acid added at 0.47% of the molar amount of iron phosphate.

[0208] 2) Spray dry the slurry obtained in step 1) to obtain the spray material.

[0209] The spray drying process conditions are as follows: atomizing disc speed 14000 rpm, inlet air temperature 250℃, and outlet air temperature 90℃.

[0210] 3) The spray material obtained in step 2) is sintered once in a nitrogen atmosphere furnace. After the temperature drops to room temperature, the sintered material is pulverized by airflow to obtain Ti-V co-doped lithium iron phosphate cathode material, which is the cathode active material of this embodiment.

[0211] The temperature of the first sintering treatment was 780℃, and the constant temperature reaction was carried out for 8 hours. During the air jet milling process, the frequency of the classifier wheel of the air jet mill was adjusted to 120Hz, and the milling pressure was 0.5MPa.

[0212] Example 2 This embodiment is basically the same as embodiment 1, except that: Step 2, the method for preparing lithium iron phosphate materials, includes the following steps: 1) Weigh out iron phosphate, lithium carbonate, sucrose, polyvinyl alcohol, ammonium dihydrogen phosphate and dopant in sequence, add deionized water, homogenize and then feed the slurry into a sand mill to obtain a slurry with a particle size Dv50 of 400nm.

[0213] The iron-to-phosphorus ratio of iron phosphate is 0.966, the molar ratio of Li in lithium carbonate to Fe in iron phosphate is 1.03:1, and the total mass content of titanium (Ti) and vanadium (V) in the dopant is 1% of the mass of iron phosphate. Sucrose and polyvinyl alcohol are both carbon sources, with sucrose added at 4% of the mass of iron phosphate, polyvinyl alcohol added at 10% of the mass of iron phosphate, and ammonium dihydrogen phosphate added at 0.8% of the molar mass of iron phosphate.

[0214] 2) Spray dry the slurry obtained in step 1) to obtain the spray material.

[0215] The spray drying process conditions are as follows: atomizing disc speed 15000 rpm, inlet air temperature 240℃, and outlet air temperature 100℃.

[0216] 3) The spray material obtained in step 2) is sintered once in a nitrogen atmosphere furnace. After the temperature drops to room temperature, the sintered material is pulverized by airflow to obtain Ti-V co-doped lithium iron phosphate cathode material, which is the cathode active material of this embodiment.

[0217] The temperature of the first sintering treatment is 800℃, and the constant temperature reaction is 10h; during the air jet milling process, the frequency of the classifier wheel of the air jet mill is adjusted to 120Hz, and the milling pressure is 0.5MPa.

[0218] Example 3 This embodiment is basically the same as embodiment 1, except that: Step 2, the method for preparing lithium iron phosphate materials, includes the following steps: A method for preparing lithium iron phosphate materials includes the following steps: 1) Weigh out iron phosphate, lithium carbonate, glucose, PEG2000, 85wt% phosphoric acid and dopant in sequence, add deionized water, homogenize and then feed the slurry into a sand mill to obtain a slurry with a particle size Dv50 of 450nm.

[0219] The iron-to-phosphorus ratio of iron phosphate is 0.977, the molar ratio of Li in lithium carbonate to Fe in iron phosphate is 1.01:1, and the total mass content of titanium (Ti) and vanadium (V) in the dopant is 0.5% of the mass of iron phosphate. Glucose and PEG2000 are both carbon sources, with glucose added at 5% of the mass of iron phosphate, PEG2000 added at 10% of the mass of iron phosphate, and 85wt% phosphoric acid added at 0.71% of the molar amount of iron phosphate.

[0220] 2) Spray dry the slurry obtained in step 1) to obtain the spray material.

[0221] The spray drying process conditions are as follows: atomizing disc speed 13000 rpm, inlet air temperature 260℃, and outlet air temperature 110℃.

[0222] 3) The spray material obtained in step 2) is sintered once in a nitrogen atmosphere furnace. After the temperature drops to room temperature, the sintered material is pulverized by airflow to obtain Ti-V co-doped lithium iron phosphate cathode material, which is the cathode active material of this embodiment.

[0223] The temperature of the first sintering treatment was 820℃, and the constant temperature reaction was carried out for 10 hours. During the air jet milling process, the frequency of the classifier wheel of the air jet mill was adjusted to 120Hz, and the milling pressure was 0.5MPa.

[0224] Example 4 This embodiment is basically the same as embodiment 1, except that: In step 2, during the preparation of lithium iron phosphate materials: In step 1), the total mass content of titanium (Ti) and vanadium (V) in the dopant is 0.2% of the mass of iron phosphate.

[0225] Example 5 This embodiment is basically the same as embodiment 1, except that: During step 1, in the process of preparing the dopant: In step (3), “ethylene glycol” is replaced with triethanolamine.

[0226] Example 6 This embodiment is basically the same as embodiment 1, except that: During step 1, in the process of preparing the dopant: In step (3), “ethylene glycol” is replaced with terephthalic acid.

[0227] Example 7 This embodiment is basically the same as embodiment 1, except that: During step 1, in the process of preparing the dopant: In step (2), “ammonium metavanadate” is replaced with “lithium metavanadate”.

[0228] In step (3), “ethylene glycol” is replaced with “a mixture of glycerol and 2 terephthalic acids in a molar ratio of 1:1”.

[0229] Example 8 This embodiment is basically the same as embodiment 1, except that: During step 1, in the process of preparing the dopant: In step (4), the mixed solution obtained in step (3) is reacted at room temperature for 12 hours.

[0230] Example 9 This embodiment is basically the same as embodiment 1, except that: During step 1, in the process of preparing the dopant: In step (4), the mixed solution obtained in step (3) is heated to 80°C and reacted for 2 hours.

[0231] Example 10 This embodiment is basically the same as embodiment 1, except that: During step 1, in the process of preparing the dopant: In step (3), the pH of the system is adjusted to 4 using 0.1 mol / L ammonia.

[0232] Example 11 This embodiment is basically the same as embodiment 1, except that: During step 1, in the process of preparing the dopant: In step (3), the pH of the system is adjusted to 7 using 0.1 mol / L ammonia.

[0233] Example 12 This embodiment is basically the same as embodiment 1, except that: During step 1, in the process of preparing the dopant: In step (3), the ratio of the molar amount of ethylene glycol added to the system, the total molar amount of titanium and vanadium in the first and second solutions is 1:1, and the molar ratio of titanium in the first solution to vanadium in the second solution is 0.003:0.01.

[0234] Example 13 This embodiment is basically the same as embodiment 1, except that: During step 1, in the process of preparing the dopant: In step (3), the ratio of the molar amount of ethylene glycol added to the system, the total molar amount of titanium and vanadium in the first solution and the second solution is 5:1, and the molar ratio of titanium in the first solution and vanadium in the second solution is 0.01:0.003.

[0235] Example 14 This embodiment is basically the same as embodiment 1, except that: During step 1, in the process of preparing the dopant: In step (3), the ratio of the molar amount of ethylene glycol added to the system, the total molar amount of titanium and vanadium in the first solution and the second solution is 3:1, and the molar ratio of titanium in the first solution and vanadium in the second solution is 0.006:0.006.

[0236] Example 15 This embodiment is basically the same as embodiment 1, except that: In step 2, during the preparation of lithium iron phosphate materials: In step 1): The iron-to-phosphorus ratio of ferric phosphate is 0.958, the molar ratio of Li in lithium carbonate to Fe in ferric phosphate is 1.10:1, the added glucose mass is 2.5% of the ferric phosphate mass, the added PEG 2000 mass is 2.5% of the ferric phosphate mass, and the added 85wt% phosphoric acid molar amount is 1.18% of the ferric phosphate molar amount (corresponding to 1% when the supplementary phosphorus source is pure phosphoric acid).

[0237] Example 16 This embodiment is basically the same as embodiment 1, except that: In step 2, during the preparation of lithium iron phosphate materials: In step 1): The molar ratio of Li in lithium carbonate to Fe in iron phosphate is 1.06:1, and the molar amount of 85wt% phosphoric acid added is 0.24% of the molar amount of iron phosphate (corresponding to 0.2% when the supplementary phosphoric acid source is pure phosphoric acid).

[0238] Example 17 This embodiment is basically the same as embodiment 1, except that: In step 2, during the preparation of lithium iron phosphate materials: Step 1) is: Ferrous sulfate, lithium carbonate, glucose, PEG2000, 85wt% phosphoric acid, and dopant were weighed in sequence, deionized water was added, and after homogenization, the slurry was fed into a sand mill to obtain a slurry with a particle size Dv50 of 500nm.

[0239] The molar ratio of Fe in ferrous sulfate to P in 85wt% phosphoric acid is 0.958, the molar ratio of Li in lithium carbonate to Fe in ferrous sulfate is 1.02:1, and the total mass content of titanium (Ti) and vanadium (V) in the dopant is 0.7% of the mass of ferrous sulfate. Glucose and PEG2000 are both carbon sources, with the added mass of glucose being 8% of the total mass of ferrous sulfate and 85wt% phosphoric acid, and the added mass of PEG2000 being 4% of the total mass of ferrous sulfate and 85wt% phosphoric acid.

[0240] Comparative Example 1 The comparative example is basically the same as Example 1, except that: The step of preparing the dopant in step 1 is excluded; In step 2, during the preparation of lithium iron phosphate materials: Replace the dopant in step 1) with titanium dioxide, and the mass content of titanium in titanium dioxide is 0.7% of the mass of iron phosphate.

[0241] Comparative Example 2 The comparative example is basically the same as Example 1, except that: The step of preparing the dopant in step 1 is excluded; In step 2, during the preparation of lithium iron phosphate materials: Replace the dopant in step 1) with ammonium metavanadate, in which the vanadium content is 0.7% of the mass of iron phosphate.

[0242] Comparative Example 3 The comparative example is basically the same as Example 1, except that: The step of preparing the dopant in step 1 is excluded; In step 2, during the preparation of lithium iron phosphate materials: Replace the dopant in step 1) with ammonium metavanadate and titanium dioxide in a molar ratio of 1:1. The total mass content of titanium (Ti) and vanadium (V) in the ammonium metavanadate and titanium dioxide dopant is 0.7% of the mass of iron phosphate.

[0243] II. Performance Testing 1. Appearance The positive electrode active materials prepared in each example and comparative example were tested using a scanning electron microscope (SEM) manufactured by Zeiss of Germany, model Supra 55.

[0244] Figure 2 This is a scanning electron microscope (SEM) image of the positive electrode active material prepared in Example 1. From... Figure 2 It can be seen that the lithium iron phosphate particles (i.e., positive electrode active materials) prepared in Example 1 have a relatively smooth and rounded surface and are composed of particle gradations of different sizes.

[0245] 2.Phase of matter The positive electrode active materials prepared in each example and comparative example were tested using an X-ray diffractometer (XRD) manufactured by Bruker in Germany.

[0246] The testing method is as follows: Before starting the sample test, ensure that the equipment has a suitable test program. The program settings refer to the following parameters: filter (Ni filter, placed in the front), Solar slit (0.04 rad), divergence slit (1°), light shield (20 mm), laser blade position (height), sample stage rotation (1 rpm), fluorescence elimination (7.5~75 keV). The scanning program settings are: start angle (15°), end angle (80°), step size (0.01), step time (25.5 s), and test time (12 min). Full spectrum fitting is performed according to the Rietveld method: the calculated spectrum is matched with the actual diffraction pattern (PDF #40-1499) using the least squares method. Rietveld refinement: instrument zero point and sample displacement, background function and peak shape parameters, cell parameters (a, b, c), atomic coordinates (x, y, z), placing Ti and V at the 4c ​​position of Fe (Wyckoff position), setting the total occupancy constraint (Fe + Ti + V = 1); after refining to obtain the precise coordinates (x, y, z) of each atom, the bond length (unit: Å) is calculated based on crystallographic formulas.

[0247] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the positive electrode active material prepared in Example 1. Figure 3It can be seen that the XRD pattern of the lithium iron phosphate material (i.e., the positive electrode active material) prepared in Example 1 is consistent with the standard lithium iron phosphate pattern (PDF#40-1499), with no impurity peaks, indicating that the lithium iron phosphate material prepared by this method is pure phase, and the refined data shows that there is a Ti-OV structure inside.

[0248] The bond lengths obtained from the XRD Rietveld refined data of Example 1 and Comparative Example 3 are compared in Table 1.

[0249] Table 1

[0250] As shown in Table 1, in Example 1, the Ti-O bond length (approximately 1.96 Å) and the VO bond length (approximately 1.97 Å) differ by only about 0.01 Å, essentially being the same. This indicates that Ti and V are bridged by O to form Ti-OV bridging bonds, and both are in similar coordination fields, exhibiting a Ti-OV structure. In contrast, in Comparative Example 3, the Ti-O bond length (approximately 2.02 Å) and the VO bond length (approximately 1.93 Å) differ by about 0.09 Å, indicating that Ti and V are in different local coordination environments within the crystal lattice.

[0251] 3. Particle size The volumetric particle sizes Dv50, Dv10, and Dv90 of the positive electrode active materials prepared in each example and comparative example were tested using a laser particle size analyzer (Malvern Master Size 2000). The test reference standard was GB / T19077-2016 / ISO13320:2009.

[0252] The test results are shown in Table 2 and Figure 4 As shown.

[0253] Figure 4 This is a particle size distribution diagram of the positive electrode active material prepared in Example 1. From... Figure 4 It can be seen that the particle size of the lithium iron phosphate material (i.e. the positive electrode active material) prepared in Example 1 is between 300nm and 5.2μm, and the particle size distribution shows a bimodal distribution with Dv50=1.282nm.

[0254] 4. Compacted density During the compression process under external force, as the powder moves and deforms, larger voids are filled, increasing the contact area between particles. This generates attractive forces between atoms and enhances the mechanical wedging effect between particles, thus forming a compact with a certain density and strength. 1g of the positive electrode active material powder prepared in each embodiment or comparative example is placed in a compaction mold of known diameter (model CATALOG#3619 manufactured by Carver, USA). The mold has two stainless steel sheets, each 0.13mm thick, at the top and bottom. The powder is placed in the middle, and a 3T pressure is applied using a compaction density meter (model UTM-7305 manufactured by Sansi Zongheng, China). The corresponding powder thickness is measured simultaneously, and the compaction density is calculated using the formula ρ=m / v. Specific procedures can be performed according to standard GB / T24533-2009.

[0255] The test results are shown in Table 2.

[0256] 5. Electrochemical performance The positive electrode active materials prepared in each embodiment and comparative example were used to fabricate positive electrode sheets and assembled into CR2430 coin cells. The electrochemical performance of each CR2430 coin cell was then tested. Specifically: The preparation method of the positive electrode sheet includes: mixing the positive electrode active material (i.e., the positive electrode active material prepared in each embodiment or comparative example), the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) in a ratio of positive electrode active material: Super P: PVDF = 95 wt%: 3 wt%: 2 wt%. Then, the mixture is added to N-methylpyrrolidone (NMP) and stirred until it reaches a uniform flowability, resulting in a positive electrode slurry with a solid content of 60%. Next, the positive electrode slurry is coated on one side of a 12 μm thick aluminum foil surface and dried in a forced-air drying oven at 80°C for 12 h. The dried electrode sheet is then punched into small round pieces with a diameter of 14 mm, which are the positive electrode sheets.

[0257] The method for preparing the CR2430 coin cell includes: using a 0.5mm thick lithium metal sheet as the negative electrode, an electrolyte of model LBC338A1 produced by Shenzhen Xinzhoubang Technology Co., Ltd. as the electrolyte, and a 0.5mm thick polypropylene film (PP film) as the separator, and assembling them with the positive electrode in an argon-filled glove box to form the CR2430 coin cell.

[0258] Electrochemical performance testing: The CR2430 button cell battery charge-discharge performance was tested using a CT-4008-5V50mA-164 battery testing system. The voltage range was 3.75V-2.0V. The charging process was as follows: 0.1C constant current and constant voltage charging to 3.75V cutoff, resting for 10 minutes, 0.1C constant current discharging to 2.0V cutoff (this value represents the 0.1C discharge capacity), resting for 10 minutes, 1C constant current and constant voltage charging to 3.75V cutoff, resting for 10 minutes, 1C constant current discharging to 2.0V cutoff (this value represents the 1C discharge capacity), and finally, 1C constant current discharging to 3.2V. The percentage of the 1C 3.2V plateau was calculated using the following formula: 1C 3.2V platform percentage = (platform capacity at 3.2V during 1C constant current discharge / 1C discharge capacity) 100%.

[0259] The electrochemical performance tests are shown in Table 2.

[0260] Table 2

[0261] As can be seen from Table 2, the positive electrode active materials prepared in each embodiment of this application have significant advantages in 1C discharge capacity and corresponding energy efficiency (1C 3.2V platform ratio) compared with the conventional doping methods of Comparative Examples 1-3, due to the use of dopants prepared by the preparation method of this application.

[0262] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0263] In the description of the embodiments of this application, technical terms such as "first", "second", "I", "II" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0264] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0265] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0266] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces), unless otherwise explicitly specified.

Claims

1. A positive electrode active material, characterized in that, include: The core, comprising the chemical formula LiFe 1-x-y Ti x V y The material is PO4, wherein 0.003≤x≤0.01, 0.003≤y≤0.01, and the core contains Ti-OV bridging bonds; An outer shell, which covers at least a portion of the outer surface of the core, the outer shell comprising a carbon layer.

2. The positive electrode active material according to claim 1, characterized in that, The Ti-OV bridging bond exists in the chemical formula LiFe. 1-x-y Ti x V y The interior of PO4 material; And / or, the Ti-OV bridging bond is obtained by copolymerization of a first solution, a second solution and a coupling agent, wherein the first solution contains -Ti-O- and the second solution contains metavanadate ions; And / or, the Ti and V doping is carried out in the chemical formula LiFe 1-x-y Ti x V y In the crystal lattice of PO4 materials; And / or, the Dv50 of the positive electrode active material is 800-1800 nm.

3. The positive electrode active material according to claim 2, characterized in that, The first solution is a solution formed by dissolving a titanium salt in a first solvent, wherein the titanium salt includes at least one of soluble titanium salts, and the first solvent includes at least one of an alcohol solvent and water; And / or, the second solution is a solution formed by dissolving metavanadate in a second solvent, wherein the metavanadate includes at least one of ammonium metavanadate and lithium metavanadate, and the second solvent includes at least one of water and 0.1-1 wt% ammonia water; And / or, the coupling agent comprises at least one of an organic ligand containing -OH and an organic ligand containing -COOH; optionally, the coupling agent comprises at least one of ethylene glycol, triethanolamine, glycerol, and terephthalic acid. And / or, the Dv50 of the positive electrode active material is 1000-1500 nm.

4. A method for preparing a positive electrode active material as described in any one of claims 1 to 3, characterized in that, include: The first solution, the second solution, and the coupling agent were copolymerized to obtain the dopant; The dopant includes the Ti-OV bridging bond; The first solution contains -Ti-O-, and the second solution contains metavanadate ions.

5. The preparation method according to claim 4, characterized in that, The first solution is a solution formed by dissolving a titanium salt in a first solvent, wherein the titanium salt includes at least one of soluble titanium salts, and the first solvent includes at least one of an alcohol solvent and water; And / or, the second solution is a solution formed by dissolving metavanadate in a second solvent, wherein the metavanadate includes at least one of ammonium metavanadate and lithium metavanadate, and the second solvent includes at least one of water and 0.1-1 wt% ammonia water; And / or, the coupling agent includes at least one of an organic ligand containing -OH and an organic ligand containing -COOH; optionally, the coupling agent includes at least one of ethylene glycol, triethanolamine, glycerol, and terephthalic acid.

6. The preparation method according to claim 4, characterized in that, The reaction temperature for the copolymerization reaction is from room temperature to 80°C, and can be selected as 50-70°C; And / or, the reaction time of the copolymerization reaction is 2-12 hours, optionally 2-6 hours; And / or, the pH of the copolymerization reaction is 4-7; And / or, the molar amount of the coupling agent participating in the copolymerization reaction is a mol, and the total molar amount of titanium and vanadium is b mol, wherein a and b satisfy: 1≤a / b≤5; And / or, the molar ratio of titanium in the first solution and vanadium in the second solution participating in the copolymerization reaction is x:y.

7. The preparation method according to any one of claims 4 to 6, characterized in that, The method for preparing the positive electrode active material further includes: The phosphorus source, iron source, lithium source, carbon source and the dopant are ground, spray-dried and sintered to obtain the positive electrode active material.

8. The preparation method according to claim 6, characterized in that, Based on the mass of the iron source, the total mass content of titanium and vanadium in the dopant is 0.2-1%, optionally 0.3-1%; And / or, the mass content of the carbon source is 5-15% of the mass of the iron source; And / or, the molar ratio of lithium in the lithium source to iron in the iron source is (1.01-1.10):1; And / or, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is (0.955-0.985):1; And / or, both the phosphorus source and the iron source include ferric phosphate, and when both the phosphorus source and the iron source are ferric phosphate, the ground material further includes a supplementary phosphorus source; optionally, the supplementary phosphorus source accounts for 0.2-1% of the molar ratio of the ferric phosphate. And / or, the sintering is carried out in a nitrogen or inert gas atmosphere; And / or, the sintering temperature is 720-820℃, and the sintering time is 5-10h.

9. A positive electrode sheet, characterized in that, It includes the positive electrode active material as described in any one of claims 1 to 3, or the positive electrode active material prepared by the preparation method as described in any one of claims 4 to 8.

10. A battery, characterized in that, Including the positive electrode sheet as described in claim 9.

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