Lithium iron phosphate material, preparation method and application thereof

Abstract

The application discloses a lithium iron phosphate material and a preparation method and application thereof. The lithium iron phosphate material comprises a plurality of lithium iron phosphate particles, the lithium iron phosphate particle comprises a coating layer and a core, and the coating layer at least partially covers the outer surface of the core; the core comprises a core body and a surface layer, and the surface layer at least partially covers the outer surface of the core body; wherein the core body of the lithium iron phosphate particle is doped with titanium elements; and the surface layer of the lithium iron phosphate particle is doped with vanadium elements.

Description

Technical Field

[0001] This application relates to the field of energy materials technology, and in particular to a lithium iron phosphate material, its preparation method and application. Background Technology

[0002] Lithium iron phosphate (LiFePO4), as a cathode material for lithium-ion batteries, possesses stable structure, high theoretical capacity, good cycle performance, abundant raw material sources, good safety performance, and environmental friendliness, making it the most promising cathode material for large-scale application in energy storage and power batteries. However, its theoretical capacity is only 170 mAh / g, which is relatively low, and its conductivity is poor, resulting in poor rate discharge performance. To address this issue, extensive research and development efforts have focused on developing high-capacity and high-conductivity lithium iron phosphate materials. However, the highest actual capacity of commercially available lithium iron phosphate materials is currently only around 160 mAh / g, which cannot meet the high energy density requirements of long-range electric vehicles.

[0003] One current development strategy for high-capacity lithium iron phosphate materials is to reduce the particle size, shorten the lithium-ion migration path, and thus improve capacity utilization. However, this comes at the cost of reduced powder compaction density, which, in the same volume of lithium battery, actually reduces volumetric energy density. Furthermore, as the number of cycles increases, the crystal structure of the cathode material undergoes continuous lithium-ion insertion and extraction, causing partial lattice distortion and microcracks. Combined with electrolyte corrosion, this leads to particle breakage, ultimately resulting in a sharp deterioration in the cycle performance of the lithium battery.

[0004] Therefore, it is necessary to develop a high-capacity lithium iron phosphate material with long cycle performance. Summary of the Invention

[0005] This application aims to at least partially address one of the technical problems in related technologies. Therefore, the purpose of this application is to provide a lithium iron phosphate material, its preparation method, and its application. This application prepares a lithium iron phosphate material by adjusting the proportion and distribution of raw materials with different particle sizes. The core of the material particles is doped with titanium, while the surface layer and the inner walls of the pores are doped with vanadium, which is beneficial for improving the diffusion capacity of lithium ions. Simultaneously, the surface layer of the particles can act as a protective layer, reducing the direct corrosion of the particle structure by the electrolyte and lowering the probability of particle breakage, thereby improving the cycle performance of lithium batteries.

[0006] In a first aspect, this application discloses a lithium iron phosphate material. According to an embodiment of this application, the lithium iron phosphate material comprises a plurality of lithium iron phosphate particles, each lithium iron phosphate particle comprising a coating layer and a core, the coating layer at least partially covering the outer surface of the core; the core comprises a core body and a surface layer, the surface layer at least partially covering the outer surface of the core body; wherein the core body of the lithium iron phosphate particle is doped with titanium; and the surface layer of the lithium iron phosphate particle is doped with vanadium.

[0007] According to embodiments of this application, different elements are doped into the core and surface of lithium iron phosphate particles to achieve different effects. Specifically, doping the core of the lithium iron phosphate particles with titanium not only improves the electrical conductivity of the lithium iron phosphate material but also enhances the diffusion capacity of lithium ions within it. Doping the surface of the lithium iron phosphate particles with vanadium serves as a protective layer, reducing the direct corrosion of the lithium iron phosphate material structure by the electrolyte and lowering the probability of breakage, thereby improving the chemical stability of the lithium iron phosphate material. Furthermore, the coating layer increases the electrical conductivity of the lithium iron phosphate material, enhances electron conduction, and helps improve the electrical conductivity of the lithium iron phosphate material, thus increasing the battery's discharge rate and power output.

[0008] In some embodiments of this application, the lithium iron phosphate material may also satisfy at least one of the following characteristics:

[0009] In some embodiments of this application, the lithium iron phosphate particles have a porous structure.

[0010] In some embodiments of this application, the porosity of the lithium iron phosphate particles is 10-20%.

[0011] In some embodiments of this application, vanadium is doped into the inner wall layer of the pore.

[0012] In some embodiments of this application, the core of the lithium iron phosphate particle includes pores, and except for the inner wall layer of the pores, the core of the lithium iron phosphate particle is not doped with vanadium.

[0013] In some embodiments of this application, the surface layer of the lithium iron phosphate particles has the general chemical formula LiFe. x1 Ti y1 V z PO4, where x1+y1+z=1 and 0.01≤y1≤0.05, 0.01≤z≤0.05.

[0014] In some embodiments of this application, the core of the lithium iron phosphate particle has the general formula LiFe x2 Ti y2PO4, where x2+y2=1 and 0.01≤y2≤0.05.

[0015] In some embodiments of this application, 0.02 ≤ z ≤ 0.05.

[0016] In some embodiments of this application, 0.02≤y2≤0.05.

[0017] In some embodiments of this application, 0.01≤y1≤0.03.

[0018] In some embodiments of this application, y = 0.03, 0.01 ≤ z ≤ 0.05.

[0019] In some embodiments of this application, y = 0.03, 0.01 ≤ y1 ≤ 0.05.

[0020] In some embodiments of this application, y = 0.03, 0.03 ≤ z ≤ 0.05.

[0021] In some embodiments of this application, y = 0.03, 0.01 ≤ y1 ≤ 0.03.

[0022] In some embodiments of this application, x1 and x2 may be the same or different.

[0023] In some embodiments of this application, the surface thickness of the lithium iron phosphate particles is 20nm-500nm.

[0024] In some embodiments of this application, the thickness of the inner wall layer of the hole is 20nm-500nm.

[0025] In some embodiments of this application, the coating layer of the lithium iron phosphate particles includes carbon, i.e., a carbon coating layer.

[0026] In some embodiments of this application, the core of the lithium iron phosphate particles further comprises carbon.

[0027] In some embodiments of this application, the volume average particle size Dv50 of the lithium iron phosphate particles is 3μm-7μm.

[0028] In some embodiments of this application, the surface layer of the lithium iron phosphate particles has a chemical formula including at least one of the following: LiFe 0.98 Ti 0.01 V 0.01 PO4, LiFe 0.97 Ti 0.01 V 0.02 PO4, LiFe 0.95 Ti 0.02 V 0.03 PO4, LiFe 0.93 Ti0.03 V 0.04 PO4 or LiFe 0.92 Ti 0.03 V 0.05 PO 4。

[0029] In some embodiments of this application, the core of the lithium iron phosphate particles has a chemical formula including at least one of the following: LiFe 0.99 Ti 0.01 PO4, LiFe 0.98 Ti 0.02 PO4, LiFe 0.97 Ti 0.03 PO4, LiFe 0.96 Ti 0.04 PO4 or LiFe 0.95 Ti 0.05 PO4.

[0030] In a second aspect of this application, a method for preparing the lithium iron phosphate material described in the first aspect is proposed. According to an embodiment of this application, the method includes: mixing a lithium source compound, an iron source compound, a titanium source compound, and a phosphorus source compound to obtain the core; and forming the surface layer and the coating layer on the surface of the core using a vanadium source compound and a carbon source compound to obtain the lithium iron phosphate material.

[0031] Therefore, by doping the core and surface of lithium iron phosphate particles with titanium and vanadium respectively, a unique lithium iron phosphate material can be obtained. In this lithium iron phosphate material, titanium doping in the core improves the material's conductivity and lithium-ion diffusion capacity, thereby improving battery performance and charge / discharge rate. Simultaneously, vanadium doping in the surface forms a protective layer, effectively mitigating electrolyte corrosion of the lithium iron phosphate material structure, reducing the risk of breakage, and extending battery cycle life. Furthermore, the coating layer formed using carbon source compounds increases the conductivity of the lithium iron phosphate material, enhances electron conduction, and helps improve the material's electrical conductivity, thereby increasing the battery's discharge rate and power output.

[0032] In some embodiments of this application, the method may also satisfy at least one of the following features:

[0033] In some embodiments of this application, the molar ratio of the iron source compound, lithium source compound, titanium source compound and phosphorus source compound is (0.95~0.99):1:(0.01~0.05):1.

[0034] In some embodiments of this application, the molar ratio of the iron source compound to the vanadium source compound is (0.95-0.99):(0.01-0.05).

[0035] In some embodiments of this application, the amount of carbon source compound added is 10% to 15% of the total mass of lithium source compound, iron source compound, titanium source compound and phosphorus source compound.

[0036] In some embodiments of this application, the lithium source compound includes at least one of lithium carbonate, lithium acetate, lithium hydroxide, lithium oxalate, dilithium hydroxide, and lithium nitrate.

[0037] In some embodiments of this application, the iron source compound includes at least one selected from ferric phosphate, ferric nitrate, ferric hydroxide, ferric chloride, ferric sulfate, ferrous oxalate, and ferric oxide.

[0038] In some embodiments of this application, the titanium source compound includes at least one of titanium dioxide and tetramethyl titanate.

[0039] In some embodiments of this application, the phosphorus source compound includes at least one of iron phosphate, phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0040] In some embodiments of this application, the vanadium source compound includes at least one of vanadium pentoxide and ammonium metavanadate.

[0041] In some embodiments of this application, the carbon source compound includes at least one selected from sucrose, glucose, soluble starch, urea, epoxy resin, polyvinyl alcohol, phenolic resin, carbon black, acetylene black, and citric acid.

[0042] In some embodiments of this application, the materials in the mixing process further include carbon source compounds.

[0043] In some embodiments of this application, prior to the formation of the surface layer and the coating layer, the core is further subjected to a first crushing process.

[0044] In some embodiments of this application, before obtaining the core, the mixture is further subjected to a first ball milling process and a first calcination process.

[0045] In some embodiments of this application, the formation of the surface layer and the coating layer on the surface of the core using vanadium source compound and carbon source compound is carried out by: subjecting the vanadium source compound, carbon source compound and the core to a second ball milling process; and subjecting the product of the second ball milling process to a second calcination process.

[0046] In some embodiments of this application, after the second roasting treatment, a second crushing treatment is further included in the second roasting product.

[0047] In some embodiments of this application, the first crushing process or the second crushing process is performed in a ball mill.

[0048] In some embodiments of this application, the first ball milling process or the second ball milling process is performed in a ball mill.

[0049] In some embodiments of this application, during the first ball milling process, the rotation speed is 1000-1500 r / min and the time is 18-23 h.

[0050] In some embodiments of this application, during the second ball milling process, the rotation speed is 1800-2200 r / min and the time is 15-20 h.

[0051] In some embodiments of this application, the temperature of the first calcination treatment is 350-400°C and the time is 3-5 hours.

[0052] In some embodiments of this application, the temperature of the second calcination treatment is 500–750°C, and the time is 5–10 hours.

[0053] In some embodiments of this application, the protective atmosphere includes nitrogen during the first and second roasting processes.

[0054] In some embodiments of this application, prior to the first calcination treatment and the second calcination treatment, the process further includes: spray drying the first ball-milled product and the second ball-milled product, respectively.

[0055] In some embodiments of this application, the inlet air temperature of the spray drying process is 200-250°C, and the outlet air temperature is ≤120°C.

[0056] In a third aspect of this application, the present invention provides a lithium iron phosphate material. According to an embodiment of this application, the lithium iron phosphate material is prepared by the method described in the second aspect.

[0057] Therefore, the lithium iron phosphate material of this application is composed of a core of lithium iron phosphate doped with titanium and a surface layer of lithium iron phosphate doped with vanadium. The titanium doping in the core improves the material's conductivity and lithium-ion diffusion capacity, thereby improving battery performance and charge / discharge rate. Simultaneously, the vanadium doping in the surface layer forms a protective layer, effectively mitigating electrolyte corrosion of the lithium iron phosphate material structure, reducing the risk of breakage, and extending battery cycle life. Furthermore, the coating layer increases the conductivity of the lithium iron phosphate material, enhances electron conduction, and helps improve the material's electrical conductivity, thereby increasing the battery's discharge rate and power output.

[0058] In a fourth aspect of this application, the present invention provides a positive electrode sheet. According to embodiments of this application, the positive electrode sheet comprises the lithium iron phosphate material described in the first or third aspect, or the lithium iron phosphate material prepared by the method described in the second aspect.

[0059] As mentioned above, the lithium iron phosphate material of this application has advantages such as high electrical conductivity, fast lithium-ion diffusion capability, and long cycle life. Therefore, these advantages enable the cathode sheet made of the lithium iron phosphate material to provide higher power density, faster charge and discharge rates, and longer service life, thereby providing a more reliable and efficient energy storage solution for battery applications.

[0060] In some embodiments of this application, the positive electrode further includes a current collector, and the lithium iron phosphate material is located on the surface of the current collector.

[0061] In a fifth aspect of this application, the present invention provides a battery. According to an embodiment of this application, the battery includes the positive electrode sheet described in the fourth aspect.

[0062] As mentioned above, the lithium iron phosphate material of this application has advantages such as high electrical conductivity, fast lithium-ion diffusion capability, and high cycle life. Therefore, these advantages enable batteries made from the lithium iron phosphate material to have high power density, high cycle stability, fast charging capability, and high safety.

[0063] In a sixth aspect of this application, the present invention provides an electrical device. According to an embodiment of this application, the electrical device includes the battery described in the fifth aspect.

[0064] Therefore, the electrical device has all the advantages of the battery, which will not be elaborated here.

[0065] 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

[0066] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0067] Figure 1 This is a schematic diagram of the cross-sectional structure of the lithium iron phosphate material of this application;

[0068] Figure 2 This is a particle size distribution diagram of the lithium iron phosphate material of Example 1 of this application;

[0069] Figure 3 The images show the surface and cross-sectional morphology of the lithium iron phosphate material in Experimental Example 1 of this application.

[0070] Figure 4 The images show the surface and cross-sectional morphology of the lithium iron phosphate material in Example 10 of this application.

[0071] Figure 5 The images show the surface and cross-sectional morphology of the lithium iron phosphate material in Comparative Example 1 of this application.

[0072] Figure description: 01 is the coating layer, 02 is the surface layer, 03 is the core, 04 is the inner wall layer of the pore, and 05 is the pore. Detailed Implementation

[0073] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0074] 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.

[0075] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0076] 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.

[0077] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0078] To prepare a high-capacity lithium iron phosphate material with long cycle performance, this application prepared a lithium iron phosphate material by adjusting the proportion and distribution of raw materials with different particle sizes. The core of the material particles is doped with titanium, and the surface and inner walls of the pores are doped with vanadium, which is beneficial to improving the diffusion ability of lithium ions. At the same time, the surface of the particles and the inner walls of the pores can act as a protective layer to reduce the direct corrosion of the particle structure by the electrolyte and reduce the probability of particle breakage, thereby improving the cycle performance of lithium batteries.

[0079] Specifically, this invention proposes a lithium iron phosphate material, a method for preparing the lithium iron phosphate material, a positive electrode, a battery, and an electrical device, which will be described in detail below.

[0080] Lithium iron phosphate materials

[0081] This application discloses a lithium iron phosphate material. According to an embodiment of this application, the lithium iron phosphate material comprises a plurality of lithium iron phosphate particles, each lithium iron phosphate particle comprising a coating layer and a core, the coating layer at least partially covering the outer surface of the core; the core comprises a core body and a surface layer, the surface layer at least partially covering the outer surface of the core body; wherein, the core body of the lithium iron phosphate particle is doped with titanium; and the surface layer of the lithium iron phosphate particle is doped with vanadium.

[0082] According to embodiments of this application, different elements are doped into the core and surface of lithium iron phosphate particles to achieve different effects. Specifically, doping the core of the lithium iron phosphate particles with titanium not only improves the electrical conductivity of the lithium iron phosphate material but also enhances the diffusion capacity of lithium ions within it. Doping the surface of the lithium iron phosphate particles with vanadium serves as a protective layer, reducing the direct corrosion of the lithium iron phosphate material structure by the electrolyte and lowering the probability of breakage, thereby improving the chemical stability of the lithium iron phosphate material. Furthermore, the coating layer increases the electrical conductivity of the lithium iron phosphate material, enhances electron conduction, and helps improve the electrical conductivity of the lithium iron phosphate material, thus increasing the battery's discharge rate and power output.

[0083] In this application, "a number" refers to one, two, or more. The lithium iron phosphate material of this application can be composed of a single lithium iron phosphate particle or two or more lithium iron phosphate particles.

[0084] In this application, "lithium iron phosphate particles" refers to particles with a coating layer and a core structure, wherein the core includes a core body and a surface layer, the core body is doped with titanium, and the surface layer is doped with vanadium; it also refers to small particles obtained by crushing by the method described in this application; "lithium iron phosphate material" refers to a material composed of several lithium iron phosphate particles.

[0085] In some embodiments of this application, the lithium iron phosphate particles have a porous structure with a porosity of 10-20%. Therefore, the porous structure provides a larger surface area, which is beneficial for electrolyte penetration and wetting, improves the contact between the electrolyte and the lithium iron phosphate particles, and enhances the efficiency of ion transport and reaction within the lithium iron phosphate particles, laying the foundation for improved battery performance and cycle life. Furthermore, the porous structure provides a certain degree of elasticity and space, mitigating the risk of stress concentration and structural damage to the lithium iron phosphate particles.

[0086] In some embodiments of this application, vanadium is also doped into the inner wall layer of the pores. This accelerates the lithium-ion migration rate while mitigating the direct corrosion of the lithium iron phosphate particle structure by the electrolyte, reducing the probability of particle breakage and thus improving the chemical stability of the lithium iron phosphate particles.

[0087] It should be noted that the pores exist in the core of the lithium iron phosphate particles. Although the coating layer covers the outer surface of the core, the pore structure can still be seen on the surface of the coating layer. This is because the thickness of the coating layer is generally only 2 to 5 nanometers, which is insufficient to fill the pores. Even if the carbon coating layer covers the pores, the electrolyte can still pass through the carbon coating layer and penetrate into the pores in the presence of the electrolyte.

[0088] The lithium iron phosphate particle structure diagram described in this application is as follows: Figure 1 As shown, 01 is the coating layer of the lithium iron phosphate particle, 02 is the surface layer of the lithium iron phosphate particle, 03 is the core of the lithium iron phosphate particle, 04 is the inner wall layer of the pore of the lithium iron phosphate particle, and 05 is the pore. The surface layer 02 and the inner wall layer 04 of the pore are doped with vanadium, and the core 03 is doped with titanium.

[0089] In some embodiments of this application, the core of the lithium iron phosphate particle includes pores. Except for the inner wall layer of the pores, the core of the lithium iron phosphate particle is not doped with vanadium; that is, vanadium is only present in the surface layer of the lithium iron phosphate particle and the inner wall layer of the pores. Doping vanadium only in the surface layer and the inner wall layer of the pores of the lithium iron phosphate particle avoids the formation of too many impurity phases due to simultaneous co-doping of vanadium and titanium, which would significantly affect the internal lithium iron phosphate lattice and lead to structural instability. Therefore, the lithium iron phosphate material of this application has good electrical conductivity and lithium-ion diffusion capability, and reduces the direct corrosion of its structure by the electrolyte, lowering the probability of lithium iron phosphate particle breakage, thereby improving the chemical stability of the lithium iron phosphate material.

[0090] It should be noted that the core of the lithium iron phosphate particles is doped with titanium, while vanadium is only present in the surface layer and the inner wall layer of the pores of the lithium iron phosphate particles.

[0091] In some embodiments of this application, the surface layer of the lithium iron phosphate particles has the general formula LiFe x1 Ti y1 V z PO4, where x1+y1+z=1 and 0.01≤y1≤0.05, 0.01≤z≤0.05. For example, 0.02≤z≤0.05, 0.03≤z≤0.05, where z can be 0.01, 0.02, 0.03, 0.04, or 0.05, and y1≤z. When z is 0.01, y1 is 0.01 and x1 is 0.98; when z is 0.02, y1 is 0.01 or 0.02 and x1 is 0.97 or 0.96; when z is 0.03, y1 is 0.01, 0.02 or 0.03 and x1 is 0.96, 0.95 or 0.94; when z is 0.04, y1 is 0.01, 0.02, 0.03 or 0.04 and x1 is 0.95, 0.94 or 0.93 or 0.92; when z is 0.05, y1 is 0.01, 0.02, 0.03, 0.04 or 0.05 and x1 is 0.94, 0.93 or 0.92 or 0.91 or 0.9. Therefore, the lithium iron phosphate material has good chemical stability, which can avoid direct corrosion of the lithium iron phosphate material structure by the electrolyte, reduce the probability of lithium iron phosphate material breakage, and thus improve the cycle life and long-term stability of the battery.

[0092] In some embodiments of this application, 0.01≤y1≤0.03.

[0093] In some embodiments of this application, the chemical formula of the surface layer of the lithium iron phosphate particles includes at least one of the following: LiFe 0.98 Ti 0.01 V 0.01 PO4, LiFe 0.97 Ti 0.01 V 0.02 PO4, LiFe 0.95 Ti 0.02 V 0.03 PO4, LiFe 0.93 Ti 0.03 V 0.04 PO4 or LiFe 0.92 Ti 0.03 V 0.05 PO 4。

[0094] In some embodiments of this application, the core of the lithium iron phosphate particle has the general formula LiFe x2 Ti y2PO4, where x2 + y2 = 1 and 0.01 ≤ y2 ≤ 0.05. For example, 0.01 ≤ y2 ≤ 0.04, 0.02 ≤ y2 ≤ 0.05, 0.02 ≤ y2 ≤ 0.04, where y2 can be 0.01, 0.02, 0.03, 0.04, or 0.05. When y2 is 0.01, x2 is 0.99; when y2 is 0.02, x2 is 0.98; when y2 is 0.03, x2 is 0.97; when y2 is 0.04, x2 is 0.96; and when y2 is 0.05, x2 is 0.95. Therefore, the lithium iron phosphate material has good electrical conductivity and lithium-ion diffusion capability. This means that lithium ions can migrate and transport more quickly within the lithium iron phosphate material, thereby improving the battery's charge / discharge rate and response performance.

[0095] In some embodiments of this application, the chemical formula of the core of the lithium iron phosphate particle includes at least one of the following: LiFe 0.99 Ti 0.01 PO4, LiFe 0.98 Ti 0.02 PO4, LiFe 0.97 Ti 0.03 PO4, LiFe 0.96 Ti 0.04 PO4 or LiFe 0.95 Ti 0.05 PO4.

[0096] In some embodiments of this application, y = 0.03, 0.01 ≤ z ≤ 0.05. For example, y = 0.03, 0.02 ≤ z ≤ 0.05; y = 0.03, 0.03 ≤ z ≤ 0.05. Specifically, y = 0.03, z = 0.01; y = 0.03, z = 0.02; y = 0.03, z = 0.03; y = 0.03, z = 0.04; y = 0.03, z = 0.05. Therefore, the lithium iron phosphate material not only has better chemical stability, but also better electrical conductivity and lithium-ion diffusion capability.

[0097] In some embodiments of this application, x1 and x2 may be the same or different.

[0098] In some embodiments of this application, the surface thickness of the lithium iron phosphate particles is 20nm-500nm.

[0099] In some embodiments of this application, the thickness of the inner wall layer of the hole is 20nm-500nm.

[0100] In some embodiments of this application, the coating layer of the lithium iron phosphate particles includes carbon, i.e., a carbon coating layer, which can increase the electrical conductivity of the lithium iron phosphate material and enhance the electron conduction ability. This helps to improve the conductivity of the lithium iron phosphate material and increase the discharge rate and power output of the battery.

[0101] In some embodiments of this application, the volume average particle size Dv50 of the lithium iron phosphate particles is 3μm-7μm. For example, 3.5μm-7μm, 4μm-7μm, 4.5μm-7μm, 4.5μm-6.5μm, 5μm-6.5μm, 5μm-6μm, etc.

[0102] In this application, the volume average particle size Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50%. For example, the volume average particle size Dv50 test method can refer to the standard GB / T 19077-2016 and be measured using a laser particle size analyzer (e.g., Malvern Master Size 3000).

[0103] Methods for preparing lithium iron phosphate materials

[0104] This application proposes a method for preparing the aforementioned lithium iron phosphate material. According to an embodiment of this application, the method includes: mixing a lithium source compound, an iron source compound, a titanium source compound, and a phosphorus source compound to obtain the core; and using a vanadium source compound and a carbon source compound to form the surface layer and the coating layer on the surface of the core to obtain the lithium iron phosphate material.

[0105] Therefore, this method allows for the doping of titanium and vanadium elements into the core and surface layers of lithium iron phosphate particles, respectively, resulting in a unique lithium iron phosphate material. In this material, titanium doping in the core improves the material's conductivity and lithium-ion diffusion capacity, thereby enhancing battery performance and charge / discharge rates. Simultaneously, vanadium doping in the surface layer forms a protective layer, effectively mitigating electrolyte corrosion of the lithium iron phosphate material structure, reducing the risk of breakage, and extending battery cycle life. Furthermore, the coating layer formed using carbon source compounds increases the conductivity of the lithium iron phosphate material, enhances electron conduction, and helps improve the material's electrical conductivity, ultimately increasing the battery's discharge rate and power output.

[0106] In some embodiments of this application, the molar ratio of the iron source compound, lithium source compound, titanium source compound, and phosphorus source compound is (0.95–0.99):1:(0.01–0.05):1. For example, (0.96–0.99):1:(0.01–0.04):1, (0.95–0.98):1:(0.02–0.05):1, (0.96–0.98):1:(0.02–0.04):1, specifically 0.99:1:0.01:1, 0.98:1:0.02:1, 0.97:1:0.03:1, 0.96:1:0.04:1, 0.95:1:0.05:1, 0.99:1:0.01:1. Therefore, by changing the molar ratio of the iron source compound to the titanium source compound within this range, the prepared lithium iron phosphate material can exhibit better electrical conductivity and enhanced lithium-ion diffusion capability. This means that lithium ions can migrate and transport more rapidly within the lithium iron phosphate material, thereby improving the battery's charge / discharge rate and response performance.

[0107] In some embodiments of this application, the molar ratio of the iron source compound to the vanadium source compound is (0.95–0.99):(0.01–0.05). For example, (0.95–0.98):(0.02–0.05), (0.95–0.97):(0.03–0.05), specifically 0.99:1:0.01:1, 0.98:1:0.02:1, 0.97:1:0.03:1, 0.96:1:0.04:1, 0.95:1:0.05:1, 0.99:1:0.01:1. Therefore, by changing the molar ratio of the iron source compound to the vanadium source compound within this range, the vanadium source compound can form a protective layer on the surface of the lithium iron phosphate particles, reducing the direct corrosion of the lithium iron phosphate particle structure by the electrolyte, reducing the probability of lithium iron phosphate particles breaking, thereby improving the chemical stability of lithium iron phosphate particles, and thus improving the cycle life and long-term stability of the battery.

[0108] In some embodiments of this application, the amount of the carbon source compound added is 10%-15% relative to the total mass of the iron source compound, lithium source compound, titanium source compound, and phosphorus source compound, for example, 10%, 11%, 12%, 13%, 14%, or 15%. This increases the electrical conductivity of the lithium iron phosphate material and enhances its electron conduction ability, which helps improve the conductivity of the lithium iron phosphate material and increase the battery's discharge rate and power output.

[0109] In some embodiments of this application, the materials in the mixing process may further include a carbon source compound. The amount of the carbon source compound added is 5%-8% relative to the total mass of the iron source compound, lithium source compound, titanium source compound, and phosphorus source compound, for example, 5%, 6%, 7%, or 8%. The role of the carbon source compound is to generate particles of a suitable size, preventing the particles from becoming too large.

[0110] In some embodiments of this application, the specific type of lithium source compound is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the lithium source compound may include, but is not limited to, at least one of lithium carbonate, lithium acetate, lithium hydroxide, lithium oxalate, dilithium hydroxide, and lithium nitrate.

[0111] In some embodiments of this application, the specific type of iron source compound is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the iron source compound may include, but is not limited to, at least one of ferric phosphate, ferric nitrate, ferric hydroxide, ferric chloride, ferric sulfate, ferrous oxalate, and ferric oxide.

[0112] In some embodiments of this application, the specific type of titanium source compound is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the titanium source compound may include, but is not limited to, at least one of titanium dioxide and tetramethyl titanate.

[0113] In some embodiments of this application, the specific type of phosphorus source compound is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the phosphorus source compound may include, but is not limited to, at least one of iron phosphate, phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0114] In some embodiments of this application, the specific type of vanadium source compound is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the vanadium source compound may include, but is not limited to, at least one of vanadium pentoxide and ammonium metavanadate.

[0115] In some embodiments of this application, the specific types of carbon source compounds are not particularly limited, and those skilled in the art can select them according to actual needs. As some specific examples, the carbon source compounds may include, but are not limited to, at least one of sucrose, glucose, soluble starch, urea, epoxy resin, polyvinyl alcohol, phenolic resin, carbon black, acetylene black, and citric acid.

[0116] In some embodiments of this application, in order to enable the core to fully contact the vanadium source compound and the carbon source compound, before forming the surface layer and the coating layer, the core is further subjected to a first crushing process to break it into smaller particles, so as to fully contact the vanadium source compound and the carbon source compound, thereby forming a protective layer on the surface of each particle, thus improving the stability of the particles and reducing the probability of the particles breaking in the electrolyte.

[0117] In some embodiments of this application, prior to obtaining the core, the mixture is further subjected to a first ball milling process, which is carried out in a ball mill. During the ball milling process, the kinetic-energized grinding balls move at high speed within a sealed container, which helps to achieve uniform dispersion of the material, promotes the collision and crushing of material particles, ensures the uniformity of material particle size, and thus improves the quality and performance of the final core.

[0118] In some embodiments of this application, the ball mill rotates at a speed of 1000–1500 r / min, and the milling time is 18–23 h. For example, the ball mill rotates at speeds of 1000 r / min, 1050 r / min, 1100 r / min, 1150 r / min, 1200 r / min, 1250 r / min, 1300 r / min, 1350 r / min, 1400 r / min, 1450 r / min, and 1500 r / min; and the milling time is 18 h, 19 h, 20 h, 21 h, 22 h, and 23 h.

[0119] In some embodiments of this application, after the first ball milling process and before obtaining the core, the process further includes subjecting the first ball milling product to a first calcination process. The calcination process allows the compounds in the material to react, forming a core with an olivine structure similar to that of lithium iron phosphate.

[0120] In some embodiments of this application, the temperature of the first calcination treatment is 350–400°C, the time is 3–5 hours, and the protective atmosphere includes nitrogen. For example, the temperature of the first calcination treatment is 350°C, 355°C, 360°C, 365°C, 370°C, 375°C, 380°C, 385°C, 390°C, 395°C, or 400°C; and the time is 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours.

[0121] In some embodiments of this application, the formation of the surface layer and coating layer on the core using vanadium source compounds and carbon source compounds is carried out in the following manner: the vanadium source compound, carbon source compound, and core are subjected to a second ball milling treatment; the product of the second ball milling treatment is subjected to a second calcination treatment. The purpose of the second ball milling treatment is to ensure uniform dispersion of the core, vanadium source compound, and carbon source compound, guaranteeing the homogeneity of the three during the second calcination. The purpose of the second calcination is to form a protective surface layer and coating layer on the surface of the core, and to further promote the fusion and growth of small particles formed during the first calcination treatment and / or the small particles formed by the added vanadium source compound and carbon source compound under calcination to form larger particles under high temperature.

[0122] In some embodiments of this application, the second ball milling process is performed in a ball mill with a rotational speed of 1800–2200 r / min and a milling time of 15–20 h. For example, the rotational speed of the ball mill is 1800 r / min, 1850 r / min, 1900 r / min, 1950 r / min, 2000 r / min, 2050 r / min, 2100 r / min, 2150 r / min, or 2200 r / min; and the milling time is 15 h, 16 h, 17 h, 18 h, 19 h, or 20 h.

[0123] In some embodiments of this application, the temperature of the second calcination treatment is 500℃~750℃, the time is 5~10h, and the protective atmosphere includes nitrogen. For example, the temperature of the second calcination treatment is 500℃~600℃, 530℃~580℃, and can be 500℃, 520℃, 530℃, 550℃, 580℃, 600℃, 630℃, 650℃, 680℃, 700℃, 730℃, or 750℃.

[0124] In some embodiments of this application, the temperature of the second calcination treatment is 500℃~600℃. By controlling the temperature, the degree of fusion of small particles can be controlled, thereby forming a porous structure inside the lithium iron phosphate particles. Therefore, it can not only increase the electrolyte wetting range and accelerate lithium ion migration, but also reduce the direct corrosion of the particle structure by the electrolyte and the probability of particle breakage, thus improving cycle performance.

[0125] In some embodiments of this application, after the second calcination treatment, a second crushing treatment is further performed on the product of the second calcination treatment. Therefore, the resulting lithium iron phosphate material can have a smaller size, which is beneficial for improving the material's reactivity, ion diffusion rate, and battery power density.

[0126] In some embodiments of this application, prior to the first and second calcination treatments, the process further includes: spray drying the first ball-milled product and the second ball-milled product, respectively, wherein the inlet air temperature of the spray drying treatment is 200–250°C, the outlet air temperature is ≤120°C, and the spray drying time is 5–30 seconds. Therefore, the solvent can be rapidly evaporated and removed from the solution, and particle agglomeration can be prevented, thereby obtaining a uniformly dispersed powder.

[0127] Positive electrode plate, battery, electrical equipment

[0128] This invention proposes a positive electrode. According to embodiments of this application, the positive electrode comprises the lithium iron phosphate material described above or lithium iron phosphate material prepared by the method described above. As mentioned above, the lithium iron phosphate material of this application has advantages such as high conductivity, fast lithium-ion diffusion capability, and high cycle life. Therefore, these advantages enable the positive electrode made of the lithium iron phosphate material to provide higher power density, faster charge and discharge rates, and a longer service life.

[0129] In some embodiments of this application, the positive electrode further includes a current collector, and the lithium iron phosphate material is located on the surface of the current collector.

[0130] In some embodiments, the positive electrode may also optionally include a binder, a conductive agent, and other optional additives.

[0131] As an example, conductive agents may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, SuperP(SP), graphene, and carbon nanofibers.

[0132] As an example, the adhesive may include one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0133] This invention proposes a battery. According to an embodiment of this application, the battery includes the aforementioned positive electrode. As previously stated, the lithium iron phosphate material of this application has advantages such as high conductivity, fast lithium-ion diffusion capability, and high cycle life. Therefore, these advantages enable batteries made from the lithium iron phosphate material to possess advantages such as high power density, high cycle stability, fast charging capability, and high safety.

[0134] In some embodiments, the battery may include an electrolyte that serves to conduct ions. The electrolyte may include an electrolyte salt and a solvent.

[0135] As an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0136] As an example, the solvent may include one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0137] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0138] This invention proposes an electrical device. According to an embodiment of this application, the electrical device includes the battery described above. Compared with the prior art, this electrical device has advantages such as high power density, high cycle stability, fast charging capability, and high safety.

[0139] Specifically, the aforementioned electrical equipment can include, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0140] The embodiments of this application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0141] Example 1: Preparation of Lithium-ion Battery 1

[0142] Lithium-ion battery 1 is prepared using the following steps:

[0143] 1. Preparation of cathode materials

[0144] ① Lithium iron phosphate doped with titanium and carbon (using the chemical formula LiFe) x2 Ti y (PO4 / C indicates) according to LiFe 0.99 Ti 0.01 To achieve the required stoichiometric ratio in PO4 / C, lithium, iron, titanium, and phosphorus sources are weighed out. The amount of carbon source added is 7% relative to the total mass of the iron, lithium, titanium, and phosphorus sources. These are then uniformly mixed in a ball mill to obtain the raw material. An appropriate amount of pure water is added as a dispersant, and the raw material is ball-milled (ball-to-material ratio 4:1, speed 1300 r / min, time 20 h) to mill the raw material into particles of a suitable size. The lithium source is lithium carbonate or lithium hydroxide; the iron source is ferrous oxalate, ferric phosphate, or ferric oxide; the titanium source is titanium dioxide or tetramethyl titanate; the phosphorus source is lithium dihydrogen phosphate or ammonium dihydrogen phosphate; and the carbon source is glucose, sucrose, or citric acid.

[0145] ② The particles obtained after ball milling are spray-dried (pump speed 10mL / min, set temperature 200℃) to form powder with a certain particle size;

[0146] ③ The above powder is placed in a vacuum atmosphere sintering furnace for low-temperature calcination (protective atmosphere is nitrogen, 350℃, 5h). After calcination, the product after low-temperature calcination is crushed by ball mill to obtain pre-calcined material.

[0147] ④ A vanadium source and a carbon source are added to the pre-calcined material according to an atomic ratio of Fe:V = 0.99:0.01. The amount of carbon source added is 14% of the total mass of the iron, lithium, titanium, and phosphorus sources. The resulting mixture is then ball-milled again (ball-to-material ratio 4:1, rotation speed 2000 r / min, time 20 h) to mill the mixture into particles of a suitable size. The vanadium source is vanadium pentoxide.

[0148] ⑤ The ball-milled particles are spray-dried (pump speed 10 mL / min, set temperature 200℃) to form powder with a certain particle size;

[0149] ⑥ The above powder is placed in a vacuum atmosphere sintering furnace for high-temperature calcination (protective atmosphere is nitrogen, 550℃, 10h). After calcination, the product after high-temperature calcination is crushed using a ball mill to obtain high-pressure lithium iron phosphate material.

[0150] 2. Preparation of the positive electrode sheet

[0151] ① Weigh the corresponding amounts of high-pressure lithium iron phosphate material, conductive carbon black, and polyvinylidene fluoride prepared in step 1 into a mixing tank according to the mass ratio of 95%:2%:3%, and then add an appropriate amount of N-methylpyrrolidone (NMP) and stir for 5 hours to obtain a uniform slurry with suitable viscosity.

[0152] ② The slurry is evenly coated onto the aluminum foil by extrusion coating to form a coating layer, and then the positive electrode sheet is obtained after being fully dried in an oven.

[0153] 3. Manufacturing lithium-ion batteries

[0154] ① Weigh the corresponding amounts of artificial graphite, conductive carbon black, and sodium carboxymethyl cellulose in a mixing tank at a mass ratio of 95%:2.5%:2.5%, add an appropriate amount of deionized water, and stir for 6 hours to obtain a uniform slurry with suitable viscosity; then coat the slurry onto a copper foil with a thickness of 10μm, and place it in a vacuum oven to dry at 150℃ for 16 hours to obtain a negative electrode sheet;

[0155] ② The positive electrode sheet prepared in step 2 and the negative electrode sheet prepared in the above steps are placed in a press for pressing, and then a punch is used to cut Φ15mm positive electrode discs and Φ18mm negative electrode discs respectively.

[0156] ③ The positive electrode wafer and the negative electrode wafer are placed in a glove box filled with argon protective atmosphere for battery assembly. 1 mol / L lithium hexafluorophosphate is dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in a molar ratio of 1:1, and the resulting solution is used as the electrolyte. The positive electrode wafer, the negative electrode wafer, the polyethylene separator, and other components are assembled together, and then the electrolyte is injected to finally obtain lithium-ion battery 1.

[0157] Example 2: Lithium-ion battery 2

[0158] The lithium-ion battery 2 was prepared according to the method described in Example 1, except that in step 1 of preparing the positive electrode material, the method was followed according to LiFe 0.98 Ti 0.02 The required stoichiometric ratio for PO4 / C is determined by weighing out the lithium source, iron source, titanium source, phosphorus source, and carbon source.

[0159] Example 3: Lithium-ion battery 3

[0160] The lithium-ion battery 3 was prepared according to the method described in Example 1, except that in step 1 of preparing the positive electrode material, the method was followed according to LiFe 0.97 Ti 0.03 The required stoichiometric ratio for PO4 / C is determined by weighing out the lithium source, iron source, titanium source, phosphorus source, and carbon source.

[0161] Example 4: Lithium-ion battery 4

[0162] The lithium-ion battery 4 was prepared according to the method described in Example 1, except that in step 1 of preparing the positive electrode material, the method was followed according to LiFe 0.96 Ti 0.04 The required stoichiometric ratio for PO4 / C is determined by weighing out the lithium source, iron source, titanium source, phosphorus source, and carbon source.

[0163] Example 5: Lithium-ion battery 5

[0164] The lithium-ion battery 5 was prepared according to the method described in Example 1, except that in step 1 of preparing the positive electrode material, the method was followed according to LiFe 0.95 Ti 0.05 The required stoichiometric ratio for PO4 / C is determined by weighing out the lithium source, iron source, titanium source, phosphorus source, and carbon source.

[0165] Example 6: Lithium-ion battery 6

[0166] Lithium-ion battery 6 is prepared according to the method described in Example 1, with the difference that: 1) in step 1 of preparing the positive electrode material, according to LiFe 0.97 Ti 0.03 1) Weigh the lithium source, iron source, titanium source, phosphorus source and carbon source according to the required stoichiometric ratio in PO4 / C; 2) In step 4 of preparing the cathode material, add the vanadium source according to the atomic ratio Fe:V = 0.98:0.02.

[0167] Example 7: Lithium-ion battery 7

[0168] The lithium-ion battery 7 was prepared according to the method described in Example 1, with the difference that: 1) in step 1 of preparing the positive electrode material, according to LiFe 0.97 Ti 0.03 1) Weigh out the lithium source, iron source, titanium source, phosphorus source and carbon source according to the required stoichiometric ratio in PO4 / C; 2) In step 4 of preparing the cathode material, add the vanadium source according to the atomic ratio Fe:V = 0.97:0.03.

[0169] Example 8: Lithium-ion battery 8

[0170] Lithium-ion battery 8 was prepared according to the method described in Example 1, with the difference being: 1) in step 1 of preparing the positive electrode material, according to LiFe 0.97Ti 0.03 1) Weigh out the lithium source, iron source, titanium source, phosphorus source and carbon source according to the required stoichiometric ratio in PO4 / C; 2) In step 4 of preparing the cathode material, add the vanadium source according to the atomic ratio Fe:V = 0.96:0.04.

[0171] Example 9: Lithium-ion battery 9

[0172] Lithium-ion battery 9 was prepared according to the method described in Example 1, with the difference being: 1) in step 1 of preparing the positive electrode material, according to LiFe 0.97 Ti 0.03 1) Weigh the lithium source, iron source, titanium source, phosphorus source and carbon source according to the required stoichiometric ratio in PO4 / C; 2) In step 4 of preparing the cathode material, add the vanadium source according to the atomic ratio Fe:V = 0.95:0.05.

[0173] Example 10: Lithium-ion battery 10

[0174] The lithium-ion battery 10 was prepared according to the method described in Example 1, except that the high-temperature calcination temperature was 600°C.

[0175] Example 11: Lithium-ion battery 11

[0176] The difference between Example 11 and Example 1 is that in Example 11, the titanium source compound and the vanadium source compound are simultaneously mixed in step 1 to prepare lithium iron phosphate material. The specific process for preparing the cathode material is as follows:

[0177] ①According to LiFe 0.99 Ti 0.01 To prepare PO4 / C, the required stoichiometric ratio of lithium, iron, titanium, phosphorus, and carbon sources are weighed out, with the carbon source accounting for 10% of the total mass of the iron, lithium, titanium, and phosphorus sources. A vanadium source is then weighed out according to an atomic ratio of Fe:V = 0.99:0.01. The lithium, iron, titanium, phosphorus, carbon, and vanadium sources are uniformly mixed in a ball mill to obtain the raw material. An appropriate amount of pure water is then added as a dispersant, and the raw material is ball-milled (ball-to-material ratio 4:1, speed 1300 r / min, time 20 h) to mill the raw material into particles of a suitable size. The lithium source is lithium carbonate or lithium hydroxide; the iron source is ferrous oxalate, ferric phosphate, or ferric oxide; the titanium source is titanium dioxide or tetramethyl titanate; the phosphorus source is lithium dihydrogen phosphate or ammonium dihydrogen phosphate; and the carbon source is glucose, sucrose, or citric acid.

[0178] ② The ball-milled particles are spray-dried (pump speed 10mL / min, set temperature 200℃) to form powder with a certain particle size;

[0179] ③ The above powder is placed in a vacuum atmosphere sintering furnace for low-temperature calcination (protective atmosphere is nitrogen, 350℃, 5h). After calcination, the product after low-temperature calcination is crushed by ball mill to obtain pre-calcined material.

[0180] ④ Spray dry the pre-burned material (pump speed 10mL / min, set temperature 200℃) to form powder with a certain particle size;

[0181] ⑤ The above powder is placed in a vacuum atmosphere sintering furnace for high-temperature calcination (protective atmosphere is nitrogen, 550℃, 10h). After calcination, the product after high-temperature calcination is crushed using a ball mill to obtain lithium iron phosphate material.

[0182] The preparation of the negative electrode and the lithium-ion battery are the same as in Example 1, and a lithium-ion battery 11 is obtained.

[0183] Comparative Example 1: Lithium-ion battery 12

[0184] The difference between Comparative Example 1 and Example 1 is that no vanadium source compound was added in Comparative Example 1. The specific process is as follows:

[0185] The lithium-ion battery 12 is prepared using the following steps:

[0186] 1. Preparation of cathode materials

[0187] ①According to LiFe 0.99 Ti 0.01 To prepare PO4 / C, the required stoichiometric ratio of lithium, iron, titanium, phosphorus, and carbon sources is determined by weighing out the following materials: the carbon source is 10% of the total mass of the iron, lithium, titanium, and phosphorus sources. These materials are then uniformly mixed in a ball mill to obtain the raw material. An appropriate amount of pure water is added as a dispersant, and the raw material is ball-milled (ball-to-material ratio 4:1, speed 1300 r / min, time 20 h) to achieve appropriately sized particles. The lithium source is lithium carbonate or lithium hydroxide; the iron source is ferrous oxalate, ferric phosphate, or ferric oxide; the titanium source is titanium dioxide or tetramethyl titanate; the phosphorus source is lithium dihydrogen phosphate or ammonium dihydrogen phosphate; and the carbon source is glucose, sucrose, or citric acid.

[0188] ② The ball-milled particles are spray-dried (pump speed 10mL / min, set temperature 200℃) to form powder with a certain particle size;

[0189] ③ The above powder is placed in a vacuum atmosphere sintering furnace for low-temperature calcination (protective atmosphere is nitrogen, 350℃, 5h). After calcination, the product after low-temperature calcination is crushed by ball mill to obtain pre-calcined material.

[0190] ④ Spray dry the pre-burned material (pump speed 10mL / min, set temperature 200℃) to form powder with a certain particle size;

[0191] ⑤ The above powder is placed in a vacuum atmosphere sintering furnace for high-temperature calcination (protective atmosphere is nitrogen, 600℃, 10h). After calcination, the product after high-temperature calcination is crushed using a ball mill to obtain lithium iron phosphate material.

[0192] 2. Preparation of the positive electrode sheet

[0193] ① Weigh the corresponding amounts of high-pressure lithium iron phosphate material, conductive carbon black, and polyvinylidene fluoride prepared in step 1 into a mixing tank according to the mass ratio of 95%:2%:3%, and then add an appropriate amount of N-methylpyrrolidone (NMP) and stir for 5 hours to obtain a uniform slurry with suitable viscosity.

[0194] ② The slurry is evenly coated onto the aluminum foil by extrusion coating to form a coating layer, and then the positive electrode sheet is obtained after being fully dried in an oven;

[0195] 3. Manufacturing lithium-ion batteries

[0196] ① Weigh the corresponding amounts of artificial graphite, conductive carbon black, and sodium carboxymethyl cellulose in a mixing tank at a mass ratio of 95%:2.5%:2.5%, add an appropriate amount of deionized water, and stir for 6 hours to obtain a uniform slurry with suitable viscosity; then coat the slurry onto a copper foil with a thickness of 10μm, and place it in a vacuum oven to dry at 150℃ for 16 hours to obtain a negative electrode sheet;

[0197] ② The positive electrode sheet prepared in step 2 and the negative electrode sheet prepared in the above steps are placed in a press for pressing, and then a punch is used to cut Φ15mm positive electrode discs and Φ18mm negative electrode discs respectively.

[0198] ③ The positive electrode wafer and the negative electrode wafer are placed in a glove box filled with argon protective atmosphere for battery assembly. 1 mol / L lithium hexafluorophosphate is dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in a molar ratio of 1:1, and the resulting solution is used as the electrolyte. The positive electrode wafer, the negative electrode wafer, the polyethylene separator, and other components are assembled together, and then the electrolyte is injected to finally obtain the lithium-ion battery 12.

[0199] Test Experiment

[0200] 1. Particle size distribution test

[0201] The particle size distribution of the lithium iron phosphate material prepared in Example 1 was measured using a laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000) according to the laser diffraction method for particle size distribution (GB / T19077-2016). The experimental results are as follows: Figure 2As shown, it can be seen that the lithium iron phosphate material of the present invention has a particle size Dv50 of about 5 to 6 μm by adjusting the proportion and distribution of raw materials with different particle sizes.

[0202] 2. Powder compaction test

[0203] Using a powder compaction tester (model LD43.305) from Shanghai Lisheng Company, the powder compaction density of lithium iron phosphate materials prepared according to the methods described in Examples 1 to 11 and Comparative Example 1 was measured under a pressure of 3 kN, in accordance with the standard method GBT 24533-2019. The experimental results are shown in Table 1.

[0204] 3. Rate discharge capacity test

[0205] At 25°C, the lithium-ion batteries 1 to 12 prepared in the above examples and comparative examples were charged to 3.75V at a rate of 0.5C and then discharged to 2.5V at a rate of 0.5C. The discharge capacity at this time was recorded. Then, they were charged to 3.75V at a rate of 1C and then discharged to 2.5V at a rate of 1C. The discharge capacity at this time was recorded. The experimental results are shown in Table 1.

[0206] 4. Cyclic capacity retention test

[0207] At 25°C, the lithium-ion batteries 1 to 12 prepared in the above examples and comparative examples were charged to 3.65V at a 1C rate and then discharged to 2.5V at a 1C rate. The capacity of the first cycle was taken as the initial capacity, and the capacity of the 250th cycle was divided by the initial capacity to obtain the retention rate value. The experimental results are shown in Table 1.

[0208] Table 1 shows that, compared with Comparative Example 1, the powder compaction, discharge capacity, and cycle capacity retention of Examples 1-11 are significantly improved.

[0209] From Examples 1 to 5, as the titanium doping amount in the core part of the material particles increases, the discharge capacity and cycle capacity first increase and then decrease. This is because the crystal structure of lithium iron phosphate materials requires a certain amount of element doping, while too much Ti will form some impurities, which is not conducive to the performance of the material properties. Therefore, the optimal titanium doping amount in the solid part of the material particles is y = 0.3.

[0210] Based on Examples 1 and 6-9, and with the optimal titanium doping amount (y = 0.3) in the core of the material particles, the vanadium content in the surface layer and inner wall of the pores of the material particles was increased. The results in the table show that the discharge capacity and cycle capacity initially increased and then decreased. Similarly, excessive vanadium doping can lead to the formation of some impurities, which is not conducive to the performance of the material properties. Therefore, the optimal vanadium doping amount in the surface layer and inner wall of the pores of the material particles is z = 0.4.

[0211] Compared to Example 11, which simultaneously added titanium and vanadium sources to prepare lithium iron phosphate material and lithium-ion battery 11, the lithium iron phosphate material prepared by adding titanium and vanadium sources in stages has better powder compaction. The prepared lithium-ion battery 8 has better discharge capacity and cycle capacity retention. This shows that only when titanium is doped in the core of the lithium iron phosphate material and vanadium is doped in the surface layer of the lithium iron phosphate material can the prepared lithium-ion battery have better cycle performance.

[0212] Table 1. Particle size distribution of lithium iron phosphate, powder compaction, and electrochemical test results of lithium-ion batteries.

[0213]

[0214]

[0215] 5. SEM (Scanning Electron Microscopy) Test

[0216] SEM analysis was performed on the lithium iron phosphate materials prepared in Example 1, Example 10, and Comparative Example 1, and the experimental results are as follows: Figure 3 , Figure 4 and Figure 5 As shown, by Figure 3 The surface and cross-sectional morphology of the lithium iron phosphate material particles prepared in Example 1 show that the lithium iron phosphate material particles of this application are approximately spherical and have a porous structure. Using ImageJ software to statistically analyze the cross-sectional pore area ratio of particles (≥300 particles), the average area porosity is approximately 10-20%. Figure 4 As can be seen, the lithium iron phosphate material particles prepared by the method described in Example 10 have an approximately solid spherical structure. Compared with the method in Example 1, the method in Example 10 only changed the high-temperature calcination temperature, indicating that temperature is an important factor affecting the formation of porous structures.

[0217] Comparative Example 1 ( Figure 5 The lithium iron phosphate material prepared as shown in the figure has an irregular morphology and a solid structure with no surface structure.

[0218] The spherical porous structure formed in Example 1 is more conducive to increasing the electrolyte wetting range and accelerating lithium ion migration, thereby fully utilizing the material properties. Furthermore, the doping of titanium in the core of the particle and the doping of vanadium in the outer surface layer and the inner wall surface of the pores (which can be detected by X-ray photoelectron spectroscopy) further enhances the diffusion ability of lithium ions. At the same time, the special surface layer formed in Example 1 can serve as a protective layer, reducing the direct corrosion of the particle structure by the electrolyte and lowering the probability of particle breakage, thereby improving the cycle performance of the lithium battery.

[0219] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0220] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A lithium iron phosphate material, characterized in that, The device comprises several lithium iron phosphate particles, each lithium iron phosphate particle including a coating layer and a core, the coating layer at least partially covering the outer surface of the core; the core includes a core body and a surface layer, the surface layer at least partially covering the outer surface of the core body; in, The core of the lithium iron phosphate particles is doped with titanium. The surface of the lithium iron phosphate particles is doped with vanadium. The surface of the lithium iron phosphate particles has the general formula LiFe x1 Ti y1 V z PO4, where x1+y1+z=1 and 0.01≤y1≤0.05, 0.01≤z≤0.05; The core of the lithium iron phosphate particles has the general formula LiFe x2 Ti y2 PO4, where x2+y2=1 and 0.01≤y2≤0.

05.

2. The lithium iron phosphate material according to claim 1, characterized in that, The lithium iron phosphate particles have a porous structure; The porosity of the lithium iron phosphate particles is 10-20%.

3. The lithium iron phosphate material according to claim 2, characterized in that, Vanadium is doped into the inner wall layer of the pore.

4. The lithium iron phosphate material according to claim 1, characterized in that, The core of the lithium iron phosphate particle includes pores, and except for the inner wall layer of the pores, the core of the lithium iron phosphate particle is not doped with vanadium.

5. The lithium iron phosphate material according to claim 1, characterized in that, 0.02≤z≤0.05； 0.02≤y2≤0.05。 6. The lithium iron phosphate material according to claim 5, characterized in that, 0.01≤y1≤0.03。 7. The lithium iron phosphate material according to claim 1, characterized in that, The surface thickness of the lithium iron phosphate particles is 20nm-500nm; The coating layer of the lithium iron phosphate particles includes carbon.

8. A method for preparing the lithium iron phosphate material according to any one of claims 1 to 7, characterized in that, include: The core is obtained by mixing lithium source compound, iron source compound, titanium source compound and phosphorus source compound; The surface layer and the coating layer are formed on the surface of the core using vanadium source compounds and carbon source compounds to obtain the lithium iron phosphate material.

9. The method according to claim 8, characterized in that, The molar ratio of the iron source compound, lithium source compound, titanium source compound, and phosphorus source compound is (0.95~0.99):1:(0.01~0.05):1; The molar ratio of the iron source compound to the vanadium source compound is (0.95~0.99):(0.01~0.05); The amount of carbon source compound added is 10% to 15% of the total mass of lithium source compound, iron source compound, titanium source compound and phosphorus source compound.

10. A positive electrode plate, characterized in that, Includes the lithium iron phosphate material as described in any one of claims 1 to 7.

11. The positive electrode sheet according to claim 10, characterized in that, It further includes a current collector, wherein the lithium iron phosphate material is located on the surface of the current collector.

12. A battery, characterized in that, Includes the positive electrode sheet as described in claim 10 or 11.

13. An electrical appliance, characterized in that, Includes the battery as described in claim 12.

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