Iron source, lithium iron phosphate material and preparation method and application thereof

Abstract

The invention belongs to the technical field of new energy, and particularly relates to an iron source, a lithium iron phosphate material and a preparation method and application thereof. According to the invention, by designing the core-shell structure of the iron source Fe2O3 coated Fe3O4 and limiting the content of ferroferric oxide in the iron source, the iron source is applied to the preparation of the lithium iron phosphate material, an inner layer structure rich in microcracks and pores is easily obtained, the lithium ion transport kinetics and the wettability of an electrolyte are improved, and the rate and capacity performance of the lithium iron phosphate material are broken through.

Description

Technical Field

[0001] This application belongs to the field of new energy technology, specifically relating to an iron source, lithium iron phosphate material, its preparation method and application. Background Technology

[0002] Lithium iron phosphate cathode materials have become the mainstream choice in the field of power batteries due to their advantages such as high safety, long cycle life, and low cost. However, their inherent low ion diffusion rate and poor electronic conductivity make it difficult to balance compaction density with capacity utilization and rate performance: high compaction requires dense particle stacking, but this blocks ion transport channels; while increasing porosity to improve ion transport significantly reduces electrode compaction density and volumetric energy density, becoming a core bottleneck restricting the development of high-power batteries.

[0003] Currently, modifications to lithium iron phosphate cathode materials often only address one aspect. For example, increasing the conductive carbon layer on the surface (such as graphene or carbon nanotubes) can improve electronic conductivity, but this introduces low-density inactive materials, significantly reducing the electrode's volumetric energy density. Increasing sintering temperature or extending holding time to promote particle melting and growth improves compaction but can also lead to excessively large primary particle sizes, prolonged lithium-ion diffusion paths, difficulty in achieving maximum capacity, and the generation of magnetic impurities (such as Fe2P) at high temperatures, posing safety hazards. Furthermore, some studies have proposed using multi-stage particle size mixing, blending large, medium, and nanoparticles in proportion. This allows small particles to fill the gaps between large particles, increasing compaction density while leveraging the high capacity of small particles, achieving simultaneous increases in capacity and compaction. However, the finished product is difficult to mix uniformly to achieve good gradation, and it fails to address the shortcomings of large particles, such as poor electrolyte wetting and low capacity. In addition, blending iron sources with different activities, such as iron oxide red and ferrous oxalate, is expected to combine their respective compaction and capacity advantages. However, in actual production, the difference in reaction kinetics between different iron sources can lead to local overburning or underburning. Overburning will form Fe2P impurity phase, resulting in excessive magnetic foreign matter and affecting battery safety performance. Underburning is likely to lead to poor crystallinity, poor reaction kinetics, and poor rate performance of the finished product. Summary of the Invention

[0004] This application provides an iron source, lithium iron phosphate material, its preparation method and application, to solve the problem of difficulty in balancing capacity utilization, rate performance and compaction density of lithium iron phosphate material.

[0005] Therefore, this application provides the following technical solution: In a first aspect, this application provides an iron source with a core-shell structure, the inner layer comprising Fe2O3 and the outer shell comprising Fe3O4, wherein the mass percentage of Fe3O4 is 65%-75% based on the mass of the iron source.

[0006] In one optional embodiment, the Fe3O4 content is 67%-73% by mass, based on the mass of the iron source; And / or, the Fe2O3 mass percentage content is 25%-35%, optionally 27%-33%.

[0007] Secondly, this application provides a method for preparing the above-mentioned iron source, comprising the following steps: S1, Iron oxide is etched using an etchant to obtain the precursor; The etching agent includes at least one of ammonium maleate, ammonium oxalate, citric acid, malic acid, and ascorbic acid. S2, the obtained precursor is sintered in the presence of a reducing agent.

[0008] In one optional embodiment, in S1, the etching temperature is 40-90°C and the etching time is 0.5-4h; And / or, the mass concentration of the etchant is 10%-30%; And / or, in S2, the reducing substance includes at least one of a solid reducing substance and a gaseous reducing substance.

[0009] In one optional embodiment, in S2, the sintering temperature is 300-500°C and the sintering time is 1-4 hours; And / or, in S2, the solid reducing substance includes a first carbon source, the amount of which accounts for 6%-10% of the precursor mass; And / or, the first carbon source includes at least one of sucrose, glucose, starch, and citric acid; And / or, the sintering atmosphere is at least one of nitrogen, argon, and helium; And / or, the gaseous reducing substance includes a reducing gas, the volume percentage of which is 5%-10%; optionally, the reducing gas includes at least one of hydrogen or carbon monoxide.

[0010] In an optional embodiment, in S1, the iron oxide comprises large particles with a particle size Dv50 of 1-5 μm and small particles with a particle size Dv50 of 100-600 nm. Optionally, the large and small particles are etched and sintered separately to obtain large-particle iron sources and small-particle iron sources, respectively.

[0011] In one alternative implementation, for large iron oxide particles, the processing conditions satisfy at least one of the following: (1) The etching temperature is 40-60℃ and the etching time is 2-4h; (2) The mass concentration of the etching agent is 10%-20%; (3) The etching agent includes at least one of ammonium maleate, citric acid and malic acid; (4) The sintering temperature is 400-500℃ and the sintering time is 2-4h.

[0012] In one optional embodiment, for iron oxide particles, the treatment conditions satisfy at least one of the following: (1) The etching temperature is 60-90℃ and the etching time is 0.5-1.5h; (2) The mass concentration of the etching agent is 20%-30%; (3) The etching agent includes at least one of ammonium oxalate and ascorbic acid; (4) The sintering temperature is 300-400℃ and the sintering time is 1-2h.

[0013] Thirdly, a lithium iron phosphate material is provided, comprising a core and a carbon coating layer located on at least a portion of the surface of the core; the core comprises lithium iron phosphate. The compaction density of the lithium iron phosphate material is ≥2.55 g / cm³. 3 XRD diffraction peak intensity I (020) / I (200) ≥2.9; BET is 10-15m 2 / g.

[0014] In one optional embodiment, the carbon coating layer comprises 0.5%-5% by mass, optionally 1%-3%, based on the mass of the lithium iron phosphate material. And / or, the compacted density of the lithium iron phosphate material is 2.55-2.65 g / cm³. 3 XRD diffraction peak intensity I (020) / I (200) It ranges from 2.9 to 3.2; And / or, the iron source used to prepare the lithium iron phosphate material is the iron source described above or the iron source prepared by the preparation method described above.

[0015] Fourthly, a method for preparing the above-mentioned lithium iron phosphate material is provided, comprising the following steps: S11, mix iron source, lithium source, phosphorus source, second carbon source, additives and crystal face inducer of different particle sizes, and slurry to obtain mixed slurry; Wherein, the iron source is the iron source described above or the iron source prepared by the preparation method described above; The amount of the crystal plane inducer added is 0.2%-0.8% of the iron source mass; S12, the resulting mixed slurry is spray-dried and sintered.

[0016] In one alternative embodiment, the Li / Fe molar ratio in the mixed slurry is 1.0-1.1, and the Fe / P molar ratio is 0.95-0.99. And / or, the amount of the additive added is 0-2.0% of the mass of the iron source; And / or, the amount of the second carbon source added accounts for 10%-35% of the mass of the iron source; And / or, in the iron source, the mass ratio of large-particle iron source to small-particle iron source is 1-9:1; And / or, the solid content of the mixed slurry is 15wt%-45wt%.

[0017] In an optional embodiment, in S11, the large-particle iron source and the small-particle iron source are respectively mixed with the lithium source, the phosphorus source, the second carbon source, the additive, and the crystal surface inducer, slurryed, and ground to obtain large-particle slurry and small-particle slurry, and then mixed to obtain a mixed slurry. Optionally, during the preparation of the large particle slurry, the grinding speed is 500 rpm to 2000 rpm; the grinding time is 3 min to 30 min; and the slurry particle size Dv50 is 0.8 μm to 2.5 μm. Optionally, during the preparation of the small particle slurry, the grinding speed is 500rpm-2000rpm; the grinding time is 0.5h-3h, and the slurry particle size Dv50 is 100nm-500nm.

[0018] In an optional embodiment, in S12, the sintering includes: holding at 250℃-400℃ for 3h-5h; holding at 550℃-600℃ for 1h-3h; holding at 630℃-680℃ for 7h-10h; and holding at 720℃-750℃ for 1h-3h. And / or, the sintering atmosphere is at least one of nitrogen, argon, and helium; And / or, after sintering, a pulverization step is also included, pulverizing the product to a particle size Dv50 of 0.8μm-3.0μm; And / or, the inlet air temperature of the spray dryer is 180-240℃, the outlet air temperature is 80-150℃, and the feed rate is 0.5-5L / h.

[0019] In one optional embodiment, the lithium source includes at least one of lithium carbonate, lithium phosphate, lithium oxalate, lithium dihydrogen phosphate, and lithium hydroxide. And / or, the phosphorus source includes at least one of monoammonium phosphate, lithium phosphate, lithium dihydrogen phosphate, and phosphoric acid; And / or, the second carbon source includes at least one of sucrose, starch, glucose, citric acid, cyclodextrin, maltose, polyethylene glycol, polyvinylpyrrolidone, acetylene black, Ketjen black, and graphene; And / or, the additive includes at least one of titanium dioxide, magnesium oxide, niobium oxide, and aluminum oxide; And / or, the crystal plane inducer includes at least one of lithium zirconate and lithium titanate.

[0020] Fifthly, a secondary battery is provided, comprising the lithium iron phosphate material described above or the lithium iron phosphate material prepared by the above preparation method.

[0021] Sixthly, an electrical device is provided, including the aforementioned secondary battery.

[0022] The technical solution of this application has the following advantages: The iron source provided in this application has a core-shell structure with an inner layer comprising Fe2O3 and an outer shell comprising Fe3O4. The Fe3O4 content is 65%-75% by mass of the iron source.

[0023] This application, through the design of the Fe2O3@Fe3O4 core-shell structure of the iron source and the limitation of the content of iron tetroxide in the iron source, uses it in the preparation of lithium iron phosphate materials, which easily obtains an inner layer structure rich in microcracks and pores, improves lithium-ion transport dynamics and electrolyte wettability, and breaks through the rate and capacity performance of lithium iron phosphate materials.

[0024] 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

[0025] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a SEM image of the lithium iron phosphate material obtained in Example 1 of this application; Figure 2 This is the XRD pattern of the lithium iron phosphate material obtained in Example 1 of this application; Figure 3 This is a SEM image of the cross-section of the large-particle iron source obtained in Example 1 of this application. Detailed Implementation

[0027] 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.

[0028] 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 belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms “comprising” and “having” and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0029] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0030] 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.

[0031] 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.

[0032] 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, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0033] 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).

[0034] As described in the background section, existing lithium iron phosphate materials struggle to simultaneously achieve optimal capacity utilization, rate performance, and compaction density. For instance, existing patent literature discloses a method for preparing graphene-coated lithium iron phosphate cathode materials. Graphene coating effectively controls grain growth, and its excellent conductivity accelerates the electron migration rate of the composite material, effectively improving the conductivity of the electrode material. However, the graphene carbon source used in this method is expensive, making industrial application difficult, and it fails to improve the compaction density of the finished product.

[0035] Another patent document discloses a method for preparing lithium iron phosphate cathode materials by mixing iron phosphate and iron oxide as an iron source. This method combines the high capacity of the iron phosphate process with the high compaction of the iron oxide process. Under appropriate mixing ratios, it can effectively improve the compaction density of the material and ensure the high capacity of the finished product. However, this process involves iron phosphate, which has a high unit price, resulting in high production costs. Furthermore, physical mixing can easily lead to problems such as localized inhomogeneity and fluctuations in product performance.

[0036] To address the problems existing in the aforementioned related technologies, according to a first aspect of this application, an iron source is provided, wherein the microstructure of the iron source is a core-shell structure, the inner layer comprising Fe2O3 and the outer shell comprising Fe3O4, and the mass percentage content of Fe3O4 is 65%-75% based on the mass of the iron source.

[0037] As an example, the mass percentage of Fe3O4 in the iron source can be 65%, 67%, 69%, 70%, 72%, 74%, 75%, or within any of the above values.

[0038] Based on the aforementioned technical means, this application, through the design of the Fe2O3@Fe3O4 core-shell structure of the iron source and the limitation of the Fe3O4 content in the iron source, utilizes it in the preparation of lithium iron phosphate materials. This easily yields an inner structure rich in microcracks and pores, improving lithium-ion transport kinetics and electrolyte wettability, thus overcoming the rate and capacity performance limitations of lithium iron phosphate materials. If the mass percentage of Fe3O4 is less than 65%, it leads to excessive internal porosity, reducing the compaction density of the finished product; if the mass percentage of Fe3O4 is greater than 75%, it results in a lower internal porosity, making lithium-ion transport to the interior difficult and deteriorating rate performance.

[0039] In one optional embodiment, the Fe3O4 content is 67%-73% by mass, based on the mass of the iron source; And / or, the Fe2O3 mass percentage content is 25%-35%, optionally 27%-33%.

[0040] As an example, the mass percentage of Fe2O3 may be 25%, 27%, 29%, 30%, 32%, 34%, 35%, or within any of the above values.

[0041] Based on the above technical means, by limiting the content of ferric oxide and ferric oxide in the iron source, the electrical performance of lithium iron phosphate materials prepared from the iron source can be further improved, achieving a better balance among various properties.

[0042] According to another aspect of this application, a method for preparing the above-mentioned iron source is provided, comprising the following steps: S1, Iron oxide is etched using an etchant to obtain the precursor; The etching agent includes at least one of ammonium maleate, ammonium oxalate, citric acid, malic acid, and ascorbic acid. S2, the obtained precursor is sintered in the presence of a reducing agent.

[0043] Based on the aforementioned technical methods, the iron oxide raw material (iron oxide red raw material) is first pretreated with an etchant to construct a highly porous Fe2O3@FeOOH core-shell structure in situ on the iron oxide red surface. Subsequently, by mixing with a first carbon source, sintering induces the directional transformation of the iron source, forming a Fe2O3@Fe3O4 core-shell structure. During sintering, the outer Fe3O4 layer, with its highly symmetric crystal structure, forms a dense spherical outer layer, significantly improving particle size distribution. The inner Fe2O3 layer inherits its porous structure, enhancing electrolyte wettability. This method is simple to operate, does not use expensive raw materials, and is easy to promote and apply in the future.

[0044] In one optional embodiment, in S1, the etching temperature is 40-90°C and the etching time is 0.5-4h; As an example, the etching temperature can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or within any range of the above values; the etching time can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, or within any range of the above values.

[0045] In one optional embodiment, the mass concentration of the etchant is 10%-30%. As an example, the mass concentration of the etchant can be 10%, 12%, 14%, 15%, 17%, 19%, 20%, 22%, 24%, 25%, 27%, 29%, 30%, or within any range of the above values. In this application, the solvent in the etchant is water.

[0046] Based on the above technical means, this application can achieve a uniform and controllable etching effect on particles of different sizes by limiting the etching temperature, etching time and etchant concentration, thereby obtaining a high-porosity Fe2O3@FeOOH core-shell structure.

[0047] In one optional embodiment, in S2, the reducing substance includes at least one of a solid reducing substance and a gaseous reducing substance; In one optional embodiment, in S2, the sintering temperature is 300-500°C and the sintering time is 1-4 hours; As an example, the sintering temperature can be 300℃, 350℃, 400℃, 450℃, 500℃, or within any range of the above values; the sintering time can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, or within any range of the above values.

[0048] Based on the above technical means, this application can achieve a better reduction effect on particles of different sizes by limiting the sintering temperature and time, so that the Fe2O3@FeOOH core-shell structure is transformed into the Fe2O3@Fe3O4 core-shell structure, and the two components are controlled within a suitable range.

[0049] In an optional embodiment, in S2, the solid reducing substance includes a first carbon source, the amount of which accounts for 6%-10% of the precursor mass; As an example, the amount of the first carbon source is 6%, 7%, 8%, 9%, 10% of the precursor mass, or within any of the above values.

[0050] According to the above-mentioned technical means, the first carbon source in this application is used to provide a reducing atmosphere to reduce FeOOH and part of Fe2O3 to divalent iron, so that Fe2O3 and Fe3O4 in the final core-shell structure are within a set range.

[0051] In one optional embodiment, the first carbon source includes at least one selected from sucrose, glucose, starch, and citric acid; In one optional embodiment, the sintering atmosphere is at least one of nitrogen, argon, and helium; In one optional embodiment, the gaseous reducing substance includes a reducing gas, the volume percentage of which is 5%-10%; optionally, the reducing gas includes at least one of hydrogen or carbon monoxide.

[0052] According to the above-mentioned technical means, the gaseous reducing substance of this application is used to provide a reducing atmosphere to reduce FeOOH and part of Fe2O3 to divalent iron, so that Fe2O3 and Fe3O4 in the final core-shell structure are within a set range.

[0053] In an optional embodiment, in S1, the iron oxide comprises large particles with a particle size Dv50 of 1-5 μm and small particles with a particle size Dv50 of 100-600 nm. As an example, the particle size Dv50 of the large iron oxide particles can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, or within any range of the above values; the particle size Dv50 of the small particles can be 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, or within any range of the above values.

[0054] Based on the above-mentioned technical means, by limiting the size of the particles in iron oxide, iron sources with different particle sizes can be directly prepared, achieving particle gradation. When used in the preparation of lithium iron phosphate, the compaction density of the material can be improved.

[0055] In one alternative embodiment, the large and small particles are etched and sintered separately to obtain large-particle iron sources and small-particle iron sources, respectively.

[0056] In one alternative implementation, for large iron oxide particles, the processing conditions satisfy at least one of the following: (1) The etching temperature is 40-60℃ and the etching time is 2-4h; (2) The mass concentration of the etching agent is 10%-20%; (3) The etching agent includes at least one of ammonium maleate, citric acid and malic acid; (4) The sintering temperature is 400-500℃ and the sintering time is 2-4h.

[0057] In one optional embodiment, for iron oxide particles, the treatment conditions satisfy at least one of the following: (1) The etching temperature is 60-90℃ and the etching time is 0.5-1.5h; (2) The mass concentration of the etching agent is 20%-30%; (3) The etching agent includes at least one of ammonium oxalate and ascorbic acid; (4) The sintering temperature is 300-400℃ and the sintering time is 1-2h; (5) The first carbon source accounts for 6%-10% of the precursor mass.

[0058] Based on the aforementioned technical methods, this application processes large and small iron particles independently to avoid over-etching or insufficient etching, ensuring etching uniformity. Large particles require low-temperature and long-term etching to prevent localized over-reaction and form a more uniform core-shell structure. Small particles, however, have a fast reaction rate, and prolonged etching can easily lead to over-dissolution; therefore, a strong acid is used to rapidly activate the surface. During pre-sintering, the ion diffusion path within the bulk phase of large particles is longer, requiring higher temperatures to provide sufficient energy. Small particles, on the other hand, have high surface energy, and excessively high sintering temperatures can easily lead to agglomeration and over-sintering, damaging the core-shell structure.

[0059] According to another aspect of this application, a lithium iron phosphate material is provided, comprising a core and a carbon coating layer located on at least a portion of the surface of the core; the core comprises lithium iron phosphate. The compaction density of the lithium iron phosphate material is ≥2.55 g / cm³. 3 XRD diffraction peak intensity I (020) / I (200) ≥2.9; BET is 10-15m 2 / g.

[0060] Based on the above technical methods, the XRD diffraction peak intensity I (020) / I (200) A ratio greater than 2.9 indicates a higher exposure rate of the (010) active crystal face, which fundamentally improves the lithium-ion transport dynamics of the material. By limiting the surface area, the electrolyte wetting performance can be improved. Combined with the limitation of the material compaction density, the technical bottleneck of lithium iron phosphate material compaction density and rate and capacity performance can be overcome.

[0061] In one optional embodiment, the carbon coating layer accounts for 0.5%-5% of the mass of the lithium iron phosphate material, and optionally 1%-3%; And / or, the compacted density of the lithium iron phosphate material is 2.55-2.65 g / cm³. 3 XRD diffraction peak intensity I (020) / I (200) It ranges from 2.9 to 3.2; And / or, the iron source used to prepare the lithium iron phosphate material is the iron source described above or the iron source prepared by the preparation method described above.

[0062] According to another aspect of this application, a method for preparing the above-mentioned lithium iron phosphate material is provided, comprising the following steps: S11, mix iron source, lithium source, phosphorus source, second carbon source, additives and crystal face inducer of different particle sizes, and slurry to obtain mixed slurry; Wherein, the iron source is the iron source described above or the iron source prepared by the preparation method described above; The amount of the crystal plane inducer added is 0.2%-0.8% of the iron source mass; S12, the resulting mixed slurry is spray-dried and sintered.

[0063] As an example, the amount of the crystal facet inducer added is 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% of the iron source mass, or within any range of the above values. Excessive addition will generate impurities, blocking the lithium-ion diffusion path and reducing rate performance; insufficient addition will result in insufficient exposure of the (010) crystal facets and a longer lithium-ion diffusion path.

[0064] Based on the above technical means, the use of crystal facet inducers during the slurry preparation process can induce the implementation of crystal facet directional growth technology in the subsequent sintering process. The crystal facet inducers can induce the crystal to preferentially nucleate along the lithium ion diffusion channel (b-axis), improve the exposure rate of the (010) crystal facet, and fundamentally improve the lithium ion transport dynamics. The additives can improve the electronic conductivity of lithium iron phosphate materials and improve the rate performance of the products. Fe3O4 with a core-shell structure of iron source outer layer forms a dense spherical outer layer during sintering due to its high symmetry crystal structure and low reaction activation energy, achieving better particle size distribution and significantly improving the compaction density of the material. Fe2O3 in the iron source inner layer, due to the different growth rates of different crystal faces, is easy to obtain an inner layer structure rich in microcracks and pores, improving the wettability of the electrolyte. The design of the core-shell structure of the iron source and the synergistic control of different iron source particle size distributions simultaneously break through the performance bottleneck of compaction density and rate capacity of lithium iron phosphate. This method overcomes the contradiction of not being able to achieve compaction density, capacity and rate in traditional processes, and provides a cathode solution for power batteries that has the characteristics of high compaction, high rate and capacity.

[0065] In one alternative embodiment, the Li / Fe molar ratio in the mixed slurry is 1.0-1.1, and the Fe / P molar ratio is 0.95-0.99. And / or, the amount of the additive added is 0-2.0% of the iron source mass; as an example, the amount of the additive added is 0%, 0.2%, 0.5%, 0.7%, 0.9%, 1%, 1.3%, 1.5%, 1.8%, 2% of the iron source mass, or within any range of the above values. If the amount added is too high, it cannot completely penetrate the crystal lattice, leading to agglomeration at grain boundaries to form impurity phases and reduce capacity; if the amount added is too low, the improvement in electronic conductivity is limited.

[0066] And / or, the amount of the second carbon source added accounts for 10%-35% of the mass of the iron source. If the carbon source is too low, an effective carbon coating layer cannot be formed, and the material has poor conductivity. If the carbon source is too high, it will lead to a reduction in the proportion of active material and a decrease in capacity. And / or, in the iron source, the mass ratio of large-particle iron source to small-particle iron source is 1-9:1; As an example, the mass ratio of large-particle iron source to small-particle iron source in the iron source can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or within any range of the above values. This mass ratio range can achieve a better particle size distribution effect and improve the compaction of the finished product.

[0067] And / or, the solids content of the mixed slurry is 15wt%-45wt%. As an example, the solids content of the slurry can be 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, or within any range of these values. Excessive solids content will result in excessive slurry viscosity, easily clogging pipes; excessively low solids content will reduce production capacity.

[0068] In an optional embodiment, in S11, the large-particle iron source and the small-particle iron source are respectively mixed with the lithium source, the phosphorus source, the second carbon source, the additive, and the crystal surface inducer, slurryed, and ground to obtain large-particle slurry and small-particle slurry, and then mixed to obtain a mixed slurry. Based on the above technical means, iron sources of different sizes are pulped and ground separately. Since the particle size of the particles is different, pulping and grinding them separately can more accurately control the particle size.

[0069] Optionally, during the preparation of the large particle slurry, the grinding speed is 500 rpm to 2000 rpm; the grinding time is 3 min to 30 min; and the slurry particle size Dv50 is 0.8 μm to 2.5 μm. Optionally, during the preparation of the small particle slurry, the grinding speed is 500rpm-2000rpm; the grinding time is 0.5h-3h, and the slurry particle size Dv50 is 100nm-500nm.

[0070] In an optional embodiment, in S12, the sintering includes: holding at 250℃-400℃ for 3h-5h; holding at 550℃-600℃ for 1h-3h; holding at 630℃-680℃ for 7h-10h; and holding at 720℃-750℃ for 1h-3h. And / or, the sintering atmosphere is at least one of nitrogen, argon, and helium; And / or, after sintering, a pulverization step is also included, pulverizing the product to a particle size Dv50 of 0.8μm-3.0μm, which can achieve a good balance between compaction, capacity and rate performance; And / or, the inlet air temperature of the spray dryer is 180-240℃, the outlet air temperature is 80-150℃, and the feed rate is 0.5-5L / h. Excessive inlet and outlet air temperatures can easily lead to side reactions, while excessively low temperatures result in slow drying efficiency.

[0071] In one optional embodiment, the lithium source includes at least one of lithium carbonate, lithium phosphate, lithium oxalate, lithium dihydrogen phosphate, and lithium hydroxide. And / or, the phosphorus source includes at least one of monoammonium phosphate, lithium phosphate, lithium dihydrogen phosphate, and phosphoric acid; And / or, the second carbon source includes at least one of sucrose, starch, glucose, citric acid, cyclodextrin, maltose, polyethylene glycol, polyvinylpyrrolidone, acetylene black, Ketjen black, and graphene; And / or, the additive includes at least one of titanium dioxide, magnesium oxide, niobium oxide, and aluminum oxide; And / or, the crystal plane inducer includes at least one of lithium zirconate and lithium titanate.

[0072] According to another aspect of this application, a secondary battery is provided, comprising the lithium iron phosphate material described above or the lithium iron phosphate material prepared by the above preparation method.

[0073] According to another aspect of this application, an electrical device is provided, including the aforementioned secondary battery.

[0074] The secondary battery and electrical equipment provided in this application have the same advantages as the lithium iron phosphate material or its preparation method provided in this application, since they adopt the lithium iron phosphate material provided in this application or the lithium iron phosphate material provided by the preparation method described above. These advantages will not be repeated here.

[0075] The following describes the secondary battery and electrical equipment of this application.

[0076] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0077] [Positive electrode plate] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes the positive active material of the first aspect of this application.

[0078] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0079] The positive electrode active material layer includes a positive electrode active material. The positive electrode active material can be selected from materials capable of absorbing and releasing lithium.

[0080] In some embodiments, the positive electrode active material layer in the positive electrode sheet of the present application does not exclude other positive electrode active materials other than the lithium iron phosphate material provided by the present application. For example, other positive electrode active materials can adopt positive electrode active materials for batteries well-known in the art. The specific type of the positive electrode active material is not specifically limited and can be selected according to requirements. As an example, the positive electrode active material can include, but is not limited to, NCM ternary materials, lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium iron pyrophosphate (Li2FeP2O7), lithium cobalt oxide (LiCoO2), spinel-type lithium manganese oxide (LiMn2O4), spinel-type lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), layered lithium manganese oxide (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, such as 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, such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.), lithium-rich materials (such as lithium-rich nickel cobalt manganese oxides), manganese dioxide (MnO2), vanadium oxides, sulfur oxides, silicate oxides, and at least one of their respective modified compounds. These materials can be used alone or in combination of two or more.

[0081] The modified compounds for the above-mentioned positive electrode active materials can be modified by doping, surface coating, or both doping and coating.

[0082] 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.).

[0083] In some embodiments, the positive electrode active material 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.

[0084] In some embodiments, the positive electrode active material layer 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.

[0085] 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.

[0086] [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 comprising a negative electrode active material. In some optional embodiments, the negative electrode sheet can be directly made of a lithium-containing metal sheet. The lithium-containing metal sheet can be lithium metal or an alloy formed of lithium metal with other metals or non-metallic elements.

[0087] 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.

[0088] 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.).

[0089] 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.

[0090] 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).

[0091] 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.

[0092] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0093] 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.

[0094] [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.

[0095] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] [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.

[0100] 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.

[0101] 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.

[0102] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0103] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0104] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0105] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0106] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0107] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0108] In some embodiments, the aforementioned electrical device may also include a battery module or battery pack assembled from the aforementioned secondary batteries. The secondary batteries, battery modules, or battery packs can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0109] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements. An example electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0110] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0111] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0112] Example 1 This embodiment provides an iron source, lithium iron phosphate, and their preparation method. The specific steps and operating parameters are as follows: Iron oxide red particles with a particle size Dv50 of 3 μm were dispersed in a 15 wt% ammonium maleate solution and heated to 50 °C. After etching for 3 h, the mixture was filtered and dried to obtain the precursor Fe2O3@FeOOH. Glucose at a mass fraction of 7% of the precursor was added, and the temperature was increased to 450 °C at a rate of 2 °C / min and held for 3 h to obtain large-particle iron source Fe2O3@Fe3O4. Iron oxide red particles with a particle size Dv50 of 300 nm were dispersed in a 25 wt% ammonium oxalate solution and heated to 75 °C. After etching for 1 h, the mixture was filtered and dried to obtain the precursor Fe2O3@FeOOH. Glucose at a mass fraction of 8% of the precursor was added, and the temperature was increased to 350 °C at a rate of 5 °C / min and held for 1.5 h to obtain small-particle iron source Fe2O3@Fe3O4. The mass fractions of Fe3O4 in the large-particle and small-particle Fe2O3@Fe3O4 iron sources were measured to be 68% and 70%, respectively. The obtained large-particle iron source was destroyed, and the SEM characterization results of its cross-section are as follows: Figure 3 As shown in the figure, a clear core-shell structure can be seen.

[0113] Large-particle iron source Fe2O3@Fe3O4, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, starch, polyethylene glycol, lithium zirconate, and water were mixed in the mixing tank of a sand mill. The Li / Fe ratio was 1.03, the Fe / P ratio was 0.97, and the amount of titanium dioxide, starch, polyethylene glycol, and lithium zirconate as additives accounted for 1.1% of the large-particle iron source, 10.7% of the carbon source, 9.5% of the carbon source, and 0.5% of the crystal facet inducer, lithium zirconate. The solid content of the large-particle slurry was 32%. The sand mill speed was set to 1200 rpm, and after sand milling for 15 minutes, a sample was taken to test the particle size Dv50, which was 1.8 μm. Sand milling was then stopped, and the slurry was poured out to obtain the large-particle slurry. Small-particle iron source Fe2O3@Fe3O4, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, starch, polyethylene glycol, lithium zirconate, and water were mixed in the mixing tank of a sand mill. The Li / Fe ratio was 1.05, the Fe / P ratio was 0.98, and the additives included titanium dioxide (1.1% of the small-particle iron source), starch (9.5% of the small-particle iron source), polyethylene glycol (8.6% of the small-particle iron source), and lithium zirconate (0.5% of the iron source as a crystal face inducing agent). The solid content of the small-particle slurry was 32%. The sand mill speed was set to 1500 rpm, and after sand milling for 1.5 hours, a sample was taken to test the particle size Dv50, which was 350 nm. Sand milling was then stopped, and the slurry was poured out to obtain the small-particle slurry. The large and small-particle slurries were mixed to obtain a mixed slurry. The mass ratio of large-particle iron source to small-particle iron source in the mixed slurry was 4. Pour the mixed slurry into the feed tank of the spray dryer, turn on the nitrogen valve, set the inlet air temperature of the spray dryer to 200℃ and the outlet air temperature to 120℃, and wait for the temperature to stabilize. Then start spray drying at a feed rate of 2L / h. After all the slurry has dried, remove the sprayed material from the outlet.

[0114] The sprayed material was placed in a graphite sagger and then placed in a box furnace for high-temperature sintering. The sintering atmosphere was nitrogen with a gas flow rate of 2 L / min. The temperature was increased to 350°C at a rate of 3°C / min and held for 4 hours. Then, the temperature was increased to 580°C at a rate of 2°C / min and held for 2 hours. The temperature was then increased to 650°C and held for 8 hours. Finally, the temperature was increased to 730°C and held for 2 hours. The mixture was then cooled to room temperature. The resulting lithium iron phosphate sintered material was then pulverized to obtain lithium iron phosphate material.

[0115] The SEM image of the lithium iron phosphate material obtained in this embodiment is as follows: Figure 1 As shown, the compacted density of the powder is 2.58 g / cm³. 3 The particle size Dv50 is 1.53 μm, and the BET is 12.8 μm. 2 / g, the carbon layer content was found to be 1.32% of the total material mass using a carbon-sulfur analyzer. XRD test results are as follows: Figure 2As shown, the XRD diffraction peak intensity I (020) / I (200) It is 3.07.

[0116] Example 2 This embodiment provides an iron source, lithium iron phosphate, and their preparation method. The specific steps and operating parameters are as follows: Iron oxide red particles with a particle size Dv50 of 4.5 μm were dispersed in an 18 wt% ammonium maleate solution and heated to 55 °C. After etching for 3.2 h, the solution was filtered and dried to obtain the precursor Fe2O3@FeOOH. 6% glucose was added to the precursor, and the temperature was increased to 420 °C at a rate of 2 °C / min and held for 2.5 h to obtain the large-particle iron source Fe2O3@Fe3O4. Iron oxide red particles with a particle size Dv50 of 400 nm were dispersed in a 28 wt% ammonium oxalate solution and heated to 85 °C. After etching for 1.5 h, the solution was filtered and dried to obtain Fe2O3@FeOOH. 9.5% glucose was added to the solution, and the temperature was increased to 380 °C at a rate of 5 °C / min and held for 2 h to obtain the small-particle iron source Fe2O3@Fe3O4. Tests showed that the mass fraction of Fe3O4 in the large-particle and small-particle Fe2O3@Fe3O4 iron sources was 66% and 72%, respectively.

[0117] Large-particle iron source Fe2O3@Fe3O4, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, starch, polyethylene glycol, lithium zirconate, and water were mixed in the mixing tank of a sand mill. The Li / Fe ratio was 1.08, the Fe / P ratio was 0.98, and the amount of titanium dioxide, starch, polyethylene glycol, and lithium zirconate added accounted for 16.7% and 14.5% of the large-particle iron source, respectively. The solid content of the large-particle slurry was 42%. The sand mill speed was set to 1200 rpm, and after sand milling for 30 minutes, a sample was taken to test the particle size Dv50, which was 2.4 μm. Sand milling was then stopped, and the slurry was poured out to obtain the large-particle slurry. Small-particle iron source Fe2O3@Fe3O4, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, starch, polyethylene glycol, lithium zirconate, and water were mixed in the mixing tank of a sand mill. The Li / Fe ratio was 1.09, the Fe / P ratio was 0.99, and the additives included titanium dioxide (1.8% of the small-particle iron source), starch (15.5% of the small-particle iron source), polyethylene glycol (12.9% of the small-particle iron source), and lithium zirconate (0.8% of the iron source). The solid content of the small-particle slurry was 44%. The sand mill was set to 1000 rpm, and after 2 hours of sand milling, a sample was taken to test the particle size Dv50, which was 500 nm. The sand milling was then stopped, and the slurry was poured out to obtain the small-particle slurry. The large and small-particle slurries were mixed to obtain a mixed slurry. The mass ratio of large to small-particle iron source in the mixed slurry was 2.

[0118] Pour the mixed slurry into the feed tank of the spray dryer, turn on the nitrogen valve, set the inlet air temperature of the spray dryer to 240℃ and the outlet air temperature to 120℃, and wait for the temperature to stabilize. Then start spray drying at a feed rate of 2L / h. After all the slurry has dried, remove the sprayed material from the outlet.

[0119] The sprayed material was placed in a graphite sagger and then placed in a box furnace for high-temperature sintering. The sintering atmosphere was nitrogen with a gas flow rate of 2 L / min. The temperature was increased to 400℃ at a rate of 3℃ / min and held for 3 hours. Then, the temperature was increased to 600℃ at a rate of 2℃ / min and held for 2 hours. The temperature was then increased to 680℃ and held for 7 hours. Finally, the temperature was increased to 740℃ and held for 2 hours. The mixture was then cooled to room temperature. The resulting lithium iron phosphate sintered material was then pulverized to obtain lithium iron phosphate material.

[0120] Example 3 This embodiment provides an iron source, lithium iron phosphate, and their preparation method. The specific steps and operating parameters are as follows: Iron oxide red particles with a particle size Dv50 of 1.2 μm were dispersed in a 12 wt% ammonium maleate solution and heated to 45 °C. After etching for 4 h, the mixture was filtered and dried to obtain the precursor Fe2O3@FeOOH. 10% glucose was added to the precursor, and the temperature was increased to 490 °C at a rate of 2 °C / min and held for 3.5 h to obtain the large-particle iron source Fe2O3@Fe3O4. Iron oxide red particles with a particle size Dv50 of 200 nm were dispersed in a 20 wt% ammonium oxalate solution and heated to 65 °C. After etching for 0.5 h, the mixture was filtered and dried to obtain the precursor Fe2O3@FeOOH. 6.5% glucose was added to the precursor, and the temperature was increased to 310 °C at a rate of 5 °C / min and held for 1 h to obtain the small-particle iron source Fe2O3@Fe3O4. Tests showed that the mass fraction of Fe3O4 in the large-particle and small-particle Fe2O3@Fe3O4 iron sources was 74% and 67%, respectively.

[0121] Large-particle iron source Fe2O3@Fe3O4, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, starch, polyethylene glycol, lithium zirconate, and water were mixed in the mixing tank of a sand mill. The Li / Fe ratio was 1.01, the Fe / P ratio was 0.955, and the amount of titanium dioxide, starch, polyethylene glycol, and lithium zirconate added accounted for 0.4% of the large-particle iron source, 8.8% of the carbon source, 5.7% of the carbon source, and 0.2% of the crystal facet inducer, lithium zirconate. The solid content of the large-particle slurry was 20%. The sand mill speed was set to 1800 rpm, and after sand milling for 10 minutes, a sample was taken to test the particle size Dv50, which was 1.2 μm. Sand milling was then stopped, and the slurry was poured out to obtain the large-particle slurry. Small-particle iron source Fe2O3@Fe3O4, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, starch, polyethylene glycol, lithium zirconate, and water were mixed in the mixing tank of a sand mill. The Li / Fe ratio was 1.02, the Fe / P ratio was 0.965, and the additives included titanium dioxide (0.4% of the small-particle iron source), starch (6.5% of the small-particle iron source), polyethylene glycol (4.8% of the small-particle iron source), and lithium zirconate (0.2% of the iron source as a crystal facet inducer). The solid content of the small-particle slurry was 17%. The sand mill was set to 800 rpm, and after 3 hours of sand milling, a sample was taken to test the particle size Dv50, which was 200 nm. The sand milling was then stopped, and the slurry was poured out to obtain the small-particle slurry. The large and small-particle slurries were mixed to obtain a mixed slurry. The mass ratio of large-particle iron source to small-particle iron source in the mixed slurry was 8.

[0122] Pour the mixed slurry into the feed tank of the spray dryer, turn on the nitrogen valve, set the inlet air temperature of the spray dryer to 240℃ and the outlet air temperature to 110℃, and wait for the temperature to stabilize. Then start spray drying at a feed rate of 2L / h. After all the slurry has dried, remove the sprayed material from the outlet.

[0123] The sprayed material was placed in a graphite sagger and then placed in a box furnace for high-temperature sintering. The sintering atmosphere was nitrogen with a gas flow rate of 2 L / min. The temperature was increased to 300℃ at a rate of 3℃ / min and held for 5 hours. Then, the temperature was increased to 560℃ at a rate of 2℃ / min and held for 2 hours. The temperature was then increased to 630℃ and held for 10 hours. Finally, the temperature was increased to 720℃ and held for 1.5 hours. The material was then cooled to room temperature. The resulting lithium iron phosphate sintered material was then pulverized to obtain lithium iron phosphate material.

[0124] Example 4 This embodiment provides an iron source, lithium iron phosphate, and a method for preparing the same. The difference between this embodiment and Embodiment 1 is that no additives are used in the preparation of lithium iron phosphate.

[0125] Example 5 This embodiment provides an iron source, lithium iron phosphate, and its preparation method. Compared with Example 1, the difference lies in the different additives. In the lithium iron phosphate preparation process, an equal amount of niobium oxide is used instead of titanium oxide.

[0126] Example 6 This embodiment provides an iron source, lithium iron phosphate, and their preparation method. Compared with Example 1, the difference lies in that the Fe3O4 content in both the large and small particle iron sources is 70%. The specific operation for preparing the large particle iron source is as follows: Iron oxide red particles with a particle size Dv50 of 3 μm were dispersed in a 15 wt% ammonium maleate solution and heated to 50 °C. After etching for 3 h, the mixture was filtered and dried to obtain the precursor Fe2O3@FeOOH. Glucose at a mass fraction of 7% of the precursor was added, and the temperature was increased to 450 °C at a rate of 2 °C / min and held for 3.5 h to obtain the large-particle iron source Fe2O3@Fe3O4. Testing showed that the mass fraction of Fe3O4 in the large-particle iron source Fe2O3@Fe3O4 was 70%.

[0127] All other steps and parameters are consistent with those in Example 1.

[0128] Example 7 This embodiment provides an iron source, lithium iron phosphate, and their preparation method. The specific steps and operating parameters are as follows: Iron oxide red particles with Dv50 values ​​of 3 μm and 300 nm were mixed at a mass ratio of 4:1, dispersed in a 20 wt% ammonium maleate solution, and heated to 50 °C. After etching for 3 h, the mixture was filtered and dried to obtain the precursor Fe2O3@FeOOH. Glucose at a mass fraction of 7% of the precursor was added, and the temperature was increased to 375 °C at a rate of 2 °C / min and held for 2.5 h to obtain a core-shell structured iron source Fe2O3@Fe3O4. The particles were sieved using an ultrasonic vibrating screen to obtain large Fe2O3@Fe3O4 particles with a Dv50 of 3.4 μm and small Fe2O3@Fe3O4 particles with a Dv50 of 420 nm. The mass fractions of Fe3O4 in the large and small Fe2O3@Fe3O4 particles were measured to be 66% and 72%, respectively.

[0129] All other steps and parameters are consistent with those in Example 1.

[0130] Example 8 This embodiment provides an iron source, lithium iron phosphate, and their preparation method. The specific steps and operating parameters are as follows: Iron oxide red particles with a particle size Dv50 of 3 μm were dispersed in a 15 wt% ammonium maleate solution and heated to 50 °C. After etching for 3 h, the mixture was filtered and dried to obtain the precursor Fe2O3@FeOOH. Glucose at a mass fraction of 7% of the precursor was added, and the temperature was increased to 450 °C at a rate of 2 °C / min and held for 3 h to obtain large-particle iron source Fe2O3@Fe3O4. Iron oxide red particles with a particle size Dv50 of 300 nm were dispersed in a 25 wt% ammonium oxalate solution and heated to 75 °C. After etching for 1 h, the mixture was filtered and dried to obtain the precursor Fe2O3@FeOOH. Small-particle iron source Fe2O3@Fe3O4 was obtained under a reducing gas atmosphere (a mixture of hydrogen and nitrogen, with a hydrogen volume percentage of 8%), at a rate of 5 °C / min, and held for 1.5 h. Tests showed that the mass fraction of Fe3O4 in the large-particle and small-particle Fe2O3@Fe3O4 iron sources was 70% and 72%, respectively.

[0131] All other steps and parameters are consistent with those in Example 1.

[0132] Comparative Example 1 This comparative example provides an iron source, lithium iron phosphate, and their preparation method. The specific steps and operating parameters are as follows: Iron oxide red particles with a particle size Dv50 of 3 μm were dispersed in a 15 wt% ammonium maleate solution and heated to 50 °C. After etching for 6 h, the solution was filtered and dried to obtain the precursor Fe2O3@FeOOH. 12% glucose was added to the precursor, and the temperature was increased to 550 °C at a rate of 2 °C / min and held for 5 h to obtain large-particle iron source Fe2O3@Fe3O4. Iron oxide red particles with a particle size Dv50 of 300 nm were dispersed in a 25 wt% ammonium oxalate solution and heated to 75 °C. After etching for 4 h, the solution was filtered and dried to obtain the precursor Fe2O3@FeOOH. 8% glucose was added to the precursor, and the temperature was increased to 350 °C at a rate of 5 °C / min and held for 5 h to obtain small-particle iron source Fe2O3@Fe3O4. The mass fraction of Fe3O4 in the large-particle and small-particle Fe2O3@Fe3O4 iron sources was 90% and 80%, respectively.

[0133] All other steps and parameters are consistent with those in Example 1.

[0134] Comparative Example 2 This comparative example provides an iron source, lithium iron phosphate, and their preparation method. The specific steps and operating parameters are as follows: Iron oxide red particles with a diameter of 3 μm were dispersed in a 15 wt% ammonium maleate solution and heated to 50 °C. After etching for 30 min, the mixture was filtered and dried to obtain the precursor Fe₂O₃@FeOOH. Glucose at a mass fraction of 8% of the precursor was added, and the temperature was increased to 450 °C at a rate of 2 °C / min and held for 1 h to obtain large-particle iron source Fe₂O₃@Fe₃O₄. Iron oxide red particles with a diameter of 300 nm were dispersed in a 10 wt% ammonium oxalate solution and heated to 75 °C. After etching for 0.5 h, the mixture was filtered and dried to obtain the precursor Fe₂O₃@FeOOH. Glucose at a mass fraction of 8% of the precursor was added, and the temperature was increased to 300 °C at a rate of 5 °C / min and held for 1.5 h to obtain small-particle iron source Fe₂O₃@Fe₃O₄. The mass fractions of Fe₃O₄ in the large-particle and small-particle Fe₂O₃@Fe₃O₄ iron sources were 45% and 60%, respectively.

[0135] All other steps and parameters are consistent with those in Example 1.

[0136] Comparative Example 3 This comparative example provides an iron source, lithium iron phosphate, and their preparation method. Compared with Example 1, the difference is that the mass ratio of large-particle iron source to small-particle iron source in the mixed slurry is 0.25, while other steps and parameters are consistent with Example 1.

[0137] Comparative Example 4 This comparative example provides an iron source, lithium iron phosphate, and their preparation method. Compared with Example 1, the difference is that the amount of lithium zirconate, the crystal facet inducer, added during the preparation of large-particle slurry and small-particle slurry accounts for 0.1% of the iron source.

[0138] Comparative Example 5 This comparative example provides an iron source, lithium iron phosphate, and their preparation method. Compared with Example 1, the difference is that the mass ratio of large-particle iron source to small-particle iron source in the mixed slurry is 15:1, while other steps and parameters remain the same as in Example 1.

[0139] Comparative Example 6 This comparative example provides an iron source, lithium iron phosphate, and their preparation method. Compared with Example 1, the difference is that conventional iron sources are used: pure Fe2O3 with a particle size Dv50 of 3 μm and pure Fe2O3 with a particle size Dv50 of 350 nm are used instead of the iron source with a core-shell structure in this application; other steps and parameters are consistent with Example 1.

[0140] Test case XRD testing method: The XRD diffractometer was a Bruker D8 Advance. The sample was ground into powder, sieved, and then filled into a glass sample cell. The scanning angle was 15°-80°, and the scanning speed was 5° / min. The test pattern was compared with the standard PDF card to determine the positions of the (020) and (200) crystal planes. After background subtraction, the ratio I between the two was calculated. (020) / I (200) .

[0141] Particle size testing method: Particle size Dv50 was determined according to standard GB / T 19077-2016 using a laser particle size analyzer (Malvern Master Size 2000).

[0142] Compacted density test method: Compaction is performed in accordance with standard GB / T 30835-2014, using a powder compaction density meter, with a test pressure of 3T.

[0143] Specific surface area testing method: The specific surface area is determined according to standard GB / T 19587-2017, using the gas adsorption BET method. After the sample is heated and purged to remove gas, it undergoes low-temperature physical adsorption in liquid nitrogen. When adsorption reaches equilibrium, the instrument measures the amount of adsorption in the monolayer on the sample surface, and then the specific surface area of ​​the sample is calculated using the adsorption theory BET.

[0144] Carbon content test method: Referring to standard GB / T 20123-2006, the high-frequency combustion infrared absorption method is adopted. The sample is burned in a high-temperature oxygen stream, and carbon is converted into CO2. The CO2 content is determined by infrared detector, and the carbon mass fraction is calculated.

[0145] Fe3O4 content test in large and small particle iron sources: The obtained Fe2O3@Fe3O4 core-shell structure XRD test spectrum was refined using GSAS software. By optimizing the background, half-width at half-maximum, atomic coordinates, occupancy and anisotropic temperature factor, the fitted graph can match the test curve well, and the relative mass fraction of Fe2O3 and Fe3O4 is obtained.

[0146] Electrical performance testing: The lithium iron phosphate cathode material powder, acetylene black, and PVDF provided in the examples and comparative examples were mixed uniformly at a mass ratio of 90:5:5. This mixture was then coated onto a 0.02 mm thick aluminum foil, dried, and cold-pressed to obtain the cathode sheet. Button batteries were then assembled in a nitrogen-filled glove box, using porous polyethylene as the separator, lithium foil as the anode material, and LiPF6 dissolved in a 1:1:1 mixture of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate at a concentration of 1 mol / L. Finally, charge-discharge performance tests were conducted on a Xinwei electrochemical workstation with a voltage range of 2.5 V-3.75 V. The battery was charged to the cutoff voltage with a constant current, and then discharged to the lower limit voltage at the same rate. The first charge-discharge cycle was conducted at a rate of 0.1C, the second at 1C, and the third at 5C. The 1C and 5C discharge capacities of the material were obtained, and the rate performance was expressed as 5C capacity / 1C capacity.

[0147] The test results are shown in the table below: Table 1

[0148] Table 2

[0149] The embodiments of this application overcome the performance bottlenecks of lithium iron phosphate's compaction density and rate capacity through the synergistic control of Fe2O3@Fe3O4 core-shell structure design and multi-scale particle gradation. When the Fe3O4 ratio is controlled within a reasonable range and a reasonable ratio of large and small iron source particles is designed, the compaction density of the finished lithium iron phosphate material can reach 2.55 g / cm³. 3 The above BET is within 10-15m. 2 Between / g, I (020) / I (200) The ratios were all above 2.9, indicating a high (010) crystal facet exposure rate. Electrochemical tests showed that the 1C capacity of the finished products could reach over 140 mAh / g, and the rate performance was over 85%. However, in the comparative example, due to the imbalance of the proportions of the components in the Fe2O3@Fe3O4 core-shell structure and the deviation of the particle size distribution, the resulting product could not simultaneously achieve both compaction density and capacity. At the same time, the lower amount of crystal facet inducer added would reduce the I content in the product. (020) / I (200) A ratio below 2.9 significantly reduces the finished product capacity, and using conventional iron sources also leads to excessive internal porosity, making it difficult to improve compaction.

[0150] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. An iron source, characterized in that, The micro-morphology of the iron source is a core-shell structure, the inner layer comprises Fe2O3, and the shell comprises Fe3O4, and the mass percentage of the Fe3O4 is 65%-75% based on the mass of the iron source.

2. The iron source of claim 1, wherein The mass percentage of the Fe3O4 is 67%-73% based on the mass of the iron source; And / or, the mass percentage of the Fe2O3 is 25%-35%, and optionally 27%-33%.

3. A method of producing the iron source as claimed in claim 1 or 2, characterized by, Comprising the following steps: S1, etching the iron oxide using an etchant to obtain a precursor; The etchant comprises at least one of ammonium maleate, ammonium oxalate, citric acid, malic acid and ascorbic acid; S2, sintering the obtained precursor in the presence of a reducing substance.

4. The method of claim 3, wherein the iron source is prepared by, In S1, the etching temperature is 40-90℃, and the etching time is 0.5-4h; And / or, the mass concentration of the etchant is 10%-30%; And / or, in S2, the reducing substance comprises at least one of a solid reducing substance and a gaseous reducing substance.

5. The method of claim 4, wherein the iron source is prepared by, In S2, the sintering temperature is 300-500℃, and the sintering time is 1-4h; And / or, in S2, the solid reducing substance comprises a first carbon source, and the amount of the first carbon source accounts for 6%-10% of the mass of the precursor; Optionally, the first carbon source comprises at least one of sucrose, glucose, starch and citric acid; And / or, the gaseous reducing substance comprises a reducing gas, and the volume percentage of the reducing gas is 5%-10%; optionally, the reducing gas comprises at least one of hydrogen and carbon monoxide; And / or, the sintering atmosphere is at least one of nitrogen, argon and helium.

6. The method of claim any one of claims 3-5, wherein the iron source is prepared by, In S1, the iron oxide comprises large particles with a particle size Dv50 of 1-5μm and small particles with a particle size Dv50 of 100-600nm; Optionally, the large particles and the small particles are etched and sintered separately to obtain large particle iron sources and small particle iron sources, respectively.

7. The method of producing an iron source according to claim 6, wherein For the large particle iron oxide, the processing conditions satisfy at least one of the following: (1) the etching temperature is 40-60℃, and the etching time is 2-4h; (2) the mass concentration of the etchant is 10%-20%; (3) the etchant comprises at least one of ammonium maleate, citric acid and malic acid; (4) the sintering temperature is 400-500℃, and the sintering time is 2-4h.

8. The method of producing an iron source according to claim 6, wherein For the small particle iron oxide, the processing conditions satisfy at least one of the following: (1) the etching temperature is 60-90℃, and the etching time is 0.5-1.5h; (2) the mass concentration of the etchant is 20%-30%; (3) the etchant comprises at least one of ammonium oxalate and ascorbic acid; (4) the sintering temperature is 300-400℃, and the sintering time is 1-2h.

9. A lithium iron phosphate material, characterized in that, Comprising an inner core and a carbon coating layer located on at least part of the surface of the inner core; the inner core comprises lithium iron phosphate; The compaction density of the lithium iron phosphate material is ≥ 2.55 g / cm 3 ; the XRD diffraction peak intensity I (020) / I (200) ≥ 2.9; the BET is 10-15 m 2 / g.

10. The lithium iron phosphate material of claim 9, wherein, The mass percentage of the carbon coating layer is 0.5%-5% based on the mass of the lithium iron phosphate material, and optionally 1%-3%. and / or the compaction density of the lithium iron phosphate material is 2.55-2.65 g / cm3 3 ; the XRD diffraction peak intensity I (020) / I (200) is 2.9-3.2; And / or, the iron source used in the preparation of the lithium iron phosphate material is the iron source of claim 1 or 2 or the iron source prepared by the preparation method of any one of claims 3-8.

11. A method of producing the lithium iron phosphate material according to claim 9 or 10, characterized in that Comprising the following steps: S11, mixing the iron source, lithium source, phosphorus source, second carbon source, additive, and crystal face inducer of different particle sizes, slurry preparation, to obtain a mixed slurry; Wherein, the iron source is the iron source of claim 1 or 2 or the iron source prepared by the preparation method of any one of claims 3-8; The addition amount of the crystal face inducer is 0.2%-0.8% of the mass of the iron source; S12, the mixed slurry is spray dried and sintered.

12. The method of claim 11, wherein the lithium iron phosphate material is prepared by the steps of: The molar ratio of Li / Fe in the mixed slurry is 1.0-1.1, and the molar ratio of Fe / P is 0.95-0.99; ​ And / or, the addition amount of the additive is 0-2.0% of the mass of the iron source; And / or, the addition amount of the second carbon source is 10%-35% of the mass of the iron source; And / or, in the iron source, the mass ratio of large particle iron source to small particle iron source is 1-9:1; And / or, the solid content of the mixed slurry is 15wt%-45wt%.

13. The method of claim 11, wherein the lithium iron phosphate material is prepared by the steps of: In S11, the large particle iron source and the small particle iron source are mixed with the lithium source, the phosphorus source, the second carbon source, the additive, and the crystal face inducer, respectively, slurry preparation, grinding, to obtain a large particle slurry and a small particle slurry, mixing the two to obtain a mixed slurry; ​ Optionally, in the preparation of the large particle slurry, the grinding speed is 500rpm-2000rpm; the grinding time is 3min-30min, and the particle size Dv50 of the slurry is ground to 0.8μm-2.5μm; Optionally, in the preparation of the small particle slurry, the grinding speed is 500rpm-2000rpm; the grinding time is 0.5h-3h, and the particle size Dv50 of the slurry is ground to 100nm-500nm.

14. The method of claim 11-13, wherein the lithium iron phosphate material is prepared by the steps of: In S12, the sintering includes: 250℃-400℃, holding for 3h-5h; 550℃-600℃, holding for 1h-3h; 630℃-680℃, holding for 7h-10h; 720℃-750℃, holding for 1h-3h; ​ And / or, the sintering atmosphere is at least one of nitrogen, argon, and helium; And / or, after sintering, it further includes a step of crushing to a particle size Dv50 of 0.8μm-3.0μm of the product; And / or, the inlet air temperature of the spray drying is 180-240℃, the outlet air temperature is 80-150℃, and the feeding speed is 0.5-5L / h.

15. The method of claim 14, wherein the lithium iron phosphate material is prepared by a process comprising: The lithium source includes at least one of lithium carbonate, lithium phosphate, lithium oxalate, lithium dihydrogen phosphate, and lithium hydroxide; ​ And / or, the phosphorus source includes at least one of monoammonium phosphate, lithium phosphate, lithium dihydrogen phosphate, and phosphoric acid; And / or, the second carbon source includes at least one of sucrose, starch, glucose, citric acid, cyclodextrin, maltose, polyethylene glycol, polyvinylpyrrolidone, acetylene black, ketjen black, and graphene; And / or, the additive includes at least one of titanium oxide, magnesium oxide, niobium oxide, and aluminum oxide; And / or, the crystal face inducer includes at least one of lithium zirconate and lithium titanate.

16. A secondary battery characterized by comprising: The lithium iron phosphate material of claim 9 or 10 or the lithium iron phosphate material prepared by the preparation method of any one of claims 11-15.

17. An electrical device, comprising: The secondary battery of claim 16.

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