Lithium iron phosphate preparation method, positive electrode active material, positive electrode plate, battery, and electrical device

Abstract

A lithium iron phosphate preparation method, a positive electrode active material, a positive electrode plate, a battery, and an electrical device. The lithium iron phosphate preparation method comprises: adding a first iron phosphate, a second iron phosphate, and a lithium source into a solvent, so as to obtain a slurry; and sintering the slurry, so as to obtain lithium iron phosphate. The specific surface area S1 of the first iron phosphate satisfies 7 m2 / g ≤ S1 ≤ 9.5 m2 / g, and the grain size D1 of the first iron phosphate satisfies 50 nm ≤ D1 ≤ 65 nm; the specific surface area S2 of the second iron phosphate satisfies 8.5 m2 / g ≤ S2 ≤ 11.5 m2 / g, and the grain size D2 of the second iron phosphate satisfies 30 nm ≤ D2 ≤ 50 nm; the specific surface area of the second iron phosphate is greater than the specific surface area of the first iron phosphate, and the grain size of the second iron phosphate is less than the grain size of the first iron phosphate. The technical solution of the present application can achieve lithium iron phosphate having high compaction density and high capacity.

Description

Preparation method of lithium iron phosphate, positive electrode active material, positive electrode sheet, battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410256782.9 filed on March 6, 2024, entitled “Method for preparing lithium iron phosphate, positive electrode active material, positive electrode sheet, battery and electrical device,” and the entire contents of that application are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and more specifically, to a preparation method of lithium iron phosphate, a positive electrode active material, a positive electrode sheet, a battery, and an electrical device. Background Art

[0004] In recent years, lithium-ion batteries have been used in an increasingly diverse range of applications, including energy storage and power supply applications such as wind, hydro, thermal, and solar power plants, as well as in electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. This significant advancement in lithium-ion batteries has also led to higher performance requirements across all aspects of their application.

[0005] Lithium iron phosphate, as a positive electrode active material, is crucial to the performance of lithium-ion batteries. Therefore, how to improve the compaction density and capacity of lithium iron phosphate is a technical problem that needs to be solved urgently.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a preparation method of lithium iron phosphate, a positive electrode active material, a positive electrode sheet, a battery and an electrical device, which improve the compaction density and capacity of lithium iron phosphate.

[0008] In a first aspect, a method for preparing lithium iron phosphate is provided, comprising: adding a first iron phosphate, a second iron phosphate, and a lithium source to a solvent to obtain a slurry; sintering the slurry to obtain lithium iron phosphate; wherein the specific surface area S1 of the first iron phosphate satisfies: 7m 2 / g≤S1≤9.5m 2 / g, the size D1 of the first ferric phosphate grains satisfies: 50nm≤D1≤65nm; the specific surface area S2 of the second ferric phosphate satisfies: 8.5m 2 / g≤S2≤11.5m 2 / g, the size D2 of the second iron phosphate grains satisfies: 30nm≤D2≤50nm, the specific surface area of ​​the second iron phosphate is greater than the specific surface area of ​​the first iron phosphate, and the size of the second iron phosphate grains is smaller than the size of the first iron phosphate grains.

[0009] In the embodiment of the present application, the first iron phosphate and the second iron phosphate have different grain sizes and specific surface areas, the specific surface area of ​​the first iron phosphate is smaller than the specific surface area of ​​the second iron phosphate, and the size of the grains of the first iron phosphate is larger than the size of the grains of the second iron phosphate. By matching the first iron phosphate and the second iron phosphate with corresponding specific surface areas and grain sizes, lithium iron phosphate with high compaction density and high capacity can be prepared.

[0010] In a possible embodiment, the specific surface area S1 of the first iron phosphate satisfies: 8.5 m 2 / g≤S1≤9.5m 2 / g, and / or the size D1 of the first iron phosphate grains satisfies: 50nm≤D1≤60nm. Further limiting the specific surface area and grain size of the first iron phosphate is conducive to obtaining lithium iron phosphate with higher capacity at a lower sintering temperature.

[0011] In a possible implementation, the specific surface area S2 of the second iron phosphate satisfies: 10m 2 / g≤S2≤11.5m 2 / g, and / or the size D2 of the second iron phosphate grains satisfies: 30nm≤D2≤40nm. Further limiting the specific surface area and grain size of the second iron phosphate is conducive to obtaining lithium iron phosphate with higher capacity at a lower sintering temperature.

[0012] In a possible implementation, the iron-to-phosphorus ratio A1 of the first ferric phosphate satisfies: 0.96≤A1≤0.975; and / or the iron-to-phosphorus ratio A2 of the second ferric phosphate satisfies: 0.96≤A2≤0.975.

[0013] When the iron-phosphorus ratio of the first iron phosphate and / or the second iron phosphate is greater than or equal to 0.96, it is beneficial to the preparation and generation of lithium iron phosphate, and can reduce the risk of the presence of impurities other than lithium iron phosphate in the prepared product; when the iron-phosphorus ratio of the first iron phosphate and / or the second iron phosphate is not greater than 0.975, the risk of excessive grain growth of lithium iron phosphate due to excessive iron-phosphorus ratio can be reduced.

[0014] In a possible implementation, the mass ratio of the first iron phosphate to the second iron phosphate is 1:1 to 9:1.

[0015] When the mass ratio of the first iron phosphate to the second iron phosphate is greater than or equal to 1:1, the first iron phosphate has a suitable mass content, which is conducive to obtaining lithium iron phosphate with a high compaction density; when the mass ratio of the first iron phosphate to the second iron phosphate is less than or equal to 9:1, the second iron phosphate has a suitable mass content, which is conducive to obtaining lithium iron phosphate with a high capacity.

[0016] In one possible implementation, the sintering temperature T1 satisfies: T1<800° C. In this technical solution, the reaction between the first iron phosphate, the second iron phosphate, the lithium source, and the carbon source can be completed at a temperature below 800° C., which is beneficial for energy conservation.

[0017] In a possible implementation, the sintering temperature T1 satisfies: 750° C. ≤ T1 ≤ 790° C. The above temperature setting is beneficial to the reaction between the first iron phosphate, the second iron phosphate, the lithium source, and the carbon source to generate lithium iron phosphate, and is also beneficial to saving energy.

[0018] In one possible implementation, the total sintering time t satisfies: 14h≤t≤18h. This time setting is conducive to the full progress of the reaction and reduces the risk of abnormal growth of lithium iron phosphate grains due to the reaction time.

[0019] In a possible implementation, the sintering treatment of the slurry includes: grinding and demagnetizing the slurry; spray drying the demagnetized slurry to obtain dry powder; and sintering the dry powder to obtain the lithium iron phosphate.

[0020] Grinding the slurry can make the first iron phosphate, the second iron phosphate, the lithium source, and the carbon source in the slurry mixed more evenly, and demagnetizing the slurry can remove the magnetism in the slurry; spray drying the demagnetized slurry to obtain dry powder for subsequent sintering; sintering the dry powder facilitates the reaction between the first iron phosphate, the second iron phosphate, the lithium source, and the carbon source to generate lithium iron phosphate.

[0021] In one possible implementation, sintering the dry powder includes heating the dry powder to a sintering temperature T1 within 5 to 6 hours in an inert atmosphere, and maintaining the dry powder at the sintering temperature T1 for 9 to 12 hours to obtain the lithium iron phosphate. This sintering process of first heating the dry powder and then sintering the powder at a constant temperature helps reduce agglomeration in the sintered product.

[0022] In a possible implementation, the preparation method further includes: after sintering the dry powder, performing air flow pulverization on the sintered material.

[0023] By performing air flow pulverization on the sintered material, the sintered material can be pulverized into materials with smaller particles, thereby obtaining lithium iron phosphate secondary particles with a suitable size.

[0024] In one possible implementation, the molar ratio of the iron content in the first and second iron phosphates to the lithium content in the lithium source is 1:1 to 1:1.05. Thus, the first and second iron phosphates, as well as the lithium source, have a suitable molar ratio, facilitating the production of lithium iron phosphate through the reaction.

[0025] In one possible implementation, adding the first iron phosphate, the second iron phosphate, and the lithium source to a solvent to obtain a slurry includes adding the first iron phosphate, the second iron phosphate, the lithium source, and a carbon source to the solvent to obtain the slurry. The addition of the carbon source facilitates obtaining a lithium iron phosphate having a carbon coating during a subsequent sintering process, thereby enabling the lithium iron phosphate to have better electrical conductivity.

[0026] In one possible implementation, the ratio of the sum of the mass of the first iron phosphate and the second iron phosphate to the mass of the carbon source is 1:0.1 to 1:0.105. In this way, the surface of the lithium iron phosphate is coated with a suitable mass content of carbon, thereby having good conductivity.

[0027] In a possible implementation, the carbon source includes at least one of sucrose, glucose, dextrin, citric acid, fructose, or starch. This facilitates flexible selection of a specific carbon source according to actual needs.

[0028] A second aspect of the present application provides a positive electrode active material, which includes lithium iron phosphate prepared by the preparation method described in any embodiment of the first aspect of the present application.

[0029] In one possible embodiment, the compaction density of the lithium iron phosphate powder at 3T is greater than or equal to 2.45 g / cm 3 .

[0030] In one possible implementation, at a temperature of 25° C., the discharge capacity of the lithium iron phosphate at 0.1C is greater than or equal to 156 mAh / g.

[0031] In the positive electrode active material of the embodiment of the present application, the positive electrode active material has a higher compaction density and a higher discharge capacity. The positive electrode active material has relatively excellent performance, which is beneficial to improving the performance of the battery.

[0032] In one possible embodiment, the volume average particle size Dv50 of the lithium iron phosphate satisfies: 0.8 μm ≤ Dv50 ≤ 1.8 μm. In this way, the lithium iron phosphate powder has a suitable particle size, which is convenient for subsequent applications of the lithium iron phosphate.

[0033] In the embodiment of the present application, the lithium iron phosphate with a combination of large and small particle sizes prepared by the preparation method of the present application has a higher compaction density and a higher capacity, which is beneficial to improving the volume energy density and rate performance of the battery.

[0034] The third aspect of the present application provides a positive electrode plate, comprising: a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer comprising lithium iron phosphate prepared by the preparation method described in any embodiment of the first aspect, or the positive electrode active material described in the second aspect.

[0035] The fourth aspect of the present application provides a battery, comprising the positive electrode sheet described in any one of the embodiments of the third aspect.

[0036] The fifth aspect of the present application provides an electrical device comprising the battery described in the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0038] FIG1 is a schematic diagram of a method for preparing lithium iron phosphate according to an embodiment of the present application;

[0039] FIG2 is a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application;

[0040] FIG3 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0041] FIG4 is a schematic structural diagram of a battery cell according to an embodiment of the present application;

[0042] FIG5 is a schematic diagram of a battery according to an embodiment of the present application;

[0043] FIG6 is a schematic structural diagram of a battery according to an embodiment of the present application;

[0044] FIG7 is a schematic structural diagram of an electric device according to an embodiment of the present application;

[0045] FIG8 is a graph showing the first charge and discharge curve at a rate of 0.1C according to an embodiment of the present application;

[0046] FIG. 9 is a SEM image of lithium iron phosphate according to an embodiment of the present application.

[0047] Reference numerals:

[0048] 1-Electrical device;

[0049] 11-shell, 12-electrode assembly, 13-cover plate;

[0050] 100-battery cell, 121-positive electrode sheet, 122-positive electrode current collector, 123-positive electrode film layer, 400-battery, 401-upper box, 402-lower box, 500-motor, 600-controller. DETAILED DESCRIPTION

[0051] Below, the preparation method of lithium iron phosphate, positive electrode active material, positive electrode sheet, battery and electric device of the present application are described in detail with appropriate reference to the drawings, but there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0052] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of specific range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0055] Unless otherwise specified, all steps of the present application may be performed sequentially, randomly, or optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0056] The terms "above", "below", "greater than" or "less than" as used in this application are inclusive of the number, for example, "at least one" means one or more, and "at least one of A and B" means "A", "B" or "A and B".

[0057] The development of battery technology needs to consider many design factors, such as capacity, energy density, cycle life, reliability, etc. Among them, the performance of the positive electrode active material has a great influence on the performance of the battery. Lithium iron phosphate (LiFeO4) with an olivine-type crystalline structure has outstanding advantages such as large discharge specific capacity, long cycle life, good safety performance, low price, non-toxicity and no environmental pollution, so it has a wide range of application scenarios. However, compared with ternary materials, the compaction density and capacity of lithium iron phosphate are relatively low, resulting in limited improvement in battery performance. In some treatment methods, the compaction density of lithium iron phosphate is increased by increasing the sintering temperature and extending the holding time. However, this treatment method will lead to a higher risk of abnormal growth of lithium iron phosphate grains, resulting in a decrease in the capacity of lithium iron phosphate. Therefore, how to provide a preparation method for lithium iron phosphate to improve the compaction density and capacity of lithium iron phosphate is a technical problem that needs to be solved urgently.

[0058] In view of this, the present application provides a method for preparing lithium iron phosphate. In the method for preparing lithium iron phosphate, a first iron phosphate and a second iron phosphate with specific specific surface area and grain size are used in combination, and the prepared lithium iron phosphate has both high compaction density and high capacity.

[0059] The preparation method of lithium iron phosphate, positive electrode active material, positive electrode plate, battery cell, battery and electrical device of the present application are described below with reference to the accompanying drawings.

[0060] [Preparation method of lithium iron phosphate]

[0061] FIG1 is a schematic diagram of a method for preparing lithium iron phosphate according to an embodiment of the present application. For example, as shown in FIG1 , the present application provides a method 100 for preparing lithium iron phosphate, and the method 100 includes the following steps.

[0062] Step 110 : adding the first iron phosphate, the second iron phosphate, and a lithium source into a solvent to obtain a slurry.

[0063] The specific surface area S1 of the first iron phosphate satisfies: 7m 2 / g≤S1≤9.5m 2 / g. S1 can be 7m 2 / g、8m 2 / g、8.5m 2 / g、9m 2 / g, 9.5m 2 / g or any value within the above range.

[0064] The size D1 of the first ferric phosphate crystals satisfies the following: 50 nm ≤ D1 ≤ 65 nm. D1 can be 50 nm, 60 nm, 65 nm, or any value within the aforementioned range.

[0065] The specific surface area S2 of the second iron phosphate satisfies: 8.5m 2 / g≤S2≤11.5m 2 / g. S2 can be 8.5m 2 / g, 9.5m 2 / g、10m 2 / g、11m 2 / g, 11.5m 2 / g or any value within the above range.

[0066] The size D2 of the second ferric phosphate crystals satisfies the following: 30 nm ≤ D2 ≤ 50 nm. D2 can be 30 nm, 40 nm, 45 nm, 50 nm, or any value within the aforementioned range. The specific surface area of ​​the second ferric phosphate is greater than the specific surface area of ​​the first ferric phosphate, and the size of the second ferric phosphate crystals is smaller than the size of the first ferric phosphate crystals.

[0067] The first iron phosphate and the second iron phosphate are single crystal materials, and the size of the grain refers to the size of a single grain.

[0068] The specific surface areas of the first ferric phosphate and the second ferric phosphate may be specific surface areas obtained by a BET specific surface area adsorption method.

[0069] There is a certain correspondence between the specific surface area and the size of the grains. For grains of the same size, the specific surface area varies slightly under the influence of different preparation processes. For example, for the second iron phosphate, when the size D2 of the second iron phosphate grains is in the range of 30nm to 50nm, due to the influence of the preparation process, the specific surface area of ​​the second iron phosphate will basically not exceed 11.5m 2 / g.

[0070] The specific surface area of ​​the second iron phosphate is greater than that of the first iron phosphate, and the reaction activity of the second iron phosphate is high. During the sintering process, the second iron phosphate reacts with the lithium source before the first iron phosphate, so the second iron phosphate reacts with the lithium source to form crystal nuclei, and the first iron phosphate reacts with the lithium source and crystallizes on the basis of the crystal nuclei formed by the second iron phosphate. In addition, the size of the second iron phosphate grains is smaller than the size of the first iron phosphate grains, so during the sintering process, the second iron phosphate reacts with the lithium source to form small and numerous crystals, which is beneficial to the subsequent reaction of the first iron phosphate with the lithium source to form more uniform grains, thereby facilitating the formation of more uniform lithium iron phosphate grains with appropriate particle size, reducing the formation of abnormally large grains, and thus facilitating the acquisition of lithium iron phosphate with higher compaction density and higher capacity.

[0071] When the first iron phosphate is used for sintering, the obtained lithium iron phosphate particles are larger, and the larger particles of lithium iron phosphate are easier to compact, which helps to improve the compaction density of the lithium iron phosphate; when the second iron phosphate is used for sintering, the obtained iron phosphate particles are smaller, and the smaller particles of lithium iron phosphate have a lithium ion escape path of suitable length, which helps the transmission and diffusion of lithium ions and helps to improve the capacity of the lithium iron phosphate; the combination of the first iron phosphate and the second iron phosphate helps to improve the compaction density and capacity of the lithium iron phosphate.

[0072] The specific surface area S1 of the first iron phosphate is not less than 7m 2 / g, the first iron phosphate has a suitable specific surface area, so that the first iron phosphate has a more suitable reaction activity, which is beneficial to reducing the risk of difficulty in generating lithium iron phosphate at a certain sintering temperature due to the low specific surface area of ​​the first iron phosphate, and is beneficial to reducing the risk of abnormal growth of lithium iron phosphate grains due to high sintering temperature; when the specific surface area S1 of the first iron phosphate is not greater than 9.5m 2 / g, the specific surface areas of the first iron phosphate and the second iron phosphate have a certain difference, which facilitates the second iron phosphate to react preferentially with the lithium source.

[0073] The specific surface area S2 of the second iron phosphate is not less than 8.5m 2 / g, the specific surface areas of the first iron phosphate and the second iron phosphate have a certain difference, which facilitates the second iron phosphate to react preferentially with the lithium source.

[0074] It should be noted that the "first" in the first iron phosphate and the "second" in the second iron phosphate are only used for distinction, indicating that the first iron phosphate and the second iron phosphate have different properties, for example, different specific surface areas, grain sizes, iron-phosphorus ratios, etc.

[0075] Optionally, in step 110 , a carbon source may be added to the solvent to prepare a carbon coating layer of a certain thickness on the surface of the lithium iron phosphate.

[0076] As an example, the solvent is water.

[0077] Step 120 , sintering the slurry to obtain lithium iron phosphate.

[0078] In step 120 , the slurry is sintered to facilitate the reaction of the first iron phosphate, the second iron phosphate, and the lithium source in the slurry to generate lithium iron phosphate.

[0079] In an embodiment of the present application, the first iron phosphate and the second iron phosphate have different grain sizes and specific surface areas. The specific surface area of ​​the first iron phosphate is smaller than the specific surface area of ​​the second iron phosphate, and the size of the grains of the first iron phosphate is larger than the size of the grains of the second iron phosphate. By combining the first iron phosphate and the second iron phosphate, lithium iron phosphate with high compaction density and high capacity can be prepared.

[0080] Generally speaking, as the specific surface area of ​​iron phosphate increases, the compacted density and capacity of the prepared iron phosphate increase. However, when the specific surface area of ​​iron phosphate reaches a certain value, the compacted density and capacity of the prepared iron phosphate are difficult to further increase. By using the combination of the first iron phosphate and the second iron phosphate with a specific specific surface area and grain size in the embodiment of the present application, the compacted density and capacity of lithium iron phosphate can be improved, so that a compacted density greater than or equal to 2.45 g / cm can be obtained. 3 , at a temperature of around 25°C, the discharge capacity at 0.1C is greater than or equal to 156mAh / g of lithium iron phosphate.

[0081] In some embodiments, the specific surface area S1 of the first iron phosphate satisfies: 8.5 m 2 / g≤S1≤9.5m 2 / g, and / or, a size D1 of the first ferric phosphate crystals satisfies: 50nm≤D1≤60nm.

[0082] As an example, the specific surface area S1 of the first iron phosphate is 8.5 m 2 / g, and the grain size D1 is 50nm.

[0083] In the above embodiment, the following three situations may be included: the specific surface area S1 of the first iron phosphate satisfies: 8.5m 2 / g≤S1≤9.5m 2 / g, the grain size D1 is not specifically limited; the size D1 of the first ferric phosphate grains satisfies: 50nm≤D1≤60nm, and the specific surface area is not specifically limited; or the specific surface area S1 of the first ferric phosphate satisfies: 8.5m 2 / g≤S1≤9.5m 2 / g, and the size D1 of the crystallites of the first iron phosphate satisfies: 50nm≤D1≤60nm.

[0084] Further limiting the specific surface area and grain size of the first iron phosphate is conducive to obtaining lithium iron phosphate with higher capacity at a lower sintering temperature.

[0085] In some embodiments, the specific surface area S2 of the second iron phosphate satisfies: 10 m 2 / g≤S2≤11.5m 2 / g, and / or, the size D2 of the second iron phosphate crystals satisfies: 30nm≤D1≤40nm.

[0086] As an example, the specific surface area S2 of the second iron phosphate is 10 m 2 / g, and the grain size D2 is 30nm.

[0087] Further limiting the specific surface area and grain size of the second iron phosphate is conducive to obtaining lithium iron phosphate with higher capacity at a lower sintering temperature.

[0088] In some embodiments, the iron-phosphorus ratio A1 of the first ferric phosphate satisfies: 0.96≤A1≤0.975; and / or the iron-phosphorus ratio A2 of the second ferric phosphate satisfies: 0.96≤A2≤0.975.

[0089] As some examples, A1 and / or A2 may also be any value between 0.963 and 0.973, for example, 0.963, 0.97, 0.973 or any value within the above range.

[0090] The iron-phosphorus ratio refers to the molar ratio of iron to phosphorus in ferric phosphate. According to the national standard HG / T4701-2021, the iron-phosphorus ratio (M) can be calculated using the following formula: M = (w1 / w2) × 0.5545, where w1 is the mass content of Fe and w2 is the mass content of P.

[0091] The iron-phosphorus ratio of the first iron phosphate and the second iron phosphate may be the same or different, as long as the iron-phosphorus ratio of the first iron phosphate and the second iron phosphate meets the above range.

[0092] When A1 or A2 is not less than 0.96, it is beneficial to the preparation and production of lithium iron phosphate, and can reduce the risk of the presence of impurities other than lithium iron phosphate in the prepared product; when A1 or A2 is not greater than 0.975, the risk of excessive grain growth of lithium iron phosphate due to an excessively large iron-phosphorus ratio can be reduced.

[0093] In this embodiment, by setting the iron-phosphorus ratio of the first iron phosphate, and / or the iron-phosphorus ratio of the second iron phosphate to meet the above range, the phosphorus element has a suitable mass proportion, which is conducive to obtaining lithium iron phosphate with a suitable grain size, reducing the risk of generating impurities, and thus obtaining lithium iron phosphate with higher capacity and compaction density.

[0094] In some embodiments, the mass ratio of the first iron phosphate to the second iron phosphate is 1:1 to 9:1.

[0095] The mass ratio of the first ferric phosphate to the second ferric phosphate can be 1:1, 6:4, 2:1, 7:3, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or any value within the above range.

[0096] The mass ratio of the first iron phosphate to the second iron phosphate refers to the mass ratio of the first iron phosphate to the second iron phosphate added during the preparation of lithium iron phosphate.

[0097] When the mass ratio of the first iron phosphate to the second iron phosphate is greater than or equal to 1:1, the first iron phosphate has a suitable mass content, which is conducive to obtaining lithium iron phosphate with a high compaction density; when the mass ratio of the first iron phosphate to the second iron phosphate is less than or equal to 9:1, the second iron phosphate has a suitable mass content, which is conducive to obtaining lithium iron phosphate with a high capacity.

[0098] In some embodiments, the mass ratio of the first iron phosphate to the second iron phosphate is 1:1 to 7:3, which is conducive to obtaining lithium iron phosphate with a high compaction density.

[0099] In some embodiments, the sintering temperature T1 satisfies: T1<800° C. In this technical solution, the reaction between the first iron phosphate, the second iron phosphate, and the lithium source can be completed at a temperature lower than 800° C., which is beneficial to energy conservation.

[0100] In some embodiments, the temperature T1 of the sintering process satisfies: 750° C. ≤ T1 ≤ 790° C. T1 can be 750° C., 760° C., 780° C., 790° C., or any value within the above range.

[0101] When the temperature T1 is greater than or equal to 750°C, the first iron phosphate, the second iron phosphate and the lithium source can react to generate lithium iron phosphate; when T1 is less than or equal to 790°C, it is beneficial to react at a lower temperature and save energy.

[0102] By setting 750° C. ≤ T1 ≤ 790° C., it is beneficial for the reaction among the first iron phosphate, the second iron phosphate and the lithium source to generate lithium iron phosphate, and it is also beneficial for saving energy.

[0103] In some embodiments, the total time t of the sintering process satisfies: 14 h ≤ t ≤ 18 h.

[0104] The total sintering time t can be 14 h, 15 h, 16 h, 18 h or any value within the above range.

[0105] The above time setting is conducive to the full progress of the reaction and can also reduce the risk of abnormal growth of lithium iron phosphate grains due to the reaction time process.

[0106] In some embodiments, the slurry is subjected to a sintering treatment, including: grinding and demagnetizing the slurry; spray drying the demagnetized slurry to obtain dry powder; and sintering the dry powder to obtain lithium iron phosphate.

[0107] Grinding the slurry can make the first iron phosphate, the second iron phosphate and the lithium source in the slurry more evenly mixed, which facilitates the subsequent reaction between the first iron phosphate, the second iron phosphate and the lithium source.

[0108] As an example, the slurry is sent to a sand mill and ground twice, namely, coarse grinding and fine grinding, to make the slurry more uniform.

[0109] Demagnetizing the slurry can remove the magnetism in the slurry and reduce the impact of magnetism on the preparation of lithium iron phosphate.

[0110] As an example, the ground slurry is sent to a demagnetizer for demagnetization to remove magnetic foreign matter in the slurry.

[0111] The demagnetized slurry is spray-dried to obtain a dry powder for subsequent sintering. As an example, the demagnetized slurry is placed in a spray dryer, and the inlet and outlet temperatures of the spray dryer are controlled to obtain a dried powder. The dried powder includes the first iron phosphate, the second iron phosphate, and a lithium source.

[0112] The dry powder is sintered to facilitate a reaction between the first iron phosphate, the second iron phosphate, and the lithium source, thereby generating lithium iron phosphate. As an example, the sintering process is performed in an inert atmosphere, such as nitrogen.

[0113] In some embodiments, after the grinding process, the volume average particle size Dv50 of the slurry satisfies: 400 nm ≤ Dv50 ≤ 600 nm.

[0114] The volume average particle size of the slurry may refer to the volume average particle size of particles of the first iron phosphate, the second iron phosphate, the lithium source, the carbon source, etc. in the slurry.

[0115] The volume average particle size Dv50 of the slurry may be 400 nm, 500 nm, 600 nm, or any value within the above range.

[0116] In this embodiment, the first iron phosphate, the second iron phosphate, the lithium source, and the carbon source in the slurry are more evenly distributed, and the slurry has better uniformity, which facilitates obtaining dry powder with a suitable particle size during the spray drying process.

[0117] In some embodiments, the volume average particle size Dv50 of the dry powder satisfies: 10 μm ≤ Dv50 ≤ 20 μm.

[0118] The volume average particle size Dv50 of the dry powder may be 10 μm, 15 μm, 20 μm, or any value within the above range.

[0119] By setting the volume average particle size of the dry powder to meet the above range, the reaction between the first iron phosphate, the second iron phosphate and the lithium source is facilitated, thereby facilitating the preparation of lithium iron phosphate.

[0120] In some embodiments, the inlet temperature T2 of the spray drying process satisfies: 190°C≤T2≤200°C, and the outlet temperature T3 of the spray drying process satisfies: 80°C≤T3≤90°C.

[0121] The inlet temperature can refer to the temperature at the slurry inlet of the spray drying equipment. The outlet temperature can refer to the temperature at the dry powder outlet of the spray drying equipment.

[0122] T2 may be 190°C, 195°C, 200°C or any value within the above ranges, and T3 may be 80°C, 85°C, 90°C or any value within the above ranges.

[0123] By setting the feed inlet temperature and the discharge outlet temperature of the drying process to meet the above range, it is convenient to obtain dry powder with a suitable particle size.

[0124] In some embodiments, the dry powder is sintered, including: in an inert atmosphere, heating the dry powder to a sintering temperature T1 within 5 to 6 hours, and keeping the dry powder at the sintering temperature T1 for 9 to 12 hours to obtain lithium iron phosphate.

[0125] The sintering treatment method of first heating the product and then sintering the product at a constant temperature is beneficial to reducing the agglomeration phenomenon in the sintered product.

[0126] In some embodiments, the dry powder may be directly placed in a sintering device at a temperature T1 to undergo a sintering process.

[0127] In some embodiments, the preparation method further includes: after sintering the dry powder, performing air flow milling on the sintered material, and the volume average particle size Dv50 of the lithium iron phosphate after the air flow milling satisfies: 0.8μm≤Dv50≤1.8μm.

[0128] The volume average particle size Dv50 of the lithium iron phosphate powder after airflow milling can be 0.8 μm, 1 μm, 1.5 μm, 1.8 μm, or any value within the above range.

[0129] By performing air flow pulverization on the sintered material, the sintered material can be pulverized into materials with smaller particles, thereby obtaining lithium iron phosphate powder with a suitable size.

[0130] As an example, after air flow crushing, screening and demagnetization, the final product lithium iron phosphate is obtained.

[0131] In some embodiments, the solid content B of the slurry satisfies: 40%≤B≤50%, so as to facilitate uniform mixing of the slurry.

[0132] The solid content B of the slurry may be 40%, 45%, 50% or any value within the above range.

[0133] In some embodiments, the molar ratio of the iron content in the first and second iron phosphates to the lithium content in the lithium source is 1:1 to 1:1.05. Thus, the first and second iron phosphates, as well as the lithium source, have a suitable molar ratio, facilitating the preparation of lithium iron phosphate through the reaction.

[0134] In some embodiments, adding the first iron phosphate, the second iron phosphate, and the lithium source to a solvent to obtain a slurry includes: adding the first iron phosphate, the second iron phosphate, the lithium source, and the carbon source to a solvent to obtain a slurry.

[0135] By adding a carbon source, lithium iron phosphate with a carbon coating layer can be obtained during the subsequent sintering process, so that the lithium iron phosphate can have better conductive properties.

[0136] In some embodiments, the ratio of the sum of the mass of the first ferric phosphate and the second ferric phosphate to the mass of the carbon source is 1:0.1 to 1:0.105.

[0137] The ratio of the sum of the masses of the first ferric phosphate and the second ferric phosphate to the mass of the carbon source can be 1:0.1, 1:0.101, 1:0.105, or any value within the above range.

[0138] By setting the ratio of the sum of the masses of the first iron phosphate and the second iron phosphate to the mass of the carbon source to meet the above range, it is possible to prepare lithium iron phosphate whose surface is coated with carbon having a suitable mass content, so that the lithium iron phosphate has better conductivity; it is also beneficial to reduce the impact of the excessively high mass content of the carbon source on the capacity of the lithium iron phosphate.

[0139] In some embodiments, the carbon source includes at least one of sucrose, glucose, dextrin, citric acid, fructose, or starch. This allows for flexible configuration of the carbon source based on actual needs.

[0140] In some embodiments, the slurry also includes a dispersant, which can reduce the viscosity of the mixed slurry and facilitate subsequent operations.

[0141] In some embodiments, the slurry further includes an additive, which may include a compound of at least one of Ti, Ga, Sr, W, Mg, Si, Y, Zr, B, Mo, or La. In the above solution, the inclusion of the additive in the slurry facilitates obtaining lithium iron phosphate doped with the above elements, thereby enabling the lithium iron phosphate to have better performance, and the battery can have properties such as ionic conductivity and high rate capability.

[0142] In some embodiments, the lithium source includes at least one of lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide, lithium phosphate, lithium acetate, or lithium oxalate.

[0143] [Positive electrode active material]

[0144] An embodiment of the present application provides a positive electrode active material, which includes lithium iron phosphate prepared by the method for preparing lithium iron phosphate according to any of the above embodiments.

[0145] In some embodiments, the compaction density of lithium iron phosphate powder at 3T is greater than or equal to 2.45 g / cm 3 .

[0146] In some embodiments, at a temperature of 25° C., the discharge capacity of the lithium iron phosphate at 0.1C is greater than or equal to 156 mAh / g.

[0147] In the above scheme, the lithium iron phosphate prepared by the preparation method of the present application can have both high compaction density and high capacity.

[0148] The compacted density of lithium iron phosphate powder can be 2.45g / cm 3 , 2.5g / cm 3 , 2.55g / cm 3 Or any value within the above range; at a temperature of 25°C, the discharge capacity of lithium iron phosphate at 0.1C can be 156mAh / g, 158mAh / g or any value within the above range.

[0149] Unless otherwise specified, the compaction density in this application refers to the compaction density of lithium iron phosphate powder under a pressure of 3T.

[0150] In some embodiments, the volume average particle size Dv50 of the lithium iron phosphate is 0.8 μm to 1.8 μm.

[0151] Specifically, the volume average particle size Dv50 of the lithium iron phosphate can be 0.8 μm, 1 μm, 1.5 μm, 1.8 μm, or any value within the above range.

[0152] In some embodiments, the lithium iron phosphate has a carbon coating.

[0153] [Positive electrode]

[0154] The present application provides a positive electrode sheet. Figure 2 is a schematic structural diagram of a positive electrode sheet according to one embodiment of the present application. As shown in Figure 2, the positive electrode sheet 121 includes a positive electrode current collector 122 and a positive electrode film layer 123 disposed on at least one side of the positive electrode current collector 122. The positive electrode film layer 123 includes lithium iron phosphate prepared according to the lithium iron phosphate preparation method described in any of the above embodiments, or the positive electrode active material described in any of the above embodiments.

[0155] Typically, a battery cell consists of a positive electrode sheet 121, a separator, a negative electrode sheet, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte transfers ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0156] The positive electrode sheet 121 includes a positive electrode current collector 122 and a positive electrode film layer 123 disposed on at least one surface of the positive electrode current collector 122 . The positive electrode film layer 123 includes lithium iron phosphate.

[0157] As an example, the positive electrode current collector 122 has two opposite surfaces in its thickness direction, and the positive electrode film layer 123 is disposed on either or both of the two opposite surfaces of the positive electrode current collector 122 .

[0158] In some embodiments, the positive electrode current collector 122 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 material base layer and a metal layer formed on at least one surface of the polymer material base layer. 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 material substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0159] In some embodiments, the positive electrode film 123 further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0160] In some embodiments, the positive electrode film layer 123 further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0161] In some embodiments, the positive electrode sheet 121 can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, and the positive electrode slurry is coated on the positive electrode current collector 122. After drying, cold pressing and other processes, the positive electrode sheet 121 can be obtained.

[0162] [Negative electrode]

[0163] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0164] As an example, the negative electrode current collector has two surfaces opposite to each other in its 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.

[0165] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0166] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. 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. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional 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.

[0167] In some embodiments, the negative electrode film layer further includes a binder. The binder can 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).

[0168] In some embodiments, the negative electrode film layer further includes a conductive agent, which can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0169] In some embodiments, the negative electrode film layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0170] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0171] [Electrolytes]

[0172] The electrolyte acts as a conductive medium between the positive electrode 121 and the negative electrode. The present application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0173] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0174] In some embodiments, the electrolyte salt can 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0175] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0176] In some embodiments, the electrolyte further includes electrolyte additives. For example, the electrolyte additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0177] [Isolation film]

[0178] In some embodiments, the battery cell further includes a separator. This application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0179] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0180] In some embodiments, the positive electrode sheet 121 , the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0181] [Battery Cell]

[0182] An embodiment of the present application provides a battery cell, comprising the positive electrode sheet in any of the above embodiments.

[0183] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0184] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0185] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square, or any other shape. Figure 3 is a schematic diagram of a battery cell according to one embodiment of the present application. For example, as shown in Figure 3, the battery cell is a square battery cell.

[0186] Figure 4 is a schematic structural diagram of a battery cell according to an embodiment of the present application. As shown in Figure 4, the outer packaging of the battery cell 100 includes a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet 121, the negative electrode sheet, and the isolation film can be formed into an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte impregnates the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 100 may be one or more, and those skilled in the art can select according to specific actual needs.

[0187] In some embodiments, the battery cells 100 may be assembled into a battery module. The battery module may contain one or more battery cells 100. The specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0188] [Battery]

[0189] An embodiment of the present application provides a battery, comprising the battery cell in any of the above embodiments, or the pole piece in any of the above embodiments.

[0190] Figure 5 is a schematic diagram of a battery according to one embodiment of the present application, and Figure 6 is a schematic diagram of the structure of a battery according to one embodiment of the present application. Referring to Figures 5 and 6, a battery 400 may include a battery box and a plurality of battery cells 100 disposed within the battery box. The battery box includes an upper box body 401 and a lower box body 402. The upper box body 401 can be placed over the lower box body 402 to form an enclosed space for accommodating the battery cells 100. The plurality of battery cells 100 can be arranged in any manner within the battery box.

[0191] [Electrical devices]

[0192] An embodiment of the present application provides an electrical device, comprising the battery in any of the above embodiments.

[0193] The electrical device may include at least one of the positive electrode sheet 121, the battery cell 100, or the battery 400 according to the embodiment of the present application. The battery cell 100 or the battery 400 may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0194] FIG7 is a schematic structural diagram of an electric device according to an embodiment of the present application. For example, as shown in FIG7 , the electric device 1 is a vehicle 1, and the vehicle 1 can be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor 500, a controller 600 and a battery 400 can be provided inside the vehicle 1, and the controller 600 is used to control the battery 400 to supply power to the motor 500. For example, a battery 400 can be provided at the bottom, front or rear of the vehicle 1. The battery 400 can be used to power the vehicle 1, for example, the battery 400 can be used as an operating power source for the vehicle 1, for the circuit system of the vehicle 1, for example, for the working power requirements during the start-up, navigation and operation of the vehicle 1. In another embodiment of the present application, the battery 400 can not only be used as an operating power source for the vehicle 1, but also as a driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0195] As the electrical device, the positive electrode sheet 121 , the battery cell 100 or the battery 400 can be selected according to its usage requirements.

[0196] The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirement for a high capacity battery, a battery cell 100 or a battery 400 may be used.

[0197] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use the battery cell 100 as a power source.

[0198] [Example]

[0199] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0200] Example 1

[0201] The preparation method of lithium iron phosphate in Example 1 is as follows:

[0202] (1) The first iron phosphate, the second iron phosphate, the lithium source, and the carbon source are mixed with water in proportion, stirred and homogenized to obtain a slurry with a solid content B of 45%, wherein the mass ratio of the first iron phosphate to the second iron phosphate is 1:1, the molar ratio of the iron element in the first iron phosphate and the second iron phosphate to the lithium element in the lithium source is 1:1.05, the mass ratio of the sum of the mass of the first iron phosphate and the second iron phosphate to the mass of the carbon source is 1:0.105, and the specific surface area S1 of the first iron phosphate is 8.5 m 2 / g, the grain size D1 is 60nm, the iron-phosphorus ratio in the first iron phosphate is 0.964, and the specific surface area S2 of the second iron phosphate is 10m 2 / g, the grain size D2 is 40nm, the iron-phosphorus ratio of the second iron phosphate is 0.967; the lithium source is lithium carbonate, the carbon source is glucose and polyethylene glycol (PEG), and the mass ratio of glucose to PEG is 4:1;

[0203] (2) Grind the slurry thoroughly, control the grinding particle size Dv50 at 0.52 μm, and send it into the finished product tank after demagnetization for 90 minutes;

[0204] (3) spray drying the slurry in the finished product tank to obtain a dry powder with a volume average particle size Dv50 of 12 μm;

[0205] (4) feeding the dry powder into a kiln for sintering under the following conditions: under nitrogen protection, with an oxygen content of less than 30 ppm, a furnace pressure of 20-30 Pa, and a bowl thickness of 10 cm; the total sintering time t is 18 hours, wherein the temperature is raised to 790°C in 6 hours, then kept at 790°C for 12 hours, and cooled to less than 80°C before being taken out of the kiln to obtain the sintered material;

[0206] (5) The sintered material was crushed, screened, and demagnetized to obtain finished lithium iron phosphate with a volume average particle size Dv50 of 1.246 μm and Dv99 of 8.207 μm. The compaction density of the obtained lithium iron phosphate powder under a pressure of 3T was 2.60 g / cm 3 At a temperature of 25°C, the first discharge capacity at 0.1C reaches 156.7mAh / g.

[0207] In Examples 2-9, the preparation method of lithium iron phosphate is substantially the same as that of Example 1, and the differences are briefly described below.

[0208] Example 2

[0209] The difference between Example 2 and Example 1 is that the mass ratio of the first iron phosphate to the second iron phosphate is 6:4.

[0210] In step (1), the mass ratio of the sum of the mass of the first iron phosphate and the second iron phosphate to the mass of the carbon source is 1:0.104; in step (2), the particle size Dv50 of the slurry is 0.55 μm; in step (4), the temperature is raised to 775°C in 6 hours and then kept at 775°C for 12 hours; in step (5), a finished product lithium iron phosphate with a volume average particle size Dv50 of 1.239 μm and a Dv99 of 8.222 μm is obtained. The compacted density of the obtained lithium iron phosphate powder under a pressure of 3T is 2.56 g / cm 3 At a temperature of 25°C, the first discharge capacity at 0.1C reaches 156.6mAh / g.

[0211] Example 3

[0212] The difference between Example 3 and Example 1 is that the mass ratio of the first iron phosphate to the second iron phosphate is 7:3.

[0213] In step (1), the mass ratio of the sum of the mass of the first iron phosphate and the second iron phosphate to the mass of the carbon source is 1:0.103; in step (2), the particle size Dv50 of the slurry is 0.53 μm; in step (4), the total sintering time t is 16.5 h, the temperature is raised to 765°C in 5.5 hours, and then kept at 765°C for 11 hours; in step (5), a finished product lithium iron phosphate with a volume average particle size Dv50 of 1.473 μm and a Dv99 of 8.124 μm is obtained. The compaction density of the obtained lithium iron phosphate powder under a pressure of 3T is 2.53 g / cm 3 At a temperature of 25°C, the first discharge capacity at 0.1C reaches 157.1mAh / g.

[0214] Example 4

[0215] The difference between Example 4 and Example 1 is that the mass ratio of the first iron phosphate to the second iron phosphate is 9:1.

[0216] In step (1), the mass ratio of the sum of the mass of the first iron phosphate and the second iron phosphate to the mass of the carbon source is 1:0.1; in step (2), the particle size Dv50 of the slurry is 0.5 μm; in step (4), the total sintering time t is 14 hours, the temperature is raised to 750°C in 5 hours, and then kept at 750°C for 9 hours; in step (5), a finished lithium iron phosphate with a volume average particle size Dv50 of 1.221 μm and a Dv99 of 7.096 μm is obtained. The compaction density of the obtained lithium iron phosphate powder under a pressure of 3T is 2.45 g / cm 3 At a temperature of 25°C, the first discharge capacity at 0.1C reaches 156.8mAh / g.

[0217] Example 5

[0218] The difference between Example 5 and Example 1 is that the total sintering time t is 14 hours, the temperature is raised to 765° C. in 5 hours, and then kept at 765° C. for 9 hours.

[0219] In step (1), the mass ratio of the sum of the mass of the first iron phosphate and the second iron phosphate to the mass of the carbon source is 1:0.1; in step (2), the particle size Dv50 of the slurry is 0.51 μm; in step (5), a finished product of lithium iron phosphate having a volume average particle size Dv50 of 1.112 μm and a Dv99 of 8.585 μm is obtained. The compaction density of the obtained lithium iron phosphate powder under a pressure of 3T is 2.45 g / cm 3 At a temperature of 25°C, the first discharge capacity at 0.1C reaches 159.8mAh / g.

[0220] During the sintering process, the higher the sintering temperature, the greater the loss of the carbon source. In Examples 1-5, in order to provide a certain carbon coating layer on the surface of the lithium iron phosphate, the mass ratio of the sum of the mass of the first iron phosphate and the second iron phosphate to the mass of the carbon source is slightly different.

[0221] Examples 6-7

[0222] The difference between Example 6-7 and Example 1 is that the specific surface area and the size of the crystal grains of the first iron phosphate, as well as the specific surface area and the size of the crystal grains of the second iron phosphate are different.

[0223] Examples 8-9

[0224] The difference between Example 8-9 and Example 1 is that the iron-phosphorus ratio of the first iron phosphate and the second iron phosphate is different.

[0225] Examples 10-11

[0226] The difference between Example 10-11 and Example 1 is that the specific surface area and the size of the crystal grains of the first iron phosphate are different.

[0227] Examples 12-13

[0228] The difference between Example 12-13 and Example 1 is that the specific surface area and grain size of the second iron phosphate are different.

[0229] Comparative Example 1

[0230] In Comparative Example 1, the second iron phosphate was not added. The compacted density of the obtained lithium iron phosphate powder under a pressure of 3T was 2.45 g / cm 3 At a temperature of 25°C and a 0.1C first discharge capacity of 152.6 mAh / g.

[0231] Comparative Example 2

[0232] In Comparative Example 2, the first iron phosphate was not added. The compacted density of the obtained lithium iron phosphate powder under a pressure of 3T was 2.31 g / cm 3 At a temperature of 25°C and a 0.1C first discharge capacity of 160.6 mAh / g.

[0233] Comparative Example 3

[0234] In Comparative Example 3, the specific surface area S1 of the first iron phosphate is 6.5 m 2 / g, the size of the grain D1 is 85nm; the specific surface area S2 of the second iron phosphate is 8m 2 / g, and the grain size D2 is 70nm. The compaction density of the obtained lithium iron phosphate powder under 3T pressure is 2.43g / cm 3 , at a temperature of 25°C and a 0.1C first discharge capacity of 155mAh / g.

[0235] Comparative Example 4

[0236] In Comparative Example 4, the specific surface area S1 of the first iron phosphate is 7 m 2 / g, the grain size D1 is 65nm; the specific surface area S2 of the second iron phosphate is 8m 2 / g, and the grain size D2 is 70nm. The compaction density of the obtained lithium iron phosphate powder under 3T pressure is 2.45g / cm 3 , at a temperature of 25°C, the first discharge capacity at 0.1C is 152mAh / g.

[0237] Comparative Example 5

[0238] In Comparative Example 5, the specific surface area S1 of the first iron phosphate is 6.5 m 2 / g, the grain size D1 is 85nm; the specific surface area S2 of the second iron phosphate is 8.5m 2 / g, and the grain size D2 is 50nm. The compaction density of the obtained lithium iron phosphate powder under 3T pressure is 2.45g / cm 3 At a temperature of 25°C and a 0.1C first discharge capacity of 154.6 mAh / g.

[0239] Table 1 Relevant parameters of the preparation methods of Examples and Comparative Examples

[0240] Table 2 Experimental results of the comparative examples of the embodiments

[0241] [Preparation of lithium-ion half-cells]

[0242] Preparation of positive electrode sheets: Lithium iron phosphate powder, conductive agent carbon black (SP), and positive electrode binder polyvinylidene fluoride (PVDF) are dissolved in solvent N-methylpyrrolidone (NMP) in a weight ratio of 90%:5%:5%, and the mixture is thoroughly stirred and mixed to prepare a positive electrode slurry. The positive electrode slurry is coated on Al foil, and then dried, cold pressed, and cut to obtain positive electrode sheets.

[0243] Preparation of negative electrode sheet: The negative electrode sheet is a lithium sheet.

[0244] Preparation of diaphragm: PE porous polymer film is used as the isolation membrane.

[0245] Electrolyte: Dissolve EC / EMC / DMC in 1M LiPF6 at a volume ratio of 1:1:1 and stir evenly to obtain 1 mol / L LiPF6 electrolyte.

[0246] The positive electrode sheet, the negative electrode sheet, the separator and the electrolyte are assembled into a lithium-ion half-cell.

[0247] [Grain size test]

[0248] Diffraction patterns were measured using a Bruker D8 DISCOVER X-ray diffractometer. The convolution method in JEDA software was used to deconvolute the full spectrum and obtain the sample's grain size information. As an example, a diffraction pattern was obtained using a Bruker D8 DISCOVER X-ray diffractometer. TOPAS software was used during data refinement to calculate peak shape using the convolution method. The full spectrum was fitted using the basic instrument parameter method, and the sample's grain size information was deconvoluted from the full spectrum.

[0249] [Iron-phosphorus ratio test]

[0250] The Fe content and P content were tested by potassium dichromate titration and quinolyl gravitational method respectively, and then the iron-phosphorus ratio was calculated according to the formula: Fe content × 0.5546 / P content. The specific operation can refer to the standard: HG / T 4701-2021.

[0251] [Volume particle size distribution test]

[0252] Take an appropriate amount of the sample to be tested (the sample concentration is sufficient to ensure 8-12% shading), add 20 ml of deionized water, and simultaneously ultraviolet (53KHz / 120W) for 5 minutes to ensure that the sample is completely dispersed. Then, the sample is measured using a Malvern 3000 (MasterSizer 3000) laser particle size analyzer in accordance with GB / T19077-2016 / ISO 13320:2009 standard.

[0253] [Test of compaction density]

[0254] A certain amount of powder is placed in a compaction die of known diameter (for example, the Sansi Zongheng UTM7305). A metal sheet is placed above and below the die, with the powder placed in the middle. A pressure of 3T is applied while measuring the corresponding powder thickness. The compaction density is calculated using the formula ρ = m / v. Specific procedures can be performed in accordance with the standard: GB / T24533-2009.

[0255] [0.1C rate performance test]

[0256] At room temperature (25°C), charge the battery at a constant current of 0.1C to 3.75V, then charge at a constant voltage of 3.75V to a current of 50uA and leave it for 5 minutes; then discharge at 0.1C to 2.0V and cycle twice; make 4 batteries at the same time and take the average of the two middle groups of results as the result.

[0257] [1C rate performance test]

[0258] At room temperature (25°C), charge the battery to 3.75V at a constant current of 0.1C, then charge it to a current of 50uA at a constant voltage of 3.75V, and let it sit for 5 minutes; then discharge it to 2.0V at 0.1C, make 4 batteries at the same time, and take the average of the two middle groups of results as the result; then charge the battery to 3.75V at a constant current of 1C, then charge it to a current of 50uA at a constant voltage of 3.75V, and let it sit for 5 minutes; then discharge it to 2.0V at 0.1C, make 4 batteries at the same time, and take the average of the two middle groups of results as the result.

[0259] Figure 8 is a graph showing the initial charge-discharge curve at a 0.1C rate for an embodiment of the present application, and Figure 9 is a SEM image of the lithium iron phosphate for an embodiment of the present application. Specifically, Figures 8 and 9 are schematic diagrams of the relevant tests for Example 1 of the present application. Combined with Figure 9, the lithium iron phosphate has a relatively uniform particle size distribution.

[0260] As shown in Examples 1-9 and Comparative Examples 1-5, in the preparation method of lithium iron phosphate of the present invention, by combining the first iron phosphate and the second iron phosphate with specific specific surface area and grain size, lithium iron phosphate with high compaction density and high capacity can be prepared. The compaction density of the lithium iron phosphate powder can reach or even exceed 2.45g / cm 3 The capacity of the battery at 0.1C exceeds 156mAh / g, and the capacity of the battery at 1C exceeds 135mAh / g.

[0261] As shown in Examples 1-4, the temperature and time of the sintering treatment can be set according to the mass ratio of the first iron phosphate to the second iron phosphate, so as to obtain lithium iron phosphate with high compaction density and capacity.

[0262] As shown in Examples 1 and 5, reducing the temperature and time of the sintering treatment can obtain lithium iron phosphate with a smaller particle size, and the compaction density of the lithium iron phosphate is slightly increased, while the capacity is greatly increased.

[0263] Combined with Examples 6-7 and 10-13, the specific surface area of ​​the first iron phosphate is set to 7m 2 / g~9.5m 2 / g, the grain size is 50nm~65nm, and the specific surface area of ​​the second iron phosphate is 8.5m 2 / g~11.5m 2 / g, and the grain size is 30nm to 50nm, which is conducive to the preparation of lithium iron phosphate with high compaction density and high capacity.

[0264] As shown in Examples 8-9, by setting the iron-phosphorus ratio of the first iron phosphate and the second iron phosphate within the range of 0.96 to 0.975, it is advantageous to prepare lithium iron phosphate with high compaction density and high capacity at a temperature less than 800°C.

[0265] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing lithium iron phosphate, characterized in that: include: adding the first iron phosphate, the second iron phosphate, and a lithium source into a solvent to obtain a slurry; The slurry is sintered to obtain lithium iron phosphate; wherein, The specific surface area S1 of the first iron phosphate satisfies: 7m 2 / g≤S1≤9.5m 2 / g, the size D1 of the first ferric phosphate crystals satisfies: 50nm≤D1≤65nm; The specific surface area S2 of the second iron phosphate satisfies: 8.5m 2 / g≤S2≤11.5m 2 / g, the size D2 of the second iron phosphate grains satisfies: 30nm≤D2≤50nm, the specific surface area of ​​the second iron phosphate is greater than the specific surface area of ​​the first iron phosphate, and the size of the second iron phosphate grains is smaller than the size of the first iron phosphate grains.

2. The preparation method according to claim 1, characterized in that The specific surface area S1 of the first iron phosphate satisfies: 8.5m 2 / g≤S1≤9.5m 2 / g, and / or, the size D1 of the first ferric phosphate grains satisfies: 50nm≤D1≤60nm.

3. The preparation method according to claim 1 or 2, characterized in that The specific surface area S2 of the second iron phosphate satisfies: 10m 2 / g≤S2≤11.5m 2 / g, and / or, the size D2 of the second ferric phosphate crystals satisfies: 30nm≤D2≤40nm.

4. The preparation method according to any one of claims 1 to 3, characterized in that The iron-to-phosphorus ratio A1 of the first ferric phosphate satisfies: 0.96≤A1≤0.975; and / or the iron-to-phosphorus ratio A2 of the second ferric phosphate satisfies: 0.96≤A2≤0.

975.

5. The preparation method according to any one of claims 1 to 4, characterized in that The mass ratio of the first ferric phosphate to the second ferric phosphate is 1:1 to 9:

1.

6. The preparation method according to any one of claims 1 to 5, characterized in that The temperature T1 of the sintering process satisfies: T1<800°C.

7. The preparation method according to claim 6, characterized in that The temperature T1 of the sintering process satisfies: 750°C≤T1≤790°C.

8. The preparation method according to any one of claims 1 to 7, characterized in that The total time t of the sintering process satisfies: 14h≤t≤18h.

9. The preparation method according to any one of claims 1 to 8, characterized in that The sintering treatment of the slurry comprises: performing grinding and demagnetization treatment on the slurry; The demagnetized slurry is spray-dried to obtain a dry powder; The dry powder is sintered to obtain the lithium iron phosphate.

10. The preparation method according to claim 9, characterized in that The sintering process of the dry powder comprises: In an inert atmosphere, the dry powder is heated to the sintering temperature T1 within 5 to 6 hours, and the dry powder is kept at the sintering temperature T1 for 9 to 12 hours to obtain the lithium iron phosphate.

11. The preparation method according to claim 9 or 10, characterized in that: The preparation method further comprises: After the dry powder is sintered, the sintered material is subjected to air flow milling.

12. The preparation method according to any one of claims 1 to 11, characterized in that The molar ratio of the iron content in the first iron phosphate and the second iron phosphate to the lithium content in the lithium source is 1:1 to 1:1.

05.

13. The preparation method according to any one of claims 1 to 12, characterized in that The step of adding the first iron phosphate, the second iron phosphate, and the lithium source to a solvent to obtain a slurry comprises: The first ferric phosphate, the second ferric phosphate, the lithium source, and a carbon source are added to the solvent to obtain the slurry.

14. The preparation method according to claim 13, characterized in that The ratio of the sum of the mass of the first ferric phosphate and the second ferric phosphate to the mass of the carbon source is 1:0.1 to 1:0.

105.

15. The preparation method according to claim 13 or 14, characterized in that: The carbon source includes at least one of sucrose, glucose, dextrin, citric acid, fructose or starch.

16. A positive electrode active material, characterized in that The positive electrode active material includes lithium iron phosphate prepared by the preparation method according to any one of claims 1 to 15.

17. The positive electrode active material according to claim 16, characterized in that The compaction density of the lithium iron phosphate powder at 3T is greater than or equal to 2.45 g / cm 3 .

18. The positive electrode active material according to claim 17, characterized in that At a temperature of 25° C., the discharge capacity of the lithium iron phosphate at 0.1C is greater than or equal to 156 mAh / g.

19. The positive electrode active material according to any one of claims 16 to 18, characterized in that The volume average particle size Dv50 of the lithium iron phosphate satisfies: 0.8 μm≤Dv50≤1.8 μm.

20. A positive electrode plate, characterized in that: include: A positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, The positive electrode film layer comprises lithium iron phosphate prepared by the preparation method according to any one of claims 1 to 15 or the positive electrode active material according to any one of claims 16 to 19.

21. A battery, characterized in that: Including the positive electrode sheet according to claim 20.

22. An electrical device, characterized in that: Comprising the battery of claim 21.

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