Lithium iron phosphate positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application provides a lithium iron phosphate positive electrode material, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion batteries. The preparation method of the lithium iron phosphate positive electrode material comprises the following steps: mixing and grinding raw materials containing a lithium source, an iron source, a phosphorus source and a carbon source to obtain a first precursor; mixing the first precursor with an alkali metal chloride to obtain a second precursor; and sintering, cooling and washing the second precursor to obtain the lithium iron phosphate positive electrode material. By using the alkali metal chloride to reduce the sintering temperature, on the one hand, the process energy consumption is reduced, and on the other hand, the lithium iron phosphate particles can be combined more closely, the compaction density is improved, the discharge capacity of the lithium iron phosphate positive electrode material is improved, and the electrochemical performance of the lithium ion battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a lithium iron phosphate positive electrode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] In the positive electrode material of lithium ion batteries, lithium iron phosphate (LiFePO4) has become one of the mainstream positive electrode materials because of its good thermal stability and safety, and it also has the advantages of long cycle life, environmental protection, low cost, etc.

[0003] Although lithium iron phosphate material has been applied to commercial batteries, there are still some performance problems, such as low ion and electron conductivity of lithium iron phosphate material, poor low-temperature performance and rate performance of the battery, which limit the application of lithium iron phosphate material in the next generation of lithium ion batteries. At present, it is generally recognized that the electrochemical performance is closely related to the morphology and crystal orientation of LiFePO4 particles. When the particle size is less than 100 nm, the phase transition of nano lithium iron phosphate material no longer follows the two-phase mechanism with phase interface, but changes into a non-equilibrium solid solution mechanism. Since there is no structure mismatch in the solid solution, the rate performance and cycle stability of lithium iron phosphate material will be significantly improved. At the same time, the Li + The increase in the number of transmission channels and the reduction in length make the Li-Fe anti-site defects have less impact on Li + transport. Therefore, it is necessary to provide a method for regulating the crystal nucleus growth of nano lithium iron phosphate material to prepare lithium iron phosphate positive electrode material with excellent electrochemical performance. SUMMARY

[0004] The purpose of the present application is to provide a lithium iron phosphate positive electrode material, a preparation method thereof and a lithium ion battery, mainly for regulating the crystal nucleus growth of lithium iron phosphate to obtain better particle size and compaction, improve its discharge capacity and improve its electrochemical performance.

[0005] To achieve the above purpose, the technical solutions of the present application are as follows:

[0006] The present application provides a preparation method of a lithium iron phosphate positive electrode material, comprising:

[0007] Mixing and grinding raw materials containing lithium source, iron source, phosphorus source and carbon source to obtain a first precursor;

[0008] Mixing the first precursor with an alkali metal chloride to obtain a second precursor;

[0009] Sintering, cooling and washing the second precursor to obtain the lithium iron phosphate positive electrode material.

[0010] Preferably, the lithium source comprises at least one of lithium hydroxide, lithium carbonate, lithium phosphate, lithium sulfate, lithium acetate, lithium phosphate, lithium fluoride;

[0011] And / or, the iron source comprises at least one of ferric nitrate, ferrous oxalate, iron phosphate, ferrous phosphate, iron hydroxyl oxide, iron hydroxide;

[0012] And / or, the phosphorus source comprises at least one of phosphoric acid, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, ferrous phosphate, lithium phosphate, lithium dihydrogen phosphate;

[0013] And / or, the carbon source comprises at least one of glucose, sucrose, starch, polyethylene glycol;

[0014] And / or, the alkali metal chloride comprises at least one of zinc chloride, magnesium chloride, lithium chloride, rubidium chloride.

[0015] Preferably, the molar ratio of Li element:Fe element:P element in the lithium source, iron source, and phosphorus source is (0.9-1.3):1:(1-1.04);

[0016] And / or, the molar ratio of the carbon source and the lithium source is (0.95-1.1):1;

[0017] And / or, the mass of the alkali metal chloride is 0.1%-10% of the mass of the first precursor.

[0018] Preferably, the grinding method comprises wet ball milling with a ball mill;

[0019] And / or, the particle size of the first precursor is ≤50nm;

[0020] And / or, the preparation method of the second precursor comprises dry ball milling the first precursor with the alkali metal chloride for 4h-6h.

[0021] Further preferably, the wet ball milling time is 6h-10h;

[0022] And / or, after the wet ball milling, the method further comprises drying the wet ball milling product at 50℃-80℃ to obtain the first precursor.

[0023] Preferably, the sintering comprises first sintering and second sintering.

[0024] Further preferably, the first sintering comprises increasing the temperature from room temperature to 350℃-410℃ at a temperature increasing rate of 3℃ / min-7℃ / min under the protection of inert gas, and holding for 3h-5h;

[0025] And / or, the second sintering comprises: under the protection of inert gas, increasing the temperature from room temperature to 470-530 DEG C at a temperature increasing rate of 3 DEG C / min-7 DEG C / min, and keeping the temperature for 7-10 hours.

[0026] Preferably, the washing comprises: washing the cooled product 4-5 times with water, and then drying to obtain the lithium iron phosphate positive electrode material.

[0027] The application provides a lithium iron phosphate positive electrode material prepared by the above method.

[0028] And / or, the compaction density of the lithium iron phosphate positive electrode material is 2.13 g / cm 3 -2.60 g / cm 3 ;

[0029] And / or, the D50 particle size of the lithium iron phosphate positive electrode material is 1.52-9.23 mu m.

[0030] The application also provides a lithium ion battery comprising the above lithium iron phosphate positive electrode material.

[0031] The application has the following advantages:

[0032] In the preparation method of the lithium iron phosphate positive electrode material, the alkali metal chloride is added as a cosolvent to reduce the sintering temperature of the lithium iron phosphate positive electrode material, which reduces the energy consumption of the preparation process and makes the particles combine more closely, thereby improving the compaction density of the positive electrode material, increasing the discharge capacity, and improving the electrochemical performance of the lithium ion battery. At the same time, the low sintering temperature cannot overcome the energy barrier of the simultaneous doping of alkali metal ions and chloride ions into the lithium iron phosphate material, so the alkali metal chloride exists in a stable state, and is removed by washing, so that there is no other impurity element doped in the lithium iron phosphate positive electrode material.

[0033] Further, by adjusting the temperature and temperature increasing rate of the first sintering and the second sintering, the growth of the lithium iron phosphate crystal nucleus can be controlled, especially as the sintering temperature and the temperature increasing rate increase, the crystallinity of the crystal nucleus increases, the order degree of the lithium iron phosphate crystal nucleus arrangement increases, and the compaction density increases, so that the lithium iron phosphate material obtained has the shortest b-axis length, the diffusion distance of lithium ions is reduced, and the 0.1C and 1C discharge capacities are the highest. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation on the scope of the application.

[0035] Figure 1 The XRD patterns of the lithium iron phosphate materials prepared in Examples 1-3 and Comparative Examples 1-3 are shown below.

[0036] Figure 2 Here is a SEM image of the lithium iron phosphate material prepared in Example 1;

[0037] Figure 3 SEM image of the lithium iron phosphate material prepared in Example 2;

[0038] Figure 4 Here is a SEM image of the lithium iron phosphate material prepared in Example 3;

[0039] Figure 5 The image shows the SEM-EDS energy spectrum of the lithium iron phosphate material prepared in Example 3. Detailed Implementation

[0040] As used in this article:

[0041] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus. The conjunction "composed of" excludes any unnamed elements, steps, or components.

[0042] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0043] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0044] "Quality parts" refers to the basic unit of measurement indicating the mass ratio relationship of multiple components, 1 part can represent any unit mass, such as 1g, 2.689g, etc. If we say that the mass of component A is a parts, and the mass of component B is b parts, it means that the mass ratio of component A to component B is a:b. Alternatively, the mass of component A is aK, and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that unlike the mass parts, the sum of the mass parts of all components is not limited to 100 parts.

[0045] "and / or" is used to indicate that one or both of the described cases can occur, for example, A and / or B includes (A and B) and (A or B).

[0046] The application provides a preparation method of a lithium iron phosphate positive electrode material, comprising:

[0047] S1, mixing, grinding raw materials containing lithium source, iron source, phosphorus source and carbon source to obtain a first precursor;

[0048] S2, mixing the first precursor with alkali metal chloride to obtain a second precursor;

[0049] S3, sintering, cooling and washing the second precursor to obtain the lithium iron phosphate positive electrode material.

[0050] In an embodiment of the application, the grinding in S1 includes wet ball milling with a ball mill.

[0051] Specifically, after mixing the lithium source, iron source, phosphorus source and carbon source, a premix material is obtained, and then the premix material and anhydrous ethanol are added to the ball mill for wet ball milling for 6-10h, and then the ball milling product is dried at 50-80℃ to obtain the first precursor.

[0052] In an embodiment of the application, the particle size of the first precursor obtained in S1 is ≤50nm, which is used for subsequent preparation of nanoscale lithium iron phosphate positive electrode material.

[0053] In an embodiment of the application, the molar ratio of Li element:Fe element:P element in the lithium source, iron source and phosphorus source in S1 is (0.9-1.3):1:(1-1.04), for example, it can be 0.9:1:1, 1:1.01:1, 1.1:1:1.02, 1.2:1:1.03, 1.3:1:1.04 or any value between (0.9-1.3):1:(1-1.04).

[0054] In an embodiment of the present application, the molar ratio of the carbon source and the lithium source in S1 is (0.95-1.1):1, for example, it can be 0.95:1, 0.96:1, 0.98:1, 1:1, 1.1:1, or any value between (0.95-1.1):1.

[0055] In an embodiment of the present application, the alkali metal chloride in S2 includes at least one of zinc chloride, magnesium chloride, lithium chloride, rubidium chloride; the mass of the alkali metal chloride is 0.1%-10% of the mass of the first precursor, for example, it can be 0.1%, 1%, 3%, 5%, 7%, 10%, or any value between 0.1%-10%.

[0056] In an embodiment of the present application, the first precursor and the alkali metal chloride in S2 are dry ball-milled for 4h-6h to obtain the second precursor in powder form.

[0057] In an embodiment of the present application, the sintering in S3 includes first sintering and second sintering.

[0058] The first sintering includes: under the protection of inert gas, increasing the temperature from room temperature to 350℃-410℃ at a temperature increasing rate of 3℃ / min-7℃ / min, for example, it can be 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, or any value between 3℃ / min-7℃ / min, and holding for 3h-5h, more preferably for 4h.

[0059] The second sintering includes: under the protection of inert gas, increasing the temperature from room temperature to 470℃-530℃ at a temperature increasing rate of 3℃ / min-7℃ / min, for example, it can be 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, or any value between 470℃-530℃, and holding for 7h-10h, more preferably for 8h.

[0060] It should be noted that the sintering temperature used in the present application is lower than the sintering temperature of the prior art for preparing lithium iron phosphate material, on the one hand, in order to reduce the sintering energy consumption, on the other hand, at a low sintering temperature, after the particles contact each other, the atoms between the particles can diffuse to each other, so that the combination between the particles is more compact.

[0061] In an embodiment of the present application, the washing in S3 includes: washing the product obtained after sintering and cooling for 4-5 times, and then drying to obtain the lithium iron phosphate positive electrode material.

[0062] The embodiments of the present application will be described in detail below with specific examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be obtained by commercial purchase.

[0063] Example 1

[0064] The present embodiment provides a lithium iron phosphate material, and a preparation method thereof includes the following steps:

[0065] (1) 7.46 g of lithium carbonate, 81.2 g of iron nitrate, 23.24 g of ammonium dihydrogen phosphate, and 17.28 g of glucose were weighed and uniformly mixed to obtain a mixture.

[0066] (2) 30 mL of anhydrous ethanol was added to the mixture of step (1), and ball milling was performed for 6 h, and then drying was performed at 60°C to obtain a powdery first precursor.

[0067] (3) 0.1% of zinc chloride by mass was added to the first precursor, and ball milling was performed for 4 h to obtain a powdery second precursor.

[0068] (4) The powdery second precursor of step (3) was sintered under a nitrogen atmosphere, and the sintering was specifically divided into a first sintering stage and a second sintering stage; in the first sintering stage, the temperature was raised from room temperature to 350°C at a rate of 3°C / min, and sintering was performed for 4 h; in the second sintering stage, the temperature was sintered from room temperature to 470°C at a rate of 3°C / min, and sintering was performed for 8 h, and then natural cooling was performed to room temperature to obtain a sintered material.

[0069] (5) The sintered material obtained in step (4) was washed with distilled water for 4-5 times, and then drying was performed to obtain a lithium iron phosphate positive electrode material.

[0070] Example 2

[0071] The present embodiment provides a lithium iron phosphate material, and a preparation method thereof is the same as that of Example 1, except that 0.1% of magnesium chloride by mass was added to the first precursor in step (3).

[0072] In the first sintering stage of step (4), the temperature was raised from room temperature to 380°C at a rate of 5°C / min, and sintering was performed for 4 h; in the second sintering stage, the temperature was sintered from room temperature to 500°C at a rate of 5°C / min, and sintering was performed for 8 h.

[0073] Example 3

[0074] The present example provides a lithium iron phosphate material, the preparation method of which is the same as that of Example 1, except that in step (3), 0.1% of lithium chloride is added to the first precursor by mass;

[0075] The first sintering stage in step (4) is to increase the temperature from room temperature to 410°C at a rate of 7°C / min, and sinter for 4h; the second sintering stage is to sinter from room temperature to 530°C at a rate of 7°C / min, and sinter for 8h.

[0076] Example 4

[0077] The present example provides a lithium iron phosphate material, the preparation method of which is the same as that of Example 3, except that in step (3), 10% of lithium chloride is added to the first precursor by mass.

[0078] Example 5

[0079] The present example provides a lithium iron phosphate material, the preparation method of which is the same as that of Example 3, except that in step (4), the first sintering stage is to increase the temperature from room temperature to 380°C at a rate of 7°C / min, and sinter for 4h; the second sintering stage is to sinter from room temperature to 500°C at a rate of 7°C / min, and sinter for 8h.

[0080] Example 6

[0081] The present example provides a lithium iron phosphate material, the preparation method of which is the same as that of Example 3, except that in step (4), the first sintering stage is to increase the temperature from room temperature to 350°C at a rate of 7°C / min, and sinter for 4h; the second sintering stage is to sinter from room temperature to 470°C at a rate of 7°C / min, and sinter for 8h.

[0082] Comparative Example 1

[0083] The present comparative example provides a lithium iron phosphate material, the preparation method of which is the same as that of Example 1, except that in step (4), the first sintering stage is to increase the temperature from room temperature to 350°C at a rate of 1°C / min, and sinter for 4h; the second sintering stage is to sinter from room temperature to 470°C at a rate of 1°C / min, and sinter for 8h.

[0084] Comparative Example 2

[0085] The present comparative example provides a lithium iron phosphate material, the preparation method of which is the same as that of Example 1, except that in step (4), the first sintering stage is to increase the temperature from room temperature to 350°C at a rate of 10°C / min, and sinter for 4h; the second sintering stage is to sinter from room temperature to 470°C at a rate of 10°C / min, and sinter for 8h.

[0086] Comparative Example 3

[0087] The comparative example 4 provides a lithium iron phosphate material, which is prepared by the method of the example 1, except that after step (2), the first precursor is directly subjected to the first sintering and the second sintering in step (4).

[0088] The comparative example 4 provides a lithium iron phosphate material, which is prepared by the method of the example 1, except that after step (2), the first precursor is directly subjected to the first sintering and the second sintering in step (4).

[0089] The comparative example 4 provides a lithium iron phosphate material, which is prepared by the method of the example 1, except that after step (2), the first precursor is directly subjected to the first sintering and the second sintering in step (4).

[0090] Test part

[0091] The lithium iron phosphate materials prepared in the above examples and comparative examples are subjected to phase characterization (XRD) test and morphology characterization (SEM) test.

[0092] The XRD diffractometer uses Cu target Kα radiation, λ = 0.15406 nm, and the XRD spectrum of the lithium iron phosphate sample is obtained by testing; the SEM image of the sample is obtained by field emission scanning electron microscope and energy dispersive spectrometer.

[0093] Figure 1 The XRD spectrum of the lithium iron phosphate material prepared in the examples 1-3 and the comparative examples 1-3 is given. It can be seen from the XRD spectrum that there is no impurity phase in the lithium iron phosphate material synthesized in the examples of the present application.

[0094] Figure 2 、 Figure 3 、 Figure 4 The SEM images of the lithium iron phosphate materials prepared in the examples 1-3 are given respectively. It can be seen from the SEM images that with the increase of the sintering temperature and the heating rate, especially with the increase of the first sintering temperature, the second sintering temperature and the heating rate of each stage, the particle size of the prepared lithium iron phosphate material gradually increases, and the adhesion effect of the particles gradually weakens.

[0095] Figure 5 The SEM-EDS energy spectrum of the lithium iron phosphate material prepared in the example 3 is given. The EDS energy spectrum is compared with the XRD spectrum of the lithium iron phosphate material prepared in the example 3. Figure 1The XRD results are combined, and it is known that the lithium iron phosphate material synthesized and prepared in the application does not have magnesium, zinc, rubidium, chlorine and other elements doped, and the carbon, oxygen, phosphorus, iron elements are uniformly distributed, which further indicates that there is no other impurity phase in the synthesized lithium iron phosphate material. This may be because the alkali metal chloride as a complexing agent reduces the sintering temperature, and thus cannot overcome the energy barrier of the simultaneous doping of alkali metal ions and chloride ions into the lithium iron phosphate material, so the alkali metal chloride exists in a stable state, and after subsequent water washing, it is successfully separated from the lithium iron phosphate material, ensuring that there is no other impurity phase in the lithium iron phosphate.

[0096] The lithium iron phosphate material prepared in each of the above examples and comparative examples was also subjected to particle size D50, compaction density, a, b, and c axes of the crystal grain, and electrochemical performance tests, and the test results are shown in Table 1. Among them, the electrochemical performance test process is as follows:

[0097] Preparation of button-type half cell: the lithium iron phosphate material prepared in each of the above examples and comparative examples was used as a positive electrode material, mixed with a conductive agent (conductive carbon black SP) and a binder (polyvinylidene fluoride PVDF) at a mass ratio of 93:3:4, and then a solvent N-methyl pyrrolidone (NMP) was added for homogenization to obtain a positive electrode slurry; the positive electrode slurry was coated on an aluminum foil current collector, dried, rolled, and die-cut to obtain a positive electrode sheet; a metal lithium sheet was used as a negative electrode sheet, and a sw-b005 electrolyte was used to assemble a button-type half cell in a glove box.

[0098] The prepared button-type half cell was subjected to electrochemical performance test using a LAND electrochemical tester, and the charge-discharge voltage window was 2.0V-4.2V.

[0099] Table 1: Test results of lithium iron phosphate materials in each example and comparative example

[0100]

[0101]

[0102] According to Table 1: compared with Comparative Examples 1-4, the lithium iron phosphate material prepared in Examples 1-3 and Examples 5-6 has the shortest b-axis length, reducing the diffusion distance of lithium ions. In Example 4, 10% lithium chloride was added to the first precursor, so that the b-axis length of the lithium iron phosphate material prepared is higher than that of Comparative Examples 1-3, but lower than that of Comparative Example 4, because the sintering temperature of Example 4 is higher, and when the amount of lithium chloride added reaches a limit, the lithium chloride crystals may tend to agglomerate, and the complexing effect is lower than that of a lower amount.

[0103] Meanwhile, the example 1 and the comparative examples 1-2 are compared, in the temperature rising rate range of 1-10 ℃ / min, with the increase of the temperature rising rate, the D50 particle size of the sintered sample gradually decreases, the compaction density also gradually decreases, but the discharge gram capacity of 0.1C gradually increases; the example 3 and the comparative example 3 are compared, because the temperature rising rate of the comparative example 3 is too high, so that the D50 particle size and the compaction density of the comparative example 3 are smaller than the results of the example 3, but the discharge gram capacity of 0.1C is higher than the example 3.

[0104] The example 5, the example 6 and the example 3 are compared, it can be known that with the increase of the sintering temperature, the unit cell volume increases, the D50 particle size gradually increases, and the compaction density improves.

[0105] With the increase of the sintering temperature and the temperature rising rate, the diffusion effect increases, the crystallinity of the lithium iron phosphate crystal nucleus improves, the order degree of the lithium iron phosphate crystal nucleus arrangement increases, and the compaction density gradually improves.

[0106] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

[0107] In addition, those skilled in the art can understand that although some of the embodiments herein include certain features included in other embodiments rather than other features, the combination of the features of different embodiments means that it is within the scope of the present application and forms different embodiments. For example, any one of the above claimed embodiments can be used in any combination. The information disclosed in the background section is only intended to deepen the understanding of the overall background of the present application, and should not be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a lithium iron phosphate cathode material, characterized in that, The application relates to a lithium iron phosphate positive electrode material and a preparation method thereof. Mixing and grinding raw materials containing a lithium source, an iron source, a phosphorus source and a carbon source to obtain a first precursor; Mixing the first precursor with an alkali metal chloride to obtain a second precursor; Sintering, cooling and washing the second precursor to obtain the lithium iron phosphate positive electrode material; The alkali metal chloride comprises at least one of sodium chloride, potassium chloride, zinc chloride, magnesium chloride, lithium chloride and rubidium chloride; The sintering comprises first sintering and second sintering; The first sintering comprises: under the protection of an inert gas, increasing the temperature from room temperature to 350-410 DEG C at a temperature increasing rate of 3-7 DEG C / min, and keeping the temperature for 3-5 h; The second sintering comprises: under the protection of an inert gas, increasing the temperature from room temperature to 470-530 DEG C at a temperature increasing rate of 3-7 DEG C / min, and keeping the temperature for 7-10 h.

2. The method for preparing the lithium iron phosphate cathode material as described in claim 1, characterized in that, The lithium source comprises at least one of lithium hydroxide, lithium carbonate, lithium phosphate, lithium sulfate, lithium acetate, lithium hydrogen phosphate and lithium fluoride; And / or, the iron source comprises at least one of ferric nitrate, ferrous oxalate, iron phosphate, ferrous phosphate, iron hydroxyl oxide and iron hydroxide; And / or, the phosphorus source comprises at least one of phosphoric acid, triammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, ferrous phosphate, lithium phosphate and lithium dihydrogen phosphate; And / or, the carbon source comprises at least one of glucose, sucrose, starch and polyethylene glycol.

3. The method of claim 1, wherein the lithium iron phosphate cathode material is prepared by the steps of: mixing lithium carbonate, iron oxide, and phosphoric acid; and heating the mixture at a temperature of 600 to 800°C for 6 to 10 hours. The molar ratio of Li element:Fe element:P element in the lithium source, the iron source and the phosphorus source is (0.9-1.3):1:(1-1.04); And / or, the molar ratio of the carbon source and the lithium source is (0.95-1.1):1; And / or, the mass of the alkali metal chloride is 0.1%-10% of the mass of the first precursor.

4. The method of claim 1, wherein the lithium iron phosphate cathode material is prepared by the steps of: mixing lithium carbonate, iron oxide, and phosphoric acid; and heating the mixture at a temperature of 600 to 800°C for 6 to 10 hours. The grinding mode comprises: wet ball milling by adopting a ball mill; And / or, the particle size of the first precursor is less than or equal to 50 nm; And / or, the preparation method of the second precursor comprises: dry ball milling the first precursor and the alkali metal chloride for 4-6 h.

5. The method of claim 4, wherein the lithium iron phosphate cathode material is prepared by the steps of: mixing lithium carbonate, iron oxide, and phosphoric acid; and heating the mixture at a temperature of 600 to 800°C for 6 to 10 hours. The wet ball milling time is 6-10 h; And / or, after the wet ball milling is completed, the product of the wet ball milling is further subjected to drying treatment at 50-80 DEG C to obtain the first precursor.

6. The method of producing a lithium-iron-phosphate cathode material according to any one of claims 1 to 5, characterized in that The washing comprises: water washing the cooled product for 4-5 times, and then performing drying treatment to obtain the lithium iron phosphate positive electrode material.

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