Iron phosphate pre-embedded lithium intermediate, carbon-coated lithium iron phosphate positive electrode material and preparation method of carbon-coated lithium iron phosphate positive electrode material

Abstract

The invention discloses an iron phosphate pre-embedded lithium intermediate and a carbon-coated lithium iron phosphate positive electrode material and a preparation method thereof, and the preparation method comprises the following steps: taking iron phosphate and lithium hydroxide as raw materials, burdening according to a molar ratio of Li: P = (1.00-1.05): 1, dispersing in deionized water to form slurry, carrying out hydrothermal reaction for 4-15 hours at 110-150 DEG C under a nitrogen condition, cooling, filtering and drying after the reaction is finished, and thus obtaining the carbon-coated lithium iron phosphate positive electrode material with the iron phosphate pre-embedded lithium intermediate and the carbon-coated lithium iron phosphate positive electrode material. The iron phosphate pre-intercalation lithium intermediate is obtained. The intermediate is composed of an iron phosphate phase, a lithium pyrophosphate phase and a ferroferric oxide phase, and the lithium pyrophosphate phase and the ferroferric oxide phase are uniformly distributed in the iron phosphate pre-embedded lithium intermediate. According to the prepared iron phosphate pre-embedded lithium intermediate, the lithium element is uniformly dispersed in the intermediate, and uniform distribution of the lithium element can be realized from a molecular level in a subsequent process of preparing a lithium iron phosphate positive electrode material through a solid-phase reaction, so that pure-phase lithium iron phosphate is obtained.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, and particularly relates to a lithium iron phosphate pre-intercalation intermediate and a carbon-coated lithium iron phosphate cathode material and its preparation method. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is widely used in electric vehicles and energy storage systems as a cathode material for lithium-ion batteries due to its advantages such as high safety, long cycle life, low cost, and environmental friendliness. However, its low intrinsic electronic conductivity and lithium-ion diffusion coefficient limit its high-rate performance. Existing improvement technologies mainly focus on material nanosizing to shorten the ion diffusion path and surface carbon coating to improve electronic conductivity.

[0003] Soluble brine thermal synthesis can directly synthesize nano-precursors with good crystallinity and controllable morphology, but its hydrothermal conditions are harsh, making operation difficult and costly. Traditional dry mixing of carbon sources easily leads to uneven coating and particle agglomeration, affecting the final performance. Existing processes often use expensive additives and involve multiple independent steps, lacking systematic optimization.

[0004] Chinese patent application CN115028153 A discloses a low-cost, equimolar, lithium-reserving hydrothermal method for producing lithium iron phosphate. This method involves adding a suitable neutralizing agent to a solution of iron source:phosphorus source:lithium source in a 1:1:1 equimolar ratio, followed by conventional hydrothermal process steps: high-temperature hydrothermal reaction in an autoclave under antioxidant conditions, followed by cooling, filtration, washing, drying, and pulverization to obtain the lithium iron phosphate cathode material. However, this method uses a large amount of auxiliary materials and generates significant wastewater, resulting in excessively high process costs. Furthermore, it requires stringent experimental conditions and highly sophisticated equipment, making large-scale production difficult. Summary of the Invention

[0005] To overcome the problems in the prior art, the present invention provides an iron phosphate pre-lithium intercalation intermediate and a carbon-coated lithium iron phosphate cathode material and a method for preparing the same. The present invention first synthesizes an iron phosphate pre-lithium intercalation intermediate in which lithium elements are uniformly dispersed. In the subsequent solid-phase reaction to prepare the lithium iron phosphate cathode material, the uniform distribution of lithium elements can be achieved by mixing at the molecular level, resulting in pure phase lithium iron phosphate.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: The present invention provides an iron phosphate pre-lithiation intermediate, which is composed of an iron phosphate phase, a lithium pyrophosphate phase and a magnetite phase, wherein the lithium pyrophosphate phase and the magnetite phase are uniformly distributed in the iron phosphate pre-lithiation intermediate.

[0007] In this invention, the lithium iron phosphate pre-intercalation intermediate comprises an iron phosphate phase, a lithium pyrophosphate phase, and a magnetite phase. The lithium pyrophosphate phase is uniformly distributed. During the subsequent milling process of lithium iron phosphate prepared from the intermediate, lithium does not need to migrate further to obtain uniformly distributed lithium iron phosphate, thus shortening the milling time. Simultaneously, during the spray drying process to prepare the fractions, the uniform distribution of lithium in the intermediate also avoids lithium enrichment, ultimately resulting in pure-phase lithium iron phosphate.

[0008] As an optional implementation, in the intermediate provided by the present invention, the intermediate is spherical and the particle size is less than 7 μm.

[0009] As an optional implementation, in the intermediate provided by the present invention, the lithium pyrophosphate phase is coated or embedded in the iron phosphate phase and the iron oxide phase.

[0010] In this invention, lithium exists in the form of lithium pyrophosphate phase, and the lithium pyrophosphate phase is coated or embedded in the iron phosphate phase and the iron oxide phase.

[0011] Based on the same technical concept, the present invention also provides a method for preparing the above-mentioned iron phosphate pre-lithiation intermediate, comprising the following steps: using iron phosphate and lithium hydroxide as raw materials, dispersing them in deionized water at a molar ratio of Li:P = (1.00~1.05):1 to form a slurry, and hydrothermally reacting at 110~150℃ for 4~15h under nitrogen conditions. After the reaction is completed, the mixture is cooled, filtered, and dried to obtain the iron phosphate pre-lithiation intermediate.

[0012] In this invention, iron phosphate and lithium hydroxide are used as raw materials, and the iron phosphate pre-lithiation intermediate containing lithium pyrophosphate phase can be prepared by reacting them at 110-150°C according to the above ratio.

[0013] As an optional implementation, in the preparation method provided by the present invention, the lithium hydroxide is selected from crystalline particles with a particle size of less than 10 mm.

[0014] As an optional implementation method, in the preparation method provided by the present invention, the nitrogen pressure in the reactor is 0.2 to 3.0 MPa.

[0015] In this invention, nitrogen cannot be introduced into the reactor if the nitrogen pressure is lower than the vapor pressure. Therefore, after nitrogen is introduced, the pressure inside the reactor needs to exceed the saturated vapor pressure of water vapor at the corresponding reactor temperature.

[0016] Based on the same technical concept, the present invention also provides a carbon-coated lithium iron phosphate cathode material, which is prepared from the above-mentioned lithium iron phosphate pre-intercalation intermediate.

[0017] Based on the same technical concept, the present invention also provides a method for preparing the above-mentioned carbon-coated lithium iron phosphate cathode material, wherein the above-mentioned lithium iron phosphate pre-intercalation intermediate is mixed with a carbon source and then dispersed by sand milling, and then spray dried to obtain lithium iron phosphate precursor powder. The lithium iron phosphate precursor powder is then calcined at high temperature under an inert atmosphere. After complete calcination, the carbon-coated lithium iron phosphate cathode material is obtained.

[0018] As an optional implementation, in the preparation method provided by the present invention, the amount of carbon source added is 1% to 10% of the mass of the intermediate.

[0019] In this invention, the addition of a carbon source can improve the conductivity of the cathode material. Too low a carbon source will not have an obvious effect, while too high a carbon source will affect the compaction density of the material.

[0020] As an optional implementation method, in the preparation method provided by the present invention, the inlet temperature is controlled at 180-220°C and the outlet temperature is controlled at 90-120°C during the spray drying process.

[0021] As an optional implementation method, in the preparation method provided by the present invention, the calcination temperature is 650-900°C and the calcination time is 5-15 hours.

[0022] In this invention, controlling the calcination temperature helps to promote the complete crystal transformation of lithium iron phosphate and reduce impurities.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The lithium iron phosphate pre-intercalation intermediate in this invention contains a lithium pyrophosphate phase, which has high reactivity, low melting point, and is easy to undergo crystal transformation. It can directly provide lithium and iron sources and is uniformly distributed in the lithium iron phosphate pre-intercalation intermediate. In the subsequent solid-phase reaction to prepare lithium iron phosphate cathode material, it can be mixed at the molecular level, which greatly promotes the reaction process and ensures that the elements are uniformly distributed in the crystal structure.

[0024] (2) In this invention, iron phosphate and lithium source with extremely low solubility are used as raw materials to prepare iron phosphate pre-lithiated intermediate through hydrothermal method. The lithium element is uniformly distributed in the iron phosphate intermediate. Compared with the existing technology of preparing lithium iron phosphate using soluble phosphorus source, iron source and lithium source, it will not generate a large amount of wastewater and is more suitable for industrial production. Moreover, the lithium element is uniformly distributed, and the subsequent sand milling and calcination processes do not require further lithium migration to obtain lithium iron phosphate with uniform element distribution. At the same time, the lithium / phosphorus molar ratio in the raw materials of this invention is consistent with the lithium to phosphorus stoichiometry ratio in the target lithium iron phosphate material prepared based on the pre-lithiated intermediate. During the sand milling process of the intermediate, no additional lithium source is required. Compared with the traditional solid-state method using lithium carbonate as lithium source (which requires grinding micron-sized lithium carbonate to nano-sized during grinding), the sand milling time of this patented method is shorter, which can significantly improve the sand milling efficiency of solid-state method for preparing lithium iron phosphate.

[0025] (3) The lithium iron phosphate pre-intercalation intermediate in this invention exhibits better high temperature resistance. Compared with the lithium iron phosphate material prepared by the traditional solid-state method, the primary particles at the same sintering temperature are smaller and have no adhesion phenomenon, which can better exert the electrochemical performance of the material.

[0026] (4) The lithium iron phosphate cathode material prepared using the lithium iron phosphate pre-intercalation intermediate has both the advantages of nanostructure and uniform carbon coating, and the electronic and ion conduction capabilities are greatly improved. The material has a discharge specific capacity of more than 160 mAh / g at a 0.1C rate and an initial discharge efficiency of ≥95%.

[0027] (5) The preparation method of the present invention has low requirements for raw materials, all of which are cheap and readily available. The process is simple, energy consumption is low, it is suitable for large-scale production, and the entire production process is environmentally friendly. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The image shown is a scanning electron microscope (SEM) image of the lithium iron phosphate pre-intercalation intermediate prepared in the embodiments of the present invention. Figure 2 The XRD pattern of the lithium iron phosphate pre-intercalation intermediate prepared in the embodiments of the present invention; Figure 3 The images shown are scanning electron microscope (SEM) images of the lithium iron phosphate cathode material prepared in Example 1 of this invention, with the left image being a low-power image and the right image being a high-power image. Figure 4 The images shown are scanning electron microscope (SEM) images of the lithium iron phosphate cathode material prepared in Example 2 of this invention, with the left image being a low-power image and the right image being a high-power image. Figure 5 The images shown are scanning electron microscope (SEM) images of the lithium iron phosphate cathode material prepared in Example 3 of this invention, with the left image being a low-power image and the right image being a high-power image. Figure 6 The images shown are scanning electron microscope (SEM) images of the lithium iron phosphate cathode material prepared in Comparative Example 1 of this invention, with the left image being a low-power image and the right image being a high-power image. Figure 7The images shown are scanning electron microscope (SEM) images of the lithium iron phosphate cathode material prepared in Comparative Example 2 of this invention, with the left image being a low-power image and the right image being a high-power image. Figure 8 The images shown are scanning electron microscope (SEM) images of the lithium iron phosphate cathode material prepared in Comparative Example 3 of this invention, with the left image being a low-power image and the right image being a high-power image. Figure 9 The images show the XRD patterns of the lithium iron phosphate cathode materials prepared in Example 2 and Comparative Example 3 of this invention. Detailed Implementation

[0030] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0033] Example 1 The preparation method of lithium iron phosphate cathode material includes the following steps: (1) Hydrothermal preparation of lithium iron phosphate pre-intercalation intermediate: S1: Accurately weigh FePO4 and LiOH·H2O (crystalline particles with a particle size less than 10 mm) according to a Li:P molar ratio of 1.02:1, add deionized water and stir to form a homogeneous slurry. Transfer the slurry to a high-pressure reactor, evacuate the reactor, and purge with nitrogen to maintain the pressure inside the reactor at 0.3 MPa. React at 120℃ and 300 r / min for 10 hours. After the reaction is complete, the product is separated into solid and liquid phases and dried in a vacuum drying oven at 80℃ for 12 hours to obtain the lithium iron phosphate pre-intercalation intermediate.

[0034] (2) Preparation of lithium iron phosphate cathode material S2: Weigh 1000g of the above intermediate and mix it with 81.04g of glucose. Add it to 2000ml of deionized water and grind and disperse it in a sand mill for 1.5 hours. The particle size D50 of the ground slurry is 190nm.

[0035] S3: Spray dry the ground slurry, set the inlet temperature to 200℃ and the outlet temperature to 100℃, and collect the spray-dried material, i.e., spray material.

[0036] S4: Place the sprayed material in a tube furnace under nitrogen protection, heat it to 770°C at a rate of 3°C / min, and hold it at this temperature for 10 hours. Then, allow it to cool naturally to room temperature to obtain the final product, LiFePO4 / C composite material.

[0037] Example 2 The preparation method of lithium iron phosphate cathode material includes the following steps: (1) Hydrothermal preparation of lithium iron phosphate pre-intercalation intermediate: S1: Accurately weigh FePO4 and LiOH·H2O (crystalline particles with a particle size less than 10 mm) according to a Li:P molar ratio of 1.02:1, add deionized water and stir to form a homogeneous slurry. Transfer the slurry to a high-pressure reactor, evacuate the reactor, and purge with nitrogen to maintain the pressure inside the reactor at 0.3 MPa. React at 120℃ and 300 r / min for 10 hours. After the reaction is complete, the product is separated into solid and liquid phases and dried in a vacuum drying oven at 80℃ for 12 hours to obtain the lithium iron phosphate pre-intercalation intermediate.

[0038] (2) Preparation of lithium iron phosphate cathode material S2: Weigh 1000g of the above intermediate and mix it with 81.04g of glucose. Add it to 2000ml of deionized water and grind and disperse it in a sand mill for 1.5 hours. The particle size D50 of the ground slurry is 190nm.

[0039] S3: Spray dry the ground slurry, set the inlet temperature to 200℃ and the outlet temperature to 100℃, and collect the spray-dried material, i.e., spray material.

[0040] S4: Place the sprayed material in a tube furnace under nitrogen protection, heat it to 790°C at a rate of 3°C / min, and hold it at this temperature for 10 hours. Then, allow it to cool naturally to room temperature to obtain the final product, LiFePO4 / C composite material.

[0041] Example 3 The preparation method of lithium iron phosphate cathode material includes the following steps: (1) Hydrothermal preparation of lithium iron phosphate pre-intercalation intermediate: S1: Accurately weigh FePO4 and LiOH·H2O (crystalline particles with a particle size less than 10 mm) according to a Li:P molar ratio of 1.03:1, add deionized water and stir to form a homogeneous slurry. Transfer the slurry to a high-pressure reactor, evacuate the reactor, and purge with nitrogen to maintain the pressure inside the reactor at 0.5 MPa. React at 130℃ and 300 r / min for 8 hours. After the reaction is complete, the product is separated into solid and liquid phases and dried in a vacuum drying oven at 80℃ for 12 hours to obtain the lithium iron phosphate pre-intercalation intermediate.

[0042] (2) Preparation of lithium iron phosphate cathode material S2: Weigh 1000g of the above intermediate and mix it with 81.04g of glucose. Add it to 2000ml of deionized water and grind and disperse it in a sand mill for 1.5 hours. The particle size D50 of the ground slurry is 190nm.

[0043] S3: Spray dry the ground slurry, set the inlet temperature to 200℃ and the outlet temperature to 100℃, and collect the spray-dried material, i.e., spray material.

[0044] S4: Place the sprayed material in a tube furnace under nitrogen protection, heat it to 770°C at a rate of 3°C / min, hold it at this temperature for 6 hours, and then let it cool naturally to room temperature to obtain the final product, LiFePO4 / C composite material.

[0045] Comparative Example 1 Using traditional solid-phase mixing process: S1. FePO4, Li2CO3, glucose and dopant are mixed according to the stoichiometric ratio of Li:P molar ratio of 1.02:1, added to 2000mL of deionized water, and ground and dispersed in a sand mill for 2.5 hours. The particle size D50 of the ground slurry is 190nm.

[0046] S2: Spray dry the ground slurry, set the inlet temperature to 200℃ and the outlet temperature to 100℃, and collect the spray-dried material, i.e., spray material.

[0047] S3: The sprayed material is placed in a tube furnace under nitrogen protection and heated to 770°C at a rate of 3°C / min. It is then held at this temperature for 6 hours and naturally cooled to room temperature to obtain the final product, LiFePO4 / C composite material.

[0048] Comparative Example 2 The only difference between Comparative Example 3 and Comparative Example 1 is that the Li:P molar ratio of the lithium iron phosphate cathode material was changed to 1.03:1.

[0049] S1: FePO4, Li2CO3, glucose and dopant were mixed according to the stoichiometric ratio of Li:P molar ratio of 1.03:1, added to 2000mL of deionized water, and ground and dispersed in a sand mill for 2.5 hours. The particle size D50 of the ground slurry was 190nm.

[0050] Comparative Example 3 The only difference between Comparative Example 2 and Comparative Example 1 is that the sintering process of the lithium iron phosphate cathode material was changed.

[0051] S3: Place the sprayed material in a tube furnace under nitrogen protection, heat it to 790°C at a rate of 3°C / min, and hold it at this temperature for 10 hours. Then, allow it to cool naturally to room temperature to obtain the final product, LiFePO4 / C composite material.

[0052] Performance testing Figure 1 The electron microscopy (SEM) results for the lithium iron phosphate pre-intercalation intermediate prepared in Example 1 show that the material morphology is nearly spherical with a particle size of less than 7 μm. The intermediate of this invention inherits the morphology of lithium iron phosphate. SEM comparison reveals numerous pores on the surface of the lithium iron phosphate particles. The reduction in pores on the surface of the intermediate particles after in-situ hydrothermal intercalation indicates that the lithium pyrophosphate and iron oxide phases generated after the reaction are uniformly distributed within the particles. This intermediate exhibits a shorter grinding time during the sand milling process. Compared to the traditional solid-state method using lithium carbonate as the lithium source, the shorter grinding time significantly improves the grinding efficiency of the solid-state method for preparing lithium iron phosphate.

[0053] Figure 2 The XRD crystal diffraction pattern of the iron phosphate pre-lithiation intermediate prepared in Example 1 is shown in the XRD crystal diffraction pattern of the intermediate. It can be seen that the material is composed of iron phosphate phase, lithium pyrophosphate phase and iron oxide phase. This indicates that during the hydrothermal synthesis process, iron phosphate reacts with lithium hydroxide to produce new phases, namely lithium pyrophosphate phase and iron oxide phase. The generated lithium pyrophosphate phase and iron oxide phase are uniformly distributed at the molecular level in the iron phosphate pre-lithiation intermediate. Specifically, the lithium pyrophosphate phase coats or inserts into the iron phosphate phase and iron oxide phase.

[0054] A novel phase, lithium pyrophosphate, is generated in the hydrothermal synthesis intermediate. This material exhibits high reactivity, a low melting point, and readily undergoes crystal transformation. Furthermore, it can directly provide lithium and iron sources, allowing for molecular-level mixing during subsequent solid-state reactions to prepare lithium iron phosphate cathode materials. This significantly promotes the reaction process and ensures uniform elemental distribution within the crystal structure. These factors directly influence the final energy density, rate performance, and cycle stability of the prepared lithium iron phosphate cathode material.

[0055] Figure 3-5 The images show SEM images of the lithium iron phosphate cathode materials prepared in Examples 1-3, respectively. They exhibit a near-spherical morphology with good sphericity and structural stability. At the same sintering temperature, the primary particles of the lithium iron phosphate material prepared from the intermediate are smaller and show no adhesion. The secondary particles of the lithium iron phosphate cathode material prepared by the milling, spraying, and sintering processes are all near-spherical, with a primary particle size <300 nm. The hydrothermal lithium intercalation intermediate demonstrates better high-temperature resistance. Figure 6-8 The images shown are SEM images of lithium iron phosphate cathode materials in Comparative Examples 1-3. The comparison shows that the primary particles prepared by the traditional solid-state method are smaller than those prepared by the same sintering temperature.

[0056] Figure 9 XRD pattern analysis of the cathode materials in Example 2 and Comparative Example 3; The XRD pattern shows that the lithium iron phosphate material prepared from the intermediate has sharp diffraction peaks, good crystallinity, no impurities, and is a pure phase lithium iron phosphate cathode material, corresponding to PDF#01-081-1173 card.

[0057] Button production The positive electrode materials prepared in the examples and comparative examples were mixed with Super-P and PVDF at a mass ratio of 80:10:10 in an appropriate amount of NMP, coated onto aluminum foil, dried, punched, and sheared to obtain the positive electrode sheet. A CR2016 coin cell was prepared using a lithium sheet as the negative electrode, LiPF6 / EC+DEC (volume ratio 1:1) as the electrolyte, and a Celgard 2325 membrane as the separator.

[0058] Performance testing Test method for initial charge and discharge specific capacity: At room temperature (25℃), charge and discharge the coin cell at 0.1C (1C=150mA / g) for one cycle, with a voltage range of 2.5V-4.0V. The results are shown in Table 1.

[0059] The specific surface area of ​​the lithium iron phosphate cathode materials prepared in the examples and comparative examples was tested. Table 1: Specific surface area and coin cell performance test results of samples prepared in the examples and comparative examples

[0060] As can be seen from the data in Table 1, the cathode materials prepared by the method of this invention all have low specific surface areas (<15m²). 2 / g). As can be seen from the examples and comparative examples, the hydrothermal synthesis intermediate of the present invention has better high-temperature resistance during sintering than the traditional solid-state sintering. The lithium iron phosphate material prepared by increasing the sintering temperature to 790℃ still exhibits good electrical properties.

[0061] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the inventive concept, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A lithium iron phosphate pre-intercalation intermediate, characterized in that, The intermediate is composed of an iron phosphate phase, a lithium pyrophosphate phase, and a magnetite phase, wherein the lithium pyrophosphate phase and the magnetite phase are uniformly distributed in the iron phosphate pre-lithiation intermediate.

2. The lithium iron phosphate pre-intercalation intermediate according to claim 1, characterized in that, The intermediate is spherical with a particle size of less than 7 μm and a specific surface area of ​​<15 m². 2 / g.

3. The lithium iron phosphate pre-intercalation intermediate according to claim 1, characterized in that, The lithium pyrophosphate phase is coated or embedded in the iron phosphate phase and the iron oxide phase.

4. A method for preparing a lithium iron phosphate pre-intercalation intermediate as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Using iron phosphate and lithium hydroxide as raw materials, the mixture is prepared in a molar ratio of Li:P = (1.00~1.05):1 and dispersed in deionized water to form a slurry. Under nitrogen conditions, the mixture is hydrothermally reacted at 110~150℃ for 4~15h. After the reaction is completed, the mixture is cooled, filtered and dried to obtain the iron phosphate pre-lithium intercalation intermediate.

5. The method for preparing the lithium iron phosphate pre-intercalation intermediate according to claim 4, characterized in that, The lithium hydroxide is selected from crystalline particles with a particle size of less than 10 mm.

6. The method for preparing the lithium iron phosphate pre-intercalation intermediate according to claim 4, characterized in that, The nitrogen pressure inside the reactor is 0.2–3.0 MPa.

7. A carbon-coated lithium iron phosphate cathode material, characterized in that, It is prepared from the lithium iron phosphate pre-intercalation intermediate according to any one of claims 1 to 3.

8. A method for preparing the carbon-coated lithium iron phosphate cathode material as described in claim 7, characterized in that, The lithium iron phosphate pre-intercalation intermediate according to any one of claims 1 to 3 is mixed with a carbon source and then dispersed by sand milling, and then spray dried to obtain lithium iron phosphate precursor powder. The lithium iron phosphate precursor powder is then calcined at high temperature under an inert atmosphere. After complete calcination, carbon-coated lithium iron phosphate cathode material is obtained.

9. The method for preparing carbon-coated lithium iron phosphate cathode material according to claim 8, characterized in that, The amount of carbon source added is 1% to 10% of the intermediate mass; the inlet temperature is controlled at 180 to 220°C and the outlet temperature is controlled at 90 to 120°C during the spray drying process.

10. The method for preparing carbon-coated lithium iron phosphate cathode material according to claim 8, characterized in that, The roasting temperature is 650–900℃, and the roasting time is 5–15 hours.

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