Method for preparing lithium iron phosphate positive electrode material at low cost

Abstract

The invention relates to a low-cost method for preparing a lithium iron phosphate positive electrode material, which comprises the following steps: (a) adding a surfactant into a phosphorus source at normal temperature in a nitrogen atmosphere to form a phosphorus solution, mixing and stirring a lithium source and the phosphorus solution to obtain a phosphorus-lithium solution, adding an alkali solution into the phosphorus-lithium solution to adjust the pH value to 6-7, and stirring to obtain a mixed solution, stirring and mixing the mixed solution with an iron source to obtain turbid liquid A; (b) in a nitrogen atmosphere, heating the microreactor to a certain temperature and keeping the temperature constant, simultaneously feeding the suspension A and the alkali liquor into the microreactor in a double-strand manner, adjusting the pH value to 7.5-9, and carrying out hydrothermal reaction to obtain a hydrothermal product; (c) carrying out post-treatment on the hydrothermal product to obtain lithium iron phosphate; and (d) mixing and calcining the lithium iron phosphate and the carbon source to obtain LiFePO4 / C. According to the preparation method disclosed by the invention, the reaction time is greatly shortened, the use amount of a lithium source in the raw materials is effectively reduced, the cost is relatively low, and the prepared lithium iron phosphate can reach a nanoscale and is relatively good in dispersity and uniformity and excellent in electrochemical performance.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery positive electrode materials, and specifically relates to a method for preparing lithium iron phosphate positive electrode materials at low cost. Background Art

[0002] Olivine lithium iron phosphate is a material with excellent electrochemical properties, and its theoretical capacity can reach 170mAh g -1 , energy density is 550 Wh·kg -1 , the PO bond energy is large, which ensures that this material has good thermal stability and chemical stability. In addition, the raw materials for synthesizing lithium iron phosphate are widely available, the production cost is low and it is environmentally friendly, and it also has good recyclability. Therefore, lithium iron phosphate power batteries have been widely used in the field of electric vehicles and have good application prospects.

[0003] At present, the synthesis methods of positive electrode material lithium iron phosphate mainly include solid phase reaction method, carbon thermal reduction method, sol-gel method, coprecipitation method, etc. Among them, the solid phase method has been widely used in industrial production and the technology is relatively mature. The liquid phase synthesis method is attracting attention as an emerging lithium iron phosphate synthesis method. Compared with the solid phase method, its low reaction temperature and controllable morphology and particle size are conducive to the preparation of lithium iron phosphate with higher electrochemical performance.

[0004] However, the liquid phase synthesis method generally has problems such as high energy consumption, high temperature and high pressure resistance of the reaction equipment, and long reaction time, which cannot be mass-produced and restricts the industrialization process. In addition, there are also problems such as agglomeration, poor consistency and dispersibility, which affect the electrochemical performance of the material.

[0005] Patent CN 112408354 A provides a method for preparing lithium iron phosphate positive electrode materials, and the preparation time is as long as 5 h~8 h; Patent CN 107293728 A provides a method for preparing carbon-coated lithium iron phosphate using a one-step hydrothermal method using water-soluble starch, and the lithium-phosphorus ratio is 3.0~3.3:1, and the preparation time is as long as 6 h~10 h. The above patents all use liquid phase synthesis methods, and their preparation methods have defects such as large amount of raw materials, high cost, and long reaction time. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing lithium iron phosphate positive electrode materials at low cost, which greatly shortens the reaction time, effectively reduces the amount of lithium source in the raw materials, and prepares lithium iron phosphate positive electrode materials with excellent electrochemical properties at the nanoscale at low cost.

[0007] The technical solution adopted by the present invention to solve the above problem is: a method for preparing lithium iron phosphate positive electrode material at low cost, comprising the following steps: (a) adding a surfactant to a phosphorus source at room temperature and in a nitrogen atmosphere to form a phosphorus liquid, mixing a certain proportion of a lithium source with the phosphorus liquid and stirring to form a phosphorus-lithium liquid, adding an alkali solution to the phosphorus-lithium liquid to adjust the pH to 6-7 and stirring to form a mixed solution, and stirring the mixed solution with an iron source to obtain a suspension A; (b) In a nitrogen atmosphere, the microreactor is heated to a certain temperature and kept at a constant temperature, and the suspension A and the alkali solution are simultaneously fed into the microreactor in two streams, and the pH is adjusted to 7.5-9 to perform a hydrothermal reaction to obtain a hydrothermal product; (c) filtering, washing and vacuum drying the hydrothermal product to obtain a lithium iron phosphate material; (d) The lithium iron phosphate material and the carbon source are mixed and calcined under nitrogen protection to obtain LiFePO4 / C material.

[0008] Among them, adding a surfactant to the phosphorus source facilitates reducing the particle size of the mixed solution (containing lithium phosphate and lithium dihydrogen phosphate, etc.) formed when the alkali solution is subsequently added, thereby improving its dispersibility.

[0009] In step (a), an alkali solution is added to adjust the pH to 6-7 so that the mixed solution produces a mixture of lithium phosphate and lithium dihydrogen phosphate, which is convenient for the subsequent addition of an iron source to produce a suspension with a smaller particle size; in step (b), the pH is adjusted to 7.5-9 so that the Fe and P elements are precipitated as completely as possible.

[0010] Preferably, the phosphorus source is at least one of phosphoric acid and lithium dihydrogen phosphate, the lithium source is at least one of lithium sulfate, lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide or lithium phosphate, and the iron source is at least one of ferrous chloride, ferrous sulfate and ferrous nitrate.

[0011] Preferably, the molar ratio of the lithium source, the iron source and the phosphorus source is 1.5-2.0:1:1.

[0012] Preferably, the surfactant is at least one of polyvinyl alcohol, hexadecyltrimethylammonium bromide, sorbitan fatty acid ester, and sodium lauryl sulfate, and the added amount is 0.50%wt. to 0.80%wt. of the total weight of the raw materials.

[0013] Preferably, the alkali solution is at least one of aqueous ammonia and sodium hydroxide.

[0014] Preferably, the carbon source is at least one of glucose, sucrose, ascorbic acid and starch, and the amount of the carbon source is 4.00% wt. to 10.00% wt. of the total weight of the raw material.

[0015] Preferably, in step (a), the phosphorus liquid is the base liquid, the lithium source feeding time is 3 min to 5 min, the lithium source and the phosphorus liquid are mixed and stirred for 5 min to 10 min, and the stirring rate is 1000 r·min -1 ~1500r·min-1 ; Phosphorus lithium solution is the bottom solution, the alkali solution feeding time is 3min~5min, the phosphorus lithium solution and alkali solution stirring time is 5min~10min, and the stirring rate is 1000 r·min -1 ~1500r·min -1 ; The mixed liquid is the bottom liquid, the iron source feeding time is 3min~5min, the mixing time of the mixed liquid and the iron source is 5min~10min, and the stirring rate is 1000r·min -1 ~1500r·min -1 .

[0016] Preferably, in step (b), the microreactor has a constant temperature range of 180°C to 220°C, a pressure of 1.80 MPa to 2.20 MPa, and a hydrothermal reaction time of 10 min to 25 min.

[0017] Preferably, in step (c), the vacuum drying temperature is 50°C to 80°C, and the time is 5.0 h to 7.0 h.

[0018] Preferably, in step (d), the calcination temperature is 500° C. to 700° C., and the calcination time is 4.0 h to 7.0 h.

[0019] A lithium iron phosphate positive electrode material is prepared by using the above-mentioned method for preparing a lithium iron phosphate positive electrode material at a low cost.

[0020] Compared with the prior art, the advantages of the present invention are: The invention discloses a method for preparing lithium iron phosphate positive electrode material at low cost, adopts a microreactor and a double-stream feeding method to improve the dispersibility and consistency of liquid-liquid reaction, effectively improves reaction efficiency, greatly shortens reaction time, adopts low-cost ammonia water or sodium hydroxide to adjust the pH of the reaction system, effectively reduces the amount of lithium source in the raw material, greatly reduces the raw material cost, and can prepare lithium iron phosphate positive electrode material with excellent electrochemical performance at the nano level. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a scanning electron microscope image of LiFePO4 / C in Example 1 of the present invention.

[0022] Figure 2 This is a scanning electron microscope image of LiFePO4 / C in comparative example 1 of the present invention.

[0023] Figure 3 This is a scanning electron microscope image of LiFePO4 / C in comparative example 2 of the present invention.

[0024] Figure 4 It is the XRD analysis diagram of LiFePO4 / C in Example 1-3 of the present invention and Comparative Example 1-2.

[0025] Figure 5 It is a comparison chart of the electrochemical performance of LiFePO4 / C in Examples 1-3 of the present invention and Comparative Examples 1-2. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to the accompanying drawings. Example 1

[0027] A method for preparing a lithium iron phosphate positive electrode material at a low cost, wherein the lithium: iron: phosphorus = 1.5:1:1 (molar ratio) is reacted in a microreactor, and the pH is adjusted with ammonia water to prepare the lithium iron phosphate positive electrode material, comprising the following steps: (1) Prepare 0.375 mol·L in oxygen-free water -1 Lithium hydroxide solution.

[0028] (2) Prepare 0.25 mol·L in oxygen-free water -1 Phosphoric acid solution.

[0029] (3) Prepare 0.375 mol·L in oxygen-free water -1 of aqueous ammonia solution.

[0030] (4) Prepare 0.25 mol·L -1 of ferrous sulfate aqueous solution.

[0031] (5) To 0.25 mol·L -1 0.60 wt.% polyvinyl alcohol based on the total weight of the raw materials was added to the phosphoric acid solution to obtain a phosphorus solution.

[0032] (6) Add an equal volume of 0.375 mol·L phosphoric acid to the phosphorus solution. -1 Lithium hydroxide solution, lithium hydroxide feeding time is 5 min, at 1100 r·min -1 Under the stirring rate condition, the mixture was stirred for 8 min to obtain a phosphorus-lithium solution.

[0033] (7) Add 0.375 mol·L lithium phosphate solution -1 Ammonia solution, pH adjusted to 6.80, ammonia feeding time for 5 min, at 1100 r min -1 The mixture was stirred at a stirring rate of 1.04 % for 8 min to obtain a mixed solution.

[0034] (8) In a nitrogen environment, add an equal volume of 0.25 mol·L phosphoric acid to the mixed solution at a feeding time of 5 min. -1 The ferrous sulfate solution was stirred for 10 min to obtain suspension A.

[0035] (9) In a nitrogen environment, the microreactor was kept at a constant temperature of 200 °C, and the suspension A was mixed with 0.375 mol·L -1 Ammonia solution was simultaneously fed into the microreactor, the pH was adjusted to 8.2, and a hydrothermal reaction was carried out. The reaction time was 15 min and the pressure was 1.80 MPa to obtain a hydrothermal product.

[0036] (10) The hydrothermal product was filtered, washed with oxygen-free water, and dried in a vacuum drying oven at 60 °C for 6 h to obtain lithium iron phosphate material.

[0037] (11) The lithium iron phosphate material was mixed with 4.00%wt starch from the total weight of the raw materials, and the mixed solid was placed in a tube furnace in a nitrogen atmosphere at 8°C min -1 The heating rate was increased to 600°C, and the calcination temperature was kept constant at 600°C for 6.5 hours to obtain LiFePO4 / C material. Example 2

[0038] A method for preparing a lithium iron phosphate positive electrode material at a low cost, wherein the lithium: iron: phosphorus = 2.0:1:1 (molar ratio) is reacted in a microreactor, and the pH is adjusted with ammonia water to prepare the lithium iron phosphate positive electrode material, comprising the following steps: (1) Prepare 0.125 mol·L in oxygen-free water -1 Lithium sulfate solution.

[0039] (2) Prepare 0.25 mol·L in oxygen-free water -1 Lithium dihydrogen phosphate solution.

[0040] (3) Prepare 0.50 mol·L in oxygen-free water -1 of aqueous ammonia solution.

[0041] (4) Prepare 0.25 mol·L -1 of ferrous sulfate aqueous solution.

[0042] (5) To 0.25 mol·L -1 0.50%wt. of hexadecyltrimethylammonium bromide based on the total weight of the raw materials was added to the lithium dihydrogen phosphate solution to obtain phosphorus liquid.

[0043] (6) Add 0.125 mol·L lithium dihydrogen phosphate in an equal volume to the phosphorus solution. -1 Lithium sulfate solution, lithium sulfate feeding time is 4 min, at 1200 r·min -1 Under the stirring rate condition, the mixture was stirred for 6 min to obtain a phosphorus-lithium solution.

[0044] (7) Add 0.50 mol·L lithium phosphate solution -1The pH of the ammonia solution was adjusted to 6.2, and the ammonia feeding time was 4 min. -1 The mixture was stirred for 6 min at a stirring rate of 1.04 % to obtain a mixed solution.

[0045] (8) In a nitrogen environment, add 0.25 mol·L lithium dihydrogen phosphate (LDP) in an equal volume to the mixed solution at a feeding time of 4 min. -1 The ferrous sulfate solution was stirred for 8 min to obtain suspension A.

[0046] (9) In a nitrogen environment, the microreactor was kept at a constant temperature of 210 °C, and the suspension A was mixed with 0.50 mol·L -1 Ammonia solution was simultaneously fed into the microreactor, the pH was adjusted to 8.2, and a hydrothermal reaction was carried out. The reaction time was 13 min and the pressure was 2.00 MPa to obtain a hydrothermal product.

[0047] (10) The hydrothermal product was filtered, washed, and dried in a vacuum drying oven at 65 °C for 5.5 h to obtain lithium iron phosphate material.

[0048] (11) The lithium iron phosphate material was mixed with 6.00%wt glucose in the total weight of the raw materials, and the mixed solid was placed in a tubular furnace in a nitrogen atmosphere. The calcination temperature was 650°C and the heating rate was 5°C min. -1 , constant temperature time is 6.0h, and LiFePO4 / C material is obtained. Example 3

[0049] A method for preparing a lithium iron phosphate positive electrode material at a low cost, wherein the lithium: iron: phosphorus = 1.5:1:1 (molar ratio) is reacted in a microreactor, and the pH is adjusted with sodium hydroxide to prepare the lithium iron phosphate positive electrode material, comprising the following steps: (1) Prepare 0.0625 mol·L in oxygen-free water -1 Lithium carbonate solution.

[0050] (2) Prepare 0.25 mol·L in oxygen-free water -1 Lithium dihydrogen phosphate solution.

[0051] (3) Prepare 0.375 mol·L in oxygen-free water -1 of sodium hydroxide solution.

[0052] (4) Prepare 0.25 mol·L -1 of ferrous nitrate solution.

[0053] (5) To 0.25 mol·L -1 0.70 wt.% sodium dodecyl sulfate based on the total weight of the raw materials was added to the lithium dihydrogen phosphate solution to obtain a phosphorus liquid.

[0054] (6) Add 0.0625 mol·L lithium dihydrogen phosphate in an equal volume to the phosphorus solution. -1 Lithium carbonate solution, lithium carbonate feeding time is 3 min, at 1500 r·min -1 Under the stirring rate condition, stir for 5 min to obtain lithium phosphorus solution.

[0055] (7) Add 0.375 mol·L lithium phosphate solution -1 Sodium hydroxide solution, pH adjusted to 6.5, sodium hydroxide feed time was 3 min, at 1200 r min -1 The mixture was stirred at a stirring rate of 7 min to obtain a mixed solution.

[0056] (8) In a nitrogen environment, add 0.25 mol·L lithium dihydrogen phosphate (LDP) in an equal volume to the mixed solution at a feeding time of 3 min. -1 Ferrous nitrate solution, at 1150 r·min -1 The mixture was stirred for 8 min under stirring rate conditions to obtain suspension A.

[0057] (9) In a nitrogen environment, the microreactor was kept at a constant temperature of 220 °C, and the suspension A and 0.375 mol·L -1 Sodium hydroxide solution was simultaneously fed into the microreactor, the pH was adjusted to 8.2, and a hydrothermal reaction was carried out. The reaction time was 10 min and the pressure was 2.20 MPa to obtain a hydrothermal product.

[0058] (10) The hydrothermal product was filtered, washed, and dried in a vacuum drying oven at 70 °C for 5.0 h to obtain a lithium iron phosphate material; (11) The lithium iron phosphate material was mixed with 8.00% wt. sucrose, and the mixed solid was placed in a tubular furnace in a nitrogen atmosphere. The calcination temperature was 550 °C and the heating rate was 5 °C min. -1 , constant temperature time is 7.0 h, and LiFePO4 / C material is obtained.

[0059] Comparative Example 1 A method for preparing a lithium iron phosphate positive electrode material, wherein the lithium iron phosphate positive electrode material is prepared by reacting in a microreactor at a ratio of lithium: iron: phosphorus = 3:1:1 (molar ratio), without the need for adjusting the pH with an alkali solution, and comprising the following steps: (1) Prepare 0.75 mol·L in oxygen-free water -1 Lithium hydroxide solution.

[0060] (2) Prepare 0.25 mol·L in oxygen-free water -1 Phosphoric acid solution.

[0061] (3) Prepare 0.25 mol·L -1 of ferrous sulfate aqueous solution.

[0062] (4) To 0.25 mol·L -1 0.60 wt.% polyvinyl alcohol based on the total weight of the raw materials was added to the phosphoric acid solution to obtain a phosphorus solution.

[0063] (5) Add 0.75 mol·L -1 Lithium hydroxide solution, pH end point adjusted to 6.80, lithium hydroxide feeding time for 5 min, at 1100 r min -1 Under the stirring rate condition, the mixture is stirred for 8 min to obtain a phosphorus-lithium solution, which is a mixed solution.

[0064] (6) In a nitrogen environment, add an equal volume of 0.25 mol·L phosphoric acid to the mixed solution for 5 min. -1 The ferrous sulfate solution was stirred for 10 min to obtain suspension A.

[0065] (7) In a nitrogen environment, the microreactor was kept at a constant temperature of 200 °C, and the suspension A was mixed with 0.75 mol·L -1 Lithium hydroxide solution was simultaneously fed into the microreactor, the pH was adjusted to 8.2, and a hydrothermal reaction was carried out. The reaction time was 15 min and the pressure was 1.80 MPa to obtain a hydrothermal product.

[0066] (8) The hydrothermal product was filtered, washed, and dried in a vacuum drying oven at 60 °C for 6 h to obtain lithium iron phosphate material.

[0067] (9) The lithium iron phosphate material was mixed with 4.00% wt. starch of the total weight of the raw materials, and the mixed solid was placed in a tubular furnace in a nitrogen atmosphere. The calcination temperature was 600 °C and the heating rate was 8 °C min. -1 , constant temperature time is 6.5 h, and LiFePO4 / C material is obtained.

[0068] Comparative Example 2 A method for preparing a lithium iron phosphate positive electrode material, reacting in a kettle reactor at a ratio of lithium: iron: phosphorus = 1.5:1:1 (molar ratio), and adjusting the pH with sodium hydroxide to prepare the lithium iron phosphate positive electrode material, comprising the following steps: (1) Prepare 0.0625 mol·L in oxygen-free water -1 Lithium carbonate solution.

[0069] (2) Prepare 0.25 mol·L in oxygen-free water -1 Lithium dihydrogen phosphate solution.

[0070] (3) Prepare 0.375 mol·L in oxygen-free water -1 of sodium hydroxide solution.

[0071] (4) Prepare 0.25 mol·L -1 of ferrous nitrate aqueous solution.

[0072] (5) To 0.25 mol·L -1 0.70 wt.% sodium dodecyl sulfate based on the total weight of the raw materials was added to the lithium dihydrogen phosphate solution to obtain a phosphorus solution.

[0073] (6) Add 0.0625 mol·L lithium dihydrogen phosphate in an equal volume to the phosphorus solution. -1 Lithium carbonate solution, lithium carbonate feeding time is 3 min, at 1500 r·min -1 Under the stirring rate condition, stir for 5 min to obtain lithium phosphorus solution.

[0074] (7) Add 0.375 mol·L lithium phosphate solution -1 Sodium hydroxide solution was added to adjust the pH to 6.50. The sodium hydroxide feeding time was 3 min and the temperature was kept at 1200 r·min. -1 The mixture was stirred at a stirring rate of 1.04 % for 7 min to obtain a mixed solution.

[0075] (8) In a nitrogen environment, add 0.25 mol·L lithium dihydrogen phosphate (LDP) in an equal volume to the mixed solution at a feeding time of 3 min. -1 Ferrous nitrate solution, at 1150 r·min -1 The mixture was stirred at a stirring rate of 1.04 % for 8 min to obtain suspension A.

[0076] (9) In a nitrogen environment, suspension A and 0.375 mol·L -1 Sodium hydroxide solution was simultaneously fed into the tank reactor to adjust the pH to 9.00 and the reactor was heated at 5 °C min -1 The heating rate was increased to 220°C, and the reaction was carried out at 220°C for 7.0 h to obtain a hydrothermal product.

[0077] (10) The hydrothermal product was filtered, washed, and dried in a vacuum drying oven at 70 °C for 5.0 h to obtain lithium iron phosphate material.

[0078] (11) The lithium iron phosphate material was mixed with 8.00%wt. sucrose, and the mixed solid was placed in a tubular furnace in a nitrogen atmosphere. The calcination temperature was 550 °C and the heating rate was 5 °C min. -1 , constant temperature time is 7.0h, and LiFePO4 / C material is obtained.

[0079] The LiFePO4 / C materials prepared in Example 1 and Comparative Examples 1-2 were characterized by microscopic morphology. Figure 1 This is a scanning electron microscope image of LiFePO4 / C in Example 1 of the present invention. Figure 2 The scanning electron microscope image of LiFePO4 / C in comparative example 1 of the present invention and the scanning electron microscope image of LiFePO4 / C in comparative example 2 of the present invention are shown in FIG. Figures 1 to 3 It can be seen that compared with Comparative Example 2, the LiFePO4 / C prepared in Example 1 and Comparative Example 1 is smaller and has better dispersibility, indicating that the reaction method using a microreactor can effectively reduce the particle size of lithium iron phosphate.

[0080] XRD analysis was performed on the LiFePO4 / C materials prepared in Examples 1-3 and Comparative Examples 1-2. Figure 4 As shown, from Figure 4 It can be seen that the lithium iron phosphate materials prepared in Examples 1 to 3 and Comparative Example 1 are all pure phase lithium iron phosphate, and no impurities are found. Comparative Example 1 contains a sodium iron phosphate impurity phase, which indicates that compared with the traditional kettle reactor, the use of a microreactor can effectively promote the combination of lithium iron phosphate and avoid the generation of impurities.

[0081] The electrochemical performance (specific capacity) of the LiFePO4 / C materials prepared in Examples 1-3 and Comparative Examples 1-2 was characterized. Figure 5 To characterize the results, the data of each sample are shown in Table 1.

[0082] Table 1

[0083] from Figure 5 , Table 1 shows that the electrochemical performance of Examples 1 to 3 and Comparative Example 1 is basically the same, indicating that compared with the mainstream lithium iron phosphate preparation method with a lithium:phosphorus:iron ratio of 3:1:1 on the market, the electrochemical performance of lithium iron phosphate prepared in a microreactor with a lithium:phosphorus:iron ratio of 1.5 to 2.0:1:1 (molar ratio) is basically the same, further highlighting the advantages of the microreactor in terms of small amount of raw materials and low cost. The electrochemical performance of LiFePO4 / C in Comparative Example 2 is significantly lower than that of Examples 1-3, further indicating that compared with the traditional kettle reactor, the reaction mode of the microreactor can effectively improve the electrochemical performance of lithium iron phosphate.

[0084] In addition to the above embodiments, the present invention also includes other implementation modes. Any technical solutions formed by equivalent transformation or equivalent replacement should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing lithium iron phosphate positive electrode material at low cost, characterized in that: The following steps are involved: (a) adding a surfactant to a phosphorus source at room temperature and in a nitrogen atmosphere to form a phosphorus liquid, mixing a lithium source with the phosphorus liquid and stirring to form a phosphorus-lithium liquid, adding an alkali solution to the phosphorus-lithium liquid to adjust the pH to 6-7 and stirring to form a mixed liquid, and stirring the mixed liquid with an iron source to obtain a suspension A; (b) In a nitrogen atmosphere, the microreactor is heated to a certain temperature and kept at a constant temperature, and the suspension A and the alkali solution are simultaneously fed into the microreactor in two streams, and the pH is adjusted to 7.5-9 to perform a hydrothermal reaction to obtain a hydrothermal product; (c) filtering, washing and vacuum drying the hydrothermal product to obtain a lithium iron phosphate material; (d) The lithium iron phosphate material and the carbon source are mixed and calcined under nitrogen protection to obtain LiFePO4 / C material.

2. The method for preparing lithium iron phosphate positive electrode material at low cost according to claim 1, characterized in that: The phosphorus source is at least one of phosphoric acid and lithium dihydrogen phosphate, the lithium source is at least one of lithium sulfate, lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide or lithium phosphate, and the iron source is at least one of ferrous chloride, ferrous sulfate and ferrous nitrate.

3. The method for preparing lithium iron phosphate positive electrode material at low cost according to claim 1, characterized in that: The molar ratio of the lithium source, the iron source and the phosphorus source is 1.5-2.0:1:

1.

4. The method for preparing lithium iron phosphate positive electrode material at low cost according to claim 1, characterized in that: The surfactant is at least one of polyvinyl alcohol, hexadecyltrimethylammonium bromide, sorbitol fatty acid ester, and sodium lauryl sulfate, and the added amount is 0.50% wt. to 0.80% wt. of the total weight of the raw materials.

5. The method for preparing lithium iron phosphate positive electrode material at low cost according to claim 1, characterized in that: The alkali solution is at least one of ammonia water and sodium hydroxide.

6. The method for preparing lithium iron phosphate positive electrode material at low cost according to claim 1, characterized in that: The carbon source is at least one of glucose, sucrose, ascorbic acid and starch, and the amount of the carbon source is 4.00% wt. to 10.00% wt. of the total weight of the raw material.

7. The method for preparing lithium iron phosphate positive electrode material at low cost according to claim 1, characterized in that: In step (a), phosphorus liquid is the base liquid, the lithium source feeding time is 3min~5min, the lithium source and phosphorus liquid are mixed and stirred for 5min~10min, and the stirring rate is 1000r·min -1 ~1500r·min -1 ; The phospholipid-lithium solution is the bottom solution, the alkali solution feeding time is 3min~5min, the phospholipid-lithium solution and alkali solution stirring time is 5min~10min, and the stirring rate is 1000 r·min -1 ~1500 r·min -1 ; The mixed liquid is the bottom liquid, the iron source feeding time is 3min~5min, the mixed liquid and iron source stirring time is 5min~10min, and the stirring rate is 1000r·min -1 ~1500r·min -1 .

8. The method for preparing lithium iron phosphate positive electrode material at low cost according to claim 1, characterized in that: In step (b), the constant temperature range of the microreactor is 180°C~220°C, the pressure is 1.80 Mpa~2.20 Mpa; and the hydrothermal reaction time is 10 min~25 min.

9. The method for preparing lithium iron phosphate positive electrode material at low cost according to claim 1, characterized in that: In step (c), the vacuum drying temperature is 50°C to 80°C, and the time is 5.0h to 7.0h; in step (d), the calcination temperature is 500°C to 700°C, and the calcination time is 4.0h to 7.0h.

10. A lithium iron phosphate positive electrode material, characterized in that: The lithium iron phosphate positive electrode material is prepared by the method for preparing the lithium iron phosphate positive electrode material at low cost according to any one of claims 1 to 9.

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