Preparation method of lithium manganese iron phosphate positive electrode material
The Fe3(PO4)2·6H2O precursor was synthesized by the precipitation method and the LiFe0.75Mn0.25PO4/C positive electrode material was synthesized, which solved the problems of low lithium ion diffusion rate and poor electronic conductivity of the LFMP positive electrode material, and achieved higher electrochemical performance and cyclic stability.
Patent Information
- Application Number
- CN202411788669.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-06
- Publication Date
- 2025-03-14
AI Technical Summary
Lithium iron manganese phosphate (LiFe1-xMnxPO4, LFMP) cathode material has problems with low lithium ion diffusion rate and poor electronic conductivity, which hinders its widespread application in lithium-ion batteries.
Fe3(PO4)2·6H2O precursor was synthesized by precipitation method, and LiFe0.75Mn0.25PO4/C positive electrode material was synthesized by wet ball milling, vacuum drying, calcining, etc., and the pH value was adjusted to control the particle morphology and electrochemical properties.
The smaller and more uniform particle size, higher electron conductivity, larger lithium ion diffusion coefficient, better rate performance and cycle stability of the LiFe0.75Mn0.25PO4/C cathode material are achieved.
Smart Images
Figure HDA0005174756470000011 
Figure HDA0005174756470000012 
Figure HDA0005174756470000021
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a method for preparing a lithium iron manganese phosphate positive electrode material. Background Art
[0002] Lithium iron manganese phosphate (LiFe 1-x Mn x PO 4 LFMP) cathode materials are widely used in lithium-ion batteries due to their high safety, low cost and high energy density. However, the low lithium ion diffusion rate and poor electronic conductivity of LFMP hinder its application. In order to solve the problems of poor electronic conductivity and low lithium ion diffusion coefficient, a lot of modification research has been done. The study found that particle minimization, surface coating of conductive materials (carbon or metal particles) and cation doping, especially Mn 2+ Replace Fe 2+ It has been shown to be effective in improving LiFePO 4 The low energy density and electrochemical performance of LiFe x Mn 1-x PO 4 Can be a good successor to LiFePO 4 Outstanding rate performance and LiMnPO 4 Higher working potential. Therefore, olivine structure LiFe x Mn 1-x PO 4 The research on positive electrode materials has received widespread attention.
[0003] In addition, the synthesis process of LiFe x Mn 1-x PO 4 Control of particle morphology also plays an important role. The solid phase method is to synthesize materials by fully mixing certain materials in proportion and then sintering them at high temperature for a long time. This preparation method is easy to implement in industrial production processes, but the resulting materials have problems such as large particle size and uneven distribution, and the process is relatively time-consuming and labor-intensive. Liquid phase methods such as coprecipitation, hydrothermal or solvothermal, and sol-gel processes can well control particle size and morphology. However, hydrothermal or solvothermal methods require high temperature and high pressure, and the sol-gel process steps are extremely cumbersome. Therefore, it remains a huge challenge. Summary of the invention
[0004] In view of the shortcomings of the prior art, the present invention provides a method for preparing a lithium manganese iron phosphate positive electrode material. The method first uses iron powder and phosphoric acid solution as raw materials by a precipitation method, adds a surfactant and an alkaline solution to adjust the pH to synthesize Fe 3 (PO 4 ) 26H 2 O precursor; then use it as an iron source, add lithium source, manganese source, phosphorus source and a small amount of carbon source, and synthesize LiFe through a series of steps including wet ball milling, vacuum drying and calcination. 0.75 Mn 0.25 PO 4 / C positive electrode material.
[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions:
[0006] The present invention discloses a method for preparing a lithium manganese iron phosphate positive electrode material, comprising the following steps:
[0007] (1) dissolving iron powder in a phosphoric acid solution, adding a surfactant, adjusting the pH value with an alkaline lithium compound, and after the reaction is completed, filtering to obtain an iron source;
[0008] (2) mixing a lithium source, a manganese source, an iron source, a phosphorus source and a carbon source, grinding, refining, drying and cooling to obtain a precursor;
[0009] (3) Sintering the precursor at high temperature in an argon atmosphere and cooling it to room temperature after sintering to obtain LiFe 0.75 Mn 0.25 PO 4 / C positive electrode material.
[0010] Preferably, in step (1), the molar ratio of iron to phosphoric acid is 1:2.5, the mass percentage concentration of phosphoric acid is 20%, and after the pH value is adjusted, the reaction time is 0.5 to 4 hours, and the reaction temperature is 70°C to 90°C; the concentration of the alkaline lithium compound is 0.5 to 1.0 mol / L, and the pH range is 4 to 9.
[0011] Preferably, in step (1), the surfactant mainly comprises one or more mixtures of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride and octadecyltrimethylammonium chloride.
[0012] Preferably, in step (1), the alkaline lithium compound mainly comprises one or more mixtures of lithium hydroxide, lithium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate.
[0013] Preferably, in step (2), the amount of carbon source added is 10-20wt% of the total mass of the raw material, and the total mass of the raw material is the sum of the mass of the lithium source, the manganese source, and the iron source; in step (3), the prepared LiFe 0.75 Mn 0.25 PO 4 The molar ratio of lithium source, manganese source, iron source and phosphorus source in the / C positive electrode material is (1-1.05):0.25:0.75:1.
[0014] Preferably, the lithium source is one or more mixtures of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate and lithium phosphate.
[0015] Preferably, the manganese source is Mn(H 2 PO 4 ) 2 ·2H 2 O.
[0016] Preferably, the phosphorus source is lithium dihydrogen phosphate, lithium phosphate or a mixture of one or more thereof.
[0017] Preferably, the carbon source is a mixture of one or more of sucrose, glucose, polyvinyl alcohol, soluble starch, citric acid, ascorbic acid, polypropylene alcohol, polyethylene glycol, carbon black, acetylene black, carbon nanotubes, and graphene.
[0018] Preferably, in step (3), the sintering temperature is 600-700°C.
[0019] The present invention has the following beneficial effects:
[0020] 1. The present invention proposes a method for preparing ferrous phosphate and an environmentally friendly lithium iron manganese phosphate positive electrode material. 3 (PO 4 ) 2 6H 2 O precursor, and then mixed with manganese source and lithium source by ball milling, freeze-dried and calcined to prepare Li 1-1.05 Fe 0.75 Mn 0.25 PO 4 / C positive electrode material, the alkaline substance used to adjust the pH in the preparation process can be recycled, no waste is discharged, and the preparation process is green and environmentally friendly. In the past, high-pollution raw materials containing sulfuric acid, oxalate, nitrate and ammonium ion compounds were usually used for preparation in the preparation of lithium batteries, while the present invention uses low-pollution raw materials to prepare lithium-ion battery positive electrode materials.
[0021] 2. The present invention uses a coprecipitation method to generate a uniform long flake iron source, and then performs wet ball milling to synthesize the LFMP positive electrode material. By adjusting different synthesis temperatures, Fe with different morphologies is synthesized. 3 (PO 4 ) 2 6H 2 O, uniform long flake Fe 3 (PO 4 ) 2 6H 2 O particles have smaller particle size, more uniform morphology and higher crystallinity. 0.75Mn 0.25 PO 4 / C positive electrode materials have smaller and more uniform particle size, higher electronic conductivity, larger lithium ion diffusion coefficient, and better rate performance and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 The rate performance diagram of the materials finally prepared in Example 1, Comparative Example 1 and Comparative Example 2 at a rate of 0.2-10C;
[0023] Figure 2 The cycle performance diagram of the materials finally prepared in Example 1, Comparative Example 1 and Comparative Example 2 at 1C rate for 700 cycles;
[0024] Figure 3 The morphology of the positive electrode materials prepared in Example 1, Comparative Example 1 and Comparative Example 2;
[0025] Figure 4 The diffusion of lithium ions in the positive electrode materials prepared in Example 1, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION
[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0027] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.
[0028] The present invention discloses a method for preparing a lithium manganese iron phosphate positive electrode material, comprising the following steps:
[0029] (1) Dissolve iron powder in phosphoric acid solution, add surfactant, adjust pH value with alkaline lithium compound, and after the reaction is completed, let stand and filter to dry to obtain iron source; wherein the mass percentage concentration of phosphoric acid is 20%, after the pH value is adjusted, the reaction time is 0.5 to 4 hours, and the reaction temperature is 70°C to 90°C; the concentration of alkaline lithium compound is 0.5 to 1.0 mol / L, and the pH range is 4 to 9. 3 PO 4 The molar ratio is 1:2.5.
[0030] Furthermore, the surfactant mainly includes one or more mixtures of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.
[0031] The alkaline lithium compounds mainly include lithium hydroxide (LiOH), lithium dihydrogen phosphate (LiH 2 PO 4 )、Lithium dihydrogen phosphate (Li 2 HPO 4 ), lithium phosphate (Li 3 PO 4 ) or a mixture of one or more of ).
[0032] (2) A lithium source, a manganese source, an iron source, a phosphorus source and a carbon source are mixed, ground, dried and cooled to room temperature to obtain a precursor; the amount of the carbon source added is 10 to 20 wt% of the total mass of the raw materials, and the total mass of the raw materials is the sum of the masses of the lithium source, the manganese source and the iron source.
[0033] Furthermore, the lithium source is lithium carbonate (Li 2 CO 3 ), lithium hydroxide (LiOH), lithium dihydrogen phosphate (LiH 2 PO 4 ), lithium phosphate (Li 3 PO 4 ) or a mixture thereof. The manganese source is Mn(H 2 PO 4 ) 2 ·2H 2 O. The phosphorus source is lithium dihydrogen phosphate (LiH 2 PO 4 ), lithium phosphate (Li 3 PO 4 ). The carbon source is a mixture of one or more of sucrose, glucose, polyvinyl alcohol, soluble starch, citric acid, ascorbic acid, polypropylene alcohol, polyethylene glycol, carbon black, acetylene black, carbon nanotubes, and graphene.
[0034] (3) The precursor is sintered at high temperature in an argon atmosphere at a temperature of 600-700°C for 10 h, and then cooled to room temperature to obtain Li 1～1.05 Fe 0.75 Mn 0.25 PO 4 / C positive electrode material, the molar ratio of lithium source, manganese source, iron source and phosphorus source in the material is (1-1.05): 0.25: 0.75: 1. The specific sintering process is: calcining at 400°C for 3-4h, and then calcining at 600-700°C for 10h.
[0035] The present invention will be further described below in conjunction with specific embodiments.
[0036] Example 1
[0037] A method for synthesizing long flake Fe by precipitation method 3 (PO 4 ) 2 6H 2 O as an iron source for preparation of LiFe 0.75 Mn 0.25 PO 4 The preparation method of / C positive electrode material, the steps are as follows:
[0038] S1.Fe:H 3 PO 4 The molar ratio is 1:2.5. At 40°C, the iron powder is stirred and dissolved in 20% phosphoric acid (85% phosphoric acid is dissolved in a certain amount of deionized water) with a mass percentage concentration. After reacting for 4 hours, it is filtered to obtain a light green solution.
[0039] S2. Add 0.0312 g CTAB (hexadecyltrimethylammonium bromide), 0.8 mol / L LiOH·H 2 The pH of the aqueous solution was adjusted to 5.5, and the mixture was stirred vigorously at 80°C for 4 h. After standing for 12 h, a light blue solid was obtained by filtration, which was then dried in vacuo to obtain the iron source.
[0040] S3. Weigh the iron source, Mn(H 2 PO 4 ) 2 ·2H 2 O. Li 2 CO 3 , glucose (15wt%) was dissolved in 15mL of deionized water and ethanol, V 水 :V 乙醇 =2:1, ball milled at 400 rpm for 10 h, and then dried to obtain the precursor.
[0041] S4. The above precursor was calcined at 400°C for 3h and 600°C for 10h in a tube furnace at a heating rate of 5°C / min under argon atmosphere to obtain LiFe 0.75 Mn 0.25 PO 4 / C positive electrode material. The morphology of the prepared positive electrode material is shown in Figure 3 shown.
[0042] Example 2
[0043] Preparation of LiFe 0.75 Mn 0.25 PO4 The process of preparing the / C positive electrode material is the same as that of Example 1, except that the iron source is ferroferric oxide.
[0044] Example 3
[0045] Preparation of LiFe 0.75 Mn 0.25 PO 4 The process of using 0.8 mol / L LiOH·H 2 O aqueous solution was adjusted to pH 8-9.
[0046] Example 4
[0047] Preparation of LiFe 0.75 Mn 0.25 PO 4 The process of preparing the / C positive electrode material is the same as that of Example 1, except that the calcination temperatures are 650°C and 700°C respectively.
[0048] Comparative Example 1
[0049] Preparation of LiFe 0.75 Mn 0.25 PO 4 The process of preparing the positive electrode material of / C is the same as that of Example 1, except that the reaction temperature of step S2 is changed to 70°C. The morphology of the prepared positive electrode material is shown in Figure 3 shown.
[0050] Comparative Example 2
[0051] Preparation of LiFe 0.75 Mn 0.25 PO 4 The process of preparing the positive electrode material of / C is the same as that of Example 1, except that the reaction temperature of step S2 is changed to 90°C. The morphology of the prepared positive electrode material is shown in Figure 3 shown.
[0052] Performance Testing
[0053] The cathode materials finally prepared in Example 1, Comparative Example 1 and Comparative Example 2 are respectively recorded as LFMP / C-80°C, LFMP / C-70°C and LFMP / C-90°C. The electrochemical properties of the three materials are tested respectively. The test results are shown in FIG. Figure 1 , 2 shown.
[0054] Electronic conductivity and Li + Migration rate Figure 4 And as shown in Table 1.
[0055] Table 1 LiFe 0.75 Mn 0.25 PO 4 Conductivity and Li / C cathode materials + Mobility
[0056] sample <![CDATA[LogD Li + ]]> <![CDATA[Average D Li + (cm 2 s -1 )]]> LFMP / C-70℃ -9.733 <![CDATA[8.20×10 -10 ]]> LFMP / C-80℃ -9.705 <![CDATA[1.00×10 -9 ]]> LFMP / C-90℃ -10.176 <![CDATA[3.37×10 -10 ]]>
[0057] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.
Claims
1. A method for preparing a lithium manganese iron phosphate positive electrode material, characterized in that: The following steps are involved: (1) dissolving iron powder in a phosphoric acid solution, adding a surfactant, adjusting the pH value with an alkaline lithium compound, and after the reaction is completed, filtering to obtain an iron source; (2) mixing a lithium source, a manganese source, an iron source, a phosphorus source and a carbon source, grinding, refining, drying and cooling to obtain a precursor; (3) Sintering the precursor at high temperature in an argon atmosphere and cooling it to room temperature after sintering to obtain LiFe 0.75 Mn 0.25 PO4 / C positive electrode material.
2. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: In step (1), the molar ratio of iron to phosphoric acid is 1:2.5, the mass percentage concentration of phosphoric acid is 20%, and after the pH value is adjusted, the reaction time is 0.5 to 4 hours, and the reaction temperature is 70° C. to 90° C.; the concentration of the alkaline lithium compound is 0.5 to 1.0 mol / L, and the pH range is 4 to 9.
3. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: In step (1), the surfactant mainly comprises one or more mixtures of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride and octadecyltrimethylammonium chloride.
4. A method for preparing a lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 3, characterized in that: In step (1), the alkaline lithium compound mainly includes one or more mixtures of lithium hydroxide, lithium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate.
5. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: In step (2), the amount of carbon source added is 10-20wt% of the total mass of the raw materials, and the total mass of the raw materials is the sum of the mass of the lithium source, the manganese source, and the iron source; in step (3), the prepared LiFe 0.75 Mn 0.25 The molar ratio of lithium source, manganese source, iron source and phosphorus source in the PO4 / C positive electrode material is (1-1.05):0.25:0.75:
1.
6. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The lithium source is one or more mixtures of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate and lithium phosphate.
7. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The manganese source is Mn(H2PO4)2·2H2O.
8. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The phosphorus source is lithium dihydrogen phosphate, lithium phosphate or a mixture of one or more thereof.
9. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The carbon source is a mixture of one or more of sucrose, glucose, polyvinyl alcohol, soluble starch, citric acid, ascorbic acid, polypropylene alcohol, polyethylene glycol, carbon black, acetylene black, carbon nanotubes and graphene.
10. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: In step (3), the sintering temperature is 600-700°C.