A precursor and a method of making the same

Abstract

This invention discloses a precursor and its preparation method, belonging to the field of lithium-ion battery cathode material technology; the molecular formula of the organic-inorganic hybrid manganese-iron precursor is Mn. x Fe y [C6H5PO3]·nH2O, where x+y=1, and 0.2≤x≤0.9, 0<n≤2. The organic-inorganic hybrid manganese-iron precursor prepared in this invention achieves a highly uniform atomic-level distribution of the two metal elements by uniformly complexing manganese and iron ions at the molecular level using phenylphosphonic acid ligands. This solves the phase separation and structural instability problems caused by elemental segregation in lithium manganese iron phosphate materials, thus laying a uniform and controllable compositional and structural foundation for the subsequent synthesis of high-performance cathode materials.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials technology, specifically a precursor and its preparation method. Background Technology

[0002] Currently, lithium iron phosphate (LFP) has become the mainstream choice in the market due to its excellent safety performance, but its low energy density severely restricts the upper limit of battery energy. As battery energy density gradually reaches its ceiling, lithium manganese iron phosphate (LiMnxFeyPO4), as a new type of lithium battery cathode material, is gradually becoming a rising star in the field of lithium battery cathode materials due to its high energy density, long cycle life and high safety.

[0003] However, its practical application still faces multiple challenges: although the introduction of manganese can improve the working voltage and power density, it will induce structural defects such as the Jahn-Teller effect and lattice distortion; more importantly, changes in charge and discharge rates will significantly alter its electrochemical reaction pathway, leading to capacity decay and a decrease in rate performance, which seriously restricts its commercialization process.

[0004] To address these issues, a manganese-iron coprecipitation precursor process is employed. This process allows for precise control of the manganese-iron element ratio and synthesis pathway, achieving atomic-level uniform distribution of manganese and iron. This avoids the risk of phase separation from the outset, ensuring the material's structural stability. However, there are currently no unified industry standards for precursor synthesis processes. Precursor production is technically challenging, requiring long-term R&D and process accumulation, thus presenting significant barriers to entry. Summary of the Invention

[0005] In view of this, the present invention provides an organic-inorganic hybrid manganese iron precursor and its preparation method. By complexing manganese iron with phenylphosphonic acid in the liquid phase, an organic-inorganic hybrid precursor with uniform elemental distribution is prepared, achieving atomic-level uniform distribution of manganese and iron in the precursor. The resulting lithium manganese iron phosphate product has uniform distribution of manganese and iron phases and exhibits good electrochemical performance when applied in secondary batteries.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention discloses a precursor having the molecular formula Mn. x Fe y [C6H5PO3]·nH2O, where x+y=1, and 0.2≤x≤0.9, 0<n≤2.

[0008] As a further aspect of this invention: 0.5 ≤ x ≤ 0.8. Lithium manganese iron phosphate materials prepared within this ratio range can balance high operating voltage and structural stability, avoiding lattice distortion caused by excessive manganese and insufficient energy density caused by excessive iron.

[0009] Secondly, this invention discloses a method for preparing the above-described organic-inorganic hybrid manganese-iron precursor, comprising the following steps: S1. Prepare organic molecule solutions; S2. Prepare a mixed salt solution of manganese and iron sources, and introduce an inert gas for atmosphere protection. S3. The organic molecular solution and the pH adjusting agent solution are added dropwise to the mixed salt solution in a parallel flow to carry out the reaction. The resulting slurry is filtered, washed and dried to obtain the organic-inorganic hybrid manganese iron precursor.

[0010] As a further aspect of the present invention: in step S1, the organic molecule is phenylphosphonic acid, with the molecular formula C6H7O3P; the concentration of the organic molecule solution is 0.5–2.0 mol / L. Phenylophosphonic acid possesses both complexing and carbon source precursor functions, enabling the in-situ formation of a conductive carbon network during sintering; the limited concentration range ensures the kinetics of the complexing reaction and the stability of the system, avoiding incomplete complexation due to excessively low concentration or side reactions caused by excessively high concentration.

[0011] As a further aspect of the present invention: in step S2, the iron source is at least one selected from ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous oxalate, and ferrous acetate; the manganese source is at least one selected from manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate; the total concentration of manganese and iron in the manganese-iron mixed solution is 0.5–2 mol / L. This provides a variety of soluble manganese / iron sources to suit different raw material costs and process routes; the concentration range balances reaction efficiency and system stability, avoiding low production capacity due to excessive dilution and uneven precipitation due to excessive concentration.

[0012] As a further aspect of the present invention: in step S2, the protective gas atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0013] As a further aspect of the present invention: in step S3, the pH adjuster includes at least one of ammonia water and sulfuric acid solution, and the pH value is controlled between 3.0 and 6.0. This pH range limitation ensures that the complexation reaction proceeds at a suitable acidity, avoiding incomplete complexation due to excessively low pH and the occurrence of hydroxide precipitation side reactions due to excessively high pH.

[0014] Thirdly, the present invention discloses a lithium manganese iron phosphate material, which is prepared from the above-mentioned organic-inorganic hybrid manganese iron precursor.

[0015] Fourthly, this invention discloses a method for preparing lithium iron phosphate material. The method involves uniformly mixing the aforementioned organic-inorganic hybrid manganese iron precursor with a lithium source and a carbon source, followed by sand milling, spray drying, sintering, and pulverization to obtain the lithium manganese iron phosphate material. During sintering, the phenylphosphonic acid groups in the precursor are converted in situ to phosphate groups, while the organic ligands carbonize to form a conductive carbon layer. This method is directly compatible with existing lithium iron phosphate production lines, exhibiting extremely high process compatibility and industrialization potential.

[0016] As a further aspect of the present invention: the carbon source is at least one selected from glucose, polyethylene glycol, polyvinyl alcohol, citric acid, tannic acid, and starch. The composite carbon source can synergistically improve the uniformity and conductivity of the carbon layer, while tannic acid has both dispersing and complexing functions; the type and amount of carbon source are flexibly adjustable and can be optimized according to performance indicators such as target specific surface area, residual carbon content, and resistivity.

[0017] Compared with the prior art, the beneficial effects of the present invention are: The organic-inorganic hybrid manganese-iron precursor prepared in this invention achieves a highly uniform atomic distribution of the two metal elements by uniformly complexing manganese and iron ions at the molecular level using phenylphosphonic acid ligands. This solves the phase separation and structural instability problems caused by element segregation in lithium manganese iron phosphate materials, thus laying a uniform and controllable composition and structural foundation for the subsequent synthesis of high-performance cathode materials.

[0018] The preparation method provided by this invention, employing a liquid-phase complexation process with co-current dropwise addition and pH synergistic control, enables the efficient and controllable synthesis of the aforementioned precursor, and achieves one-step sintering synthesis of lithium manganese iron phosphate based on this precursor. Compared with traditional multi-step co-precipitation and two-stage sintering processes, this process significantly shortens the production cycle, reduces energy consumption and costs, and, because the precursor itself possesses both structure-guiding and carbon source functions, makes the synthesis process more efficient, produces better product consistency, and can be directly adapted to existing lithium iron phosphate production lines, demonstrating outstanding process compatibility and industrialization potential. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart of the preparation method of carbon-coated lithium manganese iron phosphate, the precursor of this application. Figure 2 SEM image of the organic-inorganic hybrid manganese-iron precursor material prepared in Example 1; Figure 3 SEM image of the lithium manganese iron phosphate material prepared in Example 1; Figure 4 The image shows a SEM image of the lithium manganese iron phosphate material prepared in Example 2. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0022] In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail; unless otherwise specified, the parts in the following embodiments refer to parts by weight.

[0023] Example 1 Phenyline phosphonic acid was dissolved in deionized water to prepare a 1.5 mol / L solution A. Manganese sulfate and ferrous sulfate were dissolved in deionized water at a molar ratio of Mn to Fe of 6:4 to prepare solution B with a total concentration of Mn and Fe of 1.5 mol / L. Nitrogen gas was continuously introduced to maintain the atmosphere and prevent the oxidation of metal ions. Solution A and ammonia solution were added dropwise to solution B under co-current flow, with the pH controlled at 6 during the reaction. The resulting colloidal suspension was continuously stirred under flowing nitrogen for approximately 3 hours, followed by multiple centrifugal washings with acetone and vacuum drying at 100°C to obtain the chemical formula Mn. 0.6 Fe 0.4 [C6H5PO3]·H2O precursor; The aforementioned precursor and lithium carbonate were weighed according to a Li:(Mn+Fe) molar ratio of 1.125, and an organic composite carbon source (75% glucose and 25% tannic acid) equivalent to 6% of the precursor mass was added. The mixture was ball-milled for 4 hours using deionized water as the dispersion medium. The milled slurry was diluted with water to a solid content of 25% and then atomized and dried. The two-fluid drying parameters were set to an inlet air temperature of 180℃. The dried material was placed in a tube furnace and heated to 680℃ at a rate of 5℃ / min, then held for sintering for 12 hours to obtain carbon-coated lithium manganese iron phosphate cathode material.

[0024] Example 2 Phenyline phosphonic acid was dissolved in deionized water to prepare a 1.5 mol / L solution A. Manganese sulfate and ferrous sulfate were dissolved in deionized water at a molar ratio of Mn to Fe of 7:3 to prepare solution B with a total concentration of Mn and Fe of 1.5 mol / L. Nitrogen gas was continuously introduced to maintain the atmosphere and prevent the oxidation of metal ions. Solution A and ammonia solution were added dropwise to solution B under co-current flow, with the pH controlled at 6 during the reaction. The resulting colloidal suspension was continuously stirred under flowing nitrogen for approximately 3 hours, followed by multiple centrifugal washings with acetone and vacuum drying at 100°C to obtain the chemical formula Mn. 0.7 Fe 0.3 [C6H5PO3]·H2O precursor; The aforementioned precursor and lithium carbonate were weighed according to a Li:(Mn+Fe) molar ratio of 1.125, and an organic composite carbon source (75% glucose and 25% tannic acid) equivalent to 6% of the precursor mass was added. The mixture was ball-milled for 4 hours using deionized water as the dispersion medium. The milled slurry was diluted with water to a solid content of 25% and then atomized and dried. The two-fluid drying parameters were set to an inlet air temperature of 180℃. The dried material was placed in a tube furnace and heated to 680℃ at a rate of 5℃ / min, then held for sintering for 12 hours to obtain carbon-coated lithium manganese iron phosphate cathode material.

[0025] Example 3 Phenyline phosphonic acid was dissolved in deionized water to prepare a 1.5 mol / L solution A. Manganese sulfate and ferrous sulfate were dissolved in deionized water at a molar ratio of Mn to Fe of 3:1 to prepare solution B with a total concentration of Mn and Fe of 1.5 mol / L. Nitrogen gas was continuously introduced to maintain the atmosphere and prevent the oxidation of metal ions. Solution A and ammonia solution were added dropwise to solution B under co-current flow, with the pH controlled at 6 during the reaction. The resulting colloidal suspension was continuously stirred under flowing nitrogen for approximately 3 hours, followed by multiple centrifugal washings with acetone and vacuum drying at 100°C to obtain the chemical formula Mn. 0.75 Fe 0.25 [C6H5PO3]·H2O precursor; The aforementioned precursor and lithium carbonate were weighed according to a Li:(Mn+Fe) molar ratio of 1.125, and an organic composite carbon source (75% glucose and 25% tannic acid) equivalent to 6% of the precursor mass was added. The mixture was ball-milled for 4 hours using deionized water as the dispersion medium. The milled slurry was diluted with water to a solid content of 25% and then atomized and dried. The two-fluid drying parameters were set to an inlet air temperature of 180℃. The dried material was placed in a tube furnace and heated to 680℃ at a rate of 5℃ / min, then held for sintering for 12 hours to obtain carbon-coated lithium manganese iron phosphate cathode material.

[0026] Example 4 Phenyline phosphonic acid was dissolved in deionized water to prepare a 1.0 mol / L solution A. Manganese sulfate and ferrous sulfate were dissolved in deionized water at a molar ratio of Mn to Fe of 6:4 to prepare solution B with a total concentration of Mn and Fe of 1.0 mol / L. Nitrogen gas was continuously introduced to maintain the atmosphere and prevent the oxidation of metal ions. Solution A and dilute sulfuric acid solution were added dropwise to solution B in a parallel flow, with the pH controlled at 4 during the reaction. The resulting colloidal suspension was continuously stirred under flowing nitrogen for approximately 3 hours, followed by multiple centrifugal washings with acetone and vacuum drying at 100°C to obtain the chemical formula Mn. 0.6 Fe 0.4 [C6H5PO3]·H2O precursor; The aforementioned precursor and lithium carbonate were weighed according to a Li:(Mn+Fe) molar ratio of 1.125, and an organic carbon source (glucose) equivalent to 6% of the precursor mass was added. Using deionized water as the dispersion medium, the mixture was ball-milled for 4 hours. The milled slurry was diluted with water to a solid content of 25% and then atomized and dried. The two-fluid drying parameters were set to an inlet air temperature of 180℃. The dried material was placed in a tube furnace and heated to 680℃ at a rate of 5℃ / min, then held at that temperature for sintering for 12 hours to finally obtain carbon-coated lithium manganese iron phosphate cathode material.

[0027] Comparative Example 1 Using commercially available lithium manganese iron phosphate cathode material (LiMn) 0.6 Fe 0.4 PO4 (grade LMFP64) was used as a control sample.

[0028] Comparative Example 2 Phenyline phosphonic acid was dissolved in deionized water to prepare a 1.5 mol / L solution A. Manganese sulfate and ferrous sulfate were dissolved in deionized water at a molar ratio of Mn to Fe of 1:9 to prepare solution B with a total concentration of Mn and Fe of 1.5 mol / L. Nitrogen gas was continuously introduced to maintain the atmosphere and prevent the oxidation of metal ions. Solution A and ammonia solution were added dropwise to solution B under co-current flow, with the pH controlled at 6 during the reaction. The resulting colloidal suspension was continuously stirred under flowing nitrogen for approximately 3 hours, followed by multiple centrifugal washings with acetone and vacuum drying at 100°C to obtain the chemical formula Mn. 0.1 Fe 0.9 [C6H5PO3]·H2O precursor; The aforementioned precursor and lithium carbonate were weighed according to a Li:(Mn+Fe) molar ratio of 1.125, and an organic composite carbon source (75% glucose and 25% tannic acid) equivalent to 6% of the precursor mass was added. The mixture was ball-milled for 4 hours using deionized water as the dispersion medium. The milled slurry was diluted with water to a solid content of 25% and then atomized and dried. The two-fluid drying parameters were set to an inlet air temperature of 180℃. The dried material was placed in a tube furnace and heated to 680℃ at a rate of 5℃ / min, then held for sintering for 12 hours to obtain carbon-coated lithium manganese iron phosphate cathode material.

[0029] Comparative Example 3 Phenyline phosphonic acid was dissolved in deionized water to prepare a 1.5 mol / L solution A. Manganese sulfate and ferrous sulfate were dissolved in deionized water at a molar ratio of Mn to Fe of 95:5 to prepare solution B with a total concentration of Mn and Fe of 1.5 mol / L. Nitrogen gas was continuously introduced to maintain the atmosphere and prevent the oxidation of metal ions. Solution A and ammonia solution were added dropwise to solution B under co-current flow, with the pH controlled at 6 during the reaction. The resulting colloidal suspension was continuously stirred under flowing nitrogen for approximately 3 hours, followed by multiple centrifugal washings with acetone and vacuum drying at 100°C to obtain the chemical formula Mn. 0.95 Fe 0.05 [C6H5PO3]·H2O precursor; The aforementioned precursor and lithium carbonate were weighed according to a Li:(Mn+Fe) molar ratio of 1.125, and an organic composite carbon source (75% glucose and 25% tannic acid) equivalent to 6% of the precursor mass was added. The mixture was ball-milled for 4 hours using deionized water as the dispersion medium. The milled slurry was diluted with water to a solid content of 25% and then atomized and dried. The two-fluid drying parameters were set to an inlet air temperature of 180℃. The dried material was placed in a tube furnace and heated to 680℃ at a rate of 5℃ / min, then held for sintering for 12 hours to obtain carbon-coated lithium manganese iron phosphate cathode material.

[0030] Test case The lithium manganese iron phosphate cathode materials prepared in Examples 1-4 and Comparative Examples 1-2 were used to prepare electrodes and assemble batteries for testing according to the following general procedures: According to the ratio of positive electrode material: conductive agent: binder = 8:1:1, an appropriate amount of NMP is added as a dispersant, and the mixture is quickly stirred to form a viscous slurry. This slurry is then evenly coated onto aluminum foil that has been wiped clean with alcohol, and baked in a forced-air drying oven at 100℃ for 10 hours. The aluminum foil coated with active material is then rolled using a roller press to form 14mm electrode sheets. Finally, the dried positive electrode sheets are selected and weighed. The positive electrode shell, positive electrode material, separator, electrolyte, lithium sheet, pad, gasket, electrolyte, and negative electrode shell are assembled sequentially into a CR2032 coin cell. Test conditions: The specific capacity, specific capacity, and coulombic efficiency of the first 0.1C charge are tested within a voltage range of 2.0 to 4.5V.

[0031] Test conditions: The specific capacity, first-cycle 0.1C charge capacity, and first-cycle 0.1C charge efficiency were tested within a voltage range of 2.0–4.5V. The test performance and results are shown in Table 1.

[0032] Table 1

[0033] As can be seen from Table 1, the specific surface areas of Examples 1-4 are concentrated in the range of 18.65–22.68 m². 2 The powder resistivity ranged from 28.61 to 39.88 Ω·cm, generally lower than that of Comparative Example 3 (30.06 m). 2The resistivity (82.31 Ω·cm) indicates that the material prepared by the precursor of this invention has better electronic conductivity while maintaining a suitable specific surface area. Comparative Example 3, due to its excessively high manganese content, suffers from severe structural distortion, leading to a significant increase in resistivity. Furthermore, the 226 MPa powder compaction density of Examples 1-4 is 2.29–2.35 g / cc, higher than Comparative Example 3 (2.21 g / cc) and comparable to Comparative Example 1 (2.28 g / cc) and Comparative Example 2 (2.45 g / cc), indicating that the material prepared by this precursor process has good compaction processing performance and is suitable for high-energy-density electrode fabrication. The 0.1C charge specific capacity of Examples 1-4 ranged from 160.11 to 161.85 mAh / g, and the discharge specific capacity ranged from 150.32 to 154.37 mAh / g, both superior to Comparative Example 1 (159.01 / 148.37 mAh / g), Comparative Example 2 (158.76 / 148.96 mAh / g), and Comparative Example 3 (158.30 / 145.06 mAh / g). Example 1 exhibited the best electrochemical performance (161.85 / 154.37 mAh / g), indicating that a Mn / Fe ratio of 6:4 achieved a good balance between material structural stability and electrochemical activity. The first-cycle coulombic efficiency of Examples 1-4 ranged from 93.55% to 95.38%, both higher than Comparative Example 3 (91.64%) and Comparative Example 1 (93.30%), and close to or better than Comparative Example 2 (93.82%). Example 1 achieved a success rate of 95.38%, indicating that its electrochemical reaction has high reversibility and few side reactions, and that structural defects and interfacial side reactions are effectively suppressed.

[0034] In summary, the organic-inorganic hybrid manganese-iron precursor prepared by this invention significantly improves the conductivity, compaction density, and electrochemical performance of lithium manganese iron phosphate cathode material through molecular-level uniform complexation of manganese and iron. In particular, its comprehensive performance is optimal in the range of Mn / Fe ratio of 0.6 to 0.7, and it has good application prospects and industrialization value.

[0035] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0036] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A precursor, characterized in that, Its molecular formula is Mn x Fe y [C6H5PO3]·nH2O, where x+y=1, and 0.2≤x≤0.9, 0<n≤2.

2. The precursor according to claim 1, characterized in that, x+y=1, 0.5≤x≤0.8, 0<n≤2.

3. A method for preparing the precursor as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Prepare organic molecule solutions; S2. Prepare a mixed salt solution of manganese and iron sources, and introduce an inert gas for atmosphere protection. S3. The organic molecular solution and the pH adjusting agent solution are added dropwise to the mixed salt solution in a parallel flow to carry out the reaction. The resulting slurry is filtered, washed and dried to obtain the organic-inorganic hybrid manganese iron precursor.

4. The preparation method according to claim 3, characterized in that, In step S1, the organic molecule is phenylphosphonic acid, with the molecular formula C6H7O3P; the concentration of the organic molecule solution is 0.5–2.0 mol / L.

5. The preparation method according to claim 3, characterized in that, In step S2, the iron source is at least one of ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous oxalate, and ferrous acetate; the manganese source is at least one of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate; and the total concentration of manganese and iron in the manganese-iron mixed solution is 0.5–2 mol / L.

6. The preparation method according to claim 3, characterized in that, In step S2, the protective gas atmosphere is a nitrogen atmosphere or an argon atmosphere.

7. The preparation method according to claim 3, characterized in that, In step S3, the pH adjuster includes at least one of ammonia water and sulfuric acid solution, and the pH value is controlled between 3.0 and 6.

0.

8. A lithium manganese iron phosphate material, characterized in that, It is prepared from the organic-inorganic hybrid manganese-iron precursor according to any one of claims 1-2.

9. A method for preparing lithium iron phosphate material, characterized in that, The organic-inorganic hybrid manganese iron precursor, including any one of claims 1-2, is mixed evenly with a lithium source and a carbon source, and then subjected to sand milling, spray drying, sintering, and pulverization to obtain the lithium manganese iron phosphate material.

10. The preparation method according to claim 9, characterized in that, The carbon source is at least one of glucose, polyethylene glycol, polyvinyl alcohol, citric acid, tannic acid, and starch.

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