Preparation method and application of high-conductivity molybdenum phosphide doped lithium manganese iron phosphate composite material
Highly conductive molybdenum phosphide-doped lithium manganese iron phosphate composite materials were prepared through solvothermal and hydrothermal processes, which solved the problems of poor conductivity and structural distortion of lithium manganese iron phosphate materials, achieved significant improvement in material performance and industrial application prospects.
Patent Information
- Application Number
- CN202510886223.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-30
- Publication Date
- 2025-09-26
AI Technical Summary
Lithium manganese iron phosphate materials have poor conductivity and structural distortion caused by the Jahn-Teller effect, which hinder their commercial application.
The MoS2@C precursor was in situ synthesized by a solvothermal method and converted into MoP@C material by precisely controlling the phosphating temperature and time. Molybdenum-doped LiMn0.6Fe0.4-xMoxPO4 positive electrode material was grown on its surface by combining a hydrothermal process to construct a three-dimensional conductive network and suppress the Jahn-Teller effect of Mn3+.
The electronic conductivity and structural stability of the material are significantly improved, the lithium ion transmission rate is improved, and the process conditions are mild, environmentally friendly and easy to scale up.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of lithium-ion battery manufacturing, and in particular relates to a preparation method and application of a high-conductivity molybdenum phosphide-doped lithium manganese iron phosphate composite material. Background Art
[0002] As an upgraded material system of lithium iron phosphate, lithium manganese iron phosphate successfully increases the operating voltage platform to ~4.1V (vs. Li) by adopting the strategy of partially replacing Fe sites with Mn elements while maintaining the inherent high safety and structural stability of LFP materials. + / Li), resulting in a theoretical energy density approximately 20% higher than that of LFP, making it considered a highly promising cathode material for next-generation lithium-ion batteries. However, the practical application of LMFP materials still faces several key challenges, primarily stemming from their unique crystal structure and electrochemical reaction mechanisms.
[0003] First, LMFP inherits the olivine crystal structure of LFP. In this structure, PO4 tetrahedrons and MO6 (M=Mn / Fe) octahedrons are connected only by sharing vertices, resulting in a discontinuous electron conduction path and extremely low intrinsic electronic conductivity (~10^-9S / cm). This inherent low conductivity seriously restricts the rate performance of the material. More importantly, during the electrochemical cycle, the high-spin state of Mn 3+ The asymmetric occupation of orbital electrons in the MO6 molybdenum oxide (LMFP) leads to a significant Jahn-Teller effect, causing severe distortion of the MO6 octahedron and lattice volume mutation, which in turn seriously deteriorates the battery's cycling stability. These intrinsic structural defects and reaction mechanism issues together constitute the main technical bottleneck hindering the commercial application of LMFP materials.
[0004] Existing modification technologies mainly rely on high-temperature carbonization treatment of carbon source materials such as glucose to improve the conductivity of materials. However, this method has obvious limitations: on the one hand, it is difficult to achieve uniform coating of the carbon layer in the traditional solid-phase carbonization process, resulting in imperfect conductive network construction; on the other hand, a simple carbon coating strategy can only partially improve the electron conduction problem, but cannot effectively solve the problem of material conductivity caused by Mn during charge and discharge. 3+ The structural distortion problem caused by the Jahn-Teller effect. The deficiency of this single modification method seriously restricts the improvement of the comprehensive performance of lithium manganese iron phosphate materials. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a preparation method and application of a highly conductive molybdenum phosphide-doped lithium manganese iron phosphate composite material.
[0006] In order to solve the problems of poor conductivity and Jahn-Teller distortion of lithium iron manganese phosphate materials, the technical solution proposed by the present invention is as follows:
[0007] A preparation method and application of a high-conductivity molybdenum phosphide-doped lithium manganese iron phosphate composite material, the molecular formula of which is LiMn 0.6 Fe 0.4-x Mo x PO4 / MoP@C.
[0008] A method for preparing a highly conductive molybdenum phosphide-doped lithium manganese iron phosphate composite material comprises the following steps:
[0009] (1) A soluble molybdenum salt and citric acid were dissolved in a deionized water solution in a certain proportion to form a uniform metal salt solution A. Thioacetamide and a surfactant were then dissolved in dimethylformamide to form a solution B. Solution B was added dropwise to the metal salt solution A, and after ultrasonic stirring, the solution was transferred to a Teflon-lined autoclave and heated at a temperature of 160-220°C for 8-20 hours. After cooling to room temperature, the solution was removed and, after solid-liquid separation, the solid was washed several times with anhydrous ethanol and deionized water, and dried overnight to obtain a black-brown powder MoS2@C material.
[0010] (2) The black-brown material and sodium hypophosphite in step (1) are ground evenly, mixed and placed in a porcelain boat, and subjected to high-temperature sintering and phosphating treatment under atmosphere to obtain a MoP@C conductive precursor material.
[0011] (3) Dissolve soluble iron salt, soluble manganese salt, ammonium molybdate, phosphoric acid and lithium hydroxide in deionized water in a certain proportion to form solution C. Then, ultrasonically disperse the conductive precursor material obtained in step (2) in solution C in a certain mass ratio and transfer it to a Teflon-lined autoclave. The hydrothermal temperature is 180-220°C and maintained for 8-20 hours. After cooling to room temperature, take it out, separate the solid and liquid, and use anhydrous ethanol and deionized water to make it dissolve in water.
[0012] Preferably, the soluble molybdenum salt in step (1) is one or more of ammonium tetrathiomolybdate, sodium molybdate, ammonium molybdate, and potassium molybdate. The surfactant is one or more of cetyltrimethylammonium bromide, cocamidopropyl betaine, and sodium dodecylbenzenesulfonate.
[0013] Preferably, in step (1), the molar ratio of the molybdenum salt to the citric acid is 1:1.5-3.5, the molar ratio of thioacetamide to the surfactant is 1:0.2-0.4, and the ratio of thioacetamide to the molybdenum salt is 3-5:1. Solution B is added dropwise to the metal salt solution A for 10 minutes to 1 hour, and the volume occupancy of the Teflon liner is 40% to 70%.
[0014] Preferably, the high-temperature sintering atmosphere in step (2) is nitrogen, argon, or a hydrogen-argon mixture, and the phosphating temperature is 550-850°C. The sintering time is 8-16 hours. More preferably, the temperature is 600-820°C, and the sintering time is 12-14 hours.
[0015] Preferably, the soluble iron salt in step (3) is one or more of ferrous sulfate heptahydrate, ferrous chloride, and ferrous nitrate, and the soluble manganese salt is one or more of manganese sulfate monohydrate, manganese chloride tetrahydrate, and manganese nitrate. The ratio of manganese salt to iron salt to ammonium molybdate to phosphoric acid is 0.6:0.4-x:x:1, where x is 0.001-0.1, and the total molar ratio of manganese salt to lithium salt is 1:1.03-1.09.
[0016] Preferably, the amount of the MoP@C conductive precursor material added in step (3) is 3%-8% of the mass ratio of the theoretical synthesis of LMFP, the ultrasonic dispersion time is 30min-1h, and the volume occupancy of the Teflon liner is 30%-60%.
[0017] The beneficial effects of the present invention are mainly reflected in the following three aspects:
[0018] (1) Innovative material preparation process:
[0019] The MoS2@C precursor was synthesized in situ by the solvent thermal method, and converted into a highly conductive MoP@C composite material by precisely controlling the phosphating temperature and time. Subsequently, a hydrothermal process was combined to uniformly grow molybdenum-doped LiMn on the surface of the MoP@C material. 0.6 Fe 0.4-x Mo x PO4 positive electrode material realizes precise control of material components and optimized design of structure.
[0020] (2) Significantly improved electrochemical performance:
[0021] In the prepared molybdenum phosphide-doped lithium manganese iron phosphate composite material, the MoP@C component constructs a three-dimensional conductive network, which increases the electronic conductivity of the material by 2-3 orders of magnitude. At the same time, the high-valence Mo-O bond can effectively inhibit the Mn 3+ Jahn-Teller effect, improving Mn 3+ The three-dimensional stretching state of the -O bond significantly improves the structural stability and lithium ion transmission rate of the material.
[0022] (3) Excellent industrial application prospects:
[0023] This preparation process features mild reaction conditions, good reproducibility, and high yield. The raw materials used are all industrial-grade chemicals, resulting in significant cost advantages. The entire process is environmentally friendly, emits no toxic or hazardous substances, and is easily scalable. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 This is the 0.1C charge-discharge curve at 25°C for the lithium battery made of highly conductive molybdenum phosphide-doped lithium manganese iron phosphate in Example 1 of the present invention.
[0025] Figure 2 This is the 0.1C charge and discharge curve at 25°C of the lithium battery made from the unmodified lithium manganese iron phosphate in Comparative Example 1 of the present invention. DETAILED DESCRIPTION
[0026] Example 1
[0027] (1) 0.1 mol ammonium molybdate and 0.3 mol citric acid were dissolved in 40 ml deionized solution to form solution A. 0.4 mol thioacetamide and 0.08 mol hexadecyltrimethylammonium bromide were dissolved in 20 ml dimethylformamide solution to form solution B. Solution B was added dropwise to metal salt solution A over a period of 15 min and ultrasonically dispersed for 30 min. The solution was then transferred into a 100 ml Teflon-lined autoclave and maintained at 180 °C for 12 h. After cooling to room temperature, the solution was centrifuged and washed three times with anhydrous ethanol and deionized water to obtain MoS2@C precursor. 0.5 g of the precursor was ground and mixed with 2 g of sodium hypophosphite, and then sintered at 650 °C for 12 h under argon atmosphere to obtain MoP@C conductive material. Subsequently, 0.039 mol ferrous nitrate, 0.06 mol manganese nitrate, 0.001 mol ammonium molybdate, 0.1 mol phosphoric acid, and 0.106 mol lithium hydroxide monohydrate were dissolved in 80 ml deionized water to form a uniform metal salt solution C. 0.785g MoP@C conductive material was ultrasonically dispersed in metal salt solution C for 30min, and then transferred into a 100ml Teflon-lined autoclave at 200℃ for 8h. After cooling to room temperature, it was washed with anhydrous ethanol and deionized water three times respectively, and dried in a vacuum oven at 90℃ for 12h to finally obtain LiMn 0.6 Fe 0.39 Mo 0.01 PO4 / MoP@C materials.
[0028] Comparative Example 1
[0029] (1) 0.04 mol of ferrous nitrate, 0.06 mol of manganese nitrate, 0.1 mol of phosphoric acid, 0.785 g of conductive carbon black, and 0.106 mol of lithium hydroxide monohydrate were dissolved in 80 ml of deionized water to form a uniform metal salt solution D. After ultrasonic dispersion for 30 min, the solution was transferred into a 100 ml Teflon-lined autoclave at 200 ° C for 8 h. After cooling to room temperature, the solution was washed with anhydrous ethanol and deionized water three times respectively, and dried in a vacuum oven at 90 ° C for 12 h to obtain LiMn 0.6 Fe 0.4 PO4@Cb material.
[0030] Comparative Example 2
[0031] (1) 0.04 mol of ferrous nitrate, 0.06 mol of manganese nitrate, 0.1 mol of phosphoric acid, 0.106 mol of glucose, 0.785 g of lithium hydroxide monohydrate were dissolved in 80 ml of deionized water to form a uniform metal salt solution E. After ultrasonic dispersion for 30 min, the solution was transferred to a 100 ml Teflon-lined autoclave at 200°C for 8 h. After cooling to room temperature, the solution was washed three times with anhydrous ethanol and deionized water, respectively, and dried in a vacuum oven at 90°C for 12 h.
[0032] (2) The dried material from step (1) was placed in a magnetic boat and sintered at 670°C for 4 hours under a nitrogen atmosphere to obtain the final LiMn 0.6 Fe 0.4 PO4@C material.
[0033] Comparative Example 3
[0034] (1) 0.039 mol of ferrous nitrate, 0.06 mol of manganese nitrate, 0.001 mol of ammonium molybdate, 0.1 mol of phosphoric acid, 0.785 g of glucose, and lithium hydroxide monohydrate were dissolved in 80 ml of deionized water to form a uniform metal salt solution F. After ultrasonic dispersion for 30 min, the solution was transferred to a 100 ml Teflon-lined autoclave at 200°C for 8 h. After cooling to room temperature, the solution was washed three times with anhydrous ethanol and deionized water, respectively, and dried in a vacuum oven at 90°C for 12 h.
[0035] (2) The dried material from step (1) was placed in a magnetic boat and sintered at 670°C for 4 hours under a nitrogen atmosphere to obtain the final LiMn 0.6 Fe 0.39 Mo 0.01 PO4@C material.
[0036] Example 2
[0037] (1) 0.15 mol ammonium molybdate and 0.3 mol citric acid were dissolved in 40 ml of deionized water to form solution A. 0.6 mol thioacetamide and 0.12 mol hexadecyltrimethylammonium bromide were dissolved in 20 ml of dimethylformamide solution to form solution B. Solution B was added dropwise to metal salt solution A over a period of 15 min and ultrasonically dispersed for 30 min. The solution was transferred into a 100 ml Teflon-lined autoclave and maintained at 180 °C for 12 h. After cooling to room temperature, the solution was centrifuged and washed three times with anhydrous ethanol and deionized water to obtain the MoS2@C-2 precursor. 0.5 g of the precursor was ground and mixed with 2 g of sodium hypophosphite, and then sintered at 650 °C for 12 h under argon atmosphere to obtain the MoP@C-2 conductive material. Subsequently, 0.039 mol of ferrous nitrate, 0.06 mol of manganese nitrate, 0.001 mol of ammonium molybdate, 0.1 mol of phosphoric acid, and 0.106 mol of lithium hydroxide monohydrate were dissolved in 80 ml of deionized water to form a uniform metal salt solution C. 0.785 g of MoP@C conductive material was ultrasonically dispersed in the metal salt solution C for 30 min, and then transferred into a 100 ml Teflon-lined autoclave at 200 ° C for 8 h. After cooling to room temperature, it was washed with anhydrous ethanol and deionized water three times respectively, and dried in a vacuum oven at 90 ° C for 12 h to finally obtain LiMn 0.6 Fe 0.39 Mo 0.01 PO4 / MoP@C-2 material.
[0038] Example 3
[0039] (1) 0.1 mol ammonium molybdate and 0.3 mol citric acid were dissolved in 40 ml deionized solution to form solution A. 0.4 mol thioacetamide and 0.08 mol hexadecyltrimethylammonium bromide were dissolved in 20 ml dimethylformamide solution to form solution B. Solution B was added dropwise to metal salt solution A over a period of 15 min and ultrasonically dispersed for 30 min. The solution was then transferred into a 100 ml Teflon-lined autoclave and maintained at 180 °C for 12 h. After cooling to room temperature, the solution was centrifuged and washed three times with anhydrous ethanol and deionized water to obtain MoS2@C precursor. 0.5 g of the precursor was ground and mixed with 2 g of sodium hypophosphite, and then sintered at 650 °C for 12 h under argon atmosphere to obtain MoP@C conductive material. Subsequently, 0.038 mol ferrous nitrate, 0.06 mol manganese nitrate, 0.002 mol ammonium molybdate, 0.1 mol phosphoric acid, and 0.106 mol lithium hydroxide monohydrate were dissolved in 80 ml deionized water to form a uniform metal salt solution C. 0.785 g MoP@C conductive material was ultrasonically dispersed in metal salt solution C for 30 min, then transferred into a 100 ml Teflon-lined autoclave at 200 ° C for 8 h, cooled to room temperature, washed with anhydrous ethanol and deionized water three times respectively, and dried in a vacuum oven at 90 ° C for 12 h to obtain
[0040] LiMn0.6 Fe 0.38 Mo 0.02 PO4 / MoP@C materials.
[0041] The materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were assembled into batteries by the following method:
[0042] To evaluate the electrochemical properties of the materials, the positive electrode materials of Examples 1-3 and Comparative Examples 1-3 were mixed with acetylene black (AB) and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) solvent was added and stirred at 800r / min for 2h to prepare a uniform slurry. The slurry was evenly coated on the aluminum foil current collector using an automatic coating machine, and after vacuum drying at 85°C for 4h, it was punched into pole pieces with a diameter of 12mm, and then dried again at 105°C for 4h to completely remove moisture. Subsequently, CR2032 button batteries were assembled in a strictly controlled argon glove box (H2O / O2<0.1ppm), with a metal lithium sheet as the negative electrode and a Celgard2300 diaphragm as the isolation layer. The electrochemical test was performed after standing for 12h to ensure that the electrolyte was fully infiltrated. This standardized preparation process ensures the reliability and comparability of the experimental data. After assembly, the battery was aged for 12 hours and then subjected to charge and discharge tests at a voltage of 2.5-4.5 V and a current density of 0.1 C. The test results are shown in Table 1.
[0043] Table 1 Electrochemical performance of the embodiment and the comparative example
[0044]
[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.
Claims
1. A highly conductive molybdenum phosphide-doped lithium manganese iron phosphate composite material, characterized in that: The molecular formula of the highly conductive molybdenum phosphide-doped lithium iron manganese phosphate material is LiMn 0.6 Fe 0.4-x Mo x PO4 / MoP@C (x is 0.001-0.1), where the MoP doping amount is 1% to 8%.
2. A method for preparing a highly conductive molybdenum phosphide-doped lithium manganese iron phosphate composite material, characterized in that: The following steps are involved: (1) A soluble molybdenum salt and citric acid were dissolved in a deionized water solution in a certain proportion to form a uniform metal salt solution A. Thioacetamide and a surfactant were then dissolved in dimethylformamide to form a solution B. Solution B was added dropwise to the metal salt solution A, and after ultrasonic stirring, the solution was transferred to a Teflon-lined autoclave and heated at a temperature of 160-220°C for 8-20 hours. After cooling to room temperature, the solution was removed and, after solid-liquid separation, the solid was washed several times with anhydrous ethanol and deionized water, and dried overnight to obtain a black-brown powder MoS2@C material. (2) The black-brown material and sodium hypophosphite in step (1) are ground evenly, mixed and placed in a porcelain boat, and subjected to high-temperature sintering and phosphating treatment under atmosphere to obtain a MoP@C conductive precursor material. (3) Soluble iron salt, soluble manganese salt, ammonium molybdate, phosphoric acid and lithium hydroxide are dissolved in deionized water in a certain proportion to form solution C. Then the conductive precursor material obtained in step (2) is ultrasonically dispersed in solution C in a certain mass ratio and transferred to a Teflon-lined autoclave. The hydrothermal temperature is 180-220°C and maintained for 8-20 hours. After cooling to room temperature, the solid is taken out and, after solid-liquid separation, the solid is washed several times with anhydrous ethanol and deionized water and vacuum dried at 90°C for 12 hours to obtain LiMn 0.6 Fe 0.4- x Mo x PO4 / MoP@C positive electrode material.
3. The method for preparing a high-conductivity molybdenum phosphide-doped lithium manganese iron phosphate composite material according to claim 2, characterized in that: The soluble molybdenum salt in step (1) is one or more of ammonium tetrathiomolybdate, sodium molybdate, ammonium molybdate, and potassium molybdate. The surfactant is one or more of hexadecyltrimethylammonium bromide, cocamidopropyl betaine, and sodium dodecylbenzenesulfonate.
4. The method for preparing a high-conductivity molybdenum phosphide-doped lithium manganese iron phosphate composite material according to claim 2, characterized in that: In step (3), the soluble iron salt is one or more of ferrous sulfate heptahydrate, ferrous chloride, and ferrous nitrate, and the soluble manganese salt is one or more of manganese sulfate monohydrate, manganese chloride tetrahydrate, and manganese nitrate. The molar ratio of manganese salt to iron salt to ammonium molybdate to phosphoric acid is 0.6:0.4-x:x:1, where x is 0.001-0.1, and the total molar ratio of manganese salt to lithium salt is 1:1.03-1.
09.
5. The method for preparing a high-conductivity molybdenum phosphide-doped lithium manganese iron phosphate composite material according to claim 2, characterized in that: In step (1), the molar ratio of the molybdenum salt to the citric acid is 1:1.5-3.5, the molar ratio of thioacetamide to the surfactant is 1:0.2-0.4, and the ratio to the molybdenum salt is 3-5:
1.
6. The method for preparing a high-conductivity molybdenum phosphide-doped lithium manganese iron phosphate composite material according to claim 2, characterized in that: In step (2), the high-temperature sintering atmosphere is nitrogen, argon, or a hydrogen-argon mixture, the phosphating temperature is 550-850° C., and the sintering time is 8-16 hours.
7. The method for preparing a high-conductivity molybdenum phosphide-doped lithium manganese iron phosphate composite material according to claim 2, characterized in that: The ammonium molybdate in step (3) mainly plays a doping role in place of Fe in LMFP, and has a different role from the molybdenum salt added in the synthesis of the MoP@C conductive precursor material in step (1).
8. The method for preparing a high-conductivity molybdenum phosphide-doped lithium manganese iron phosphate composite material according to claim 2, characterized in that: The amount of the MoP@C conductive precursor material added in step (3) is 3%-8% of the mass ratio of the theoretical synthesis of LMFP.