LiMn 0.6 Fe 0.4 PO4 / C and methods of making and using same

Abstract

This invention discloses LiMn 0.6 Fe 0.4 This research relates to PO4 / C, its preparation method, and its applications, belonging to the field of electrode material preparation technology. A LiMn... 0.6 Fe 0.4 The preparation method of PO4 / C is as follows: manganese acetate, ferrous sulfate, ammonium dihydrogen phosphate, lithium acetate, and citric acid are dissolved in water to prepare a suspension; the suspension is ball-milled to form a nanoscale dispersion to obtain a ball-milled suspension; the ball-milled suspension is subjected to a hydrothermal reaction to obtain LiMn. 0.6 Fe 0.4 PO4 / C. This invention uses low-cost manganese acetate, ferrous sulfate, ammonium dihydrogen phosphate, lithium acetate, and citric acid as raw materials. When prepared via a hydrothermal method, no surfactants such as PEG are required. The resulting LiMn... 0.6 Fe 0.4 PO4 / C has small particle size, large specific surface area and high stability.

Description

Technical Field

[0001] This invention relates to the field of electrode material preparation technology, and more specifically to LiMn 0.6 Fe 0.4 PO4 / C, its preparation methods, and applications. Background Technology

[0002] The depletion of traditional energy sources and environmental degradation have spurred demand for the development of clean new energy sources, consequently elevating the strategic importance of lithium resources and leading to the booming development of the lithium battery industry. Among numerous electrode materials, LiMn... 0.6 Fe 0.4 PO4 / C, with its combination of high stability and high energy density, can significantly improve battery cycle life and energy output efficiency, meeting the requirements of long-range and high-safety applications, and has become a typical representative of new electrode materials.

[0003] Typically, LiMn 0.6 Fe 0.4 The preparation processes of PO4 / C include high-temperature solid-state methods, spray drying methods, sol-gel methods, and hydrothermal methods. Among these, the hydrothermal method has advantages due to its low reaction temperature, short process flow, simple operation, and stable product. Compared with traditional preparation processes such as high-temperature solid-state methods and spray drying methods, the hydrothermal method saves on equipment energy consumption and process costs. However, existing hydrothermal methods usually still require the protection of inert gases to prevent excessive oxidation of raw materials during the reaction, and additional carbon sources are needed to coat the surface with a C layer to enhance the stability of the product.

[0004] To simplify the hydrothermal process and reduce its cost, it is usually necessary to process LiMn. 0.6 Fe 0.4 The source materials for each element in PO4 / C are carefully selected, such as LiH2PO4, FeSO4, and MnO. Simultaneously, substances that simultaneously inhibit oxidation and act as a source of the C layer, such as ascorbic acid and oxalic acid, need to be added. However, studies have shown that the LiMn prepared by the above method... 0.6 Fe 0.4 PO4 / C still suffers from poor electrochemical performance. Summary of the Invention

[0005] To address the above problems, this invention provides a LiMn 0.6 Fe 0.4 This invention relates to PO4 / C, its preparation method, and applications. Using low-cost manganese acetate, ferrous sulfate, ammonium dihydrogen phosphate, lithium acetate, and citric acid as raw materials, a hydrothermal method is employed for preparation. No surfactants such as PEG are required to assist in the preparation. The resulting LiMn... 0.6 Fe 0.4PO4 / C has small particle size, large specific surface area, and high stability, which solves the problem of LiMn prepared by existing technology. 0.6 Fe 0.4 PO4 / C still suffers from poor electrochemical performance.

[0006] The first objective of this invention is to provide a LiMn 0.6 Fe 0.4 The preparation method of PO4 / C includes the following steps:

[0007] A suspension was prepared by dissolving manganese acetate, ferrous sulfate, ammonium dihydrogen phosphate, lithium acetate, and citric acid in water. The suspension was then ball-milled to form a nanoscale dispersion, resulting in a ball-milled suspension. The ball-milled suspension was then subjected to a hydrothermal reaction, during which olivine-type LiMn was formed. 0.6 Fe 0.4 PO4, citric acid in LiMn 0.6 Fe 0.4 A uniform graphitized carbon layer was formed on the PO4 surface to obtain LiMn. 0.6 Fe 0.4 PO4 / C.

[0008] Specifically, this invention involves subjecting the ball-milled suspension to a hydrothermal reaction. During the hydrothermal process, the interactions between ions are enhanced, and iron ions, manganese ions, and phosphate ions combine to form a crystal structure. Simultaneously, lithium ions are embedded into the crystal structure, gradually forming olivine-type LiMn. 0.6 Fe 0.4 The PO4 crystal structure, citric acid gradually releases CO2 and H2O under hydrothermal temperature, thus effectively reducing the damage to the material's pore structure. After hydrothermal treatment, citric acid C6H8O7 forms a uniform graphitized carbon layer, yielding LiMn. 0.6 Fe 0.4 PO4 / C.

[0009] Manganese acetate, as a Mn source, and lithium acetate, as a Li source, both possess a weak reducing property due to their inherent CH3COO structure, which helps inhibit the excessive oxidation of Mn and Fe during hydrothermal processes. Furthermore, during hydrothermal processes, they can adsorb onto the crystal nucleus surface, inhibiting excessive grain growth and forming nanoscale particles. Ammonium dihydrogen phosphate, acting as both a P and O source, with C6H8O7, inhibits the excessive oxidation of Mn and Fe while also serving as a carbon source in the LiMn... 0.6 Fe 0.4 A uniform C layer is formed on the PO4 surface, thereby producing LiMn. 0.6 Fe 0.4 PO4 / C.

[0010] In a preferred embodiment of the present invention, the molar ratio of manganese acetate to ferrous sulfate is 1.5:1 to 1.5.

[0011] In a preferred embodiment of the present invention, the molar ratio of manganese acetate to ammonium dihydrogen phosphate is 3:5 to 5.2.

[0012] In a preferred embodiment of the present invention, the molar ratio of manganese acetate to lithium acetate is 1:4.5 to 5.5.

[0013] In a preferred embodiment of the present invention, the molar ratio of manganese acetate to citric acid is 12:8 to 11.

[0014] When there is too little citric acid, impurities such as Fe will be produced. 3+ Or Mn 3+ This reduces conductivity; excessive citric acid provides too much carbon source, resulting in an excessively thick carbon layer that hinders ion migration. The Mn / Fe ratio is LiMn... 0.6 Fe 0.4 The key to PO4 materials lies in their ability to directly determine their core performance. Excessive ferrous sulfate increases solubility loss, while insufficient ferrous sulfate hinders lithium ion adsorption. Insufficient ammonium dihydrogen phosphate generates electrochemically inert impurities such as Mn / Fe oxides, exacerbating cation mixing and blockage; excessive addition may generate impurities affecting morphology. A slight excess of lithium acetate helps compensate for lithium loss, while excessive addition generates impurities.

[0015] In a preferred embodiment of the present invention, in the hydrothermal reaction treatment, the reaction temperature is 170℃~200℃, and the reaction time is 9h~12h, thereby ensuring that LiMn 0.6 Fe 0.4 PO4 / C has sufficient crystallinity while avoiding excessive crystal growth and structural instability.

[0016] In a preferred embodiment of the present invention, during ball milling, the mass ratio of grinding balls to suspension is 1–3:1; the ball milling speed is 600 rpm–1000 rpm; and the ball milling time is 2 h–5 h. By controlling the ratio of grinding balls to suspension, the ball milling speed, and the ball milling time during the ball milling process, maximum nanoscale dispersion of the solution is achieved, which helps to form a uniform and dense graphitized carbon layer through hydrothermal treatment, thereby improving lithium capacity and cycle life.

[0017] In a preferred embodiment of the present invention, the stirring time after adding manganese acetate is 30-40 minutes, the stirring time after adding ferrous sulfate is 30-40 minutes, the stirring time after adding ammonium dihydrogen phosphate is 1-1.5 hours, the stirring time after adding lithium acetate is 1-1.5 hours, and the stirring time after adding citric acid is 1-1.5 hours; stirring after each addition of raw materials is beneficial for complete dispersion. The dissolution temperature is 40°C-60°C.

[0018] The second objective of this invention is to provide LiMn prepared by the above-described preparation method. 0.6 Fe 0.4 PO4 / C, LiMn 0.6 Fe 0.4 The particle size of PO4 / C ranges from 50 nm to 500 nm. When the particle size is less than 500 nm, the diffusion path of lithium ions is effectively shortened, the elements are evenly distributed, the crystallinity is good, and the structure is complete, ensuring that lithium ions can quickly and stably shuttle through the crystal lattice. If the particle size is too small, such as less than 50 nm, it will cause agglomeration and faster capacity decay. If the particle size is too large, such as greater than 1 micrometer, it will lead to a decrease in capacity and poor conductivity.

[0019] A third objective of this invention is to provide the aforementioned LiMn 0.6 Fe 0.4 The application of PO4 / C in electrode materials can be specifically applied in the lithium extraction industry using electro-adsorption from high Mg / Li ratio salt lake brine.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) In this invention, a hydrothermal method is used, with low-cost manganese acetate, ferrous sulfate, ammonium dihydrogen phosphate, and lithium acetate as LiMn. 0.6 Fe 0.4 The raw materials for each component in PO4. Manganese acetate serves as the Mn source, and lithium acetate as the Li source. The inherent CH3COO structure of both has weak reducing properties, which helps to inhibit the excessive oxidation of Mn and Fe during hydrothermal processes and prevent the formation of impurity phases, such as Fe. 3+ Or Mn 3+ This reduces the conductivity of the material and allows it to adsorb onto the crystal nucleus surface during hydrothermal reaction, inhibiting excessive grain growth and forming nanoscale particles. Ammonium dihydrogen phosphate, as both a P and O source, provides a relatively stable reaction environment in the mixed reaction stage due to its weak acidity. Lithium acetate, as a direct source of Li, reduces the possibility of forming unstable intermediates with ammonium dihydrogen phosphate. Furthermore, no surfactants such as PEG are needed. Additionally, the added C6H8O7 forms relatively stable complexes with Mn and Fe, effectively inhibiting excessive oxidation of both during hydrothermal reaction, and its application cost is far lower than ascorbic acid. Simultaneously, it provides a milder pH environment than ascorbic acid and oxalic acid during hydrothermal reaction, promoting the growth of LiMn. 0.6 Fe 0.4PO4 / C directional crystallization. Existing technologies using oxalic acid rapidly decompose to produce CO and CO2 at 157℃, while the C6H8O7 used in this invention is more stable, gradually releasing CO2 and H2O under hydrothermal conditions, effectively reducing damage to the material's pore structure. Furthermore, uniformly mixed C6H8O7 can form a uniform graphitized carbon layer after hydrothermal treatment, eliminating the need for additional glucose as a LiMn agent. 0.6 Fe 0.4 The source of the external C layer of PO4 / C.

[0022] (2) This invention employs ball milling to further disperse the suspension formed after mixing the raw materials at the nanoscale. This method, while ensuring uniform mixing of all components, effectively prevents excessive lattice expansion during hydrothermal crystallization, which could lead to a loose structure and contributes to the preparation of LiMn with small particle size, large specific surface area, and high stability. 0.6 Fe 0.4 PO4 / C.

[0023] (3) Compared with traditional material preparation processes such as high-temperature solid-state method and spray drying method, which require the synthesis of precursors and then long-term high-temperature sintering and solidification for carbon coating, the present invention uses hydrothermal method to prepare LiMn 0.6 Fe 0.4 PO4 / C, achieved in LiMn by simply adding C6H8O7. 0.6 Fe 0.4 The formation of a C layer on the PO4 surface effectively simplifies the process and reduces process costs. Attached Figure Description

[0024] Figure 1 This refers to LiMn in Examples 1, 2, and 3. 0.6 Fe 0.4 Phase characterization of PO4 / C, where (a) is the XRD pattern in the range of 10° to 90°, and LMFP-8, LMFP-9, LMFP-10, and LMFP-11 correspond to LiMn prepared with C6H8O7 molar ratios of 8, 9, 10, and 11, respectively. 0.6 Fe 0.4 PO4 / C; (b) is the XRD pattern in the range of 20° to 40°.

[0025] Figure 2 In the example, (a) shows LiMn in Example 3. 0.6 Fe 0.4 SEM images of PO4 / C: (b) is the distribution map of Mn, (c) is the distribution map of Fe, (d) is the distribution map of O, (e) is the distribution map of P, and (f) is the distribution map of C.

[0026] Figure 3In Example 3, (a) is LiMn 0.6 Fe 0.4 Transmission images of PO4 / C; (a1) is a magnified view of point A in (a), (a2) is a magnified view of point B in (a), and (b) is a transmission image of LiMn in Example 3. 0.6 Fe 0.4 Electron diffraction pattern of PO4 / C.

[0027] Figure 4 The LiMn in Example 3 0.6 Fe 0.4 XPS characterization of the elemental composition and valence state of PO4 / C; where (a) is the full XPS spectrum; (b) is the C1s orbital energy spectrum; (c) is the Fe2p orbital energy spectrum; and (d) is the Mn2p orbital energy spectrum. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] LiMn prepared by hydrothermal method 0.6 Fe 0.4 The process flow of PO4 / C includes three key control steps: raw material mixing, ball milling dispersion, and hydrothermal reaction.

[0031] Step 1: Under constant temperature of 40℃, add 20 mol of NH4H2PO4, 60 mol of CH3COOLi·H2O, 12 mol of Mn(CH3COO)2·4H2O, 8 mol of FeSO4·7H2O, and 8 mol of C6H8O7 to 200 mL of deionized water in a molar ratio of 20:60:12:8:8. Stir for 30 min, 30 min, 1 h, 1 h, and 1 h after each addition to ensure complete dispersion and form a uniform suspension.

[0032] Step 2: Mix the suspension and grinding balls at a mass ratio of 1:1, and ball mill at 600 rpm for 3 hours to ensure that the suspension reaches nanoscale dispersion, thus obtaining the ball-milled suspension.

[0033] Step 3: Transfer the ball-milled suspension to a hydrothermal reactor and react at 170℃ for 9 hours. After the reaction is complete, filter for 0.5 hours, washing with deionized water during this period, and then dry under vacuum for 4 hours to obtain LiMn. 0.6 Fe 0.4 PO4 / C powder, designated as LMFP-8.

[0034] LiMn 0.6 Fe 0.4 All PO4 / C powder tests were conducted within a potential window of -1.2V to 1.2V. The LiMn prepared in this embodiment was tested... 0.6 Fe 0.4 PO4 / C exhibits excellent electrochemical performance and stability, with an initial discharge specific capacity of 128 mAh / g at 0.2C, and a capacity retention of over 86% after 50 cycles. This is comparable to the paper "Heat-rate-controlled hydrothermal crystallization of high-performance LiMn" published by Song YJ et al. in *Ceramics International*, Volume 46, Issue 4, 2020. 0.7 Fe 0.3 In the section "PO4cathode material for lithium-ion batteries", LiMn is prepared using LiOH, H3PO4, PEG 400, MnSO4·H2O, FeSO4·7H2O, H2C2O4·2H2O and similar substances as raw materials. 0.6 Fe 0.4 PO4 / C, performance improved by approximately 8%.

[0035] Example 2

[0036] LiMn prepared by hydrothermal method 0.6 Fe 0.4 The process flow of PO4 / C includes three key control steps: raw material mixing, ball milling dispersion, and hydrothermal reaction.

[0037] In the raw material mixing step, under constant temperature of 50℃, 20 mol of NH4H2PO4, 60 mol of CH3COOLi·H2O, 12 mol of Mn(CH3COO)2·4H2O, 8 mol of FeSO4·7H2O and 10 mol of C6H8O7 were added to 200 mL of deionized water in a molar ratio of 20:60:12:8:10. After each addition, the mixture was stirred for 30 min, 30 min, 1 h, 1 h and 1 h respectively to form a uniform suspension.

[0038] During ball milling dispersion, the suspension and grinding balls are mixed at a mass ratio of 1:1 and ball milled at a speed of 600 rpm for 3 hours to ensure that the suspension reaches nanoscale dispersion, thus obtaining the ball-milled suspension.

[0039] During the hydrothermal reaction, the ball-milled suspension was transferred to a hydrothermal reactor and reacted at 170°C for 9 hours. After the reaction was complete, it was filtered for 0.5 hours, during which time it was washed with deionized water, and then dried under vacuum for 4 hours to obtain LiMn. 0.6 Fe 0.4 PO4 / C powder, designated as LMFP-10.

[0040] LiMn 0.6 Fe 0.4 All PO4 / C powder tests were conducted within a potential window of -1.2V to 1.2V. The LiMn prepared in this embodiment was tested... 0.6 Fe 0.4 PO4 / C exhibits excellent electrochemical performance and stability, with an initial discharge specific capacity of 131 mAh / g at 0.2C, and retaining over 90% of its capacity after 50 cycles. This is comparable to the paper "Heat-rate-controlled hydrothermal crystallization of high-performance LiMn" published by Song YJ et al. in *Ceramics International*, Volume 46, Issue 4, 2020. 0.7 Fe 0.3 In the section "PO4cathode material for lithium-ion batteries", LiMn is prepared using LiOH, H3PO4, PEG 400, MnSO4·H2O, FeSO4·7H2O, H2C2O4·2H2O and similar substances as raw materials. 0.6 Fe 0.4 PO4 / C offers approximately a 10% performance improvement.

[0041] Example 3

[0042] LiMn prepared by hydrothermal method 0.6 Fe 0.4 The process flow of PO4 / C includes three key control steps: raw material mixing, ball milling dispersion, and hydrothermal reaction.

[0043] In the raw material mixing step, under constant temperature of 50℃, 20 mol of NH4H2PO4, 60 mol of CH3COOLi·H2O, 12 mol of Mn(CH3COO)2·4H2O, 8 mol of FeSO4·7H2O and 9 mol of C6H8O7 were added to 200 mL of deionized water in a molar ratio of 20:60:12:8:9. After each addition, the mixture was stirred for 30 min, 30 min, 1 h, 1 h and 1 h respectively to form a uniform suspension.

[0044] During ball milling dispersion, the suspension and grinding balls are mixed at a mass ratio of 1:1 and ball milled at a speed of 600 rpm for 3 hours to ensure that the suspension reaches nanoscale dispersion, thus obtaining the ball-milled suspension.

[0045] During the hydrothermal reaction, the ball-milled suspension was transferred to a hydrothermal reactor and reacted at 170°C for 9 hours. After the reaction was complete, it was filtered for 0.5 hours, during which time it was washed with deionized water, and then dried under vacuum for 4 hours to obtain LiMn. 0.6 Fe 0.4 PO4 / C powder, designated as LMFP-9.

[0046] Example 4

[0047] LiMn prepared by hydrothermal method 0.6 Fe 0.4 The process flow of PO4 / C includes three key control steps: raw material mixing, ball milling dispersion, and hydrothermal reaction.

[0048] In the raw material mixing step, under constant temperature of 50℃, 20 mol of NH4H2PO4, 60 mol of CH3COOLi·H2O, 12 mol of Mn(CH3COO)2·4H2O, 8 mol of FeSO4·7H2O and 11 mol of C6H8O7 were added to 200 mL of deionized water in a molar ratio of 20:60:12:8:11. After each addition, the mixture was stirred for 30 min, 30 min, 1 h, 1 h and 1 h respectively to form a uniform suspension.

[0049] During ball milling dispersion, the suspension and grinding balls are mixed at a mass ratio of 1:1 and ball milled at a speed of 600 rpm for 3 hours to ensure that the suspension reaches nanoscale dispersion, thus obtaining the ball-milled suspension.

[0050] During the hydrothermal reaction, the ball-milled suspension was transferred to a hydrothermal reactor and reacted at 170°C for 9 hours. After the reaction was complete, it was filtered for 0.5 hours, during which time it was washed with deionized water, and then dried under vacuum for 4 hours to obtain LiMn. 0.6 Fe 0.4 PO4 / C powder, designated as LMFP-11.

[0051] Example 5

[0052] LiMn prepared by hydrothermal method 0.6 Fe 0.4 The process flow of PO4 / C includes three key control steps: raw material mixing, ball milling dispersion, and hydrothermal reaction.

[0053] In the raw material mixing step, under a constant temperature of 50℃, 20 mol of NH4H2PO4, 60 mol of CH3COOLi·H2O, 12 mol of Mn(CH3COO)2·4H2O, 8 mol of FeSO4·7H2O, and 10 mol of C6H8O7 were added sequentially to 200 mL of deionized water in a molar ratio of 20:60:12:8:10. After each addition, the mixture was stirred for 30 min, 30 min, 1 h, 1 h, and 1 h respectively to form a homogeneous suspension.

[0054] During ball milling dispersion, the suspension and grinding balls are mixed at a mass ratio of 2:1 and ball milled at 800 rpm for 3 hours to ensure that the suspension reaches nanoscale dispersion, thus obtaining the ball-milled suspension.

[0055] During the hydrothermal reaction, the ball-milled suspension was transferred to a hydrothermal reactor and reacted at 170°C for 10 hours. After the reaction was complete, the mixture was filtered for 0.5 hours, during which it was washed with deionized water, and then dried under vacuum for 4 hours to obtain LiMn. 0.6 Fe 0.4 PO4 / C powder.

[0056] LiMn 0.6 Fe 0.4 All PO4 / C powder tests were conducted within a potential window of -1.2V to 1.2V. The LiMn prepared in this embodiment was tested... 0.6 Fe 0.4 PO4 / C exhibits excellent electrochemical performance and stability, with an initial discharge specific capacity of 139 mAh / g at 0.2C. After 50 cycles, the capacity retention remains above 92%. This is comparable to the paper "Heat-rate-controlled hydrothermal crystallization of high-performance LiMn" published by Song YJ et al. in *Ceramics International*, Volume 46, Issue 4, 2020. 0.7 Fe 0.3 In the section "PO4cathode material for lithium-ion batteries", LiMn is prepared using LiOH, H3PO4, PEG 400, MnSO4·H2O, FeSO4·7H2O, H2C2O4·2H2O and similar substances as raw materials. 0.6 Fe 0.4 PO4 / C offers a performance improvement of approximately 17%.

[0057] Example 6

[0058] LiMn prepared by hydrothermal method 0.6 Fe 0.4 The process flow of PO4 / C includes three key control steps: raw material mixing, ball milling dispersion, and hydrothermal reaction.

[0059] In the raw material mixing step, under a constant temperature of 50℃, 20.8 mol of NH4H2PO4, 54 mol of CH3COOLi·H2O, 12 mol of Mn(CH3COO)2·4H2O, 12 mol of FeSO4·7H2O, and 10 mol of C6H8O7 were added sequentially to 200 mL of deionized water in a molar ratio of 20.8:54:12:12:10. After each addition, the mixture was stirred for 40 min, 40 min, 1.5 h, 1.5 h, and 1.5 h, respectively, to form a homogeneous suspension.

[0060] During ball milling dispersion, the suspension and grinding balls are mixed at a mass ratio of 3:1 and ball milled at 1000 rpm for 2 hours to ensure that the suspension reaches nanoscale dispersion, thus obtaining the ball-milled suspension.

[0061] During the hydrothermal reaction, the ball-milled suspension was transferred to a hydrothermal reactor and reacted at 180°C for 12 hours. After the reaction was complete, the mixture was filtered for 0.5 hours, during which it was washed with deionized water, and then dried under vacuum for 4 hours to obtain LiMn. 0.6 Fe 0.4 PO4 / C powder.

[0062] LiMn 0.6 Fe 0.4 All PO4 / C powder tests were conducted within a potential window of -1.2V to 1.2V. The LiMn prepared in this embodiment was tested... 0.6 Fe 0.4 PO4 / C exhibits excellent electrochemical performance and stability, with an initial discharge specific capacity of 133 mAh / g at 0.2C. After 50 cycles, the capacity retention remains above 92%. This is comparable to the paper "Heat-rate-controlled hydrothermal crystallization of high-performance LiMn" published by Song YJ et al. in *Ceramics International*, Volume 46, Issue 4, 2020. 0.7 Fe 0.3 In the section "PO4cathode material for lithium-ion batteries", LiMn is prepared using LiOH, H3PO4, PEG 400, MnSO4·H2O, FeSO4·7H2O, H2C2O4·2H2O and similar substances as raw materials. 0.6 Fe 0.4 PO4 / C offers an approximately 12% performance improvement.

[0063] Example 7

[0064] Adopting such Figure 1 The hydrothermal method for preparing LiMn shown 0.6 Fe 0.4 The process flow of PO4 / C includes three key control steps: raw material mixing, ball milling dispersion, and hydrothermal reaction.

[0065] In the raw material mixing step, under a constant temperature of 50℃, 20.4 mol of NH4H2PO4, 66 mol of CH3COOLi·H2O, 12 mol of Mn(CH3COO)2·4H2O, 10 mol of FeSO4·7H2O, and 10 mol of C6H8O7 were added sequentially to 200 mL of deionized water in a molar ratio of 20.4:66:12:10:10. After each addition, the mixture was stirred for 35 min, 35 min, 80 min, 70 min, and 80 min respectively to form a homogeneous suspension.

[0066] During ball milling dispersion, the suspension and grinding balls are mixed at a mass ratio of 1:1 and ball milled at a speed of 600 rpm for 5 hours to ensure that the suspension reaches nanoscale dispersion, thus obtaining the ball-milled suspension.

[0067] During the hydrothermal reaction, the ball-milled suspension was transferred to a hydrothermal reactor and reacted at 200°C for 9 hours. After the reaction was complete, it was filtered for 0.5 hours, during which time it was washed with deionized water, and then dried under vacuum for 4 hours to obtain LiMn. 0.6 Fe 0.4 PO4 / C powder.

[0068] LiMn 0.6 Fe 0.4 All PO4 / C powder tests were conducted within a potential window of -1.2V to 1.2V. The LiMn prepared in this embodiment was tested... 0.6 Fe 0.4 PO4 / C exhibits excellent electrochemical performance and stability, with an initial discharge specific capacity of 131 mAh / g at 0.2C. After 50 cycles, the capacity retention remains above 90%. This is comparable to the paper "Heat-rate-controlled hydrothermal crystallization of high-performance LiMn" published by Song YJ et al. in *Ceramics International*, Volume 46, Issue 4, 2020. 0.7 Fe0.3 In the section "PO4cathode material for lithium-ion batteries", LiMn is prepared using LiOH, H3PO4, PEG 400, MnSO4·H2O, FeSO4·7H2O, H2C2O4·2H2O and similar substances as raw materials. 0.6 Fe 0.4 PO4 / C offers approximately a 10% performance improvement.

[0069] from Figure 1 As shown in (a), within the range of 2θ from 10° to 90°, the XRD curves of the materials prepared in Examples 1 to 4 all exhibit relatively obvious characteristic peaks, and the C element exists in an amorphous form, without significantly affecting the material structure. Furthermore, as the dosage of C6H8O7 increases from 8 mmol to 10 mmol, the characteristic peaks gradually become sharper, and the fit with the PDF standard card provided by the International Center for Diffraction Data (ICDD) database improves, indicating an increase in the crystallinity of the material and a more complete olivine crystal form. Figure 1 In (b), when the dosage of C6H8O7 was increased to 11 mmol, the characteristic peaks showed no significant change and remained in good agreement with the standard card. Within the range of 2θ from 20° to 40°, the characteristic peaks shifted to the left with increasing C6H8O7 dosage, and the agreement with the PDF standard card improved. When the dosage of C6H8O7 was increased from 10 mmol to 11 mmol, the intensity of the characteristic peaks slightly decreased, and the sharpness of the characteristic peaks near 24° and 40° slightly decreased. These results indicate that, using Mn(CH3COO)2·4H2O, FeSO4·7H2O, NH4H2PO4, CH3COOLi·H2O, and C6H8O7 as raw materials, a hydrothermal method was successfully used to prepare olivine orthorhombic LiMn with uniform elemental distribution, small particle size, and good crystallinity. 0.6 Fe 0.4 The microstructure of LMFP-10, a PO4 / C material, was characterized, and its appearance and elemental distribution are as follows: Figure 2 As shown, the material particles exhibit an irregular olivine morphology, which matches their characteristic structure. Figure 3 In (a) of the study, transmission electron microscopy was used to further reveal the lattice parameters and surface C-layer characteristics of the material. The results show that LiMn 0.6 Fe 0.4 The lattice spacing of PO4 / C is approximately 4.01 Å, corresponding to LiMn. 0.6 Fe 0.4 The (120) crystal plane and Pmnb space group structure of PO4 indicate that the material has good crystal structure stability. Furthermore, the surface is coated with an amorphous C layer with a thickness of less than 4 nm. Figure 3As shown in (b), the electron diffraction pattern reveals the (101), (040), (140), and (161) crystal planes of the material, which are consistent with its orthorhombic crystal system, olivine structure of the Pmnb space group, and PDF standard card, confirming that LiMn 0.6 Fe 0.4 PO4 / C materials are polycrystalline with high crystallinity, and the Mn content in the material is high. 2+ with Fe 2+ The combination was good and no structural distortion occurred.

[0070] Figure 4 The LiMn in Example 3 was analyzed using XPS. 0.6 Fe 0.4 The chemical valence states of each element in the PO4 / C sample were determined. The test data were fitted using Advantage software and corrected for charge using the standard C1s peak at 284.8 eV. Figure 4 As can be seen from the XPS full spectrum of (a) in Example 3, LiMn 0.6 Fe 0.4 Characteristic signals of Li1s, C1s, O1s, Fe2p, Mn2p, and P2p were detected in the PO4 / C sample, and the Fe:Mn molar ratio was approximately 4:6, consistent with the raw material molar ratio in the hydrothermal preparation method, indicating that Mn... 2 + Fe 2+ No significant segregation or excessive oxidation occurred during the hydrothermal preparation process, confirming the effectiveness of the hydrothermal method for preparing LiMn. 0.6 Fe 0.4 The controllability of PO4 / C materials and the role of C6H8O7 as an oxidation inhibitor and C layer lead to the formation of stable LiMn. 0.6 Fe 0.4 PO4 / C material. Furthermore, the P2p and O1s orbitals correspond to PO4. 3- The presence of functional groups indicates good bonding between P and O, PO4 3- The structure is complete. Figure 4 In (b), the high-resolution XPS spectrum of C1s yielded two characteristic peaks. The standard characteristic peak at a binding energy of 284.8 eV was attributed to the presence of C-C or C=C bonds, while the peak at 286.5 eV corresponded to CO bonds, indicating that the carbon layer on the sample surface is rich in functional groups. Figure 4 In (c), the high-resolution spectrum of Fe2p shows two distinct characteristic peaks at 710.9 eV and 724.3 eV, corresponding to Fe2p, respectively. 3 / 2 and Fe2p 1 / 2 The orbitals indicate that the oxidation state of Fe in the material is +2. The two peaks at 715.1 eV and 728.0 eV correspond to Fe... 2+ The satellite peak. Figure 4 In (d), the high-resolution spectrum of Mn2p shows distinct characteristic peaks at 641.3 eV and 642.7 eV, corresponding to Mn2p, respectively. 3 / 2 Mn in the orbit 2+ and Mn 3+ The peak values ​​at 653.3 eV and 654.6 eV correspond to Mn2p, respectively. 1 / 2 Mn in the orbit 2+ and Mn 3+ The peak value at 647.3 eV corresponds to the satellite peak of Mn2p. Among them, Mn... 2+ Mn generated by spin splitting 3+ The charge / discharge capacity of the material is determined by Mn. 2+ The Jahn-Teller effect is the main reason for the high Mn content in the crystal structure of materials. 3+ / Mn 2+ The ratio will bring better electrochemical performance to the material, by Figure 4 As can be seen from this, Mn 3+ The peak area is higher than that of Mn 2+ Furthermore, Mn was not detected. 4+ The presence of Mn indicates that the Mn in the material has not been over-oxidized.

[0071] The preparation process of this invention mainly includes three key controlled steps: raw material mixing, ball milling dispersion, and hydrothermal reaction. Specifically, Mn(CH3COO)2·4H2O, FeSO4·7H2O, NH4H2PO4, CH3COOLi·H2O, and C6H8O7 are used as raw materials to form a homogeneous suspension under specific reaction conditions. C6H8O7 plays a dual crucial role in inhibiting excessive oxidation of Mn and Fe during the hydrothermal reaction and in forming an external C layer. The suspension is dispersed to the maximum nanoscale using ball milling. By precisely controlling the reaction temperature and time, LiMn can be directly generated solely through a hydrothermal method. 0.6 Fe 0.4 The target of PO4 / C effectively shortens the LiMn 0.6 Fe 0.4 The PO4 / C preparation process reduces processing costs. The resulting LiMn... 0.6 Fe 0.4 The PO4 / C powder exhibits excellent charge / discharge capacity of >120 mAh / g and cycle performance with a capacity retention of >85% at 0.2C.

[0072] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0073] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A LiMn 0.6 Fe 0.4 The method for preparing PO4 / C is characterized by, Includes the following steps: Manganese acetate, ferrous sulfate, ammonium dihydrogen phosphate, lithium acetate, and citric acid were dissolved in water to prepare a suspension; the suspension was then ball-milled to form a nanoscale dispersion to obtain a ball-milled suspension. The ball-milled suspension was subjected to a hydrothermal reaction, during which olivine-type LiMn was formed. 0.6 Fe 0.4 PO4, citric acid in LiMn 0.6 Fe 0.4 A uniform graphitized carbon layer was formed on the PO4 surface to obtain LiMn. 0.6 Fe 0.4 PO4 / C; The molar ratio of manganese acetate to ferrous sulfate is 1.5:1 to 1.5; The molar ratio of manganese acetate to ammonium dihydrogen phosphate is 3:5 to 5.2; The molar ratio of manganese acetate to lithium acetate is 1:4.5 to 5.5; The molar ratio of manganese acetate to citric acid is 12:8-11.

2. A LiMn according to claim 1 0.6 Fe 0.4 The method for preparing PO4 / C is characterized by, In the hydrothermal reaction treatment, the reaction temperature is 170℃~200℃ and the reaction time is 9h~12h.

3. A LiMn according to claim 1 0.6 Fe 0.4 The method for preparing PO4 / C is characterized by, During ball milling, the ball milling speed is 600 rpm to 1000 rpm; the ball milling time is 2 h to 5 h.

4. A LiMn according to claim 1 0.6 Fe 0.4 The method for preparing PO4 / C is characterized by, The preparation method of the suspension is as follows: the stirring time after adding manganese acetate is 30 min to 40 min, the stirring time after adding ferrous sulfate is 30 min to 40 min, the stirring time after adding ammonium dihydrogen phosphate is 1 h to 1.5 h, the stirring time after adding lithium acetate is 1 h to 1.5 h, and the stirring time after adding citric acid is 1 h to 1.5 h; the dissolution temperature is 40℃ to 60℃.

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