A magnesium-aluminum co-modified lithium manganese iron phosphate cathode material, a preparation method and application thereof

Abstract

The application discloses a magnesium-aluminum co-modified manganese iron lithium phosphate positive electrode material and a preparation method and application thereof, and relates to the technical field of battery positive electrode material preparation. x Fe y Mg m Al n PO4, wherein 0.5<=x<0.7, 0.3<=y<0.5, 0.01<=m<=0.04, 0.005<=n<=0.02, and x+y+m+n=1. In the application, magnesium and aluminum are doped into transition metal sites, magnesium doping can effectively inhibit Jahn-Teller effect, and is helpful to stabilize the material crystal structure and improve the cycle stability; aluminum doping can introduce holes, and significantly improve the intrinsic conductivity of the material; and co-doping can simultaneously solve the problems of poor material stability and low conductivity.

Description

Technical Field

[0001] This invention relates to the field of battery cathode material preparation technology, specifically to a magnesium-aluminum co-modified manganese iron phosphate cathode material, its preparation method, and its application. Background Technology

[0002] With the depletion of traditional fossil fuels and the increasingly severe environmental pollution problems, the development and utilization of clean energy have been widely promoted. To achieve the goal of a clean and low-carbon energy transition, advanced energy storage technology has become a key link connecting the supply and demand of renewable energy. Among various energy storage technologies, lithium-ion batteries, with their advantages of high energy density, long cycle life, and high conversion efficiency, occupy a central position in the clean energy technology revolution and have been widely used in portable consumer electronics, new energy vehicles, and grid energy storage. As a core component of lithium-ion batteries, the cathode material's performance directly determines the overall performance of the battery. Lithium manganese iron phosphate cathode materials integrate the core characteristics of lithium iron phosphate and lithium manganese phosphate, possessing not only a higher voltage platform and potential high energy density but also relatively low raw material costs, making it one of the key research directions in the field of lithium-ion battery cathode materials in recent years.

[0003] However, current technologies for preparing lithium manganese iron phosphate still face several key technical bottlenecks: firstly, the material's electronic conductivity and ion diffusion coefficient are relatively low, directly affecting its rate performance; secondly, manganese dissolution easily occurs during charge-discharge cycles, severely restricting the improvement of battery cycle stability. Therefore, developing high-performance LiMnFePO4 with high conductivity, high cycle capacity retention, and a simple preparation process is crucial. x Fe 1-x PO4 cathode material has important theoretical value and practical application significance for promoting the high-quality development of the lithium-ion battery industry. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a magnesium-aluminum co-modified manganese iron phosphate cathode material, its preparation method, and its application, thereby solving the problem of poor conductivity and cycle stability of existing battery cathode materials.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A magnesium-aluminum co-modified lithium manganese iron phosphate cathode material is provided, with the chemical formula LiMn. x Fe y Mg m Al n PO4, where 0.5≤x<0.7, 0.3≤y<0.5, 0.01≤m≤0.04, 0.005≤n≤0.02, and x+y+m+n=1.

[0006] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, the chemical formula of this cathode material is LiMn. 0.585 Fe 0.385 Mg 0.02 Al 0.01 PO4, LiMn 0.685 Fe 0.285 Mg 0.02 Al 0.01 PO4, LiMn 0.485 Fe 0.485 Mg 0.02 Al 0.01 PO4, LiMn 0.5925 Fe 0.3925 Mg 0.01 Al 0.005 PO4 or LiMn 0.57 Fe 0.37 Mg 0.04 Al 0.02 PO4.

[0007] This invention also provides a method for preparing the above-mentioned magnesium-aluminum co-modified lithium manganese iron phosphate cathode material, comprising the following steps: (1) According to the stoichiometric ratio, manganese iron phosphate precursor, lithium-containing compound, glucose and magnesium aluminum hydrotalcite are mixed evenly to obtain mixed powder; (2) The mixed powder obtained in step (1) is pre-fired and sintered, then ground and sieved to obtain magnesium-aluminum co-modified manganese iron lithium phosphate cathode material.

[0008] Furthermore, in step (1), the chemical formula of the manganese iron phosphate precursor is Mn a Fe b PO4, where 0.5≤a≤0.7, 0.3≤b≤0.5, and a+b=1.

[0009] Furthermore, in step (1), the lithium-containing compound is at least one of lithium carbonate, lithium hydroxide monohydrate, lithium oxalate, and lithium dihydrogen phosphate.

[0010] Furthermore, in step (1), the chemical formula of magnesium aluminum hydrotalcite is [Mg 2 / 3 Al 1 / 3 [(OH)2](CO3) 1 / 6 0.6H2O. Furthermore, in step (1), the molar ratio of lithium ions to manganese iron phosphate precursor in the lithium-containing compound is (1.01-1.05):1; the molar ratio of magnesium aluminum hydrotalcite to manganese iron phosphate precursor is (0.015-0.06):(0.94-0.985).

[0011] Furthermore, in step (1), the mixture is ball-milled until homogeneous.

[0012] Furthermore, the ball milling speed is 400-600 rpm, and the ball milling time is 5-9 hours.

[0013] Furthermore, the ball milling speed was 500 rpm, and the ball milling time was 8 hours.

[0014] Furthermore, in step (2), the sample is preheated at 300-400℃ for 2-4 hours.

[0015] Furthermore, in step (2), sintering is carried out at 600-700℃ for 6-10 hours. Furthermore, in step (2), pre-firing and sintering are carried out in a nitrogen atmosphere.

[0016] Furthermore, in step (2), the sample is passed through a 220-mesh sieve.

[0017] This invention also provides the application of the above-mentioned magnesium-aluminum co-modified lithium manganese iron phosphate cathode material in the preparation of lithium battery cathodes.

[0018] The present invention also provides a lithium battery cathode, comprising the above-mentioned magnesium-aluminum co-modified lithium manganese iron phosphate cathode material.

[0019] The present invention has the following beneficial effects: 1. Introducing dopants with different valence states and ionic radii into transition metal sites can effectively control crystal structure, improve conductivity, and suppress Jahn-Teller distortion. Mg 2+ Due to its stable electrochemical properties and suitable ionic radius, Mg has become one of the ideal doping elements in this field. 2+ Doping into the Fe / Mn sites of lithium manganese iron phosphate can suppress the Ginger-Taylor effect and improve the structural stability of the material. Furthermore, Mg... 2+ Its radius is only 0.066 nm, smaller than Fe. 2+ The 0.074 nm doping can increase the Li-O bond length in the LiO6 octahedron, thereby broadening the Li... + Diffusion channels; with increasing Mg doping concentration, the cell parameter b decreases from 1.0407 nm to 1.0398 nm, and this structural change further promotes Li diffusion. + The migration and diffusion of Al. 3+Doping into the Fe sites of lithium iron phosphate can provide holes and enhance the intrinsic conductivity of the material. However, simply doping with magnesium or aluminum alone cannot effectively solve problems such as the Jahn-Teller effect, poor conductivity, and low ion diffusion rate. Therefore, this invention proposes a magnesium-aluminum layered double hydroxide (TLD) co-modification strategy. This invention incorporates magnesium and aluminum doping into the transition metal sites. Magnesium doping effectively suppresses the Jahn-Teller effect, helping to stabilize the material's crystal structure and improve its cycling stability; aluminum doping introduces holes, significantly improving the material's intrinsic conductivity. This co-doping approach simultaneously addresses the problems of poor material stability and low conductivity.

[0020] 2. In magnesium-aluminum hydrotalcite, magnesium and aluminum elements are uniformly distributed at the molecular level. By utilizing the synergistic diffusion effect of magnesium and aluminum elements, the problem of aluminum segregation during the calcination process can be avoided. Therefore, in the synthesis process, magnesium-aluminum hydrotalcite is used as a modifier for element doping to achieve uniform distribution of doped magnesium and aluminum elements in the finished material.

[0021] 3. In addition, the preparation process used in this invention has the technical advantages of simple process, high controllability and easy large-scale production. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope image of the positive electrode material prepared in Example 1; Figure 2 The X-ray diffraction pattern of the precursor in Example 1 is shown below. Figure 3 The X-ray diffraction pattern of the cathode material prepared in Example 1; Figure 4 This is a diagram showing the room temperature first-cycle charge-discharge curve of the cathode material prepared in Example 1; Figure 5 The graph shows the room temperature electrochemical cycling performance of the cathode material prepared in Example 1. Detailed Implementation

[0023] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0024] Example 1: A magnesium-aluminum co-modified lithium manganese iron phosphate cathode material (LiMn) 0.585 Fe 0.385 Mg 0.02 Al 0.01 PO4), its preparation method includes the following steps: (1) The manganese iron phosphate precursor (Mn)0.6 Fe 0.4 PO4, 16.5g), lithium compounds (lithium carbonate, 4.26g), glucose (2.12g), magnesium aluminum hydrotalcite ([Mg... 2 / 3 Al 1 / 3 [(OH)2](CO3) 1 / 6 0.6H2O (0.27g) and 100mL of ethanol were placed in a ball mill and mixed evenly. The ball milling speed was 500rpm and the ball milling time was 8h. After drying, the mixed powder was obtained. (2) The mixed powder obtained in step (1) is pre-fired and sintered in a nitrogen atmosphere. It is pre-fired at 350°C for 3 hours and then sintered at 680°C for 8 hours. After grinding and sieving, magnesium-aluminum co-modified manganese iron lithium phosphate cathode material is obtained.

[0025] Example 2: A magnesium-aluminum co-modified lithium manganese iron phosphate cathode material (LiMn) 0.685 Fe 0.285 Mg 0.02 Al 0.01 PO4), its preparation method includes the following steps: (1) The manganese iron phosphate precursor (Mn) 0.7 Fe 0.3 PO4, 16.5g), lithium compounds (lithium carbonate, 4.3g), glucose (2.12g), magnesium aluminum hydrotalcite ([Mg... 2 / 3 Al 1 / 3 [(OH)2](CO3) 1 / 6 0.6H2O (0.27g) and 100mL of ethanol were placed in a ball mill and mixed evenly. The ball milling speed was 400rpm and the ball milling time was 9h. After drying, the mixed powder was obtained. (2) The mixed powder obtained in step (1) is pre-fired and sintered in a nitrogen atmosphere. It is pre-fired at 300°C for 4 hours and then sintered at 600°C for 10 hours. After grinding and passing through a 220-mesh sieve, magnesium-aluminum co-modified manganese iron lithium phosphate cathode material is obtained.

[0026] Example 3: A magnesium-aluminum co-modified lithium manganese iron phosphate cathode material (LiMn) 0.485 Fe 0.485 Mg 0.02 Al 0.01 PO4), its preparation method includes the following steps: (1) The manganese iron phosphate precursor (Mn) 0.5 Fe 0.5 PO4, 16.5g), lithium compounds (lithium carbonate, 4.38g), glucose (2.12g), magnesium aluminum hydrotalcite ([Mg... 2 / 3Al 1 / 3 [(OH)2](CO3) 1 / 6 0.6H2O (0.27g) and 100mL of ethanol were placed in a ball mill and mixed evenly. The ball milling speed was 600rpm and the ball milling time was 5h. After drying, the mixed powder was obtained. (2) The mixed powder obtained in step (1) is pre-fired and sintered in a nitrogen atmosphere. It is pre-fired at 400°C for 2 hours and then sintered at 700°C for 6 hours. After grinding and passing through a 220-mesh sieve, magnesium-aluminum co-modified manganese iron lithium phosphate cathode material is obtained.

[0027] Example 4: A magnesium-aluminum co-modified lithium manganese iron phosphate cathode material (LiMn) 0.5925 Fe 0.3925 Mg 0.01 Al 0.005 PO4), its preparation method includes the following steps: (1) The manganese iron phosphate precursor (Mn) 0.6 Fe 0.4 PO4, 16.75g), lithium compounds (lithium carbonate, 4.22g), glucose (2.12g), magnesium aluminum hydrotalcite ([Mg... 2 / 3 Al 1 / 3 [(OH)2](CO3) 1 / 6 0.6H2O (0.13g) and 100mL of ethanol were placed in a ball mill and mixed evenly. The ball milling speed was 500rpm and the ball milling time was 8h. After drying, the mixed powder was obtained. (2) The mixed powder obtained in step (1) is pre-fired and sintered in a nitrogen atmosphere. It is pre-fired at 350°C for 4 hours and then sintered at 680°C for 10 hours. After grinding and passing through a 220-mesh sieve, magnesium-aluminum co-modified manganese iron lithium phosphate cathode material is obtained.

[0028] Example 5: A magnesium-aluminum co-modified lithium manganese iron phosphate cathode material (LiMn) 0.57 Fe 0.37 Mg 0.04 Al 0.02 PO4), its preparation method includes the following steps: (1) The manganese iron phosphate precursor (Mn) 0.6 Fe 0.4 PO4, 16g), lithium compounds (lithium carbonate, 4.26g), glucose (2.12g), magnesium aluminum hydrotalcite ([Mg... 2 / 3 Al 1 / 3 [(OH)2](CO3) 1 / 60.6H2O (0.54g) and 100mL of ethanol were placed in a ball mill and mixed evenly. The ball milling speed was 500rpm and the ball milling time was 8h. After drying, the mixed powder was obtained. (2) The mixed powder obtained in step (1) is pre-fired and sintered in a nitrogen atmosphere. It is pre-fired at 350°C for 4 hours and then sintered at 680°C for 10 hours. After grinding and passing through a 220-mesh sieve, magnesium-aluminum co-modified manganese iron lithium phosphate cathode material is obtained.

[0029] Comparative Example 1: A lithium iron phosphate cathode material (LiMn) 0.6 Fe 0.4 PO4), its preparation method includes the following steps: (1) The manganese iron phosphate precursor (Mn) 0.6 Fe 0.4 PO4 (17g), lithium-containing compound (lithium carbonate, 4.26g), glucose (2.12g) and 100mL ethanol were placed in a ball mill and mixed evenly. The ball milling speed was 500rpm and the ball milling time was 8h. After drying, the mixed powder was obtained. (2) The mixed powder obtained in step (1) is pre-fired and sintered in a nitrogen atmosphere. It is pre-fired at 350°C for 3 hours and then sintered at 680°C for 8 hours. After grinding and sieving, lithium manganese iron phosphate cathode material is obtained.

[0030] Comparative Example 2: A magnesium-modified lithium iron phosphate cathode material (LiMn) 0.59 Fe 0.39 Mg 0.02 PO4), its preparation method includes the following steps: (1) The manganese iron phosphate precursor (Mn) 0.6 Fe 0.4 PO4 (16.66 g), lithium-containing compound (lithium carbonate, 4.26 g), glucose (2.12 g), magnesium oxide (0.08 g) and 100 mL of ethanol were placed in a ball mill and mixed evenly. The ball milling speed was 500 rpm and the ball milling time was 8 h. After drying, the mixed powder was obtained. (2) The mixed powder obtained in step (1) is pre-fired and sintered in a nitrogen atmosphere. It is pre-fired at 350°C for 3 hours and then sintered at 680°C for 8 hours. After grinding and sieving, magnesium-modified manganese iron phosphate cathode material is obtained.

[0031] Comparative Example 3: An aluminum-modified lithium iron phosphate cathode material (LiMn) 0.595 Fe 0.395 Al 0.01 PO4), its preparation method includes the following steps: (1) The manganese iron phosphate precursor (Mn) 0.6 Fe 0.4 PO4 (16.83 g), lithium-containing compounds (lithium carbonate, 4.26 g), glucose (2.12 g), alumina (0.051 g) and 100 mL of ethanol were placed in a ball mill and mixed evenly. The ball milling speed was 500 rpm and the ball milling time was 8 h. After drying, the mixed powder was obtained. (2) The mixed powder obtained in step (1) is pre-fired and sintered in a nitrogen atmosphere. It is pre-fired at 350°C for 3 hours and then sintered at 680°C for 8 hours. After grinding and sieving, aluminum-modified manganese iron phosphate cathode material is obtained.

[0032] Comparative Example 4: A magnesium-aluminum co-modified lithium manganese iron phosphate cathode material (LiMn) 0.585 Fe 0.385 Mg 0.02 Al 0.01 PO4), its preparation method includes the following steps: (1) The manganese iron phosphate precursor (Mn) 0.6 Fe 0.4 PO4 (16.5g), lithium-containing compounds (lithium carbonate, 4.26g), glucose (2.12g), magnesium oxide (0.08g), aluminum oxide (0.051g), and 100mL of ethanol were placed in a ball mill and mixed evenly. The ball milling speed was 500rpm and the ball milling time was 8h. The mixture was then dried to obtain a mixed powder. (2) The mixed powder obtained in step (1) is pre-fired and sintered in a nitrogen atmosphere. It is pre-fired at 350°C for 3 hours and then sintered at 680°C for 8 hours. After grinding and sieving, magnesium-aluminum co-modified manganese iron lithium phosphate cathode material is obtained.

[0033] Test case I. The morphology of the cathode material prepared in Example 1 was characterized using a Zeiss Supra 55 field emission scanning electron microscope (FET). The results are shown in [Figure 1]. Figure 1 .

[0034] Depend on Figure 1 It is known that the finished material of the present invention is an agglomerate composed of multiple primary particles. The particle size of the primary particles is submicron, and there are many pores in the material, which is beneficial to the wetting of the electrolyte and the transport of lithium ions.

[0035] II. The cathode material and the raw material ferromanganese phosphate precursor prepared in Example 1 were characterized using a Rigaku Uitima III X-ray diffractometer (Japan). The results are shown in [Figure Number]. Figure 2 and Figure 3 ( Figure 2 and Figure 3In the figure, the horizontal axis represents the diffraction angle 2θ, in degrees (°); the vertical axis represents the diffraction peak intensity, in absolute units (a.u.).

[0036] Depend on Figure 2 and Figure 3 It can be seen that the XRD diffraction peaks of the manganese iron phosphate precursor correspond well with the PDF standard card 97-006-2220 of MnPO4·H2O; the XRD diffraction peaks of the cathode material prepared in Example 1 correspond well with the PDF standard card 74-0375 of LiMnPO4.

[0037] III. The electrochemical performance of the cathode materials prepared in Examples 1-5 and Comparative Examples 1-4 was tested. The specific testing methods are as follows: Using the prepared positive electrode material as the positive electrode active material, it was mixed with conductive carbon black and polyvinylidene fluoride binder at a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry. This slurry was then coated onto the surface of an aluminum foil current collector. o After drying at C, the material is rolled and vacuum dried in a vacuum oven at 120°C for 12 h. Electrode sheets with a diameter of 1 cm are obtained using a stamping machine as positive electrodes, lithium metal sheets are used as negative electrodes, polyethylene film is used as separators, and 1 mol / L LiPF6+EC+DMC is used as electrolyte. Button batteries are assembled in a UniLab type glove box (H2O<1ppm, O2<1ppm) of M. Braun.

[0038] Electrochemical performance was tested using a Wuhan Landian CT2001A battery tester, with a voltage range of 2.3-4.5 V (vs. Li). + / Li), 1 C = 170 mA·g -1 .

[0039] See results Figure 4 (Test conditions: voltage 2.3-4.5V, temperature 25℃) Figure 5 (Test conditions: voltage 2.3-4.5V, 0.1C activation for 3 weeks, 1C cycle for 200 cycles) and Table 1.

[0040] Table 1. Electrochemical performance of the cathode materials prepared in Examples 1-5 and Comparative Examples 1-4

[0041] See the results Figure 4 , Figure 5 As shown in Table 1, the magnesium-aluminum co-modified lithium manganese iron phosphate cathode material LiMn prepared by this invention... x Fe y Mg m Al nPO4 not only improved the specific capacity in the first week, but also enhanced the cycling stability of the material.

[0042] This invention employs magnesium-aluminum hydrotalcite for dual-element doping. Magnesium doping not only suppresses the Jameer-Taylor effect and improves the structural stability of the material, but also increases the lithium-oxygen bond length, enhancing the lithium-ion diffusion rate. Aluminum doping provides additional holes, significantly contributing to the improvement of the material's intrinsic conductivity. Compared to single doping with magnesium or aluminum, dual doping addresses the main pain points in lithium manganese iron phosphate, thereby significantly improving the specific capacity and cycle stability of the lithium manganese iron phosphate cathode material.

[0043] Compared to dual doping using separate magnesium and aluminum sources (such as magnesium oxide and aluminum oxide), doping with magnesium-aluminum hydrotalcite significantly improves the uniformity of element distribution and largely avoids aluminum segregation during calcination. Furthermore, the preparation method of this invention is simple, highly controllable, and easy to scale up for mass production.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A magnesium-aluminum co-modified lithium manganese iron phosphate cathode material, characterized in that, The chemical formula is LiMn x Fe y Mg m Al n PO4, where 0.5≤x<0.7, 0.3≤y<0.5, 0.01≤m≤0.04, 0.005≤n≤0.02, and x+y+m+n=1.

2. The magnesium-aluminum co-modified manganese iron phosphate cathode material according to claim 1, characterized in that, The chemical formula is LiMn 0.585 Fe 0.385 Mg 0.02 Al 0.01 PO4, LiMn 0.685 Fe 0.285 Mg 0.02 Al 0.01 PO4, LiMn 0.485 Fe 0.485 Mg 0.02 Al 0.01 PO4, LiMn 0.5925 Fe 0.3925 Mg 0.01 Al 0.005 PO4 or LiMn 0.57 Fe 0.37 Mg 0.04 Al 0.02 PO4.

3. The method for preparing the magnesium-aluminum co-modified lithium manganese iron phosphate cathode material according to any one of claims 1-2, characterized in that, Includes the following steps: (1) According to the stoichiometric ratio, manganese iron phosphate precursor, lithium-containing compound, glucose and magnesium aluminum hydrotalcite are mixed evenly to obtain mixed powder; (2) The mixed powder obtained in step (1) is pre-fired and sintered, then ground and sieved to obtain magnesium-aluminum co-modified manganese iron lithium phosphate cathode material.

4. The preparation method of the magnesium-aluminum co-modified lithium manganese iron phosphate cathode material according to claim 3, characterized in that, In step (1), the chemical formula of the manganese iron phosphate precursor is Mn a Fe b PO4, where 0.5≤a≤0.7, 0.3≤b≤0.5, and a+b=1.

5. The preparation method of the magnesium-aluminum co-modified lithium manganese iron phosphate cathode material according to claim 3, characterized in that, In step (1), the lithium-containing compound is at least one of lithium carbonate, lithium hydroxide monohydrate, lithium oxalate, and lithium dihydrogen phosphate.

6. The preparation method of the magnesium-aluminum co-modified lithium manganese iron phosphate cathode material according to claim 3, characterized in that, In step (1), the chemical formula of magnesium aluminum hydrotalcite is [Mg 2 / 3 Al 1 / 3 [(OH)2](CO3) 1 / 6 0.6H2O.

7. The preparation method of the magnesium-aluminum co-modified lithium manganese iron phosphate cathode material according to claim 3, characterized in that, In step (2), preheat at 300-400℃ for 2-4 hours.

8. The preparation method of the magnesium-aluminum co-modified lithium manganese iron phosphate cathode material according to claim 3, characterized in that, In step (2), sintering is carried out at 600-700℃ for 6-10 hours.

9. The application of the magnesium-aluminum co-modified manganese iron phosphate cathode material according to any one of claims 1-2 in the preparation of lithium battery cathodes.

10. A lithium battery positive electrode, characterized in that, Including the magnesium-aluminum co-modified manganese iron phosphate cathode material as described in any one of claims 1-2.

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