Preparation method of high-compaction-density lithium manganese iron phosphate positive electrode material

Abstract

The invention discloses a high-compaction-density lithium manganese iron phosphate positive electrode material and a preparation method thereof, and belongs to the technical field of lithium ion battery materials. Raw materials are divided into a material A and a material B for pretreatment; wherein a magnesium source dopant is added into the material A, and a titanium source or a titanium / magnesium composite dopant is added into the material B; the slurries of the two routes are respectively ground and spray-dried, and then are mixed and sintered according to a specific proportion. According to the method, Mg < 2 + > and Ti < 4 + > exert a synergistic effect through step-by-step differential doping, and large and small grain grading is physically formed, so that the intrinsic conductivity, the ion mobility and the compaction density of the lithium manganese iron phosphate material are synchronously improved. The positive electrode material prepared by the invention has the characteristics of high compaction density, high discharge capacity and excellent rate capability, and is simple in process and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material preparation, specifically relating to a method for preparing a high-density lithium manganese iron phosphate cathode material. Background Technology

[0002] In recent years, the resurgence of lithium iron phosphate (LFP) cathodes has spurred research into the application of lithium manganese iron phosphate (LMFP) materials, which are considered promising replacements for LFP cathodes as the next generation of cathode materials for large-scale applications, possessing broad market prospects. LFP cathode materials combine the high safety and low cost of LFP with the high power of ternary materials. As an upgraded product of LFP, LFP cathode materials have a higher voltage platform due to the presence of manganese ions, theoretically increasing energy density by 20%. Furthermore, their cycle life and safety performance are comparable to LFP, and their low-temperature performance is superior. They also inherit the low cost and high safety advantages of olivine-structured cathode materials.

[0003] However, lithium iron phosphate materials have some inherent defects. Current research has found that due to the addition of Mn, the electronic conductivity and ion mobility of LMFP are lower than those of LFP. Currently, some improvements have been made by reducing the particle size of the material through nano-sizing and increasing carbon coating, but this further reduces the compaction density of lithium manganese iron phosphate cathode materials, increases their specific surface area, and affects the processing characteristics of the material.

[0004] Currently, the main methods for improving the electrochemical performance of LMFPs include carbon coating, nano-sizing, and ion doping. However, existing doping techniques are mostly single and uniform, making it difficult to simultaneously improve conductivity and optimize compaction density. Designing an innovative fabrication process that can synergistically address the low conductivity and low compaction density issues of LMFPs has become a pressing technical challenge for those skilled in the art. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a method for preparing high-density lithium manganese iron phosphate cathode material, thereby resolving the technical issues present in the prior art.

[0006] This invention is achieved through the following technical solution:

[0007] This invention proposes a method for preparing a high-density lithium manganese iron phosphate cathode material, which is made from material A and material B. Both material A and material B include a lithium source, an iron source, a manganese source, a carbon source, glucose, PEG, and additives. The proportions of each raw material meet the following requirements: the molar ratio of manganese / iron is 8:2 to 5:5; the molar ratio of (manganese + iron) / phosphorus is 0.96 to 0.98; the molar ratio of lithium / (manganese + iron) is 1.02 to 1.05; and the glucose:PEG ratio is 2:8 to 5:5. The additive in material A is magnesium oxide, and the additive in material B is magnesium oxide and titanium dioxide.

[0008] The preparation method includes the following steps:

[0009] S1: Pulping; Material A and Material B are mixed with deionized water to prepare slurries; ① Weigh out 50% solids content deionized water and start stirring; the deionized water is prepared according to a solids content of 25-37%; ② Add the prepared raw materials slowly in the order of lithium source, iron source and manganese source, carbon source and additives; each raw material must be completely dispersed before adding the next raw material; after all materials are added, continue stirring for a certain period of time to ensure full dispersion, and obtain slurry A and slurry B respectively;

[0010] S2: Grinding and spray drying: The slurry A and slurry B obtained in S1 are put into a grinding equipment for grinding until the particle size D50 is 0.25-0.4μm. After the particle size is qualified, the ground slurry A and slurry B are put into a spray drying equipment for spray drying. During the spray drying process, the inlet and outlet air temperatures are strictly controlled. The inlet air temperature is 190-220℃ and the outlet air temperature is 80-100℃, so that the moisture content of the material after spray drying is 1.0%-1.5%, and spray-dried material A and spray-dried material B are obtained.

[0011] S3. Sintering: Mix the sprayed material A and sprayed material B in a ratio of 8:2 to 4:6. After thorough mixing, transfer the mixture to the kiln for sintering. Set the kiln sintering temperature to 750 to 820℃ and keep it at a constant temperature for about 10 hours. Nitrogen gas is introduced throughout the sintering process, and the oxygen content is controlled at 1PPM to 3PPM.

[0012] S4. Crushing: The semi-finished material after the sintering of S3 is transferred to the crushing equipment for crushing; the final product is obtained after the particle size test is qualified.

[0013] Preferably, the lithium source in material A and material B is lithium carbonate and lithium dihydrogen phosphate, the manganese source is manganese carbonate and manganese oxide, and PEG and glucose are carbon sources; the iron source in material A is spherical iron phosphate, and the additive is magnesium oxide; the iron source in material B is flake iron phosphate, and the additives are magnesium oxide and titanium dioxide.

[0014] Preferably, in step S1, lithium carbonate is slowly added and then dispersed for 10-30 minutes; lithium dihydrogen phosphate is first dissolved in water and then slowly added and dispersed for 10-30 minutes; manganese carbonate, manganese oxide, and spherical iron phosphate are slowly added and then dispersed for 10-30 minutes; magnesium oxide, glucose, and PEG are slowly added and then dispersed for 30-50 minutes.

[0015] Preferably, in step S3, the sintering heating rate is 1.5℃ / min.

[0016] Preferably, in step S4, the acceptable range for the particle size D50 is 1.0 to 1.5 μm.

[0017] The method for preparing high-density lithium manganese iron phosphate cathode material proposed in this invention can bring the following beneficial effects:

[0018] 1. This invention employs ion doping, which introduces defects into the original crystal lattice structure. These defects expand the lithium-ion diffusion channels, lower the activation energy for electron transfer, and reduce the band gap, fundamentally improving the material's conductivity. Mg doping elongates the Li-O covalent bonds in the LiO6 octahedron of the olivine structure. The larger interstitial sites facilitate lithium-ion migration, enhancing ionic conductivity and increasing the battery's discharge capacity and rate performance. Simultaneously, the magnesium ion size is between that of Mn... 2+ With Mn 3+ In the intermediate stage, the conversion from divalent to trivalent manganese can be facilitated, alleviating the structural collapse caused by the valence state transformation of manganese, stabilizing the material structure, and inhibiting manganese dissolution. When high-valence metals such as Ti are doped, lattice distortion is caused, leading to changes in the growth space and bonding mode of subsequent ions, slowing down the crystal growth rate, and requiring the overcoming of higher energy barriers, thereby inhibiting particle growth.

[0019] 2. This invention employs two materials: single Mg doping and Ti / Mg dual doping. The particle size of the finished products is controlled by adjusting the carbon source and grinding particle size. The two spray-dried materials are then mixed and particle size gradation is performed to obtain a lithium manganese iron phosphate cathode material with high compaction density and electrical performance. The product has a smaller crystal particle size and more regular particle morphology, resulting in improved battery material safety performance. Furthermore, the electrical performance data is higher than that of traditional preparation methods, exhibiting higher voltage efficiency and a longer discharge platform. The raw materials for both materials in this invention are widely available, with a high degree of selectivity for the main raw materials, resulting in lower preparation costs.

[0020] In summary, this invention achieves Mg... 2+ and Ti 4+By leveraging synergistic effects and physically creating a particle size distribution, the intrinsic conductivity, ion mobility, and compaction density of lithium manganese iron phosphate materials are simultaneously improved. The cathode material prepared by this invention features high compaction density, high discharge capacity, and excellent rate performance. The process is simple and suitable for industrial production. Attached Figure Description

[0021] Figure 1 The image shown is a SEM image of the lithium manganese iron phosphate product prepared in Example 1 of this invention, magnified 20,000 times. Detailed Implementation

[0022] To more clearly explain the overall concept of this invention, the following description is provided in conjunction with the appendix to the specification. Figure 1 Detailed explanations will be provided using examples.

[0023] Example 1

[0024] A method for preparing a high-density lithium manganese iron phosphate cathode material, comprising material A and material B, wherein material A consists of 1 kg of spherical iron phosphate, 0.071 kg of manganese oxide, 1.092 kg of manganese carbonate, 1.057 kg of lithium dihydrogen phosphate, 0.252 kg of lithium carbonate, 0.0067 kg of magnesium oxide, 0.1472 kg of PEG, 0.1728 kg of glucose, and 9.3 kg of deionized water; wherein lithium carbonate and lithium dihydrogen phosphate are the lithium source, manganese carbonate and manganese oxide are the manganese source, spherical iron phosphate is the iron source, and PEG and glucose are the carbon source. Material B consists of 1 kg of flake ferric phosphate, 0.71 kg of manganese oxide, 1.092 kg of manganese carbonate, 1.057 kg of lithium dihydrogen phosphate, 0.252 kg of lithium carbonate, 0.0067 kg of magnesium oxide, 0.0026 kg of titanium dioxide, 0.1472 kg of PEG, 0.1728 kg of glucose, and 9.3 kg of deionized water. Lithium carbonate and lithium dihydrogen phosphate serve as lithium and iron sources, manganese carbonate and manganese oxide as manganese sources, flake ferric phosphate as an iron source, PEG and glucose as carbon sources, and magnesium oxide and titanium dioxide as additives. The deionized water is prepared with a solids content of 25-37%.

[0025] After material A and material B are prepared, proceed with the following steps:

[0026] S1: Preparation of Slurry A: Weigh 50% deionized water and start stirring. Slowly add lithium carbonate from material A and disperse for 10-30 minutes. Then add lithium dihydrogen phosphate and disperse for 10-30 minutes. Lithium dihydrogen phosphate needs to be dissolved in water before being added slowly. Next, slowly add manganese carbonate, manganese oxide, and spherical iron phosphate and disperse for 10-30 minutes. Finally, slowly add magnesium oxide, glucose, and PEG and disperse for 30-50 minutes. After all materials are added, continue stirring for a certain period of time to ensure full dispersion. Slurry A is now obtained.

[0027] S2: Preparation of Slurry B: Weigh a portion of deionized water and slowly add lithium carbonate from material B, dispersing for 10-30 minutes; then add lithium dihydrogen phosphate from material B (dissolved in water first, then added slowly), dispersing for 10-30 minutes; next, slowly add manganese carbonate, manganese oxide, and flake ferric phosphate from material B, dispersing for 10-30 minutes; finally, slowly add magnesium oxide, titanium dioxide, glucose, and PEG from material B, dispersing for 30-50 minutes; after all materials are added, continue stirring for a certain period of time to ensure thorough dispersion; thus, slurry B is prepared.

[0028] S3: Grinding and Spray Drying: Slurries A and B obtained in S1 and S2 are respectively transferred to grinding equipment for grinding. After the particle size D50 reaches 0.25-0.4μm, the viscosity of the slurry is tested. If the viscosity is qualified, the slurry is transferred to spray drying equipment for spray drying to obtain spray-dried material A and spray-dried material B. During the spray drying process, the inlet and outlet air temperatures are strictly controlled. The inlet air temperature is 190-220℃, and the outlet air temperature is 80-100℃, so that the moisture content of the spray-dried material is 1.0%-1.5%.

[0029] S4: Sintering: The spray-dried material A and spray-dried material B, which have been spray-dried in S3, are mixed in a certain ratio, ranging from 8:2 to 4:6. After being thoroughly mixed, the mixture is transferred to the kiln sintering equipment for sintering. Nitrogen gas is purged throughout the sintering process, and the oxygen content is controlled between 1 and 3 ppm. The sintering heating rate is 1.5℃ / min, and the temperature is raised to the kiln sintering temperature set at 750-820℃. The temperature is held for about 10 hours, and then the semi-finished material is discharged according to the normal kiln cooling process.

[0030] S5: Crushing: The semi-finished material after sintering is transferred to a crushing device for crushing. The acceptable particle size D50 range is 1.0~1.5um. After passing the particle size test, the final product is obtained. The final product is then vacuum-packed.

[0031] Example 2:

[0032] Material B contains only 0.0067 kg of magnesium oxide as an additive and no titanium dioxide; otherwise, it is the same as in Example 1.

[0033] Example 3:

[0034] Material B contains only 0.0026 kg of titanium dioxide as an additive and no magnesium oxide. The remaining steps are the same as in Example 1.

[0035] Example 4:

[0036] Material B contains no additives, and the remaining steps are the same as in Example 1.

[0037] Comparative Example 1:

[0038] Materials A and B do not contain any additives, and the remaining steps are the same as in Example 1.

[0039] Comparative Example 2:

[0040] Material A contains no additives, while Material B contains only 0.0026 kg of titanium dioxide and no magnesium oxide. The remaining steps are the same as those in Comparative Example 1.

[0041] Comparative Example 3:

[0042] Material A contains no additives, while Material B contains only 0.0067 kg of magnesium oxide and no titanium dioxide. The remaining steps are the same as those in Comparative Example 1.

[0043] Comparative Example 4:

[0044] Material A contains no additives, while Material B contains 0.0067 kg of magnesium oxide and 0.0026 kg of titanium dioxide as additives. The remaining steps are the same as those in Comparative Example 1.

[0045] The lithium manganese iron phosphate cathode materials obtained in Examples 1-4 and Comparative Examples 1-4 were subjected to powder compaction density testing and electrochemical performance testing. The performance comparison table is shown in Table 1. Using a battery testing system, their discharge capacity at 0.1C and 1C rates and their initial coulombic efficiency were tested.

[0046] Table 1. Performance Comparison of Lithium Manganese Iron Phosphate Products Obtained in Examples and Comparative Examples

[0047]

[0048] As shown in Table 1, the lithium manganese iron phosphate materials prepared in Examples 1-4 of this invention significantly outperformed Comparative Examples 1-4 in terms of compaction density and various electrochemical properties. Example 1 exhibited the best performance, demonstrating that the dual-doping gradation scheme of "adding magnesium oxide to material A while adding both magnesium oxide and titanium dioxide to material B" has the best synergistic effect. Comparing Example 1 with Comparative Examples 1-4 shows that adding dopants only to material B (Comparative Examples 2, 4) or only to one material route (Comparative Example 3) is less effective than differentiated doping in both routes (Examples 1-3). Even Example 4, where only magnesium oxide was added to material A and no dopants were added to material B, outperformed Comparative Example 1, which did not add any dopants, indicating that adding Mg doping to one route can improve performance, but not as effectively as differentiated doping in both routes. This confirms the non-obviousness and technical superiority of the core concept of "stepwise differentiated doping." Furthermore, this invention, by grinding and proportioning the two materials separately, makes it easier to adjust the particle size gradation and improve compaction; from Figure 1It can be seen that the material prepared by the present invention is composed of particles of different sizes, forming a good gradation structure, with a large number of small particles filling between the large particles, which is beneficial to improving the compaction density of the material.

[0049] In summary, this invention achieves a "dual-gradation" of chemical composition and physical particle size distribution by separately incorporating Mg doping (to improve conductivity) and Ti / Mg doping (to inhibit growth and refine particle size) into materials A and B, and then mixing them before sintering. Material A, predominantly Mg-doped, forms larger particles with good ion channels, while material B, with Ti doping to inhibit growth, forms smaller particles filling the gaps, together constructing a highly conductive and highly compacted electrode microstructure. Through this particle size distribution design, small particles effectively fill the voids between larger particles, enabling the powder compaction density of the lithium manganese iron phosphate cathode material prepared by this invention to reach 2.34 g / cm³. 3 The above-mentioned optimal solution can reach 2.41 g / cm³. 3 The concentration was significantly higher than that of the control group (~2.28 g / cm³). 3 ). At the same time, due to Mg 2+ and Ti 4+ The synergistic doping effect enhances the intrinsic conductivity of the material. The product in this example exhibits a discharge capacity exceeding 150 mAh / g at 0.1C, with an initial efficiency exceeding 96%, while maintaining a high capacity output (>140 mAh / g) at 1C, demonstrating excellent rate performance.

[0050] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a high-density lithium manganese iron phosphate cathode material, characterized in that, Made from material A and material B, both of which include lithium source, iron source, manganese source, carbon source, glucose, PEG and additives; the proportions of each raw material meet the following requirements: manganese / iron molar ratio of 8:2 to 5:5; (manganese + iron) / phosphorus molar ratio of 0.96 to 0.98; lithium / (manganese + iron) molar ratio of 1.02 to 1.05; glucose:PEG ratio of 2:8 to 5:5; the additive for material A is magnesium oxide, and the additive for material B is magnesium oxide and titanium dioxide; The preparation method includes the following steps: S1: Pulping; Material A and Material B are mixed with deionized water to prepare slurries; ① Weigh out 50% solids content deionized water and start stirring; the deionized water is prepared according to a solids content of 25-37%; ② Add the prepared raw materials slowly in the order of lithium source, iron source and manganese source, carbon source and additives; each raw material must be completely dispersed before adding the next raw material; after all materials are added, continue stirring for a certain period of time to ensure full dispersion, and obtain slurry A and slurry B respectively; S2: Grinding and spray drying: The slurry A and slurry B obtained in S1 are put into a grinding equipment for grinding until the particle size D50 is 0.25-0.4μm. After the particle size is qualified, the ground slurry A and slurry B are put into a spray drying equipment for spray drying. During the spray drying process, the inlet and outlet air temperatures are strictly controlled. The inlet air temperature is 190-220℃ and the outlet air temperature is 80-100℃, so that the moisture content of the material after spray drying is 1.0%-1.5%, and spray-dried material A and spray-dried material B are obtained. S3. Sintering: Mix the sprayed material A and sprayed material B in a ratio of 8:2 to 4:

6. After thorough mixing, transfer the mixture to the kiln for sintering. Set the kiln sintering temperature to 750 to 820℃ and keep it at a constant temperature for about 10 hours. Nitrogen gas is introduced throughout the sintering process, and the oxygen content is controlled at 1PPM to 3PPM. S4. Crushing: The semi-finished material after the sintering of S3 is transferred to the crushing equipment for crushing; the final product is obtained after the particle size test is qualified.

2. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The lithium source in materials A and B is lithium carbonate and lithium dihydrogen phosphate, the manganese source is manganese carbonate and manganese oxide, and PEG and glucose are carbon sources; the iron source in material A is spherical iron phosphate, and the additive is magnesium oxide; the iron source in material B is flake iron phosphate, and the additives are magnesium oxide and titanium dioxide.

3. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S1, lithium carbonate is slowly added and dispersed for 10-30 minutes; lithium dihydrogen phosphate is first dissolved in water and then slowly added and dispersed for 10-30 minutes; manganese carbonate, manganese oxide, and spherical iron phosphate are slowly added and dispersed for 10-30 minutes; magnesium oxide, glucose, and PEG are slowly added and dispersed for 30-50 minutes.

4. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S3, the sintering heating rate is 1.5℃ / min.

5. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S4, the acceptable range for the particle size D50 is 1.0 to 1.5 μm.

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