Lithium manganese iron phosphate material with solid-hollow composite structure as well as preparation method and application of lithium manganese iron phosphate material

Abstract

The invention belongs to the technical field of lithium ion battery positive electrode materials, and discloses a lithium manganese iron phosphate material with a solid-hollow composite structure and a preparation method thereof.The preparation method adopts a step-by-step reaction and co-sintering method, and comprises the steps that firstly, heterogeneous nucleation is achieved through the solubility product difference of manganese phosphate to form a hollow lithium manganese phosphate precursor; subsequently adding an iron source, a titanium source and other raw materials, and performing spray drying and inert atmosphere sintering to construct a composite structure of solid particles and hollow particles; the lithium manganese iron phosphate material with the solid-hollow composite structure has the characteristics that solid particles provide mechanical support, hollow microspheres increase ion conduction channels and a compact structure formed by a three-dimensional network, and the compaction density gt of a pole piece is realized; 2.5 g / cm < 3 > and 2C rate capacity retention rate gt; and the method has important new energy automobile and large-scale energy storage industrialization application value.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to a solid-hollow composite structure lithium manganese iron phosphate material and its preparation method. Background Technology

[0002] With the global energy structure transitioning towards cleaner and lower-carbon energy sources, lithium-ion batteries, as the core energy storage medium, are experiencing explosive growth in demand in areas such as new energy vehicles, large-scale energy storage, and consumer electronics, indicating extremely broad prospects for technological development. Currently, innovation in cathode materials is key to improving battery performance, and among various approaches, lithium manganese iron phosphate (LiMn) stands out. x Fe 1- x PO4 (LMFP) material has become one of the most promising next-generation cathode materials due to its unique advantages of combining high safety with a high voltage platform (~4.1V), and is expected to maintain low cost while improving energy density.

[0003] However, the commercial application of LMFP faces two major challenges. On the one hand, it inherits the inherent defects of low intrinsic electronic conductivity and slow ion diffusion rate of phosphate materials, resulting in poor rate performance and low-temperature performance of the battery. On the other hand, the introduction of manganese brings about the Jahn-Teller effect and manganese dissolution problem. The former causes lattice distortion and destroys structural stability, while the latter leads to loss of active lithium and damages the negative electrode interface, which seriously deteriorates the cycle life.

[0004] To improve the conductivity of LMFPs, traditional techniques typically employ nano-sizing and carbon coating strategies. However, nanoscale particles significantly reduce the material's tap density and electrode compaction density, resulting in a substantial decrease in the battery's volumetric energy density, failing to meet the high driving range requirements of end-user applications. Therefore, overcoming the limitations of traditional modification strategies and developing an LMFP material that simultaneously achieves high energy density, excellent rate performance, and long cycle life has become a core technological bottleneck restricting its large-scale industrial application. Summary of the Invention

[0005] The purpose of this invention is to provide a solid-hollow composite lithium manganese iron phosphate material and its preparation method. This method constructs a composite structure of solid and hollow particles in one step through stepwise reaction and co-sintering, achieving synergistic optimization of high solid density, excellent rate performance and long cycle life, and breaking through the bottleneck of reduced volumetric energy density caused by traditional nano-modification.

[0006] This invention provides a method for preparing a solid-hollow composite structure lithium manganese iron phosphate material, the method comprising the following steps:

[0007] 1) Disperse lithium, manganese, phosphorus and carbon sources in deionized water to carry out a self-sacrificial template reaction to obtain hollow spherical lithium manganese phosphate precursor slurry;

[0008] 2) The precursor slurry is obtained by dispersing iron source, lithium source, phosphorus source, carbon source and titanium dioxide into hollow spherical lithium manganese phosphate precursor slurry;

[0009] 3) Spray dry the precursor slurry to obtain precursor powder;

[0010] 4) The precursor powder is sintered to obtain a solid-hollow composite structure lithium manganese iron phosphate material.

[0011] In the above preparation method, the lithium source is either lithium phosphate or lithium carbonate; the manganese source is either manganese sulfate or manganese acetate; the phosphorus source is either phosphoric acid or ammonium phosphate; the carbon source is either sucrose or glucose; and the iron source is either ferric oxide or ferrous oxalate.

[0012] In step 1) of the above preparation method, the molar ratio of the lithium source, manganese source, phosphorus source and carbon source is 1.05~1.1:0.69~0.71:0.29~0.31:0.02~0.04, and the molar concentration of the manganese source dispersed in deionized water is 5~8 mol / L.

[0013] In step 1) of the above preparation method, the reaction temperature of the self-sacrificing template reaction is 180~200℃, the reaction time is 6~12h, and the reaction atmosphere is Ar or N2.

[0014] In step 2) of the above preparation method, the molar ratio of the iron source, lithium source, phosphorus source, carbon source and titanium dioxide is 1.05~1.1:0.69~0.71:0.29~0.31:0.02~0.04:0.01~0.05.

[0015] In step 3) of the above preparation method, the inlet temperature of the spray dryer is 150~280℃ and the outlet temperature is 80~120℃.

[0016] In step 4) of the above preparation method, the sintering temperature is 650~750℃, the sintering time is 5~10h, and the sintering atmosphere is either Ar or N2.

[0017] This invention provides a solid-hollow composite structure lithium manganese iron phosphate material prepared by the above preparation method. The solid-hollow composite structure lithium manganese iron phosphate material contains solid particles and hollow particles, and the outer surfaces of the solid particles and hollow particles are coated with an amorphous carbon layer.

[0018] The solid particles have a particle size D50 of 1~8μm and a mass percentage of 20~85%; the hollow particles have a D50 of 0.05~2μm and a mass percentage of 15~80%; in the solid-hollow composite lithium manganese iron phosphate material, the mass percentage of hollow particles and solid particles is 96~98%, and the mass percentage of the amorphous carbon layer is 2~4wt%.

[0019] The Ti content in the solid-hollow composite lithium manganese iron phosphate material is 0.4–0.6 wt%.

[0020] This invention provides the application of the solid-hollow composite structure lithium manganese iron phosphate material in lithium-ion batteries.

[0021] The present invention provides a lithium-ion battery cathode, wherein the lithium-ion battery cathode is prepared using the solid-hollow composite structure lithium manganese iron phosphate material as the active material.

[0022] The positive electrode of the lithium-ion battery uses aluminum foil as a carrier, and the active material loading is 1.5~3.0 mg / cm³. 2 .

[0023] The present invention provides a lithium-ion battery, which is assembled using the above-mentioned lithium-ion battery positive electrode as the positive electrode.

[0024] This invention first utilizes the difference in solubility product of manganese phosphate to achieve heterogeneous nucleation and form a hollow lithium manganese phosphate precursor. Subsequently, after adding raw materials such as iron and titanium sources, it is spray-dried and sintered in an inert atmosphere to construct a composite structure of solid particles with a D50 of 1~8 μm and hollow particles with a D50 of 0.05~2 μm.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The compaction density of lithium manganese iron phosphate is increased by the supporting effect of solid particles;

[0027] 2. Hollow particles provide excellent ion conductivity, improving the rate performance of lithium manganese iron phosphate materials;

[0028] 3. The combined effect of carbon coating and hollow structure buffering can effectively suppress manganese leaching and volumetric strain, thus improving the material's cycle performance. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of the lithium manganese iron phosphate material prepared in Example 1;

[0030] Figure 2 A comparison of the charge-discharge curves of Example 1 and Comparative Example 1 at a 2C rate;

[0031] Figure 3 Comparison of cyclic trends for Example 1, Comparative Example 1, and Comparative Example at a 2C scaling factor. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0033] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0034] Example 1

[0035] A method for preparing a solid-hollow composite lithium manganese iron phosphate material, the method comprising the following steps:

[0036] 1) 1.1 mol lithium carbonate, 0.7 mol manganese sulfate, 0.3 mol phosphoric acid and 0.03 mol sucrose were dispersed in 100 mL of deionized water and subjected to a self-sacrificial template reaction at 180 °C under argon atmosphere for 10 h to obtain hollow spherical lithium manganese phosphate precursor slurry;

[0037] 2) 1.05 mol ferric oxide, 0.7 mol lithium carbonate, 0.3 mol ammonium phosphate, 0.03 mol sucrose and 0.05 mol titanium dioxide were added to the hollow spherical lithium manganese phosphate precursor slurry and dispersed to obtain the precursor slurry. The precursor slurry was then ball-milled for 4 hours to obtain the precursor slurry.

[0038] 3) The precursor slurry was spray-dried at an inlet temperature of 200°C and an outlet temperature of 100°C to obtain precursor powder.

[0039] 4) The precursor powder was sintered in a nitrogen atmosphere at a temperature of 700℃ for 8 hours to obtain a solid-hollow composite lithium manganese iron phosphate material.

[0040] Example 2

[0041] A method for preparing a solid-hollow composite lithium manganese iron phosphate material, the method comprising the following steps:

[0042] The preparation method in this embodiment is the same as in Example 1, except that the lithium source is replaced with lithium phosphate.

[0043] Example 3

[0044] A method for preparing a solid-hollow composite lithium manganese iron phosphate material, the method comprising the following steps:

[0045] The preparation method in this embodiment is the same as in Example 1, except that the manganese source is replaced with manganese sulfate.

[0046] Comparative Example 1

[0047] A method for preparing lithium manganese iron phosphate material, the method comprising the following steps:

[0048] 1) Disperse 1.1 mol lithium carbonate, 0.5 mol ferrous oxalate, 0.5 mol manganese dioxide and 1 mol ammonium dihydrogen phosphate in 100 mL of deionized water and ball mill for 4 h to obtain precursor slurry.

[0049] 2) The precursor slurry was spray-dried at an inlet temperature of 200°C and an outlet temperature of 100°C to obtain precursor powder.

[0050] 3) The precursor powder was sintered in a nitrogen atmosphere at a temperature of 700°C for 8 hours to obtain lithium manganese iron phosphate material.

[0051] Comparative Example 2

[0052] A method for preparing lithium manganese iron phosphate material, the method comprising the following steps:

[0053] The difference between this comparative example and Comparative Example 1 is that in step 1), lithium carbonate, ferrous oxalate, manganese dioxide, and ammonium dihydrogen phosphate are replaced with equimolar amounts of lithium hydroxide, iron oxide, manganese carbonate, and lithium hydrogen phosphate.

[0054] Application Example 1

[0055] The method for preparing lithium-ion battery cathode sheets using the cathode materials prepared in the above embodiments and comparative examples as active materials includes the following steps:

[0056] The materials prepared in Examples 1-3 and Comparative Examples 1-2, polyvinylidene fluoride, and conductive carbon black were homogenized in a mass ratio of 18:1:1 and coated onto an aluminum foil carrier to obtain a loading of 3 mg / cm³. 2 The positive electrode plate.

[0057] The lithium-ion battery uses the positive electrode sheet prepared as the active material in the above embodiments and comparative examples as the positive electrode. The negative electrode of the lithium-ion battery is Shanshan CGS-16; the separator is Enjie ceramic-coated separator with a thickness of 7μm and a ceramic coating of 3μm; the electrolyte is KLD-LMFP03A; and the assembly form is CR2032 coin cell.

[0058] Test Example 1

[0059] Compacted density test:

[0060] The powder compaction density was tested using a Yuaneng PRCD-3100 powder compaction density meter, in accordance with GB / T 44330-2024 "Determination of Powder Compacted Density of Cathode Materials for Lithium-ion Batteries". A CAN-CALOA-0150DS roller press was used to apply a pressure of 20 MPa to the cathode sheets prepared as active materials in each example and comparative sample for cold pressing. The powder layer thickness H was measured using a micrometer. The electrode compaction density was calculated using the following formula:

[0061] ρ=m / (S×H);

[0062] In the formula, m is the sample mass and S is the cross-sectional area of ​​the mold. The test was repeated 3 times, and the test results are shown in Table 1 below:

[0063] Table 1 Powder compaction density and electrode compaction density

[0064]

[0065] As can be seen from Table 1, the compaction density of lithium manganese iron phosphate material and the compaction density of electrode sheet prepared by the preparation method of the present invention are both greater than those of Comparative Example 1, indicating that the method of preparing lithium manganese iron phosphate of the present invention can improve the compaction density of powder.

[0066] Test Example 2

[0067] Battery performance test:

[0068] The lithium-ion batteries prepared using the examples and comparative examples as active materials were subjected to performance testing using a Xinwei CT-4008Tn-mA charge-discharge tester. All tests were conducted at 25±0.5°C, and the test results are shown in Table 2 below.

[0069] Table 2 Comparison of charge and discharge performance

[0070]

[0071] Table 3 2C Rate Performance and Capacity Retention

[0072]

[0073] In each embodiment, hollow spherical lithium manganese phosphate precursor slurry was prepared by self-sacrificing template method. The carbon source was hydrothermally carbonized to form a solid carbon sphere template. The lithium manganese phosphate precursor underwent heterogeneous nucleation and growth on the surface of the carbon sphere to form a core-shell structure. During the hydrothermal process, the carbon template was consumed in situ to form a hollow spherical lithium manganese phosphate precursor. In contrast, each comparative example only involved ball milling of the raw materials, which did not trigger a chemical reaction that could form a hollow structure.

[0074] As can be seen from the above 2C first-cycle discharge capacity and rate performance of lithium-ion batteries, the discharge specific capacity of each embodiment is significantly greater than that of each comparative example. Hollow and solid particles synergistically improve the rate performance of lithium manganese iron phosphate material. At the same time, the cycle retention rate after 100 cycles is also higher than that of comparative examples 1 and 2, indicating that the introduction of hollow spheres effectively suppresses manganese dissolution and volume strain, and improves the cycle performance of the material.

[0075] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0076] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a solid-hollow composite structure lithium manganese iron phosphate material, characterized in that, The preparation method includes the following steps: 1) Disperse lithium, manganese, phosphorus and carbon sources in deionized water to carry out a self-sacrificial template reaction to obtain hollow spherical lithium manganese phosphate precursor slurry; 2) The precursor slurry is obtained by dispersing iron source, lithium source, phosphorus source, carbon source and titanium dioxide into hollow spherical lithium manganese phosphate precursor slurry; 3) Spray dry the precursor slurry to obtain precursor powder; 4) The precursor powder is sintered to obtain a solid-hollow composite structure lithium manganese iron phosphate material.

2. The preparation method of the solid-hollow composite structure lithium manganese iron phosphate material according to claim 1, characterized in that, The lithium source is either lithium phosphate or lithium carbonate; the manganese source is either manganese sulfate or manganese acetate; the phosphorus source is either phosphoric acid or ammonium phosphate; the carbon source is either sucrose or glucose; and the iron source is either ferric oxide or ferrous oxalate.

3. The method for preparing the solid-hollow composite structure lithium manganese iron phosphate material according to claim 1 or 2, characterized in that, In step 1), the molar ratio of the lithium source, manganese source, phosphorus source and carbon source is 1.05~1.1:0.69~0.71:0.29~0.31:0.02~0.04, and the molar concentration of the manganese source dispersed in deionized water is 5~8 mol / L.

4. The preparation method of the solid-hollow composite structure lithium manganese iron phosphate material according to claim 1, characterized in that, In step 1), the reaction temperature of the self-sacrificing template reaction is 180~200℃, the reaction time is 6~12h, and the reaction atmosphere is Ar or N2.

5. The method for preparing the solid-hollow composite structure lithium manganese iron phosphate material according to claim 2, characterized in that, In step 2), the molar ratio of the iron source, lithium source, phosphorus source, carbon source and titanium dioxide is 1.05~1.1:0.69~0.71:0.29~0.31:0.02~0.04:0.01~0.

05.

6. The method for preparing the solid-hollow composite structure lithium manganese iron phosphate material according to claim 1, characterized in that, In step 3), the inlet temperature of the spray dryer is 150~280℃ and the outlet temperature is 80~120℃.

7. The method for preparing the solid-hollow composite structure lithium manganese iron phosphate material according to claim 1, characterized in that, In step 4), the sintering temperature is 650~750℃, the sintering time is 5~10h, and the sintering atmosphere is either Ar or N2.

8. A solid-hollow composite lithium manganese iron phosphate material prepared by the preparation method according to any one of claims 1-7, characterized in that, The solid-hollow composite lithium manganese iron phosphate material comprises solid particles and hollow particles, the outer surfaces of which are coated with an amorphous carbon layer.

9. The solid-hollow composite lithium manganese iron phosphate material according to claim 8, characterized in that, The solid particles have a particle size D50 of 1~8μm and a mass percentage of 20~85%; the hollow particles have a D50 of 0.05~2μm and a mass percentage of 15~80%; the solid-hollow composite lithium manganese iron phosphate material has a mass percentage of 96~98% for both hollow and solid particles, and a mass percentage of 2~4wt% for the amorphous carbon layer; the solid-hollow composite lithium manganese iron phosphate material contains 0.4~0.6wt% Ti.

10. The application of a solid-hollow composite lithium manganese iron phosphate material as described in claim 8 in lithium-ion batteries.

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