Lithium ferric manganese phosphate precursor and preparation method thereof as well as lithium ferric manganese phosphate and preparation method thereof

Abstract

The invention provides a lithium ferric manganese phosphate precursor and a preparation method thereof, and lithium ferric manganese phosphate and a preparation method thereof, and relates to the technical field of lithium ion battery positive electrode materials. A preparation method of a lithium ferric manganese phosphate precursor comprises the following steps: (1) respectively providing ferric salt, phosphorus salt and manganese salt, dissolving the ferric salt, the phosphorus salt and the manganese salt in pure water, uniformly stirring at normal temperature, adding organic fuel, and uniformly stirring to obtain a precursor solution; (2) sintering the precursor solution under the ultrasonic action to obtain a lithium ferric manganese phosphate precursor; the sintering temperature ranges from 350 DEG C to 750 DEG C, the sintering time ranges from 0.5 h to 2 h, and the ultrasonic power ranges from 1000 W to 2000 W. The synthesized lithium ferric manganese phosphate precursor has a fine and uniform three-dimensional pore structure, and the compaction density of the lithium ferric manganese phosphate positive electrode material and the capacity of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery positive electrode materials, and in particular to a lithium iron manganese phosphate precursor and a preparation method thereof, and lithium iron manganese phosphate and a preparation method thereof. Background Art

[0002] In the field of power batteries, due to the demand for lightweight vehicles and longer cruising range, higher energy density has become a key indicator of concern to consumers. The performance of power battery energy density is often closely related to the positive electrode material. Positive electrode materials with low initial efficiency and low gram capacity will directly lead to a decrease in power battery capacity and initial efficiency, and then lead to a decrease in energy density.

[0003] Among them, in addition to the current mainstream ternary lithium and lithium iron phosphate, new materials represented by lithium iron manganese phosphate are also one of the new solutions expected by the industry. At present, the methods for preparing lithium iron manganese phosphate mainly include high-temperature solid-phase method and co-precipitation method. Among them, the high-temperature solid-phase method is more widely used and more suitable for industrial production, but the solid-phase reaction is difficult to control the nucleation rate of the product phase and the diffusion rate of the phase ions, and the consistency of the final product is poor. And the co-precipitation method has poor consistency due to the high temperature solid-phase method. 3+ , Mn 3+ The precipitation pH in aqueous solution is quite different, and it is difficult for FePO4·2H2O and MnPO4·H2O to form a uniform solid solution during precipitation. The synthesized lithium iron manganese phosphate is of low quality. Therefore, it is difficult to prepare high-performance lithium iron manganese phosphate materials by the above two methods. Summary of the invention

[0004] 1. Technical issues to be solved

[0005] In view of the deficiencies in the prior art, the present invention provides a lithium iron manganese phosphate precursor and a preparation method thereof, lithium iron manganese phosphate and a preparation method thereof, which solve the technical problem that the lithium iron manganese phosphate battery prepared by the prior method has poor electrical performance.

[0006] (II) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] In one aspect, the present invention provides a method for preparing a lithium manganese iron phosphate precursor, comprising the following steps:

[0009] (1) Preparation of lithium iron manganese phosphate precursor solution

[0010] Provide iron salt, phosphorus salt and manganese salt respectively, dissolve them in water, stir them evenly at room temperature, then add organic fuel, stir them evenly to obtain a precursor solution;

[0011] (2) Preparation of lithium iron manganese phosphate precursor

[0012] The precursor solution is sintered under ultrasonic action to obtain a lithium iron manganese phosphate precursor;

[0013] The sintering temperature is 350-750° C., the sintering time is 0.5-2 hours, and the ultrasonic power is 1000-2000W.

[0014] The preparation method of the above-mentioned lithium iron manganese phosphate precursor is to perform ultrasonic treatment on the precursor solution during the sintering synthesis process of the precursor solution, so that a large number of cavitation bubbles are introduced into the precursor solution. Under the action of the shock wave generated by the ultrasound, the cavitation bubbles collapse into small bubbles, and the small bubbles are evenly dispersed in the fluid medium under the mechanical effect of the ultrasound and the shock wave and microjets generated when the cavitation bubbles collapse; similarly, the ultrasonic treatment also destroys the large bubbles generated by the decomposition of the organic fuel, making them small bubbles and evenly dispersed in the fluid medium; and the small bubbles will form a three-dimensional pore structure during the solidification process of the material; therefore, the lithium iron manganese phosphate precursor synthesized under the action of ultrasound has a fine and uniformly distributed three-dimensional pore structure, thereby improving the compaction density of the lithium iron manganese phosphate positive electrode material and improving the capacity of the battery.

[0015] In addition, shock waves and micro jets will also form strong mechanical stirring, which helps to obtain a uniform honeycomb structure composed of holes. In addition, the above preparation method preferably uses easily dispersible phosphorus iron manganese raw materials, which are mutually dissolved under liquid phase conditions to achieve uniform mixing of phosphorus iron manganese at the atomic level.

[0016] In the above-mentioned preparation method of lithium iron manganese phosphate precursor, the organic fuel also plays a core role in the performance of the final product, which can not only act as a reducing agent, but also as a chelating agent and microstructure template. The organic fuel contains a chelating agent, which can prevent the precipitation of metal ions and maintain the uniformity of composition between all components, which helps to form a strong coordination bond and keep the metal cations uniformly fixed in their positions during the combustion process.

[0017] In any embodiment, in step (1), the manganese salt is selected from any one of manganese sulfate, manganese carbonate, manganese nitrate, manganese chloride, manganese oxalate, acid manganese phosphate, and manganese phosphate, or a combination of at least two of them. The manganese salt raw materials are easily soluble in water, and are mutually soluble in liquid phase conditions to achieve uniform mixing with other raw materials at the atomic level.

[0018] In any embodiment, in step (1), the iron salt is selected from any one of ferrous sulfate, ferrous oxalate, ferric nitrate, ferrous chloride, ferric chloride, ferric perchlorate, ferrous dihydrogen phosphate, ferric formate, ferric citrate, ferric lactate, and ferric tartrate, or a combination of at least two thereof. The above iron salt raw materials are easily soluble in water, and are mutually soluble in liquid phase conditions to achieve uniform mixing with other raw materials at the atomic level.

[0019] In any embodiment, in step (1), the phosphate salt is selected from any one of acid manganese phosphate, ferrous dihydrogen phosphate, phosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, and sodium pyrophosphate, or a combination of at least two thereof.

[0020] The above raw materials are easily dispersed in aqueous solution, and are mutually soluble in liquid phase conditions to achieve uniform mixing with other raw materials at the atomic level.

[0021] In any embodiment, in step (1), the organic fuel is selected from any one of glycine, urea, polyethylene glycol, alanine, citric acid, glycerol, agar, and hexamethylene diisocyanate, or a combination of at least two thereof.

[0022] The organic fuel is selected from substances containing carboxyl, hydroxyl and fatty amine (hydrazine) groups, which can react with oxidants to initiate combustion reactions and have a great influence on the microstructure of the final oxidized material. This is related to the gel network formed by the organic fuel and its decomposition characteristics. It is an important factor affecting the properties of synthetic materials and can change the combustion temperature, reducing ability, coordination state of metal ions, etc., thereby affecting the composition and properties of the final product.

[0023] In any embodiment, in the precursor solution of step (1), the total concentration of iron ions and manganese ions is 1 to 4 mol / L.

[0024] In any embodiment, in the precursor solution of step (1), the molar ratio of the total molar number of iron ions and manganese ions to the organic fuel is 1:(0.5-2).

[0025] In a second aspect, the present invention provides a lithium iron manganese phosphate precursor prepared by the preparation method described in the first aspect, wherein the chemical formula of the lithium iron manganese phosphate precursor is αFPO4·(1-α)MP2O7, and the molar ratio of FPO4 to MP2O7 is α:(1-α); wherein α is 0 to 1, and F and M are independently selected from any one or two of Mn and Fe.

[0026] The above-mentioned lithium iron manganese phosphate precursor is iron manganese bimetallic phosphate pyrophosphate, rather than ammonium iron manganese phosphate, iron manganese oxalate, and iron manganese phosphate. The above-mentioned precursor has uniform composition, simple synthesis process, low gas production during sintering, and does not contain NH4 + , thereby avoiding the generation of ammonia during sintering and improving the electrochemical performance of lithium iron manganese phosphate positive electrode materials.

[0027] In a third aspect, the present invention provides a method for preparing lithium iron manganese phosphate, comprising the following steps:

[0028] The lithium source, the carbon source and the lithium iron manganese phosphate precursor described in the second aspect are dispersed in water respectively, dried after being evenly dispersed, and then calcined in an inert gas atmosphere to obtain lithium iron manganese phosphate.

[0029] The above-mentioned preparation method of lithium iron manganese phosphate uses a lithium iron manganese phosphate precursor with a fine and uniformly distributed three-dimensional pore structure to prepare lithium iron manganese phosphate. Therefore, the lithium iron manganese phosphate has a fine and uniformly distributed pore structure, which makes the lithium iron manganese phosphate positive electrode material have a higher compaction density and a higher battery capacity.

[0030] In a fourth aspect, the present invention provides a lithium iron manganese phosphate prepared by the preparation method described in the third aspect, wherein the lithium iron manganese phosphate has a flat state.

[0031] The above-mentioned lithium iron manganese phosphate has a flat state, which expands the ac dimension and reduces the b-axis dimension, thereby reducing the transmission path of lithium ions and improving the electrical properties of the lithium iron manganese phosphate material. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 The XRD pattern of the lithium manganese iron phosphate precursor prepared in Example 1;

[0034] Figure 2 This is a SEM image of the lithium manganese iron phosphate precursor prepared in Example 1;

[0035] Figure 3 The XRD comparison diagram of lithium iron manganese phosphate prepared by the precursor synthesized in Example 1 and commercially available lithium iron manganese phosphate in Comparative Example 1 is shown in FIG.

[0036] Wherein, a-lithium iron manganese phosphate prepared from the precursor synthesized in Example 1, b-commercially available lithium iron manganese phosphate in Comparative Example 1;

[0037] Figure 4 This is a SEM image of lithium manganese iron phosphate prepared from the precursor synthesized in Example 1;

[0038] Figure 5 The SEM image of the commercial lithium iron manganese phosphate provided in Comparative Example 1;

[0039] Figure 6 This is a comparison chart of the electrical properties of lithium iron manganese phosphate prepared from the precursor synthesized in Example 1 and commercially available lithium iron manganese phosphate 0.2C in Comparative Example 1.

[0040] Among them, c is lithium iron manganese phosphate prepared from the precursor synthesized in Example 1, and d is commercially available lithium iron manganese phosphate in Comparative Example 1. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The embodiments of the present application solve the technical problem of low capacity of lithium iron manganese phosphate batteries prepared by existing methods by providing a lithium iron manganese phosphate precursor and a preparation method thereof, lithium iron manganese phosphate and a preparation method thereof.

[0043] The technical solution in the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows:

[0044] At present, the precursors of lithium iron manganese phosphate on the market mainly include iron manganese oxalate and ammonium iron manganese phosphate. The precursors are prone to produce a large amount of waste gas emissions during sintering, such as carbon dioxide, ammonia, and water vapor, causing the material to present an uneven porous state, thereby making the compaction density of the positive electrode material low. The lithium iron manganese phosphate precursor proposed by the present invention can avoid the above defects.

[0045] The preparation method of lithium iron manganese phosphate precursor is as follows: in the sintering synthesis process of the precursor solution, the precursor solution is ultrasonically treated, so that a large number of cavitation bubbles are introduced into the precursor solution, and the cavitation bubbles collapse into small bubbles under the action of the shock wave generated by the ultrasound, and the small bubbles are uniformly dispersed in the fluid medium under the mechanical effect of the ultrasound and the shock wave and microjet generated when the cavitation bubbles collapse; similarly, the ultrasonic treatment also destroys the large bubbles generated by the decomposition of organic fuel, making them small bubbles and uniformly dispersed in the fluid medium; and the small bubbles will form a three-dimensional pore structure during the solidification process of the material; therefore, the lithium iron manganese phosphate precursor synthesized under the action of ultrasound has a fine and uniformly distributed three-dimensional pore structure. Therefore, the lithium iron manganese phosphate prepared from the precursor has a fine and uniformly distributed pore structure, and the lithium iron manganese phosphate positive electrode material has a high compaction density, thereby ensuring that the battery has a high capacity.

[0046] In addition, shock waves and micro jets will also form strong mechanical stirring, which helps to obtain a uniform honeycomb structure composed of holes. In addition, the above preparation method preferably uses easily soluble phosphorus, iron and manganese raw materials, which are mutually dissolved under liquid phase conditions to achieve uniform mixing at the atomic level.

[0047] In addition, the ultrasonic-assisted solution combustion synthesis technology is used to effectively solve the problems of difficult control of the reaction process, uneven temperature and concentration of the reaction system, and difficult combustion synthesis of multi-component reaction systems. The prepared precursor has uniform composition, simple synthesis process, low gas production during sintering, and does not contain NH4+ , thereby avoiding the generation of ammonia during sintering and improving the electrochemical performance of lithium manganese iron phosphate positive electrode materials.

[0048] The lithium iron manganese phosphate precursor obtained by the above preparation method is an iron manganese bimetallic phosphate pyrophosphate material, rather than ammonium iron manganese phosphate, iron manganese oxalate, and iron manganese phosphate. The precursor of the present invention has uniform composition, simple synthesis process, low gas production during sintering, and does not contain NH4 + , thereby avoiding the generation of ammonia during sintering and improving the electrochemical performance of lithium iron manganese phosphate positive electrode materials.

[0049] Therefore, the present invention uses manganese iron phosphate pyrophosphate as a precursor of lithium manganese iron phosphate, which can avoid the generation of waste gas such as ammonia, and the synthetic product has a higher compaction density than the manganese iron oxalate precursor. The solution combustion synthesis method with a simple reaction process is adopted, and the preparation process adopts liquid phase batching to ensure that the raw materials are evenly mixed and the uniformity of the final product composition and microstructure is guaranteed.

[0050] By introducing ultrasonic technology, a large number of cavitation bubbles are introduced into the solution, and due to the mechanical effect of ultrasound and the shock waves and microjets generated when the cavitation bubbles collapse, strong mechanical stirring will be formed, which is helpful to obtain a uniform honeycomb structure composed of mesopores.

[0051] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0052] Example 1

[0053] This embodiment provides a method for preparing a lithium iron manganese phosphate precursor 0.4FePO4·0.6MnP2O7, comprising the following steps:

[0054] According to the stoichiometric ratio of the lithium iron manganese phosphate precursor molecular formula 0.4FePO4·0.6MnP2O7, 0.4 mol FeSO4, 0.4 mol (NH4)3PO4, and 0.6 mol Mn (H2PO4)2 were weighed respectively, dissolved in 0.5 L pure water, and stirred evenly at room temperature; then 0.2 mol urea and 0.8 mol citric acid were weighed and added to the above solution, and stirred evenly to obtain a precursor solution;

[0055] The precursor solution was placed in a gold furnace at 550°C. At the same time, the top of an ultrasonic transducer (20kHz, 1500W) was immersed 2cm below the surface of the precursor solution to perform ultrasonic treatment. The solution self-propagated and a large amount of foam and gas were generated during the self-propagation combustion. After the self-propagation combustion was completed, the ultrasonic transducer was removed and the temperature was kept for 2 hours to obtain the lithium iron manganese phosphate precursor 0.4FePO4·0.6MnP2O7.

[0056] Take 30g of lithium iron manganese phosphate precursor 0.4FePO4·0.6MnP2O7, 8.48g LiOH·H2O, 3.6g glucose, and 0.3g carbon nanotubes (CNTs), disperse them in 63g pure water, ball mill for 5h, then dry at 100℃, and then calcine at 700℃ in a nitrogen atmosphere for 10h to obtain lithium iron manganese phosphate.

[0057] XRD and SEM tests were performed on the lithium iron manganese phosphate precursor 0.4FePO4·0.6MnP2O7:

[0058] The XRD pattern of lithium iron manganese phosphate precursor 0.4FePO4·0.6MnP2O7 is as follows Figure 1 As shown, the peak shape is sharp and matches well with the standard card.

[0059] The SEM image of the lithium iron manganese phosphate precursor 0.4FePO4·0.6MnP2O7 is as follows Figure 2 As shown by Figure 2 It can be seen that the lithium iron manganese phosphate precursor has a fine and uniform three-dimensional pore structure. This is because the precursor solution is subjected to ultrasonic treatment during the self-propagating combustion synthesis process, so that a large number of cavitation bubbles are introduced into the precursor solution. Under the action of the shock wave generated by the ultrasound, the cavitation bubbles collapse into small bubbles. The small bubbles are evenly dispersed in the fluid medium under the mechanical effect of the ultrasound and the shock wave and microjet generated when the cavitation bubbles collapse; similarly, the ultrasonic treatment also destroys the large bubbles generated by the decomposition of urea and citric acid, making them small bubbles and evenly dispersed in the fluid medium; and the small bubbles will form a three-dimensional pore structure during the solidification process of the material; therefore, the lithium iron manganese phosphate precursor synthesized under the action of ultrasound has a fine and uniform three-dimensional pore structure. The pore structure of the lithium iron manganese phosphate prepared by the lithium iron manganese phosphate precursor with a fine and uniform three-dimensional pore structure is fine and uniform, so the prepared positive electrode material has a higher compaction density, thereby making the battery capacity higher.

[0060] In addition, ultrasonic treatment also improves the uniformity of Fe and Mn distribution in the precursor solution.

[0061] The present invention adopts liquid phase method to mix materials, which can also ensure the uniformity of iron and manganese distribution;

[0062] Example 2

[0063] This embodiment provides a method for preparing a lithium iron manganese phosphate precursor 2FePO4·0.8MnP2O7. The preparation method is the same as that of embodiment 1 except that the stoichiometric ratio of the phosphorus iron manganese raw materials is different according to the molecular formula.

[0064] Example 3

[0065] This embodiment provides a method for preparing a lithium iron manganese phosphate precursor 0.4FePO4·0.6MnP2O7. The preparation method is the same as that of Example 1 except that 0.2 mol urea and 0.8 mol citric acid are replaced with 1 mol glycine.

[0066] Example 4

[0067] This embodiment provides a method for preparing a lithium iron manganese phosphate precursor 0.4FePO4·0.6MnP2O7. The preparation method is the same as that of embodiment 1 except that the heat treatment temperature of the gold furnace is changed from 550°C to 650°C.

[0068] Example 5

[0069] This embodiment provides a method for preparing a lithium iron manganese phosphate precursor 0.6MnPO4·0.4FeP2O7. The preparation method is the same as that of Example 1 except that 0.4 mol FeSO4, 0.4 mol (NH4)3PO4, and 0.6 mol Mn(H2PO4)2 are replaced by 0.6 mol MnSO4, 0.6 mol (NH4)3PO4, and 0.4 mol Fe(H2PO4)2 respectively.

[0070] Example 6

[0071] This embodiment provides a method for preparing a lithium iron manganese phosphate precursor 0.4FePO4·0.6MnP2O7. The preparation method is the same as that of embodiment 1 except that the ultrasonic transducer (20kHz, 1500W) and the ultrasonic power are replaced with (20kHz, 2000W).

[0072] Comparative Example 1

[0073] This comparative example provides a commercially available lithium iron manganese phosphate material LMFP64.

[0074] Comparative Example 2

[0075] The only difference between this comparative example and Example 1 is that no ultrasonic treatment is introduced during the synthesis process.

[0076] Batteries were prepared using the lithium iron manganese phosphate of Example 1 and Comparative Example 1, and the performance of the batteries was tested.

[0077] Battery preparation:

[0078] Positive electrode sheet: The positive electrode material, conductive carbon black and binder PVDF prepared in the experiment were weighed in a mass ratio of 8:1:1 and mixed evenly. The dispersant NMP was added and quickly ground and mixed evenly in an agate mortar to form a paste-like slurry. The slurry was placed on aluminum foil and coated with a scraper to make it evenly attached to the surface of the aluminum foil. It was then placed in an oven and dried at 80°C for 12 hours. After drying, it was compacted with a tablet press and then cut into small discs with a slicer to obtain the positive electrode sheet required for the experiment.

[0079] Negative electrode sheet: The negative electrode sheet used is a metal lithium sheet produced by Tianjin Zhongneng Lithium Industry. The thickness of the lithium sheet is 0.5mm and the diameter is 12mm.

[0080] Diaphragm: The diaphragm used is celgard2400 produced by CELGARD Company of the United States.

[0081] Electrolyte: The electrolyte used is produced by Tianci, and the composition is 1.10 mol / L LiPF6 EC+DMC+DEC solution (volume ratio EC:DMC:DEC=1:1:1)

[0082] Battery assembly: The button cell was assembled in an Etelux-Lab2000 glove box (H2O<1ppm, O2<1ppm). The assembly steps are as follows: Place the spring and metal gasket in the positive electrode shell in turn, place the positive electrode sheet in the center of the gasket, drip two drops of electrolyte on the positive electrode material, place the prepared circular diaphragm and drip a drop of electrolyte on the other side of the diaphragm, place the metal lithium sheet on the diaphragm, buckle the negative electrode shell on it, and seal it with a sealing machine to complete the assembly.

[0083] Figure 3 The XRD comparison diagram of lithium iron manganese phosphate and commercially available lithium iron manganese phosphate in Example 1 shows that the diffraction peaks of the two groups of samples correspond to the standard card, no impurity peaks appear, and the diffraction peaks are obvious, indicating that the crystallinity is high. The lithium iron manganese phosphate positive electrode material is a mixed solid solution of lithium iron phosphate and lithium manganese phosphate. 2+ The radius is smaller than Mn 2+ Therefore, the diffraction peak of the sample is shifted to a lower angle than that of the lithium iron phosphate standard card, and to a higher angle than that of the lithium manganese phosphate standard card.

[0084] Figure 4 and Figure 5 The SEM images of the lithium iron manganese phosphate of Example 1 and the commercially available lithium iron manganese phosphate show that the two are quite different. Figure 4It is known that the lithium iron manganese phosphate particle structure prepared by the lithium iron manganese phosphate precursor of the present invention presents a slightly flattened morphology. The lithium ions of the lithium iron manganese phosphate material diffuse along the b axis, so the slightly flattened lithium iron manganese phosphate particle morphology expands the ac dimension and reduces the scale in the b axis direction, thereby reducing the transmission path of the lithium ions. Therefore, the lithium iron manganese phosphate material prepared by the present invention has excellent electrical properties.

[0085] Figure 6 The battery performance of lithium iron manganese phosphate prepared from the precursor prepared in Example 1 is compared with that of commercially available lithium iron manganese phosphate. Figure 6 It can be seen that the lithium iron manganese phosphate prepared in Example 1 does have obvious advantages in capacity and cycle. This is because, on the one hand, the lithium iron manganese phosphate precursor synthesized under ultrasound has a fine and uniform three-dimensional pore structure. The pore structure of the lithium iron manganese phosphate prepared from the lithium iron manganese phosphate precursor is fine and uniform, and the prepared positive electrode material has a higher compaction density, thereby making the battery capacity higher; on the other hand, the lithium iron manganese phosphate particles prepared in Example 1 are flat, which expands the ac direction dimension and reduces the b-axis direction dimension, thereby reducing the transmission path of lithium ions, thereby improving the electrical properties of the lithium iron manganese phosphate material.

[0086] In addition, the lithium iron manganese phosphate particles of the present application are of different sizes, which is more conducive to improving the compaction density of the positive electrode material and the capacity of the battery. However, the commercially available lithium iron manganese phosphate particles are smaller in size and have poor primary particle grading, which is not conducive to improving the compaction density.

[0087] The electrochemical performance and compaction of the lithium iron manganese phosphate batteries prepared in Example 1 and Comparative Example 2 were tested, and the results are shown in Table 1. The electrochemical performance and compaction of the precursor prepared by introducing ultrasound are improved, because the introduction of ultrasound helps to form a more uniform precursor and a three-dimensional pore structure, thereby increasing the compaction density, high capacity, and excellent first efficiency.

[0088] Table 1 Test results of electrical properties of lithium manganese iron phosphate batteries in Example 1 and Comparative Example 2

[0089] First effect% Gram capacity mAh / g Compacted g / cc Example 1 95.2 158.2 2.35 Comparative Example 2 90.7 139.8 1.99

[0090] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0091] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a lithium iron manganese phosphate precursor, characterized in that: The steps include: (1) Preparation of lithium iron manganese phosphate precursor solution Provide iron salt, phosphorus salt and manganese salt respectively, dissolve them in water, stir them evenly at room temperature, then add organic fuel, stir them evenly to obtain a precursor solution; (2) Preparation of lithium iron manganese phosphate precursor The precursor solution is sintered under ultrasonic action to obtain a lithium iron manganese phosphate precursor; The sintering temperature is 350-750° C., the sintering time is 0.5-2 hours, and the ultrasonic power is 1000-2000W.

2. The preparation method according to claim 1, characterized in that In the step (1), the manganese salt is selected from any one of manganese sulfate, manganese carbonate, manganese nitrate, manganese chloride, manganese oxalate, acid manganese phosphate, and manganese phosphate, or a combination of at least two thereof.

3. The preparation method according to claim 1, characterized in that: In the step (1), the iron salt is selected from any one of ferrous sulfate, ferrous oxalate, ferric nitrate, ferrous chloride, ferric chloride, ferric perchlorate, ferrous dihydrogen phosphate, ferric formate, ferric citrate, ferric lactate, and ferric tartrate, or a combination of at least two thereof.

4. The preparation method according to claim 1, characterized in that: In the step (1), the phosphate salt is selected from any one of acid manganese phosphate, ferrous dihydrogen phosphate, phosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, and sodium pyrophosphate, or a combination of at least two thereof.

5. The preparation method according to claim 1, characterized in that: In the step (1), the organic fuel is selected from any one of glycine, urea, polyethylene glycol, alanine, citric acid, glycerol, agar, and hexamethylene diisocyanate, or a combination of at least two thereof.

6. The preparation method according to claim 1, characterized in that: In the precursor solution of step (1), the total concentration of iron ions and manganese ions is 1 to 4 mol / L.

7. The preparation method according to claim 1, characterized in that: In the precursor solution of step (1), the molar ratio of the total molar number of iron ions and manganese ions to the organic fuel is 1:(0.5-2).

8. A lithium manganese iron phosphate precursor prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The chemical formula of the lithium iron manganese phosphate precursor is αFPO4·(1-α)MP2O7, and the molar ratio of FPO4 to MP2O7 is α:(1-α); wherein α is 0 to 1, and F and M are independently selected from any one or two of Mn and Fe.

9. A method for preparing lithium manganese iron phosphate, characterized in that: The steps include: The lithium source, the carbon source and the lithium iron manganese phosphate precursor according to claim 8 are dispersed in water respectively, dried after being evenly dispersed, and then calcined in an inert gas atmosphere to obtain lithium iron manganese phosphate.

10. Lithium iron manganese phosphate prepared by the preparation method according to claim 9, characterized in that: The lithium iron manganese phosphate has a flat state.

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