Lithium manganese iron phosphate material and preparation method thereof

Abstract

The invention relates to the technical field of materials, and discloses a lithium manganese iron phosphate material and a preparation method thereof.The lithium manganese iron phosphate material is prepared through the steps that firstly, metal ions generated by ionization of metal salt through functionalized carbon microspheres and sulfydryl of the functionalized carbon microspheres are chelated and adsorbed, and then the lithium manganese iron phosphate material is prepared through a hydrothermal method; in-situ growth of lithium iron manganese phosphate on the surfaces of carbon microspheres is achieved, finally, the carbon microspheres are converted into carbon dioxide to be removed in a sintering mode in air, lithium iron manganese phosphate with a hollow structure is prepared, the hollow structure can provide a buffer space for inward expansion of lithium iron manganese phosphate in the charging and discharging process of a battery, and the lithium iron manganese phosphate with the hollow structure is prepared. And the problem that the cycle performance of the battery is reduced due to volume expansion is solved, so that the lithium manganese iron phosphate material prepared by the method has excellent cycle life, and the capacity retention ratio is 95% or above after 1000 cycles.

Description

Technical Field

[0001] The present invention relates to the technical field of materials, and particularly relates to a lithium iron manganese phosphate material and a preparation method thereof. Background Art

[0002] Under the background of the rapid development of the global new energy industry, as the core energy storage carrier, the performance improvement and cost optimization of lithium-ion batteries have become the key breakthrough directions. As a new type of cathode material, lithium iron manganese phosphate shows broad application potential in the fields of power batteries and energy storage by virtue of its unique advantages, and is gradually becoming the focus of industry attention. Compared with lithium iron phosphate, lithium iron manganese phosphate has a higher energy density and can provide a longer cruising range. At the same time, lithium iron manganese phosphate has a relatively high discharge voltage platform, which helps to improve the voltage and power output of the battery system. However, the defects of lithium iron manganese phosphate are also very obvious. With the increase in the number of charge-discharge cycles, its capacity retention rate will gradually decrease, which is mainly due to its poor structural stability and easy volume expansion during the charge-discharge process. Therefore, improving the volume expansion effect of lithium iron manganese phosphate is of great significance for its further application in the field of electrode materials.

[0003] Currently, improving the preparation method of lithium iron manganese phosphate is an important way to enhance its electrochemical performance. The invention patent with the publication number CN105514422A discloses a precursor, lithium iron manganese phosphate and its preparation method and application. By mixing and reacting a water-soluble divalent manganese source, a divalent iron source, a divalent metal M salt and a precipitating agent, then dispersing the prepared pre-powder in water, adding a ferrous salt for heat treatment, and finally mixing and roasting with a water-soluble lithium source, a phosphorus source and an organic carbon source, lithium iron manganese phosphate with excellent cycle performance can be prepared. Therefore, excellent lithium iron manganese phosphate with cycle performance can be prepared by starting from the preparation path. Summary of the Invention

[0004] In order to solve the problems mentioned in the background art, the purpose of the present invention is to provide a lithium iron manganese phosphate material and a preparation method thereof.

[0005] The purpose of the present invention can be achieved by the following technical solutions: A preparation method of a lithium iron manganese phosphate material, comprising the following steps: First step: Add a manganese salt, an iron salt, a lithium salt and phosphoric acid to purified water, mechanically stir and mix evenly. After forming a uniform salt solution, add functionalized carbon microspheres to the salt solution. After adding, place it in an ultrasonic oscillator for ultrasonic oscillation treatment. Then, carry out a hydrothermal reaction on the formed mixed solution at a temperature of 180 - 200 °C for 12 - 16 h to form a carbon microsphere composite material; Step 2: Place the carbon microsphere composite in a sintering furnace and perform sintering treatment in an air atmosphere to obtain the lithium iron manganese phosphate material.

[0006] As a further solution of the present invention, in the first step, the manganese salt is manganese chloride or manganese sulfate; the iron salt is ferric chloride or ferric sulfate; the lithium salt is lithium chloride.

[0007] As a further solution of the present invention, in the first step, the mass ratio of the manganese salt, iron salt, lithium salt, phosphoric acid and functionalized carbon microspheres is 0.3 - 0.6:0.3 - 0.6:0.06 - 0.12:0.5 - 1:1.

[0008] As a further solution of the present invention, in the first step, the preparation method of the functionalized carbon microspheres is as follows: Step 1: Prepare the aqueous phase Add carboxymethyl xylan to purified water, stir and mix to prepare an aqueous phase solution with a mass fraction of 2 - 4%. Step 2: Prepare the oil phase Stir and mix n - hexane and Span60 evenly at a temperature of 40 - 60 °C, then continue to add Tween60 and stir until dissolved to form an oil phase solution. Step 3: Cross - linking treatment Add p - toluenesulfonic acid and dithiothreitol to the aqueous phase solution, stir at a temperature of 80 - 90 °C for 12 - 24 h, then slowly add the formed mixture to the oil phase solution. After adding, continue to stir for 1 - 2 h, add a demulsifier for demulsification, separate the microspheres to obtain the functionalized carbon microspheres.

[0009] As a further solution of the present invention, in the first step, the preparation method of the carboxymethyl xylan is as follows: Add xylan to tetrahydrofuran, stir and disperse evenly, then continue to add an aqueous sodium hydroxide solution. After adding, raise the temperature to 60 - 65 °C, add chloroacetic acid under stirring conditions. After adding, keep stirring for 2 - 4 h, stop heating, cool to room temperature, then add hydrochloric acid for neutralization, filter out the product, and obtain carboxymethyl xylan through washing and desalting processes.

[0010] As a further solution of the present invention, the mass fraction of the aqueous sodium hydroxide solution is 20 - 30%.

[0011] As a further solution of the present invention, in the first step, the frequency of the ultrasonic oscillation is 80 - 100 kHz and the time is 1 - 2 h.

[0012] As a further solution of the present invention, in the second step, the temperature of the sintering treatment is 600 - 700 °C and the time is 1 - 3 h.

[0013] In the above technical solution, first, chloroacetic acid was used as an acidifying reagent to carboxylate xylan to prepare carboxymethyl xylan. Then, dithiothreitol was used as a cross-linking agent and p-toluenesulfonic acid was used as a catalyst to catalyze the condensation of the carboxyl substituents in the structure of carboxymethyl xylan and the substituted hydroxyl groups in the structure of dithiothreitol, realizing the cross-linking of xylan. Finally, functionalized carbon microspheres containing a large number of thiol chelating functional groups in the structure were prepared by the microemulsion method.

[0014] Next, the functionalized carbon microspheres were mixed with manganese salts, iron salts, lithium salts, and phosphoric acid. Under ultrasonic conditions, the metal ions generated by the ionization of the metal salts would chelate and adsorb with the thiols of the functionalized carbon microspheres, thereby attaching a large amount of metal cations to the surface of the carbon microspheres. Then, through the hydrothermal method, the in-situ growth of lithium manganese iron phosphate on the surface of the carbon microspheres was realized. Finally, by sintering in air, the carbon microspheres were converted into carbon dioxide and removed, and finally, a lithium manganese iron phosphate material with a hollow morphology was formed.

[0015] A lithium manganese iron phosphate material was prepared by the above preparation method.

[0016] Advantages of the present invention: The lithium manganese iron phosphate prepared by the present invention has a hollow structure. This hollow structure can provide a buffer space for the inward expansion of lithium manganese iron phosphate during the charge and discharge process of the battery, slowing down the problem of the decline in the battery cycle performance caused by volume expansion. Therefore, the lithium manganese iron phosphate material prepared by the present invention has excellent cycle life, and the capacity retention rate is above 95% after 1000 cycles.

[0017] Of course, it is not necessary for any product implementing the present invention to achieve all the above-mentioned advantages simultaneously. Description of the drawings

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 It is the electron microscope image of the lithium manganese iron phosphate in Embodiment 2, where (A) is the scanning electron microscope image and (B) is the transmission electron microscope image. Detailed implementation manners

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0021] Preparation Example 1 Preparation of carboxymethyl xylan: Add 1.5 g of xylan to tetrahydrofuran, stir and disperse evenly, then continue to add 5 mL of an aqueous sodium hydroxide solution with a mass fraction of 30%. After adding, raise the temperature to 65 °C, add 0.8 g of chloroacetic acid under stirring conditions. After adding, keep stirring for 3 h, stop heating, and after cooling to room temperature, add hydrochloric acid for neutralization, filter out the product, and obtain carboxymethyl xylan through washing and desalting processes.

[0022] Preparation Example 2 Preparation of functionalized carbon microspheres: Step 1. Prepare the aqueous phase Add carboxymethyl xylan to purified water, stir and mix to prepare an aqueous solution with a mass fraction of 2%; Step 2. Prepare the oil phase Mix 30 mL of n-hexane and 1 g of Span60 evenly under stirring at a temperature of 50 °C, then continue to add 2 g of Tween60, and stir until dissolved to form an oil phase solution; Step 3. Crosslinking treatment Add 0.1 g of p-toluenesulfonic acid and 0.5 g of dithiothreitol to 5 mL of the aqueous solution, stir at a temperature of 90 °C for 16 h, then slowly add the formed mixture to the oil phase solution. After adding, continue to stir for 2 h, add a demulsifier to demulsify, separate the microspheres, and obtain functionalized carbon microspheres.

[0023] The preparation method of carboxymethyl xylan can be seen in Preparation Example 1.

[0024] Example 1 A preparation method of lithium iron manganese phosphate material, comprising the following steps: First step: Add 0.3 g of manganese chloride, 0.3 g of iron chloride, 0.06 g of lithium chloride and 0.5 g of phosphoric acid to purified water, mechanically stir and mix evenly. After forming a uniform salt solution, add 1 g of functionalized carbon microspheres to the salt solution. After adding, place it in an ultrasonic oscillator, control the frequency at 100 kHz, carry out ultrasonic oscillation treatment for 1 h, and then carry out hydrothermal reaction on the formed mixture at a temperature of 180 °C for 16 h to form a carbon microsphere composite material; Step 2: Place the carbon microsphere composite in a sintering furnace, control the temperature at 600 °C, and perform sintering treatment for 3 h in an air atmosphere to obtain the lithium iron manganese phosphate material.

[0025] Example 2 A preparation method of a lithium iron manganese phosphate material includes the following steps: Step 1: Add 0.5 g of manganese chloride, 0.5 g of iron chloride, 0.1 g of lithium chloride, and 0.8 g of phosphoric acid to purified water, mechanically stir and mix evenly. After forming a uniform salt solution, add 1 g of functionalized carbon microspheres to the salt solution. After adding, place it in an ultrasonic oscillator for ultrasonic oscillation treatment. Then, carry out hydrothermal reaction on the formed mixed solution at a temperature of 190 °C for 12 h to form a carbon microsphere composite. Step 2: Place the carbon microsphere composite in a sintering furnace, control the temperature at 650 °C, and perform sintering treatment for 2 h in an air atmosphere to obtain the lithium iron manganese phosphate material.

[0026] Figure 1 This is the electron microscopy image of the lithium iron manganese phosphate material, where (A) is the scanning electron microscopy image and (B) is the transmission electron microscopy image. It can be clearly observed from the figure that the lithium iron manganese phosphate material has an obvious hollow structure.

[0027] Example 3 A preparation method of a lithium iron manganese phosphate material includes the following steps: Step 1: Add 0.6 g of manganese chloride, 0.6 g of iron chloride, 0.12 g of lithium chloride, and 1 g of phosphoric acid to purified water, mechanically stir and mix evenly. After forming a uniform salt solution, add 1 g of functionalized carbon microspheres to the salt solution. After adding, place it in an ultrasonic oscillator for ultrasonic oscillation treatment. Then, carry out hydrothermal reaction on the formed mixed solution at a temperature of 200 °C for 12 h to form a carbon microsphere composite. Step 2: Place the carbon microsphere composite in a sintering furnace, control the temperature at 700 °C, and perform sintering treatment for 1 h in an air atmosphere to obtain the lithium iron manganese phosphate material.

[0028] Test Example Stir and mix evenly the lithium iron manganese phosphate materials prepared in Examples 1 - 3, commercially available lithium iron manganese phosphate, conductive carbon black, and polyvinylidene fluoride according to a mass ratio of 8:1:1. Then, add N-methylpyrrolidone and stir until a uniform paste-like material is formed. Coat it on the surface of aluminum foil, dry, press into a sheet to make a positive electrode sheet. Use metallic lithium as the negative electrode sheet, select LB-301 as the electrolyte, and assemble it into a button battery in a glove box filled with high-purity argon. Perform electrochemical tests at a current density of 0.1 A / g, and the results are recorded in Table 1: Table 1 - Electrochemical Performance Test Results Note: The commercially available lithium iron manganese phosphate was purchased from Shenzhen LiYou New Energy Technology Co., Ltd.

[0029] Analysis of the test results shows that, compared with the commercially available conventional lithium iron manganese phosphate, the lithium iron manganese phosphate prepared by the present invention has more excellent cycle stability, and the capacity retention rate after 1000 cycles is above 95%.

[0030] In this article, specific examples are used to elaborate on the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The protection scope of the present invention patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that have no substantial difference from the literal description of the claims, then these other embodiments should also be included within the scope of the claims.

[0031] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements will not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A preparation method of lithium iron manganese phosphate material, characterized in that, It includes the following steps: First step: Add manganese salt, iron salt, lithium salt and phosphoric acid into purified water, mechanically stir and mix evenly. After forming a uniform salt solution, add functionalized carbon microspheres into the salt solution. After adding, place it in an ultrasonic oscillator for ultrasonic oscillation treatment. Then, carry out hydrothermal reaction on the formed mixed solution at a temperature of 180 - 200 °C for 12 - 16 h to form a carbon microsphere composite material; Second step: Place the carbon microsphere composite material in a sintering furnace and carry out sintering treatment in an air atmosphere to obtain the lithium iron manganese phosphate material.

2. The preparation method of the lithium iron manganese phosphate material according to claim 1, characterized in that In the first step, the manganese salt is manganese chloride or manganese sulfate; the iron salt is iron chloride or iron sulfate; the lithium salt is lithium chloride.

3. The preparation method of the lithium iron manganese phosphate material according to claim 1, wherein, In the first step, the mass ratio of the manganese salt, iron salt, lithium salt, phosphoric acid and functionalized carbon microspheres is 0.3 - 0.6:0.3 - 0.6:0.06 - 0.12:0.5 - 1:

1.

4. The preparation method of the lithium iron manganese phosphate material according to claim 1, characterized in that, In the first step, the preparation method of the functionalized carbon microspheres is as follows: Step one: Prepare the aqueous phase Add carboxymethyl xylan into purified water, stir and mix to prepare an aqueous phase solution with a mass fraction of 2 - 4%; Step two: Prepare the oil phase Stir and mix n - hexane and Span60 evenly at a temperature of 40 - 60 °C, then continue to add Tween60 and stir to dissolve to form an oil phase solution; Step three: Cross - linking treatment Add p - toluenesulfonic acid and dithiothreitol into the aqueous phase solution, stir at a temperature of 80 - 90 °C for 12 - 24 h, then slowly add the formed mixed solution into the oil phase solution. After adding, continue to stir for 1 - 2 h, add a demulsifier for demulsification, separate out the microspheres to obtain functionalized carbon microspheres.

5. The preparation method of the lithium iron manganese phosphate material according to claim 4, characterized in that, In the first step, the preparation method of the carboxymethyl xylan is as follows: Add xylan into tetrahydrofuran, stir and disperse evenly, then continue to add an aqueous sodium hydroxide solution. After adding, raise the temperature to 60 - 65 °C, add chloroacetic acid under stirring conditions. After adding, keep stirring for 2 - 4 h, stop heating, cool to room temperature, then add hydrochloric acid for neutralization, filter out the product, and obtain carboxymethyl xylan through washing and desalting processes.

6. The preparation method of the lithium iron manganese phosphate material according to claim 5, characterized in that, The mass fraction of the aqueous sodium hydroxide solution is 20 - 30%.

7. The preparation method of the lithium iron manganese phosphate material according to claim 1, characterized in that, In the first step, the frequency of the ultrasonic oscillation is 80 - 100 kHz and the time is 1 - 2 h.

8. The preparation method of the lithium iron manganese phosphate material according to claim 1, characterized in that In the second step, the temperature of the sintering treatment is 600 - 700 °C and the time is 1 - 3 h.

9. A lithium iron manganese phosphate material, characterized in that, It is prepared by using the preparation method described in any one of claims 1 - 8.

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