CN117886296A

CN117886296A - Ammonium ferromanganese phosphate, lithium ferromanganese phosphate, and preparation methods and applications thereof

Info

Publication number: CN117886296A
Application number: CN202410068667.9A
Authority: CN
Inventors: 武开鹏; 张云; 吕威; 孙小波
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2024-01-17
Filing date: 2024-01-17
Publication date: 2024-04-16

Abstract

The invention provides ammonium ferromanganese phosphate and lithium ferromanganese phosphate as well as a preparation method and application thereof, belonging to the technical field of inorganic material preparation; the invention ensures that metal ions and NH in solution are realized through the rust reaction of iron powder and manganese powder in water, the hydrolysis reaction of ammonium ions and the regulation and control of ammonia water on the pH value of a reaction system ₃ And PO (PO) ₄ ^3‑ The combination of the manganese iron ammonium phosphate and the Fe and Mn can be completely converted into the product, so that the uniform mixing of Fe, mn and P atomic levels is realized, ammonium ions in the reaction solution can be recycled, and the atomic economy is greatly improved; the manganese iron hydrogen phosphate obtained by calcining the manganese iron ammonium phosphate is calcined with a lithium source and a carbon source, and the finally prepared manganese iron lithium phosphate material has spherical secondary particles, high purity, high tap density and uniform distribution, and the particle size of the particles is nano-scale, and has higher proportionThe lithium ion battery has good specific discharge capacity and rate capability, and can improve the electrochemical performance of the lithium ion battery when being applied to the lithium ion battery.

Description

Ammonium ferromanganese phosphate, lithium ferromanganese phosphate, and preparation methods and applications thereof

Technical Field

The invention belongs to the technical field of inorganic material preparation, and particularly relates to ammonium ferromanganese phosphate and lithium ferromanganese phosphate as well as a preparation method and application thereof.

Background

Under the international background of resource shortage, energy conservation and emission reduction, the lithium ion battery becomes the most popular chemical energy storage device in the current research due to the advantages of high specific energy, no memory effect, high safety, long cycle life and the like, and as a core component for determining the capacity and cost of the battery, the optimization of the anode material of the lithium ion battery is important for improving the performance of the battery; currently, there are many positive electrode materials of lithium ion batteries in the market, wherein the positive electrode material of lithium iron manganese phosphate has the advantages of excellent multiplying power performance of lithium iron phosphate and high voltage platform of lithium manganese phosphate, and the advantages of low cost, high safety and the like, so that the positive electrode material is outstanding in various positive electrode materials.

At present, the synthesis method of the lithium iron manganese phosphate mainly comprises a solid phase method, a coprecipitation method and a hydrothermal method, and the solid phase method is mainly used for directly mixing raw materials such as an iron source, a manganese source, a phosphorus source, a lithium source and the like and then sintering and synthesizing the raw materials at a high temperature to form the lithium iron manganese phosphate material, but the method is high in energy consumption, the particle size of a product is difficult to control, and even mixing at an atomic level cannot be realized; the hydrothermal method needs a high-temperature and high-pressure environment, has high requirements on production equipment, and has the problems of complicated production operation, poor safety, high energy consumption, low productivity and the like; the coprecipitation method firstly adopts a wet method to synthesize the ferromanganese phosphate precursor, and then the ferromanganese phosphate precursor is mixed with a lithium source for sintering, the synthesis route has mild conditions, and the prepared product has uniform element distribution, accurate and adjustable proportion and stable quality, and is a route which is favored at present.

The manganese iron ammonium phosphate contains three elements of Fe, mn and P simultaneously, has proper stoichiometric ratio and stable physical and chemical properties, is an ideal precursor for preparing the manganese iron lithium phosphate, and the current method for preparing the manganese iron ammonium phosphate mainly comprises a coprecipitation method and a mechanical activation method, wherein the coprecipitation method is to carry out coprecipitation reaction under proper pH value and temperature conditions by mixing ferrous salt, manganese salt and phosphorus source, so as to generate the manganese iron ammonium phosphate; the mechanical activation method is to mix manganese salt, ferric salt and phosphorus source, and mechanically activate the mixture in a ball mill to fully mix, crush and react the raw materials to generate ammonium ferromanganese phosphate; however, both methods use metal salts as raw materials, and therefore, a large amount of anions which cannot be utilized are generated, and the atom utilization rate is low.

Disclosure of Invention

The invention aims to provide ammonium ferromanganese phosphate, lithium ferromanganese phosphate, and a preparation method and application thereof, and solves the problems in the background technology.

In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:

the first aspect of the invention provides a preparation method of ammonium ferromanganese phosphate, which comprises the following steps: under the inert atmosphere and stirring conditions, adding iron powder and manganese powder with the molar ratio of 1.5-9:1 into a proper amount of ammonium salt solution, then adding a solution containing a metal ion-free phosphorus source and an ammonium source, adding ammonia water to keep the pH of a reaction system alkaline, continuously stirring for reaction, keeping the reaction system pH weak acidic when the bubble generation rate in the reaction system is slowed down, adjusting the adding amount of the ammonia water to keep stirring until the reaction is finished, filtering out a solid product, washing and drying to obtain the manganese ferric ammonium phosphate.

Preferably, the inert atmosphere is argon or nitrogen, the reaction stirring speed is 300-600rpm, the reaction temperature is 25-80 , the reaction time after complete feeding is 1-4h, and the alkalescence is that: the pH value is 7.0< and less than or equal to 8.5, and the weak acidity is as follows: the pH value is more than or equal to 5.0 and less than or equal to 6.5.

Preferably, the ammonium salt solution is one or more of ammonium sulfate solution, ammonium chloride solution and ammonia water, the solution containing the metal ion-free phosphorus source and the ammonium source is one or more of ammonium phosphate solution, monoammonium phosphate solution and diammonium phosphate solution, and the molar amounts of the phosphorus source and the ammonium source in the solution containing the metal ion-free phosphorus source and the ammonium source are 1-1.2 times of the total molar amount of the manganese powder and the iron powder.

Preferably, the concentration of the ammonium salt solution is 0.1-1mol/L, the concentration of the solution containing the metal ion-free phosphorus source and the ammonium source is 0.5-1mol/L, and the concentration of the ammonia water is 1-2mol/L.

The second aspect of the invention provides the ammonium ferromanganese phosphate prepared by the preparation method, and the chemical formula of the ammonium ferromanganese phosphate is NH ₄ Fe _x Mn _1-x PO ₄ 0<x0.4

The third aspect of the invention provides a preparation method for preparing lithium iron manganese phosphate by adopting the ammonium iron manganese phosphate, which comprises the following steps:

1) Calcining the ferromanganese ammonium phosphate according to claim 5 under argon or nitrogen at 200-400 for 3-8h to obtain ferromanganese hydrogen phosphate powder;

2) Dispersing the ferromanganese hydrogen phosphate powder, the lithium source and the carbon source in the step 1) in a solvent, and calcining for 6-8 hours at 600-800 in an inert atmosphere after sanding and spray drying to obtain the lithium ferromanganese phosphate.

Preferably, in the step 2), the lithium source is one or more of lithium carbonate, lithium hydroxide and lithium acetate, the carbon source is one or more of glucose, sucrose, starch and cellulose, the molar quantity of the lithium source is 1-1.03 times of the total molar quantity of iron and manganese in the manganese iron hydrogen phosphate, and the mass of the carbon source is 1% -20% of the mass of the manganese iron hydrogen phosphate powder.

Preferably, in the step 2), the solvent is at least one of water and ethanol, and the total mass of the ferric manganese hydrogen phosphate powder, the lithium source and the carbon source solid accounts for 20% -40% of the total mass of the solid and the solvent.

The fourth aspect of the invention provides a lithium iron manganese phosphate prepared by the preparation method, and the chemical formula of the lithium iron manganese phosphate is LiFe _y Mn _1-y PO ₄ 0<y0.4

The fifth aspect of the invention provides application of lithium iron manganese phosphate in a positive electrode material of a lithium ion battery.

The invention has the beneficial effects that:

1. the invention utilizes the rust reaction of iron powder and manganese powder in water to generate Fe ²⁺ Mn ²⁺ The metal ions and NH in the solution are realized through the hydrolysis reaction of ammonium ions and the regulation and control of ammonia water on the pH value of the reaction system ₄ ⁺ And PO (PO) ₄ ^3- Combining to generate ferromanganese ammonium phosphate, fe and Mn can be completely converted into products, realizing uniform mixing of Fe, mn and P atomic levels and accurate adjustment of stoichiometric ratio of Fe, mn and P in the ferromanganese ammonium phosphate, and remaining ammonium ions in the reaction solution can continue to circulateThe ring utilization greatly improves the atom economy, the process flow is simple and easy to control, the requirement on equipment is low, and the reaction condition is mild;

2. the invention regulates and controls the pH of the reaction system to be alkaline by ammonia water in the early and middle stages of the reaction to exert NH ₃ The metal ions generated by the rust reaction are reacted in the form of a complex (M (NH) ₃ ) ₂ ²⁺ M=mn, fe) exists in the solution instead of forming hydroxide precipitates to coat the surfaces of the metal particles, thereby promoting the adequate corrosion of the metal, generating a large number of bubbles, gradually slowing down the bubble generation rate along with the progress of the reaction, gradually reducing the pH value of the system due to the formation of the ammonium ferromanganese phosphate precipitates, and regulating the reaction system to a specific weak acid environment by ammonia water at the later stage of the reaction to ensure the adequate precipitation of the ammonium ferromanganese phosphate, thereby improving the yield of the product;

3. the ferromanganese ammonium phosphate obtained by the preparation method has high purity, no impurity phase and nano lamellar structure, so that the ferromanganese ammonium phosphate material synthesized by adopting the ferromanganese ammonium phosphate as a precursor has high purity, spherical secondary particles and high tap density, the particle size of the particles is nano-scale and uniformly distributed, the paths of lithium ion transmission are shortened by the fine particles, and the specific discharge capacity and the rate capability of the ferromanganese ammonium phosphate material are effectively improved;

4. the metal ions in the ferromanganese ammonium phosphate prepared by the preparation method are +2, so that when the ferromanganese ammonium phosphate is used as a precursor for sintering, no additional carbothermic reduction is needed, the use amount of a carbon source is reduced, and NH in the ferromanganese ammonium phosphate is reduced ₄ ⁺ The lithium manganese iron phosphate material is separated in the form of ammonia gas, so that the prepared lithium manganese iron phosphate material has a porous structure, and the porous structure is not only beneficial to the infiltration of electrolyte, but also improves Li ⁺ The accessibility in the microsphere fully plays the property of the material, can also improve the specific surface area of the material, increase the surface active site and improve the specific energy of the lithium iron manganese phosphate material;

5. the invention carries out low-temperature presintering on the ferromanganese ammonium phosphate to remove adsorbed water, crystal water and ammonia, so as to obtain ferromanganese hydrogen phosphate powder, and then adopts sanding, spray drying and solid-phase sintering processes to synthesize the ferromanganese phosphate material.

Drawings

FIG. 1 shows XRD patterns of ammonium ferromanganese phosphate samples A1, A2, A3 and B1 prepared in examples 1, 2, 3 and comparative examples;

FIG. 2 is an SEM image of a sample A1 of ammonium ferromanganese phosphate prepared in example 1;

FIG. 3 is an SEM image of a sample B1 of ammonium ferromanganese phosphate prepared in comparative example;

FIG. 4 is XRD patterns of lithium iron manganese phosphate samples C1 and D1 prepared in example 1 and comparative example;

FIG. 5 is an SEM image of a lithium iron manganese phosphate sample C1 prepared according to example 1;

FIG. 6 is an SEM image of a lithium iron manganese phosphate sample D1 prepared in comparative example;

fig. 7 is a charge-discharge graph of test cell 1 and test cell 2 at 0.2C magnification;

fig. 8 is a graph of the rate performance of test cell 1 and test cell 2.

Detailed Description

The present invention is described in detail below by way of examples, which are necessary to be pointed out herein for further illustration of the invention and are not to be construed as limiting the scope of the invention, since numerous insubstantial modifications and adaptations of the invention will be to those skilled in the art in light of the foregoing disclosure. In the examples which follow, reagents and apparatus not specifically described are commercially available, and experimental procedures not specifically described are carried out according to the manufacturer's instructions or techniques conventional in the art, unless otherwise defined, all technical and scientific terms used herein have the same meaning as familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to those described herein can be used in the present invention; the endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For a range of values, one or more new ranges of values can be obtained in combination with each other between the endpoints of each range, between the endpoints of each range and the individual point values, and between the individual point values, and are to be considered as specifically disclosed herein;

the first aspect of the invention provides a preparation method of ammonium ferromanganese phosphate, which comprises the following steps:

adding iron powder and manganese powder with the molar ratio of 1.5-9:1 into 0.1-1mol/L ammonium salt solution at the temperature of 25-80 under inert atmosphere according to the stirring rate of 300-600rpm, then adding a solution containing a metal ion-free phosphorus source and an ammonium source with the concentration of 0.5-1mol/L and the molar amount of both the phosphorus source and the ammonium source being 1-1.2 times of the total molar amount of the manganese powder and the iron powder, adding 1-2mol/L ammonia water to keep the pH of the reaction system weakly alkaline, continuously stirring for reaction until the bubble generation rate in the reaction system is slowed down, adjusting the adding amount of the ammonia water to enable the pH of the reaction system to be weakly acidic, continuously stirring for reaction for 1-4h, filtering out a solid product, washing and drying to obtain manganese iron ammonium phosphate.

In some preferred embodiments of the invention, the inert atmosphere is argon or nitrogen, the inert atmosphere acting to avoid Fe ²⁺ Is oxidized by (a); the reaction stirring rate may also be selected to be 350rpm, 400rpm, 450rpm, 500rpm, 550rpm; the reaction temperature can be 30 , 40 , 50 ,60 , 70 and the reaction time can be 1.5h, 2h, 2.5h, 3h and 3.5h.

In some preferred embodiments of the invention, the weak basicity is: the pH value is 7.0< and less than or equal to 8.5, and the weak acidity is as follows: pH is more than or equal to 5.0 and less than or equal to 6.5; the weak basicity may also be selected as: 7.3, 7.5, 7.8, 8.0, 8.2, 8.4; the weak acidity can also be selected from 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.4;

in some preferred embodiments of the present invention, the ammonium salt solution is one or more of an ammonium sulfate solution, an ammonium chloride solution, and aqueous ammonia, and the solution containing the metal ion-free phosphorus source and the ammonium source is one or more of an ammonium phosphate solution, an ammonium dihydrogen phosphate solution, and an ammonium dihydrogen phosphate solution.

In some preferred embodiments of the present invention, the ammonium salt solution may be further selected to be 0.2mol/L, 0.3mol/L, 0.4mol/L, 0.5mol/L, 0.6mol/L, 0.7mol/L, 0.8mol/L, 0.9mol/L, the concentration of the solution containing the metal ion-free phosphorus source and the ammonium source may be further selected to be 0.6mol/L, 0.7mol/L, 0.8mol/L, 0.9mol/L, and the concentration of the aqueous ammonia may be further selected to be 1.2mol/L, 1.3mol/L, 1.4mol/L, 1.5mol/L, 1.6mol/L, 1.7mol/L, 1.8mol/L, 1.9mol/L.

The preparation method has the technical principle that:

NH in ammonium salt solution ₄ ⁺ Hydrolysis reaction takes place to generate NH ₃ (equation (1)), then the added metal simple substance M (M=Mn, fe) is rusted with water, and M is generated on the surface of the metal particle ²⁺ Three types of fine particles (reaction formula (2)), H.OH-at this time, NH in alkaline environment ₃ Is a strong complexation of M formed in reaction formula (2) ²⁺ Will be preferentially with NH ₃ Complexing reaction to generate M (NH) ₃ ) ₂ ²⁺ Complexes (equation (3)); m (NH) ₃ ) ₂ ²⁺ The complex is transferred deep into the solution with stirring and reacts with the PO in the solution ₄ ^3- And NH ₄ ⁺ The combination forms a precipitate (equation (4)), which in turn will react with NH ₃ Release into solution with M ²⁺ Combining to form a complete cycle; in addition, H.generated in this process may combine two by two to generate hydrogen (reaction formula (5)), and the entire reaction process is as follows:

NH ₄ ⁺ +OH ^- NH ₃ +H ₂ O (1)

M+H ₂ OM ²⁺ +H+OH- (2)

M ²⁺ +2NH ₃ M(NH ₃ ) ₂ ²⁺ (3)

M(NH ₃ ) ₂ ²⁺ +PO ₄ ^3- +NH ₄ ⁺ NH ₄ MPO ₄ +2NH ₃ (4)

2HH ₂ (5)

it should be noted that the function of the ammonium salt solution is to provide an environment of "ammonium/ammonia" to promote the rusting reaction of the metal powder, which can be recycled in the solution and contains a metal ion-free phosphorus sourceAnd an ammonium source is used to provide a pure phase NH generation ₄ MPO ₄ Required NH ₄ ⁺ And PO (PO) ₄ ^3-

The invention also provides the manganese ammonium iron phosphate prepared by the preparation method of the manganese ammonium iron phosphate, and the chemical formula of the manganese ammonium iron phosphate is NH ₄ Fe _x Mn _1-x PO ₄ 0<x is less than or equal to 0.4, the purity is high, the impurity phase is avoided, and the nano-sheet structure is provided.

The invention also provides the lithium iron manganese phosphate prepared by adopting the ammonium iron manganese phosphate, and the chemical formula of the lithium iron manganese phosphate is LiFe _y Mn _1-y PO ₄ 0<y is less than or equal to 0.4, the material has spherical secondary particles, high tap density, uniform distribution of particle size in nano scale, and excellent specific discharge capacity and rate capability.

The invention also provides a preparation method of the lithium iron manganese phosphate, which comprises the following steps:

1) Placing the ammonium ferromanganese phosphate under argon or nitrogen, and calcining for 3-8 hours at the temperature of 200-400 to obtain ferromanganese hydrogen phosphate powder;

In some preferred embodiments of the present invention, the lithium source is one or more of lithium carbonate, lithium hydroxide and lithium acetate, the carbon source is one or more of glucose, sucrose, starch and cellulose, the molar amount of the lithium source is 1-1.03 times of the total molar amount of iron and manganese in the ferromanganese hydrogen phosphate, and the mass of the carbon source is 1% -20% of the mass of the ferromanganese hydrogen phosphate powder; the molar amount of the lithium source can be 1.01 times and 1.02 times of the total molar amount of iron and manganese in the ferromanganese hydrogen phosphate; the carbon source mass can be selected from 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16% and 18% of the mass of the ferromanganese hydrogen phosphate powder.

In some preferred embodiments of the present invention, the solvent is at least one of water and ethanol, and the total mass of the ferric manganese hydrogen phosphate powder, the lithium source and the carbon source is 20% -40% of the total mass of the solid and the solvent; the total mass of the solid can also account for 25%, 30% and 35% of the total mass of the solid and the solvent.

The lithium iron manganese phosphate provided by the invention is used as a positive electrode material for a lithium ion battery, so that the lithium ion battery has excellent specific capacity and cycle performance.

Hereinafter, the ammonium ferromanganese phosphate, lithium ferromanganese phosphate, and the preparation methods and applications thereof will be further described by the following specific examples.

Example 1

1) Under the conditions of nitrogen atmosphere, stirring speed of 400rpm and temperature of 60 , 14.76g of metal manganese powder and 10g of metal iron powder are weighed and added into 1000mL of ammonium sulfate solution with concentration of 0.5mol/L, 985mL of ammonium dihydrogen phosphate solution with concentration of 0.5mol/L is added, 1mol/L of ammonia water solution is added, the feeding speed is controlled, the pH value of a reaction system is maintained to be 7.5, continuous stirring is carried out, the reaction is carried out, the bubble generation speed is observed to be slow, the feeding speed of ammonia water is regulated, the pH value of the reaction system is reduced to 6.0, the reaction is carried out for 2 hours after the complete feeding, the solid product is filtered out, washing and drying are carried out, and the product with the expression of NH is obtained ₄ Fe _0.4 Mn _0.6 PO ₄ H ₂ Ammonium ferromanganese O phosphate sample A1;

2) Calcining the ammonium ferromanganese phosphate sample A1 prepared in the step 1) for 4 hours at the temperature of 300 in an argon atmosphere to obtain ferric ferromanganese phosphate powder;

3) According to the molar ratio (Fe+Mn): li=1:1.02, the mass of glucose is 10% of the mass of the ferromanganese hydrogen phosphate powder, lithium carbonate and glucose prepared in the step 2) are dispersed in water, so that the total mass of the ferromanganese hydrogen phosphate powder, lithium carbonate and glucose solid accounts for 30% of the total mass of the solid and the solvent, and the product is sintered for 8 hours at 600 in argon atmosphere after sanding and spray drying, thus obtaining the product with the expression of LiFe _0.4 Mn _0.6 PO ₄ Lithium iron manganese phosphate sample C1.

Example 2

Stirring under nitrogen atmosphere17.22g of manganese metal powder and 7.5g of iron metal powder are weighed under the conditions of 600rpm and 40 and added into 1667mL of ammonium sulfate solution with the concentration of 0.3mol/L, 470mL of ammonium dihydrogen phosphate solution with the concentration of 1.0mol/L is added, 2mol/L of ammonia water solution is added, the feeding speed is controlled, the pH value of a reaction system is maintained to be 7.5, stirring is continuously carried out for reaction, the bubble generation rate is observed to be slow, the feeding speed of ammonia water is regulated to reduce the pH value of the reaction system to 6.5, stirring is continuously carried out for 4 hours after the feeding is complete, a solid product is filtered out, washing and drying are carried out, and the NH is obtained ₄ Fe _0.3 Mn _0.7 PO ₄ H ₂ Ammonium ferromanganese O phosphate sample A2;

2) Calcining the ammonium ferromanganese phosphate sample A2 prepared in the step 1) for 3 hours at the temperature of 350 in an argon atmosphere to obtain ferric ferromanganese phosphate powder;

3) According to the molar ratio (Fe+Mn): li=1:1.03, wherein the mass of sucrose is 5% of the mass of the ferromanganese hydrogen phosphate powder, lithium hydroxide and sucrose prepared in the step 2) are dispersed in ethanol, so that the total mass of the ferromanganese hydrogen phosphate powder, the lithium hydroxide and the sucrose accounts for 30% of the total mass of the solid and the solvent, and the product is sintered for 6 hours at 700 in argon atmosphere after sanding and spray drying, thus obtaining the product with the expression of LiFe _0.3 Mn _0.7 PO ₄ Lithium iron manganese phosphate sample C2.

Example 3

Under the conditions of nitrogen atmosphere, stirring speed of 500rpm and temperature of 30 , 19.67g of metal manganese powder and 5g of metal iron powder are weighed and added into 1667mL of ammonium sulfate solution with concentration of 0.3mol/L, 985mL of ammonium dihydrogen phosphate solution with concentration of 0.5mol/L is added, 2mol/L of ammonia water solution is added, the feeding speed is controlled, the pH value of a reaction system is maintained to be 7.5, continuous stirring is carried out, the reaction is carried out, the bubble generation speed is observed to be slow, the feeding speed of ammonia water is regulated, the pH value of the reaction system is reduced to 5.0, the reaction is carried out for 2 hours after the complete feeding, the solid product is filtered out, washing and drying are carried out, and the product with the expression of NH is obtained ₄ Fe _0.2 Mn _0.8 PO ₄ H ₂ Ammonium ferromanganese O phosphate sample A3;

2) Calcining the ammonium ferromanganese phosphate sample A3 prepared in the step 1) for 4 hours at 400 in an argon atmosphere to obtain ferromanganese hydrogen phosphate powder;

3) Dispersing the ferromanganese hydrogen phosphate powder, lithium hydroxide and glucose in the step 2) in water according to the molar ratio (Fe+Mn) of Li=1:1.03, wherein the mass of glucose is 5% of the mass of the ferromanganese hydrogen phosphate powder, so that the total mass of the ferromanganese hydrogen phosphate powder, the lithium hydroxide and the glucose solid accounts for 30% of the total mass of the solid and the solvent, and calcining for 6 hours at 800 in argon atmosphere after sanding and spray drying, thereby obtaining the product with the expression of LiFe _0.2 Mn _0.8 PO ₄ Lithium iron manganese phosphate sample C3.

Comparative example

1) Dissolving manganese sulfate and ferrous sulfate metal salt in water according to a molar ratio of 6:4 to obtain a base solution, and under a nitrogen atmosphere, performing the following steps: adding 0.5mol/L ammonium dihydrogen phosphate solution into the base solution at a molar ratio of P=1:1.1, controlling the stirring speed to be 400rpm, controlling the reaction temperature to be 60 , adding 1mol/L ammonia water solution, controlling the feeding speed to enable the pH value in the reaction system to be 6.0, continuously stirring and reacting for 2 hours after the feeding is complete, and obtaining the expression of NH after the reaction is finished, and performing solid-liquid separation, washing and drying ₄ Fe _0.4 Mn _0.6 PO ₄ H ₂ Ammonium ferromanganese O phosphate sample B1;

2) Calcining the ammonium ferromanganese phosphate sample B1 prepared in the step 1) at 300 for 4 hours in an argon atmosphere to obtain ferromanganese hydrogen phosphate powder;

3) According to the molar ratio (Fe+Mn): li=1:1.02, the mass of glucose is 10% of the mass of the ferromanganese hydrogen phosphate powder, lithium carbonate and glucose are dispersed in water, so that the total mass of the ferromanganese hydrogen phosphate powder, the lithium carbonate and the glucose accounts for 30% of the total mass of the solid and the solvent, and the product with the expression of LiFe is obtained through sanding, spray drying and calcination at 600 for 8 hours in Ar atmosphere _0.4 Mn _0.6 PO ₄ Lithium iron manganese phosphate sample D1.

Experimental example 1

The products of example 1, example 2 and example 3 were preparedThe obtained ferromanganese ammonium phosphate samples A1, A2 and A3 and the ferromanganese ammonium phosphate sample B1 prepared in the comparative example 1 are subjected to X-ray diffraction (XRD) characterization analysis, and the results are shown in figure 1, and as can be seen from figure 1, each characteristic diffraction peak of the ferromanganese ammonium phosphate samples A1, A2, A3 and B1 prepared in the examples 1, 2, 3 and 3 corresponds to the standard ferromanganese ammonium phosphate, so that the ferromanganese ammonium phosphate is successfully prepared and no impurity phase exists. Although the invention and the comparative example can successfully prepare the ferromanganese ammonium phosphate, the preparation process of the invention has extremely high atom economy, fe and Mn elements can be completely utilized and converted into products from metal powder, filtrate can be recycled, and the comparative example can inevitably generate a large amount of NH ₄ ⁺ SO ₄ ^2- And waste water of the waste water causes resource waste.

Experimental example 2

The results of Scanning Electron Microscope (SEM) observation of the sample A1 of ferromanganese ammonium phosphate prepared in example 1 and the sample B1 of ferromanganese ammonium phosphate prepared in comparative example 1 are shown in fig. 2 and 3, and as can be seen from fig. 2: the sample A1 of the ammonium ferromanganese phosphate prepared in the example 1 has a nano-lamellar structure, the lamellar layer thickness is about 50nm, and as can be seen from FIG. 3: the comparative example was prepared so that the sample B1 of ferromanganese ammonium phosphate was not in a nano-sheet structure, and consisted of blocks stacked on each other, and the thickness of the single block was about 2-3 m. The morphology of the precursor has important influence on the morphology and performance of the positive electrode material, and the nano sheet-like structure ferromanganese ammonium phosphate prepared by the method can be crushed into particles with finer three-dimensional dimensions through the sanding process, so that Li can be shortened ⁺ The transmission path of the lithium iron manganese phosphate material is favorable for improving the electrochemical performance of the lithium iron manganese phosphate material, and the three scales of the ammonium iron manganese phosphate prepared by the comparative example are all in micron order, and particles with small particle size are difficult to obtain by the same sanding process, so that the precursor of the ammonium iron manganese phosphate prepared by the invention is more excellent in shape.

Experimental example 3

The lithium iron manganese phosphate sample C1 prepared in example 1 and the lithium iron manganese phosphate sample D1 prepared in comparative example 1 were subjected to X-ray diffraction (XRD) characterization analysis, and as shown in fig. 4, as can be seen from fig. 4, each of the characteristic diffraction peaks of the lithium iron manganese phosphate samples C1 and D1 prepared in example 1 and comparative example corresponds to standard lithium iron manganese phosphate, which indicates that lithium iron manganese phosphate was successfully prepared and that no impurity phase exists.

Experimental example 4

The results of Scanning Electron Microscope (SEM) observation of the lithium iron manganese phosphate sample C1 prepared in example 1 and the lithium iron manganese phosphate sample D1 prepared in comparative example 1 are shown in fig. 5 and 6, and as can be seen from fig. 5: the lithium iron manganese phosphate sample C1 prepared in the embodiment 1 consists of secondary spherical particles formed by primary particles, wherein the primary particles are fine and have uniform particle size distribution; as can be seen from fig. 6: the lithium iron manganese phosphate sample D1 prepared in the comparative example consists of secondary spherical particles formed by primary particles, and the primary particles have larger particle size and uneven distribution; further, the method is illustrated that the preparation of the lithium iron manganese phosphate by adopting the ammonium iron manganese phosphate precursor with the nano lamellar morphology can effectively reduce the particle size in the product, the fine particles shorten the path of lithium ion transmission, and the discharge specific capacity and the rate capability of the lithium iron manganese phosphate material are improved.

Experimental example 5

The lithium iron manganese phosphate material sample C1 prepared in the embodiment 1 of the invention and the lithium iron manganese phosphate material sample D1 prepared in the comparative example are used as positive electrode materials of lithium ion batteries to prepare and assemble CR2032 button batteries, and a new battery test system is used for testing the charge and discharge performance of the batteries:

1. preparation of button cell:

grinding a lithium iron manganese phosphate material and a conductive agent Super P in a mortar for 20 minutes to uniformly mix the materials, then adding a binder polyvinylidene fluoride (PVDF) solution and a proper amount of Nitrogen Methyl Pyrrolidone (NMP) solvent, grinding for 10 minutes, uniformly coating the obtained slurry on a carbon-coated aluminum foil, drying the aluminum foil in a vacuum oven at 120 for 8 hours, and then performing punch forming by a punching machine to obtain a round positive electrode plate with the diameter of 12mm, wherein the mass ratio of the lithium iron manganese phosphate material to the conductive agent to the binder is 8:1:1, a step of; the positive electrode plate is taken as a positive electrode, the metal lithium plate is taken as a negative electrode, the polypropylene porous membrane is taken as a diaphragm, equal amount of mixed liquid of 1mol/L LiPF6, ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) is taken as electrolyte, and a 2032 button cell is formed in a glove box filled with argon.

The battery with the lithium iron manganese phosphate material sample prepared in example 1 as the battery positive electrode material is used as the test battery 1, and the battery with the lithium iron manganese phosphate material sample prepared in comparative example as the battery positive electrode material is used as the test battery 2.

2. Performance test and results:

(1) The test battery 1 and the test battery 2 are respectively subjected to constant current charge and discharge test under the multiplying power of 0.2C, the voltage test range is 2.0-4.5V, and the result is shown in figure 7; as shown in FIG. 7, the two are at 3.5V, 4.1V (vs. Li ⁺ near/Li) there are two pairs of typical charge-discharge platforms, corresponding to Fe ²⁺ /Fe ³⁺ Mn ²⁺ /Mn ³⁺ Is a redox reaction of (a); the first discharge capacities of test cell 1 and test cell 2 at 0.2C were 148.24 mAh.g, respectively ^-1 And 144.95 mAh.g ^-1 Furthermore, the voltage difference between the charge and discharge platform of test cell 1 was slightly less than test cell 2, indicating that test cell 1 had less electrochemical polarization.

(2) The specific capacities of the test cells 1 and 2 were measured at respective rates of 0.2C, 0.5C, 1C, 2C, 5C, and 10C, and as shown in fig. 8, it was found from fig. 8 that the specific capacities of the test cells 1 at respective rates of 0.2C, 0.5C, 1C, 2C, 5C, and 10C were 148.24mahg ^-1 146.65mAhg ^-1 144.90mAhg ^-1 141.28mAhg ^-1 136.08mAhg ^-1 130.30mAhg ^-1 Specific discharge capacities of the test battery 2 at rates of 0.2C, 0.5C, 1C, 2C, 5C, and 10C were 144.95 mAh.g, respectively ^-1 139.94mAhg ^-1 132.99mAhg ^-1 127.16mAhg ^-1 112.62mAhg ^-1 92.07mAhg ^-1 The method comprises the steps of carrying out a first treatment on the surface of the As can be seen from the above test results, even at low rates, both have comparable specific discharge capacities, but as the rates increase, the difference in specific discharge capacities between the two increases more and more, and the test battery 1 has more excellent rate than the test battery 2Can further illustrate that the lithium iron manganese phosphate prepared by the invention has more excellent specific discharge capacity and rate capability, which is due to the fact that the lithium iron manganese phosphate material has finer primary particles, thereby leading Li to ⁺ With a shorter diffusion path.

It should be understood that the foregoing description is only a preferred embodiment of the present invention, and not intended to limit the invention to the particular embodiment, but it is to be understood that the invention may be embodied with the technical solutions described in the foregoing embodiments, and that several simple deductions, substitutions, or equivalent substitutions of some technical features may be made by those skilled in the art without departing from the spirit and principles of the present invention, and any modifications, equivalent substitutions, improvements, etc. made in the foregoing embodiments are intended to be included in the scope of the present invention.

Claims

1. A preparation method of ammonium ferromanganese phosphate is characterized in that: the method comprises the following steps: under the inert atmosphere and stirring conditions, adding iron powder and manganese powder with the molar ratio of 1.5-9:1 into a proper amount of ammonium salt solution, then adding a solution containing a metal ion-free phosphorus source and an ammonium source, adding ammonia water to keep the pH of a reaction system weakly alkaline, continuously stirring for reaction, keeping the reaction system at a low bubble generation rate, adjusting the addition amount of the ammonia water to keep the pH of the reaction system weakly acidic, continuously stirring until the reaction is finished, filtering out a solid product after the reaction, washing and drying to obtain the manganese ferric ammonium phosphate.

2. The method for preparing the ammonium ferromanganese phosphate according to claim 1, which is characterized in that: the inert atmosphere is argon or nitrogen, the reaction stirring speed is 300-600rpm, the reaction temperature is 25-80 , the reaction time after complete feeding is 1-4h, and the alkalescence is that: the pH value is 7.0< and less than or equal to 8.5, and the weak acidity is as follows: the pH value is more than or equal to 5.0 and less than or equal to 6.5.

3. The method for preparing the ammonium ferromanganese phosphate according to claim 1, which is characterized in that: the ammonium salt solution is one or more of ammonium sulfate solution, ammonium chloride solution and ammonia water, the solution containing the metal ion-free phosphorus source and the ammonium source is one or more of ammonium phosphate solution, monoammonium phosphate solution and diammonium phosphate solution, and the molar quantity of the phosphorus source and the ammonium source in the solution containing the metal ion-free phosphorus source and the ammonium source is 1-1.2 times of the total molar quantity of the manganese powder and the iron powder.

4. The method for preparing the ammonium ferromanganese phosphate according to claim 1, which is characterized in that: the concentration of the ammonium salt solution is 0.1-1mol/L, the concentration of the solution containing the metal ion-free phosphorus source and the ammonium source is 0.5-1mol/L, and the concentration of the ammonia water is 1-2mol/L.

5. An ammonium ferromanganese phosphate, characterized in that: prepared by the method of any one of claims 1-5, having the formula NH ₄ Fe _x Mn _1-x PO ₄ 0<x0.4

6. A preparation method of lithium iron manganese phosphate is characterized in that: the method comprises the following steps:

7. The method for preparing lithium iron manganese phosphate according to claim 6, wherein the method comprises the following steps: in the step 2), the lithium source is one or more of lithium carbonate, lithium hydroxide and lithium acetate, the carbon source is one or more of glucose, sucrose, starch and cellulose, the molar weight of the lithium source is 1-1.03 times of the total molar weight of iron and manganese in the manganese iron hydrogen phosphate, and the mass of the carbon source is 1-20% of the mass of the manganese iron hydrogen phosphate powder.

8. The method for preparing lithium iron manganese phosphate according to claim 6, wherein: in the step 2), the solvent is at least one of water and ethanol, and the total mass of the ferric manganese hydrogen phosphate powder, the lithium source and the carbon source solid accounts for 20-40% of the total mass of the solid and the solvent.

9. A lithium iron manganese phosphate, characterized in that: prepared by the method of any one of claims 7-9, having the chemical formula LiFe _y Mn _1-y PO ₄ 0<y0.4

10. Use of the lithium iron manganese phosphate according to claim 9 in a positive electrode material of a lithium ion battery.