CN117440928A

CN117440928A - Manganese iron phosphate precursor, manganese iron lithium phosphate positive electrode material, preparation method and application

Info

Publication number: CN117440928A
Application number: CN202380010870.4A
Authority: CN
Inventors: 李爱霞; 谢英豪; 余海军; 李长东
Original assignee: Hunan Brunp Recycling Technology Co Ltd; Guangdong Brunp Recycling Technology Co Ltd
Current assignee: Hunan Brunp Recycling Technology Co Ltd; Guangdong Brunp Recycling Technology Co Ltd
Priority date: 2023-09-13
Filing date: 2023-09-13
Publication date: 2024-01-23

Abstract

The disclosure belongs to the technical field of lithium batteries, and particularly relates to a manganese iron phosphate precursor, a manganese iron phosphate lithium anode material, a preparation method and application. According to the method, by utilizing the characteristic that Ksp of iron phosphate and Ksp of aluminum phosphate precipitation are similar, the iron phosphate and the aluminum phosphate are synthesized firstly by a coprecipitation method, so that the iron phosphate and the aluminum phosphate are mixed uniformly, then, the iron phosphate and the manganese chloride react to prepare a stable manganese phosphate iron precursor, and aluminum chloride generated in the reaction process can be volatilized directly. The synthesis route provided by the disclosure can effectively solve the problem of non-uniformity of the manganese phosphate precursor caused by directly adopting manganese phosphate and ferric phosphate to carry out coprecipitation, the iron-manganese ratio of the prepared manganese phosphate precursor is closer to a target value, and the specific capacity and the cycle performance of the lithium manganese phosphate further prepared by utilizing the precursor can be effectively improved. The whole process flow is simple and easy to implement, the process cost is low, and the method has very good industrial application prospect.

Description

Manganese iron phosphate precursor, manganese iron lithium phosphate positive electrode material, preparation method and application

Technical Field

The disclosure belongs to the technical field of lithium batteries, and particularly relates to a manganese iron phosphate precursor, a manganese iron phosphate lithium anode material, a preparation method and application.

Background

Along with the wider and wider application range of the lithium ion battery in society, the requirements of people on the battery are diversified, such as higher energy density, higher rate capability, good low-temperature performance and the like. The energy density of the lithium ion battery depends on the battery material, and currently commonly used lithium ion battery anode materials include ternary materials (such as nickel cobalt lithium manganate) and lithium iron phosphate. At present, the energy density of the lithium iron phosphate battery is close to the limit of a theoretical value, and the lifting space is relatively small. In order to further improve the electrochemical performance of lithium ion batteries, in recent years, it is considered to select a polyanionic material lithium manganese phosphate with an olivine structure to replace the lithium iron phosphate battery. However, lithium manganese phosphate has lower electron conductivity and ion diffusion coefficient than lithium iron phosphate, which limits the application of the battery at high rate and low temperature. Meanwhile, the manganese ions have the problems of Jahn-Teller effect, ion elution and the like.

In order to alleviate the problems, the advantages of lithium iron phosphate, lithium manganese phosphate and the like are combined, and the two materials are compounded to form a lithium iron manganese phosphate solid solution (LiMn _x Fe _1-x PO ₄ X is atomic ratio) is a more efficient method. The lithium iron manganese phosphate has the same crystal structure as that of the lithium iron phosphate, and the discharge voltage of the battery is higher (may be 4.1V) due to the manganese ions, so that the energy density of the lithium iron manganese phosphate is higher than that of the phosphoric acidThe iron lithium is about 20% higher, so the solid solution material is expected to replace the iron lithium phosphate to be used as the anode material of the next generation lithium ion battery for large-scale application.

At present, most of the methods for producing the lithium iron manganese phosphate on a large scale are high-temperature solid phase methods: mixing raw materials such as a lithium source, a manganese source, an iron source, a phosphorus source, a carbon source and the like according to a certain proportion, ball milling and drying, heating to a set temperature in an inert or reducing atmosphere in a muffle furnace, and reacting for a period of time to obtain the lithium manganese iron phosphate material. However, the method is difficult to accurately control the proportion of iron and manganese, and transition metal is difficult to uniformly distribute in a main structure of the material, so that Mn is caused ³⁺ The Jahn-Teller effect is severe, affecting the cycle and rate performance of the battery. K due to ferric phosphate and manganese phosphate _SP The values are greatly different, and the co-precipitation is difficult to form the manganese iron phosphate precursor under the conventional liquid phase reaction system, and although some students can successfully synthesize the manganese iron phosphate precursor under the severe conditions, the process is complex, the cost is high, and the method is difficult to apply to industrial production.

Therefore, it is needed to develop a simple and easy synthesis method with low process cost, and make the iron-manganese ratio in the prepared lithium iron manganese phosphate closer to the target value, so as to improve the electrochemical performance of the high-manganese iron manganese phosphate battery.

In view of this, the present disclosure is specifically proposed.

Disclosure of Invention

The purpose of the present disclosure includes providing a manganese iron phosphate precursor, a manganese iron lithium phosphate positive electrode material, a preparation method and application, and aims to significantly improve the specific capacity and the cycle performance of a manganese iron lithium phosphate battery.

In order to achieve the above object of the present disclosure, the following technical solutions may be adopted:

in a first aspect, the present disclosure provides a method for preparing a manganese iron phosphate precursor, comprising: mixing ferric aluminum phosphate obtained by a coprecipitation method with manganese chloride and a fluxing agent, and reacting at 185-300 ℃.

In some embodiments of the present disclosure, a process for utilizing an iron aluminum phosphate to manganese iron phosphate precursor includes: mixing ferric aluminum phosphate, manganese chloride and a fluxing agent, reacting at 185-300 ℃ to obtain a dihydrate manganese iron phosphate precursor, and carrying out high-temperature treatment on the dihydrate manganese iron phosphate precursor to remove crystal water in the dihydrate manganese iron phosphate precursor.

In some embodiments of the present disclosure, the fluxing agent is a mixture of potassium chloride and sodium chloride.

In some embodiments of the present disclosure, in the fluxing agent, the mass fraction of potassium chloride is 40% -55%, and the mass fraction of sodium chloride is 45% -60%.

In some embodiments of the present disclosure, the molar ratio of iron aluminum phosphate to the total amount of flux is 1: (0.4-0.8).

In some embodiments of the present disclosure, the molar ratio of iron aluminum phosphate to manganese chloride is 1: (1.5-1.7).

In some embodiments of the present disclosure, ferric aluminum phosphate is mixed with manganese chloride and a fluxing agent, reacted for 2h to 6h under the condition of 250 ℃ to 300 ℃ in an inert atmosphere, cooled, washed and dried to obtain the dihydrate manganese iron phosphate precursor.

In some embodiments of the present disclosure, the process of high temperature treatment includes: and (3) treating the dihydrate ferromanganese phosphate precursor for 1-4 hours at the temperature of 600-700 ℃.

In some embodiments of the present disclosure, the high temperature treatment is performed under an inert atmosphere.

In some embodiments of the present disclosure, the process of preparing the iron aluminum phosphate comprises: adding ferric salt solution, aluminum salt solution, phosphoric acid solution and precipitant solution into a reactor for coprecipitation reaction.

In some embodiments of the present disclosure, the molar ratio of iron, aluminum, and phosphorus elements in the reaction system is (0.5-0.8) by controlling the concentrations and addition rates of the iron salt solution, the aluminum salt solution, and the phosphorus source solution: (0.2-0.5): (1.0-1.1).

In some embodiments of the present disclosure, the reaction temperature of the coprecipitation reaction is 45 ℃ to 90 ℃ and the reaction time is 3h to 6h.

In some embodiments of the present disclosure, the pH of the coprecipitation reaction system is controlled to be 2.8 to 3.5 by controlling the rate of addition of the precipitant solution.

In some embodiments of the present disclosure, the precipitant solution is an aqueous ammonia solution having a concentration of 2mol/L to 6 mol/L.

In some embodiments of the present disclosure, during the reaction of the coprecipitation reaction, the rotation speed is controlled to be 100r/min to 400r/min, and washing and drying are performed after the reaction is completed.

In some embodiments of the present disclosure, the iron salt is selected from at least one of iron acetate, iron carbonate, iron oxalate, iron chloride, iron nitrate, and iron sulfate.

In some embodiments of the present disclosure, the aluminum salt is selected from at least one of aluminum nitrate, aluminum sulfate, aluminum chloride, and aluminum carbonate.

In some embodiments of the present disclosure, the phosphorus source is selected from at least one of phosphoric acid, ammonium phosphate, monoammonium phosphate, and monoammonium phosphate.

In a second aspect, the present disclosure provides a solution further comprising a manganese iron phosphate precursor, prepared by the preparation method in the above embodiment.

In a third aspect, the present disclosure provides a method for preparing a lithium iron manganese phosphate positive electrode material, including: the ferromanganese phosphate precursor and the lithium source in the above embodiment are used for reaction.

In some embodiments of the present disclosure, there is provided: mixing and calcining the manganese iron phosphate precursor, a lithium source and a carbon source, wherein the calcining temperature is controlled to be 800-900 ℃ and the calcining time is controlled to be 6-20 h.

In some embodiments of the present disclosure, the molar ratio of the lithium element to the total amount of ferromanganese is (1.0-1.2) by controlling the amounts of the ferromanganese phosphate precursor and the lithium source: 1.

in some embodiments of the present disclosure, the mass ratio of the amount of carbon source to the total amount of the manganese iron phosphate precursor and the lithium source is (5-13): 100.

in some embodiments of the present disclosure, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

In some embodiments of the present disclosure, the carbon source is selected from at least one of sucrose, glucose, soluble starch, citric acid, phenolic resin, graphite, and carbon black.

In some embodiments of the present disclosure, the calcination is performed under inert atmosphere conditions.

In a third aspect, the present disclosure provides a solution further including a lithium iron manganese phosphate positive electrode material, which is prepared by the preparation method in the above embodiment.

In a fourth aspect, the present disclosure provides a positive electrode sheet, including the lithium iron manganese phosphate positive electrode material in the above embodiment.

In a fifth aspect, the present disclosure provides a lithium battery, including the positive electrode sheet in the foregoing embodiment.

The method utilizes the characteristic that Ksp of ferric phosphate and Ksp of aluminum phosphate precipitation are similar, firstly synthesizes uniform ferric aluminum phosphate by a coprecipitation method, then utilizes ferric aluminum phosphate, manganese chloride and fluxing agent to react to prepare stable ferric manganese phosphate precursor, and aluminum chloride generated in the reaction process can be volatilized directly. The synthesis route provided by the disclosure can effectively solve the problem of non-uniformity of the manganese phosphate precursor caused by directly adopting manganese phosphate and ferric phosphate to carry out coprecipitation, the iron-manganese ratio of the prepared manganese phosphate precursor is closer to a target value, and the specific capacity and the cycle performance of the lithium manganese phosphate further prepared by utilizing the precursor can be effectively improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present disclosure and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person of ordinary skill in the art.

Fig. 1 is a process flow diagram of a method for preparing a manganese iron phosphate precursor provided in an embodiment of the disclosure;

fig. 2 is a process flow diagram of a method for preparing a lithium iron manganese phosphate positive electrode material according to an embodiment of the present disclosure;

FIG. 3 is an EDS diagram of the precursor prepared in example 1.

Detailed Description

Embodiments of the present disclosure will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present disclosure and should not be construed as limiting the scope of the present disclosure. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

The endpoints of the ranges and any values disclosed in this disclosure are not limited to the precise range or value, and such range or value should be understood to encompass values approaching those range or value. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

The embodiment of the disclosure provides a preparation method of a lithium iron manganese phosphate positive electrode material, as shown in fig. 1, firstly, a synthesis route provided by the disclosure is adopted to synthesize a precursor of manganese iron phosphate, and as the synthesis route is improved, the uniformity of the precursor is higher, and the proportion of iron and manganese is closer to a target value. Referring to fig. 2, the specific capacity and cycle performance of the positive electrode material can be significantly improved by preparing the lithium iron manganese phosphate positive electrode material by reacting the lithium source with the manganese iron phosphate precursor.

The method specifically comprises the following steps:

s1, preparing aluminum iron phosphate

The coprecipitation method is adopted to prepare the aluminum ferric phosphate, the specific operation process is not limited, and the metal iron and aluminum can be deposited in an aqueous solution system by controlling the pH value. By utilizing the characteristic that Ksp of ferric phosphate and Ksp of aluminum phosphate precipitate are similar, ferric phosphate aluminum is synthesized firstly by a coprecipitation method, so that ferric phosphate aluminum is uniformly mixed.

In some embodiments of the present disclosure, a process for preparing aluminum iron phosphate comprises: adding ferric salt solution, aluminum salt solution, phosphoric acid solution and precipitant solution into a reactor for coprecipitation reaction. The ferric salt solution, the aluminum salt solution, the phosphorus source solution and the precipitator solution can be added in a parallel flow mode, or the ferric salt solution and the aluminum salt solution can be mixed and then added into the reactor in parallel flow with the phosphorus source solution and the precipitator solution, so that the reaction can be carried out more uniformly.

In some embodiments of the present disclosure, the iron salt is selected from at least one of iron acetate, iron carbonate, iron oxalate, iron chloride, iron nitrate, and iron sulfate, and may be any one or several of the above; the aluminum salt is at least one selected from aluminum nitrate, aluminum sulfate, aluminum chloride and aluminum carbonate, and can be any one or more of the above; the phosphorus source is at least one selected from phosphoric acid, ammonium phosphate, monoammonium phosphate and monoammonium phosphate, and can be any one or more of the above. In actual operation, the ferric salt, the aluminum salt and the phosphorus source are respectively mixed and dissolved with water, the ferric salt solution and the aluminum salt solution are added into the reactor, and then the phosphorus source solution and the precipitant solution are added dropwise.

Further, the kind of the precipitant solution is not limited, and may be an aqueous ammonia solution, but is not limited thereto. The concentration of the aqueous ammonia solution may be 2mol/L to 6mol/L, for example, 2mol/L, 3mol/L, 4mol/L, 5mol/L, 6mol/L, etc.

In some embodiments of the present disclosure, the molar ratio of iron, aluminum, and phosphorus elements in the reaction system is (0.5-0.8) by controlling the concentrations and addition rates of the iron salt solution, aluminum salt solution, and phosphorus source solution: (0.2-0.5): (1.0-1.1) so that the finally prepared positive electrode material has more excellent electrochemical performance. Specifically, the molar ratio of iron, aluminum, and phosphorus elements may be 0.5:0.5:1.0, 0.6:0.4:1.0, 0.7:0.3:1.0, 0.8:0.2:1.0, 0.5:0.5:1.05, 0.6:0.4:1.05, 0.7:0.3:1.05, 0.8:0.2:1.05, 0.5:0.5:1.1, 0.6:0.4:1.1, 0.7:0.3:1.1, 0.8:0.2:1.1, etc.

In some embodiments of the present disclosure, the reaction temperature of the coprecipitation reaction is 45 ℃ to 90 ℃, the reaction time is 3h to 6h, and the rotation speed is controlled to be 100r/min to 400r/min; meanwhile, the pH value of the coprecipitation reaction system is 2.8-3.5 by controlling the adding rate of the precipitant solution. By further controlling the reaction conditions of coprecipitation, the reaction is fully carried out, and after the reaction is completed, washing and drying are carried out, so that a uniform product is obtained.

Specifically, the reaction temperature of the coprecipitation reaction may be 45 ℃, 50 ℃, 60 ℃, 70 ℃,80 ℃, 90 ℃, etc.; the reaction time can be 3h, 4h, 5h, 6h and the like; the control rotation speed can be 100r/min, 200r/min, 300r/min, 400r/min and the like; the pH of the coprecipitation reaction system may be 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, etc.

S2, preparing a manganese iron phosphate precursor

Reacting ferric aluminum phosphate with manganese chloride to prepare a ferric manganese phosphate precursor, preparing a stable ferric manganese phosphate precursor by utilizing the reaction of ferric aluminum phosphate and manganese chloride, wherein aluminum chloride generated in the reaction process can be directly volatilized.

It should be noted that if co-precipitation is directly performed by using manganese phosphate and ferric phosphate, the problem of non-uniformity of the precursor of manganese ferric phosphate is caused, and the synthesis route provided by the disclosure can effectively avoid the problem, so that the ratio of iron to manganese of the prepared precursor of manganese ferric phosphate is closer to the target value, and the specific capacity and the cycle performance of the lithium manganese ferric phosphate further prepared by using the precursor can be effectively improved.

In some embodiments of the present disclosure, a process for utilizing an iron aluminum phosphate to manganese iron phosphate precursor includes: mixing ferric aluminum phosphate, manganese chloride and a fluxing agent, reacting at 185-300 ℃ to obtain a dihydrate manganese iron phosphate precursor, and performing high-temperature treatment on the dihydrate manganese iron phosphate precursor to remove crystal water in the dihydrate manganese iron phosphate precursor to obtain the manganese iron phosphate precursor. The addition of the fluxing agent can reduce the eutectic point, so that the reaction can be carried out at a lower temperature, and a more stable ferric manganese phosphate precursor is formed after low-temperature heat treatment.

Specifically, the reaction temperature for preparing the manganese iron phosphate dihydrate precursor may be 185 ℃, 200 ℃, 250 ℃, 300 ℃ or the like.

In some embodiments of the present disclosure, the fluxing agent is a mixture of potassium chloride and sodium chloride, and the use of a mixture of potassium chloride and sodium chloride is effective to reduce the reaction temperature. Further, in the flux, the mass fraction of potassium chloride is 40% -55%, for example, 40%, 45%, 50%, 55%, etc., the mass fraction of sodium chloride is 45% -60%, for example, 45%, 50%, 55%, 60%, etc., and the total amount of potassium chloride and sodium chloride is 100%.

In some embodiments of the present disclosure, the molar ratio of iron aluminum phosphate to the total amount of flux is 1: (0.4-0.8), the molar ratio of the ferric aluminum phosphate to the manganese chloride is 1: (1.5-1.7). By further controlling the use amount of the raw materials, the prepared precursor has better uniformity, and the electrochemical performance of the finally prepared anode material is improved. Specifically, the molar ratio of the iron aluminum phosphate to the total amount of the fluxing agent can be 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8 and the like, and the molar ratio of the iron aluminum phosphate to the manganese element in the manganese chloride can be 1:1.5, 1:1.6, 1:1.7 and the like.

In the process of synthesizing the ferric manganese phosphate dihydrate precursor, the specific operation process can adopt the following modes: mixing ferric aluminum phosphate, manganese chloride and a fluxing agent, reacting for 2-6 hours in an inert atmosphere (such as nitrogen, argon and the like) at the temperature of 250-300 ℃, cooling, cleaning and drying to obtain the dihydrate manganese iron phosphate precursor. Specifically, the reaction time may be 2h, 3h, 4h, 5h, 6h, or the like.

In some embodiments of the present disclosure, the process of high temperature treatment includes: and (3) treating the ferric manganese phosphate dihydrate precursor for 1-4 hours at 600-700 ℃ in an inert atmosphere (such as nitrogen, argon and the like) so as to sufficiently remove crystal water in the precursor. Specifically, the treatment temperature may be 600 ℃, 650 ℃, 700 ℃, etc., and the treatment time may be 1h, 2h, 3h, 4h, etc.

S3, preparing lithium iron manganese phosphate anode material

And (3) reacting the manganese iron phosphate precursor prepared in the step (S2) with a lithium source to prepare the manganese iron phosphate lithium anode material.

In some embodiments of the present disclosure, there is provided: mixing and calcining the manganese iron phosphate precursor, a lithium source and a carbon source, wherein the calcining temperature is controlled to be 800-900 ℃ and the calcining time is controlled to be 6-20 h. And doping lithium into the manganese iron phosphate precursor, adding a carbon source into the manganese iron phosphate precursor, and calcining at high temperature to obtain the manganese iron phosphate anode material, wherein the carbon source is carbonized and coated on the surface of the manganese iron phosphate, so that the crystal structure of the manganese iron phosphate is further stabilized.

Specifically, the calcination temperature may be 800 ℃, 850 ℃, 900 ℃, etc., and the calcination time may be 6 hours, 8 hours, 10 hours, 15 hours, 20 hours, etc.

In some embodiments of the present disclosure, the molar ratio of the lithium element to the total amount of ferromanganese is (1.0-1.2) by controlling the amounts of the ferromanganese phosphate precursor and the lithium source: 1, the mass ratio of the dosage of the carbon source to the total amount of the manganese iron phosphate precursor and the lithium source is (5-13): 100. by further controlling the dosage ratio of the raw materials, the reaction is more sufficient, the carbon coating amount is more appropriate, and the cycle performance of the positive electrode material is further improved.

Specifically, the molar ratio of lithium element to total ferromanganese can be 1.0:1, 1.1:1, 1.2:1, etc. by controlling the dosage of the ferromanganese phosphate precursor and the lithium source; the mass ratio of the amount of carbon source to the total amount of the manganese iron phosphate precursor and the lithium source may be 5:100, 8:100, 10:100, 13:100, etc.

In some embodiments of the present disclosure, the lithium source is at least one selected from the group consisting of lithium carbonate, lithium hydroxide, and lithium acetate, and may be any one or several of the above; the carbon source is at least one selected from sucrose, glucose, soluble starch, citric acid, phenolic resin, graphite and carbon black, and can be any one or more of the above.

In some embodiments of the present disclosure, the calcination is performed under an inert atmosphere, which is not limited in kind and may be nitrogen, argon, or the like.

The preparation method of the lithium iron manganese phosphate positive electrode material provided by the embodiment of the disclosure avoids the defects of high process cost and relatively complex process in the traditional process, and can greatly reduce energy consumption, reduce synthesis cost and simplify the manufacturing process.

The embodiment of the disclosure also provides a lithium iron manganese phosphate anode material, which is prepared by the preparation method, and can obtain lithium iron manganese phosphate with a target iron-manganese ratio and can also improve compaction density and energy density.

The embodiment of the disclosure also provides a positive electrode plate, which comprises the above lithium iron manganese phosphate positive electrode material, and can be prepared by adopting a conventional preparation method, for example, the lithium iron manganese phosphate positive electrode material, a conductive agent, a dispersing agent, a binder and the like are formed into positive electrode slurry, the positive electrode slurry is coated on a positive electrode current collector, and a coating is formed after drying. The electrochemical performance of the prepared positive electrode plate is improved due to the improvement of the performance of the positive electrode material.

The embodiment of the disclosure also provides a lithium battery, which comprises the positive electrode plate, and can also comprise a negative electrode plate, electrolyte, a diaphragm and the like to form a complete lithium battery. The lithium battery has more excellent electrochemical performance due to the improvement of the performance of the positive electrode material.

The features and capabilities of the present disclosure are described in further detail below in connection with the examples.

Example 1

The embodiment provides a preparation method of a manganese iron phosphate precursor and a manganese iron lithium phosphate positive electrode material, which comprises the following steps:

(1) Preparing 0.5mol/L aqueous solution of sulfuric acid, 0.5mol/L aqueous solution of aluminum sulfate, 1mol/L aqueous solution of phosphoric acid and 4mol/L aqueous solution of ammonia, adding the 4 solutions into a coprecipitation reactor in parallel under stirring to carry out coprecipitation reaction, controlling the flow rates of the aqueous solution of sulfuric acid, the aqueous solution of aluminum sulfate and the aqueous solution of phosphoric acid to be 120mL/min, controlling the adding speed of the aqueous ammonia to ensure that the pH value of the reaction solution to be 3.1+/-0.2, the reaction temperature to be 70 ℃, the stirring speed to be 200r/min, washing the reaction solution with deionized water after 4 hours, and drying the reaction solution at 80 ℃ for 6 hours to obtain the aluminum ferric phosphate.

(2) Uniformly mixing the ferric aluminum phosphate, the manganese chloride and the fluxing agent in the step (1) according to the molar ratio of 1:1.6:0.6, putting the mixture into a muffle furnace, introducing nitrogen gas, preserving heat for 4 hours at the temperature of 250 ℃, cooling the mixture along with the furnace, cleaning the mixture by using deionized water, and drying the mixture at the temperature of 100 ℃ for 4 hours to obtain the manganese iron dihydrate precursor. Wherein the fluxing agent is a mixture of 50% by mass of potassium chloride and 50% by mass of sodium chloride. And (3) under the nitrogen atmosphere, preserving the heat of the dihydrate ferromanganese phosphate precursor for 3 hours at the temperature of 650 ℃, and removing the crystal water of the dihydrate ferromanganese phosphate precursor to obtain the ferromanganese phosphate precursor.

(3) And (3) weighing lithium carbonate and the manganese iron phosphate precursor in the step (2), uniformly mixing according to the molar ratio of the lithium source to the manganese iron phosphate precursor of 1.2:1, adding 7wt% of sucrose (namely, the mass ratio of the sucrose to the total amount of the lithium source and the manganese iron phosphate precursor is 7:100), heating to 850 ℃ in a nitrogen atmosphere, calcining for 10 hours, and cooling to room temperature to obtain the manganese iron phosphate lithium anode material.

The EDS diagram of the precursor prepared in example 1 is shown in fig. 3, and it can be seen from the EDS diagram that the manganese element and the iron element in the precursor are uniformly distributed, and the atomic percentage contents of the manganese element, the iron element, the phosphorus element and the oxygen element in the precursor are respectively 20.83%,19.10%,19.61% and 40.46%.

Example 2

(1) Preparing 0.6mol/L aqueous solution of ferric nitrate, 0.4mol/L aqueous solution of aluminum nitrate, 1.1mol/L aqueous solution of monoammonium phosphate and 2mol/L aqueous solution of ammonia respectively, adding the 4 solutions into a coprecipitation reactor in parallel under stirring to carry out coprecipitation reaction, controlling the flow rates of the aqueous solution of ferric sulfate, the aqueous solution of aluminum sulfate and the aqueous solution of phosphoric acid to be 120mL/min, controlling the adding speed of the aqueous ammonia to ensure that the pH=2.8+/-0.2 of the reaction solution, the reaction temperature to be 90 ℃, the stirring speed to be 400r/min, washing with deionized water after 3 hours of reaction, and drying at 80 ℃ for 6 hours to obtain the ferric aluminum phosphate.

(2) The iron aluminum phosphate, the manganese chloride and the fluxing agent in the step (1) are mixed according to the mol ratio of 1:1.7: and 0.8, uniformly mixing, putting into a muffle furnace, introducing nitrogen, preserving heat for 2 hours at the temperature of 300 ℃, cooling along with the furnace, cleaning with deionized water, and drying for 4 hours at the temperature of 100 ℃ to obtain the dihydrate manganese iron phosphate precursor. Wherein the fluxing agent is a mixture of 55% by mass of potassium chloride and 45% by mass of sodium chloride. And (3) under the nitrogen atmosphere, preserving the heat of the dihydrate ferromanganese phosphate precursor for 1h at the temperature of 700 ℃ and removing the crystal water of the dihydrate ferromanganese phosphate precursor to obtain the ferromanganese phosphate precursor.

(4) And (3) weighing lithium carbonate and the manganese iron phosphate precursor in the step (3), uniformly mixing according to the molar ratio of a lithium source to the manganese iron phosphate precursor of 1.2:1, adding 13wt% of sucrose, heating to 900 ℃ in a nitrogen atmosphere, calcining for 6 hours, and cooling to room temperature to obtain the manganese iron lithium phosphate anode material.

Example 3

(1) Preparing 0.8mol/L aqueous solution of sulfuric acid, 0.2mol/L aqueous solution of aluminum sulfate, 1.1mol/L aqueous solution of phosphoric acid and 6mol/L aqueous solution of ammonia respectively, adding the 4 solutions into a coprecipitation reactor in parallel under stirring to carry out coprecipitation reaction, controlling the flow rates of the aqueous solution of sulfuric acid, the aqueous solution of aluminum sulfate and the aqueous solution of phosphoric acid to be 120mL/min, controlling the adding speed of the aqueous ammonia to ensure that the pH value of the reaction solution to be 3.5+/-0.2, the reaction temperature to be 45 ℃, the stirring speed to be 100r/min, washing the reaction solution with deionized water after the reaction is carried out for 6 hours, and drying the reaction solution at 80 ℃ for 6 hours to obtain the ferric aluminum phosphate.

(2) The iron aluminum phosphate, the manganese chloride and the fluxing agent in the step (1) are mixed according to the mol ratio of 1:1.5: and 0.4, uniformly mixing, putting into a muffle furnace, introducing nitrogen, preserving heat for 6 hours at 185 ℃, cooling along with the furnace, cleaning with deionized water, and drying for 4 hours at 100 ℃ to obtain the dihydrate manganese iron phosphate precursor. Wherein the fluxing agent is a mixture of 40% by mass of potassium chloride and 60% by mass of sodium chloride. And (3) under the nitrogen atmosphere, preserving the heat of the dihydrate ferromanganese phosphate precursor for 4 hours at the temperature of 600 ℃ and removing the crystal water of the dihydrate ferromanganese phosphate precursor to obtain the ferromanganese phosphate precursor.

(3) And (3) weighing lithium carbonate and the manganese iron phosphate precursor in the step (2), uniformly mixing according to the molar ratio of a lithium source to the manganese iron phosphate precursor of 1:1, adding 5wt% of sucrose, heating to 800 ℃ in a nitrogen atmosphere, calcining for 20 hours, and cooling to room temperature to obtain the manganese iron lithium phosphate anode material.

Example 4

The only difference from example 1 is that: the cosolvent in step (2) is replaced by sodium chloride.

Example 5

The only difference from example 1 is that: the reaction temperature in step (2) was 400 ℃.

Comparative example 1

The comparative example provides a preparation method of a lithium iron manganese phosphate positive electrode material, which comprises the following steps:

(1) Preparing 0.5mol/L of aqueous solution of ferric sulfate, 0.5mol/L of aqueous solution of manganese sulfate, 1mol/L of aqueous solution of phosphoric acid and 4mol/L of aqueous solution of ammonia, adding the 4 solutions into a coprecipitation reactor in parallel under stirring to carry out coprecipitation reaction, maintaining the ratio of Fe to Mn of metal salt to be 1:1 by controlling the flow, controlling the adding speed of the aqueous ammonia to ensure that the pH value of the reaction solution is=3.1+/-0.2, the reaction temperature is 70 ℃, the stirring speed is 200r/min, washing with deionized water after 4 hours, and drying at 80 ℃ for 6 hours to obtain the manganese iron phosphate precursor.

(2) And (3) weighing lithium carbonate and the manganese iron phosphate precursor in the step (1), uniformly mixing according to the molar ratio of a lithium source to the manganese iron phosphate precursor of 1.2:1, adding 7wt% of sucrose, heating to 850 ℃ in a nitrogen atmosphere, calcining for 10 hours, and cooling to room temperature to obtain the manganese iron lithium phosphate anode material.

Comparative example 2

taking lithium carbonate, ferric sulfate, manganese nitrate and ammonium phosphate as raw materials, weighing the raw materials according to the stoichiometric ratio of 1.2:0.5:0.5:1 of the molar ratio of lithium to iron to manganese to phosphorus, adding 7% of sucrose as a carbon source after uniformly mixing, calcining for 20 hours at 850 ℃ under the protection of nitrogen atmosphere according to a high-temperature solid-phase method synthesis route to obtain the lithium manganese iron phosphate anode material, wherein the molar ratio of iron to manganese element is 1:1.

Comparative example 3

The only difference from example 1 is that: no fluxing agent is added in step (2).

Comparative example 4

The only difference from example 1 is that: the reaction temperature in step (2) was 170 ℃.

Test example 1

The performance of the lithium manganese iron phosphate cathode materials prepared in the examples and comparative examples was tested, and the results are shown in table 1.

The testing method comprises the following steps: the lithium iron manganese phosphate anode materials obtained in the examples and the comparative examples are mixed by taking acetylene black as a conductive agent and PVDF as a binder according to the mass ratio of 8:1:1, and a certain amount of organic solvent NMP is added, and the mixture is coated on an aluminum foil after stirring to prepare the anode sheet. A negative electrode adopts a metal lithium sheet; the separator is a Celgard2400 polypropylene porous membrane; the electrolyte is prepared from EC, DMC and EMC in a mass ratio of 1:1:1, and the solute is LiPF ₆ ，LiPF ₆ The concentration of (2) is 1.0mol/L; inside the glove box, 2023 type button cell was assembled. Performing charge-discharge cycle performance test on the battery, and testing the discharge specific capacities of 0.1C and 1C within the range of 2.2-4.3V of cut-off voltage; the results of the electrochemical properties are shown in Table 1.

TABLE 1 basic Properties of lithium iron manganese phosphate Material

Examples 1-7 are lithium iron manganese phosphate prepared by the present disclosure, and comparative examples 1-2 are lithium iron manganese phosphate prepared by a conventional method, and from the data, it can be seen that the lithium iron manganese phosphate positive electrode material of the present disclosure has high compaction density, and can be applied to lithium ion batteries to remarkably improve the specific capacity of the lithium ion batteries and improve the cycle performance of the lithium ion batteries.

Industrial applicability

According to the method, by utilizing the characteristic that Ksp of ferric phosphate and Ksp of aluminum phosphate precipitation are similar, ferric aluminum phosphate is synthesized firstly by a coprecipitation method, so that ferric aluminum phosphate is uniformly mixed, then, ferric aluminum phosphate and manganese chloride are utilized to react to prepare a stable ferric manganese phosphate precursor, and aluminum chloride generated in the reaction process can be volatilized directly. And doping lithium into the lithium iron manganese phosphate precursor, adding a carbon source, and performing high-temperature calcination to obtain the lithium iron manganese phosphate anode material. Has the advantages of low process cost, simple and easy process and is suitable for industrial application.

Claims

1. The preparation method of the ferric manganese phosphate precursor is characterized by comprising the following steps of: mixing ferric aluminum phosphate obtained by a coprecipitation method with manganese chloride and a fluxing agent, and reacting at 185-300 ℃.

2. The method of preparing as claimed in claim 1, wherein the process of preparing the iron-manganese phosphate precursor using the iron-aluminum phosphate comprises: mixing the aluminum iron phosphate with manganese chloride and a fluxing agent, reacting at 185-300 ℃ to obtain a manganese iron phosphate dihydrate precursor, and carrying out high-temperature treatment on the manganese iron phosphate dihydrate precursor to remove crystal water in the manganese iron phosphate dihydrate precursor.

3. The method of claim 2, wherein the fluxing agent is a mixture of potassium chloride and sodium chloride.

4. A production method according to claim 3, wherein in the flux, the mass fraction of potassium chloride is 40% -55%, and the mass fraction of sodium chloride is 45% -60%.

5. The method according to any one of claims 2 to 4, wherein the molar ratio of the iron aluminum phosphate to the total amount of the fluxing agent is 1: (0.4-0.8).

6. The method according to any one of claims 2 to 5, wherein the molar ratio of the iron aluminum phosphate to the manganese chloride is 1: (1.5-1.7).

7. The preparation method according to any one of claims 2 to 6, wherein the ferric aluminum phosphate, the manganese chloride and the fluxing agent are mixed, reacted for 2 to 6 hours under the condition of an inert atmosphere and 250 to 300 ℃, cooled, washed and dried to obtain the manganese iron dihydrate precursor.

8. The method according to any one of claims 2 to 7, wherein the high temperature treatment process comprises: and (3) treating the ferric manganese phosphate dihydrate precursor for 1-4 hours at the temperature of 600-700 ℃.

9. The method according to claim 8, wherein the high temperature treatment is performed under an inert atmosphere.

10. The method of any one of claims 1-9, wherein the process of preparing the aluminum iron phosphate comprises: adding ferric salt solution, aluminum salt solution, phosphoric acid solution and precipitant solution into a reactor for coprecipitation reaction.

11. The production method according to claim 10, wherein the molar ratio of iron, aluminum and phosphorus elements in the reaction system is made to be (0.5-0.8) by controlling the concentrations and addition rates of the iron salt solution, the aluminum salt solution and the phosphorus source solution: (0.2-0.5): (1.0-1.1).

12. The method according to claim 10 or 11, wherein the reaction temperature of the coprecipitation reaction is 45 ℃ to 90 ℃ and the reaction time is 3h to 6h.

13. The method according to any one of claims 10 to 12, wherein the pH of the coprecipitation reaction system is controlled to be 2.8 to 3.5 by controlling the rate of addition of the precipitant solution.

14. The method of claim 13, wherein the precipitant solution is an aqueous ammonia solution having a concentration of 2mol/L to 6 mol/L.

15. The method according to any one of claims 10 to 14, wherein the rotation speed is controlled to be 100r/min to 400r/min during the coprecipitation reaction, and washing and drying are performed after the completion of the reaction.

16. The method of any one of claims 10-15, wherein the iron salt is selected from at least one of iron acetate, iron carbonate, iron oxalate, iron chloride, iron nitrate, and iron sulfate.

17. The production method according to any one of claims 10 to 16, wherein the aluminum salt is selected from at least one of aluminum nitrate, aluminum sulfate, aluminum chloride, and aluminum carbonate.

18. The method of any one of claims 10-17, wherein the phosphorus source is selected from at least one of phosphoric acid, ammonium phosphate, monoammonium phosphate, and monoammonium phosphate.

19. An iron manganese phosphate precursor prepared by the method of any one of claims 1-18.

20. The preparation method of the lithium iron manganese phosphate anode material is characterized by comprising the following steps of: the reaction of a manganese iron phosphate precursor according to claim 19 with a lithium source.

21. The method of manufacturing as claimed in claim 20, comprising: and mixing and calcining the manganese iron phosphate precursor, a lithium source and a carbon source, wherein the calcining temperature is controlled to be 800-900 ℃ and the calcining time is controlled to be 6-20 h.

22. The production method according to claim 20 or 21, wherein the molar ratio of the total amount of lithium element and ferromanganese is (1.0-1.2) by controlling the amounts of the ferromanganese phosphate precursor and the lithium source: 1.

23. the production method according to claim 21 or 22, wherein a mass ratio of the amount of the carbon source to the total amount of the manganese iron phosphate precursor and the lithium source is (5-13): 100.

24. the method of any one of claims 20-23, wherein the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

25. The method of any one of claims 21-24, wherein the carbon source is selected from at least one of sucrose, glucose, soluble starch, citric acid, phenolic resin, graphite, and carbon black.

26. The method of any one of claims 21 to 25, wherein the calcination is performed under inert atmosphere conditions.

27. A lithium iron manganese phosphate cathode material prepared by the preparation method of any one of claims 20 to 26.

28. A positive electrode sheet comprising the lithium iron manganese phosphate positive electrode material according to claim 27.

29. A lithium battery comprising the positive electrode sheet of claim 28.