Modified iron phosphate material, method for preparing same, and use thereof

Abstract

The application relates to a modified iron phosphate material and a preparation method and application thereof, and belongs to the technical field of inorganic material preparation. The preparation method of the modified iron phosphate material is as follows: firstly, a metal ruthenium-doped iron phosphate material is prepared by adopting a sol-gel method; and then, the surface of the material is modified by adopting nano-graphite powder to obtain a graphene-coated metal ruthenium-doped iron phosphate material. + The composite chelating agent is adopted in the ruthenium doping process, so that the ruthenium ions are uniformly distributed and stably exist in the iron phosphate material; the uniform doping of the ruthenium ions causes defects in the iron phosphate crystal structure, Li The graphene coating can prevent the agglomeration between particles, and the graphene coating can also improve the overall electrochemical performance of the material due to the high conductivity of the graphene.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic material preparation, and relates to a modified iron phosphate material, a preparation method thereof and application thereof in battery preparation. BACKGROUND

[0002] Iron phosphate (FePO4) is a monoclinic crystal powder, mainly exists in the form of hydrate FePO4·2H2O, and is generally white or light pink. It has good thermal performance and long service life, and a lithium battery positive electrode prepared by taking the iron phosphate as a precursor is widely used in the fields of electric vehicles, portable devices and energy storage systems. The main production process of the lithium battery positive electrode material iron lithium phosphate powder is a high-temperature solid-phase synthesis method. The conventional operation process for producing the iron lithium phosphate powder by the high-temperature solid-phase synthesis method comprises the following steps: first, battery-grade iron phosphate powder, lithium carbonate powder, a carbon source such as sucrose, pure water or ethanol and a small amount of an additive are mixed to form a slurry, and the slurry is ground to a fine powder and dried to obtain iron lithium phosphate fine powder.

[0003] The iron phosphate has strong thermal stability and can maintain stability even under high-temperature conditions, thereby improving the safety of a lithium ion battery. Moreover, the iron phosphate has good environmental protection performance, is non-toxic, does not contain heavy metals, is insoluble in water, cannot form flammable and explosive organic matters and belongs to green chemistry. Furthermore, the iron phosphate is simple to prepare, low in cost and can be mass-produced within a certain range. Although the iron phosphate has many advantages, the iron phosphate also has some problems as a battery positive electrode. (1) The electronic conductivity of the iron phosphate is poor, so the maximum charge-discharge power of the iron phosphate battery is limited. (2) The theoretical capacity of lithium ions in the interlayer of the iron phosphate is as high as 170 mAh / g, but the diffusion rate of the lithium ions is low, and the theoretical capacity cannot be achieved at a high rate, so the theoretical specific capacity cannot be achieved.

[0004] Therefore, the modification method of the iron phosphate has always been a hot topic, and various new doping technologies or coating methods emerge in an endless stream. The co-doping of Mn, Co, Ni and other multi-metal elements can improve the electrical conductivity of the iron phosphate and improve the lithium storage capacity. The modification methods mainly include coating modification and doping modification. SUMMARY

[0005] The application relates to a modified iron phosphate material, a preparation method thereof and application thereof, and belongs to the technical field of inorganic material preparation. The preparation method of the modified iron phosphate material is as follows: a metal ruthenium-doped iron phosphate material is prepared by adopting a sol-gel method, and then the iron phosphate material is surface-modified by adopting nano-graphite powder to obtain a graphene-coated metal ruthenium-doped iron phosphate material. In the process of ruthenium doping, a composite chelating agent is adopted, so that the ruthenium ions are uniformly distributed and stably exist in the iron phosphate material. The uniform doping of the ruthenium ions causes defects in the crystal structure of the iron phosphate, Li +And the electron can be stored and released more effectively; the coating of graphene can prevent the agglomeration between particles, and since graphene has high conductivity, the coating of graphene can also improve the overall electrochemical performance of the material.

[0006] The object of the present application can be achieved by the following technical solutions.

[0007] A modified iron phosphate material, and a preparation method thereof, comprising the following steps:

[0008] (1) sequentially adding a composite chelating agent, an aqueous ferric nitrate solution into an aqueous phosphoric acid solution, and mixing to obtain a mixed solution;

[0009] (2) adding ruthenium dioxide into the mixed solution, stirring until uniform, then adding ammonia water to adjust the pH value, and continuing to stir until a gel is formed; the gel is calcined at high temperature, and then ground to obtain a doped powder, i.e. a metal ruthenium-doped iron phosphate material;

[0010] (3) mixing the doped powder, nano-graphite powder and an additive, and then putting them into a grinding machine for first grinding; after nitrogen is introduced, the mixture is calcined by heating, and then second grinding is performed to obtain a modified iron phosphate material, i.e. a graphene-coated metal ruthenium-doped iron phosphate material;

[0011] The composite chelating agent in step (1) is composed of citric acid, ascorbic acid and sodium ethylenediaminetetra-methylene phosphonate with a mass ratio of 1:1:1-2.

[0012] Further, the molar concentration of the aqueous phosphoric acid solution in step (1) is 1.0-1.5 mol / L, and the molar concentration ratio of the aqueous ferric nitrate solution to the aqueous phosphoric acid solution is 0.98-1.02:1.

[0013] Further, the composite chelating agent accounts for 3-5wt% of the aqueous phosphoric acid solution in step (1).

[0014] Further, the ruthenium dioxide accounts for 1-5wt% of the mixed solution in step (2), the pH value is 8-8.5, and the stirring speed is 500-800r / min.

[0015] Further, the temperature and time of high-temperature calcination in step (2) are 500-700℃ and 2-3h respectively, and the particle size of the doped powder is 10-50μm.

[0016] Further, the mass ratio among the doped powder, nano-graphite powder and additive in step (3) is 1-3:0.3-1:0.05-0.1, and the additive is composed of ethanol and glycerol with a mass ratio of 1:1.

[0017] Further, the first grinding time in the step (3) is 5-6h, the temperature and time of the temperature rising calcination are 800-1000℃ and 6-8h respectively, and the second grinding time is 3-4h.

[0018] Further, the modified iron phosphate material is applied to prepare a lithium ion battery.

[0019] The beneficial effects of the present application are as follows:

[0020] The present application adopts a composite chelating agent composed of citric acid, ascorbic acid and sodium ethylenediaminetetramethylene phosphonate, which can form stable complex with metal ions (such as ruthenium ions), thereby helping the uniform distribution and stable existence of metal ions in the iron phosphate material, making the iron phosphate material have good chemical stability and thermal stability, being able to resist high reaction temperature, and making the iron phosphate crystal lattice structure have defects, Li + and electrons can be effectively stored and released; in addition, the coating of graphene can prevent the agglomeration between particles, and since graphene has high conductivity, the coating of graphene can also improve the overall electrochemical performance of the material. DETAILED DESCRIPTION

[0021] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined application purposes, the specific embodiments, structures, features and effects according to the present application are described in detail as follows.

[0022] Example 1

[0023] A modified iron phosphate material, and a preparation method of the modified iron phosphate material, the preparation method comprising the following steps:

[0024] (1) adding a composite chelating agent and an aqueous ferric nitrate solution into an aqueous phosphoric acid solution in sequence and mixing to obtain a mixed solution;

[0025] (2) adding ruthenium dioxide into the mixed solution and stirring until uniform, then adding ammonia water to adjust the pH value, and continuing to stir until a gel is formed, grinding the gel after high-temperature calcination to obtain a doped powder;

[0026] (3) mixing the doped powder, nano-graphite powder and an additive, then putting them into a grinder to perform first grinding, introducing nitrogen and then performing temperature rising calcination, and then performing second grinding to obtain the modified iron phosphate material;

[0027] The composite chelating agent in the step (1) is composed of citric acid, ascorbic acid and sodium ethylenediaminetetramethylene phosphonate with a mass ratio of 1:1:1;

[0028] The molar concentration of the aqueous phosphoric acid solution in the step (1) is 1.0mol / L, and the molar concentration ratio of the aqueous ferric nitrate solution to the aqueous phosphoric acid solution is 0.98:1.

[0029] The complex chelating agent in step (1) accounts for 3wt% of the aqueous phosphoric acid solution;

[0030] The ruthenium dioxide in step (2) accounts for 1wt% of the mixed solution, the pH value is 8, and the stirring speed is 500r / min;

[0031] The temperature and time of high-temperature calcination in step (2) are 500℃ and 2h respectively, and the particle size of the doped powder is 10μm;

[0032] The mass ratio among the doped powder, nano-graphite powder and additive in step (3) is 1:0.3:0.05, and the additive is composed of ethanol and glycerol with a mass ratio of 1:1;

[0033] The time of the first grinding in step (3) is 5h, the temperature and time of the temperature-rising calcination are 800℃ and 6h respectively, and the time of the second grinding is 3h;

[0034] The particle size of the nano-graphite powder is 6.5nm.

[0035] Example 2

[0036] A modified iron phosphate material, and a preparation method thereof, the preparation method comprising the following steps:

[0037] (1) sequentially adding a complex chelating agent and an aqueous ferric nitrate solution into an aqueous phosphoric acid solution and mixing to obtain a mixed solution;

[0038] (2) adding ruthenium dioxide into the mixed solution and stirring uniformly, then adding ammonia water to adjust the pH value, continuing to stir until a gel is formed, calcining the gel at high temperature, and grinding to obtain a doped powder;

[0039] (3) mixing the doped powder, nano-graphite powder and additive, then putting them into a grinder for the first grinding, introducing nitrogen and then performing temperature-rising calcination, and then performing the second grinding to obtain the modified iron phosphate material;

[0040] The complex chelating agent in step (1) is composed of citric acid, ascorbic acid and sodium ethylenediaminetetra-methylene phosphonate with a mass ratio of 1:1:1.5;

[0041] The aqueous phosphoric acid solution in step (1) has a molar concentration of 1.3mol / L, and the molar concentration ratio of the aqueous ferric nitrate solution to the aqueous phosphoric acid solution is 1:1;

[0042] The complex chelating agent in step (1) accounts for 4wt% of the aqueous phosphoric acid solution;

[0043] The ruthenium dioxide in the step (2) accounts for 3wt% of the mixed solution, the pH value is 8.3, and the stirring speed is 650r / min;

[0044] The temperature and time of the high-temperature calcination in the step (2) are 600℃ and 2.5h respectively, and the particle size of the doped powder is 35μm;

[0045] The mass ratio among the doped powder, the nano-graphite powder and the additive in the step (3) is 2:0.6:0.07, and the additive is composed of ethanol and glycerol with a mass ratio of 1:1;

[0046] The time of the first grinding in the step (3) is 5.5h, the temperature and time of the high-temperature calcination are 900℃ and 7h respectively, and the time of the second grinding is 3.5h;

[0047] The particle size of the nano-graphite powder is 6.5nm.

[0048] Example 3

[0049] A modified iron phosphate material, and a preparation method thereof, the preparation method comprising the following steps:

[0050] (1) sequentially adding a composite chelating agent and an aqueous ferric nitrate solution into an aqueous phosphoric acid solution and mixing to obtain a mixed solution;

[0051] (2) adding ruthenium dioxide into the mixed solution and stirring uniformly, then adding ammonia water to adjust the pH value, continuing to stir until a gel is formed, calcining the gel at high temperature, and grinding to obtain a doped powder;

[0052] (3) mixing the doped powder, a nano-graphite powder and an additive, then putting them into a grinder to perform the first grinding, introducing nitrogen, and then performing the high-temperature calcination, and subsequently performing the second grinding to obtain the modified iron phosphate material;

[0053] The composite chelating agent in the step (1) is composed of citric acid, ascorbic acid and sodium ethylenediaminetetramethylene phosphonate with a mass ratio of 1:1:2;

[0054] The molar concentration of the aqueous phosphoric acid solution in the step (1) is 1.5mol / L, and the molar concentration ratio of the aqueous ferric nitrate solution to the aqueous phosphoric acid solution is 1.02:1;

[0055] The composite chelating agent accounts for 5wt% of the aqueous phosphoric acid solution in the step (1);

[0056] The ruthenium dioxide in the step (2) accounts for 5wt% of the mixed solution, the pH value is 8.5, and the stirring speed is 800r / min;

[0057] The temperature and time of the high-temperature calcination in the step (2) are 700℃ and 3h respectively, and the particle size of the doped powder is 50μm;

[0058] The mass ratio among the doped powder, the nano-graphite powder and the additive in the step (3) is 3:1:0.1, and the additive is composed of ethanol and glycerol with a mass ratio of 1:1;

[0059] The time of the first grinding in the step (3) is 6h, the temperature and time of the high-temperature calcination are 1000℃ and 8h respectively, and the time of the second grinding is 4h;

[0060] The particle size of the nano-graphite powder is 6.5nm.

[0061] Comparative Example 1: Different from Example 2, the composite chelating agent in the step (1) only includes citric acid, without ascorbic acid and ethylenediaminetetra-methylene phosphonic acid sodium.

[0062] Comparative Example 2: Different from Example 2, the composite chelating agent in the step (1) only includes ascorbic acid, without citric acid and ethylenediaminetetra-methylene phosphonic acid sodium.

[0063] Comparative Example 3: Different from Example 2, the composite chelating agent in the step (1) only includes ethylenediaminetetra-methylene phosphonic acid sodium, without citric acid and ascorbic acid.

[0064] Comparative Example 4: Different from Example 2, the composite chelating agent in the step (1) is composed of citric acid and ascorbic acid with a mass ratio of 1:1.

[0065] Comparative Example 5: Different from Example 2, the composite chelating agent in the step (1) is composed of citric acid and ethylenediaminetetra-methylene phosphonic acid sodium with a mass ratio of 1:1.5.

[0066] Comparative Example 6: Different from Example 2, the composite chelating agent in the step (1) is composed of ascorbic acid and ethylenediaminetetra-methylene phosphonic acid sodium with a mass ratio of 1:1.5.

[0067] Comparative Example 7: Different from Example 2, the composite chelating agent in the step (1) is composed of citric acid, ascorbic acid and ethylenediaminetetra-methylene phosphonic acid sodium with a mass ratio of 1.5:1:1.

[0068] Comparative Example 8: Different from Example 2, the composite chelating agent in the step (1) is composed of citric acid, ascorbic acid and ethylenediaminetetra-methylene phosphonic acid sodium with a mass ratio of 1:1.5:1.

[0069] Comparative Example 9: Based on Example 2, a preparation method of a modified iron phosphate material comprises the following steps:

[0070] (1) adding a complex chelating agent, an aqueous ferric nitrate solution into an aqueous phosphoric acid solution in sequence and mixing to obtain a mixed solution;

[0071] (2) adding ruthenium dioxide into the mixed solution and stirring until uniform, then adding ammonia water to adjust the pH value, and continuing to stir until a gel is formed, and grinding the powder obtained after calcining the gel at high temperature to obtain the modified ferric phosphate material;

[0072] The complex chelating agent in step (1) is composed of citric acid, ascorbic acid and sodium ethylenediaminetetramethylene phosphonate in a mass ratio of 1:1:1.5;

[0073] The molar concentration of the aqueous phosphoric acid solution in step (1) is 1.3 mol / L, and the molar concentration ratio of the aqueous ferric nitrate solution to the aqueous phosphoric acid solution is 1:1;

[0074] The complex chelating agent in step (1) accounts for 4wt% of the aqueous phosphoric acid solution;

[0075] The ruthenium dioxide in step (2) accounts for 3wt% of the mixed solution, the pH value is 8.3, and the stirring speed is 650r / min;

[0076] The temperature and time of high-temperature calcination in step (2) are 600℃ and 2.5h respectively, and the particle size of the doped powder is 35μm.

[0077] Performance test

[0078] Electrochemical performance test: the electrochemical performance of Examples 1-3 and Comparative Examples 1-9 was tested according to the patent CN111874885B, and the test results are shown in Table 1.

[0079] Table 1 test results

[0080]

[0081] From Table 1, it can be seen that the charge and discharge capacity of Examples 1-3 is greater than that of Comparative Examples 1-9, the coulombic efficiency of Examples 1-3 is also greater than that of Comparative Examples 1-9, and the 1C rate 50-week capacity retention rate of Examples 1-3 is greater than that of Comparative Examples 1-9. In Comparative Examples 1-3, only one chelating agent is added, in Comparative Examples 4-6, one of the chelating agents is removed, and the uneven distribution of ruthenium dioxide in ferric phosphate affects the electrochemical performance; Comparative Examples 7-8 exceed the range of chelating agents in the examples and affect the electrochemical performance; in Comparative Example 9, graphene coating is not used, agglomeration occurs between the particles and the conductivity decreases, which affects the electrochemical performance.

[0082] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, as long as the changes or modifications do not deviate from the technical solution of the present application. Any modification, change, equivalent change and modification of the above embodiments made according to the technical essence of the present application still belong to the scope of the technical solution of the present application.

Claims

1. A modified iron phosphate material characterized in that, The preparation method of the modified iron phosphate material comprises the following steps: (1) sequentially adding a composite chelating agent, an aqueous ferric nitrate solution into an aqueous phosphoric acid solution and mixing to obtain a mixed solution; (2) adding ruthenium dioxide into the mixed solution and stirring until uniform, then adding ammonia water to adjust the pH value, and continuing to stir until a gel is formed, grinding the gel after high-temperature calcination to obtain a doped powder; wherein the temperature and time of high-temperature calcination are 500-700℃ and 2-3h respectively, and the particle size of the doped powder is 10-50μm; (3) mixing the doped powder, nano-graphite powder and an additive, then putting them into a grinder for first grinding, then passing nitrogen and calcining, and then second grinding to obtain the modified iron phosphate material; the mass ratio of the doped powder, nano-graphite powder and additive is 1-3:0.3-1:0.05-0.1, and the additive is composed of ethanol and glycerol with a mass ratio of 1:1; The composite chelating agent in step (1) is composed of citric acid, ascorbic acid and sodium ethylenediaminetetramethylene phosphonate with a mass ratio of 1:1:1-2.

2. The modified iron phosphate material of claim 1, wherein, The molar concentration of the aqueous phosphoric acid solution in step (1) is 1.0-1.5mol / L, and the molar concentration ratio of the aqueous ferric nitrate solution to the aqueous phosphoric acid solution is 0.98-1.02:

1.

3. The modified iron phosphate material of claim 1, wherein, The composite chelating agent in step (1) accounts for 3-5wt% of the aqueous phosphoric acid solution.

4. The modified iron phosphate material of claim 1, wherein, The ruthenium dioxide in step (2) accounts for 1-5wt% of the mixed solution, the pH value is 8-8.5, and the stirring speed is 500-800r / min.

5. The modified iron phosphate material of claim 1, wherein, The time of first grinding in step (3) is 5-6h, the temperature and time of calcination are 800-1000℃ and 6-8h respectively, and the time of second grinding is 3-4h.

6. The modified iron phosphate material according to any one of claims 1-5 for use in the preparation of a lithium ion battery.

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