CN111422851A - Lithium iron phosphate and preparation method thereof - Google Patents
Lithium iron phosphate and preparation method thereof Download PDFInfo
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- CN111422851A CN111422851A CN202010136005.2A CN202010136005A CN111422851A CN 111422851 A CN111422851 A CN 111422851A CN 202010136005 A CN202010136005 A CN 202010136005A CN 111422851 A CN111422851 A CN 111422851A
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Abstract
The invention belongs to the technical field of synthesis of battery materials, and particularly relates to lithium iron phosphate and a preparation method thereof. The invention obtains soluble amorphous ferric phosphate by reacting a solution containing phosphate ions with an iron source and an oxidant, and then obtains the lithium iron phosphate by liquid phase synthesis. The preparation method of the lithium iron phosphate has the advantages of low energy consumption, low production cost and simple steps, and the obtained lithium iron phosphate has the advantages of high compaction density and good electrochemical performance.
Description
Technical Field
The invention belongs to the technical field of synthesis of battery materials, and particularly relates to lithium iron phosphate and a preparation method thereof.
Background
The lithium iron phosphate is used as the material of the lithium iron phosphate anode material of the lithium ion battery, and the synthesis method determines the quality of the obtained lithium ion battery. The iron phosphate has a structure similar to that of lithium iron phosphate and becomes the most common raw material or precursor, and the prepared lithium iron phosphate has the characteristics of good electrochemical performance, high compaction density, good consistency and the like.
At present, iron phosphate used for preparing lithium iron phosphate is obtained by reacting phosphate with iron salt and then calcining at high temperature to obtain iron phosphate crystals, and the preparation process has high energy consumption and high cost for environmental treatment, so that a new iron phosphate preparation method with low energy consumption and environmental friendliness is urgently needed.
Common preparation methods of the lithium iron phosphate positive electrode material include a high-temperature solid phase method, a mechanochemical method and a microwave method. The method has high requirements on equipment and a complex preparation process, and has poor consistency of prepared lithium iron phosphate and easy generation of impurity phases due to limited mixing uniformity, so that the performance of the prepared lithium iron phosphate material is influenced. The mechanochemical method is that particles are crushed by the action of mechanical force, the contact area of reactants is increased, a crushed and compact powder mixture is obtained, and then a lithium iron phosphate material is obtained through solid phase reaction. The microwave method is characterized in that each salt is prepared according to the molecular formula atomic ratio of the lithium iron phosphate, and the lithium iron phosphate is synthesized by microwave heating.
Disclosure of Invention
The invention aims to provide lithium iron phosphate and a preparation method thereof, and aims to solve the technical problems that the cost is high, the steps are complicated, the lithium iron phosphate obtained by synthesis is easy to generate impurity phases and the like in the conventional lithium iron phosphate synthesis process.
In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:
the invention provides a preparation method of lithium iron phosphate on one hand, which comprises the following steps:
reacting the solution containing phosphate ions with an iron source and an oxidant, and carrying out solid-liquid separation to obtain amorphous iron phosphate;
reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution to obtain a lithium iron phosphate precursor;
and sintering the lithium iron phosphate precursor to obtain the lithium iron phosphate.
As a preferable technical scheme of the invention, the pH value of the solution containing phosphate ions is 4.0-4.5.
In a preferred embodiment of the present invention, the molar ratio of the phosphate ions to the iron atoms or iron ions in the iron source is 1:1.
As a preferred technical scheme of the invention, in the step of reacting the solution containing phosphate ions with the iron source and the oxidant, the reaction temperature is 60-90 ℃.
As a preferable technical scheme of the invention, in the step of reacting the solution containing phosphate ions with the iron source and the oxidant, the reaction time is 2h-3 h.
As a preferred technical solution of the present invention, in the step of reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution, the solution is an acidic solution.
In a further preferred embodiment of the present invention, in the step of reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution, the solution is an acidic solution, and the acidic solution is at least one selected from a phosphoric acid solution, a nitric acid solution, a hydrochloric acid solution, and an oxalic acid solution.
In a preferred embodiment of the present invention, the iron source is at least one selected from iron salts and iron oxides.
In a preferred embodiment of the present invention, the oxidant is at least one selected from hydrogen peroxide, oxygen, ozone, sodium hypochlorite and sodium peroxide.
As a preferable technical scheme of the invention, in the step of reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution, the molar ratio of the amorphous iron phosphate to the lithium source to the carbon source is (0.95-1.05): (0.95-1.05): 0.01-0.02).
As a preferred technical scheme of the present invention, in the step of reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution, the reaction temperature is 50 ℃ to 70 ℃.
As a preferred technical scheme of the invention, in the step of reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution, the reaction time is 4h-5 h.
In a preferred embodiment of the present invention, the lithium source is at least one selected from the group consisting of lithium phosphate, lithium dihydrogen phosphate, lithium hydroxide, lithium carbonate, lithium nitrate, lithium nitrite, lithium acetate, lithium oxide, and lithium oxalate.
In a preferred embodiment of the present invention, the carbon source is at least one selected from sucrose, glucose, oxalic acid, salicylic acid, citric acid, tartaric acid, malic acid, glycine, ethylenediaminetetraacetic acid, and succinic acid.
As a preferred technical scheme of the invention, the sintering temperature is 500-700 ℃.
As a preferable technical scheme of the invention, the sintering time is 6-12 h.
The invention also provides lithium iron phosphate which is prepared by the preparation method of the lithium iron phosphate.
In the traditional preparation method of the lithium iron phosphate, the used raw material iron phosphate is crystalline iron phosphate obtained by reacting phosphate with iron salt and calcining at high temperature. The crystalline iron phosphate has a relatively stable phase state, the molecular arrangement of the crystalline iron phosphate is relatively compact and regular, the intermolecular force is relatively large, and the solubility of the crystalline iron phosphate is obviously lower than that of the amorphous iron phosphate, so that the crystalline iron phosphate with poor solubility is used for synthesizing the lithium iron phosphate by adopting a high-temperature solid phase method, and the method has the problems of high energy consumption, easy environmental pollution, high cost, easy generation of impurity phases, poor performance of the obtained lithium iron phosphate and the like. In order to avoid synthesizing lithium iron phosphate by using a high-temperature solid-phase method, the solution containing phosphate ions is reacted with an iron source and an oxidant, and the amorphous iron phosphate is prepared without a calcining step.
The lithium iron phosphate is synthesized by taking amorphous ferric phosphate as a raw material through a liquid phase method, and primary particles of the lithium iron phosphate areNanoparticles having a small interparticle gap and a compacted density of 2.45g/cm3-2.50g/cm3The charge gram capacity of 0.1C is 161mAh/g, the discharge gram capacity is 159mAh/g, and the electrochemical catalyst has the advantages of high purity and good comprehensive electrochemical performance.
Drawings
FIG. 1 is an XRD pattern of amorphous iron phosphate obtained in example 2;
FIG. 2 is an SEM photograph of lithium iron phosphate obtained in example 2;
fig. 3 is a charge-discharge curve diagram of lithium iron phosphate obtained in example 2.
Detailed Description
In order to make the objects, technical solutions and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described, and the embodiments described below are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive step in connection with the embodiments of the present invention shall fall within the scope of protection of the present invention. Those whose specific conditions are not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer; the reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
In the description of the present invention, it should be understood that the weight of the related components mentioned in the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, it is within the scope of the disclosure that the content of the related components is scaled up or down according to the embodiments of the present invention. Specifically, the weight described in the embodiments of the present invention may be a unit of mass known in the chemical field such as μ g, mg, g, kg, etc.
In addition, unless the context clearly uses otherwise, an expression of a word in the singular is to be understood as including the plural of the word. The terms "comprises" or "comprising" are intended to specify the presence of stated features, quantities, steps, operations, elements, portions, or combinations thereof, but are not intended to preclude the presence or addition of one or more other features, quantities, steps, operations, elements, portions, or combinations thereof.
The embodiment of the invention provides a preparation method of lithium iron phosphate, which comprises the following steps:
s1, reacting the solution containing phosphate ions with an iron source and an oxidant, and carrying out solid-liquid separation to obtain amorphous iron phosphate;
s2, reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution to obtain a lithium iron phosphate precursor;
and S3, sintering the lithium iron phosphate precursor to obtain the lithium iron phosphate.
In the traditional preparation method of the lithium iron phosphate, the used raw material iron phosphate is crystalline iron phosphate obtained by reacting phosphate with iron salt and calcining at high temperature. The crystalline iron phosphate has a relatively stable phase state, the molecular arrangement of the crystalline iron phosphate is relatively compact and regular, the intermolecular force is relatively large, and the solubility of the crystalline iron phosphate is obviously lower than that of the amorphous iron phosphate, so that the crystalline iron phosphate with poor solubility is used for synthesizing the lithium iron phosphate by adopting a high-temperature solid phase method, and the method has the problems of high energy consumption, easy environmental pollution, high cost, easy generation of impurity phases, poor performance of the obtained lithium iron phosphate and the like. In order to avoid synthesizing lithium iron phosphate by using a high-temperature solid-phase method, the solution containing phosphate ions is reacted with an iron source and an oxidant, and amorphous iron phosphate can be obtained through solid-liquid separation without a calcining step.
In S1, the solution containing phosphate ions may specifically be a phosphate solution, a phosphoric acid solution, or the like, and is used to provide phosphate ions for the subsequent preparation of iron phosphate.
In order to separate the iron phosphate obtained by the reaction from the solution in the form of a precipitate before the reaction with the iron source and the oxidizing agent while preventing the formation of iron hydroxide, it is preferable in some embodiments to adjust the pH of the phosphate ion-containing solution to 4.0 to 4.5. In particular, typical but not limiting pH values are 4.0, 4.1, 4.2, 4.3, 4.4, 4.5. The substance for adjusting the pH value of the solution containing phosphate ions is an alkaline substance, preferably at least one of ammonia water, sodium hydroxide and potassium hydroxide, and can avoid introducing redundant impurities to influence the purity of the obtained amorphous iron phosphate.
In some embodiments, the phosphate ion-containing solution and the iron source are added in a molar ratio of 1:1 phosphorus to iron, and the oxidizing agent is added in excess. After phosphate ions and iron atoms/iron ions react under the full oxidation action of an oxidant to generate iron phosphate, redundant phosphate ions or iron ions are not generated in a reaction system, so that the production cost is saved, and the problems of environmental pollution and the like caused by redundant waste liquid generated in the production process can be avoided.
Further, the iron source is iron salt and/or iron oxide, preferably a substance with high iron content, low cost, no by-product generation or easy separation of the generated by-product, such as at least one of ferric sulfate, ferrous sulfate, ferric nitrate, ferrous nitrate, ferric oxide, ferrous oxide, ferric chloride, ferrous chloride, ferric carbonate, and ferrous carbonate.
Further, by utilizing the characteristic of strong oxidizing property of the oxidizing agent, iron ions can be completely oxidized into ferric iron under the acidic condition, so that the ferric iron ions and phosphate ions are fully reacted to generate iron phosphate precipitate. Preferably, a substance which does not introduce new metal impurity ions, has low price, wide source, easily controlled reaction process, greenness and innocuity is used as an oxidant, such as at least one of hydrogen peroxide, oxygen, ozone, sodium hypochlorite and sodium peroxide.
The reaction temperature of the reaction system is properly increased, which is beneficial to accelerating the reaction rate and saving the production time and the production efficiency. Thus, in some embodiments, the reaction of the phosphate ion-containing solution with the iron source and the oxidizing agent is carried out under heating, preferably at a temperature of 60 ℃ to 90 ℃. Specifically, typical but not limiting reaction temperatures are 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃.
By controlling the reaction time of the reaction system, on one hand, the phosphate ions and the iron ions can be ensured to fully react under the action of the oxidant, and on the other hand, the energy consumption increase and the introduction of impurities caused by overlong reaction time can be avoided. Thus, in some embodiments, the time for the phosphate ion-containing solution to react with the iron source and the oxidizing agent is controlled to be between 2h and 3 h. In particular, typical, but not limiting, reaction times are 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, 3 h.
Furthermore, the impurity content in the obtained amorphous iron phosphate can be further reduced by adding the iron source and the oxidant in a spraying mode, and the impurity content of the synthesized lithium iron phosphate can be lower and the electrochemical performance can be improved by taking the iron source and the oxidant as raw materials for synthesizing the lithium iron phosphate.
In S2, since the present invention uses a liquid phase method to prepare lithium iron phosphate, amorphous iron phosphate should react with a lithium source and a carbon source under a solution condition.
In some embodiments, in order to facilitate the reaction of the amorphous iron phosphate with the lithium source and the carbon source, an acidic solution is preferably used as a liquid phase reaction system. This is because amorphous iron phosphate can be dissolved in an acidic solution to generate phosphoric acid and iron ions, which facilitates subsequent reactions.
Further, the acid solution is at least one selected from phosphoric acid solution, nitric acid solution, hydrochloric acid solution and oxalic acid solution; among them, a nitric acid solution is preferable. This is because the nitric acid solution can completely dissolve the amorphous iron phosphate, thereby improving the production efficiency. And nitrate ions formed in the process that the amorphous iron phosphate is dissolved in the nitric acid solution are attached to the lithium iron phosphate precursor and can be removed through volatilization in the sintering process, so that the impurity introduction of the lithium iron phosphate is reduced.
Further, it is preferable that the amorphous iron phosphate is completely dissolved in an acidic solution and then reacted with a lithium source and a carbon source. This is because if the amorphous iron phosphate is not completely dissolved, the reaction system is too thick and is not uniformly mixed with the lithium source, which leads to poor performance of the synthesized lithium iron phosphate.
Further, the components are preferably mixed more uniformly by adopting a stirring mode in the process of reacting the amorphous iron phosphate with the lithium source and the carbon source, and the stirring speed is 40rpm-60 rpm. Specifically, typical, but not limiting, stirring rates are 40rpm, 45rpm, 50rpm, 55rpm, 60 rpm.
During the reaction with amorphous iron phosphate, a lithium source is used to provide lithium ions. In some embodiments, the lithium source is selected from at least one of lithium phosphate, lithium dihydrogen phosphate, lithium hydroxide, lithium carbonate, lithium nitrate, lithium nitrite, lithium acetate, lithium oxide, lithium oxalate.
In the reaction process of the amorphous iron phosphate, the carbon source has the following functions: (1) forming a carbon coating layer on the surface of the lithium iron phosphate, wherein the carbon coating layer is used for inhibiting the growth of lithium iron phosphate crystal grains and increasing the specific surface area; (2) enhancing the conductivity of the electrons among and on the surface of the obtained lithium iron phosphate particles; (3) as a reducing agent, the generation of Fe is avoided, and the purity of the obtained lithium iron phosphate is improved; (4) and the lithium iron phosphate serves as a nucleating agent, so that the particle size of the obtained lithium iron phosphate is reduced. In some embodiments, the carbon source is selected from at least one of sucrose, glucose, oxalic acid, salicylic acid, citric acid, tartaric acid, malic acid, glycine, ethylenediaminetetraacetic acid, succinic acid.
In some embodiments, in order to stabilize the solution system and prevent the formation of precipitates, a complexing agent is further added during the reaction of the amorphous iron phosphate with the lithium source and the carbon source.
Further, the complexing agent is selected from one of polyacrylamide, polyacrylic acid, EDTA, oxalic acid, citric acid and gluconic acid, and oxalic acid and/or glucose with low cost and wide sources are preferred.
The reaction rate and the production efficiency are improved by heating the reaction system of the amorphous iron phosphate with the lithium source and the carbon source, and thus, in some embodiments, the reaction temperature is set to 50 ℃ to 70 ℃. Specifically, typical but not limiting reaction temperatures are 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃.
By controlling the reaction time of the amorphous iron phosphate, the lithium source and the carbon source, the amorphous iron phosphate can be fully reacted with the lithium source and the carbon source, and unnecessary energy consumption caused by overlong reaction time is avoided. Thus, in some embodiments, the reaction time is controlled to be between 4h and 5 h. In particular, typical, but not limiting, reaction times are 4h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h, 5 h.
In S3, the precursor of the lithium iron phosphate is sintered, and the carbon-coated lithium iron phosphate material is synthesized by a carbothermic method, so that the obtained lithium iron phosphate crystal is more stable.
Increasing the sintering temperature can improve the uniformity of the obtained lithium iron phosphate material and the compactness of the carbon coating layer, but too high sintering temperature can cause the shape and size of the lithium iron phosphate material to change difficultly and affect the service life of equipment, so in some embodiments, the sintering temperature is preferably 500 ℃ to 700 ℃. Specifically, typical, but not limiting, sintering temperatures are 500 deg.C, 550 deg.C, 600 deg.C, 650 deg.C, 700 deg.C.
The formation of a dense lithium iron phosphate material is facilitated by optimizing the time of the sintering process, which in some embodiments is preferably 6h to 12 h. In particular, typical but not limiting sintering times are 6h, 7h, 8h, 9h, 10h, 11h, 12 h.
In order to clearly understand the details of the above-described implementation and operation of the present invention for those skilled in the art and to significantly embody the advanced performance of the embodiments of the present invention, the above-described technical solution is illustrated by a plurality of embodiments below.
Example 1
A preparation method of lithium iron phosphate comprises the following steps:
(1) adding ammonia water into a phosphoric acid solution of which the thickness is 100m L to adjust the pH value of the solution to 4.5, adding ferrous oxide and hydrogen peroxide, heating and reacting for 2 hours at the temperature of 80 ℃, and filtering to obtain flocculent iron phosphate, namely amorphous iron phosphate;
(2) and (2) dissolving flocculent iron phosphate in phosphoric acid to obtain an iron phosphate solution, adding a lithium phosphate solution, a glucose solution and oxalic acid, reacting for 4.5 hours at 62 ℃, filtering, and calcining the obtained precipitate for 2 hours at 600 ℃ under the protection of nitrogen to obtain the lithium iron phosphate. Wherein the molar ratio of the added phosphoric acid, the ferrous oxide, the lithium phosphate and the glucose is 1:1.001:0.995: 0.014.
Example 2
A preparation method of lithium iron phosphate comprises the following steps:
(1) adding nitric acid into 80m L sodium phosphate solution to adjust pH to 4.8, adding ferrous oxide and hydrogen peroxide, heating at 76 deg.C for 2.8h, and filtering to obtain flocculent iron phosphate, i.e. amorphous iron phosphate, with XRD pattern shown in figure 1;
(2) dissolving flocculent ferric phosphate by adding nitric acid to obtain a ferric phosphate solution, adding a lithium phosphate solution, a glucose solution and oxalic acid, reacting for 4.3h at 66 ℃, filtering, and calcining the obtained precipitate for 4h at 650 ℃ under the protection of nitrogen to obtain the lithium iron phosphate (the SEM image is shown in figure 2). Wherein the molar ratio of the added sodium phosphate to the added ferrous oxide to the added lithium phosphate to the added glucose is 0.996:1.002:1: 0.015.
Example 3
A preparation method of lithium iron phosphate comprises the following steps:
(1) adding hydrochloric acid into 90m L potassium phosphate solution to adjust the pH value of the solution to 4, adding iron oxide red and hydrogen peroxide, heating and reacting at 65 ℃ for 2.5h, and filtering to obtain flocculent iron phosphate, namely amorphous iron phosphate;
(2) and (2) dissolving flocculent iron phosphate with hydrochloric acid to obtain an iron phosphate solution, adding a lithium hydroxide solution, a sucrose solution and oxalic acid, reacting for 4.8h at 50 ℃, filtering, and calcining the obtained precipitate for 8h at 550 ℃ under the protection of nitrogen to obtain the lithium iron phosphate. Wherein the molar ratio of the potassium phosphate to the ferrous oxide to the lithium hydroxide to the sucrose is 0.998:1.009:0.995: 0.018.
Example 4
A preparation method of lithium iron phosphate comprises the following steps:
(1) taking 50m L ammonium phosphate solution, adding oxalic acid to adjust the pH of the solution to 4.3, adding iron oxide red and hydrogen peroxide, heating and reacting for 3 hours at 90 ℃, and filtering to obtain flocculent iron phosphate, namely amorphous iron phosphate;
(2) and dissolving flocculent iron phosphate with oxalic acid to obtain an iron phosphate solution, adding a lithium hydroxide solution, a sucrose solution and glucose, reacting for 5 hours at 58 ℃, filtering, and calcining the obtained precipitate for 7 hours at 500 ℃ under the protection of nitrogen to obtain the lithium iron phosphate. Wherein the molar ratio of the addition amount of the ammonium phosphate, the ferrous oxide, the lithium hydroxide and the sucrose is 0.995:1:1.003: 0.013.
Example 5
A preparation method of lithium iron phosphate comprises the following steps:
(1) adding phosphoric acid into 70m L sodium phosphate solution to adjust the pH value of the solution to 4.2, adding ferrous carbonate and hydrogen peroxide, heating and reacting for 2.6h at 83 ℃, and filtering to obtain flocculent iron phosphate, namely amorphous iron phosphate;
(2) and (2) dissolving flocculent iron phosphate in phosphoric acid to obtain an iron phosphate solution, adding a lithium carbonate solution and a glucose solution, reacting for 4.6h at 52 ℃, filtering, and calcining the obtained precipitate for 6h at 580 ℃ under the protection of nitrogen to obtain the lithium iron phosphate. Wherein the molar ratio of the added sodium phosphate to the added ferrous carbonate to the added lithium carbonate to the added glucose is 0.997:1.004:1.002: 0.02.
Example 6
A preparation method of lithium iron phosphate comprises the following steps:
(1) adding ammonia water into a phosphoric acid solution with the concentration of 60m L to adjust the pH value of the solution to 5, adding ferrous carbonate and hydrogen peroxide, heating and reacting for 2.4 hours at the temperature of 60 ℃, and filtering to obtain flocculent iron phosphate, namely amorphous iron phosphate;
(2) and (2) dissolving flocculent iron phosphate in phosphoric acid to obtain an iron phosphate solution, adding a lithium carbonate solution and a glucose solution, reacting for 4 hours at 70 ℃, filtering, and calcining the obtained precipitate for 3 hours at 700 ℃ under the protection of nitrogen to obtain the lithium iron phosphate. Wherein the molar ratio of the added phosphoric acid, the ferrous carbonate, the lithium carbonate and the glucose is 0.998:1.003:1: 0.012.
Comparative example 1
A preparation method of lithium iron phosphate comprises the following steps:
(1) adding ammonia water into a 100m L phosphoric acid solution to adjust the pH value of the solution to 4.5, adding ferrous oxide and hydrogen peroxide, heating and reacting for 2 hours at 80 ℃, filtering, and calcining the obtained precipitate for 3 hours at 300 ℃ to obtain crystalline iron phosphate;
(2) and (2) uniformly mixing the crystalline iron phosphate prepared in the step (1) with powdery lithium phosphate and glucose, and calcining at 600 ℃ for 6 hours under the protection of nitrogen to obtain the lithium iron phosphate. Wherein the molar ratio of the added iron phosphate, lithium phosphate and glucose is 1.001:0.995: 0.014.
Comparative example 2
A preparation method of lithium iron phosphate comprises the following steps:
(1) adding nitric acid into 80m L sodium phosphate solution to adjust the pH value of the solution to 4.8, adding ferrous oxide and hydrogen peroxide, heating and reacting for 2.8h at 76 ℃, filtering, and calcining the obtained precipitate for 2h at 400 ℃ to obtain crystalline iron phosphate;
(2) and (2) uniformly mixing the crystalline iron phosphate prepared in the step (1) with powdery lithium phosphate and glucose, and calcining at 650 ℃ for 8 hours under the protection of nitrogen to obtain the lithium iron phosphate. Wherein the molar ratio of the added iron phosphate to the added lithium phosphate to the added glucose is 0.996:1.002: 0.015.
Comparative example 3
A preparation method of lithium iron phosphate comprises the following steps:
(1) adding hydrochloric acid into 90m L potassium phosphate solution to adjust the pH value of the solution to 4, adding iron oxide red and hydrogen peroxide, heating and reacting for 2.5h at 65 ℃, filtering, and calcining the obtained precipitate for 4h at 500 ℃ under the protection of nitrogen to obtain crystalline iron phosphate;
(2) and (2) uniformly mixing the crystalline iron phosphate prepared in the step (1) with powdery lithium hydroxide and sucrose, and calcining at 550 ℃ for 9 hours to obtain the lithium iron phosphate. Wherein the molar ratio of the added iron phosphate, the added lithium hydroxide and the added sucrose is 1.009:0.995: 0.018.
Half cells were prepared under the same conditions in examples 1 to 6 and comparative examples 1 to 3, and subjected to charge and discharge tests; meanwhile, the compacted densities of the lithium iron phosphate obtained in examples 1 to 6 and comparative examples 1 to 3 were measured, and the specific test procedure for the compacted densities was as follows:
(1) cleaning a filler grinding tool used by a base, a hollow cavity, two round cakes and the like of a powder tablet press by using a paper towel, and measuring the inner diameter d of the hollow cavity by using a digital display caliper;
(2) the grinder of the powder tablet press was assembled before any sample was filled and then the vernier caliper was gently placed vertically. Measuring from the surface of the hollow cavity to the uppermost circle inside by selecting any three directionsThe depth of the cavity in the surface of the cake was averaged and recorded as h0；
(3) A lithium iron phosphate sample of a certain mass was weighed with an electronic analytical balance and recorded as m. Pouring the uppermost round cake into the hollow cavity after the uppermost round cake in the grinding tool cavity is taken out, and putting the round cake back. After assembly, it is placed on a tablet press for tableting. And (3) rocking the rocker up and down to adjust the pressure of the tablet press, staying for a corresponding time after the pressure reaches the pressure value displayed by the pressure gauge, unscrewing the knob to release the pressure, and taking out the grinding tool. Measuring the depth from the surface of the hollow cavity to the surface of the uppermost round cake in the hollow cavity in any three directions, and taking the average value to record as h1；
(4) Calculating the average height h of the pressed powder obtained by tabletting, wherein the formula is h ═ h0-h1；
(5) Calculating the compaction density rho according to the following calculation formula:
ρ＝40m/(πd2*h)
the compacted densities of the lithium iron phosphate obtained in examples 1 to 6 and comparative examples 1 to 3, and the charge and discharge test results of the half-cell made of the obtained lithium iron phosphate are shown in table 1.
TABLE 1 compacted density and charge-discharge test results of lithium iron phosphate obtained in examples 1 to 6 and comparative examples 1 to 3
| Examples | Compacted density (g/cm)3) | First discharge capacity (mAh/g) |
| Example 1 | 2.459 | 159.9 |
| Example 2 | 2.473 | 160 |
| Example 3 | 2.461 | 159.2 |
| Example 4 | 2.495 | 160.9 |
| Example 5 | 2.460 | 159.8 |
| Example 6 | 2.489 | 159 |
| Comparative example 1 | 2.143 | 135.5 |
| Comparative example 2 | 2.189 | 139.2 |
| Comparative example 3 | 2.172 | 137.6 |
As can be seen from table 1, the compaction density of the lithium iron phosphate prepared in examples 1 to 6 of the present invention is significantly higher than that of comparative examples 1 to 3, and therefore, the lithium iron phosphate material prepared by the method for preparing lithium iron phosphate using amorphous iron phosphate according to the present invention has a higher compaction density and the obtained half cell has a higher charge-discharge capacity, and therefore, the electrochemical performance of the lithium iron phosphate material prepared by the method for preparing lithium iron phosphate using amorphous iron phosphate according to the present invention can be improved.
It can be seen that the electrochemical performance of the lithium iron phosphate prepared by the amorphous iron phosphate of the present invention is superior to that of the lithium iron phosphate prepared by the crystalline iron phosphate, because the lithium iron phosphate prepared by the liquid phase method has high compaction density, is less affected by defect obstruction, longer transmission distance, etc. during the discharge process, and L i in the middle part of the particles+Can be completely separated, the reversible capacity of the material is higher, and the rate capability is good; in the process of high-rate charge and discharge, the electrode is not easy to polarize.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A preparation method of lithium iron phosphate is characterized by comprising the following steps:
reacting the solution containing phosphate ions with an iron source and an oxidant, and carrying out solid-liquid separation to obtain amorphous iron phosphate;
reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution to obtain a lithium iron phosphate precursor;
and sintering the lithium iron phosphate precursor to obtain the lithium iron phosphate.
2. The method for producing lithium iron phosphate according to claim 1, wherein the pH of the phosphate ion-containing solution is 4.0 to 4.5; and/or
The molar ratio of phosphate ions in the solution containing phosphate ions to iron atoms or iron ions in the iron source is 1:1.
3. The method for preparing lithium iron phosphate according to claim 1, wherein in the step of reacting the solution containing phosphate ions with the iron source and the oxidant, the reaction temperature is 60 ℃ to 90 ℃; and/or
And in the step of reacting the solution containing phosphate ions with an iron source and an oxidant, the reaction time is 2-3 h.
4. The method for preparing lithium iron phosphate according to claim 1, wherein in the step of reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution, the solution is an acidic solution; and/or
And in the step of reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution, the solution is an acidic solution, and the acidic solution is at least one selected from a phosphoric acid solution, a nitric acid solution, a hydrochloric acid solution and an oxalic acid solution.
5. The method for preparing lithium iron phosphate according to any one of claims 1 to 4, wherein the iron source is at least one selected from iron salts and iron oxides; and/or
The oxidant is at least one selected from hydrogen peroxide, oxygen, ozone, sodium hypochlorite and sodium peroxide.
6. The method for preparing lithium iron phosphate according to any one of claims 1 to 4, wherein in the step of reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution, the molar ratio of the amorphous iron phosphate to the lithium source to the carbon source is (0.95-1.05): (0.95-1.05): 0.01-0.02).
7. The method for preparing lithium iron phosphate according to any one of claims 1 to 4, wherein in the step of reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution, the reaction temperature is 50 ℃ to 70 ℃; and/or
And in the step of reacting the amorphous iron phosphate with a lithium source and a carbon source in a solution, the reaction time is 4-5 h.
8. The method for producing lithium iron phosphate according to any one of claims 1 to 4, wherein the lithium source is at least one selected from the group consisting of lithium phosphate, lithium dihydrogen phosphate, lithium hydroxide, lithium carbonate, lithium nitrate, lithium nitrite, lithium acetate, lithium oxide, and lithium oxalate; and/or
The carbon source is at least one selected from sucrose, glucose, oxalic acid, salicylic acid, citric acid, tartaric acid, malic acid, glycine, ethylenediamine tetraacetic acid and succinic acid.
9. The method for preparing lithium iron phosphate according to any one of claims 1 to 4, wherein the sintering temperature is 500 ℃ to 700 ℃; and/or
The sintering time is 6-12 h.
10. The lithium iron phosphate prepared by the method for preparing lithium iron phosphate according to any one of claims 1 to 9.
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