Lithium iron phosphate positive electrode material, lithium ion battery, preparation method and application

Abstract

The invention discloses a lithium iron phosphate positive electrode material, a lithium ion battery, a preparation method and application. The preparation method of the lithium iron phosphate positive electrode material comprises the following steps: carrying out acid dissolution on iron-containing waste residues by utilizing an acid solution, carrying out solid-liquid separation, and collecting a liquid phase to prepare a metal salt solution A; mixing the metal salt solution A, an impurity removal agent and iron powder, reacting, carrying out solid-liquid separation, and collecting a liquid phase to prepare a metal salt solution B; wherein the metal salt solution B contains ferrous ions, the pH of the metal salt solution B is increased to 0.5-2.5 by adopting an alkaline reagent, and a metal salt solution C is prepared; mixing the metal salt solution C, the lithium-containing solution and the phosphate radical-containing solution, carrying out a co-precipitation reaction, collecting a precipitate, and drying to obtain a precursor; and mixing the precursor with a carbon source, and sintering to prepare the lithium iron phosphate positive electrode material. The preparation method provided by the invention takes iron-containing waste residues as raw materials, turns waste into wealth, is low in cost and is suitable for industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries and relates to a lithium iron phosphate positive electrode material, a lithium ion battery, a preparation method and an application. Background Art

[0002] The properties of lithium battery cathode materials directly affect the performance of lithium-ion batteries. As a cathode material for lithium-ion batteries, lithium iron phosphate is widely used in electrochemical devices such as electric vehicles and energy storage due to its low cost, high safety performance and long cycle life.

[0003] Scrap iron slag usually contains a certain amount of iron. Even after the initial smelting and other industrial processes, the remaining iron in the scrap iron slag still has recycling value. Recycling these iron elements can reduce dependence on primary iron ore and turn waste into treasure. Summary of the invention

[0004] Based on this, a lithium iron phosphate positive electrode material, a lithium ion battery, a preparation method and an application are provided using iron-containing waste slag as raw material.

[0005] In some embodiments, a method for preparing a lithium iron phosphate positive electrode material is provided, comprising the following steps:

[0006] The iron-containing waste slag is acid-dissolved by using an acid solution, the solid-liquid separation is performed, and the liquid phase is collected to prepare a metal salt solution A;

[0007] The metal salt solution A, the impurity remover and the iron powder are mixed, reacted, solid-liquid separated, and the liquid phase is collected to prepare a metal salt solution B; wherein the metal salt solution B contains ferrous ions,

[0008] Using an alkaline reagent to increase the pH of the metal salt solution B to 0.5-2.5 to prepare a metal salt solution C;

[0009] The metal salt solution C, the lithium-containing solution and the phosphate-containing solution are mixed to perform a coprecipitation reaction, and the precipitate is collected and dried to obtain a precursor;

[0010] The precursor is mixed with a carbon source and sintered to prepare the lithium iron phosphate positive electrode material.

[0011] In some embodiments, the method for preparing a lithium iron phosphate positive electrode material provides one or more of the following characteristics:

[0012] The iron-containing waste slag is steelmaking waste slag;

[0013] The mass ratio of the iron-containing waste slag to the acid in the acid solution is 1:(0.5-7);

[0014] The mass ratio of the impurity remover to the iron-containing waste slag is (2-5):120;

[0015] The mass ratio of the iron powder to the iron-containing waste slag is (20-25):120;

[0016] The mass ratio of the precursor to the carbon source is 1:0.05-0.2.

[0017] In some embodiments, in the method for preparing a lithium iron phosphate positive electrode material provided, the impurity remover comprises one or both of sodium sulfide and ammonium fluoride.

[0018] In some embodiments, in the method for preparing a lithium iron phosphate positive electrode material provided, in the step of mixing the metal salt solution C with the lithium-containing solution and the phosphate-containing solution, the Fe 2+ , Li + PO4 3- The molar ratio is (0.9~1.2):(2.6~3.2):(0.9~1.2).

[0019] In some embodiments, the method for preparing a lithium iron phosphate positive electrode material provides one or more of the following characteristics:

[0020] The acid in the acid solution comprises one or more of sulfuric acid, hydrochloric acid and nitric acid;

[0021] The molar concentration of the acid solution is 1 mol / L to 4 mol / L;

[0022] The lithium-containing solution contains one or more of lithium carbonate, lithium hydroxide, lithium bicarbonate, lithium sulfate, lithium phosphate, lithium dihydrogen phosphate and lithium chloride;

[0023] The solubility of the lithium-containing solution is 0.5 mol / L to 5 mol / L;

[0024] The phosphate-containing solution contains one or more of phosphoric acid, sodium phosphate, lithium phosphate, lithium dihydrogen phosphate and ammonium dihydrogen phosphate;

[0025] The solubility of the phosphate-containing solution is 0.5 mol / L to 5 mol / L.

[0026] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the metal salt solution A, the impurity remover, and the iron powder are mixed, and a reaction step is carried out, wherein the reaction includes a precipitation reaction to remove impurity metal ions, and the impurity metal ions include one or more of chromium ions, nickel ions, manganese ions, zinc ions, magnesium ions, calcium ions, and copper ions.

[0027] In some embodiments, the method for preparing a lithium iron phosphate positive electrode material provides one or more of the following characteristics:

[0028] The temperature for carrying out the coprecipitation reaction is 75-95°C;

[0029] The coprecipitation reaction is carried out for 1 h to 6 h;

[0030] The pH value for the coprecipitation reaction is 3.5 to 6.5;

[0031] The carbon source comprises one or more of glucose, starch, sucrose, polyethylene glycol and polyvinyl pyrrolidone;

[0032] The sintering temperature is 750°C to 800°C;

[0033] The sintering time is 8h~12h.

[0034] In some embodiments, a lithium iron phosphate positive electrode material is provided, which is prepared by the preparation method.

[0035] In some embodiments, there is provided a use of the lithium iron phosphate positive electrode material in preparing a lithium ion battery.

[0036] In some embodiments, a lithium-ion battery is provided, comprising the lithium iron phosphate positive electrode material.

[0037] The preparation method provided in the above application uses iron-containing waste slag as raw material, turns waste into treasure, has low cost, and is suitable for industrial application. The iron salt solution obtained by removing the impurity metal ions in the iron-containing waste slag raw material is co-precipitated with the lithium-containing solution and the phosphate-containing solution, and carbon-coated to obtain a lithium iron phosphate positive electrode material with high capacity and excellent performance that can be used in lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the implementation methods and examples of the present application and to more completely understand the present application and its beneficial effects, the following is a brief introduction to the drawings required for use in the description of the implementation methods or examples. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0039] Figure 1 A flow chart of a method for preparing a lithium iron phosphate positive electrode material in one embodiment;

[0040] Figure 2 is the XRD pattern of the reaction product obtained in step (5) of Example 1;

[0041] Figure 3 is a SEM image of the reaction product obtained in step (5) of Example 1;

[0042] Figure 4 This is the XRD diagram of the lithium iron phosphate positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0043] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0045] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0046] The terms "and / or", "or / and", and "and / or" used in this application include any one of two or more related listed items, and also include any and all combinations of related listed items, which include any combination of any two related listed items, any more related listed items, or all related listed items. For example, "A and / or B" includes three parallel solutions: A, B, and "a combination of A and B".

[0047] In the present application, "plurality", "multiple", "multiple times", "multiples", etc., unless otherwise specified, refer to a number greater than 2 or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0048] The terms "combination thereof", "any combination thereof", "any combination thereof" and the like used in this application include all suitable combinations of any two or more of the listed items.

[0049] In this application, the "suitable" mentioned in "suitable combination", "suitable method", "any suitable method", etc. is based on the ability to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0050] In the present application, "preferred", "better", "more preferred" and "suitable" are only used to describe implementation methods or examples with better effects. It should be understood that they do not constitute limitations on the scope of protection of the present application.

[0051] In the present application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present application.

[0052] In this application, "optionally", "optional", and "optional" mean optional or dispensable, that is, any one of the two parallel schemes of "yes" or "no". If multiple "options" appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent.

[0053] In the present invention, in the "first aspect", "second aspect", "third aspect", "fourth aspect", etc., the terms "first", "second", "third", "fourth", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0054] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0055] In the present application, when it comes to numerical intervals (i.e., numerical ranges), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1 to 10, indicating that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges included therein.

[0056] The temperature parameters in this application, unless otherwise specified, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0057] In the present application, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass volume percentage.

[0058] The "room temperature" in this application generally refers to 5°C to 30°C, preferably 25±5°C.

[0059] The "base water" in this application refers to deionized water.

[0060] The main methods for preparing lithium iron phosphate are currently high-temperature solid phase method, sol-gel method and hydrothermal / solvothermal method. However, the raw materials of the high-temperature solid phase method are mixed by high-energy grinding, which has poor uniformity, the product yield of the sol-gel method is low during the production process, and the hydrothermal / solvothermal method requires high-temperature and high-pressure reaction equipment, which is not conducive to large-scale production applications.

[0061] In some embodiments, a method for preparing a lithium iron phosphate positive electrode material is provided, comprising the following steps:

[0062] The iron-containing waste slag is acid-dissolved by using an acid solution, the solid-liquid separation is performed, and the liquid phase is collected to prepare a metal salt solution A;

[0063] The metal salt solution A, the impurity remover and the iron powder are mixed, reacted, solid-liquid separated, and the liquid phase is collected to prepare the metal salt solution B; wherein the metal salt solution B contains ferrous ions,

[0064] The pH of the metal salt solution B is adjusted to 0.5-2.5 by using an alkaline reagent to prepare a metal salt solution C;

[0065] The metal salt solution C, the lithium-containing solution and the phosphate-containing solution are mixed to perform a coprecipitation reaction, and the precipitate is collected and dried to obtain a precursor;

[0066] The precursor is mixed with a carbon source and sintered to prepare a lithium iron phosphate positive electrode material.

[0067] In some embodiments, in the method for preparing a lithium iron phosphate positive electrode material provided, the iron-containing waste slag is steelmaking waste slag.

[0068] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the mass ratio of the iron-containing waste slag to the acid in the acid solution is 1:(0.5~7), for example, the mass ratio of the iron-containing waste slag to the acid in the acid solution can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7 or a range selected from any two of the foregoing ratios.

[0069] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the mass ratio of the impurity remover to the iron-containing waste slag is (2~5):120. For example, the mass ratio of the impurity remover to the iron-containing waste slag can be 2:120, 3:120, 4:120, 5:120 or a range selected from any two of the foregoing ratios.

[0070] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the mass ratio of iron powder to iron-containing waste slag is (20~25):120. For example, the mass ratio of iron powder to iron-containing waste slag can be 20:120, 21:120, 22:120, 23:120, 24:120, 25:120 or a range selected from any two of the foregoing ratios.

[0071] It should be noted that in order to ensure that the iron slag can be completely dissolved, excess acid needs to be added. In addition, during the acid dissolution process, iron is easily oxidized. The added iron powder is used to neutralize the excess acid and reduce the oxidized iron ions.

[0072] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the mass ratio of the precursor to the carbon source is 1:(0.05~0.2), for example, the mass ratio of the precursor to the carbon source can be 1:0.05, 1:0.1, 1:0.15, 1:0.2 or a range selected from any two of the foregoing ratios.

[0073] In some embodiments, in the method for preparing a lithium iron phosphate positive electrode material provided, the impurity remover comprises one or both of sodium sulfide and ammonium fluoride.

[0074] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the metal salt solution A, the impurity remover, and the iron powder are mixed, and in the reaction step, the reaction includes a precipitation reaction to remove impurity metal ions, and the impurity metal ions include one or more of chromium ions, nickel ions, manganese ions, zinc ions, magnesium ions, calcium ions, and copper ions. The impurity remover containing one or both of sodium sulfide and ammonium fluoride at a specific content will react with the metal impurity ions to form a precipitate. In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, in the step of mixing the metal salt solution C with the lithium-containing solution and the phosphate-containing solution, the Fe 2+ , Li + PO4 3- The molar ratio is (0.9~1.2):(2.6~3.2):(0.9~1.2).

[0075] In some embodiments, in the method for preparing a lithium iron phosphate positive electrode material provided, the acid in the acid solution comprises one or more of sulfuric acid, hydrochloric acid and nitric acid.

[0076] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the molar concentration of the acid solution is 1 mol / L~4 mol / L. For example, the molar concentration of the acid solution can be 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or a range selected from any two of the foregoing values.

[0077] In some embodiments, in the step of adjusting the pH of the metal salt solution B to 0.5-2.5 using an alkaline reagent, the added alkaline reagent comprises one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia water.

[0078] In some embodiments, in the method for preparing a lithium iron phosphate positive electrode material provided, the lithium-containing solution contains one or more of lithium carbonate, lithium hydroxide, lithium bicarbonate, lithium sulfate, lithium phosphate, lithium dihydrogen phosphate and lithium chloride.

[0079] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the solubility of the lithium-containing solution is 0.5 mol / L~5 mol / L. For example, the solubility of the lithium-containing solution can be 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L or a range selected from any two of the foregoing values.

[0080] In some embodiments, in the method for preparing a lithium iron phosphate positive electrode material provided, the phosphate-containing solution contains one or more of phosphoric acid, sodium phosphate, lithium phosphate, lithium dihydrogen phosphate, and ammonium dihydrogen phosphate.

[0081] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the solubility of the phosphate solution is 0.5 mol / L~5 mol / L. For example, the solubility of the phosphate solution can be 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L or a range selected from any two of the foregoing values.

[0082] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the temperature for the coprecipitation reaction is 75°C~95°C. For example, the temperature for the coprecipitation reaction can be 75°C, 80°C, 85°C, 90°C, 95°C or a range selected from any two of the foregoing values.

[0083] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the coprecipitation reaction time is 1h~6h. For example, the coprecipitation reaction time can be 1h, 2h, 3h, 4h, 5h, 6h or a range selected from any two of the foregoing values.

[0084] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the pH value of the coprecipitation reaction is 3.5~6.5. For example, the pH value of the coprecipitation reaction can be 3.5, 4, 4.5, 5, 5.5, 6, 6.5 or a range selected from any two of the foregoing values.

[0085] In some embodiments, in the method for preparing a lithium iron phosphate positive electrode material provided, the carbon source comprises one or more of glucose, starch, sucrose, polyethylene glycol, and polyvinyl pyrrolidone.

[0086] In some embodiments, in the method for preparing the lithium iron phosphate positive electrode material provided, the sintering temperature is 750°C to 800°C.

[0087] In some embodiments, in the preparation method of the lithium iron phosphate positive electrode material provided, the sintering time is 8h~12h. For example, the sintering time can be 8h, 9h, 10h, 11h, 12h or a range selected from any two of the foregoing values.

[0088] In some embodiments, a lithium iron phosphate positive electrode material is provided, which is prepared by the aforementioned preparation method.

[0089] The lithium iron phosphate is prepared by a coprecipitation method using a raw material containing waste iron slag, and the provided lithium iron phosphate positive electrode material has uniform particle size and excellent electrochemical performance. In some embodiments, the use of the lithium iron phosphate positive electrode material in the preparation of a lithium ion battery is provided.

[0090] In some embodiments, a lithium-ion battery is provided, comprising the aforementioned lithium iron phosphate positive electrode material.

[0091] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0092] Example 1

[0093] This embodiment provides a lithium iron phosphate positive electrode material, and the preparation method is as follows:

[0094] (1) Take 160g of concentrated sulfuric acid and slowly add it to 1200mL of water. Then weigh 120g of waste iron slag and add it to the above sulfuric acid solution. Heat it to 80℃ and dissolve it for 6h. Cool it to room temperature and filter it to obtain solution A (corresponding to metal salt solution A).

[0095] (2) Add 2.4 g of sodium sulfide and 20 g of iron powder to the above solution A, stir, and then filter to obtain solution B (corresponding to metal salt solution B);

[0096] (3) Lithium hydroxide solution (alkaline reagent) is added dropwise to solution B, and the pH value of the solution is finally controlled to be 1.5 to obtain solution C (corresponding to metal salt solution C, which contains ferrous ions);

[0097] (4) Take 240 g of lithium phosphate and disperse it in 1000 mL of deionized water to obtain a lithium-containing solution for standby use; weigh 43 g of concentrated phosphoric acid and disperse it in 1000 mL of deionized water to obtain a lithium-containing solution for standby use.

[0098] (5) Add 4000 mL of bottom water into the reactor, then heat it to 95°C, and then simultaneously add solution C, the lithium-containing solution and the phosphate-containing solution into the reactor to carry out a co-precipitation reaction. After the addition is completed, the pH of the solution is controlled to 4.5 and maintained at this temperature for 4 h. Then, the temperature is cooled to room temperature, filtered, and the precipitate is collected, washed with deionized water, and dried at 60°C to obtain a reaction product (corresponding to the precursor).

[0099] (6) Take 20 g of the above reaction product and 1.6 g of glucose (carbon source) and mix and grind them in deionized water. When the particle size reaches 400±10 nm, it can be spray-dried. Then, the dried powder is sintered under nitrogen atmosphere at 780°C for 4 h. Then, it is naturally cooled to room temperature to obtain lithium iron phosphate positive electrode material.

[0100] The reaction product obtained in step (5) of the above embodiment was characterized by an X-ray diffractometer (Rigaku Ultima IV X-ray diffractometer, Japan) and observed by a scanning electron microscope (Zeiss Sigma360). The results can be found in Figure 2 and Figure 3 .from Figure 2 It can be seen from the results that the diffraction peak of the product is consistent with the diffraction peak of lithium iron phosphate, indicating that the reaction product is a pure phase lithium iron phosphate material. Figure 3 It can be seen that the particle size of the reaction product is uniform. Under an electron microscope, the primary particle size is about 200 nm, and the reaction product has a rod-shaped particle morphology. The crystal structure of the lithium iron phosphate positive electrode material obtained in step (6) is characterized. The results can be found in Figure 4 .from Figure 4 It can be seen from the results that the diffraction peak of the obtained lithium iron phosphate positive electrode material is consistent with the position of the diffraction peak of lithium iron phosphate, indicating that the reaction product is a pure phase lithium iron phosphate positive electrode material.

[0101] Electrochemical performance test

[0102] 1. Preparation of Lithium-ion Batteries

[0103] Then the lithium iron phosphate positive electrode material was made into a button cell for electrochemical performance testing. The test conditions were 0.1C charge and discharge, and the voltage range was 2.0V~3.65V. The test results are shown in Table 1.

[0104] (a) Pole preparation:

[0105] Weigh the three substances according to the mass ratio of lithium iron phosphate positive electrode material: conductive agent (super-p) and polyvinylidene fluoride (PVDF) = 8:1:1, and dry grind them in an agate mortar for 15 minutes to mix the three materials evenly, then transfer them to a glass bottle, add an appropriate amount of N-methylpyrrolidone (NMP) to adjust the viscosity of the slurry, seal it, and stir it continuously at 600rmp for 6 hours to form a uniform slurry, then apply it on the rough side of the copper foil that has been cleaned and dried in advance by a scraper method, with a coating thickness of about 200μm, then transfer it to a 110℃ oven for pre-drying for 2 hours, and then place it in a 100℃ vacuum drying oven for drying for 12 hours; after natural cooling, use a slicer to punch out discs with a diameter of 12mm, weigh, seal and place them in a drying dish for later use.

[0106] (b) Battery assembly:

[0107] CR2032 button cells were assembled in a glove box filled with high-purity argon atmosphere, where the contents of H2O and O2 were both less than 0.1ppm. The electrolyte was 1M LiPF6 (ethylene carbonate EC: ethyl methyl carbonate EMC: dimethyl carbonate DMC = 1:1:1 vol%), and the separator was PP separator.

[0108] 2.Battery performance test:

[0109] The electrochemical performance of CR2032 button cells was tested using a BlueDian battery test system. The charge and discharge cutoff voltage range was 2.0 V to 3.65 V. The test rates were 0.1 C / 0.1 C and 1 C / 1 C, respectively. The test results are shown in Table 1.

[0110] Example 2

[0111] This embodiment provides a lithium iron phosphate positive electrode material, and the preparation method is as follows:

[0112] (1) Take 160g (1.6mol) of concentrated sulfuric acid and slowly add it to 1200mL of water. Then weigh 120g (1.72mol, calculated as 80%) of waste iron slag and add it to the above sulfuric acid solution. Heat it to 90℃ and dissolve it for 6h. Cool it to room temperature and filter it to obtain solution A (corresponding to metal salt solution A).

[0113] (2) Add 4.1 g (0.11 mol) of the impurity remover ammonium fluoride and 23.4 g (0.42 mol) of iron powder to the above solution, stir, and then filter to obtain solution B (corresponding to metal salt solution B);

[0114] (3) Add sodium hydroxide solution (alkaline reagent) to solution B, and finally control the pH value of the solution to 0.5 to obtain solution C (corresponding to metal salt solution C, which contains ferrous ions);

[0115] (4) Take 348.3 g (2.72 mol) of lithium sulfate and disperse it in 1000 mL of deionized water to obtain a lithium-containing solution for standby use; weigh 243.4 g (2.11 mol) of concentrated phosphoric acid and disperse it in 1000 mL of deionized water to obtain a phosphate-containing solution for standby use.

[0116] (5) Add 4000 mL of bottom water into the reactor, then heat it to 90°C, and then simultaneously add solution C, the lithium-containing solution and the phosphate-containing solution into the reactor to carry out a co-precipitation reaction. After the addition is completed, the pH value of the solution is controlled to be 5.2, and maintained at this temperature for 4 hours, then cooled to room temperature, filtered, and the precipitate is collected, washed with deionized water, and dried at 60°C to obtain a reaction product (corresponding to the precursor).

[0117] (6) Take 20 g of the above reaction product and 1.6 g of glucose (carbon source) and mix and grind them in deionized water. When the particle size reaches 400±10 nm, it can be spray-dried. Then, the dried powder is sintered under nitrogen atmosphere at 780°C for 4 h. Then, it is naturally cooled to room temperature to obtain lithium iron phosphate positive electrode material.

[0118] The electrochemical performance test was carried out in the same manner as in Example 1. The test results are shown in Table 1.

[0119] Example 3

[0120] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material, and the preparation method is as follows:

[0121] (1) Take 160g (1.6mol) of concentrated sulfuric acid and slowly add it to 1200mL of water. Then weigh 120g (1.72mol, calculated as 80%) of waste iron slag and add it to the above sulfuric acid solution. Heat it to 90℃ and dissolve it for 6h. Cool it to room temperature and filter it to obtain solution A (corresponding to metal salt solution A).

[0122] (2) Add 3.2 g (0.086 mol) of the impurity remover ammonium fluoride and 23.4 g (0.42 mol) of iron powder to the above solution, stir, and then filter to obtain solution B (corresponding to metal salt solution B);

[0123] (3) Lithium hydroxide solution (alkaline reagent) is added dropwise to solution B, and the pH value of the solution is finally controlled to be 0.5, thereby obtaining solution C (corresponding to metal salt solution C, which contains ferrous ions);

[0124] (4) Take 243.8 g (3.27 mol) of lithium carbonate and disperse it in 1000 mL of deionized water to obtain a lithium-containing solution for standby use; weigh 243.4 g (2.11 mol) of concentrated phosphoric acid and disperse it in 1000 mL of deionized water to obtain a phosphate-containing solution for standby use.

[0125] (5) Add 4000 mL of bottom water into the reactor, then heat it to 95°C, and then simultaneously add solution C, the lithium-containing solution and the phosphate-containing solution into the reactor to carry out a co-precipitation reaction. After the addition is completed, the pH of the solution is controlled to 5.5 and maintained at this temperature for 6 h. Then, the temperature is cooled to room temperature, filtered, and the precipitate is collected, washed with deionized water, and dried at 60°C to obtain a reaction product (corresponding to the precursor).

[0126] (6) Take 20 g of the above reaction product and 1.6 g of glucose (carbon source) and mix and grind them in deionized water. When the particle size reaches 400±10 nm, it can be spray-dried. Then, the dried powder is sintered under nitrogen atmosphere at 780°C for 4 h. Then, it is naturally cooled to room temperature to obtain lithium iron phosphate positive electrode material.

[0127] The electrochemical performance test was carried out in the same manner as in Example 1. The test results are shown in Table 1.

[0128] Example 4

[0129] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material, and the preparation method is as follows:

[0130] (1) Take 160g (1.6mol) of concentrated sulfuric acid and slowly add it to 1200mL of water. Then weigh 120g (1.72mol, calculated as 80%) of waste iron slag and add it to the above sulfuric acid solution. Heat it to 90℃ and dissolve it for 6h. Cool it to room temperature and filter it to obtain solution A (corresponding to metal salt solution A).

[0131] (2) Add 4.2 g (0.054 mol) of sodium sulfide and 23.4 g (0.42 mol) of iron powder to the above solution, stir, and then filter to obtain solution B (corresponding to metal salt solution B);

[0132] (3) Lithium hydroxide solution (alkaline reagent) is added dropwise to solution B, and the pH value of the solution is finally controlled to be 2.0, thereby obtaining solution C (corresponding to metal salt solution C, which contains ferrous ions);

[0133] (4) Take 240 g (2.07 mol) of lithium phosphate and disperse it in 1000 mL of deionized water to obtain a lithium-containing solution for standby use; weigh 33.4 g (0.29 mol) of concentrated phosphoric acid and disperse it in 1000 mL of deionized water to obtain a phosphate-containing solution for standby use.

[0134] (5) Add 4000 mL of bottom water into the reactor, then heat it to 85°C, and then simultaneously add solution C, the lithium-containing solution and the phosphate-containing solution into the reactor to carry out a co-precipitation reaction. After the addition is completed, the pH value of the solution is controlled to be 5.5, and maintained at this temperature for 2 h, then cooled to room temperature, filtered, and the precipitate is collected, washed with deionized water, and dried at 60°C to obtain a reaction product (corresponding to the precursor).

[0135] (6) Take 20 g of the above reaction product and 1.6 g of glucose (carbon source) and mix and grind them in deionized water. When the particle size reaches 400±10 nm, it can be spray-dried. Then, the dried powder is sintered under nitrogen atmosphere at 780°C for 4 h. Then, it is naturally cooled to room temperature to obtain lithium iron phosphate positive electrode material.

[0136] The electrochemical performance test was carried out in the same manner as in Example 1. The test results are shown in Table 1.

[0137] Comparative Example 1

[0138] The difference from Example 1 is that lithium iron phosphate is prepared by a high-temperature solid phase method, and the preparation method is as follows:

[0139] Weigh 15g of battery-grade lithium carbonate, 60g of battery-grade anhydrous ferric phosphate and 5g of glucose, disperse them in deionized water, and then transfer them to a sand mill for grinding for 0.5h until the particle size reaches 400nm. The slurry is spray-dried and then sintered at 780°C in a tubular furnace under an inert atmosphere for 8h. After cooling naturally, lithium iron phosphate, a positive electrode material for lithium-ion batteries, is obtained.

[0140] The electrochemical performance test was carried out in the same manner as in Example 1. The test results are shown in Table 1.

[0141] Comparative Example 2

[0142] The difference from Example 1 is that the iron slag solution is not impurity-removed, and the preparation method is as follows:

[0143] (1) Take 160g of concentrated sulfuric acid and slowly add it to 1200mL of water. Then weigh 120g of waste iron slag and add it to the above sulfuric acid solution. Heat it to 80℃ and dissolve it for 6h. Cool it to room temperature and filter it to obtain solution A (corresponding to metal salt solution A).

[0144] (2) Add 20 g of iron powder to the above solution A, stir, and then filter to obtain solution B (corresponding to metal salt solution B);

[0145] (3) Lithium hydroxide solution (alkaline reagent) is added dropwise to solution B, and the pH value of the solution is finally controlled to be 1.5 to obtain solution C (corresponding to metal salt solution C, which contains ferrous ions);

[0146] (4) Take 240 g of lithium phosphate and disperse it in 1000 mL of deionized water to obtain a lithium-containing solution for standby use; weigh 43 g of concentrated phosphoric acid and disperse it in 1000 mL of deionized water to obtain a lithium-containing solution for standby use.

[0147] (5) Add 4000 mL of bottom water to the reactor, then heat it to 95°C, and then simultaneously drop solution C, the lithium-containing solution and the phosphate-containing solution into the reactor to perform a coprecipitation reaction. After the dropwise addition is completed, the pH of the solution is controlled to 4.5, and maintained at this temperature for 4 hours, then cooled to room temperature, filtered, and then washed with deionized water, and dried at 60°C to obtain a reaction product (corresponding to the precursor).

[0148] (6) Take 20 grams of the above reaction product and 1.6 g of glucose, mix and grind them in deionized water. When the particle size reaches 400±10 nm, spray drying can be carried out. Then, the dried powder is sintered under nitrogen atmosphere at a sintering temperature of 780°C for 4 hours. Then, it is naturally cooled to room temperature to obtain lithium iron phosphate positive electrode material.

[0149] The electrochemical performance test was carried out in the same manner as in Example 1. The test results are shown in Table 1.

[0150] Comparative Example 3

[0151] The difference from Example 1 is that no carbon coating is performed. The preparation method is as follows:

[0152] (1) Take 160g of concentrated sulfuric acid and slowly add it to 1200mL of water. Then weigh 120g of waste iron slag and add it to the above sulfuric acid solution. Heat it to 80℃ and dissolve it for 6h. Cool it to room temperature and filter it to obtain solution A (corresponding to metal salt solution A).

[0153] (2) Add 2.4 g of sodium sulfide and 20 g of iron powder to the above solution A, stir, and then filter to obtain solution B (corresponding to metal salt solution B);

[0154] (3) Lithium hydroxide solution (alkaline reagent) is added dropwise to solution B, and the pH value of the solution is finally controlled to be 1.5 to obtain solution C (corresponding to metal salt solution C, which contains ferrous ions);

[0155] (4) Take 240 g of lithium phosphate and disperse it in 1000 mL of deionized water to obtain a lithium-containing solution for standby use; weigh 43 g of concentrated phosphoric acid and disperse it in 1000 mL of deionized water to obtain a lithium-containing solution for standby use.

[0156] (5) Add 4000 mL of bottom water to the reactor, then heat it to 95°C, and then simultaneously drop solution C, the lithium-containing solution and the phosphate-containing solution into the reactor to perform a coprecipitation reaction. After the dropwise addition is completed, the pH of the solution is controlled to 4.5, and maintained at this temperature for 4 hours, then cooled to room temperature, filtered, and then washed with deionized water, and dried at 60°C to obtain a reaction product (corresponding to the precursor).

[0157] The electrochemical performance of the reaction product obtained by the same method as in Example 1 was tested. The test results are shown in Table 1.

[0158] Test results analysis

[0159] Table 1 below shows the test results of the electrochemical performance of button cells prepared using the lithium iron phosphate positive electrode materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3.

[0160] Table 1

[0161]

[0162] The results show that the button-type batteries prepared using the lithium iron phosphate positive electrode materials of Examples 1 to 4 have high specific charge and discharge capacity, high initial efficiency, and excellent electrochemical performance. The lithium iron phosphate positive electrode material prepared by the high-temperature solid phase method in Comparative Example 1, the lithium iron phosphate positive electrode material in Comparative Example 2 was not impurity-removed, and the lithium iron phosphate positive electrode material in Comparative Example 3 was not carbon-coated. The button-type batteries prepared using the lithium iron phosphate positive electrode materials of Comparative Examples 1 to 3 have low specific charge and discharge capacity and low initial efficiency.

[0163] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0164] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description and drawings may be used to interpret the content of the claims.

Claims

1. A method for preparing a lithium iron phosphate positive electrode material, characterized in that: The following steps are involved: The iron-containing waste slag is acid-dissolved by using an acid solution, the solid-liquid separation is performed, and the liquid phase is collected to prepare a metal salt solution A; The metal salt solution A, the impurity remover and the iron powder are mixed, reacted, solid-liquid separated, and the liquid phase is collected to prepare a metal salt solution B; wherein the metal salt solution B contains ferrous ions, Using an alkaline reagent to increase the pH of the metal salt solution B to 0.5-2.5 to prepare a metal salt solution C; The metal salt solution C, the lithium-containing solution and the phosphate-containing solution are mixed to perform a coprecipitation reaction, and the precipitate is collected and dried to obtain a precursor; The precursor is mixed with a carbon source and sintered to prepare the lithium iron phosphate positive electrode material.

2. The preparation method according to claim 1, characterized in that: Meet one or more of the following characteristics: The iron-containing waste slag is steelmaking waste slag; The mass ratio of the iron-containing waste slag to the acid in the acid solution is 1:(0.5-7); The mass ratio of the impurity remover to the iron-containing waste slag is (2-5):120; The mass ratio of the iron powder to the iron-containing waste slag is (20-25):120; The mass ratio of the precursor to the carbon source is 1:0.05-0.

2.

3. The preparation method according to claim 1 or 2, characterized in that: The impurity remover comprises one or both of sodium sulfide and ammonium fluoride.

4. The preparation method according to any one of claims 1 to 3, characterized in that In the step of mixing the metal salt solution C with the lithium-containing solution and the phosphate-containing solution, Fe 2+ , Li + PO4 3- The molar ratio is (0.9~1.2):(2.6~3.2):(0.9~1.2).

5. The preparation method according to any one of claims 1 to 4, characterized in that Meet one or more of the following characteristics: The acid in the acid solution comprises one or more of sulfuric acid, hydrochloric acid and nitric acid; The molar concentration of the acid solution is 1 mol / L to 4 mol / L; The lithium-containing solution contains one or more of lithium carbonate, lithium hydroxide, lithium bicarbonate, lithium sulfate, lithium phosphate, lithium dihydrogen phosphate and lithium chloride; The solubility of the lithium-containing solution is 0.5 mol / L to 5 mol / L; The phosphate-containing solution contains one or more of phosphoric acid, sodium phosphate, lithium phosphate, lithium dihydrogen phosphate and ammonium dihydrogen phosphate; The solubility of the phosphate-containing solution is 0.5 mol / L to 5 mol / L.

6. The preparation method according to any one of claims 1 to 5, characterized in that The metal salt solution A, the impurity remover and the iron powder are mixed and a reaction step is carried out, wherein the reaction includes a precipitation reaction to remove impure metal ions, and the impurity metal ions include one or more of chromium ions, nickel ions, manganese ions, zinc ions, magnesium ions, calcium ions and copper ions.

7. The preparation method according to any one of claims 1 to 6, characterized in that Meet one or more of the following characteristics: The temperature for carrying out the coprecipitation reaction is 75°C to 95°C; The coprecipitation reaction is carried out for 1 h to 6 h; The pH value for the coprecipitation reaction is 3.5 to 6.5; The carbon source comprises one or more of glucose, starch, sucrose, polyethylene glycol and polyvinyl pyrrolidone; The sintering temperature is 750°C to 800°C; The sintering time is 8h~12h.

8. A lithium iron phosphate positive electrode material, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the lithium iron phosphate positive electrode material according to claim 8 in the preparation of lithium ion batteries.

10. A lithium ion battery, characterized in that: Contains the lithium iron phosphate positive electrode material as described in claim 8.

Images