Modified lithium iron phosphate material and preparation and application thereof

Abstract

The invention relates to the technical field of recycling of waste lithium ion batteries, in particular to a modified lithium iron phosphate material as well as preparation and application thereof. The method comprises the following steps: firstly, dispersing waste lithium iron phosphate powder into a mixed solution of absolute ethyl alcohol and ammonia water to obtain a lithium iron phosphate solution; then, uniformly mixing a titanium source with a lithium iron phosphate solution, and after reaction, performing post-treatment to obtain TiO2 coating modified LiFePO4 powder: LiFePO4-coated TiO2 powder; and finally, calcining the LiFePO4-coated TiO2 powder in a nitrogen atmosphere to obtain the modified lithium iron phosphate material. The preparation method provided by the invention has the characteristics of greenness, safety and low cost, the system adopts an efficient gradient utilization strategy, the sustainable development requirement is completely met, and the preparation method is completely matched with the efficient treatment and recycling targets of wastes.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling and reusing waste lithium-ion batteries, and in particular to a modified lithium iron phosphate material and a preparation and application thereof. Background Art

[0002] How to properly handle the recycling of used batteries and the lithium resource crisis is one of the key technical barriers to solving the future energy storage problem. Compared with lithium resources on land, the lithium reserves in seawater are 16,000 times that of land. Considering this high reserve, various research institutions have carried out technical development of lithium extraction from seawater. However, since the lithium concentration in seawater is only 0.17ppm, the cost and output of lithium extraction from seawater are very different. In addition, due to the rich variety of ions in seawater, including Na and Mg ions with similar chemical properties to Li ions, the lithium extraction process is accompanied by other impurity ions. Therefore, how to reduce the cost of lithium extraction from seawater and improve the selectivity of lithium extraction has become the key to the development of seawater lithium extraction technology.

[0003] Zhou Haoshen et al. (Yang, SX; Zhang, F.; Ding, He, P.*; Zhou, HS*Lithium Metal Extraction from Seawater. Joule, 2018, 2(9), 1648-1651.) from Nanjing University proposed a system for extracting lithium from seawater using solar panels as the driving force of electricity and based on lithium-ion solid electrolyte film. However, the disadvantage is that the solid electrolyte film is expensive and the system needs to be sealed, which is not conducive to practical application in an open ocean environment. Therefore, it is still crucial to develop an open ocean lithium extraction system. Summary of the invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a modified lithium iron phosphate material and its preparation and application. The present invention modifies waste lithium iron phosphate electrode materials by coating with titanium dioxide to obtain a highly selective and stable lithium ion insertion and extraction process; the preparation method is green, safe, and low-cost, and the system adopts an efficient cascade utilization strategy, which fully meets the requirements of sustainable development and is fully consistent with the goals of efficient waste management and resource utilization.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] The first object of the present invention is to provide a method for preparing a modified lithium iron phosphate material, comprising the following steps:

[0007] (S1) dispersing waste lithium iron phosphate powder in a mixed solution of anhydrous ethanol and aqueous ammonia to obtain a lithium iron phosphate solution;

[0008] (S2) mixing the titanium source with the lithium iron phosphate solution prepared in step (S1), and performing post-treatment after the reaction to obtain LiFePO4 powder modified with a TiO2 coating: LiFePO4@TiO2 powder;

[0009] (S3) The LiFePO4@TiO2 powder is placed in a nitrogen atmosphere for calcination to obtain a modified lithium iron phosphate material.

[0010] In the present invention, in the LiFePO4@TiO2 powder, the TiO2 coating layer plays an excellent buffering role in the process of lithium ion embedding and de-embedding of waste lithium iron phosphate electrode materials, effectively reduces the desolvation energy of lithium ions at the electrode interface, enhances the selectivity of lithium ions, and significantly improves the charge and discharge rate and cycle stability of waste lithium iron phosphate electrode materials.

[0011] In one embodiment of the present invention, in step (S1), the volume ratio of anhydrous ethanol to aqueous ammonia is 300-350:1;

[0012] The dosage ratio of waste lithium iron phosphate powder to the mixed solution of anhydrous ethanol and ammonia water is 0.5-1 mg:1 mL.

[0013] In one embodiment of the present invention, the dispersion is ultrasonic dispersion for a time of 0.5 to 3 hours.

[0014] In one embodiment of the present invention, in step (S2), the titanium source is selected from one of isopropyl titanate, n-butyl titanate, and titanium tetrachloride;

[0015] The volume ratio of the titanium source to the mixed solution of anhydrous ethanol and ammonia water is 1:100-150;

[0016] During the reaction, the temperature is 35-42°C and the reaction time is 40-48h;

[0017] The post-treatment is to use anhydrous ethanol for washing after the reaction is completed, and then centrifuge and dry in an oven.

[0018] In one embodiment of the present invention, during the mixing process of the titanium source and the lithium iron phosphate solution, the temperature is 35 to 42° C., and the environment is a temperature control device such as a water bath, an oil bath or a heating jacket;

[0019] The mixing process includes two stages: a fast stirring stage and a low-speed stirring stage;

[0020] The speed in the rapid stirring stage is 500-1000 rpm / min, and the speed in the slow stirring stage is 100-200 rpm / min.

[0021] In one embodiment of the present invention, the washing is performed with anhydrous ethanol for 3 times, and the temperature during the drying process is 40-60°C.

[0022] In one embodiment of the present invention, in step (S3), during the calcination treatment, the temperature is 400-500° C., the heating rate is 1-5° C. / min, and the time is 1-5 h.

[0023] The second object of the present invention is to provide a modified lithium iron phosphate material prepared by the above method, wherein the modified lithium iron phosphate material is a titanium dioxide-coated lithium iron phosphate electrode material, and the coating layer is titanium dioxide with controllable thickness.

[0024] The third object of the present invention is to provide a modified lithium iron phosphate material for use in preparing a cathode electrode.

[0025] A fourth object of the present invention is to provide a method for preparing a cathode electrode, comprising the following steps:

[0026] (A1) grinding and mixing conductive carbon black, polyvinylidene fluoride, modified lithium iron phosphate material and N-methyl pyrrolidone to obtain a mixed slurry;

[0027] (A2) Scrape the mixed slurry onto the conductive carbon cloth (1*2cm 2 ) and dried to obtain a LiFePO4@TiO2 electrode;

[0028] (A3) Using the LiFePO4@TiO2 electrode prepared in step (A2) as a working electrode, an activated carbon electrode as a counter electrode, and Ag / AgCl as a reference electrode, delithiation treatment is performed in a magnesium chloride solution to obtain a cathode electrode: FePO4@TiO2 electrode.

[0029] In one embodiment of the present invention, in step (A1), the mass ratio of conductive carbon black, polyvinylidene fluoride and modified lithium iron phosphate material is 1-2:1:7-8, and the solid content of the mixed slurry is 75-85% (preferably, the solid content of the mixed slurry is 80%);

[0030] In step (A2), the scraping amount of the mixed slurry is 1 mg / cm 2 ~100mg / cm 2 ; The drying process is in a dry atmosphere, the temperature is 100-110°C, and the time is 12-24h;

[0031] In step (A3), the concentration of magnesium chloride is 0.5 mol / L. During the delithiation process, it is electrochemically charged to 0.8 V.

[0032] The fifth object of the present invention is to provide a cathode electrode prepared by the above method.

[0033] The sixth object of the present invention is to provide a cathode electrode for use in preparing a lithium extraction system.

[0034] The present invention is based on the principle of primary cells. A metal element that can undergo self-corrosion reaction in seawater / brine and function as an electron donor is selected as the anode, and a FePO4@TiO2 electrode is selected as the cathode. The anode and the cathode are placed in a quartz electrolytic cell filled with seawater or brine. As the anode metal element self-corrodes and discharges to generate electrons, they quickly flow to the cathode through an external circuit. To maintain electrical neutrality, the FePO4@TiO2 cathode captures a lithium ion from the seawater / brine while receiving an electron, thereby realizing the extraction of lithium ions.

[0035] In the present invention, the main anode reaction of the lithium extraction system (selecting metal elements (such as Fe, Mg, and Al metal electrodes) that can undergo self-corrosion reactions in seawater / brine as electron donors as anodes, FePO4@TiO2 electrodes as cathodes, and placing the anodes and cathodes in a quartz electrolytic cell filled with seawater or brine) is:

[0036] Metal(0)→Metal(n+)+e - ;

[0037] The main cathode reaction of the lithium extraction system is:

[0038] FePO4@TiO2+Li + +e - →LiFePO4@TiO2;

[0039] In general, the present invention establishes a sustainable coupling pathway for the recovery of lithium-ion battery electrode materials and the extraction of lithium resources from unconventional water sources.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) In theory, by modifying the oxidative coating layer, the desolvation energy barrier for lithium ions to embed at the electrode interface can be increased, thereby improving the material's selectivity for lithium ions and regenerating the electrochemical properties of spent lithium-ion battery electrode materials.

[0042] (2) In terms of technology, in order to address the recycling problem of waste lithium iron phosphate positive electrode materials, a simple, green and efficient modification method was developed, and a self-driven electrochemical seawater / brine lithium extraction system was constructed, which effectively expanded the cascade utilization scenarios of lithium iron phosphate electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The preparation flow chart of modified lithium iron phosphate material;

[0044] Figure 2XRD diagrams of waste lithium iron phosphate powder, LiFePO4@TiO2 powder and modified lithium iron phosphate material in Example 1;

[0045] Figure 3 The XPS graphs of the waste lithium iron phosphate powder and LiFePO4@TiO2 powder in Example 1;

[0046] Figure 4 The cyclic voltammetry test curve of LiFePO4@TiO2 electrode in different cationic electrolytes in Example 2;

[0047] Figure 5 The lithium extraction redox curve of the cathode electrode in the electrochemical brine lithium extraction system in Example 2;

[0048] Figure 6 This is the ICP-MS analysis diagram of the electrolyte after delithiation in Example 2. DETAILED DESCRIPTION

[0049] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] In the following embodiments, waste lithium iron phosphate powder is obtained by the following method: waste lithium iron phosphate is disassembled after being discharged to obtain active powder of the positive terminal.

[0051] Unless otherwise specified, all reagents used are commercially available reagents, and all detection means and methods used are conventional detection means and methods in the art.

[0052] Example 1

[0053] This embodiment provides a method for preparing a modified lithium iron phosphate material (sol-gel combined with low temperature heat treatment, such as Figure 1 As shown), comprising the following steps:

[0054] (S1) preparing a mixed solution consisting of 600 mL of anhydrous ethanol and 1.8 mL of aqueous ammonia (28 wt%), weighing 450 mg of waste lithium iron phosphate powder and adding it to the solution, and ultrasonically dispersing for 1 h to obtain a lithium iron phosphate solution;

[0055] (S2) The lithium iron phosphate solution obtained in step (S1) is transferred to an environment at a water bath temperature of 40°C, and then 1 mL of isopropyl titanate is added as a titanium source. After rapid stirring at a speed of 500 rpm for 30 min, the stirring rate is slowed down to 150 rpm, and the reaction is continued for 40 h. After the reaction is completed, anhydrous ethanol is used as a detergent, and after centrifugation (washing and centrifugation 3 times), it is placed in an oven for drying (50°C) to obtain an amorphous TiO2 coating-modified LiFePO4 powder: LiFePO4@TiO2 powder;

[0056] (S3) The LiFePO4@TiO2 powder obtained in step (S2) is calcined at 450°C in a nitrogen atmosphere in a tubular furnace at a heating rate of 5°C / min and kept warm for 3 hours to obtain a modified lithium iron phosphate material.

[0057] pass Figure 2 It can be found that the XRD peak shape did not change significantly before and after modification, indicating that the modification method did not destroy the intrinsic structure of the lithium iron phosphate electrode material.

[0058] pass Figure 3 It can be found that in the XPS peak spectra of the samples before and after modification, there is an obvious Ti 2p peak, indicating the existence of the TiO2 layer.

[0059] Example 2

[0060] This embodiment provides a method for preparing a cathode electrode, comprising the following steps:

[0061] (A1) Conductive carbon cloth (1*2cm 2 ) as a current collector, the modified lithium iron phosphate material, conductive carbon black and polyvinylidene fluoride prepared in Example 1 were put into an agate mortar in a mass ratio of 7:2:1, 100 μL of N-methylpyrrolidone was added and ground for 15 min to obtain a mixed slurry; then, the ground mixed slurry was evenly scraped on the conductive carbon cloth with a surgical scraper (the scraping amount was 50 mg / cm 2 ), place the conductive carbon cloth in a vacuum drying oven and dry it at 110°C for 20 h to obtain a LiFePO4@TiO2 electrode.

[0062] The LiFePO4@TiO2 electrode was tested to determine its effect on the insertion and extraction of lithium ions. The details are as follows:

[0063] (A101) Prepare three electrolytes: 0.5M LiNO3, 0.5M NaNO3, and a mixture of equal volumes of 0.5M LiNO3 and 0.5M NaNO3.

[0064] (A102) The three-electrode method was used for testing, with the LiFePO4@TiO2 electrode prepared in step (A1) as the working electrode, the Ag / AgCl electrode as the reference electrode, and the Pt electrode as the counter electrode; the three electrolytes prepared in step (A2) were respectively tested for cyclic voltammetry curves using an electrochemical workstation, with the scanning voltage range set to -0.2 to 0.8 V and the scanning rate set to 1 mV / s.

[0065] like Figure 4As shown, the prepared TiO2 coating-modified LiFePO4 electrode exhibits a lithium ion redox peak in a lithium and sodium mixed solution, and has significant lithium ion selectivity; indicating that the TiO2 coating effectively improves the lithium insertion and sodium resistance properties of the LiFePO4 electrode.

[0066] (A2) The LiFePO4@TiO2 electrode prepared in step (A1) was used as the working electrode, the activated carbon electrode was used as the counter electrode, and the Ag / AgCl electrode was used as the reference electrode. -1 The electrode was electrochemically charged to 0.8 V at a current of 0.5 mA in a magnesium chloride solution using a constant current charging mode of an electrochemical workstation, and then delithiation treatment was performed to obtain a cathode electrode: FePO4@TiO2 electrode.

[0067] (A201) The FePO4@TiO2 electrode was tested to determine its lithium extraction redox curve. Specifically, the FePO4@TiO2 electrode prepared as above was used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the Pt electrode was used as the counter electrode. The electrode was electrochemically charged to 0.8V at a current of 0.5 mA. The brine from a salt lake in Qinghai was used as the electrolyte containing a lithium source. The lithium extraction redox curve is shown in FIG. Figure 5 As shown, through Figure 5 It can be found that the constant current discharge curve in real salt lake water has an obvious redox platform, which means that the lithium ion embedding process can be completed.

[0068] (A202) The electrolyte after delithiation is subjected to ICP-MS analysis to analyze the ion concentration (including the concentration of Li, Na, and Mg ions) therein; the results are as follows: Figure 6 As shown, through Figure 6 It can be found that the results of ICP-MS show that only Li ions exist in the released liquid, and the concentrations of Na and Mg ions are lower than the detection line of the instrument, indicating its high selectivity for Li ions.

[0069] The cathode electrode provided in this embodiment can be further applied to electrochemical lithium extraction from seawater / brine.

[0070] Example 3

[0071] This embodiment provides a method for preparing a modified lithium iron phosphate material, comprising the following steps:

[0072] (S1) preparing a mixed solution consisting of 540 mL of anhydrous ethanol and 1.8 mL of aqueous ammonia (28 wt%), weighing 450 mg of waste lithium iron phosphate powder and adding it to the solution, and ultrasonically dispersing it for 1 h to obtain a lithium iron phosphate solution;

[0073] (S2) The lithium iron phosphate solution obtained in step (S1) was transferred to an environment at a water bath temperature of 35°C, and then 1 mL of isopropyl titanate was added as a titanium source. After rapid stirring at a speed of 500 rpm for 30 min, the stirring rate was slowed down to 150 rpm, and the reaction was continued for 44 h. After the reaction was completed, anhydrous ethanol was used as a detergent, and after centrifugation (washing and centrifugation 3 times), it was placed in an oven for drying (50°C) to obtain an amorphous TiO2 coating-modified LiFePO4 powder: LiFePO4@TiO2 powder;

[0074] (S3) The LiFePO4@TiO2 powder obtained in step (S2) is calcined at 500°C in a nitrogen atmosphere in a tubular furnace at a heating rate of 1°C / min and kept at this temperature for 1 hour to obtain a modified lithium iron phosphate material.

[0075] Example 4

[0076] This embodiment provides a method for preparing a modified lithium iron phosphate material, comprising the following steps:

[0077] (S1) preparing a mixed solution consisting of 630 mL of anhydrous ethanol and 1.8 mL of aqueous ammonia (28 wt%), weighing 450 mg of waste lithium iron phosphate powder and adding it to the solution, and ultrasonically dispersing it for 1 h to obtain a lithium iron phosphate solution;

[0078] (S2) The lithium iron phosphate solution obtained in step (S1) is transferred to an environment at a water bath temperature of 42° C., and then 1 mL of isopropyl titanate is added as a titanium source. After rapid stirring at a speed of 500 rpm for 30 min, the stirring rate is slowed down to 150 rpm, and the reaction is continued for 48 h. After the reaction is completed, anhydrous ethanol is used as a detergent, and after centrifugation (washing and centrifugation 3 times), it is placed in an oven for drying (50° C.) to obtain an amorphous TiO2 coating-modified LiFePO4 powder: LiFePO4@TiO2 powder;

[0079] (S3) The LiFePO4@TiO2 powder obtained in step (S2) is calcined at 400°C in a nitrogen atmosphere in a tubular furnace at a heating rate of 3°C / min and kept warm for 5 hours to obtain a modified lithium iron phosphate material.

[0080] The performance of the modified lithium iron phosphate material prepared in Example 3 and Example 4 is comparable to that of the modified lithium iron phosphate material prepared in Example 1.

[0081] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the explanation of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a modified lithium iron phosphate material, characterized in that: The following steps are involved: (S1) dispersing waste lithium iron phosphate powder in a mixed solution of anhydrous ethanol and aqueous ammonia to obtain a lithium iron phosphate solution; (S2) mixing the titanium source with the lithium iron phosphate solution prepared in step (S1), and performing post-treatment after the reaction to obtain LiFePO4 powder modified with a TiO2 coating: LiFePO4@TiO2 powder; (S3) The LiFePO4@TiO2 powder is placed in a nitrogen atmosphere for calcination to obtain a modified lithium iron phosphate material.

2. The method for preparing a modified lithium iron phosphate material according to claim 1, characterized in that: In step (S1), the volume ratio of anhydrous ethanol to aqueous ammonia is 300-350:1; The dosage ratio of waste lithium iron phosphate powder to the mixed solution of anhydrous ethanol and ammonia water is 0.5-1 mg:1 mL.

3. The method for preparing a modified lithium iron phosphate material according to claim 1, characterized in that: In step (S2), the titanium source is selected from one of isopropyl titanate, n-butyl titanate, and titanium tetrachloride; The volume ratio of the mixed solution of the titanium source, anhydrous ethanol and ammonia water is 1:100-150; During the reaction, the temperature is 35-42°C and the reaction time is 40-48 hours.

4. The method for preparing a modified lithium iron phosphate material according to claim 1, characterized in that: In step (S3), during the calcination process, the temperature is 400-500°C, the heating rate is 1-5°C / min, and the time is 1-5h.

5. A modified lithium iron phosphate material prepared by the method according to any one of claims 1 to 4.

6. Use of the modified lithium iron phosphate material as claimed in claim 5 in preparing a cathode electrode.

7. A method for preparing a cathode electrode, characterized in that: The following steps are involved: (A1) grinding and mixing conductive carbon black, polyvinylidene fluoride, the modified lithium iron phosphate material according to claim 5 and N-methylpyrrolidone to obtain a mixed slurry; (A2) coating the mixed slurry on a conductive carbon cloth and drying it to obtain a LiFePO4@TiO2 electrode; (A3) Using the LiFePO4@TiO2 electrode prepared in step (A2) as a working electrode, an activated carbon electrode as a counter electrode, and Ag / AgCl as a reference electrode, delithiation treatment is performed in a magnesium chloride solution to obtain a cathode electrode: FePO4@TiO2 electrode.

8. The method for preparing a cathode electrode according to claim 7, characterized in that: In step (A1), the mass ratio of conductive carbon black, polyvinylidene fluoride and modified lithium iron phosphate material is 1-2:1:7-8, and the solid content of the mixed slurry is 75-85%; In step (A2), the scraping amount of the mixed slurry is 1 mg / cm 2 ~100mg / cm 2 ; The drying process is in a dry atmosphere, the temperature is 100-110°C, and the time is 12-24h; In step (A3), the concentration of magnesium chloride is 0.5 mol / L. During the delithiation process, it is electrochemically charged to 0.8 V.

9. A cathode electrode, characterized in that: It is prepared by the method according to claim 8.

10. Use of the cathode electrode as claimed in claim 9 in constructing a self-driven seawater / brine lithium extraction system.

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