Method for recycling lithium and iron from waste lithium iron phosphate batteries and lithium iron phosphate prepared from recycled materials

Abstract

The invention relates to the technical field of recycling treatment of waste lithium ion batteries, in particular to a method for recycling lithium and iron from waste lithium iron phosphate batteries and lithium iron phosphate prepared from recycled materials. The method comprises the following steps: taking a lithium-containing solution as a raw material, inserting an anode and a cathode into the lithium-containing solution, electrifying for electrolysis under sunlight irradiation, carrying out solid-liquid separation after electrolysis is completed, adding carbonate into the lithium-containing solution for reaction, and carrying out solid-liquid separation after the reaction is completed to obtain lithium carbonate, wherein the anode is a conductive material modified by a piezoelectric and photoelectric double-activity material. The conductive material modified by the piezoelectric and photoelectric double-activity material is used as the anode material, solar energy is converted into electric energy, lithium ions and iron ions are selectively recycled from the waste lithium iron phosphate battery, and the method is environment-friendly and clean.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling and processing of waste lithium-ion batteries, and in particular to a method for recycling lithium and iron from waste lithium iron phosphate batteries and lithium iron phosphate prepared by using the recycled materials. Background Art

[0002] According to statistics released by the International Energy Agency (IEA), driven by the decarbonization of transportation, the stock of electric vehicles (EVs) has surged from 17,000 in 2010 to 16.2 million in 2021. Lithium-ion batteries (LIBs) have the advantages of high capacity and high power density and are considered to be the key components that determine the driving performance of the entire vehicle. Among commercial lithium-ion batteries, lithium iron phosphate (LiFePO 4 , LFP) batteries are widely used, accounting for more than 32% of the entire LIB market share due to their superior safety, earth-abundant iron sources and relatively low production costs. Waste batteries are a valuable resource because the concentration of key elements, especially lithium, contained in waste LFP batteries exceeds that in minerals. For example, it only takes 23 tons of waste LFP batteries to produce one ton of lithium, while the corresponding brine or ore requires 750 tons or 250 tons.

[0003] Existing battery recycling technologies mainly include pyrometallurgy, biometallurgy and hydrometallurgy, each of which has its own limitations. Pyrometallurgy is a mature technical route, but it consumes a lot of energy and produces a lot of waste gas in the process. The recovery cycle of biometallurgy is relatively long. Although hydrometallurgy can effectively recover lithium and iron ions, it consumes a lot of chemical reagents and has the risk of causing secondary pollution. In recent years, electrochemical recovery methods have gradually attracted widespread attention in the industry due to their environmental friendliness and high selectivity, but electrochemical recovery requires a lot of electricity. Fortunately, solar energy is inexhaustible, and photoelectrochemistry can convert solar energy into electrical energy. Therefore, how to use solar energy for the recovery of waste lithium iron phosphate batteries is a technical problem that needs to be solved in this field. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for recovering lithium and iron from waste lithium iron phosphate batteries and lithium iron phosphate prepared using recycled materials. The present invention uses a conductive material modified with a material having both piezoelectric and photoelectric activity as an anode material to convert solar energy into electrical energy, which is used to selectively recover lithium ions (in the form of lithium carbonate) and iron ions (in the form of iron phosphate) from waste lithium iron phosphate batteries, which is environmentally friendly and clean.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for recovering lithium and iron from waste lithium iron phosphate batteries, the method comprising the following steps:

[0007] The acidic leachate of the positive active material of the waste lithium iron phosphate battery is used as the electrolyte, an anode and a cathode are inserted into the electrolyte, and then the anode and the cathode are energized for electrolysis under sunlight. After the electrolysis is completed, the electrolysis material is subjected to solid-liquid separation, the liquid is a lithium-containing solution, and the solid is an iron-containing sediment. Then, carbonate is added to the lithium-containing solution for reaction, and lithium carbonate is obtained by solid-liquid separation after the reaction is completed; wherein, the acidic leachate of the positive active material of the waste lithium iron phosphate battery is a solution obtained by leaching a target solid substance with an acid solution, the target solid substance includes the positive electrode sheet of the waste lithium iron phosphate battery and / or a substance peeled off from the positive electrode sheet, and the anode is a conductive material modified by a material having both piezoelectric and photoelectric activity.

[0008] The present invention uses a conductive material modified with a material having both piezoelectric and photoelectric activities as an anode material to convert solar energy into electrical energy, which is used to selectively recover lithium ions (in the form of lithium carbonate) and iron ions (in the form of iron phosphate) from waste lithium iron phosphate batteries, thereby being environmentally friendly and clean.

[0009] Further, the acid solution includes at least one of an aqueous solution of p-toluenesulfonic acid, an aqueous solution of methanesulfonic acid, an aqueous solution of citric acid, an aqueous solution of succinic acid, an aqueous solution of malic acid, an aqueous solution of aspartic acid, and an aqueous solution of oxalic acid;

[0010] And / or, the concentration of the acid solution is 1-4 mol / L;

[0011] And / or, the solid-liquid ratio of the target solid substance to the acid solution is (20-60) g:1 L; and / or, the time for leaching the target solid substance with the acid solution is 60 min to 240 min.

[0012] Furthermore, the electrolyte is in a stirring state with a stirring rate of 500-3000 rpm.

[0013] Furthermore, the material having piezoelectric and photoelectric dual activity includes CdS, ZnO, CdTe, MoS 2 At least one of;

[0014] And / or, the conductive material includes fluorine-doped tin oxide.

[0015] Furthermore, the anode is fluorine-doped tin oxide modified by a CdS nanorod array having piezoelectric and photoelectric dual activity; the preparation method of the anode comprises the following steps:

[0016] A. Place FTO conductive glass in Na2 After soaking in S aqueous solution, it was washed with ethanol and ultrapure water in turn and dried, and then immersed in CdCl 2 Soak in an aqueous solution, then wash with ethanol and ultrapure water in turn and blow dry;

[0017] B. Repeat step A for multiple times to obtain a CdS seed layer, and then place it in a Cd(NO 3 ) 2 , CH 4 N 2 The reaction is carried out in a reactor of S and GSH aqueous solution at 100-300° C. for 12-48 hours to obtain a fluorine-doped tin oxide electrode modified by a CdS nanorod array having both piezoelectric and photoelectric activities.

[0018] Furthermore, in the method for preparing the anode, in step A, the immersion time is 1 to 5 minutes; in step B, the continuous ion layer adsorption reaction in step A is repeated 5 to 15 times.

[0019] Furthermore, the cathode is at least one of graphite, titanium sheet, stainless steel sheet, boron-doped diamond, and platinum sheet;

[0020] And / or, direct current is passed through the anode and the cathode to perform electrolysis.

[0021] Furthermore, the electrolysis temperature is 20-80°C, the electrolysis time is 1-10h, and the electrolysis voltage is 0-0.4V;

[0022] And / or, the iron-containing deposit comprises FePO 4 ;

[0023] And / or, the carbonate comprises sodium carbonate, the carbonate is added in the form of a carbonate solution, the mass fraction of the carbonate in the carbonate solution is 20% to 40%, and the reaction temperature is 80 to 100°C.

[0024] In a second aspect, the present invention provides a lithium iron phosphate prepared using recycled materials, wherein the recycled materials include FePO4 obtained by the method for recovering lithium and iron from waste lithium iron phosphate batteries according to the first aspect. 4 and lithium carbonate.

[0025] Furthermore, the preparation method of lithium iron phosphate comprises the following steps:

[0026] FePO 4 and Li 2 CO 3The lithium iron phosphate is obtained by mixing and grinding with conductive carbon in a ball mill, and then transferring the mixture to a tubular furnace and calcining it under a protective gas atmosphere, wherein the grinding time is 3 to 5 hours, the protective gas includes argon, the calcination temperature is 500° C. to 700° C., and the calcination time is 12 to 48 hours.

[0027] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0028] (1) The present invention uses a conductive material modified with a material having both piezoelectric and photoelectric activities as an anode material to convert solar energy into electrical energy, which is used to selectively recover lithium ions (in the form of lithium carbonate) and iron ions (in the form of iron phosphate) from waste lithium iron phosphate batteries, thereby being environmentally friendly and clean.

[0029] (2) The present invention proposes a piezoelectric-assisted photoelectrochemical method for recovering LFP, which is used to selectively recover lithium ions (in the form of lithium carbonate) and iron ions (in the form of iron phosphate) from waste LFP batteries. Compared with the traditional recovery method, this method uses a material with piezoelectric and photoelectric dual activity as a photoelectrode, uses inexhaustible sunlight as an energy source, and stirs the solution to not only significantly increase the contact frequency between ions and electrodes, but also stirs to bend the nanorod array of the material with piezoelectric and photoelectric dual activity to generate a piezoelectric cell to promote the rapid separation and transfer of photogenerated charges, thereby significantly improving the electrolysis efficiency and thus the recovery efficiency.

[0030] (3) The recycling method provided by the present invention reduces the amount of reagents used and waste generated in traditional recycling methods, and provides a green and simple method for recycling and utilizing waste LFP batteries. The leaching solution of this method is an organic weak acid, which reduces the subsequent large-scale water neutralization process and produces less waste, making it an environmentally friendly recycling method. In addition, this method does not require additional oxidants: in the stirring-assisted photoelectrochemical process, no oxidants need to be added, which further reduces the secondary pollution that may be generated in the process.

[0031] (4) The recovery method provided by the present invention realizes efficient selective leaching and recovery of lithium ions and iron ions, with the Fe recovery rate reaching 99.8% and the Li recovery rate reaching 99.4%. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 A flow chart of a method for recovering lithium and iron from waste lithium iron phosphate batteries and preparing lithium iron phosphate using the recovered materials provided in Example 1 of the present invention;

[0034] Figure 2 Electron microscopic images of the top surface (a) and cross section (b) of the CdS nanorod array in the fluorine-doped tin oxide electrode modified with the CdS nanorod array provided by the present invention;

[0035] Figure 3 This is a simulated diagram of the piezoelectric field distribution of CdS nanorods under external force in the fluorine-doped tin oxide electrode modified by the CdS nanorod array provided by the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. 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. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0037] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0038] In a first aspect, the present invention provides a method for recovering lithium and iron from waste lithium iron phosphate batteries, the method comprising the following steps:

[0039] The acidic leachate of the positive active material of the waste lithium iron phosphate battery is used as the electrolyte, an anode and a cathode are inserted therein, and then the anode and the cathode are energized for electrolysis under sunlight. After the electrolysis is completed (when the mass of the iron-containing sediment no longer increases, it indicates that the electrolysis is completed), the electrolytic material is subjected to solid-liquid separation, the liquid is a lithium-containing solution, and the solid is an iron-containing sediment, and then carbonate is added to the lithium-containing solution for reaction. After the reaction is completed, lithium carbonate is obtained by solid-liquid separation; wherein, the acidic leachate of the positive active material of the waste lithium iron phosphate battery is a solution obtained by leaching a target solid substance with an acid solution, the target solid substance includes the positive electrode sheet of the waste lithium iron phosphate battery and / or a substance peeled off from the positive electrode sheet, and the anode is a conductive material modified by a material having both piezoelectric and photoelectric activity.

[0040] The present invention uses a conductive material modified with a material having both piezoelectric and photoelectric activities as an anode material to convert solar energy into electrical energy, which is used to selectively recover lithium ions (in the form of lithium carbonate) and iron ions (in the form of iron phosphate) from waste lithium iron phosphate batteries, thereby being environmentally friendly and clean.

[0041] The electrolysis mechanism of the method for recovering lithium and iron from waste lithium iron phosphate batteries provided by the present invention is as follows: the material with piezoelectric and photoelectric dual activity (such as CdS) has piezoelectric and photoelectric dual activity, and under solution stirring and light irradiation, the photoanode with piezoelectric and photoelectric dual activity can generate photogenerated electrons and holes, wherein the photogenerated electrons are transferred to the graphite cathode through an external circuit to undergo a reduction reaction, and the photogenerated holes on the surface of the photoanode with piezoelectric and photoelectric dual activity undergo an oxidation reaction with ferrous ions to generate ferric ions and then react with phosphate to form ferric phosphate precipitates, thereby precipitating the iron ions and phosphate in the leachate.

[0042] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional embodiment, the acid solution includes at least one of an aqueous solution of p-toluenesulfonic acid, an aqueous solution of methanesulfonic acid, an aqueous solution of citric acid, an aqueous solution of succinic acid, an aqueous solution of malic acid, an aqueous solution of aspartic acid and an aqueous solution of oxalic acid.

[0043] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional implementation, the concentration of the acid solution is 1-4 mol / L, preferably 2-3 mol / L, and more preferably 2 mol / L.

[0044] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional embodiment, the solid-liquid ratio of the target solid substance to the acid solution is (20-60) g:1L, for example, it can be 20g:1L, 30g:1L, 40g:1L, 50g:1L or 60g:1L, preferably (30-50) g:1L, and more preferably 40g:1L.

[0045] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional implementation, the time for leaching the target solid substance with an acid solution is 60 minutes to 240 minutes, for example, it can be 60 minutes, 90 minutes, 120 minutes, 150 minutes, 180 minutes, 210 minutes or 240 minutes.

[0046] Specifically, the positive electrode sheet of the waste lithium iron phosphate battery or the material peeled off from the positive electrode sheet is obtained by the existing conventional method. It is usually necessary to first fully discharge the waste lithium iron phosphate battery on a battery tester, and then immerse it in a salt solution to reduce the risk of short circuit and spontaneous combustion, such as immersing it in 35wt% NaCl for 2 days to prevent short circuit and spontaneous combustion when the battery is mechanically opened. Then, for safety reasons, the battery is disassembled in a drying room (dew point -40°C), and the positive electrode sheet is collected, or the material on the positive electrode sheet is further collected. Once the battery is opened, the material is crushed, ground and sieved (sieve size 0.074mm) to obtain fine powder and coarse particles. The coarse particles are mainly composed of aluminum, copper collector foil, etc., and the fine powder is mainly composed of LFP (cathode) and graphite (anode) and residual Al / Cu foil.

[0047] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional embodiment, the electrolyte is in a stirring state, and the stirring rate is 500-3000rpm (for example, it can be 500rpm, 1000rpm, 1500rpm, 2000rpm, 2500rpm or 3000rpm), preferably 1000-1500rpm.

[0048] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional embodiment, the material having piezoelectric and photoelectric dual activity includes CdS, ZnO, CdTe, MoS 2 At least one of .

[0049] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional implementation, the conductive material includes fluorine-doped tin oxide (FTO).

[0050] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional embodiment, the anode is fluorine-doped tin oxide (FTO) modified by CdS nanorod arrays having piezoelectric and photoelectric dual activity; the preparation method of the anode comprises the following steps:

[0051] A. Place FTO conductive glass in Na 2 After soaking in S aqueous solution, it was washed with ethanol and ultrapure water in turn and dried, and then immersed in CdCl 2Soak in an aqueous solution, then wash with ethanol and ultrapure water in turn and blow dry;

[0052] B. Repeat step A for multiple times to obtain a dense CdS seed layer, and then place it in a Cd(NO 3 ) 2 , CH 4 N 2 S and GSH (glutathione) aqueous solution in a reactor, react at 100-300° C. (for example, 100° C., 200° C. or 300° C.) for 12-48 h (for example, 12 h, 16 h, 20 h, 24 h, 28 h, 32 h, 36 h, 40 h, 44 h or 48 h) to obtain a fluorine-doped tin oxide (CdSNR / FTO) electrode modified with a CdS nanorod array having both piezoelectric and photoelectric dual activity.

[0053] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional embodiment, in the method for preparing the anode, in step A, the immersion time is 1 to 5 minutes; in step B, the continuous ion layer adsorption reaction of step A is repeated 5 to 15 times, for example, 5 times, 10 times or 15 times. If the number of times is too small, the obtained seed layer is too thin, and if the number of times is too large, the obtained seed layer is too thick. If the seed layer is too thin: (1) the growth of nanorods may not be uniform because the seed layer cannot provide enough crystal nucleation points; (2) the nanorods may break or tilt during the growth process due to lack of sufficient support and adhesion; (3) the orientation of the nanorods may deteriorate because the seed layer is too thin to effectively guide the nanorods to grow in a specific direction. If the seed layer is too thick: (1) the growth of nanorods may become disorderly, because a too thick seed layer may lead to too many crystal nucleation points, thus affecting the orderly arrangement of nanorods; (2) the spacing between nanorods may decrease, causing them to squeeze or fuse with each other, affecting their performance; (3) a too thick seed layer may increase the stress during the growth process, which may cause defects in the crystal structure of the nanorods. Therefore, the seed layer thickness has a great influence on the spatial orientation of CdS nanorods. When the seed layer is thin or thick, the spatial orientation of the nanorods is poor. When the seed layer thickness is moderate, CdS nanorods with uniform density and good spatial orientation can be obtained.

[0054] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional implementation, the cathode is at least one of graphite, titanium sheet, stainless steel sheet, boron-doped diamond, and platinum sheet.

[0055] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional implementation, direct current is applied to the anode and the cathode for electrolysis. In the present invention, the purpose of applying current is to form a directional electric field to drive the electrons converted from light energy to form a directional movement under the action of an external current. A very small direct current is used, and the loss of electric energy is negligible relative to the entire electrochemical process.

[0056] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional embodiment, the electrolysis temperature is 20-80°C (for example, it can be 20°C, 40°C, 60°C or 80°C, preferably 40-60°C), the electrolysis time is 1-10h (for example, it can be 1h, 3h, 5h, 7h or 10h, preferably 4-6h), and the electrolysis voltage is 0-0.4V, preferably 0.2-0.32V.

[0057] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional embodiment, the iron-containing sediment includes FePO 4 .

[0058] In the above method for recovering lithium and iron from waste lithium iron phosphate batteries, as an optional implementation, the carbonate includes sodium carbonate, the carbonate is added in the form of a carbonate solution, the mass fraction of the carbonate in the carbonate solution is 20% to 40%, and the reaction temperature is 80 to 100°C.

[0059] In a second aspect, the present invention provides a lithium iron phosphate prepared using recycled materials, wherein the recycled materials include FePO4 obtained by the method for recovering lithium and iron from waste lithium iron phosphate batteries according to the first aspect. 4 and lithium carbonate.

[0060] In the lithium iron phosphate prepared using the recycled material, as an optional implementation, the preparation method of the lithium iron phosphate includes the following steps:

[0061] FePO 4 and Li 2 CO 3 The lithium iron phosphate is obtained by mixing and grinding the lithium iron phosphate with conductive carbon (SuperP) in a ball mill, and then transferring the mixture into a tube furnace and calcining the mixture under a protective gas atmosphere.

[0062] In the lithium iron phosphate prepared from the recycled material, as an optional embodiment, the grinding time is 3 to 5 hours, and FePO 4 :Li 2 CO 3The molar ratio of carbon to carbon is 2:1:4, the protective gas includes argon, the calcination temperature is 500°C to 700°C (for example, 500°C, 550°C, 600°C, 650°C or 700°C), and the calcination time is 12 to 48h (for example, 12h, 18h, 24h, 30h, 36h, 42h or 48h).

[0063] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0064] In the following examples and comparative examples 1-2:

[0065] The preparation method of fluorine-doped tin oxide (FTO) modified by CdS nanorod array with piezoelectric and photoelectric dual activity comprises the following steps: ultrasonically cleaning FTO conductive glass in water, ethanol, acetone and aqueous solution for 5 minutes, then drying in an oven at 80°C, and then heating the cleaned FTO conductive glass in 50mM Na 2 The mixture was immersed in 50 mM CdCl 2 The solution was immersed in water for 1 min, then washed with ethanol and ultrapure water in turn and dried; the above continuous ion layer adsorption reaction was repeated 10 times to obtain a dense CdS seed layer, which was then placed in a 5 mM Cd (NO 3 ) 2 +5mM CH 4 N 2 The reaction was carried out in a reactor containing S+3mM GSH aqueous solution at 200°C for 24h to obtain a CdSNR / FTO (fluorine-doped tin oxide modified with CdS nanorod arrays having piezoelectric and photoelectric dual activity) electrode. The electron microscope image of the electrode is shown in FIG. Figure 2 As shown in the figure, the finite element simulation of the piezoelectric field distribution of CdS nanorods under external force is carried out by using the comsol software, as shown in the figure. Figure 3 shown.

[0066] Recovery rate (%) = actual recovery mass / theoretical recovery mass × 100%, specifically: take the fine powder in step (1), measure the actual content of lithium iron element, and calculate the theoretical lithium iron recovery mass; take the recovered lithium carbonate and iron phosphate, measure the actual lithium iron element mass, and calculate the actual lithium iron recovery mass.

[0067] Example 1

[0068] This embodiment provides a method for recovering lithium and iron from waste lithium iron phosphate batteries. The process flow is as follows: Figure 1 As shown, the specific steps include:

[0069] (1) First, the spent lithium iron phosphate batteries were fully discharged on a battery tester and then immersed in a 35 wt% NaCl aqueous solution for 2 days to prevent short circuit and spontaneous combustion when the battery was mechanically opened. Then, for safety reasons, the battery was disassembled in a drying room (dew point -40 ° C). Once opened, the materials were crushed, ground and sieved (sieve size 0.074 mm) to obtain fine powder and coarse particles. The coarse particles were mainly composed of aluminum, copper current collector foil, etc., and the fine powder was mainly composed of LFP (cathode) and graphite (anode) as well as residual Al / Cu foil;

[0070] (2) weighing the fine powder obtained in step 1, adding it to a 2 mol / L TsOH (p-toluenesulfonic acid) aqueous solution, stirring at room temperature for 90 min, and obtaining a leaching solution containing lithium / ferrous ions, wherein the volume ratio of the mass of the fine powder to the TsOH (p-toluenesulfonic acid) aqueous solution is 40 g:1 L;

[0071] (3) The leaching solution containing lithium / ferrous ions obtained in step 2 is used as an electrolyte, an anode and a cathode are inserted therein, fluorine-doped tin oxide modified with a CdS nanorod array having piezoelectric and photoelectric dual activity is used as the anode material, and graphite is used as the cathode material. Then, under the conditions of simultaneous sunlight irradiation and stirring at 1500 rpm, direct current is passed through the anode and the cathode, and electrolysis is performed at a temperature of 60° C. and a voltage of 0.2 V for 5 hours. The reaction formula is as follows:

[0072] Anode: Fe 2+ -e - →Fe 3+

[0073] Solution: Fe 3+ +PO4 3- →FePO4↓;

[0074] (4) After the electrolysis is completed, the electrolysis product is filtered to obtain a brown filter residue (FePO 4 , Fe recovery rate 99.8%) and colorless transparent filtrate (solution containing lithium ions), and then 30wt% Na 2 CO 3 The aqueous solution was reacted at 90°C for 1 h, cooled to room temperature and filtered to obtain a white residue (Li 2 CO 3 , Li recovery rate 99.4%).

[0075] This embodiment also provides a method of using FePO recovered by this embodiment. 4 and Li 2 CO 3 The prepared lithium iron phosphate comprises the following steps:

[0076] The FePO obtained in step (4) of this example 4 and Li 2 CO 3 The mixture was mixed with conductive carbon (SuperP) in a ball mill at a molar ratio of 2:1:4 for 4 h, and then transferred to a tube furnace and sintered at 600 °C for 24 h under an argon atmosphere to obtain LFP powder.

[0077] Embodiment 2-5

[0078] The method for recovering lithium and iron from waste lithium iron phosphate batteries provided in Examples 2-5 is different from that in Example 1 only in that the volume ratio (solid-to-liquid ratio) of the mass of the fine powder and the aqueous solution of TsOH (p-toluenesulfonic acid) in step (2) is different, and the rest of the settings are the same as those in Example 1. The specific solid-to-liquid ratios of each example can be seen in Table 1, and the recovery rates of lithium ions and iron ions can also be seen in Table 1.

[0079] Table 1 Solid-liquid ratio and ion recovery rate of Examples 1-5

[0080]

[0081] Embodiment 6-8

[0082] The method for recovering lithium and iron from waste lithium iron phosphate batteries provided in Examples 6-8 is different from that in Example 1 only in that the concentration of the acid solution in step (2) is different, and the rest of the settings are the same as those in Example 1. The specific acid solution concentrations of each example can be seen in Table 2, and the recovery rates of lithium ions and iron ions can also be seen in Table 2.

[0083] Table 2 Acid solution concentration and ion recovery rate of Examples 1, 6-8

[0084] project Example 6 Example 1 Example 7 Example 8 Concentration (mol / L) 1 2 3 4 Fe recovery rate 87.6％ 99.8％ 90.2％ 82.1％ Li recovery rate 78.6％ 99.4％ 94.4％ 91.3％

[0085] Examples 9-12

[0086] The method for recovering lithium and iron from waste lithium iron phosphate batteries provided in Examples 9-12 is different from that in Example 1 only in that the electrolysis voltage in step (3) is different, and the rest of the settings are the same as those in Example 1. The specific voltages of each example can be seen in Table 3, and the recovery rates of lithium ions and iron ions can also be seen in Table 3.

[0087] Table 3 Voltage and ion recovery rate of Examples 1, 9-12

[0088] project Example 9 Example 10 Example 1 Embodiment 11 Example 12 Voltage (V) 0 0.1 0.2 0.32 0.4 Fe recovery rate 65.3％ 73.2％ 99.8％ 92.6％ 87.2％ Li recovery rate 72.6％ 83.2％ 99.4％ 89.6％ 87.4％

[0089] It can be seen from Example 9 that without power supply, the Fe recovery rate and the Li recovery rate are still high, indicating that the method for recovering lithium and iron from waste lithium iron phosphate batteries provided by the present invention can convert solar energy into electrical energy, which can be used to selectively recover lithium ions (in the form of lithium carbonate) and iron ions (in the form of iron phosphate) from waste lithium iron phosphate batteries, which is environmentally friendly and clean.

[0090] Examples 13-15

[0091] The method for recovering lithium and iron from waste lithium iron phosphate batteries provided in Examples 13-15 is different from that in Example 1 only in that the electrolysis temperature in step (3) is different, and the rest of the settings are the same as those in Example 1. The specific electrolysis temperature of each example can be seen in Table 4, and the recovery rates of lithium ions and iron ions can also be seen in Table 4.

[0092] Table 4 Electrolysis temperature and ion recovery rate of Examples 1, 13-15

[0093] project Example 13 Embodiment 14 Example 1 Embodiment 15 Temperature(℃) 20 40 60 80 Fe recovery rate 91.1％ 97.6％ 99.8％ 98.2％ Li recovery rate 92.3％ 98.5％ 99.4％ 97.4％

[0094] Examples 16-21

[0095] The method for recovering lithium and iron from waste lithium iron phosphate batteries provided in Examples 16-21 is different from that in Example 1 only in that the stirring rate in step (3) is different, and the rest of the settings are the same as those in Example 1. The specific stirring rates of each example can be seen in Table 5, and the recovery rates of lithium ions and iron ions can also be seen in Table 5.

[0096] Table 5 Stirring rate and ion recovery rate of Examples 1, 16-21

[0097]

[0098]

[0099] Embodiment 22

[0100] The method for recovering lithium and iron from waste lithium iron phosphate batteries provided in this embodiment is different from that in Embodiment 1 only in that p-toluenesulfonic acid is replaced by oxalic acid.

[0101] The Fe recovery rate was 92.5% and the Li recovery rate was 96.3%.

[0102] Embodiment 23

[0103] The method for recovering lithium and iron from waste lithium iron phosphate batteries provided in this embodiment is different from that in embodiment 1 only in that the fluorine-doped tin oxide modified with CdS nanorod arrays is modified to MoS 2 Nanorod array-modified fluorine-doped tin oxide, MoS 2The preparation method of fluorine-doped tin oxide modified by nanorod array comprises the following steps: 2 MoO 4 ·2H 2 O) is a molybdenum source, thioacetamide (CH 3 CSNH 2 ) is the sulfur source, silicotungstic acid (H 4 O 40 S W 12 ·xH 2 O) was used as a catalyst and the reaction was carried out at 180°C for 24 hours.

[0104] The Fe recovery rate was 85.1% and the Li recovery rate was 84.8%.

[0105] Comparative Example 1

[0106] This comparative example uses a conventional electrolysis method to recover iron and lithium. The only difference from Example 1 is that the anode material is boron-doped diamond and the cathode material is titanium sheet. Direct current is then passed through the anode and cathode, and electrolysis is performed for 6 hours at a temperature of 60°C and a voltage of 2.5V.

[0107] The Fe recovery rate was 98.2% and the Li recovery rate was 97.4%.

[0108] By comparing Example 1 with Comparative Example 1, it can be seen that the electric energy consumed by recovering iron and lithium using the conventional electrolysis method (electric energy supplied by the power supply) is much greater than that of Example 1, indicating that the present invention converts solar energy into electric energy by using a fluorine-doped tin oxide material modified with a CdS nanorod array as a photoanode material, which is used to selectively recover lithium ions (in the form of lithium carbonate) and iron ions (in the form of iron phosphate) from waste lithium iron phosphate batteries, thereby reducing the consumption of electric energy supplied by the power supply.

[0109] Comparative Example 2

[0110] The method for recovering lithium and iron from waste lithium iron phosphate batteries provided in this comparative example is different from that in Example 1 only in that p-toluenesulfonic acid is replaced by hydrochloric acid.

[0111] The Fe recovery rate was 89.6% and the Li recovery rate was 91.3%.

[0112] Comparative Example 3

[0113] The method for recovering lithium and iron from waste lithium iron phosphate batteries provided in this embodiment is different from that in embodiment 1 only in that the preparation method of fluorine-doped tin oxide (FTO) modified by CdS nanorod arrays having piezoelectric and photoelectric dual activity is different, and specifically comprises the following steps: ultrasonically cleaning the FTO conductive glass in water, ethanol, acetone, and aqueous solution for 5 minutes in sequence, and then drying it in an oven at 80°C, and then placing it in a 5 mM Cd(NO3 ) 2 +5mM CH 4 N 2 The reaction mixture was placed in a reactor containing S+3 mM GSH aqueous solution at 200°C for 24 h to obtain a CdSNR / FTO (fluorine-doped tin oxide modified with CdS nanorod arrays having both piezoelectric and photoelectric activity) electrode.

[0114] The Fe recovery rate was 87.6% and the Li recovery rate was 86.9%.

[0115] By comparing Example 1 with Comparative Example 3, it can be seen that Example 1 can significantly improve the Fe recovery rate and Li recovery rate by using fluorine-doped tin oxide (FTO) modified by CdS nanorod array obtained by first preparing the seed layer as the anode. The inventor speculates that the reason may be that by adding the process of first preparing the CdS seed layer, the distribution of the CdS nanorod array can be made more vertical, thereby improving its electrochemical performance, and ultimately improving the Fe recovery rate and Li recovery rate.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recovering lithium and iron from waste lithium iron phosphate batteries, characterized in that: The method comprises the following steps: The acidic leachate of the positive active material of the waste lithium iron phosphate battery is used as the electrolyte, an anode and a cathode are inserted into the electrolyte, and then the anode and the cathode are energized for electrolysis under sunlight. After the electrolysis is completed, the electrolysis material is subjected to solid-liquid separation, the liquid is a lithium-containing solution, and the solid is an iron-containing sediment. Then, carbonate is added to the lithium-containing solution for reaction, and lithium carbonate is obtained by solid-liquid separation after the reaction is completed; wherein, the acidic leachate of the positive active material of the waste lithium iron phosphate battery is a solution obtained by leaching a target solid substance with an acid solution, the target solid substance includes the positive electrode sheet of the waste lithium iron phosphate battery and / or a substance peeled off from the positive electrode sheet, and the anode is a conductive material modified by a material having both piezoelectric and photoelectric activity.

2. The method for recovering lithium and iron from waste lithium iron phosphate batteries according to claim 1, characterized in that: The acid solution comprises at least one of an aqueous solution of p-toluenesulfonic acid, an aqueous solution of methanesulfonic acid, an aqueous solution of citric acid, an aqueous solution of succinic acid, an aqueous solution of malic acid, an aqueous solution of aspartic acid, and an aqueous solution of oxalic acid; And / or, the concentration of the acid solution is 1-4 mol / L; and / or, the solid-to-liquid ratio of the target solid substance to the acid solution is (20-60) g:1 L; And / or, the time for leaching the target solid matter with the acid solution is 60 minutes to 240 minutes.

3. The method for recovering lithium and iron from waste lithium iron phosphate batteries according to claim 1, characterized in that: The electrolyte is in a stirring state, and the stirring rate is 500-3000 rpm.

4. The method for recovering lithium and iron from waste lithium iron phosphate batteries according to claim 1, characterized in that: The material having both piezoelectric and photoelectric activity includes at least one of CdS, ZnO, CdTe, and MoS2; And / or, the conductive material includes fluorine-doped tin oxide.

5. The method for recovering lithium and iron from waste lithium iron phosphate batteries according to claim 1, characterized in that: The anode is fluorine-doped tin oxide modified by a CdS nanorod array having piezoelectric and photoelectric dual activity; the preparation method of the anode comprises the following steps: A. Soak the FTO conductive glass in a Na2S aqueous solution, wash it with ethanol and ultrapure water in turn and blow it dry, then soak it in a CdCl2 aqueous solution, then wash it with ethanol and ultrapure water in turn and blow it dry; B. Repeat step A for multiple times to carry out continuous ion layer adsorption reaction to obtain a CdS seed layer, which is then placed in a reactor containing Cd(NO3)2, CH4N2S and GSH aqueous solution, and reacted at 100-300°C for 12-48h to obtain a fluorine-doped tin oxide electrode modified with a CdS nanorod array having both piezoelectric and photoelectric dual activity.

6. The method for recovering lithium and iron from waste lithium iron phosphate batteries according to claim 5, characterized in that: In the method for preparing the anode, in step A, the immersion time is 1 to 5 minutes; in step B, the continuous ion layer adsorption reaction in step A is repeated 5 to 15 times.

7. The method for recovering lithium and iron from waste lithium iron phosphate batteries according to claim 1, characterized in that: The cathode is at least one of graphite, titanium sheet, stainless steel sheet, boron-doped diamond, and platinum sheet; And / or, direct current is passed through the anode and the cathode to perform electrolysis.

8. The method for recovering lithium and iron from waste lithium iron phosphate batteries according to claim 1, characterized in that: The electrolysis temperature is 20-80°C, the electrolysis time is 1-10h, and the electrolysis voltage is 0-0.4V; and / or, the iron-containing deposit comprises FePO4; And / or, the carbonate comprises sodium carbonate, the carbonate is added in the form of a carbonate solution, the mass fraction of the carbonate in the carbonate solution is 20% to 40%, and the reaction temperature is 80 to 100°C.

9. A lithium iron phosphate prepared using recycled materials, characterized in that: The recycled material includes FePO4 and lithium carbonate obtained by the method for recovering lithium and iron from waste lithium iron phosphate batteries according to any one of claims 1 to 8.

10. The lithium iron phosphate prepared using recycled materials according to claim 9, characterized in that: The preparation method of lithium iron phosphate comprises the following steps: FePO4 and Li2CO3 are mixed and ground with conductive carbon in a ball mill, and then the mixture is transferred to a tubular furnace and calcined under a protective gas atmosphere to obtain the lithium iron phosphate, wherein the grinding time is 3 to 5 hours, the protective gas includes argon, the calcination temperature is 500°C to 700°C, and the calcination time is 12 to 48 hours.

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