Method for recycling high-value waste lithium iron phosphate battery cathode material

Abstract

The application relates to a method for recycling high-value waste lithium iron phosphate battery positive electrode materials, mainly comprising the following steps: adding lithium iron phosphate positive electrode materials, ammonium chloride and hydrogen peroxide into a ball mill tank for grinding, controlling the mass ratio of ammonium chloride and lithium iron phosphate positive electrode materials to be 5:2-7:2, and the volume-mass ratio of hydrogen peroxide and lithium iron phosphate positive electrode materials to be (18-22):1 mL / g; after grinding, the mixture is washed out of the ball mill tank with deionized water, and then water immersion treatment is carried out to fully leach metal lithium; excessive ammonium fluoride is added into the filtrate, and after reaction, reaction liquid and product lithium fluoride are obtained; the reaction liquid is subjected to adsorption treatment by using defluorination resin, the defluorination resin is regenerated by elution, the effluent and the eluent are combined and concentrated to obtain an ammonium chloride solution which can be reused in the chlorination reaction stage. Through the H2O2-strengthened mechanical chlorination coupling fluorination reaction, near-full recovery of the waste lithium iron phosphate battery positive electrode materials and high value of the product are realized, and the process is simpler and more environmentally friendly.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste lithium iron phosphate battery recycling, and particularly relates to a method for recycling high-value waste lithium iron phosphate battery positive electrode materials. BACKGROUND

[0002] In recent years, the production of lithium ion batteries has increased significantly driven by the popularity of digital products and electric vehicles. Lithium iron phosphate (LiFePO4, LFP) batteries have attracted much attention due to their low cost, superior cycle performance, and enhanced safety. However, due to the high cost of existing recycling methods, large-scale recycling still faces obstacles. Therefore, it is particularly important to improve the economic efficiency of lithium extraction from waste lithium iron phosphate to support the sustainability of the system. Therefore, the near-full recovery of waste LFP positive electrode materials and the high value of the products are the main problems currently faced.

[0003] In the prior art, the method for extracting valuable elements from waste LFP batteries is usually divided into complete leaching and selective leaching. Among them, the complete leaching process requires an acidic environment, usually using strong acids such as H3PO4 or H2SO4 to maintain the dissolution of all elements in LFP, and then separating them according to their different properties. However, the leaching process uses excessive acid, and the residual acid liquid discharged into the water body will cause serious pollution to the environment, and the leached Li and Fe need additional steps for separation, so the complete leaching process has the problems of high recovery cost, long processing flow, poor leaching selectivity, environmental pollution, etc. The selective leaching process has the advantages of being able to be carried out under weakly acidic or neutral conditions, which can reduce the cost and the impact on the environment.

[0004] With the development of technology, mechanochemistry has been proved to be able to destroy the structure of LFP, reduce the particle size and improve the leaching efficiency of metal. For example, CN116573655A discloses a stripping and recycling method for lithium positive electrode material in lithium iron phosphate battery. In the technical scheme, the obtained active positive electrode powder is mixed with grinding reagent and put into an instrument for grinding. The metal ions in the grinding reagent replace lithium in LiFePO4 to generate LiCl, and solid powder is obtained. After the grinding reaction is completed, the solid powder is transferred to a beaker containing deionized water for leaching. After leaching is completed, solid-liquid separation is realized by vacuum filtration, and finally metallic lithium is recovered in the form of lithium carbonate. CN110760682A discloses a process for selectively recycling lithium from waste lithium iron phosphate batteries by mechanochemical activation. In the technical scheme, the positive electrode material and grinding aid are added to the ball mill jar for grinding, and then the leaching agent is added. After leaching for 1 hour, a lithium-containing solution and a leaching residue containing iron, phosphorus and carbon powder are obtained. At this time, phosphorus and iron combine to form iron phosphate precipitate. Then, the pH value of the lithium-containing solution is adjusted to 11-13 by adding sodium hydroxide, and then sodium phosphate is added. Metallic lithium is recovered in the form of lithium phosphate precipitate. The above process relies on the high energy generated by mechanochemical activation to change the physical and chemical properties of the material, and selectively leaches lithium through chemical reaction of the leaching agent. Compared with the complete leaching process, the amount of reagents such as acid is reduced, and the process flow is simplified. However, the selectively leached metallic lithium is mainly recovered in the form of lithium carbonate or lithium phosphate. Since lithium carbonate or lithium phosphate still has a certain solubility in aqueous solution, the recovery efficiency of lithium is still low. Moreover, the amount of chemical additives and leaching agents added during the reaction process, such as ammonium chloride, carbonate and phosphate, is large, which cannot be recycled and reused, resulting in high cost of recycling process and low added value of recovered products. This is also the main reason why the technology cannot be industrialized at present, and it is also a major challenge faced by enterprises.

[0005] Therefore, how to achieve near-full recovery of waste LFP positive electrode material and high value of the product is a technical problem that needs to be solved urgently in the industry. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art and provide a method for high-value recycling of waste lithium iron phosphate battery positive electrode material. The method realizes near-full recovery of waste lithium iron phosphate battery positive electrode material and high value of the product through H2O2-strengthened mechanical chlorination coupled with fluorination reaction.

[0007] The above invention purpose of the present application is realized by the following technical scheme:

[0008] A method for high-value recycling of waste lithium iron phosphate battery positive electrode material, comprising the following steps:

[0009] Step A, after pretreatment of waste lithium iron phosphate battery, lithium iron phosphate positive material is obtained;

[0010] Step B, lithium iron phosphate positive material, ammonium chloride and hydrogen peroxide are added into a ball mill tank for grinding, the mass ratio of ammonium chloride and lithium iron phosphate positive material is controlled to be 5:2-7:2, and the volume mass ratio of hydrogen peroxide and lithium iron phosphate positive material is (18-22):1 mL / g;

[0011] Step C, after grinding, the mixture is washed out from the ball mill tank with deionized water, and then water immersion treatment is carried out to fully leach the metal lithium; after water immersion, filtration is carried out to obtain a lithium chloride-containing filtrate and a filter residue containing iron phosphate; wherein the filter residue is used for characterization experiment after washing, drying and grinding, and the filtrate, i.e. the leaching solution, is used for ICP-OES determination of Fe 2+ / Fe 3+ and Li + chlorination efficiency after homogenization;

[0012] Step D, excess ammonium fluoride is added to the filtrate of step C, and after a period of reaction, a reaction solution and a precipitate are obtained by filtration, and the precipitate is washed, dried and ground to obtain the product lithium fluoride; ammonium fluoride is used as a precipitant to realize the conversion of LiCl to LiF without introducing impurity ions, and the filtered LiF is washed, dried and ground for characterization experiment; Step E, the reaction solution of step D is adjusted to pH 5.0-6.5, and then a defluorination resin is used for cyclic adsorption treatment of the reaction solution, and the effluent is collected; when the defluorination resin adsorption reaches saturation, aluminum chloride solution is used for elution regeneration of the defluorination resin, and the eluate is collected; the collected effluent and eluate are combined and concentrated to obtain an ammonium chloride solution.

[0013] In the above technical solution, in step B, the ball-to-material ratio is (14-16):1, the grinding time is 11-13h, and the ball milling speed is 550-650rpm; by optimizing the above process conditions, the chlorination and recovery efficiency of metal lithium is improved.

[0014] In the above technical solution, in step C, the leaching temperature is 55-65 degrees, and the leaching time is 60-100 minutes; when the leaching temperature is further increased, the Li leaching efficiency decreases, but the Fe leaching efficiency increases, which may accelerate the phase change or structural rearrangement of the positive material at high temperature, resulting in inhibition of Li diffusion; considering energy consumption and economic benefits, the above temperature and time are selected to realize the separation of Li and Fe.

[0015] In the above technical solution, in step E, the defluorination resin is purchased from Xi'an Lanxiao Science and Technology New Material Co., Ltd., and the model number is LX-760.

[0016] In the technical scheme, in step E, 10% aluminum chloride solution is used to elute and regenerate the defluorination resin at a flow rate of 1 BV / h, and the regeneration treatment capacity is 2-3 BV.

[0017] In the technical scheme, in step A, the pretreatment step is: disassembling and separating the waste lithium iron phosphate battery to obtain the positive pole piece, and then pyrolyzing the positive pole piece to separate the positive material and aluminum foil, thereby obtaining the lithium iron phosphate positive material.

[0018] The technical concept of the application is as follows:

[0019] Firstly, ammonium chloride is added in the mechanical ball milling process to realize partial chlorination of metal lithium, and under the natural ball milling condition, only a small part of Li-O bonds will be broken, which is far from meeting the needs of Li chlorination and resource conversion, therefore, H2O2 is added to strengthen the mechanical chlorination effect and improve the chlorination efficiency of Li, and after subsequent water immersion treatment, Li is fully leached out while Fe is rarely leached out, so that Li and Fe are separated to obtain a filtrate containing LiCl and a filter residue containing FePO4.

[0020] Secondly, the H2O2 in the application 2- In the NH4Cl mechanical chlorination reaction system, the chlorination reaction coupling fluorination reaction of ammonium chloride + ammonium fluoride is selected, which has multiple considerations: on the one hand, ammonium chloride is selected to provide Cl - ions for the combination of metal Li (LiCl is generated by chlorination reaction) and H + ions produced by partial hydrolysis to make the solution system present weak acidity, and the oxidation performance of H2O2 is greatly improved under weak acidic conditions, so that divalent iron Fe 2+ is oxidized to trivalent iron Fe 3+ , which promotes the breaking of Li-O bonds and releases Li from the structure of LiFePO4, but has little effect on Fe-O bonds, thereby improving the chlorination efficiency of Li, while the chlorination efficiency of Fe is not affected, and the two can be separated subsequently; on the other hand, ammonium fluoride is selected, and the chlorination coupling fluorination reaction realizes the conversion of LiCl to high-value product LiF, and the recovery efficiency of Li in the form of LiF is much higher than that in the form of Li2CO3 or Li2PO4, and the high added value, recovery rate and purity of LiF are higher than those of Li2CO3 or Li2PO4. - - - - ​​​NH4Cl was successfully derivatized; when the defluorination resin reached saturation, AlCl3 solution was used for regeneration, and the Al in the regeneration solution... 3+ F in the resin - (1) The resin is desorbed and forms an Al-F complex, thereby realizing the regeneration and recycling of the resin; (2) The main solute of the LiF conversion liquid is converted into NH4Cl. The NH4Cl in this part and the NH4Cl remaining after the chlorination reaction, as well as the NH4Cl derived in the defluorination process, are all recycled and reused, thereby greatly reducing the consumption of materials and reducing costs.

[0021] Furthermore, the ability of H2O2 to enhance mechanical ball milling is a known prior art, but in the H2O of this invention... 2- In the NH4Cl mechanical chlorination reaction system, the inventors, through numerous experiments, discovered for the first time the mechanism of H2O2-enhanced mechanical chlorination, namely, the free radicals generated during the H2O2 oxidation process [H2O2→·OH→HO2·→O2]. - ·→ 1 O2 may play a crucial role in the breaking of LiFePO4 bonds, thereby enhancing the efficiency of mechanical chlorination. However, the strong reactivity of these free radicals means they have short lifespans, making them difficult to capture and quantify directly. This poses a challenge to how H2O2 can enhance the formation and reaction mechanism of free radicals during the mechanical chlorination of LFP, namely, which free radicals can enhance the breaking of Li-O bonds without affecting the breaking of Fe-O bonds, and which free radicals simultaneously enhance the breaking of both Li-O and Fe-O bonds. To address this, the inventors considered adding appropriate amounts of five different types of quenchers: methanol (MeOH), n-butanol (NBA), tert-butanol (TBA), p-benzoquinone (BQ), and furfuryl alcohol (FFA). By comparing the chlorination efficiency of Li and Fe before and after the addition of the quenchers, the existence and formation mechanism of free radicals were confirmed for the first time, and the reaction pathway between free radicals and LiFePO4 was deduced.

[0022] In summary, this application achieves the following technical effects:

[0023] This invention utilizes a mechanical chlorination coupled with fluorination reaction enhanced by H₂O₂ to successfully convert 96.79% of Li into the high-value product LiF, with a purity of 99.50%. 99.89% of F is then exchanged using a defluorinating resin. - Each liter of LiF conversion residue can successfully generate 0.63g of NH4Cl for reuse in mechanical chlorination reactions. This achieves near-total recovery and high-value utilization of waste lithium iron phosphate battery cathode materials, with a simpler and more environmentally friendly process, demonstrating excellent prospects for industrial application. Attached Figure Description

[0024] Figure 1 This is a comparison chart of the chlorination efficiency of metallic Li and Fe under different conditions.

[0025] Figure 2 is the chlorination efficiency comparison chart of metal Li and Fe under different quenching agents of experimental example 1-5.

[0026] Figure 3 is the XRD pattern of LFP sample (a), filter residue sample (b) produced by H2O-NH4Cl mechanical chlorination system of comparative example 2, LFP sample (c) after ball milling of H2O2-NH4Cl mechanical chlorination system of example 1 and filter residue sample (d) produced by H2O2-NH4Cl mechanical chlorination system of example 1.

[0027] Figure 4 is the FT-IR spectrum of LFP sample (a), filter residue sample (b) produced by H2O-NH4Cl mechanical chlorination system of comparative example 2, LFP sample (c) after ball milling of H2O2-NH4Cl mechanical chlorination system of example 1 and filter residue sample (d) produced by H2O2-NH4Cl mechanical chlorination system of example 1.

[0028] Figure 5 is the XPS pattern of samples before and after ball milling of H2O2-NH4Cl mechanical chlorination system of example 1.

[0029] Figure 6 is the XRD pattern of Gibbs free energy change and temperature relationship (a), LiF (b), reused NH4Cl (c), Li2CO3 (d) in the reaction process of H2O2-NH4Cl mechanical chlorination system of example 1.

[0030] Figure 7 is the reaction mechanism diagram of the method for recycling positive electrode material of waste lithium iron phosphate battery according to the application. DETAILED DESCRIPTION

[0031] The application will be further described in detail below with reference to the accompanying drawings.

[0032] Experimental materials:

[0033] 1. Chemical reagents:

[0034] Ammonium chloride (NH4Cl), hydrogen peroxide (H2O2, 30%), ammonium fluoride (NH4F);

[0035] The defluorinated resin was purchased from Xi'an Lanxiao Science and Technology New Material Co., Ltd., and the model number was LX-760;

[0036] Deionized water (resistivity of 18.2 MΩ·cm).

[0037] 2. Instruments and equipment:

[0038] Planetary ball mill, purchased from Hunan Fokas Experimental Instrument Co., Ltd., model F-P400;

[0039] Ion chromatography (IC, Thermo Scientific ICS-1100, USA) was used.

[0040] X-ray diffractometer (XRD, Malvern Panalytical Empyrean, Netherlands);

[0041] Fourier transform infrared spectrometer (FT-IR, Thermo Fisher Scientific Nicolet iS20, USA).

[0042] 3. Waste lithium iron phosphate battery:

[0043] The sample waste lithium iron phosphate battery of the embodiment was provided by a new energy environmental protection technology company in Shenzhen.

[0044] After pretreatment of the waste lithium iron phosphate battery, LFP positive electrode material was obtained, and the element content of the LFP positive electrode material is shown in Table 1.

[0045] Table 1. Element content of LFP positive electrode material

[0046] Element Fe Li P Al Content % 33.89 4.12 17.48 0.19

[0047] The specific steps for pretreating the waste lithium iron phosphate battery are as follows:

[0048] First, discharge to 1V using Shenzhen Xinxin BTS-5V6A, then discharge for 48 hours using 5-10% NaCl solution, and after detecting that the voltage is 0, disassemble the positive plate in an inert atmosphere glove box. After cutting the positive plate, pyrolyze the PVDF in a tube furnace to remove the PVDF, and the pyrolysis conditions are pyrolysis temperature 450℃, holding time 60min, heating rate 10℃ / min, thereby realizing the separation of aluminum foil and positive electrode material, and obtaining lithium iron phosphate positive electrode material.

[0049] Take 0.1g of lithium iron phosphate positive electrode material (hereinafter referred to as LFP) as a sample, and use it for the following examples and comparative examples.

[0050] Example 1:

[0051] A method for recycling waste lithium iron phosphate battery positive electrode material with high value, comprising the following steps:

[0052] Step A, after pretreatment of the waste lithium iron phosphate battery, LFP is obtained and is ready for use.

[0053] Step B, take 0.1 g LFP into 100 mL ball mill tank, and add 0.3 g ammonium chloride, 2.0 mL hydrogen peroxide and quenching agent for grinding, control the ball-to-material ratio to be 15:1, the grinding time is 12 h, and the ball milling speed is 600 rpm;

[0054] The mass ratio of ammonium chloride to LFP is 3:1, and the volume-to-mass ratio of hydrogen peroxide to LFP is 20:1 mL / g;

[0055] Step C, after grinding, the mixture is washed out of the ball mill tank with deionized water, and then water immersion treatment is carried out, the leaching temperature is 55-65 degrees, the leaching time is 60-100 min, so that the metal lithium is fully leached out; after water immersion, the filter residue containing lithium chloride and the filter residue containing iron phosphate are obtained; the filter residue is washed, dried and ground for characterization experiment, and the leaching solution is homogenized and then the chloride efficiency of Fe 2+ / Fe 3+ and Li + is determined by ICP-OES.

[0056] Step D, add excess ammonium fluoride to the filtrate of step C, ammonium fluoride as a precipitating agent, realizes the conversion of LiCl to LiF without introducing impurity ions, filter to obtain the reaction liquid and precipitate, and the precipitate is washed, dried, ground to obtain the product LiF, and used for characterization experiment.

[0057] Step E, adjust the pH of the reaction liquid of step D to 5.0-6.5, then use fluoride removal resin LX-760 to treat the reaction liquid by cyclic adsorption, and collect the effluent; when the fluoride removal resin adsorption reaches saturation, use 10% aluminum chloride solution at a flow rate of 1 BV / h to elute and regenerate the fluoride removal resin, the regeneration treatment capacity is 2-3 BV, and the eluate is collected; combine the collected effluent and eluate, and recover ammonium chloride after concentration treatment.

[0058] In this embodiment, the reaction liquid obtained in step D contains two parts of NH4Cl: unreacted residual NH4Cl and NH4Cl produced in the conversion process of LiF; all of these two parts of NH4Cl and NH4Cl derived in the defluorination process of step E are recovered and reused in the mechanical chlorination reaction stage of step B, thereby greatly reducing the consumption of materials and reducing costs.

[0059] Result analysis: 96.79% of Li is successfully converted into high-value LiF with a purity of 99.50%. 99.89% of F -, 0.63 g of NH4Cl can be successfully derived from the conversion of the residual solution per liter of LiF for reuse in the mechanical chlorination reaction of Step B. The mechanical chlorination coupled with fluorination reaction enhanced by H2O2 realizes near-full recovery and high-value production of waste lithium iron phosphate battery cathode materials, and the process is simpler and more environmentally friendly.

[0060] Example 2:

[0061] A method for high-value recovery of waste lithium iron phosphate battery cathode material, comprising the following steps:

[0062] Step A: After pretreatment of the waste lithium iron phosphate battery, LFP is obtained for standby use.

[0063] Step B: Take 0.1 g of LFP and put it into a 100 mL ball mill jar, and add 0.25 g of ammonium chloride, 1.8 mL of hydrogen peroxide and a quencher for grinding, control the ball-to-material ratio to be 14:1, the grinding time is 13 h, and the ball milling speed is 550 rpm.

[0064] Step C: After grinding, the mixture is washed out of the ball mill jar with deionized water, and then water immersion treatment is carried out, the leaching temperature is 55-65 degrees, the leaching time is 60-100 minutes, so that the metal lithium is fully leached out; After water immersion, filter to obtain a filtrate containing lithium chloride and a filter residue containing iron phosphate; The filter residue is washed, dried and ground for characterization experiments, and the filtrate, i.e. the leaching solution, is homogenized and then the chloride efficiency of Fe 2+ / Fe 3+ and Li + is determined by ICP-OES.

[0065] Step D: Add excess ammonium fluoride to the filtrate of Step C, ammonium fluoride as a precipitant, realizes the conversion of LiCl to LiF without introducing impurity ions, filter to obtain a reaction solution and a precipitate, the precipitate is washed, dried, ground to obtain the product LiF, and used for characterization experiments.

[0066] Step E: Adjust the pH of the reaction solution of Step D to 5.0-6.5, then use the defluorination resin LX-760 of Blue Xia Technology to treat the reaction solution by cyclic adsorption, and collect the effluent; When the defluorination resin adsorption reaches saturation, use 10% aluminum chloride solution at a flow rate of 1 BV / h to elute and regenerate the defluorination resin, the regeneration treatment capacity is 2-3 BV, and the eluate is collected; Combine the collected effluent and eluate, and recover ammonium chloride after concentration treatment.

[0067] Results analysis: 95.49% of Li is successfully converted to high-value LiF with a purity of 99.37%. 99.73% of F -, 0.62 g of NH4Cl can be successfully derived from the conversion residue per liter of LiF and reused in the mechanical chlorination reaction of Step B.

[0068] Example 3:

[0069] A method for recycling high-value waste lithium iron phosphate battery cathode material, comprising the following steps:

[0070] A method for recycling high-value waste lithium iron phosphate battery cathode material, comprising the following steps:

[0071] Step A, after pretreatment of waste lithium iron phosphate battery, LFP is obtained for standby.

[0072] Step B, take 0.1 g of LFP and put it into a 100 mL ball mill jar, add 0.35 g of ammonium chloride, 2.2 mL of hydrogen peroxide and a quencher, control the ball-to-material ratio to be 16:1, the grinding time is 11 h, and the ball milling speed is 650 rpm.

[0073] Step C, after grinding, the mixture is washed out of the ball mill jar with deionized water, then water immersion treatment is carried out, the leaching temperature is 55-65 degrees, the leaching time is 60-100 minutes, so that the lithium metal is fully leached; after water immersion, filter to obtain a filtrate containing lithium chloride and a filter residue containing iron phosphate; the filter residue is washed, dried and ground for characterization experiment, and the filtrate, i.e. leaching solution, is homogenized and then ICP-OES is used to determine the chlorination efficiency of Fe 2+ / Fe 3+ and Li + .

[0074] Step D, add excess ammonium fluoride to the filtrate of Step C, ammonium fluoride as a precipitating agent, realizes the conversion of LiCl to LiF without introducing impurity ions, filter to obtain a reaction liquid and a precipitate, the precipitate is washed, dried, ground to obtain product LiF, and used for characterization experiment.

[0075] Step E, adjust the pH of the reaction liquid of Step D to 5.0-6.5, then use the defluorination resin LX-760 of Blue Xia Technology to treat the reaction liquid by cyclic adsorption, collect the effluent; when the defluorination resin adsorption reaches saturation, use 10% aluminum chloride solution at a flow rate of 1 BV / h to elute and regenerate the defluorination resin, the regeneration treatment capacity is 2-3 BV, collect the eluate; combine the collected effluent and eluate, and recover ammonium chloride after concentration treatment.

[0076] Results analysis: 96.07% of Li is successfully converted into high-value LiF with a purity of 99.46%. 99.56% of F -0.61 g of NH4Cl could be successfully derived from the conversion of the residual solution per liter of LiF to the mechanical chlorination reaction of Step B.

[0077] Comparative Example:

[0078] The main steps of the following Comparative Examples 1 and 2 are the same as those of Example 1, except that:

[0079] Comparative Example 1 (H2O2-mechanical system)

[0080] In Step B, 0.1 g of lithium iron phosphate positive electrode material was placed in a 100 mL ball mill jar, and then 0.3 g of hydrogen peroxide was added for grinding; no ammonium chloride was used in this step.

[0081] Comparative Example 2 (H2O-NH4Cl mechanical chlorination system)

[0082] In Step B, 0.1 g of lithium iron phosphate positive electrode material was placed in a 100 mL ball mill jar, and then 0.3 g of ammonium chloride and 2.0 mL of water were added for grinding; no hydrogen peroxide was used in this step.

[0083] Experimental Example:

[0084] The main steps of the following Experimental Examples 1-5 are the same as those of Example 1, except that the types of quenching agents in Step B are different:

[0085] The quenching agent of Experimental Example 1 is methanol (MeOH);

[0086] The quenching agent of Experimental Example 2 is n-butanol (NBA);

[0087] The quenching agent of Experimental Example 3 is tert-butanol (TBA);

[0088] The quenching agent of Experimental Example 4 is p-benzoquinone (BQ);

[0089] The quenching agent of Experimental Example 5 is furfuryl alcohol (FFA).

[0090] The above Examples 1-3, Comparative Examples 1-3, and Experimental Examples 1-5 were subjected to the following experiments, respectively:

[0091] I. Detection method:

[0092] 1. The concentrations of metals Fe, Mn, and Li in the filtrate after water immersion were measured by inductively coupled plasma optical emission spectrometry (ICP-OES, PerkinElmer Avio 550 Max, USA), and the leaching efficiency / chlorination efficiency LE of different metals in LFP was calculated using the following formula (1): 2+ LE = (C0-Ct) / C0 3+ where C0is the initial concentration of the metal in the LFP, and Ctis the concentration of the metal in the filtrate after water immersion. + i 1. The concentrations of metals Fe, Mn, and Li in the filtrate after water immersion were measured by inductively coupled plasma optical emission spectrometry (ICP-OES, PerkinElmer Avio 550 Max, USA), and the leaching efficiency / chlorination efficiency LE of different metals in LFP was calculated using the following formula (1):

[0093] ​

[0094] where C i and V i are the metal ion concentration (mg / L) and the filtrate volume (L), respectively. m and w% are the mass of LFP (mg) and the mass fraction of metals in LFP, respectively.

[0095] 2. The concentration of F in the residual solution of LiF conversion was determined by ion chromatography (IC, Thermo Scientific ICS-1100, USA). -

[0096] 3. Characterization was performed by X-ray diffractometer (XRD, Malvern Panalytical Empyrean, Netherlands). Data were collected by step scanning with a scanning speed of 10° / min and a scanning angle (2q) of 10°-80°.

[0097] 4. Functional group information in the sample was obtained by Fourier transform infrared spectrometer (FT-IR, Thermo Fisher Scientific Nicolet iS20, USA).

[0098] 5. XPS spectra were obtained by X-ray photoelectron spectrometer (XPS, Thermo Fisher Escalab Xi+, USA).

[0099] II. Experimental content:

[0100] 1. Chlorination efficiency of metal Li and Fe under different conditions

[0101] In order to improve the chlorination and recovery efficiency of Li, the effects of different process conditions, such as ball-to-material ratio, mass ratio of NH4Cl to LFP, H2O2 volume, ball milling speed and grinding time, on the chlorination efficiency of Li and Fe in the mechanical chlorination process were experimentally studied, and the results are shown in Figure 1 .

[0102] Appropriate increase of ball-to-material ratio helps to improve the chlorination efficiency of Li. More ZrO2 balls can increase the interface area and make the material stress uniform. When the ball-to-material ratio is 15:1, the chlorination efficiency of Li is 89.74% ( Figure 1 a). With the continuous increase of ball-to-material ratio, the chlorination efficiency of Li begins to decrease, and the chlorination efficiency of Fe increases. This is because too many balls will cause agglomeration, hindering the reaction.

[0103] The effect of mass ratio of NH4Cl to LFP on chlorination efficiency is shown in Figure 1 ​NH4Cl and LFP is 1:1, the chlorination efficiency of Li is 86.49% and the chlorination efficiency of Fe is 0.2%. When the mass ratio of NH4Cl and LFP is 3:1, the chlorination efficiency of Li increases to 97.14% and the chlorination efficiency of Fe is only 0.01%. However, when the mass ratio continues to increase, the chlorination efficiency of Li decreases slightly. This is because the reaction is a flow-solid reaction, which follows the shrinking core model. During mechanical chlorination, a liquid layer is formed around the solid particles, and the chlorination process of Li is a diffusion-controlled process. The high concentration of NH4Cl in the solution reduces the diffusion rate, hindering the chlorination process of Li. Considering the economy, the mass ratio of NH4Cl to LFP is 3:1.

[0104] The effect of the volume of H2O2 on the chlorination efficiency is shown in Figure 1 c. The chlorination efficiency of Li increases with the increase of H2O2 until 2.0 mL. At this time, the chlorination efficiency of Li reaches 97.14%, and the chlorination efficiency of Fe decreases to 0.01%. With the continuous increase of the volume of H2O2, the chlorination efficiency of Li begins to decrease. It is found during the experiment that an appropriate amount of liquid medium can prevent LFP from adhering to the inner wall of the ball mill jar and the surface of the small ball, thereby promoting the mechanical chlorination reaction. However, too much liquid in the system will reduce the energy transfer during the ball milling impact. Therefore, the appropriate amount of H2O2 in the system is 2.0 mL.

[0105] In addition, the effect of ball mill speed on the chlorination efficiency of Li and Fe is shown in Figure 1 d. The chlorination efficiency of Li reaches 97.14% at 600 rpm, and then decreases with the increase of speed. This is because the speed is too high, part of the LFP material is brought to the blind spot of the ball mill jar, and the reaction is not complete. Considering the energy consumption, it is determined that 600 rpm is the ideal speed to achieve high Li chlorination efficiency and low Fe chlorination efficiency.

[0106] Figure 1 e shows the effect of grinding time on the chlorination efficiency of Li and Fe. When the ball milling time is less than 9h, the chlorination efficiency of Li is about 80%, and the chlorination efficiency of Li significantly increases with the continuous extension of the ball milling time. After 12h of ball milling, a critical point is reached, which is beneficial for the detachment of Li from the framework. After 12h of ball milling, the chlorination efficiency of Li is 97.14%, and does not increase with the increase of ball milling time. Too long ball milling time will cause the material to be overground, resulting in too many small particles, which may cause the material to agglomerate or block in the reaction system, thereby reducing the chlorination efficiency of Li. Considering the time and economic cost, the ideal ball milling time is determined to be 12h.

[0107] In summary, Example 1 determines that the optimal conditions for selective chlorination are a ball-to-material ratio of 15:1, a mass ratio of NH4Cl to LFP of 3:1, a volume-to-mass ratio of H2O2 to LFP of 20:1 mL / g, a rotation speed of 600 rpm, and a grinding time of 12 h.

[0108] Meanwhile, the chlorination / leaching efficiency of lithium and iron in Comparative Examples 1-3 and Comparative Example 1-2 is shown in Table 1.

[0109] In Example 1-3, the chlorination efficiency of lithium metal reaches more than 95%, and the highest is 97.14%, while the chlorination efficiency of Fe is 0.01%, and is always less than 0.1% under the synergistic effect of mechanical ball milling, H2O2 and quenching agent.

[0110] Under the same leaching experimental conditions, Comparative Example 1 is a H2O2-mechanical ball milling system without the addition of NH4Cl, and the leaching efficiency of Li is reduced to 40.07%, and the leaching efficiency of Fe is 1.88%. This shows that the H2O2-NH4Cl mechanical chlorination system using NH4Cl plays an important role in strengthening the chlorination efficiency of Li. On the one hand, it provides combined Cl - ions (chlorination reaction to generate LiCl), and on the other hand, the H + ions produced by partial hydrolysis make the solution system weakly acidic, and the oxidation performance of H2O2 is greatly improved under weakly acidic conditions, which oxidizes divalent iron Fe 2+ to trivalent iron Fe 3 , which promotes the rupture of Li-O bonds after oxidation, releases Li from the LiFePO4 structure, and has little effect on Fe-O bonds, thereby further improving the chlorination efficiency of Li, while the chlorination efficiency of Fe is not affected.

[0111] Comparative Example 2 is a H2O-NH4Cl mechanical chlorination system using only NH4Cl, and the leaching efficiency of Li is 35.01%, and the leaching efficiency of Fe is 0.26, which shows that only the synergistic effect of NH4Cl and H2O2 can form a H2O2-NH4Cl mechanical chlorination system to achieve the best chlorination efficiency of Li.

[0112] Table 1. Chlorination / leaching efficiency of lithium and iron in Examples 1-3 and Comparative Examples 1-3

[0113]

[0114] (II) Experiment on the mechanism of NH4Cl+H2O2 synergistically strengthening LFP mechanical chlorination

[0115] The breaking of Li-O bond in the process of mechanochemistry has been a difficult problem. Under the condition of natural ball milling, only a small part of Li-O bond will be broken, which is far from meeting the needs of Li chlorination and resource conversion. The role of NH4Cl in the reaction system is to provide Cl - ion and part of the hydrolysis of H + ion makes the solution weakly acidic, and the oxidation performance of H2O2 is greatly improved under weakly acidic conditions, which oxidizes divalent iron Fe 2+ to trivalent iron Fe 3 . After oxidation, it will promote the breaking of Li-O bond, release Li from the structure of LiFePO4, and has little effect on Fe-O bond.

[0116] The inventors also found in experiments that the free radicals produced by H2O2 may play an important role in the breaking of LiFePO4 bond, thereby strengthening the mechanical chlorination efficiency. The reaction is as follows:

[0117] Fe 2+ +H2O2→Fe 3+ +OH - +·OH(2)

[0118] H2O2→2H2O+O2(3)

[0119] Fe 2+ +·OH→Fe 3+ +OH-(4)

[0120] ·OH+H2O2→2H2O+HO2·(5)

[0121] Fe 3+ + HO2·→Fe 2+ + H + + O2 (6)

[0122] Fe 2+ +HO2·+H + →Fe 3+ +H2O2(7)

[0123] HO2·→O2 - ·+H + (8)

[0124] HO2·+·OH→H2O+ 1 O2(9)

[0125] Fe 2+ +O2→Fe 3+ +O2 - ·(10)

[0126] 2Fe 2++ H2O2→ 2Fe 3+ + 2OH - (11)

[0127] H2O2→·OH→HO2·→O2 - ·→ 1 O2(12)

[0128] However, the strong reactivity of these radicals means that their lifetime is short, making it difficult to directly capture and quantify them. This poses a challenge to how H2O2 strengthens the formation and reaction mechanism of radicals in the mechanical chlorination process of LFP. That is, which radicals can strengthen the breaking of Li-O bonds without affecting the breaking of Fe-O bonds, and which radicals can simultaneously strengthen the breaking of Li-O bonds and Fe-O bonds. To this end, the inventors added an appropriate amount of different types of quenchers: methanol (MeOH), n-butanol (NBA), tert-butanol (TBA), p-benzoquinone (BQ), and furfuryl alcohol (FFA). By comparing the chlorination efficiency of Li and Fe before and after adding the quenchers, the existence and formation mechanism of the radicals were confirmed, and the reaction pathway of the radicals with LFP was inferred.

[0129] The chlorination efficiency of Li and Fe under different quenchers in Experimental Examples 1-5 was measured, respectively, and the results are shown in Table 2 and Figure 2 .

[0130] Table 2. Chlorination efficiency of Li and Fe under different quenchers

[0131]

[0132]

[0133] Since methanol (MeOH), n-butanol (NBA), and tert-butanol (TBA) are quenchers for hydroxyl radicals ·OH, p-benzoquinone (BQ) is a quencher for hydrogen peroxide radicals HO2· and superoxide radicals O2 - ·, and furfuryl alcohol (FFA) is a quencher for singlet oxygen radicals 1 O2; it can be known that: Figure 3

[0134] 1. When methanol (MeOH), n-butanol (NBA), and tert-butanol (TBA) are selected as quenchers, respectively, that is, ·OH is quenched, it is equivalent to the entire radical chain reaction being blocked (H2O2→·OH→HO2·→O2 - ·→ 1 ​The results showed that the chlorination efficiency of Li decreased to varying degrees, while the chlorination efficiency of Fe did not change significantly. This is because the quenching effect of these three alcohols is relatively poor, and due to the limited capacity of the container during the experiment, a sufficient amount of quencher could not be added (adding too much liquid would cause it to spill during ball milling) to prevent the chain reaction of free radicals, leading to H2O2→·OH→HO2·→O2. - ·→ 1 The reaction pathway of O2 can still proceed, only slightly obstructed;

[0135] 2. When p-benzoquinone (BQ) is chosen as the quencher, i.e., free radicals HO2·, O2 - ·and 1 O2 generation is limited (HO2·→O2) - ·→ 1 (O2 pathway is blocked), the chlorination efficiency of Li also decreases, while the chlorination efficiency of Fe is significantly improved due to the destruction of Fe-O bonds by the strongly oxidizing ·OH;

[0136] (3) When furfuryl alcohol (FFA) is selected as the quencher, i.e. free radicals 1 When O2 is quenched, the efficiency of lithium decreases significantly, and the same applies when BQ is used as the quencher, and the chlorination efficiency of Fe is even higher.

[0137] The above experimental results indicate that the system contains three coexisting free radicals: ·OH, HO2·, and O2. - • is the main cause of Fe-O bond breaking, while methanol, n-butanol, and tert-butanol act as quenchers of •OH. The addition of these three alcohols will, to some extent, prevent the generation of •OH and subsequent free radicals (H2O2→·OH→HO2·→O2). - ·→ 1 O2); while free radicals 1 O2 is the main cause of Li-O bond breaking, exhibiting strong electron affinity. 1 O2 can polarize the Li-O bond, weakening its strength and ultimately leading to its breakage. The stability of Fe-O is due to PO4. 3- It retained its structure and trapped the surrounding Fe. 3+ FePO4 was formed, achieving the directional enrichment of Fe and P.

[0138] (III) Main reaction pathway of the H2O2-NH4Cl mechanical chlorination system

[0139] like Figure 3 and Figure 4As shown, the XRD and FT-IR spectra of samples before and after mechanical chlorination under different conditions are analyzed: LFP sample (a), filter residue sample from the H2O-NH4Cl mechanical chlorination system of Comparative Example 2 (b), LFP sample after ball milling from the H2O2-NH4Cl mechanical chlorination system of Example 1 (c), and filter residue sample from the H2O2-NH4Cl mechanical chlorination system of Example 1 (d). Wherein:

[0140] Figure 3 In Example 1, the XRD pattern of the filter residue sample produced by the H2O-NH4Cl mechanical chlorination system is shown. Figure 3 b) It was observed that the main phase was FePO4, which is consistent with the result that only a small portion of Li was chlorinated and leached. In the H2O2-NH4Cl mechanical chlorination system of Example 1, the XRD patterns of the LFP samples before and after ball milling ( Figure 3 c) shows that NH4Cl and FePO4 are the main phases, with LiCl phase present. The main phase of the filter residue sample produced by the H2O2-NH4Cl mechanical chlorination system is FePO4 (… Figure 3 d). The XRD pattern confirmed the oxidation transformation of LiFePO4 to FePO4, indicating that Li deintercalation occurred.

[0141] Figure 4 From Figure 4 a to Figure 4 b, Peak position change is not obvious. 469.02cm -1 and 502.05cm -1 The peak at the location and Li + The movement is related to its intensity, which varies with Li. x The decrease in x in FePO4 leads to a decrease in ( Figure 4 a and 4c). In the LFP sample of the H2O2-NH4Cl mechanical chlorination system, the octahedral FeO6 in LiFePO4 is at 636.56 cm⁻¹. -1 The stretching vibration at that point shifted to 655.18 cm. -1 Location. In LiFePO4, at 969.01 cm⁻¹. -1 PO4 at the location 3- The symmetric stretching vibration mode band gradually shifts to 957.12 cm⁻¹ in FePO₄. -1 Location: 1401.41cm -1 The peak at the location and PO4 3- The antisymmetric stretching is related to Li deintercalation and FePO4 formation; 3170.36 cm -1 The peak at 3403.52 cm⁻¹ is due to the vibration of the NH bond in excess NH₄Cl. -1The peak at this location may correspond to the symmetric stretching vibration of the OH bond, indicating that the sample may contain water or hydroxyl groups. After removing the NH4Cl component, the peak at 3170.36 cm⁻¹... -1 The corresponding peak disappeared, while the positions of other peaks did not change significantly.

[0142] To further confirm the main reaction pathway in the mechanical chlorination process, XPS analysis was performed on samples of the H2O2-NH4Cl mechanical chlorination system from Example 1 before and after mechanical ball milling. Figure 5 As shown in the Li 1s spectrum, the characteristic peaks of Li shifted after mechanical chlorination, moving from a high binding energy (56.20 eV) to a low binding energy (56.10 eV), indicating the deintercalation of Li in LiFePO4. After the reaction, the main peaks of Fe 2p3 / 2 and Fe 2p1 / 2 in the LFP cathode material shifted from 711.61 eV to 712.58 eV and from 724.54 eV to 726.53 eV, respectively, clearly shifting towards higher binding energies. This indicates that Fe(II) in LFP was oxidized to Fe(III) during mechanical chlorination. However, the P 2p spectrum shows almost no change in peak position and pre-peak position, indicating that its structure is highly similar to that before mechanical chlorination. This further confirms that the conversion of LiFePO4 to FePO4 is accompanied by the deintercalation of Li.

[0143] (iv) Chlorination coupled with fluorination reaction to achieve high-value product utilization and near-full recovery

[0144] 1. LiF conversion and NH4Cl regeneration mechanism

[0145] First, ammonium chloride (NH4Cl) is added during the H2O2-enhanced ball milling process to provide Cl- for the bonding of metallic Li. - The reaction involves chlorination to produce LiCl, followed by the use of ammonium fluoride (NH4F) as a precipitant for Li in the filtrate, converting LiCl into the high-value product LiF. During the chlorination-coupled fluorination reaction, NH4F and LiCl dissolve in water and dissociate into NH4+. + ,F - and Li + ,Cl - (Equations 13 and 14). When the two substances are mixed in water, a double displacement reaction occurs, NH4+. + With Cl - Combine to form NH4Cl, Li + With F - The reaction process, which combines to form Li (Formulas 15 and 16), is shown below:

[0146] LiCl→Li + + Cl - (13)

[0147] NH4F→NH4 + + F - (14)

[0148] Li + + F - →LiF (15)

[0149] NH4 + + Cl - →NH4Cl (16)

[0150] like Figure 6 As shown, from the perspective of lattice energy analysis, Li has a small ionic radius. + With F, which has a high charge density - The strong attraction generated is the main reason for the high lattice energy of LiF. Analysis from the perspective of Gibbs free energy (see...) Figure 6 a) The formation of LiF precipitate reduces the number of ions in the solution, leading to a decrease in system entropy. The energy released during this process compensates for the heat absorbed during dissolution, promoting the forward reaction. In terms of solubility differences, LiCl, NH4F, and NH4Cl are readily soluble in water, while LiF has significantly lower solubility than the other three salts, causing it to precipitate preferentially and promoting the forward reaction.

[0151] The reaction mechanism of H2O2-enhanced mechanical chlorination coupled with fluorination to treat waste LiFePO4 and prepare high-value LiF is as follows: Figure 7 As shown, under the action of mechanical force, H2O2 is produced 1 O2 can selectively break low-energy Li-O bonds in LiFePO4, releasing Li + With Cl - They combine to form LiCl. Similar to the charging process of an LFP battery, LiFePO4 is oxidized to FePO4, while the crystal structure remains unchanged. The conversion of LiCl to LiF is due to the addition of NH4F, which increases the ionic radius of the smaller Li ions. + With F, which has a high charge density - Furthermore, the formation of low-solubility LiF precipitates increases the entropy of the system, thereby promoting the forward direction of the metathesis reaction. During the defluorination process, the aluminum-loaded functional groups in the regenerated resin affect the F... - It exhibits strong selective adsorption, releasing an equal amount of Cl during ion exchange. - With NH4 + They combine to form NH4Cl.

[0152] 2. High-value utilization of LiF products and recycling of NH4Cl and defluorination resins

[0153] NH4Cl is produced in the fluorination reaction, i.e. LiF conversion process, and F - in the residual LiF conversion solution is removed by a defluorination resin. In the ion exchange process, the functional groups on the resin release an equivalent amount of Cl - , F - is adsorbed on the resin to remove F - in the residual LiF conversion solution. When the defluorination resin is saturated, an aluminum AlCl3 solution is used for regeneration to restore its performance. Al 3+ in the regeneration solution desorbs F - in the resin to form an Al-F complex, thereby achieving regeneration and recycling of the resin.

[0154] Meanwhile, the main solute in the LiF conversion solution is converted into NH4Cl, and this part of NH4Cl and the remaining NH4Cl from the chlorination reaction and NH4Cl derived from the defluorination process are all recycled and reused, thereby greatly reducing the consumption of materials and lowering costs. XRD patterns show that the repeatedly used NH4Cl is well crystallized (see Figure 6 c).

[0155] On the other hand, most of the existing lithium-ion battery recycling processes choose carbonates or phosphates to obtain products Li2CO3 or Li2PO4, and the solubility of Li2CO3 and Li2PO4 is much higher than that of LiF, which leads to waste of recovered Li. In order to verify the difference in solubility, the lithium concentration in saturated Li2CO3 solution and saturated LiF solution under the same conditions was tested respectively:

[0156] At room temperature, the solubility of Li2CO3 is 1.33 grams, and the Li + concentration in the saturated Li2CO3 solution is calculated as follows:

[0157]

[0158] Moles of Li + = 2 x Moles of Li2CO3 = 2 x 0.0180 mol = 0.0360 mol

[0159] At room temperature, the solubility of LiF is 0.13 grams, and the Li + concentration in the saturated LiF solution is calculated as follows:

[0160]

[0161] Moles of Li + = Moles of LF = 0.00501 mol

[0162] Therefore, the concentration of Li in the saturated Li2CO3 solution + The concentration is much higher than that in the saturated LiF solution. This indicates that the efficiency of recovering Li in the form of LiF is much higher than that of the prior art product Li2CO3 under the same conditions.

[0163] In addition, LiF has a higher value than Li2CO3. LiF is widely used in fluxes, glazes, dosimetry, brazing, and aluminum casting processes. More importantly, LiF plays a key role in solid-state batteries by improving the interface, increasing ionic conductivity, and enhancing electrochemical stability. Figure 6 The XRD pattern of b shows that LiF is well crystallized.

[0164] The price of each ton of battery-grade Li2CO3 is 76350 yuan RMB, while the price of each ton of battery-grade LiF is 143500 yuan RMB (https: / / new-energy.smm.cn / , accessed on January 25, 2025).

[0165] Take 1 ton of product as an example:

[0166]

[0167]

[0168] LiF has high purity, high yield, simple process, low production cost, high added value, and good economic benefits. However, the recovery process of Li2CO3 is complex, the energy consumption is high, the purity and yield are relatively low, resulting in high production cost and relatively poor economic benefits, making it difficult to realize industrialization.

[0169] The above-described embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for high-value recycling of waste lithium iron phosphate battery cathode materials, characterized in that, Includes the following steps: Step A: After pretreatment of the waste lithium iron phosphate batteries, lithium iron phosphate cathode material is obtained; Step B: Add lithium iron phosphate cathode material, ammonium chloride and hydrogen peroxide to a ball mill jar for grinding, and control the mass ratio of ammonium chloride to lithium iron phosphate cathode material to be 5:2~7:2, and the volume mass ratio of hydrogen peroxide to lithium iron phosphate cathode material to be (18~22):1 mL / g; Step C: After grinding, the mixture is washed out of the ball mill jar with deionized water, and then subjected to water immersion treatment to fully leach out the lithium metal; after water immersion, it is filtered to obtain a filtrate containing lithium chloride and a filter residue containing iron phosphate; the filter residue is washed, dried and ground and then used for characterization experiments, and the filtrate is homogenized and the chlorination efficiency of lithium metal and iron is determined. Step D: Add excess ammonium fluoride to the filtrate from step C. After reacting for a period of time, filter to obtain the reaction solution and precipitate. The precipitate is washed, dried, and ground to obtain the product lithium fluoride. Step E: Adjust the pH of the reaction solution from step D to 5.0-6.5, then use a fluoride removal resin to perform cyclic adsorption treatment on the reaction solution and collect the effluent; when the fluoride removal resin reaches saturation, use an aluminum chloride solution to elute and regenerate the fluoride removal resin and collect the eluent; combine the collected effluent and eluent, and after concentration treatment, obtain an ammonium chloride solution. In step C, the leaching temperature is 55-65 degrees Celsius, and the leaching time is 60-100 minutes.

2. The method for high-value recycling of waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that: In step B, the ball-to-material ratio is (14~16):1, the grinding time is 11-13 hours, and the ball mill speed is 550-650 rpm.

3. The method for high-value recycling of waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that: In step E, the defluorinating resin is eluted and regenerated using a 10% aluminum chloride solution at a flow rate of 1 BV / h, with a regeneration capacity of 2-3 BV.

4. The method for high-value recycling of waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that: In step A, the pretreatment step is as follows: the waste lithium iron phosphate battery is discharged and disassembled to obtain the positive electrode sheet, and then the positive electrode sheet is subjected to pyrolysis treatment to separate the positive electrode material and aluminum foil, thereby obtaining the lithium iron phosphate positive electrode material.

Images