A method for directly repairing and regenerating waste lithium iron phosphate positive electrode based on two-electron lithiation reagent

Abstract

This invention discloses a direct repair and regeneration method for waste lithium iron phosphate cathodes based on a two-electron lithiation reagent, comprising the following steps: (1) disassembling the recycled waste lithium iron phosphate battery after complete discharge, separating and collecting the cathode active material; (2) adding an aromatic ketone dilithium reagent to the cathode active material, stirring and reacting for 1-4 hours, then centrifuging, washing, and drying to obtain a lithified regenerated lithium iron phosphate cathode; wherein: the molar ratio of lithium in the aromatic ketone dilithium reagent to the molar ratio of lithium missing in the cathode active material is ≥1; the aromatic ketone dilithium reagent is composed of aromatic ketone dilithium and an organic solvent; the molar ratio of aromatic ketone molecules to lithium in the aromatic ketone dilithium is 1:2. This invention can achieve twice the lithiation efficiency with the same amount of aromatic chemical reagent consumption, which is beneficial to reducing the material input in the repair and regeneration process. Moreover, the electrochemical performance of the regenerated layered lithium iron phosphate cathode material obtained by this invention is comparable to that of commercial lithium iron phosphate cathodes.

Description

Technical Field

[0001] This invention relates to a direct repair and regeneration technology for spent cathode materials of retired lithium-ion batteries, and particularly to a two-electron chemical lithiation repair and regeneration method for spent lithium iron phosphate cathode materials. Background Technology

[0002] Over the past few decades, advancements in electrochemical theory and the development of the lithium-ion battery industry have significantly transformed the world and human lifestyles. However, the limited electrochemical lifespan of commercially available lithium-ion batteries means that a peak in their retirement is approaching in the coming years. Proper recycling and reuse of retired lithium-ion batteries are essential to fully realize their economic value and reduce resource waste and potential environmental pollution.

[0003] Lithium iron phosphate (LiFePO4) with an olivine structure is currently the most widely used, safest, and most cost-effective cathode chemistry system in automotive power batteries. During the electrochemical charging process of lithium-ion batteries, the active Li... + LiFePO4 cathode phase is extracted to form lithium-poor FePO4 phase, Li + Under the influence of an internal electric field, ions are inserted into the graphite anode via the electrolyte's ion transport pathway, completing the conversion of electrical energy into chemical energy; the discharge process is the reverse. The stable FeO6 and PO4 structural units in the LiFePO4 cathode ensure that problems such as active material dissolution and crystal structure collapse occur virtually during long-term lithium-ion insertion / extraction. However, the graphite anode consumes some Li during the first week. + The formation of a solid electrolyte interface, which continuously breaks down and regenerates during subsequent cycles, means that the capacity degradation mechanism of lithium-ion batteries based on LiFePO4 cathodes is mainly the loss of lithium reserves.

[0004] For low-value-added cathodes like LiFePO4, which do not contain precious transition metals, the economic value of metal smelting is very limited, and the economic value of the smelting products is often insufficient to cover the cost. Common methods for recycling waste LiFePO4 cathodes primarily involve the selective extraction of the more valuable lithium element, which often involves the use of corrosive chemicals or high-temperature roasting. For example, the invention patent with authorization announcement number CN216808939U requires the use of oxidants and acid leaching solutions for selective lithium extraction. It should be noted that 70%-80% of the residual energy is still retained in the spent LiFePO4 cathode. This residual energy is lost due to the breaking of chemical bonds during both metal smelting and lithium extraction processes, which is a significant reason for the limited economic value of recycling spent LiFePO4 cathodes. From the perspective of the failure mechanism, spent LiFePO4 cathodes can be directly repaired and regenerated from old to new cathodes by supplementing with an active lithium source. This repair strategy can achieve high economic benefits with relatively low energy and material input. For example, the invention patent with authorization announcement number CN112349989B utilizes aromatic hydrocarbon-based lithiation reagents to achieve chemical lithium replenishment and regeneration of lithium-depleted waste cathodes. However, these conventional aromatic hydrocarbon lithiation reagents only involve single-electron reactions, resulting in limited lithiation capacity per unit size. Moreover, polycyclic aromatic hydrocarbons have strong biotoxic effects on humans and aquatic organisms.

[0005] Based on the above reasons, this application is hereby submitted. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a green and non-toxic remediation and regeneration technology for spent lithium iron phosphate cathode materials from lithium-ion batteries, possessing two-electron lithiation capability. This technology focuses on the 0.59V vs. Li value of spent lithium iron phosphate cathode materials. + The present invention utilizes lithiation potential matching (above 0.59V vs. Li) to determine the over-lithiation potential of Li. + The aromatic ketone dilithiation reagent ( / Li) is used to chemically lithiate spent lithium iron phosphate cathodes at room temperature, restoring their electrochemical performance. The advantage of this method is that the selected aromatic ketone lithiation reagent not only has good biocompatibility but also enables two-electron lithium replenishment, further reducing the amount of lithiation reagent and solvent used, thus achieving lower material input.

[0007] The technical solution adopted in this invention is as follows:

[0008] A method for repairing and regenerating lithium iron phosphate cathode material from waste lithium-ion batteries includes the following steps:

[0009] (1) Disassemble the recycled waste lithium iron phosphate batteries after they are fully discharged, and separate and collect the positive electrode active materials;

[0010] (2) Add an aromatic ketone dilithium reagent to the positive electrode active material, stir the reaction for 1-4 hours, centrifuge, wash, and dry to obtain the lithiated regenerated lithium iron phosphate positive electrode; wherein:

[0011] The ratio of the molar amount of lithium in the aromatic ketone dilithium reagent to the molar amount of lithium missing in the positive electrode active material is ≥1;

[0012] The aromatic ketone dilithium reagent is composed of aromatic ketone dilithium and an organic solvent; the molar ratio of aromatic ketone molecules to lithium in the aromatic ketone dilithium is 1:2.

[0013] Furthermore, in the above technical solution, the discharge method of the waste lithium iron phosphate battery mentioned in step (1) can be one of electrochemical discharge or salt solution immersion discharge; the separation method can be one of mechanical separation or organic solvent separation.

[0014] Furthermore, in the above technical solution, the concentration of aromatic ketone dilithium in the aromatic ketone dilithium reagent in step (2) is 0.01 to 2.0 mol / L.

[0015] Furthermore, in the above technical solution, the aromatic ketone dilithium mentioned in step (2) can be at least one of benzophenone dilithium or 9-fluorenone dilithium, preferably 9-fluorenone dilithium.

[0016] Furthermore, in the above technical solution, the organic solvent is an aprotic solvent, such as any one of ethylene glycol dimethyl ether (DME), tetrahydrofuran (THF), acetonitrile, N,N-dimethylformamide, etc.

[0017] Furthermore, in the above technical solution, the aromatic ketone dilithium reagent provided by the present invention is prepared by a chemical reaction between an aromatic ketone and metallic lithium in an organic solvent; wherein: the organic solvent is an aprotic solvent, such as any one of ethylene glycol dimethyl ether (DME), tetrahydrofuran (THF), acetonitrile, N,N-dimethylformamide, etc.

[0018] Furthermore, in the above technical solution, the aromatic ketone dilithium reagent is prepared by the following method, with the following steps:

[0019] At room temperature, the aromatic ketone is dissolved in an organic solvent and mixed well. Then, lithium metal is added at a stoichiometric ratio of 1:2 (aromatic ketone to lithium metal molar ratio). The mixture is stirred until it reacts completely to obtain a homogeneous solution, which is the aromatic ketone dilithium reagent.

[0020] More preferably, in the above technical solution, the reaction time is 20-40 minutes, and more preferably 30 minutes.

[0021] Specifically, in the above technical solution, step (2) controls the ratio of the molar amount of lithium in the aromatic ketone dilithium reagent to the molar amount of lithium missing in the positive electrode active material to be ≥1. In actual operation, this can be achieved by using an excess of aromatic ketone dilithium reagent.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention provides a method for direct repair and regeneration of waste lithium iron phosphate cathode based on aromatic ketone lithiation reagent, which can achieve twice the lithiation efficiency with the same amount of aromatic chemical reagent consumption, which is beneficial to reduce the material input in the repair and regeneration process.

[0024] (2) The present invention uses a moderately reducing aromatic ketone lithiation reagent for chemical lithiation. The matching redox potential avoids the occurrence of ineffective overlithiation behavior, thus eliminating the need to pre-determine the Li content of waste lithium iron phosphate cathodes, which facilitates low-cost and high-throughput industrial applications.

[0025] (3) The aromatic ketone lithium reagent used in this invention has less biotoxicity than the aromatic hydrocarbon lithium reagent and is a low-toxicity green lithium reagent.

[0026] (3) The electrochemical performance of the regenerated layered lithium iron phosphate cathode material obtained by the present invention is comparable to that of commercial lithium iron phosphate cathode, which indicates that it has initial industrialization potential. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This invention relates to a technical roadmap for the direct repair and regeneration of waste lithium iron phosphate cathodes using chemical lithiation with a two-electron aromatic ketone lithiation reagent.

[0029] Figure 2 These are the X-ray diffraction patterns of the lithium iron phosphate cathode before and after the repair and regeneration of nonafluorenone dilithium provided in Example 1 of this invention;

[0030] Figure 3 This is the first-cycle charge-discharge curve of the lithium iron phosphate cathode material before and after the repair and regeneration of nonafluorenone dilithium provided in Example 1 of the present invention;

[0031] Figure 4This is a graph showing the electrochemical cycle stability test results of the lithium iron phosphate cathode material after repair and regeneration with nonafluorenone dilithium provided in Example 1 of this invention;

[0032] Figure 5 This is the X-ray diffraction pattern of the lithium iron phosphate cathode before and after the repair and regeneration of benzophenone dilithium provided in Example 2 of the present invention;

[0033] Figure 6 The first-cycle charge-discharge curves of the lithium iron phosphate cathode material before and after the repair and regeneration of benzophenone dilithium provided in Example 2 of this invention are shown.

[0034] Figure 7 This is a graph showing the electrochemical cycle stability test results of the lithium iron phosphate cathode material before and after the repair and regeneration of benzophenone dilithium provided in Example 2 of the present invention. Detailed Implementation

[0035] The present invention will be further described in detail below through implementation examples. These implementation examples are carried out based on the technology of the present invention. Detailed implementation methods and specific operating procedures are provided to illustrate the inventiveness of the present invention, but the scope of protection of the present invention is not limited to the following implementation examples.

[0036] The equipment and raw materials used in this invention are all commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0037] To address the problems of inefficient energy utilization and high pollution associated with destructive metallurgical technologies, as well as the insufficient lithium replenishment capacity and high toxicity of lithiation reagents in existing direct remediation and regeneration technologies, this invention provides a technical route for the direct remediation and regeneration of waste lithium iron phosphate cathodes using a two-electron aromatic ketone lithiation reagent through chemical lithiation. Figure 1 As shown.

[0038] The aromatic ketone dilithium (9-fluorenone dilithium or benzophenone dilithium) reagent provided by this invention is prepared by chemical reaction of aromatic ketones with metallic lithium in organic solvents (such as ethylene glycol dimethyl ether, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, etc.). The concentration of the aromatic ketone dilithium reagent is 0.01–2.0 mol / L.

[0039] The electrochemical performance of the regenerated cathodes prepared in the following examples was tested according to the following methods:

[0040] The prepared recycled cathode material, Super P and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 80:10:10 to form a slurry, which was then uniformly coated onto an aluminum foil current collector to obtain the working electrode. Using lithium metal as the counter electrode, polypropylene (purchased from Celgard, USA) as the separator, and 1 mol / L ternary electrolyte (1M LiPF6 EC / DEC / DMC (volume ratio 1:1:1)) as the electrolyte, the 2016 type coin cell was assembled in a glove box.

[0041] Example 1

[0042] This embodiment describes a method for directly repairing recycled waste lithium iron phosphate cathode materials using a 9-fluorenone dilithium reagent. The specific steps are as follows:

[0043] (1) Waste lithium iron phosphate / graphite pouch cells that have been cycled at 1C for 3000 cycles are discharged to 2.0V on an electrochemical charge-discharge apparatus and then disassembled to obtain spent lithium iron phosphate positive electrode sheets. The obtained positive electrode sheets are first soaked in dimethyl carbonate for 0.5h to remove residual lithium salts, and then spent lithium iron phosphate powder is obtained by physical crushing and solvent separation.

[0044] (2) Dissolve 1.8g of 9-fluorenone powder in 100mL of tetrahydrofuran (THF) in a glove box to form a pale yellow solution; add 138.8mg of lithium metal to the solution and stir for 30min to obtain a 0.1mol / L 9-fluorenone dilithium solution.

[0045] (3) Disperse 1g of the failed lithium iron phosphate cathode powder obtained in step (1) in 50mL THF, then add 100mL of the 9-fluorenone dilithium reagent prepared in step (2) to the dispersion, continue stirring and reacting for 30min, then centrifuge the mixed solution, retain the supernatant for subsequent recycling, wash the precipitate three times with THF and then dry it to obtain the regenerated lithium iron phosphate cathode.

[0046] Figure 2 This is an X-ray diffraction pattern of the lithium iron phosphate cathode before and after regeneration of lithium nonafluorenone dilithium, as provided in Example 1 of this invention. Figure 2 It can be seen that the XRD pattern before repair and regeneration contains obvious diffraction peaks related to lithium-poor FePO4. After chemical lithiation regeneration with nonafluorenone dilithium, the transformation of FePO4 to LiFePO4 was achieved.

[0047] Figure 3 This is the first-cycle charge-discharge curve of the lithium iron phosphate cathode material before and after regeneration of nonafluorenone dilithium provided in Example 1 of this invention. Figure 3It can be seen that the initial charge capacity of the failed LiFePO4 cathode is only about 110 mAh / g, indicating that there are many lithium defect sites in its crystal structure. After regeneration by nonafluorenone dilithium, the active lithium in the lithiation reagent diffuses into the cathode lattice, increasing its charge capacity to about 158 ​​mAh / g, confirming the effectiveness of nonafluorenone dilithium in lithium replenishment.

[0048] Figure 4 This is a graph showing the electrochemical cycle stability test results of the repaired and regenerated lithium iron phosphate cathode material provided in Example 1 of this invention. Figure 4 It can be seen that after chemical lithiation repair and regeneration with nonafluorenone dilithium, the regenerated cathode can achieve a capacity retention rate of over 80% during a long-term cycle of 160 cycles, indicating that this two-electron lithiation reagent can achieve a good repair effect.

[0049] Example 2

[0050] This embodiment presents a method for directly repairing recycled waste lithium iron phosphate cathode materials using benzophenone dilithium reagent. The specific steps are as follows:

[0051] (1) Waste lithium iron phosphate / graphite pouch batteries that have been cycled at 0.5C for 5000 cycles were soaked in saline solution for 24 hours and then manually disassembled to obtain the failed positive electrode sheet. The obtained positive electrode sheet was first soaked in dimethyl carbonate for 0.5 hours to remove residual lithium salt, and then the failed lithium iron phosphate positive electrode powder was obtained by physical crushing, solvent dissolution, low-speed centrifugation and other means.

[0052] (2) Dissolve 1.82g of benzophenone powder in 100mL of ethylene glycol dimethyl ether (DME) in a glove box to form a slightly yellow solution; add 138.8mg of lithium metal to the solution and stir for 30min to obtain a 0.1mol / L benzophenone dilithium solution.

[0053] (3) Disperse 1g of the failed lithium iron phosphate cathode powder obtained in step (1) in 50mL of DME, then add 100mL of the benzophenone dilithium reagent prepared in step (2) to the dispersion, continue stirring and reacting for 30min, then centrifuge the mixed solution, retain the supernatant for subsequent recycling, wash the precipitate three times with DME and then dry it to obtain the regenerated lithium iron phosphate cathode powder.

[0054] Figure 5 This is an X-ray diffraction pattern of the lithium iron phosphate cathode before and after the regeneration of benzophenone-based dilithium, as provided in Example 2 of this invention. Figure 5 It can be seen that the XRD pattern before regeneration contains obvious diffraction peaks related to lithium-poor FePO4. After chemical lithiation regeneration with benzophenone dilithium, the transformation of FePO4 to LiFePO4 was achieved.

[0055] Figure 6 This is the first-cycle charge-discharge curve of the lithium iron phosphate cathode material before and after the repair and regeneration of benzophenone dilithium provided in Example 2 of the present invention. Figure 6 It can be seen that the initial charge capacity of the failed LiFePO4 cathode is only about 110 mAh / g, indicating that there are many lithium defect sites in its crystal structure. After regeneration by benzophenone dilithium, the active lithium in the lithiation reagent diffuses into the cathode lattice, increasing its charge capacity to about 145 mAh / g, confirming the effectiveness of benzophenone dilithium for lithium replenishment.

[0056] Figure 7 This is a graph showing the electrochemical cycle stability test results of the lithium iron phosphate cathode material before and after the regeneration and repair of benzophenone-based dilithium, as provided in Example 2 of this invention. Figure 7 It can be seen that after chemical lithiation repair and regeneration with benzophenone dilithium, the regenerated cathode can achieve a capacity retention rate of over 80% during a long-term cycle of 160 cycles, indicating that this two-electron lithiation reagent can achieve a good repair effect.

Claims

1. A method for repairing and regenerating lithium iron phosphate cathode material from waste lithium-ion batteries, characterized in that: The method includes the following steps: (1) Disassemble the recycled waste lithium iron phosphate batteries after they are fully discharged, and separate and collect the positive electrode active materials; (2) Add an aromatic ketone dilithium reagent to the positive electrode active material, stir and react for 1-4 h, then centrifuge, wash, and dry to obtain a lithiated regenerated lithium iron phosphate positive electrode; wherein: The ratio of the molar amount of lithium in the aromatic ketone dilithium reagent to the molar amount of lithium missing in the positive electrode active material is ≥1; The aromatic ketone dilithium reagent is composed of aromatic ketone dilithium and an organic solvent; the molar ratio of aromatic ketone molecules to lithium in the aromatic ketone dilithium is 1:2; The aromatic ketone dilithium reagent is at least one of benzophenone dilithium or 9-fluorenone dilithium.

2. The method according to claim 1, characterized in that: The concentration of the aromatic ketone dilithium in the aromatic ketone dilithium reagent in step (2) is 0.01 to 2.0 mol / L.

3. The method according to claim 1, characterized in that: The aromatic ketone dilithium is 9-fluorenone dilithium.

4. The method according to claim 1, characterized in that: The organic solvent is an aprotic solvent.

5. The method according to claim 4, characterized in that: The organic solvent is any one of ethylene glycol dimethyl ether, tetrahydrofuran, acetonitrile, and N,N-dimethylformamide.

6. The method according to claim 4, characterized in that: The aromatic ketone dilithium reagent was prepared by the following method, with the steps as follows: At room temperature, the aromatic ketone is dissolved in an organic solvent and mixed well. Then, lithium metal is added at a stoichiometric ratio of 1:2 (aromatic ketone to lithium metal molar ratio). The mixture is stirred until it reacts completely to obtain a homogeneous solution, which is the aromatic ketone dilithium reagent.

7. The method according to claim 6, characterized in that: The reaction time is 20-40 min.

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