Method for stripping positive electrode material of waste lithium iron phosphate battery

Abstract

The invention discloses a stripping method for a positive electrode material of a waste lithium iron phosphate battery, and belongs to the technical field of lithium battery recycling. The stripping method comprises the following steps: discharging, disassembling and screening the waste lithium iron phosphate battery to obtain a negative electrode; the sodium persulfate solution is subjected to electrolytic pre-activation, and the sodium persulfate solution obtained after electrolytic pre-activation serves as electrolyte; the cathode electrode is placed in the electrolyte, stirring treatment is conducted under the water bath condition, solid-liquid separation and drying are conducted, and then current collector aluminum foil and positive electrode material powder are obtained. Oriented degradation of polyvinylidene fluoride is achieved under the mild condition through the synergistic effect of an external electric field and an active oxidizing agent in the electrolyte; the positive electrode material and the aluminum foil are efficiently separated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery recycling, and particularly relates to a stripping method for positive electrode material of waste lithium iron phosphate battery. BACKGROUND

[0002] With the rapid development of new energy vehicles and energy storage industries, lithium iron phosphate (LiFePO4) batteries are widely used due to their high safety, long cycle life and low cost. However, a large number of batteries are retired at the end of their service life, generating a considerable amount of waste lithium iron phosphate positive electrode material. This type of positive electrode material is mainly composed of active material LiFePO4, conductive agent carbon powder and binder polyvinylidene fluoride (PVDF), and is tightly attached to the aluminum foil current collector. PVDF has very high chemical inertness and thermal stability, making the combination between the positive electrode material and the current collector very firm, which brings great difficulty to the subsequent material separation and metal recovery.

[0003] Currently, the separation of waste lithium iron phosphate positive electrode material mainly relies on high-temperature calcination, organic solvent dissolution or mechanical stripping. High-temperature calcination achieves stripping by thermal decomposition of PVDF, but this method has high energy consumption and can cause damage to the crystal structure of LiFePO4 and loss of lithium elements. Although the organic solvent method can dissolve the binder at a relatively low temperature, it often uses NMP, DMF and other high-boiling organic solvents, which have the problems of high toxicity, high cost and difficult recovery. Mechanical stripping is simple to operate, but has low stripping efficiency and can easily damage the material.

[0004] Therefore, it is a key requirement in the current technical research and industrial application of this field to develop an electrochemical stripping method with high controllability, high stripping efficiency, good aluminum foil retention and environmental friendliness, to achieve efficient separation and resource recovery of waste lithium iron phosphate positive electrode material under mild conditions. SUMMARY

[0005] To solve the technical problems of high cost, large acid consumption and complex operation in the stripping of aluminum foil and positive electrode material during the recycling process of waste lithium iron phosphate battery, the application provides a stripping method for positive electrode material of waste lithium iron phosphate battery, which is a green electrochemical recycling method that can achieve efficient stripping of positive electrode material. This method does not require high-temperature calcination or organic solvent treatment, and has the advantages of low energy consumption, little pollution and complete stripping.

[0006] To achieve the above purpose, the application provides the following technical solutions:

[0007] The application provides a stripping method for positive electrode material of waste lithium iron phosphate battery, comprising the following steps:

[0008] After the waste lithium iron phosphate battery is discharged, disassembled and sieved, a cathode electrode is obtained;

[0009] Electrolytic pre-activation is performed on the sodium persulfate solution, and the electrolytic pre-activated sodium persulfate solution is used as an electrolyte to activate the sodium persulfate solution and generate a free radical system with strong oxidizing property;

[0010] The cathode electrode is placed in the electrolyte, and stirring treatment (peeling reaction) is performed under water bath conditions; the active free radicals in the electrolyte can promote oxidative degradation of the binder PVDF (polyvinylidene fluoride), thereby destroying the combination between the positive active material and the aluminum foil, and after the peeling reaction is completed, solid-liquid separation is performed, and after drying, the current collector aluminum foil and the positive material powder are obtained. The current collector aluminum foil obtained by the method has a smooth surface and no obvious corrosion, and can be directly recycled; the peeled positive material powder can be used for regeneration or resource treatment after washing and drying.

[0011] The present application utilizes the two-stage mechanism of electrolytic pre-activation + free radical synergistic oxidation to realize the directional degradation and efficient peeling of the binder PVDF in the waste lithium iron phosphate positive material. In the electrolytic pre-activation stage, sodium persulfate (Na2S2O8) is decomposed under an applied electric field to generate sulfate radicals (SO4•⁻) and hydroxyl radicals (•OH) with strong oxidizing ability. Unlike traditional continuous electrolysis, no cathode electrode is added in this stage, and only the electrolyte is pre-activated for a short time to make the free radical concentration in the system reach a stable balance. After the electrolytic pre-activation is completed, the electrolytic device is removed, and the waste lithium iron phosphate cathode electrode is put into the pre-activated solution and stirred under water bath conditions. The active free radicals continue to have oxidative chain scission reaction with PVDF in the absence of an external electric field, causing the directional rupture of C-F and C-C bonds, the gradual degradation of the bonding layer, and the natural peeling of the positive active material from the aluminum foil. Due to the mild system potential, the aluminum foil surface is almost not corroded, maintaining the original metal luster.

[0012] Compared with the prior art, the present application has the following characteristics:

[0013] 1. "Space-time separation mechanism" of electrolytic pre-activation and subsequent self-peeling: existing electrochemical peeling methods (such as Fenton electrochemical system or continuous power-on system) require oxidation and peeling to be performed simultaneously under the action of electric current, and the electric current needs to be continuously maintained throughout the process, which has high energy consumption and uneven electrode interface reaction.

[0014] The present application realizes the "energy storage reaction" of free radicals in the solution by the strategy of electrolytic pre-activation followed by peeling without electricity, which not only significantly reduces the energy consumption, but also avoids electrode polarization and side reactions, making the reaction more stable and controllable. The electrolysis of the present application only exists in the pre-activation treatment stage; the peeling stage is performed under no electric field conditions.

[0015] 2. Short peeling time, high efficiency, and good aluminum foil retention: due to the high concentration of active radical systems (SO4•⁻, •OH) in the pre-activation solution, the peeling reaction can quickly attack the binder PVDF once it starts, achieving complete separation within a short time (5-10 min). Compared with the continuous electrolysis system (which requires long-time power supply to maintain the reaction), the peeling reaction of the present application can be completed in a short time, and the reaction is mild and does not corrode the aluminum foil. Experiments show that the peeling rate is as high as 100%, and the aluminum foil can be directly recycled. The peeling stage can achieve complete separation in a short time without external current, and the process is mild and highly selective.

[0016] Further, the step of discharging, disassembling and screening the waste lithium iron phosphate battery is: placing the waste lithium iron phosphate battery in a saturated NaCl solution, standing to discharge, taking out and drying, disassembling to obtain an aluminum shell, a cathode electrode, an anode electrode and a separator; the obtained cathode electrode is dried again for standby.

[0017] Further, the standing time is 24 hours.

[0018] Further, the concentration of the sodium persulfate solution is 0.1 mol / L-0.4 mol / L; preferably, the concentration of the sodium persulfate solution is 0.3 mol / L-0.4 mol / L.

[0019] Further, the electrolytic pre-activation is carried out under constant current conditions, the current is 1-4 A, and the time is 60-180 s; preferably, the current during electrolytic pre-activation is 2-4 A, and the time is 120-180 s.

[0020] Further, the temperature of the water bath is 30-60℃, and the time of the water bath is 5.5-25 min; preferably, the temperature of the water bath is 30-50℃, and the time of the water bath is 10-15 min.

[0021] Further, the stirring treatment speed is 200 rpm-600 rpm; preferably, the stirring treatment speed is 400 rpm-600 rpm.

[0022] The present application realizes the directional degradation of the binder polyvinylidene fluoride (PVDF) under mild conditions through the synergistic effect of the applied electric field and the active oxidizing agent in the electrolyte, which enables the efficient separation of the positive electrode material and the aluminum foil. Compared with the traditional high-temperature calcination method, the organic solvent dissolution method or the mechanical peeling method, the present application has the following advantages and technical effects:

[0023] (1) Green and environmentally friendly: no strong acid, high temperature and organic solvent are needed, avoiding secondary pollution;

[0024] (2) High peeling efficiency: the active substance and the aluminum foil combination layer are quickly degraded, and the separation is complete;

[0025] (3) The aluminum foil remains intact: the electrochemical reaction is mild, and no obvious corrosion occurs on the surface of the aluminum foil, which can be directly recycled;

[0026] (4) Simple operation and low energy consumption: efficient stripping under low-temperature, acid-free and solvent-free conditions is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and serve as an explanation of the illustrative embodiments of the present application, and are not intended to limit the present application. In the drawings:

[0028] Figure 1 A flowchart of a method for stripping a positive electrode material of a waste lithium iron phosphate battery according to the present application;

[0029] Figure 2 A physical diagram of the cathode electrode obtained after discharging, disassembling and screening treatment of the waste lithium iron phosphate battery, the current collector aluminum foil obtained by stripping according to the method of Example 1, and the current collector aluminum foil obtained by stripping according to the method of Comparative Example 2, wherein "electrolytic stripping" represents the current collector aluminum foil obtained by stripping according to the method of Example 1, and "alkali stripping" represents the current collector aluminum foil obtained by stripping according to the method of Comparative Example 2. DETAILED DESCRIPTION

[0030] The various illustrative embodiments of the present application will now be described in detail below. This detailed description is not intended to limit the present application, but rather to explain certain aspects, features, and embodiments of the present application.

[0031] It should be understood that the terms used herein are merely for describing particular embodiments and are not intended to limit the present application. In addition, for numerical ranges in the present application, it should be understood that each intermediate value between the upper limit and the lower limit of the range is specifically disclosed. Each smaller range within the larger range is also included in the present application. The upper limit and the lower limit of these smaller ranges can be included or excluded independently.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In the case of conflict between any document incorporated by reference and the present specification, the present specification controls.

[0033] Many modifications and variations to the illustrative embodiments described herein will be apparent to those skilled in the art from consideration of the specification and practice of the subject technology. Additional embodiments of the technology will be apparent to those skilled in the art from consideration of the specification and practice of the subject technology. The specification and examples given herein are by way of illustration only and are not intended to limit the scope of the subject technology.

[0034] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having" or the like are open-ended expressions that are intended to denote the presence of stated features, elements, integers, steps or the like, but do not preclude the presence or addition of one or more other features, elements, integers, steps, acts, objects, or the like.

[0035] The embodiment of the present application provides a stripping method of waste lithium iron phosphate battery positive electrode material, a flow chart is shown as Figure 1 The embodiment of the present application provides a stripping method of waste lithium iron phosphate battery positive electrode material, a flow chart is shown as

[0036] The waste lithium iron phosphate battery is subjected to discharge, disassembly and screening treatment, and then a cathode electrode is obtained.

[0037] The sodium persulfate (Na2S2O8) solution is subjected to electrolytic pre-activation, and the electrolytic pre-activated sodium persulfate solution is used as an electrolyte.

[0038] The cathode electrode is placed in the electrolyte, and stirring treatment is performed under water bath condition, then solid-liquid separation is performed, and after drying, the current collector aluminum foil and the positive electrode material powder are obtained.

[0039] The embodiment of the present application provides a stripping method of waste lithium iron phosphate battery positive electrode material, a flow chart is shown as

[0040] In the preferred embodiment of the present application, the step of obtaining the cathode electrode by subjecting the waste lithium iron phosphate battery to discharge, disassembly and screening treatment is as follows: the waste lithium iron phosphate battery is placed in a saturated NaCl solution, and is subjected to discharge by standing for 24 hours; after being taken out, the waste lithium iron phosphate battery is subjected to drying, disassembly to obtain an aluminum shell, a cathode electrode, an anode electrode and a separator, and the obtained cathode electrode is subjected to drying again for standby.

[0041] In the preferred embodiment of the present application, before the cathode electrode is placed in the electrolyte, the cathode electrode is further cut into a sheet with a size of 2cm*2cm, and the step of drying is performed, for example, the drying temperature is 50-80℃.

[0042] In the preferred embodiment of the present application, the concentration of the Na2S2O8 solution is 0.1mol / L-0.4mol / L; preferably, the concentration of the Na2S2O8 solution is 0.3mol / L-0.4mol / L.

[0043] In the preferred embodiment of the present application, the electrolytic pre-activation is performed under constant current condition, the current is 1-4A, and the time is 60-180s; preferably, the current during the electrolytic pre-activation is 2-4A, and the time is 120-180s.

[0044] In the preferred embodiment of the present application, when the Na2S2O8 solution is electrolytically pre-activated, platinum sheets are used as the anode and titanium plates are used as the cathode; after the electrolytic pre-activation is completed, the platinum sheets and the titanium plates are removed.

[0045] In the preferred embodiment of the present application, the temperature of the water bath is 30-60℃, and the time of the water bath is 5.5-25min; preferably, the temperature of the water bath is 30-50℃, and the time of the water bath is 10-15min.

[0046] In the preferred embodiment of the present application, the stirring speed is 200rpm-600rpm; preferably, the stirring speed is 400rpm-600rpm.

[0047] For example, the stripping method of the positive electrode material of the waste lithium iron phosphate battery is as follows:

[0048] (1) After the waste lithium iron phosphate battery is treated by discharging, disassembling, screening and the like, a cathode electrode is obtained, the cathode electrode is cut into a 2cm×2cm sheet, and the sheet is dried at 50-80℃ for standby;

[0049] (2) A sodium persulfate (Na2S2O8) solution with different concentrations (0.1mol / L-0.4mol / L) is prepared as an electrolyte, poured into an electrolytic cell, platinum sheets are used as the anode, titanium plates are used as the cathode, a current is applied under a constant current condition (2-4A), and the electrolyte is electrolyzed for 120-180s, so as to activate the Na2S2O8 solution and generate a free radical system with strong oxidizing property;

[0050] (3) After the electrolytic pre-treatment in step (2) is completed, the electrodes are removed, and the cathode electrode sheet cut in step (1) is placed in the electrolytic cell, stirred at a speed of 200rpm-600rpm under a water bath temperature of 30-60℃ for 5.5-25min, and the active free radicals in the electrolyte can promote the oxidative degradation of the binder PVDF, so as to destroy the combination between the positive active material and the aluminum foil;

[0051] (4) After the stripping reaction in step (3) is completed, solid-liquid separation is performed, and the aluminum foil current collector and the positive electrode material powder are obtained after drying at 60-80℃. The aluminum foil surface obtained by the method of the present application is smooth and has no obvious corrosion, and can be directly recycled; the positive electrode material powder stripped off can be used for regeneration or resource treatment after washing and drying.

[0052] In the present application, the stripping rate (Y) is calculated as follows:

[0053]

[0054] ​B0 and B1 represent the weight (g) of the cathode electrode before and after the auxiliary baking treatment, respectively. The difference between B0 and B1 represents the actual mass of the collected cathode active material. Al defined as the weight (g) of the aluminum foil within the battery electrode. Al The difference between B0 and B1 reflects the theoretical weight of the cathode material that can be extracted from the battery electrode.

[0055] Unless otherwise specified, the room temperature in the present application is 25±2℃.

[0056] The raw materials used in the embodiments of the present application are all commercially available.

[0057] It should be noted that the details not described in the present application are all conventional operating means in the art, and are not the focus of the present application, for example, the specific preparation method of 0.1 mol / L sodium persulfate (Na2S2O8) solution is completed by using a conventional method.

[0058] The technical solutions of the present application are further illustrated by the following examples.

[0059] Example 1

[0060] The present embodiment provides a stripping method for waste lithium iron phosphate battery positive electrode material, and the steps are as follows:

[0061] (1) After the waste lithium iron phosphate battery is discharged, disassembled and sieved, a cathode electrode is obtained (the waste lithium iron phosphate battery is placed in a saturated NaCl solution, and is left to stand for 24 hours for discharge, and is taken out for drying, and is disassembled to obtain an aluminum shell, a cathode electrode, an anode electrode and a separator, and the obtained cathode electrode is dried again for standby), the obtained cathode electrode is cut into a 2cm×2cm sheet, and is dried at 60℃ for standby;

[0062] (2) 0.1 mol / L sodium persulfate (Na2S2O8) solution is prepared as an electrolyte, and is poured into an electrolytic cell, a platinum sheet is used as an anode, and a titanium plate is used as a cathode, an electric current of 3A is applied under constant current conditions, and the electrolyte is electrolyzed for 180 s;

[0063] (3) After the electrolytic pretreatment in step (2) is completed, the electrode is taken out, and the cut cathode electrode sheet in step (1) is placed in the electrolytic cell, and is stirred at a water bath temperature of 50℃ and a stirring speed of 200 rpm for 5.5 min;

[0064] (4) After the stripping reaction in step (3) is completed, solid-liquid separation is carried out, and after drying at 70℃, the complete current collector aluminum foil and the positive electrode material powder (the positive electrode material powder is a lithium iron phosphate positive electrode material, the same below) are obtained.

[0065] Example 2

[0066] The embodiment provides a stripping method of a positive electrode material of a waste lithium iron phosphate battery, and the steps are as follows:

[0067] (1) After the waste lithium iron phosphate battery is subjected to discharge, disassembly and screening treatment (same as in embodiment 1), a cathode electrode is obtained, the obtained cathode electrode is cut into a 2cm*2cm sheet, and the sheet is dried at 60°C for standby;

[0068] (2) 0.1mol / L Na2S2O8 solution is prepared as an electrolyte, poured into an electrolytic tank, a platinum sheet is used as an anode, a titanium plate is used as a cathode, a current of 3A is applied under a constant current condition, and electrolysis is performed on the electrolyte for 120s;

[0069] (3) After the electrolytic pretreatment in step (2) ends, the electrode is taken out, the cathode electrode sheet cut in step (1) is placed in the electrolytic tank, stirring is performed at a water bath temperature of 50°C and a stirring speed of 400rpm for 20min;

[0070] (4) After the stripping reaction in step (3) ends, solid-liquid separation is performed, and after drying at 70°C, an integrated current collector aluminum foil and a positive electrode material powder are obtained.

[0071] Comparative example 1

[0072] The comparative example provides a stripping method of a positive electrode material of a waste lithium iron phosphate battery, and the steps are as follows:

[0073] (1) After the waste lithium iron phosphate battery is subjected to discharge, disassembly and screening treatment (same as in embodiment 1), a cathode electrode is obtained, the obtained cathode electrode is cut into a 2cm*2cm sheet, and the sheet is dried at 60°C for standby;

[0074] (2) 0.1mol / L Na2S2O8 solution is prepared as an electrolyte, poured into an electrolytic tank, a platinum sheet is used as an anode, a titanium plate is used as a cathode, a current of 3A is applied under a constant current condition, and electrolysis is performed on the electrolyte for 30s;

[0075] (3) After the electrolytic pretreatment in step (2) ends, the electrode is taken out, the cathode electrode sheet cut in step (1) is placed in the electrolytic tank, stirring is performed at a water bath temperature of 50°C and a stirring speed of 200rpm for 5.5min;

[0076] (4) After the stripping reaction in step (3) ends, solid-liquid separation is performed, and after drying at 70°C, an integrated current collector aluminum foil and a positive electrode material powder are obtained.

[0077] Example 3

[0078] The embodiment provides a stripping method of a positive electrode material of a waste lithium iron phosphate battery, and the steps are as follows:

[0079] (1) After the waste lithium iron phosphate battery is treated by discharging, disassembling and screening (same as in Example 1), a cathode electrode is obtained, and the obtained cathode electrode is cut into a 2 cm x 2 cm sheet and dried at 50°C for standby;

[0080] (2) A 0.2 mol / L Na2S2O8 solution is prepared as an electrolyte, poured into an electrolytic tank, a platinum sheet is used as an anode, a titanium plate is used as a cathode, and a current of 3 A is applied under constant current conditions to electrolyze the electrolyte for 120 s;

[0081] (3) After the electrolytic pretreatment in step (2) is completed, the electrode is taken out, and the cut cathode electrode sheet in step (1) is placed in the electrolytic tank and stirred at a speed of 400 rpm for 5.5 min at a water bath temperature of 50°C;

[0082] (4) After the stripping reaction in step (3) is completed, solid-liquid separation is performed, and the complete current collector aluminum foil and positive material powder are obtained after drying at 80°C.

[0083] Example 4

[0084] The present example provides a stripping method for a positive material of a waste lithium iron phosphate battery, and the steps are as follows:

[0085] (1) After the waste lithium iron phosphate battery is treated by discharging, disassembling and screening (same as in Example 1), a cathode electrode is obtained, and the obtained cathode electrode is cut into a 2 cm x 2 cm sheet and dried at 80°C for standby;

[0086] (2) A 0.2 mol / L Na2S2O8 solution is prepared as an electrolyte, poured into an electrolytic tank, a platinum sheet is used as an anode, a titanium plate is used as a cathode, and a current of 1 A is applied under constant current conditions to electrolyze the electrolyte for 120 s;

[0087] (3) After the electrolytic pretreatment in step (2) is completed, the electrode is taken out, and the cut cathode electrode sheet in step (1) is placed in the electrolytic tank and stirred at a speed of 500 rpm for 15 min at a water bath temperature of 30°C;

[0088] (4) After the stripping reaction in step (3) is completed, solid-liquid separation is performed, and the complete current collector aluminum foil and positive material powder are obtained after drying at 60°C.

[0089] Example 5

[0090] The present example provides a stripping method for a positive material of a waste lithium iron phosphate battery, and the steps are as follows:

[0091] (1) After the waste lithium iron phosphate battery is treated by discharging, disassembling and screening (same as in Example 1), a cathode electrode is obtained, and the obtained cathode electrode is cut into a 2 cm x 2 cm sheet and dried at 70°C for standby;

[0092] (2) Preparation of 0.2 mol / L Na2S2O8 solution as electrolyte, pour into the electrolytic cell, with platinum as anode, with titanium plate as cathode, under constant current conditions, apply current 2A, electrolysis of electrolyte for 90 s;

[0093] (3) After the electrolytic pretreatment in step (2) is completed, the electrode is taken out, and the cut cathode electrode sheet in step (1) is placed in the electrolytic cell, stirred at a speed of 500 rpm for 10 min at a water bath temperature of 50 ℃;

[0094] (4) After the stripping reaction in step (3) is completed, solid-liquid separation is performed, and the complete current collector aluminum foil and positive electrode material powder are obtained after drying at 70 ℃.

[0095] Example 6

[0096] The present embodiment provides a stripping method for positive electrode material of waste lithium iron phosphate battery, the steps are as follows:

[0097] (1) After the waste lithium iron phosphate battery is discharged, disassembled and sieved (same as example 1), the cathode electrode is obtained, and the obtained cathode electrode is cut into a sheet with a size of 2 cm x 2 cm, and dried at 60 ℃ for standby;

[0098] (2) Preparation of 0.3 mol / L Na2S2O8 solution as electrolyte, pour into the electrolytic cell, with platinum as anode, with titanium plate as cathode, under constant current conditions, apply current 4A, electrolysis of electrolyte for 60 s;

[0099] (3) After the electrolytic pretreatment in step (2) is completed, the electrode is taken out, and the cut cathode electrode sheet in step (1) is placed in the electrolytic cell, stirred at a speed of 200 rpm for 25 min at a water bath temperature of 40 ℃;

[0100] (4) After the stripping reaction in step (3) is completed, solid-liquid separation is performed, and the complete current collector aluminum foil and positive electrode material powder are obtained after drying at 70 ℃.

[0101] Example 7

[0102] The present embodiment provides a stripping method for positive electrode material of waste lithium iron phosphate battery, the steps are as follows:

[0103] (1) After the waste lithium iron phosphate battery is discharged, disassembled and sieved (same as example 1), the cathode electrode is obtained, and the obtained cathode electrode is cut into a sheet with a size of 2 cm x 2 cm, and dried at 60 ℃ for standby;

[0104] (2) Preparation of 0.3 mol / L Na2S2O8 solution as electrolyte, pour into the electrolytic tank, with platinum as anode, with titanium plate as cathode, under constant current conditions, apply current 3 A, electrolysis of electrolyte for 120 s;

[0105] (3) After the electrolytic pretreatment in step (2) is completed, the electrode is taken out, and the cut cathode electrode sheet in step (1) is placed in the electrolytic tank, stirred at a speed of 400 rpm at a water bath temperature of 30 ℃ for 10 min;

[0106] (4) After the stripping reaction in step (3) is completed, solid-liquid separation is performed, and the complete current collector aluminum foil and positive electrode material powder are obtained after drying at 70 ℃.

[0107] Example 8

[0108] The present embodiment provides a stripping method for positive electrode material of waste lithium iron phosphate battery, the steps are as follows:

[0109] (1) After the waste lithium iron phosphate battery is discharged, disassembled and sieved (same as example 1), the cathode electrode is obtained, and the obtained cathode electrode is cut into a sheet with a size of 2 cm x 2 cm, and dried at 60 ℃ for standby;

[0110] (2) Preparation of 0.3 mol / L Na2S2O8 solution as electrolyte, pour into the electrolytic tank, with platinum as anode, with titanium plate as cathode, under constant current conditions, apply current 4 A, electrolysis of electrolyte for 120 s;

[0111] (3) After the electrolytic pretreatment in step (2) is completed, the electrode is taken out, and the cut cathode electrode sheet in step (1) is placed in the electrolytic tank, stirred at a speed of 600 rpm at a water bath temperature of 50 ℃ for 10 min;

[0112] (4) After the stripping reaction in step (3) is completed, solid-liquid separation is performed, and the complete current collector aluminum foil and positive electrode material powder are obtained after drying at 70 ℃.

[0113] Example 9

[0114] The present embodiment provides a stripping method for positive electrode material of waste lithium iron phosphate battery, the steps are as follows:

[0115] (1) After the waste lithium iron phosphate battery is discharged, disassembled and sieved (same as example 1), the cathode electrode is obtained, and the obtained cathode electrode is cut into a sheet with a size of 2 cm x 2 cm, and dried at 60 ℃ for standby;

[0116] (2) Preparation of 0.4 mol / L Na2S2O8 solution as electrolyte, pour into the electrolytic tank, with platinum as anode, with titanium plate as cathode, under constant current conditions, apply current 2 A, electrolysis of electrolyte for 30 s;

[0117] (3) After the electrolytic pretreatment in step (2) is completed, the electrode is taken out, and the cathode electrode sheet cut in step (1) is placed in the electrolytic tank, stirred at a speed of 300 rpm at a water bath temperature of 60 ℃ for 20 min;

[0118] (4) After the stripping reaction in step (3) is completed, solid-liquid separation is performed, and the complete current collector aluminum foil and positive electrode material powder are obtained after drying at 70 ℃.

[0119] Example 10

[0120] The present embodiment provides a stripping method for positive electrode material of waste lithium iron phosphate battery, the steps are as follows:

[0121] (1) After the waste lithium iron phosphate battery is discharged, disassembled and sieved (same as example 1), the cathode electrode is obtained, and the obtained cathode electrode is cut into a sheet with a size of 2 cm x 2 cm and dried at 60 ℃ for standby;

[0122] (2) Preparation of 0.4 mol / L Na2S2O8 solution as electrolyte, pour into the electrolytic tank, with platinum as anode, with titanium plate as cathode, under constant current conditions, apply current 4 A, electrolysis of electrolyte for 120 s;

[0123] (3) After the electrolytic pretreatment in step (2) is completed, the electrode is taken out, and the cathode electrode sheet cut in step (1) is placed in the electrolytic tank, stirred at a speed of 500 rpm at a water bath temperature of 40 ℃ for 10 min;

[0124] (4) After the stripping reaction in step (3) is completed, solid-liquid separation is performed, and the complete current collector aluminum foil and positive electrode material powder are obtained after drying at 70 ℃.

[0125] Example 11

[0126] The present embodiment provides a stripping method for positive electrode material of waste lithium iron phosphate battery, the steps are as follows:

[0127] (1) After the waste lithium iron phosphate battery is discharged, disassembled and sieved (same as example 1), the cathode electrode is obtained, and the obtained cathode electrode is cut into a sheet with a size of 2 cm x 2 cm and dried at 60 ℃ for standby;

[0128] (2) Prepare a 0.4 mol / L Na2S2O8 solution as an electrolyte, pour it into the electrolytic cell, use a platinum sheet as the anode, and use a titanium plate as the cathode. Apply a current of 2 A under constant current conditions, and electrolyze the electrolyte for 180 s;

[0129] (3) After the electrolytic pretreatment in step (2) is completed, remove the electrode, and place the cathode electrode sheet cut in step (1) in the electrolytic cell. Stir at a speed of 400 rpm for 10 min at a water bath temperature of 50 ℃;

[0130] (4) After the peeling reaction in step (3) is completed, perform solid-liquid separation, and dry at 70 ℃ to obtain an integrated current collector aluminum foil and a positive electrode material powder.

[0131] Comparative Example 2

[0132] As a comparison, the current collector aluminum foil and the lithium iron phosphate positive electrode material are peeled off by using a traditional alkali solution method. The specific steps are as follows:

[0133] (1) After the waste lithium iron phosphate battery is discharged, disassembled, and sieved (the same as in Example 1), a cathode electrode is obtained;

[0134] (2) The cathode electrode obtained in step (1) is washed with 18MΩ ultrapure water and dried at a temperature of 60 ℃ for 2 h;

[0135] (3) The cathode electrode after drying in step (2) is cut into a size of 10 mm x 10 mm, immersed in a 2.5M sodium hydroxide solution, and the current collector aluminum foil and the lithium iron phosphate positive electrode material are peeled off.

[0136] The aluminum foil obtained by the electrochemical peeling method of the present application and the aluminum foil obtained by the alkali solution peeling method of Comparative Example 2 have obvious differences in appearance (as shown in Figure 2 ). The aluminum foil peeled off by the present application has a clear aluminum metal luster on the surface, and the aluminum foil is complete; the aluminum foil peeled off by the alkali solution method of Comparative Example 2 is dark on the surface, has no brightness of the original aluminum metal, and the aluminum foil is curled. In the lithium iron phosphate positive electrode material treated by the alkali solution method, the aluminum foil reacts with the sodium hydroxide solution, and the aluminum is partially dissolved and lost.

[0137] Comparative Example 3

[0138] As a comparison, the waste lithium iron phosphate positive electrode material is peeled off by using an electrolytic method (CN114039119A). The specific steps are as follows:

[0139] (1) The recovered waste lithium iron phosphate battery is discharged and disassembled to obtain positive electrode sheets, negative electrode sheets, shells, and separators;

[0140] (2) The positive electrode material obtained by splitting is placed in an electrolytic cell with an electrolyte concentration of 4 g / L, wherein the electrolyte used is anhydrous sodium sulfate, and both the positive and negative electrodes are graphite electrodes;

[0141] (3) Electrolytic stripping is performed at a voltage of 10V. After stripping for 20 minutes with a stirring rate of 400rpm, the aluminum foil is taken out. After solid-liquid separation, the filtrate is further electrolytically stripped, and the filter cake is the stripped lithium iron phosphate cathode material.

[0142] The methods in the embodiments of this invention differ significantly from those in Comparative Example 3: This invention does not continuously apply an electric field during the stripping process. Instead, it first performs short-term electrolytic pre-activation on the sodium persulfate solution, generating a highly active free radical system in situ in the solution through electrochemical action. After electrolytic activation, the electrolytic device is removed, and the electrode is then placed in the pre-activated solution. The oxidative chain scission of PVDF and the stripping of the positive electrode material are completed under conditions without external current. This invention, through the separation mechanism of "electrolytic pre-activation - field-free stripping," allows the stripping process to proceed in a low-energy, low-potential environment, avoiding electrode side reactions and aluminum foil surface damage caused by continuous current application, while significantly shortening the stripping time.

[0143] Comparative Example 4

[0144] In contrast, a free radical system was used to greenly strip the cathode material from spent lithium iron phosphate batteries (CN114024054A). The specific steps are as follows:

[0145] (1) Discharge and disassemble the waste lithium iron phosphate batteries to obtain positive electrode plates, negative electrode plates, shells, separators, etc.;

[0146] (2) After cutting the positive electrode obtained from the splitting, put it into a stripping solution consisting of 0.5wt% potassium persulfate, 3%wt% sodium persulfate and 1wt% ferrous sulfate, and stir at 300rpm for 20min.

[0147] (3) Then the aluminum foil is taken out and dried, the stripping liquid is separated into solid and liquid, the filtrate is added with stripping liquid to continue stripping, and the filter cake is the stripped lithium iron phosphate cathode material.

[0148] Comparative Example 4 relies on the persulfate-ferrous system to continuously generate free radicals during the reaction process. The stripping efficiency is greatly affected by the component ratio, iron ion concentration and the stability of the reaction system. At the same time, the high concentration of various chemical reagents used in this method may still have a certain oxidizing effect on the aluminum foil.

[0149] The present application adopts an "electrolytic pre-activation-electric field-free stripping" mode, generates a free radical system in-situ in a solution through electrolysis for a short time, and completes the stripping process under mild conditions after the electric field is removed, without adding iron salts and other accelerators. The generation of free radicals in the stripping process of the present application is controllable, the solution composition is simple, there is no electrochemical or chemical corrosion to the aluminum foil, and the stripping efficiency is high, the reaction time is short, and the energy consumption is significantly reduced.

[0150] The experimental conditions and stripping rates of Examples 1-12 are shown in Table 1.

[0151] Table 1

[0152]

[0153] As can be seen from Table 1, the electrolysis time of Comparative Example 1 is shorter (compared with Example 1), so that the number of generated free radicals is insufficient to promote the stripping of the positive electrode material, and therefore the stripping rate of Comparative Example 1 is lower.

[0154] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any changes or replacements that can be easily thought of by those skilled in the art within the technical range disclosed by the present application should be covered within the protection scope of the present application.

Claims

1. A method for stripping cathode material from waste lithium iron phosphate batteries, characterized in that, Includes the following steps: The cathode electrode is obtained by discharging, dismantling and screening waste lithium iron phosphate batteries; The sodium persulfate solution was pre-activated by electrolysis, and the pre-activated sodium persulfate solution was used as the electrolyte. The cathode electrode is placed in the electrolyte and stirred under water bath conditions to separate the solid and liquid. After drying, current collector aluminum foil and positive electrode material powder are obtained.

2. The method for stripping the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that, The steps for discharging, dismantling, and screening waste lithium iron phosphate batteries are as follows: place the waste lithium iron phosphate batteries in a saturated NaCl solution, let them stand, take them out and dry them, and then dismantle them to obtain an aluminum shell, cathode electrode, anode electrode, and separator.

3. The method for stripping the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that, The concentration of the sodium persulfate solution is 0.1 mol / L to 0.4 mol / L.

4. The method for stripping the cathode material of waste lithium iron phosphate batteries according to claim 3, characterized in that, The concentration of the sodium persulfate solution is 0.3 mol / L to 0.4 mol / L.

5. The method for stripping the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that, The electrolytic preactivation is carried out under constant current conditions, with a current of 1-4A and a time of 60-180s.

6. The method for stripping the cathode material of waste lithium iron phosphate batteries according to claim 5, characterized in that, The electrolytic preactivation is carried out under constant current conditions, with a current of 2-4A and a time of 120-180s.

7. The method for stripping the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that, The water bath temperature is 30-60℃, and the water bath time is 5.5-25 minutes.

8. The method for stripping the cathode material of waste lithium iron phosphate batteries according to claim 7, characterized in that, The temperature of the water bath is 30-50℃, and the water bath time is 10-15 minutes.

9. The method for stripping the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that, The stirring speed is 200 rpm to 600 rpm.

10. The method for stripping the cathode material of waste lithium iron phosphate batteries according to claim 9, characterized in that, The stirring speed is 400 rpm to 600 rpm.

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