Direct recovery method for waste lithium iron phosphate positive electrode based on primary battery reaction

Abstract

The invention relates to a waste lithium iron phosphate positive electrode direct recovery method based on primary battery reaction, and the method comprises the following steps: S1, dissolving a film removing agent and a soluble lithium salt in water to prepare a lithium supplement regeneration liquid; s2, the waste lithium iron phosphate pole piece is soaked in the lithium supplement regeneration liquid; and S3, taking out the soaked waste pole piece, repeatedly washing with clear water, and drying to obtain the regenerated positive electrode material. The regenerated positive electrode material is obtained through the recovery method, and the obtained regenerated positive electrode material can be further used for preparing a regenerated positive electrode plate and a button battery. The method does not need to additionally add a reducing agent or apply external voltage, and has good compatibility with the existing battery recovery industry. The whole reaction can be completed in an electrolyte environment, no extra energy consumption exists in the lithiation process, the problems that a traditional recycling method is tedious in process, high in energy consumption, low in economic benefit and the like are effectively solved, and remarkable technical and economic advantages are achieved.

Description

Technical Field

[0001] The invention relates to a method for directly recovering waste lithium iron phosphate positive electrodes based on primary cell reactions, belongs to the field of rechargeable and dischargeable lithium ion secondary batteries, and can be used in the fields of energy, industry, scientific research, etc. Background Art

[0002] With the rapid development of new energy vehicles and smart grids, lithium-ion batteries with lithium iron phosphate (LFP) cathode materials have been widely used in power batteries and energy storage systems due to their high safety, long cycle life and low cost. In recent years, both the installed capacity of power batteries and the installed capacity of energy storage systems have shown a trend of sustained growth. However, this growth has also brought about the recycling and treatment of a large number of retired batteries. Among waste lithium-ion batteries, cathode materials have become the focus of recycling due to their high added value. At present, the recycling methods for cathode materials are mainly divided into two paths: element extraction and direct regeneration. In contrast, direct regeneration and repair can significantly improve economic benefits while maintaining the material structure, and has greater application potential. Lithium iron phosphate has a unique olivine crystal structure, which has good stability during the cycle process. The direct recovery methods for waste lithium iron phosphate mainly include high-temperature calcination and solution immersion. The high-temperature calcination method achieves regeneration by treating waste materials at high temperatures, but the process is complicated, energy consumption is high, and there is a certain amount of carbon emissions, which is not conducive to achieving green recycling (such as patent CN116053631A). The solution immersion method uses a reducing agent to reduce the iron phosphate in the waste material to lithium iron phosphate through wet chemical means. However, the existing solution immersion method has major limitations: when the reducing agent is weak in reducing property, heating is usually required to promote the reaction (such as patent CN117088347A), thereby further increasing energy consumption; and when the reducing agent is strong in reducing property, it is often not stable enough and expensive (such as document ACSSustainable Chem.Eng.2021,9,48,16384). These problems have limited the promotion of the solution immersion method in industrialization to a certain extent.

[0003] Therefore, the current direct recycling method still has problems such as complex process, high energy consumption, and high economic cost, which cannot meet the needs of industrial application. Developing an efficient, green and low-cost direct recycling method for lithium iron phosphate positive electrodes can not only improve the reuse efficiency of retired batteries, but also promote the sustainable development of the field of waste lithium battery recycling. It is an important issue that needs to be solved urgently. Summary of the invention

[0004] Based on the defects existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for directly recovering waste lithium iron phosphate positive electrodes based on primary cell reaction, which is a simple, efficient and environmentally friendly method for recovering waste lithium iron phosphate positive electrode materials.

[0005] The current collector aluminum in waste lithium iron phosphate has strong reducing properties, but because the dense oxide film naturally formed on its surface has an extremely high protective effect, the actual oxidation potential of metallic aluminum in the electrolyte is much higher than the theoretical oxidation potential, making it difficult to directly reduce the iron phosphate phase in the waste lithium iron phosphate, and regeneration cannot be achieved.

[0006] The inventors found through research that the halogen anions in the electrolyte can act as nucleophiles to react with Al3+ with high charge density and small ion radius in the alumina crystal, thereby weakening the bond between Al3+ and O 2 -The electrostatic interaction between them. This mechanism will destroy the local structure of the oxide film, causing the oxide film to lose its protective function, and then the metal aluminum inside will be directly exposed to the electrolyte and undergo oxidation reaction. The degree of failure of the oxide film is closely related to the nucleophilic ability of the halogen anion and the anion concentration in the solution. At the same time, the oxidation process of aluminum foil is also affected by the solution environment. The corrosion potential of aluminum in different electrolytes has significant differences.

[0007] Based on the above characteristics, the inventors have innovatively designed an efficient and green method for spontaneous regeneration of waste lithium iron phosphate positive electrode materials. This method only requires the waste lithium iron phosphate electrode to be immersed in a special electrolyte to achieve automatic regeneration of the material. In this special electrolyte, the corrosion potential of aluminum can be adjusted to be lower than the reduction potential of the iron phosphate in the waste lithium iron phosphate. When the waste electrode is immersed in the electrolyte, the halogen anions will effectively destroy the oxide film on the surface of the current collector, and the active components in the electrolyte further increase the potential on the surface of the aluminum foil, thereby activating the strong reducing property of metallic aluminum. Through this process, metallic aluminum spontaneously undergoes redox reaction with the iron phosphate in the waste lithium iron phosphate: metallic aluminum is oxidized to trivalent aluminum ions, and lithium-deficient iron phosphate is reduced to lithium iron phosphate, thereby successfully achieving the re-lithiation of the waste lithium iron phosphate positive electrode.

[0008] Based on the above objectives and principles, this application provides the following technical solutions:

[0009] One of the technical solutions of the present application provides a method for directly recovering waste lithium iron phosphate positive electrodes based on the reaction of the primary battery. The specific steps of the method are as follows:

[0010] S1: dissolving the film removal agent and soluble lithium salt in water to prepare a lithium replenishing regeneration solution;

[0011] S2: Soak the waste lithium iron phosphate electrode in lithium replenishment regeneration solution;

[0012] S3: Take out the used electrode after soaking, wash it repeatedly with clean water and then dry it to obtain regenerated positive electrode material.

[0013] Furthermore, the defilming agent in step S1 is selected from at least any one of soluble metal chloride, soluble metal bromide, soluble metal iodide, soluble medium-strong acid, and soluble strong base, preferably soluble metal chloride; the concentration of the defilming agent in the lithium replenishing regeneration solution is 0.005M-0.2M, preferably 0.01M-0.05M.

[0014] Furthermore, the soluble lithium salt in step S1 is selected from at least one of lithium nitrate and lithium sulfate; the total concentration of lithium ions in the lithium replenishing regeneration solution is not less than 0.1M to ensure the reaction speed.

[0015] Furthermore, the soaking time in step S2 is determined by the concentration of lithium ions in the soaking solution, and the lower limit of the soaking time is 20 min / lithium ion concentration (M). Taking the lithium ion concentration of 1 M and the film removal agent concentration of 0.01 M as an example, the minimum soaking time is 20 min.

[0016] After the inventors used a film remover to remove the oxide film on the surface of the metal aluminum current collector, the metal aluminum and the iron phosphate in the waste lithium iron phosphate can form a primary battery, and then a spontaneous self-discharge reaction occurs, that is, the 0-valent metal aluminum is oxidized to +3-valent aluminum ions or aluminate, and the trivalent iron in the iron phosphate is reduced to divalent iron. At the same time, the lithium ions in the solution spontaneously enter the lattice of the lithium iron phosphate to re-lithiate the iron phosphate. With LiCl as the film remover and LiNO 3 Taking lithium source as an example, the reaction of the membrane removal process is:

[0017] 3LiCl+2Al 2 O 3 =AlCl 3 +3LiAlO 2 ;

[0018] The self-discharge recovery reaction of iron phosphate and Al is:

[0019] 3LiNO 3 +3FePO 4 +Al=Al(NO 3 ) 3 +3LiFePO 4 .

[0020] The second technical solution of the present application provides a regenerated positive electrode material prepared by the above method.

[0021] The third technical solution of the present application provides a regenerated positive electrode plate, comprising the above-mentioned regenerated positive electrode.

[0022] Furthermore, the method for preparing the regenerated positive electrode sheet comprises the following steps:

[0023] The regenerated positive electrode, Super P and PVDF are prepared into slurry, and the slurry is coated on aluminum foil and dried to obtain a regenerated positive electrode plate.

[0024] Furthermore, the mass ratio of the regenerated positive electrode, Super P and PVDF is 90:5:5; the slurry coating is performed by coating with a doctor blade on a wet film preparation device, and the thickness of the slurry is 100 to 200 microns, preferably 150 microns.

[0025] Furthermore, the drying is carried out at 60-100° C. for 10-15 hours; preferably, the drying is carried out in an oven at 80° C. for 12 hours.

[0026] A fourth technical solution of the present application provides a button battery, wherein the positive electrode of the button battery is the above-mentioned regenerated positive electrode plate.

[0027] Furthermore, the preparation steps of the button battery are: cutting the regenerated positive electrode sheet into discs, using metallic lithium as a counter electrode, and equipping a 2025 type button battery.

[0028] Furthermore, the diameter of the disc is preferably 12 mm; the electrolyte of the button battery is preferably a commercial electrolyte, the formula of which is 1M LiPF 6 in EC:DEC=1:1.

[0029] Compared with the prior art, this application has at least the following advantages and beneficial effects:

[0030] (1) The method of the present invention is easy to operate, does not require the addition of additional reducing agents and the application of external voltage, and has good compatibility with the existing battery recycling industry.

[0031] (2) The entire reaction can be completed in an electrolyte environment, and the lithiation process does not consume any additional energy. It is both highly efficient and environmentally friendly, and effectively solves the problems of traditional recycling methods such as complicated processes, high energy consumption, and low economic benefits. It has significant technical and economic advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Flow chart for regenerating positive electrode for this application;

[0033] Figure 2 This is the LSV curve of aluminum foil in 0.1M LiCl electrolyte. During the test, the working electrode is Al, the counter electrode is Pt, and the reference electrode is calomel electrode;

[0034] Figure 3This is the LSV curve of aluminum foil in 0.1M LiNO3 electrolyte. During the test, the working electrode is Al, the counter electrode is Pt, and the reference electrode is calomel electrode.

[0035] Figure 4 This is the LSV curve of aluminum foil in 0.01M LiCl electrolyte. During the test, the working electrode is Al, the counter electrode is Pt, and the reference electrode is calomel electrode;

[0036] Figure 5 This is a photograph of the aluminum foil separated in Example 1. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below in conjunction with specific embodiments. It should be noted that the following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, several variations and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0038] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0039] The flow chart of regenerating the positive electrode in the embodiment of the present application is as follows Figure 1 As shown, the specific steps are:

[0040] S1: dissolving the film removal agent and soluble lithium salt in water to prepare a lithium replenishing regeneration solution;

[0041] S2: Soak the waste lithium iron phosphate electrode in lithium replenishment regeneration solution;

[0042] S3: Take out the used electrode after soaking, wash it repeatedly with clean water and then dry it to obtain regenerated positive electrode material.

[0043] Examples 1 to 5 and Comparative Examples 1 to 6 of the present application are as follows:

[0044] Example 1: Soak the waste lithium iron phosphate positive electrode in 0.01M LiCl+1M LiNO 3 The regenerated positive electrode sample E1 was obtained by placing the regenerated positive electrode in an electrolyte (lithium replenishing regeneration solution, all electrolytes mentioned below refer to lithium replenishing regeneration solution) for 30 minutes, washing and drying.

[0045] Example 2: Soak the waste lithium iron phosphate positive electrode in 0.03M LiCl+3M LiNO 3 The regenerated positive electrode sample E2 was obtained after being placed in the electrolyte for 10 min and then washed and dried.

[0046] Example 3: Soak the waste lithium iron phosphate positive electrode in 0.01M LiOH+1M LiNO 3 The regenerated positive electrode sample E3 was obtained after being placed in the electrolyte for 30 min and then washed and dried.

[0047] Example 4: Soaking the waste lithium iron phosphate positive electrode in 0.005M LiBr+2M LiNO 3 The regenerated positive electrode sample E4 was obtained after being placed in the electrolyte for 10 min and then washed and dried.

[0048] Example 5: Soak the waste lithium iron phosphate positive electrode in 0.2M LiCl+1M Li 2 SO 4 The regenerated positive electrode sample E5 was obtained after being placed in the electrolyte for 25 min and then washed and dried.

[0049] Comparative Example 1: Soak the waste lithium iron phosphate positive electrode in 0.01M LiOH+1M LiNO 3 The regenerated positive electrode sample C1 was obtained after being placed in the electrolyte for 10 min and then washed and dried.

[0050] Comparative Example 2: Soak the waste lithium iron phosphate positive electrode in 0.001M LiCl+2M LiNO 3 The regenerated positive electrode sample C2 was obtained after being placed in the electrolyte for 20 min and then washed and dried.

[0051] Comparative Example 3: Soak the waste lithium iron phosphate positive electrode in 0.3M LiCl+2M LiNO 3 The regenerated positive electrode sample C3 was obtained after being placed in the electrolyte for 30 min and then washed and dried.

[0052] Comparative Example 4: Soak the waste lithium iron phosphate positive electrode in 1M LiCl+1M LiNO 3 The regenerated positive electrode sample C4 was obtained after being placed in the electrolyte for 10 min and then washed and dried.

[0053] Comparative Example 5: Soaking the waste lithium iron phosphate positive electrode in 1M LiNO 3 The regenerated positive electrode sample C5 was obtained after being placed in the electrolyte for 30 min and then washed and dried.

[0054] Comparative Example 6: directly using the waste lithium iron phosphate positive electrode as the positive electrode sample C6.

[0055] The regenerated positive electrode samples of the above-mentioned Examples 1-5 and Comparative Examples 1-6 were used to prepare positive electrode sheets and button cells in the following manner:

[0056] (1) Prepare a slurry with a ratio of regenerated positive electrode sample: Super P: PVDF = 90:5:5, and coat the slurry on aluminum foil with a thickness of 150 μm;

[0057] (2) placing the positive electrode sheet obtained in (1) in an oven at 80°C for 12 hours;

[0058] (3) The dried positive electrode was cut into discs with a diameter of 12 mm. Metal lithium was used as the counter electrode and a commercial electrolyte (formula 1M LiPF 6 in EC:DEC=1:1) as the electrolyte, equipped with 2025 type button cells. The button cells were electrochemically tested at a voltage range of [2.5V, 3.8V] with a current of 15mA / g, and the batteries were charged first and then discharged.

[0059] The contents of the electrochemical test include:

[0060] Instrument: Xinwei battery tester;

[0061] Method: Galvanostatic method (constant current test method). Using this method, the following data can be directly obtained and recorded on the above instrument.

[0062] (1) First-cycle charge capacity: The amount of charge that a battery can hold per unit mass or volume of active material during the first charge, usually expressed in milliampere-hours per gram (mAh / g) or milliampere-hours per cubic centimeter (mAh / cm 3 )express.

[0063] (2) First-cycle discharge capacity: The first-cycle discharge capacity refers to the amount of charge released by the active material per unit mass or volume during the first discharge of the battery, also expressed in (mAh / g) or (mAh / cm 3 )express.

[0064] (3) First efficiency (%): First efficiency (first efficiency) refers to the ratio of the discharge capacity to the charge capacity of the battery in the first charge and discharge cycle, usually expressed as a percentage (%). It reflects the irreversible loss of the battery in the first cycle.

[0065] from Figures 2 to 4 It can be seen that in the presence of chloride ions ( Figure 2 ), Al foil is oxidized at a very low potential (all lower than 0V vs. SCE), and the potential is related to the chloride ion concentration ( Figure 4 ), while in the lithium nitrate environment ( Figure 3 ) Since the oxide film is not removed, it is not oxidized even at 0.8V vs. SCE, while the potential at which iron phosphate in waste lithium iron phosphate is reduced is about 0.3V vs. SCE.

[0066] It can be seen from Table 1 that the first cycle coulombic efficiency of the batteries of Examples 1 to 5 is greater than 98%, and the first cycle charging capacity is greater than 155 mAh / g, indicating that they are no longer lithium-deficient; and Figure 5 It can be seen from the figure that the separated aluminum foil is heavily corroded, indicating that Al, as a reducing agent, participates in the process of re-lithiation of iron phosphate; in Comparative Example 1, due to insufficient immersion time, lithium replenishment was not complete, so its charge specific capacity was low, the discharge specific capacity was normal, and the first efficiency was less than 100%; in Comparative Example 2, due to the low concentration of the defilming agent, the slow removal of the oxide film limited the reaction rate, so the waste electrode was not completely lithiated within a given time, so the charge specific capacity became low, and the discharge specific capacity was normal; in Comparative Examples 3 and 4, due to the high concentration of the defilming agent, the applicant found that the defilming agent itself would react with iron phosphate, causing the olivine structure to be destroyed, so the charge and discharge capacity were greatly reduced; in Comparative Example 5, since no defilming agent was added, iron phosphate could not form a primary battery with metallic aluminum, so its charge and discharge capacity was close to that of the untreated Comparative Example 6.

[0067] Table 1 The first cycle charge and discharge specific capacity and first cycle coulombic efficiency of the above embodiments and comparative examples

[0068]

[0069] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for directly recovering waste lithium iron phosphate positive electrodes based on primary cell reaction, characterized in that: The specific steps of this method are as follows: S1: dissolving the film removal agent and soluble lithium salt in water to prepare a lithium replenishing regeneration solution; S2: Soak the waste lithium iron phosphate electrode in lithium replenishment regeneration solution; S3: Take out the used electrode after soaking, wash it repeatedly with clean water and then dry it to obtain regenerated positive electrode material.

2. The method for directly recovering waste lithium iron phosphate positive electrodes based on primary cell reaction according to claim 1, characterized in that: The film removing agent in step S1 is selected from at least any one of soluble metal chlorides, soluble metal bromides, soluble metal iodides, soluble medium-strong acids, and soluble strong bases.

3. The method for directly recovering waste lithium iron phosphate positive electrodes based on primary cell reaction according to claim 1, characterized in that: The soluble lithium salt in step S1 is selected from at least one of lithium nitrate and lithium sulfate.

4. The method for directly recovering waste lithium iron phosphate positive electrodes based on primary cell reaction according to claim 1, characterized in that: The concentration of the film remover in the lithium replenishing regeneration solution is 0.005M-0.2M; the total concentration of lithium ions in the lithium replenishing regeneration solution is not less than 0.1M.

5. According to the method for directly recovering waste lithium iron phosphate positive electrodes based on primary battery reaction according to claim 1, the lower limit of the immersion time in step S2 is 20 min / lithium ion concentration (M).

6. A regenerated positive electrode material, characterized in that: The waste lithium iron phosphate positive electrode is prepared by the direct recovery method of waste lithium iron phosphate positive electrode based on primary battery reaction as described in any one of claims 1 to 5.

7. A regenerated positive electrode plate, characterized in that: The invention comprises the regenerated positive electrode material as described in claim 6; the preparation method of the regenerated positive electrode plate comprises the following steps: preparing the regenerated positive electrode, Super P and PVDF into slurry, coating the slurry on aluminum foil and drying it to obtain the regenerated positive electrode plate.

8. A regenerated positive electrode plate according to claim 7, characterized in that: In the preparation method, the mass ratio of the regenerated positive electrode, Super P and PVDF is 90:5:5; the thickness of the slurry coating is 100 to 200 microns.

9. A regenerated positive electrode sheet according to claim 7, characterized in that: In the preparation method, the drying temperature is 60-100° C. and the drying time is 10-15 hours.

10. A button battery, characterized in that: The positive electrode of the button battery is the regenerated positive electrode plate as claimed in claim 7; the counter electrode of the button battery is metallic lithium; the electrolyte formula of the button battery is 1M LiPF6 in EC:DEC=1:1.

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