A method for recycling lithium iron phosphate

Abstract

The present invention relates to the field of recycling useful components of waste storage batteries, and more particularly, to a method for recycling and regenerating lithium iron phosphate. The method for recycling and regenerating lithium iron phosphate includes: soaking and discharging the battery cells of lithium iron phosphate batteries in a buffer solution to obtain discharged battery cells; separating the positive electrode plates from the discharged battery cells and removing the current collectors from the positive electrode plates; the pH of the buffer solution is 2.0 to 8.0; the soaking time is 30 to 120 minutes; the magnitude of the discharge current during the discharging process is 0.01 to 0.5 times the rated capacity of the lithium iron phosphate battery; the voltage of the discharged battery cells is -1.0 to -1.8 V. The method for recycling and regenerating lithium iron phosphate is simple and easy to operate, can recover the consumed lithium in various waste lithium iron phosphate batteries in different states and re-embed it into the lithium iron phosphate positive electrode without an additional lithium source, and the obtained repaired lithium iron phosphate has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the field of regeneration of useful components of waste storage batteries, and more particularly, to a method for recycling and regenerating lithium iron phosphate. Background Art

[0002] Olivine-type lithium iron phosphate (LiFePO4 or LFP) has become one of the most widely used cathode materials for lithium-ion batteries (LIBs) due to its high thermal stability, long cycle life, and low cost. LFP batteries account for more than one-third of the entire LIBs market. The global demand for LIBs is expected to reach 440 GWh within 5 years. However, after 3 to 10 years of use, millions of tons of waste LIBs will be generated. Effective recycling and reuse of waste LIBs can help recover valuable materials, reduce energy consumption for natural resource extraction, and reduce environmental pollution. Although the charge storage capacity of waste LFP may be greatly lost, the morphology and crystal structure of its particles generally remain unchanged. This failure mechanism provides a potential opportunity to directly recover waste LFP to form new LFP particles, which is convenient for manufacturing new batteries.

[0003] Due to the low raw material and manufacturing costs of lithium iron phosphate (LFP) batteries, from the perspective of transition metal elements, the recycling value of traditional wet and pyrometallurgical methods is relatively small, and a large number of retired LFP batteries face the current situation of difficult resource treatment. Direct regeneration is a very promising new recycling strategy developed in recent years, which aims to achieve material regeneration through direct repair of the active material structure. The regenerated new cathode material can be directly used to manufacture new batteries, thus realizing the closed-loop development of lithium batteries. However, different waste batteries have experienced different usage conditions. The lithium ions in the LFP cathode are gradually consumed and cannot be intercalated back into the LFP structure, resulting in capacity attenuation, that is, the cathode is a mixed phase of LFP and FePO4 (LiFePO4 / FePO4). The active lithium consumed by LFP batteries usually exists in the form of SEI film and metallic lithium on the surface of the anode. Due to the lack of lithium ions, even if the battery is discharged to zero volts, such as discharged to 2.0 V, there is still a large amount of lithium-deficient FePO4 in the cathode. Existing lithium supplementation and regeneration generally require additional lithium sources and high-temperature heat treatment to make up for the loss of lithium, and the lithium sources required for batteries in different states of health (SOH) vary greatly, and the economic advantage is not obvious enough for low-cost LFP. Therefore, it is necessary to develop a new direct regeneration strategy to improve the economic benefits of resource recycling and reuse of lithium iron phosphate, so as to drive the efficient recycling of a large number of low-value LFP batteries.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a method for recycling and regenerating lithium iron phosphate. The method for recycling and regenerating lithium iron phosphate has the advantages of being simple and easy to operate, capable of recovering the consumed lithium in various waste lithium iron phosphate batteries in different states, and not requiring an additional lithium source.

[0006] In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:

[0007] A method for recycling and regenerating lithium iron phosphate, comprising the following steps:

[0008] Soak and discharge the battery cell of the lithium iron phosphate battery in a buffer solution to obtain a discharged battery cell; separate the positive electrode sheet in the discharged battery cell and remove the current collector in the positive electrode sheet;

[0009] The pH of the buffer solution is 2.0 - 8.0;

[0010] The soaking time is 30 - 120 min;

[0011] The magnitude of the discharge current during the discharge treatment is 0.01 - 0.5 times the rated capacity of the lithium iron phosphate battery;

[0012] The voltage of the discharged battery cell is -1.0 - -1.8 V.

[0013] The method for recycling and regenerating lithium iron phosphate is simple and easy to operate, can recover the consumed lithium in various waste lithium iron phosphate batteries in different states, and re-embed it into the lithium iron phosphate positive electrode without requiring an additional lithium source. The repaired lithium iron phosphate obtained has excellent electrochemical performance.

[0014] Preferably, the pH of the buffer solution is 4.0 - 6.0.

[0015] Preferably, the buffer solution includes at least one of citric acid, sodium citrate, tartaric acid, salicylic acid, malic acid, oxalic acid, and ascorbic acid.

[0016] Preferably, the magnitude of the discharge current during the discharge treatment is 0.05 - 0.2 times the rated capacity of the lithium iron phosphate battery.

[0017] Preferably, the discharge treatment mode includes a constant current discharge mode and / or a pulse discharge mode.

[0018] Preferably, the ratio of the pulse time to the interval time in the pulse discharge mode is (5 - 10):1.

[0019] Preferably, the voltage of the discharged battery cell is -1.2 - -1.5 V.

[0020] Preferably, the voltage of the lithium iron phosphate battery is 0 - 2.5 V.

[0021] Preferably, the discharging treatment specifically includes:

[0022] Connect the positive electrode tab of the battery cell of the lithium iron phosphate battery after soaking to the positive electrode of an external power source; connect the negative electrode tab of the battery cell of the lithium iron phosphate battery after soaking in parallel with an inert electrode, and then connect it to the negative electrode of the external power source, and use the buffer solution as the electrolyte for discharging.

[0023] Preferably, the inert electrode includes at least one of a platinum electrode, a nickel electrode, a rhodium electrode, and a graphite electrode.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The recycling and regeneration method of lithium iron phosphate provided by the present invention dissolves the irreversible lithium in the negative electrode or on the surface through a buffer solution, and then embeds the dissolved lithium ions back into the lithium iron phosphate positive electrode material through a discharging method. It can recycle the consumed lithium in waste lithium iron phosphate batteries in various different health states and re-embed it into the lithium iron phosphate positive electrode. There is no need to additionally supplement a lithium source. The repaired lithium iron phosphate material obtained has excellent electrochemical performance and realizes the maximum utilization of lithium resources. Description of the Drawings

[0026] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 It is the XRD pattern of the lithium iron phosphate provided by the embodiment of the present invention;

[0028] Figure 2 It is the SEM photograph of the lithium iron phosphate provided by the embodiment of the present invention;

[0029] Figure 3 It is the XRD pattern of the lithium iron phosphate provided by the comparative example of the present invention. Detailed Embodiments

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0031] A method for recycling and regenerating lithium iron phosphate includes the following steps:

[0032] Soak and discharge the battery cells of lithium iron phosphate batteries in a buffer solution to obtain discharged battery cells; separate the positive electrode sheets in the discharged battery cells and remove the current collectors in the positive electrode sheets;

[0033] The pH of the buffer solution is 2.0 to 8.0 (such as 2.0, 3.0, 4.0, 5.0, 6.0, 7.0 or 8.0);

[0034] The soaking time is 30 to 120 min (such as 30 min, 45 min, 60 min, 90 min, 100 min or 120 min);

[0035] The magnitude of the discharge current in the discharge treatment is 0.01 to 0.5 times the rated capacity of the lithium iron phosphate battery (such as 0.01 times, 0.03 times, 0.05 times, 0.08 times, 0.1 times, 0.2 times, 0.3 times, 0.4 times or 0.5 times);

[0036] The voltage of the discharged battery cell is -1.0 to -1.8 V (such as -1.0 V, -1.1 V, -1.2 V, -1.3 V, -1.4 V, -1.5 V, -1.6 V, -1.7 V or -1.8 V).

[0037] In the method for recycling and regenerating lithium iron phosphate, the irreversible lithium in the negative electrode or on the surface is dissolved by a buffer solution, and then the dissolved lithium ions are re-embedded into the lithium iron phosphate positive electrode material in the form of discharge. The consumed lithium in waste lithium iron phosphate batteries in various different health states can be recovered and re-embedded into the lithium iron phosphate positive electrode. No additional lithium source needs to be supplemented. The repaired lithium iron phosphate material obtained has excellent electrochemical performance and realizes the maximum utilization of lithium resources.

[0038] Preferably, the pH of the buffer solution is 4.0 to 6.0.

[0039] Preferably, the buffer solution includes at least one of citric acid, sodium citrate, tartaric acid, salicylic acid, malic acid, oxalic acid, and ascorbic acid.

[0040] Preferably, the magnitude of the discharge current during the discharge treatment is 0.05 to 0.2 times the rated capacity of the lithium iron phosphate battery.

[0041] Preferably, the mode of the discharge treatment includes a constant current discharge mode and / or a pulse discharge mode.

[0042] Preferably, the ratio of the pulse time to the interval time in the pulse discharge mode is (5 - 10):1 (such as 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1).

[0043] Preferably, the voltage of the empty battery cell is -1.2 to -1.5V.

[0044] Preferably, the voltage of the lithium iron phosphate battery is 0 to 2.5V (such as 0V, 0.5V, 1.0V, 1.5V, 2.0V, or 2.5V).

[0045] Preferably, the discharge treatment specifically includes:

[0046] Connect the positive electrode tab of the battery cell of the lithium iron phosphate battery after soaking to the positive pole of the external power supply; after connecting the negative electrode tab of the battery cell of the lithium iron phosphate battery after soaking in parallel with the inert electrode, connect it to the negative pole of the external power supply, and perform discharge with the buffer solution as the electrolyte.

[0047] Preferably, the inert electrode includes at least one of a platinum electrode, a nickel electrode, a rhodium electrode, and a graphite electrode.

[0048] Hereinafter, the embodiments of the present invention will be described in detail in conjunction with examples and comparative examples.

[0049] Example 1

[0050] The method for recycling and regenerating lithium iron phosphate provided in this example includes the following steps:

[0051] A batch of used soft-pack lithium iron phosphate batteries with a rated capacity of 50Ah and a remaining capacity of 34Ah are discharged to 2.0V, and then the aluminum-plastic film is peeled off to obtain the exposed battery cells.

[0052] Dissolve citric acid / sodium citrate in water to obtain a buffer solution with a pH value of 2.0, and soak the above-mentioned battery cells in the prepared buffer solution to dissolve the lithium in or on the surface of the graphite negative electrode in the solution.

[0053] Connect the positive electrode tab of the battery cell to the positive electrode of the external power supply, connect the negative electrode tab of the battery cell in parallel with the graphite electrode and then to the negative electrode of the external power supply. Use the buffer solution as the electrolyte and discharge at a constant current of 10 A until -1.5 V.

[0054] Separate the discharged positive electrode sheet from the battery cell, send the positive electrode sheet into a crusher for crushing, and then through vibrating screening. The aluminum slag is intercepted and separated by the sieve mesh, and the current collector on the sieve mesh is separated. The material passing through the sieve mesh enters an air flow mill. The main component of the material passing through the sieve mesh is lithium iron phosphate, and the lithium iron phosphate recovered is finally obtained through classification.

[0055] Example 2

[0056] The difference from Example 1 is that the pH value of the buffer solution is 8.0.

[0057] Example 3

[0058] The difference from Example 1 is that the pH value of the buffer solution is 4.0.

[0059] Example 4

[0060] The difference from Example 3 is that the magnitude of the constant current discharge current is 25 A.

[0061] Example 5

[0062] The difference from Example 3 is that the magnitude of the constant current discharge current is 0.5 A.

[0063] Example 6

[0064] The difference from Example 3 is that the cut-off voltage of the constant current discharge is -1.0 V.

[0065] Example 7

[0066] The difference from Example 3 is that the cut-off voltage of the constant current discharge is -1.8 V.

[0067] Example 8

[0068] The difference from Example 3 is that the discharge adopts a pulse discharge mode, and the ratio of the pulse discharge to the interval time is 10:1.

[0069] Example 9

[0070] The difference from Example 8 is that the discharge adopts a pulse discharge mode, and the ratio of the pulse discharge to the interval time is 5:1.

[0071] Example 10

[0072] The difference from Example 9 is that the remaining capacity of the used waste lithium iron phosphate battery is 25 Ah.

[0073] Example 11

[0074] It is different from Example 9 in that the remaining capacity of the used waste lithium iron phosphate battery is 38 Ah.

[0075] Example 12

[0076] It is different from Example 1 in that the negative electrode tab of the battery cell is connected in parallel with the platinum electrode and then connected to the negative electrode of the external power supply.

[0077] Example 13

[0078] It is different from Example 1 in that the negative electrode tab of the battery cell is connected in parallel with the nickel electrode and then connected to the negative electrode of the external power supply.

[0079] Example 14

[0080] It is different from Example 1 in that the negative electrode tab of the battery cell is connected in parallel with the rhodium electrode and then connected to the negative electrode of the external power supply.

[0081] Comparative Example 1

[0082] The recycling and regeneration method of lithium iron phosphate provided in this comparative example includes the following steps:

[0083] A batch of waste soft-pack lithium iron phosphate batteries with a rated capacity of 50 Ah and a remaining capacity of 34 Ah are discharged to 2.0 V, then the aluminum-plastic film is peeled off, and then the positive and negative electrode plates in the battery cell are separated. The positive electrode plate is sent to a crusher for crushing, and then through vibrating screening, the lithium iron phosphate positive electrode material enters the next process, and the aluminum slag is intercepted and separated by the screen, and the current collector on the screen is separated; the material passing through the screen enters an air-flow mill again. The main component of the material passing through the screen is lithium iron phosphate, and the lithium iron phosphate obtained by recycling is finally obtained through classification.

[0084] The recycled lithium iron phosphate is subjected to XRD testing and coin cell charge-discharge testing. Coin cell manufacturing method: Weigh the positive electrode active material, conductive agent SP, and binder PVDF according to a mass ratio of 90:5:5. Dissolve the binder PVDF in the NMP solvent, then add the positive electrode active material and conductive agent SP to the above-mentioned dissolved PVDF colloidal solution, disperse evenly, and coat it on the aluminum foil current collector. After baking, rolling, and cutting, a positive electrode plate is obtained. The positive electrode plate is assembled with a separator, a lithium sheet, and an electrolyte into a coin cell; Coin cell charge-discharge testing method: Use a Neware testing system to perform charge-discharge testing on the battery. Charge it at a constant current and constant voltage of 0.2C to 3.8 V, with a cut-off current of 0.05C, let it stand for 10 min, and then discharge it at a constant current of 0.2C to 2.5 V for cut-off. It can be seen from the XRD test that there are more iron phosphate phases in the recycled lithium iron phosphate, and the specific capacity of the first charge is only 105.5 mAh / g.

[0085] Experimental Example

[0086] The recycled lithium iron phosphate obtained in Example 3 and Comparative Example 1 was placed on the sample stage of an X-ray diffractometer for XRD testing. XRD testing can distinguish the ratio of the content of the lithium iron phosphate phase to the content of the iron phosphate phase (LFP / FP) in the lithium iron phosphate material, and at the same time can characterize whether the crystal structure of the recycled lithium iron phosphate cathode is complete. The results are shown in Figure 1 and Figure 3 . It can be seen from Figure 1 and Figure 3 that there are obvious diffraction peaks of the iron phosphate phase in the lithium iron phosphate material obtained in Comparative Example 1, and there are no diffraction peaks of the iron phosphate phase in the lithium iron phosphate material obtained by this technical solution, indicating that the lithium in the negative electrode is effectively intercalated into the lithium iron phosphate material of the positive electrode, and a repaired lithium iron phosphate material with a complete crystal structure is obtained; the results of observing the recycled lithium iron phosphate cathode material obtained in Example 9 under a scanning electron microscope are shown in Figure 2 .

[0087] The recycled and repaired lithium iron phosphate obtained in the examples and comparative examples was made into a button cell. The manufacturing method of the button cell: Weigh the cathode active material, conductive agent SP, and binder PVDF according to a mass ratio of 90:5:5. Dissolve the binder PVDF in the NMP solvent, then add the cathode active material and conductive agent SP to the dissolved PVDF colloidal solution, disperse evenly, and coat it on the aluminum foil current collector. After baking, rolling, and cutting, a positive electrode sheet is obtained. Assemble the positive electrode sheet with a separator, lithium sheet, and electrolyte into a button cell; The charge-discharge test method for the button cell: Use a Neware test system to conduct charge-discharge tests on the battery. Charge it at a constant current and constant voltage of 0.2C to 3.8V, with a cut-off current of 0.05C, let it stand for 10 minutes, and then discharge it at a constant current of 0.2C until it reaches 2.5V cut-off. Charge-discharge tests were carried out. The initial charge capacity characterizes the content of lithium ions that can be removed in the lithium iron phosphate structure, that is, the lithium content LixFePO4 in the lithium iron phosphate material. The results are shown in Table 1

[0088] Table 1 Performance of Lithium Iron Phosphate

[0089]

[0090]

[0091] By comparing the examples and comparative examples, it can be seen that the technical solution of the present invention dissolves the irreversible lithium in or on the negative electrode through a buffer solution, and then re-inserts the dissolved lithium ions into the lithium iron phosphate cathode material through a discharge form. The consumed lithium in waste lithium iron phosphate batteries in various different health states can be recycled and re-inserted into the lithium iron phosphate cathode. There is no need to additionally supplement a lithium source. The repaired lithium iron phosphate material obtained has excellent electrochemical performance and realizes the maximum utilization of lithium resources

[0092] Although the present invention has been illustrated and described with reference to specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it; those of ordinary skill in the art should understand that: without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention; therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for recycling and regenerating lithium iron phosphate, characterized in that, It includes the following steps: Soak and discharge the battery cells of the lithium iron phosphate battery in a buffer solution to obtain discharged battery cells; separate the positive electrode plates in the discharged battery cells, and remove the current collectors in the positive electrode plates; The pH of the buffer solution is 2.0 - 8.0; the buffer solution includes at least one of citric acid, sodium citrate, tartaric acid, salicylic acid, malic acid, oxalic acid, and ascorbic acid; The soaking time is 30 - 120 min; The magnitude of the discharge current in the discharge treatment is 0.01 - 0.5 times the rated capacity of the lithium iron phosphate battery; the discharge treatment specifically includes: connecting the positive electrode tab of the battery cell of the lithium iron phosphate battery after soaking to the positive electrode of an external power source; connecting the negative electrode tab of the battery cell of the lithium iron phosphate battery after soaking in parallel with an inert electrode and then connecting it to the negative electrode of the external power source, and discharging with the buffer solution as the electrolyte; The voltage of the discharged battery cell is -1.0 - -1.8 V.

2. The recycling method of lithium iron phosphate according to claim 1, wherein The pH of the buffer solution is 4.0 - 6.

0.

3. The recycling method of lithium iron phosphate according to claim 1, characterized in that, The magnitude of the discharge current in the discharge treatment is 0.05 - 0.2 times the rated capacity of the lithium iron phosphate battery.

4. The recycling method of lithium iron phosphate according to claim 1, characterized in that, The discharge mode in the discharge treatment includes a constant current discharge mode and / or a pulse discharge mode.

5. The recycling method of lithium iron phosphate according to claim 4, characterized in that, The ratio of the pulse time to the interval time in the pulse discharge mode is (5 - 10):

1.

6. The recycling method of lithium iron phosphate according to claim 1, characterized in that, The voltage of the discharged battery cell is -1.2 - -1.5 V.

7. The method for recycling lithium iron phosphate according to claim 1, characterized in that, The voltage of the lithium iron phosphate battery is 0 - 2.5 V.

8. The recycling method of lithium iron phosphate according to claim 1, characterized in that, The inert electrode includes at least one of a platinum electrode, a nickel electrode, a rhodium electrode, and a graphite electrode.

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