Method for directly regenerating waste lithium iron phosphate positive electrode material

Abstract

The invention discloses a method for directly regenerating a waste lithium iron phosphate positive electrode material, which comprises the following steps: uniformly mixing waste lithium iron phosphate powder and a lithium source according to a certain molar ratio, and then fully grinding at room temperature; and carrying out top-speed Joule thermal shock on the uniformly mixed powder obtained by grinding in a nitrogen atmosphere, cooling, washing with distilled water to remove salt, and drying in a vacuum oven to obtain the repaired and regenerated lithium iron phosphate positive electrode material. The method is efficient, energy-saving and environment-friendly, and the waste lithium iron phosphate positive electrode material can be effectively regenerated; the lithium iron phosphate positive electrode material regenerated by the method is excellent in electrochemical performance and can reach the commercialization level, and the lithium ion battery prepared from the positive electrode material can be repeatedly used.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery materials, and in particular relates to a method for directly regenerating waste lithium iron phosphate positive electrode materials. Background Art

[0002] With the explosive growth of new energy vehicles, my country's power batteries will usher in a "retirement wave". It is estimated that by 2025, the total amount of retired new energy vehicle power batteries will exceed 800,000 tons. Therefore, if the recycling and reuse of waste lithium iron phosphate batteries can be effectively completed and the "internal circulation" of lithium resources can be realized, it will not only greatly reduce the environmental pressure brought by the future battery retirement wave, but also bring considerable economic benefits. The positive electrode material occupies the highest cost in the battery and directly determines the energy density of the battery. Therefore, the problem of recycling waste lithium iron phosphate batteries is mainly concentrated on the positive electrode material.

[0003] At present, the main methods used for recycling positive electrode materials are wet recycling, pyrometallurgical recycling, and repair and regeneration. Wet recycling is the most widely studied and effective recycling method. It can effectively reduce the loss of various elements and the recovered single substances or compounds have higher purity, but it also has the problem of long recycling process and low economic benefits. The pyrometallurgical recycling process is short and the operation is relatively simple, which can reduce energy consumption, but this recycling method cannot effectively recycle single lithium and is prone to produce various polluting gases. With the development of technology and the change of research ideas, researchers have begun to focus on the development of repair and regeneration recycling processes in order to pursue short processes, high efficiency, and high added value for waste lithium iron phosphate battery positive electrode materials. This method will not destroy the inherent crystal structure of waste lithium iron phosphate. The process is simple and environmentally friendly and has high economic benefits, but it also has problems such as poor battery cycle stability and high cost of added reducing agents.

[0004] At present, researchers at home and abroad have carried out related work. For example, by adding lithium carbonate, 3,4-dihydroxybenzonitrile dilithium and other lithium salts to waste lithium iron phosphate, or adding some reducing substances to it, the repaired materials show excellent electrochemical properties, but there are also problems such as high energy consumption and the lithium-ion batteries prepared cannot be reused. Summary of the invention

[0005] The purpose of the present invention is to provide a method for directly regenerating waste lithium iron phosphate positive electrode materials. The method is efficient, energy-saving and environmentally friendly, and can effectively regenerate waste lithium iron phosphate positive electrode materials; the lithium iron phosphate positive electrode materials regenerated by this method have excellent electrochemical properties and can reach commercial levels, and the lithium-ion batteries prepared using the positive electrode materials can be reused.

[0006] To achieve the above-mentioned object of the invention, the present invention provides a method for directly regenerating waste lithium iron phosphate positive electrode material, comprising the following steps:

[0007] (1) mixing waste lithium iron phosphate powder (SLFP) and a lithium source uniformly in a certain molar ratio, and then grinding them fully at room temperature;

[0008] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to extremely rapid Joule thermal shock in a nitrogen atmosphere and then cooling, washing with distilled water to remove salt, and drying in a vacuum oven to obtain a repaired and regenerated lithium iron phosphate positive electrode material (RLFP).

[0009] Preferably, in step (1), the lithium source is one or more of lithium fluoride, lithium carbonate, lithium acetate, and lithium iodide.

[0010] Preferably, in step (1), the molar ratio between the waste lithium iron phosphate powder and lithium fluoride is 1:(0.3-0.8).

[0011] Preferably, in step (2), the current of the extreme Joule heating is 10A to 100A, the voltage is 30V, and the heating time is 1s to 100s.

[0012] Preferably, in step (2), the drying temperature is 60° C. to 120° C., and the drying time is 12 to 24 hours.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) The extremely fast Joule thermal shock technology in the present invention is realized by using carbon paper, carbon felt and carbon boat as carriers and adopting a pulse power supply; the present invention obtains a regenerated lithium iron phosphate positive electrode material by using a simple and fast extremely fast Joule thermal shock technology and by regulating the type of lithium salt, the content of lithium salt, the heating temperature and the heating time. The electrochemical performance of the lithium iron phosphate positive electrode material regenerated by the method is excellent and can reach the commercial level, and the lithium ion battery prepared by using the positive electrode material can be reused;

[0015] (2) The waste lithium iron phosphate powder (SLFP) used in the present invention has not been pretreated, so the structure of lithium iron phosphate is retained, simplifying the experimental process; by adding a lithium source to the SLFP and then regenerating the SLFP by extremely fast Joule thermal shock, the lithium source can supplement the missing Li in the SLFP, thereby ensuring the integrity of the positive electrode material and improving the electrochemical performance of the repaired lithium iron phosphate powder (RLFP);

[0016] (3) The method of the present invention is efficient, energy-saving and environmentally friendly. It can not only directly regenerate waste lithium iron phosphate positive electrode materials, but also achieve fine control of the Li / Fe content of RLFP samples, making it easy to achieve large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1These are SEM images of the SLFP used in Example 1 of the present invention and the RLFP positive electrode material obtained after repair, (a) is a SLFP with a scale of 1 μm, (b) is a RLFP with a scale of 1 μm, (c) is a SLFP with a scale of 500 nm, and (d) is a RLFP with a scale of 500 nm;

[0018] Figure 2 This is an ICP image of the SLFP used in Example 1 of the present invention and the repaired RLFP positive electrode material;

[0019] Figure 3 This is a rate performance diagram of the SLFP used in Example 1 of the present invention and the repaired RLFP positive electrode material at a current density of 0.1C to 3C;

[0020] Figure 4 This is a long cycle performance diagram of the RLFP positive electrode material repaired in Example 1 of the present invention at a current density of 1C. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with specific embodiments.

[0022] Embodiment 1

[0023] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0024] (1) 0.316 g SLFP and 0.020 g LiF (molar ratio of 1:0.4) were placed in a mortar and ground thoroughly for 30 min at room temperature;

[0025] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, setting the heating current to 35 A, the voltage to 30 V, and the heating time to 30 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 120° C. for 12 h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material (RLFP).

[0026] The SLFP and the RLFP prepared in this example were subjected to characterization tests, wherein Figure 1 (a) and Figure 1 (c) SEM images show that the SLFP cathode material particles are irregular in shape and the particle size distribution is in the range of 0.2 to 0.5 μm; Figure 1 (b) and Figure 1 (d) SEM image shows that after regeneration, RLFP maintains the morphology and size of SLFP, and the particle shape is more regular.

[0027] Figure 2The ICP results showed that the molar ratio of Li / Fe in SLFP was only 0.70, while that in RLFP increased to 1.05, indicating that the structure and composition of SLFP were fully restored after regeneration.

[0028] The SLFP and the RLFP prepared in Example 1 were used as positive electrode materials for lithium-ion batteries to test their electrochemical performance. The counter electrode tested was a metal lithium sheet, and the electrolyte was 1M lithium hexafluorophosphate (LiPF6) dissolved in a mixture of diethyl carbonate (DEC) / ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (1:1:1 vol / vol). Figure 3 The results show that at current densities of 0.1C to 3C, the discharge specific capacity of RLFP is better than that of SLFP, and it has better rate performance.

[0029] Figure 4 The long cycle performance diagram of RLFP shows that the cycle retention rate of RLFP is 87.80% after 500 cycles, showing excellent cycle stability.

[0030] Embodiment 2

[0031] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0032] (1) 0.316 g SLFP and 0.052 g Li2CO3 (molar ratio of 1:0.35) were placed in a mortar and ground thoroughly for 30 min at room temperature;

[0033] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, with the heating current set to 35 A, the voltage set to 30 V, and the heating time set to 30 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 120° C. for 12 h to obtain a sample that is the regenerated lithium iron phosphate positive electrode material.

[0034] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a button cell and the electrochemical performance was tested. The charge and discharge results showed that the regenerated lithium iron phosphate cathode material could obtain 135 mAh g at a current density of 1C. -1 The discharge capacity.

[0035] Embodiment 3

[0036] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0037] (1) 0.316 g SLFP and 0.053 g CH3COOLi (molar ratio of 1:0.4) were placed in a mortar and ground thoroughly for 30 min at room temperature;

[0038] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, setting the heating current to 30 A, the voltage to 30 V, and the heating time to 100 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 120° C. for 12 h to obtain a sample that is the regenerated lithium iron phosphate positive electrode material.

[0039] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a button cell and the electrochemical performance was tested. The charge and discharge results showed that the regenerated lithium iron phosphate cathode material could obtain 130 mAh g at a current density of 1C. -1 The discharge capacity.

[0040] Embodiment 4

[0041] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0042] (1) 0.316 g SLFP and 0.020 g LiF (molar ratio of 1:0.4) were placed in a mortar and ground thoroughly for 30 min at room temperature;

[0043] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, setting the heating current to 100 A, the voltage to 30 V, and the heating time to 35 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 120° C. for 12 h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material.

[0044] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a button cell and the electrochemical performance was tested. The charge and discharge results showed that the regenerated lithium iron phosphate cathode material could obtain 125 mAh g at a current density of 1C. -1 The discharge capacity.

[0045] Embodiment 5

[0046] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0047] (1) 0.316 g SLFP and 0.020 g LiF (molar ratio of 1:0.4) were placed in a mortar and ground thoroughly for 30 min at room temperature;

[0048] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, setting the heating current to 30 A, the voltage to 30 V, and the heating time to 100 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 120° C. for 12 h to obtain a sample that is the regenerated lithium iron phosphate positive electrode material.

[0049] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a button cell and the electrochemical performance was tested. The charge and discharge results showed that the regenerated lithium iron phosphate cathode material could obtain 130 mAh g at a current density of 1C. -1 The discharge capacity.

[0050] Embodiment 6

[0051] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0052] (1) 0.316 g SLFP and 0.106 g CH3COOLi (molar ratio of 1:0.8) were placed in a mortar and ground thoroughly at room temperature for 30 min;

[0053] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, setting the heating current to 30 A, the voltage to 30 V, and the heating time to 35 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 120° C. for 12 h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material.

[0054] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a button cell and the electrochemical performance was tested. The charge and discharge results showed that the regenerated lithium iron phosphate cathode material could obtain 140 mAh g at a current density of 1C. -1 The discharge capacity.

[0055] Embodiment 7

[0056] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0057] (1) 0.316 g SLFP and 0.106 g CH3COOLi (molar ratio of 1:0.8) were placed in a mortar and ground thoroughly at room temperature for 30 min;

[0058] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, with a heating current of 10 A, a voltage of 30 V, and a heating time of 35 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 120° C. for 12 h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material.

[0059] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a button cell and the electrochemical performance was tested. The charge and discharge results showed that the regenerated lithium iron phosphate cathode material could obtain 125 mAh g at a current density of 1C. -1 The discharge capacity.

[0060] Embodiment 8

[0061] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0062] (1) 0.316 g SLFP and 0.020 g LiF (molar ratio of 1:0.4) were placed in a mortar and ground thoroughly for 30 min at room temperature;

[0063] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, setting the heating current to 10 A, the voltage to 30 V, and the heating time to 1 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 120° C. for 12 h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material (RLFP).

[0064] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a button cell and the electrochemical performance was tested. The charge and discharge results showed that the regenerated lithium iron phosphate cathode material could obtain 120 mAh g at a current density of 1C. -1 The discharge capacity.

[0065] Embodiment 9

[0066] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0067] (1) 0.316 g SLFP and 0.015 g LiF (molar ratio of 1:0.3) were placed in a mortar and ground thoroughly for 30 min at room temperature;

[0068] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, setting the heating current to 30 A, the voltage to 30 V, and the heating time to 10 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 120° C. for 12 h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material (RLFP).

[0069] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a button cell and the electrochemical performance was tested. The charge and discharge results showed that the regenerated lithium iron phosphate cathode material could obtain 130 mAh g at a current density of 1C. -1 The discharge capacity.

[0070] Embodiment 10

[0071] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0072] (1) 0.316 g SLFP, 0.010 g LiF: 0.027 g CH3COOLi (molar ratio of 1:0.2:0.2) were placed in a mortar and ground thoroughly at room temperature for 30 min;

[0073] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, setting the heating current to 35 A, the voltage to 30 V, and the heating time to 30 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 120° C. for 12 h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material (RLFP).

[0074] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a button cell and the electrochemical performance was tested. The charge and discharge results showed that the regenerated lithium iron phosphate cathode material could obtain 140 mAh g at a current density of 1C. -1 The discharge capacity.

[0075] Embodiment 11

[0076] A method for directly regenerating waste lithium iron phosphate positive electrode material comprises the following steps:

[0077] (1) 0.316 g SLFP and 0.188 g LiI (molar ratio of 1:0.5) were placed in a mortar and ground thoroughly for 30 min at room temperature;

[0078] (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to an extremely rapid Joule thermal shock in a nitrogen atmosphere, setting the heating current to 35 A, the voltage to 30 V, and the heating time to 30 s; cooling after heating, washing the directly regenerated material with distilled water for desalination, and drying it in a vacuum oven at 60° C. for 24 h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material (RLFP).

[0079] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a button cell and the electrochemical performance was tested. The charge and discharge results showed that the regenerated lithium iron phosphate cathode material could obtain 140 mAh g at a current density of 1C. -1 The discharge capacity.

Claims

1. A method for directly regenerating waste lithium iron phosphate positive electrode materials, characterized in that: The following steps are involved: (1) mixing waste lithium iron phosphate powder and lithium source uniformly in a certain molar ratio, and then grinding them fully at room temperature; (2) subjecting the uniformly mixed powder obtained by grinding in step (1) to extremely rapid Joule thermal shock in a nitrogen atmosphere and then cooling, washing with distilled water to remove salt, and drying in a vacuum oven to obtain a repaired and regenerated lithium iron phosphate positive electrode material.

2. A method for directly regenerating waste lithium iron phosphate positive electrode materials according to claim 1, characterized in that: In step (1), the lithium source is one or more of lithium fluoride, lithium carbonate, lithium acetate, and lithium iodide.

3. A method for directly regenerating waste lithium iron phosphate positive electrode material according to claim 2, characterized in that: In step (1), the molar ratio between the waste lithium iron phosphate powder and lithium fluoride is 1:(0.3-0.8).

4. A method for directly regenerating waste lithium iron phosphate positive electrode material according to claim 1 or 2, characterized in that: In step (2), the current of the extreme Joule heating is 10A to 100A, the voltage is 30V, and the heating time is 1s to 100s.

5. A method for directly regenerating waste lithium iron phosphate positive electrode material according to claim 1 or 2, characterized in that: In step (2), the drying temperature is 60° C. to 120° C., and the drying time is 12 to 24 hours.

Images