A method for directly regenerating waste lithium iron phosphate induced by internal stress

Abstract

The present invention discloses a method for directly regenerating waste lithium iron phosphate induced by internal stress, which comprises the following steps: mixing waste lithium iron phosphate cathode material, lithium source and ion source for inducing internal stress generation according to a certain molar ratio, and grinding to obtain powder I; after wrapping powder I with carbon-based material, subjecting it to rapid Joule heating sintering to generate internal stress induction to obtain powder II; using deionized water to desalt powder II at room temperature, and drying in a vacuum drying oven to obtain regenerated lithium iron phosphate cathode material. The lithium source is one or more of lithium iodide, lithium chloride, lithium carbonate, lithium fluoride, lithium hydroxide; the ion source for inducing internal stress generation is one or more of sodium iodide, sodium chloride, sodium carbonate, sodium hydroxide. This method has short time consumption and less pollution, can quickly repair the structural defects of waste lithium iron phosphate and supplement the lacking active lithium; the obtained regenerated lithium iron phosphate has excellent electrochemical performance and can reach the commercial level.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and particularly relates to a method for directly regenerating waste lithium iron phosphate by internal stress induction. Background Art

[0002] Lithium iron phosphate (LiFePO4) has become one of the most widely used cathode materials due to its excellent properties such as low cost, high safety and stability. However, a large number of lithium iron phosphate batteries will be retired in large quantities after the end of their cycle life. Improper treatment will cause environmental pollution and waste of resources. Therefore, recycling these batteries is of great significance for environmental protection, resource conservation and economic efficiency.

[0003] At present, there are mainly two main routes for the treatment of waste lithium-ion battery cathode materials: the recovery of valuable elements in the battery and the direct regeneration of electrode materials. The recovery methods of valuable elements in the battery include pyrometallurgical recovery and hydrometallurgical recovery. Pyrometallurgical recovery mainly extracts metals and their compounds from waste batteries by high-temperature means. The process flow is relatively short and the operation is relatively simple. It has low requirements for raw materials and is suitable for large-scale waste battery treatment. However, the disadvantages of pyrometallurgy are obvious, with high energy consumption and a large amount of waste gas generation; Hydrometallurgical recovery is to extract solid metal substances in electrode materials with acid-base solutions, and it is also the most widely used recovery technology. This technology can effectively recover various valuable metal ions in waste batteries, but a large amount of chemical reagents are consumed during the recovery process.

[0004] The direct regeneration of electrode materials is mainly to supplement the missing active lithium ions in the cathode material and simultaneously repair its crystal structure. Due to the stable structure of lithium iron phosphate and the low economic effect of recovering valuable metals, the current research direction mainly focuses on direct regeneration.

[0005] At present, relevant work has been carried out by researchers at home and abroad. For example, by adding lithium salts such as lithium carbonate and lithium hydroxide to waste lithium iron phosphate and adding some reducing substances, the repaired materials all show good electrochemical performance, but there are also problems with the poor cycle performance of the prepared lithium-ion batteries. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for directly regenerating waste lithium iron phosphate by internal stress induction. This method takes a short time, has less pollution, can quickly repair the structural defects of waste lithium iron phosphate and supplement the missing active lithium; the regenerated lithium iron phosphate obtained by this method has excellent electrochemical performance and can reach the commercial level.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is: a method for directly regenerating waste lithium iron phosphate by internal stress induction, comprising the following steps:

[0008] (1) Mix the waste lithium iron phosphate cathode material (SLFP), lithium source, and ion source that induces internal stress in a certain molar ratio, and grind them to obtain Powder I;

[0009] (2) After wrapping the Powder I obtained in step (1) with a carbon-based material, subject it to rapid Joule heating sintering to induce internal stress to obtain Powder II; Use deionized water to desalt Powder II at room temperature, and dry it in a vacuum drying oven to obtain the regenerated lithium iron phosphate cathode material (RLFP-N).

[0010] Preferably, in step (1), the lithium source is one or more of lithium iodide, lithium chloride, lithium carbonate, lithium fluoride, and lithium hydroxide.

[0011] Preferably, in step (1), the ion source that induces internal stress is one or more of sodium iodide, sodium chloride, sodium carbonate, and sodium hydroxide.

[0012] Preferably, in step (1), the molar ratio between the waste lithium iron phosphate cathode material and the ion source that induces internal stress is 1:(0.14 - 0.32).

[0013] Preferably, in step (1), the molar ratio between the waste lithium iron phosphate cathode material and the lithium source is 1:(0.06 - 0.16).

[0014] Preferably, in step (2), the carbon-based material is the substance that generates Joule heat, and the carbon-based material is carbon cloth, carbon felt, carbon paper, or carbon boat.

[0015] Preferably, in step (2), the Joule heating sintering temperature is 600 - 1100 °C, the heating time is 20 - 100 s, and the sintering atmosphere is one of nitrogen, argon, and argon / hydrogen mixed atmosphere.

[0016] Preferably, in step (2), the drying temperature is 60 °C - 120 °C, and the drying time is 12 - 24 h.

[0017] In the present invention, the internal stress induction is mainly achieved by doping sodium into the Li site during rapid heating, while forming an internal induction force to make the remaining Li supplement to the missing Li site. At the same time, the addition of I can act as a reducing agent to reduce Fe(III) occupying the Li site to Fe(II) to repair its structure.

[0018] Compared with the prior art solutions, the present invention has the following advantages:

[0019] (1) The present invention obtains a regenerated lithium iron phosphate cathode material through a simple method of internal stress induction, and by regulating the types of lithium salts and sodium salts, the ratio of lithium salts to sodium salts, the reaction time, and the reaction temperature. The regenerated lithium iron phosphate obtained by this method has excellent electrochemical performance and can reach the commercial level;

[0020] (2) The present invention uses a rapid thermal shock method. The ion source that induces the generation of internal stress is added to generate internal stress to induce lithium ions to be supplemented into the waste lithium iron phosphate. At the same time, the doping of sodium can improve the cycle stability of the regenerated lithium iron phosphate (RLFP-N);

[0021] (3) The method of the present invention is efficient, energy-saving and environmentally friendly. It can not only directly regenerate the waste lithium iron phosphate cathode material, but also finely regulate the Na doping content of the RLFP sample, and is easy to realize large-scale production. Description of the Drawings

[0022] Figure 1 are SEM images of the RLFP-N cathode material obtained after repair in Example 1 of the present invention and the SLFP used. (a) is RLFP-N at a scale of 1 μm, and (b) is SLFP at a scale of 500 nm;

[0023] Figure 2 are XRD images of the RLFP-N cathode material obtained after repair in Example 1 of the present invention and the SLFP used;

[0024] Figure 3 are rate performance graphs of the RLFP-N cathode material obtained after repair in Example 1 of the present invention and the SLFP used at a current density of 0.1C to 5C;

[0025] Figure 4 are long cycle performance graphs of the RLFP-N cathode material obtained after repair in Example 1 of the present invention and the SLFP used at a current density of 1C. Detailed Embodiments

[0026] The following further describes the present invention in detail with reference to the drawings and specific embodiments.

[0027] Example 1

[0028] A method for directly regenerating waste lithium iron phosphate by internal stress induction includes the following steps:

[0029] (1) Put 0.395 g of SLFP, 0.259 g of NaI, and 0.100 g of LiI (the molar ratio among the three is 1:0.28:0.12) into a mortar and grind them thoroughly at room temperature for 30 min to obtain powder I;

[0030] (2) The powder I obtained by grinding in step (1) is wrapped with carbon paper and subjected to rapid Joule heating sintering, that is, rapid thermal shock is performed in a nitrogen atmosphere to induce internal stress to obtain powder II, the heating temperature is 800°C, and the heating time is 20s; after heating, the powder II is cooled, washed with distilled water to remove salt, and dried in a vacuum oven at 120°C for 12h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material (RLFP-N).

[0031] The SLFP and the RLFP-N prepared in this example were characterized and tested. Figure 1 (b) SEM image shows that the particles of SLFP cathode material are irregular in shape; Figure 1 (a) The image shows that after regeneration, RLFP-N maintains the morphology of SLFP, and the particle shape is more regular.

[0032] SLFP and RLFP-N prepared in this example 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 the current density of 0.1C to 3C, the discharge specific capacity of RLFP-N is better than that of SLFP, and it has better rate performance.

[0033] Figure 4 The long cycle performance diagram of RLFP shows that the cycle retention rate of RLFP-N is 93.36% after 100 cycles, showing excellent cycle stability.

[0034] Embodiment 2

[0035] A method for directly regenerating waste lithium iron phosphate by inducing internal stress, comprising the following steps:

[0036] (1) 0.395 g SLFP, 0.117 g NaCl, and 0.021 g LiCl (the molar ratio of the three is 1:0.32:0.08) were placed in a mortar and ground thoroughly at room temperature for 30 min to obtain powder I;

[0037] (2) The powder I obtained by grinding in step (1) is wrapped with carbon cloth and subjected to rapid Joule heating sintering, that is, rapid thermal shock is performed in a nitrogen atmosphere to induce internal stress to obtain powder II, the heating temperature is 600°C, and the heating time is 40s; after heating, the powder II is cooled, washed with distilled water to remove salt, and dried in a vacuum oven at 100°C for 16h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material.

[0038] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a coin cell for electrochemical performance testing. The charge-discharge results showed that the regenerated lithium iron phosphate cathode material could obtain a discharge specific capacity of 130 mAh g -1 at a current density of 1C.

[0039] Example 3

[0040] A method for directly regenerating waste lithium iron phosphate by internal stress induction, comprising the following steps:

[0041] (1) 0.395 g of SLFP, 0.185 g of Na2CO3, and 0.055 g of Li2CO3 (molar ratio of the three is 1:0.14:0.06) were placed in a mortar and ground thoroughly at room temperature for 30 min to obtain powder I;

[0042] (2) After the powder I obtained by grinding in step (1) was wrapped with a carbon boat, it was sintered by rapid Joule heating, that is, internal stress induction was generated by rapid thermal shock in a nitrogen atmosphere to obtain powder II. The heating temperature was 900 °C and the heating time was 60 s; after heating, it was cooled. The powder II was washed with distilled water to remove salts and then dried in a vacuum oven at 90 °C for 18 h. The obtained sample was the regenerated lithium iron phosphate cathode material.

[0043] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a coin cell for electrochemical performance testing. The charge-discharge results showed that the regenerated lithium iron phosphate cathode material could obtain a discharge specific capacity of 127 mAh g -1 at a current density of 1C.

[0044] Example 4

[0045] A method for directly regenerating waste lithium iron phosphate by internal stress induction, comprising the following steps:

[0046] (1) 0.395 g of SLFP, 0.060 g of NaOH, and 0.024 g of LiOH (molar ratio of the three is 1:0.24:0.16) were placed in a mortar and ground thoroughly at room temperature for 30 min to obtain powder I;

[0047] (2) After the powder I obtained by grinding in step (1) was wrapped with a carbon felt, it was sintered by rapid Joule heating, that is, internal stress induction was generated by rapid thermal shock in an argon atmosphere to obtain powder II. The heating temperature was 1100 °C and the heating time was 20 s; after heating, it was cooled. The powder II was washed with distilled water to remove salts and then dried in a vacuum oven at 80 °C for 20 h. The obtained sample was the regenerated lithium iron phosphate cathode material.

[0048] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a coin cell for electrochemical performance testing. The charge-discharge results showed that the regenerated lithium iron phosphate cathode material could obtain a discharge specific capacity of 139 mAh g -1 at a current density of 1C.

[0049] Example 5

[0050] A method for directly regenerating waste lithium iron phosphate by internal stress induction, comprising the following steps:

[0051] (1) Put 0.395 g of SLFP, 0.300 g of NaI, and 0.013 g of LiF (the molar ratio among the three is 1:0.32:0.08) into a mortar and grind thoroughly at room temperature for 30 min to obtain Powder I;

[0052] (2) After wrapping the Powder I obtained by grinding in step (1) with carbon paper, it was sintered by rapid Joule heating, that is, internal stress induction was generated by rapid thermal shock in an argon / hydrogen mixed gas atmosphere to obtain Powder II. The heating temperature was 800 °C and the heating time was 100 s; after heating, it was cooled. The Powder II was washed with distilled water to remove salts and then dried in a vacuum oven at 60 °C for 24 h. The obtained sample was the regenerated lithium iron phosphate cathode material.

[0053] The regenerated lithium iron phosphate cathode material obtained in this example was assembled into a coin cell for electrochemical performance testing. The charge-discharge results showed that the regenerated lithium iron phosphate cathode material could obtain a discharge specific capacity of 133 mAh g -1 at a current density of 1C.

Claims

1. A method for directly regenerating waste lithium iron phosphate induced by internal stress, characterized in that, The method includes the following steps: (1) Mixing and grinding waste lithium iron phosphate cathode materials, a lithium source, and an ion source for inducing internal stress in a certain molar ratio to obtain powder I; the ion source for inducing internal stress is one or more of sodium iodide, sodium chloride, sodium carbonate, and sodium hydroxide; the molar ratio between the waste lithium iron phosphate cathode materials and the ion source for inducing internal stress is 1:(0.14 - 0.32); (2) Wrapping the powder I obtained in step (1) with a carbon-based material, and after rapid Joule heating sintering to induce internal stress, obtaining powder II; using deionized water to desalt the powder II at room temperature, and drying it in a vacuum drying oven to obtain regenerated lithium iron phosphate cathode materials.

2. The method for directly regenerating waste lithium iron phosphate induced by internal stress according to claim 1, wherein In step (1), the lithium source is one or more of lithium iodide, lithium chloride, lithium carbonate, lithium fluoride, and lithium hydroxide.

3. A method for directly regenerating waste lithium iron phosphate induced by internal stress according to claim 1 or 2, characterized in that, In step (1), the molar ratio between the waste lithium iron phosphate cathode materials and the lithium source is 1:(0.06 - 0.16).

4. A method for directly regenerating waste lithium iron phosphate induced by internal stress according to claim 1 or 2, characterized in that, In step (2), the carbon-based material is the substance that generates Joule heat, and the carbon-based material is carbon cloth, carbon felt, carbon paper, or a carbon boat.

5. A method for directly recycling waste lithium iron phosphate induced by internal stress according to claim 1 or 2, characterized in that In step (2), the Joule heating sintering temperature is 600 - 1100°C, the heating time is 20 - 100 s, and the sintering atmosphere is one of nitrogen, argon, and an argon / hydrogen mixed atmosphere.

6. The method for directly regenerating waste lithium iron phosphate induced by internal stress according to claim 1 or 2, characterized in that In step (2), the drying temperature is 60°C - 120°C, and the drying time is 12 - 24 h.

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