Method for directly regenerating waste lithium iron phosphate through internal stress induction

Abstract

The invention discloses a method for directly regenerating waste lithium iron phosphate through internal stress induction. The method comprises the following steps: mixing and grinding a waste lithium iron phosphate positive electrode material, a lithium source and an ion source for inducing internal stress generation according to a certain molar ratio to obtain powder I; after the powder I is wrapped with a carbon-based material, internal stress induction is generated after rapid Joule heating sintering, and powder II is obtained; and desalting the powder II by using deionized water at normal temperature, and drying in a vacuum drying oven to obtain the regenerated lithium iron phosphate positive electrode material. The lithium source is one or more of lithium iodide, lithium chloride, lithium carbonate, lithium fluoride and lithium hydroxide; the ion source for inducing the generation of the internal stress is one or more of sodium iodide, sodium chloride, sodium carbonate and sodium hydroxide. The method is short in time consumption and less in pollution, and can quickly repair the structural defects of the waste lithium iron phosphate and supplement lacked active lithium; the obtained regenerated lithium iron phosphate has excellent electrochemical performance and can reach the commercialization level.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and in particular to a method for directly regenerating waste lithium iron phosphate by inducing internal stress. 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 at the end of their cycle life, and improper handling 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 two main routes for the treatment of waste lithium-ion battery positive electrode materials: the recovery of valuable elements in the battery and the direct regeneration of electrode materials. There are two ways to recover valuable elements in the battery: pyrometallurgical recovery and wet recovery. Pyrometallurgical recovery mainly uses high temperature means to extract metals and their compounds from waste batteries. The process is short and relatively simple to operate, with 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 generated; wet recovery uses acid and alkali solutions to extract solid metal substances in electrode materials, and 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] Direct regeneration of electrode materials is mainly achieved by replenishing the active lithium ions missing in the positive electrode material and repairing its crystal structure at the same time. Since lithium iron phosphate has a stable structure and the economic effect of recycling valuable metals is not high, the current research direction is mainly focused on direct regeneration.

[0005] At present, researchers at home and abroad have carried out related work. For example, by adding lithium carbonate, lithium hydroxide and other lithium salts to waste lithium iron phosphate, and adding some reducing substances to it, the repaired materials show good electrochemical properties, but there are also lithium-ion batteries with poor cycle performance. Summary of the invention

[0006] The purpose of the present invention is to provide a method for directly regenerating waste lithium iron phosphate by inducing internal stress. The method is time-saving and less polluting, and can quickly repair the structural defects of waste lithium iron phosphate and supplement the missing active lithium. The regenerated lithium iron phosphate obtained by the method has excellent electrochemical properties and can reach commercial level.

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

[0008] (1) mixing and grinding waste lithium iron phosphate cathode material (SLFP), a lithium source, and an ion source that induces internal stress according to a certain molar ratio to obtain powder I;

[0009] (2) The powder I obtained in step (1) is wrapped with a carbon-based material, and then subjected to rapid Joule heating sintering to induce internal stress to obtain powder II; powder II is desalted using deionized water at room temperature, and then dried in a vacuum drying oven to obtain a regenerated lithium iron phosphate positive electrode 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 for inducing 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 positive electrode material and the ion source inducing internal stress is 1:(0.14-0.32).

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

[0014] Preferably, in step (2), the carbon-based material is a 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. to 120° C., and the drying time is 12 to 24 hours.

[0017] In the present invention, internal stress induction is mainly achieved by rapidly heating the sodium to form an internal induction force to supplement the remaining Li to the missing Li position. At the same time, the addition of I can act as a reducing agent to reduce the Fe(III) occupying the Li position 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 positive electrode material by a simple internal stress induction method and by regulating the types of lithium salt and sodium salt, the ratio of lithium salt and sodium salt, the reaction time, and the reaction temperature. The regenerated lithium iron phosphate obtained by the method has excellent electrochemical properties and can reach commercial level;

[0020] (2) The rapid thermal shock method used in the present invention generates an ion source that induces internal stress to induce lithium ions to be added to the waste lithium iron phosphate. At the same time, sodium doping 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 waste lithium iron phosphate positive electrode materials, but also achieve fine control of the Na doping content of RLFP samples, making it easy to achieve large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 These 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 the RLFP-N with a scale of 1 μm, and (b) is the SLFP with a scale of 500 nm;

[0023] Figure 2 It is the XRD image of the RLFP-N positive electrode material obtained after repair in Example 1 of the present invention and the SLFP used;

[0024] Figure 3 This is a rate performance diagram of the RLFP-N positive electrode 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 This is a long cycle performance diagram of the RLFP-N positive electrode material obtained after repair in Example 1 of the present invention and the SLFP used at a current density of 1C. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] Embodiment 1

[0028] A method for directly regenerating waste lithium iron phosphate by inducing internal stress, comprising the following steps:

[0029] (1) 0.395 g SLFP, 0.259 g NaI, and 0.100 g LiI (the molar ratio of the three is 1:0.28:0.12) were placed in a mortar and ground 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 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.

[0039] Embodiment 3

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

[0041] (1) 0.395 g SLFP, 0.185 g Na2CO3, and 0.055 g Li2CO3 (the 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) The powder I obtained by grinding in step (1) is wrapped in a carbon boat 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 900°C, and the heating time is 60s; after heating, the powder II is cooled, washed with distilled water to remove salt, and dried in a vacuum oven at 90°C for 18h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material.

[0043] 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 127 mAh g at a current density of 1C. -1 The discharge capacity.

[0044] Embodiment 4

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

[0046] (1) 0.395 g SLFP, 0.060 g NaOH, and 0.024 g LiOH (the 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) The powder I obtained by grinding in step (1) is wrapped with carbon felt and subjected to rapid Joule heating sintering, that is, rapid thermal shock is performed in an argon atmosphere to induce internal stress to obtain powder II, the heating temperature is 1100°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 80°C for 20h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material.

[0048] 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 139 mAh g at a current density of 1C. -1 The discharge capacity.

[0049] Embodiment 5

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

[0051] (1) 0.395 g SLFP, 0.300 g NaI, and 0.013 g LiF (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;

[0052] (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 an argon / hydrogen mixed gas atmosphere to induce internal stress to obtain powder II, the heating temperature is 800°C, and the heating time is 100s; after heating, the powder II is cooled, washed with distilled water to remove salt, and dried in a vacuum oven at 60°C for 24h to obtain a sample, which is the regenerated lithium iron phosphate positive electrode material.

[0053] 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 133 mAh g at a current density of 1C. -1 The discharge capacity.

Claims

1. A method for direct regeneration of waste lithium iron phosphate by internal stress induction, characterized in that: The following steps are involved: (1) mixing and grinding waste lithium iron phosphate positive electrode material, a lithium source and an ion source that induces internal stress according to a certain molar ratio to obtain powder I; (2) The powder I obtained in step (1) is wrapped with a carbon-based material, and then subjected to rapid Joule heating sintering to induce internal stress to obtain powder II; powder II is desalted using deionized water at room temperature, and then dried in a vacuum drying oven to obtain a regenerated lithium iron phosphate positive electrode material.

2. The method for direct regeneration of waste lithium iron phosphate by internal stress induction according to claim 1, characterized in that: 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 direct regeneration of waste lithium iron phosphate by internal stress induction according to claim 1 or 2, characterized in that: In step (1), the ion source for inducing internal stress is one or more of sodium iodide, sodium chloride, sodium carbonate, and sodium hydroxide.

4. A method for direct regeneration of waste lithium iron phosphate by internal stress induction according to claim 1 or 2, characterized in that: In step (1), the molar ratio between the waste lithium iron phosphate positive electrode material and the ion source inducing internal stress is 1:(0.14-0.32).

5. A method for direct regeneration of waste lithium iron phosphate by internal stress induction according to claim 1 or 2, characterized in that: In step (1), the molar ratio between the waste lithium iron phosphate positive electrode material and the lithium source is 1:(0.06-0.16).

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

7. A method for direct regeneration of waste lithium iron phosphate by internal stress induction 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 argon / hydrogen mixed atmosphere.

8. A method for direct regeneration of waste lithium iron phosphate by internal stress induction 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.

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