Direct regeneration technology of waste lithium iron phosphate positive electrode material

Abstract

The lithium iron phosphate battery has the characteristics of small volume, high energy density, good safety and the like, so that the lithium iron phosphate battery is always widely applied to the fields of electric automobiles and energy storage. Along with the increase of the service life, the scrap quantity of the lithium iron phosphate battery is increasing year by year. Therefore, how to efficiently and environment-friendly recycle the waste lithium iron phosphate battery is very important. The invention designs a direct regeneration technology of a lithium iron phosphate positive electrode material, which comprises the following steps: uniformly stirring waste lithium iron phosphate powder, a silane coupling agent with a reducing group and a lithium source in deionized water, transferring into a reaction kettle, and regenerating lithium iron phosphate by a hydrothermal method. The reducing group on the silane coupling agent can reduce Fe (III) into Fe (II), and at the same time, a SiO2 coating is formed to prevent the active substance from being in direct contact with the electrolyte. The method is simple to operate, low in energy consumption and free of additional pollution, so that the method for directly regenerating the lithium iron phosphate positive electrode material by using the silane coupling agent is more economical and environment-friendly.

Description

[0001] Technical field: The present invention belongs to the field of waste lithium-ion battery recycling, and specifically relates to a direct regeneration technology for waste lithium iron phosphate positive electrode materials. Background technology:

[0002] Lithium iron phosphate batteries have gradually become an important part of the power battery field due to their high safety, good stability, economy, and environmental protection. Due to the large-scale production and application of lithium iron phosphate batteries, the scrap volume of lithium iron phosphate batteries is increasing year by year. If they are discarded or buried at will without effective treatment and recycling, it may cause waste of resources and environmental pollution. At present, common recycling methods are divided into three categories: wet method, pyrolysis and direct regeneration. Pyrolysis recycling is to recover the metal in the form of metal compounds by high-temperature calcination. Although this method has a simple process and a short process, it consumes a lot of energy during the calcination process and is prone to produce a large amount of waste gas and waste residue. Wet recovery is to selectively leach the metal in the positive electrode material by acid, alkali or microorganisms, and then prepare the valuable metal compound or single substance by extraction separation or coprecipitation. Although this method has low energy consumption and can achieve a high metal extraction rate, it is easy to produce a large amount of leaching wastewater during the recovery process. Compared with lithium cobalt oxide and ternary positive electrode materials, lithium iron phosphate positive electrode materials do not contain valuable metals such as cobalt and nickel, and the resulting recycled products are not economical. Therefore, the direct regeneration method of restoring the original electrochemical properties of the waste lithium iron phosphate positive electrode materials after certain treatment is more economical and environmentally friendly. The main reason for the failure of lithium iron phosphate batteries is the loss of lithium in long-term cycles, which leads to the attenuation of battery capacity, and the loss of lithium will cause the formation of Fe(III) in the block crystal structure, thereby causing Li-Fe anti-site defects. Therefore, by adding lithium sources to supplement lithium and using reducing agents to simultaneously repair anti-site defects, direct regeneration of lithium iron phosphate positive electrode materials can be achieved. Summary of the invention:

[0003] Based on the above problems, this paper proposes a direct regeneration technology for lithium iron phosphate positive electrode materials, which includes the following steps:

[0004] (1) Add 10 ml of deionized water to waste LiFePO4 positive electrode material powder, lithium salt, and silane coupling agent containing reducing groups and stir at room temperature for 1-6 hours;

[0005] (2) The liquid obtained in step (1) was transferred to a reactor for hydrothermal reaction, cooled, washed with deionized water for 3 times, centrifuged, dried in an oven at 60° C. for 12 h, and then ground to obtain regenerated LiFePO4 positive electrode material powder.

[0006] Preferably, in step (1), the lithium salt used can be one of lithium chloride, lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, etc.

[0007] Preferably, the silane coupling agent in step (1) can be one of 3-aminopropyltriethoxysilane (KH550), N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KH792), N-(β-aminoethyl)-3-aminopropylmethyldimethoxysilane (KH602), and 3-aminopropylmethyldiethoxysilane (KH-902).

[0008] Preferably, in step (1), the mass ratio of lithium salt to waste LiFePO4 is 1:1 to 1:4.

[0009] Preferably, in step (1), the solid-to-liquid ratio of waste LiFePO4 to silane coupling agent is 10-40 g / L.

[0010] Preferably, in step (2), the temperature of the hydrothermal reaction is 100-300°C.

[0011] Preferably, in step (2), the hydrothermal reaction time is 1-12 h.

[0012] In summary, the present invention discloses a technology for directly regenerating waste lithium iron phosphate using a silane coupling agent. The regeneration result is optimized by adjusting the amount of lithium source, silane coupling agent, and the temperature and time of the hydrothermal reaction. The reducing group on the silane coupling agent can reduce Fe(III) to Fe(II), and while repairing waste LiFePO4, a SiO2 coating is formed by chemical coupling. The SiO2 layer can prevent direct contact between the electrolyte and the positive electrode material, and inhibit the corrosion of the electrolyte to the positive electrode material during the cycle. Description of the drawings:

[0013] Figure 1 This is the XRD diagram of the waste lithium iron phosphate positive electrode material before and after repair in Example 1.

[0014] Figure 2 (a) The XPS spectrum of Fe in the waste lithium iron phosphate in Example 2. (b) The XPS spectrum of Fe in the regenerated lithium iron phosphate positive electrode material.

[0015] Figure 3 (a) is the XPS spectrum of F after 50 cycles of commercial lithium iron phosphate in Example 3. (b) is the XPS spectrum of F after 50 cycles of regenerated lithium iron phosphate.

[0016] Figure 4 It is the cycling performance of the lithium iron phosphate positive electrode material regenerated in Example 4 at 1C current density. Specific implementation method:

[0017] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and accompanying drawings:

[0018] Embodiment 1:

[0019] This embodiment provides a direct regeneration technology for waste lithium iron phosphate positive electrode materials, which specifically includes the following steps:

[0020] (1) 12.5 mg LiCl and 25 mg waste LiFePO4 were dissolved in 10 ml deionized water, and then 800 μl 3-aminopropyltriethoxysilane (KH550) was added and stirred at room temperature for 1 h.

[0021] (2) The solution was transferred to a reactor and subjected to hydrothermal treatment at 160° C. for 6 h. The solution after the reaction was washed with deionized water for multiple times, filtered, and dried to obtain regenerated LiFePO4. Figure 1 From the XRD diagrams of the waste lithium iron phosphate positive electrode material before and after repair, it can be seen that the FePO4 phase disappears in the repaired LiFePO4 positive electrode material.

[0022] Embodiment 2:

[0023] A direct regeneration technology for waste lithium iron phosphate positive electrode materials includes the following implementation steps:

[0024] (1) 25 mg LiCl and 25 mg waste LiFePO4 were dissolved in 10 ml deionized water, and then 1200 μl 3-aminopropyltriethoxysilane (KH550) was added and stirred at room temperature for 1 h.

[0025] (2) The solution was transferred to a reactor and subjected to hydrothermal treatment at 200° C. for 2 h. The solution after the reaction was washed with deionized water for multiple times, filtered, and dried to obtain regenerated LiFePO4. Figure 2 The XPS spectrum shows the disappearance of Fe(III) and the recovery of the composition and structure of the regenerated LiFePO4 positive electrode material.

[0026] Embodiment 3:

[0027] This embodiment is similar to Embodiment 2, except that LiCl in Step 1 is replaced with Li2CO3, and other conditions remain unchanged. Figure 3 By comparing the XPS spectra of F in commercial lithium iron phosphate and regenerated lithium iron phosphate after 50 cycles, it can be seen that the LiF concentration of the regenerated LiFePO4 positive electrode material decreases after cycling, indicating that LiF formation is inhibited.

[0028] Embodiment 4:

[0029] This embodiment is based on the embodiment 2, except that KH550 in step 1 is replaced by KH602, and the other conditions remain unchanged. The regenerated LiFePO4 positive electrode material powder is slurried with Super P and PVDF (polyvinylidene fluoride) in a mass ratio of 8:1:1, and the obtained slurry is evenly coated on aluminum foil. After drying in a vacuum drying oven at 60°C for 12 hours, the slurry is cut into pieces with an area of ​​1.13 cm 2 The metal lithium sheet was used as the negative electrode sheet, 1M LiPF6 was dissolved in a solution with a volume ratio of EC (ethylene carbonate) : DMC (dimethyl carbonate) = 3:7 as the electrolyte, and button cells were assembled in a glove box. The battery test was carried out with the voltage controlled at 2.5-4.2V. Figure 4 It can be seen that the cycle performance of the regenerated LiFePO4 positive electrode material has been greatly improved.

Claims

1. A direct regeneration technology for lithium iron phosphate positive electrode material, characterized in that: By replenishing the lithium source and adding a silane coupling agent with a reducing group to reduce Fe(III) to Fe(II), the original performance of the waste lithium iron phosphate positive electrode material can be restored.

2. This patent relates to a technology that can repair waste lithium iron phosphate positive electrode materials, and the uniform SiO2 coating formed by chemical coupling of silane coupling agents can prevent direct contact between active substances and electrolytes, inhibiting the corrosion of electrolytes on positive electrode materials during the cycle. The steps of repairing waste lithium iron phosphate positive electrode materials using this technology include: Step 1: Add 10 ml of deionized water to waste LiFePO4 positive electrode material powder, lithium salt, and silane coupling agent containing reducing groups and stir at room temperature for 1-6 hours; Step 2: The liquid obtained in step 1 is transferred to a reactor for hydrothermal reaction, cooled, centrifuged, washed with deionized water for 3 times, and dried in an oven at 60°C for 12 hours. After uniform grinding, the regenerated LiFePO4 positive electrode material powder is obtained.

3. The direct regeneration technology of waste lithium iron phosphate positive electrode material according to claim 2, characterized in that: In step 1, the lithium salt used can be one of lithium chloride, lithium hydroxide, lithium carbonate and lithium dihydrogen phosphate.

4. The direct regeneration technology of waste lithium iron phosphate positive electrode material according to claim 2, characterized in that: In step 1, the silane coupling agent used can be one of 3-aminopropyltriethoxysilane (KH550), N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KH792), N-(β-aminoethyl)-3-aminopropylmethyldimethoxysilane (KH602), and 3-aminopropylmethyldiethoxysilane (KH-902).

5. The direct regeneration technology of waste lithium iron phosphate positive electrode material according to claim 2, characterized in that: In step 1, the mass ratio of lithium salt to waste lithium iron phosphate positive electrode material is 1:1 to 1:

4.

6. The direct regeneration technology of waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: In step 2, the temperature of the hydrothermal reaction is 100-300°C.

7. The direct regeneration technology of waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: In step 2, the hydrothermal reaction time is 1-12 h.

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