Difunctional organic lithium salt, preparation method thereof and application of difunctional organic lithium salt in regeneration of waste lithium iron phosphate

Abstract

The invention relates to a difunctional organic lithium salt, a preparation method thereof and application of the difunctional organic lithium salt in regeneration of waste lithium iron phosphate. Firstly, benzene-containing organic molecules, inorganic lithium salt, an organic solvent and the like are used as raw materials, difunctional organic lithium salt with a lithium carboxylate (COO-Li +) and lithium phenolate (Ph-O-Li +) composite structure is prepared, then the waste lithium iron phosphate positive electrode material and the difunctional organic lithium salt are evenly mixed according to a certain proportion, the obtained mixture is heated to 650-800 DEG C to be subjected to high-temperature calcination, and the waste lithium iron phosphate positive electrode material is obtained. And repeatedly cleaning with absolute ethyl alcohol and deionized water, and drying to finally obtain the regenerated lithium iron phosphate which has a crystal structure equivalent to that of the original lithium iron phosphate and has high specific capacity, excellent rate capability and good cycle stability. In the regeneration process of the waste lithium iron phosphate, the difunctional organic lithium salt can supplement lithium vacancies and realize carbon coating, so that the defects of the waste lithium iron phosphate are repaired, the regenerated lithium iron phosphate can be directly used for manufacturing battery positive electrodes and lithium batteries, and an important support is provided for sustainable development of the lithium battery industry.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries and composite materials, and particularly relates to a bifunctional organic lithium salt, a preparation method thereof and application of the bifunctional organic lithium salt in recycling waste lithium iron phosphate. BACKGROUND

[0002] With the gradual transformation of global energy structure towards clean and low-carbon, as the core component of new energy vehicles and energy storage systems, the market size of lithium ion batteries presents explosive growth, and the problem of waste lithium battery treatment gradually emerges. The finiteness of strategic resources such as lithium, iron and phosphorus and the environmental risks (such as heavy metal pollution, electrolyte leakage, etc.) caused by improper disposal of waste batteries make efficient and green battery recycling technology a key link in the sustainable development of the industrial chain.

[0003] Lithium battery recycling mainly targets the positive electrode material. The current mainstream waste lithium iron phosphate LiFePO4 positive electrode material recycling technology includes pyrometallurgical method, hydrometallurgical method and direct regeneration method. Although the pyrometallurgical method has a simple process flow, it has extremely high energy consumption (>1500℃), and lithium is easy to volatilize and lose during high-temperature recycling, resulting in a lithium recovery rate usually lower than 60%. Although the hydrometallurgical method can achieve a high lithium recovery rate (up to more than 90%), the use of strong corrosive reagents leads to rising recycling costs, and more importantly, iron, phosphorus and other elements in waste batteries are recycled in the form of low-value-added products. In comparison, the direct regeneration method restores the performance of the material through lithium compensation and lattice repair, and has the advantages of low energy consumption and high value, and is considered as the most potential technical path for industrialization. The solid-phase sintering process in the common direct regeneration technology on the market has the following key defects: ① Traditional inorganic lithium salt (such as Li2CO3, LiOH) can only provide lithium source compensation and cannot solve the problem of the increase of Fe 3+ oxidation state ratio (XPS analysis shows that Fe 3+ / Fe 2+ >2:1) of LiFePO4 caused by long-term cycling. High-valence Fe 3+ will destroy the intrinsic electron conduction path of the material, resulting in a significant decrease in the first efficiency of the regenerated material (<90%) and the deterioration of the rate performance (2C discharge capacity <110mAh / g). Although the introduction of a reducing agent (such as H2, glucose) can repair Fe 2+ activity, it increases the process complexity and impurity risk.

[0004] ② The thermal decomposition temperature of inorganic lithium salt is high (such as Li2CO3 needs >720℃), so the entire treatment process is at high temperature (>600℃) for a long time, which not only causes serious lithium volatilization loss (recovery rate <85%), but also aggravates Fe 3+Oxidation tends to generate inactive Fe2O3 impurities (XRD characteristic peak 2θ=33.2°), and metal impurities such as Al 3+ , Cu 2+ , etc. form insulating phase LiAlO2 (XRD 2θ=18.5°) at high temperature, further hindering lithium ion transmission.

[0005] ③The existing technology often relies on external carbon source (such as sucrose, PVDF carbon residue) to achieve carbon coating, but the carbon layer is unevenly distributed (SEM shows agglomeration phenomenon), and the interface bonding force with LiFePO4 particles is weak (peeling strength <1.5N / cm), which is easy to fall off during the cycle process, resulting in poor long-term stability of the electrode (200-week capacity retention rate <80%), which seriously restricts the large-scale application.

[0006] In summary, it is urgent to develop a suitable lithium salt to achieve multiple purposes such as supplementing lithium vacancies and reducing trivalent iron, which has great significance for the recycling of lithium ion batteries and the development of lithium battery industry. SUMMARY

[0007] The present application mainly aims at the problems of resource waste, environmental pollution, complex recycling process, and low economic benefit of recycling of the current waste lithium battery, and provides a brand new bifunctional organic lithium salt, which utilizes efficient and low-cost regenerated waste lithium iron phosphate positive electrode material, and promotes the healthy and sustainable development of lithium battery and power battery, new energy vehicle and other industries.

[0008] The bifunctional organic lithium salt is obtained by reaction of a benzene-containing organic molecule and an inorganic lithium salt, and the bifunctional organic lithium salt has a complex structure of lithium carboxylate (COO - Li + ) and lithium phenoxide (Ph-O-Li + ).

[0009] Specifically, the preparation method of the bifunctional organic lithium salt comprises the following steps: mixing the benzene-containing organic molecule and the inorganic lithium salt in proportion in the presence of an organic solvent to make them fully react, and obtaining the target product, the bifunctional organic lithium salt, after solid-liquid separation.

[0010] More specifically, first, the benzene-containing organic molecule is uniformly mixed with the organic solvent, then the inorganic lithium salt is added in batches for reaction, and finally the solid product is centrifuged and dried.

[0011] In the above scheme, the benzene-containing organic molecule is lithium salicylate. The benzene ring itself is a rigid and stable structure, which can enhance the thermal stability and chemical stability of the entire organic lithium salt molecule as the core skeleton of the molecule, facilitating storage and subsequent use. The core purpose of "containing benzene" is to utilize the unique electronic effect (conjugation effect) of the benzene ring to stabilize the structure and utilize its rigid skeleton to create a new reagent with superior performance, which has both lithium supplementing and reducing functions. If an aliphatic molecule (such as citric acid) without a benzene ring is used, it cannot form this stable lithium phenoxide structure, and the technical effects of the present application cannot be achieved.

[0012] In the above scheme, the inorganic lithium salt is selected from at least one of lithium hydride and lithium hydroxide, preferably lithium hydride. The inorganic lithium salt can provide lithium ions (Li + ), which is the most direct effect. In addition, the lithium ions provided by the inorganic lithium salt (such as LiH, LiOH) undergo acid-base neutralization or similar reactions with the acidic hydrogen (from the carboxyl group -COOH and the phenolic hydroxyl group -OH) in the benzene-containing organic molecule (such as salicylic acid), generating the target product - the bifunctional organic lithium salt. The inorganic lithium salt is the "engine" of the synthesis reaction, which "installs" lithium elements onto the organic molecular skeleton through chemical reactions, thereby generating the final product - the bifunctional organic lithium salt with specific structure and function. The selection of the inorganic lithium salt and the control of the reaction conditions affect the success or failure of the synthesis reaction and the quality of the product.

[0013] In the above scheme, the organic solvent is selected from at least one of tetrahydrofuran and anhydrous ethanol, preferably tetrahydrofuran.

[0014] In the process of synthesizing the bifunctional organic lithium salt, the molar ratio of the benzene-containing organic molecule to the inorganic lithium salt is 0.5-3.0.

[0015] In the process of synthesizing the bifunctional organic lithium salt, stirring is also required, and the stirring speed is 300-800 rad / s.

[0016] After the reaction is completed, the mixture is first centrifuged, and then the solid product is placed in a vacuum drying oven for sufficient drying, with the drying temperature being 60-120℃.

[0017] The present application also provides the use of the above-mentioned bifunctional organic lithium salt in regenerating waste lithium iron phosphate positive electrode materials.

[0018] Specifically, the specific method of the application includes: mixing the bifunctional organic lithium salt and the waste lithium iron phosphate, then grinding thoroughly, and then sintering at high temperature under a protective atmosphere to obtain regenerated lithium iron phosphate that can be used to make battery positive electrodes.

[0019] In the above scheme, the proportion of the bifunctional organic lithium salt in the mixture is 5wt%-15wt%.

[0020] In the above scheme, the protective atmosphere is an inert atmosphere such as argon or nitrogen.

[0021] In the above scheme, high-temperature sintering is performed by one-step sintering, the sintering temperature is 650-800 DEG C, the sintering time is 6-14 h, and the heating rate is 2 DEG C / min-5 DEG C / min.

[0022] In the above scheme, after sintering, the solid product is naturally cooled to room temperature, then repeatedly washed with ultrapure water and anhydrous ethanol, and then fully vacuum dried at 50-80 DEG C to obtain the regenerated lithium iron phosphate LiFePO4 cathode material with complete olivine structure.

[0023] The core of the present application is to realize the "lithium supplement-reduction" synergistic regeneration by molecular design and process optimization, and finally efficiently and low-cost recycle the waste lithium iron phosphate material. Compared with the traditional recycling method, the progress of the present application mainly lies in the following points: (1) The multifunctional organic lithium salt is used to directly regenerate the waste lithium iron phosphate cathode material, and the whole process has the advantages of low energy consumption, high efficiency, environmental friendliness, simple process, easy to scale, etc. More importantly, the lithium iron phosphate material obtained after regeneration has the same crystal structure as the original lithium iron phosphate, and has high specific capacity, excellent rate performance and good cycle stability and other electrochemical properties.

[0024] (2) The bifunctional organic lithium salt provided by the present application can supplement lithium vacancies while realizing carbon coating, thereby repairing the defects of the waste lithium iron phosphate, and ensuring that the regenerated lithium iron phosphate cathode material has excellent electrochemical performance.

[0025] (3) The process flow of the present application has significant scalability, not only simple synthesis steps and strong operability, but also low cost, and is very suitable for large-scale production, providing an efficient and environmentally friendly solution for the recycling of waste lithium ion batteries, and providing important support for the sustainable development of lithium ion battery and new energy automobile industry.

[0026] (4) The lithium iron phosphate regenerated by the method of the present application can be directly used to make lithium ion battery cathode and lithium battery, and the lithium battery product has the characteristics of high specific capacity, good rate performance, good reversibility, long cycle life, etc., and has broad application prospects in the field of large-scale energy storage equipment. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The principle diagram for regenerating the waste lithium iron phosphate cathode material by using the bifunctional organic lithium salt.

[0028] Figure 2 The infrared spectrum of the bifunctional organic lithium salt.

[0029] Figure 3XRD spectra of waste lithium iron phosphate and regenerated lithium iron phosphate cathode materials.

[0030] Figure 4 Raman spectra of waste lithium iron phosphate and regenerated lithium iron phosphate cathode materials.

[0031] Figure 5 XPS spectra of waste lithium iron phosphate and regenerated lithium iron phosphate cathode materials.

[0032] Figure 6 Electrochemical performance graphs of waste lithium iron phosphate and regenerated lithium iron phosphate cathode materials. DETAILED DESCRIPTION

[0033] In order for those skilled in the art to fully understand the technical solutions and beneficial effects of the present application, further detailed description will be made below in combination with specific embodiments. It needs to be emphasized that the following embodiments are only a part of the present application, and on this basis, there can be many other embodiments of the present application, and any improvement made based on these embodiments will fall within the protection scope of the present application.

[0034] The raw materials in the present application are all ordinary commercially available, and those not specially mentioned are all analytical pure.

[0035] With the rapid development of electric vehicles and energy storage markets, the demand for lithium ion batteries has increased dramatically, and the recycling problem of waste lithium ion batteries has become increasingly prominent. Lithium iron phosphate LiFePO4 as an important cathode material is widely used in batteries due to its high safety, long cycle life and low cost. At present, the regeneration of waste lithium iron phosphate cathode material faces many difficulties and challenges, including complex recycling process, high energy consumption and performance degradation of regenerated materials. Traditional recycling methods usually use hydrometallurgy or pyrometallurgy process, which not only has high energy consumption, but also may produce harmful waste, making it difficult to meet the requirements of green and sustainable development.

[0036] In order to solve these problems, the present application provides a bifunctional organic lithium salt which can be used for directly regenerating waste lithium iron phosphate cathode material, and the preparation method thereof comprises: S1. Dissolve lithium salicylate in organic solvents such as tetrahydrofuran, ethanol, etc., and stir uniformly at a speed of 300-800 rad / s to form a mixed solution.

[0037] S2. Add inorganic lithium salts such as lithium hydride and lithium hydroxide to the mixed solution in step S1 in batches, and stir uniformly at a speed of 300-800 rad / s to form a milky white suspension. The molar ratio of benzene organic molecules to inorganic lithium salts in the suspension is controlled between 0.5-3.0, such as 0.5, 0.63, 0.85, 0.98, 1.15, 1.8, 2.1, 2.65, 3.0, etc.

[0038] S3. Centrifugal separation of the suspension described in step S2, collect the solid product and transfer to a vacuum drying oven (P < 10 Pa) and dry at 60-120℃ for 8-24h to obtain an organic lithium salt with the dual function of lithium compensation and reduction.

[0039] The dual functional organic lithium salt can be used to directly regenerate waste lithium iron phosphate cathode material, and the specific method comprises: S4. According to the mass percentage ratio of 5wt%-15wt%:95wt%-85wt%, mix the dual functional organic lithium salt with waste lithium iron phosphate and grind thoroughly, and transfer the obtained mixed powder to a tube furnace, heat from room temperature to 650-800℃ at a heating rate of 2℃ / min-5℃ / min in an inert atmosphere of argon, nitrogen, etc., and keep sintering at this temperature for 6-14h, and then naturally cool to room temperature. In some embodiments, the amount of dual functional organic lithium salt is 5wt%, 7.5wt%, 9.2wt%, 11wt%, 15wt%, etc., and the amount of waste lithium iron phosphate is 95wt%, 92.5wt%, 90.8wt%, 89wt%, 85wt%, etc.

[0040] S5. Take out the sintered product and wash repeatedly with ultrapure water and anhydrous ethanol several times, and then transfer it to a vacuum drying oven (P < 10 Pa) and dry at 50-80℃ for 8-24h to obtain regenerated lithium iron phosphate LiFePO4 cathode material with complete olivine structure.

[0041] Example 1 The organic molecule containing benzene selected in this embodiment is lithium salicylate, the organic solvent selected is tetrahydrofuran, and the inorganic lithium salt selected is lithium hydride.

[0042] The specific method for preparing a dual functional organic lithium salt and regenerating waste lithium iron phosphate cathode material using these raw materials is as follows: 1) Dissolve 0.9g of lithium salicylate in 30mL of tetrahydrofuran solvent, stir at a speed of 400rad / s for about 15 minutes until the solution is clear.

[0043] 2) Add 0.059g of lithium hydride to the mixed solution obtained in the previous step in three portions, and stir at a speed of 500rad / s for about 15h until the reaction is complete to obtain a blended suspension.

[0044] 3) Centrifugal separation of the suspension prepared in the previous step, and the solid material obtained is transferred to a vacuum drying oven (P < 10 Pa) and dried at 60℃ for 12h to obtain a yellowish powder, which is the dual functional organic lithium salt or lithium compensation agent.

[0045] 4) Accurately weigh 24 mg of the yellowish powder prepared in the previous step, 276 mg of the waste lithium iron phosphate powder (i.e., S-LFP in the figure), and add them to a mortar for grinding, and then press into a tablet.

[0046] 5) Transfer the tablet prepared in the previous step to a tube furnace, and perform one-step high-temperature sintering by filling argon. The sintering temperature is 700°C, the heating rate is 5°C / min, the sintering time is 8 h, and after sintering, the temperature is naturally cooled to room temperature.

[0047] 6) Take out the sintered product and grind it with a mortar to obtain a powder, sequentially wash it with anhydrous ethanol and deionized water, and then transfer it to a vacuum drying oven (P < 10 Pa) for vacuum drying at 60°C for 10 h, to finally obtain a regenerated lithium iron phosphate powder (i.e., R-LFP in the figure).

[0048] Example 2 Example 2 is basically the same as Example 1, except that in step 4), 15 mg of the yellowish powder is mixed with 285 mg of the waste lithium iron phosphate powder (of the same batch as in Example 1, and the same below).

[0049] Example 3 Example 3 is basically the same as Example 1, except that in step 4), 30 mg of the yellowish powder is mixed with 270 mg of the waste lithium iron phosphate powder.

[0050] Example 4 Example 4 is basically the same as Example 1, except that in step 5), the sintering temperature is reduced to 650°C.

[0051] Example 5 Example 5 is basically the same as Example 1, except that in step 5), the sintering temperature is increased to 750°C.

[0052] Example 6 Example 5 is basically the same as Example 1, except that in step 5), the sintering temperature is increased to 800°C.

[0053] Comparative Example 1 1) Accurately weigh 0.9 g of lithium salicylate, 276 mg of the waste lithium iron phosphate powder, and add them to a mortar for grinding, and then press into a tablet.

[0054] 2) Transfer the tablet prepared in the previous step to a tube furnace, and perform one-step high-temperature sintering by filling argon. The sintering temperature is 700°C, the heating rate is 5°C / min, the sintering time is 8 h, and after sintering, the temperature is naturally cooled to room temperature.

[0055] 3) Take out the sintered product and grind it in a mortar to obtain powder. Wash it with anhydrous ethanol and deionized water in sequence, then transfer it to a vacuum drying oven (P<10Pa) and dry it at 60℃ for 10h to finally obtain regenerated lithium iron phosphate powder.

[0056] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that lithium salicylate in step 1) is replaced with an equimolar amount of lithium tartrate.

[0057] Comparative Example 3 Comparative Example 3 is basically the same as Comparative Example 1, except that lithium salicylate is replaced with an equimolar amount of lithium tartrate.

[0058] To fully understand the structure and properties of the products obtained in each step of the various embodiments and comparative examples of the present invention, samples were taken and subjected to a series of tests, including infrared (IR), X-ray diffraction (XRD), Raman spectroscopy, and XPS. The test results of Example 1 are used as an example for explanation below.

[0059] Figure 2 The infrared spectrum of the bifunctional organolithium salt prepared in Example 1 is shown in Figures a and b. As can be seen from Figures a and b: (1) In the range of 1800-3000cm -1 Within the range, organolithium salts at 1561 cm⁻¹ -1 and 1536cm -1 Two characteristic peaks appeared at the location, namely lithium carboxylate (COO). - Li + ) symmetry (V s ) and the opposite (V) as ) Absorption of stretching vibration characteristics.

[0060] (2) In the range of 4000-3000cm -1 Within the range, the raw material lithium salicylate is at 3370cm. -1 and 3098cm -1 The stretching vibration peak of the hydroxyl group (-OH) disappears in the organolithium salt, confirming that the hydrogen of the phenolic hydroxyl group is replaced by lithium, forming lithium phenoxy (Ph-O-Li). + ).

[0061] (3) Organic lithium salts at 3580cm -1 and 3550cm -1 The weak peak at the position may originate from trace amounts of residual hydroxyl groups or Li-O vibrations, but its intensity is significantly reduced, further supporting the conclusion that a substitution reaction has occurred.

[0062] (4) Lithium salicylate at 677cm -1 and 460cm -1The Li-O vibration peak in the original LiPF6 disappeared in the organic lithium salt, indicating that the coordination mode of lithium changed after the reaction, forming a new complex structure of lithium carboxylate and lithium phenoxide.

[0063] Figure 3 XRD patterns of the waste lithium iron phosphate in Example 1 and the regenerated lithium iron phosphate using the bifunctional organic lithium salt. As can be seen from the figure, compared with the lithium iron phosphate standard card, the waste lithium iron phosphate contains impurity peaks at positions of 18°C, 23°C, 31°C, etc.; while the regenerated lithium iron phosphate using the bifunctional organic lithium salt is completely matched with the standard card (PDF #83-2092), and its main peaks are respectively located at positions of 17°C, 20°C, 25°C, 29°C, 35°C, etc., which is a typical olivine structure, and this result fully proves that the waste lithium iron phosphate is repaired.

[0064] Figure 4 Raman spectra of the waste lithium iron phosphate in Example 1 and the regenerated lithium iron phosphate using the bifunctional organic lithium salt. As can be seen from the figure, both S-LFP and R-LFP materials appear characteristic peaks at about 1350 cm -1 (D peak) and 1580 cm -1 (G peak), which respectively correspond to the disordered structure (sp 3 hybrid carbon) and the ordered graphite structure (sp 2 hybrid carbon) in the carbon material. The ID / IG value (D peak and G peak intensity ratio) of the waste lithium iron phosphate is 1.04, while the ID / IG value of the regenerated lithium iron phosphate is significantly reduced to 0.96. The reduction of the ID / IG value indicates that after the regeneration treatment of the bifunctional organic lithium salt, the graphitization degree of the carbon component in the waste lithium iron phosphate material is improved, and the structural order is enhanced.

[0065] Figure 5 XPS spectra of the waste lithium iron phosphate in Example 1 and the regenerated lithium iron phosphate using the bifunctional organic lithium salt. As can be seen from the figure, the peaks of the waste lithium iron phosphate at 711.3 eV and 725.1 eV respectively represent the trivalent iron in Fe 2p 3 / 2 and Fe 2p 1 / 2 . This indicates that the waste lithium iron phosphate contains a large amount of trivalent iron, which is mainly caused by the long-term cycle charging and discharging of the battery. The peaks of the regenerated lithium iron phosphate using the bifunctional organic lithium salt at positions of 710.8 eV and 723.8 eV respectively represent the divalent iron in Fe 2p 3 / 2 and Fe 2p 1 / 2 , and there is no peak representing trivalent iron. This proves that the trivalent iron in the waste lithium iron phosphate is reduced by the bifunctional organic lithium salt, reducing the lithium-iron anti-site, so that the regenerated lithium iron phosphate is obtained.

[0066] Based on the above analysis and test results, the following conclusions are obtained:Figure 1 The principle diagram of the bifunctional organic lithium salt regenerating waste lithium iron phosphate cathode material. After the waste lithium iron phosphate powder is mixed with the bifunctional organic lithium salt, the two are fully contacted, and under the condition of high-temperature sintering, the bifunctional organic lithium salt can fill the lithium vacancies of the waste lithium iron phosphate, and the phenolic oxygen lithium functional group in the bifunctional organic lithium salt has a certain reduction effect, which can reduce the trivalent iron to divalent iron. High-temperature sintering can reduce the lithium-iron anti-site, and the bifunctional organic lithium salt also has a certain carbon-coating function. After high-temperature sintering, the material is cleaned alternately with deionized water and anhydrous ethanol to wash off the excess lithium salt on the surface, and then dried to obtain regenerated lithium iron phosphate cathode material with a typical olivine structure.

[0067] Application Example The regenerated lithium iron phosphate prepared in Example 1 was used as an active material to prepare a cathode of a lithium ion battery. The specific method was as follows: the active material, acetylene black and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, and then coated on an aluminum foil, and then dried to obtain a cathode sheet; in the same way, the waste lithium iron phosphate in Example 1 was used to prepare a cathode sheet as a control; two kinds of cathode sheets and pure lithium sheet electrodes were assembled into half-cells, and then electrochemical performance tests were carried out, and the results are shown in Figure 6 .

[0068] Figure 6 The rate performance test results of a show that the discharge specific capacity of the regenerated lithium iron phosphate (0.2C: 165.87 mAh / g, 0.5C: 160.0 mAh / g, 1C: 153.23 mAh / g, 2C: 144.4 mAh / g, 5C: 129.6 mAh / g) is significantly better than that of the waste lithium iron phosphate (0.2C: 80.5 mAh / g, 0.5C: 79.4 mAh / g, 1C: 72.0 mAh / g, 2C: 63.2 mAh / g, 5C: 51.2 mAh / g), and when the rate is switched from 5C back to 0.2C, the capacity of the regenerated lithium iron phosphate can recover to 166.7 mAh / g, indicating that its excellent rate performance meets the use standard of commercial lithium iron phosphate.

[0069] Figure 6 b shows the charge-discharge curves of the regenerated lithium iron phosphate at 0.2C to 5C, and the clear and stable platform in the figure reflects the good redox reaction reversibility, proving that lithium ions can be efficiently inserted and extracted.

[0070] Figure 6The 5C long cycle test results in c further prove that the discharge specific capacity of the regenerated lithium iron phosphate is much higher than that of the waste lithium iron phosphate, and the regenerated lithium iron phosphate still maintains a capacity retention rate of up to 91.1% after 500 cycles, showing excellent cycle stability. Referring to the above method, the regenerated lithium iron phosphate powders prepared in examples 2-6 and comparative examples 1-3 are assembled into half batteries, and then electrochemical performance tests are respectively carried out, and the results are as follows:

[0071] As can be seen from the above, the regenerated lithium iron phosphate provided by various embodiments of the present application has been significantly improved in terms of rate performance, reaction reversibility and cycle stability, proving that the dual-functional organic lithium salt and the corresponding lithium iron phosphate regeneration process provided by the present application effectively repair the key structural defects such as the amount of lithium deficiency, the high content of trivalent iron (Fe 3+ ) and the excessive Li / Fe anti-site in the waste lithium iron phosphate positive electrode material, thereby endowing the regenerated lithium iron phosphate material with excellent comprehensive electrochemical performance.

Claims

1. A bifunctional organolithium salt characterized in that: The bifunctional organolithium salt has both a lithium carboxylate COO - Li + and a lithium phenoxide Ph-O-Li + complex structure.

2. A process for the preparation of the bifunctional organolithium salt of claim 1, characterized in that The method comprises: mixing and reacting a benzene-containing organic molecule with an inorganic lithium salt in the presence of an organic solvent, and obtaining a bifunctional organic lithium salt after solid-liquid separation.

3. The production method according to claim 2, characterized by: First, the benzene-containing organic molecule is mixed uniformly with the organic solvent, then the inorganic lithium salt is added in batches for reaction, and finally the solid product is separated by centrifugation and dried.

4. The production method according to claim 2, characterized by: The benzene-containing organic molecule is specifically lithium salicylate, the inorganic lithium salt is selected from at least one of lithium hydride and lithium hydroxide, and the organic solvent is selected from at least one of tetrahydrofuran and anhydrous ethanol.

5. The production method according to claim 2, wherein: The molar ratio of the benzene-containing organic molecule to the inorganic lithium salt is 0.5-3.

0.

6. The production method according to claim 3, characterized by: The raw materials need to be stirred during mixing and reaction, and the stirring speed is 300-800 rad / s; after the reaction is completed, the mixture is centrifuged, and then fully vacuum dried at 60-120℃.

7. The bifunctional organic lithium salt of claim 1 is used in the regeneration of waste lithium iron phosphate.

8. Use according to claim 7, wherein The application comprises: mixing the bifunctional organic lithium salt and the waste lithium iron phosphate, then fully grinding the mixture, sintering the obtained mixture at high temperature under a protective atmosphere, and obtaining regenerated lithium iron phosphate.

9. Use according to claim 8, wherein: The proportion of the bifunctional organic lithium salt in the mixture is 5wt%-15wt%.

10. The use according to claim 8, characterized in that: The protective atmosphere required for high-temperature sintering is selected from any one of argon and nitrogen, the sintering temperature is 650-800℃, the sintering time is 6-14h, the heating rate is 2℃ / min-5℃ / min, the sintering is naturally cooled to room temperature after completion, then the product is repeatedly washed with ultrapure water and anhydrous ethanol, and finally fully dried at 50-80℃, obtaining regenerated lithium iron phosphate with complete olivine structure.

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