A lithium iron ferrite lithium supplement and its preparation method

Abstract

The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a lithium ferrite lithium supplement and a preparation method thereof. The lithium ferrite lithium supplement comprises the following components: an iron salt, an organic ligand, a lithium salt, a regulator, and a biomass graphene quantum dot; first, defective Fe-MOFs are synthesized as a template, which is mixed with the lithium salt, the iron salt, and the biomass graphene quantum dot, and then calcined in a nitrogen atmosphere to obtain the lithium ferrite lithium supplement. As a synthesis template, Fe-MOFs can make the distribution of lithium ions uniform, reduce the local stress and volume change inside the battery. At the same time, the introduction of the biomass graphene quantum dot can improve the conductivity of the lithium supplement, and can synergistically act with Fe-MOFs to improve the overall performance of the lithium supplement, providing an efficient and green solution for the optimization of lithium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a lithium ferrite lithium supplement and a preparation method thereof. Background Art

[0002] Existing lithium-ion battery technologies face multiple challenges, including irreversible loss of lithium ions, structural degradation of electrode materials, and complex and costly preparation processes. During charge and discharge, some lithium ions are irreversibly consumed to form a solid electrolyte interface (SEI) film or participate in side reactions, resulting in a gradual decrease in battery capacity. These irreversibly lost lithium ions can no longer participate in subsequent electrochemical reactions, causing the battery performance to gradually decay. At the same time, the electrode materials undergo volume changes and structural degradation during repeated lithium ion insertion and extraction processes, reducing the mechanical stability of the battery, thereby affecting its cycle life and increasing the internal resistance, seriously affecting the overall performance of the battery.

[0003] The lithium supplement technology aims to restore and improve battery performance by supplementing the consumed lithium ions in the battery. However, traditional lithium supplement technologies are difficult to ensure the uniform distribution of the lithium supplement, resulting in regions with too high or too low local lithium concentration inside the battery. This non-uniform distribution will exacerbate the local stress and volume changes of the battery, further affecting the cycle stability and safety of the battery. In addition, the preparation process of the lithium supplement usually requires high-temperature long-term calcination, with complex steps and high energy consumption. This not only increases the production cost but also may introduce impurities, affecting the purity and performance consistency of the lithium supplement. Traditional preparation processes often use organic solvents and high-temperature calcination, generating harmful gases and waste liquids that pollute the environment, restricting the sustainability of large-scale applications. The improvements in environmental protection and efficient preparation in the prior art are limited, restricting the wide application of the lithium supplement. Summary of the Invention

[0004] In view of the above situation, to overcome the defects of the prior art, the present invention provides a lithium ferrite lithium supplement and a preparation method thereof. The present invention uses defective Fe-MOFs as a synthesis template, mixes with lithium salts, iron salts, and biomass graphene quantum dots, and calcines in a nitrogen atmosphere to obtain the lithium ferrite lithium supplement, solving the problem of irreversible loss of lithium ions existing in the existing lithium-ion battery technology. At the same time, it enables the uniform distribution of lithium ions, reduces the local stress and volume changes inside the battery, and adopts mild reaction conditions and environmentally friendly reagents, reducing energy consumption and production costs.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a lithium ferrite lithium supplement, and the lithium ferrite lithium supplement includes the following components: iron salts, organic ligands, lithium salts, regulators, and biomass graphene quantum dots.

[0006] Preferably, the iron salt is one or more of ferric chloride, ferric nitrate, ferric sulfate, and ferric oxalate.

[0007] Preferably, the organic ligand is any one of terephthalic acid, biphenyl-4,4'-dicarboxylic acid, trimesic acid, 2-aminoterephthalic acid, and 2,5-dihydroxyterephthalic acid.

[0008] Preferably, the lithium salt is one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, lithium sulfide, lithium oxide, and lithium acetate.

[0009] Preferably, the regulator is any one of benzoic acid, formic acid, and acetic acid.

[0010] Furthermore, the preparation method of the biomass graphene quantum dots includes the following steps:

[0011] ① Wash the biomass waste with clean water, dry it, put it into a crusher, crush it into biomass powder with a diameter of 2 mm, and then put it into an oven for carbonization at 300 °C for 40 - 60 min to obtain carbonized biomass;

[0012] ② Weigh 4 - 6 g of the carbonized biomass obtained in step ①, slowly add it to 100 mL of concentrated sulfuric acid, slowly stir and dropwise add 50 mL of 0.5 mol / L ammonium persulfate solution, slowly stir at 200 - 300 rpm at room temperature for 2 - 4 h, add 100 mL of deionized water and mix evenly, raise the temperature to 90 - 95 °C and continue stirring for 10 - 20 min, dropwise add 100 mL of 3 wt% H 2 O 2 solution, continue stirring for 20 min, filter to obtain a precipitate, wash it three times with deionized water, ultrasonically exfoliate it at 300 W for 30 - 40 min, and filter to obtain biomass graphene;

[0013] ③ Disperse the biomass graphene obtained in step ② in 200 - 300 mL of deionized water, add 2 mL of 1 wt% ammonia water, stir at 350 - 450 rpm for 30 min, then transfer it to a high-pressure reaction kettle with a polytetrafluoroethylene inner liner, heat it at 200 °C for 6 - 8 h, filter the product after cooling to room temperature, wash the product three times alternately with ethanol and deionized water, and dry it to obtain biomass graphene quantum dots.

[0014] Preferably, in step ①, the biomass waste is any one of corn straw, wheat straw, and cotton straw.

[0015] The present invention also proposes a preparation method of a lithium iron ferrite lithium supplement agent, which specifically includes the following steps:

[0016] S1. Weigh iron salts, organic ligands and regulators, dissolve them in DMF, mix evenly, transfer to a reaction kettle, heat at 140 - 160 °C for 12 - 24 h, after cooling to room temperature, wash three times alternately with ethanol and water, and obtain Fe-MOFs after drying;

[0017] S2. Add the Fe-MOFs prepared in step S1 into ethanol to disperse evenly, then add lithium salts, iron salts and biomass graphene quantum dots, stir at 300 - 400 rpm in a closed environment for 2 - 4 h, freeze-dry to obtain a reaction precursor, place it in a nitrogen atmosphere, heat to 600 - 800 °C at a heating rate of 5 - 8 °C / min and calcine for 1 - 2 h, and obtain a lithium supplement agent after cooling to room temperature.

[0018] Preferably, in step S1, the dosage ratio of iron salts, organic ligands, regulators and DMF is 10 mmol: 10 mmol: 20 - 50 mmol: 20 - 30 mL.

[0019] Preferably, in step S2, the dosage ratio of Fe-MOFs, ethanol, lithium salts, iron salts and biomass graphene quantum dots is 2 - 4 g: 60 - 100 mL: 0.1 - 0.2 mol: 0.1 mol: 0.2 - 0.5 g.

[0020] The beneficial effects achieved by the present invention are as follows:

[0021] The present invention significantly improves the performance and service life of lithium-ion batteries by using lithium ferrite as a lithium supplement agent. The lithium ferrite lithium supplement agent can effectively supplement the consumed lithium ions in the battery, reduce irreversible losses, and improve the actual capacity and energy density of the battery. As a precursor material, iron-based metal-organic frameworks (Fe-MOFs) have a high specific surface area and a highly ordered pore structure, enabling lithium ferrite to have higher structural order and dispersion during the formation process, providing more active sites, and significantly enhancing the electrochemical performance and stability of the lithium supplement agent. The introduction of Fe-MOFs also improves the uniform distribution of lithium ions and reduces the damage caused by local stress and volume changes inside the battery. The introduction of biomass graphene quantum dots further enhances the conductivity of the electrode material. Biomass graphene quantum dots not only have excellent conductivity themselves, but their nanoscale size and high surface area can synergistically interact with the Fe-MOFs structure to further improve the overall performance of the lithium supplement agent. The synergistic effect of graphene quantum dots and Fe-MOFs ensures the structural stability of the electrode material, reduces the increase in internal resistance and performance degradation, and improves the cycle stability and safety of the battery. Generally speaking, the present invention optimizes the composition and preparation method of the lithium supplement agent, uses mild reaction conditions and environmentally friendly reagents, avoids high-temperature long-term calcination processes, reduces energy consumption and production costs, and has better sustainability and environmental friendliness. This technical solution not only solves a number of problems in the prior art, but also provides an efficient and green solution for the optimization of lithium-ion batteries, with broad application prospects and economic value. Brief Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only those of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 It is the transmission electron microscope image of the biomass graphene quantum dots prepared in Example 1;

[0024] Figure 2 It is the XRD pattern of the biomass graphene quantum dots prepared in Example 1;

[0025] Figure 3 It is the transmission electron microscope image of the lithium ferrite lithium supplement agent prepared in Example 1;

[0026] Figure 4 It is the XRD pattern of the lithium ferrite lithium supplement agent prepared in Example 1. Detailed Description of the Embodiments

[0027] The present invention will be further described in detail below through examples and comparative examples. However, it should not be understood that the scope of the present invention is limited to the following examples. All technologies implemented based on the above content of the present invention belong to the scope of the present invention.

[0028] In the experimental methods in the following examples, unless otherwise specified, they are all conventional methods; in the test materials used in the following examples and comparative examples, unless otherwise specified, they are all purchased from commercial channels.

[0029] Example 1: In this example, a lithium ferrite lithium supplement is proposed. The lithium ferrite lithium supplement includes the following components: ferric chloride, terephthalic acid, lithium carbonate, benzoic acid, and biomass graphene quantum dots.

[0030] The preparation method of the biomass graphene quantum dots includes the following steps:

[0031] ① Wash the corn straw with clean water, dry it, put it into a pulverizer, and pulverize it into biomass powder with a diameter of 2 mm. Then put it into an oven and carbonize it at 300 °C for 40 min to obtain carbonized biomass.

[0032] ② Weigh 6 g of the carbonized biomass obtained in step ①, slowly add it to 100 mL of concentrated sulfuric acid, slowly stir and dropwise add 50 mL of 0.5 mol / L ammonium persulfate solution, slowly stir at 300 rpm at room temperature for 4 h, add 100 mL of deionized water and mix evenly, heat up to 95 °C and continue stirring for 20 min, dropwise add 100 mL of 3 wt% H 2 O 2 solution, continue stirring for 20 min, filter to obtain a precipitate, wash it three times with deionized water, ultrasonically exfoliate it at 300 W for 40 min, and filter to obtain biomass graphene.

[0033] ③ Disperse the biomass graphene obtained in step ② in 300 mL of deionized water, add 2 mL of 1 wt% ammonia water, stir at 400 rpm for 30 min, then transfer it to a high-pressure reaction kettle with a polytetrafluoroethylene inner liner, heat it at 200 °C for 8 h, filter the product after cooling to room temperature, wash the product three times alternately with ethanol and deionized water, and dry it to obtain biomass graphene quantum dots.

[0034] This example also proposes a preparation method of a lithium ferrite lithium supplement, which specifically includes the following steps:

[0035] S1. Weigh 10 mmol of ferric chloride, 10 mmol of terephthalic acid, and 40 mmol of benzoic acid, dissolve them in 20 mL of DMF, mix them evenly, transfer them to a reaction kettle, heat them at 160 °C for 12 h, cool to room temperature, and wash them three times alternately with ethanol and water, and dry them to obtain Fe-MOFs.

[0036] S2. Weigh 4 g of the Fe-MOFs prepared in step S1, disperse them evenly in 100 mL of ethanol, then add 0.2 mol of lithium carbonate, 0.1 mol of ferric chloride, and 0.4 g of biomass graphene quantum dots. Stir magnetically at 400 rpm for 2 h in a closed container, and then perform freeze-drying to obtain a reaction precursor. Place it in a nitrogen atmosphere and heat it to 800 °C at a heating rate of 5 °C / min for 2 h. After cooling to room temperature, a lithium supplement agent is obtained.

[0037] Example 2: This example presents a lithium ferrite lithium supplement agent, which includes the following components: ferric nitrate, trimesic acid, lithium nitrate, acetic acid, and biomass graphene quantum dots.

[0038] The preparation method of the biomass graphene quantum dots includes the following steps:

[0039] ①. Wash wheat straw with clean water, dry it, put it into a pulverizer, and pulverize it into biomass powder with a diameter of 2 mm. Then put it into an oven and carbonize it at 300 °C for 60 min to obtain carbonized biomass.

[0040] ②. Weigh 5 g of the carbonized biomass obtained in step ①, slowly add it to 100 mL of concentrated sulfuric acid, slowly stir and dropwise add 50 mL of 0.5 mol / L ammonium persulfate solution. Stir magnetically at 200 rpm at room temperature for 2 h, add 100 mL of deionized water and mix evenly. Heat it to 90 °C and continue stirring for 10 min. Dropwise add 100 mL of 3 wt% H 2 O 2 solution, continue stirring for 20 min, filter to obtain a precipitate, wash it three times with deionized water, ultrasonically exfoliate it at 300 W for 30 min, and filter to obtain biomass graphene.

[0041] ③. Disperse the biomass graphene obtained in step ② in 200 mL of deionized water, add 2 mL of 1 wt% ammonia water, stir magnetically at 350 rpm for 30 min, then transfer it to a high-pressure reaction kettle with a polytetrafluoroethylene inner liner, heat it at 200 °C for 6 h, filter the product after cooling to room temperature, wash the product three times alternately with ethanol and deionized water, and dry it to obtain biomass graphene quantum dots.

[0042] This example also presents a preparation method of a lithium ferrite lithium supplement agent, which specifically includes the following steps:

[0043] S1. Weigh 10 mmol of ferric chloride, 10 mmol of terephthalic acid, and 50 mmol of benzoic acid, dissolve them in 30 mL of DMF, mix evenly, transfer them to a reaction kettle, heat them at 140 - 160 °C for 12 - 24 h, cool to room temperature, and wash them three times alternately with ethanol and water, and dry to obtain Fe-MOFs.

[0044] S2. Weigh 2 g of the Fe-MOFs prepared in step S1, disperse them evenly in 60 mL of ethanol, then add 0.1 mol of lithium carbonate, 0.1 mol of ferric chloride, and 0.2 g of biomass graphene quantum dots. Stir the mixture in a closed container at 300 rpm for 4 h, and then perform freeze-drying to obtain a reaction precursor. Place it in a nitrogen atmosphere and heat it to 700 °C at a heating rate of 8 °C / min for 1 h. After cooling to room temperature, a lithium supplement agent is obtained.

[0045] Example 3: This example presents a lithium ferrite lithium supplement agent, and the lithium ferrite lithium supplement agent includes the following components: ferric sulfate, biphenyl-4,4'-dicarboxylic acid, lithium acetate, formic acid, and biomass graphene quantum dots.

[0046] The preparation method of the biomass graphene quantum dots includes the following steps:

[0047] ①. Wash the cotton straw with clean water, dry it, put it into a pulverizer, and pulverize it into biomass powder with a diameter of 2 mm. Then place it in an oven and carbonize it at 300 °C for 50 min to obtain carbonized biomass.

[0048] ②. Weigh 4 g of the carbonized biomass obtained in step ①, slowly add it to 100 mL of concentrated sulfuric acid, slowly stir and dropwise add 50 mL of 0.5 mol / L ammonium persulfate solution. Stir slowly at 260 rpm at room temperature for 3 h, add 100 mL of deionized water and mix evenly. Heat it to 92 °C and continue stirring for 10 - 20 min. Dropwise add 100 mL of 3 wt% H 2 O 2 solution, continue stirring for 20 min, filter to obtain a precipitate, wash it three times with deionized water, perform ultrasonic exfoliation at 300 W for 35 min, and filter to obtain biomass graphene.

[0049] ③. Disperse the biomass graphene obtained in step ② in 250 mL of deionized water, add 2 mL of 1 wt% ammonia water, stir at 450 rpm for 30 min, then transfer it to a high-pressure reaction kettle with a polytetrafluoroethylene inner lining, heat it at 200 °C for 7 h, filter the product after cooling to room temperature, wash the product three times alternately with ethanol and deionized water, and dry it to obtain biomass graphene quantum dots.

[0050] This example also presents a preparation method of a lithium ferrite lithium supplement agent, which specifically includes the following steps:

[0051] S1. Weigh 10 mmol of ferric chloride, 10 mmol of terephthalic acid, and 20 mmol of benzoic acid, dissolve them in 25 mL of DMF, mix evenly, transfer them to a reaction kettle, heat at 150 °C for 16 h, cool to room temperature, and wash them three times alternately with ethanol and water, and dry to obtain Fe-MOFs.

[0052] S2. Weigh 3 g of the Fe-MOFs prepared in step S1, disperse them evenly in 80 mL of ethanol, then add 0.15 mol of lithium salt, 0.1 mol of iron salt, and 0.5 g of biomass graphene quantum dots. Stir magnetically at 360 rpm for 3 h in a sealed container, and then perform freeze-drying to obtain a reaction precursor. Place it in a nitrogen atmosphere, heat it to 600 °C at a heating rate of 7 °C / min, calcine for 1.5 h, and cool to room temperature to obtain a lithium supplement agent.

[0053] Comparative Example 1: This comparative example presents a lithium ferrite lithium supplement agent. The difference from Example 1 is that Fe-MOFs are not used, and the other components, component contents, and experimental steps are the same as those in Example 1. The lithium ferrite lithium supplement agent includes the following components: ferric chloride, lithium carbonate, and biomass graphene quantum dots.

[0054] The preparation method of the biomass graphene quantum dots includes the following steps:

[0055] ①. Wash the corn straw with clean water, dry it, put it into a crusher, and crush it into biomass powder with a diameter of 2 mm. Then put it into an oven and carbonize it at 300 °C for 40 min to obtain carbonized biomass.

[0056] ②. Weigh 6 g of the carbonized biomass obtained in step ①, slowly add it to 100 mL of concentrated sulfuric acid, slowly stir and dropwise add 50 mL of 0.5 mol / L ammonium persulfate solution, stir magnetically at 300 rpm at room temperature for 4 h, add 100 mL of deionized water and mix evenly, heat up to 95 °C and continue stirring for 20 min, dropwise add 100 mL of 3 wt% H 2 O 2 solution, continue stirring for 20 min, filter to obtain a precipitate, wash it three times with deionized water, perform ultrasonic exfoliation at 300 W for 40 min, and filter to obtain biomass graphene.

[0057] ③. Disperse the biomass graphene obtained in step ② in 300 mL of deionized water, add 2 mL of 1 wt% ammonia water, stir magnetically at 400 rpm for 30 min, then transfer it to a high-pressure reaction kettle with a polytetrafluoroethylene inner liner, heat it at 200 °C for 8 h, cool to room temperature and filter to obtain the product, wash the product three times alternately with ethanol and deionized water, and dry it to obtain biomass graphene quantum dots.

[0058] This comparative example also presents a preparation method of a lithium ferrite lithium supplement agent, which specifically includes the following steps:

[0059] S1. Add 0.2 mol of lithium carbonate, 0.1 mol of ferric chloride, and 0.4 g of biomass graphene quantum dots into 100 mL of ethanol. Stir the mixture in a closed container at 400 rpm for 2 h, and then obtain the reaction precursor by freeze-drying. Place it in a nitrogen atmosphere and heat it to 800 °C at a heating rate of 5 °C / min for calcination for 2 h. After cooling to room temperature, a lithium supplement agent is obtained.

[0060] Comparative Example 2: This comparative example presents a lithium ferrite lithium supplement agent. The difference from Example 1 is only that no biomass graphene quantum dots are added, and the other components, component contents, and experimental steps are the same as those in Example 1.

[0061] Experimental Example 1: Observe the microscopic morphology of the biomass graphene quantum dots prepared in Example 1 using a transmission electron microscope; at the same time, analyze the structural characteristics of the biomass graphene quantum dots prepared in Example 1 using X-ray diffraction.

[0062] Figure 1 is the transmission electron microscope image of the biomass graphene quantum dots prepared in Example 1. As shown in the figure, the biomass graphene quantum dots have a small particle size and are evenly distributed, with a diameter of about 4 nm. Figure 2 is the XRD pattern of the biomass graphene quantum dots prepared in Example 1. As shown in the figure, the diffraction peak at 25.4° corresponds to the (002) diffraction plane of the graphene quantum dots. The above analysis indicates the successful preparation of the biomass graphene quantum dots.

[0063] Experimental Example 2: Observe the microscopic morphology of the lithium ferrite lithium supplement agent prepared in Example 1 using a transmission electron microscope; at the same time, analyze the structural characteristics of the lithium ferrite lithium supplement agent prepared in Example 1 using X-ray diffraction.

[0064] Figure 3 is the transmission electron microscope image of the lithium ferrite lithium supplement agent prepared in Example 1. As shown in the figure, the MOF structure collapses, but the overall still forms cubic nanoparticles with a small particle size and a diameter of about 120 nm. Figure 4 is the XRD pattern of the lithium ferrite lithium supplement agent prepared in Example 1. As shown in the figure, the diffraction peaks in the figure correspond to the reflections of the (221), (220), (311), (317), (400), (417), (419), (422), (440), and (511) planes of lithium ferrite, respectively. At the same time, the reflection of the (002) diffraction plane of the graphene quantum dots can be observed, indicating the successful preparation of the lithium ferrite lithium supplement agent.

[0065] Experimental Example 3: Performance test:

[0066] (1) Half-cell performance test: The lithium ferrite lithium supplement agents prepared in Examples 1-3 and Comparative Examples 1-2 were respectively mixed with conductive carbon black, PVDF, and NMP in a mass ratio of 90:5:5:60 to form a positive electrode slurry, which was uniformly coated on an aluminum foil substrate, vacuum dried at 80 °C for 12 h, rolled and cut to obtain a positive electrode sheet, and a lithium sheet was used as the negative electrode. In a CR2032 button battery case, the positive electrode sheet, lithium sheet, and polyethylene film (separator) were assembled together, and 1 mol / L LiPF6 / EC+DMC+EMC electrolyte was added and sealed. In a constant temperature oven at 25 °C, it was charged to 4.5 V at a current of 0.1 C, and then discharged to 2.0 V at the same current, and the first charge specific capacity and the first charge-discharge efficiency were recorded. The test data are shown in Table 1.

[0067] Table 1 Half-cell performance test data

[0068]

[0069]

[0070] As shown in Table 1, in the half-cell test, the first charge specific capacity of Examples 1-3 was significantly higher than that of Comparative Example 1 and Comparative Example 2. This indicates that the lithium ferrite lithium supplement agents synthesized in the examples can store more electric charge during the first charge process. At the same time, the first charge-discharge efficiency of Examples 1-3 was significantly lower than that of Comparative Example 1 and Comparative Example 2, indicating that the lithium supplement agents prepared in Examples 1-3 effectively compensated for the lithium ion loss caused by side reactions during the first charge process. Although this would reduce the first discharge efficiency, it played a positive role in compensating for the initial irreversible lithium loss.

[0071] (2) Full-cell performance test: The lithium ferrite lithium supplement agents prepared in Examples 1-3 and Comparative Examples 1-2 were respectively mixed with lithium iron phosphate, conductive carbon black, PVDF, and N-methylpyrrolidone in a mass ratio of 10:90:5:5:60 and mixed evenly to form a positive electrode slurry, which was uniformly coated on an aluminum foil substrate, vacuum dried at 80 °C for 12 h, rolled and cut to obtain a positive electrode sheet. Graphite, conductive carbon black, CMC, SBR, and deionized water were mixed evenly in a mass ratio of 94:2:2:2:100 to form a negative electrode slurry, which was uniformly coated on a copper foil substrate, vacuum dried at 80 °C for 12 h, rolled and cut to obtain a negative electrode sheet. The obtained positive electrode sheet, negative electrode sheet, and polyethylene film were wound into the electrode core of a lithium ion battery, and 1 mol / L LiPF 6 / EC+DMC+EMC electrolyte was injected into the aluminum shell of the battery and sealed to prepare a 1 Ah lithium ion battery.

[0072] Test conditions: Constant current charge at 1C to 4.5V in an incubator at 25°C, then constant current discharge at 1C from 4.5V to 2.0V, test its first charge-discharge capacity and the capacity retention rate after 200 cycles (1C), and calculate the unit lithium supplementation capacity. The test data are shown in Table 2.

[0073] Table 2 Test data of the full cell performance

[0074]

[0075] According to the experimental data, the lithium ferrite lithium supplement agents of Examples 1-3 perform excellently in terms of the first charge specific capacity, the first discharge specific capacity, and the capacity retention rate after 200 cycles. Among them, the first charge specific capacity and the first discharge specific capacity of the examples are significantly higher than those of the comparative example, indicating that they have higher initial capacities; the capacity retention rate after 200 cycles is between 97.47% and 98.13%, showing excellent cycle stability. In contrast, the cycle capacity retention rate of the comparative example is significantly lower, verifying the significant advantages of the lithium ferrite lithium supplement agent of the embodiments of the present invention in improving battery performance and extending service life, and having good application prospects.

[0076] The above describes the present invention and its implementation manners. Such description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual application is not limited thereto. Generally speaking, if those of ordinary skill in the art are inspired by it and design similar manners and embodiments to this technical solution without creative efforts without departing from the purpose of the present invention, they should fall within the protection scope of the present invention.

Claims

1. A lithium ferrite lithium supplement, characterized in that: The raw materials for the lithium ferrite lithium supplementation agent reaction include the following components: iron salt, organic ligand, lithium salt, regulator and biomass graphene quantum dots; The method for preparing biomass graphene quantum dots comprises the following steps: ①, wash the biomass waste, dry and crush it into biomass powder, and then carbonize it at 300℃ for 40~60 min to obtain carbonized biomass; ②, the carbonized biomass obtained in step ①, slowly add concentrated sulfuric acid, slowly stir and drop ammonium persulfate solution, slowly stir at room temperature for 2-4 h, add deionized water and mix evenly, heat to 90-95 ° C and continue stirring for 10-20 min, drop H2O2 solution, continue stirring for 20 min, filter to obtain precipitate, wash and ultrasonically peel for 30-40 min, filter to obtain biomass graphene; ③, the biomass graphene obtained in step ② was dispersed in deionized water, ammonia water was added and stirred for 30 min, then transferred to a high-pressure reactor, heated at 200 ° C for 6-8 h, cooled to room temperature and filtered to obtain the product, and then washed and dried to obtain biomass graphene quantum dots; The iron salt is one or more of ferric chloride, ferric nitrate, ferric sulfate and ferric oxalate; The organic ligand is any one of terephthalic acid, biphenyl-4-4'-dicarboxylic acid, trimesic acid, 2-aminoterephthalic acid and 2,5-dihydroxyterephthalic acid; The lithium salt is one or more of lithium carbonate, lithium nitrate, lithium sulfate and lithium acetate; The regulator is any one of benzoic acid, formic acid and acetic acid; In the step ①, the biomass waste is any one of corn straw, wheat straw, and cotton straw; The preparation of the lithium ferrite lithium supplement comprises the following steps: S1. Weigh the iron salt, organic ligand and regulator, dissolve them in DMF, mix them evenly, transfer them to a reactor and heat them at 140-160°C for 12-24 h. After cooling to room temperature, wash them alternately with ethanol and water three times, and dry them to obtain Fe-MOFs. S2. Add the Fe-MOFs prepared in step S1 into ethanol and disperse them evenly, then add lithium salt, iron salt and biomass graphene quantum dots, stir in a closed container for 2-4 h, freeze-dry to obtain a reaction precursor, place it in a nitrogen atmosphere, heat it to 600-800°C at a heating rate of 5-8°C / min, calcine it for 1-2 h, and cool it to room temperature to obtain a lithium supplement.

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