A lithium supplement and a method for preparing the same

Abstract

The application discloses a lithium supplement and a preparation method thereof, wherein the preparation method of the lithium supplement comprises the following steps: (1) preparing a carbon source dispersion liquid, wherein the carbon source dispersion liquid comprises a dispersing agent, a nano carbon material and water, and the pH value of the carbon source dispersion liquid is adjusted to 12-13; (2) under the condition that the temperature of the carbon source dispersion liquid is kept at 40-60 DEG C, an iron-containing solution and an alkaline solution are simultaneously added dropwise into the carbon source dispersion liquid, the pH value of the system is controlled, after the dropwise addition is completed, impurities are removed and dried to obtain C@Fe3O4; (3) C@Fe3O4, micro-sized LiOH.H2O and nano-sized Al2O3 are uniformly mixed to serve as a precursor, the precursor is sintered and crushed twice in sequence to obtain a primary powder; and (4) a stabilizer is added into the primary powder, and after uniform mixing, sintering and crushing are carried out to obtain the lithium supplement. The lithium supplement can improve the first charge-discharge efficiency of a lithium iron phosphate battery, and meanwhile, does not substantially affect the discharge capacity and the cycle stability.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a lithium replenishing agent and its preparation method. Background Technology

[0002] During the first charge of a lithium-ion battery, a solid electrolyte interphase (SEI) film forms on the surface of the negative electrode. This process irreversibly consumes the active lithium in the positive electrode material, leading to a loss of specific capacity during the first cycle. Currently, the most widely used commercial graphite anode material experiences an irreversible capacity loss of approximately 10%. For silicon-based and tin-based anode materials with higher theoretical specific capacities, this loss rate can exceed 30%, severely limiting the improvement of lithium-ion battery energy density. To address this issue, lithium replenishment technology, due to its ability to effectively compensate for irreversible capacity loss and restore the reversible capacity of the positive electrode material, demonstrates significant application value and research significance.

[0003] Existing lithium replenishment technologies are mainly divided into two categories: positive electrode lithium replenishment and negative electrode lithium replenishment. Among them, positive electrode lithium replenishment technology has greater application advantages due to its simple process and strong environmental adaptability. This technology introduces high-capacity lithium replenishment additives during the positive electrode slurry preparation stage, enabling the additive material to release excess lithium ions during subsequent charging to compensate for the capacity loss in the first cycle. Among many positive electrode lithium replenishment additives, Li5FeO4 has attracted much attention due to its excellent theoretical performance: 1) extremely high lithium storage capacity (each mole of Li5FeO4 can provide 5 Li ions). + 2) Outstanding specific capacity (up to 867 mAh / g).

[0004] Studies have shown that incorporating an appropriate amount of Li5FeO4 into conventional cathode materials can significantly improve the first coulombic efficiency and overall energy density of lithium-ion batteries. However, existing Li5FeO4 materials still face problems such as excessively large particle size and unsatisfactory conductivity. Summary of the Invention

[0005] This application provides a method for preparing a lithium replenishing agent. The prepared lithium replenishing agent can improve the first charge and discharge efficiency of lithium iron phosphate batteries, while not having a substantial impact on discharge capacity and cycle stability, thereby improving the overall performance of lithium-ion batteries.

[0006] A method for preparing a lithium supplement includes the following steps:

[0007] (1) Prepare a carbon source dispersion, wherein the carbon source dispersion includes a dispersant, nano-carbon material and water, and adjust the pH value of the carbon source dispersion to 12-13.

[0008] (2) While maintaining the temperature of the carbon source dispersion at 40-60℃, iron-containing solution and alkaline solution are added dropwise to the carbon source dispersion simultaneously. When the volume of alkaline solution consumed accounts for 55%-65% of the total volume of alkaline solution, the pH is adjusted to 10-11 using iron-containing solution and alkaline solution. The iron-containing solution and alkaline solution are then added dropwise. After the addition is completed, the mixture is allowed to stand to remove impurities and dry to obtain C@Fe3O4.

[0009] (3) C@Fe3O4, micron-sized LiOH·H2O and nano-sized Al2O3 are mixed evenly and used as a precursor. Under nitrogen protection, the precursor is sintered and pulverized twice to obtain primary powder.

[0010] (4) Add a stabilizer to the primary powder, mix evenly, and then sinter and pulverize to obtain the lithium supplement agent.

[0011] Several alternative methods are provided below, but they are not intended as additional limitations on the overall solution above. They are merely further additions or optimizations. Provided there are no technical or logical contradictions, each alternative method can be combined individually with respect to the overall solution above, or multiple alternative methods can be combined with each other.

[0012] In this application, C@Fe3O4 is a crystalline particle formed by the combination of carbon material and Fe3O4. The particles of C@Fe3O4 material are uniform, with a size of about 80-150 nm, high specific surface area, and good conductivity. The lithium replenishment agent prepared using C@Fe3O4 material has a good lithium replenishment effect, and the lithium iron phosphate battery with the addition of this lithium replenishment agent achieves a coulombic efficiency of over 99% for the first time.

[0013] The dispersant is at least one selected from polyvinylpyrrolidone, sodium carboxymethyl cellulose, polymaleic anhydride, sodium polystyrene sulfonate, and sodium naphthalene sulfonate. All dispersants are water-soluble substances and can dissolve in water to form a solution.

[0014] The nano-carbon material is at least one of carbon black, carbon nanotubes, porous carbon, and graphene. The nano-carbon material is mixed with a dispersant in the form of an aqueous slurry, and the content of the nano-carbon material in the aqueous slurry is 20-30%. The nano-carbon material is mixed with a dispersant in the form of an aqueous slurry and diluted with water to obtain a carbon source dispersion.

[0015] The carbon source dispersion is kept at a temperature of 40-60℃ using an oil bath. During the addition of iron-containing and alkaline solutions, the carbon source dispersion is continuously stirred. That is, during the addition of iron-containing and alkaline solutions, the system is always stirred to ensure that the substances are mixed evenly. Nitrogen gas is introduced for protection during the mixing process.

[0016] The pH value is crucial during the growth of C@Fe3O4 crystals. By adding an iron-containing solution and an alkaline solution to the carbon source dispersion, the pH value of the carbon source dispersion system can be adjusted. The iron-containing solution has an acidic pH value, while the alkaline solution has an alkaline pH value.

[0017] In this application, pH control is divided into two stages. In the early stage of the reaction, the pH is controlled to be alkaline, that is, pH 12-13. In the later stage of the reaction, the pH is reduced to control the pH at 10-11. The dividing point between the early and late stages of the reaction is when the volume of alkaline solution consumed accounts for 55%-65% of the total volume of alkaline solution. For example, 200 mL of alkaline solution is added dropwise to the carbon source dispersion. The pH is adjusted within the range of 110 mL-130 mL after the alkaline solution is added. The period before the pH adjustment is the early stage of the reaction, and the period after the pH adjustment is the late stage of the reaction.

[0018] Throughout the process, before and after adjusting the pH to 10-11, the ratio of the dropping rate of the iron-containing solution to the alkaline solution is controlled to prevent drastic changes in the pH value of the system during the dropping process, allowing it to remain stable around a certain pH value. Controlling the pH value in the early and later stages of the reaction can result in smaller, more uniform crystal particles with clearer particle boundaries.

[0019] C@Li5FeO4 is formed by the combination of Li and C@Fe3O4. Its particle size depends on the particle size of C@Fe3O4 crystals. The particle size and distribution uniformity of C@Fe3O4 crystals affect the particle size and size uniformity of C@Li5FeO4. Smaller crystal size means a larger specific surface area, which can improve the efficiency of catalytic reaction, increase the reactivity and catalytic activity of the material, and help improve electron conductivity and ion diffusion rate. Uniform particle distribution helps to improve the cycle stability and safety of the battery.

[0020] After the addition is completed, the crystals are allowed to stand for 2 to 3 hours to promote aging. After standing, the crystals are filtered and washed at least twice with a 1 mol / L NaOH aqueous solution to remove any possible sulfides. Then, the crystals are further removed by washing with a large amount of water and filtration with hot water at 70°C. Finally, the crystals are dried in a forced-air drying oven for 24 hours to obtain C@Fe3O4.

[0021] The stabilizer is asphalt powder or phenolic resin powder. The introduction of the stabilizer can promote the uniform distribution of carbon source on the material surface and form a uniform carbon coating layer, thereby optimizing the phase composition and electrochemical performance of the product C@Fe3O4 and enabling it to play a greater role in lithium replenishment applications.

[0022] High-purity nitrogen gas is introduced during the sintering process to ensure that the oxygen content is below 1 ppm, thus ensuring that the preparation of C@Li5FeO4 is carried out in an oxygen-free environment, thereby obtaining better material properties.

[0023] Optionally, the mass fraction of the dispersant in the carbon source dispersion is 0.05-0.5%, and the carbon content is 1.1%-1.5%. Optionally, the mass fraction of the dispersant in the carbon source dispersion is 0.2-0.5%, and the carbon content is 1.1%-1.5%.

[0024] The carbon content in the carbon source dispersion is crucial for the consistency and stability of the subsequent synthesis of C@Fe3O4 nanocrystal particles. Precise control of carbon content helps to control the growth of nanoparticles, thereby optimizing their electrochemical performance.

[0025] The carbon content in the carbon source dispersion also has a significant impact on many properties of the lithium supplement. Appropriate carbon coating can effectively disperse particles and prevent them from agglomerating, thereby increasing the specific surface area of ​​the material, promoting charge transfer and ion diffusion, and improving the charge and discharge performance of the material. At the same time, the carbon layer, as a protective layer, can alleviate the volume change of the material and enhance the structural stability.

[0026] The solute in the iron-containing solution is at least one selected from ferric sulfate, ferric nitrate, and ferric chloride. The solute in the alkaline solution is at least one selected from sodium hydroxide, ammonia, and calcium hydroxide. Water is used as the solvent for both the iron-containing and alkaline solutions. The solute in the iron-containing solution is a water-soluble iron salt. Dissolving the iron salt in water forms a solution containing iron ions, which is the iron-containing solution. The solute in the alkaline solution is various alkaline substances. Dissolving these substances in water forms an alkaline solution, which is added simultaneously with the iron-containing solution to the carbon source dispersion to provide a growth environment for C@Fe3O4.

[0027] The particle size D of the micron-sized LiOH·H2O 50 The average particle size of the nano-sized Al2O3 is less than 150 nm, with a particle size of less than 20 μm.

[0028] Optionally, the molar concentration of the iron-containing solution is 1 to 3 mol / L, and the molar concentration of the alkaline solution is 1 to 3 mol / L.

[0029] Optionally, the molar concentration of the iron-containing solution is the same as that of the alkaline solution.

[0030] Optionally, the volume ratio of the carbon source dispersion, the iron-containing solution, and the alkaline solution is 3-10:100:150-280.

[0031] Optionally, the volume ratio of the carbon source dispersion, the iron-containing solution, and the alkaline solution is 4-6:100:180-220.

[0032] Optionally, the iron-containing solution is an aqueous solution of FeSO4·7H2O, and the alkaline solution is an aqueous solution of NaOH. The molar concentration of the FeSO4·7H2O aqueous solution is 1–3 mol / L, and the molar concentration of the NaOH aqueous solution is 1–3 mol / L. During the entire dropping process, the dropping rate ratio of the FeSO4·7H2O aqueous solution to the NaOH aqueous solution is 1:2–2.1. The dropping rate of the FeSO4·7H2O aqueous solution is 4–6 mL / min, and the dropping rate of the NaOH aqueous solution is 8–12 mL / min.

[0033] Optionally, in the precursor, the molar ratio of Fe in C@Fe3O4 to Li in micron-sized LiOH·H2O is 1:5 to 5.5; and the amount of nano-sized Al2O3 added in the precursor is 0.05 to 0.1%.

[0034] Optionally, the precursor is sintered twice at a temperature of 400℃ to 800℃ for a time of 20 to 32 hours.

[0035] Optionally, the temperature for the two sintering processes of the precursor is 480℃~550℃.

[0036] Optionally, the stabilizer is in powder form, and the stabilizer material is at least one of asphalt, phenolic resin, polyethylene glycol resin, needle coke, and glucose. After introducing the stabilizer, the sintering temperature is 350°C, and the sintering time is 20 to 24 hours.

[0037] The stabilizer's D 50 The particle size is 0.2–5 μm, preferably 0.2–2 μm.

[0038] This application also provides a lithium replenishing agent, which is prepared using the preparation method described above.

[0039] This application also provides a lithium-ion battery cathode material, which contains the aforementioned lithium replenishing agent. The lithium-ion battery cathode material contains lithium iron phosphate, and the amount of the lithium replenishing agent added is 2-4 wt% based on lithium iron phosphate.

[0040] The lithium replenishing agent provided in this application can improve the initial charge and discharge efficiency of lithium iron phosphate batteries without substantially affecting the discharge capacity and cycle stability, thereby improving the overall performance of lithium-ion batteries. Attached Figure Description

[0041] Figure 1 A flowchart for preparing lithium supplements;

[0042] Figure 2 A flowchart for the preparation of C@Fe3O4;

[0043] Figure 3 SEM image of C@Fe3O4 prepared in Example 1;

[0044] Figure 4 SEM image of C@Li5FeO4 prepared in Example 1;

[0045] Figure 5 The initial charge-discharge curves of LFP and LFP(LFO) obtained from the performance test in Example 1 are shown.

[0046] Figure 6 SEM images of C@Fe3O4 prepared in Examples 2-5;

[0047] Figure 7 SEM images of C@Fe3O4 prepared in Examples 6-11;

[0048] Figure 8 SEM images of C@Fe3O4 prepared in Examples 12-15;

[0049] Figure 9 SEM images of C@Fe3O4 prepared in Examples 16-20;

[0050] Figure 10 XRD patterns of C@Li5FeO4 prepared in Comparative Example 3 and Example 23;

[0051] Figure 11 Electrochemical impedance spectroscopy (EIS) spectra of half-cells using C@Li5FeO4 and those not using C@Li5FeO4. Detailed Implementation

[0052] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0053] To better describe and illustrate the embodiments of this application, reference may be made to one or more accompanying drawings, but the additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the inventive creations of this application, the embodiments or preferred methods described herein.

[0054] It should be noted that when a component is said to be "connected" to another component, it can be directly connected to the other component or it can be connected to a component in between. When a component is said to be "set on" another component, it can be directly set on the other component or it may be set to a component in between.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0056] Example 1

[0057] A method for preparing a lithium supplement, see [link to relevant documentation]. Figure 1 As shown, it includes the following steps:

[0058] I. Preparation of C@Fe3O4, see process details below. Figure 2 As shown, the specific steps include the following:

[0059] (1) Preparation of carbon source dispersion mother liquor: Weigh 1.87g of carbon black dispersion (the carbon black content in the carbon black dispersion is 25%), add 2.27g of water, and then add 0.05g of polyvinylpyrrolidone (i.e., dispersant), stir evenly to obtain carbon source dispersion mother liquor. In the carbon source dispersion mother liquor, the mass fraction of carbon black is 11.15% and the mass fraction of polyvinylpyrrolidone is 1%.

[0060] (2) In a 500mL three-necked flask equipped with a magnetic stir bar and a dropping funnel, add 0.50g of carbon source dispersion mother liquor and 5g of water, and stir at a stirring speed of 500rpm to obtain carbon source dispersion. The carbon source dispersion is heated in an oil bath at 50℃ while nitrogen gas is introduced for protection. Ammonia water is added dropwise to adjust the pH value and maintain the pH value at 12.

[0061] (3) Weigh 55.6g of FeSO4·7H2O and dissolve it in 100g of deionized water to prepare an aqueous solution of FeSO4·7H2O with a molar concentration of 2mol / L. Weigh 16g of NaOH and dissolve it in 200g of deionized water to prepare an aqueous solution of NaOH with a molar concentration of 2mol / L.

[0062] Simultaneously add FeSO4·7H2O aqueous solution and NaOH aqueous solution to the carbon source dispersion using a dropping funnel. Adjust the pH to 12.6 (i.e., the pH in the early stage of the reaction) using the FeSO4·7H2O aqueous solution and NaOH aqueous solution. Continue adding FeSO4·7H2O aqueous solution and NaOH aqueous solution. When the volume of NaOH aqueous solution consumed is 120 mL (this volume includes the volume consumed when adjusting the pH), adjust the pH to 10.2 (i.e., the pH in the later stage of the reaction). Continue adding FeSO4·7H2O aqueous solution and NaOH aqueous solution.

[0063] No drop rate limit is imposed when adjusting pH; otherwise, the drop rate of FeSO4·7H2O aqueous solution is 5 mL / min, and the drop rate of NaOH aqueous solution is 10 mL / min.

[0064] (4) After the addition is complete, the mixed solution is allowed to stand for 3 hours, and then filtered twice with 1 mol / L NaOH aqueous solution to remove any possible sulfides. Then, hot water at 70°C is used to wash the solution with a large amount of water and filter to further remove residual sulfur, sodium and other impurities. The material is then placed in a forced-air drying oven and dried for 24 hours to obtain C@Fe3O4.

[0065] C@Fe3O4 appears as a yellowish-black powder, containing 68% Fe, 4% carbon, and 2000 ppm each of S and Na.

[0066] See the SEM image of C@Fe3O4. Figure 3 As shown, the synthesized nanoparticles are small in size, uniformly distributed, and have a clear crystal structure.

[0067] II. Preparation of C@Li5FeO4

[0068] (1) 11.628g LiOH·H2O (micron powder grade, particle size D) was used. 50 Using 1g C@Fe3O4 (with an average particle size of less than 20μm) as the reaction raw material, 0.008g of nano-sized Al2O3 (with an average particle size of less than 150nm) was introduced as an additive, and a uniform precursor was formed by high-speed mixing.

[0069] (2) The prepared precursor was placed in a high-temperature vacuum tube furnace and sintered at high temperature under an inert atmosphere. The temperature of the first sintering was 500℃ and the sintering time was 24h. After the first sintering, it was crushed and then sintered a second time at a temperature of 490℃ for 20h. It was crushed again to obtain powder.

[0070] (3) Add 0.01g of asphalt powder (D) to the powder. 50 A 1 μm particle size particle was used as a stabilizer, mixed evenly, sintered at 350℃ for 20 h, and then pulverized and demagnetized to obtain C@Li5FeO4, which is a lithium supplement. SEM images of C@Li5FeO4 are shown below. Figure 4 As shown.

[0071] Performance testing of C@Li5FeO4: C@Li5FeO4 was added to an electrode prepared by lithium iron phosphate (LFP), conductive agent acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. The amount of C@Li5FeO4 added was 3 wt% of lithium iron phosphate. The electrode was assembled into a half cell with lithium sheet tail as the negative electrode and tested at 0.1C.

[0072] See Figure 5 As shown, the initial charge capacity of the half-cell using C@Li5FeO4 is higher than that of the half-cell without C@Li5FeO4, and the initial coulombic efficiency of the half-cell using C@Li5FeO4 (99.0%) is also higher than that of the half-cell without C@Li5FeO4 (98.3%). Figure 5 In the figure, LFP (LFO) is the curve of the half-cell using C@Li5FeO4, and LFP is the curve of the half-cell without C@Li5FeO4.

[0073] C@Li5FeO4 can produce a pre-lithiation effect on the cathode of the half-cell, providing additional irreversible capacity and effectively compensating for the lithium consumption caused by the SEI film. The discharge capacities of the two half-cells are similar, indicating that the addition of C@Li5FeO4 did not have a significant negative impact on the discharge capacity of the cathode.

[0074] See Figure 11 As shown, the electrochemical impedance spectroscopy (EIS) spectra of half-cells using C@Li5FeO4 and those without C@Li5FeO4 are presented. Although the electronic conductivity of the half-cell using C@Li5FeO4 is not high, its ionic conductivity is good. In the high-frequency region of the EIS spectrum, the observed semi-circular shape is mainly due to the charge transfer resistance at the electrode interface, while in the low-frequency region, the slope of the straight section reflects the impedance of the lithium-ion diffusion process. Although the use of C@Li5FeO4 leads to a slight increase in the charge transfer resistance at the electrode interface, the lithium-ion diffusion impedance is simultaneously reduced. This phenomenon can be confirmed by the change in the slope in the low-frequency region. Nevertheless, the overall impedance change is not significant, indicating that the addition of C@Li5FeO4 does not adversely affect the cycle stability of the battery.

[0075] Examples 2-20

[0076] Table 1

[0077]

[0078]

[0079] In Examples 2-20, the experimental conditions were the same as in Example 1, except for the pH values ​​at the beginning and end of the reaction. Examples 2-20 mainly compared the effects of different pH values ​​at the beginning and end of the reaction on the morphology of C@Fe3O4 crystal particles.

[0080] Examples 2-5 investigated the effect of pH values ​​of 9-13 on the morphology of C@Fe3O4 crystal particles during the early stage of the reaction. (See also...) Figure 6 As shown, (a1) and (a2) are SEM images of C@Fe3O4 crystal particles from Example 2, (b1) and (b2) are SEM images of C@Fe3O4 crystal particles from Example 3, (c1) and (c2) are SEM images of C@Fe3O4 crystal particles from Example 4, and (d1) and (d2) are SEM images of C@Fe3O4 crystal particles from Example 5. Figure 6 It can be seen that within the pH range of 12 to 13, C@Fe3O4 crystal particles exhibit a smaller size (approximately 0.1 to 0.3 μm), a more uniform distribution, and clearer crystal boundaries.

[0081] Examples 6-11 investigated the effect of more precise pH control (between 12 and 13) on the morphology of C@Fe3O4 crystals during the early stage of the reaction. (See also...) Figure 7 As shown, (a) is a SEM image of C@Fe3O4 crystal particles from Example 6, (b) is a SEM image of C@Fe3O4 crystal particles from Example 7, (c) is a SEM image of C@Fe3O4 crystal particles from Example 8, (d) is a SEM image of C@Fe3O4 crystal particles from Example 9, (e) is a SEM image of C@Fe3O4 crystal particles from Example 10, and (f) is a SEM image of C@Fe3O4 crystal particles from Example 11. Figure 7 It can be seen that when the pH value is precisely controlled at approximately 12.6 in the early stage of the reaction, the synthesized crystal particles exhibit optimal characteristics in terms of size miniaturization, uniform distribution, and clarity of crystal structure.

[0082] Examples 12-15 investigated the effect of pH 8-11 during the later stages of the reaction on the morphology of C@Fe3O4 crystal particles. (See also...) Figure 8 As shown, (a1) and (a2) are SEM images of C@Fe3O4 crystal particles from Example 12, (b1) and (b2) are SEM images of C@Fe3O4 crystal particles from Example 13, (c1) and (c2) are SEM images of C@Fe3O4 crystal particles from Example 14, and (d1) and (d2) are SEM images of C@Fe3O4 crystal particles from Example 15. Figure 8It can be seen that when the pH value is controlled in the range of 10 to 11 in the later stage of the reaction, the crystal particles are small in size, uniformly distributed, and have a clear structure.

[0083] Examples 16-20 investigated the effect of more precise pH control (between 10 and 11) on the morphology of C@Fe3O4 crystals during the later stages of the reaction. See also... Figure 9 As shown, (a) is a SEM image of C@Fe3O4 crystal particles from Example 16, (b) is a SEM image of C@Fe3O4 crystal particles from Example 17, (c) is a SEM image of C@Fe3O4 crystal particles from Example 18, (d) is a SEM image of C@Fe3O4 crystal particles from Example 19, and (e) is a SEM image of C@Fe3O4 crystal particles from Example 20. Figure 9 It can be seen that the pH value in the later stage of the reaction has a significant impact on the morphology and size of the crystals. When the pH value is close to 10, the morphology of the C@Fe3O4 crystal particles is more ideal.

[0084] Example 21

[0085] In the carbon source dispersion, sodium carboxymethyl cellulose was used as the dispersant, and carbon nanomaterials were carbon nanotubes. In the mother liquor of the carbon source dispersion, the mass fraction of sodium carboxymethyl cellulose was 1.5%, and the mass fraction of carbon nanotubes was 8%. Other conditions were the same as in Example 1.

[0086] Example 22

[0087] In the carbon source dispersion, sodium styrene sulfonate was used as the dispersant, and graphene was used as the nano-carbon material. In the mother liquor of the carbon source dispersion, the mass fraction of sodium styrene sulfonate was 1.5%, the mass fraction of graphene was 8%, and other conditions were the same as in Example 1.

[0088] Comparative Example 1

[0089] When the carbon black content in the carbon source dispersion mother liquor is 10.0% and the mass fraction of polyvinylpyrrolidone (PVP) is 1%, the carbon content in C@Fe3O4 is extremely low, only 1%.

[0090] Comparative Example 2

[0091] When the carbon black content in the carbon source dispersion mother liquor is 12.5% ​​and the mass fraction of polyvinylpyrrolidone is 1%, the carbon content in C@Fe3O4 is too high.

[0092] Comparative Example 3

[0093] The C@Fe3O4, LiOH·H2O (micron grade), and Al2O3 (nano grade) obtained in Example 1 were thoroughly ground into powder and sintered at 500°C for 32 hours. The resulting product was named C@Li5FeO4-1.

[0094] Example 23

[0095] The C@Fe3O4, LiOH·H2O (micron-grade), and Al2O3 (nano-grade) obtained in Example 1 were thoroughly mixed and ground into powder. The first sintering temperature was 500℃, and the sintering time was 32 h. After the first sintering, the powder was pulverized again, and then a second sintering was performed at 490℃ for 20 h. The powder was pulverized again, and 1% (by weight) of asphalt micron powder was added to the resulting powder and mixed thoroughly. Subsequently, the mixture was placed in a tube furnace for final sintering at 350℃ for 20 h. The obtained product was named C@Li5FeO4-2.

[0096] XRD patterns of C@Li5FeO4 prepared under different sintering methods in Comparative Example 3 and Example 23 are shown in [reference]. Figure 10 As shown, the Li5FeO4 peak in C@Li5FeO4-2 is more prominent, accompanied by characteristic peaks of LiFeO2. Observing the spectrum of C@Li5FeO4-1, it was found that the peak of C@Li5FeO4 is weaker, while the characteristic peak of LiFeO2 is very obvious. This finding indicates that in high-temperature reactions, extending the reaction time can promote the phase transformation of LiFeO2 to Li5FeO4. Example 23, due to the use of a two-stage calcination method, involves pulverizing the material after high-temperature sintering and then sintering again, which helps to remix the incompletely reacted LiOH and LiFeO2, thereby achieving a better sintering effect.

[0097] In addition, the introduction of pitch powder during the sintering process is beneficial to the uniform coating of Li5FeO4 by the carbon source. Pitch powder, as a stabilizer, can enhance the thermal stability and hydrophobicity of the material, thereby improving the electrical conductivity and initial charge-discharge efficiency of the material, and thus enhancing the overall electrochemical performance.

[0098] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0099] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a lithium supplement, characterized in that, Includes the following steps: (1) Prepare a carbon source dispersion, wherein the carbon source dispersion includes a dispersant, nano-carbon material and water, and adjust the pH value of the carbon source dispersion to 12~13; (2) While maintaining the temperature of the carbon source dispersion at 40~60℃, iron-containing solution and alkaline solution are added dropwise to the carbon source dispersion simultaneously. When the volume of alkaline solution consumed accounts for 55%~65% of the total volume of alkaline solution, the pH is adjusted to 10~11 using iron-containing solution and alkaline solution. The iron-containing solution and alkaline solution are then added dropwise. After the addition is completed, the mixture is allowed to stand to remove impurities and dry to obtain C@Fe3O4. The pH of the iron-containing solution is acidic, and the pH of the alkaline solution is alkaline. The pH of the carbon source dispersion system is adjusted using the iron-containing solution and the alkaline solution. In the early stage of the reaction, the pH is controlled at 12-13, and in the later stage of the reaction, the pH is controlled at 10-11. The dividing point between the early and late stages of the reaction is when the volume of alkaline solution consumed accounts for 55%-65% of the total volume of alkaline solution. (3) C@Fe3O4, micron-sized LiOH·H2O and nano-sized Al2O3 are mixed evenly and used as a precursor. Under nitrogen protection, the precursor is sintered and pulverized twice to obtain primary powder. When the precursor is sintered twice in sequence, the sintering temperature is 400℃~800℃ each time and the sintering time is 20~32 hours each time. (4) Add a stabilizer to the primary powder, mix evenly, and then sinter and pulverize to obtain the lithium supplement. The stabilizer is in powder form and the material of the stabilizer is at least one of asphalt, phenolic resin, polyethylene glycol resin, needle coke, and glucose. The sintering temperature after introducing the stabilizer is 350°C and the sintering time is 20-24 hours.

2. The method for preparing the lithium supplement as described in claim 1, characterized in that, The dispersant is at least one of polyvinylpyrrolidone, sodium carboxymethyl cellulose, polymaleic anhydride, sodium polystyrene sulfonate, and sodium naphthalene sulfonate, and the nano-carbon material is at least one of carbon black, carbon nanotubes, porous carbon, and graphene.

3. The method for preparing the lithium supplement as described in claim 1, characterized in that, The mass fraction of the dispersant in the carbon source dispersion is 0.05-0.5%, and the carbon content is 1.1%-1.5%.

4. The method for preparing the lithium supplement as described in claim 1, characterized in that, The solute in the iron-containing solution is at least one of ferric sulfate, ferric nitrate, and ferric chloride, and the solute in the alkaline solution is at least one of sodium hydroxide, ammonia, and calcium hydroxide.

5. The method for preparing the lithium supplement as described in claim 1, characterized in that, The molar concentration of the iron-containing solution is 1~3 mol / L, the molar concentration of the alkaline solution is 1~3 mol / L, and the volume ratio of the carbon source dispersion, the iron-containing solution, and the alkaline solution is 3~10:100:150~280.

6. The method for preparing the lithium supplement as described in claim 1, characterized in that, In the precursor, the molar ratio of Fe in C@Fe3O4 to Li in micron-sized LiOH·H2O is 1:5~5.5; the amount of nano-sized Al2O3 added in the precursor is 0.05~0.1%.

7. A lithium supplement, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. A lithium-ion battery cathode material, characterized in that, The lithium-ion battery cathode material contains lithium iron phosphate, and the amount of lithium-ion battery cathode material added is 2-4 wt% based on lithium iron phosphate.

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