Graphite-coated passivated lithium powder for lithium supplement of negative electrode of lithium battery and preparation method of graphite-coated passivated lithium powder

Abstract

The graphite-coated passivated lithium powder comprises 5-95 wt% of active substance graphite and 5-95 wt% of metal lithium powder, a finished product is core-shell structure composite powder with middle metal lithium powder and outer coated graphite powder, the macroscopic morphology is gray black, the microscopic particle size is 0.1-200 microns, the composite powder is good in fluidity, uniform in dispersion and free of agglomeration and hardening phenomena, and the preparation method comprises seven steps and conditions of three stages. The composite material has the advantages that the composite material can be compounded with nano lithium drops, dendritic crystal growth and volume change of lithium are inhibited, the structural stability and electrochemical performance of the composite material are improved, and the graphite powder can be fully and uniformly mixed with the lithium and paraffin emulsion, so that the lithium can be effectively loaded or embedded into pores and surfaces of the graphite; meanwhile, paraffin wrapped with lithium particles can be effectively dissolved and washed away, solid-liquid separation can be achieved, and pure lithium-graphite composite powder is obtained; in addition, adverse effects on subsequent battery manufacturing can be prevented, the particle size distribution of a final product can be controlled, and batch consistency and electrochemical performance uniformity are ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery materials, and particularly relates to a graphite-coated passivated lithium powder for lithium supplement of a lithium battery negative electrode and a preparation method thereof. BACKGROUND

[0002] With the rapid development of lithium ion batteries and the in-depth research of solid-state batteries, prelithiation has been one of the focuses of research and breakthrough. Prelithiation refers to actively introducing an additional lithium source into the battery system (mainly the negative electrode side) before the formal charging and discharging cycle of the lithium ion battery through physical or chemical methods to compensate for the irreversible lithium loss in the first charging process. Graphite is the main negative electrode material currently used in lithium ion batteries. For graphite negative electrode lithium supplement, there are mainly two types of technical routes:

[0003] One is the stabilized lithium metal powder (passivated lithium powder) lithium supplement type: this type of method is to mix micron-sized lithium metal powder (passivated lithium powder) with a special surface treatment, negative electrode graphite, conductive agent and binder to make a slurry, and coat to form an electrode, that is, the passivated lithium powder is added to the negative electrode during slurry preparation. The principle is that after the battery is injected with liquid, the passivated lithium powder will react with the electrolyte to pre-supplement lithium for the negative electrode, and the advantage is that the lithium supplement amount can be accurately controlled and easily integrated into the existing production line. However, it has problems such as extreme sensitivity of lithium powder to water and oxygen, requirement of extremely high production environment (dry room, even glove box) for oxygen-free atmosphere, difficulty in uniform dispersion, and high cost of preparing passivated lithium powder. Moreover, in the process of lithium supplement, the passivated lithium powder as an additive has difficulty in uniform mixing with the negative electrode active material graphite. For example, the patent CN119786551A Passivated lithium powder and preparation method thereof, negative electrode sheet, battery and electric equipment adopts this idea, but the passivation layer required by the patent is F fluoride or an organic substance.

[0004] The second is the lithium foil and lithium compound supplement type: this type of method uses other lithium-rich compounds as a lithium source, or adds an extra thin lithium foil in contact with the negative electrode during assembly to release lithium ions through chemical reaction or electrochemical method. However, this process of mechanical lamination has problems such as reaction control, safety and cost. For example, the patent CN114361398B Method for preparing lithium-supplemented negative electrode and lithium-supplemented negative electrode uses "ultra-thin lithium or lithium alloy film" as a lithium source, and "transfers part of the ultra-thin lithium / lithium alloy film to the upper and lower surfaces of the negative electrode by means of the rolling of the concave-convex roller". This process does not use passivated lithium powder, and the lithium exists on the surface of the electrode sheet, so the lithium supplement effect is limited, and there is a problem of lithium dendrite.

[0005] Therefore, it is of great significance to develop a graphite-coated passivated lithium powder for lithium supplement of a lithium battery negative electrode and a preparation method thereof. SUMMARY

[0006] The objective of this invention is to overcome the shortcomings of the prior art and provide a graphite-coated passivated lithium powder for lithium battery anode replenishment and its preparation method.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] Graphite-coated passivated lithium powder comprises 5-95 wt% graphite as active material and 5-95 wt% lithium metal powder. The finished product is a core-shell structured composite powder with a highly active pure lithium metal powder core and an outer coating of graphite powder. It exhibits a typical metallic gray-black morphology, with visible particle sizes of 0.1-200 μm. The composite powder demonstrates good flowability, uniform dispersion, and no agglomeration or caking. Its preparation method specifically includes the following stages, steps, and conditions:

[0009] Phase 1: Environmental and Raw Material Pretreatment

[0010] (1) Environmental preparation: dew point room and glove box, so that the dew point in the dew point room is <-40℃ and the corresponding water content is <120ppm, which can ensure the quality and safety of the reaction;

[0011] (2) Preheating with paraffin solvent: Paraffin is used as an inert medium and the first solvent to ensure that air is isolated, heat is conducted and lithium droplets are dispersed;

[0012] (3) Pre-melting of lithium sheets: Lithium sheets are added to heated paraffin wax to form a lithium-paraffin mixture;

[0013] Second-stage compounding and emulsification:

[0014] (4) Mechanical stirring: a high-speed dispersion process is adopted, and the lithium-paraffin mixture is thoroughly stirred with dispersion blades, which can improve the subsequent ultrasonic emulsification effect;

[0015] (5) First ultrasonic emulsification: using the emulsification effect of ultrasound, the molten lithium sheet is broken into droplets of micron or even nanometer scale and uniformly dispersed in paraffin to form an emulsion, which can greatly increase the specific surface area and lay the foundation for subsequent uniform composite with graphite.

[0016] (6) Adding graphite powder, with graphite as a carrier or buffer framework, is intended to be combined with nano-lithium droplets to inhibit the growth of lithium dendrites and volume changes, thereby improving the structural stability and electrochemical performance of the composite material.

[0017] (7) Second ultrasonic emulsification: The solution after adding graphite is subjected to a second ultrasonic emulsification to form a lithium-paraffin-graphite composite slurry, which can ensure that the graphite powder and the lithium-paraffin emulsion are fully and uniformly mixed, so that lithium is effectively loaded or embedded into the pores and surface of graphite.

[0018] Third stage cleaning and post-treatment:

[0019] (8) Solvent replacement and separation: Add a second solvent, n-hexane, cyclohexane, or alkylbenzene, to the solution after the second ultrasonic emulsification and graphite addition to clean and replace the paraffin. These solvents are good solvents for paraffin and do not react with lithium, and can effectively dissolve and wash away the paraffin that encapsulates lithium particles.

[0020] (9) Selection of separation method: (9.1) Static precipitation: Static precipitation separates the static precipitate. Static precipitation is suitable for systems with larger particles and faster settling speed, and is more economical; (9.2) High-speed centrifugation: High-speed centrifugation can separate fine composite powder more quickly and thoroughly, and is more efficient. The high-speed centrifugation precipitate is used to obtain pure lithium-graphite composite solid.

[0021] (10) Collect solid precipitates, and combine the precipitates separated by static sedimentation and the precipitates separated by high-speed centrifugation;

[0022] (11) Vacuum drying to remove residual solvent. The collected and combined precipitates are vacuum dried at a low temperature of 60-80°C and under negative pressure. This can completely remove residual n-hexane and trace amounts of water, preventing them from having an adverse effect on subsequent battery manufacturing.

[0023] (12) Selective sieving: the undersize material is the target powder with a particle size <0.2μm, controlling the particle size distribution of the final product to ensure batch consistency and uniformity of electrochemical performance. The oversize material is the large particles that can be removed due to agglomeration or abnormal growth, resulting in the final product composite powder.

[0024] The innovative aspects of this invention are as follows:

[0025] (1) In this invention, graphite is added directly during the lithium powder preparation stage to obtain a composite powder. Conventional negative electrode lithium replenishment usually involves adding lithium powder as an additional additive or mechanically pressing it onto the surface of the negative electrode sheet during the negative electrode slurry preparation process.

[0026] (2) This invention uses ultrasonic emulsification to prepare lithium powder, which is divided into two stages and incorporates mechanical stirring pretreatment, as well as powder drying methods such as static setting or high-speed centrifugation. Conventional lithium powder preparation processes include melt stirring, high-speed dispersion, and spraying. Only the patent "CN105826545B Method for Preparing Lithium Powder or Lithium Alloy Powder" involves ultrasonic preparation of lithium powder, which uses metals such as "Be, Mg, Ti, Zr, V, Nb, Cr, Cu, Al, Sn and Sr" as passivation layers, but does not involve specific process steps.

[0027] Compared with the prior art, the present invention has the following advantages or effects:

[0028] Because of the use of graphite composites and secondary ultrasonic emulsification, it can be combined with nano-lithium droplets to inhibit lithium dendrite growth and volume changes, thereby improving the structural stability and electrochemical performance of the composite material. It also ensures that the graphite powder is fully and uniformly mixed with the lithium and paraffin emulsion, allowing lithium to be effectively loaded or embedded into the pores and surface of the graphite. At the same time, due to the use of solvent replacement and separation, it can effectively dissolve and wash away the paraffin coating the lithium particles, and achieve solid-liquid separation to obtain pure lithium-graphite composite powder. In addition, due to the setting of drying and sieving, it can thoroughly remove residual n-hexane and trace moisture to prevent them from having an adverse effect on subsequent battery manufacturing, and control the particle size distribution of the final product to ensure batch consistency and uniformity of electrochemical performance. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process flow for preparing graphite-coated passivated lithium powder for lithium replenishment in the negative electrode of a lithium battery, based on the present invention.

[0030] Figure 2 This is an electron microscope schematic diagram of the graphite-coated passivated lithium powder of Example 1, which is used for lithium replenishment of the negative electrode of a lithium battery according to the present invention.

[0031] The percentages mentioned in this application are by mass. PVDF refers to polyvinylidene fluoride, and NMP refers to methylpyrrolidone. These two are commonly used binders and solvents in commercial lithium batteries, respectively.

[0032] The present invention will now be described in further detail with reference to the accompanying drawings. Detailed Implementation

[0033] like Figures 1~2 As shown, the graphite-coated passivated lithium powder includes 5-95 wt% active material graphite and 5-95 wt% metallic lithium powder. The finished product is a core-shell structured composite powder with highly active pure metallic lithium powder in the middle and graphite powder on the outside. The macroscopic morphology is gray-black, which is common in metallic powders. The microparticle size is 0.1-200 μm. The composite powder has good flowability, uniform dispersion, and no agglomeration or caking.

[0034] The graphite-coated passivated lithium powder of the present invention can be further...

[0035] The preferred microparticle size is 200 nm, or 0.2 μm.

[0036] The composite powder has an adjustable ratio of lithium powder and graphite, and can directly serve as a negative electrode active material to supplement lithium in the negative electrode.

[0037] The preparation method of graphite-coated passivated lithium powder specifically includes the following stages, steps, and conditions:

[0038] Phase 1: Environmental and Raw Material Pretreatment

[0039] (1) Environmental preparation: dew point room and glove box, so that the dew point in the dew point room is <-40℃ and the corresponding water content is <120ppm, which can ensure the quality and safety of the reaction;

[0040] (2) Preheating with paraffin solvent: Paraffin is used as an inert medium and the first solvent to ensure that air is isolated, heat is conducted and lithium droplets are dispersed;

[0041] (3) Pre-melting of lithium sheets: Lithium sheets are added to heated paraffin wax to form a lithium-paraffin mixture;

[0042] Second-stage compounding and emulsification:

[0043] (4) Mechanical stirring: a high-speed dispersion process is adopted, and the lithium-paraffin mixture is thoroughly stirred with dispersion blades, which can improve the subsequent ultrasonic emulsification effect;

[0044] (5) First ultrasonic emulsification: using the emulsification effect of ultrasound, the molten lithium sheet is broken into droplets of micron or even nanometer scale and uniformly dispersed in paraffin to form an emulsion, which can greatly increase the specific surface area and lay the foundation for subsequent uniform composite with graphite.

[0045] (6) Adding graphite powder, with graphite as a carrier or buffer framework, is intended to be combined with nano-lithium droplets to inhibit the growth of lithium dendrites and volume changes, thereby improving the structural stability and electrochemical performance of the composite material.

[0046] (7) Second ultrasonic emulsification: The solution after adding graphite is subjected to a second ultrasonic emulsification to form a lithium-paraffin-graphite composite slurry, which can ensure that the graphite powder and the lithium-paraffin emulsion are fully and uniformly mixed, so that lithium is effectively loaded or embedded into the pores and surface of graphite.

[0047] Third stage cleaning and post-treatment:

[0048] (8) Solvent replacement and separation: Add a second solvent, n-hexane, cyclohexane, or alkylbenzene, to the solution after the second ultrasonic emulsification and graphite addition to clean and replace the paraffin. These solvents are good solvents for paraffin and do not react with lithium, and can effectively dissolve and wash away the paraffin that encapsulates lithium particles.

[0049] (9) Selection of separation method: (9.1) Static precipitation: Static precipitation separates the static precipitate. Static precipitation is suitable for systems with larger particles and faster settling speed, and is more economical; (9.2) High-speed centrifugation: High-speed centrifugation can separate fine composite powder more quickly and thoroughly, and is more efficient. The high-speed centrifugation precipitate is used to obtain pure lithium-graphite composite solid.

[0050] (10) Collect solid precipitates, and combine the precipitates separated by static sedimentation and the precipitates separated by high-speed centrifugation;

[0051] (11) Vacuum drying to remove residual solvent. The collected and combined precipitates are vacuum dried at a low temperature of 60~80°C and under negative pressure. This can completely remove residual n-hexane and trace amounts of water, preventing them from having an adverse effect on subsequent battery manufacturing.

[0052] (12) Selective sieving: the undersize material is the target powder with a particle size <0.2μm, controlling the particle size distribution of the final product to ensure batch consistency and uniformity of electrochemical performance. The oversize material is the large particles that can be removed due to agglomeration or abnormal growth, resulting in the final product composite powder.

[0053] The preparation method of the present invention can be further described as follows:

[0054] In step (2), the preheating temperature of the paraffin solvent is 200~300°C.

[0055] The rated power of the ultrasonic equipment in steps (5) and (7) is 1500W, and the adjustable range is 5%~95%.

[0056] In step (9.2), the high-speed centrifugation speed is above 150,000 RPM.

[0057] In step (11), the vacuum drying process involves a vacuum degree higher than -0.08 MPa and a temperature of 60~100℃.

[0058] The method of using the composite powder described in claims 1 to 3 for lithium replenishment of lithium battery anode is to mix graphite-coated passivated lithium powder with conductive agent and binder to form a slurry, and then coat it onto the lithium battery anode, controlling the compaction density to be 1.3 to 1.7 g / cm³.

[0059] Example 1

[0060] Graphite passivated lithium powder anode (Li:C=9:1 wt), prepared by coating passivated lithium powder:

[0061] First, the experiment was conducted in a dry room with a dew point temperature below -45°C, and all critical operations were performed in a glove box filled with high-purity argon to keep the ambient water content at an extremely low level.

[0062] In a 250 mL reaction vessel, 30 mL of liquid paraffin was added as the first solvent and reaction medium, and melted under heating at 220°C. Subsequently, 1.5 g of commercial lithium flakes were added to the molten paraffin and initially dispersed by mechanical stirring. Next, the mixture was pre-treated using an ultrasonic emulsification process, with the power set at 30% of the rated power for 10 minutes, breaking down and dispersing the molten lithium flakes into micron / nano-scale droplets, forming a uniform lithium / paraffin emulsion.

[0063] Then, 0.16 grams of graphite powder were precisely added to the emulsion, and a second ultrasonic emulsification was immediately performed. This step was performed at 50% power for 20 minutes to utilize stronger shear force to fully and uniformly combine the graphite powder with the lithium droplets, forming a stable lithium-paraffin-graphite three-phase slurry.

[0064] After compounding, 1000 mL of n-hexane was added to the system as a second solvent. Hexane, as a good solvent for paraffin, effectively dissolves and elutes the paraffin coating on the surface of the composite powder. The washed mixture was allowed to stand for 12 hours, and solid-liquid separation was achieved by gravity sedimentation. After sedimentation, the upper layer of clear n-hexane containing paraffin was carefully poured off, and the solid precipitate at the bottom was collected.

[0065] The resulting precipitate was transferred to a vacuum drying oven and dried at 80°C for 6 hours to completely remove residual n-hexane solvent. Finally, the dried block product was sieved through a standard 300-mesh sieve (approximately 48 μm pore size) to obtain a final product with good flowability—lithium / graphite composite powder—for subsequent material characterization and electrochemical testing.

[0066] Negative electrode preparation

[0067] The first stage is negative electrode pulping.

[0068] Formulation (by mass): Active material: graphite 96~97.5%; Conductive agent: conductive carbon black (e.g., SP); Binder: PVDF (polyvinylidene fluoride) 1.5~2%

[0069] Solvent: N-methylpyrrolidone (NMP) in appropriate amount, to adjust the solid content to 45-55%.

[0070] The solid content should be controlled between 45% and 55%, which directly affects the viscosity and coating performance of the slurry.

[0071] A) PVDF adhesive preparation: In a planetary mixer, first add a portion of NMP solvent. While stirring slowly, gradually add the measured amount of PVDF powder to prevent clumping. After the addition is complete, increase the speed and stir under vacuum for 1-2 hours until the PVDF is completely dissolved, forming a homogeneous, semi-transparent adhesive.

[0072] b) Wet mixing of active material, conductive agent, and graphite: The conductive agent and active material are slowly added to the PVDF adhesive prepared in step a under high-speed stirring. The viscosity of the adhesive is used to fully disperse the conductive agent under high-speed shear force, breaking its agglomerates and forming a conductive paste.

[0073] c) After all the ingredients are added, switch to high speed / revolution mode and vacuum stir for 1-3 hours to ensure that all components are highly uniformly mixed.

[0074] d) Viscosity Adjustment and Discharge: Check the viscosity and solid content of the slurry. If the viscosity is too high, add a small amount of NMP for fine adjustment. After the slurry is qualified, discharge it to the transfer tank and perform degassing treatment (static degassing or centrifugal degassing) to remove the gas entrained during the stirring process.

[0075] Phase Two: Electrode Forming

[0076] Coating: Current collector: Electrolytic 8μm thick copper foil.

[0077] Equipment: Slot extrusion coating machine.

[0078] Key parameter: Areal density. The mass of active material per unit area is precisely controlled by adjusting the slit size of the coating head, coating speed, and slurry pumping pressure. The areal density deviation between the two sides of the electrode must be strictly controlled to <±1.5%.

[0079] Environment: It needs to be carried out in a dry room with low humidity, such as dew point < -30℃, to prevent NMP from absorbing moisture.

[0080] Drying: Equipment: 3-5 temperature zone high-pressure convection oven. Process: Temperature is set from low to high. The low temperature zone allows NMP to evaporate slowly, avoiding surface crust formation and "cracking"; the high temperature zone ensures the electrode is completely dry.

[0081] Cold pressing: Equipment: Roller press. The purpose is to improve the bonding strength between the electrode and the current collector, increase the compaction density of the active material, and improve the volumetric energy density of the battery. It results in a smooth and even electrode surface with uniform thickness. The key parameter is compaction density. By adjusting the roller gap and pressure, the electrode is rolled to the target thickness. The typical compaction density range for graphite anodes is 1.5 ~ 1.7 g / cm³.

[0082] Phase 3: Post-processing

[0083] Cutting / Slitting: Depending on the battery type (e.g., cylindrical, square, pouch), use a die-cutting machine or slitting machine to cut the entire roll of electrode sheets into the required size and shape.

[0084] Vacuum drying: Purpose: To remove trace amounts of moisture adsorbed by the electrodes from the air and trace amounts of solvent remaining after baking. Process: Place the cut electrodes in a vacuum oven and bake at 120~150℃ for 4~12 hours. This step is crucial for ensuring low moisture content in the battery, extending its lifespan, and improving safety.

[0085] Example 2

[0086] The graphite passivated lithium powder anode (Li:C=1:9 wt) was prepared using the same process as in Example 1, except for the different preparation parameters of the target lithium powder.

[0087] Preparation of coated lithium powder:

[0088] First, the experiment was conducted in a dry room with a dew point temperature below -45°C, and all critical operations were performed in a glove box filled with high-purity argon to keep the ambient water content at an extremely low level.

[0089] In a 250 mL reaction vessel, 90 mL of liquid paraffin was added as the first solvent and reaction medium, and melted at 220°C. Subsequently, 0.16 g of commercial lithium flakes were added to the molten paraffin and initially dispersed by mechanical stirring. Next, the mixture was pre-treated using an ultrasonic emulsification process, with the power set at 50% of the rated power for 10 minutes, breaking down and dispersing the molten lithium flakes into micron / nano-scale droplets, forming a uniform lithium / paraffin emulsion.

[0090] Then, 1.5 grams of graphite powder were precisely added to the emulsion, and a second ultrasonic emulsification was immediately performed. This step was performed at 80% power for 10 minutes to utilize stronger shear force to fully and uniformly combine the graphite powder with the lithium droplets, forming a stable lithium-paraffin-graphite three-phase slurry.

[0091] The subsequent process is the same as in Example 1, resulting in the final negative electrode and button cell.

[0092] Example 3

[0093] - Graphite passivated lithium powder anode (Li:C=1:1 wt), all other processes are the same as in Example 1, only the preparation parameters of the target lithium powder are different.

[0094] Preparation of coated lithium powder:

[0095] First, the experiment was conducted in a dry room with a dew point temperature below -45°C, and all critical operations were performed in a glove box filled with high-purity argon to keep the ambient water content at an extremely low level.

[0096] In a 250 mL reaction vessel, 60 mL of liquid paraffin was added as the first solvent and reaction medium, and melted under heating at 220°C. Subsequently, 0.8 g of commercial lithium flakes were added to the molten paraffin and initially dispersed by mechanical stirring. Next, the mixture was pre-treated using an ultrasonic emulsification process, with the power set at 30% of the rated power for 10 minutes, breaking down and dispersing the molten lithium flakes into micron / nano-scale droplets, forming a uniform lithium / paraffin emulsion.

[0097] Then, 0.8 grams of graphite powder were precisely added to the emulsion, and a second ultrasonic emulsification was immediately performed. This step was performed at 50% power for 20 minutes to utilize stronger shear force to fully and uniformly combine the graphite powder with the lithium droplets, forming a stable lithium-paraffin-graphite three-phase slurry.

[0098] The subsequent process is the same as in Example 1, resulting in the final negative electrode and button cell.

[0099] Summary of Comparative Analysis of Results for Each Case

[0100] Sample Primary efficiency Capacity retention @ 100 cycles Comparative Example 1 97.5% 98.2% Comparative Example 2 85.3% 83.4% Example 1 92.5% 91.6% Example 2 98.2% 95.2% Example 3 90.3% 93.5%

[0101] Comparative Example 1 uses a coin cell half-cell commonly used in electrochemical research and development. Its positive electrode uses commercially available LFP (lithium iron phosphate), and its negative electrode uses pure lithium foil. This effectively provides an unlimited supply of lithium for replenishment, ignoring SEI formation and electrolyte side reactions, resulting in high initial efficiency and capacity retention. Comparative Example 2 uses a coin cell full cell also commonly used in electrochemical research and development. Its positive electrode uses commercially available LFP, and its negative electrode uses pure graphite. Its initial efficiency is mainly limited by the active lithium consumed by the solid electrolyte interphase (SEI) film formed during the first charge-discharge cycle of the graphite negative electrode. Similarly, due to the continuous consumption of the SEI film and the formation of dead lithium in the graphite during multiple charge-discharge cycles, Comparative Example 2 has lower initial efficiency and capacity retention.

[0102] The composite powder described in Example 1 has a Li:C ratio of 9:1 wt. With lithium as the main material and graphite as a small amount of modifier, its initial efficiency and capacity retention are close to those of a pure lithium anode. However, the high proportion of lithium weakens the passivation effect of the lithium powder, increases safety risks, and raises the cost of the composite material. It also suffers from the same problem as pure lithium anodes: the tendency to develop lithium dendrites.

[0103] The composite powder described in Example 2 has a Li:C ratio of 1:9 wt. In this case, graphite is the main material, and lithium is used as a small amount of modifying material. The initial efficiency and capacity retention are close to those of pure graphite anodes. However, compared to pure graphite anodes, both initial efficiency and capacity retention are significantly improved. This is because the lithium in the composite powder can effectively act as a lithium replenisher, supplementing the lithium ions consumed by the formation of the SEI film and dead lithium during multiple charge-discharge cycles of the graphite anode. Furthermore, the more graphite present, the better the passivation effect and air stability of the composite powder, making it more suitable for large-scale industrial production.

[0104] Based on the above data and analysis, Example 3 adjusted the Li:C ratio to 1:1, and the data matched the above analysis, with the first-efficiency performance and capacity retention at a moderate level. Furthermore, Example 3 demonstrates that the composite powder described in this invention has a highly adjustable composite ratio of graphite and lithium. Electron microscopy images show that the powder has uniform particle size and good dispersibility.

[0105] As described above, the present invention can be well implemented. The above embodiments are only the best implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are all included within the protection scope of the present invention.

Claims

1. Graphite-coated passivated lithium powder, characterized in that... It includes 5-95 wt% active material graphite and 5-95 wt% lithium metal powder. The finished product is a core-shell structured composite powder with highly active pure lithium metal powder in the middle and graphite powder on the outside. The macroscopic morphology is gray-black, which is common in metals. The microscopic particle size is 0.1-200 μm. The composite powder has good flowability, uniform dispersion, and no agglomeration or caking.

2. The composite powder according to claim 1, characterized in that... The composite powder has a particle size of 0.2 μm.

3. The composite powder according to claim 1, characterized in that... The ratio of highly active pure lithium metal powder, graphite, and lithium metal powder in the composite powder is appropriately adjusted so that it can directly serve as the negative electrode active material to replenish lithium to the negative electrode of the lithium battery.

4. A method for preparing graphite-coated passivated lithium powder, characterized in that... Specifically, it includes the following stages, steps, and conditions: Phase 1: Environmental and Raw Material Pretreatment (1) Environmental preparation: dew point room and glove box, so that the dew point in the dew point room is <-40℃ and the corresponding water content is <120 ppm, which can ensure the quality and safety of the reaction; (2) Preheating with paraffin solvent: Paraffin is used as an inert medium and the first solvent to ensure that air is isolated, heat is conducted and lithium droplets are dispersed; (3) Pre-melting of lithium sheets: Lithium sheets are added to heated paraffin wax to form a lithium-paraffin mixture; Second-stage compounding and emulsification: (4) Mechanical stirring: a high-speed dispersion process is adopted, and the lithium-paraffin mixture is thoroughly stirred with dispersion blades, which can improve the subsequent ultrasonic emulsification effect; (5) First ultrasonic emulsification: using the emulsification effect of ultrasound, the molten lithium sheet is broken into droplets of micron or even nanometer scale and uniformly dispersed in paraffin to form an emulsion, which can greatly increase the specific surface area and lay the foundation for subsequent uniform composite with graphite. (6) Adding graphite powder, with graphite as a carrier or buffer framework, is intended to be combined with nano-lithium droplets to inhibit the growth of lithium dendrites and volume changes, thereby improving the structural stability and electrochemical performance of the composite material. (7) Second ultrasonic emulsification: The solution after adding graphite is subjected to a second ultrasonic emulsification to form a lithium-paraffin-graphite composite slurry, which can ensure that the graphite powder and the lithium-paraffin emulsion are fully and uniformly mixed, so that lithium is effectively loaded or embedded into the pores and surface of graphite. Third stage cleaning and post-treatment: (8) Solvent replacement and separation: Add a second solvent, n-hexane, cyclohexane, or alkylbenzene, to the solution after the second ultrasonic emulsification and graphite addition to clean and replace the paraffin. These solvents are good solvents for paraffin and do not react with lithium, and can effectively dissolve and wash away the paraffin that encapsulates lithium particles. (9) Selection of separation method: (9.1) Static precipitation: Static precipitation separates the static precipitate. Static precipitation is suitable for systems with larger particles and faster settling speed, and is more economical; (9.2) High-speed centrifugation: High-speed centrifugation can separate fine composite powder more quickly and thoroughly, and is more efficient. The high-speed centrifugation precipitate is used to obtain pure lithium-graphite composite solid. (10) Collect solid precipitates, and combine the precipitates separated by static sedimentation and the precipitates separated by high-speed centrifugation; (11) Vacuum drying to remove residual solvent. The collected and combined precipitates are vacuum dried at a low temperature of 60~80°C and under negative pressure. This can completely remove residual n-hexane and trace amounts of water, preventing them from having an adverse effect on subsequent battery manufacturing. (12) Selective sieving: the undersize material is the target powder with a particle size <0.2μm, controlling the particle size distribution of the final product to ensure batch consistency and uniformity of electrochemical performance. The oversize material is the large particles that can be removed due to agglomeration or abnormal growth, resulting in the final product composite powder.

5. The method according to claim 4, characterized in that: In step (2), the preheating temperature of the paraffin solvent is 200~300°C.

6. The method according to claim 1, characterized in that: The rated power of the ultrasonic equipment in steps (5) and (7) is 1500W, and the adjustable range is 5%~95%.

7. The method according to claim 1, characterized in that: In step (9.2), the high-speed centrifugation speed is above 150,000 RPM.

8. The method according to claim 1, characterized in that: In step (11), the vacuum drying process involves a vacuum degree higher than -0.08 MPa and a temperature of 60~100℃.

9. The method according to claim 1, characterized in that... The method of using the composite powder described in claims 1 to 3 for lithium replenishment in lithium battery anodes involves mixing graphite-coated passivated lithium powder with a conductive agent and a binder to form a slurry, which is then coated onto the lithium battery anode, with the compaction density controlled at 1.3 to 1.7 g / cm³.

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