Low-expansion fast-charging modified graphite negative electrode material and preparation method and application thereof

Abstract

This invention discloses a low-expansion, fast-charging modified graphite anode material, its preparation method, and its application. The method includes the following steps: A solution of alkaline earth metal fluorides is spray-dried to uniformly deposit onto the surface of crushed, pulverized, and granulated coke raw material, yielding a coke material containing alkaline earth metal fluorides; the coke material is then subjected to low-temperature activation treatment at 800-1000°C under an inert atmosphere to obtain a product; the product is mixed uniformly with the alkaline earth metal fluoride solution and impregnated, followed by graphitization under an inert atmosphere to obtain the modified graphite anode material. This invention introduces alkaline earth metal fluorides for doping modification during the preparation process, thereby promoting impurity removal, improving graphitization efficiency, and ultimately preparing an anode material with a low coefficient of expansion.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and particularly relates to a low-expansion fast-charging modified graphite anode material, its preparation method, and its application. Background Technology

[0002] In lithium-ion battery anode materials, the coefficient of thermal expansion of graphite significantly affects the battery's longevity and safety. Traditional graphitization processes typically require high temperatures of around 3000℃ to obtain an optimal graphite structure. However, high-temperature graphitization is energy-intensive, difficult to control impurity removal, and not conducive to low-cost production.

[0003] In the prior art, the patent application with publication number CN115377414A and invention title "Carbon anode material and its preparation method, lithium-ion battery anode, lithium-ion battery and electrical equipment" uses asphalt liquid phase to coat graphite anode, but the carbon material anode has a lower first efficiency and the overall energy density is lower than that of low expansion graphite anode material. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a low-expansion fast-charging modified graphite anode material, its preparation method and application.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for preparing a low-expansion, fast-charging modified graphite anode material includes the following steps: (1) The alkaline earth metal fluoride solution is uniformly deposited onto the surface of the coke raw material that has been crushed, pulverized and granulated by spray drying process to obtain coke material containing alkaline earth metal fluoride; (2) The coke material containing alkaline earth metal fluorides is subjected to low-temperature activation treatment at 800~1000℃ under an inert atmosphere to obtain the product; (3) The product is mixed evenly with an alkaline earth metal fluoride solution and impregnated, and then graphitized under an inert atmosphere to obtain a modified graphite anode material.

[0006] Furthermore, the coke raw material is pitch coke and / or petroleum coke.

[0007] Furthermore, the alkaline earth metal fluoride is magnesium fluoride and / or calcium fluoride.

[0008] Furthermore, the alkaline earth metal fluoride mentioned in step (1) is magnesium fluoride, and the amount of magnesium fluoride added is 0.5-3% of the mass of the coke raw material.

[0009] Furthermore, the alkaline earth metal fluoride mentioned in step (3) is calcium fluoride, and the amount of calcium fluoride added is 0.5-3% of the mass of the coke raw material.

[0010] Further, in step (2), the temperature is increased to 800-1000℃ at a heating rate of 8-12℃ / min and held for 1.5-2.5h.

[0011] Furthermore, the impregnation treatment time in step (3) is 20~30 hours; the graphitization temperature is 1800~2500℃ and the time is 5~8 hours.

[0012] The present invention also provides a low-expansion fast-charging modified graphite anode material, which is prepared by the preparation method described above.

[0013] The present invention also provides a battery negative electrode comprising the aforementioned low-expansion fast-charging modified graphite negative electrode material.

[0014] The present invention also provides a lithium-ion battery, which includes the aforementioned battery negative electrode.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention prepares graphite anode materials with large interlayer spacing through staged heat treatment. During the preparation process, alkaline earth metal fluorides (magnesium fluoride / calcium fluoride) are introduced for doping modification to promote the removal of impurities and improve graphitization efficiency, thereby preparing anode materials with low expansion coefficient. This material has broad application prospects in high-end fast-charging long-cycle battery cells. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a specific capacity diagram of the modified graphite anode material prepared in Example 2; Figure 2 This is an electron microscope image of the modified graphite anode material prepared in Example 2; Figure 3 The results show the expansion rates of the graphite anode materials in the examples and comparative examples. Detailed Implementation

[0018] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0019] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0020] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0021] In some specific embodiments, the preparation method of the low-expansion fast-charging modified graphite anode material of the present invention includes the following steps: (1) The alkaline earth metal fluoride (e.g., magnesium fluoride) solution is spray-dried to uniformly deposit onto the surface of the coke raw material that has been crushed, pulverized and granulated, so as to obtain coke material containing alkaline earth metal fluoride.

[0022] In some embodiments, the coke raw materials are preferably pitch coke and petroleum coke, wherein petroleum coke accounts for 10-30% of the mass of pitch coke.

[0023] In this invention, the main characteristics of pitch coke are: the carbon content is usually above 90%, which provides good electrochemical performance, which is very beneficial for the preparation of lithium-ion battery anode materials; the impurity content is low, especially sulfur, nitrogen and other impurities, which helps to improve electrochemical stability and conductivity; its structure is similar to hard carbon, with some pores and disordered structure inside, which is conducive to the insertion and extraction of lithium ions, giving it good cycle performance and rate performance.

[0024] In some embodiments, the particle size is controlled at 8-15 μm during the granulation process.

[0025] In some embodiments, the amount of magnesium fluoride added is 0.5-3% of the mass of the coke raw material.

[0026] By using a spray drying process, liquid is dispersed into fine droplets and dried rapidly to form microparticles containing alkaline earth metal fluorides. This method can uniformly distribute magnesium fluoride in the microstructure.

[0027] (2) The coke material containing alkaline earth metal fluorides is subjected to low-temperature activation treatment at 800~1000℃ under an inert atmosphere to obtain the product.

[0028] In some embodiments, the temperature is increased to 800-1000°C at a heating rate of 8-12°C / min and held for 1.5-2.5 hours.

[0029] During the low-temperature activation process, magnesium fluoride can promote local carbon rearrangement in pitch coke, transforming pitch coke into primary graphite microcrystals and forming magnesium fluoride-coated microregions in pitch coke.

[0030] (3) The product is mixed evenly with an alkaline earth metal fluoride (e.g., calcium fluoride) solution and impregnated, and then graphitized under an inert atmosphere to obtain a modified graphite anode material.

[0031] In some embodiments, the amount of calcium fluoride added is 0.5-3% of the mass of the coke raw material.

[0032] In some embodiments, the immersion treatment time is 20 to 30 hours.

[0033] The product is impregnated in an alkaline earth metal fluoride solution, allowing the solution to fully penetrate the pores of the carbon material. After impregnation, the material is dried to remove moisture, followed by graphitization. The alkaline earth metal fluoride can promote the structural rearrangement of the carbon material at high temperatures, promote carbon migration, lower the graphitization activation energy, and facilitate the formation of a graphitized structure.

[0034] Mg in magnesium fluoride 2+ With its small radius and strong polarization ability, calcium fluoride primarily functions to form surface micropores, activate edges, and create precursor structures that are more easily graphitized. With a melting point of approximately 1400 degrees Celsius, calcium fluoride exhibits fluidity at high temperatures, effectively promoting microcrystal growth. Magnesium fluoride is used to induce the formation of carbon framework defects and activate microstructures at low temperatures, while calcium fluoride promotes the ordering of graphite crystals and the reconstruction of layered structures at high temperatures, thus achieving a synergistic optimization of fast ion diffusion and high structural stability.

[0035] In some embodiments, the graphitization temperature is 1800~2500℃ and the time is 5~8h.

[0036] The role of alkaline earth metal fluorides (calcium fluoride / magnesium fluoride) in this invention is as follows: (1) Impact on cycle performance: 1) Enhanced Structural Stability: Doping with alkaline earth metal fluorides improves the structural stability of carbon materials. During graphitization, alkaline earth metal fluorides effectively suppress the formation of dislocations or defects in the graphite layer, resulting in a more ordered and durable graphite structure. This more stable structure better maintains the material's integrity during charge-discharge cycles, reducing capacity decay and increasing cycle life.

[0037] 2) Reduced side reactions: Alkaline earth metal fluorides can form a stable passivation layer on the graphite surface, reducing side reactions between the negative electrode material and the electrolyte. This passivation layer helps reduce electrolyte decomposition reactions, thereby reducing irreversible capacity loss and improving coulombic efficiency and long-term stability.

[0038] 3) Improved lithium insertion / extraction kinetics: Alkaline earth metal fluoride doping can adjust the microstructure of graphite, providing more lithium insertion sites or improving lithium-ion diffusion channels, thereby enhancing the lithium-ion insertion and extraction rates. This is significantly helpful for long-term high-rate charge and discharge, improving battery stability under fast charging and long-cycle conditions.

[0039] (2) Effect on expansion properties: 1) Reduced volume expansion: Alkaline earth metal fluoride-doped graphite exhibits less volume expansion. This may be because the doped graphite structure has a denser and more stable interlayer structure, which can disperse stress during the charging and discharging process. The presence of alkaline earth metal fluorides can suppress excessive interlayer spacing changes in the graphite anode during charging and discharging, reduce volume expansion, and enhance the mechanical stability of the anode material.

[0040] 2) Mitigating Dendrite Growth: At high rates, excessive lithium insertion can lead to lithium metal deposition and even dendrite formation, thus affecting battery safety and lifespan. Doping with alkaline earth metal fluorides creates a passivation layer on the surface, making it easier for lithium ions to be uniformly inserted into the graphite layer rather than deposited on the negative electrode surface. This helps reduce dendrite growth and indirectly lowers the risk of expansion.

[0041] 3) Lower lithium insertion volume change: Alkaline earth metal fluoride doping can alter the interlayer spacing of graphite, making it more stable during lithium-ion insertion and extraction, thereby reducing the expansion effect of the anode material. Especially after long-term use, volume change and battery expansion are often not significant, thus improving the overall stability and reliability of the cell.

[0042] (3) Impact on fast charging performance: Unmodified graphite surfaces have carbon-based defects and mostly contain organic components. After modification with alkaline earth metal fluorides, the residual trace amounts of F on the surface form a LiF-rich inorganic SEI, which lowers the desolvation energy barrier. The proportion of organic matter in the formed SEI film decreases, while the proportion of inorganic matter such as LfF and Li2CO3 increases. The SEI has the characteristics of being more dense, stable, electronically insulating, and having higher ion conductivity.

[0043] Example 1 Pitch coke is mixed with 10% petroleum coke by mass, crushed to millimeter size and dried. It is then pulverized using a roller mill to control the particle size D50 to approximately 8μm, followed by granulation to further reduce the D50 to 13-15μm, yielding the coke raw material.

[0044] A 10wt% magnesium fluoride (MgF2) solution (magnesium fluoride accounts for 0.5% of the total mass of coke raw materials) is prepared and uniformly deposited onto the surface of the coke raw materials through a spray drying process (dispersing the liquid into fine droplets and drying it rapidly) while stirring the coke raw materials to form coke material containing magnesium fluoride.

[0045] The sample was then transferred to an atmosphere furnace, and nitrogen was used as a protective gas throughout the process to raise the temperature to 1000℃ at a rate of 10℃ / min and hold it at that temperature for 2 hours to obtain the product (without graphitization).

[0046] Example 2 Pitch coke is mixed with 10% petroleum coke by mass, crushed to millimeter size and dried. It is then pulverized using a roller mill to control the particle size D50 to approximately 8μm, followed by granulation to further reduce the D50 to 13-15μm, yielding the coke raw material.

[0047] A 10wt% magnesium fluoride (MgF2) solution (magnesium fluoride accounts for 0.5% of the total mass of coke raw materials) is prepared and uniformly deposited onto the surface of the coke raw materials through a spray drying process (dispersing the magnesium fluoride solution into fine droplets and drying it rapidly) while stirring the coke raw materials to form coke material containing magnesium fluoride.

[0048] The sample was then transferred to an atmosphere furnace, and under nitrogen protection, the temperature was increased to 1000℃ at a rate of 10℃ / min and held for 2 hours for low-temperature activation to obtain the product. The obtained product was mixed evenly with a 10wt% calcium fluoride (CaF2) solution (calcium fluoride accounts for 0.5% of the total mass of the coke raw material), impregnated for 24 hours, dried, and then placed in a graphitization furnace for graphitization under an argon protective atmosphere at 2500℃ for 6 hours. After cooling to room temperature, the modified graphite anode material was obtained.

[0049] Electron micrograph of the modified graphite anode material is shown below. Figure 2 This indicates that the particle composite degree is relatively good.

[0050] Comparative Example 1 Pure petroleum coke was crushed to millimeter size and dried. The particle size (D50) was controlled to approximately 8 μm by roller milling, followed by granulation to further reduce D50 to 13-15 μm. The material was then placed in a graphitization furnace and graphitized under an argon protective atmosphere at 2500℃ for 6 hours, before being cooled to room temperature to obtain the graphite anode material.

[0051] Comparative Example 2 The only difference from Example 2 is that magnesium fluoride is replaced with magnesium chloride and calcium fluoride is replaced with calcium chloride.

[0052] Comparative Example 3 Pitch coke is mixed with 10% petroleum coke by mass, crushed to millimeter size and dried. It is then pulverized using a roller mill to control the particle size D50 to approximately 8μm, followed by granulation to further reduce the D50 to 13-15μm, yielding the coke raw material.

[0053] The sample was then transferred to an atmosphere furnace, where nitrogen was used as a protective gas throughout the process. The temperature was increased to 1000℃ at a rate of 10℃ / min and held for 2 hours for low-temperature activation to obtain the product. The product was then placed in a graphitization furnace and graphitized under an argon protective atmosphere at 2500℃ for 6 hours, and then cooled to room temperature to obtain the modified graphite anode material.

[0054] Performance testing: 1. The graphitization degree and powder OI value of the graphite anode material were obtained by testing the examples and comparative examples according to the national standard GB / T 24533 2019 "Graphite Anode Materials for Lithium-ion Batteries".

[0055] 2. Preparation of coin cell batteries: A binder, conductive agent, and solvent were added to the graphite anode material obtained in the examples and comparative examples. The mixture was stirred and stirred until homogeneous to form a slurry. The resulting slurry was coated onto copper foil, dried, and rolled to obtain the coin cell anode sheet. The binder was LA132 binder, the conductive agent was conductive agent SP, and the solvent was double-distilled water; the weight ratio of graphite anode material, conductive agent SP, LA132 binder, and double-distilled water was 98:1:4:220. A lithium metal sheet was used as the positive electrode, a composite membrane of polyethylene (PE), polypropylene (PP), and polyethylene propylene (PEP) was used as the separator, and LiPF6 / EC+DEC (1:1) was used as the electrolyte. Simulated battery assembly was performed in an argon-filled glove box.

[0056] The prepared coin cells were installed on a Wuhan Bluepoint CT2001A battery tester and charged at a 0.1C rate. The charge / discharge voltage range was 0.005V to 2.0V, and the initial discharge capacity was measured. The specific capacity of the modified graphite anode material prepared in Example 2 is as follows: Figure 1 .

[0057] 3. Cyclic expansion test: Anode formulation C (graphite anode material obtained in the examples and comparative examples): SP:CMC:SBR = 95.8:1:1.2:2; Cathode formulation LFP:SP:PVDF = 96:2:2; ① The negative electrode sheet was sealed in a sample bag and stored at room temperature (25±2℃). After standing for 48 hours, the expansion ratio was calculated to obtain the expansion ratio after 48 hours of cold pressing. ② After baking at 45℃±5℃ for 12 hours, the expansion ratio was calculated to obtain the expansion ratio after 12 hours of baking. ③ It was compacted to 1.6 g / cm³ according to the design. 3 The cells are rolled and then fully charged with a constant current and constant voltage of 1 / 3C. The expansion ratio is calculated, which is the cell after full charge. ④ After the cells are classified by capacity, they are cycled for 50 cycles according to the specified cycle test procedure. After the cycle, the expansion ratio is calculated to obtain the expansion ratio from rolling to the cycle. The data is then processed to obtain the final result. Figure 3Cyclic testing procedure: 50 cycles of 0.5C constant current and constant voltage charging (cutoff voltage 3.65V) and 0.5C constant current discharging (cutoff voltage 2.5V). The expansion rate is calculated according to GB / T 44027.2-2024 "Determination Methods for Carbon Materials - Part 2: Determination of Expansion Rate" to assess its structural stability.

[0058] Performance data for the examples and comparative examples are shown in Table 1.

[0059] Table 1

[0060] Example 2 has the lowest OI value and the best fast charging performance.

[0061] Comparing Examples 1-2 and Comparative Example 2, it can be seen that introducing alkaline earth metal fluorides through staged heat treatment can help adjust the structure and properties of carbon materials. The main effects are: establishing controllable microporous channels to improve fast-charging performance; increasing the local interlayer spacing, which reduces the compression of the graphite layered structure during lithium ion insertion / extraction, thereby reducing the expansion rate; lowering the graphitization activation energy; constructing "controllable inorganic residue" to adjust the SEI; and alkaline earth metal fluorides can form a stable passivation layer on the graphite surface, reducing side reactions between the negative electrode material and the electrolyte. This passivation layer helps reduce the decomposition reaction of the electrolyte, thereby reducing irreversible capacity loss and improving coulombic efficiency and long-term stability.

[0062] Compared to different halide systems, fluorides exhibit stronger structural control over graphite compared to chlorides. Fluorides, in particular, efficiently disrupt local sp² conjugation and form stable C–F bonds, introducing active defects. This demonstrates superior performance compared to chloride systems, which only exhibit mild surface-level reactions, in improving fast-charging kinetics, interfacial stability, and structural controllability. Therefore, Example 2 shows a higher capacity and better fast-charging performance than Comparative Example 2.

[0063] The electrode expansion data shows that Example 2 exhibits the lowest rebound after cold pressing, baking, charging, and cycling, demonstrating that the alkaline earth metal fluoride-modified low-expansion graphite anode material with staged heat treatment can suppress excessive interlayer spacing changes during charging and discharging, reduce volume expansion, and enhance the mechanical stability of the anode material.

[0064] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a low-expansion, fast-charging modified graphite anode material, characterized in that, Includes the following steps: (1) The alkaline earth metal fluoride solution is uniformly deposited onto the surface of the coke raw material that has been crushed, pulverized and granulated by spray drying process to obtain coke material containing alkaline earth metal fluoride; (2) The coke material containing alkaline earth metal fluorides is subjected to low-temperature activation treatment at 800~1000℃ under an inert atmosphere to obtain the product; (3) The product is mixed evenly with an alkaline earth metal fluoride solution and impregnated, and then graphitized under an inert atmosphere to obtain a modified graphite anode material.

2. The preparation method of the low-expansion fast-charging modified graphite anode material according to claim 1, characterized in that, The coke raw material is pitch coke and / or petroleum coke.

3. The preparation method of the low-expansion fast-charging modified graphite anode material according to claim 1, characterized in that, The alkaline earth metal fluoride is magnesium fluoride and / or calcium fluoride.

4. The preparation method of the low-expansion fast-charging modified graphite anode material according to claim 3, characterized in that, The alkaline earth metal fluoride mentioned in step (1) is magnesium fluoride, and the amount of magnesium fluoride added is 0.5-3% of the mass of the coke raw material.

5. The preparation method of the low-expansion fast-charging modified graphite anode material according to claim 3, characterized in that, The alkaline earth metal fluoride mentioned in step (3) is calcium fluoride, and the amount of calcium fluoride added is 0.5-3% of the mass of the coke raw material.

6. The preparation method of the low-expansion fast-charging modified graphite anode material according to claim 1, characterized in that, Step (2) Heat to 800-1000℃ at a heating rate of 8-12℃ / min and hold for 1.5-2.5h.

7. The method for preparing the low-expansion fast-charging modified graphite anode material according to claim 1, characterized in that, Step (3) The impregnation treatment time is 20~30 hours; the graphitization temperature is 1800~2500℃ and the time is 5~8 hours.

8. A low-expansion, fast-charging modified graphite anode material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 7.

9. A battery negative electrode, characterized in that, It comprises the low-expansion fast-charging modified graphite anode material as described in claim 8.

10. A lithium-ion battery, characterized in that, It includes the battery negative electrode as described in claim 9.

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