Graphite and hydrophilic oxide composite material, preparation method and application thereof and lithium ion battery

Abstract

The invention belongs to the field of battery materials, and particularly relates to a graphite and hydrophilic oxide composite material, a preparation method and application thereof and a lithium ion battery, and the preparation method of the graphite and hydrophilic oxide composite material comprises the following steps: obtaining a dispersion liquid in which graphite, hydrophilic nanoparticles and a stabilizer are dispersed; forming liquid drops from the dispersion liquid, and assembling the liquid drops on the surface of the modified substrate to form primary particles; and then roasting the primary particles to prepare the graphite and hydrophilic oxide particle composite material. The hydrophilic oxide is an oxide of at least one element of silicon, titanium, tin and iron; the stabilizer is at least one of polyethylene glycol, polyacrylic acid and polyvinylpyrrolidone; the modified substrate comprises an alkali-etched substrate and a modified material which is compounded on the surface of the alkali-etched substrate and is shown as a formula 1 (). According to the scheme, the electrochemical performance such as fast charge and the process stability of the material can be improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically to the field of graphite materials for lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries (LIBs) operate based on the presence of Li in the electrode material. + The anisotropic transport properties of commonly used graphite anodes, particularly during the insertion and extraction of lithium, limit fast-charging performance. Their low physicochemical potential (≈0.1V) can also induce lithium deposition and dendrite formation, posing safety hazards to the battery. Furthermore, polarization heating during fast charging raises the battery temperature above 60°C, accelerating electrolyte decomposition, causing SEI film rupture, and affecting battery cycle life. Despite these challenges in applying graphite in fast-charging scenarios, it remains the preferred choice for current industrial applications due to its comprehensive considerations of energy density, stability, and convenience.

[0003] Electrode structure design is considered an effective strategy to promote ion charge transport dynamics. The electrode surface is the site of initial electrochemical reactions and electron-ion exchange. Various inorganic / organic substances are constructed on the material surface, thereby affecting the structural composition of the SEI film and influencing Li + Desolvation process, improves Li + / Electron transport capability. Depending on whether the constructed interface is compatible with Li + Interfacial materials can be categorized into reactive and non-reactive interfaces. Reactive interfacial layers can react with Li... + It reacts and participates in the formation of SEI during (de)lithiation. The non-reactive interface layer is compatible with lithium metal and LiC6, and can remain stable and promote interface transport during (de)lithiation. Most of them are core-shell structures with graphite as the core and forming a shell on the outer surface.

[0004] A typical example of a core-shell structure is the amorphous carbon-coated graphite anode. The amorphous carbon shell effectively isolates the electrolyte, forming a stable SEI film and alleviating stress caused by volume expansion, thus improving electrode cycle stability. Simultaneously, the carbon shell exhibits good conductivity, which is beneficial for the transport and diffusion of electrons and lithium ions, enhancing fast-charging performance. Furthermore, core-shell structures coated with non-reactive metal oxides are also a recent research hotspot. Jiang et al. reported a hard carbon / alumina dual-coated graphite (AG@HC@Al2O3) anode material for high-rate lithium-ion batteries. The hard carbon acts as the inner layer of the dual coating to improve rate performance, while the alumina outer layer acts as an artificial SEI film, effectively blocking electron entry, inhibiting electrolyte decomposition, and improving interfacial wettability. Kim et al. reported a graphite anode material coated with oxygen-deficient black titanium oxide, which maintained a capacity of 98.2% after cycling at 5C rate. Transition metals can also serve as a shell for graphite. Tallman et al. coated nanoscale Ni onto graphite electrodes using DC magnetron sputtering, thereby increasing the overpotential for Li nucleation and suppressing Li deposition. Compared to bare graphite electrodes, the Ni-coated graphite electrodes exhibited 50% less Li deposition, and the corresponding full-cell test showed a capacity retention of 90% after 300 cycles at 6C. Additionally, the organic polymer shell can serve as an artificial SEI film on the graphite surface to improve Li. + Transport. Zheng et al. proposed a recycled graphite electrode coated with a PMMA layer. During the (de)lithiation process, a composite SEI structure consisting of an inner PMMA layer and an outer natural SEI is formed. This composite SEI structure can reduce electrolyte decomposition and inhibit lithium deposition, thus the electrode exhibits excellent electrochemical cycling performance (at 1 mA / cm). 2 Under the given current density conditions, after 180 cycles, the Coulomb efficiency remains almost above 97%. .

[0005] Common methods for synthesizing core-shell structures include one-pot synthesis, sol-gel synthesis, self-assembly, and template synthesis. In the one-pot synthesis, the reaction and structure formation occur simultaneously in a container, without the need for pre-synthesizing the core and separating the intermediate phase, significantly saving cost and time, making it suitable for large-scale production. However, the one-pot method is extremely demanding in controlling temperature, concentration, stirring rate, and additives, and the core-shell structure formation is completed in only one step, making it difficult to precisely control parameters such as the number of shell layers, shell thickness, and core size. The sol-gel method uses metal alkoxides or inorganic salts as precursors, which undergo hydrolysis and condensation reactions in the liquid phase to form a sol, which is then aged to transform into a gel. Finally, it is dried and calcined to form a uniform shell layer on the surface of the pre-formed core particles. This method can achieve shell coating with complex chemical compositions, resulting in continuous, dense, and homogeneous shell components. The shell thickness can be controlled at the nanoscale by adjusting the precursor concentration and reaction time. However, the drawbacks include the multiple steps involved in the process, the requirement for high temperatures during calcination to obtain a well-crystallized shell which can easily damage the core material structure, and the tendency for shell shrinkage and cracking during drying and calcination. More importantly, the organic solvents used as precursors are mostly toxic, which is detrimental to the environment. Self-assembly, on the other hand, utilizes intermolecular forces or the guiding effect of surfactants to spontaneously and orderly adsorb or assemble the shell precursor onto the surface of the core particle, forming a core-shell structure (often involving surface functionalization to enhance interactions). The reaction conditions are mild, allowing for the acquisition of core-shell particles with uniform size and atomic / molecular thickness at low temperatures. In the battery field, self-assembly can be used to construct ion channels and high specific surface area structures, improving ion transport and catalytic reaction efficiency in batteries, showing great potential. The disadvantages are that its preparation process requires specific surface functionalization treatment of the core particle (introducing specific functional groups) to promote assembly, resulting in high costs. Secondly, the application of shell materials is limited, only suitable for materials that can exist stably in solution and effectively interact with the core surface. Finally, the finished shell has weak adhesion and may peel off during battery cycling. While hard template methods can precisely control the morphology, size, and thickness of the shell, promoting the adjustment and optimization of core-shell material properties, the strong acid etching used may corrode or damage the shell structure and is difficult to completely remove. Soft template methods use vesicles composed of amphiphilic surfactants and block agents as templates, offering a simple preparation process that does not require etching with strong acid corrosive agents. However, their stability is poor; the dynamic aggregates formed by weak intermolecular interactions are easily affected by external conditions, making morphology difficult to control. Furthermore, template removal is also difficult, and residual surfactants or polymers are detrimental to battery applications (increasing interfacial resistance, forming unstable SEI films, and blocking ion transport).

[0006] [1]Dan. JL, Jin. CX, Wen. LJ et al. A double-layer-coated graphiteanode material for high-rate lithium-ion batteries. Solid State Sci, 2023, (141), 107220.

[0007] [2]Kim DS, Chung DJ, Bae J, et al. Surface engineering of graphiteanode material with black TiO2-x for fast chargeable lithium ion battery. Electrochimica acta, 2017, (258) 336-342.

[0008] [3]Killian. R, Tallman. B. Z, Lei. W, et al. Anode OverpotentialControl via Interfacial Modification: Inhibition of Lithium Plating onGraphite Anodes. ACS Appl. Mater. Interfaces. 2019, 11(50), 46864-46874.

[0009] [4]Zheng. G, Wang. C, Pei. A, et al. High-performance lithium metalnegative electrode with a soft and flowable polymer coating. ACS Energy Lett, 2016, 1(6): 1247-1255. Summary of the Invention

[0010] To address the problems existing in the prior art, the primary objective of this invention is to provide a method for preparing graphite@hydrophilic oxide composite materials, aiming to obtain graphite@hydrophilic oxide composite materials with excellent morphology and properties based on a simple evaporation-driven assembly method.

[0011] The second objective of this invention is to provide a graphite@hydrophilic oxide composite material prepared by the aforementioned method and its application in lithium-ion batteries.

[0012] A third objective of this invention is to provide a lithium-ion battery comprising the graphite@hydrophilic oxide composite material.

[0013] For dispersion systems containing graphite and hydrophilic oxide particles, ring-shaped pinning and other problems easily form during self-assembly, which can lead to the failure of coating structure construction and unsatisfactory material morphology and uniformity. To address this problem, this invention, after in-depth research, provides the following improvement:

[0014] A method for preparing graphite@hydrophilic oxide composite material involves obtaining a dispersion liquid containing graphite, hydrophilic oxide and stabilizer; forming droplets from the dispersion liquid and assembling them on the surface of a modified substrate to form primary particles; and then calcining the primary particles to obtain the graphite@hydrophilic nanoparticle composite material.

[0015] The hydrophilic oxide particles are oxides of at least one element selected from silicon, titanium, tin, and iron.

[0016] The stabilizer is at least one of polyethylene glycol (PEG), polyacrylic acid (PAA), and polyvinylpyrrolidone (PVP);

[0017] The modified substrate includes an alkaline-etched substrate and a modified material of formula 1 composite on its surface;

[0018] Formula 1

[0019] In R1 to R4, at least one substituent is a fluoroalkyl group, and the remaining substituents are alkyl, alkoxy, or fluoroalkyl groups.

[0020] In the dispersion, the total percentage of graphite and hydrophilic nanoparticles is 0.8 wt.%~4 wt.%; the weight ratio of hydrophilic oxide to graphite is 1:2~5; the stabilizer is 0.8 wt.%~4 wt.% of the total weight of hydrophilic oxide and graphite.

[0021] This invention innovatively forms droplets from a dispersion of graphite, hydrophilic oxide particles, and a stabilizer, and then drives the droplets to assemble on the modified surface of a specially modified substrate through evaporation. This allows the hydrophilic oxide particles in the droplets to distribute on the surface of the graphite agglomerates based on the interaction between the droplets and the modified substrate, forming a core-shell structure. Further calcination of this structure allows for the simple acquisition of a graphite@hydrophilic oxide particle composite material with excellent structure and morphological uniformity, while also exhibiting excellent fast charging, high rate stability, and batch stability.

[0022] In this invention, the particle size of graphite ranges from 80nm to 200nm, preferably from 100nm to 150nm;

[0023] Hydrophilic oxides include at least one of silicon dioxide, titanium dioxide, tin dioxide, and iron oxide;

[0024] Preferably, the particle size of the hydrophilic oxide is between 5 nm and 30 nm, and more preferably between 10 nm and 20 nm.

[0025] Preferably, the hydrophilic oxide comprises particles A and particles B, wherein particle A is silicon dioxide with a D50 of 5-15 nm, and particle B is titanium dioxide with a D50 of 20-30 nm.

[0026] The research of this invention shows that the combination of composite hydrophilic oxides with special materials and particle sizes, in conjunction with the self-assembly preparation process described in this invention, can more effectively prevent direct contact between the electrolyte and the graphite core, improve mechanical strength, and thus synergistically improve the fast charging and process stability of the prepared material.

[0027] In this invention, the weight ratio of particle A to particle B in the hydrophilic oxide is 1:1 to 5; more specifically, it can be 1:2 to 3.

[0028] Preferably, the weight ratio of hydrophilic nanoparticles to graphite in the dispersion can be 1:3~4.

[0029] Preferably, the total percentage of graphite and hydrophilic nanoparticles in the dispersion is 1 wt.% to 3.5 wt.%; more preferably 1 to 1.5 wt.%. Studies have shown that the preferred content helps to further combine with the self-assembly process described in this invention, thereby further improving the fast-charging performance and process stability of the prepared material.

[0030] Preferably, conductive carbon black nanoparticles are also added to the dispersion; the particle size D50 of the conductive carbon black nanoparticles is 20~50nm, and the amount added is 10%~40% of the total mass of the hydrophilic nanoparticles and the conductive carbon black nanoparticles.

[0031] In this invention, the use of the conductive agent can complement the self-assembly process described herein, facilitating the formation of an electrically conductive bridge between graphite and hydrophilic oxides, optimizing the electron transport pathway, and contributing to further optimization of the electrochemical properties of the prepared material, such as fast charging.

[0032] A further optimization of this invention involves adjusting the pH of the dispersion to 8.0~10.0, and more specifically, to 9±0.5. The methods for adjusting the pH can be known, for example, through the appropriate use of ammonia, sodium hydroxide, potassium hydroxide, or tetramethylammonium hydroxide solution.

[0033] In this invention, the optimized dispersion system, combined with the evaporation self-assembly coating process described herein, enables hydrophilic particles to be simultaneously and uniformly enriched at the gas-liquid-solid three-phase interface and coated with a hydrophobic graphite core, which is a key prerequisite.

[0034] In this invention, the stabilizer in the dispersion can be PEG and PAA in a weight ratio of 1 to 3:1. Studies have shown that the preferred composite stabilizer helps to further optimize the network structure of graphite and hydrophilic polymers in the system, helps to further synergize with the evaporation self-assembly process, helps to further synergistically strengthen the interfacial structure of the material, and further synergistically strengthens the electrochemical properties of the prepared material, such as fast charging.

[0035] In this invention, the stabilizer is 2 wt.% to 3 wt.% of the total weight of the hydrophilic oxide-graphite; more specifically, it can be 2 to 2.5 wt.%.

[0036] In this invention, a dispersion is sprayed onto the surface of a modified substrate to form droplets, wherein the size of the composite particles formed after the droplets are dried is 10μm~200μm.

[0037] In this invention, in Formula 1, R1 is C6~C 16 The alkyl halogroup, R2 to R4, is individually a C1 to C4 alkyl or alkoxy group; preferably, R1 is a C1 to C4 alkyl or alkoxy group. m F 2m+1 C n H 2n , where m is an integer from 6 to 10, and n is an integer from 1 to 3; R2 to R4 are individually C1 to C3 alkoxy groups.

[0038] In this invention, the modified substrate is prepared by pre-treating the substrate with an alkaline solution to obtain an alkaline-etched substrate, and then immersing it in a solution of Formula 1 to obtain the modified substrate.

[0039] Preferably, the alkaline solution is an aqueous solution of an alkali metal hydroxide with a concentration of 2-6 wt.%.

[0040] Preferably, the alkaline treatment is performed at room temperature for 2-4 hours.

[0041] Preferably, the substrate is a 6061 aluminum alloy plate;

[0042] Preferably, in the solution of Formula 1, the concentration of Formula 1 is 0.1~0.6 wt.%, more preferably 0.2~0.4 wt.%.

[0043] Preferably, the impregnation temperature is 75~95℃;

[0044] Preferably, the soaking time is 2 to 4 hours.

[0045] In this invention, the assembly time of the nascent particles is 10-30 minutes;

[0046] Preferably, the roasting atmosphere is at least one of nitrogen, argon, or a mixture thereof;

[0047] Preferably, the calcination temperature is 700~1200℃, and more preferably 1050~1150℃;

[0048] Preferably, the roasting time is 3 to 6 hours.

[0049] Preferably, before calcination, the process includes a first pre-calcination process at a temperature of 100-200°C and a second pre-calcination process at a temperature of 300-400°C. Studies have shown that the preferred two-stage pre-calcination combined with the subsequent calcination process can further adapt to the characteristics of the evaporation self-assembly process, help to further improve the interface and ion and electron conduction pathways, and help to further optimize the fast charging and stability of the prepared material.

[0050] In this invention, the first pretreatment stage can take 20-60 minutes. The second pre-calcination stage can take 30-120 minutes.

[0051] In this invention, the calcination process is conducted in an atmosphere containing 1-5 vol% ammonia. Studies have shown that the calcination atmosphere can be further combined and synergistically integrated with the evaporation self-assembly process described in this invention, which helps to further improve the interface and ion and electron conduction pathways, and helps to further optimize the fast charging and stability of the prepared materials.

[0052] The present invention also provides a graphite@hydrophilic oxide composite material prepared by the aforementioned preparation method.

[0053] The present invention also provides an application of the graphite@hydrophilic oxide composite material prepared by the above preparation method, which is used as a negative electrode active material to prepare a lithium-ion battery.

[0054] The present invention also provides a lithium-ion battery comprising the graphite@hydrophilic oxide composite material obtained by the preparation method described above.

[0055] Beneficial effects:

[0056] This invention innovatively prepares a dispersion by mixing graphite, hydrophilic nanoparticles, and a stabilizer. The dispersion sample droplets are then evaporation-driven to assemble on the modified surface of a specially modified substrate. This allows the hydrophilic nanoparticles in the droplets to be distributed on the surface of the graphite agglomerate core droplets based on the interaction between the droplets and the modified substrate, forming a core-shell structure. Further calcination of this structure provides a simple method to obtain a graphite@hydrophilic nanoparticle composite material with excellent structure and morphological uniformity, while also exhibiting excellent fast charging, high rate stability, and batch stability.

[0057] This invention significantly simplifies the preparation process of core-shell structures and has a wide range of applications. The main material in the method provided by this invention is not limited to artificial graphite particles but has universal applicability, and can be replaced with silicon-based particles or lithium-ion battery anode materials such as silicon-carbon anodes. In addition to inorganic oxides, the shell layer can also be made of organic polymers. The shape and size of the core-shell structure particles can be rationally controlled by adjusting the concentration of the dispersion droplets and the volume of each droplet added. The type of main particles can be designed more flexibly according to the desired function of the core-shell structure particles. Many basic materials that cannot be prepared into aggregates in existing technologies can also obtain aggregates through the method of this invention, thereby optimizing functionality and discovering new properties. Attached Figure Description

[0058] Figure 1 This is a high-speed photograph of droplets ejected from the spray nozzle of Example 2 contacting the surface of the modified substrate;

[0059] Figure 2 This is a partial SEM image (scale bar is 20 μm) of the aggregates obtained in Example 2. Detailed Implementation

[0060] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0061] The raw materials used in the embodiments of the present invention are all obtained through conventional commercial channels.

[0062] Example 1

[0063] (1) Preparation of dispersion:

[0064] 1 g of hydrophilic oxide particles (SiO2 nanoparticles, D50 = 10.4 nm in this case) and 4 g of artificial graphite nanoparticles (D50 = 117.7 nm) were added to deionized water, along with 0.12 g of polyethylene glycol (PEG) stabilizer. The mixture was then sonicated to obtain a dispersion. The total percentage concentration of hydrophilic oxide and graphite in the dispersion was 1 wt.%.

[0065] (2) Preparation of modified substrate:

[0066] The 6061 aluminum alloy substrate was polished with 600-mesh and 800-mesh metallographic abrasives, cleaned, and then etched with 4 wt.% NaOH alkaline solution for 3 ± 0.5 h to obtain a rough structure. Subsequently, the substrate was immersed in a modifying solution (the modifying solution is of formula 1A). The modified substrate was obtained by treating water in an ultrasonic bath at 40°C for 30 minutes, wherein the weight percentage of Formula 1A was 0.2 wt.%. The substrate was then reacted at 80°C for 2.5 hours. Finally, the substrate was dried to obtain the modified substrate.

[0067] (3) Based on the spraying method, the dispersion of step 1 is sprayed onto the modified substrate of step 2. During the spraying process, the atomizing pressure is 0.36MPa, the liquid flow rate is 5mL / min, the temperature is room temperature of 20℃, and the relative humidity of the environment during the spraying process is 50%. The outlet of the spraying device is set above the surface of the modified substrate of step 2, and the distance difference in the height direction is 200±10mm.

[0068] After the droplets ejected from the spray nozzle contacted the modified substrate surface, the droplets maintained a constant contact angle and evaporated, resulting in a smaller overall size. After 28 minutes, the solvent evaporated completely, and the solute was collected, yielding SiO2 & graphite aggregates with an average particle size of 27.3 μm.

[0069] (4) Roasting:

[0070] The SiO2 & graphite agglomerates obtained in step 3 were calcined in a carbonization kiln at 1150℃ and under N2 atmosphere for 5 hours to obtain the graphite@hydrophilic oxide composite material.

[0071] Example 2

[0072] Compared with Example 1, the difference lies in that the concentration of the dispersion obtained in step 1 is changed, and the total percentage concentration of hydrophilic oxide and graphite in the dispersion is 3.5 wt.%.

[0073] Simultaneously, the parameters of the spraying process in step 3 were adjusted. During the spraying process, the atomizing gas pressure was 0.22 MPa and the liquid flow rate was 15 mL / min. After the solvent evaporated completely, the solute was collected, resulting in larger SiO2 & graphite aggregates with an average particle size of 128.3 μm.

[0074] The obtained SiO2 & graphite agglomerates were characterized by SEM, and the results were as follows: Figure 2 . Figure 2 The overall morphology of the obtained single SiO2 & graphite aggregate particles is shown. The outer, more fragmented portion consists of smaller hydrophilic SiO2 nanoparticles, maintaining the original morphological characteristics. The obtained SiO2 & graphite aggregates are larger entities formed by hydrophobic particles nucleating at the center and coated with an outer layer.

[0075] Example 3

[0076] Compared to Example 1, the only difference is that the hydrophilic oxide particles in step 1 are changed. The experimental groups are as follows:

[0077] Group A: The hydrophilic oxide particles are SnO2, and their D50 = 10.2 nm;

[0078] Group B: The hydrophilic oxide particles are TiO2, and their D50 = 28.7 nm;

[0079] Group C: The hydrophilic oxide particles are Fe3O4; the weight ratio of hydrophilic oxide particles to graphite is 1:3.5; the total weight of hydrophilic oxide and graphite remains unchanged;

[0080] Group D: The hydrophilic oxide particles included 0.3g of hydrophilic SiO2 nanoparticles (D50=10.4nm) and 0.7g of hydrophilic TiO2 nanoparticles (D50=28.7nm); other operations and parameters were the same as in Example 1.

[0081] Group E: Mix 1g of hydrophilic SiO2 nanoparticles (D50=10.4nm) with 0.25g of conductive carbon black nanoparticles (D50=40nm) to replace 1g of SiO2 in Example 1, and the remaining steps are the same.

[0082] Example 4

[0083] Compared to Example 1, the only difference is the type of modifier; the experimental groups are as follows:

[0084] Group A: The stabilizer is polyvinylpyrrolidone (PVP); the stabilizer dosage is 0.1g;

[0085] Group B: Stabilizer is polyacrylic acid (PAA);

[0086] Group C: The stabilizer is a combination of PEG and PAA in a weight ratio of 5:2;

[0087] The stabilizer dosage and other operations and parameters for each group were the same as in Example 1.

[0088] Example 5

[0089] Compared to Example 1, the only difference is that step 4 employs a three-stage gradient heating process for the calcination treatment: the temperature is increased to 150°C (labeled T1) at a rate of 2°C / min and held for 40 min; then increased to 350°C (labeled T2) at a rate of 5°C / min and held for 60 min; finally, the temperature is increased to 1100°C (labeled T3) at a rate of 5°C / min and held for 5 h, followed by natural cooling. All other operating parameters are the same as in Example 1.

[0090] Example 6

[0091] Compared with Example 1, the only difference is that in step 4, the calcination atmosphere is replaced with a 3 vol% ammonia-N2 mixture, while other operations and parameters are the same as in Example 1.

[0092] Example 7

[0093] Compared with Example 1, the only difference is that in step 1, ammonia water is used to adjust the pH of the dispersion to 9±0.2, and all other operations and parameters are the same as in Example 1.

[0094] Comparative Example 1

[0095] Compared with Example 1, the only difference is that no stabilizer was added during the preparation of the dispersion in step 1.

[0096] Comparative Example 2

[0097] Compared with Example 1, the only difference is that in step 1, an equal weight of hexadecyltrimethylammonium bromide (CTAB) is used as a stabilizer, and all other operations and parameters are the same as in Example 1.

[0098] Comparative Example 3

[0099] Compared with Example 1, the only difference is that the total percentage concentration of hydrophilic oxide and graphite in the dispersion is 6 wt.%, and all other operations and parameters are the same as in Example 1.

[0100] Comparative Example 4

[0101] Compared with Example 1, the only difference is that in step 2, the modification in step 2 is not performed, and the substrate is directly subjected to step 3 and subsequent processing. All other operations and parameters are the same as in Example 1.

[0102] Comparative Example 5

[0103] Compared with Example 1, the only difference is that in step 2, polydimethylsiloxane is used instead of form 1A; all other operations and parameters are the same as in Example 1.

[0104] 1. Electrode preparation:

[0105] a. Slurry preparation: The active material to be tested (the graphite hydrophilic oxide composite material finally prepared in each example and comparative example), conductive carbon black, and binder polyvinylidene fluoride (PVDF) were accurately weighed at a mass ratio of 8:1:1. N-methyl-2-pyrrolidone (NMP, battery grade, moisture <50ppm) was used as the solvent, and the solid content was controlled at 35wt%. The mixture was placed in a planetary mixer (Thinky, ARE-310) and stirred at 2000 rpm for 30 minutes to ensure initial mixing.

[0106] b. Homogenization and degassing: The slurry is then transferred to a vacuum planetary mixer and stirred at 500 rpm for 2 hours under a vacuum of -0.095 MPa to completely remove air bubbles and obtain a homogeneous slurry with good flowability.

[0107] c. Coating and Drying: The slurry was uniformly coated onto a 10 μm thick electrolytic copper foil using an automatic coating machine (MTI, MSK-AFA-III). The wet film thickness was set to 150 μm. The coated electrode was immediately transferred to a forced-air drying oven at 80°C for pre-drying for 30 minutes, and then placed in a vacuum drying oven at 120°C (vacuum degree < -0.09 MPa) for drying for 12 hours.

[0108] d. Rolling and cutting: The dried electrode sheets are rolled using a double roller press (MTI, MSK-2150) at a pressure of 10 MPa until the compacted density is approximately 1.5 g / cm³. 3 Finally, electrode discs with a diameter of 12.0 mm were cut using a stamping machine, and the mass of each electrode disc was weighed using a precision balance (accuracy 0.01 mg) to ensure that the areal loading of the active material was controlled at 1.20 ± 0.05 mg / cm². 2 The electrode sheets were stored in a vacuum environment at 120℃ for later use (test electrode sheets).

[0109] 2. Button cell (CR2032) assembly:

[0110] All assembly steps were carried out in a glove box filled with high-purity argon gas (Ar, O2 < 0.1 ppm, H2O < 0.1 ppm).

[0111] a. Battery assembly preparation: A lithium metal sheet (15.6 mm in diameter, 0.45 mm in thickness) was used as the counter / reference electrode, a Celgard 2400 polypropylene membrane (19 mm in diameter) was used, and the electrolyte was a 1.0 mol / L LiPF6 carbonate-based mixed solvent, which was prepared by mixing ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) in a volume ratio of 1:1:1. Additionally, 10 vol% of fluoroethylene carbonate (FEC) was added as a film-forming additive.

[0112] b. Assembly sequence: Place the battery negative electrode shell, lithium sheet, separator with 80.0 μL electrolyte added, test electrode plate, gasket, spring, and positive electrode shell into the assembly mold in sequence. Use a sealing machine (MTI, MSK-110) to seal under 4.0 MPa pressure and let stand for 12 hours to ensure full wetting.

[0113] 3. Electrochemical test parameters:

[0114] All tests were conducted on the LAND battery testing system in a constant temperature chamber at 25.0±0.5℃.

[0115] First Coulomb efficiency test:

[0116] Voltage window: 0.01 V ~ 1.5 V (vs. Li + / Li)

[0117] Procedure: After resting, activate once with a small current of 0.05C (1C = 372 mA / g). Then perform the formal test: discharge at a constant current of 0.1C (CC) to 0.005 V, then discharge at a constant voltage (CV) until the current drops to 0.01C, and record the discharge capacity (Q_dis). Then charge at a constant current of 0.1C to 1.5 V, and record the charging capacity (Q_ch).

[0118] Calculate: ICE = (Q_ch / Q_dis) × 100%.

[0119] Ratio performance test:

[0120] Procedure: After completing the first cycle test, the battery was subjected to 5 charge-discharge cycles each at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C rates (all in CC mode, cutoff voltage 0.005~1.5V). The discharge capacity of the 5th cycle was recorded at each rate. Finally, the battery was returned to 0.1C for 5 cycles, and the capacity recovery rate was calculated.

[0121] Long-cycle stability test:

[0122] Procedure: After three activation cycles at 0.5C, switch to 1C for constant current charge-discharge cycling, for 500 cycles. Capacity retention is calculated by dividing the discharge capacity of the 500th cycle by the discharge capacity of the 5th cycle.

[0123] Electrochemical impedance spectroscopy (EIS) testing:

[0124] Equipment and conditions: An electrochemical workstation (Princeton, VersaSTAT 4) was used to complete three 0.1C cycles and charge the battery to 50% SOC (~0.2 V vs. Li). + Tested under the condition of / Li). Frequency range: 100 kHz to 10 mHz, AC disturbance amplitude: 5.0 mV.

[0125] Data processing: Equivalent circuit fitting (R(QR)(QR) model) was performed using ZView software to obtain the charge transfer resistance (Rct). Lithium-ion diffusion coefficient (D_Li) + Based on the Warburg impedance in the low-frequency region, the formula D = (R2 T 2 ) / (2A 2 n 4 F 4 C 2 σ_w 2 ) Calculate, where σ_w is the sum of Z' and ω -1 / 2 The slope of the linear fit.

[0126] 3.2: Electrochemical Test Results and Data Analysis

[0127]

[0128]

[0129]

[0130] The method described in this invention is a highly efficient, reliable, and highly designable core-shell material preparation process. It not only successfully prepares uniformly coated core-shell structures but also, through material selection (such as TiO2, SiO2) and structure / process optimization (such as dual-size densification, conductive network construction, stepped calcination, atmosphere doping, and pH control), can directionally and synergistically enhance key indicators of the final anode material, such as first-efficiency performance, cycle life, and rate performance. The outstanding performance of Example 3E, particularly its rate performance and interfacial kinetic parameters, provides a highly valuable solution for the design of anode materials for fast-charging lithium-ion batteries.

[0131] Preferred embodiments demonstrate ultra-high process reproducibility: in embodiments employing the fine control scheme of the present invention, batch-to-batch differences are controlled to an extremely low level.

[0132] The basic implementation examples confirm that the method itself has good stability: all examples following the basic process route of this invention have low RSD values ​​(≤0.35%). This confirms that even without additional optimization methods, the core method of "superhydrophobic surface-driven self-assembly" established by this invention has reliable process stability and can stably prepare core-shell materials with excellent performance.

[0133] The comparative examples exhibited poor stability due to process defects: the process of Comparative Example 4 was uncontrollable, with an RSD as high as 2.12%, and its standard deviation (8.06) was dozens of times that of the examples. This demonstrates that reproducible production is impossible on non-superhydrophobic surfaces due to the dominance of disordered deposition such as the "coffee ring effect." The remaining comparative examples generally had RSD values ​​(0.44%-0.82%) worse than all the examples due to the use of inappropriate dispersants, incorrect concentrations, or insufficient surface modification. This indicates that deviations from any critical parameter can introduce additional, non-negligible process fluctuations.

[0134] All the data together provide strong support for the innovation, practicality, and technological advancement of this invention.

Claims

1. A method for preparing graphite@hydrophilic oxide composite materials, characterized in that, A dispersion containing graphite, hydrophilic nanoparticles, and a stabilizer was obtained; the dispersion was formed into droplets and assembled on the surface of a modified substrate to form primary particles; the primary particles were then calcined to obtain the graphite@hydrophilic oxide particle composite material. The hydrophilic oxide is an oxide of at least one element selected from silicon, titanium, tin, and iron; The stabilizer is at least one of polyethylene glycol, polyacrylic acid, and polyvinylpyrrolidone; The modified substrate includes an alkaline-etched substrate and a modified material of formula 1 composite on its surface; Formula 1 In R1 to R4, at least one substituent is a fluoroalkyl group, and the remaining substituents are alkyl, alkoxy, or fluoroalkyl groups. In the dispersion, the total percentage of graphite and hydrophilic nanoparticles is 0.8 wt.%~4 wt.%; the weight ratio of hydrophilic oxide to graphite is 1:2~5; the stabilizer is 0.8 wt.%~4 wt.% of the total weight of hydrophilic oxide and graphite.

2. The preparation method according to claim 1, characterized in that, The particle size of graphite ranges from 80nm to 200nm, preferably from 100nm to 150nm; Hydrophilic oxides include at least one of silicon dioxide, titanium dioxide, tin dioxide, and iron oxide; Preferably, the particle size of the hydrophilic oxide is between 5 nm and 30 nm; Preferably, the hydrophilic oxide comprises particles A and particles B, wherein particles A are silicon dioxide with a D50 of 5-15 nm; and particles B are titanium dioxide with a D50 of 20-30 nm. Preferably, in the hydrophilic oxide, the weight ratio of particle A to particle B is 1:1~5; Preferably, the stabilizer in the dispersion can be PEG and PAA in a weight ratio of 1 to 3:1; Preferably, the stabilizer is 2 wt.% to 3 wt.% of the total weight of the hydrophilic oxide-graphite mixture; Preferably, the dispersion further contains conductive carbon black nanoparticles; the particle size D50 of the conductive carbon black nanoparticles is 20~50nm, and the amount added is 10%~40% of the total mass of the hydrophilic nanoparticles and the conductive carbon black nanoparticles. Preferably, the pH of the dispersion is adjusted to 8.0~10.

0.

3. The preparation method according to claim 1, characterized in that, The dispersion is sprayed onto the surface of the modified substrate to form droplets, and the composite particles formed after the droplets are dried have a size of 10μm~200μm.

4. The preparation method according to claim 1, characterized in that, In Equation 1, R1 is C6~C 16 The alkyl halogroup, R2 to R4, is individually a C1 to C4 alkyl or alkoxy group; preferably, R1 is a C1 to C4 alkyl or alkoxy group. m F 2m+1 C n H 2n , where m is an integer from 6 to 10, and n is an integer from 1 to 3; R2 to R4 are individually C1 to C3 alkoxy groups.

5. The preparation method according to claim 1, characterized in that, The modified substrate is prepared by pretreating the substrate with an alkaline solution to obtain an alkaline-etched substrate, and then immersing it in a solution of Formula 1 to obtain the modified substrate. Preferably, the alkaline solution is an aqueous solution of an alkali metal hydroxide with a concentration of 2-6 wt.%. Preferably, the alkaline treatment is performed at room temperature for 2-4 hours. Preferably, the substrate is a 6061 aluminum alloy plate; Preferably, in the solution of Formula 1, the concentration of Formula 1 is 0.1~0.6 wt.%; Preferably, the impregnation temperature is 75~95℃; Preferably, the soaking time is 2 to 4 hours.

6. The preparation method according to claim 1, characterized in that, The assembly time for the initial particles is 10-30 minutes; Preferably, the roasting temperature is 700~1200℃; Preferably, the roasting time is 3-6 hours; Preferably, before roasting, the process further includes a first pre-roasting process at a temperature of 100~200℃ and a second pre-roasting process at a temperature of 300~400℃. Preferably, the pre-baking time for the first stage can be 20-60 min; the pre-baking time for the second stage can be 30-120 min.

7. The preparation method according to claim 1, characterized in that, The roasting process is carried out in an atmosphere containing 1-5% ammonia.

8. A graphite@hydrophilic oxide composite material prepared by the preparation method according to any one of claims 1 to 7.

9. An application of the graphite@hydrophilic oxide composite material according to claim 8, characterized in that, It was used as the negative electrode active material to prepare lithium-ion batteries.

10. A lithium-ion battery, characterized in that, The graphite@hydrophilic oxide composite material obtained by the preparation method according to any one of claims 1 to 7.

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