Preparation of nano-TiO2-encapsulated graphite electrodes based on sol-gel method

Abstract

The application aims to provide a preparation method of nanometer titanium dioxide uniformly coated graphite negative electrode material. + The method is simple in process, and the titanium dioxide as a fast ion conductor can provide a high-speed transmission channel for the graphite electrode, thereby improving the high-rate charge and discharge performance of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology for electrochemical energy storage devices such as lithium-ion batteries, sodium-ion batteries, or supercapacitors, and specifically to a composite electrode material and its preparation method for in-situ coating of nano-titanium dioxide (TiO2) on the surface of graphite by a sol-gel method. Background Technology

[0002] Graphite is currently the mainstream anode material for lithium-ion batteries due to its advantages such as low cost, good conductivity, and stable lithium-ion insertion / extraction potential plateau. However, during cycling, Li... + The high desolvation energy and slow mass transfer rate on the surface of pure graphite limit the application of graphite electrodes in high-performance, long-life batteries.

[0003] Coating the surface of graphite with a stable metal oxide (such as MoO3, Al2O3, etc.) is an effective strategy to improve its electrochemical performance. TiO2 has good chemical stability and a high lithium-ion diffusion coefficient. Common coating methods include hydrothermal methods (LI Y, XUE J, SHEN Q, et al. Chemical Engineering Journal, 423, 2021, 130188) and mechanical mixing methods (RHEE DY, KIM J, MOON J, et al. Journal of Alloys and Compounds, 843, 2020, 156042.). However, hydrothermal methods and simple mechanical mixing are difficult to achieve a uniform and firm distribution of TiO2 on the graphite surface. Titanium dioxide tends to agglomerate into large particles, resulting in high interfacial impedance and limited improvement effect. Therefore, developing a simple, uniformly distributed, and firmly bonded TiO2-coated graphite material preparation method is of great significance. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a simple, uniformly distributed, and firmly bonded method for preparing nano-TiO2-coated graphite electrode materials. This method involves in-situ initiation of titanium alkoxide hydrolysis-condensation in a graphite dispersion system, causing the titanium dioxide hydrate precursor to uniformly gel and distribute on the surface of graphite particles. Subsequent calcination forms crystallized nano-TiO2, thereby significantly improving the electrochemical stability and rate performance of the composite material.

[0005] The objective of this invention is achieved through the following technical solution: A method for preparing a nano-TiO2-coated graphite electrode material, characterized by comprising the following steps: (1) Synthesis of precursor C@TiO(OH)2·nH2O: Graphite powder was dispersed in a mixed solution composed of deionized water, anhydrous ethanol, glacial acetic acid and surfactant. The mixture was ultrasonically treated to ensure full dispersion and obtain a uniform suspension. Titanate ester was slowly added dropwise to the suspension under continuous stirring. After the addition was complete, the mixture was stirred continuously under heating until the suspension system gelled and solidified into a block. The obtained block was dried, ground and sieved to obtain precursor powder C / TiO(OH)2·nH2O. (2) Synthesis of C@TiO2 composite material: The precursor powder obtained in step (1) is placed in a tube furnace or muffle furnace under an inert atmosphere or an air atmosphere for high-temperature calcination; after calcination, it is naturally cooled to room temperature, and the calcined product is washed and dried to finally obtain the graphite composite material C@TiO2 coated with nano TiO2.

[0006] Further, in step (1), the volume ratio of deionized water, anhydrous ethanol, and glacial acetic acid in the mixed solution is (1~5):(10~30):(0.5~3). The surfactant is one of sodium dodecylbenzenesulfonate, polyethylene glycol, and hexadecyltrimethylammonium bromide, and its addition amount is 0.1%~5% of the graphite mass. The molar ratio of graphite to titanium in the titanate is 1:(0.01~0.2).

[0007] Further, in step (1), the titanate ester is tetrabutyl titanate, isopropyl titanate, or ethyl titanate, and the dropping rate is 0.05-0.5 mL / s. After the dropping is completed, the mixture is stirred at 40-80℃ and 100-1000 r / min for 1-12 hours until the gel solidifies.

[0008] Optionally, in step (1), after the gel solidifies, it is manually ground or ground in a ball mill for 10 to 60 minutes and then passed through a 100 to 300 mesh sieve.

[0009] Furthermore, in step (2), the calcination atmosphere is nitrogen, argon, or air. The calcination procedure is as follows: the temperature is increased to 280-800°C at a heating rate of 1-10°C / min, and held at that temperature for 2-8 hours.

[0010] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the above-described method, employing glacial acetic acid as a chelating agent to effectively inhibit the excessively rapid hydrolysis of titanate esters, control the hydrolysis-condensation rate, and facilitate the formation of a uniform and dense sol. The surfactant forms an adsorption layer on the graphite surface, ensuring uniform dispersion of graphite in the system, while simultaneously increasing the interaction between the graphite six-membered rings and Ti. 4+The binding force of ions provides the basis for in-situ coating. TiO(OH)2·nH2O, generated by the hydrolysis of titanate at the graphite / solution interface, forms a three-dimensional network gel through condensation, encapsulating the graphite particles. The subsequent calcination process crystallizes amorphous hydrated titanium dioxide into nano-TiO2, and the high temperature further strengthens the physical or weak chemical bond between the TiO2 layer and the graphite surface.

[0011] In-situ gelation was used to achieve molecular-level contact and uniform coating of TiO2 precursor on graphite surface. The prepared C@TiO2 composite material combines the high electrical conductivity of graphite with the high ionic conductivity of TiO2. By adjusting the amount of titanium source, hydrolysis conditions, and calcination temperature, the thickness, crystalline phase, and microstructure of the TiO2 coating layer can be effectively controlled, thereby greatly improving the rate performance of the material. Attached Figure Description

[0012] Figure 1 TEM images of C@TiO2 (2wt%) (b)(c) and pure graphite (a) samples prepared in this invention.

[0013] Figure 2 EDX image of the C@TiO2 (2wt%) sample prepared in this invention.

[0014] Figure 3 XRD pattern of C@TiO2 (2wt%) prepared in this invention corresponding to a graphite-free sample.

[0015] Figure 4 Comparison of rate performance between C@TiO2 (2wt%) and pure graphite electrodes prepared in this invention.

[0016] Figure 5 Comparison of high-rate cycling performance between C@TiO2 (2wt%) prepared in this invention and pure graphite electrode. Detailed Implementation

[0017] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above-described invention. Example

[0018] (1) Weigh 20 g of artificial graphite powder and disperse it in a beaker containing a mixed solution of 2 mL deionized water, 60 mL anhydrous ethanol, 1 mL glacial acetic acid, and 0.01 g sodium dodecylbenzenesulfonate (SDBS). Sonicate the solution for 1 hour to form a uniform black suspension. While stirring in an ice-water bath (0°C), pipette 2.5 mL of tetraethyl titanate and add it dropwise at a rate of 0.05 mL / s. After the addition is complete, remove the ice bath and heat the reaction system to 60°C, stirring continuously for 12 hours. The viscosity of the system gradually increases, eventually solidifying into a black blocky gel. Dry the resulting gel block in a 60°C oven for 12 hours, then ball mill it for 10 minutes and pass it through a 100-mesh sieve to obtain the black precursor powder C@TiO(OH)2·nH2O.

[0019] (2) The precursor powder was placed in a tube furnace and heated to 280°C at a rate of 5°C / min under an argon atmosphere, and held at that temperature for 8 hours. After calcination, the furnace was cooled to room temperature. The calcined product was washed three times with deionized water and ethanol, respectively, and then vacuum dried at 80°C for 12 hours to obtain the final product C@TiO2 composite material. Example

[0020] (1) Weigh 3.0 g of natural graphite powder and disperse it in a beaker containing a mixed solution of 2 mL deionized water, 5 mL anhydrous ethanol, 1 mL glacial acetic acid, and 0.01 g sodium dodecylbenzenesulfonate (SDBS). Sonicate the solution for 30 minutes to form a uniform black suspension. While stirring at room temperature (25℃), pipette 0.25 mL of isopropyl titanate and add it dropwise at a rate of 0.25 mL / s. After the addition is complete, heat the reaction system to 80℃ and stir continuously for 4 hours. The viscosity of the system gradually increases, eventually solidifying into a black blocky gel. Dry the resulting gel block in an 80℃ oven for 24 hours, then manually grind it for 5 minutes and pass it through a 300-mesh sieve to obtain the black precursor powder C@TiO(OH)2·nH2O.

[0021] (2) The precursor powder was placed in a tube furnace and heated to 500°C at a rate of 5°C / min under an argon atmosphere, and held at that temperature for 5 hours. After calcination, the furnace was cooled to room temperature. The calcined product was washed three times with deionized water and ethanol, respectively, and then vacuum dried at 80°C for 12 hours to obtain the final product C@TiO2 (2wt%) composite material. Example

[0022] (1) Weigh 6.0 g of natural graphite powder and disperse it in a beaker containing a mixed solution of 2 mL deionized water, 5 mL anhydrous ethanol, 1 mL glacial acetic acid, and 0.1 g cetyltrimethylammonium bromide (CTAB). Sonicate the solution for 30 minutes to form a uniform black suspension. While stirring at room temperature (25°C), pipette 0.25 mL of isopropyl titanate and add it dropwise at a rate of 0.01 mL / s. After the addition is complete, heat the reaction system to 80°C and stir continuously for 1 hour. The viscosity of the system gradually increases, eventually solidifying into a black blocky gel. Dry the resulting gel block in a 70°C oven for 12 hours, then manually grind it and pass it through a 200-mesh sieve to obtain the black precursor powder C@TiO(OH)2·nH2O.

[0023] (2) The precursor powder was placed in a tube furnace and heated to 280°C at a rate of 2°C / min under an argon atmosphere, and held at that temperature for 8 hours. After calcination, the furnace was cooled to room temperature. The calcined product was washed three times with deionized water and ethanol, respectively, and then vacuum dried at 80°C for 12 hours to obtain the final product C@TiO2 (1wt%) composite material. Example

[0024] (1) Weigh 5.0 g of artificial graphite powder and disperse it in a mixed solution consisting of 1 mL of deionized water, 10 mL of anhydrous ethanol, 3 mL of glacial acetic acid, and 0.1 g of polyethylene glycol-400 (PEG-400). Sonicate the solution for 1.5 hours. Add 2.0 mL of tetrabutyl titanate dropwise at a rate of 0.5 mL / s while stirring at room temperature (25℃). After the addition is complete, stir the solution at 50℃ for 10 hours until complete gelation. Dry, grind, and sieve the solution to obtain the precursor powder C@TiO(OH)2·nH2O.

[0025] (2) The precursor powder was placed in a muffle furnace and heated to 450°C in air at a rate of 2°C / min. The temperature was maintained for 4 hours to obtain the C@TiO2 composite material.

[0026] Figure 1 These are scanning electron microscope (TEM) comparison images of C@TiO2 (2 wt%) prepared in Example 2 of this invention and pure graphite anode material. Wherein: (a) shows the typical surface morphology of uncoated, pristine graphite particles. (b) and (c) show the surface morphology of the C@TiO2 composite material prepared by the method of this invention. The images clearly show that nano-titanium dioxide is uniformly and continuously coated on the surface of the graphite particles, demonstrating that the sol-gel process of this invention can achieve uniform surface coating.

[0027] Figure 2This is the energy-dispersive X-ray spectroscopy (EDX) elemental distribution diagram of C@TiO2 (2 wt%) prepared in Example 2 of this invention. The diagram visually demonstrates the uniform spatial distribution of carbon (C), titanium (Ti), and oxygen (O) in the composite material, further confirming at the elemental level the uniform and complete distribution of the titanium dioxide nanocoating layer on the graphite substrate surface, with the titanium element signal highly overlapping with the graphite particle outline.

[0028] Figure 3 This is the X-ray diffraction (XRD) pattern of pure titanium dioxide product obtained using the same preparation process of this invention but without the addition of a graphite substrate. Analysis of the diffraction peak positions and intensities in the pattern confirms that the titanium dioxide crystalline phase formed after calcination is a mixture of anatase and trace amounts of brookite.

[0029] Figure 4 This figure compares the rate performance of the C@TiO2 composite anode material (C@TiO2, 2wt%) prepared in this invention with that of a pure graphite electrode at different charge-discharge rates. The figure shows the change and recovery of the discharge specific capacity of the two electrodes during charge-discharge processes from low rates (0.1C, 0.2C) to high rates (1C, 2C, 5C, 10C). The C@TiO2 composite material exhibits higher capacity retention and superior rate performance than pure graphite at high rates, demonstrating the positive effect of TiO2 coating on improving interfacial ion transport kinetics.

[0030] Figure 5 This is a comparison of the long-cycle performance of the C@TiO2 composite anode material (C@TiO2, 2wt%) prepared in this embodiment of the invention and a pure graphite electrode at a charge-discharge rate (10C). The figure shows the capacity decay trend of the two electrodes during 1000 cycles. The C@TiO2 composite material exhibits a significantly better specific capacity than pure graphite, with no capacity decay, demonstrating the crucial role of TiO2 coating in improving rate performance.

[0031] Obviously, the above description is merely an embodiment of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent.

Claims

1. A method for preparing a nano-TiO2-coated graphite anode material, characterized in that: The preparation steps of the material are as follows: 1-6g of powdered graphite was dispersed in deionized water containing glacial acetic acid, anhydrous ethanol, and a surfactant. The dispersion was performed ultrasonically for 30-60 min. Then, 0.25-2 mL of isopropyl titanate was slowly added dropwise while stirring. Stirring and heating continued until the suspension completely formed a sol-gel mass. After drying, grinding, and sieving, C@TiO(OH)2·nH2O powder was obtained. 2) The aforementioned C@TiO(OH)2·nH2O powder was placed in a tube furnace and heated at 1-10 °C for 1 min under an argon atmosphere. -1 The temperature was increased from room temperature to 260-800 ℃ and held for 2-8 h, then naturally cooled to obtain the graphite anode material C@TiO2 coated with nano-TiO2.

2. The preparation method of a nano-TiO2-coated graphite anode material as described in claim 1, characterized in that: Step 1) The volume ratio of deionized water to anhydrous ethanol and glacial acetic acid is (1~5):(10~30):(0.5~3), and the amount of surfactant is 0.1%~5% of the graphite mass.

3. The preparation method of a nano-TiO2-coated graphite anode material as described in claim 1, characterized in that: The surfactant is one of the following: sodium dodecylbenzenesulfonate, polyethylene glycol, or hexadecyltrimethylammonium bromide.

4. The method for preparing a nano-TiO2-coated graphite anode material as described in claim 1, characterized in that: After ultrasonic dispersion, the above mixed solution was added dropwise at a rate of 0.05-0.5 mL / s with isopropyl titanate.

5. The method for preparing a nano-TiO2-coated graphite anode material as described in claim 1, characterized in that: After adding isopropyl titanate, the heating temperature is 40-80 ℃, the stirring speed is 100-1000 r / min, and the stirring time is 1-12 h.

6. The method for preparing a nano-TiO2-coated graphite anode material as described in claim 1, characterized in that: The precursor was placed in an oven for sol-gel drying at a temperature of 60-80℃ for 6-24 hours.

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