CN113651356B - Preparation method and application of core-shell cavity structure titanium dioxide graphene composite - Google Patents

Abstract

The invention relates to a preparation method and application of a core-shell cavity structure titanium dioxide graphene composite, and belongs to the technical field of nanomaterials. The aim is to improve the electrochemical cycling stability and cycling specific capacity of the material. The main scheme includes firstly using potassium chloride as a salt template and metal-free phthalocyanine as carbon and nitrogen sources to prepare a mixture of graphene and potassium chloride salt by ionothermal method, and then using isopropyl titanate in ethanol. Hydrolysis, under the action of hexadecylamine surfactant, uniformly grows a layer of titanium dioxide on the surface of graphene, and finally obtains a core-shell cavity structure titanium dioxide graphene composite after centrifugation, washing and drying. And successfully applied to lithium-ion batteries, showing good long-cycle stability and high cycle specific capacity, excellent electrochemical performance.

Description

Preparation method and application of core-shell cavity structure titanium dioxide graphene composite

technical field

The invention relates to a preparation method of a core-shell cavity structure titanium dioxide graphene composite and its application as an anode material of a lithium ion battery, and belongs to the technical field of nanomaterials.

Background technique

Global oil resources and other traditional energy sources are increasingly scarce, and there is an urgent need to develop and utilize new types of renewable energy, such as solar energy, wind energy and tidal power. But the power system requires stable and continuous power supply, but wind and solar energy are intermittent and unstable in nature, which promotes the development and research of rechargeable secondary batteries. Traditional lead-acid batteries, nickel-cadmium batteries and nickel-hydride batteries all have some deficiencies, such as short service life, environmental pollution and low energy density, which greatly limit their large-scale commercial applications. At present, the main task of the battery industry is to find rechargeable secondary batteries to replace traditional lead-acid batteries and nickel-cadmium batteries, and it is urgent to develop non-toxic and non-polluting electrode materials and battery separators, as well as non-polluting batteries. Compared with traditional secondary chemical batteries, lithium-ion batteries (LIBS) have dominated electronic products. With the advancement of technology, the rapid application and development of various electric vehicles and electronic products have made people more interested in lithium-ion batteries. In order to pursue higher pursuit, the development of materials with high safety, good cycle stability and high specific capacity has become the goal of people's pursuit of excellent electrochemical performance of lithium-ion batteries.

There are many safety hazards based on traditional carbon materials as the anode of lithium batteries. For example, the intercalation and deintercalation process of lithium ions will lead to the volume change of the electrode surface and the formation of lithium dendrites, which may easily lead to short circuit or explosion of the battery. As the anode material of lithium ion battery, it is generally compounded with other transition metal oxides, and the graphene composite is used as the anode of lithium ion battery. Transition metal oxides such as titanium dioxide and manganese dioxide are the research hotspots.

Ti-based materials have high reversible Li-ion storage capacity, long cycle life and high safety as low-cost electrode materials that can effectively avoid Li metal deposition. In addition, Ti-based material has a certain oxygen absorption function at high temperature, which has obvious safety, therefore, it is considered as an ideal anode material. Among them, _TiO2 has high safety, suitable lithium storage voltage platform, stable structure, low power consumption, low raw material price, simple preparation method, and high theoretical electrochemical performance index. In addition, _TiO2 , which is an anode material for lithium-ion batteries (LIBS), has a high operating voltage of about 1.75 V, which can suppress the generation of lithium dendrites and improve safety. However, _TiO2 still has some disadvantages in practical applications. Because it is a semiconducting material (bandgap*3.2eV), both the electronic conductivity and ionic conductivity are low, which leads to the decrease of lithium ion diffusion and deintercalation performance; in addition, it exists on the surface of _TiO2 , especially nano-type TiO2 ₂ The hydroxyl groups on the surface of the material will react with the electrolyte during charging and discharging. These affect its electrochemical performance, resulting in reduced cycling performance and rate performance. Therefore, coating graphene with TiO2 can give full play to the advantages of both materials, mainly focusing on improving the electronic conductivity and ionic conductivity of _TiO2 materials, complementing each other's shortcomings, the synthesis has long cycle life, high safety, good A core-shell cavity structure titanium dioxide-graphene composite lithium battery anode material with electronic conductivity and ionic conductivity.

SUMMARY OF THE INVENTION

The invention provides a preparation method of a core-shell cavity structure titanium dioxide graphene composite and its application as an anode material of a lithium ion battery, aiming at improving the electrochemical cycle stability and cycle specific capacity of the material.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

The invention discloses a preparation method of a core-shell cavity structure titanium dioxide graphene composite and its application as an anode material of a lithium ion battery. Firstly, potassium chloride salt is used as a template, and a two-dimensional structure with a regular cubic structure is obtained by a salt template method. Thin graphene sheets are then hydrolyzed by isopropyl titanate at room temperature to uniformly grow a layer of titanium dioxide on the surface of the cube graphene, and finally wash off the potassium chloride by washing with water to obtain a core-shell cavity structure titanium dioxide graphite Graphene composite body, the inner layer of the cavity is a graphene thin layer, and the outer surface of the graphene is uniformly coated with a layer of titanium dioxide core-shell hollow structure composite body.

The invention provides a method for preparing a core-shell cavity structure titanium dioxide graphene composite, the specific steps are as follows:

Step (1): Measure 200-220 ml of ethanol and mix and stir with 40-50 ml of cyclohexane, then add 0.10-0.20 g of metal-free phthalocyanine, mix and stir until the metal-free phthalocyanine is fully dissolved, and let the reaction vessel soak at the same time In an ice-water bath environment (-1 to 1°C), continuously add 50-60 ml of saturated potassium chloride solution dropwise, and continue to stir, after the dropwise addition, age in an ice-bath environment, and wash with ethanol after aging (all cyclohexane was washed away), filtered with a microporous filter membrane (organic), and then the product was collected and dried under vacuum at 60-80 °C for 8 h. The final composite precursor of phthalocyanine particles and potassium chloride salt, Denoted as Pc/KCl;

Step (2): transfer the composite precursor of phthalocyanine particles and potassium chloride salt prepared in step (1) into a quartz tube for drying, place in a tube furnace for high-temperature sintering, and sinter in a tube furnace in an inert gas atmosphere. The composite precursor was calcined at 700℃ for 8h and then cooled to room temperature naturally to carbonize the composite precursor into two-dimensional thin graphene sheets with regular cubic structure;

Step (3): Take 1-2 g of the two-dimensional thin-layer graphene sheet with a regular cubic structure in step (2), add it to 150-170 ml of ethanol solution, and then add 0.1-0.3 g of hexadecane amine, and then continue to stir, then dropwise 10 μl of deionized water every 10min, and continue to stir for 24 hours to obtain a uniform dispersion solution of the titanium dioxide graphene complex; finally, a core-shell cavity structure is obtained by centrifugation and drying. Titanium dioxide graphene composite, denoted as 24-G@TiO ₂ .

In the above technical scheme, metal-free phthalocyanine is used as carbon source and nitrogen source, potassium chloride (melting point is 750°C) is used as salt template, and the mixture of graphene and potassium chloride salt is prepared by anti-solvent method.

In the above technical solution, in step (2), the inert gas atmosphere is Ar gas or nitrogen gas; the heating program for sintering in the tube furnace is: at room temperature, argon gas is passed for 1 h, and then the temperature is increased at a heating rate of 5°C·min ^-1 The temperature was raised to 300 °C, then kept for 1 h, then raised to 700 °C at a rate of 2 °C·min ^-1 , held for 8 h, and then cooled to room temperature naturally.

In the above technical solution, in step (3), hexadecylamine is used as the surfactant, and the hydrolysis time of titanium dioxide is 24 h.

The invention also discloses the application of the core-shell cavity structure titanium dioxide-graphene composite prepared by the above preparation method, that is, it is used as an anode material of a lithium ion battery.

Compared with the prior art, the beneficial effects of the present invention are embodied in:

1. The core-shell cavity structure titanium dioxide-graphene composite of the present invention adopts conventional medicines, and is prepared by salt template, calcination and hydrolysis, and the product preparation method and equipment are simple, and the raw materials used are also easy to obtain. It is practically used in lithium ion batteries. It shows excellent long-cycle stability, and can maintain a capacity of 180 mAh·g ^-1 after 4000 cycles of stable cycling. Both the long-cycle capability and the final high capacity are better than those reported so far.

2. The present invention explores the effect of different titania hydrolysis times on electrochemical performance, followed by the cycle diagrams of composite materials with different hydrolysis times. According to the specific capacity of the battery, we find that the optimal hydrolysis time is 24 h.

3. What the present invention uses is high-concentration ethanol with a concentration of 99.7%. The purpose is to wash away the cyclohexane without washing the potassium chloride salt particles covered inside. If the cyclohexane cannot be washed completely It will lead to the risk of explosion during subsequent high temperature sintering in the tube furnace. If it is washed with water, the salt will be washed off; or other organic solvents will be washed, even after washing off the cyclohexane, the organic solvent itself will remain, so it will have a great impact on the product.

Description of drawings

Fig. 1 is the SEM images of the two-dimensional thin-layer graphene sheets sintered at different temperatures of 500 ℃, 700 ℃ and 900 ℃ obtained in Example 1 of the present invention, corresponding to Fig. 1(a), Fig. 1(b) and Fig. 1(b) respectively. Figure 1(c);

2 is a SEM image of a core-shell cavity structure titanium dioxide graphene composite 18-G@TiO ₂ obtained in Example 1, with a magnification of ×2000;

3 is a SEM image of a core-shell cavity structure titanium dioxide-graphene composite 24-G@TiO ₂ obtained in Example 1, with a magnification of ×2000;

4 is a SEM image of a core-shell cavity structure titanium dioxide-graphene composite 30-G@TiO ₂ obtained in Example 1, with a magnification of ×2000;

2.5V（相对于 Li/Li ⁺）的锂离子电池的长循环性能图；Figure 5 shows the core-shell cavity structure titanium dioxide graphene composites 18-G@TiO ₂ , 24-G@TiO ₂ and 30-G@TiO ₂ under different time gradients obtained in Example 1 of the present invention at 1 A·g ^- At a current density of ¹ , the tested voltage range is 0.01V

Long-cycle performance graph of Li-ion battery at 2.5V (vs. Li/Li ⁺ );

6 is a thermogravimetric analysis diagram (TG-DTG) of C in the core-shell G@TiO ₂ composite obtained in Example 1 of the present invention.

7 is an impedance diagram of a lithium-ion battery of 24-G@TiO ₂ obtained in Example 1 of the present invention in an initial state, with 2 cycles, 3 cycles, and 4 cycles.

FIG. 8 is a graph showing the rate cycling performance of the 24-G@TiO ₂ obtained in Example 1 of the present invention under different current densities.

FIG. 9 is a CV curve diagram of the first and second cycles of the lithium-ion battery obtained in Example ₁ of the present invention at a scan rate of 0.1 mv/s.

Figure 10 shows the 24-G@TiO ₂ obtained in Example 1 of the present invention at different scan speeds of 0.1 mv·s ^-1 , 0.4 mv·s ^-1 , 0.6 mv·s ^-1 , 0.8 mv·s ^-1 and 1 mv· Li-ion battery CV curves at s ^-1 .

Detailed ways

The embodiments of the present invention are described in detail below with reference to the accompanying drawings and specific implementations. This embodiment is implemented on the premise of the technical solutions of the present invention, and provides detailed implementation modes and specific operation processes, but the protection scope of the present invention is It is not limited to the following examples.

The experimental methods used in the following examples are conventional methods unless otherwise specified.

The reagents, materials, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

The core-shell cavity structure titanium dioxide graphene composite is used as the battery anode, and the specific experimental part of the battery electrode is as follows:

Manufactured by mixing 80% active material, 10% conducting agent (Super P) and 10% binder polyvinylidene difluoride (PVDF) using N-methyl-2-pyrrolidone (NMP) as solvent Working electrode, the resulting slurry was pasted on Cu foil and dried in a vacuum oven at 70 °C for 12 h. To perform electrochemical measurements of Li-ion batteries, 1 M LiPF6 was prepared in a 1:1 (v/v) mixed solution containing ethylene carbonate and diethyl carbonate (EC/DEC) using a Celgard 2500 membrane as the separator, and the It was used as the electrolyte to form a CR2032 button cell in an argon-filled glove box. Voltage electrostatic discharge charge curves were measured in the voltage range of 1.0-3.0 V (vs. Li/Li ⁺ ) using the LAND-CT2001A battery test system.

Example 1

220 ml的乙醇与40

50 ml的环己烷混合搅拌，然后加入0.10

0.20 g无金属酞菁混合搅拌至无金属酞菁充分溶解，同时让反应容器浸泡在冰水浴环境下（-1至1℃）,连续滴加50-60 ml饱和氯化钾溶液，并且持续搅拌，滴加结束后，在冰浴环境下陈化，陈化结束后用乙醇清洗（将环己烷全部清洗掉），用微孔过滤膜（有机系）过滤，然后收集产品到60℃-80℃真空干燥8 h，最终的到酞菁颗粒和氯化钾盐的复合前驱体，记为Pc/KCl；Step (1): Measure 200

220 ml of ethanol with 40

50 ml of cyclohexane mixed and stirred, then added 0.10

0.20 g of metal-free phthalocyanine was mixed and stirred until the metal-free phthalocyanine was fully dissolved. At the same time, the reaction vessel was immersed in an ice-water bath environment (-1 to 1 °C), and 50-60 ml of saturated potassium chloride solution was continuously added dropwise and stirred continuously. , after the dropwise addition, age in an ice bath environment, wash with ethanol after ageing (all cyclohexane is washed away), filter with a microporous filter membrane (organic), and then collect the product to a temperature of 60°C-80°C. After drying under vacuum for 8 h, the final composite precursor of phthalocyanine particles and potassium chloride salt was recorded as Pc/KCl;

Step (2): transfer the composite precursor of phthalocyanine particles and potassium chloride salt prepared in step (1) into a quartz tube for drying, place in a tube furnace for high-temperature sintering, and sinter in a tube furnace in an inert gas atmosphere. The composite precursor was calcined at 700 °C for 8 h and then naturally cooled to room temperature to carbonize the composite precursor into a two-dimensional thin graphene sheet with a regular cubic structure;

2 g，加入到150-170 ml的乙醇溶液中超声，然后加入0.1-0.3 g的十六胺，再持续搅拌，然后每隔10min滴加10 μl的去离子水，通过控制不同的水解时间，从而使二氧化钛在石墨烯表面的厚度不一样，设置了3组不同水解时间的对比实验，分别为水解时间18h、24h、30h，都会得到二氧化钛石墨烯复合体均匀的分散溶液；最后通过离心、烘干最终得到一种核壳空腔结构二氧化钛石墨烯复合体，记为18-G@TiO2 、24-G@TiO2 、30-G@TiO2。通过探究电化学性能的差异，从而得出了最佳水解包覆时间为24h。Step (3): take the two-dimensional thin-layer graphene sheet 1 with a regular cubic structure in step (2)

2 g, add it to 150-170 ml of ethanol solution and sonicate, then add 0.1-0.3 g of hexadecylamine, continue to stir, and then dropwise add 10 μl of deionized water every 10 minutes, by controlling different hydrolysis times, As a result, the thickness of titanium dioxide on the graphene surface is different, and three sets of comparative experiments with different hydrolysis times are set up. The hydrolysis time is 18h, 24h, and 30h, respectively, and a uniform dispersion solution of the titanium dioxide-graphene composite will be obtained. Finally, a core-shell cavity structure titanium dioxide-graphene composite was obtained, denoted as 18-G@TiO2, 24-G@TiO2, 30-G@TiO2. By exploring the difference in electrochemical performance, the optimal hydrolysis coating time is 24h.

Fig. 1 is the SEM images of the two-dimensional thin-layer graphene sheets sintered at different temperatures of 500 ℃, 700 ℃ and 900 ℃ obtained in Example 1 of the present invention, corresponding to Fig. 1(a), Fig. 1(b) and Fig. 1(b) respectively. Figure 1(c). From Fig. 1(b), it can be clearly seen that the cubic salt particles of potassium chloride salt sintered at 700 °C are very uniform, the morphology is regular, and the surface of the cubic salt particles is evenly wrapped with a layer of graphene.

Comparison samples at 500 °C and 900 °C were also made in a tube furnace in an inert gas atmosphere. From the SEM Figure 1(a), it can be seen that the crystal surface of the potassium chloride salt cubic salt sintered at 500 °C is smooth and has no metal carbon. The source molecule has adsorption and spreading behavior on the crystal plane; it can be seen from Figure 1(c) that at 900 °C, after calcination, metal-free phthalocyanine is cracked to obtain a two-dimensional carbon material structure. At this temperature, molten salt chloride passes through sodium solid - Liquid-solid stage, it can be seen that the cubic crystals presented by the molten salt are not perfect. Therefore, the sample at the optimal sintering temperature of 700 °C was selected for further research.

FIG. 2 is a scanning photograph of the 18-G@TiO ₂ obtained in Example 1, and the magnification is ×2000. In the process of synthesizing core-shell cavity structure titania-graphene composites from cube-structured two-dimensional thin-layer graphene sheets, after 18 hours of hydrolysis of isopropyl titanate, the cubic-structured two-dimensional thin-layer graphite The surface of the olefin layer is evenly coated with a thin layer of titanium dioxide, and after centrifugation, water washing and other operations, the structure shown in Figure 2 is obtained. It can be seen from the figure that although the surface-coated TiO2 of the synthesized 18-G@ _TiO2 composites is very uniform, it is very thin.

FIG. 3 is a scanning photograph of the 24-G@TiO ₂ obtained in Example 1, and the magnification is ×2000. In the process of synthesizing core-shell cavity structure titanium dioxide graphene composite material from two-dimensional thin-layer graphene sheets with cubic structure, after 24 hours of hydrolysis of isopropyl titanate, the two-dimensional thin-layer graphite in cubic structure The surface of the olefin sheet layer is evenly coated with a layer of titanium dioxide, and after centrifugation, water washing and other operations, the structure shown in Figure 2 is obtained. It can be seen from the figure that the surface-coated titanium dioxide of the synthesized 24-G@TiO ₂ composites is very uniform. After washing with water, some core-shell cavities still maintain a cubic structure, and some core-shell cavities have been opened. a window.

FIG. 4 is a scanning photograph of the 30-G@TiO ₂ obtained in Example 1, with a magnification of ×2000. It can be seen from the figure that the surface-coated TiO2 of the synthesized 30-G@ _TiO2 composite is not uniform, and rod-shaped TiO2 appears, indicating that the hydrolysis time of isopropyl titanate is too long, resulting in excessive TiO2 adhered to the cubes. The graphene surface, causing the structure to collapse somewhat.

2.5 V（相对于 Li/Li ⁺））。对比发现，18-G@TiO₂可以稳定循环4000圈，电池的首次放电比容量为325 mAh·g^-1，循环曲线呈现出前100圈先下降然后开始持续稳定上升至3500圈后保持稳定，最后容量可以保持在139 mAh·g^-1，容量保持率为42.1％；24-G@TiO₂ 也可以稳定循环4000圈，电池的首次放电比容量为380 mAh·g^-1，循环曲线呈现出前100圈先下降然后开始持续稳定上升至3000圈后保持稳定，最后容量可以保持在180 mAh·g^-1，容量保持率为46.6％；Figure 5 shows the cycle performance of 18-G@TiO ₂ , 24-G@TiO ₂ , and 30-G@TiO ₂ obtained in Example 1 after being assembled into a CR2032 battery at a current density of (1 A·g ^-1 , the test voltage range is 0.01

2.5 V (vs. Li/Li ⁺ )). By comparison, it is found that 18-G@TiO ₂ can be cycled stably for 4000 cycles, and the first discharge specific capacity of the battery is 325 mAh·g ^-1 . The capacity can be maintained at 139 mAh·g ^-1 , and the capacity retention rate is 42.1%; 24-G@TiO ₂ can also be stably cycled for 4000 cycles, the first discharge specific capacity of the battery is 380 mAh·g ^-1 , and the cycle curve shows the top 100 The cycle first decreased and then began to rise steadily to 3000 cycles and then remained stable. The final capacity could be maintained at 180 mAh·g ^-1 , and the capacity retention rate was 46.6%;

30-G@TiO ₂ can also be cycled stably for about 4000 cycles. The first discharge specific capacity of the battery is 300 mAh·g ^-1 , and the cycle curve shows that the first 100 cycles first decrease and then start to rise steadily to 3500 cycles and then remain stable, and the final capacity can be maintained at 130.3 mAh·g ^-1 with a capacity retention rate of 43.3%; by comparing the respective long-cycle performances of 18-G@TiO ₂ , 24-G@TiO ₂ , and 30-G@TiO ₂ , we can obtain The 24-G@TiO ₂ has the best electrochemical performance and capacity. After 4000 cycles of long cycle, it can maintain a capacity of 180 mAh·g ^-1 , which is better than the current capacity in terms of long cycle capacity and final high capacity. material that has already been reported. Therefore, we mainly focus on 24-G@TiO ₂ in the following other characterization tests.

700℃，升温速率为10℃·min^-1。可以观察到核壳TiO₂ @G复合材料在30-700℃温度范围内质量百分比明显下降，且出现了两个平台，说明在升温过程中，24-G@TiO₂中的水分子首先蒸发，导致质量百分比下降；然后复合材料中的碳由于与空气发生反应，生成二氧化碳气体，同时也考虑到复合材料本身的氧化，由此可以得到在24-G@TiO₂中C的含量为8.12％。Figure 6 shows that in order to explore the content of C in the synthesized 24-G@TiO ₂ , the thermogravimetric analysis (TG-DTG) was carried out in this Example 1 under an air atmosphere, and the temperature range was 30

700°C, the heating rate is 10°C·min ^-1 . It can be observed that the mass percentage of the core-shell _TiO2 @G composite decreases significantly in the temperature range of 30-700 °C, and two plateaus appear, indicating that during the heating process, the water molecules in 24-G@ _TiO2 evaporate first, As a result, the mass percentage decreased; then the carbon in the composite material reacted with air to generate carbon dioxide gas, and the oxidation of the composite material itself was also considered, so the content of C in 24-G@TiO ₂ was 8.12%.

Figure 7 is the electrochemical impedance spectrum (EIS) of the core-shell cavity structure titanium dioxide-graphene composite material obtained in Example 1. It can be clearly seen from the EIS diagram that the first black impedance curve has an obvious large section in the high frequency region. , which is the typical impedance generated by charge transfer; the impedance curves of the 2nd, 3rd, 4th, and 3500th circles form two small semicircles in the previous large circle area, and the radius of the semicircle during the cycle gradually decreases, which means that the charge transfer resistance (Rct) decreases gradually. This obvious change indicates the enhanced interparticle and electrical contact between graphene and _TiO2 nanosheets, which is related to the special core-shell cavity structure of the composite, as can be seen from the figure, the small semicircle 3 bars in front The lines are almost coincident, indicating that this is due to the charge transfer resistance generated by the intercalation of lithium ions on the surface of the active material; the three semicircular lines in the back do not overlap, indicating that there has always been a change in the SEI film under different charge and discharge cycles; Finally, the sloping line in the low-frequency region is parallel and gradually stabilized after 2 to 4 cycles, indicating good structural stability. It shows that the cubic structure of the core-shell cavity structure TiO2-graphene composite material always maintains a stable structure that is conducive to Li + diffusion during the charge-discharge cycle. In short, the EIS results reveal stable and efficient electronic and ionic conduction in 24-G@ _TiO2 , a material with excellent Li+ storage capacity.

FIG. 8 is a graph of the rate curves of the 24-G@TiO ₂ obtained in this example when used as a lithium-ion battery at different current densities. It can be clearly seen from the figure that the specific capacity of 24-G@TiO ₂ can reach 225mAh·g ^-1 at a low current density of 0.2 A·g ^-1 . As the current density increases, the specific capacity of the battery also increases. When the current density is 5 A·g ^-1 , the capacity can be maintained at about 100 mAh·g ^-1 , and the average discharge capacity can still reach 45% of 0.2 A·g ^-1 , indicating that 24 The special core-shell cavity cubic structure of -G@TiO ₂ has excellent adaptability to the charge-discharge current; then with the decrease of the current density, the capacity gradually increases. It can be seen from the figure that when the current density becomes At 0.2 A·g ^-1 , the capacity can be quickly recovered with almost no decay, indicating that the battery has good capacity retention, good cycle stability, high reversibility, and good rate performance.

Fig. 9 shows the CV curve of 24-G@TiO ₂ in this example at a sweep rate of 0.1 A·g ^-1 . From the figure, we can clearly see that this is the CV curve of titanium dioxide, which also has a typical CV curve. The carbon redox peak also proves that the composite material of titanium dioxide and graphene of this material, in the second circle, the area of the CV curve is reduced, which proves the formation of the SEI film.

Figure 10 shows the CV curves of 24-G@TiO ₂ under different sweep numbers. From the figure, we can see that the curve has good repeatability and obvious oxidation and reduction peaks, and as the sweep number increases, The area of the curve also increases, and after the first four cycles, the CV curve shows two corresponding peaks at different scan rates, indicating a typical Ti ⁴⁺ /Ti ³⁺ redox pair. In contrast, the voltage hysteresis becomes severe at higher scan rates; this phenomenon is common in titania-graphene composites and is attributed to a sharp increase in the polarization reaction.

In summary, by controlling different hydrolysis times, the differences in electrochemical performance were explored, and the optimal hydrolysis coating time was 24h. The performance of the core-shell composite material 24-G@TiO2 prepared by the present invention was also explored when applied to the negative electrode material for lithium ion batteries. The performance characteristics: it can cycle stably for 4000 cycles, the capacity can be maintained at 180 mAh·g ^-1 , and the capacity can be maintained at 180 mAh·g -1 . The retention rate is 46.6%, the rate performance is very good, and the electrochemical performance is very excellent, which is better than the electrochemical performance of the related titanium dioxide carbon materials that have been reported so far.

Claims (5)

1. a core-shell cavity structure titanium dioxide graphene composite preparation method, is characterized in that: at first with potassium chloride as salt template, with metal-free phthalocyanine as carbon source and nitrogen source, prepare graphene by ionothermal method and potassium chloride salt mixture, then use isopropyl titanate to hydrolyze in ethanol, under the action of hexadecylamine surfactant, make a layer of titanium dioxide evenly grow on the surface of graphene, and finally centrifuge, wash, dry, Finally, a core-shell cavity structure titanium dioxide graphene composite is obtained; Specifically include the following steps: Step (1): Measure 200-220 ml of ethanol and mix and stir with 40-50 ml of cyclohexane, then add 0.10-0.20 g of metal-free phthalocyanine, mix and stir until the metal-free phthalocyanine is fully dissolved, and at the same time let the reaction vessel soak In an ice-water bath environment -1 to 1 °C, continuously add 50-60 ml of saturated potassium chloride solution dropwise, and continue to stir, after the dropwise addition, age in an ice bath environment, wash with ethanol after aging, All the cyclohexane was washed away, filtered with a microporous filter membrane, and then the product was collected and dried under vacuum at 60-80 °C for 8 h. The final composite precursor of phthalocyanine particles and potassium chloride salt was recorded as Pc/KCl; Step (2): transfer the Pc/KCl prepared in step (1) into a quartz tube for drying, place it in a tube furnace for high temperature sintering, and calcine at 700°C for 8 hours in a tube furnace with an inert gas atmosphere, and then naturally After cooling to room temperature, the composite precursor was carbonized into a two-dimensional thin graphene sheet with a regular cubic structure, denoted as G/KCl; Step (3): Take 1-2 g of the two-dimensional thin-layer graphene sheet with a regular cubic structure in step (2), add it to 150-170 ml of ethanol solution, and then add 0.1-0.3 g of hexadecane amine, and then continue to stir, then dropwise 10 μl of deionized water every 10 min, and continue to stir for 24 hours to obtain a uniform dispersion solution of the titanium dioxide graphene complex; finally, a core-shell cavity is obtained by centrifugation and drying. Structural titanium dioxide graphene composite, denoted as G@TiO ₂ ; Using metal-free phthalocyanine as the carbon source and nitrogen source, and potassium chloride as the salt template, a mixture of graphene and potassium chloride salt was prepared by ionothermal method, denoted as G/KCl. 2. the preparation method of a kind of core-shell cavity structure titanium dioxide graphene composite body according to claim 1, is characterized in that: in step (2), inert gas atmosphere is Ar gas or nitrogen; The program was as follows: at room temperature, argon was introduced for 1 h, then heated to 300 °C at a heating rate of 5 °C·min ^-1 , then held for 1 h, and then raised to 700 °C at a rate of 2 °C·min ^-1 for 8 h. Then naturally cooled to room temperature. 3. the preparation method of a kind of core-shell cavity structure titanium dioxide graphene composite body according to claim 2, is characterized in that: in step (3), adopt hexadecylamine as surfactant, and titanium dioxide hydrolysis time is 24 h. 4. A core-shell cavity structure titanium dioxide graphene composite prepared by the preparation method according to any one of claims 1 to 3. 5. An application of the core-shell cavity structure titanium dioxide-graphene composite according to claim 4, characterized in that it is used as an anode material for a lithium ion battery.

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