Preparation and application of titanium dioxide / sodium titanate / carbon composite material

Abstract

The invention belongs to the technical field of electrode materials, and particularly discloses preparation and application of a titanium dioxide / sodium titanate / carbon composite material, and the preparation comprises the following steps: preparing a graphene oxide aqueous solution and a sodium hydroxide solution; taking a sodium hydroxide solution, adding tetrabutyl titanate, and carrying out a hydrothermal reaction; cooling to room temperature, centrifugally washing for three times, and drying in vacuum; deionized water is taken, tetrabutyl titanate is added, and a hydrothermal reaction is carried out; cooling to room temperature, centrifugally washing with water for three times, and drying in vacuum; adding a sodium titanate precursor and a titanium dioxide precursor into the graphene oxide aqueous solution, fully stirring, carrying out centrifugal treatment, and drying; and placing in a tube test furnace, and carrying out heat treatment under an inert gas condition. By adopting the preparation and the application of the titanium dioxide / sodium titanate / carbon composite material, the problem that the existing titanium-based sodium ion battery negative electrode material is generally insufficient in chemical kinetic characteristics can be solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and in particular relates to the preparation and application of a titanium dioxide / sodium titanate / carbon composite material. Background Art

[0002] Titanium is the all-around champion in the metal world, and its compounds are widely used in various industries. Titanium dioxide (TiO2) and sodium titanate (Na2Ti3O7) as electrode materials have been widely studied in the field of secondary ion batteries in recent years. At present, researchers mainly improve their electrochemical properties through nanostructure design, doping modification and composite material preparation. For example, by preparing nanowires, nanotubes or mesoporous structures to increase the specific surface area and ion diffusion rate; by doping nitrogen, carbon or other metal elements to improve its conductivity and structural stability; or by compounding with carbonaceous materials to enhance electron transport capacity. Sodium titanate is considered to be a promising negative electrode material for sodium ion batteries due to its open layered structure and high theoretical specific capacity. Researchers have improved its cycle stability and rate performance by regulating morphology, optimizing synthesis process and surface modification. However, there are still some problems with the existing technology. First, the theoretical specific capacity of titanium dioxide is low (about 335mAh g -1 ) and poor conductivity, limiting its application in high-energy-density batteries. Secondly, sodium titanate is prone to structural collapse and volume expansion during charge and discharge, resulting in insufficient cycling stability. Further optimizing the material structure, developing low-cost preparation processes, and exploring its performance in actual battery systems are key to promoting its industrial application.

[0003] Therefore, the art needs to develop a preparation and application of titanium dioxide / sodium titanate / carbon composite materials that can effectively solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation and application of a titanium dioxide / sodium titanate / carbon composite material, which can solve the problem of insufficient chemical kinetic properties commonly found in existing titanium-based sodium ion battery negative electrode materials.

[0005] To achieve the above object, the present invention provides a preparation method of a titanium dioxide / sodium titanate / carbon composite material, comprising the following steps:

[0006] Step S1, preparing a graphene oxide aqueous solution and a sodium hydroxide solution;

[0007] Step S2: Take 40-70 mL of sodium hydroxide solution and add tetrabutyl titanate to make the volume concentration of tetrabutyl titanate 0.05-0.22 g mL -1 Too low a concentration will result in insufficient crystallinity of sodium titanate, while too high a concentration will result in incomplete hydrolysis of sodium titanate.

[0008] After the hydrothermal reaction, the mixture was cooled to room temperature and washed three times with deionized centrifugal water; then vacuum dried at 60°C for 12 hours to obtain a sodium titanate precursor;

[0009] Step S3: Take 40-70 mL of ionized water and add tetrabutyl titanate to make the concentration of tetrabutyl titanate 0.05-0.22 g mL -1 Too low a concentration will result in insufficient crystallinity of titanium dioxide, while too high a concentration will result in incomplete hydrolysis of sodium titanate. Carry out hydrothermal reaction;

[0010] After the hydrothermal reaction, the product was cooled to room temperature and washed three times with deionized water by centrifugation; then vacuum dried at 60°C for 12 hours to obtain a titanium dioxide precursor;

[0011] Step S4: adding sodium titanate precursor and titanium dioxide precursor to the graphene oxide aqueous solution, wherein the mass concentration of sodium titanate precursor and titanium dioxide precursor is controlled to be 1-4 mg mL -1 The suspension of titanium dioxide and sodium titanate was stirred thoroughly for 12-24 hours, then centrifuged and dried in vacuum at 60°C for 12 hours.

[0012] Step S5: Place the sample in a tube test furnace and perform heat treatment under inert gas conditions to ensure that the carbonaceous material is effectively retained during the carbonization process. In an oxidizing atmosphere, the carbonaceous material will turn into oxides and disappear, thus obtaining a titanium dioxide / sodium titanate / carbon composite material.

[0013] The obtained titanium dioxide / sodium titanate / carbon composite material has the following characteristics:

[0014] 1) Size characteristics:

[0015] Titanium dioxide / sodium titanate / carbon composites are nanocomposites, and graphene is a nanoscale carbonaceous material. The nanostructure of titanium dioxide / sodium titanate supported on a carbonaceous substrate provides more channels for electron transport in the electrode material. The nanomaterials provide more active sites, enhancing the electrochemical stability of the electrode material. To fully maximize the electrochemical activity of titanium dioxide / sodium titanate, the carbonaceous substrate content is preferably controlled below 20%.

[0016] 2)Structure and performance characteristics:

[0017] Titanium dioxide and sodium titanate achieve energy storage through intercalation reactions, so the volume strain is large during the electrochemical reaction. Graphene mainly achieves energy storage through ion adsorption / desorption, so its electrochemical stability is relatively excellent. The synergistic effect of the two constituent unit materials enables it to exhibit electrochemical characteristics of high capacity and long cycle performance.

[0018] 3) Process characteristics: The composite material is obtained by combining the hydrothermal method, which is traditional, simple and easy to implement.

[0019] 5) Cost characteristics: The main components of titanium dioxide / sodium titanate / carbon composite materials are titanium dioxide, sodium titanate, and graphene. Titanium is a conventional transition metal with a high abundance in the earth's crust, and carbon is a human-friendly element. Therefore, developing related technologies for their composite materials has advantages in improving the electrochemical properties of their composite materials and reducing the cost of electrode materials.

[0020] Preferably, in step S1, the concentration of the graphene oxide aqueous solution is 2-5 mg / mL. If the mass concentration of graphene oxide is too low, the dispersion of titanium dioxide and sodium titanate will be insufficient. If the concentration is too high, the carbon content of the composite material will increase, resulting in a decrease in the electrochemical activity of the composite material.

[0021] The concentration of sodium hydroxide solution is 9-12 mol L -1 Too low a concentration of sodium hydroxide will affect the crystallinity of sodium titanate, while too high a concentration will cause a waste of sodium hydroxide.

[0022] Preferably, in step S2, the hydrothermal reaction temperature is 160-200°C, and the hydrothermal time is 16-24h; if the hydrothermal temperature is too low, the pressure in the reactor will be insufficient and the crystallinity of the product will be poor; if the temperature is too high, energy consumption will increase, resulting in waste.

[0023] The centrifugal speed is 6000-10000 r / min, and the centrifugal time is 5-10 min;

[0024] In step S3, the hydrothermal reaction temperature is 160-200°C, and the hydrothermal time is 16-24h. If the hydrothermal temperature is too low, the pressure in the reactor will be insufficient and the crystallinity of the product will be poor. If the temperature is too high, energy consumption will increase, resulting in waste.

[0025] The centrifugal speed is 6000-10000 r / min, and the centrifugal time is 5-10 min;

[0026] In step S4, the centrifugal speed is 6000-10000 r / min, and the centrifugal time is 5-10 min.

[0027] Preferably, in step S5, the inert gas includes, but is not limited to, argon and nitrogen; the heat treatment temperature is 600-900°C, and the heat treatment time is 1-3 hours. If the treatment temperature is too low, the crystallinity of titanium dioxide and sodium titanate will not be complete. If the treatment temperature is too high or the treatment time is too long, it will increase energy consumption and waste resources, leading to increased preparation costs.

[0028] The present invention also provides an application of the titanium dioxide / sodium titanate / carbon composite material obtained by preparing the titanium dioxide / sodium titanate / carbon composite material in a sodium ion battery.

[0029] The above application is specifically as follows: the obtained titanium dioxide / sodium titanate / carbon composite material, conductive carbon black or carbon nanotubes and polyvinylidene fluoride are mixed in N-methylpyrrolidone at a mass ratio of 7-8.5:2-1:1-0.5, stirred for 0.2-1h, and stirred until uniform; the obtained uniform electrode slurry is coated on copper foil with a loading capacity of 3-12 mg / cm 2 If the loading amount is too low, the cycle stability is insufficient and there is no production reference value. If it is too high, the active material near the current collector cannot fully exert its electrochemical activity. Therefore, the loading amount should be appropriate.

[0030] After coating, the electrode is placed in a vacuum drying oven and dried at 60-120°C for 24-48 hours, and then punched into a circular electrode sheet with a diameter of 12 mm (as the negative electrode) or the corresponding electrode sheet size of a card battery; finally, in a glove box, the electrode is assembled with sodium foil to form a two-electrode system battery model CR2025 button battery or the corresponding card battery.

[0031] The present invention adopts the preparation and application of the above-mentioned titanium dioxide / sodium titanate / carbon composite material, and the beneficial effects are as follows:

[0032] 1. The titanium-based composite material of the present invention has a high sodium storage capacity. By introducing carbon into the composite material, the present invention provides favorable conditions for the dispersion and distribution of titanium dioxide and sodium titanate, which can significantly increase the specific surface area of ​​the composite material and effectively improve the sodium storage capacity of the composite material. A sodium ion battery assembled using the composite material prepared in this invention as the active material can achieve a reversible capacity of 110.8 mAh / g at a current density of 0.05 A / g.

[0033] 2. The composite material of the present invention can alleviate the volume strain of titanium dioxide and sodium titanate during electrochemical processes. The introduction of graphene can provide abundant electron transport channels and have a positive effect on the dispersion and distribution of titanium dioxide and sodium titanate. The unique spatial structure of the flake sodium titanate carrying titanium dioxide on the graphene surface provides abundant active sites and a stable electrochemical structure for carrier adsorption / desorption and embedding / ejection, and can effectively alleviate the volume expansion of the electrode material during the electrochemical reaction.

[0034] 3. The composite material of the present invention has good electrochemical structural stability, and the obtained electrode sheet has excellent cycle performance. The microstructure and intrinsic properties of the material determine its electrochemical performance. The titanium dioxide / sodium titanate / carbon composite material combines the monomer structure and performance advantages of titanium dioxide, sodium titanate, and graphene. The introduction of sodium titanate enriches the effective electrochemical sites of titanium dioxide, and the reaction sites and transport channels of the carriers introduced by graphene are used to improve the transport kinetics of sodium ions and the reversibility of the electrochemical reaction of the electrode material through structural regulation of the composite material, thereby obtaining a sodium ion battery with excellent cycle performance. When the current density is 0.1Ag -1 When the cycle is repeated for 1000 times, the reversible capacity retention rate reaches 83.6%.

[0035] 4. The composite material of the present invention has good reversibility, and the obtained electrode active material has excellent rate performance. Titanium dioxide / sodium titanate / carbon composite material has better structural stability than titanium dioxide / sodium titanate composite material and has more abundant electron migration channels, which can improve the thermodynamic stability and ion deintercalation kinetics of electrode material, thereby accelerating the transport of ions / electrons and improving the specific capacity of composite electrode material. It can be seen from the rate curve that at 0.05, 0.1, 0.3, 0.5, 0.8, 1.0, 5.0, 10.0Ag -1 At a current density of 1.5 GHz, the specific capacity of the titanium dioxide / sodium titanate / carbon composite material is as high as 546.21 mAh g -1 、492.61mAh g -1 , 425.21mAh g -1 、368.91mAh g -1 , 295.11mAh g -1 , 209.21mAhg -1 、157.61mAh g -1 、98.1mAh g -1 , and then return to a low current density of 0.3Ag -1 Under the condition of high current density, the capacity is almost unchanged, which once again shows that the obtained titanium dioxide / sodium titanate / carbon composite material has good electrochemical reaction reversibility.

[0036] 5. The preparation steps of the present invention are simple, the reaction conditions are mild and easy to control, and the raw materials used are low in cost, making it suitable for large-scale production. The hydrothermal reaction used in the preparation process of the composite material can be completed in an ordinary blast drying oven, and all heat treatment processes are carried out in a tubular furnace, and the temperature range belongs to medium and low temperature heating. The equipment is conventional and there are no overly harsh conditions. This provides the possibility for conventional chemical plants to have ton-level reactors for large-scale production; the base material in the composite material is carbon material, which provides a guarantee for its low cost and environmental friendliness. The transition metal titanium is a conventional non-strategic resource metal and is extremely environmentally friendly, which also creates favorable conditions for the large-scale production of the composite material.

[0037] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a SEM morphology image of the titanium dioxide / sodium titanate / carbon composite material prepared in Example 1 of the preparation and application of a titanium dioxide / sodium titanate / carbon composite material of the present invention;

[0039] Figure 2 The XRD pattern of the titanium dioxide / sodium titanate / carbon composite material prepared in Example 1 of the preparation and application of the titanium dioxide / sodium titanate / carbon composite material of the present invention;

[0040] Figure 3 Thermogravimetric curves of the titanium dioxide / sodium titanate / carbon composite material and titanium dioxide / sodium titanate prepared in Example 1 of the preparation and application of a titanium dioxide / sodium titanate / carbon composite material of the present invention;

[0041] Figure 4 This is the constant current charge-discharge curve of titanium dioxide / sodium titanate / graphene in Example 1 of the preparation and application of a titanium dioxide / sodium titanate / carbon composite material of the present invention;

[0042] Figure 5 This is the constant current charge and discharge curve of titanium dioxide / sodium titanate in Example 1 of the preparation and application of a titanium dioxide / sodium titanate / carbon composite material of the present invention;

[0043] Figure 6 The rate performance curve of titanium dioxide / sodium titanate / graphene in Example 1 of the preparation and application of a titanium dioxide / sodium titanate / carbon composite material of the present invention;

[0044] Figure 7 The cycle performance curve of titanium dioxide / sodium titanate / graphene in Example 1 of the preparation and application of a titanium dioxide / sodium titanate / carbon composite material of the present invention;

[0045] Figure 8This is a SEM morphology image of the titanium dioxide / sodium titanate / carbon composite material prepared in Example 2 of the preparation and application of a titanium dioxide / sodium titanate / carbon composite material of the present invention;

[0046] Figure 9 This is a SEM morphology image of the titanium dioxide / sodium titanate / carbon composite material prepared in Example 3 of the preparation and application of a titanium dioxide / sodium titanate / carbon composite material of the present invention;

[0047] Figure 10 This is a SEM morphology image of a titanium dioxide / sodium titanate / carbon composite material prepared in Comparative Example 1 of the preparation and application of a titanium dioxide / sodium titanate / carbon composite material of the present invention;

[0048] Figure 11 This is a SEM morphology image of the titanium dioxide / sodium titanate / carbon composite material prepared in comparative example 2 of the preparation and application of a titanium dioxide / sodium titanate / carbon composite material of the present invention. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0050] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0051] Example 1

[0052] A preparation method of a titanium dioxide / sodium titanate / carbon composite material comprises the following steps:

[0053] Step S1: prepare a graphene oxide aqueous solution with a concentration of 3.5 mg / mL and a graphene oxide aqueous solution with a concentration of 10 mol L -1 of sodium hydroxide solution;

[0054] Step S2: Take 50 mL of sodium hydroxide solution and add tetrabutyl titanate to make the volume concentration of tetrabutyl titanate 0.15 g mL -1 , carry out hydrothermal reaction, the hydrothermal reaction temperature is 180℃, and the hydrothermal time is 20h;

[0055] After the hydrothermal reaction, the mixture was cooled to room temperature and washed three times with water by deionized water centrifugation (parameter 8000r / min, 8min); then vacuum dried at 60°C for 12h to obtain a sodium titanate precursor;

[0056] Step S3: Remove 50 mL of ionized water and add tetrabutyl titanate to make the concentration of tetrabutyl titanate 0.15 g mL -1 , carry out hydrothermal reaction, the hydrothermal reaction temperature is 180℃, and the hydrothermal time is 20h;

[0057] After the hydrothermal reaction, the product was cooled to room temperature and washed three times with deionized water by centrifugation (parameter 8000r / min, 8min); then vacuum dried at 60°C for 12h to obtain a titanium dioxide precursor;

[0058] Step S4: adding sodium titanate precursor and titanium dioxide precursor to the graphene oxide aqueous solution, wherein the mass concentration of sodium titanate precursor and titanium dioxide precursor is controlled to 3 mg mL -1 The suspension was stirred for 18 h, then centrifuged (parameter 8000 r / min, 8 min), and vacuum dried at 60 °C for 12 h;

[0059] Step S5: Place the sample in a tube test furnace and perform heat treatment under inert gas (argon or nitrogen) at a temperature of 800° C. for 2 hours to obtain a titanium dioxide / sodium titanate / carbon composite material.

[0060] like Figure 1 As shown, the titanium dioxide / sodium titanate heterostructure is relatively evenly dispersed on the graphene surface, and the sodium titanate particles are about 30 nm.

[0061] like Figure 2 As shown, titanium dioxide / sodium titanate / carbon composites were successfully synthesized.

[0062] like Figure 3 As shown, the mass content of graphene in the composite material is about 5.4%. The preparation process of titanium dioxide / sodium titanate is: no graphene is involved in the whole process, and other parameters and operations are the same as in Example 1.

[0063] Electrode preparation / battery assembly: Titanium dioxide / sodium titanate / carbon composite material, conductive carbon black, and polyvinylidene fluoride were mixed in N-methylpyrrolidone at a mass ratio of 7:2:1 and stirred for 0.5 h. The resulting uniform electrode slurry was coated on copper foil with a loading of 4 mg / cm 2 After preparation, it was dried in a vacuum drying oven at 60°C for 12 hours, punched into circular electrode sheets with a diameter of 12 mm, and matched with metallic sodium in a glove box to form a two-electrode battery system, model CR2025, with a voltage test range of 0.01-3V.

[0064] like Figure 4-Figure 5 As shown in the figure, after the third cycle, the curves overlap and the performance begins to stabilize. This is due to the formation of the SEI film, and the charge and discharge platform of the material is about 0.59V.

[0065] like Figure 6 As shown, at a current density of 0.05Ag -1 , 0.1Ag -1 , 0.3Ag -1, 0.5Ag -1 , 0.8Ag -1 , 1.0Ag -1 , 3.0Ag -1 , 5.0Ag -1 , the reversible capacity can reach 546.2mAh g -1 , 492.6mAh g -1 , 425.2mAh g -1 , 368.9mAhg -1 , 295.1mAh g -1 , 209.2mAh g -1 , 157.6mAh g -1 , 98.1mAh g -1 .

[0066] like Figure 7 As shown in FIG, after 1000 cycles, the capacity retention rate reaches 83.6%. It can be seen that the titanium dioxide / sodium titanate / carbon electrode material battery prepared in this example exhibits good cycle stability.

[0067] Example 2

[0068] A preparation method of a titanium dioxide / sodium titanate / carbon composite material comprises the following steps:

[0069] Step S1: prepare a graphene oxide aqueous solution with a concentration of 5 mg / mL and a graphene oxide aqueous solution with a concentration of 12 mol L -1 of sodium hydroxide solution;

[0070] Step S2: Take 70 mL of sodium hydroxide solution and add tetrabutyl titanate to make the volume concentration of tetrabutyl titanate 0.22 g mL -1 , carry out hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the hydrothermal time is 24h;

[0071] After the hydrothermal reaction, the mixture was cooled to room temperature and washed three times with water by deionized water centrifugation (parameter 10000r / min, 10min); then vacuum dried at 60°C for 12h to obtain a sodium titanate precursor;

[0072] Step S3: Remove 70 mL of ionized water and add tetrabutyl titanate to make the concentration of tetrabutyl titanate 0.22 g mL -1 , carry out hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the hydrothermal time is 24h;

[0073] After the hydrothermal reaction, the product was cooled to room temperature and washed three times with deionized water by centrifugation (parameter 10000r / min, 10min); then vacuum dried at 60°C for 12h to obtain a titanium dioxide precursor;

[0074] Step S4: adding sodium titanate precursor and titanium dioxide precursor to the graphene oxide aqueous solution, wherein the mass concentration of sodium titanate precursor and titanium dioxide precursor is controlled to 4 mg mL -1 The suspension was stirred for 24 h, then centrifuged (parameter 10000 r / min, 10 min), and vacuum dried at 60 ° C for 12 h;

[0075] Step S5: Place the sample in a tube test furnace and perform heat treatment under inert gas (argon or nitrogen) at a temperature of 900° C. for 3 hours to obtain a titanium dioxide / sodium titanate / carbon composite material.

[0076] Electrode preparation / battery assembly:

[0077] The obtained titanium dioxide / sodium titanate / carbon composite material, conductive carbon black and polyvinylidene fluoride were mixed in N-methylpyrrolidone at a mass ratio of 8.5:2:0.5 and stirred for 0.5 hours. The obtained uniform electrode slurry was coated on copper foil with a loading of 8 mg / cm 2 After preparation, it was dried in a vacuum drying oven at 60°C for 12 hours, punched into circular electrode sheets with a diameter of 12 mm, and matched with metallic sodium in a glove box to form a two-electrode battery system, model CR2025, with a voltage test range of 0.01-3V.

[0078] like Figure 8 As shown, the titanium dioxide / sodium titanate / carbon composite prepared in Example 1 exhibits more severe agglomeration than the titanium dioxide / sodium titanate / carbon composite prepared in Example 1, which is related to the temperature and duration of the hydrothermal reaction. When the mass ratio of the titanium dioxide / sodium titanate / carbon composite, conductive carbon black, and polyvinylidene fluoride was adjusted from 7:2:1 to 8.5:1:0.5, the battery maintained a specific capacity of 77.1% after 1,000 cycles.

[0079] As can be seen, the electrochemical performance of the composite material obtained in Example 2 is lower than that of Example 1, and the overall battery performance has declined. The structural characteristics of the composite material determine that the carrier transport efficiency is lower than that of Example 1. At the same time, the reduced proportion of the conductive agent leads to a decrease in electron collection efficiency, ultimately resulting in the electrochemical performance of the battery electrode material being inferior to that of Example 1.

[0080] Example 3

[0081] A preparation method of a titanium dioxide / sodium titanate / carbon composite material comprises the following steps:

[0082] Step S1: prepare a graphene oxide aqueous solution with a concentration of 2 mg / mL and a graphene oxide aqueous solution with a concentration of 9 mol L -1 of sodium hydroxide solution;

[0083] Step S2: Take 40 mL of sodium hydroxide solution and add tetrabutyl titanate to make the volume concentration of tetrabutyl titanate 0.05 g mL -1 , carry out hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the hydrothermal time is 24h;

[0084] After the hydrothermal reaction, the mixture was cooled to room temperature and washed three times with water by deionized water centrifugation (parameter 10000r / min, 10min); then vacuum dried at 60°C for 12h to obtain a sodium titanate precursor;

[0085] Step S3: Remove 40 mL of ionized water and add tetrabutyl titanate to make the concentration of tetrabutyl titanate 0.05 g mL -1 , carry out hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the hydrothermal time is 24h;

[0086] After the hydrothermal reaction, the product was cooled to room temperature, centrifuged with deionized water (7000 r / min, 10 min) and washed three times; then vacuum dried at 60°C for 12 h to obtain a titanium dioxide precursor;

[0087] Step S4: adding sodium titanate precursor and titanium dioxide precursor to the graphene oxide aqueous solution, wherein the mass concentration of sodium titanate precursor and titanium dioxide precursor is controlled to 1 mg mL -1 The suspension was stirred for 24 h, then centrifuged (parameter 6000 r / min, 5 min), and vacuum dried at 60 °C for 12 h;

[0088] Step S5: Place the sample in a tube test furnace and perform heat treatment under inert gas (argon or nitrogen) at a temperature of 700° C. for 3 hours to obtain a titanium dioxide / sodium titanate / carbon composite material.

[0089] Electrode preparation / battery assembly: The obtained titanium dioxide / sodium titanate / carbon composite material, conductive carbon black and polyvinylidene fluoride (mass ratio of 8:1:1) were mixed in N-methylpyrrolidone and stirred for 0.5 hours. The obtained uniform electrode slurry was coated on copper foil with a loading of 3.5 mg / cm 2 , in a vacuum drying oven, at 90°C, keep warm for 18 hours, punch out circular electrode sheets with a diameter of 12 mm, and form a two-electrode system with sodium metal in a glove box. The battery assembly model is CR2025 button battery, and the voltage test range is 0.01-3V.

[0090] like Figure 9 As shown, the dispersion of titanium dioxide / sodium titanate is not as good as that of Example 1 and Example 2, and is not evenly dispersed on the graphene surface. This is related to the insufficient amount of metal ions and the short reaction time. -1The reversible capacity is 465.3 mAh g -1 , after 1000 cycles, the capacity retention rate is 52.4%.

[0091] The microstructure and distribution of titanium dioxide / sodium titanate / carbon, the primary active materials in the electrode material, directly impact its overall performance. Because the process parameters were lower than those in Example 1, its electrochemical performance was relatively low. Due to the lower amount of titanium dioxide / sodium titanate formed, the graphene content in the composite material was relatively high. Furthermore, adjusting the electrode ingredient ratio still failed to compensate for the reduction in active sites in the electrode material, resulting in a lower specific capacity than in Example 1.

[0092] Comparative Example 1

[0093] A preparation method of a titanium dioxide / sodium titanate / carbon composite material comprises the following steps:

[0094] Step S1: prepare a graphene oxide aqueous solution with a concentration of 8 mg / mL and a graphene oxide aqueous solution with a concentration of 14 mol L -1 of sodium hydroxide solution;

[0095] Step S2: Take 70 mL of sodium hydroxide solution and add tetrabutyl titanate to make the volume concentration of tetrabutyl titanate 0.3 g mL -1 , carry out hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the hydrothermal time is 24h;

[0096] After the hydrothermal reaction, the mixture was cooled to room temperature and washed three times with water by deionized water centrifugation (parameter 10000r / min, 10min); then vacuum dried at 60°C for 12h to obtain a sodium titanate precursor;

[0097] Step S3: Remove 70 mL of ionized water and add tetrabutyl titanate to make the concentration of tetrabutyl titanate 0.4 g mL -1 , carry out hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the hydrothermal time is 24h;

[0098] After the hydrothermal reaction, the product was cooled to room temperature and washed three times with deionized water by centrifugation (parameter 10000r / min, 10min); then vacuum dried at 60°C for 12h to obtain a titanium dioxide precursor;

[0099] Step S4: adding sodium titanate precursor and titanium dioxide precursor to the graphene oxide aqueous solution, wherein the mass concentration of sodium titanate precursor and titanium dioxide precursor is controlled to 6 mg mL -1 , fully stirred for 36 h, then centrifuged (parameter 10000 r / min, 10 min), and vacuum dried at a temperature of 60 ° C for 12 h;

[0100] Step S5: Place the sample in a tube test furnace and perform heat treatment under inert gas (argon or nitrogen) at a temperature of 900° C. for 3.5 hours to obtain a titanium dioxide / sodium titanate / carbon composite material.

[0101] Electrode preparation / battery assembly: The obtained titanium dioxide / sodium titanate / carbon composite material, conductive carbon black and polyvinylidene fluoride (mass ratio 7:2:1) were mixed in N-methylpyrrolidone and stirred for 0.5 h. The slurry was coated on copper foil with a loading of about 2.5 mg / cm 2 , vacuum drying, 60℃, 12h, punched into circular electrode sheets with a diameter of 12mm, and composed of a two-electrode system with sodium metal in a glove box. The battery assembly model is CR2025 button battery, and the voltage test range is 0.01-3V.

[0102] like Figure 10 As shown in Figure 2, the titanium dioxide / sodium titanate / carbon agglomerates severely, and it is impossible to obtain a nano-scale composite material with excellent structure. Because the titanium dioxide / sodium titanate / carbon structure is not ideal, its intrinsic electrochemical performance is not fully exerted, and its specific capacity is only 386.9 mAh g -1 (0.05Ag -1 ).

[0103] Comparative Example 2

[0104] A preparation method of a titanium dioxide / sodium titanate / carbon composite material comprises the following steps:

[0105] Step S1: prepare a graphene oxide aqueous solution with a concentration of 1.5 mg / mL and a graphene oxide aqueous solution with a concentration of 7 mol L -1 of sodium hydroxide solution;

[0106] Step S2: Take 70 mL of sodium hydroxide solution and add tetrabutyl titanate to make the volume concentration of tetrabutyl titanate 0.05 g mL -1 , hydrothermal reaction was carried out, the hydrothermal reaction temperature was 150 ° C, and the hydrothermal time was 16 h;

[0107] After the hydrothermal reaction, the mixture was cooled to room temperature and washed three times with water by deionized water centrifugation (parameter 6000r / min, 5min); then vacuum dried at 60°C for 12h to obtain a sodium titanate precursor;

[0108] Step S3: Remove 70 mL of ionized water and add tetrabutyl titanate to make the concentration of tetrabutyl titanate 0.05 g mL -1 , hydrothermal reaction was carried out, the hydrothermal reaction temperature was 160℃, and the hydrothermal time was 16h;

[0109] After the hydrothermal reaction, the product was cooled to room temperature and washed three times with deionized water by centrifugation (parameter 6000r / min, 5min); then vacuum dried at 60°C for 12h to obtain a titanium dioxide precursor;

[0110] Step S4: adding sodium titanate precursor and titanium dioxide precursor to the graphene oxide aqueous solution, wherein the mass concentration of sodium titanate precursor and titanium dioxide precursor is controlled to 1 mg mL -1 , fully stirred for 12 h, then centrifuged (parameter 6000 r / min, 5 min), and vacuum dried at a temperature of 60 ° C for 12 h;

[0111] Step S5: Place the sample in a tube test furnace and perform heat treatment under inert gas (argon or nitrogen) at a temperature of 600° C. for 0.5 h to obtain a titanium dioxide / sodium titanate / carbon composite material.

[0112] Electrode preparation / battery assembly:

[0113] Mix titanium dioxide / sodium titanate / carbon composite material, conductive carbon black or carbon nanotubes and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of 8.5:1:0.5 and stir for 0.1h until uniform. Coat the obtained uniform electrode slurry on copper foil with a loading of 2mg / cm 2 If the loading is too low, the cycle stability will be insufficient and the material will have no production reference value. If the loading is too high, the active material near the current collector will not be able to fully exert its electrochemical activity. Therefore, the loading should be appropriate. After coating, the electrode is placed in a vacuum drying oven and dried at 60°C for 12 hours. It is then punched into a circular electrode sheet with a diameter of 12mm (as the negative electrode) or the corresponding electrode sheet size for a card battery. Finally, it is assembled into a two-electrode system with sodium foil in a glove box. The battery assembly model is CR2025 button cell or the corresponding card battery.

[0114] like Figure 11 As shown in the figure, due to the changes in the preparation process of titanium dioxide / sodium titanate / carbon composite materials, titanium dioxide / sodium titanate as the main electrode active material, the electrochemical performance of the composite material is reduced due to insufficient metal ion source and insufficient processing time and temperature, resulting in a low final specific capacity of the battery.

[0115] Based on the test data of Examples 1-3 and Comparative Examples 1-2, the following summary and analysis are made:

[0116] Structural considerations: The morphology of the titanium dioxide / sodium titanate / carbon composite directly impacts its electrochemical applications. Comparing the examples with the comparative examples reveals that to ensure efficient synergy between titanium dioxide / sodium titanate and graphene, and a relatively uniform composite structure, the amount of metal ions used should be neither too high nor too low, and the optimal amount of tetrabutyl titanate should be appropriate.

[0117] Cost considerations: The amount of raw materials used influences the difficulty of process implementation and the feasibility of large-scale production. Therefore, the amount of titanate and graphene used should be within a reasonable range. The temperature and time of the hydrothermal reaction should be sufficient to ensure the composite material structure, and the temperature and time of the annealing treatment should be sufficient to ensure the dispersion of titanium dioxide / sodium titanate and the electrochemical performance.

[0118] Process factors: The process setting directly determines the possibility of large-scale application of materials, so the process should be simplified and the conditions should be minimized. Therefore, the recommended process parameters are: the mass concentration of graphene oxide aqueous solution is 2-5 mg / mL, the carbonization temperature is 600-900℃, the processing time is 1-3 hours, and the volume concentration of tetrabutyl titanate is 0.05-0.22 g mL -1 , the hydrothermal reaction temperature is 160-200℃, and the hydrothermal time is 16-24h.

[0119] Therefore, the present invention adopts the preparation and application of the above-mentioned titanium dioxide / sodium titanate / carbon composite material to solve the problem of insufficient chemical kinetic properties commonly existing in existing titanium-based sodium ion battery negative electrode materials.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. Preparation of a titanium dioxide / sodium titanate / carbon composite material, characterized in that: The following steps are involved: Step S1, preparing a graphene oxide aqueous solution and a sodium hydroxide solution; Step S2: Take 40-70 mL of sodium hydroxide solution and add tetrabutyl titanate to make the volume concentration of tetrabutyl titanate 0.05-0.22 g mL -1 , to carry out a hydrothermal reaction; After the hydrothermal reaction, the mixture was cooled to room temperature and washed three times with deionized centrifugal water; then vacuum dried at 60°C for 12 hours to obtain a sodium titanate precursor; Step S3: Take 40-70 mL of ionized water and add tetrabutyl titanate to make the concentration of tetrabutyl titanate 0.05-0.22 g mL -1 , to carry out a hydrothermal reaction; After the hydrothermal reaction, the product was cooled to room temperature and washed three times with deionized water by centrifugation; then vacuum dried at 60°C for 12 hours to obtain a titanium dioxide precursor; Step S4: adding sodium titanate precursor and titanium dioxide precursor to the graphene oxide aqueous solution, wherein the mass concentration of sodium titanate precursor and titanium dioxide precursor is controlled to be 1-4 mg mL -1 The suspension was stirred thoroughly for 12-24 hours, then centrifuged and dried under vacuum at 60°C for 12 hours; Step S5: placing the product in a tube test furnace and performing heat treatment under inert gas conditions to obtain a titanium dioxide / sodium titanate / carbon composite material.

2. The preparation of a titanium dioxide / sodium titanate / carbon composite material according to claim 1, characterized in that: In step S1, the concentration of the graphene oxide aqueous solution is 2-5 mg / mL, and the concentration of the sodium hydroxide solution is 9-12 mol L -1 .

3. The preparation of a titanium dioxide / sodium titanate / carbon composite material according to claim 1, characterized in that: In step S2, the hydrothermal reaction temperature is 160-200° C., the hydrothermal time is 16-24 h; the centrifugal speed is 6000-10000 r / min, and the centrifugal time is 5-10 min; In step S3, the hydrothermal reaction temperature is 160-200° C., the hydrothermal time is 16-24 h; the centrifugal speed is 6000-10000 r / min, and the centrifugal time is 5-10 min; In step S4, the centrifugal speed is 6000-10000 r / min, and the centrifugal time is 5-10 min.

4. The preparation of a titanium dioxide / sodium titanate / carbon composite material according to claim 1, characterized in that: In step S5, the inert gas includes but is not limited to argon and nitrogen; the heat treatment temperature is 600-900° C., and the heat treatment time is 1-3 hours.

5. Use of the titanium dioxide / sodium titanate / carbon composite material prepared according to any one of claims 1 to 4 in a sodium ion battery.

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