A mesoporous sodium titanate / carbon composite electrode material and its preparation method and application

Abstract

The present invention relates to a mesoporous sodium titanate / carbon composite electrode material and its preparation method and application. The composite electrode material has a mesopore diameter of 3-5 nm and a specific surface area of ​​100-600 m 2 / g, including pure phase sodium titanate and coated carbon; using a surfactant as a template, a chelating agent, a titanium source, and a sodium source are added to a solvent, mixed and dried, and then calcined to obtain the composite electrode material. Compared with the existing technology, the present invention realizes the synthesis of mesoporous sodium titanate / carbon composite electrode materials and their application in batteries for the first time. The preparation process is simple, easy to scale up production, and highly controllable. The pore size, specific surface area, and mesostructure of the obtained material are all adjustable. As a sodium battery positive electrode or sodium ion battery negative electrode material, it has the advantages of high first-cycle coulombic efficiency, low operating voltage, excellent rate performance, and good cycle stability. Rechargeable sodium batteries or sodium ion batteries containing these materials have the advantages of high energy density and power density, showing broad market application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery electrode materials, and in particular to a mesoporous sodium titanate / carbon composite electrode material and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries, with their abundant resources and low cost, offer enormous potential for applications such as large-scale energy storage and smart grids. However, their energy density, power density, and long-cycle stability remain shortcomings in their practical development and require further improvement. Anode materials play a crucial role in the energy density and stability of batteries. The ideal anode material should have a low discharge voltage and a high theoretical capacity. Furthermore, first-cycle coulombic efficiency, power characteristics, and cycle stability are also important performance indicators.

[0003] Titanium-based anode materials have attracted great interest due to their high sodium storage activity, high stability, low cost and non-toxicity. 0.23 As a semiconductor material, TiO2 has a lower discharge voltage platform (0.3V vs Na / Na + ), which can produce higher operating voltage and energy density in actual batteries, but it is rarely reported in existing research. 0.23 The composite structure of TiO2 and Ti3C2 is used in sodium batteries, but its synthesis method is complicated and requires a high-temperature hydrothermal reaction (Nano Energy, 2018, 46, 20-28); there are also reports of electrochemically embedding sodium ions into TiO2 by a molten salt method, which has harsh synthesis conditions and is not conducive to large-scale production (J. Mater. Chem. A, 2015, 3, 16495-16500). At the same time, the Na obtained by these synthesis methods 0.23 TiO2 is micron-sized, which is not conducive to its sodium storage performance. 12 As a potential sodium storage material, M-Na4Ti5O 12 and T-Na4Ti5O 12 Both structures have certain electrochemical properties, but the micron-sized Na4Ti5O synthesized in these studies 12 Nanoparticles have poor performance when used in sodium ion batteries and are far from meeting the requirements of practical use (J. Electrochem. Soc., 2012, 12, A2016-A2023; Chem. Mater., 2014, 26, 7067-7072). 14 As a titanate material, it has not yet been used in sodium-ion batteries. Summary of the Invention

[0004] The present invention aims to provide a mesoporous sodium titanate / carbon composite electrode material and a preparation method and application thereof, which are used for assembling sodium batteries or sodium ion batteries.

[0005] The purpose of the present invention can be achieved by the following technical solution: a mesoporous sodium titanate / carbon composite electrode material with a mesopore diameter of 3-5nm and a specific surface area of ​​100-600m 2 / g, including pure phase sodium titanate and coated carbon.

[0006] Preferably, the pure phase sodium titanate comprises Na 0.23 TiO2、Na4Ti5O 12 、Na4Ti3O8、Na8Ti5O 14 , the corresponding mesoporous sodium titanate / carbon composite electrode materials are mesoporous Na 0.23 TiO2 / C composite electrode materials, mesoporous Na4Ti5O 12 / C composite electrode materials, preparation of mesoporous Na4Ti3O8 / C composite electrode materials and mesoporous Na8Ti5O 14 / C composite electrode material.

[0007] Preferably, in the composite electrode material, the total mass of carbon is 5%-20% of the mass of the composite electrode material.

[0008] Further preferably, the mesoporous Na 0.23 In the TiO2 / C composite electrode material, the total mass of carbon is mesoporous Na 0.23 5%-10% of the mass of TiO2 / C composite electrode material.

[0009] Further preferably, the mesoporous Na4Ti5O 12 In the / C composite electrode material, the total mass of carbon is mesoporous Na4Ti5O 12 / C composite electrode material mass 5%-20%.

[0010] Further preferably, in the mesoporous Na4Ti3O8 / C composite electrode material, the total mass of carbon is mesoporous Na4Ti5O 12 / C composite electrode material mass 5%-20%.

[0011] Further preferably, the mesoporous Na8Ti5O 14 In the / C composite electrode material, the total mass of carbon is mesoporous Na4Ti5O 12 / C composite electrode material mass 10%-20%.

[0012] A preparation method of the above-mentioned mesoporous sodium titanate / carbon composite electrode material uses a surfactant as a template, adds a complexing agent, a titanium source and a sodium source to a solvent, mixes and dries, and then calcines to obtain the mesoporous sodium titanate / carbon composite electrode material.

[0013] The preparation of the mesoporous sodium titanate / carbon composite electrode material provided by the present invention is based on a commercial surfactant as a template, and is obtained by a one-step calcination process after solution mixing and drying. By changing different titanium sources and sodium sources, four different stoichiometric ratios of mesoporous sodium titanate (Na 0.23 TiO2、Na4Ti5O 12 , Na4Ti3O8 and Na8Ti5O 14 ) are synthesized by the corresponding pure phase Na 0.23 TiO2、Na4Ti5O 12 , Na4Ti3O8 and Na8Ti5O 14 and the carbon composition of the coating.

[0014] Preferably, the surfactant is dissolved in a solvent, stirred, and then a complexing agent and a titanium source are added, followed by the sodium source. After stirring and dissolving, the solvent is dried, and the black solid is collected to obtain a composite precursor. The precursor is placed in an inert atmosphere and calcined to obtain the mesoporous sodium titanate / carbon composite electrode material.

[0015] Preferably, the surfactant is one or more of polyethylene oxide-polypropylene oxide, polyethylene oxide-polybutylene oxide, polyethylene oxide-polystyrene or polyethylene oxide-polymethyl methacrylate diblock copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and polypropylene oxide-polyethylene oxide-polypropylene oxide triblock copolymer.

[0016] Preferably, the solvent is one or more of water, methanol, ethanol, n-propanol, isopropanol, and n-butanol.

[0017] Preferably, the complexing agent is one or more of citric acid, ethylenediaminetetraacetic acid, phenolic resin, and acetylacetone.

[0018] Preferably, the titanium source is one or more of titanium sulfate, titanium tert-butoxide, titanium methoxide, titanium tetrachloride, tetrabutyl titanate, isopropyl titanate, tetraethyl titanate or titanium acetylacetonate.

[0019] Preferably, the sodium source is one or more of sodium acetate, sodium citrate, sodium sulfate, sodium carbonate, sodium propionate, and sodium butyrate.

[0020] Preferably, the molar ratio of the titanium source to the sodium source is (3-5):(1-2).

[0021] Further preferably, the mesoporous Na 0.23 When TiO2 / C composite electrode material is used, the molar ratio of titanium source to sodium source is (4-5):(1-2).

[0022] Further preferably, the mesoporous Na4Ti5O 12 / C composite electrode material, the molar ratio of titanium source to sodium source is (4-5):(1-2).

[0023] Further preferably, when preparing the mesoporous Na4Ti3O8 / C composite electrode material, the molar ratio of the titanium source to the sodium source is (3-4):(1-2).

[0024] Further preferably, the mesoporous Na8Ti5O 14 / C composite electrode material, the molar ratio of titanium source to sodium source is (3-4):(1-2).

[0025] Preferably, the inert atmosphere is nitrogen or argon.

[0026] Preferably, the calcination process is to increase the temperature to 500-800° C. at a heating rate of 1-5° C. / min and maintain the temperature for 0.5-3 hours.

[0027] An application of the above-mentioned mesoporous sodium titanate / carbon composite electrode material is to use the composite electrode material to prepare a sodium ion battery or a sodium battery.

[0028] Preferably, the composite electrode material is used as the positive electrode of a sodium battery or the negative electrode of a sodium ion battery.

[0029] Preferably, the sodium ion battery and sodium battery are room temperature sodium / sodium ion batteries that can be charged and discharged, including a positive electrode sheet, a negative electrode sheet, an electrolyte, a diaphragm and a shell, the diaphragm is a glass fiber diaphragm, polyethylene, a polypropylene microporous membrane, or a composite diaphragm thereof, and the electrolyte is a soluble sodium salt organic solution; in the sodium battery, the mesoporous sodium titanate / carbon composite electrode material is the positive electrode, and metallic sodium is used as the negative electrode of the sodium battery; in the sodium ion battery, the mesoporous sodium titanate / carbon composite electrode material is the negative electrode, and the sodium ion active material that can be inserted / extracted is used as the positive electrode of the sodium ion battery.

[0030] Further preferably, the soluble sodium salt organic solution is obtained by dissolving a sodium salt in an organic solvent, the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate and sodium nitrate, and the organic solvent is one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-cyclopentanediol, ethylene glycol dimethyl ether and triethylene glycol dimethyl ether.

[0031] Further preferably, the active material capable of inserting / removing sodium ions comprises transition metal oxides, phosphates, pyrophosphates, sulfates, and fluorophosphates.

[0032] Further preferably, the battery shells are made of aluminum shell, aluminum-plastic film (soft-pack battery), stainless steel and composite materials thereof, and are button-shaped, cylindrical or square.

[0033] Preferably, the sodium battery positive electrode sheet is obtained by filling a slurry obtained by uniformly mixing a positive electrode material with a conductive agent, a binder and a dispersant onto a current collector, and the current collector is copper foil; the sodium ion battery negative electrode sheet is obtained by filling a slurry obtained by uniformly mixing a negative electrode material with a conductive agent, a binder and a dispersant onto a current collector, and the current collector is copper foil; the positive electrode sheet is obtained by filling a slurry obtained by uniformly mixing a positive electrode material with a conductive agent, a binder and a dispersant onto a current collector, and the current collector is aluminum foil.

[0034] Further preferably, the conductive agent in the sodium ion battery or sodium battery is one or more of acetylene black, Super P or graphite; the binder is one or more of sodium carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride or styrene-butadiene rubber; and the dispersant is one or more of water, ethanol, isopropanol or 1-methyl-2-pyrrolidone.

[0035] Mesoporous structures can effectively shorten the ion transmission distance and have excellent ion transmission characteristics. They have been widely designed, studied and applied in energy storage materials. However, there has been no report on the design of mesoporous structures for electrode materials such as sodium titanate. Therefore, the present invention synthesizes a mesoporous sodium titanate electrode material with a nanoscale size through a soft template synthesis method, which is very meaningful for application in sodium batteries or sodium ion batteries, thereby obtaining high first-cycle coulombic efficiency, high capacity, excellent rate characteristics and cycle stability. The composite electrode material of the present invention presents a two-dimensional sheet structure, and the rich mesoporous structure can release more active sites, effectively shorten the ion transmission path, and increase the ion transmission rate; at the same time, it alleviates volume expansion, which is beneficial to structural stability. The mesoporous sodium titanate / carbon composite electrode material has high reversible capacity, excellent kinetic characteristics, high first-cycle coulombic efficiency and excellent cycle stability.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] 1. The presence of mesopores in the composite electrode material of the present invention can effectively enhance ion transport, release more active sites, and alleviate volume expansion, thereby facilitating structural stability.

[0038] 2. The preparation process of the present invention is simple, easy to scale up, and highly controllable. The pore size, specific surface area, and mesostructure of the obtained material are all adjustable.

[0039] 3. This invention realizes the synthesis of mesoporous sodium titanate / carbon composite materials and their application in batteries for the first time;

[0040] 4. The composite electrode material of the present invention, as a positive electrode material for sodium batteries or a negative electrode material for sodium ion batteries, has the advantages of high first-cycle coulombic efficiency, low operating voltage, excellent rate performance and good cycle stability. The rechargeable sodium battery or sodium ion battery containing this material has the advantages of high energy density and power density, showing broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The mesoporous Na prepared in Example 1 0.23 XRD pattern of TiO2 / C composite electrode material;

[0042] Figure 2 The mesoporous Na prepared in Example 1 0.23 SEM image of TiO2 / C composite electrode material;

[0043] Figure 3 The mesoporous Na prepared in Example 1 0.23 TEM image of TiO2 / C composite electrode material;

[0044] Figure 4 The mesoporous Na prepared in Example 1 0.23 Figure 2 shows nitrogen adsorption and desorption of TiO2 / C composite electrode materials;

[0045] Figure 5 The mesoporous Na prepared in Example 1 0.23 Pore ​​size distribution diagram of TiO2 / C composite electrode material;

[0046] Figure 6 The mesoporous Na prepared in Example 1 0.23 Charge and discharge curves of TiO2 / C composite electrode materials;

[0047] Figure 7 The mesoporous Na prepared in Example 1 0.23 Charge and discharge curves of TiO2 / C composite electrode materials at different rates;

[0048] Figure 8 The mesoporous Na prepared in Example 1 0.23 Cycling stability diagram of TiO2 / C composite electrode material;

[0049] Figure 9 The mesoporous Na4Ti5O prepared in Example 2 12 XRD pattern of / C composite electrode material;

[0050] Figure 10The mesoporous Na4Ti5O prepared in Example 2 12 SEM images of / C composite electrode materials;

[0051] Figure 11 The mesoporous Na4Ti5O prepared in Example 2 12 TEM image of / C composite electrode material;

[0052] Figure 12 The mesoporous Na4Ti5O prepared in Example 2 12 Figure 2: Nitrogen adsorption and desorption of C / C composite electrode materials;

[0053] Figure 13 The mesoporous Na4Ti5O prepared in Example 2 12 Pore ​​size distribution of / C composite electrode materials;

[0054] Figure 14 The mesoporous Na4Ti5O prepared in Example 2 12 / C composite electrode material charge and discharge curves;

[0055] Figure 15 The mesoporous Na4Ti5O prepared in Example 2 12 / C composite electrode material charge and discharge curves at different rates;

[0056] Figure 16 The mesoporous Na4Ti5O prepared in Example 2 12 Cycling stability diagram of / C composite electrode material;

[0057] Figure 17 is the XRD pattern of the mesoporous Na4Ti3O8 / C composite electrode material prepared in Example 3;

[0058] Figure 18 is a SEM image of the mesoporous Na4Ti3O8 / C composite electrode material prepared in Example 3;

[0059] Figure 19 is a TEM image of the mesoporous Na4Ti3O8 / C composite electrode material prepared in Example 3;

[0060] Figure 20 This is a diagram showing nitrogen adsorption and desorption of the mesoporous Na4Ti3O8 / C composite electrode material prepared in Example 3;

[0061] Figure 21 is a pore size distribution diagram of the mesoporous Na4Ti3O8 / C composite electrode material prepared in Example 3;

[0062] Figure 22is a charge-discharge curve diagram of the mesoporous Na4Ti3O8 / C composite electrode material prepared in Example 3;

[0063] Figure 23 3 is a charge-discharge curve diagram of the mesoporous Na4Ti3O8 / C composite electrode material prepared in Example 3 at different rates;

[0064] Figure 24 is a cycle stability diagram of the mesoporous Na4Ti3O8 / C composite electrode material prepared in Example 3;

[0065] Figure 25 The mesoporous Na8Ti5O prepared in Example 4 14 XRD pattern of / C composite electrode material;

[0066] Figure 26 The mesoporous Na8Ti5O prepared in Example 4 14 SEM images of / C composite electrode materials;

[0067] Figure 27 The mesoporous Na8Ti5O prepared in Example 4 14 TEM image of / C composite electrode material;

[0068] Figure 28 The mesoporous Na8Ti5O prepared in Example 4 14 Figure 2 shows nitrogen adsorption and desorption of C / C composite electrode materials;

[0069] Figure 29 The mesoporous Na8Ti5O prepared in Example 4 14 Pore ​​size distribution of / C composite electrode materials;

[0070] Figure 30 The mesoporous Na8Ti5O prepared in Example 4 14 / C composite electrode material charge and discharge curves;

[0071] Figure 31 The mesoporous Na8Ti5O prepared in Example 4 14 / C composite electrode material charge and discharge curves at different rates;

[0072] Figure 32 The mesoporous Na8Ti5O prepared in Example 4 14 Cycling stability diagram of / C composite electrode material;

[0073] Figure 33 1 is a performance comparison chart of the mesoporous sodium titanate / carbon composite electrode materials prepared in Examples 1 to 4;

[0074] Figure 34The mesoporous Na prepared in Comparative Example 1 0.23 SEM image of TiO2 / C composite electrode material;

[0075] Figure 35 The mesoporous Na prepared in Comparative Example 2 0.23 SEM image of TiO2 / C composite electrode material. DETAILED DESCRIPTION

[0076] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following embodiments.

[0077] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0078] Example 1

[0079] The mesoporous Na used in the present invention 0.23 The synthesis steps of TiO2 / C composite electrode material are as follows:

[0080] 1.5g Pluronic F127 (PEO 106 PPO 70 PEO 106 , M w =12600 g mol -1 ) was dissolved in 30ml of water and stirred in an oil bath at 40℃ for 2 hours to obtain a clear solution. Then 3.8g of citric acid was added and stirred in an oil bath at 40℃ for 2 hours to completely dissolve the citric acid. Then 1.5ml of tetrabutyl titanate was added and stirred in an oil bath at 40℃ for 2 hours. When the solution became transparent and clear, 0.242g of sodium acetate was added and stirred for 2 hours. After that, it was dried in a drying oven at 100℃ for 24 hours. After cooling to room temperature, the black solid was collected to obtain a sodium titanate / citric acid complex precursor. The precursor was ground evenly and pre-calcined in a tubular furnace in an argon atmosphere. Then the temperature was raised to 800℃ and calcined for 3h at a heating rate of 2℃ / min to obtain mesoporous Na 0.23 TiO2 / C composite electrode material.

[0081] Figure 1 Mesoporous Na 0.23 The X-ray diffraction (XRD) pattern of TiO2 / C composite electrode material is similar to that of Monoclinic Na 0.23 The standard card of TiO2 (PDF#22-1404) corresponds to that of TiO2, and the poor crystallinity is due to its small particles and carbon coating. The diffraction peak at 24.37° shows the highest intensity, indicating that the (110) crystal plane is Na0.23 Dominant crystal plane of TiO2 crystal. Figure 2 Mesoporous Na 0.23 The SEM image of the TiO2 / C composite electrode material shows the presence of abundant pores on its surface. Figure 3 Mesoporous Na 0.23 The TEM image of the TiO2 / C composite electrode material shows a two-dimensional layered structure, in which the black particles of about 5-10nm in size are Na 0.23 TiO2 crystals are wrapped in an outer layer of carbon and are rich in voids. The carbon content is Na 0.23 5-15% of the mass of TiO2 / C composite electrode material. Figure 4 The mesoporous Na obtained in Example 1 0.23 Nitrogen adsorption and desorption isotherms of TiO2 / C composite electrode materials. The adsorption curve is an IV curve, which is a typical adsorption isotherm for mesoporous materials. The obvious adsorption at relative pressures of 0.5-0.8 corresponds to mesopores. The specific surface area of ​​the material is 559.7 m 2 / g. Figure 5 The mesoporous Na obtained in Example 1 0.23 The pore size distribution curve of the TiO2 / C composite electrode material shows that the material has a uniform pore size of approximately 3.9nm.

[0082] The prepared mesoporous Na 0.23 TiO2 / C composite electrode material is used as the positive electrode active material, mixed with acetylene black and sodium carboxymethyl cellulose in a mass ratio of 80:10:10, and deionized water is used as a dispersant. The above mixture is mixed evenly to form a slurry and coated on the copper foil. After vacuum drying at 80°C, a positive electrode sheet with a diameter of 13 mm is cut to obtain a sodium metal sheet as the negative electrode (diameter of 16 mm), a glass fiber membrane (Whatman GF / D) as a diaphragm, and 1M NaSO3CF3 dissolved in DGM as the electrolyte. A stainless steel shell is used as the outer shell to assemble into a CR2025 button battery. The sodium battery assembled by the above process was subjected to charge and discharge tests at room temperature in the potential range of 0.01-3.0 V. Its charge and discharge curves and rate performance are shown in Figure 2. Figure 6 and Figure 7 As shown. 0.1Ag -1 The lower discharge platform is lower than 0.2V, and the reversible specific capacity is about 170mAh g -1 , with a first-cycle coulombic efficiency of 73.3%. At 2.0A g -1 At a high current density, its reversible specific capacity is still about 43 mAh g -1 . Figure 8 At 0.2A g -1 The cycle stability diagram at the bottom shows that the capacity is still about 150 mAh g after 200 cycles. -1, the capacity retention rate is close to 100%.

[0083] Example 2

[0084] The mesoporous Na4Ti5O used in the present invention 12 The synthesis steps of the / C composite electrode material are as follows:

[0085] 1.5g of Pluronic F127 was dissolved in 30ml of water and stirred in an oil bath at 40℃ for 2 hours to obtain a clear solution. 3.8g of citric acid was then added and stirred in an oil bath at 40℃ for 2 hours to completely dissolve the citric acid. 1.5ml of tetrabutyl titanate was then added and stirred in an oil bath at 40℃ for 2 hours. When the solution became transparent and clear, 0.41g of sodium acetate was added and stirred for 2 hours. The solvent was evaporated in a drying oven at 100℃ for 24 hours and the solution was cooled to room temperature before collecting a black solid to obtain a sodium titanate / citric acid composite precursor. The precursor was ground uniformly and pre-calcined in a tube furnace under an argon atmosphere. The temperature was then raised to 800℃ and calcined for 3 hours at a heating rate of 2℃ / min to obtain mesoporous Na4Ti5O 12 / C composite electrode material.

[0086] Figure 9 Mesoporous Na4Ti5O 12 The X-ray diffraction (XRD) pattern of the / C composite electrode material is similar to that of the Monoclinic C2 / m(12) type Na4Ti5O 12 The diffraction peak (2theta = 14.03°) shows the highest intensity, indicating that the (001) crystal plane is Na4Ti5O 12 Predominant crystal face. Figure 10 Mesoporous Na4Ti5O 12 The SEM image of the / C composite electrode material shows the presence of abundant pores on its surface. Figure 11 Mesoporous Na4Ti5O 12 The TEM image of the / C composite electrode material shows a two-dimensional layered structure, in which the black particles of about 5-10nm in size are Na4Ti5O 12 The crystal is wrapped by the outer layer of carbon and has a large number of voids. The total amount of carbon is Na4Ti5O 12 / C composite electrode material mass 5-15%. Figure 12 The mesoporous Na4Ti5O obtained in Example 2 12 Nitrogen adsorption and desorption isotherms of the / C composite electrode material. The adsorption curve is an IV curve, which is a typical adsorption isotherm for mesoporous materials. The obvious adsorption at relative pressures of 0.5-0.8 corresponds to mesopores. The specific surface area of ​​the material is 105.1m2 / g. Figure 13 The mesoporous Na4Ti5O obtained in Example 2 12 The pore size distribution curve of the Mg / C composite electrode material shows that the material has a uniform pore size of approximately 3.6 nm.

[0087] The prepared mesoporous Na4Ti5O 12 / C composite electrode material is used as the positive electrode active material, the positive electrode material is mixed with acetylene black and sodium carboxymethyl cellulose in a mass ratio of 80:10:10, deionized water is used as a dispersant, the above mixture is mixed evenly into a slurry and coated on the copper foil. After vacuum drying at 80°C, the positive electrode sheet with a diameter of 13mm is cut, the sodium metal sheet is used as the negative electrode (diameter of 16mm), the glass fiber membrane (Whatman GF / D) is used as the diaphragm, and 1M NaSO3CF3 dissolved in DGM is used as the electrolyte. The stainless steel shell is used as the outer shell and assembled into a CR2025 button battery. The sodium battery assembled by the above process is subjected to charge and discharge tests at room temperature in the potential range of 0.01-3.0V. Its charge and discharge curves and rate performance are shown in the figure. Figure 14 and Figure 15 As shown. 0.1Ag -1 The lower discharge platform is lower than 0.2V, and the reversible specific capacity is about 260mAh g -1 , with an initial coulombic efficiency of 84.2%. -1 At a high current density, its reversible specific capacity is still about 114 mAh g -1 . Figure 16 At 0.2A g -1 The cycle stability diagram at the bottom shows that the capacity is still about 211 mAh g after 200 cycles. -1 .

[0088] Example 3

[0089] The synthesis steps of the mesoporous Na4Ti3O8 / C composite electrode material used in the present invention are as follows:

[0090] 1.5g of Pluronic F127 was dissolved in 30ml of water and stirred in a 40°C oil bath for 2 hours to obtain a clear solution. 3.8g of citric acid was then added and stirred in a 40°C oil bath for 2 hours to completely dissolve the citric acid. 1.5ml of tetrabutyl titanate was then added and stirred in a 40°C oil bath for another 2 hours until the solution became clear. 0.484g of sodium acetate was then added and stirred for another 2 hours. The solution was then dried in a 100°C oven for 24 hours to evaporate the solvent. The solution was cooled to room temperature and a black solid was collected to obtain a sodium titanate / citric acid composite precursor. This precursor was ground uniformly and pre-calcined in a tube furnace under an argon atmosphere. The temperature was then increased to 800°C and calcined for 3 hours at a rate of 2°C / min to obtain a mesoporous Na4Ti3O8 / C composite electrode material.

[0091] Figure 17 This is the X-ray diffraction (XRD) pattern of the mesoporous Na4Ti3O8 / C composite electrode material, which corresponds to the standard card (PDF#38-0730) of Monoclinic C2 / m(12) type Na4Ti3O8. The poor crystallinity is due to its small particles and carbon coating. Figure 18 This is the SEM image of the mesoporous Na4Ti3O8 / C composite electrode material, from which it can be seen that there are abundant pores on its surface. Figure 19 This is a TEM image of a mesoporous Na4Ti3O8 / C composite electrode material, showing a two-dimensional lamellar structure. The black particles, approximately 5-10 nm in size, are Na4Ti3O8 crystals, encapsulated by an outer layer of carbon and interspersed with numerous voids. The total amount of carbon accounts for 5-15% of the mass of the Na4Ti3O8 / C composite electrode material. Figure 20 This is the nitrogen adsorption and desorption isotherm of the mesoporous Na4Ti3O8 / C composite electrode material obtained in Example 2. The adsorption curve is an IV curve, which is a typical adsorption isotherm for mesoporous materials. The obvious adsorption at a relative pressure of 0.5-0.8 corresponds to the mesopores. The specific surface area of ​​the material is 128.5m 2 / g. Figure 21 This is the pore size distribution curve of the mesoporous Na4Ti3O8 / C composite electrode material obtained in Example 2. The curve shows that the material has a uniform pore size of about 3.5 nm.

[0092] The prepared mesoporous Na4Ti3O8 / C composite electrode material was used as the positive electrode active material, mixed with acetylene black and sodium carboxymethyl cellulose in a mass ratio of 80:10:10, and deionized water was used as a dispersant. The above mixture was mixed evenly into a slurry and coated on the copper foil. After vacuum drying at 80°C, a positive electrode sheet with a diameter of 13 mm was cut to obtain a sodium metal sheet as the negative electrode (diameter of 16 mm), a glass fiber membrane (Whatman GF / D) as a diaphragm, and 1M NaSO3CF3 dissolved in DGM as the electrolyte. A stainless steel shell was used as the outer shell to assemble a CR2025 button battery. The sodium battery assembled by the above process was subjected to charge and discharge tests at room temperature in the potential range of 0.01-3.0 V. Its charge and discharge curves and rate performance are shown in Figure 2. Figure 22 and Figure 23 As shown. 0.1Ag -1 The lower discharge platform is lower than 0.2V, and the reversible specific capacity is about 238mAh g -1 , the first week coulombic efficiency is 80.3%. -1 At a high current density, its reversible specific capacity is still about 98.3 mAh g -1 . Figure 24 At 0.2A g -1 The cycle stability diagram at the bottom shows that the capacity is still about 168.2 mAh g after 200 cycles. -1 , the capacity retention rate is close to 100%.

[0093] Example 4

[0094] The mesoporous Na8Ti5O used in the present invention 14 The synthesis steps of the / C composite electrode material are as follows:

[0095] 1.5g of Pluronic F127 was dissolved in 30ml of water and stirred in an oil bath at 40℃ for 2 hours to obtain a clear solution. 3.8g of citric acid was then added and stirred in an oil bath at 40℃ for 2 hours to completely dissolve the citric acid. 1.5ml of tetrabutyl titanate was then added and stirred in an oil bath at 40℃ for 2 hours. When the solution became transparent and clear, 0.51g of sodium acetate was added and stirred for 2 hours. The solvent was evaporated in a drying oven at 100℃ for 24 hours and the solution was cooled to room temperature before collecting a black solid to obtain a sodium titanate / citric acid complex precursor. The precursor was ground uniformly and pre-calcined in a tube furnace under an argon atmosphere. The temperature was then raised to 800℃ and calcined for 3 hours at a heating rate of 2℃ / min to obtain mesoporous Na8Ti5O 14 / C composite electrode material.

[0096] Figure 25 Mesoporous Na8Ti5O 14The X-ray diffraction (XRD) pattern of the / C composite electrode material is similar to that of the Triclinic type Na8Ti5O 14 The diffraction peak (2theta = 11.99°) shows the highest intensity, indicating that the (100) crystal plane is Na8Ti5O 14 Predominant crystal face. Figure 26 Mesoporous Na8Ti5O 14 The SEM image of the / C composite electrode material shows the presence of abundant pores on its surface. Figure 27 Mesoporous Na8Ti5O 14 The TEM image of the / C composite electrode material shows a two-dimensional layered structure, in which the black particles of about 5-10 nm in size are Na8Ti5O 14 The crystal is wrapped by an outer layer of carbon and has a large number of voids. The total amount of carbon is Na8Ti5O 14 / C composite electrode material mass 5-15%. Figure 28 The mesoporous Na8Ti5O obtained in Example 3 14 Nitrogen adsorption and desorption isotherms of the / C composite electrode material. The adsorption curve is an IV curve, which is a typical adsorption isotherm for mesoporous materials. The obvious adsorption at relative pressures of 0.5-0.8 corresponds to mesopores. The specific surface area of ​​the material is 115.7m 2 / g. Figure 29 The mesoporous Na8Ti5O obtained in Example 3 14 The pore size distribution curve of the Mg / C composite electrode material shows that the material has a uniform pore size of approximately 4.3 nm.

[0097] The prepared mesoporous Na8Ti5O 14 / C composite electrode material is used as the positive electrode active material, mixed with acetylene black and sodium carboxymethyl cellulose in a mass ratio of 80:10:10, and deionized water is used as a dispersant. The above mixture is mixed evenly to form a slurry and applied to the copper foil. After vacuum drying at 80°C, the positive electrode sheet with a diameter of 13 mm is cut, the sodium metal sheet is used as the negative electrode (diameter of 16 mm), the glass fiber membrane (Whatman GF / D) is used as the diaphragm, and 1M NaSO3CF3 dissolved in DGM is used as the electrolyte. The stainless steel shell is used as the outer shell and assembled into a CR2025 button battery. The sodium battery assembled by the above process was charged and discharged at room temperature in the potential range of 0.01-3.0V. Its charge and discharge curve and rate performance are shown in the figure. Figure 30 and Figure 31 As shown. 0.1Ag -1 The lower discharge platform is lower than 0.2V, and the reversible specific capacity is about 126mAh g -1, with a first-cycle Coulombic efficiency of 76.2%. At 2.0A g -1 At a high current density, its reversible specific capacity is still about 23.3 mAh g -1 . Figure 32 At 0.2Ag -1 The cycle stability diagram at the bottom shows that the capacity is still about 74.2 mAh g after 200 cycles. -1 , the capacity retention rate is close to 100%.

[0098] Example 5

[0099] Compared with Example 1, most of the steps are the same, except that in this example, F127 is replaced by an equimolar amount of hexadecyltrimethylammonium bromide (CTAB).

[0100] Example 6

[0101] Compared with Example 2, most of the steps are the same, except that in this example, F127 is replaced by an equimolar amount of hexadecyltrimethylammonium bromide (CTAB).

[0102] Example 7

[0103] Compared with Example 3, most of the steps are the same, except that in this example, F127 is replaced by an equimolar amount of hexadecyltrimethylammonium bromide (CTAB).

[0104] Example 8

[0105] Compared with Example 4, most of the steps are the same, except that in this example, F127 is replaced by an equimolar amount of hexadecyltrimethylammonium bromide (CTAB).

[0106] Example 9

[0107] Compared with Example 1, most of the steps are the same, except that in this example, the amount of citric acid is changed to 4.6 g.

[0108] Example 10

[0109] Compared with Example 2, most of the steps are the same, except that in this example, the amount of citric acid is changed to 4.6 g.

[0110] Example 11

[0111] Compared with Example 3, most of the steps are the same, except that in this example, the amount of citric acid is changed to 4.6 g.

[0112] Example 12

[0113] Compared with Example 4, most of the contents are the same, except that in this example, the amount of citric acid is changed to 4.6 g.

[0114] Example 13

[0115] Compared with Example 1, most of the steps are the same, except that the calcination temperature is changed to 700°C in this example.

[0116] Example 14

[0117] Compared with Example 2, most of the steps are the same, except that the calcination temperature is changed to 700°C in this example.

[0118] Example 15

[0119] Compared with Example 3, most of the steps are the same, except that the calcination temperature is changed to 700°C in this example.

[0120] Example 16

[0121] Compared with Example 4, most of the steps are the same, except that the calcination temperature is changed to 700°C in this example.

[0122] Example 17

[0123] Compared with Example 1, most of the above are the same, except that in this example, 1M NaPF6 dissolved in EC:DEC (volume ratio of 1:1) is used as the electrolyte.

[0124] Example 18

[0125] Compared with Example 2, most of the steps are the same, except that in this example, 1 M NaPF6 dissolved in EC:DEC (volume ratio of 1:1) is used as the electrolyte.

[0126] Example 19

[0127] Compared with Example 3, most of the steps are the same, except that in this example, 1 M NaPF6 dissolved in EC:DEC (volume ratio of 1:1) is used as the electrolyte.

[0128] Example 20

[0129] Compared with Example 4, most of the above are the same, except that in this example, 1M NaPF6 dissolved in EC:DEC (volume ratio of 1:1) is used as the electrolyte.

[0130] Example 21

[0131] Compared with Example 1, most of the above are the same, except that in this example, the prepared mesoporous Na 0.23TiO2 / C composite electrode material was used as the negative electrode active material. The negative electrode material was mixed with acetylene black and sodium carboxymethyl cellulose in a mass ratio of 80:10:10, using deionized water as a dispersant. The mixture was mixed evenly to form a slurry, which was then applied to copper foil. Commercial sodium vanadium fluorophosphate was used as the positive electrode active material. The positive electrode active material was mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 70:20:10, using 1-methyl-2-pyrrolidone as a dispersant. The mixture was mixed evenly to form a slurry, which was then applied to aluminum foil. After vacuum drying at 80°C, the negative and positive electrode sheets were cut to 13 mm in diameter. A glass fiber membrane (Whatman GF / D) was used as the separator, and 1 M NaPF6 dissolved in DGM was used as the electrolyte. A stainless steel case was used as the outer shell, and the battery was assembled into a CR2025 button cell. The sodium battery assembled using the above process was tested for charge and discharge at room temperature within a potential range of 1.5-3.6 V.

[0132] Example 22

[0133] Compared with Example 2, most of the above are the same, except that in this example, the prepared mesoporous Na4Ti5O 12 A 1.5-μm / C composite electrode material was used as the negative electrode active material. The negative electrode material was mixed with acetylene black and sodium carboxymethyl cellulose in a mass ratio of 80:10:10, using deionized water as a dispersant. The mixture was mixed evenly to form a slurry, which was then applied to copper foil. Commercial sodium vanadium fluorophosphate was used as the positive electrode active material. The positive electrode active material was mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 70:20:10, using 1-methyl-2-pyrrolidone as a dispersant. The mixture was mixed evenly to form a slurry, which was then applied to aluminum foil. After vacuum drying at 80°C, the resulting negative and positive electrode sheets were cut to 13 mm in diameter. A glass fiber membrane (Whatman GF / D) was used as the separator, and 1 M NaPF6 dissolved in DGM was used as the electrolyte. A stainless steel case was used as the outer shell, and the cells were assembled into CR2025 button cells. The sodium battery assembled using the above process was subjected to charge and discharge tests at room temperature within a potential range of 1.5-3.6 V.

[0134] Example 23

[0135] Compared with Example 3, most of them are the same, except that in this example, the prepared mesoporous Na4Ti3O8 / C composite electrode material is used as the negative electrode active material, the negative electrode material is mixed with acetylene black and sodium carboxymethyl cellulose in a mass ratio of 80:10:10, deionized water is used as a dispersant, the above mixture is mixed evenly into a slurry and applied to copper foil. Commercial sodium vanadium fluorophosphate is used as the positive electrode active material, the positive electrode active material is mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 70:20:10, 1-methyl-2-pyrrolidone is used as a dispersant, the above mixture is mixed evenly into a slurry and applied to aluminum foil. After vacuum drying at 80°C, the negative and positive electrode sheets with a diameter of 13 mm are cut, a glass fiber membrane (Whatman GF / D) is used as a diaphragm, and 1MNaPF6 dissolved in DGM is used as the electrolyte. A stainless steel shell is used as the outer shell and assembled into a CR2025 button battery. The sodium battery assembled by the above process was subjected to charge and discharge tests at room temperature within a potential range of 1.5-3.6V.

[0136] Example 24

[0137] Compared with Example 4, most of the above are the same, except that in this example, the prepared mesoporous Na8Ti5O 14 A 1.5-μm / C composite electrode material was used as the negative electrode active material. The negative electrode material was mixed with acetylene black and sodium carboxymethyl cellulose in a mass ratio of 80:10:10, using deionized water as a dispersant. The mixture was mixed evenly to form a slurry, which was then applied to copper foil. Commercial sodium vanadium fluorophosphate was used as the positive electrode active material. The positive electrode active material was mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 70:20:10, using 1-methyl-2-pyrrolidone as a dispersant. The mixture was mixed evenly to form a slurry, which was then applied to aluminum foil. After vacuum drying at 80°C, the resulting negative and positive electrode sheets were cut to 13 mm in diameter. A glass fiber membrane (Whatman GF / D) was used as the separator, and 1 M NaPF6 dissolved in DGM was used as the electrolyte. A stainless steel case was used as the outer shell, and the cells were assembled into CR2025 button cells. The sodium battery assembled using the above process was subjected to charge and discharge tests at room temperature within a potential range of 1.5-3.6 V.

[0138] Example 25

[0139] Compared with Example 21, most of the contents are the same, except that in this example, 1 M NaCl4 dissolved in EC:DEC (volume ratio of 1:1) is used as the electrolyte.

[0140] Example 26

[0141] Compared with Example 22, most of the steps are the same, except that in this example, 1 M NaCl4 dissolved in EC:DEC (volume ratio of 1:1) is used as the electrolyte.

[0142] Example 27

[0143] Compared with Example 23, most of the steps are the same, except that in this example, 1 M NaCl4 dissolved in EC:DEC (volume ratio of 1:1) is used as the electrolyte.

[0144] Example 28

[0145] Compared with Example 24, most of the contents are the same, except that in this example, 1 M NaCl4 dissolved in EC:DEC (volume ratio of 1:1) is used as the electrolyte.

[0146] Comparative Example 1:

[0147] Compared with Example 1, most of the steps are the same, except that the introduction of F127 is omitted in this example.

[0148] like Figure 34 As shown in the figure, when no F127 template is added, the synthesized material is non-porous micron-sized block particles without mesopores.

[0149] Comparative Example 2:

[0150] Compared with Example 1, most of the steps are the same except that the introduction of citric acid is omitted in this example.

[0151] like Figure 35 As shown, when citric acid is not added, the synthesized material is irregular micron-sized crystalline block particles without mesopore formation.

[0152] Comparative Example 3:

[0153] Compared with Example 2, most of the steps are the same, except that the introduction of F127 is omitted in this example.

[0154] Comparative Example 4:

[0155] Compared with Example 2, most of the above are the same, except that the introduction of citric acid is omitted in this example.

[0156] Compared with Example 3, most of the steps are the same, except that the introduction of F127 is omitted in this example.

[0157] Comparative Example 6:

[0158] Compared with Example 3, most of the above are the same, except that the introduction of citric acid is omitted in this example.

[0159] Compared with Example 4, most of the steps are the same, except that the introduction of F127 is omitted in this example.

[0160] Comparative Example 8:

[0161] Compared with Example 4, most of the steps are the same except that the introduction of citric acid is omitted in this example.

[0162] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a mesoporous sodium titanate / carbon composite electrode material, characterized in that: The mesoporous sodium titanate / carbon composite electrode material has a mesopore diameter of 3-5 nm and a specific surface area of ​​100-600 m 2 / g, including pure phase sodium titanate and coated carbon; The pure phase sodium titanate includes Na 0.23 TiO2、Na4Ti5O 12 , Na4Ti3O8 or Na8Ti5O 14 ; The size of the pure phase sodium titanate is 5-10 nm; The preparation method of the mesoporous sodium titanate / carbon composite electrode material is as follows: using a surfactant as a template, adding a complexing agent, a titanium source and a sodium source to a solvent, mixing and drying, and then calcining to obtain the mesoporous sodium titanate / carbon composite electrode material; Specifically, a surfactant is dissolved in a solvent, and after stirring, a complexing agent and a titanium source are added, and then a sodium source is added. After stirring and dissolving, the solvent is dried, and a black solid is collected to obtain a composite precursor. The precursor is placed in an inert atmosphere and calcined to obtain the mesoporous sodium titanate / carbon composite electrode material; The surfactant is one or more of polyethylene oxide-polypropylene oxide, polyethylene oxide-polybutylene oxide, polyethylene oxide-polystyrene or polyethylene oxide-polymethyl methacrylate diblock copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and polypropylene oxide-polyethylene oxide-polypropylene oxide triblock copolymer; The solvent is one or more of water, methanol, ethanol, n-propanol, isopropanol, and n-butanol; The complexing agent is one or more of citric acid, ethylenediaminetetraacetic acid, phenolic resin, and acetylacetone; The titanium source is one or more of titanium sulfate, titanium tert-butoxide, titanium methoxide, titanium tetrachloride, tetrabutyl titanate, isopropyl titanate, tetraethyl titanate or titanium acetylacetonate; The sodium source is one or more of sodium acetate, sodium citrate, sodium sulfate, sodium carbonate, sodium propionate and sodium butyrate.

2. The method for preparing the mesoporous sodium titanate / carbon composite electrode material according to claim 1, characterized in that: In the composite electrode material, the total mass of carbon accounts for 5%-20% of the mass of the composite electrode material.

3. The method for preparing the mesoporous sodium titanate / carbon composite electrode material according to claim 1, characterized in that: The molar ratio of the titanium source to the sodium source is (3-5): (1-2); the calcination process is 1-5 o C / min heating rate to 500-800 o C, constant temperature for 0.5-3 h.

4. An application of a mesoporous sodium titanate / carbon composite electrode material prepared by the preparation method according to any one of claims 1 to 2, characterized in that: The composite electrode material is used to prepare a sodium ion battery or a sodium battery.

5. The use of the mesoporous sodium titanate / carbon composite electrode material according to claim 4, characterized in that: The sodium ion battery and sodium battery include a positive electrode sheet, a negative electrode sheet, an electrolyte, a diaphragm and a shell. The diaphragm is a glass fiber diaphragm, a polyethylene, a polypropylene microporous membrane, or a composite diaphragm thereof, and the electrolyte is a soluble sodium salt organic solution. In the sodium battery, the mesoporous sodium titanate / carbon composite electrode material is the positive electrode, and metallic sodium serves as the negative electrode of the sodium battery. In the sodium ion battery, the mesoporous sodium titanate / carbon composite electrode material is the negative electrode, and the active material that can insert / extract sodium ions serves as the positive electrode of the sodium ion battery.

6. The use of the mesoporous sodium titanate / carbon composite electrode material according to claim 5, characterized in that: The soluble sodium salt organic solution is obtained by dissolving sodium salt in an organic solvent, wherein the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium trifluoromethanesulfonate, and the organic solvent is one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, and triethylene glycol dimethyl ether.

Images