CN111470535B - Niobium pentoxide yolk structure nano material with controllable core volume and preparation method thereof - Google Patents
Niobium pentoxide yolk structure nano material with controllable core volume and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a niobium pentoxide yolk structure nano material with controllable core volume and a preparation method thereof. The invention uses the niobium pentoxide core with the heteroatom carbon shell confinement volume controllable, and can effectively regulate and control the space utilization rate of the nano yolk material and solve the problem of volume expansion. Heteroatom functional groups on the heteroatom carbon shell are beneficial to the infiltration of electrolyte and the transmission of ions.
Description
Technical Field
The invention relates to the technical field of electrode materials of lithium ion hybrid capacitors, in particular to a niobium pentoxide yolk structure nano material with controllable core volume for heteroatom carbon shell confinement of a lithium ion hybrid capacitor and a preparation method thereof.
Background
With the continuous and intensive research on energy storage devices, a lithium ion hybrid capacitor (HSC) having advantages of both a lithium ion battery (LIC) and a Super Capacitor (SC) has been proposed and attracted extensive attention. HSC is an energy storage device that combines the negative electrode of the lithium ion intercalation type faradaic behavior with the positive electrode of the electric double layer type non-faradaic behavior. Existing studies have demonstrated that the combination of two different energy storage mechanisms allows HSCs to combine the advantages of LIC and SC. In particular, HSCs have not only higher energy and power densities, but also excellent cycling and rate performance. However, the kinetic imbalance of the energy storage mechanism also causes the development of the cathode material to have certain limiting factors: that is, the HSC negative electrode material does not only need to have excellent lithium storageThe ability to incorporate fast lithium insertion compatible with fast non-faraday energy storage reactions is also needed. Based on the conditions, niobium pentoxide (Nb) with special crystal form channel 2 O 5 ) Become a research hotspot.
Nb 2 O 5 As a promising energy storage material, it has been explored to a large extent. Firstly, compared with the traditional titanate material (170 mAh g) used for HSC negative electrode -1 ），Nb 2 O 5 Not only has higher theoretical specific capacity (-200 mAh g) -1 ) And also has a low plateau voltage (< 2 V，vs Li/Li + ) And special intercalation pseudocapacitance behavior. It is clear that Li + Nb embedded in quadrature phase 2 O 5 Is a capacitive process. In particular, li + The embedding process can take place not only at the surface but also within the bulk crystal structure and is not limited by solid diffusion. This particular property is due to the open two-dimensional tube structure and NbO in the crystal x Unique open channels (similar to nanopores) in the lamellae allow Li + Fast transmission of (2). Nb 2 O 5 Unique Li in non-aqueous electrolytes + The intercalation process is typical of lithium ion battery capacitance, but at a rate close to that of supercapacitors. This makes Li + Embedded Nb 2 O 5 The process has the characteristics of a battery and a super capacitor, and provides basis for a new energy storage concept. But Nb 2 O 5 There are also some difficulties that limit their development. First, nb 2 O 5 The electrochemical performance of the material is extremely dependent on the crystal form and the nanometer structure. Among the numerous crystal forms, orthorhombic niobium pentoxide (T-Nb) 2 O 5 ) Has the crystal structure most suitable for lithium ion to pass and the best electrochemical performance. But its lattice formation generally requires a high temperature (f)>600. Annealing treatment at the temperature of C), the nano material is easy to collapse or sinter at high temperature, and the shape and the performance of the material are negatively influenced. Second, nb 2 O 5 Has poor conductivity (300K is-3.4 multiplied by 10) -6 S cm -1 ) Reduce the electrochemical activity thereofUtilization rate of sexual sites and rate capability of materials.
Disclosure of Invention
The invention aims to provide a niobium pentoxide yolk structure nano material with a controllable core volume of a heteroatom carbon shell confinement for a lithium ion hybrid capacitor and a preparation method thereof.
The technical solution for realizing the purpose of the invention is as follows: niobium pentoxide and tetrabutylammonium hydroxide are prepared into a niobium pentoxide template under a hydrothermal condition, then dopamine hydrochloride is used for coating the surface of the niobium pentoxide template, carbonization is carried out under the protection of nitrogen, and the obtained double-layer concentric nanospheres are etched in hydrofluoric acid to remove part of niobium pentoxide nuclei, so that the yolk structure is obtained. The method comprises the following specific steps:
1) Adding niobium chloride (NbCl) 5 ) Dissolving in isopropanol, adding tetrabutylammonium hydroxide (TBA) under magnetic stirring, and reacting the obtained mixed solution at the constant temperature of 150-220 ℃ for 24 hours to obtain niobium pentoxide (Nb) 2 O 5 ) Nanospheres;
2) Mixing niobium pentoxide nanospheres and dopamine hydrochloride according to a mass ratio of 1-2: 1 in a tris buffer solution, stirring for 6 hours, centrifuging, drying, and adding the sample to N 2 Under protection, heating to 500 ℃ at the temperature rising speed of 1 ℃ per minute, keeping the temperature for 2 hours, and cooling to obtain Nb 2 O 5 @ NC nanospheres;
3) Mixing Nb with 2 O 5 And dispersing the @ NC nanospheres in a hydrofluoric acid solution, stirring for 12 h, and annealing the sample subjected to centrifugal separation and drying at 700 ℃ for two hours to obtain the nano material.
Further, the mass ratio of niobium chloride to tetrabutylammonium hydroxide is 5 to 10:1, and the concentration of the niobium chloride in the isopropanol is 3 to 10 g mL -1 . Because the concentration of niobium chloride directly affects the size of the diameter of the niobium pentoxide template and its independence during hydrothermal processing: the niobium chloride concentration is too small, resulting in nanospheres having small diameters and non-uniform sizes. When the carbon source coats the surface, the carbon source is easy to agglomerate; niobium chloride with excessive concentration is nanometerThe diameter of the ball is too large, and the carbon source is not easy to be completely and uniformly coated.
Further, the mass ratio of the dopamine hydrochloride to the niobium pentoxide is 1 to 1. When the dopamine hydrochloride is excessive, the generated carbon shell is too thick, so that the transmission of ions is not facilitated, and the ion mobility and the electrochemical energy storage effect are reduced; when the dopamine hydrochloride is too little, the carbon shell is too thin, cannot play a limiting effect during charging and discharging of the material, is extremely easy to break, and reduces the stability of the material.
Further, nb 2 O 5 The mass ratio of the @ NC nanospheres to the hydrofluoric acid solution is 1: 1-9, preferably 1: 2-6, and the concentration of the hydrofluoric acid solution is 4 mol L -1 . The size of niobium pentoxide nuclei is directly controlled by the consumption of hydrofluoric acid, wherein the nuclei with overlarge volume have large volume change in the charge-discharge process, so that the structural stability of the material is damaged; the too small core reduces the space utilization rate of the material and the specific capacity of the material for energy storage.
Compared with the prior art, the invention has the beneficial effects that:
(1) The niobium pentoxide nanospheres are simultaneously used as a template and an energy storage main body, so that the preparation process of the conventional yolk structure is simplified.
(2) The volume of the niobium pentoxide core is controllable, the cavity size of the yolk structure can be well regulated, and the contradiction between the space utilization rate and the volume effect is effectively balanced.
(3) The limited domain coating of the heteroatom carbon shell enhances the stability of the material structure. Compared with a pure carbon shell, the electrolyte has better electrolyte wettability.
(4) The preparation process of the yolk structure is beneficial to improving the conventional preparation mode.
Drawings
FIG. 1 is a transmission electron microscope image of the niobium pentoxide nanospheres synthesized in example 1.
FIG. 2 is a transmission electron micrograph of the heteroatom-carbon shell coated niobium pentoxide synthesized in example 1.
FIG. 3 shows T-Nb synthesized in example 1 2 O 5 Scanning electron microscope picture of @ NC-5 nanosphere.
FIG. 4 shows T-Nb synthesized in example 1 2 O 5 Transmission electron microscopy images of the @ NC-5 nanospheres.
FIG. 5 shows T-Nb synthesized in example 2 2 O 5 Transmission electron micrograph of @ NC-3 nanosphere.
FIG. 6 shows T-Nb synthesized in example 3 2 O 5 Transmission electron micrograph of @ NC-7 nanosphere.
FIG. 7 shows T-Nb synthesized in example 4 2 O 5 Scanning electron microscope image of @ NC nanosphere.
FIG. 8 shows T-Nb synthesized in example 1 2 O 5 Mapping graph of @ NC-5 nanospheres.
FIG. 9 shows T-Nb synthesized in example 1 2 O 5 XRD patterns of @ NC-5 nanospheres.
FIG. 10 shows T-Nb prepared in example 1 2 O 5 XPS analysis of the @ NC nanospheres electron spectrum fit plot of the full spectrum elements.
FIG. 11 shows T-Nb prepared in example 1 2 O 5 XPS analysis of @ NC nanospheres electron spectrum fit of the N1s element.
FIG. 12 shows T-Nb prepared in examples 1 to 3 2 O 5 Graph of rate performance of @ NC nanospheres at different current densities.
FIG. 13 shows T-Nb prepared in example 1 2 O 5 Energy density versus power density plot for a @ NC-5 nanosphere assembled lithium ion hybrid capacitor.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in detail below with reference to examples.
The invention relates to a zero-dimensional confinement material T-Nb which takes niobium pentoxide with controllable content as a core and nitrogen-doped carbon as a shell 2 O 5 @ NC-x (x is Nb) 2 O 5 The remaining amount). The electrochemical performance of the composite material can be well improved by the unique characteristics of the core-shell structure. (1) The introduction of the core-shell structure (the size and tap density of the gap between the core shells are controlled by directly etching the core structure) effectively relieves the volume expansion effect caused in the lithium ion intercalation process, and enhances the cycle performance of the material. (2) Cycling and conductivity properties of carbon shell to materialHas better improving effect. The carbon shell can effectively reduce the sintering phenomenon of the material when the crystal form is regulated and controlled by high-temperature annealing, thereby improving the problems of material pulverization and falling off in the process of multiple charging and discharging cycles and the like. In addition, as a functional additive, the introduction of the carbon material inevitably improves the conductivity of the material. And (3) the N heteroatom carbon shell has better electrochemical activity. N is doped into the carbon lattice, so that a shorter carbon-nitrogen bond C-N can be formed, and two free p electrons can be provided to enter a carbon pi bond, so that the electrochemical activity is improved. T-Nb 2 O 5 The composition and structure advantages possessed by @ NC will facilitate its expression in electrochemical energy storage. The invention uses the niobium pentoxide core with the heteroatom carbon shell confinement volume controllable, and can effectively regulate and control the space utilization rate of the nano yolk material and solve the problem of volume expansion. Heteroatom functional groups on the heteroatom carbon shell are beneficial to the infiltration of electrolyte and the transmission of ions.
1. The preparation process comprises the following steps:
example 1:
1) 0.4 g of NbCl was weighed 5 Dissolved in 60 mL of isopropanol and 0.4 g of aqueous TBA (10 wt%) was added with magnetic stirring. The solution was transferred into a 100 mL autoclave and thermostatted at 200 ℃ for 24 h. After cooling to room temperature, the product was dried at 60 ℃ after centrifugation and washing several times. The obtained Nb is collected by centrifugation 2 O 5 The TEM image is shown in FIG. 1, and can be seen in FIG. 1: the diameter of the nanosphere is about 500 nm, the surface is not smooth, and the coating growth of dopamine hydrochloride is facilitated.
2) Niobium pentoxide nanospheres (80 mg), dopamine hydrochloride (50 mg) were dispersed in tris buffer solution under magnetic stirring. After stirring for 6 h, the centrifuged and dried sample was placed in N 2 Under protection, heating to 500 ℃ at a heating speed of 1 ℃ per minute, and keeping the temperature for 2 hours. After cooling, the sample was collected. The TEM image of the product obtained is shown in fig. 2, as can be seen in fig. 2: the thickness of the heteroatom carbon shell is about 20 nm, and the heteroatom carbon shell is completely coated on the surface of the niobium pentoxide.
3) Weighing 1 g of Nb 2 O 5 @ NC nanospheres dispersed in 3.75 g dilute hydrofluoric acid solution (4 mol L) -1 ) Neutralizing and stirring for 12 h, annealing the sample subjected to centrifugal separation and drying at 700 ℃ for two hours, and naming the sample as T-Nb 2 O 5 @ NC-5. The SEM image of the product obtained is shown in fig. 3, as can be seen in fig. 3: uniform and independent spheres can be observed at large scale. The TEM image of the product obtained is shown in fig. 4, as can be seen in fig. 3: the etched structure retains 50% by volume of the niobium pentoxide core, and has a more suitable cavity and burr-like core surface.
FIG. 8 shows T-Nb synthesized in example 1 2 O 5 Mapping graph for @ NC-5 nanospheres. As can be seen from fig. 8: c and N elements and Nb and O elements distributed in the core are uniformly distributed on the carbon shell.
FIG. 9 shows T-Nb synthesized in example 1 2 O 5 XRD patterns of @ NC-5 nanospheres. As can be seen from fig. 9: the prepared niobium pentoxide has an orthorhombic structure suitable for lithium ion intercalation.
FIG. 10 shows T-Nb prepared in example 1 2 O 5 XPS analysis of the @ NC yolk sphere electron spectrum fit of the full spectrum elements. As can be seen from fig. 10: the prepared active carbon material mainly comprises Nb, O, C and N elements.
FIG. 11 shows T-Nb prepared in example 1 2 O 5 XPS analysis of the @ NC yolk sphere electron spectrum fit of the N1s element. As can be seen from fig. 11: the N1s spectrum peak is divided into two peaks, which shows that the surface of the carbon shell contains rich nitrogen-containing functional groups, and the surface activity of the two peaks can provide rich pseudo-capacitance, so that the capacitance performance of the carbon material is enhanced, and the infiltration between the material and electrolyte is enhanced.
Example 2:
1) 0.4 g of NbCl was weighed 5 Dissolved in 60 mL of isopropanol and 0.4 g of aqueous TBA (10 wt%) was added with magnetic stirring. The solution was transferred into a 100 mL autoclave and thermostatted at 200 ℃ for 24 h. After cooling to room temperature, the product was dried at 60 ℃ after centrifugation and washing several times.
2) Niobium pentoxide nanospheres (80 mg) and dopamine hydrochloride (50 mg) were dispersed in tris (hydroxymethyl) aminomethane under magnetic stirring. After stirring for 6 h, the centrifuged and dried sample was placed in N 2 Under the protection of the air conditioner, the air conditioner is protected,heating to 500 ℃ at the temperature rising speed of 1 ℃ per minute, and keeping the temperature for 2 hours. After cooling, the sample was collected.
3) Weighing 1 g of Nb 2 O 5 @ NC nanospheres dispersed in 5.25 g dilute hydrofluoric acid solution (4 mol L) -1 ) Neutralizing and stirring for 12 h, annealing the centrifugally separated and dried sample at 700 ℃ for two hours, and naming the sample as T-Nb 2 O 5 @ NC-3. The TEM image of the product obtained is shown in fig. 5, as can be seen in fig. 5: the etched structure retains 30% by volume of niobium pentoxide nuclei, with relatively suitable cavities and burr-like nuclear surfaces.
Example 3:
1) 0.4 g of NbCl was weighed 5 Dissolved in 60 mL of isopropanol and 0.4 g of aqueous TBA (10 wt%) was added with magnetic stirring. The solution was transferred into a 100 mL autoclave and thermostatted at 200 ℃ for 24 h. After cooling to room temperature, the product was dried at 60 ℃ after centrifugation and washing several times.
2) Niobium pentoxide nanospheres (80 mg) and dopamine hydrochloride (50 mg) were dispersed in tris (hydroxymethyl) aminomethane under magnetic stirring. After stirring for 6 h, the centrifuged and dried sample was placed in N 2 Under protection, heating to 500 ℃ at a heating speed of 1 ℃ per minute, and keeping the temperature for 2 hours. After cooling, the sample was collected.
3) Weighing 1 g of Nb 2 O 5 @ NC nanospheres dispersed in 2.25 g dilute hydrofluoric acid solution (4 mol L) -1 ) Neutralizing and stirring for 12 h, annealing the centrifugally separated and dried sample at 700 ℃ for two hours, and naming the sample as T-Nb 2 O 5 @ NC-3. The TEM image of the product obtained is shown in fig. 6, as can be seen in fig. 6: after etching, the structure is kept to be 70% of niobium pentoxide core by volume, and the structure is provided with more proper cavities and burr-shaped core surfaces.
Example 4:
1) 0.8 g of NbCl was weighed 5 Dissolved in 60 mL of isopropanol and 0.4 g of aqueous TBA (10 wt%) was added with magnetic stirring. The solution was transferred into a 100 mL autoclave and thermostatted at 200 ℃ for 24 h. After cooling to room temperature, the product was dried at 60 ℃ after centrifugation and washing several times.
2) Niobium pentoxide nanospheres (80 mg) and dopamine hydrochloride (80 mg) were dispersed in tris (hydroxymethyl) aminomethane under magnetic stirring. After stirring for 6 h, the centrifugally separated, dried sample was placed in N 2 Under protection, heating to 500 ℃ at a heating speed of 1 ℃ per minute, and keeping the temperature for 2 hours. After cooling, the sample was collected.
3) Weighing 1 g of Nb 2 O 5 @ NC nanospheres dispersed in 2.25 g dilute hydrofluoric acid solution (4 mol L) -1 ) Neutralizing and stirring for 12 h, annealing the sample subjected to centrifugal separation and drying at 700 ℃ for two hours, and naming the sample as T-Nb 2 O 5 @ NC-3. The SEM image of the product obtained is shown in fig. 7, as can be seen in fig. 7: due to the change of parameters, the morphology of the material can not maintain a hollow sphere structure, and the material is agglomerated due to excessive Nb sources.
2. The application comprises the following steps:
the electrode materials prepared in the three examples are respectively taken for parallel tests:
mixing niobium pentoxide/heteroatom carbon shell material with controllable core volume, conductive agent and binder according to the proportion of 8:1: 1. preparing the electrode slice according to the mass ratio of (A) to (B). In LiPF 6 Button cells and hybrid capacitors are assembled in organic electrolytes.
FIG. 12 shows T-Nb prepared in examples 1, 2 and 3 2 O 5 Graph of rate performance of @ NC nanospheres at different current densities.
As can be seen from fig. 12: T-Nb prepared in example 1 2 O 5 @ NC-5 nanospheres at 0.1A g -1 It has a high level of 208 mAh g -1 And a specific capacity of 5 ag -1 Under high current, 127 mAh g can be still maintained -1 The specific capacity of (A). The capacitance of 95% can still be maintained after different current density cycles. This illustrates the T-Nb prepared in example 1 2 O 5 The @ NC yolk ball has extremely excellent rate capability and material stability.
FIG. 13 shows T-Nb prepared in example 1 2 O 5 Energy density versus power density plot for a @ NC yolk sphere assembled lithium ion hybrid capacitor.
As can be seen from fig. 13: prepared in example 1T-Nb 2 O 5 @ NC yolk ball having high energy density (56.7 Wh kg) -1 ) And power density (9753W kg) -1 ). The T-Nb prepared in example 1 is illustrated 2 O 5 The lithium ion capacitor assembled by the @ NC yolk ball has larger practical application possibility.
In conclusion, the controllable core volume effectively solves the problem that the expansion of the yolk structure in actual production is contradictory due to the space utilization rate of materials and the core volume. The heteroatom functional group on the heteroatom carbon shell also promotes the infiltration of the electrolyte, and effectively provides enough buffer space for the volume expansion of the core in the charge-discharge process.
Claims (6)
1. A preparation method of a niobium pentoxide yolk structure nano material with controllable core volume is characterized in that niobium pentoxide template is prepared from niobium chloride and tetrabutylammonium hydroxide under a hydrothermal condition, dopamine hydrochloride is used for coating the surface of the niobium pentoxide template, carbonization treatment is carried out under the protection of nitrogen, and the obtained double-layer concentric nanospheres are etched in hydrofluoric acid to remove part of niobium pentoxide cores, so that the yolk structure nano material is obtained; the method comprises the following specific steps:
1) Dissolving niobium chloride in isopropanol, adding tetrabutylammonium hydroxide under magnetic stirring, and reacting the obtained mixed solution at the constant temperature of 150-220 ℃ for 24 hours to obtain niobium pentoxide nanospheres;
2) Niobium pentoxide nanospheres and dopamine hydrochloride are mixed according to the mass ratio of 1-2: 1 in a tris buffer solution, stirring for 6 hours, centrifuging, drying, and adding the sample to N 2 Under protection, heating to 500 ℃ at the temperature rising speed of 1 ℃ per minute, keeping the temperature for 2 hours, and cooling to obtain Nb 2 O 5 @ NC nanospheres;
3) Mixing Nb with 2 O 5 And dispersing the @ NC nanospheres in a hydrofluoric acid solution, stirring for 12 h, and annealing the centrifugally separated and dried sample at 700 ℃ for two hours to obtain the nano material.
2. The method according to claim 1, wherein the mass ratio of niobium chloride to tetrabutylammonium hydroxide is 5 to 10:1.
3. the method of claim 1, wherein the concentration of niobium chloride in isopropanol is 3 to 10 g mL -1 。
4. The method according to claim 1, wherein the mass ratio of dopamine hydrochloride to niobium pentoxide is 1 to 2.
5. The method of claim 1, wherein Nb 2 O 5 The mass ratio of the @ NC nanospheres to the hydrofluoric acid solution is 1: 1-9, and the concentration of the hydrofluoric acid solution is 4 mol L -1 。
6. The method of claim 1, wherein Nb 2 O 5 The mass ratio of the @ NC nanospheres to the hydrofluoric acid solution is 1: 2-6, and the concentration of the hydrofluoric acid solution is 4 mol L -1 。
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