CN114249351A - Tetragonal niobium pentoxide material and synthesis and application thereof - Google Patents

Abstract

The invention relates to the field of lithium ion battery cathode materials, in particular to synthesis and application of a tetragonal niobium pentoxide material, which comprises the following steps of 1) coating a silicon dioxide layer on the outer surface of raw material powder by taking one or a mixture of two or a mixture of three of amorphous niobium oxide, pseudo-hexagonal niobium oxide and orthogonal niobium oxide as a raw material to obtain a raw material coated with the silicon dioxide layer; 2) calcining the raw material coated with the silicon dioxide layer at 950-1100 ℃ for 3-8 h; soaking calcined powder in 1-4mol L^‑1The solution of sodium hydroxide (NaOH) for 12 to 48 hours, then solid-liquid separation, washing and drying are carried out to obtain the tetragonal niobium oxide M-Nb₂O₅. Synthesized M-Nb₂O₅Has a g of 300mAh^‑1The specific capacity and the excellent rate performance of the composite material; the material has intrinsic high lithium ion diffusion capacity, and guarantees the ultrahigh-rate charge and discharge capacity and long cycle stability of the material.

Description

Tetragonal niobium pentoxide material and synthesis and application thereof

Technical Field

The invention relates to the field of lithium ion battery cathode materials, in particular to synthesis and application of a tetragonal-phase niobium pentoxide material.

Background

As for the negative electrode material of the lithium ion battery, the graphite negative electrode is the most common negative electrode material of the current commercial lithium ion battery, the theoretical specific capacity of the graphite negative electrode is 372mAh/g, and the graphite negative electrode has low lithium intercalation potential (<0.2V，vs.Li⁺/Li). However, at high current density, the graphite negative electrode has an increased lithium intercalation overpotential, which may cause a battery circuit and cause a battery safety problem, and thus it is not suitable for high-rate charge and discharge. Lithium titanate (Li)₄Ti₅O₁₂LTO) negative electrode has an intercalation potential of 1.55V (vs. Li)⁺Li), the volume should be reduced in the charging and discharging process, and the lithium ion battery is a negative electrode material which has high safety, long service life and can be charged and discharged rapidly. However, due to its high potential and low specific capacity (175mAh/g), its energy density is difficult to meet the demand for high specific energy batteries. The silicon-based composite negative electrode material is a novel high-specific-capacity negative electrode, the actual specific capacity of the silicon-based composite negative electrode material can reach 600-plus-2000 mAh/g, and good high-rate charge and discharge performance can be realized through material nanocrystallization. However, the inherent huge volume expansion of the material in the lithium intercalation process affects the cycle life of the material, and the problems of low coulomb charge and discharge for the first time, complex material manufacturing process and the like exist, which make the silicon-based negative electrode difficult to be realizedThe method is applied to large-scale practical application. Therefore, exploring a suitable negative electrode material is a hotspot and difficulty in developing the next generation of high-rate and high-safety energy storage technology. Recently, niobium pentoxide (Nb) has recently come into use₂O₅) Due to the considerable theoretical capacity (200 mAh/g) and the unique crystal structure, the lithium ion ultra-high-speed storage kinetics can be realized, and the lithium ion lithium cathode material is considered to be a promising cathode material. Nb depending on the calcination conditions, precursor and synthesis method₂O₅There are many crystal phases, such as TT-, T-, B-, N-, P-, M-and H-Nb₂O₅They have different effects on their lithium storage properties. The most common of which are T, M and H-Nb₂O₅Is Nb determined by Brauer et al based on stable thermodynamic states of low, medium and high temperature₂O₅Three crystal phases of (2). Orthogonal phase T-Nb₂O₅It has received the greatest attention due to its low-variation intercalation structure (no phase change), and high rate capability, but it still has a practical specific capacity of less than 200 mAh/g. Monoclinic phase H-Nb₂O₅Has a Li content of up to 250mAh/g (1.0-3.0V vs Li)⁺/Li). Tetragonal phase M-Nb₂O₅Has the characteristics similar to H-Nb₂O₅The specific capacity and the rate capability are more excellent. But due to M-Nb₂O₅The synthesis conditions are very harsh, and the synthesis is often performed with T-Nb₂O₅Or H-Nb₂O₅Mixed phases of (1).

Disclosure of Invention

Based on the existing M-Nb₂O₅Has the problems of strict synthesis conditions and the like, and the invention provides tetragonal niobium pentoxide (M-Nb)₂O₅) The composite material can be used as a negative electrode in lithium ion batteries and lithium ion capacitors.

The invention provides a tetragonal phase M-Nb₂O₅The Nb is changed by the silicon dioxide coating layer₂O₅The phase transition temperature and time at high temperature can obtain pure tetragonal phase M-Nb under wider synthesis conditions₂O₅Solves the problem of pure phase tetragonal phase M-Nb₂O₅The problem of difficult synthesis; synthesized M-Nb₂O₅Has a g of 300mAh^-1The specific capacity, excellent cycle performance and ultrahigh-rate charge and discharge capacity of the lithium ion battery are improved; the material has intrinsic high lithium ion diffusion capability.

The invention provides a complete technical scheme, a method for synthesizing tetragonal niobium oxide,

1) taking one or a mixture of two or a mixture of three of amorphous niobium oxide, pseudo-hexagonal niobium oxide and orthorhombic niobium oxide as a raw material, and coating a silicon dioxide layer on the outer surface of the raw material powder to obtain a raw material coated with the silicon dioxide layer;

2) calcining the raw material coated with the silica layer at 950-; soaking the calcined powder in 1-4mol L^-1(preferably 2mol L)^-1-3mol L^-1More preferably 3mol L^-1) Is added into sodium hydroxide (NaOH) solution for 12 to 48 hours (preferably 20 to 30 hours, more preferably 24 hours), then solid-liquid separation, washing and drying are carried out to obtain tetragonal niobium oxide M-Nb₂O₅。

The process of wrapping the outer surface of the raw material in the step 1) with the silicon dioxide layer comprises the following steps: adding one or two or three mixture powders of amorphous niobium oxide, pseudo hexagonal niobium oxide and orthorhombic niobium oxide as raw materials into a mixed powder with the volume ratio of 4-8: 2 (preferably 5-7: 2) aqueous ethanol solution, wherein the mass (g) to volume (ml) ratio of the starting material to the aqueous ethanol solution is 0.05-1: 70 (preferably 0.1-0.2: 70); weighing Cetyl Trimethyl Ammonium Bromide (CTAB), adding into the suspension, and uniformly stirring, wherein the mass ratio of CTAB to the raw materials is 1:5-20 (preferably 1: 10-15, more preferably 1: 10); then adding the mixture into an ethanol water solution in a volume ratio of 1-3: ammonia water with the mass fraction of 25% -28% of 70 (preferably 1-2: 70, more preferably 1: 70) is evenly stirred; finally, the concentration is 0.001-0.05g ml^-1(preferably 0.008-0.015g ml)^-1) Adding dropwise ethyl orthosilicate (TEOS) ethanol solution into the above solution at a volume ratio of ethyl orthosilicate ethanol solution to ethanol water solution of 1:5-20 (preferably 1:7-10, more preferably 1:7), stirring for 6-24 hr (preferably 10-24 hr), performing solid-liquid separation, and drying the solid to obtain coated productA raw material of the silicon dioxide layer.

A. The amorphous niobium oxide is synthesized by a hydrothermal method: reacting NbCl₅Adding the powder into benzyl alcohol; keeping the temperature at 180-220 ℃ for 12-48 hours, carrying out solid-liquid separation, and drying the solid to obtain amorphous niobium oxide; NbCl₅A mass (g) to volume (ml) ratio to benzyl alcohol of 0.1-0.5:18 (preferably 0.2-0.3:18, more preferably 0.24-0.25: 18);

or B, preparing one or two mixtures or three mixtures of amorphous niobium oxide, pseudo hexagonal niobium oxide and orthorhombic niobium oxide: and B, calcining the amorphous niobium oxide obtained in the step A at the temperature of 300-700 ℃ for 2-5h to obtain one or two or three of amorphous niobium oxide, pseudo-hexagonal niobium oxide and orthorhombic niobium oxide, which is called low-temperature calcined niobium oxide.

Tetragonal niobium oxide synthesized by the above synthesis method.

The tetragonal niobium oxide is applied to a lithium ion battery or a lithium ion capacitor as a negative electrode active material.

The invention has the beneficial effects that:

the invention provides a tetragonal phase M-Nb₂O₅The Nb is changed by a silicon dioxide coating layer₂O₅The phase transition temperature and time at high temperature can obtain pure tetragonal phase M-Nb under wider synthesis conditions₂O₅Solves the problem of pure tetragonal phase M-Nb₂O₅The problem of difficult synthesis; synthesized M-Nb₂O₅Has a g of 300mAh^-1The specific capacity and the excellent rate performance of the composite material; the material has intrinsic high lithium ion diffusion capacity, and guarantees the ultrahigh-rate charge and discharge capacity and long cycle stability of the material.

Drawings

FIG. 1 shows M-Nb obtained in example 1₂O₅Schematic synthesis of sample material a 2;

FIG. 2 is an XRD diffraction curve and standard characteristic peaks of sample A2 obtained in example 1;

FIG. 3 is a phase characterization of the XRD of sample materials A7-A9 of comparative examples 1-3;

FIG. 4 shows M-Nb obtained in example 1₂O₅Sample material a2 half cell GITT calculated diffusion coefficient;

FIG. 5 shows M-Nb obtained in example 1₂O₅Sample material a2 half cell charge and discharge curve;

FIG. 6 shows M-Nb obtained in example 1₂O₅Sample material a2 half cell cycle performance test;

FIG. 7 shows M-Nb obtained in example 1₂O₅Carrying out rate performance test on a sample material A2 half cell;

FIG. 8 shows M-Nb obtained in example 1₂O₅TEM topography before (left) and after (right) washing with NaOH.

Detailed Description

Example 1

Preparing raw materials:

0.243g of milled NbCl₅The powder was added to 18mL of benzyl alcohol. The resulting solution was transferred to a 22 ml teflon liner and then placed in an autoclave. The autoclave was placed at a constant temperature of 180 ℃ for 24 hours and then air-cooled to room temperature. The solid was collected by centrifugation, washed with ethanol and dried at 50 ℃ to give a starting material A1.

Synthesis of sample material:

calcining the raw material A1 at 700 ℃ for 2h to obtain T-Nb₂O₅The preparation steps of the (orthorhombic niobium pentoxide) are shown in figure 1; 0.1g of calcined material is added into a solution containing 50ml of ethanol and 20ml of deionized water, and ultrasonic treatment is carried out for 10min to form a suspension with good dispersibility. 0.02g of cetyltrimethylammonium bromide (CTAB) was weighed into the above suspension and stirred for 5 minutes. Then, 1ml of concentrated aqueous ammonia (mass fraction 28%) was added and stirred for 5 minutes. Finally, the solution will contain 0.012g ml^-110ml of ethyl silicate (TEOS) ethanol solution is slowly added into the suspension dropwise, and after 12 hours of stirring, the suspension is centrifuged, the solid is washed, and dried at 50 ℃.

The dried powder was calcined at 1050 ℃ for 5 h. Placing the calcined powder in a concentration of 3mol L^-150ml of sodium hydroxide (NaOH) solution and left for 24 hours, followed by centrifugation and solidificationWashing with deionized water, and drying to obtain pure phase M-Nb₂O₅(A2) In that respect It can be seen from FIG. 2 that it is a pure phase M-Nb₂O₅The purity is more than 99 percent, and the rest is T-Nb₂O₅And H-Nb₂O₅。

Preparing a half cell:

preparing an electrode using the sample material (a2) as an electrode active material; the material composition of the electrode is as follows: the mass ratio of the electrode material (A2), the carbon black and the PVDF is 8:1:1, the current collector is copper foil, the electrolyte is LBC0305, the battery diaphragm is Celgard2325, and the obtained electrode and the metal lithium form a half-battery to test the battery performance.

The GITT technique of FIG. 4 shows an ion diffusion coefficient of 10^-10-10^-9To (c) to (d); FIG. 5 shows that the reversible capacity reaches 300mAh g^-1(ii) a FIG. 6 shows that it is 2A g^-1The following has good cycle performance, and fig. 7 shows that it has 20C ultra high rate performance. As can be seen in fig. 8, the surface silica layer was removed after soaking in the sodium hydroxide solution, and a pure-phase niobium pentoxide material was obtained.

Example 2

The starting material used in example 2 was the starting material a1 prepared in example 1

Synthesis of sample material:

calcining the raw material A1 at 700 ℃ for 2h to obtain T-Nb₂O₅(orthogonal niobium pentoxide), 0.1g of calcined material is added into a solution containing 50ml of ethanol and 20ml of deionized water, and ultrasonic treatment is carried out for 10min to form a suspension with good dispersibility. 0.02g of cetyltrimethylammonium bromide (CTAB) was weighed into the above suspension and stirred for 5 minutes. Then, 1ml of concentrated aqueous ammonia (mass fraction 28%) was added and stirred for 5 minutes. Finally, the mixture will contain 0.008gml^-110ml of ethyl silicate (TEOS) ethanol solution is slowly dripped into the suspension, stirred for 12 hours, centrifuged, washed and dried at 50 ℃. The dried powder was calcined at 950 ℃ for 5 h. Placing the calcined powder in a concentration of 3mol L^-150ml of sodium hydroxide (NaOH) solution and standing for 24 hours, then centrifuging, washing by deionized water and drying to obtain pure phase M-Nb₂O₅(A3)。

Preparing a half cell:

from Nb₂O₅The material (a3) was used as an electrode active material to prepare a half cell, and the preparation procedure and conditions were the same as in example 1.

The obtained A3 is pure phase M-Nb₂O₅The purity is more than 95 percent, and the rest is T-Nb₂O₅(ii) a The capacity can reach 295mAh g^-1Has stable cycle performance and ultrahigh rate performance.

Example 3

The starting material used in example 3 was the starting material A1 prepared in example 1

Synthesis of sample material:

calcining the raw material A1 at 700 ℃ for 2h to obtain T-Nb₂O₅0.1g of calcined material is added into a solution containing 50ml of ethanol and 20ml of deionized water, and ultrasonic treatment is carried out for 10min to form a suspension with good dispersibility. 0.02g of cetyltrimethylammonium bromide (CTAB) was weighed into the above suspension and stirred for 5 minutes. Then, 1ml of concentrated aqueous ammonia (mass fraction 28%) was added and stirred for 5 minutes. Finally, the solution will contain 0.01g ml^-110ml of ethyl silicate (TEOS) ethanol solution is slowly dripped into the suspension, stirred for 12 hours, centrifuged, washed and dried at 50 ℃. The dried powder was calcined at 1000 ℃ for 5 h. Placing the calcined powder in a concentration of 3mol L^-150ml of sodium hydroxide (NaOH) solution and standing for 24 hours, then centrifuging, washing by deionized water and drying to obtain pure phase M-Nb₂O₅(A4) In that respect Preparing a half cell:

from Nb₂O₅The material (a4) was used as an electrode active material to prepare a half cell, and the preparation procedure and conditions were the same as in example 1.

The obtained A4 is pure phase M-Nb₂O₅The purity is more than 99 percent, and the rest is T-Nb₂O₅And H-Nb₂O₅(ii) a The capacity can reach 300mAh g^-1Has stable cycle performance and ultrahigh rate performance.

Example 4

The starting material used in example 4 was the starting material A1 prepared in example 1

Synthesis of sample material:

calcining the raw material A1 at 700 ℃ for 2h to obtain T-Nb₂O₅0.1g of calcined material is added into a solution containing 50ml of ethanol and 20ml of deionized water, and ultrasonic treatment is carried out for 10min to form a suspension with good dispersibility. 0.02g of cetyltrimethylammonium bromide (CTAB) was weighed into the above suspension and stirred for 5 minutes. Then, 1ml of concentrated aqueous ammonia (mass fraction 28%) was added and stirred for 5 minutes. Finally, the solution will contain 0.015g ml^-110ml of ethyl silicate (TEOS) ethanol solution is slowly dripped into the suspension, stirred for 12 hours, centrifuged, washed and dried at 50 ℃. The dried powder was calcined at 1100 ℃ for 5 h. Placing the calcined powder in a concentration of 3mol L^-150ml of sodium hydroxide (NaOH) solution and standing for 24 hours, then centrifuging, washing by deionized water and drying to obtain pure phase M-Nb₂O₅(A5)。

From Nb₂O₅The material (a5) was used as an electrode active material to prepare a half cell, and the preparation procedure and conditions were the same as in example 1.

The obtained A5 is pure phase M-Nb₂O₅The purity is more than 99 percent, and the rest is H-Nb₂O₅(ii) a The capacity can reach 300mAh g^-1Has stable cycle performance and ultrahigh rate performance.

Example 5

The starting material used in example 5 was the starting material A1 prepared in example 1

Synthesis of sample material:

adding 10.1g of the raw material A10 to a solution containing 50ml of ethanol and 20ml of deionized water, and carrying out ultrasonic treatment for 10min to form a suspension with good dispersibility. 0.02g of cetyltrimethylammonium bromide (CTAB) was weighed into the above suspension and stirred for 5 minutes. Then, 1ml of concentrated aqueous ammonia (mass fraction 28%) was added and stirred for 5 minutes. Finally, the solution will contain 0.012g ml^-110ml of ethyl silicate (TEOS) ethanol solution is slowly dripped into the suspension, stirred for 12 hours, centrifuged, washed and dried at 50 ℃. The dried powder was calcined at 1050 ℃ for 5 h. Placing the calcined powder in a concentration of 3mol L^-150ml of sodium hydroxide (NaOH) solution and standing for 24 hours, then centrifuging, washing by deionized water and drying to obtain pure phase M-Nb₂O₅(A6)。

From Nb₂O₅The material (a6) was used as an electrode active material to prepare a half cell, and the preparation procedure and conditions were the same as in example 1.

The obtained A6 is pure phase M-Nb₂O₅The purity is more than 99 percent, and the rest is T-Nb₂O₅And H-Nb₂O₅(ii) a The capacity can reach 300mAh g^-1Has stable cycle performance and ultrahigh rate performance.

Example 6

The starting material used in example 6 was the starting material A1 prepared in example 1

Synthesis of sample material:

calcining the raw material A1 at 700 ℃ for 2h to obtain T-Nb₂O₅The preparation steps of the (orthorhombic niobium pentoxide) are shown in figure 1; 0.1g of calcined material is added into a solution containing 50ml of ethanol and 20ml of deionized water, and ultrasonic treatment is carried out for 10min to form a suspension with good dispersibility. 0.02g of cetyltrimethylammonium bromide (CTAB) was weighed into the above suspension and stirred for 5 minutes. Then, 1ml of concentrated aqueous ammonia (mass fraction 28%) was added and stirred for 5 minutes. Finally, the solution will contain 0.001g ml^-110ml of ethyl silicate (TEOS) ethanol solution is slowly added into the suspension dropwise, and after 12 hours of stirring, the suspension is centrifuged, the solid is washed, and dried at 50 ℃.

The dried powder was calcined at 1050 ℃ for 5 h. Placing the calcined powder in a concentration of 3mol L^-150ml of sodium hydroxide (NaOH) solution and standing for 24 hours, then centrifuging, washing with solid deionized water and drying to obtain pure phase M-Nb₂O₅(A7)。

Preparing a half cell:

from Nb₂O₅The material (a7) was used as an electrode active material to prepare a half cell, and the preparation procedure and conditions were the same as in example 1.

The obtained A7 is pure phase M-Nb₂O₅The purity is more than 95 percent, and the rest is H-Nb₂O₅(ii) a It has a capacity ofUp to 295mAh g^-1Has stable cycle performance and ultrahigh rate performance.

The ethyl silicate (TEOS) concentration was chosen to be lower than in example 1, as a lower limit of experimental conditions, so that SiO is formed₂The coating is thin, the effect is slightly poor, and H-Nb is more easily generated when the coating is calcined at the same temperature₂O₅I.e. H-Nb in the product₂O₅Relatively much.

Example 7

The starting material used in example 7 was the starting material A1 prepared in example 1

Synthesis of sample material:

calcining the raw material A1 at 700 ℃ for 2h to obtain T-Nb₂O₅The preparation steps of the (orthorhombic niobium pentoxide) are shown in figure 1; 0.1g of calcined material is added into a solution containing 50ml of ethanol and 20ml of deionized water, and ultrasonic treatment is carried out for 10min to form a suspension with good dispersibility. 0.02g of cetyltrimethylammonium bromide (CTAB) was weighed into the above suspension and stirred for 5 minutes. Then, 1ml of concentrated aqueous ammonia (mass fraction 28%) was added and stirred for 5 minutes. Finally, the solution will contain 0.05g ml^-110ml of ethyl silicate (TEOS) ethanol solution is slowly added into the suspension dropwise, and after 12 hours of stirring, the suspension is centrifuged, the solid is washed, and dried at 50 ℃.

The dried powder was calcined at 1050 ℃ for 5 h. Placing the calcined powder in a concentration of 3mol L^-150ml of sodium hydroxide (NaOH) solution and standing for 24 hours, then centrifuging, washing with solid deionized water and drying to obtain pure phase M-Nb₂O₅(A8)。

Preparing a half cell:

from Nb₂O₅The material (A8) was used as an electrode active material to prepare a half cell, and the preparation procedure and conditions were the same as in example 1.

The obtained A8 is pure phase M-Nb₂O₅The purity is more than 95 percent, and the rest is T-Nb₂O₅(ii) a The capacity can reach 295mAh g^-1Has stable cycle performance and ultrahigh rate performance.

The selected concentration of ethyl silicate (TEOS) compared to example 1Higher, the upper limit of experimental conditions, so that SiO is formed₂Thick coating layer, tetragonal phase M-Nb synthesized at 1050 DEG C₂O₅The crystallinity of (a) is slightly poor.

Comparative example 1

The starting material used in comparative example 1 was the starting material A1 prepared in example 1

Synthesis of sample material:

heating the raw material A1 to 800 ℃ from room temperature at a heating rate of 5 ℃/min in an Air (Air) atmosphere; keeping the temperature for heat treatment for 2h, and then cooling to room temperature at the speed of 10 ℃/min to obtain T-Nb₂O₅And M-Nb₂O₅Mixed phase (A9).

From Nb₂O₅The material (a9) was used as an electrode active material to prepare a half cell, and the preparation procedure and conditions were the same as in example 1.

As can be seen from the XRD results of FIG. 3, the obtained A9 is T-Nb₂O₅And M-Nb₂O₅Mixed phase, the molar ratio of the two contents is about 0.8: 0.2; the mixed phase ratio capacity is 230mAh g^-1Has poor circulation stability and rate capability, and has only 50mAhg at 20C rate^-1The specific capacity of (A).

Comparative example 2

The starting material used in comparative example 2 was the starting material A1 prepared in example 1

Synthesis of sample material:

heating the raw material A1 to 850 ℃ from room temperature at a heating rate of 5 ℃/min in an Air (Air) atmosphere; keeping the temperature for heat treatment for 2H, and then cooling to room temperature at the speed of 10 ℃/min to obtain H-Nb₂O₅And M-Nb₂O₅Mixed phase (A10).

From Nb₂O₅The material (a10) was used as an electrode active material to prepare a half cell, and the preparation procedure and conditions were the same as in example 1.

As can be seen from the XRD results of FIG. 3, the obtained A10 is M-Nb₂O₅And H-Nb₂O₅Mixed phase, the molar ratio of the two contents is about 0.6: 0.4; the mixed phase ratio capacity is 250mAh g^-1Tool for measuringHas poor circulation stability and rate capability, and has only 60mAhg at 20C rate^-1The specific capacity of (A).

Comparative example 3

The starting material used in comparative example 3 was the starting material A1 prepared in example 1

Synthesis of sample material:

heating the raw material A1 to 900 ℃ from room temperature at a heating rate of 5 ℃/min in an Air (Air) atmosphere; keeping the temperature for heat treatment for 2H, and then cooling to room temperature at the speed of 10 ℃/min to obtain H-Nb₂O₅(A11)。

From Nb₂O₅The material (a11) was used as an electrode active material to prepare a half cell, and the preparation procedure and conditions were the same as in example 1.

As can be seen from the XRD results of FIG. 3, the obtained A11 is H-Nb₂O₅And M-Nb₂O₅Mixed phase, the molar ratio of the two contents is about 0.8: 0.2; the mixed phase ratio capacity is 250mAh g^-1Has poor circulation stability and rate capability, and has only 60mAhg at 20C rate^-1The specific capacity of (A).

Comparative example 4

The starting material used in comparative example 4 was the starting material A1 prepared in example 1

Calcining the raw material A1 at 700 ℃ for 2h to obtain T-Nb₂O₅0.1g of calcined material is added into a solution containing 50ml of ethanol and 20ml of deionized water, and ultrasonic treatment is carried out for 10min to form a suspension with good dispersibility. 0.02g of cetyltrimethylammonium bromide (CTAB) was weighed into the above suspension and stirred for 5 minutes. Then, 1ml of concentrated aqueous ammonia (mass fraction 28%) was added and stirred for 5 minutes. Finally, the solution will contain 0.0008g ml^-110ml of ethyl silicate (TEOS) ethanol solution is slowly dripped into the suspension, stirred for 12 hours, centrifuged, washed and dried at 50 ℃. The dried powder was calcined at 1000 ℃ for 5 h. Placing the calcined powder in a concentration of 3mol L^-150ml of sodium hydroxide (NaOH) solution and standing for 24 hours, then centrifuging, washing by deionized water and drying to obtain H-Nb₂O₅And M-Nb₂O₅Mixed phase (A12) in mol ratioThe ratio is about 0.4: 0.6.

with mixed phases of Nb₂O₅Materials as electrode active materials half cells were prepared using the same procedure and conditions as in example 1.

The resulting mixed phase Nb₂O₅A12 specific capacity 270mAh g^-1Has poor circulation stability and rate capability, and has only 60mAhg at 20C rate^-1The specific capacity of (A).

Comparative example 5

The starting material used in comparative example 5 was the starting material A1 prepared in example 1

Synthesis of sample material:

calcining the raw material A1 at 700 ℃ for 2h to obtain T-Nb₂O₅0.1g of calcined material is added into a solution containing 50ml of ethanol and 20ml of deionized water, and ultrasonic treatment is carried out for 10min to form a suspension with good dispersibility. 0.02g of cetyltrimethylammonium bromide (CTAB) was weighed into the above suspension and stirred for 5 minutes. Then, 1ml of concentrated aqueous ammonia (mass fraction 28%) was added and stirred for 5 minutes. Finally, the solution will contain 0.015g ml^-110ml of ethyl silicate (TEOS) ethanol solution is slowly dripped into the suspension, stirred for 12 hours, centrifuged, washed and dried at 50 ℃. The dried powder was calcined at 800 ℃ for 5 h. Placing the calcined powder in a concentration of 3mol L^-150ml of sodium hydroxide (NaOH) solution and standing for 24 hours, then centrifuging, washing by deionized water and drying to obtain T-Nb₂O₅And M-Nb₂O₅Mixed phase (a13) in a molar ratio of about 0.5: 0.5. .

With mixed phases of Nb₂O₅Materials as electrode active materials half cells were prepared using the same procedure and conditions as in example 1.

The resulting mixed phase Nb₂O₅Its capacity is 220mAh g^-1Has poor circulation stability and rate capability, and has only 50mAhg at 20C rate^-1The specific capacity of (A). Comparative examples 1 to 5 are niobium pentoxide materials obtained by direct calcination without silica coating, and it can be seen from the XRD patterns that the direct calcination temperature was 900 ℃ or lower by adjusting the calcination temperatureSo that the synthesis gives a tetragonal phase of M-Nb₂O₅But also includes other crystalline phases, with very low purity. When the temperature is increased to over 900 ℃, pure phase H-Nb is obtained as shown by XRD pattern₂O₅A material.

The niobium pentoxide material obtained by calcining after being coated by silicon dioxide is subjected to regulation and control of preparation parameters and conditions to obtain the tetragonal phase M-Nb with the purity of more than 90 percent₂O₅The material is calcined at 950-1100 deg.c after coating silica layer, unlike the case of calcining without coating silica layer, and high purity tetragonal phase M-Nb can be obtained₂O₅The specific capacity of the material can reach 300Ah g when the material is used for lithium ion battery electrodes^-1And excellent cycle performance and rate performance are shown.

Although the present application has been described with reference to a few embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.

Claims (5)

1. A method for synthesizing tetragonal niobium oxide is characterized in that:

1) taking one or a mixture of two or a mixture of three of amorphous niobium oxide, pseudo-hexagonal niobium oxide and orthorhombic niobium oxide as a raw material, and coating a silicon dioxide layer on the outer surface of the raw material powder to obtain a raw material coated with the silicon dioxide layer;

2) calcining the raw material coated with the silica layer at 950-; soaking the calcined powder in 1-4mol L^-1(preferably 2mol L)^-1-3mol L^-1More preferably 3mol L^-1) Is added into sodium hydroxide (NaOH) solution for 12 to 48 hours (preferably 20 to 30 hours, more preferably 24 hours), then solid-liquid separation, washing and drying are carried out to obtain tetragonal niobium oxide M-Nb₂O₅。

2. A method of synthesis according to claim 1, characterized in that:

the process of wrapping the outer surface of the raw material in the step 1) with the silicon dioxide layer comprises the following steps: adding one or two or three mixture powders of amorphous niobium oxide, pseudo hexagonal niobium oxide and orthorhombic niobium oxide as raw materials into a mixed powder with the volume ratio of 4-8: 2 (preferably 5-7: 2) aqueous ethanol solution, wherein the mass (g) to volume (ml) ratio of the starting material to the aqueous ethanol solution is 0.05-1: 70 (preferably 0.1-0.2: 70); weighing Cetyl Trimethyl Ammonium Bromide (CTAB), adding into the suspension, and uniformly stirring, wherein the mass ratio of CTAB to the raw materials is 1:5-20 (preferably 1: 10-15, more preferably 1: 10); then adding the mixture into an ethanol water solution in a volume ratio of 1-3: ammonia water with the mass fraction of 25% -28% of 70 (preferably 1-2: 70, more preferably 1: 70) is evenly stirred; finally, the concentration is 0.001-0.05g ml^-1(preferably 0.008-0.015g ml)^-1) Dropwise adding ethyl orthosilicate (TEOS) ethanol solution into the solution, wherein the volume ratio of the ethyl orthosilicate ethanol solution to the ethanol aqueous solution is 1:5-20 (preferably 1:7-10, more preferably 1:7), stirring for 6-24 hours (preferably 10-24 hours), performing solid-liquid separation, and drying the solid to obtain the raw material coated with the silicon dioxide layer.

3. A method of synthesis according to claim 1, characterized in that:

A. the amorphous niobium oxide is synthesized by a hydrothermal method: reacting NbCl₅Adding the powder into benzyl alcohol; keeping the temperature at 180-220 ℃ for 12-48 hours, carrying out solid-liquid separation, and drying the solid to obtain amorphous niobium oxide; NbCl₅A mass (g) to volume (ml) ratio to benzyl alcohol of 0.1-0.5:18 (preferably 0.2-0.3:18, more preferably 0.24-0.25: 18);

or B, preparing one or two mixtures or three mixtures of amorphous niobium oxide, pseudo hexagonal niobium oxide and orthorhombic niobium oxide: and B, calcining the amorphous niobium oxide obtained in the step A at the temperature of 300-700 ℃ for 2-5h to obtain one or two or three of amorphous niobium oxide, pseudo-hexagonal niobium oxide and orthorhombic niobium oxide, which is called low-temperature calcined niobium oxide.

4. A synthesized tetragonal niobium oxide according to the synthesis method of any one of claims 1 to 3.

5. Use of the tetragonal niobium oxide of claim 4 as a negative active material in a lithium ion battery or a lithium ion capacitor.

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