Ferrous diselenide rod-like nanoflower nitrogen-doped carbon material and preparation method and application thereof

Abstract

The application provides a ferrous diselenide rod-shaped nanoflower nitrogen-doped carbon material and a preparation method and application thereof, and belongs to the technical field of battery materials. The prepared iron selenide presents a nanoflower structure composed of nanorods, and an outer layer is covered by a nitrogen-doped carbon shell, and is a kind of self-assembled nanoflower composite material. The nanoflower structure increases the specific surface area of the material, provides abundant active sites for catalysis, the nitrogen-doped carbon shell enhances the physical confinement of polysulfides and the transmission of electrons, there is a strong chemical bond between FeSe2 and polysulfides, which can effectively anchor polysulfides, and can accelerate the catalytic conversion of polysulfides and relieve the shuttle effect. The lithium-sulfur battery using the material as a positive active material has excellent cycle stability and high sulfur loading.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery materials, in particular to a ferrous diselenide rod-shaped nanoflower nitrogen-doped carbon material and a preparation method and application thereof. BACKGROUND

[0002] With the development of industry and society, human energy consumption is increasing, and global problems such as greenhouse effect and air pollution are frequent. Therefore, human beings need to develop clean energy, and due to the instability and intermittency of clean energy, it is necessary to convert it into stable and sustainable energy through energy storage and conversion devices.

[0003] At present, lithium ion batteries are the most common commercial secondary batteries. However, the theoretical specific capacity of lithium ion batteries is generally not more than 300 mAh·g -1 With the continuous maturity of technology, the specific capacity of lithium ion batteries has approached the theoretical limit, but still cannot meet the needs of industry, so we need to develop an electrochemical energy storage system with high specific energy, high safety factor and low cost. In comparison, lithium-sulfur batteries have more advantages, with a theoretical specific energy of 2600 Wh·kg -1 and a theoretical specific capacity of 1672 mAh·g -1 The high specific capacity and energy density of lithium-sulfur batteries show broad application prospects, but there are still many problems and challenges.

[0004] Shuttle effect: in the charging and discharging process, polysulfides undergo shuttle effect, generating insulating products Li2S at the negative electrode and adhering to the surface of lithium sheet to form a passivation film. The substances adhering to the lithium sheet cannot return to the positive electrode to be converted into S8 during charging, so the loss of active substances is irreversible, resulting in capacity attenuation of the battery.

[0005] Elemental sulfur and the final discharge product are both insulating, which reduces the separation rate of electrons and ions and increases the electrochemical reaction impedance.

[0006] Sulfur has a huge volume change during charging and discharging, which destroys the structure of the battery itself, causes pulverization, increases the resistance in the battery, and degrades the cycle performance of the battery.

[0007] In order to solve the above problems, many researchers often use carbon materials as the carrier of sulfur to improve the electronic conductivity, use the porous structure and heteroatom doping of carbon as a physical and chemical barrier to enhance the adsorption of polysulfides, but the anchoring of polysulfides alone cannot well inhibit the shuttle effect of polysulfides, and will affect the electrochemical reaction rate and reduce the utilization of active substances. SUMMARY

[0008] The application aims to provide a ferrous diselenide rod-shaped nanoflower nitrogen-doped carbon material, a preparation method thereof and application thereof, so as to solve the technical problems of poor electrochemical reaction performance and poor cycle performance of the existing lithium-sulfur battery.

[0009] In order to achieve the above-mentioned application purposes, the application provides the following technical solutions.

[0010] The application provides a preparation method of a FeSe2 rod-shaped nanoflower nitrogen-doped carbon material.

[0011] 1) ammonium iron sulfate, water and glucose are mixed to obtain an A solution;

[0012] 2) a hydrazine hydrate solution and selenium powder are mixed until the solution becomes dark red brown to obtain a B solution;

[0013] 3) the B solution is added to the A solution to perform a hydrothermal reaction to obtain a black powder sample;

[0014] 4) the black powder sample is subjected to heat treatment in a protective atmosphere to obtain the FeSe2 rod-shaped nanoflower nitrogen-doped carbon material.

[0015] Further, the molar volume ratio of the ammonium iron sulfate, water and glucose is 0.5-1.5 mmol: 15-25 mL: 3-5 mmol.

[0016] Further, the dosage ratio of the hydrazine hydrate solution and the selenium powder is 4-6 mL: 1.0-3.0 mmol, and the volume fraction of the hydrazine hydrate solution is 80-85%.

[0017] Further, the molar ratio of the ammonium iron sulfate and the selenium powder is 0.5-1.5: 1.0-3.0.

[0018] Further, in the step 3), the temperature of the hydrothermal reaction is 160-200 DEG C, and the time of the hydrothermal reaction is 8-12 h.

[0019] Further, in the step 4), the temperature of the heat treatment is 300-400 DEG C, the heating rate is 10-20 DEG C / min, and the time of the heat treatment is 2-3 h.

[0020] Further, in the step 4), the protective atmosphere is nitrogen, argon or helium.

[0021] The application provides a FeSe2 rod-shaped nanoflower nitrogen-doped carbon material.

[0022] The application also provides application of the FeSe2 rod-shaped nanoflower nitrogen-doped carbon material in a lithium-sulfur battery.

[0023] The application has the following beneficial effects:

[0024] The self-assembly constructs the nitrogen-doped rod-like nanoflower carbon material in the application, wherein the petal-like thin-layer carbon material structure can increase the specific surface area of the material, has the characteristics of high porosity and large specific surface area, can fully expose the adsorption and catalysis sites, and is beneficial to the uniform loading of nanoselemide, sufficient contact with polysulfide, shortening of the electron transfer path, and rich cross-linking network for providing physical blockage for polysulfide and high-speed channel for electron conduction. Meanwhile, the gap between the nanoflowers provides a fast channel for ion transport, and nitrogen doping converts non-polar carbon material into polar carbon material, converts the adsorption of polysulfide from physical adsorption to chemical adsorption, reduces the conversion energy barrier of polysulfide, and relieves the shuttle of polysulfide.

[0025] In the application, there is a strong interaction between FeSe2 and polysulfide, which has an anchoring effect on polysulfide and greatly reduces the decomposition energy barrier of polysulfide, accelerates the conversion of polysulfide, and has a dual synergistic effect of anchoring and accelerating catalysis of polysulfide. The interaction of Fe-S bonding and Se-Li bonding provides multiple adsorption sites, and the strong interaction between them can provide stronger capture ability of polysulfide.

[0026] Compared with the prior art, the FeSe2 rod-like nanoflower nitrogen-doped carbon material of the application also has the following advantages:

[0027] 1) The FeSe2 rod-like nanoflower nitrogen-doped carbon material of the application can realize dual synergism of anchoring and catalysis, can significantly relieve the shuttle of polysulfide during battery cycling, and shows excellent long cycle stability and rate performance, thereby improving the cycle life of lithium-sulfur batteries.

[0028] 2) The structure of the nitrogen-doped rod-like nanoflower carbon material of the application not only fully exposes the adsorption and catalysis sites, realizes uniform loading of the catalyst, and provides high-speed transmission channels for ions and electrons, but also further relieves the shuttle of polysulfide by converting the adsorption of polysulfide from physical adsorption to chemical adsorption.

[0029] 3) The FeSe2 itself has catalytic properties for sulfides. The interaction of Fe-S bonding and Se-Li bonding provides multiple adsorption sites, greatly reduces the decomposition energy barrier of polysulfide, accelerates the conversion of polysulfide, and realizes dual synergism of anchoring and catalysis. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the FeSe2 rod-like nanoflower nitrogen-doped carbon material prepared in Example 1 are shown in the figures, wherein (a) is the SEM image of FeSe2@NC, (b) is the enlarged SEM image, (c) is the low-magnification TEM, (d, e) are the enlarged TEM, and (f) is the HTEM image.

[0031] Figure 2 Long cycle performance chart of FeSe2@NC / S prepared for application example 1 at 1C;

[0032] Figure 3 100 cycle chart of FeSe2@NC / S prepared for application example 1 at 0.2C;

[0033] Figure 4 100 cycle chart of SP / S prepared for comparative example 1 at 0.2C;

[0034] Figure 5 Rate performance chart of FeSe2@NC / S prepared for application example 1;

[0035] Figure 6 Rate performance chart of SP / S prepared for comparative example 1. DETAILED DESCRIPTION

[0036] The application provides a preparation method of FeSe2 rod-shaped nanoflower nitrogen-doped carbon material, comprising the following steps:

[0037] 1) mixing ferric ammonium sulfate, water and glucose to obtain an A solution;

[0038] 2) mixing a hydrazine hydrate solution and selenium powder until the solution turns into dark red brown to obtain a B solution;

[0039] 3) adding the B solution into the A solution to perform a hydrothermal reaction to obtain a black powder sample;

[0040] 4) performing heat treatment on the black powder sample under a protective atmosphere to obtain the FeSe2 rod-shaped nanoflower nitrogen-doped carbon material.

[0041] In the application, the molar volume ratio of the ferric ammonium sulfate, water and glucose is 0.5-1.5 mmol: 15-25 mL: 3-5 mmol, preferably 0.8-1.2 mmol: 18-22 mL: 3.5-4.5 mmol, and further preferably 1.0 mmol: 20 mL: 4 mmol.

[0042] In the application, the amount ratio of the hydrazine hydrate solution and selenium powder is 4-6 mL: 1.0-3.0 mmol, preferably 5 mL: 2 mmol.

[0043] In the application, the volume fraction of the hydrazine hydrate solution is 80-85%, preferably 85%.

[0044] In the present application, the molar ratio of the ferric ammonium sulfate and selenium powder is 0.5-1.5:1.0-3.0, preferably 0.8-1.2:1.6-2.4, and further preferably 1.0:2.0.

[0045] In the present application, in the step 3), the temperature of the hydrothermal reaction is 160-200℃, preferably 170-190℃, and further preferably 180℃; the time of the hydrothermal reaction is 8-12h, preferably 9-11h, and further preferably 10h.

[0046] In the present application, in the step 4), the temperature of the heat treatment is 300-400℃, preferably 320-380℃, and further preferably 350℃; the heating rate is 10-20℃ / min, preferably 12-18℃ / min, and further preferably 15℃ / min; the time of the heat treatment is 2-3h, preferably 2.5h.

[0047] In the present application, in the step 4), the protective atmosphere is nitrogen, argon or helium, preferably nitrogen.

[0048] The present application provides a FeSe2 rod-like nanoflower nitrogen-doped carbon material.

[0049] The present application also provides an application of the FeSe2 rod-like nanoflower nitrogen-doped carbon material in a lithium-sulfur battery.

[0050] The technical solutions provided by the present application will be described in detail below in conjunction with the embodiments, but they should not be understood as limiting the scope of protection of the present application.

[0051] Example 1

[0052] Preparation of the FeSe2 rod-like nanoflower nitrogen-doped carbon material:

[0053] I. 1mmol of ferric ammonium sulfate was weighed and dissolved in 20mL of deionized water, and 4mmol of glucose was added and stirred until completely dissolved to prepare an A solution. II. 5mL of a hydrazine hydrate solution (85%) was transferred to a beaker with a pipette, and 2mmol of selenium powder was weighed and slowly added to the hydrazine hydrate solution while stirring, and the stirring was continued for 30min until the solution turned dark red brown to prepare a B solution. III. The B solution was slowly added to the A solution while continuously stirring until the mixture was uniformly mixed, and a hydrothermal method was used to heat treat at 160℃ for 10h to finally obtain a black precipitate, which was washed and dried to collect a black powder sample. IV. The black powder was placed in a tube furnace and heated to 350℃ at a heating rate of 20℃ / min under nitrogen protection for 2h to finally obtain a FeSe2 rod-like nanoflower nitrogen-doped carbon material (FeSe2@NC).

[0054] Example 2

[0055] Preparation of FeSe2 rod-shaped nanoflower nitrogen-doped carbon material:

[0056] One, weigh 1 mmol of ferric ammonium sulfate, dissolve in 20 mL of deionized water, and add 3 mmol of glucose to stir until completely dissolved to prepare solution A. Two, use a pipette to transfer 5 mL of hydrazine hydrate solution (85%) into a beaker, weigh 2 mmol of selenium powder, slowly add the hydrazine hydrate solution while stirring, continue stirring for 30 min until the solution turns dark reddish brown to prepare solution B. Three, slowly add solution B to solution A while continuously stirring until the mixture is uniform, use hydrothermal method to heat treat at 180℃ for 8h, finally obtain black precipitate, wash and dry, collect black powder sample. Four, place the black powder in a tube furnace, under nitrogen protection, heat to 380℃ at a heating rate of 15℃ / min, keep for 2h, finally obtain FeSe2 rod-shaped nanoflower nitrogen-doped carbon material (FeSe2@NC).

[0057] Example 3

[0058] Preparation of FeSe2 rod-shaped nanoflower nitrogen-doped carbon material:

[0059] One, weigh 1 mmol of ferric ammonium sulfate, dissolve in 20 mL of deionized water, and add 3 mmol of glucose to stir until completely dissolved to prepare solution A. Two, use a pipette to transfer 5 mL of hydrazine hydrate solution (85%) into a beaker, weigh 2 mmol of selenium powder, slowly add the hydrazine hydrate solution while stirring, continue stirring for 30 min until the solution turns dark reddish brown to prepare solution B. Three, slowly add solution B to solution A while continuously stirring until the mixture is uniform, use hydrothermal method to heat treat at 180℃ for 8h, finally obtain black precipitate, wash and dry, collect black powder sample. Four, place the black powder in a tube furnace, under nitrogen protection, heat to 380℃ at a heating rate of 15℃ / min, keep for 2h, finally obtain FeSe2 rod-shaped nanoflower nitrogen-doped carbon material (FeSe2@NC).

[0060] Application Example 1

[0061] Preparation of lithium-sulfur battery positive electrode active material:

[0062] Sublimed sulfur and FeSe2@NC of Example 1 are weighed in a mortar in a weight ratio of 6:4 and ground for 20 min to mix uniformly. The mixed powder is placed in a reaction kettle under an argon protective atmosphere, kept at 155℃ for 12h, and then naturally cooled to room temperature to obtain FeSe2@NC / S material for use as a positive electrode material.

[0063] Application Example 2

[0064] Preparation of lithium-sulfur battery positive electrode sheet, assembly of lithium-sulfur battery full cell, and testing.

[0065] Preparation of lithium-sulfur battery positive electrode sheet: The above-mentioned sulfur positive electrode material (FeSe2@NC / S) and conductive carbon black (Super P), PVDF were weighed in turn according to the mass ratio of 8:1:1, and an appropriate amount of NMP solution was added. After mixing and stirring to uniform slurry, the mixed uniform paste slurry was coated on the surface of the current collector aluminum foil with a scraper. Then it was transferred to a vacuum oven at 60℃ for 12h, and after drying, it was taken out and made into a 12mm diameter circle sheet as a positive electrode with a puncher. FeSe2@C / S positive electrode sheet was prepared.

[0066] Comparative Example 1

[0067] Preparation of conventional carbon black-sulfur positive electrode active material:

[0068] Sublimed sulfur and Super-P (carbon black) were weighed in a mortar at a weight ratio of 6:4 and ground for 20min to mix uniformly. The mixed powder was placed in a reaction kettle under an argon protective atmosphere, kept at 155℃ for 12h, and then naturally cooled to room temperature to obtain SP / S material for use as a positive electrode material.

[0069] Comparative Example 2

[0070] Preparation of lithium-sulfur battery positive electrode sheet: The above-mentioned sulfur positive electrode material (SP / S) and conductive carbon black (Super P), PVDF were weighed in turn according to the mass ratio of 8:1:1, and an appropriate amount of NMP solution was added. After mixing and stirring to uniform slurry, the mixed uniform paste slurry was coated on the surface of the current collector aluminum foil with a scraper. Then it was transferred to a vacuum oven at 60℃ for 12h, and after drying, it was taken out and made into a 12mm diameter circle sheet as a positive electrode with a puncher. SP / S positive electrode sheet was prepared.

[0071] Full battery performance test of the positive electrode sheets obtained in Comparative Example 2 and Example 2: The lithium-sulfur battery was tested for cycle performance and rate performance on a Blue Electric CT-2001A battery system, with a charge-discharge voltage range of 1.7 to 2.8V. The assembled lithium-sulfur battery was tested for 300 cycles at a 1C rate, 100 cycles at a 0.2C rate, and rate performance tests were conducted at current densities of 0.2, 0.5, 1.0, 2.0 and 3.0C, respectively.

[0072] Figure 1 are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the FeSe2 rod-like nanoflower nitrogen-doped carbon material of Example 1 at different magnifications. It can be seen that the prepared iron selenide presents a nanoflower structure composed of nanorods (a), and from the large-scale SEM image (b), it can be seen that the size and distribution of the FeSe2@NC nanoflower are relatively uniform. The diameter of the nanorod is about 40nm as measured in the enlarged SEM image. TEM was used to further characterize the microstructure of FeSe2@NC, as shown inFigure 1 As shown in Figure c, the nanorods can be seen growing tightly together. Upon magnification, the nanorods become clearly visible (see Figure c). Figure 1 d), corresponding to the SEM image. The HTEM image is as follows: Figure 1 As shown in Figure e, the carbon shell encapsulating iron selenide can be clearly seen, and the measured lattice size is approximately 0.25 nm.

[0073] Figure 2 The image shows the long-cycle performance curve of a lithium-sulfur battery assembled using the FeSe2 rod-shaped nanoflower nitrogen-doped carbon material as the active material sulfur carrier in Example 1 at room temperature, after 300 cycles at a 1C rate. The capacity remained stable at 584.1 mAh·g after 300 cycles at a 1C current density. -1 The capacity retention rate was close to 100%, which confirms the excellent cycling stability of the FeSe2@NC / S electrode.

[0074] Figure 3 In Application Example 2, the nitrogen-doped carbon material of the present invention, FeSe2 rod-shaped nanoflowers, is used as a carrier for the active substance sulfur to jointly form the cathode material. Figure 4 Carbon black was used as a sulfur carrier to form the positive electrode material. A lithium sheet was used as the negative electrode in the lithium-sulfur battery, and the same PP separator was used to assemble a lithium-sulfur full cell. The cells were cycled 100 times at a rate of 0.2C. It can be seen that the initial capacity of the lithium-sulfur battery assembled using the positive electrode sheet from Example 2 is 1223.4 mAh·g. -1 After 100 cycles, the capacity still remains at 1039.3 mAh·g. -1 The corresponding capacity retention rate is 84.9%. In contrast, the lithium-sulfur battery assembled with the positive electrode in Comparative Example 2 has a discharge capacity of only 912.4 mAh·g at a current density of 0.2C. -1 After 100 cycles, the capacity is 615.0 mAh·g. -1 The capacity retention rate was only 67.4%. Comparative analysis shows that the sulfur carrier of this invention significantly improves the utilization rate of active materials and cycle stability.

[0075] Figure 5 and Figure 6 Lithium-sulfur full cells were assembled using the same method described above, and the rate performance of FeSe2@NC / S and SP / S at different current densities was compared. The discharge specific capacities of FeSe2@NC / S at current densities of 0.2, 0.5, 1.0, 2.0, and 3.0 C were 1122.0, 901.9, 899.7, 695.8, and 495.3 mAh·g, respectively. -1 After cycling, the current density returned to 0.2C, while the capacity remained at 1017.0 mAh·g. -1 The SP / S specific capacity at 3C current density is only 225.7 mAh·g.-1 When the current density jumps back to 0.2C, the discharge specific capacity is only 668.7 mAh·g -1 The rate performance results show that, compared with SP, FeSe2@NC is more conducive to improving the rate performance of lithium-sulfur batteries, indicating the excellent catalytic ability of FeSe2@NC. It can be predicted that the sulfur-carrier carbon material of the application has certain fast-charging ability and certain practical application value.

[0076] From the above examples, the application provides a ferrous diselenide rod-shaped nanoflower nitrogen-doped carbon material, a preparation method and application thereof. The prepared iron selenide presents a nanoflower structure composed of nanorods, and an outer layer is coated with a nitrogen-doped carbon shell, which is a kind of self-assembled nanoflower composite material. The nanoflower structure increases the specific surface area of the material, provides abundant active sites for catalysis, the nitrogen-doped carbon shell enhances the physical confinement of polysulfides and the transmission of electrons, there is a strong chemical bond between FeSe2 and polysulfides, which can effectively anchor polysulfides, and at the same time, can accelerate the catalytic conversion of polysulfides and relieve the shuttle effect. The lithium-sulfur battery using the material as a positive active material has excellent cycle stability and high sulfur loading.

[0077] The above description is only the preferred embodiments of the application, and it should be pointed out that, for ordinary skilled in the art, without departing from the principles of the application, a number of improvements and refinements can be made, and these improvements and refinements should be considered as the protection scope of the application.

Claims

1. A method for preparing FeSe2 rod-shaped nanoflower nitrogen-doped carbon material, characterized in that, Includes the following steps: 1) Mix ferric ammonium sulfate, water, and glucose to obtain solution A; 2) Mix hydrazine hydrate solution and selenium powder until the solution turns dark reddish-brown to obtain solution B; 3) Solution B was added to solution A to carry out a hydrothermal reaction, resulting in a black powder sample; 4) The black powder sample was heat-treated under a protective atmosphere to obtain FeSe2 rod-shaped nanoflower nitrogen-doped carbon material; The molar volume ratio of ammonium ferric sulfate, water, and glucose is 0.5~1.5 mmol: 15~25 mL: 3~5 mmol; The ratio of hydrazine hydrate solution to selenium powder is 4-6 mL: 1.0-3.0 mmol, and the volume fraction of the hydrazine hydrate solution is 80-85%. The molar ratio of ammonium ferric sulfate to selenium powder is 0.5~1.5:1.0~3.0; In step 4), the heat treatment temperature is 300~400℃, the heating rate is 10~20℃ / min, and the heat treatment time is 2~3h.

2. The preparation method according to claim 1, characterized in that, In step 3), the hydrothermal reaction temperature is 160~200℃ and the hydrothermal reaction time is 8~12h.

3. The preparation method according to claim 1 or 2, characterized in that, In step 4), the protective atmosphere is nitrogen, argon, or helium.

4. The FeSe2 rod-shaped nanoflower nitrogen-doped carbon material prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the FeSe2 rod-shaped nanoflower nitrogen-doped carbon material according to claim 4 in lithium-sulfur batteries.

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