CN113860271A

CN113860271A - Oxygen-doped TaN nanosheet and application thereof

Info

Publication number: CN113860271A
Application number: CN202111040332.9A
Authority: CN
Inventors: 杨硕; 张永贵; 蔡冬; 于爽; 梁策; 聂华贵; 杨植
Original assignee: Wenzhou University
Current assignee: Wenzhou University
Priority date: 2021-09-06
Filing date: 2021-09-06
Publication date: 2021-12-31

Abstract

The invention relates to the technical field of electrochemical materials, in particular to an oxygen-doped tantalum nitride (TaN) nanosheet and application thereof. The preparation method of the oxygen-doped TaN nanosheet comprises the following steps: preparing TaN nanosheets from TaN serving as a raw material; and (3) placing the TaN nanosheet in an alkaline solution for etching to obtain the oxygen-doped TaN nanosheet. Compared with bulk TaN, the oxygen-doped TaN nanosheet provided by the invention has stronger adsorption capacity on polysulfide, Ta in the material can generate strong chemical interaction with S in the polysulfide through Ta-S bonds, and the material shows extremely strong Li under the condition of oxygen doping₂S₆And (4) adsorption. The use of the lithium sulfur battery positive electrode can significantly improve the battery performance.

Description

Oxygen-doped TaN nanosheet and application thereof

Technical Field

The invention relates to the technical field of electrochemical materials, in particular to oxygen-doped TaN nanosheets and application thereof.

Background

Due to exhaustion of non-renewable resources such as coal and petroleum and indirect nature of renewable resources such as solar energy and wind energy, secondary batteries have attracted attention as an energy storage means. Among them, the lithium-sulfur battery has 1675 mAh g⁻¹Is considered to be the most promising next generation high energy storage battery. Shuttle Effect, however, Sulfur/lithium sulfide (S)₈/Li₂S), volume change of sulfur during charge and discharge, etc. have hindered further commercialization of lithium-sulfur batteries.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide oxygen-doped TaN nanosheets and application thereof.

The technical scheme adopted by the invention is as follows: an oxygen-doped TaN nanosheet, and a preparation method thereof comprises the following steps: preparing TaN nano-sheets by taking tantalum nitride as a raw material; and (3) placing the TaN nanosheet in an alkaline solution for etching to obtain the oxygen-doped TaN nanosheet.

And putting the tantalum nitride in an NMP solution for ultrasonic treatment to obtain the TaN nanosheet.

And (3) placing the tantalum nitride in an NMP solution, performing probe ultrasonic treatment under an ice bath condition, centrifuging to obtain an upper suspension containing the TaN nanosheets, and then removing a liquid part to obtain the TaN nanosheets.

The alkaline solution is a potassium hydroxide NMP solution.

The oxygen-doped TaN nanosheet is applied to preparation of a positive electrode material of a lithium-sulfur battery.

A lithium sulfur battery containing a positive electrode material comprising therein oxygen-doped TaN nanoplates as described above.

The invention has the following beneficial effects: compared with bulk TaN, the oxygen-doped TaN nanosheet provided by the invention has stronger adsorption capacity on polysulfide, Ta in the material can generate strong chemical interaction with S in the polysulfide through Ta-S bonds, and the material shows extremely strong Li under the condition of oxygen doping₂S₆And (4) adsorption. The use of the lithium sulfur battery positive electrode can significantly improve the battery performance.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is within the scope of the present invention for those skilled in the art to obtain other drawings based on the drawings without inventive exercise.

FIGS. 1 (a, d-e) TEM images of TN-O NSs, (b) TaN NSs and (c) bulk TaN; HRTEM images of (f-g) TN-O NSs, (h) TaN NSs, and (i) bulk TaN;

FIG. 2 HRTEM image of TN-O NSs and its corresponding elemental map;

FIG. 3 (a) HRTEM image of TaN NSs and (b) bulk TaN and their corresponding elemental maps;

FIG. 4 Raman spectra of bulk TaN, TaN NSs and TN-O NSs;

FIG. 5 Infrared spectra of bulk TaN, TaN NSs and TN-O NSs;

FIG. 6 XRD of bulk TaN, TaN NSs and TN-O NSs;

FIG. 7 high resolution XPS spectra of (a) N1 s and (b) Ta 4f for bulk TaN, TaN NSs, TN-O NSs (half-sat.);

FIG. 8 illustrates (a) rate capability and (b) charge-discharge plateau of the second cycle at 0.2C for bulk TaN/CNTs-S, TaN NSs/CNTs-S, TN-O NSs (half-sat.)/CNTs-S and TN-O NSs/CNTs-S anodes;

FIG. 9 (a) bulk TaN/CNTs-S, TaN NSs/CNTs-S, TN-O NSs (semi-saturated)/CNTs-S and TN-O NSs/CNTs-S positive electrode (sulfur load of 0.8 mg cm)⁻²) Cycling performance at 1C. (b) TN-O NSs/CNTs-S positive electrode (sulfur loading 4.0 mg cm)⁻²) Cycling performance at 0.1C;

FIG. 10 Li₂S₈The constant potential discharge curve of the tetraglycol dimethyl ether solution in (a) TN-O NSs/CNTs, (b) TN-O NSs (half-sat.)/CNTs, (c) TaN NSs/CNTs and (d) bulk TaN/CNTs positive electrodes;

FIG. 11 Li of bulk TaN, TaN NSs and TN-O NSs₂S₆Adsorption test, the adsorption time is 12 h;

FIG. 12 is at Li₂S₆After adsorption experiments, (a) S2 p, (b) N1S and (c) Ta 4f high-resolution XPS spectra of bulk TaN, TaN NSs and TN-O NSs;

FIG. 13 (a-d) quasi-in-situ Li 1S, N1S, and S2 p XPS spectra after discharge of TN-O NSs/CNTs-S anodes to a specified state and (e-f) quasi-in-situ Li 1S and N1S XPS spectra after discharge of bulk TaN/CNTs-S anodes to a specified state: fully charged at 2.8V, discharged to 2.1V, discharged to 1.6V.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings.

The invention provides an oxygen-doped TaN nanosheet, and a preparation method thereof comprises the following steps: preparing TaN nano sheets (TaN NSs) by taking tantalum nitride (TaN) as a raw material; and (3) placing the TaN nanosheet in an alkaline solution for etching to obtain the oxygen-doped TaN nanosheet (TN-O NSs). The Raman, FTIR, XRD and XPS characterization proves that oxygen atoms are successfully introduced into the TaN nanosheets after alkali etching. TEM also shows the introduction of TaN nanosheet edge defect structure. In electrochemical tests, the TN-O NSs/CNTs-S positive electrode shows excellent rate performance and long cycle stability, and in some embodiments of the invention, the specific capacity of the prepared oxygen-doped TaN nano sheet is kept at 500 mAh g after 500 cycles at 1C⁻¹Above, the capacity attenuation per cycle is as low as 0.093%. At 4.0 mg cm⁻²At a high sulfur loading of (2), the battery can be operated at 0.1CProviding 786 mAh g⁻¹After the 150 th cycle, 634 mAh g was still maintained⁻¹The improvement effect of oxygen doping and defect structure introduction on the performance of the battery is verified. Through an adsorption experiment and XPS, the internal mechanism of the battery is further analyzed, and the fact that TN-O NSs can generate strong chemical adsorption on polysulfide through Ta-S bonds is found, so that a shuttle effect is inhibited, and the utilization rate of active substances is improved.

Example 1:

(1) taking a proper amount of block TaN in NMP solution with the solid-to-liquid ratio of 3 mg mL⁻¹Carrying out probe ultrasonic treatment on the solution for 10 h under the ice bath condition, centrifuging for 30 min at 1000 rpm, removing large-size particles at the bottom, enriching the upper suspension at 10000 rpm to obtain the ultrasonically treated TaN nanosheet (TaN NSs), stirring and etching the TaN nanosheet in an NMP solution of saturated potassium hydroxide for 4 h, and then washing the solution to be neutral by using pure NMP to obtain the oxygen-doped TaN nanosheet (TN-O NSs).

(2) Sulfur powder was mixed homogeneously with multi-walled Carbon Nanotubes (CNTs) by grinding in a mass ratio of 7: 3. The resulting mixture is dissolved in carbon disulfide (CS)₂) Stirring for 12 h, then heating in a vacuum oven at 155 ℃ for 12 h to allow the sulfur to melt sufficiently to diffuse into the CNTs and form CNTs-S composites. The sulfur content of the CNTs-S composite material is controlled to be about 70 percent. Subsequently, a NMP solution was added to a formed slurry of 80% CNTs-S composite, 5% polyvinylidene fluoride (PVDF), 14% conductive agent, and 1% TN-O NSs. After stirring for 4 h, the slurry was coated on aluminum foil and dried in a vacuum oven at 55 ℃ overnight, and the dried aluminum foil was punched into a circular positive plate with a diameter of 14 mm, which was designated as TN-O NSs/CNTs-S composite. The sulfur loading of the positive electrode at low areal density was 0.8 mg cm⁻²The sulfur loading of the positive electrode at high areal density was 4.0 mg cm⁻²。

(3) And assembling the CR2025 button cell in an argon-filled glove box by taking TN-O NSs/CNTs-S as a positive electrode, metal lithium as a negative electrode and polypropylene as a diaphragm.

Example 2:

(1) taking a proper amount of block TaN in NMP solution, and fixingThe liquid ratio is 3 mg mL⁻¹Ultrasonically treating the solution for 10 h under an ice bath condition by a probe, centrifuging for 30 min at 1000 rpm, removing large-size particles at the bottom, enriching the upper suspension at 10000 rpm to obtain ultrasonically treated TaN NSs, respectively stirring and etching the TaN nanosheets in a semi-saturated potassium hydroxide NMP solution for 4 h, and then washing the TaN nanosheets to be neutral by pure NMP to obtain oxygen-doped TaN nanosheets (TN-O NSs (half-sat)).

(2) The sulfur powder and the multi-walled carbon nanotubes were mixed uniformly by grinding in a mass ratio of 7: 3. The resulting mixture is dissolved in carbon disulfide (CS)₂) Stirring for 12 h, then heating in a vacuum oven at 155 ℃ for 12 h to allow the sulfur to melt sufficiently to diffuse into the CNTs and form CNTs-S composites. The sulfur content of the CNTs-S composite material is controlled to be about 70 percent. Subsequently, a NMP solution was added to a formed slurry of 80% CNTs-S composite, 5% polyvinylidene fluoride (PVDF), 14% conductive agent, and 1% TN-O NSs (half-sat.). After stirring for 4 h, the slurry was coated on an aluminum foil and dried in a vacuum oven at 55 ℃ overnight, and the dried aluminum foil was punched into a circular positive plate having a diameter of 14 mm, which was designated as TN-O NSs (half-sat.)/CNTs-S composite material. The sulfur loading of the positive electrode at low areal density was 0.8 mg cm⁻²The sulfur loading of the positive electrode at high areal density was 4.0 mg cm⁻²。

(3) The CR2025 button cell is assembled in an argon-filled glove box by taking TN-O NSs (half-sat.)/CNTs-S as a positive electrode, metal lithium as a negative electrode and polypropylene as a diaphragm.

Comparative example 1:

the same steps are adopted to prepare the TaN/CNTs-S composite material by utilizing the bulk TaN, and then the composite material is assembled into the CR2025 button cell.

Comparative example 2:

the same steps are adopted to prepare TaN NSs/CNTs-S composite material by utilizing TaN NSs, and then the composite material is assembled into a CR2025 button cell.

The following are the morphology and structure characterization results for the different materials:

the morphology of TN-O NSs, TaN NSs and bulk TaN was observed with TEM. As shown in FIGS. 1a-c, the sizes of TaN NSs and TN-O NSs are significantly reduced after ultrasonic and etching treatment; in addition, it can be seen that after the alkali etching treatment, the morphology of TN-O NSs is greatly changed, and the TN-O NSs is converted into a linear structure from a block structure, while the TaN NSs which is not subjected to the alkali etching treatment has no obvious change in morphology except for size reduction; on a further magnification, as shown in FIGS. 1d and e, it can be seen that the linear TN-O NSs surface has a large number of point defect structures, and FIG. 1f shows that these points are small grains with lattice fringes. Furthermore, HRTEM images of the thicker edge of TN-O NSs line structure showed polycrystalline structure with lower crystallinity (FIG. 1 g), which is very different from the single crystal structure of TaN NSs and bulk TaN (FIG. 1h, i). Since such a linear structure can increase the specific surface area of the material, in combination with its defect-rich structure, it is expected to provide more active sites for the adsorption and catalysis of polysulfides, and it is therefore surmised that the introduction of such a structure can optimize the performance of the material in a lithium-sulfur battery.

Analysis of the elemental distribution in TN-O NSs, TaN NSs and bulk TaN (FIGS. 2 and 3) shows that after the alkali etching treatment, oxygen is introduced into TN-O NSs and uniformly distributed on the linear material, indicating that part of oxygen atoms are introduced into the material during the preparation process. The above characterization shows that the linear TaN nano material rich in oxygen defects is successfully prepared after probe ultrasonic and alkali etching treatment, and the introduction of the linear structures and oxygen elements can increase the active sites of the material, hopefully improve the physical and chemical properties of the material, and show excellent catalytic performance in the electrochemical field.

The Raman spectrum of the material is shown in FIG. 4, and the Raman peak of bulk TaN is from 50 cm to 200 cm⁻¹And 400-750 cm⁻¹The first order optical band (O); the Raman peak of the TaN NSs almost disappears, which is probably caused by the reduction of the Raman peak intensity along with the reduction of the size and the thickness of the sample, and the successful preparation of the TaN NSs is also verified from the side; notably, the Raman spectrum of TN-O NSs was at 660 cm⁻¹A new peak appears, which can be assigned to the raman peak of tantalum oxide. FTIR spectra of the materials are shown in FIG. 5, and bulk TaN has FTIR spectra of 667, 706 cm⁻¹Respectively exist one at each positionPeaks, which can be attributed to TA-N bonds in TaN, corresponding to the second order mode (O-A), first order optical band, respectively, in Raman spectrA; FTIR spectra of TN-O NSs at 832, 925 cm⁻¹Two new peaks appear at the site, which can be attributed to Ta-O bonds; 1025 cm⁻¹The new peak at (A) can be assigned to Ta-N-O. XRD of the sample As shown in FIG. 6, XRD peaks of bulk TaN and TaN PDF #74-0226 and TaN_0.43The PDF #71-0265 standard cards are consistent, which shows that the sample is of a polycrystalline structure; after ultrasonic treatment, the original XRD peak of the sample is still kept, which indicates that the original crystal structure of the sample is kept; in contrast, the TN-O NSs sample showed a new peak at 24.2 deg., which is consistent with the strong peak in the TaON PDF #72-2067 standard card, probably due to the introduction of oxygen during the alkaline etching of the material.

The XPS spectra of N1 s and Ta 4f of four samples of bulk TaN, TaN NSs, TN-O NSs (half-sat.), and TN-O NSs are shown in FIG. 7, the Ta 4f spectrum of bulk TaN has two pairs of peaks at 26.4/28.3 eV and 24.2/26.2 eV, and the two pairs of peaks can be respectively assigned as Ta in TaN_x−N_yA Ta-N bond; the N1 s spectrum of bulk TaN has two peaks at 403.6 eV and 396.5 eV, which can be respectively assigned to Ta 4p of TaN_3/2And a N-Ta bond. After the alkali etching treatment, Ta-O, N-O peaks appear at 24.8/26.7 eV and 400.0 eV in the spectrograms of Ta 4f and N1 s respectively, which shows that oxygen atoms are introduced into TaN after the alkali etching, and the results are consistent with the previous characterization results of Raman, FTIR, XRD and the like. Ta of TN-O NSs compared to bulk TaN_x−N_yTa-N peak shift to lower binding energy, and Ta 4p_3/2The N-Ta peak moves to higher binding energy, and the peak position movement indicates the reduction of Ta valence and the increase of N valence under strong electronegative oxygen doping; in addition, the intensity of these peaks was reduced after the introduction of oxygen, which is presumably because the Ta-N peak was reduced and the Ta-O, N-O peak appeared during the alkali etching due to the substitution of nitrogen in TaN by the introduced oxygen. Compared with TN-O NSs (half-sat.), the peak of N-O, Ta-O in N1 s and Ta 4f of TN-O NSs is stronger, which shows that the material is stronger in etching and more oxygen defects are introduced under stronger alkaline conditions, and shows that the etching degree can be regulated and controlled by the concentration of the alkaline solution.

In conclusion, the oxygen-doped TaN nanosheet prepared by the method introduces oxygen atoms and nanosheet edge defects in the alkali etching process.

The electrochemical performance results of the above materials are as follows:

as shown in FIG. 8a, at a rate of 0.2C, the cell with TN-O NSs/CNTs-S positive electrode provided 1221 mAh g⁻¹High specific capacity of (a); the current density is improved to 0.5C, 0.7C and 1C, and the specific capacity of the TN-O NSs/CNTs-S anode is 959 mAh g⁻¹、884 mAh g⁻¹And 817 mAh g⁻¹(ii) a When the current density returns to 0.2C, 978 mAh g can be recovered⁻¹The high specific capacity of the composite material further proves that the TN-O NSs/CNTs-S positive electrode has good capacity reversibility and stability. In contrast, at the same rate, the specific capacity of bulk TaN/CNTs-S, TaN NSs/CNTs-S and TN-O NSs (half-sat.)/CNTs-S anodes is much lower. In FIG. 8b, the constant current charge-discharge curve for TN-O NSs/CNTs-S anode at 0.2C shows two longer and flatter plateaus, which is consistent with the multi-step reduction of sulfur. Compared with two anodes of TaN/CNTs-S and TaN NSs/CNTs-S, the potential difference between the charge and discharge platforms of TN-O NSs/CNTs-S is much smaller, and the lower polarization of the TN-O NSs/CNTs-S anode is proved again. The excellent rate capability of the TN-O NSs/CNTs-S anode can benefit from abundant polysulfide adsorption and catalytic active centers, and is beneficial to improving the utilization rate of sulfur, slowing down a shuttle effect and accelerating the kinetics of sulfur species redox reaction.

In addition, the TN-O NSs/CNTs-S positive electrode also has good cycle stability. As shown in FIG. 9a, after 500 cycles at 1C, the specific capacity of the TN-O NSs/CNTs-S positive electrode was maintained at 500 mAh g⁻¹The volume attenuation rate per circle is as low as 0.093%, which is superior to bulk TaN/CNTs-S and TaN NSs/CNTs-S, TN-O NSs (half-sat.)/CNTs-S positive electrodes. It is well known that positive electrode sulfur loading is a key factor affecting the practical application of lithium sulfur batteries. Therefore, the positive electrode of TN-O NSs/CNTs-S is at 4.0 mg cm⁻²Further cycling at high sulfur loading, as shown in FIG. 9b, the cell with TN-O NSs/CNTs-S positive electrode still provided 786 mAh g at 0.1C⁻¹Is highInitial capacity, 634 mAh g was maintained after cycle 150⁻¹Indicating its excellent cycling stability at high sulfur loading.

On different substrates to Li in tetraethyl ether solution₂S₈Carrying out Li₂S potentiostatic discharge deposition to elucidate TN-O NSs vs Li₂Catalysis of the S precipitation. As shown in FIG. 10, first, constant current discharge is performed to 2.06V, consuming most of the long-chain polysulfide, and then Li is driven by 0.02V overpotential₂Nucleation and growth of S. According to the mass of sulfur in the electrolyte, calculating to obtain Li on the TN-O NSs/CNTs electrode₂S deposition capacity 180.24 mAh g_(s) ⁻¹And TN-O NSs (half-sat.)/CNTs, TaN NSs/CNTs and Li on bulk TaN/CNTs electrodes₂The S deposition capacities were 167.61 mAh g, respectively_(s) ⁻¹、136.36 mAh g_(s) ⁻¹And 130.7 mAh g_(s) ⁻¹And is far lower than TN-O NSs/CNTs electrodes, which shows the high catalytic activity of TN-O NSs. Furthermore, in the above four electrodes, TN-O NSs/CNTs was vs Li₂The S nucleation has the fastest response speed, the largest current peak value and the highest current density. These results indicate that TN-O NSs can significantly reduce Li₂Initial overpotential of S nucleation to promote subsequent Li₂S deposition kinetics. This fast Li₂S deposition behavior is critical to improve the capacity and stability of lithium sulfur batteries, especially during rapid charging and discharging.

To understand the mechanism of action of TN-O NSs and polysulfides and the mechanism of catalytic conversion of polysulfides inside the cell, adsorption experiments and XPS analysis were further developed, as shown in FIGS. 11 and 12. As can be seen from the adsorption experiments, under the same experimental conditions, the supernatant of the TN-O NSs material has the lightest color, indicating that TN-O NSs is opposite to Li₂S₆The strongest adsorption effect can be seen according to the color of the supernatant, and the material has Li pair effect₂S₆The adsorption strength of the following components in sequence from strong to weak: TN-O NSs>TaN NSs>Bulk TaN, which corresponds to the electrochemical performance in fig. 8 and 9.

The XPS spectrum of the material after the adsorption experiment is shown in FIG. 12. High at S2 pIn resolving XPS spectra (FIG. 12 a), a broad peak around 167 eV can be assigned as Li₂S₆And Li during the test₂S₆The peak generated by oxidation is weaker in bulk TaN compared with TaN NSs and TN-O NSs, and indicates that the surface of the bulk TaN material only has a small amount of Li₂S₆Adsorbed, indicating a weak adsorption of polysulfides. The peak near 161 eV can be attributed to Ta-S bond generated by the action of the material and polysulfide, and the peak in TN-O NSs is slightly shifted to high field, possibly caused by the influence of strong electronegative oxygen on Ta-S in the material^[112]。

In the N1 s high resolution XPS spectrum (FIG. 12 b), there was no significant difference between bulk TaN after adsorption of polysulfide and before adsorption (FIG. 7), mainly from 404 cm⁻¹Ta 4p of_3/2Peak sum of 396 cm⁻¹The N-Ta peak composition of (A); in contrast, the N1 s high resolution XPS of TN-O NSs, TaN NSs after adsorption of polysulfides, was significantly different from that before adsorption (FIG. 7), at 400 cm⁻¹There appeared a distinct new peak, which was suspected to be due to interaction of the material with polysulphides, 404 cm⁻¹Ta 4p of_3/2Peak sum of 396 cm⁻¹The disappearance of the N-Ta peak is probably due to the adsorption of sulfides on the material surface, and therefore the originally weak material signal is covered, which is also the result of Ta 4f high resolution XPS spectra (FIG. 12 c) with TN-O NSs and Ta in TaN NSs_x−N_yThe reason why the peak of Ta-N is significantly reduced after adsorbing polysulfide is that in Ta 4f high-resolution XPS spectrum (FIG. 12 c), TN-O NSs and TaN NSs peaks are slightly shifted to low field, which may be caused by the change of the internal electronic structure of the material due to the interaction between the material and polysulfide.

The adsorption experiments and the corresponding XPS analysis result show that compared with bulk TaN, TN-O NSs and TaN NSs have stronger adsorption on polysulfide, Ta in the material can generate strong chemical interaction with S in the polysulfide to form Ta-S, and Ta, N, O and S atoms can form more stable interaction under the condition that the material is doped with oxygen, so that TN-O NSs shows the strongest Li₂S₆Adsorption capacity.

Subsequently, in-situ XPS testing was performed in order to further analyze the internal mechanism of the battery during charging and discharging. The battery after one cycle at 0.2C was charged and discharged to different states, the positive electrode was disassembled, dried and used for quasi-in-situ XPS analysis, and the results are shown in fig. 13. During discharge, the Li 1S peak of TN-O NSs/CNTs-S positive electrode gradually shifts to low field, moving from 55.8 eV to 55.3 eV (FIG. 13 a), and since the Li 1S peak is composed of Li-S bond in lithium polysulfide on the positive electrode and Li-N bond/Li-OH bond formed by interaction between lithium polysulfide and TN-O NSs (FIG. 13 d), the shift of the Li 1S peak is caused by strong interaction between lithium polysulfide and TN-O NSs during charge and discharge. Furthermore, the N1S peak at 400.1 eV for TN-O NSs/CNTs-S anode also gradually shifted to low field during discharge, from 400.1 eV to 399.6 eV (fig. 13 b), due to the interaction of N into the material with Li in the lithium polysulphide, which is consistent with the XPS results in the adsorption experiments (fig. 12 b). In contrast, neither the Li 1S peak nor the N1S peak of the bulk TaN/CNTs-S anode shifted significantly during charging and discharging (FIG. 13e, f), indicating a stronger interaction between TN-O NSs and lithium polysulfide. In addition, in the S2 p XPS spectrum of the TN-O NSs/CNTs-S positive electrode, the peak at 167.3 eV is assigned to sulfite or thiosulfate, and the peak at 168.7 eV is assigned to sulfonyl in bis (trifluoromethyl) sulfonyl imide salt. 165-160 eV is S_B ^–1、S_T ^–1And Li₂S (FIG. 13 c), when discharged to 2.1V, corresponds to S_B ^–1And S_T ^–1The S2 p peak of (a) is enhanced, which is consistent with the conversion of sulfides inside the cell during discharge. After discharge to 1.6V, Li at 160.2 eV₂The peak of S indicates incomplete utilization of lithium sulfide, which indicates battery performance to be further improved.

The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention, and it is therefore to be understood that the invention is not limited by the scope of the appended claims.

Claims

1. An oxygen-doped TaN nanosheet, which is characterized in that the preparation method comprises the following steps: preparing TaN nanosheets from TaN serving as a raw material; and (3) placing the TaN nanosheet in an alkaline solution for etching to obtain the oxygen-doped TaN nanosheet.

2. Oxygen-doped TaN nanoplatelets according to claim 1, characterized in that: and putting the tantalum nitride in an N-methyl pyrrolidone (NMP) solution for ultrasonic treatment to obtain the TaN nano-sheet.

3. Oxygen-doped TaN nanoplatelets according to claim 2, characterized in that: and (3) placing the tantalum nitride in an NMP solution, performing probe ultrasonic treatment under an ice bath condition, centrifuging to obtain an upper suspension containing the TaN nanosheets, and then removing a liquid part to obtain the TaN nanosheets.

4. Oxygen-doped TaN nanoplatelets according to claim 1, characterized in that: the alkaline solution is a potassium hydroxide NMP solution.

5. Use of oxygen-doped TaN nanoplates as defined in any of claims 1-4 for the preparation of a lithium-sulfur battery positive electrode material.

6. A lithium sulfur battery comprising a positive electrode material, characterized in that: the oxygen-doped TaN nanosheets as defined in any one of claims 1-4 being included in the cathode material.