A self-supporting spun sulfur cathode host material rich in edge boron doping sites, preparation method and application thereof

Abstract

The present invention belongs to the technical field of lithium-sulfur batteries, and specifically discloses a self-supporting spinning sulfur cathode host material rich in edge boron doping sites, a preparation method and an application thereof. The present invention uses boron (B)-doped carbon quantum dots (CDs) as heteroatom introduction primitives to construct self-supporting carbon nanofibers (BCDs@CNF) rich in edge heteroatom doping sites. The obtained sulfur cathode host material has the following advantages: (1) The rich edge heteroatoms have stronger catalytic performance, which can efficiently accelerate the conversion of polysulfides, thereby improving the cycle stability of LSBs; (2) The host material does not contain metal-based catalysts, has lightweight characteristics, and can ensure the sulfur content in the cathode; (3) The material is easy to wet, suitable for ultra-high sulfur loading and lean electrolyte conditions, combined with its lightweight characteristics, it can effectively improve the energy density of LSBs; (4) The synthesis process has fewer steps, simple operation, and high cost performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur batteries, and specifically relates to a self-supporting spun sulfur positive electrode host material rich in edge boron doping sites, a preparation method and an application thereof, and is particularly suitable for lithium-sulfur batteries with high sulfur loading and poor electrolyte. Background Art

[0002] Lithium-sulfur batteries (LSBs) have attracted extensive attention and research due to their extremely high theoretical energy density (2600Wh / Kg). After nearly a decade of development, researchers have designed high-performance cathodes composed of sulfur and different host materials using adsorption strategies. However, the high performance of these cathodes depends on an excessively high electrolyte-to-sulfur ratio (E / S, ≥20μL / mg), which severely limits the energy density of LSBs. Therefore, it is necessary to explore strategies to reduce E / S.

[0003] The difficulty in reducing E / S is mainly caused by the contradiction between cycle performance and sulfur utilization. In order to ensure the cycle performance of the positive electrode, the host material needs to have sufficient adsorption surface to fully suppress the "shuttle effect" of soluble polysulfides (PS). However, these adsorption surfaces cannot be completely wetted by a small amount of electrolyte, resulting in the inability of lithium ions to be transferred to the unwetted surface to participate in the reaction, thereby affecting the sulfur utilization. At the same time, the electrolyte is generally difficult to penetrate into commonly used host materials, which further affects the wetting of the host material surface. Therefore, reducing E / S requires an easily wettable host material based on a low adsorption area to effectively suppress the "shuttle effect."

[0004] Studies have shown that the slow conversion of polysulfides (PS) to insoluble sulfides (Li2S2 / Li2S) is the root cause of PS aggregation and the "shuttle effect". Accelerating this process using catalytic materials (such as heteroatom-doped carbon, transition metal oxides, sulfides, phosphides, etc.) can avoid PS aggregation, thereby achieving the expected effect of low adsorption area but effectively suppressing the "shuttle effect". In addition, the easily wettable structure with ordered pores can also ensure the uniform dispersion of the electrolyte. Therefore, designing a highly catalytically active easily wettable host material is currently the main strategy to reduce E / S. However, among the commonly used catalytic materials, the metal compounds with high catalytic activity have a large mass, which affects the proportion of sulfur in the positive electrode (≤50wt%), thereby limiting the energy density of LSBs. Chinese patent CN113839024B discloses a self-supporting spun sulfur cathode host material uniformly loaded with small-sized catalysts, including self-supporting spun carbon nanofibers, and nickel-loaded nitrogen-doped carbon quantum dots (Ni@NCDs) uniformly distributed on the self-supporting spun carbon nanofibers, wherein the nickel-loaded nitrogen-doped carbon quantum dots have Ni-N bonds between nickel (Ni) and nitrogen-doped carbon quantum dots (NCDs). Based on the confining effect of carbon quantum dots, the patent evenly and stably distributes ultra-small-sized metal nickel catalysts in carbon fibers. Due to the coordination bond Ni-N between Ni and NCDs, in addition to being able to efficiently catalyze polysulfide conversion and improve cycle stability, it can also adapt to the harsh conditions of ultra-high sulfur loading and lean electrolyte. However, the metal substances in this material are heavier and still cannot guarantee the sulfur content in the cathode. Studies have shown that heteroatom-doped carbon is a commonly used lightweight catalytic material, but its activity is generally low and the catalytic performance needs to be further improved. The main improvement strategy is to increase the edge heteroatom doping sites with high catalytic activity by increasing the specific surface area or introducing a large number of micropores. However, this approach is difficult to apply to wettable carbon materials with ordered macropores and low specific surface area. Therefore, it is necessary to explore new strategies to form abundant edge heteroatom doping sites in lightweight wettable carbon materials. Summary of the invention

[0005] The main technical problem solved by the present invention is to provide a self-supporting spun sulfur cathode host material rich in edge boron doping sites. The material uses boron (B)-doped carbon quantum dots (CDs) as heteroatom introduction primitives to construct self-supporting carbon nanofibers (BCDs@CNF) rich in edge heteroatom doping sites. The obtained sulfur cathode host material has the following advantages: (1) The rich edge heteroatoms have stronger catalytic performance and can efficiently accelerate the conversion of polysulfides, thereby improving the cycle stability of LSBs; (2) The host material does not contain metal-based catalysts and has a lightweight characteristic, which can ensure the sulfur content in the cathode; (3) The material is easy to wet and is suitable for conditions of ultra-high sulfur loading and poor electrolyte (low E / S: low electrolyte / sulfur). Combined with its lightweight characteristics, it can effectively improve the energy density of LSBs; (4) The synthesis process has fewer steps, simple operation, and high cost performance.

[0006] At the same time, the present invention also provides a method for preparing a self-supporting spun sulfur cathode host material rich in edge boron doping sites.

[0007] Finally, the present invention also embodies the use of a self-supporting spun sulfur cathode host material rich in edge boron doping sites in the preparation of lithium-sulfur batteries (LSBs).

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] A self-supporting spun sulfur cathode host material (BCDs@CNF) rich in edge boron doping sites, wherein the host material comprises self-supporting spun carbon nanofibers (CNF) and boron-doped carbon quantum dots (BCDs) uniformly distributed on the self-supporting spun carbon nanofibers.

[0010] As a preferred embodiment of the present invention, the content of boron-doped carbon quantum dots in the host material is 29.4-50.0 wt %.

[0011] As a preferred embodiment of the present invention, the boron content in the boron-doped carbon quantum dots is 5-8 atomic%.

[0012] As a preferred embodiment of the present invention, the boron-doped carbon quantum dots contain at least elements such as B, N, C, and O.

[0013] As a preferred embodiment of the present invention, the average size of the boron-doped carbon quantum dots is less than 5 nm, and more preferably, the average size is ˜3.6 nm.

[0014] A method for preparing a self-supporting spun sulfur cathode host material rich in edge boron doping sites comprises the following steps:

[0015] (1) Preparation of Boron-doped Carbon Quantum Dots (BCDs)

[0016] Boron-doped carbon quantum dots were prepared by hydrothermal synthesis using 3-aminophenylborate hydrochloride as raw material.

[0017] (2) Preparation of host material (BCDs@CNF)

[0018] Boron-doped carbon quantum dots and polyacrylonitrile (PAN) were mixed and composite nanofibers were prepared by electrospinning technology;

[0019] The composite nanofiber pressed sheet is subjected to a pre-oxidation stabilization treatment and then subjected to a heat treatment to obtain the sheet.

[0020] The technical concept of the present invention is that self-supporting carbon nanofibers (CNFs) rich in edge heteroatom doping sites can be constructed by using boron-doped carbon quantum dots (BCDs) as heteroatom introduction primitives. Among them, carbon nanofibers are lightweight and easily wettable carbon materials that can be prepared on a large scale; boron-doped carbon quantum dots have the characteristics of highly crystalline core, easily controllable external heteroatoms and high compatibility. Therefore, the highly dispersed boron-doped carbon quantum dots in the precursor can make the heteroatoms evenly distributed, and the highly crystalline core can hinder the crystallinity of the precursor during the carbonization process, preventing heteroatoms from entering the carbon lattice, thereby forming more edge heteroatom doping sites.

[0021] As a preferred embodiment of the present invention, in step (1), the 3-aminophenyl boron hydrochloride is first dissolved in water (such as deionized water), and then the boron-doped carbon quantum dots are prepared by a bottom-up hydrothermal synthesis method. For example, 0.5 g of 3-aminophenyl boron hydrochloride is dissolved in 50 mL of deionized water, and the solution is transferred to a 100 mL polytetrafluoroethylene-lined reactor.

[0022] As a preferred embodiment of the present invention, in step (1), the temperature for preparing boron-doped carbon quantum dots by hydrothermal synthesis is 180-220°C and the time is 6-10 hours. Preferably, the temperature is 200°C and the time is 8 hours. After hydrothermal, the solution is naturally cooled to room temperature, and the obtained solution is subjected to rotary evaporation and freeze drying to obtain BCDs.

[0023] As a preferred embodiment of the present invention, in step (2), the mass ratio of the boron-doped carbon quantum dots to polyacrylonitrile is 1:1-3, preferably 1:2.4.

[0024] As a preferred embodiment of the present invention, in step (2), the boron-doped carbon quantum dots are first dispersed in a solvent (such as N,N-dimethylformamide, DMF), and then mixed with polyacrylonitrile to obtain a spinning solution. For example, 0.5 g of boron-doped carbon quantum dots are dissolved in 10 mL of N,N-dimethylformamide, stirred evenly, and then 1.2 g of polyacrylonitrile is added, and stirring is continued for 12 hours to obtain a spinning solution.

[0025] As a preferred embodiment of the present invention, in step (2), the technical parameters of the electrospinning technology for preparing composite nanofibers are: ambient humidity 35%-45%, temperature 30-40°C, voltage 10-20kV, push speed 0.5-1.0mL / h, receiving distance 10-20cm, receiving speed 20-40rpm. More preferably, the ambient humidity is 40%, the temperature is 35°C, the voltage is 16kV, the push speed is 0.8mL / h, the receiving distance is 15cm, and the receiving speed is 30 rpm. Other technical parameters include: the syringe (containing the spinning solution) is 20mL in size, the stainless steel needle is N23, and the oil paper is used as the receiver.

[0026] As a preferred embodiment of the present invention, in step (2), the pre-oxidation stabilization treatment is: in an air atmosphere, the temperature is increased from room temperature to 140-170°C at a heating rate of 0.5-2°C / min, and maintained for 2-4 hours; then the temperature is increased to 200-300°C at a heating rate of 0.5-2°C / min, and maintained for 20-40 minutes. More preferably, in an air atmosphere, the temperature is increased from room temperature to 150°C at a heating rate of 1°C / min, and maintained for 3 hours; then the temperature is continued to be increased to 250°C at a heating rate of 1°C / min, and maintained for 30 minutes. Before the pre-oxidation stabilization treatment, the composite nanofibers obtained by electrospinning are first dried (such as drying at 40°C for 12 hours), and then the pre-oxidation stabilization treatment is performed.

[0027] As a preferred embodiment of the present invention, in step (2), the heat treatment is: in an argon (Ar) atmosphere, the temperature is increased to 600-800°C at a heating rate of 3-10°C / min, and maintained for 2-4 hours. More preferably, in an argon atmosphere, the temperature is increased to 700°C at a heating rate of 5°C / min, and maintained for 3 hours.

[0028] A self-supporting spun sulfur cathode host material rich in edge boron doping sites for its application in the preparation of lithium-sulfur batteries.

[0029] As a preferred embodiment of the present invention, when preparing the lithium-sulfur battery, sulfur is first compounded with the host material, and then assembled to obtain the lithium-sulfur battery.

[0030] Beneficial effects of the present invention:

[0031] The present invention provides a self-supporting spun sulfur cathode host material rich in edge boron doping sites, which has the following advantages: (1) The rich edge heteroatoms have stronger catalytic performance and can efficiently accelerate the conversion of polysulfides, thereby improving the cycle stability of LSBs; (2) The host material does not contain metal-based catalysts and has a lightweight characteristic, which can ensure the sulfur content in the cathode; (3) The material is easy to wet and is suitable for conditions of ultra-high sulfur loading and poor electrolyte (low E / S: low electrolyte / sulfur). Combined with its lightweight characteristics, it can effectively improve the energy density of LSBs; (4) The synthesis process has fewer steps, simple operation, and high cost performance.

[0032] Compared with the traditional lithium-sulfur battery cathode host material, the present invention has the following advantages:

[0033] (1) BCDs@CNF has efficient catalytic performance in the catalytic conversion of polysulfides and can effectively alleviate the "shuttle effect", enabling the sulfur cathode to exhibit excellent capacity performance and coulombic efficiency under the harsh conditions of high sulfur loading and lean electrolyte.

[0034] (2) The lightweight properties of BCDs@CNF allow the sulfur content in the cathode to be as high as 75%.

[0035] The preparation method of the sulfur cathode host material provided by the present invention realizes the controllable construction of edge heteroatoms with high catalytic activity in an easily wettable self-supporting structure, and obtains a lightweight catalytic host material rich in boron (B) edge doping sites, which is suitable for improving the performance of LSBs under high sulfur loading and lean electrolyte conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The transmission electron microscopy (TEM) images and X-ray diffraction (XRD) images of BCDs in Example 1 of the present invention at different magnifications are shown;

[0037] Figure 1 (a) is a TEM image, (b) is a high-resolution TEM image, and (c) is an XRD image.

[0038] Figure 2 Transmission electron microscopy (TEM) images and X-ray energy spectrum (EDS) images of two electrode materials, BCDs@CNF in Example 1 of the present invention and B@CNF in Comparative Example 1;

[0039] Figure 2(a) is the SEM image of BCDs@CNF, (b) is the TEM image of BCDs@CNF, (c) is the EDS scanning area image of BCDs@CNF, (d) is the EDS element distribution image of BCDs@CNF, (e) is the SEM image of B@CNF, (f) is the TEM image of B@CNF, (g) is the EDS scanning area image of B@CNF, and (h) is the EDS element distribution image of B@CNF.

[0040] Figure 3 X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) diagrams of two electrode materials, BCDs@CNF in Example 1 of the present invention and B@CNF in Comparative Example 1;

[0041] Figure 3 (a) is the XRD pattern, (b) is the XPS total spectrum, (c) is the O spectrum of BCDs@CNF, and (d) is the O spectrum of B@CNF.

[0042] Figure 4 The catalytic performance test diagram of the three electrode materials BCDs@CNF in Example 1 of the present invention and B@CNF and CNF in Comparative Examples 1-2;

[0043] Figure 4 (a) is a cyclic voltammetry (CV) diagram of a symmetric battery, (b) is an electrochemical impedance spectroscopy (EIS) diagram of a symmetric battery, (c) is a constant voltage discharge diagram of an asymmetric battery, and (d) is a CV diagram of an asymmetric battery.

[0044] Figure 5 The battery performance test diagram of the three electrode materials BCDs@CNF in Example 1 of the present invention and B@CNF and CNF in Comparative Examples 1-2;

[0045] Figure 5 (a) is the charge and discharge curve at 0.2C, (b) is the discharge curve at 2C, (c) is the rate performance diagram, and (d) is the cycle performance diagram.

[0046] Figure 6 The battery performance test diagram of the BCDs@CNF electrode material under high sulfur loading and low E / S conditions in Example 1 of the present invention is as follows:

[0047] Figure 6 (a) is the charge and discharge curve, and (b) is the cycle performance diagram.

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings obtained in the embodiments and experimental examples are briefly introduced above. It should be understood that the above drawings only show some experimental examples of the present invention and should not be regarded as any limitation on the scope of protection of the claims. For ordinary technicians in this field, other related drawings can also be obtained based on these drawings without creative work. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments and experimental examples. However, it should be understood by those skilled in the art that the embodiments are only used to illustrate the technical solution of the present invention and should not be regarded as limiting the scope of protection of the present invention. Based on the following embodiments, all other implementation schemes obtained by ordinary technicians in the field without making creative work, such as modification, deformation or simple replacement, should belong to the scope of protection of the present invention.

[0050] Unless otherwise specified, the experimental methods used in the following embodiments and experimental examples are all conventional methods; the raw materials, reagents, instruments, etc. used are all commercially available unless otherwise specified. Among them, the vacuum rotary evaporator was purchased from Zhengzhou Zhengsheng Instrument Equipment Co., Ltd., model: RE-2000A; the freeze dryer was purchased from Ningbo Xinzhi Biotechnology Co., Ltd.; the electrospinning machine was purchased from Changsha Nayi Instrument Technology Co., Ltd., model: JDF05.

[0051] Example 1

[0052] The present embodiment provides a self-supporting spun sulfur cathode host material rich in edge boron doping sites (BCDs@CNF), including self-supporting spun carbon nanofibers (CNFs), and boron-doped carbon quantum dots (BCDs) uniformly distributed on the self-supporting spun carbon nanofibers.

[0053] The method for preparing a self-supporting spun sulfur cathode host material rich in edge boron doping sites in this embodiment comprises the following steps:

[0054] (1) Preparation of Boron-doped Carbon Quantum Dots (BCDs)

[0055] Boron-doped carbon quantum dots were prepared using a bottom-up hydrothermal synthesis method: 0.5 g of 3-aminophenylborate hydrochloride was dissolved in 50 mL of deionized water, and the solution was then transferred to a 100 mL polytetrafluoroethylene-lined reactor. After being hydrothermally heated at 200 °C in a forced air drying oven for 8 h, the solution was naturally cooled to room temperature. The resulting solution was rotary evaporated, freeze-dried, and the sample was collected to obtain BCDs.

[0056] (2) Preparation of host material (BCDs@CNF)

[0057] Take 0.5g BCDs and dissolve it in 10mL DMF solvent. After stirring evenly, add 1.2g polyacrylonitrile (PAN) and continue stirring for 12h to obtain a spinning solution. Pour the spinning solution into a 20mL plastic syringe (stainless steel needle N23) for electrospinning. During the electrospinning process, keep the ambient humidity at about 40%, the temperature at about 35°C, the voltage at 16kV, the push speed at 0.8mL / h, the receiving distance at 15cm, the receiving speed at 30rpm, and use oil paper as the receiver to obtain composite nanofibers.

[0058] After spinning, the composite nanofiber sample was dried at 40°C for 12 h, and then the sample was pressed into a sheet for pre-oxidation stabilization treatment: in an air atmosphere, the temperature was increased from room temperature to 150°C at a heating rate of 1°C / min, maintained for 3 h, and then continued to be increased to 250°C at a heating rate of 1°C / min, and maintained for 30 min; finally, heat treatment was carried out in a tubular furnace under Ar atmosphere protection at a heating rate of 5°C / min to 700°C, maintained for 3 h, to obtain BCDs@CNF.

[0059] Example 2

[0060] This embodiment provides a self-supporting spun sulfur cathode host material rich in edge boron doping sites (BCDs@CNF), which is prepared by a method comprising the following steps:

[0061] (1) Preparation of Boron-doped Carbon Quantum Dots (BCDs)

[0062] Boron-doped carbon quantum dots were prepared using a bottom-up hydrothermal synthesis method: 0.5 g of 3-aminophenylborate hydrochloride was dissolved in 50 mL of deionized water, and the solution was then transferred to a 100 mL polytetrafluoroethylene-lined reactor. The solution was hydrothermally heated at 180 °C in a forced air drying oven for 10 h and then naturally cooled to room temperature. The resulting solution was rotary evaporated, freeze-dried, and the sample was collected to obtain BCDs.

[0063] (2) Preparation of host material (BCDs@CNF)

[0064] Take 0.8g BCDs and dissolve it in 10mL DMF solvent. After stirring evenly, add 1.2g polyacrylonitrile (PAN) and continue stirring for 12h to obtain a spinning solution. Pour the spinning solution into a 20mL plastic syringe (stainless steel needle N23) for electrospinning. During the electrospinning process, keep the ambient humidity at about 35%, the temperature at about 30°C, the voltage at 10kV, the push speed at 1.0mL / h, the receiving distance at 10cm, the receiving speed at 20rpm, and use oil paper as the receiver to obtain composite nanofibers.

[0065] After spinning, the composite nanofiber sample was dried at 40°C for 12 h, and then the sample was pressed into a sheet for pre-oxidation stabilization treatment: in an air atmosphere, the temperature was increased from room temperature to 140°C at a heating rate of 0.5°C / min, maintained for 4 h, and then continued to be increased to 200°C at a heating rate of 0.5°C / min, and maintained for 40 min; finally, heat treatment was carried out in a tubular furnace under Ar atmosphere protection at a heating rate of 3°C / min to 600°C, maintained for 4 h, to obtain BCDs@CNF.

[0066] Example 3

[0067] This embodiment provides a self-supporting spun sulfur cathode host material rich in edge boron doping sites (BCDs@CNF), which is prepared by a method comprising the following steps:

[0068] (1) Preparation of Boron-doped Carbon Quantum Dots (BCDs)

[0069] Boron-doped carbon quantum dots were prepared using a bottom-up hydrothermal synthesis method: 0.5 g of 3-aminophenylborate hydrochloride was dissolved in 50 mL of deionized water, and the solution was then transferred to a 100 mL polytetrafluoroethylene-lined reactor. The solution was hydrothermally heated at 220 °C in a forced air drying oven for 6 h and then naturally cooled to room temperature. The resulting solution was rotary evaporated, freeze-dried, and the sample was collected to obtain BCDs.

[0070] (2) Preparation of host material (BCDs@CNF)

[0071] Take 1.2g BCDs and dissolve it in 10mL DMF solvent. After stirring evenly, add 1.2g polyacrylonitrile (PAN) and continue stirring for 12h to obtain a spinning solution. Pour the spinning solution into a 20mL plastic syringe (stainless steel needle N23) for electrospinning. During the electrospinning process, keep the ambient humidity at about 45%, the temperature at about 40°C, the voltage at 20kV, the push speed at 0.5mL / h, the receiving distance at 20cm, the receiving speed at 40rpm, and use oil paper as the receiver to obtain composite nanofibers.

[0072] After spinning, the composite nanofiber sample was dried at 40°C for 12 h, and then the sample was pressed into a sheet for pre-oxidation stabilization treatment: in an air atmosphere, the temperature was increased from room temperature to 170°C at a heating rate of 2°C / min, maintained for 2 h, and then continued to be increased to 300°C at a heating rate of 2°C / min, and maintained for 20 min; finally, heat treatment was carried out in a tubular furnace under Ar atmosphere protection at a heating rate of 10°C / min to 800°C, maintained for 2 h, and BCDs@CNF was obtained.

[0073] Comparative Example 1

[0074] This comparative example provides a B-doped CNF (B@CNF) electrode material, in which the same amount of 3-aminophenylborate hydrochloride is used instead of BCDs as a boron source and electrospun with PAN. The electrospinning process and high-temperature calcination process are consistent with those for preparing Ni@CDs-CNF in Example 1 to obtain a B@CNF electrode material.

[0075] Comparative Example 2

[0076] This comparative example provides a CNF electrode material, and the preparation method is as follows: weigh 1.2 g of polyacrylonitrile (PAN), slowly add it into 10 mL of N,N-dimethylformamide (DMF) solvent while stirring, and continue stirring for 12 hours to form a uniform slurry. The subsequent electrospinning process and high-temperature calcination process are consistent with the preparation of Ni@CDs-CNF in Example 1 to obtain a CNF electrode material.

[0077] Experimental Example 1

[0078] (1) The boron-doped carbon quantum dots (BCDs) in Example 1 were subjected to transmission electron microscopy (TEM) analysis and X-ray diffraction (XRD) analysis, respectively. The results are as follows: Figure 1 shown.

[0079] from Figure 1 (a) It can be seen that the BCDs are evenly distributed with an average size of ~3.6 nm. Figure 1 (b) It can be seen that the core of BCDs is highly crystalline. XRDs( Figure 1 (c)) shows that it has characteristic peaks of C material.

[0080] (2) The two electrode materials BCDs@CNF in Example 1 and B@CNF in Comparative Example 1 were subjected to transmission electron microscopy (TEM) analysis and X-ray energy dispersive spectroscopy (EDS) analysis, respectively. The results are as follows: Figure 2 shown.

[0081] from Figure 2 It can be seen that the morphologies of the two electrode materials are similar and the elements are evenly distributed.

[0082] (3) The two electrode materials, BCDs@CNF in Example 1 and B@CNF in Comparative Example 1, were subjected to X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS) analysis, respectively. The results are shown in FIG3 .

[0083] from Figure 3 (a) and (b) show that both electrode materials show the characteristic peaks of C material, and the proportion of heteroatoms is very similar, which can rule out the influence of morphology and heteroatom content on performance. Figure 3(c) and 3(d)) show that there are more BO bonds in BCDs@CNF.

[0084] Experimental Example 2

[0085] The performance of the three electrode materials, BCDs@CNF in the example and B@CNF and CNF in the comparative example, were evaluated by electrochemical performance and battery performance.

[0086] (1) Catalytic performance evaluation

[0087] The symmetrical battery was assembled and evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The positive and negative electrodes of the symmetrical battery were both 1 cm 2 The same electrode material is used, and the electrolyte is 40μL 0.2M Li2S6 electrolyte (the preparation method is: add S powder and Li2S powder to 10mL of lithium-sulfur electrolyte in a glove box at a molar ratio of 5:1, heat and stir at 40°C until the reaction is completely dissolved to obtain a brown-yellow solution). The CV test conditions are: at room temperature (25°C), the voltage test range is -1 to 1V, and the scan rate is 20mV / s. It is evaluated by comparing the peak current and area. The EIS test conditions are: at room temperature (25°C), the frequency test range is 100kHz-0.1Hz. It is evaluated by comparing the migration resistance. The CV and EIS test results are as follows Figure 4 As shown in (a) and (b).

[0088] The asymmetric battery was assembled and evaluated by constant voltage discharge and CV test. The positive electrode of the asymmetric battery was loaded with 1.5 mg / cm 2 Sulfur electrode material (specific composite process: 0.1g sulfur powder is dissolved in 10mL toluene, heated and stirred at 40℃ until a uniform solution is obtained, 150μL of the above solution is added dropwise to different materials, and the sulfur loading is confirmed by weighing on a 1 / 10,000 balance after drying at 60℃ on a flat heating table), the negative electrode is a lithium metal negative electrode, and the electrolyte is 40μL of a lithium sulfur electrolyte (a DOL / DME (1:1, v / v) mixture containing 1MLiTFSI and 2% LiNO3). The test conditions for constant voltage discharge are: at room temperature (25℃), the battery is first discharged at a constant current to 2.05V, and then discharged at a constant voltage at different voltages (1.95-2.06V) until the current is stable (i≤0.01mA). The peak position and peak area and their corresponding lithium sulfide (Li2S) deposition capacity are compared for evaluation. The CV test conditions are: room temperature (25°C), voltage test range 1.7-2.8V, scan rate 0.1mV / s. Compare the voltage and current values ​​corresponding to the peak. The constant voltage discharge and CV test results are shown in Figure 2. Figure 4 As shown in (c) and (d).

[0089] from Figure 4(a) It can be seen that when the scanning rate is 20mV / s, the peak currents of BCDs@CNF, B@CNF, and CNF are 23mA, 12mA, and 7mA, respectively.

[0090] from Figure 4 (b) It can be seen that the migration resistances of BCDs@CNF, B@CNF, and CNF are 13.2 mA, 21.3 mA, and 23.1 mA, respectively.

[0091] from Figure 4 (c) It can be seen that the BCDs@CNF / S cathode has an earlier peak than other cathodes and a larger peak area. The lithium sulfide deposition capacities of the three electrodes are 162.4 mAh / g, 55.0 mAh / g, and 43.4 mAh / g, respectively.

[0092] from Figure 4 (d) It can be seen that when the scan rate is 0.1mV / s, the oxidation peaks of BCDs@CNF / S, B@CNF / S, and CNF / S positive electrodes are 2.45V, 2.46V, and 2.55V, respectively, and the peak currents are 3.13mA, 3.2mA, and 1.01mA, respectively; the first reduction peaks are 2.28V, 2.25V, and 2.2V, respectively, and the peak currents are 0.84mA, 0.82mA, and 0.46mA, respectively; the second reduction peaks are 1.99V, 1.96V, and 1.88V, respectively, and the peak currents are 2.30mA, 1.90mA, and 0.66mA, respectively.

[0093] (2) Battery performance evaluation

[0094] The evaluation is carried out by assembling an asymmetric battery and performing a constant current charge and discharge test. The positive electrode of the asymmetric battery is an electrode material loaded with different amounts of sulfur, the negative electrode is a lithium metal negative electrode, and the electrolyte is 40μL of a lithium-sulfur electrolyte (the preparation process is the same as above, and the E / S is 20μL / mg and 5μL / mg (high sulfur loading and low E / S conditions)). The constant current charge and discharge test conditions are: at room temperature (25°C), the charge and discharge test voltage window is 1.5-3.0V. The evaluation is carried out by comparing the polarization of the charge and discharge curves, the capacity of the charge and discharge curves, and the cycle stability. The results are as follows Figure 5 , Figure 6 shown.

[0095] from Figure 5It can be seen that when E / S is 20μL / mg, the polarization of BCDs@CNF / S cathode is smaller than that of other cathodes. The discharge specific capacities of BCDs@CNF / S, B@CNF / S, and CNF / S cathodes at 0.2C, 0.5C, 1C, and 2C are (1151, 1046, 982, 881mAh / g), (1000, 925, 857, 755mAh / g), and (828, 790, 197, 66mAh / g), respectively. The capacity retention rates of BCDs@CNF / S, B@CNF / S, and CNF / S cathodes after 200 cycles at 0.5C are 86.5%, 73.8%, and 82%, respectively, and the average decay rates per cycle are 0.067%, 0.13%, and 0.09%, respectively.

[0096] from Figure 6 It can be seen that the BCDs@CNF / S positive electrode still shows a good charge and discharge curve and a small polarization when the sulfur content is as high as 75% (E / S is 5μL / mg), and exhibits a specific capacity of 1103mAh / g. The capacity retention rate after 32 cycles is still as high as 86.1%.

[0097] From the above experimental results, it can be seen that the self-supporting spinning sulfur cathode host material rich in edge boron doping sites provided by the present invention has the following advantages: (1) The rich edge heteroatoms have stronger catalytic performance, which can efficiently accelerate the conversion of polysulfides, thereby improving the cycle stability of LSBs; (2) The material is easy to wet and is suitable for ultra-high sulfur loading and poor electrolyte conditions (low E / S: low electrolyte / sulfur). Combined with its lightweight characteristics, it can effectively improve the energy density of LSBs. Compared with traditional lithium-sulfur battery cathode host materials, it has the following advantages: (1) BCDs@CNF has efficient catalytic performance in the catalytic conversion of polysulfides, which can effectively alleviate the "shuttle effect", so that the sulfur cathode exhibits excellent capacity performance and coulombic efficiency under the harsh conditions of high sulfur loading and poor electrolyte. (2) BCDs@CNF has lightweight characteristics, which can make the sulfur content in the cathode as high as 75wt%, and the synthesis process has few steps, simple operation, and high cost performance, which is suitable for improving the performance of LSBs under high sulfur loading and poor electrolyte conditions.

[0098] Although the technical solution of the present invention has been described in detail above with general descriptions, specific implementation methods and experimental examples, it should be noted that the embodiments and experimental examples are only used to illustrate the technical solution and technical effects of the present invention, and should not be regarded as any limitation on the protection scope of the present invention. Simple deformation, modification or improvement based on the technical concept of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A self-supporting spun sulfur cathode host material rich in edge boron doping sites, characterized in that: The host material includes self-supporting spun carbon nanofibers, and boron-doped carbon quantum dots uniformly distributed on the self-supporting spun carbon nanofibers; The preparation method of the host material comprises the following steps: (1) Preparation of Boron-doped Carbon Quantum Dots Boron-doped carbon quantum dots were prepared by hydrothermal synthesis using 3-aminophenylborate hydrochloride as raw material. (2) Preparation of host materials Boron-doped carbon quantum dots and polyacrylonitrile were mixed and composite nanofibers were prepared by electrospinning technology; The composite nanofiber pressed sheet is subjected to a pre-oxidation stabilization treatment and then subjected to a heat treatment to obtain the sheet.

2. The self-supporting spun sulfur cathode host material rich in edge boron doping sites according to claim 1, characterized in that: The content of boron-doped carbon quantum dots in the host material is 29.4-50.0 wt %.

3. The self-supporting spun sulfur cathode host material rich in edge boron doping sites according to claim 1, characterized in that: The boron content in the boron-doped carbon quantum dots is 5-8 atomic %.

4. The self-supporting spun sulfur cathode host material rich in edge boron doping sites according to claim 1, characterized in that: The boron-doped carbon quantum dots contain at least B, N, C, and O elements; And / or, the average size of the boron-doped carbon quantum dots is less than 5 nm.

5. The self-supporting spun sulfur cathode host material rich in edge boron doping sites according to claim 4, characterized in that: The average size of the boron-doped carbon quantum dots is 3.6 nm.

6. A method for preparing a self-supporting spun sulfur cathode host material rich in edge boron doping sites as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Preparation of Boron-doped Carbon Quantum Dots Boron-doped carbon quantum dots were prepared by hydrothermal synthesis using 3-aminophenylborate hydrochloride as raw material. (2) Preparation of host materials Boron-doped carbon quantum dots and polyacrylonitrile were mixed and composite nanofibers were prepared by electrospinning technology; The composite nanofiber pressed sheet is subjected to a pre-oxidation stabilization treatment and then subjected to a heat treatment to obtain the sheet.

7. The method for preparing a self-supporting spun sulfur cathode host material rich in edge boron doping sites according to claim 6, characterized in that: In step (1), the 3-aminophenylborate hydrochloride is first dissolved in water, and then the boron-doped carbon quantum dots are prepared by a bottom-up hydrothermal synthesis method; And / or, the temperature for preparing boron-doped carbon quantum dots by the hydrothermal synthesis method is 180-220° C. and the time is 6-10 h.

8. The method for preparing a self-supporting spun sulfur cathode host material rich in edge boron doping sites according to claim 7, characterized in that: The temperature for preparing boron-doped carbon quantum dots by the hydrothermal synthesis method is 200° C. and the time is 8 hours.

9. The method for preparing a self-supporting spun sulfur cathode host material rich in edge boron doping sites according to claim 6, characterized in that: In step (2), the mass ratio of the boron-doped carbon quantum dots to polyacrylonitrile is 1:1-3; and / or, dispersing boron-doped carbon quantum dots in N,N-dimethylformamide, and then mixing with polyacrylonitrile to obtain a spinning solution; And / or, the technical parameters of the electrospinning technology for preparing composite nanofibers are: ambient humidity 35%-45%, temperature 30-40°C, voltage 10-20kV, push speed 0.5-1.0mL / h, receiving distance 10-20cm, and receiving rotation speed 20-40rpm.

10. The method for preparing a self-supporting spun sulfur cathode host material rich in edge boron doping sites according to claim 9, characterized in that: The mass ratio of the boron-doped carbon quantum dots to polyacrylonitrile is 1:2.4; And / or, the technical parameters of the electrospinning technology for preparing composite nanofibers are: ambient humidity 40%, temperature 35°C, voltage 16kV, push speed 0.8mL / h, receiving distance 15cm, and receiving rotation speed 30rpm.

11. The method for preparing a self-supporting spun sulfur cathode host material rich in edge boron doping sites according to claim 6, characterized in that: In step (2), the pre-oxidation stabilization treatment is: in an air atmosphere, the temperature is raised from room temperature to 140-170°C at a heating rate of 0.5-2°C / min, maintained for 2-4 hours, and then raised to 200-300°C at a heating rate of 0.5-2°C / min, maintained for 20-40 minutes; And / or, the heat treatment is: in Ar atmosphere, heating to 600-800° C. at a heating rate of 3-10° C. / min, and maintaining for 2-4 hours.

12. The method for preparing a self-supporting spun sulfur cathode host material rich in edge boron doping sites according to claim 11, characterized in that: The pre-oxidation stabilization treatment is as follows: in an air atmosphere, the temperature is raised from room temperature to 150°C at a heating rate of 1°C / min, maintained for 3 hours, and then continued to be raised to 250°C at a heating rate of 1°C / min, maintained for 30 minutes; And / or, the heat treatment is: in Ar atmosphere, heating to 700° C. at a heating rate of 5° C. / min and maintaining for 3 h.

13. Use of the self-supporting spun sulfur cathode host material rich in edge boron doping sites according to any one of claims 1 to 5, or the self-supporting spun sulfur cathode host material rich in edge boron doping sites prepared by the method according to any one of claims 6 to 12 in the preparation of a lithium-sulfur battery.

14. The use according to claim 13, characterized in that: When preparing the lithium-sulfur battery, sulfur is first compounded with the host material and then assembled to obtain the lithium-sulfur battery.

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