Preparation method and application of In2O3@CNF material

Abstract

The present invention discloses a preparation method and application of an In2O3@CNF material. The preparation method comprises the following steps: (1) dissolving polyacrylonitrile in N,N-dimethylformamide, heating and stirring to obtain a polyacrylonitrile solution; (2) adding indium nitrate to the polyacrylonitrile solution, heating and stirring until the indium nitrate is completely dispersed, to obtain a mixed dispersion; (3) spinning the mixed dispersion using an electrostatic spinning device, stripping the collected spun fibers, and drying to obtain carbon fibers; (4) performing a low-temperature pre-oxidation treatment on the carbon fibers in an air environment to obtain pre-oxidized carbon fibers; and (5) performing high-temperature carbonization on the pre-oxidized carbon fibers under an argon atmosphere to obtain the target product. The In2O3@CNF material prepared by the method of the present invention is used as an intermediate layer of a lithium-sulfur battery, which can alleviate the shuttle effect of polysulfides in the lithium-sulfur battery and improve the cycle life of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-sulfur battery intermediate layers, specifically to a preparation method and application of an In2O3@CNF material. Background Art

[0002] Electrochemical energy storage (EES) systems stand out in the field of renewable energy storage due to their unique advantages of high efficiency, low cost, high safety and versatility. Currently, sulfur can be combined with lithium metal negative electrodes to form attractive lithium-sulfur batteries. Sulfur, a non-metallic element, has the advantages of high safety, fast reaction kinetics, good reversibility, high theoretical capacity and raw material availability. However, lithium-sulfur batteries themselves have disadvantages, such as the high insulating properties of sulfur and its discharge products, which create a very slow reaction environment and the volume change during the cycle causes the positive electrode structure to deform. In addition to these inherent problems, the alternating movement of discharge products between electrodes caused by the dissolution of polysulfides during the cycle, the so-called shuttle effect, is another potential factor leading to rapid capacity decay and increased battery impedance, which is not conducive to the cycle life of the battery.

[0003] Local fixation of polysulfides by physical confinement and chemical adsorption has been shown to be effective in preventing the shuttle effect. To this end, researchers have used various types of positive electrode composite materials to adsorb polysulfides. However, the preparation process of these composite materials is usually complicated and not suitable for industrial applications. Another effective strategy to reduce the shuttle effect is to insert a functional intermediate layer between the positive electrode and the separator. Research on intermediate layer materials has focused on the adsorption of polysulfides by carbon-based materials. These carbon materials have carefully adjusted structures and inhibit the shuttling of polysulfides by physical adsorption. However, physical adsorption using only non-polar carbon cannot completely and effectively inhibit the shuttle effect. Therefore, it is necessary to design a functional intermediate layer of metal and carbon fiber composites and use it in lithium-sulfur batteries to inhibit the shuttle effect of polysulfides and improve the electrochemical performance of lithium-sulfur batteries. Summary of the Invention

[0004] To this end, the technical problem to be solved by the present invention is to provide a preparation method and application of In2O3@CNF material to solve the problem that the existing lithium-sulfur battery intermediate layer cannot effectively inhibit the shuttle effect of polysulfides and affect the electrochemical performance of lithium-sulfur batteries.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A method for preparing In2O3@CNF material comprises the following steps:

[0007] Step (1), dissolving polyacrylonitrile in N,N-dimethylformamide, heating and stirring to obtain a polyacrylonitrile solution;

[0008] Step (2), adding indium nitrate to the polyacrylonitrile solution, heating and stirring until the indium nitrate is completely dispersed, to obtain a mixed dispersion;

[0009] Step (3), spinning the mixed dispersion using an electrospinning device, peeling off the spun fibers collected on the collector and placing them in a drying oven for drying, and obtaining carbon fibers after drying;

[0010] Step (4), performing a low-temperature pre-oxidation treatment on the carbon fiber in an air environment to obtain pre-oxidized carbon fiber;

[0011] Step (5): Carbonizing the pre-oxidized carbon fibers at high temperature in an argon atmosphere to obtain In2O3@CNF materials.

[0012] In the preparation method of the above-mentioned In2O3@CNF material, in step (1), the volume mass ratio of N,N-dimethylformamide to polyacrylonitrile in the polyacrylonitrile solution is 9 mL / g; the stirring temperature during heating and stirring is 55-65°C, and the stirring time is 4-6 hours.

[0013] In the preparation method of the above-mentioned In2O3@CNF material, in step (2), the mass ratio of indium nitrate to polyacrylonitrile in the mixed dispersion is 1:1; and the stirring temperature during heating and stirring is 55-65°C.

[0014] In the above-mentioned method for preparing In2O3@CNF material, in step (3), the electrospinning conditions are: a propeller speed of 0.6 mL / h, a distance between the ejector head and the roller collector of 15 cm, a voltage of 22 kV, and a spinning time of 5 hours. If the spinning time is too short, the prepared intermediate layer is too thin and unusable. If the spinning time is too long, the prepared intermediate layer is too thick, which will affect the ion propagation speed in the battery and cause excessive internal resistance.

[0015] In the preparation method of the above-mentioned In2O3@CNF material, in step (3), the spinning drying temperature is 55-65°C, and the drying time is 8-12 hours.

[0016] In the preparation method of the above-mentioned In2O3@CNF material, in step (4), the conditions for the low-temperature pre-oxidation treatment are: heating from room temperature to 200°C at a heating rate of 2.0°C / min and keeping warm for 60 minutes.

[0017] In the preparation method of the above-mentioned In2O3@CNF material, in step (5), the high-temperature carbonization conditions are: heating from room temperature to 650°C at a heating rate of 5°C / min and keeping warm for 3 hours.

[0018] In the preparation method of the above-mentioned In2O3@CNF material, in step (1), the volume mass ratio of N,N-dimethylformamide to polyacrylonitrile in the polyacrylonitrile solution is 9 mL / g, the stirring temperature during heating and stirring is 60°C, and the stirring time is 5 h;

[0019] In step (2), the mass ratio of indium nitrate to polyacrylonitrile in the mixed dispersion is 1:1; the stirring temperature during heating and stirring is 60° C.; if the amount of indium nitrate in the mixed dispersion is too much, spinning cannot be formed;

[0020] In step (3), the electrospinning conditions are as follows: the propeller speed is 0.6 mL / h, the distance between the ejector head and the roller collector is 15 cm, the voltage is 22 kV, the spinning time is 5 h; the spinning drying temperature is 60 ° C, and the drying time is 10 h;

[0021] In step (4), the low-temperature pre-oxidation treatment conditions are: heating from room temperature to 200°C at a heating rate of 2°C / min and keeping warm for 60 minutes; if the pre-oxidation temperature is too high, the indium nitrate will volatilize prematurely;

[0022] In step (5), the high-temperature carbonization conditions are: heating from room temperature to 650°C at a heating rate of 5°C / min and keeping the temperature for 3 hours.

[0023] An application of In2O3@CNF material, wherein the In2O3@CNF material prepared by the above-mentioned preparation method of In2O3@CNF material is used as an intermediate layer of a lithium-sulfur battery.

[0024] The electrodes of lithium-sulfur batteries are prepared by the following steps using the above-mentioned In2O3@CNF materials:

[0025] Step A, mixing sulfur and carbon nanotubes in a mass ratio of 4:1 and grinding for 30 minutes to obtain mixed powder A;

[0026] Step B, placing the mixed powder under an argon atmosphere, heating to 155°C at a heating rate of 2°C / min, and keeping the temperature for 12 hours to obtain a C / S composite positive electrode material;

[0027] Step C: mixing the C / S composite cathode material and the conductive carbon black in a mass ratio of 8:1 and grinding them for 10 minutes to obtain a mixed powder B;

[0028] Step D: Mixing the binder and N-methylpyrrolidone to obtain a transparent dispersion; the mass ratio of the binder to the conductive carbon black in step C is 1:1;

[0029] Step E: adding the mixed powder B to the transparent dispersion and stirring for 12 hours to obtain an electrode raw material slurry;

[0030] Step F: coating the electrode raw material slurry on aluminum foil with a coating thickness of 100 μm. After coating, the foil was placed in a vacuum drying oven at 60° C. and dried for 12 h to obtain an electrode.

[0031] The technical solution of the present invention achieves the following beneficial technical effects:

[0032] 1. This invention uses In2O3 as the polar material and polyacrylonitrile (PAN) as the carbon skeleton. In2O3 nanoparticles are embedded in carbon fibers via electrospinning. The material is then subjected to low-temperature pre-oxidation and high-temperature carbonization to produce an indium oxide-modified carbon skeleton interlayer material, namely the In2O3@CNF composite interlayer material. The carbon nanofibers in this composite interlayer material have excellent electrical conductivity, which helps increase the diffusion rate of lithium ions. The In2O3 nanoparticles dispersed on the carbon fibers provide abundant active sites, capable of anchoring a large number of sulfides to alleviate the shuttle effect.

[0033] 2. The preparation method of the present invention is used to prepare the In2O3@CNF composite intermediate layer material as a functional intermediate layer to alleviate the shuttle effect of polysulfides in lithium-sulfur batteries and improve the cycle life of the battery. Among them, the CNF with a conductive skeleton can effectively reduce the resistance of the positive electrode and alleviate the volume expansion during the charge and discharge process. The In2O3 nanoparticles act as active sites to adsorb polysulfides and accelerate their redox kinetics. Compared with the lithium-sulfur battery without the addition of the intermediate layer, the electrochemical performance of the electrode with the addition of the In2O3@CNF intermediate layer is significantly improved. At a current density of 0.2C, the initial discharge capacity of the electrode with a positive sulfur content of 77wt% reaches 1187.4mAh g -1 After 100 cycles, the capacity retention rate was 77.5%; when the current density increased to 1C, it still had 997mAh g -1 The initial capacity is high, and the capacity is maintained at 589.1 mAh g after 400 cycles. -1 , and has extremely stable Coulombic efficiency (Coulombic efficiency is close to 100% in 400 cycles) and low single-cycle capacity decay rate (0.1%). BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the preparation process of the In2O3@CNF intermediate layer in an embodiment of the present invention;

[0035] Figure 2 TG curve of C / S of the positive electrode material prepared in the embodiment of the present invention;

[0036] Figure 3a SEM image of CNF prepared in the embodiment of the present invention (1 μm);

[0037] Figure 3bSEM image of In2O3@CNF prepared in the embodiment of the present invention (1μm);

[0038] Figure 3c TEM image of In2O3@CNF prepared in the embodiment of the present invention (200nm);

[0039] Figure 3d SEM image of CNF prepared in the embodiment of the present invention (500nm);

[0040] Figure 3e SEM image of In2O3@CNF prepared in the embodiment of the present invention (500nm);

[0041] Figure 3f HRTEM image of In2O3@CNF prepared in the embodiment of the present invention (5nm);

[0042] Figure 3g EDS spectrum of In2O3@CNF prepared in the embodiment of the present invention (100nm);

[0043] Figure 3h EDS image of In2O3@CNF prepared in the embodiment of the present invention (C element);

[0044] Figure 3i EDS image of In2O3@CNF prepared in the embodiment of the present invention (In element);

[0045] Figure 3j EDS image of In2O3@CNF prepared in the embodiment of the present invention (O element);

[0046] Figure 4a XRD patterns of CNF and In2O3@CNF prepared in the examples of the present invention;

[0047] Figure 4b Raman images of CNF and In2O3@CNF prepared in the examples of the present invention;

[0048] Figure 5a Nitrogen adsorption-desorption isotherms and pore size distribution curves of CNFs in the embodiments of the present invention;

[0049] Figure 5b Nitrogen adsorption-desorption isothermal pore size distribution curve of In2O3@CNF according to the embodiment of the present invention;

[0050] Figure 6a The full XPS spectrum of In2O3@CNF prepared in the embodiment of the present invention;

[0051] Figure 6b In 3d spectrum of In2O3@CNF prepared in the embodiment of the present invention;

[0052] Figure 7a In the embodiment of the present invention, the In2O3@CNF, CNF and lithium-sulfur batteries without adding an intermediate layer have a high thermal conductivity at 0.1mV s -1 The cyclic voltammetry curve below;

[0053] Figure 7b The lithium-sulfur battery of In2O3@CNF in the embodiment of the present invention is 0.1mV s -1 The cyclic voltammetry curves of different numbers of cycles are shown below;

[0054] Figure 8a First cycle charge and discharge curves of In2O3@CNF, CNF, and lithium-sulfur batteries without an intermediate layer at 0.2C in an embodiment of the present invention;

[0055] Figure 8b for Figure 8a Schematic diagram of a partial enlargement of the discharge curve;

[0056] Figure 9a Cycling performance diagram of In2O3@CNF, CNF and lithium-sulfur battery without adding intermediate layer at 0.2C in the embodiment of the present invention;

[0057] Figure 9b The charge and discharge curve of the In2O3@CNF lithium-sulfur battery at 0.2C in the embodiment of the present invention; Figure 10a Rate performance diagram of lithium-sulfur batteries with and without CNF and In2O3@CNF intermediate layers in the embodiment of the present invention;

[0058] Figure 10b Charge and discharge curves of the In2O3@CNF lithium-sulfur battery at different current densities in an embodiment of the present invention;

[0059] Figure 10c Cycling performance diagram of In2O3@CNF lithium-sulfur battery at 1C after activation at 0.1C in the embodiment of the present invention;

[0060] Figure 11a Cyclic voltammetry curves of a lithium-sulfur battery containing a CNF intermediate layer at different scan rates according to an embodiment of the present invention;

[0061] Figure 11b Cyclic voltammetry curves of a lithium-sulfur battery containing an In2O3@CNF intermediate layer at different scan rates according to an embodiment of the present invention;

[0062] Figure 11c for Figure 11a and Figure 11b Relationship between the square root of the peak potential scan rate and the peak current;

[0063] Figure 12aEIS graphs of lithium-sulfur batteries with and without CNF and In2O3@CNF intermediate layers after 100 cycles in the embodiments of the present invention;

[0064] Figure 12b EIS graphs of lithium-sulfur batteries containing CNF intermediate layers after different cycles in an embodiment of the present invention;

[0065] Figure 12c EIS graphs of lithium-sulfur batteries containing an In2O3@CNF intermediate layer after different cycles in an embodiment of the present invention;

[0066] Figure 13 Actual photos of polysulfide adsorption tests on CNF and In2O3@CNF in the examples of the present invention;

[0067] Figure 14a SEM image and sulfur element distribution diagram of the separator after 100 cycles of the lithium-sulfur battery without adding an intermediate layer in the embodiment of the present invention;

[0068] Figure 14b SEM image and sulfur element distribution diagram of the separator of the lithium-sulfur battery with a CNF intermediate layer after 100 cycles in the embodiment of the present invention;

[0069] Figure 14c SEM image and sulfur element distribution diagram of the separator of the lithium-sulfur battery with an In2O3@CNF intermediate layer added in the embodiment of the present invention after 100 cycles. DETAILED DESCRIPTION

[0070] 1. Preparation of In2O3@CNF intermediate layer

[0071] The preparation process of the In2O3@CNF intermediate layer in this embodiment is as follows Figure 1 As shown, the specific steps include:

[0072] Step (1): Weigh 1 g of polyacrylonitrile (PAN) and dissolve it in 9 mL of N,N-dimethylformamide (DMF). Stir at 60°C for 5 h to obtain a transparent PAN solution. Then, add 1 g of indium nitrate (In(NO3)3) and continue stirring at 60°C until it is completely dissolved to obtain a mixed solution.

[0073] Step (2): Pour the mixed solution into a 20 mL syringe at a propeller speed of 0.6 mL / h, set the distance between the injector head and the roller collector to 15 cm, and set the voltage to 22 kV. Spin for 5 hours to obtain carbon fibers. The spun carbon fibers are peeled from the collector and dried in a drying oven at 60°C overnight.

[0074] Step (3) The carbon fibers are then placed in a blast drying oven for low-temperature pre-oxidation. The temperature is raised from 25°C to 200°C in an air environment at a rate of 2°C / min and maintained for 1 hour. During the low-temperature pre-oxidation, polyacrylonitrile undergoes cyclization, dehydrogenation, and oxidation, stabilizing the carbon fiber structure and providing a foundation for subsequent high-temperature carbonization.

[0075] After the pre-oxidation step (4), the carbon fibers were removed from the blast drying oven and placed in a high-temperature tube furnace for high-temperature carbonization under an argon atmosphere. The temperature was raised from 25°C to 650°C at a rate of 5°C / min and the temperature was maintained for 3 hours to complete the carbonization, thereby obtaining an In2O3@CNF film.

[0076] Step (5): A film with a diameter of 12 mm was cut by a punching machine as a self-supporting intermediate layer. Lithium-sulfur batteries with a positive electrode material C / S without an intermediate layer and a positive electrode material C / S with a CNF intermediate layer were used as comparisons.

[0077] The preparation method of CNF intermediate layer is as follows: pour the transparent PAN solution directly into a 20mL syringe, the propeller speed is 1mL / h, the distance between the nozzle and the roller collector is 20cm, the voltage is set to 18kV, and the spinning is performed for 4 hours to obtain carbon fiber; then the carbon fiber is placed in a blast drying oven for low-temperature pre-oxidation treatment, and heated from room temperature to 260℃ at a heating rate of 2℃ / min in an air atmosphere, and kept warm for 1 hour; after the pre-oxidation is completed, the carbon fiber is taken out from the blast drying oven and placed in a high-temperature tubular furnace, and heated from room temperature to 700℃ at a rate of 5℃ / min in an argon atmosphere, and kept at a constant temperature for 1 hour to complete carbonization to obtain the CNF intermediate layer.

[0078] 2. Preparation of positive electrode material C / S and electrode

[0079] 2.1 Preparation of C / S cathode materials

[0080] Weigh 0.4g of sulfur and 0.1g of carbon nanotubes, put them into a mortar and grind them for 30 minutes. Pour them into a reactor and heat them to 155°C at 2°C / min under an argon atmosphere. Keep warm for 12 hours to obtain a C / S composite positive electrode material. The prepared C / S composite positive electrode material was subjected to thermogravimetric testing (the thermogravimetric tests in this embodiment were all performed using a German Netzsch STA449F5 synchronous thermal analyzer). Figure 2 As shown in FIG, the sulfur content was calculated to be 77 wt % by thermogravimetric curve. Subsequent lithium-sulfur batteries assembled all used C / S as the positive electrode.

[0081] 2.2 Preparation of electrodes

[0082] First, a sample is weighed at a mass ratio of 8:1:1 between the positive electrode material C / S, conductive carbon black (Super P), and binder (PVDF). The weighed positive electrode material C / S and conductive carbon black are mixed in a mortar and manually ground for ten minutes. The weighed PVDF is transferred to a weighing bottle, and a certain amount of N-methylpyrrolidone (NMP) is added. Stir on a magnetic stirrer until the liquid turns transparent. The ground positive electrode material C / S and conductive carbon black mixture is then poured into the weighing bottle and stirred for 12 hours. The prepared slurry is coated on aluminum foil to a thickness of 100μm, dried in a vacuum drying oven at 60°C for 12 hours, and finally punched into electrode pieces with a diameter of 10mm.

[0083] 3. Physical characterization of In2O3@CNF interlayer

[0084] 3.1 Scanning electron microscopy and transmission electron microscopy analysis

[0085] In this example, field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the micromorphology of the In2O3@CNF film, and a SU8020 scanning electron microscope from Hitachi, Japan, and a Tecnai G2 F30 instrument from FEI, USA, were used to characterize the morphology of the intermediate layer.

[0086] Figure 3a and Figure 3d The SEM image of the original carbon fiber CNF film shows a smooth fiber surface and a size of approximately 200 nm. The carbon fiber grid structure provides a good electronic conductive framework, which can alleviate the volume change of sulfur during charge and discharge. Figure 3b and Figure 3e The SEM image of In2O3@CNF film shows that compared with CNF, the fiber surface of In2O3@CNF is rough and the size is about 300nm. Figure 3c As shown, transmission electron microscopy was further used to observe that many nanoparticles grew on the surface of carbon fibers.

[0087] Figure 3g to Figure 3j This is the X-ray energy spectrum (EDS) diagram of In2O3@CNF, using the BRUCKER D8ADVANCE X-ray diffractometer from Bruker, Germany, with a test angle range of 10 to 80°. The elemental mapping of C, In and O in the figure also confirms the structure and uniform dispersion of In2O3. This embodiment attributes this distribution of In2O3 nanoparticles to the nitrate pyrolysis process. During the annealing process, In(NO3)3 decomposes into In2O3, O2 and NO2. As the gas seeps out, the In2O3 nuclei and undecomposed In(NO3)3 move to the fiber surface, eventually forming In2O3 nanoparticles. The lattice fringes of the nanoparticles are clearly shown in Figure 3fThe interplanar spacings are 0.292nm and 0.297nm, and the lattice phases are consistent with the (222) and (311) planes of In2O3. These results indicate that the small particles grown on the carbon surface are In2O3. This unique nanostructure facilitates contact with the electrolyte and electron transport, contributing to rapid charging and discharging.

[0088] 3.2 X-ray diffraction and Raman spectroscopy analysis

[0089] In this embodiment, X-ray diffraction (XRD) was used to test CNF and In2O3@CNF, and the diffraction angle range of the test was 10-80°. Figure 4a The XRD spectra of CNF and In2O3@CNF show characteristic peaks of amorphous carbon structure around 25°. In2O3@CNF shows a diffraction peak at 30.58°, which corresponds to the diffraction of the (222) crystal plane in the standard PDF card of In2O3, confirming that the particles on the carbon fiber are In2O3. The results are consistent with the EDS analysis.

[0090] Raman spectra of CNF and In2O3@CNF are shown in Figure 2. Figure 4b As shown in the figure, there are two characteristic peaks of carbon materials in both, namely D peak (1346cm -1 ) and G peak (1597cm -1 For In2O3@CNF film, the two characteristic peaks of carbon are removed and the peaks at 104.6, 126.52 and 149.4 cm -1 There are also peaks at the same time, which correspond to the characteristic peaks of In2O3 phase. In addition, the ratio of D peak to G peak of CNF (I D / I G ) is 1.12, and the I D / I G The value is 1.01, and In2O3@CNF is smaller than CNF, which indicates that the oxygen defect structure of In2O3 is introduced into carbon fibers.

[0091] 3.3 Nitrogen adsorption and desorption analysis

[0092] Figure 5a and Figure 5b The nitrogen adsorption-desorption isotherms and pore size distribution curves of CNF and In2O3@CNF are shown respectively. Figure 5bIt can be found that the adsorption-desorption isotherm of In2O3@CNF has an adsorption hysteresis loop in the middle section. The hysteresis loop is due to the capillary condensation that causes the nitrogen molecules to condense and fill the mesoporous channels at a pressure lower than normal. Since the capillary condensation begins on the liquid surface of the annular adsorption film on the pore wall, and the desorption starts from the spherical meniscus liquid surface of the pore, the adsorption and desorption isotherms do not overlap, forming a hysteresis loop. According to the classification of physical adsorption isotherms proposed by the International Union of Pure and Applied Chemistry (IUPAC), it can be divided into a type IV adsorption curve. The appearance of a hysteresis loop in the medium pressure section indicates that mesopores may exist in the material. According to Figure 5b The illustration shows that the pore size of In2O3@CNF is larger than 2 nm, proving the existence of mesopores, with a total pore volume of 0.031 cm 3 / g, larger than CNF(0.019cm 3 / g). It is speculated that the reason for the existence of mesopores in the material is the gas leakage generated during the thermal decomposition of nitrate. The specific surface areas of In2O3@CNF and CNF were calculated by BET method to be 34.4844m2 / g and 15.4518m2 / g, respectively. 2 The increase in specific surface area is due to the formation of In2O3 particles. The presence of mesopores and the rough surface area make electron transport faster, and polysulfides are easily accessible to the adsorption catalytic sites, limiting the shuttle effect.

[0093] 3.4 X-ray photoelectron spectroscopy analysis

[0094] To gain a deeper understanding of the chemical state and composition of In2O3@CNF, X-ray photoelectron spectroscopy (XPS) analysis was performed. Figure 6a From the full XPS spectrum in Figure 2, it can be seen that In2O3@CNF has characteristic peaks at 284.8eV, 445.0eV, 531.5eV, 666.1eV and 704.6eV, corresponding to C1s, In 3d, O 1s, In 3p3 and In 3p1, respectively, verifying the successful synthesis of In2O3@CNF. Figure 6b In 3d fine spectrum, In 3d appears at 452.5eV and 444.9eV respectively. 5 / 2 and In 3d 3 / 2 There are two typical peaks, which are consistent with In 3+ The valence characteristics of In2O3@CNF are consistent, verifying the existence of In2O3. When In2O3@CNF adsorbs polysulfide, the peak of In 3d shifts by 0.1eV toward the low binding energy direction, indicating that the interaction between In2O3 and polysulfide causes the electron cloud density to change.

[0095] 4. Electrochemical performance study

[0096] CNF and In2O3@CNF were used as the intermediate layers of lithium-sulfur batteries, and the effect of In2O3@CNF on the electrochemical performance of lithium-sulfur batteries was analyzed by cyclic voltammetry. Cyclic voltammetry tests were performed using a Princeton PMC1000A electrochemical workstation with a voltage range of 1.7 to 2.8 V.

[0097] 4.1 Electrolyte Configuration

[0098] Prepare 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) + 2% LiNO₃ with a 1:1 volume ratio of solvents (DOL and DME). The electrolyte needs to be prepared in an anhydrous environment, so all the following operations are performed in a glove box. First, remove a portion of the lithium salt and dry it on a hot plate at 60°C for 5 hours. Weigh 0.574g of LiTFSI and 0.05g of LiNO₃ into a glass bottle, then add 1mL of DOL and DME each, and stir for 10 hours.

[0099] 4.2 Battery Assembly

[0100] The battery assembly process was carried out in a glove box with a high-purity argon atmosphere. The oxygen and moisture contents within the glove box were controlled at <1 ppm for O2 and <1 ppm for H2O, respectively. During assembly, button cell (CR2032) batteries were assembled in the following order: negative electrode shell, spring, gasket, negative electrode, 25 μL electrolyte, separator, 25 μL electrolyte, positive electrode sheet, and positive electrode shell. For batteries containing an intermediate layer, the intermediate layer was inserted between the separator and the positive electrode sheet. To ensure that the electrolyte fully soaked the electrode materials, the assembled battery was left to rest for 12 hours. The separator consisted of a porous polypropylene (PP) film with a diameter of 19 mm.

[0101] 4.3 Cyclic voltammetry and charge-discharge curves

[0102] Figure 7a CV curves without adding intermediate layer and adding CNF and In2O3@CNF intermediate layer, scan rate 0.1mVs -1 , potential range 1.7V-2.8V. In the CV curve, the reduction peak that appears in the cathode scanning area represents the reaction of S8 being reduced to Li2S4, and Li2S4 then receiving electrons to generate Li2S2 / Li2S. The oxidation peak that appears in the anode scanning area represents the oxidation of Li2S2 / Li2S to soluble polysulfides, and some polysulfides are then oxidized to S8. Compared with the case without adding an intermediate layer and with adding a CNF intermediate layer, the peak current of In2O3@CNF is larger, indicating that the battery containing the In2O3@CNF intermediate layer has a lower electrochemical polarization. In addition, Figure 7b For In2O3@CNF battery at 0.1mV s -1The shapes and redox peaks of the first three CV curves at a scan rate of 100 nm remain almost unchanged, indicating that the battery containing the In2O3@CNF intermediate layer has high cycle reversibility.

[0103] Figure 8a The first cycle charge and discharge curves of three different configurations of lithium-sulfur batteries at a current density of 0.2C, ΔE is the median voltage difference. Through calculation and comparison, it is found that the lithium-sulfur battery containing In2O3@CNF intermediate layer has the smallest ΔE value, indicating that the reaction kinetics of the lithium-sulfur battery is accelerated, making its polarization the lowest. Figure 8b yes Figure 8a A magnified schematic diagram of the discharge platform shows that In2O3@CNF has the lowest overpotential. In lithium-sulfur batteries, capacity depends on whether soluble Li2S4 can be converted to solid Li2S2, and the overpotential is closely related to the conversion of Li2S4 to Li2S2. The In2O3@CNF interlayer has the lowest overpotential, indicating that In2O3 has a certain effect on the solid-liquid conversion of polysulfides, accelerating the conversion of soluble Li2S4, thereby improving the battery's charge and discharge capacity.

[0104] 4.4 Cycling and rate performance

[0105] In this example, the electrochemical performance of lithium-sulfur batteries without an intermediate layer and with CNF and In2O3@CNF intermediate layers was tested using a Landian charge-discharge battery tester (LandCT2001A) manufactured by Wuhan Landian Electronics Co., Ltd. The tests were conducted at room temperature with a constant current charge-discharge voltage range of 1.7 to 2.8 V.

[0106] like Figure 9a As shown in Figure 2, at a current density of 0.2C (1C = 1675 mA / g), the initial capacities of the three different configurations of batteries are significantly different. The initial capacity of the battery containing the In2O3@CNF interlayer is 1187.4 mAh g -1 , which is significantly higher than CNF (823.3 mAh g -1 ) and without adding an intermediate layer (677.2 mAh g -1 After 100 cycles, the discharge capacity of the In2O3@CNF interlayer was 920.5 mAh g -1 The capacity retention rate was 77.5%, which was higher than that of CNF (622 mAh g -1 and 75.5%) and without adding an intermediate layer (407.5 mAh g -1The lithium-sulfur battery without the interlayer exhibited poor cycling performance due to the poor conductivity of sulfur and the severe polysulfide shuttling effect. While the initial capacity improved with the CNF interlayer, capacity decay remained severe because the carbon-based material only physically adsorbs polysulfides to a limited extent. The significant improvement in initial capacity and capacity retention with the addition of the In2O3@CNF interlayer suggests that In2O3 effectively adsorbs polysulfides, accelerating their conversion and increasing the utilization of the active sulfur. Figure 9b The charge and discharge curves of the In2O3@CNF battery under different cycle cycles show that the capacity decay is small, the voltage platform is stable, and the potential hysteresis change is small.

[0107] Figure 10a The figure shows the rate performance at current densities of 0.1C, 0.2C, 0.5C, 1C and 2C. Compared with the three lithium-sulfur batteries with different configurations, the In2O3@CNF has the best rate performance. The initial capacity at different current densities is higher than the other two, indicating that the lithium-sulfur battery with the In2O3@CNF intermediate layer has a good reversible specific capacity. Importantly, even at a high current density of 2C, it can provide 768.8mAh g -1 The capacity is higher than that of CNF (428.5 mAh g -1 ) and without adding an intermediate layer (133.9 mAh g -1 At the same time, when the current density returns from 2C to 0.1C, the battery can discharge continuously and stably, and the capacity is restored to 1078.3mAhg -1 , equivalent to 70.86% of its initial capacity, showing excellent electrochemical reversibility and stability. Figure 10b It can be seen that although the current density is constantly changing, the charge and discharge platform of the battery containing the In2O3@CNF intermediate layer can be well presented. Figure 10c As shown, after 0.1C activation, the battery containing In2O3@CNF interlayer has stable cycling at 1C current density with an initial capacity of 997 mAh g -1 After 400 cycles, it still maintains 589.1mAh g -1 The reversible discharge capacity is 0.1%, the single-cycle capacity decay rate is 0.1%, and the Coulomb efficiency is close to 100%.

[0108] 4.5 Lithium Ion Diffusion Coefficient and AC Impedance

[0109] In order to further understand the role of different interlayers in accelerating the electrocatalytic conversion of polysulfides, the electrochemical performance of CNF and In2O3@CNF was measured at different scan rates (0.1 mV s -1 -0.5mV s -1) under CV, the diffusion characteristics of lithium ions were analyzed. Figure 11a and Figure 11b As shown in Figure 2, with the increase of scan rate, both the cathodic and anodic peak currents increase, and the oxidation peaks are marked as A. At 25 °C, the ion diffusion coefficient can be calculated using the classic Randles-Sevcik equation:

[0110]

[0111] In the above formula, the peak current is expressed as I p The number of electrons involved in the reaction is represented by n, the area of the electrode is represented by A, and the diffusion coefficient of lithium ions is represented by D Li Indicates that the lithium ion concentration is expressed as C Li The scan rate is represented by v. In the calculation process, the number of electrons involved in the reaction is 2, and the area of the electrode is 0.785 cm 2 , the concentration of lithium ions is 10 -4 mol / mL. D is calculated using oxidation peak A. Li , In2O3@CNF is 2.87×10 -6 cm 2 / s, which is higher than CNF (2.21×10 -6 cm 2 / s). I p The square root of the scan rate v 1 / 2 There is a linear relationship, and the slope of the fitting line is related to D Li Proportional to. Figure 11c As shown, the slope of the reduction peak for In2O3@CNF is greater than that for CNF. During the battery's charge-discharge cycle, Li2S2 / Li2S precipitates to form an insulating layer, which reduces the transport rate of lithium ions. However, in batteries containing an In2O3@CNF interlayer, the presence of the CNF carbon skeleton and In2O3 increases the number of catalytically active sites, preventing the formation of an insulating layer, increasing the diffusion rate of lithium ions, and accelerating the conversion kinetics of polysulfides.

[0112] In this example, a Princeton PMC1000A electrochemical workstation was used with a test frequency of 0.01 to 100 kHz and an amplitude of 5 mV to conduct electrochemical impedance spectroscopy (EIS) tests on lithium-sulfur batteries without an intermediate layer and with CNF and In2O3@CNF intermediate layers, in order to explore the charge transfer behavior of In2O3@CNF on the interface. The Nyquist plots of all batteries are semicircles in the medium and high frequency bands and oblique lines at low frequencies, which represent the charge transfer resistance (R ct ) and lithium diffusion impedance (Z w ).like Figure 12aAs shown in the EIS curves of three different configuration batteries after 100 cycles, it is obvious that the lithium-sulfur battery containing the In2O3@CNF intermediate layer has a lower R ct , indicating that the charge transfer between the In2O3@CNF intermediate layer and polysulfide is faster and the transfer resistance is smaller. Figure 12b and Figure 12c The EIS curves of lithium-sulfur batteries containing CNF and In2O3@CNF intermediate layers after different cycle numbers are shown. As the number of cycles increases, the impedance of both batteries continues to decrease. More importantly, the impedance of In2O3@CNF is always smaller than that of CNF, which indicates that In2O3 accelerates the conversion of polysulfides and the transmission speed of lithium ions during battery cycling.

[0113] 5. Analysis of the effect of inhibiting polysulfides

[0114] 5.1 Polysulfide adsorption test

[0115] The shuttling effect of polysulfides can seriously affect the cycling performance of lithium-sulfur batteries. During the charge-discharge cycle, polysulfides are generated and dissolve in the electrolyte, shuttling back and forth between the positive and negative electrodes, reducing sulfur utilization and causing battery capacity degradation. To test the polysulfide adsorption capacity of In2O3@CNF, equal masses of CNF and In2O3@CNF were placed in a prepared Li2S6 solution.

[0116] The lithium polysulfide Li2S6 solution in this example was prepared in an oxygen-free environment. First, a sample of Li2S and S in a 1:5 molar ratio was removed from a glove box and dissolved in a 1:1 volume ratio of DOL and DME. The sample was stirred at 60°C for 12 hours to obtain a yellow solution, which is the Li2S6 solution. The same sample mass was weighed and placed in a vacuum drying oven at 60°C for 10 hours to completely dry. After removal, the sample was placed in the lithium polysulfide solution and the color change of the solution was observed over time.

[0117] like Figure 13 As shown, the original color of Li2S6 is yellow. After 12 hours, the solution with CNF added turns light yellow, while the solution with In2O3@CNF added becomes clear. By comparison, it can be found that the adsorption performance of the In2O3@CNF middle layer is the best, indicating that In2O3 has a certain adsorption effect on polysulfides and inhibits the shuttle effect.

[0118] 5.2 Polysulfide Shuttle Effect

[0119] To further confirm that the In2O3@CNF interlayer can inhibit the shuttle of polysulfides, lithium-sulfur batteries without an interlayer and with CNF and In2O3@CNF interlayers were selected. After 100 cycles at a current density of 0.2C, the batteries were disassembled, the separators were removed, and SEM analysis was performed on the separators near the lithium metal side. Figures 14a to 14c As shown, no intermediate layer is added ( Figure 14a ) and adding CNF intermediate layer ( Figure 14b ) has some Li2S / Li2S2 particles on the separator, while the In2O3@CNF interlayer ( Figure 14c ) on the separator. In addition, the upper right corner of each figure is a distribution diagram of the sulfur element. It can be clearly seen from the figure that there is less sulfur on the separator with the In2O3@CNF intermediate layer. And through EDS element content analysis, it is known that the sulfur content on the separator without the intermediate layer and the separator with the CNF intermediate layer is 29.06% and 14.38%, respectively, while the sulfur content of the In2O3@CNF intermediate layer is only 6.61%. The above analysis results show that the polysulfide shuttled to the lithium metal surface in the battery containing the In2O3@CNF intermediate layer is significantly reduced, confirming that the In2O3 particles have a significant adsorption effect on polysulfides, effectively suppressing the shuttle effect of lithium-sulfur batteries.

[0120] In summary, this example successfully prepared a functional intermediate layer of In2O3 and carbon nanofiber composites by electrospinning and assembled it into a lithium-sulfur battery. This preparation method is simple and easy to control, and it increases the active sites of In2O3 nanoparticles on the carbon fiber surface, which can effectively inhibit the shuttle effect of polysulfides and improve the electrochemical performance of lithium-sulfur batteries. The specific conclusions are as follows:

[0121] (1) The In2O3@CNF intermediate layer was prepared by electrospinning and high-temperature carbonization. SEM and TEM images show that In2O3 nanoparticles are embedded in carbon nanofibers, forming a rough surface that is conducive to the transmission of lithium ions.

[0122] (2) In2O3@CNF contains oxygen vacancy defects, which break the charge balance state of the crystal surface and change the electronic state. The electrons around the defects are highly active and easily chemically adsorb with polysulfides to form strong covalent bonds, effectively suppressing the polysulfide shuttle effect and accelerating the conversion reaction of polysulfides, making the lithium-sulfur battery exhibit excellent electrochemical performance.

[0123] (3) The lithium-sulfur battery with an In2O3@CNF interlayer provided 1187.4 mAh g at a current density of 0.2C. -1 Excellent initial discharge capacity, which still maintains 920.5mAh g after 100 cycles -1The discharge capacity is 997mAh g at 1C. -1 It has a high initial discharge capacity and excellent cycle stability (Coulomb efficiency close to 100% in 400 cycles).

Claims

1. An application of In2O3@CNF material, characterized in that: In2O3@CNF material is used as the intermediate layer of the lithium-sulfur battery. The preparation method of In2O3@CNF material includes the following steps: Step (1), dissolving polyacrylonitrile in N, N-dimethylformamide, heating and stirring to obtain a polyacrylonitrile solution; the volume mass ratio of N, N-dimethylformamide to polyacrylonitrile in the polyacrylonitrile solution is 9 mL / g; the stirring temperature during heating and stirring is 55 to 65° C., and the stirring time is 4 to 6 hours; Step (2), adding indium nitrate to the polyacrylonitrile solution, heating and stirring until the indium nitrate is completely dispersed, to obtain a mixed dispersion; the mass ratio of indium nitrate to polyacrylonitrile in the mixed dispersion is 1:1; the stirring temperature during heating and stirring is 55 to 65°C; Step (3), spinning the mixed dispersion liquid using an electrospinning device, peeling off the spun fibers collected on the collector and placing them in a drying oven for drying, and obtaining carbon fibers after drying; the spinning conditions of the electrospinning are as follows: the propeller speed is 0.6 mL / h, the distance between the nozzle and the roller collector is 15 cm, the voltage is 22 kV, the spinning time is 5 h; the spinning drying temperature is 55-65 ° C, and the drying time is 8-12 h; Step (4), performing a low-temperature pre-oxidation treatment on the carbon fiber in an air environment to obtain a pre-oxidized carbon fiber; the conditions for the low-temperature pre-oxidation treatment are: heating from room temperature to 200°C at a heating rate of 2.0°C / min, and keeping the temperature for 60 minutes; Step (5): The pre-oxidized carbon fiber is subjected to high-temperature carbonization in an argon atmosphere. After the carbonization is completed, the In2O3@CNF material is obtained. The high-temperature carbonization conditions are: heating from room temperature to 650°C at a heating rate of 5°C / min and keeping the temperature for 3 hours.

2. The use of the In2O3@CNF material according to claim 1, characterized in that: In step (1), the volume mass ratio of N, N-dimethylformamide to polyacrylonitrile in the polyacrylonitrile solution is 9 mL / g, the stirring temperature during heating and stirring is 60° C., and the stirring time is 5 h; In step (2), the mass ratio of indium nitrate to polyacrylonitrile in the mixed dispersion is 1:1; the stirring temperature during heating and stirring is 60°C; In step (3), the electrospinning conditions are as follows: the propeller speed is 0.6 mL / h, the distance between the ejector head and the roller collector is 15 cm, the voltage is 22 kV, the spinning time is 5 h; the spinning drying temperature is 60 ° C, and the drying time is 10 h; In step (4), the conditions for the low-temperature pre-oxidation treatment are: heating from room temperature to 200°C at a heating rate of 2°C / min and keeping the temperature for 60 minutes; In step (5), the high-temperature carbonization conditions are: heating from room temperature to 650°C at a heating rate of 5°C / min and keeping the temperature for 3 hours.

3. The use of the In2O3@CNF material according to claim 1, characterized in that The electrodes of lithium-sulfur batteries are prepared by the following steps: Step A, mixing sulfur and carbon nanotubes in a mass ratio of 4:1 and grinding for 30 minutes to obtain mixed powder A; Step B, placing the mixed powder under an argon atmosphere, heating to 155°C at a heating rate of 2°C / min, and keeping the temperature for 12 hours to obtain a C / S composite positive electrode material; Step C: mixing the C / S composite cathode material and the conductive carbon black in a mass ratio of 8:1 and grinding them for 10 minutes to obtain a mixed powder B; Step D: Mixing the binder and N-methylpyrrolidone to obtain a transparent dispersion; the mass ratio of the binder to the conductive carbon black in step C is 1:1; Step E: adding the mixed powder B to the transparent dispersion and stirring for 12 hours to obtain an electrode raw material slurry; Step F: coating the electrode raw material slurry on aluminum foil with a coating thickness of 100 μm. After coating, the foil was placed in a vacuum drying oven at 60° C. and dried for 12 h to obtain an electrode.

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