Self-supporting composite material, preparation method thereof, cathode material for lithium-sulfur battery, and lithium-sulfur battery

Abstract

The present invention provides a self-supporting composite material, a preparation method thereof, a cathode material for a lithium-sulfur battery, and a lithium-sulfur battery. The self-supporting composite material includes a carrier and MoN nanowires, and one end of at least a part of the MoN nanowires is fixed on the carrier. The carrier includes a modified carbon cloth, and the contact angle of the modified carbon cloth is 10° to 25°. Compared with the unmodified carbon cloth, the surface activity of the modified carbon cloth is improved, so that the wettability of its surface is correspondingly improved, which is beneficial to the formation of MoN nanowires in the self-supporting composite material. If the above self-supporting composite material and S are prepared into a cathode material for a lithium-sulfur battery and applied to the lithium-sulfur battery, it can improve the conductivity of the S cathode, inhibit the polysulfide shuttle effect, and relieve the volume expansion of S on the basis of ensuring that the lithium-sulfur battery has a sufficiently large specific capacity and energy density, thereby improving the cycle stability and rate performance of the lithium-sulfur battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-sulfur batteries, and in particular, to a self-supporting composite material, a preparation method thereof, a cathode material of a lithium-sulfur battery, and a lithium-sulfur battery. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic devices and new energy vehicles, but their low theoretical energy density still limits their development. With the continuous improvement of the requirements for the energy density of secondary batteries, the development of high-energy-density battery systems has become an important development direction for electrochemical energy storage. Since the sulfur (S) cathode material has a theoretical specific capacity as high as 1675 mAh·g -1 , and at the same time, sulfur has abundant natural reserves and low cost; lithium has a low density and high electronegativity (-3.045 V relative to the standard hydrogen electrode), and the theoretical specific capacity of lithium can reach 3860 mAh·g -1 , therefore, the lithium-sulfur battery composed of lithium and sulfur has a theoretical capacity as high as 1675 mAh·g -1 and an energy density of 2500 Wh·kg -1 , which is much higher than that of currently commercialized lithium-ion batteries (250 mAh·g -1 ). The lithium-sulfur battery is considered to be the most promising next-generation renewable energy storage device.

[0003] However, there are many problems with current lithium-sulfur batteries, such as: (1) As a cathode material, the extremely low conductivity of S (5×10 -30 S·cm -1 ) requires it to be mixed with a certain amount of conductive agent; (2) Sulfur has a large volume expansion effect during the reaction process; (3) The intermediate product polysulfide lithium Li2S n (4≤n≤8) has a high solubility in the electrolyte, and these polysulfides diffuse from the cathode to the anode and are reduced on the anode surface, while the soluble reducing products return to the cathode to undergo an oxidation reaction again, that is, there is a "shuttling effect". The above problems result in low utilization rate of sulfur, easy deterioration of the lithium electrode surface, thus leading to rapid attenuation of its specific capacity, and further resulting in poor cycle stability and rate performance of the lithium-sulfur battery. Summary of the Invention

[0004] The main object of the present invention is to provide a self-supporting composite material, a preparation method thereof, a cathode material of a lithium-sulfur battery, and a lithium-sulfur battery to solve the problem of poor cycle stability and rate performance of the lithium-sulfur battery in the prior art.

[0005] To achieve the above object, according to one aspect of the present invention, a self-supporting composite material is provided. The self-supporting composite material includes a carrier and MoN nanowires. One end of at least part of the MoN nanowires is fixed on the carrier, and the carrier includes modified carbon cloth, and the contact angle of the modified carbon cloth is 10° to 25°.

[0006] Further, the mass of MoN nanowires per unit area of the above carrier is 25 to 65 g / m 2 .

[0007] Further, the above modified carbon cloth is oxidized modified carbon cloth.

[0008] According to another aspect of the present invention, a preparation method of the above self-supporting composite material is provided. The preparation method includes: Step S1, performing a solvothermal reaction on the modified carbon cloth and a molybdate solution to obtain a reaction product; Step S2, calcining the reaction product to obtain a self-supporting composite material, wherein the calcination is carried out in a mixed gas of an inert gas and ammonia, or a mixed gas of nitrogen and ammonia, and wherein, based on molybdenum ions, the molar concentration of the molybdate solution is 0.02 to 0.05 mol / L.

[0009] Further, based on molybdenum ions, relative to 1 m 2 of the modified carbon cloth, the mass of the molybdate is 56 to 112 g. Preferably, the molybdate is selected from any one or more of ammonium paramolybdate, sodium molybdate, and potassium molybdate. Preferably, the solvent in the molybdate solution is an organic solvent. Preferably, the organic solvent is selected from one or more of ethanol, N,N-dimethylformamide, methanol, and dimethyl sulfoxide. Preferably, the modified carbon cloth is modified graphitized carbon fiber cloth or modified carbon fiber cloth. Further preferably, the modified carbon cloth is selected from any one or more of modified HCP330P, modified HCP330N, modified HCP331P, and modified HCP331N.

[0010] Further, the temperature of the above solvothermal reaction is 180 to 220 °C, and preferably the time of the solvothermal reaction is 10 to 20 h.

[0011] Further, the volume ratio of the above inert gas to ammonia is 5 to 95:5 to 95, or the volume ratio of nitrogen to ammonia is 5 to 95:5 to 95.

[0012] Further, the temperature of the above calcination is 700 to 800 °C, and preferably the time of the calcination is 1 to 2.5 h.

[0013] Further, the above preparation method further includes oxidizing the carbon cloth to obtain modified carbon cloth, and preferably the oxidation is electrooxidation.

[0014] According to another aspect of the present invention, a cathode material for a lithium-sulfur battery is provided. The cathode material includes sulfur and a conductive agent, and the conductive agent includes the above-mentioned self-supporting composite material. Preferably, the mass ratio of sulfur to the conductive agent is 1:1 to 5:1.

[0015] According to another aspect of the present invention, a lithium-sulfur battery is provided. The lithium-sulfur battery includes a cathode and an anode, and the cathode includes the above-mentioned cathode material.

[0016] Applying the technical solution of the present invention, compared with the unmodified carbon cloth, the wettability of the surface of the modified carbon cloth (the contact angle is 10° to 25°) is correspondingly improved, which is beneficial to the formation of MoN nanowires in the self-supporting composite material. Since MoN is a good catalyst for catalyzing the conversion of polysulfides, at least part of the nanowire-shaped MoN is fixed on the modified carbon cloth to form a self-supporting composite material. If the self-supporting composite material is used as the cathode material of a lithium-sulfur battery, due to the excellent conductivity of the modified carbon cloth, on the one hand, it can improve the conductivity of S, and at the same time, as a self-supporting electrode, it avoids the use of a binder and reduces the generation of by-products during charge and discharge; moreover, the MoN nanowires in the self-supporting composite material serve as the direct host of S. Since the MoN nanowires have a sufficiently large specific surface area, they provide as many binding sites for S as possible. While improving the specific capacity and energy density of the lithium-sulfur battery, enough space is also provided between the MoN nanowires to relieve the volume change caused by charge and discharge. On the other hand, the nanowire-shaped MoN can also catalyze the rapid conversion of lithium polysulfide and slow down the polysulfide shuttle effect. The above carrier uses a carbon cloth with both high mechanical strength, good flexibility and good conductivity, and a self-supporting composite material with better performance and stronger adaptability can be obtained. Therefore, if the above self-supporting composite material and S are prepared into the cathode material of a lithium-sulfur battery and applied to the lithium-sulfur battery, on the basis of ensuring that the lithium-sulfur battery has a sufficiently large specific capacity and energy density, the conductivity of the S cathode can be improved, the polysulfide shuttle effect can be inhibited, and the volume expansion of S can be relieved, thereby improving the cycle stability and rate performance of the lithium-sulfur battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0018] Figure 1 Shows a contact angle test result diagram of an unmodified carbon cloth provided in Comparative Example 4 according to the present invention;

[0019] Figure 2 Shows a contact angle test result diagram of an oxidized modified carbon cloth provided in Example 1 according to the present invention;

[0020] Figure 3 shows Figure 2 the SEM image of the oxidized carbon cloth in

[0021] Figure 4 the SEM image of the surface morphology of a self - supporting composite material provided in Example 1 of the present invention;

[0022] Figure 5 shows Figure 4 the partially enlarged SEM image of the surface morphology of the self - supporting composite material in

[0023] Figure 6 the XRD pattern of a self - supporting composite material provided in Example 1 of the present invention;

[0024] Figure 7 shows the charge - discharge cycle diagram of the lithium - sulfur battery prepared from the self - supporting composite material of Example 1;

[0025] Figure 8 shows the charge - discharge curve diagram of the lithium - sulfur battery prepared from the self - supporting composite material of Example 1;

[0026] Figure 9 shows the SEM image of the surface morphology of a self - supporting composite material provided in Comparative Example 1 of the present invention;

[0027] Figure 10 shows Figure 9 the partially enlarged SEM image of the surface morphology of the self - supporting composite material in

[0028] Figure 11 shows the SEM image of the surface morphology of a self - supporting composite material provided in Comparative Example 2 of the present invention;

[0029] Figure 12 shows Figure 11 the partially enlarged SEM image of the surface morphology of the self - supporting composite material in; and

[0030] Figure 13 shows Figure 6 the schematic diagram of the cycling performance of the lithium - sulfur battery prepared from the self - supporting composite material at current densities of 0.1C / 0.2C / 0.5C / 1C / 2C / 3C. Detailed Description of the Invention

[0031] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0032] As analyzed in the background art, there are problems with poor cycle stability and rate performance of lithium-sulfur batteries in the prior art. To solve this problem, the present invention provides a self-supporting composite material, a preparation method thereof, a cathode material for a lithium-sulfur battery, and a lithium-sulfur battery.

[0033] In a typical embodiment of the present application, a self-supporting composite material is provided. The self-supporting composite material includes a carrier and MoN nanowires, and one end of at least part of the MoN nanowires is fixed on the carrier. The carrier includes modified carbon cloth, and the contact angle of the modified carbon cloth is 10° to 25°.

[0034] Compared with the unmodified carbon cloth, the wettability of the surface of the modified carbon cloth (contact angle of 10° to 25°) is correspondingly improved, which is beneficial to the formation of MoN nanowires in the self-supporting composite material. Since MoN is a good catalyst for catalyzing the conversion of polysulfides, at least part of the nanowire-shaped MoN is fixed on the modified carbon cloth to form a self-supporting composite material. If this self-supporting composite material is used as the cathode material of a lithium-sulfur battery, due to the excellent conductivity of the modified carbon cloth, on the one hand, it can improve the conductivity of S, and at the same time, as a self-supporting electrode, it avoids the use of binders and reduces the generation of by-products during charge and discharge; moreover, the MoN nanowires in the self-supporting composite material serve as the direct host of S. Since the MoN nanowires have a sufficiently large specific surface area, they provide as many binding sites as possible for S. While improving the specific capacity and energy density of the lithium-sulfur battery, enough space is also provided between the MoN nanowires to relieve the volume change caused by charge and discharge. On the other hand, the nanowire-shaped MoN can also catalyze the rapid conversion of lithium polysulfide and slow down the polysulfide shuttle effect. The above carrier uses carbon cloth with both high mechanical strength, good flexibility and good conductivity, and a self-supporting composite material with better performance and stronger adaptability can be obtained. Therefore, if the above self-supporting composite material and S are prepared into the cathode material of a lithium-sulfur battery and applied to a lithium-sulfur battery, on the basis of ensuring that the lithium-sulfur battery has a sufficiently large specific capacity and energy density, the conductivity of the S cathode can be improved, the polysulfide shuttle effect can be inhibited, and the volume expansion of S can be relieved, thereby improving the cycle stability and rate performance of the lithium-sulfur battery.

[0035] To ensure that there are enough MoN nanowires on the carbon cloth carrier, so as to provide as many binding sites as possible for S, catalyze the rapid conversion of lithium polysulfide to slow down the polysulfide shuttle effect and ensure the full play of the role of the carbon cloth, it is preferred that the mass of MoN nanowires per unit area of the above carrier is 25 - 65 g / m 2 .

[0036] In an embodiment of the present application, the above modified carbon cloth is oxidized modified carbon cloth.

[0037] Compared with the unmodified carbon cloth, the introduction of carboxyl groups in the above-mentioned oxidized modified carbon cloth improves its specific surface activity, thereby enhancing its surface wettability, and further increasing the formation efficiency of MoN nanowires in the self-supporting composite material.

[0038] In another typical embodiment of the present application, a method for preparing the above-mentioned self-supporting composite material is provided. The preparation method includes: Step S1, performing a solvothermal reaction on the modified carbon cloth and a molybdate solution to obtain a reaction product; Step S2, calcining the reaction product to obtain a self-supporting composite material, wherein the calcination is carried out in a mixed gas of an inert gas and ammonia, or a mixed gas of nitrogen and ammonia, and wherein, based on molybdenum ions, the molar concentration of the molybdate solution is 0.02 to 0.05 mol / L.

[0039] Compared with the unmodified carbon cloth, the surface wettability of the modified carbon cloth (contact angle is 10° - 25°) is correspondingly improved, which is beneficial for the molybdate solution in the above solvothermal reaction to combine with the modified carbon cloth, so that the surface of the modified carbon cloth contains as much molybdate as possible, and further reacts with ammonia during its calcination to obtain MoN nanowires. Further, the molar concentration of the molybdate solution needs to be controlled within the above range to form MoN nanowires. Otherwise, if the molar concentration of the molybdate solution is too small, MoN nanoparticles will be formed, and if the molar concentration of the molybdate solution is too large, MoN blocks will be formed. Since MoN is a good catalyst for catalyzing the conversion of polysulfides, by fixing at least part of the nanowire-shaped MoN on the modified carbon cloth to form a self-supporting composite material, if this self-supporting composite material is used as the cathode material of a lithium-sulfur battery, due to the excellent conductivity of the modified carbon cloth, on the one hand, it can improve the conductivity of S, and at the same time, as a self-supporting electrode, it avoids the use of a binder and reduces the generation of by-products during charge and discharge; moreover, the MoN nanowires in the self-supporting composite material serve as the direct host of S. Since the MoN nanowires have a sufficiently large specific surface area, they provide as many binding sites for S as possible. While improving the specific capacity and energy density of the lithium-sulfur battery, the space between the MoN nanowires can also relieve the volume change caused by charge and discharge. On the other hand, the nanowire-shaped MoN can also catalyze the rapid conversion of lithium polysulfide and slow down the polysulfide shuttle effect. The above carrier uses a carbon cloth with both high mechanical strength, good flexibility and good conductivity, and a self-supporting composite material with better performance and stronger adaptability can be obtained. Therefore, if the above self-supporting composite material and S are prepared into the cathode material of a lithium-sulfur battery and applied to the lithium-sulfur battery, it can improve the conductivity of the S cathode, inhibit the polysulfide shuttle effect, relieve the volume expansion of S, and thus improve the cycle stability and rate performance of the lithium-sulfur battery on the basis of ensuring that the lithium-sulfur battery has a sufficiently large specific capacity and energy density.

[0040] In one embodiment of the present application, in terms of molybdenum ions, relative to 1 m 2 of the modified carbon cloth, the mass of the molybdate is 56-112 g. Preferably, the molybdate is selected from any one or more of ammonium paramolybdate, sodium molybdate, and potassium molybdate. Preferably, the solvent in the molybdate solution is an organic solvent. Preferably, the organic solvent is selected from one or more of ethanol, N,N-dimethylformamide, methanol, and dimethyl sulfoxide. Preferably, the modified carbon cloth is a modified graphitized carbon fiber cloth or a modified carbon fiber cloth. Further preferably, the modified carbon cloth is selected from any one or more of modified HCP330P, modified HCP330N, modified HCP331P, and modified HCP331N.

[0041] By adjusting the mass of molybdenum ions on the modified carbon cloth per unit area, the amount of MoN nanowires on the modified carbon cloth can be controlled, so as to more reasonably control the specific capacity and energy density of the lithium-sulfur battery, and at the same time provide a reasonable active MoN catalyst for the lithium-sulfur battery, thereby alleviating the influence of polysulfides on the cycle stability of the lithium-sulfur battery. Together with the above-preferred modified carbon cloth, molybdate, and organic solvent, the comprehensive performance of the lithium-sulfur battery can be further improved.

[0042] To improve the efficiency of the above solvothermal reaction, preferably, the temperature of the solvothermal reaction is 180-220 °C, and preferably, the time of the solvothermal reaction is 10-20 h.

[0043] In one embodiment of the present application, the volume ratio of the above inert gas to ammonia is 5-95:5-95, or the volume ratio of nitrogen to ammonia is 5-95:5-95.

[0044] The purpose of the above ammonia is to act on the reaction product generated by the solvothermal reaction. Although pure ammonia is more conducive to the conversion of the reaction product into MoN nanowires, the ammonia concentration is too high and the corrosion of the reaction equipment is too strong. Therefore, an inert gas or nitrogen is used. On the one hand, it dilutes the ammonia, thereby reducing the corrosion of the ammonia on the reactor during calcination. On the other hand, it reduces the probability of the reaction of active components such as oxygen in the air with the reaction product to generate by-products.

[0045] To improve the interaction between the above ammonia and the reaction product to generate MoN nanowires, preferably, the temperature of the above calcination is 700-800 °C, and preferably, the time of the calcination is 1-2.5 h.

[0046] In one embodiment of the present application, the above preparation method further includes oxidizing the carbon cloth to obtain a modified carbon cloth, and preferably, the oxidation is electrooxidation.

[0047] Since the carbon cloth is made of polyacrylonitrile carbon fiber, its surface is relatively smooth, which is not conducive to the wetting of the liquid phase. If it is oxidized, acidic carboxyl groups can be introduced into the carbon cloth, thereby improving the surface activity of the carbon cloth, further enhancing its wettability, and enabling more molybdate solutions to spread on its surface.

[0048] In another typical embodiment of the present application, a cathode material for a lithium-sulfur battery is provided. The cathode material includes sulfur and a conductive agent, and the conductive agent includes the aforementioned self-supporting composite material. Preferably, the mass ratio of sulfur to the conductive agent is 1:1 to 5:1.

[0049] The above cathode material including the self-supporting composite material has excellent electrical properties.

[0050] In yet another typical embodiment of the present application, a lithium-sulfur battery is provided. The lithium-sulfur battery includes a cathode and an anode, and the cathode includes the above cathode material.

[0051] Using the above cathode material of the lithium-sulfur battery with good electrical properties in a lithium-sulfur battery can improve the energy density of the lithium-sulfur battery and enhance its cycle stability and rate performance.

[0052] The beneficial effects of the present application will be described below in conjunction with specific examples and comparative examples.

[0053] Example 1

[0054] The carbon cloth was electro-oxidized using a three-electrode system. The model of the carbon cloth was HCP330P, and the size of the carbon cloth was 3 * 4 cm. 2 Using a Pt electrode as the counter electrode, a Hg2SO4 electrode as the reference electrode, the carbon cloth as the working electrode, and 0.5M H2SO4 as the electrolyte, cyclic voltammetry (CV) scanning was performed at a scanning rate of 10 mV / s for 30 cycles at a voltage of 1.2 - 1.7V to obtain modified HCP330P. After washing the modified HCP330P to neutrality, it was dried in an oven at 80°C for standby. The SEM image of the oxidized and modified carbon cloth is as Figure 3 shown. Using the contact angle measurement method, the contact angle of the modified carbon cloth was measured to be 10° - 25°, and the contact angle test results are as Figure 2 shown.

[0055] 0.14 mmol of ammonium heptamolybdate (chemical formula: (NH4)6Mo7O 24) Dissolve it in 30 mL of N,N-dimethylformamide. After stirring evenly, add two pieces of the above-mentioned modified carbon cloth into it. Carry out solvothermal reaction at 200 °C for 15 h in a reaction kettle. Wash the reaction product with ethanol and dry it, then calcine it at 700 °C for 2 h in an Ar / NH₃ mixed gas with a volume ratio of 90:10 to obtain a self-supporting composite material. The self-supporting composite material includes carbon cloth and MoN nanowires. One end of the MoN nanowires in the transverse direction is embedded in the carbon cloth, and the mass of MoN nanowires per unit area of the carbon cloth is 40 g / m 2 , and the SEM image of the surface morphology of the self-supporting composite material is as shown in Figure 4 . The partially enlarged SEM image of the surface morphology of the self-supporting composite material is as shown in Figure 5 . It can be seen from Figure 3 , Figure 4 and Figure 5 that the surface morphology of the self-supporting composite material is nanowires. Figure 6 is the XRD pattern of the self-supporting composite material. It can be seen from Figure 6 that the self-supporting composite material contains crystals of MoN. Figure 7 is the charge-discharge cycle diagram of the lithium-sulfur battery prepared using the self-supporting composite material. Figure 8 is the charge-discharge curve diagram of the lithium-sulfur battery prepared using the self-supporting composite material. It can be seen from Figure 7 that the self-supporting composite material can improve the cycle stability of the lithium-sulfur battery.

[0056] Example 2

[0057] The difference between Example 2 and Example 1 is that

[0058] Dissolve 0.14 mmol of ammonium paramolybdate in 20 mL of N,N-dimethylformamide, and finally obtain a self-supporting composite material. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 45 g / m 2 .

[0059] Example 3

[0060] The difference between Example 3 and Example 1 is that

[0061] Dissolve 0.14 mmol of ammonium paramolybdate in 50 mL of N,N-dimethylformamide, and finally obtain a self-supporting composite material. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 42 g / m 2 .

[0062] Example 4

[0063] The difference between Example 4 and Example 1 is that

[0064] Dissolve 0.1 mmol of ammonium heptamolybdate in 21 mL of N,N-dimethylformamide to finally obtain a self-supporting composite material. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 28 g / m 2 .

[0065] Example 5

[0066] The difference between Example 5 and Example 1 is that

[0067] Dissolve 0.2 mmol of ammonium heptamolybdate in 43 mL of N,N-dimethylformamide to finally obtain a self-supporting composite material. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 65 g / m 2 .

[0068] Example 6

[0069] The difference between Example 6 and Example 1 is that

[0070] Dissolve 0.08 mmol of ammonium heptamolybdate in 17 mL of N,N-dimethylformamide to finally obtain a self-supporting composite material. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 25 g / m 2 .

[0071] Example 7

[0072] The difference between Example 7 and Example 1 is that

[0073] The model of the carbon cloth is HCP331P, and a self-supporting composite material is finally obtained. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 48 g / m 2 .

[0074] Example 8

[0075] The difference between Example 8 and Example 1 is that

[0076] Dissolve 0.98 mmol of sodium molybdate in 30 mL of N,N-dimethylformamide to finally obtain a self-supporting composite material. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 43 g / m 2 .

[0077] Example 9

[0078] The difference between Example 9 and Example 1 is that

[0079] Dissolve 0.14 mmol of ammonium heptamolybdate in 30 mL of ethanol to finally obtain a self-supporting composite material. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 45 g / m 2 .

[0080] Example 10

[0081] The difference between Example 10 and Example 1 is that

[0082] the temperature of the solvothermal reaction is 180 °C, and a self-supporting composite material is finally obtained, wherein the mass of MoN nanowires per unit area of the carbon cloth is 38 g / m 2 .

[0083] Example 11

[0084] The difference between Example 11 and Example 1 is that

[0085] the temperature of the solvothermal reaction is 220 °C, and a self-supporting composite material is finally obtained, wherein the mass of MoN nanowires per unit area of the carbon cloth is 45 g / m 2 .

[0086] Example 12

[0087] The difference between Example 12 and Example 1 is that

[0088] the temperature of the solvothermal reaction is 170 °C, and a self-supporting composite material is finally obtained, wherein the mass of MoN nanowires per unit area of the carbon cloth is 35 g / m 2 .

[0089] Example 13

[0090] The difference between Example 13 and Example 1 is that

[0091] the time of the solvothermal reaction is 10 h, and a self-supporting composite material is finally obtained, wherein the mass of MoN nanowires per unit area of the carbon cloth is 38 g / m 2 .

[0092] Example 14

[0093] The difference between Example 14 and Example 1 is that

[0094] the temperature of the solvothermal reaction is 20 h, and a self-supporting composite material is finally obtained, wherein the mass of MoN nanowires per unit area of the carbon cloth is 45 g / m 2 .

[0095] Example 15

[0096] The difference between Example 15 and Example 1 is that

[0097] the temperature of the solvothermal reaction is 8 h, and a self-supporting composite material is finally obtained, wherein the mass of MoN nanowires per unit area of the carbon cloth is 35 g / m 2 .

[0098] Example 16

[0099] Example 16 is different from Example 1 in that

[0100] The volume ratio of Ar to NH3 is 95:5, and a self-supporting composite material is finally obtained. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 35 g / m 2 .

[0101] Example 17

[0102] Example 17 is different from Example 1 in that

[0103] There is no argon, and it is all ammonia. Finally, a self-supporting composite material is obtained. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 50 g / m 2 .

[0104] Example 18

[0105] Example 18 is different from Example 1 in that

[0106] The volume ratio of Ar to NH3 is 97:3, and a self-supporting composite material is finally obtained. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 32 g / m 2 .

[0107] Example 19

[0108] Example 19 is different from Example 1 in that

[0109] The calcination temperature is 750 °C, and the calcination time is 2.5 h. Finally, a self-supporting composite material is obtained. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 45 g / m 2 .

[0110] Example 20

[0111] Example 20 is different from Example 1 in that

[0112] The calcination temperature is 800 °C, and the calcination time is 1 h. Finally, a self-supporting composite material is obtained. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 50 g / m 2 .

[0113] Example 21

[0114] Example 21 is different from Example 1 in that

[0115] The calcination temperature is 680 °C, and the calcination time is 2 h. Finally, a self-supporting composite material is obtained. Among them, the mass of MoN nanowires per unit area of the carbon cloth is 38 g / m 2 .

[0116] Comparative Example 1

[0117] The difference between Comparative Example 1 and Example 1 is that

[0118] 0.07 mmol of ammonium paramolybdate was dissolved in 30 mL of N,N-dimethylformamide, and finally the mass of MoN nanoparticles per unit area of the carbon cloth was 50 g / m 2 of the composite material. The morphology diagram of the composite material is as shown in Figure 9 shown, and the enlarged morphology diagram is as shown in Figure 10 shown. From Figure 9 、 10 it can be seen that due to the too small concentration of ammonium paramolybdate, MoN particles were formed.

[0119] Comparative Example 2

[0120] The difference between Comparative Example 2 and Example 1 is that

[0121] 0.25 mmol of ammonium paramolybdate was dissolved in 30 mL of N,N-dimethylformamide, and finally the mass of MoN blocks per unit area of the carbon cloth was 70 g / m 2 of the composite material. The morphology diagram of the composite material is as shown in Figure 11 shown, and the enlarged morphology diagram is as shown in Figure 12 shown. From Figure 11 、 12 it can be seen that due to the too large concentration of ammonium paramolybdate, MoN blocks were formed.

[0122] Comparative Example 3

[0123] By mass percentage, 50% of elemental sulfur, 10% of commercial carbon black conductive agent (Super P), 30% of MoN, and 10% of PVDF binder (polyvinylidene fluoride) were dissolved in N-methylpyrrolidone (NMP) to form the positive electrode slurry of the lithium-sulfur battery. The slurry was coated on aluminum foil and vacuum dried at 60 °C for 12 hours to obtain the aluminum foil / S positive electrode. The sulfur loading on the aluminum foil / S positive electrode was about 3 mg·cm -2 , and the MoN loading was about 1 mg·cm -2 .

[0124] Comparative Example 4

[0125] The difference between Comparative Example 4 and Example 1 is that

[0126] 0.14 mmol of ammonium paramolybdate was dissolved in 30 mL of N,N-dimethylformamide, and after stirring evenly, the unmodified carbon cloth of model HCP330P (the contact angle test results are as shown in Figure 1The one shown in [Figure] was added thereto, and a solvothermal reaction was carried out at 200 °C for 15 h in a reaction kettle. After the reaction, the product was washed with ethanol and dried, and then calcined at 700 °C for 2 h in a mixed gas of Ar / NH3 with a volume ratio of 90:10, but the self-supporting composite material of the present application was not obtained.

[0127] Fabrication of lithium-sulfur batteries: S and the self-supporting composite materials of Examples 1 to 21 above, and the materials obtained in Comparative Examples 1, 2, and 4 were respectively prepared into the positive electrode materials of lithium-sulfur batteries according to a mass ratio of 1:1, and assembled with lithium negative electrodes, separators, and lithium-sulfur electrolytes into lithium-sulfur batteries. The aluminum foil / S positive electrode, lithium negative electrode, separator, and lithium-sulfur electrolyte obtained in Comparative Example 3 were assembled into a lithium-sulfur battery.

[0128] The electrical performance of the above lithium-sulfur batteries was tested using a LAND-CT 2001A battery test system produced by Wuhan Blue Electronic Co., Ltd. at room temperature, and tested in a voltage range of 1.7 - 2.8 V at a rate of 0.1C (1C = 1675 mAh·g -1 ). The charge-discharge specific capacity of the test battery and the specific capacity retention rate after 50 cycles were tested, and the test results are listed in Table 1.

[0129] Table 1

[0130]

[0131] S and the self-supporting composite material of Example 1 were respectively prepared into the positive electrode materials of lithium-sulfur batteries according to mass ratios of 3:1, 5:1, and 6:1, and assembled with lithium negative electrodes, separators, and lithium-sulfur electrolytes into lithium-sulfur batteries. The above lithium-sulfur batteries were tested at a rate of 0.1C (1C = 1675 mAh·g -1 ) using the same electrical performance test instrument and method as above in a voltage range of 1.7 - 2.8 V. The charge-discharge specific capacity of the test battery and the specific capacity retention rate after 50 cycles were tested, and the test results are listed in Table 2.

[0132] Table 2

[0133]

[0134] The rate performance of the lithium-sulfur batteries prepared from the self-supporting composite material obtained in Example 1 above was tested at current densities of 0.1C / 0.2C / 0.5C / 1C / 2C / 3C, and the test results are as Figure 13 shown. As can be seen from the figure, the lithium-sulfur batteries prepared from the above self-supporting composite material of the present application have good rate performance and good reversibility.

[0135] From the above description, it can be seen that the above embodiments of the present invention have achieved the following technical effects:

[0136] Compared with the unmodified carbon cloth, the wettability of the surface of the modified carbon cloth (contact angle is 10° - 25°) is correspondingly improved, which is beneficial to the formation of MoN nanowires in the self-supporting composite material. Since MoN is a good catalyst for catalyzing the conversion of polysulfides, at least part of the nanowire-shaped MoN is fixed on the modified carbon cloth to form a self-supporting composite material. If this self-supporting composite material is used as the positive electrode material of a lithium-sulfur battery, due to the excellent electrical conductivity of the modified carbon cloth, on the one hand, it can improve the electrical conductivity of S, and at the same time, as a self-supporting electrode, it avoids the use of binders and reduces the generation of by-products during charge and discharge; moreover, the MoN nanowires in the self-supporting composite material serve as the direct host of S. Since the MoN nanowires have a sufficiently large specific surface area, they provide as many binding sites for S as possible. While improving the specific capacity and energy density of the lithium-sulfur battery, the space between the MoN nanowires can also relieve the volume change caused by charge and discharge. On the other hand, the nanowire-shaped MoN can also catalyze the rapid conversion of lithium polysulfide and slow down the polysulfide shuttle effect. The above carrier uses a carbon cloth with both high mechanical strength, good flexibility and good electrical conductivity, and a self-supporting composite material with better performance and stronger adaptability can be obtained. Therefore, if the above self-supporting composite material and S are prepared into the positive electrode material of a lithium-sulfur battery and applied to the lithium-sulfur battery, on the basis of ensuring that the lithium-sulfur battery has a sufficiently large specific capacity and energy density, it can improve the electrical conductivity of the S positive electrode, inhibit the polysulfide shuttle effect, relieve the volume expansion of S, and thus improve the cycle stability and rate performance of the lithium-sulfur battery.

[0137] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A self-supporting composite material, characterized in that, The self-supporting composite material includes a carrier and MoN nanowires, one end of at least a part of the MoN nanowires is fixed on the carrier, the carrier includes a modified carbon cloth, and the contact angle of the modified carbon cloth is 10° to 25°; the mass of the MoN nanowires per unit area of the carrier is 25 to 65 g / m 2 .

2. The self-supporting composite material according to claim 1, wherein The modified carbon cloth is an oxidized modified carbon cloth.

3. A method for preparing the self-supporting composite material according to claim 1 or 2, characterized in that, The preparation method includes: Step S1, subjecting the modified carbon cloth to a solvothermal reaction with a molybdate solution to obtain a reaction product; Step S2, calcining the reaction product to obtain the self-supporting composite material, wherein the calcination is carried out in a mixed gas of an inert gas and ammonia, or a mixed gas of nitrogen and ammonia, and wherein, calculated in terms of molybdenum ions, the molar concentration of the molybdate solution is 0.02 to 0.05 mol / L.

4. The preparation method according to claim 3, characterized in that Based on molybdenum ions, relative to 1 m 2 of the modified carbon cloth, the mass of molybdate is 56 to 112 g.

5. The preparation method according to claim 4, characterized in that, The molybdate is selected from any one or more of ammonium paramolybdate, sodium molybdate, and potassium molybdate.

6. The preparation method according to claim 3, characterized in that, The solvent in the molybdate solution is an organic solvent.

7. The preparation method according to claim 6, characterized in that, The organic solvent is selected from one or more of ethanol, N,N-dimethylformamide, methanol, and dimethyl sulfoxide.

8. The preparation method according to claim 3, wherein The modified carbon cloth is a modified graphitized carbon fiber cloth or a modified carbon fiber cloth.

9. The preparation method according to claim 8, wherein The modified carbon cloth is selected from any one or more of modified HCP330P, modified HCP330N, modified HCP331P, and modified HCP331N.

10. The preparation method according to claim 3, characterized in that, The temperature of the solvothermal reaction is 180 to 220 °C.

11. The preparation method according to claim 3, characterized in that The time of the solvothermal reaction is 10 to 20 h.

12. The preparation method according to claim 3, wherein The volume ratio of the inert gas to the ammonia is 5 to 95:5 to 95, or the volume ratio of the nitrogen to the ammonia is 5 to 95:5 to 95.

13. The preparation method according to claim 3, characterized in that, The temperature of the calcination is 700 to 800 °C.

14. The preparation method according to claim 3, wherein The time of the calcination is 1 to 2.5 h.

15. The preparation method according to claim 3, characterized in that, The preparation method further includes oxidizing the carbon cloth to obtain the modified carbon cloth.

16. The preparation method according to claim 15, characterized in that, The oxidation is electrooxidation.

17. A cathode material for a lithium-sulfur battery, the cathode material comprising sulfur and a conductive agent, characterized in that, The conductive agent includes the self-supporting composite material according to claim 1 or 2, and the mass ratio of the sulfur to the conductive agent is 1:1 to 5:

1.

18. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery includes a positive electrode and a negative electrode, and is characterized in that the positive electrode includes the positive electrode material according to claim 17.

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