Positive electrode material, secondary battery, and electric device

Abstract

The application discloses a positive electrode material, a secondary battery and an electric device, and belongs to the technical field of batteries. a M b , carbon nanofibers and sulfur, wherein N is at least one of Cr, Sr, W, Y, Fe, Co, Pt, Zr, Hf, Ta, Mo, Tc, Mn, Nb and Bi, M is at least one of NbO4 3‑ , VO4 3‑ , MnO4 2‑ , BiO3 3‑ , SnO3 2‑ , WO4 2‑ , MoO4 2‑ , 1<=a<=3 and 1<=b<=7. The positive electrode material can effectively improve the conductivity, effectively adsorb polysulfides and catalyze the conversion of polysulfides, thereby inhibiting the polysulfide shuttle, being favorable for the transmission of electrons and effectively improving the electrochemical performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive electrode material, a secondary battery, and an electrical device. Background Technology

[0002] Secondary batteries, such as lithium-sulfur batteries, have broad application prospects in fields such as electric vehicles and wearable devices due to their advantages such as high energy density and low cost.

[0003] The "shuttle effect" caused by the migration of soluble polysulfides generated during the charging and discharging process of lithium-sulfur batteries into the electrolyte and towards the negative electrode due to the concentration gradient leads to irreversible sulfur loss at the positive electrode, continuous corrosion of the negative electrode, and abnormal electrolyte consumption. Ultimately, this results in low discharge capacity and poor cycle stability of lithium-sulfur batteries. Therefore, addressing the "shuttle effect" of polysulfides is crucial to fully realizing the potential of lithium-sulfur batteries.

[0004] Therefore, this application is submitted. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the existing technology and provide a positive electrode material, a secondary battery and an electrical device. The positive electrode material of this application can effectively improve conductivity, effectively adsorb polysulfides and catalyze the conversion of polysulfides, thereby inhibiting polysulfide shuttle and facilitating electron transfer, which can effectively improve the electrochemical performance of the secondary battery.

[0006] To achieve the above objectives, the first aspect of this application provides a cathode material comprising N a M b Carbon nanofibers and sulfur, wherein N is at least one of Cr, Sr, W, Y, Fe, Co, Pt, Zr, Hf, Ta, Mo, Tc, Mn, Nb, and Bi, and M is NbO4. 3- VO4 3- MnO4 2- BiO3 3- SnO3 2- WO4 2- MoO4 2- At least one of them, 1≤a≤3, 1≤b≤7.

[0007] As an implementation of this application, the N a M b The mass ratio of carbon nanofibers is (0.1~2.4):1.

[0008] As an embodiment of this application, the sulfur loading of the cathode material is 0.9–20 mg / cm³. 2 .

[0009] As an embodiment of this application, the electron paramagnetic resonance spectrum of the cathode material has a characteristic peak at a g-factor of 1.99 to 2.005.

[0010] As an embodiment of this application, the electron paramagnetic resonance spectrum of the cathode material exhibits a characteristic peak at a g-factor of 1.5–1.98; and / or

[0011] The electron paramagnetic resonance spectrum of the cathode material has characteristic peaks in the range of g factor 2.006 to 4.

[0012] As an embodiment of this application, the positive electrode material is a self-supporting material, and the thickness of the positive electrode material is 30-300 μm.

[0013] As an embodiment of this application, the positive electrode material has a mesoporous structure and a microporous structure, wherein the pore size of the micropore is d1nm and the pore size of the mesopore is d2nm, satisfying: 1≤d1<2, 2≤d2≤20.

[0014] As an embodiment of this application, the density of the positive electrode material is 1.0–3.0 g / cm³. 3 .

[0015] A second aspect of this application provides a secondary battery including a positive electrode sheet, the positive electrode sheet comprising the positive electrode material described above.

[0016] A third aspect of this application provides an electrical device including the aforementioned secondary battery, wherein the secondary battery serves as the power supply for the electrical device.

[0017] The beneficial effects of this application are as follows: the cathode material of this application includes N a M b Carbon nanofibers and sulfur, where N is a high oxidation state transition metal and M is a metal acid anion, can form a three-dimensional conductive network structure, which can effectively improve conductivity, effectively adsorb polysulfides and catalyze the conversion of polysulfides, thereby inhibiting polysulfide shuttle and avoiding the loss of cathode material. At the same time, the three-dimensional conductive network structure not only provides a large space for storing elemental sulfur, but also, due to the presence of carbon nanofibers, can withstand the volume expansion of sulfur during lithiation and provide abundant electron pathways, which is conducive to electron transfer and can effectively improve the electrochemical performance of secondary batteries. Attached Figure Description

[0018] Figure 1 This is a morphological diagram of the precursor of Example 1.

[0019] Figure 2 This is a pore structure diagram of the positive electrode material in Example 1.

[0020] Figure 3The electron paramagnetic resonance spectra of the cathode materials in Examples 1-3 are shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0023] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0024] This application provides a cathode material, including N a M b Carbon nanofibers and sulfur, wherein N is at least one of Cr, Sr, W, Y, Fe, Co, Pt, Zr, Hf, Ta, Mo, Tc, Mn, Nb, and Bi, and M is NbO4. 3- VO4 3- MnO4 2- BiO3 3- SnO3 2- WO4 2- MoO4 2- At least one of them, 1≤a≤3, 1≤b≤7.

[0025] In one embodiment, the N a M b Including any one of CrNbO4, Fe2(MnO4)3, W(VO4)2, Zr3(BiO3)4, SrSnO3, CoWO4, SrMoO4, YVO4, BiVO4, MnWO4, and MnMoO4.

[0026] The cathode material of this application includes N a M bCarbon nanofibers and sulfur, where N is a high oxidation state transition metal and M is a metal acid anion, can form a three-dimensional conductive network structure, which can effectively improve conductivity, effectively adsorb polysulfides and catalyze the conversion of polysulfides, thereby inhibiting polysulfide shuttle and avoiding the loss of cathode material. At the same time, the three-dimensional conductive network structure not only provides a large space for storing elemental sulfur, but also, due to the presence of carbon nanofibers, can withstand the volume expansion of sulfur during lithiation and provide abundant electron pathways, which is conducive to electron transfer and can effectively improve the electrochemical performance of secondary batteries.

[0027] In one embodiment, the N a M b The mass ratio of carbon nanofibers is (0.1–2.4):1, for example, it can be 0.1, 0.2, 0.4, 0.8, 1, 1.5, 2, 2.4, or any two of these values. This application controls N... a M b The mass ratio of carbon nanofibers to carbon nanofibers is (0.1-2.4):1, which can form a more stable three-dimensional conductive network structure, more effectively improve conductivity, effectively adsorb polysulfides and catalyze the conversion of polysulfides, more effectively promote electron transfer, and further improve electrochemical performance.

[0028] In one embodiment, the sulfur loading of the cathode material is 0.9–20 mg / cm³. 2 For example, it could be 0.9 mg / cm³. 2 1mg / cm 2 2mg / cm 2 5mg / cm 2 10mg / cm 2 20mg / cm 2 Or a range consisting of any two of these values.

[0029] In one embodiment, the sulfur loading of the cathode material is 1.5 mg / cm³. 2 ~10mg / cm 2 Within this range, the sulfur loading can further improve the electrochemical performance.

[0030] In one embodiment, the electron paramagnetic resonance spectrum of the cathode material exhibits a characteristic peak in the g-factor range of 1.99–2.005. The presence of this characteristic peak in the g-factor range indicates the presence of oxygen vacancies in the cathode material. The presence of these oxygen vacancies can establish a surface electric field, and because they carry a positive charge, they can effectively enhance the rapid conversion of polysulfides along the surface, further adsorbing and catalyzing the conversion of polysulfides, thereby improving the electrochemical performance of the secondary battery.

[0031] In one embodiment, the electron paramagnetic resonance spectrum of the cathode material has a characteristic peak at a g-factor of 1.5 to 1.98.

[0032] In one embodiment, the electron paramagnetic resonance spectrum of the cathode material has a characteristic peak at a g-factor of 2.006 to 4.

[0033] The cathode material exhibits characteristic peaks at 1.5–1.98 and / or 2.006–4, indicating the presence of cation vacancies. These cation vacancies carry a negative charge, and their polysulfides establish an electric field perpendicular to the surface, thereby rapidly converting the polysulfides. This further enhances the adsorption and catalytic conversion of polysulfides, improving the electrochemical performance of the secondary battery.

[0034] In one embodiment, the N a M b It grows in situ on the surface and inside of the carbon nanofibers.

[0035] In one embodiment, the carbon nanofibers have particulate compounds on their surface.

[0036] In one embodiment, the cathode material is a self-supporting material with a thickness of 30-300 μm. The cathode material described in this application is a self-supporting material with excellent flexibility, which can withstand the volume expansion of sulfur during lithiation and is also conducive to electron transfer, resulting in higher energy density.

[0037] In one embodiment, the cathode material has a mesoporous structure and a microporous structure, wherein the pore size of the micropore is d1 nm and the pore size of the mesopore is d2 nm, satisfying: 1≤d1<2, 2≤d2≤20. The cathode material described in this application has a hierarchical pore structure, high specific surface area and porosity, which can effectively reduce the loss of active material, rapidly adsorb polysulfides, and improve the electrochemical performance of the secondary battery.

[0038] In one embodiment, the density of the positive electrode material is 1.0–3.0 g / cm³. 3 For example, it could be 1.0 g / cm³. 3 1.2g / cm 3 1.5g / cm 3 2g / cm 3 3g / cm 3 Or a range consisting of any two of these values.

[0039] In one embodiment, the density of the positive electrode material is 1.1–2 g / cm³. 3The cathode material described in this application has a low density, which is beneficial for obtaining secondary batteries with higher energy density and meets the requirements of lightweight design.

[0040] One embodiment of this application provides a method for preparing a positive electrode material, including the following steps:

[0041] The carbon-containing polymer, the first metal salt, and the organic acid are dissolved in water and stirred until homogeneous to obtain a mixture.

[0042] Organic solvent and hydrolysis inhibitor are added to the mixture and stirred evenly. Then, the second metal salt is added and stirred evenly. Finally, the pore-forming agent solution is added and stirred evenly to obtain the spinning solution.

[0043] The spinning solution is electrospun to obtain the spun material;

[0044] The spun fabric is oxidized and sintered to obtain the precursor;

[0045] Sulfur powder is dissolved in carbon disulfide solution to obtain sulfur powder solution;

[0046] The precursor is added to the sulfur powder solution, left to stand, removed, and the carbon disulfide solution is allowed to evaporate. The solution is then calcined to obtain the cathode material.

[0047] In one embodiment, the carbon-containing polymer includes at least one of polyacrylonitrile, polyvinylpyrrolidone, polyimide, and petroleum asphalt.

[0048] In one embodiment, the molecular weight M of the carbon-containing polymer W The range is 10,000 to 1,500,000.

[0049] In one embodiment, the organic acid includes at least one of citric acid, malic acid, and tartaric acid.

[0050] In one embodiment, the first metal salt comprises at least one of chromium acetate, tungsten ethoxide, yttrium isopropoxide, yttrium oxalate, ferric acetate, cobalt naphthenate, cobalt acetate, platinum oxide, zirconium ethoxide, hafnium oxide, tantalum butanol, molybdenum oxide, manganese acetate, strontium oxide, bismuth acetate, and bismuth neodecanoate.

[0051] In one embodiment, the first organic solvent includes at least one of N,N-dimethylformamide, acetone, water, methanol, and ethanol.

[0052] In one embodiment, the second metal salt includes niobium oxalate, vanadium oxide, manganese dioxide, bismuth trioxide, tin dioxide, ferric citrate, tungstic acid, and molybdenum trioxide.

[0053] In one embodiment, the hydrolysis inhibitor includes at least one of acetic acid, formic acid, and lactic acid.

[0054] In one embodiment, the pore-forming agent solution includes a pore-forming agent and a second organic solvent.

[0055] In one embodiment, the mass ratio of the pore-forming agent to the second organic solvent is 1:(6-10), for example, it can be 1:6, 1:7, 1:8, 1:9, 1:10 or any two of these values.

[0056] In one embodiment, the pore-forming agent includes at least one of γ-cyclodextrin, polypropylene carbonate, polyoxymethylene, starch, and polystyrene.

[0057] In one embodiment, the second organic solvent includes at least one of N,N-dimethylformamide, acetone, water, methanol, and ethanol.

[0058] In one embodiment, the sintering temperature is 800–1000°C. For example, it can be 800°C, 850°C, 900°C, 950°C, 1000°C, or a range of any two of these values.

[0059] In one embodiment, the sintering time is 1 to 6 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours or any two of these values.

[0060] In one embodiment, the oxidation temperature is 180–250°C. For example, it can be 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, or a range of any two of these values.

[0061] In one embodiment, the oxidation time is 1 to 6 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours or any two of these values.

[0062] In one embodiment, the calcination temperature is 140–180°C, for example, it can be 140°C, 150°C, 160°C, 170°C, 180°C or any two of these values.

[0063] In one embodiment, the calcination time is 6 to 24 hours, for example, it can be 6 hours, 7 hours, 8 hours, 10 hours, 12 hours, 18 hours, 20 hours, 24 hours or any two of these values.

[0064] In one embodiment, the mass ratio of the carbon-containing polymer to the first metal salt is (2-5):1, for example, it can be 2:1, 3:1, 4:1, 5:1 or any two of these values.

[0065] In one embodiment, the mass ratio of the carbon-containing polymer to the organic acid is (1 to 100):1, for example, it can be 1:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1 or any range of two of these values.

[0066] In one embodiment, the mass ratio of the carbon-containing polymer to the hydrolysis inhibitor is (1 to 100):1, for example, it can be 1:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1 or any range of two of these values.

[0067] In one embodiment, the mass ratio of the mixture to the pore-forming agent solution is (1-4):1, for example, it can be 1:1, 2:1, 3:1, 4:1, or any two of these values. In one embodiment, the mass ratio of the precursor to the sulfur powder is (1-3):(1-5), for example, it can be 3:1, 1:1, 1:3, 1:5, or any two of these values. One embodiment of this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet comprising the positive electrode material described above.

[0068] In one embodiment, the positive electrode includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector.

[0069] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0070] In one embodiment, the type of positive current collector is not particularly limited and can be any material known to be suitable for use as a positive current collector.

[0071] In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper. In one embodiment, the positive electrode current collector is a metallic material. In one embodiment, the positive electrode current collector is aluminum.

[0072] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0073] In one embodiment, the positive electrode film layer may optionally include a conductive agent and a binder.

[0074] In one embodiment, the secondary battery also includes a negative electrode and a separator.

[0075] In one embodiment, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0076] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0077] In one embodiment, there are no particular limitations on the negative current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector, etc.

[0078] In one embodiment, the negative electrode active material can be natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, or spinel-structured lithium titanate Li4Ti5O. 12 At least one of Li-Al alloys and metallic lithium.

[0079] In one embodiment, the negative electrode active material layer further includes a conductive agent and a binder.

[0080] In one embodiment, there is no limitation on the type of conductive agent mentioned in this application, and any known conductive agent may be used.

[0081] In one embodiment, the conductive agent includes at least one of carbon materials such as superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers, and needle coke.

[0082] In one embodiment, there is no limitation on the type of adhesive mentioned in this application, and any known adhesive may be used.

[0083] In one embodiment, the adhesive includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydrogenation, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer.

[0084] In one embodiment, the membrane is a polymer.

[0085] The polymers mentioned in this application include at least one of polyethylene, polystyrene, polyvinyl chloride, polyether, polyester, polyamide, polyurethane, polysulfide rubber, polyethylene terephthalate, polytetrafluoroethylene, and polyethersulfone.

[0086] In one embodiment, the secondary battery may include an outer packaging that can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0087] In one embodiment, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0088] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0089] One embodiment of this application provides an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.

[0090] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0091] The present application is further illustrated below with specific embodiments:

[0092] Example 1

[0093] A method for preparing a positive electrode material includes the following steps:

[0094] (1) 10g of polyacrylonitrile (molecular weight M) W =80000), 2.69g niobium oxalate, and 0.96g citric acid were dissolved in 20mL of water and stirred in a 70℃ water bath for 4h to obtain a mixed solution;

[0095] 1.4 g of γ-cyclodextrin was dissolved in 10 mL of N,N-dimethylformamide and stirred for 12 h to obtain a pore-forming agent solution;

[0096] (2) Add 15 mL of LDMF and 1.15 g of anhydrous acetic acid to the mixture, stir evenly, add 1.15 g of chromium acetate, stir evenly, then add the pore-forming agent solution, stir evenly to obtain the spinning solution.

[0097] (3) Electrospinning the spinning solution with a spinning voltage of 16kV, a spinning temperature of 60℃, a spinning humidity of 50%, and a needle distance of 16cm from the collector to obtain the spun material.

[0098] (4) The spun fabric was oxidized in a vacuum drying oven at 210℃ for 2 hours. The oxidized fibers were then peeled off from the aluminum foil collector, cut into regular shapes of 100*100mm, sintered, and placed in a tube furnace. The furnace was then calcined at 900℃ for 2 hours in an inert gas environment to obtain the precursor, such as... Figure 1 As shown, in the precursor, it can be clearly seen that the surface of the carbon nanofiber has many chromium niobate nanoparticles with cation vacancies that grow in situ from the inside.

[0099] (5) Use a film cutting machine to cut the precursor from step (4) into a shape of 56.1*64.5mm, and record the weight as m1;

[0100] Weigh 60g of sulfur powder and dissolve it in 100mL of carbon disulfide solution. Stir for 12h to completely dissolve the sulfur powder in the CS2 solution to obtain sulfur powder solution.

[0101] (6) Add the precursor to the sulfur powder solution, let it stand, take it out, let the carbon disulfide solution evaporate, put it into a porcelain boat, and calcine it in a tube furnace with argon gas. The calcine temperature is 155℃ and the time is 12h to obtain the positive electrode material. The weight at this time is recorded as m2.

[0102] like Figure 2 As shown, the cathode material has a mesoporous structure and a microporous structure. The pore size of the micropore is d1nm, and the pore size of the mesopore is d2nm, satisfying: 1≤d1<2, 2≤d2≤20.

[0103] Wherein, sulfur loading = ((m2-m1) / 5.61*6.45)g / cm 2 .

[0104] Example 2

[0105] The difference between Example 2 and Example 1 is that the sintering temperature of Example 2 is 800℃, while all other conditions are the same.

[0106] Example 3

[0107] The difference between Example 3 and Example 1 is that the sintering temperature of Example 3 is 1000℃, while all other aspects are the same.

[0108] like Figure 3 As shown, the electron paramagnetic resonance spectra of the cathode materials described in Examples 1 to 3 have characteristic peaks at g-factors of 1.90 to 2.005, and the electron paramagnetic resonance spectra of the cathode materials have characteristic peaks at g-factors of 1.5 to 1.89.

[0109] Examples 4-7

[0110] Examples 4-7 differ from Example 1 in that, in Examples 4-7, the amounts of niobium oxalate and chromium acetate added are varied, thereby altering the N... a M b The mass ratio of carbon nanofibers.

[0111] Examples 8-11

[0112] The difference between Examples 8-11 and Example 1 is that Examples 8-11 change the amount of sulfur powder added, thereby changing the sulfur loading.

[0113] Examples 12-15

[0114] The difference between Examples 12-15 and Example 1 is that Examples 12-15 only change the thickness.

[0115] Example 16

[0116] A method for preparing a positive electrode material includes the following steps:

[0117] (1) 10g of polyacrylonitrile (molecular weight M) W =80000), 0.865g manganese acetate and 0.96g citric acid were dissolved in 20mL of water and stirred in a 70℃ water bath for 4h to obtain a mixed solution;

[0118] 1.4 g of γ-cyclodextrin was dissolved in 10 mL of N,N-dimethylformamide and stirred for 12 h to obtain a pore-forming agent solution;

[0119] (2) Add 15 mL of LDMF and 1.15 g of anhydrous acetic acid to the mixture, stir well, add 1.22 g of ferric citrate, stir well, then add the pore-forming agent solution, stir well to obtain the spinning solution.

[0120] (3) Electrospinning the spinning solution with a spinning voltage of 16kV, a spinning temperature of 60℃, a spinning humidity of 50%, and a needle distance of 16cm from the collector to obtain the spun material.

[0121] (4) The spun fabric was oxidized in a vacuum drying oven at 210℃ for 2 hours. The oxidized fibers were then peeled off from the aluminum foil collector, cut into regular shapes of 100*100mm, sintered, and placed in a tube furnace. The furnace was then calcined at 900℃ for 2 hours in an inert gas environment to obtain the precursor, such as... Figure 1 As shown, in the precursor, it can be clearly seen that the surface of the carbon nanofiber has many chromium niobate nanoparticles with cation vacancies that grow in situ from the inside.

[0122] (5) Use a film cutting machine to cut the precursor from step (4) into a shape of 56.1*64.5mm;

[0123] Weigh 60g of sulfur powder and dissolve it in 100mL of carbon disulfide solution. Stir for 12h to completely dissolve the sulfur powder in the CS2 solution to obtain sulfur powder solution.

[0124] (6) Add the precursor to the sulfur powder solution, let it stand, take it out, let the carbon disulfide solution evaporate, put it into a ceramic boat, and calcine it in a tube furnace with argon gas. The calcine temperature is 155℃ and the time is 12h to obtain the positive electrode material.

[0125] Example 17

[0126] A method for preparing a positive electrode material includes the following steps:

[0127] (1) 10g of polyacrylonitrile (molecular weight M) W =80000), 1.55g vanadium oxalate, and 0.96g citric acid were dissolved in 20mL of water and stirred in a 70℃ water bath for 4h to obtain a mixed solution;

[0128] 1.4 g of γ-cyclodextrin was dissolved in 10 mL of N,N-dimethylformamide and stirred for 12 h to obtain a pore-forming agent solution;

[0129] (2) Add 15 mL of LDMF and 1.15 g of anhydrous acetic acid to the mixture, stir evenly, add 1.36 g of tungsten acetate, stir evenly, then add the pore-forming agent solution, stir evenly to obtain the spinning solution;

[0130] (3) Electrospinning the spinning solution with a spinning voltage of 16kV, a spinning temperature of 60℃, a spinning humidity of 50%, and a needle distance of 16cm from the collector to obtain the spun material.

[0131] (4) The spun fabric was oxidized in a vacuum drying oven at 210℃ for 2 hours. The oxidized fibers were then peeled off from the aluminum foil collector, cut into regular shapes of 100*100mm, sintered, and placed in a tube furnace. The furnace was then calcined at 900℃ for 2 hours in an inert gas environment to obtain the precursor, such as... Figure 1 As shown, in the precursor, it can be clearly seen that the surface of the carbon nanofiber has many chromium niobate nanoparticles with cation vacancies that grow in situ from the inside.

[0132] (5) Use a film cutting machine to cut the precursor from step (4) into a shape of 56.1*64.5mm;

[0133] Weigh 60g of sulfur powder and dissolve it in 100mL of carbon disulfide solution. Stir for 12h to completely dissolve the sulfur powder in the CS2 solution to obtain sulfur powder solution.

[0134] (6) Add the precursor to the sulfur powder solution, let it stand, take it out, let the carbon disulfide solution evaporate, put it into a ceramic boat, and calcine it in a tube furnace with argon gas. The calcine temperature is 155℃ and the time is 12h to obtain the positive electrode material.

[0135] Example 18

[0136] Example 18 differs from Example 1 in that it uses equimolar zirconium ethoxide to replace niobium oxalate and equimolar bismuth trioxide to replace chromium acetate; all other aspects are the same.

[0137] Example 19

[0138] Example 19 differs from Example 1 in that niobium oxalate is replaced with an equimolar amount of strontium oxide and chromium acetate is replaced with an equimolar amount of tin dioxide; all other aspects are the same.

[0139] Example 20

[0140] Example 20 differs from Example 1 in that it uses equimolar amounts of cobalt acetate instead of niobate and equimolar amounts of tungstic acid instead of chromium acetate; all other aspects are the same.

[0141] Example 21

[0142] Example 21 differs from Example 1 in that Example 20 uses equimolar amounts of strontium oxide to replace niobium oxalate and equimolar amounts of molybdenum trioxide to replace chromium acetate; all other aspects are the same.

[0143] Comparative Example 1

[0144] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses equimolar amounts of potassium acetate instead of chromium acetate, while everything else is the same.

[0145] Comparative Example 2

[0146] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses equimolar amounts of magnesium acetate instead of chromium acetate, while everything else is the same.

[0147] Table 1

[0148]

[0149]

[0150] Performance testing

[0151] Fabrication of the secondary battery: A 30μm thick lithium strip was punched into 5.81*6.65cm pieces using a stamping machine. 2 The negative electrode has a regular shape. A 9μm thick polyethylene (PE) separator is used, and a Z-shaped stacking method is employed. The positive electrode and lithium metal negative electrode of this application are located on opposite sides of the separator, with the separator between the electrodes. After stacking, tabs are welded on. The stacked electrode is then placed in an aluminum-plastic film, top-side sealed, and filled with 2g / Ah of electrolyte. It is then vacuum-sealed three times to finally obtain a lithium-sulfur stacked battery.

[0152] Initial specific capacity: The assembled stacked soft-pack batteries were measured using a 9th generation Newway battery with an initial specific capacity test at a rate of 0.1C, and the cutoff voltage was 1.8 to 2.8V.

[0153] Cycle retention rate: The assembled stacked pouch cells were subjected to a constant current charge-discharge long cycle test at a rate of 0.5C. The test voltage range was 1.8 to 2.8V, and the number of cycles to 80% was recorded.

[0154] Table 2

[0155] Group Initial specific capacity mAh / g Number of cycles <![CDATA[Positive electrode material density g / cm 3 > Example 1 1103.87 1019 1.51 Example 2 1043.63 955 1.41 Example 3 1012.45 983 1.65 Example 4 870.34 713 1.00 Example 5 924.86 873 1.54 Example 6 890.74 960 1.95 Example 7 774.76 980 3.00 Example 8 1023 523 1.76 Example 9 1024.23 870 1.85 Example 10 981.34 823 1.54 Example 11 683.89 783 1.38 Example 12 894.34 820 2.74 Example 13 936.65 993 1.26 Example 14 974.29 975 1.13 Example 15 839.93 859 1.07 Example 16 1013.34 963 1.98 Example 17 1005.93 958 1.39 Example 18 1011.57 961 1.88 Example 19 1003.84 981 1.90 Example 20 1012.39 947 2.01 Example 21 1006.93 966 1.72 Comparative Example 1 540.35 572 1.53 Comparative Example 2 743.83 595 1.74

[0156] As can be seen from Table 2, the cathode material described in this application effectively improves the electrochemical performance of the secondary battery and has a low density.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A positive electrode material, characterized in that, Including N a M b Carbon nanofibers and sulfur, wherein N is at least one of Cr, Sr, W, Y, Fe, Co, Pt, Zr, Hf, Ta, Mo, Tc, Mn, Nb, and Bi, and M is NbO4. 3- VO4 3- MnO4 2- BiO3 3- SnO3 2- WO4 2- MoO4 2- At least one of the following, 1≤a≤3, 1≤b≤7; The carbon nanofibers contain N on their surface and inside. a M b ; The cathode material has both cation vacancies and oxygen vacancies; The sulfur loading of the cathode material is 0.9~20 mg / cm³. 2 .

2. The cathode material according to claim 1, characterized in that, The N a M b The mass ratio of carbon nanofibers is (0.1~2.4):

1.

3. The cathode material according to claim 1, characterized in that, The electron paramagnetic resonance spectrum of the cathode material has a characteristic peak in the range of g factor 1.99 to 2.

005.

4. The cathode material according to claim 1, characterized in that, The electron paramagnetic resonance spectrum of the cathode material exhibits a characteristic peak in the g-factor range of 1.5 to 1.98; and / or The electron paramagnetic resonance spectrum of the cathode material has a characteristic peak at a g-factor of 2.006 to 4.

5. The positive electrode material according to claim 1, characterized in that, The positive electrode material is a self-supporting material, and the thickness of the positive electrode material is 30~300 μm.

6. The cathode material according to claim 1, characterized in that, The cathode material has a mesoporous structure and a microporous structure. The pore size of the micropore is d1 nm and the pore size of the mesopore is d2 nm, satisfying: 1 ≤ d1 < 2, 2 ≤ d2 ≤ 20.

7. The cathode material according to claim 1, characterized in that, The density of the positive electrode material is 1.0~3.0 g / cm³. 3 .

8. A secondary battery, characterized in that, It includes a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 7.

9. An electrical device, characterized in that, It includes the secondary battery as described in claim 8, wherein the secondary battery serves as the power supply for the electrical device.

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