High-volumetric-specific-capacity sulfur-based positive electrode material for lithium-sulfur secondary battery and preparation and application of high-volumetric-specific-capacity sulfur-based positive electrode material

Abstract

The invention relates to a high-volumetric-specific-capacity sulfur-based positive electrode material for a lithium-sulfur secondary battery and preparation and application of the high-volumetric-specific-capacity sulfur-based positive electrode material. The sulfur-based positive electrode material is prepared by the following steps: uniformly mixing sulfurized polyacrylonitrile with a conductive agent and metal organic salt, performing spray granulation, then mixing with elemental sulfur, and performing heating vulcanization, so as to obtain the high-volumetric-specific-capacity sulfur-based positive electrode material. The sulfur-based positive electrode material with high volume specific capacity is obtained. Compared with the prior art, the sulfur-based positive electrode material provided by the invention is high in sulfur content, remarkably improves the volumetric specific capacity and cycling stability of a secondary battery when being used as the positive electrode material of the secondary battery, is environment-friendly and low in cost, and has important practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur secondary battery materials, and relates to a sulfur-based positive electrode material with high volumetric capacity for lithium-sulfur secondary batteries, and the preparation and application thereof. Background Art

[0002] Lithium-ion batteries, due to their high overall performance and low cost, have been widely used in our daily lives as consumer batteries, power batteries, and energy storage batteries, such as in various portable devices, hybrid / electric vehicles, large-scale energy storage, and the 3C industry. With the large-scale application of electric vehicles and the rapidly increasing market demand for high-energy-density batteries, lithium-sulfur batteries have been considered as a promising next-generation secondary battery due to their ultra-high theoretical specific energy (2600Wh / kg) and theoretical specific capacity (1675mAh / g) over the past few decades.

[0003] However, composite cathodes designed from carbon / sulfur (C / S) materials typically undergo complex phase transitions involving multi-step lithium sulfide conversion and dissolution shuttling, leading to degraded reaction kinetics, capacity fading, and electrode structural damage. To address the polysulfide dissolution shuttling issue, the applicant (research group) first synthesized sulfided polyacrylonitrile (SPAN) in 2002. Its unique solid-solid conversion mechanism completely eliminates polysulfide shuttling, resulting in stable cycling and high Coulombic efficiency. However, compared to carbon / sulfur composites, the low sulfur content (<50%) is one of the factors that hinders SPAN materials from becoming high-capacity electrodes.

[0004] Based on this, researchers usually increase the sulfur content by changing the reaction conditions. However, these methods often cause excessive sulfur to adhere to the positive electrode surface, reacting with the electrolyte to form a dense interfacial passivation, resulting in low active material utilization. In addition, it is also limited by the slow and unstable electrochemical kinetics of the sulfur redox chemical process, the lack of scalable electrode composite material synthesis, and the low volumetric energy density of sulfur-based composite materials. Therefore, ensuring a high sulfur content while having both excellent reaction kinetics and excellent volumetric energy density is of great significance for improving the energy density of lithium-sulfur secondary batteries.

[0005] For example, Chinese patent application CN202410439193.4 provides a positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector. The positive electrode film layer comprises a positive electrode active material, a sodium supplement, a conductive agent, and a binder in a mass ratio of 85-92:5-10:0.5-5:1-3. The positive electrode active material comprises sodium-carbon composite sulfide polyacrylonitrile. However, the specific capacity of this sulfide polyacrylonitrile is relatively low, and further improvement is needed in terms of performance such as sulfur content and specific capacity. Summary of the Invention

[0006] The purpose of the present invention is to provide a high volumetric capacity sulfur-based positive electrode material for lithium-sulfur secondary batteries and its preparation and application. The obtained positive electrode material can significantly improve the capacity and cycle stability of the battery when it has a higher sulfur content; at the same time, the conductive agent is used to provide abundant conductive channels, and the in-situ generated metal sulfides and lithium polysulfides have excellent adsorption characteristics and catalytic conversion kinetics, thereby inhibiting the damage to the positive electrode structure, and also plays an important role in improving the volumetric capacity of the composite material.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery. The method comprises uniformly mixing sulfurized polyacrylonitrile (SPAN) with a conductive agent and a metal organic salt, spraying and granulating the mixture, and then mixing the mixture with elemental sulfur and heating and vulcanizing the mixture to obtain a high volumetric capacity sulfur-based cathode material.

[0009] Furthermore, the sulfur content in the sulfurized polyacrylonitrile is 40-70 wt.%.

[0010] Furthermore, the conductive agent is selected from one or a combination of conductive carbon black, Ketjen black, carbon nanotubes, graphene, and graphene oxide, and the mass ratio of the added amount to the sulfide polyacrylonitrile is 0.01-0.2:1.

[0011] Furthermore, the metal organic salt is one or more of metal citrate, metal oxalate or metal acetylacetonate, and the mass ratio of the added amount to the sulfide polyacrylonitrile is 0.1 to 5:1.

[0012] Furthermore, the metal elements contained in the sulfided polyacrylonitrile are one or more of iron, cobalt, nickel, manganese, zinc, vanadium, molybdenum and copper.

[0013] Furthermore, the mass ratio of the material obtained by spray granulation to elemental sulfur is 1:0.1-5.

[0014] Furthermore, the temperature of the heating vulcanization is 200-450° C., and the holding time is 0.1-12 hours.

[0015] In a second aspect, the present invention provides a high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery, which is prepared using the preparation method described in the second aspect above and has a sulfur content of 40-80 wt%, preferably 45-60 wt%.

[0016] In a third aspect, the present invention provides an application of a high volumetric capacity sulfur-based cathode material in a lithium-sulfur secondary battery.

[0017] In a fourth aspect, the present invention provides a lithium-sulfur secondary battery having a negative electrode and a positive electrode, wherein the positive electrode contains the high volumetric capacity sulfur-based positive electrode material as described in the second aspect above.

[0018] In the prior art, when the sulfur content of sulfur-based cathode materials (SPAN) prepared from polyacrylonitrile as a precursor exceeds 50 wt%, a large amount of elemental sulfur will be adsorbed on the surface, affecting the material's cycling performance and rate discharge capability. Unlike the prior art, the present invention utilizes conductive agents (carbon nanotubes, graphene) to assist spray granulation to produce micron-sized particles with abundant ion / electron transport pathways. Furthermore, metal sulfides are used to enhance the high sulfur content, effectively adsorbing lithium polysulfides during charge and discharge, ensuring a stable cathode structure. The resulting SPAN material achieves a reversible volumetric capacity of 850 mAh / L. This results in significant improvements, a simple process, ease of scalability, and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Shown are X-ray diffraction spectra of a SPAN (56.84%) precursor (b) and a SPAN composite material (FeS2 / SPAN) (a) combining iron disulfide and carbon nanotubes in Example 3 obtained by X-ray powder diffraction;

[0020] Figure 2 The figure shows a scanning electron micrograph of FeS2 / SPAN obtained by high temperature sulfurization after combining secondary particles obtained by spray drying of ferric citrate, carbon nanotubes and SPAN in Example 5 with elemental sulfur;

[0021] Figure 3 The graph shows the cycling performance of the FeS2 / SPAN sample obtained by high-temperature sulfurization of secondary particles obtained by spraying ferric citrate, carbon nanotubes and sulfurized polyacrylonitrile in Example 2;

[0022] Figure 4 The graph shows the cycling performance of the FeS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying ferric citrate, carbon nanotubes and sulfurized polyacrylonitrile in Example 5;

[0023] Figure 5 Shown is a comparison of the rate performance of the SPAN (56.84%) precursor (without iron source) and the FeS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying ferric citrate, carbon nanotubes and sulfurized polyacrylonitrile in Example 5 at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, and 0.1C;

[0024] Figure 6Shown is a charge-discharge curve of the MoS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying molybdenum acetylacetonate, carbon nanotubes, and sulfurized polyacrylonitrile in Example 10;

[0025] Figure 7 The figure shows the cycling performance of the CoS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying cobalt oxalate, carbon nanotubes and sulfurized polyacrylonitrile in Example 14;

[0026] Figure 8 1 is an X-ray diffraction spectrum of the SPAN composite material (NiS2 / SPAN) combining nickel disulfide and carbon nanotubes in Example 16 obtained by X-ray powder diffraction;

[0027] Figure 9 Shown is a charge-discharge curve of the NiS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying nickel acetylacetonate, carbon nanotubes, and sulfurized polyacrylonitrile in Example 16;

[0028] Figure 10 Shown is a graph of the cycling performance of the NiS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying nickel acetylacetonate, carbon nanotubes, and sulfurized polyacrylonitrile in Example 16;

[0029] Figure 11 This is the cycling performance diagram of the FeS2 / SPAN sample prepared in Comparative Example 1;

[0030] Figure 12 This is the cycle performance diagram of the sample obtained by directly spray granulating FeS2 with SPAN;

[0031] Figure 13 This is the cycle performance diagram of the sample prepared in Comparative Example 3. DETAILED DESCRIPTION

[0032] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0034] The terms "and / or", "or / and", and "and / or" used herein include any one of two or more related listed items, and also include any and all combinations of the related listed items, wherein the any and all combinations include any combination of two related listed items, any more related listed items, or all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that in this application, the technical solution undoubtedly includes technical solutions connected by "logical AND" and technical solutions connected by "logical OR".

[0035] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0036] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0037] Only certain numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0038] The temperature parameters in this application, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows for temperature fluctuations within the precision range of instrument control. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are permitted.

[0039] Herein, the “suitable” mentioned in “suitable combination”, “suitable method”, “any suitable method”, etc. shall be based on the ability to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0040] In this application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0041] In this application, the terms "optionally," "optional," and "optional" mean optional or dispensable, i.e., they refer to either option being selected from two parallel options: "with" or "without." If a technical solution contains multiple "optional" clauses, each "optional" clause is independent unless otherwise specified and there are no contradictions or constraints.

[0042] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0043] Unless otherwise stated, all formulations and tests herein took place at 25°C.

[0044] As used herein, the terms "comprise," "include," "contain," "have," "have," or other variations thereof are intended to encompass non-exclusive inclusions, and no distinction is made between these terms. The term "comprising" means that other steps and ingredients that do not affect the end result may be added. The compositions and methods / processes of the present invention comprise, consist of, and consist essentially of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein. As used herein, no distinction is made between the terms "efficacy," "performance," "effect," and "efficacy."

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all steps of the present application can be performed sequentially or randomly, preferably sequentially.

[0047] In the following examples, carbon nanotubes were purchased from Shanghai Haiyi Technology & Trade Co., Ltd. under the trade name TUBALL BATTH2O CMC (0.4%) R&D.

[0048] The SPAN used (sulfur content 56.84%) was prepared by the following method: the precursor PAN (molecular weight of approximately 1.5 to 1 million) was mixed with elemental sulfur in a ratio of 1:8, ethanol was added and ball-milled for 6 hours, and the resulting powder was dried and heated at 300°C in a tube furnace under a nitrogen atmosphere for 4 hours to obtain a sulfurized polyacrylonitrile positive electrode material (i.e., SPAN), with a sulfur content of 56.84%.

[0049] The preparation process of the positive electrode sheet used in lithium-sulfur secondary batteries is as follows: the sulfur-containing positive electrode material, the conductive agent (conductive carbon black, carbon nanotubes), and the binder polyacrylic acid are dispersed in solvent water in a mass ratio of 90:5:5, and then coated on the current collector. After drying, the sheet is pressed to obtain the positive electrode sheet.

[0050] Unless otherwise specified, the remaining raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0051] Example 1

[0052] SPAN (sulfur content 56.84%), 2% by mass of graphene, and ferric citrate in a mass ratio of 1:1 to SPAN were mixed evenly in water, spray-dried at 130°C to obtain secondary particles, and the secondary particles were mixed with elemental sulfur in a mass ratio of 1:10 and heated at 350°C in a tubular furnace under a nitrogen atmosphere for 2 hours to obtain a sulfur-based polyacrylonitrile positive electrode material containing iron disulfide.

[0053] The battery was then assembled in the conventional order, with a sulfur-based composite positive electrode material coated on carbon-coated aluminum foil. Commercial carbonate electrolyte (lithium hexafluorophosphate (LiPF6) concentration of 1 mol / L, ethylene carbonate / dimethyl carbonate / fluoroethylene carbonate volume ratio of 45:45:10) was used as the electrolyte. A 400-micron-thick lithium sheet was used as the negative electrode to assemble the battery, and charge and discharge tests were carried out at different current densities.

[0054] Example 2

[0055] SPAN (sulfur content 56.84%), 2% by mass of carbon nanotubes, and a 1:1 mass ratio of ferric citrate to SPAN were mixed in water and spray-dried at 130°C to obtain secondary particles. The secondary particles were then mixed with elemental sulfur at a mass ratio of 1:10 and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to obtain a sulfur-based polyacrylonitrile cathode material containing iron disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0056] Example 3

[0057] SPAN (sulfur content 56.84%), 2% by mass of carbon nanotubes, and a 1:1 mass ratio of ferric citrate to SPAN were mixed in water and spray-dried at 130°C to obtain secondary particles. The secondary particles were then mixed with elemental sulfur at a mass ratio of 1:10 and heated in a tube furnace at 400°C for 2 hours under a nitrogen atmosphere to obtain a sulfur-based polyacrylonitrile cathode material containing iron disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0058] Example 4

[0059] SPAN (sulfur content 56.84%), 2% by mass of carbon nanotubes, and a 2:1 mass ratio of ferric citrate to SPAN were mixed in water and spray-dried at 130°C to obtain secondary particles. The secondary particles were then mixed with elemental sulfur at a mass ratio of 1:10 and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to obtain a sulfur-based polyacrylonitrile cathode material containing iron disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0060] Example 5

[0061] SPAN (sulfur content 56.84%), 2% by mass of carbon nanotubes, and ferric citrate at a mass ratio of 2:1 to SPAN were mixed in water and spray-dried at 140°C to obtain secondary particles. The secondary particles were then combined with elemental sulfur at a mass ratio of 1:5 and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to obtain a sulfur-based polyacrylonitrile cathode material containing iron disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0062] Example 6

[0063] SPAN (sulfur content 56.84%), 2% carbon nanotubes (CNTs) by mass, and ferric citrate (SPAN) at a mass ratio of 2:1 were mixed in water and spray-dried at 130°C to obtain secondary particles. These particles were then mixed with elemental sulfur at a mass ratio of 1:5 and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to produce a sulfur-based composite cathode material containing iron disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0064] Example 7

[0065] SPAN (sulfur content 56.84%), 1% by mass of carbon nanotubes, 1% by mass of graphene, and ferric citrate at a mass ratio of 2:1 to SPAN were mixed in water and spray-dried at 130°C to obtain secondary particles. The secondary particles were then mixed with elemental sulfur at a mass ratio of 1:5 and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to obtain a sulfur-based composite cathode material containing iron disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0066] Example 8

[0067] SPAN (sulfur content 56.84%), 2% by mass of carbon nanotubes, and a 2:1:1 mass ratio of iron acetylacetonate and nickel acetylacetonate to SPAN were mixed in water and spray-dried at 130°C to produce secondary particles. These particles were then mixed with elemental sulfur at a 1:5 mass ratio and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to produce a sulfur-based composite cathode material containing iron disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0068] Example 9

[0069] SPAN (sulfur content 56.84%), 2% by mass of carbon nanotubes, and a 2:1:1 mass ratio of ferric citrate and cobalt citrate to SPAN were mixed in water and spray-dried at 130°C to produce secondary particles. These particles were then mixed with elemental sulfur at a 1:5 mass ratio and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to produce a sulfur-based composite cathode material containing iron disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0070] Example 10

[0071] SPAN (sulfur content 56.84%), 2% by mass of carbon nanotubes, and molybdenum acetylacetonate at a 2:1 mass ratio of SPAN to SPAN were mixed in water and spray-dried at 130°C to produce secondary particles. These particles were then mixed with elemental sulfur at a 1:5 mass ratio and heated in a tube furnace at 400°C for 2 hours under a nitrogen atmosphere to produce a sulfur-based composite cathode material containing molybdenum disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0072] Example 11

[0073] SPAN (sulfur content 56.84%), 2% by mass of carbon nanotubes, and a 1:1 mass ratio of copper acetylacetonate to SPAN were mixed in water and spray-dried at 130°C to obtain secondary particles. These particles were then mixed with elemental sulfur at a 1:5 mass ratio and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to produce a sulfur-based composite cathode material containing cobalt disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0074] Example 12

[0075] SPAN (sulfur content 56.84%), 2% carbon nanotubes (CNTs) by mass, and manganese acetylacetonate (MACET) at a 1:1 mass ratio with SPAN were mixed in water and spray-dried at 130°C to produce secondary particles. These particles were then mixed with elemental sulfur at a 1:5 mass ratio and heated in a tube furnace at 400°C for 2 hours under a nitrogen atmosphere to produce a sulfur-based composite cathode material containing cobalt disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0076] Example 13

[0077] SPAN (sulfur content 56.84%), 2% carbon nanotubes (CNTs) by mass, and vanadium oxalate (VOX) at a 1:1 mass ratio with SPAN were mixed in water and spray-dried at 130°C to produce secondary particles. These particles were then mixed with elemental sulfur at a 1:5 mass ratio and heated in a tube furnace at 400°C for 2 hours under a nitrogen atmosphere to produce a sulfur-based composite cathode material containing cobalt disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0078] Example 14

[0079] SPAN (sulfur content 56.84%), 2% by mass of carbon nanotubes, and cobalt oxalate at a mass ratio of 2:1 to SPAN were mixed in water and spray-dried at 130°C to produce secondary particles. These particles were then mixed with elemental sulfur at a mass ratio of 1:5 and heated in a tube furnace at 400°C for 2 hours under a nitrogen atmosphere to produce a sulfur-based composite cathode material containing cobalt disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0080] Example 15

[0081] SPAN (sulfur content 56.84%), 2% carbon nanotubes (CNTs) by mass, and nickel acetylacetonate (nickel acetylacetonate) at a 1:1 mass ratio of SPAN to SPAN were mixed in water and spray-dried at 130°C to produce secondary particles. These particles were then mixed with elemental sulfur at a 1:5 mass ratio and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to produce a sulfur-based composite cathode material containing cobalt disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0082] Example 16

[0083] SPAN (sulfur content 56.84%), 2% carbon nanotubes (CNTs) by mass, and nickel acetylacetonate (nickel acetylacetonate) at a 2:1 mass ratio of SPAN to SPAN were mixed in water and spray-dried at 130°C to produce secondary particles. These particles were then mixed with elemental sulfur at a 1:5 mass ratio and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to produce a sulfur-based composite cathode material containing cobalt disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0084] Example 17

[0085] SPAN (sulfur content 56.84%), 1% by mass of carbon nanotubes, 1% by mass of graphene, and nickel iron acetylacetonate at a mass ratio of 2:1 to SPAN were mixed in water and spray-dried at 130°C to obtain secondary particles. The secondary particles were then mixed with elemental sulfur at a mass ratio of 1:5 and heated in a tube furnace at 350°C for 2 hours under a nitrogen atmosphere to obtain a sulfur-based composite cathode material containing iron disulfide. Charge and discharge tests were conducted using the same method as in Example 1.

[0086] Figure 1 Shown are X-ray powder diffraction spectra of the SPAN (56.84%) precursor (b) prepared in Example 1 and the SPAN composite material (FeS2 / SPAN) (a) combining iron disulfide and carbon nanotubes, obtained in Example 3. The XRD pattern of the SPAN (56.84%) precursor shows a distinct peak (sharp peak located between 20-30°) indicating elemental sulfur, which is detrimental to the positive electrode's capacity. However, the XRD pattern of the FeS2 / SPAN cathode material shows no characteristic diffraction peaks for elemental sulfur.

[0087] Figure 2 Shown is a scanning electron micrograph of FeS2 / SPAN obtained by high-temperature sulfurization after combining the secondary particles obtained by spray drying of ferric citrate, carbon nanotubes and SPAN in Example 5 with elemental sulfur. The results show that the FeS2 nanoparticles are evenly distributed in the SPAN secondary particles.

[0088] Figure 3 The figure shows the cycle performance of the FeS2 / SPAN sample obtained by high-temperature sulfurization of secondary particles obtained by spraying ferric citrate, carbon nanotubes and sulfurized polyacrylonitrile in Example 2. After 100 cycles of FeS2 / SPAN, the capacity retention rate can reach 94.1%.

[0089] Figure 4 Shown is the cycling performance of the FeS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying ferric citrate, carbon nanotubes, and sulfurized polyacrylonitrile in Example 5. After 140 cycles, the FeS2 / SPAN sample exhibited a reversible volumetric capacity of 850 mAh / L, with a capacity retention rate of 93.9%.

[0090] Figure 5 Shown is a comparison of the rate performance at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, and 0.1C for a SPAN (56.84%) precursor (containing no iron source) derived from elemental sulfur and polyacrylonitrile and a FeS2 / SPAN sample obtained by further sulfurization of secondary particles obtained by spraying ferric citrate, carbon nanotubes, and sulfurized polyacrylonitrile in Example 5. The test results show that the FeS2 / SPAN sample exhibits a reversible specific capacity of 755.1 mAh / g at a current density of 0.1C and a reversible specific capacity of greater than 647.3 mAh / g at a high current density of 2C, surpassing the SPAN sample.

[0091] Figure 6 Shown is a charge-discharge curve of the MoS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying molybdenum acetylacetonate, carbon nanotubes, and sulfurized polyacrylonitrile in Example 10;

[0092] Figure 7 The figure shows the cycling performance of the CoS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying cobalt oxalate, carbon nanotubes and sulfurized polyacrylonitrile in Example 14;

[0093] Figure 8 1 is an X-ray diffraction spectrum of the SPAN composite material (NiS2 / SPAN) combining nickel disulfide and carbon nanotubes in Example 16 obtained by X-ray powder diffraction;

[0094] Figure 9 Shown is a charge-discharge curve of the NiS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying nickel acetylacetonate, carbon nanotubes, and sulfurized polyacrylonitrile in Example 16;

[0095] Figure 10 Shown is the cycling performance diagram of the NiS2 / SPAN sample obtained by further sulfurizing the secondary particles obtained by spraying nickel acetylacetonate, carbon nanotubes and sulfurized polyacrylonitrile in Example 16.

[0096] From the above, it can be seen that the FeS2 / SPAN sample obtained by spray granulation has the highest volumetric capacity and cycling stability.

[0097] Comparative Example 1:

[0098] SPAN (sulfur content 56.84%), 2% by mass of graphene, and iron sulfate in a mass ratio of 1:1 to SPAN were mixed evenly in water, and spray dried at 130°C to obtain secondary particles. The secondary particles were mixed with elemental sulfur in a mass ratio of 1:10 and heated at 350°C in a tubular furnace under a nitrogen atmosphere for 2 hours to obtain a sulfur-based polyacrylonitrile positive electrode material containing iron disulfide.

[0099] like Figure 11 As shown in Figure 2, when the organic iron salt (ferric citrate) in Example 1 was replaced with an inorganic iron salt (ferric sulfate), the obtained FeS2 / SPAN sample exhibited poor capacity and cycle stability.

[0100] Comparative Example 2:

[0101] SPAN (sulfur content 56.84%), 2% by mass of graphene, and iron disulfide (purchased from Adamas) with a mass ratio of 1:1 to SPAN were mixed evenly in water and spray-dried at 130°C to obtain secondary particles. The secondary particles were mixed with elemental sulfur in a mass ratio of 1:10 and heated at 350°C in a tubular furnace under a nitrogen atmosphere for 2 hours to obtain a sulfur-based polyacrylonitrile positive electrode material containing iron disulfide.

[0102] Depend on Figure 12It can be seen that the sample obtained by directly spray granulating iron disulfide and SPAN has poor cyclic stability.

[0103] Comparative Example 3:

[0104] SPAN (sulfur content 56.84%) and 2% by mass of graphene were evenly mixed in water, and secondary particles were obtained by spray drying at 130°C. The secondary particles were mixed with elemental sulfur in a mass ratio of 1:10 and heated at 350°C for 2 hours in a tubular furnace under a nitrogen atmosphere. The obtained sulfurized polyacrylonitrile secondary particles were used as the positive electrode material.

[0105] Depend on Figure 13 It can be seen that when the reaction introduction of FeS2 is omitted, the sample exhibits lower capacity and cycle stability.

[0106] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery, characterized in that: The sulfided polyacrylonitrile is uniformly mixed with a conductive agent and a metal organic salt, spray-granulated, and then mixed with elemental sulfur and heated and vulcanized to obtain a high volumetric capacity sulfur-based positive electrode material.

2. The method for preparing a high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery according to claim 1, characterized in that: The sulfur content in the sulfurized polyacrylonitrile is 40-70 wt.%.

3. The method for preparing a high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery according to claim 1, characterized in that: The conductive agent is selected from one or a combination of conductive carbon black, Ketjen black, carbon nanotubes, graphene, and graphene oxide, and the mass ratio of the added amount to the sulfide polyacrylonitrile is 0.01-0.2:

1.

4. The method for preparing a high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery according to claim 1, characterized in that: The metal organic salt is one or more of metal acetate, metal citrate, metal oxalate or metal acetylacetonate, and the mass ratio of the metal organic salt to the sulfide polyacrylonitrile is 0.1 to 5:

1.

5. The method for preparing a high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery according to claim 1, characterized in that: The metal elements contained in the sulfided polyacrylonitrile are one or more of iron, cobalt, nickel, manganese, zinc, vanadium, molybdenum and copper.

6. The method for preparing a high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery according to claim 1, characterized in that: The mass ratio of the material obtained by spray granulation to elemental sulfur is 1:0.1-5.

7. The method for preparing a high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery according to claim 1, characterized in that: The temperature of heating vulcanization is 200-450°C, and the holding time is 0.1-12h.

8. A high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery, prepared by the preparation method according to any one of claims 1 to 7, characterized in that: Its sulfur content is 40 to 80 wt%.

9. Use of the high volumetric capacity sulfur-based cathode material for a lithium-sulfur secondary battery as claimed in claim 8 in a lithium-sulfur secondary battery.

10. A lithium-sulfur secondary battery having a negative electrode and a positive electrode, characterized in that: The negative electrode is one or more of metallic lithium, lithium alloy, lithium-carbon composite negative electrode, and lithium-silicon composite negative electrode, and the positive electrode contains the high volumetric capacity sulfur-based positive electrode material as claimed in claim 8.

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