Battery pole piece with dual-mechanism synergistic effect, lithium-sulfur battery and preparation method

Abstract

The invention discloses a battery pole piece with a dual-mechanism synergistic effect, a lithium-sulfur battery and a preparation method. The positive electrode adopts a double-layer functional structure, and comprises an active layer compounded by sulfur and a high-conductivity material (carbon nanotubes, graphene, a conductive polymer and the like), and a special functional layer compounded by transition metal sulfide and selenium sulfide. According to the design, the sulfur utilization rate is increased to 80% or above through a three-dimensional conductive network, chemical adsorption and catalytic conversion of polysulfide are achieved through a heterojunction structure, and the shuttle effect is effectively inhibited. Meanwhile, the special functional layer can additionally contribute capacity, and the adverse effect on the battery performance caused by the too thick functional layer is reduced. And the cycle life and the rate capability of the battery are effectively improved under the synergistic effect of dual mechanisms of lithium ion conversion and intercalation and deintercalation.

Description

Technical Field

[0001] The present invention relates to a battery pole piece and a lithium-sulfur battery with a dual-mechanism synergistic effect, and a preparation method thereof, and belongs to the field of chemical power sources. Background Art

[0002] Lithium-sulfur batteries (LiS) have become a research hotspot for next-generation energy storage systems due to their high theoretical specific capacity (1675 mAh / g) and high energy density (2600 Wh / kg). However, LiS batteries face the following challenges in practical application: the insulating properties of sulfur lead to slow electrochemical reaction kinetics; the "shuttle effect" of polysulfides leads to capacity fading and poor cycling stability; and the volume expansion of the sulfur cathode during charge and discharge.

[0003] Existing technologies usually optimize performance by combining sulfur with conductive materials, introducing intermediate layers, or designing special positive electrode structures, but it is difficult to improve conductivity, shuttle effect, and reaction kinetics at the same time. In addition, the functional layer is limited by thickness. If it is too thin, it is difficult to effectively inhibit the diffusion of polysulfides, and if it is too thick, the battery capacity will be reduced. Therefore, it is of great significance to develop a new positive electrode structure to improve the overall performance of lithium-sulfur batteries. We selected a composite of transition metal sulfides and selenium sulfide as a special functional layer, which can not only effectively catalyze the conversion of lithium polysulfides, but also contribute additional capacity, thereby alleviating the adverse effects of excessive thickness of the functional layer on the battery capacity and improving the overall performance of lithium-sulfur batteries. Summary of the Invention

[0004] The present invention aims to provide a battery electrode and lithium-sulfur battery with a dual-mechanism synergistic effect, as well as a preparation method. The special functional layer, primarily composed of transition metal sulfides and selenium sulfide, effectively suppresses the shuttle effect by catalyzing the conversion reaction of polysulfides. Furthermore, the dual-mechanism reaction of lithium ions in the positive electrode effectively improves the battery's cycling stability and rate performance.

[0005] 1. Double-layer sulfur cathode structure:

[0006] The first layer is composed of a composite of highly conductive materials (such as carbon nanotubes, graphene, conductive polymers) and sulfur, with a thickness of 20-300 μm and a sulfur content of 40-80 wt%.

[0007] The second layer is composed of transition metal sulfides (such as CoS2, MoS2, WS2, NiS2 and FeS2) and selenium sulfide, with a thickness of 50-200 μm, which is used to catalyze the conversion reaction of polysulfides and inhibit the shuttle effect; the transition metal sulfides are in the form of nanosheets, nanoflowers or nanoparticles, and their specific surface area is ≥50m 2 / g; the transition metal sulfide in the special functional layer forms a heterojunction structure with the conductive carbon material, and synergistically suppresses the shuttle effect of polysulfides through chemical adsorption and catalytic conversion.

[0008] 2. Preparation method:

[0009] Step 1: Sulfur and conductive material are mixed in proportion, and a sulfur-conductive material composite is prepared by ball milling or hot melting method.

[0010] Step 2: Coat the composite on a current collector (such as aluminum foil) to form the first active layer.

[0011] Step 3: Mix transition metal sulfide and selenium sulfide in proportion (transition metal sulfide accounts for 10-50wt%), disperse them in a solvent, and form a second special functional layer on the surface of the first layer by scraping or spraying.

[0012] Step 4: Assemble the prepared double-layer sulfur positive electrode with the lithium negative electrode, electrolyte and separator to form a lithium-sulfur battery.

[0013] The beneficial effects of the present invention are as follows:

[0014] 1. Additional capacity contribution, alleviating the impact of excessive thickness of special functional layers on capacity

[0015] The second special functional layer, composed of a composite of transition metal sulfides and selenium sulfide, not only catalyzes the conversion of polysulfides but also serves as an additional active material to provide capacity. Compared to traditional single-layer cathode structures, this design increases the thickness of the functional layer without significantly reducing the overall battery capacity, thereby optimizing energy density and battery performance.

[0016] 2. Conversion mechanism improves sulfur utilization and specific capacity

[0017] By catalyzing the conversion reaction of polysulfides, the special functional layer promotes the efficient utilization of sulfur, reduces the loss of active materials, thereby increasing the discharge capacity and improving the energy density of the battery.

[0018] 3. De-embedding mechanism enhances rate performance and cycling stability

[0019] Transition metal sulfides participate in lithium storage through reversible extraction-intercalation reactions, contributing additional capacity and improving the battery's rate performance. At the same time, the high electrical conductivity of transition metal sulfides accelerates the transfer of electrons and lithium ions, lowering the electrode reaction energy barrier, allowing the battery to maintain a high specific capacity during high-rate discharge and enhancing cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the lithium-sulfur battery cycle diagram of Example 3. DETAILED DESCRIPTION

[0021] In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed manner below in conjunction with the accompanying drawings and preferred experimental examples, but the protection scope of the present invention is not limited to the following specific embodiments.

[0022] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0023] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0024] Example 1

[0025] In this example, the active layer was first prepared by mixing sulfur powder with a purity of ≥99.9% with multi-walled carbon nanotubes (CNTs, diameter 10-20 nm, length 10-30 μm) in a mass ratio of 7:3. The mixture was heated to 155°C under argon and held for 12 hours. The sulfur was then uniformly coated onto the CNT surface using a hot melt method. Subsequently, the sulfur-CNT composite was mixed with a PVDF binder in a mass ratio of 95:5. N-methylpyrrolidone (NMP) was added to form a slurry. The slurry was then uniformly coated onto a 15 μm-thick aluminum foil current collector at a coating speed of 5 cm / s. The mixture was then vacuum dried at 80°C for 12 hours to form a 50 μm-thick layer. The special functional layer was prepared by hydrothermal synthesis of CoS2 nanosheets: 0.1M Co(NO3)2·6H2O and 0.3M thiourea were dissolved in deionized water, reacted in a 200℃ autoclave for 24 hours, centrifuged and washed, and then dried; CoS2 nanosheets and selenium sulfide were mixed in a mass ratio of 3:7, added to ethanol and ultrasonically dispersed for 2 hours, and a special functional layer with a wet film thickness of 100μm was formed on the surface of the active layer by a doctor blade coating method. Finally, a 45μm thick special functional layer was obtained by vacuum drying at 60℃ for 6 hours. During battery assembly, the positive electrode sulfur surface loading was 3.8mg / cm 2 The electrolyte consists of 1M LiTFSI / DOL-DME (volume ratio 1:1) containing 1wt% LiNO3 additive. The separator is Celgard 2400 polypropylene film, and the negative electrode is a 200μm thick lithium metal sheet. The battery is packaged as a CR2032 button cell in an argon glove box (H2O / O2 <0.1ppm). Electrochemical testing shows that the battery has an initial discharge capacity of 1350mAh / g at a 0.2C rate, with a capacity retention rate of 92% after 100 cycles. Even at a high rate of 1C, it can still output a specific capacity of 1050mAh / g.

[0026] Example 2

[0027] In this embodiment, graphene is used as the active layer carrier: sulfur powder and graphene (specific surface area 500m 2 / g) were mixed in a 6:4 mass ratio and milled in a planetary ball mill at 400 rpm for 6 hours to uniformly disperse sulfur nanoparticles (<100 nm) between the graphene sheets. The composite was then mixed with a PVDF binder in a 93:7 mass ratio and slurried with NMP solvent. The slurry was applied to an aluminum foil current collector at a coating speed of 3 cm / s and dried at 100°C for 10 hours to form a 200μm active layer. The special functional layer was synthesized using chemical vapor deposition (CVD) of MoS2 nanoflowers: MoO3 and sulfur powder were heated at 750°C and 300°C, respectively, in a tube furnace, and reacted for 2 hours under an Ar / H2 (5% H2) carrier gas to form MoS2 nanoflowers. This MoS2 nanoflowers were then mixed with selenium sulfide in a 2:8 mass ratio, dispersed in isopropyl alcohol, and deposited on the active layer surface by spray coating (gun pressure 0.3 MPa, nozzle diameter 0.3 mm). After drying, the special functional layer had a thickness of 150μm. The sulfur surface loading during battery assembly is 4.5 mg / cm 2 The electrolyte is 1M LiTFSI / DOL-DME containing 2wt% LiNO3, and the separator is a Whatman GF / D glass fiber membrane. Performance testing shows that the battery has an initial discharge capacity of 1400mAh / g at 0.2C (sulfur utilization rate of 83.6%), a capacity retention of 90% after 100 cycles, and a discharge capacity of 980mAh / g at a 1C rate.

[0028] Example 3

[0029] Sulfur powder and polyacrylic acid (PAA) were mixed in a mass ratio of 8:2 and heated to 160°C under argon for 12 hours to produce a sulfur-based polymer (S-PAA). S-PAA was then mixed with multi-walled carbon nanotubes (CNTs) in a mass ratio of 7:3 and ball milled at 400 rpm for 6 hours to prepare a sulfur-based polymer-CNT composite. This composite was mixed with PVDF binder in a mass ratio of 95:5 and then added to N-methylpyrrolidone (NMP) solvent to form a slurry. The slurry was coated onto a 16 μm current collector at a coating speed of 5 cm / s and dried in a vacuum oven at 80°C for 12 hours to a thickness of 100 μm. CoS2 nanosheets were synthesized hydrothermally by dissolving 0.1 M Co(NO3)2·6H2O and 0.3 M thiourea in deionized water and reacting in an autoclave at 200°C for 24 hours. The resulting composite was then centrifuged, washed, and dried. CoS2 nanosheets and carbon nanotubes were mixed in a mass ratio of 3:7, added to ethanol and ultrasonically dispersed for 2 hours. A special functional layer with a wet film thickness of 400μm was formed on the surface of the active layer by a doctor blade coating method. Finally, a 60μm thick special functional layer was obtained by vacuum drying at 60℃ for 6 hours. The positive electrode sulfur surface loading was 3.8mg / cm 2The electrolyte is 1M LiTFSI / DOL-DME (volume ratio 1:1) containing 1wt% LiNO3 additive, the separator is Celgard 2400 polypropylene film, and the negative electrode is a 200μm thick lithium metal sheet. The electrochemical test results show that the reversible discharge capacity of the battery at 0.2C rate is 1380mAh / g, and the capacity retention rate after 100 cycles is 99% (such as Figure 1 As shown), it can still output a specific capacity of 1080mAh / g at a high rate of 1C.

[0030] Experiments show that the battery has a specific capacity of 1350-1400mAh / g at 0.2C, a capacity retention rate of over 90% after 100 cycles, and can still reach 1050mAh / g at 1C rate, with an areal capacity of 4-6mAh / cm 2 This design significantly improves battery performance and uses a scraping / spraying process that is compatible with existing production lines, showing good prospects for industrial application.

Claims

1. A battery pole piece with dual mechanism synergistic action, characterized in that: The invention comprises a positive electrode, wherein the positive electrode comprises: The first active layer is composed of a composite of sulfur and highly conductive materials; The second special functional layer is composed of a composite of transition metal sulfide and selenium sulfide.

2. A battery pole piece with dual mechanisms acting in synergy according to claim 1, characterized in that: The first active layer has a thickness of 20-300 μm and a sulfur content of 40-85 wt%.

3. The battery pole piece with dual-mechanism synergistic action according to claim 1, characterized in that: The thickness of the second special functional layer is 50-200 μm, and the transition metal sulfide accounts for 10-50 wt%.

4. The battery pole piece with dual mechanisms acting in synergy according to claim 1, characterized in that: The transition metal sulfide is CoS2, FeS2, MoS2, WS2 or NiS2; the transition metal sulfide is in the form of nanosheets, nanoflowers or nanoparticles, and its specific surface area is ≥50m 2 / g; the transition metal sulfide and selenium sulfide in the special functional layer form a heterojunction structure.

5. The battery pole piece with dual-mechanism synergistic action according to claim 1, characterized in that: The highly conductive material is carbon nanotube, graphene or carbon black.

6. A method for preparing a battery electrode according to any one of claims 1 to 5, characterized in that: The following steps are involved: A sulfur-conductive material composite is prepared; the composite is coated on a current collector to form a first active layer; and a second special functional layer is formed in a dispersion of transition metal sulfide and selenium sulfide.

7. A lithium-sulfur battery, characterized in that: A battery electrode comprising the battery electrode according to any one of claims 1 to 5.

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