Method for constructing stable interface of lithium-sulfur battery sulfur positive electrode material and application thereof

Abstract

The application provides a method for constructing a stable interface of a lithium-sulfur battery sulfur positive electrode material, and the electrolyte of the lithium-sulfur battery is composed of a lithium salt and a carbonate-based solvent. In the first discharge process, the carbonate reacts in situ with the lithium polysulfide intermediate and the lithium salt to form a thin and stable self-repairable positive electrode electrolyte interface phase CEI. The application also provides a lithium-sulfur battery based on the method for constructing a stable interface of a lithium-sulfur battery sulfur positive electrode material. In the first discharge process, the formed CEI serves as a fast lithium ion conducting interface, greatly improving the long cycle stability, rate performance and low temperature performance of the battery, and even the cycle stability under lithium deficiency. The application adopts a simple process, selects a commercial carbon and sulfur composite as the positive electrode material, uses a carbonate capable of undergoing a polymerization reaction with the lithium polysulfide intermediate and the lithium salt as the solvent, constructs a thin and stable self-repairable interface with fast lithium ion conductivity in situ, and is beneficial to industrial production.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a method for constructing a stable interface of sulfur cathode material in a lithium-sulfur battery, and also to a lithium-sulfur battery with a stable interface of sulfur cathode material and its preparation method. Background Technology

[0002] With the rapid growth in demand for portable electronic devices and new energy vehicles, the development of rechargeable lithium batteries with high energy density, high power density, and long cycle life is urgently needed. Compared to commercially available graphite anode materials, cathode materials are the key determinant of lithium battery performance and cost.

[0003] Lithium-sulfur batteries are considered one of the most promising rechargeable battery systems, boasting higher theoretical energy density, more readily available raw materials, and lower cost compared to commercial lithium-ion batteries. However, the shuttle effect of intermediate products (lithium polysulfides) generated during cycling in lithium-sulfur batteries leads to severe loss of active sulfur, corrosion of the lithium metal anode, and increased electrolyte viscosity, resulting in significant capacity decay and low coulombic efficiency, thus limiting the practical application of lithium-sulfur batteries. Therefore, minimizing the shuttle effect has become crucial for improving the long cycle life and commercialization of lithium-sulfur batteries.

[0004] Existing research largely focuses on the selection and preparation of multifunctional sulfur supports, employing a range of porous carbons, graphene, carbon nanotubes, metal oxides / sulfides, metal / covalent organic frameworks, and their complexes to physically or chemically anchor lithium polysulfides (LiPo) to suppress the shuttle effect and reduce LiPo diffusion into the negative electrode chamber, thereby improving the cycle performance of lithium-sulfur batteries. However, due to the limitations of the dissolution-deposition mechanism, the inherent problem of LiPo dissolution and diffusion persists, and these efforts can only effectively suppress, not completely eliminate, the shuttle effect. To completely solve this problem, we must find an effective strategy, distinct from the traditional dissolution-deposition mechanism, to fundamentally eliminate the shuttle effect.

[0005] Lithium-sulfur batteries often use ether-based electrolytes because the intermediate lithium polysulfide can exist stably in ether-based electrolytes and dissolve and diffuse relatively quickly, which is beneficial to the reaction kinetics of the sulfur cathode to some extent. However, this is also the root cause of the shuttle effect. Conventional ester-based electrolytes, on the other hand, react with lithium polysulfide to form polymer precipitates, thereby hindering the subsequent reaction [Electrochim. Acta 2013, 107, 454-460; J. Phys. Chem. C 2011, 115, 25132-25137], thus causing the battery to deactivate.

[0006] Therefore, how to effectively solve the shuttle effect problem in order to improve the cycle performance, rate performance, low temperature performance and lithium-depleted performance of lithium-sulfur batteries is an urgent technical problem to be solved. Summary of the Invention

[0007] One of the objectives of this invention is to provide a method for constructing a stable interface for a sulfur cathode material in a lithium-sulfur battery.

[0008] The second objective of this invention is to provide a lithium-sulfur battery with better long-term cycle stability, rate performance, low-temperature performance, and cycle stability under lithium-deficient conditions.

[0009] The third objective of this invention is to provide a method for preparing a lithium-sulfur battery with better long-term cycle stability, rate performance, low-temperature performance, and cycle stability under lithium-deficient conditions.

[0010] One of the technical solutions adopted to achieve the objective of this invention is: to provide a method for constructing a stable interface of sulfur cathode material in lithium-sulfur batteries. The electrolyte of the lithium-sulfur battery is composed of lithium salt and carbonate-based solvent. During the first discharge process, the carbonate-based solvent reacts in situ with lithium polysulfide intermediates and lithium salt to form a thin and stable self-healing cathode electrolyte interface phase CEI.

[0011] The overall concept of this invention is as follows: On the sulfur cathode material of lithium-sulfur batteries, by using a suitable carbonate-based raw material such as vinylene carbonate (VC) as a solvent, and utilizing its co-reaction with lithium polysulfides and lithium salts, a self-healing cathode electrolyte interface layer (CEI) is constructed in situ on the cathode surface during the initial stage of discharge. This blocks the subsequent dissolution of lithium polysulfides and achieves a completely solid-phase sulfur conversion reaction mechanism, fundamentally solving the shuttle effect problem. When applied to lithium-sulfur systems, it significantly improves their long-cycle performance, rate performance, low-temperature performance, and lithium-depleted performance.

[0012] Furthermore, the carbonate-based solvent is selected from one or more combinations of vinylene carbonate (VC), fluoroethylene carbonate (FEC), propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC).

[0013] Furthermore, the positive electrode material of the lithium-sulfur battery includes an S / C composite material, wherein the S / C composite material uses porous carbon as a sulfur carrier and is prepared by loading a certain proportion of sublimed sulfur into the porous carbon through a steam-melt method.

[0014] Furthermore, in the electrolyte, the lithium salt is selected from one or more combinations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4).

[0015] Furthermore, in the electrolyte, the concentration of lithium salt is 1–5 mol / L; the thickness of the self-healing positive electrode electrolyte interphase (CEI) is 1–40 nm. Preferably, in the electrolyte, the concentration of lithium salt is 5 mol / L, and the thickness of the self-healing positive electrode electrolyte interphase (CEI) is 1–10 nm.

[0016] The technical solution adopted to achieve the second objective of this invention is: to provide a lithium-sulfur battery, comprising: a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode comprises an S / C composite material; the electrolyte is composed of lithium salt and carbonate solvent; and the lithium-sulfur battery comprises a self-healing positive electrode electrolyte interface phase (CEI) obtained by the construction method according to the first objective of this invention.

[0017] The technical solution adopted to achieve the third objective of this invention is: to provide a method for preparing a lithium-sulfur battery, comprising the following steps:

[0018] S1. Using porous carbon as a sulfur carrier, a certain proportion of sublimed sulfur is loaded into the porous carbon by a steam-melt method to obtain an S / C composite material.

[0019] S2. Dissolve the lithium salt in a carbonate-based solvent to obtain an electrolyte with a lithium salt concentration of 1–5 mol / L;

[0020] S3. The S / C composite material is mixed with conductive carbon black and binder to obtain a positive electrode slurry. The positive electrode slurry is coated on a current collector and vacuum dried to obtain a positive electrode sheet.

[0021] S4. Under a protective atmosphere, the positive electrode sheet, a lithium metal sheet or a negative electrode made of lithium-containing material, a separator, and the electrolyte are assembled into a lithium-sulfur battery.

[0022] Furthermore, in step S1, the porous carbon support is selected from one or more combinations of ordered mesoporous carbon CMK-3, disordered mesoporous carbon BP2000, disordered mesoporous carbon KB, and disordered porous carbon treated with CO2 or alkali; the sulfur loading of the S / C composite material is 40-90 wt.%.

[0023] Preferably, step S1 includes: mixing and grinding a porous carbon support and sulfur powder, then vacuum sealing the mixture, heating it at 300–350°C for 3–12 hours, then cooling it to 155°C and holding it for 6–12 hours, and finally cooling it to room temperature to obtain the S / C composite material. Preferably, the mixture is first heated at 350°C for 6 hours, then cooled to 155°C and held for 6 hours. Here, the sulfur is first processed into a vapor state, allowing it to better penetrate the interior and deeper layers of the porous carbon support pores; then, the molten sulfur enters the pores via capillary action. Compared to directly raising the sulfur to a molten state and guiding it through capillary action, this operation makes fuller use of the pore space, resulting in better and more complete sulfur loading. This allows for a more uniform dissolution of the lithium polysulfide intermediate during the initial discharge process, which is beneficial for forming a thinner and more uniform CEI.

[0024] Furthermore, in step S2, the lithium salt is selected from one or more combinations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4).

[0025] Furthermore, the carbonate-based solvent is selected from one or more combinations of vinylene carbonate (VC), fluoroethylene carbonate (FEC), propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC).

[0026] Furthermore, in step S3, the mass ratio of the S / C composite material to the conductive carbon black and binder in the positive electrode slurry is (3-8):(1-2):1.

[0027] Preferably, the conductive carbon black is selected from one or a combination of conductive carbon black Super P, conductive carbon black Ketjen black, conductive carbon black acetylene black, conductive carbon black BP2000, and carbon nanotubes.

[0028] Preferably, the adhesive is selected from sodium carboxymethyl cellulose (CMC), sodium alginate (SA), polyacrylic acid (PAA), and polyolefins.

[0029] Preferably, the current collector is aluminum foil.

[0030] Preferably, the lithium-containing material of the negative electrode of the lithium battery includes pre-lithiated graphite or alloy negative electrodes such as silicon, germanium, and phosphorus.

[0031] Preferably, the diaphragm is selected from polyolefin membranes or glass fiber membranes; the polyolefin membrane is selected from one of polypropylene single-layer membrane (PP), polyethylene single-layer membrane (PE), and polypropylene / polyethylene / polypropylene three-layer composite membrane (PP / PE / PP);

[0032] Furthermore, the lithium-sulfur battery includes CR2016 or CR2032 coin cells.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The present invention provides a method for constructing a stable interface of sulfur cathode material for lithium-sulfur battery. The electrolyte is composed of lithium salt and carbonate-based solvent. The carbonate-based electrolyte can be used in the lithium-sulfur battery system to construct a thin, uniform, stable and Li-F-rich self-healing CEI layer on the electrode surface in situ. As a fast lithium-ion conduction interface, it greatly improves the long cycle stability, rate performance and low temperature performance of lithium-sulfur battery.

[0035] (2) The lithium-sulfur battery and its preparation method provided by the present invention adopt a simple process, select commercially available carbon and sulfur composite as the positive electrode material, and use carbonates such as vinylene carbonate (VC) that can undergo ring-opening polymerization reaction with lithium polysulfide intermediates as solvents to construct a thin and stable self-healing interface in situ, which is conducive to realizing industrial production and has the prospect of promotion and application. Attached Figure Description

[0036] Figure 1 A schematic diagram illustrating the principle of a method for constructing a stable interface for a sulfur cathode material in a lithium-sulfur battery, provided by the present invention.

[0037] Figure 2 The 5M LiTFSI-VC electrolyte prepared in Example 1 and the 5M LiTFSI-DME / DOL (v / v = 1:1) electrolyte prepared in Comparative Example 1 are examples of electrolytes prepared in this invention. 7 Li and 19 F NMR spectrum. Among them, Figure 2 (a) is 7 Li NMR spectrum, Figure 2 (b) is 19 F NMR spectrum;

[0038] Figure 3 These are TEM images of the lithium-sulfur batteries prepared in Examples 1 and 2 of this invention after cycling with LiTFSI-VC at different lithium salt concentrations; wherein, Figure 3 (f) shows the relationship between CEI film thickness and lithium salt concentration;

[0039] Figure 4 This is a TEM image of the lithium-sulfur battery prepared in Example 1 of the present invention after 5 cycles in 5M LiTFSI-VC;

[0040] Figure 5 The image shows the X-ray photoelectron spectrum of the lithium-sulfur battery prepared in Example 1 of this invention after the first discharge cycle in 5M LiTFSI-VC. Figure 5 (a) is the C1s spectrum. Figure 5 (b) is the F1s spectrum;

[0041] Figure 6 The graphs show the cycle performance of lithium-sulfur batteries fabricated using 5M and 1M LiTFSI-VC electrolytes in Examples 1 and 2 of this invention, compared to those of lithium-sulfur batteries fabricated using ether-based control group electrolytes in Comparative Examples 1 and 2. Figure 6 (a) is a comparison graph of the cycle performance of lithium-sulfur batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention. Figure 6 (b), 6(c) and 6(d) are respectively the long-cycle performance, rate performance and low-temperature performance of the lithium-sulfur battery prepared in Example 1 of the present invention in 5M LiTFSI-VC electrolyte;

[0042] Figure 7 This is a comparison of the cycling performance of the lithium-sulfur batteries prepared in Examples 3 and 4 of this invention in 5M LiTFSI-VC electrolyte, where... Figure 7 (a) is a graph showing the cycling performance of the 80 wt.% high sulfur loading lithium-sulfur battery prepared in Example 3 of the present invention in 5M LiTFSI-VC electrolyte. Figure 7 (b) is a cycle performance diagram of the lithium-sulfur battery prepared in Example 4 of the present invention, which uses lithium-less lithiform graphite as the negative electrode.

[0043] Figure 8 The graph shows the cycling performance of the lithium-sulfur battery prepared in Example 5 of this invention in 1M LiTFSI-FEC electrolyte.

[0044] Figure 9 The graph shows a comparison of the cycling performance of the lithium-sulfur batteries prepared in Examples 6-8 of this invention in 5M LiFSI-VC, 3M LiPF6-VC, 2M LiClO4-VC electrolytes and commercial ether electrolytes. Detailed Implementation

[0045] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0047] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0048] The main raw materials and parameters involved in Examples 1-8 and Comparative Examples 1 and 2 of this invention are shown in Table 1 below.

[0049] Table 1

[0050]

[0051]

[0052] Example 1

[0053] A lithium-sulfur battery is prepared, and the specific steps of the preparation method are as follows:

[0054] Step 1): Weigh commercially available CMK-3 and sulfur powder in the appropriate mass ratio, grind them evenly in a mortar, and then transfer them to a Pyrex glass tube and seal it under vacuum. Then place it in a muffle furnace and heat it at 350°C for 6 hours, then cool it down to 155°C and hold it for 6 hours, and finally cool it to room temperature to obtain an S / C composite material with a sulfur loading of 50 wt.%.

[0055] Step 2): In the glove box, weigh an appropriate amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into a reagent bottle, and add the corresponding amount of vinylene carbonate (VC) with a pipette to dissolve it and obtain a 5M LiTFSI-VC electrolyte.

[0056] Step 3): The S / C composite material is uniformly mixed with conductive carbon black (super P) and binder (CMC) at a mass ratio of 7:2:1 to obtain a slurry. The slurry is then coated onto the current collector aluminum foil and dried in a vacuum drying oven at 55°C for 12 hours to obtain the positive electrode sheet.

[0057] Step 4): Using the electrode sheet obtained above as the positive electrode, the lithium metal sheet as the counter electrode, the polypropylene membrane as the separator, and a solution containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and vinylene carbonate (VC) as the electrolyte, assemble the CR2016 button cell in an argon-filled glove box.

[0058] Example 2

[0059] A lithium-sulfur battery is prepared, and the specific steps of the preparation method are as follows:

[0060] Step 1): Weigh commercially available CMK-3 and sulfur powder in the appropriate mass ratio, grind them evenly in a mortar, and then transfer them to a Pyrex glass tube and seal it under vacuum. Then place it in a muffle furnace and heat it at 350°C for 6 hours, then cool it down to 155°C and hold it for 6 hours, and finally cool it to room temperature to obtain an S / C composite material with a sulfur loading of 50 wt.%.

[0061] Step 2): In the glove box, weigh an appropriate amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into a reagent bottle, and add the corresponding amount of vinylene carbonate (VC) with a pipette to dissolve it and obtain a 1M LiTFSI-VC electrolyte.

[0062] Step 3): The S / C composite material is uniformly mixed with conductive carbon black (super P) and binder (CMC) at a mass ratio of 7:2:1 to obtain a slurry. The slurry is then coated onto the current collector aluminum foil and dried in a vacuum drying oven at 55°C for 12 hours to obtain the positive electrode sheet.

[0063] Step 4): Using the electrode sheet obtained above as the positive electrode, the lithium metal sheet as the counter electrode, the polypropylene membrane as the separator, and a solution containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and vinylene carbonate (VC) as the electrolyte, assemble the CR2016 button cell in an argon-filled glove box.

[0064] Example 3

[0065] A lithium-sulfur battery is prepared, and the specific steps of the preparation method are as follows:

[0066] Step 1): Weigh out the macroporous disordered mesoporous carbon and sulfur powder in the appropriate mass ratio, grind them evenly in a mortar, and then transfer them to a Pierrex glass tube and seal them under vacuum. Then place it in a muffle furnace and heat it at 350℃ for 6 hours, then cool it down to 155℃ and hold it for 6 hours, and finally cool it to room temperature to obtain an S / C composite material with a sulfur loading of 80 wt.%.

[0067] Step 2): In the glove box, weigh an appropriate amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into a reagent bottle, and add the corresponding amount of vinylene carbonate (VC) with a pipette to dissolve it and obtain a 1M LiTFSI-VC electrolyte.

[0068] Step 3): The S / C composite material is uniformly mixed with conductive carbon black (super P) and binder (CMC) at a mass ratio of 7:2:1 to obtain a slurry. The slurry is then coated onto the current collector aluminum foil and dried in a vacuum drying oven at 55°C for 12 hours to obtain the positive electrode sheet.

[0069] Step 4): Using the electrode sheet obtained above as the positive electrode, the lithium metal sheet as the counter electrode, the polypropylene membrane as the separator, and a solution containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and vinylene carbonate (VC) as the electrolyte, assemble the CR2016 button cell in an argon-filled glove box.

[0070] Example 4

[0071] A lithium-sulfur battery is prepared, and the specific steps of the preparation method are as follows:

[0072] Step 1): Weigh commercially available CMK-3 and sulfur powder in the appropriate mass ratio, grind them evenly in a mortar, and then transfer them to a Pyrex glass tube and seal it under vacuum. Then place it in a muffle furnace and heat it at 350°C for 6 hours, then cool it down to 155°C and hold it for 6 hours, and finally cool it to room temperature to obtain an S / C composite material with a sulfur loading of 50 wt.%.

[0073] Step 2): In the glove box, weigh an appropriate amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into a reagent bottle, and add the corresponding amount of vinylene carbonate (VC) with a pipette to dissolve it and obtain a 1M LiTFSI-VC electrolyte.

[0074] Step 3): The S / C composite material is uniformly mixed with conductive carbon black (super P) and binder (CMC) at a mass ratio of 7:2:1 to obtain a slurry. The slurry is then coated onto the current collector aluminum foil and dried in a vacuum drying oven at 55°C for 12 hours to obtain the positive electrode sheet.

[0075] Step 4): Using the electrode sheet obtained above as the positive electrode, pre-lithiated graphite as the counter electrode, polypropylene film as the separator, and a solution containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and vinylene carbonate (VC) as the electrolyte, assemble the CR2016 coin cell in an argon-filled glove box.

[0076] Example 5

[0077] A lithium-sulfur battery is prepared, and the specific steps of the preparation method are as follows:

[0078] Step 1): Weigh commercially available CMK-3 and sulfur powder in the appropriate mass ratio, grind them evenly in a mortar, and then transfer them to a Pyrex glass tube and seal it under vacuum. Then place it in a muffle furnace and heat it at 350°C for 6 hours, then cool it down to 155°C and hold it for 6 hours, and finally cool it to room temperature to obtain an S / C composite material with a sulfur loading of 50 wt.%.

[0079] Step 2): In the glove box, weigh an appropriate amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into a reagent bottle, and add the corresponding amount of fluoroethylene carbonate (FEC) with a pipette to dissolve it and obtain a 1M LiTFSI-FEC electrolyte.

[0080] Step 3): The S / C composite material is uniformly mixed with conductive carbon black (super P) and binder (CMC) at a mass ratio of 7:2:1 to obtain a slurry. The slurry is then coated onto the current collector aluminum foil and dried in a vacuum drying oven at 55°C for 12 hours to obtain the positive electrode sheet.

[0081] Step 4): Using the electrode sheet obtained above as the positive electrode, the lithium metal sheet as the counter electrode, the polypropylene membrane as the separator, and a solution containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and fluoroethylene carbonate (FEC) as the electrolyte, assemble the CR2016 coin cell in an argon-filled glove box.

[0082] Example 6

[0083] The specific steps of preparing a lithium battery are as follows:

[0084] Step 1): Weigh out commercially available CMK-3 and sulfur powder in the appropriate mass ratio, grind them evenly in a mortar, and then transfer them to a Pyrex glass tube and seal it under vacuum. Then place it in a muffle furnace and heat it at 350°C for 6 hours, then cool it down to 155°C and hold it for 6 hours, and finally cool it to room temperature to obtain an S / C composite material with a sulfur loading of 50 wt.%.

[0085] Step 2): In the glove box, weigh an appropriate amount of lithium bis(fluorosulfonyl)imide (LiFSI) into a reagent bottle, add the corresponding amount of vinylene carbonate (VC) using a pipette, and mix thoroughly in a shaker to obtain a 5M LiFSI-VC electrolyte.

[0086] Step 3): The S / C composite material is uniformly mixed with conductive carbon black (super P) and binder (CMC) at a mass ratio of 7:2:1 to obtain a slurry. The slurry is then coated onto the current collector aluminum foil and dried in a vacuum drying oven at 55°C for 12 hours to obtain the positive electrode sheet.

[0087] Step 4): Using the electrode sheet obtained above as the negative electrode, the lithium metal sheet as the counter electrode, the polypropylene membrane as the separator, and a solution containing lithium bis(fluorosulfonyl)imide (LiFSI) and vinylene carbonate (VC) as the electrolyte, assemble the CR2016 button cell in an argon-filled glove box.

[0088] Example 7

[0089] The specific steps of preparing a lithium battery are as follows:

[0090] Step 1): Weigh commercially available CMK-3 and sulfur powder in the appropriate mass ratio, grind them evenly in a mortar, and then transfer them to a Pyrex glass tube and seal it under vacuum. Then place it in a muffle furnace and heat it at 350°C for 6 hours, then cool it down to 155°C and hold it for 6 hours, and finally cool it to room temperature to obtain an S / C composite material with a sulfur loading of 50 wt.%.

[0091] Step 2): In the glove box, weigh an appropriate amount of lithium hexafluorophosphate (LiPF6) into a reagent bottle, add the corresponding amount of vinylene carbonate (VC) with a pipette, and mix evenly in a shaker to obtain a 3M LiPF6-VC electrolyte.

[0092] Step 3): The S / C composite material is uniformly mixed with conductive carbon black (super P) and binder (CMC) at a mass ratio of 7:2:1 to obtain a slurry. The slurry is then coated onto the current collector aluminum foil and dried in a vacuum drying oven at 55°C for 12 hours to obtain the positive electrode sheet.

[0093] Step 4): Using the electrode sheet obtained above as the negative electrode, the lithium metal sheet as the counter electrode, the polypropylene membrane as the separator, and a solution containing lithium hexafluorophosphate (LiPF6) and vinylene carbonate (VC) as the electrolyte, assemble the CR2016 coin cell in an argon-filled glove box.

[0094] Example 8

[0095] The specific steps of preparing a lithium battery are as follows:

[0096] Step 1): Weigh commercially available CMK-3 and sulfur powder in the appropriate mass ratio, grind them evenly in a mortar, and then transfer them to a Pyrex glass tube and seal it under vacuum. Then place it in a muffle furnace and heat it at 350°C for 6 hours, then cool it down to 155°C and hold it for 6 hours, and finally cool it to room temperature to obtain an S / C composite material with a sulfur loading of 50 wt.%.

[0097] Step 2): In the glove box, weigh an appropriate amount of lithium perchlorate (LiClO4) into a reagent bottle, add the corresponding amount of vinylene carbonate (VC) with a pipette, and mix evenly in a shaker to obtain a 2M LiClO4-VC electrolyte.

[0098] Step 3): The S / C composite material is uniformly mixed with conductive carbon black (super P) and binder (CMC) at a mass ratio of 7:2:1 to obtain a slurry. The slurry is then coated onto the current collector aluminum foil and dried in a vacuum drying oven at 55°C for 12 hours to obtain the positive electrode sheet.

[0099] Step 4): Using the electrode sheet obtained above as the positive electrode, the lithium metal sheet as the counter electrode, the polypropylene membrane as the separator, and a solution containing lithium perchlorate (LiClO4) and vinylene carbonate (VC) as the electrolyte, assemble the CR2016 button cell in an argon-filled glove box.

[0100] Comparative Example 1

[0101] A lithium-sulfur battery is prepared, and the specific steps of the preparation method are as follows:

[0102] Step 1): Weigh commercially available CMK-3 and sulfur powder in the appropriate mass ratio, grind them evenly in a mortar, and then transfer them to a Pyrex glass tube and seal it under vacuum. Then place it in a muffle furnace and heat it at 350°C for 6 hours, then cool it down to 155°C and hold it for 6 hours, and finally cool it to room temperature to obtain an S / C composite material with a sulfur loading of 50 wt.%.

[0103] Step 2): In the glove box, weigh an appropriate amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into a reagent bottle, and add the corresponding amounts of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) with a pipette to dissolve and obtain a 5M LiTFSI-DME / DOL (v / v = 1:1) electrolyte.

[0104] Step 3): The S / C composite material is uniformly mixed with conductive carbon black (super P) and binder (CMC) at a mass ratio of 7:2:1 to obtain a slurry. The slurry is then coated onto the current collector aluminum foil and dried in a vacuum drying oven at 55°C for 12 hours to obtain the positive electrode sheet.

[0105] Step 4): Using the electrode sheet obtained above as the positive electrode, the lithium metal sheet as the counter electrode, the polypropylene membrane as the separator, and 5M LiTFSI-DME / DOL (v / v=1:1) as the control electrolyte, assemble the CR2016 button cell in an argon-filled glove box.

[0106] Comparative Example 2

[0107] A lithium-sulfur battery is prepared, and the specific steps of the preparation method are as follows:

[0108] Step 1): Weigh commercially available CMK-3 and sulfur powder in the appropriate mass ratio, grind them evenly in a mortar, and then transfer them to a Pyrex glass tube and seal it under vacuum. Then place it in a muffle furnace and heat it at 350°C for 6 hours, then cool it down to 155°C and hold it for 6 hours, and finally cool it to room temperature to obtain an S / C composite material with a sulfur loading of 50 wt.%.

[0109] Step 2): The S / C composite material is uniformly mixed with conductive carbon black (super P) and binder (CMC) at a mass ratio of 7:2:1 to obtain a slurry. The slurry is then coated onto the current collector aluminum foil and dried in a vacuum drying oven at 55°C for 12 hours to obtain the positive electrode sheet.

[0110] Step 3): Using the electrode sheet obtained above as the positive electrode, the lithium metal sheet as the counter electrode, the polypropylene membrane as the separator, and the commercially available 1M LiTFSI-DME / DOL (v / v=1:1) as the control electrolyte, CR2016 button cell is assembled in an argon-filled glove box.

[0111] Performance testing

[0112] (a) Electrolyte 7 Li and 19 F NMR spectrum

[0113] The 5M LiTFSI-VC electrolyte prepared in Example 1 was subjected to... 7 Li and 19 The electrolyte was characterized by NMR spectroscopy and compared with the 5M LiTFSI-DME / DOL (v / v = 1:1) electrolyte prepared in Comparative Example 1.

[0114] Figure 2 The 5M LiTFSI-VC electrolyte obtained in Example 1 and the 5M LiTFSI-DME / DOL (v / v = 1:1) electrolyte prepared in Comparative Example 1 are examples of electrolytes prepared in this example. 7 Li and 19 F NMR spectrum. Among them, Figure 2 (a) is 7 Li NMR spectrum, when VC is used as a solvent 7 The Li peak shifts to higher frequencies, indicating that Li + The interaction with the solvent is weakened, Li + The surrounding electron density decreases. This means there are fewer solvent molecules around the lithium ion, and during charge and discharge, Li... + It can migrate and desolvate more quickly, which helps improve the rate performance of the battery system. Li + The weaker interaction with VC can also suppress the dissolution and diffusion of lithium polysulfides in the early stage of discharge, which is conducive to the formation of a thinner CEI. Figure 2 (b) is 19 F-NMR spectroscopy, similarly, when VC is used as a solvent, 19 The F-peak shifts to higher frequencies, TFSI - The interaction between anions and solvents is also weaker.

[0115] (II) Effect of Lithium Salt Concentration in Electrolyte on CEI Film Thickness

[0116] The CEI film thickness of the lithium-sulfur batteries prepared in Examples 1 and 2 after cycling in LiTFSI-VC with lithium salt concentrations of 5M and 1M was characterized, and test results of lithium-sulfur batteries with lithium salt concentrations of 2M, 3M, and 4M were also added. Figure 3 As shown, the thickness of the CEI film gradually decreases with increasing lithium salt concentration, and the CEI film is thinnest when the lithium salt concentration is 5M, about 10nm, indicating that lithium salt participates in and affects the growth of the CEI film.

[0117] Figure 4The image shows a TEM image of the S / C cathode prepared in Example 1 after 5 cycles in a 5M LiTFSI-VC electrolyte. It can be seen that a thin and uniform CEI film forms on the cathode surface after the first discharge in this electrolyte, and its thickness remains largely unchanged and uniform after multiple cycles. The TEM results clearly demonstrate that this CEI layer, formed by the reaction of VC, lithium polysulfide, and lithium salt, is essentially formed in the early stages of discharge and its morphology is unaffected by repeated cycles.

[0118] Furthermore, Figure 5 (a) and (b) are XPS spectra of the S / C cathode in Example 1 after the first week of discharge in 5M LiTFSI-VC electrolyte. In the C1s spectrum, in addition to the control peak at 284.8 eV, four peaks appeared at 286.3, 288.5, 290.0, and 293.0 eV, corresponding to CO, ROCO2Li, Li2CO3, and CF, respectively, strongly indicating that VC and lithium salts participate in the reaction with lithium polysulfides. In the F1s spectrum, there are also two peaks at 684.6 eV and 688.7 eV, corresponding to LiF and CF, respectively. This confirms the C1s spectrum results and also indicates that this CEI film is rich in LiF, which is beneficial to its robustness and rapid LiF reaction. + Conduction.

[0119] The above results demonstrate that the sulfur cathode can form a thin, robust, dense CEI film rich in LiF in situ after cycling in the VC-based electrolyte.

[0120] (III) Cyclic Performance Testing

[0121] The batteries prepared in Examples 1 and 2 were subjected to cycle stability tests and compared with the batteries assembled using ether electrolytes in Comparative Examples 1 and 2. The charge-discharge cycle results are as follows: Figure 6 As shown in (a), batteries using ether-based electrolytes exhibited faster capacity decay, while battery performance was significantly improved in LiTFSI-VC electrolyte. In particular, the battery in Example 1 using 5M LiTFSI-VC electrolyte showed the lowest capacity decay rate, retaining 1025 mAh g⁻¹ after 200 cycles. -1 Specific capacity.

[0122] The lithium-sulfur battery prepared in Example 1 was further subjected to charge-discharge tests under different operating conditions. Figure 6 (b), 6(c) and 6(d) are charge-discharge cycle diagrams of the battery’s long-cycle performance, rate performance and low-temperature performance, respectively. Under this VC-based electrolyte system, due to the in-situ formation of CEI with stable and fast lithium-ion conduction capability, the battery exhibits extremely excellent long cycle life, high rate stability and low-temperature performance.

[0123] The lithium-sulfur batteries prepared in Examples 3 and 4 were subjected to cycle stability tests in 5M LiTFSI-VC electrolyte, wherein... Figure 7 (a) and (b) show the cycle performance of the battery under high sulfur loading and lithium-depleted conditions, respectively. The good cycle stability indicates that the high sulfur loading and lithium-depleted conditions are well adapted to this VC system.

[0124] The lithium-sulfur battery prepared in Example 5 was subjected to cycle stability testing in 1M LiTFSI-FEC electrolyte. Figure 8 The graph shows the cycle performance of the battery. The excellent cycle performance indicates that, like the VC system, the FEC system can react with lithium polysulfides and lithium salts during the first discharge process to form a thin, uniform, and stable CEI layer in situ. This fundamentally solves the shuttle effect problem of lithium polysulfides and greatly improves the cycle stability of lithium-sulfur batteries.

[0125] Furthermore, the lithium-sulfur batteries assembled with the electrolytes prepared in Examples 6-8 were subjected to cycle stability tests, and compared with batteries assembled with commercially available 1M LiTFSI-DME / DOL (v / v = 1:1) electrolytes. The test results are as follows: Figure 9 As shown, the S / C cathode exhibits excellent cycle performance in VC-based electrolytes with LiFSI, LiPF6, and LiClO4 as lithium salts, which is far superior to ether-based electrolyte systems. Among them, the electrolyte with LiPF6 as lithium salt has the best performance.

[0126] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing a lithium-sulfur battery, characterized in that, Includes the following steps: S1. After mixing and grinding porous carbon carrier and sulfur powder, vacuum seal the mixture, heat it at 300-350℃ for 3-12 hours, then cool it down to 155℃ and hold it for 6-12 hours, and finally cool it to room temperature to obtain S / C composite material. S2. Dissolve the lithium salt in a carbonate-based solvent to obtain an electrolyte with a lithium salt concentration of 5 mol / L; wherein the lithium salt is lithium bis(trifluoromethanesulfonyl)imide and the carbonate-based solvent is vinylene carbonate; S3. The S / C composite material is mixed with conductive carbon black and binder to obtain a positive electrode slurry. The positive electrode slurry is coated on a current collector and vacuum dried to obtain a positive electrode sheet. S4. Under a protective atmosphere, the positive electrode sheet, a lithium metal sheet or a negative electrode made of lithium-containing material, a separator, and the electrolyte are assembled into a lithium-sulfur battery.

2. The preparation method according to claim 1, characterized in that, In step S1, the porous carbon support is selected from one or more combinations of ordered mesoporous carbon CMK-3, disordered mesoporous carbon BP2000, and disordered mesoporous carbon KB; the sulfur loading of the S / C composite material is 40wt.%~90wt.%.

3. The preparation method according to claim 1, characterized in that, In step S1, the porous carbon support is selected from disordered porous carbon treated with CO2 or alkali; the sulfur loading of the S / C composite material is 40wt.%~90wt.%.

4. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of the S / C composite material to the conductive carbon black and binder in the positive electrode slurry is (3~8):(1~2):

1.

5. The preparation method according to claim 1, characterized in that, The lithium-sulfur battery includes CR2016 or CR2032 coin cells.

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