In-situ construction of battery positive and negative electrode protection layers in lithium-sulfur battery and preparation method of electrolyte

Abstract

The invention discloses an in-situ construction battery positive and negative electrode protection layer in a lithium-sulfur battery and an electrolyte preparation method. Wherein a soluble COF material is added and comprises COF rich in C = N, COF rich in B-O, COF containing a PEG chain and the like, so that the ionic conductivity of the electrolyte is improved and a lithium metal negative electrode is effectively protected. Through an in-situ ring-opening polymerization technology, the electrolyte has excellent cycling stability and relatively high ionic conductivity (gt; 10 <-3 > S / cm), good interface compatibility and excellent thermal stability. In addition, due to the addition of PEG-COF, the ionic conductivity and thermal stability of the electrolyte are improved, the protection on a lithium metal negative electrode is enhanced, and the growth of lithium dendrites is inhibited. The invention provides a novel electrolyte which can be applied to a lithium-sulfur battery with high energy density and long service life, and the safety and the electrochemical performance of the battery are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-sulfur batteries, and in particular to a method for in-situ constructing positive and negative electrode protective layers and electrolyte preparation in lithium-sulfur batteries. Technical Background

[0002] With the rapid development of new energy technologies, lithium-sulfur batteries (LiS) are considered one of the key candidates for the next generation of high-energy storage systems due to their high theoretical energy density (approximately 2600Wh / kg), low cost, and environmental friendliness. However, the practical application of LiS batteries still faces many challenges, including the dissolution and shuttle effect of polysulfides (LiPSs), dendritic growth of lithium metal anodes, low ionic conductivity of the electrolyte, and poor compatibility between the electrode and electrolyte interfaces. These issues lead to short battery cycle life, rapid capacity decay, and potential safety risks.

[0003] Although traditional liquid electrolytes have high ionic conductivity, they cannot effectively inhibit the shuttle effect of LiPSs, and the side reactions with lithium metal anodes will aggravate dendrite growth. Although solid electrolytes (such as polymer electrolytes and inorganic ceramic electrolytes) can alleviate the diffusion of LiPSs and improve safety, their ionic conductivity is usually low (<10 -4 S / cm) and poor interfacial contact with the electrodes limit battery performance. In recent years, quasi-solid-state electrolytes based on in-situ polymerization have attracted attention. By directly forming a polymer network within the battery, they can improve interfacial contact and inhibit LiPSs migration. However, existing in-situ polymerized electrolytes still face problems such as insufficient mechanical properties, low lithium ion transport efficiency, and limited protection of the lithium anode.

[0004] Covalent organic framework (COF) materials are used to modify separators or as sulfur host materials in lithium-sulfur batteries due to their regular pore structure, high specific surface area and designable functional groups to adsorb LiPSs. However, there is still little research on introducing COF materials as functional additives into electrolyte systems. In particular, the introduction of soluble COF materials (such as C=N COF and BO COF) may improve the ion transport efficiency by optimizing the microstructure of the electrolyte, while PEG-COF containing flexible segments can improve the solubility of the electrolyte and its interfacial compatibility with the lithium negative electrode. In addition, in situ ring-opening polymer electrolytes based on 1,3-dioxolane (DOL) monomers (such as PDOL) have been widely studied due to their high ionic conductivity and interfacial stability, but their ability to inhibit lithium dendrites and high-temperature stability still need to be further optimized.

[0005] Based on this, the present invention proposes a composite electrolyte system that combines a soluble COF material with the in-situ ring-opening polymerization technology of PDOL. By introducing a COF material (such as PEG-COF), the electrolyte's ionic conductivity (>10-3 S / cm) is enhanced, improving the uniform deposition of lithium ions and suppressing dendrite growth. Simultaneously, the in-situ polymerization process forms a stable three-dimensional network structure, enhancing the electrolyte's mechanical strength and thermal stability. This technology provides an innovative solution for the development of high-energy-density, long-life lithium-sulfur batteries. Summary of the Invention

[0006] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a method for in-situ construction of positive and negative electrode protective layers and electrolyte preparation in lithium-sulfur batteries.

[0007] The present invention adopts the following technical solution: a lithium-sulfur battery in situ constructs a positive and negative electrode protective layer of the battery, which is composed of the following raw materials in terms of mass ratio: 5% to 95% of a ring-opening polymerizable ether monomer, 0.1% to 10% of a soluble COF material, 10% to 40% of an electrolyte salt and 0.05% to 1% of an initiator.

[0008] In a further embodiment, the ring-opening polymerizable ether monomers include: 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, furans and pyrans.

[0009] In a further embodiment, the soluble COF material includes at least one of a C═N-rich COF, a BO-rich COF, and a COF containing PEG chains.

[0010] In a further embodiment, the electrolyte salt is selected from at least one of LiTFSI (lithium bis(trifluoromethylsulfonyl)imide), LiPF6 (lithium hexafluorophosphate), LiFSI (lithium bis(fluorosulfonyl)imide), and the like.

[0011] In a further embodiment, the initiator is selected from at least one of trifluoromethanesulfonate, azo initiators, tris(pentafluorophenyl)borane, titanium chloride (TiCl4) and antimony trichloride (SbCl3).

[0012] In a further embodiment, the ionic conductivity of the electrolyte is greater than 1×10 -3 S / cm, and can effectively inhibit the dendrite growth of lithium metal anode.

[0013] A method for preparing an electrolyte for a lithium-sulfur battery comprises the following steps:

[0014] An ether monomer capable of ring-opening polymerization, a soluble COF material, an electrolyte salt and an initiator are mixed to obtain an electrolyte prepolymer precursor solution; an in-situ ring-opening polymerization reaction is carried out at 80-120° C. using a Lewis acid catalyst to obtain the electrolyte.

[0015] In a further embodiment, the COF material is added in an amount of 0.1% to 10% to enhance the ionic conductivity and thermal stability of the electrolyte.

[0016] A lithium-sulfur battery is prepared using the electrolyte described above.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. Significantly improve ionic conductivity and lithium ion transmission efficiency: By introducing soluble COF materials (such as C=NCOF, BO COF, PEG-COF), the microstructure of the electrolyte is optimized. Its regular pores and high specific surface area provide a fast transmission path for lithium ions. Combined with the three-dimensional network formed by the in-situ ring-opening polymerization of PDOL, the ionic conductivity of the electrolyte reaches >10-3S / cm, which is much higher than that of traditional solid electrolytes (<10 -4 S / cm), thereby significantly reducing the internal resistance of the battery and improving the energy density and charge and discharge efficiency.

[0019] 2. Efficiently inhibits lithium metal dendrite growth and improves interfacial stability: The flexible chain segments of PEG-COF work synergistically with the functional groups of the COF material to regulate the uniform deposition of lithium ions and effectively inhibit the formation of lithium dendrites. Simultaneously, the in-situ polymerization process forms a stable and dense electrolyte / electrode interface layer on the lithium anode surface, reducing side reactions, improving the cycling stability of the lithium metal anode, and extending battery life.

[0020] 3. Enhanced thermal stability and mechanical properties to ensure battery safety: The high thermal stability of COF materials (such as B-OCOF) combined with the cross-linked structure of the PDOL polymer network enables the electrolyte to maintain excellent thermal stability even in high-temperature environments (such as 80-120°C), avoiding the decomposition risk of traditional liquid electrolytes. In addition, the three-dimensional network formed by in-situ polymerization gives the electrolyte higher mechanical strength, can adapt to changes in electrode volume, inhibit the diffusion of polysulfides (LiPSs), and further improve battery safety and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a lithium-sulfur battery cycle diagram. DETAILED DESCRIPTION

[0022] 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.

[0023] 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.

[0024] 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.

[0025] Example 1

[0026] COF synthesis steps:

[0027] First, a polyethylene glycol-modified triformylbenzene-p-phenylenediamine covalent organic framework (PEG-TpPa COF) was synthesized via a solvothermal method. The following steps were performed: 1,3,5-Triformylbenzene (TFB, 0.5 mmol, 120 mg) and polyethylene glycol diamine (PEG-NH2, Mn = 600 Da, 1.0 mmol, 600 mg) were placed in a Schlenk tube, evacuated, and then filled with nitrogen. A mixture of o-dichlorobenzene / 1,4-dioxane (volume ratio 3:1, 20 mL) and 6 M acetic acid (0.5 mL) were then added and sonicated for 10 minutes until dissolved. The reaction tube was sealed and heated at 120°C for 72 hours, resulting in a yellow precipitate. After centrifugation, the product was washed three times with tetrahydrofuran (THF) and methanol, followed by drying under vacuum at 60°C for 24 hours to obtain PEG-TpPa COF as a white powder (85% yield).

[0028] Electrolyte preparation:

[0029] 12.0 g of 1,3-dioxolane (DOL) monomer, 0.8 g of the above-synthesized PEG-TpPa COF, 8.5 g of LiTFSI and 0.15 g of aluminum trifluoromethanesulfonate initiator were mixed and ultrasonically dispersed for 30 minutes to form a homogeneous precursor solution. The precursor solution was injected into the lithium-sulfur battery module and an in-situ ring-opening polymerization reaction was carried out at 60 ° C for 24 hours to generate a PDOL-PEG-TpPa composite electrolyte. The test results show that the ionic conductivity of the electrolyte is 1.5×10-3S / cm, and the capacity retention rate of the lithium-sulfur battery after 300 cycles at a 1C rate is 91.5% (such as Figure 1 As shown), the surface of the lithium metal anode is smooth and free of dendrites.

[0030] Example 2

[0031] COF synthesis steps:

[0032] Synthesis of TpPa-1COF: 1,3,5-triformylbenzene (TFB, 0.5 mmol, 120 mg) and p-phenylenediamine (Pa-1, 0.75 mmol, 81 mg) were placed in a pressure-resistant glass tube. A mixture of o-dichlorobenzene and n-butanol (1:1 by volume, 15 mL) and 3 drops of glacial acetic acid were added. The mixture was sonicated and then frozen in liquid nitrogen and sealed. The reaction was carried out at 120°C for 72 hours to produce deep red crystals. After centrifugation, the crystals were washed three times with THF and acetone and dried in a vacuum at 100°C for 12 hours to obtain TpPa-1COF.

[0033] COF-5 Synthesis: 2,3,6,7,10,11-Hexahydroxytriphenylene (HHTP, 0.4 mmol, 142 mg) and 1,4-phenylenediboronic acid (BDBA, 0.6 mmol, 105 mg) were added to a reaction flask, along with 15 mL of anhydrous xylene and 5 mg of copper acetate catalyst. The mixture was refluxed at 140°C for 48 hours to produce a blue-green precipitate. After centrifugation, the precipitate was washed five times with acetone and dried under vacuum at 80°C for 24 hours to yield COF-5.

[0034] Electrolyte preparation:

[0035] 20.0 g of 1,3-dioxane (DX) monomer, 1.2 g of TpPa-1COF, 0.6 g of COF-5, 12.0 g of LiFSI and 0.25 g of azobisisobutyronitrile initiator were mixed and ultrasonicated for 1 hour to form a homogeneous solution. The electrolyte was added to the battery and in-situ polymerization was carried out at 60 ° C for 18 hours to form a PDOL-TpPa-1 / COF-5 composite electrolyte. The test results showed that the ionic conductivity of the electrolyte reached 2.1×10-3S / cm, and the capacity retention rate of the lithium-sulfur battery was 88% after 500 cycles at a rate of 0.5C (such as Figure 1 The high temperature (60°C) cycling stability is improved by 30% compared to traditional electrolytes.

[0036] Example 3

[0037] COF synthesis steps:

[0038] PEG-TpPa COF: synthesized according to the method of Example 1 to obtain 0.5 g of product.

[0039] TpPa-1COF: synthesized according to the method of Example 2 to obtain 0.3 g of product.

[0040] COF-5: synthesized according to the method of Example 2 to obtain 0.2 g of product.

[0041] Electrolyte preparation:

[0042] 15.0 g of 1,3-dioxolane (DOL) monomer, 0.5 g of PEG-TpPa COF, 0.3 g of TpPa-1COF, 0.2 g of COF-5, and 10.0 g of LiPF6 were mixed and stirred for 2 hours under an argon atmosphere to form a homogeneous precursor solution. After the precursor solution was injected into the battery, an in-situ ring-opening polymerization reaction was carried out at 50 ° C for 12 hours to generate a ternary composite electrolyte of PDOL-PEG-TpPa / TpPa-1 / COF-5. Performance tests showed that the ionic conductivity of the electrolyte was 1.8×10 -3 S / cm, the capacity retention rate of the lithium-sulfur battery was 65% after 200 cycles at a high rate of 2C, the polysulfide shuttle effect was reduced by 50%, and the lithium negative electrode interface impedance decreased by 40%.

Claims

1. A method for in-situ construction of positive and negative electrode protective layers in a lithium-sulfur battery, characterized in that: The invention is composed of the following raw materials according to the mass ratio: 5% to 95% of a ring-opening polymerizable ether monomer, 0.1% to 10% of a soluble COF material, 10% to 40% of an electrolyte salt and 0.05% to 1% of an initiator.

2. The method of in-situ constructing a positive and negative electrode protective layer in a lithium-sulfur battery according to claim 1, characterized in that: The ring-opening polymerizable ether monomers include: 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, furans and pyrans.

3. The method of in-situ constructing positive and negative electrode protective layers in a lithium-sulfur battery according to claim 1, wherein: The soluble COF material includes at least one of a C═N-rich COF, a BO-rich COF, and a PEG chain-containing COF.

4. The method of in-situ constructing positive and negative electrode protective layers in a lithium-sulfur battery according to claim 1, wherein: The electrolyte salt is at least one selected from LiTFSI (lithium bis(trifluoromethanesulfonyl imide), LiPF6 (lithium hexafluorophosphate), LiFSI (lithium bis(fluorosulfonyl imide), and the like.

5. The method of in-situ constructing positive and negative electrode protective layers in a lithium-sulfur battery according to claim 1, wherein: The initiator is selected from at least one of trifluoromethanesulfonate, azo initiators, tris(pentafluorophenyl)borane, titanium chloride (TiCl4) and antimony trichloride (SbCl3).

6. The method of in-situ constructing positive and negative electrode protective layers in a lithium-sulfur battery according to claim 1, wherein: The ionic conductivity of the electrolyte is greater than 1×10 -3 S / cm, and can effectively inhibit the dendrite growth of lithium metal anode.

7. A method for preparing an electrolyte for a lithium-sulfur battery, characterized in that: The following steps are involved: An ether monomer capable of ring-opening polymerization, a soluble COF material, an electrolyte salt and an initiator are mixed to obtain an electrolyte prepolymer precursor solution; an in-situ ring-opening polymerization reaction is carried out at 80-120° C. using a Lewis acid catalyst to obtain the electrolyte.

8. The method for preparing an electrolyte for a lithium-sulfur battery according to claim 7, characterized in that: The COF material is added in an amount of 0.1% to 10% to enhance the ionic conductivity and thermal stability of the electrolyte.

9. A lithium-sulfur battery, characterized in that: The electrolyte according to claims 7 to 8 is used for preparation.

Images