PDOL electrolyte based on cross-linking regulation and preparation method and application thereof

Abstract

The application discloses a kind of PDOL electrolyte based on crosslinking regulation and its preparation method and application, belong to lithium-sulfur battery electrolyte preparation technical field.The application is by introducing the 4,4'-methylene bis (N,N-diglycidyl aniline) molecule with double epoxy functional group structure in PDOL quasi-solid electrolyte system, forms crosslinking network structure in in-situ polymerization process, to enhance the mechanical strength and structural stability of PDOL electrolyte;The crosslinking structure not only can build stable continuous ion transport channel, but also can effectively inhibit the diffusion migration of lithium polysulfide in electrolyte, reduce shuttle effect.Simultaneously, crosslinking network can form stable interface environment at lithium metal negative electrode interface, induce to build uniform and dense SEI layer, to promote the uniform deposition of lithium ion and inhibit lithium dendrite growth.Through the above structure regulation, the application realizes the synergistic improvement of polysulfide inhibition and lithium negative stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery electrolyte preparation technology, specifically relating to a cross-linked PDOL electrolyte, its preparation method, and its application. Background Technology

[0002] Lithium-sulfur batteries have a high power consumption of approximately 2600 Wh•kg. -1 With its high theoretical energy density and the outstanding advantages of abundant sulfur resources, low cost, and environmental friendliness, lithium-sulfur batteries are widely regarded as a promising next-generation high-energy-density energy storage system with broad application prospects in new energy vehicles, portable electronic devices, and energy storage power stations. However, in actual operation, lithium-sulfur batteries still face multiple key technological challenges that severely restrict their industrialization process. The most critical issues include the shuttle effect caused by the migration of soluble lithium polysulfides in the electrolyte, and the inevitable dendrite growth of the lithium metal anode during repeated deposition / stripping. These problems directly lead to continuous loss of battery active materials, a significant decrease in coulombic efficiency, and a substantial reduction in cycle life. Furthermore, the growth of lithium dendrites can easily puncture the separator, causing internal short circuits, thermal runaway, and other safety hazards, seriously threatening the safety of battery use.

[0003] Currently, the liquid electrolyte system widely used in lithium-sulfur batteries has obvious limitations: on the one hand, liquid organic solvents have a strong dissolving ability for lithium polysulfides, which will accelerate the diffusion and shuttle between the positive and negative electrodes, further aggravating capacity decay; on the other hand, liquid organic solvents are generally flammable and have poor interfacial stability with the lithium metal negative electrode, which can easily induce lithium dendrite growth and membrane puncture and other safety problems.

[0004] In contrast, solid-state electrolytes (SSEs) are considered an effective strategy for improving the safety and cycle stability of lithium-sulfur batteries due to their good structural stability, high thermal safety, and ability to suppress polysulfide shuttle and lithium dendrite growth to a certain extent. However, existing solid-state electrolyte systems still generally suffer from problems such as low ionic conductivity, poor electrode-electrolyte interface contact, and limited ability to immobilize lithium polysulfides. It is difficult to achieve effective interface control on both the positive and negative electrode sides simultaneously, and thus cannot balance the rate performance and long-term cycle stability of the battery.

[0005] Therefore, constructing a solid electrolyte structure that can be formed through in-situ polymerization and has good interface compatibility, and achieving synergistic optimization of polysulfide suppression and lithium dendrite growth regulation through reasonable interface control strategies, while improving ionic conductivity and interface compatibility, is an important research direction for improving the overall performance of lithium-sulfur batteries and promoting their industrial application. Summary of the Invention

[0006] Technical Problem Solved: To address the aforementioned technical problems, this invention provides a cross-linked controlled PDOL electrolyte, its preparation method, and its application. The aim is to solve the following problems in existing lithium-sulfur batteries: loss of active material due to lithium polysulfide shuttle, rapid capacity decay; insufficient rate performance; increased battery polarization and impedance caused by the shuttle effect; uncontrolled lithium dendrite growth severely shortening battery life; poor compatibility and high interfacial impedance between the electrolyte and the positive and negative electrodes; and the difficulty in balancing safety and electrochemical performance with existing electrolytes.

[0007] Technical solution: In a first aspect, the present invention provides a method for preparing a PDOL electrolyte based on cross-linking regulation, comprising the following steps: Step 1: In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), 1,3-dioxapentane (DOL) and ethylene glycol dimethyl ether (DME) are mixed evenly at a volume ratio of 2:1 to obtain a mixed solvent; lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is added to the mixed solvent, and the concentration of LiTFSI is controlled at 1 mol / L. The mixture is stirred for 15 min until completely dissolved to obtain mixed solution A; Step 2: Add 4,4'-methylenebis(N,N-diglycidylaniline) (MDA) to mixed solution A, and stir for 15 min until MDA is completely and evenly dispersed to obtain mixed solution B; wherein, the mass of MDA is 1% of the total mass of 1,3-dioxapentane and ethylene glycol dimethyl ether; Step 3: Add lithium hexafluorophosphate (LiPF6) as an initiator to mixed solution B, control the concentration of LiPF6 to 1 mol / L, and stir continuously for 10 min to form a uniform blue precursor solution, denoted as PDOL-MDA; after in-situ polymerization of this precursor solution, PDOL electrolyte based on cross-linking regulation can be obtained.

[0008] In a second aspect, the present invention provides a PDOL electrolyte based on cross-linking regulation, which is prepared by the preparation method described in the first aspect; the electrolyte uses PDOL as the main framework and MDA as the cross-linking agent to form a three-dimensional cross-linked network structure through in-situ polymerization; LiTFSI and LiPF6 are uniformly dispersed in the electrolyte, which has good mechanical strength, interfacial wettability, ion conductivity, as well as excellent polysulfide suppression ability and lithium dendrite regulation ability.

[0009] Thirdly, the present invention provides the application of the cross-linked regulated PDOL electrolyte described in the second aspect in the preparation of lithium-sulfur batteries.

[0010] Preferably, the application includes the following steps: S1. Preparation of the positive electrode: Carbon nanotubes (CNTs) and sulfur powder were mixed at a mass ratio of 1:3 and manually ground for 30 min until homogeneous. The mixture was then placed in a tube furnace under an argon atmosphere and heated at 155 °C for 12 h. After cooling to room temperature, a C / S composite cathode material was obtained. The C / S composite cathode material, conductive agent, and binder were mixed and ground to form a uniform and viscous slurry. The slurry was uniformly coated onto a 30 μm thick aluminum foil current collector using a blade coating method, with the coating thickness controlled at 120 μm. The coating was then dried in a vacuum drying oven at 60 °C for 10 h to remove the solvent. After drying, a cathode sheet was obtained and punched into 16 mm diameter C / S circular electrode sheets for later use. S2, Assembly of lithium-sulfur batteries: In a glove box under an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm), the C / S circular electrode sheet prepared in step S1 was used as the positive electrode, Celgard 2500 polypropylene membrane was used as the separator, and a commercial lithium metal sheet (500 μm thick) was used as the negative electrode. The PDOL-MDA precursor solution was uniformly dropped onto both sides of the separator to fill the gaps between the positive electrode and the separator, and between the negative electrode and the separator, serving as the electrolyte. Subsequently, the battery was encapsulated under argon protection to obtain an unpolymerized lithium-sulfur battery semi-finished product. S3, In-situ Polymerization and Battery Molding: The lithium-sulfur battery semi-finished product was placed in a glove box for 24 hours under an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm) to allow the PDOL-MDA precursor solution to undergo an in-situ polymerization reaction inside the battery, forming a three-dimensional cross-linked network structure of PDOL electrolyte, and finally obtaining a quasi-solid-state lithium-sulfur battery.

[0011] Furthermore, in step S1, the conductive agent is Ketjen Black, and the binder is composed of polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP), wherein the ratio of PVDF to NMP is 0.75 g: 30 mL; the weight ratio of the C / S composite cathode material, conductive agent and binder is 7:2:1.

[0012] Beneficial effects: 1) Stable interface, which can meet the interface requirements of positive and negative electrodes respectively: By introducing MDA molecules with a double epoxy functional group structure into the PDOL electrolyte system, a stable cross-linked network structure is formed during in-situ polymerization, which enables the electrolyte to have both good mechanical strength and interfacial wettability, thereby significantly improving the interfacial contact and compatibility between the electrolyte and the positive and negative electrodes; This structure can effectively reduce interfacial polarization and improve ion transport efficiency, thereby improving the overall electrochemical performance of the battery; 2) Effectively suppressing the lithium polysulfide shuttle effect and improving ionic conductivity: The PDOL-MDA electrolyte on the positive electrode side constructs a stable three-dimensional polymer network through cross-linking structure, which physically confines the diffusion and migration of lithium polysulfides, thereby effectively suppressing their shuttle effect between the positive and negative electrodes, reducing the loss of active material and side reactions; at the same time, the stable polymer network can construct continuous ion transport channels, which is conducive to promoting the migration of lithium ions, thereby improving the ionic conductivity of the electrolyte and improving the positive electrode reaction kinetics; 3) Suppressing lithium dendrite growth and constructing a stable SEI to further improve ion conduction performance: The PDOL-MDA electrolyte on the negative electrode side can provide a continuous and stable ion conduction environment for lithium ions. The cross-linked network structure helps to form a dense and stable interface structure on the lithium metal surface, thereby promoting the uniform deposition of lithium ions, suppressing the nucleation and growth of lithium dendrites, and facilitating the construction of a stable solid electrolyte interface (SEI) layer, further reducing interface impedance and improving battery cycle life. 4) The process is simple and suitable for large-scale preparation: This application adopts in-situ polymerization to directly construct solid electrolytes during battery assembly, without the need for complex equipment and cumbersome steps such as multiple impregnation and coating. The overall process route is simple, the operating conditions are mild, the raw materials are readily available and the cost is low, and it has good prospects for scale-up and industrial application. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating the ring-opening principle of in-situ polymerization of PDOL-MDA precursor solution in Example 1 of the present invention. Figure 2 The graph shows the charge-discharge performance of the quasi-solid-state lithium-sulfur battery prepared in Example 1 of this invention at rates of 0.1C-2C. Figure 3 The graph shows the capacity retention performance of the quasi-solid-state lithium-sulfur battery prepared in Example 1 of this invention after 200 cycles at a 0.2C rate.

[0014] Figure 4 The stability test diagram of the symmetric cell (Li / PDOL-MDA / Li) prepared in Example 1 of the present invention under 1600 hours of cycling. Detailed Implementation

[0015] The present invention will be described in detail below with reference to specific embodiments: Example 1

[0016] A cross-linked controlled PDOL electrolyte and its in-situ polymerization preparation method specifically include the following steps: Step 1: In an argon-atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm, argon purity 99.999%), 2 mL of 1,3-dioxapentane and 1 mL of ethylene glycol dimethyl ether were mixed thoroughly to obtain a mixed solvent; lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to the mixed solvent, and the concentration of LiTFSI was controlled at 1 mol / L. The mixture was stirred for 15 min until LiTFSI was completely dissolved to obtain mixed solution A; Step 2: Add 0.03 g of MDA to mixed solution A and continue stirring for 15 min until the MDA is completely and evenly dispersed to obtain mixed solution B; Step 3: Add lithium hexafluorophosphate (LiPF6) to mixed solution B, control the concentration of LiPF6 to 1 mol / L, stir for 10 min to form a uniform blue precursor solution, denoted as PDOL-MDA.

[0017] The application of the cross-linked regulated PDOL electrolyte prepared by the above in-situ polymerization method in the preparation of lithium-sulfur batteries involves the following specific steps: S1. Carbon nanotubes and sulfur powder are mixed at a mass ratio of 1:3 and manually ground for 30 min until uniformly mixed. The mixture is then placed in a tube furnace and heated at 155℃ for 12 h under an argon atmosphere. After cooling to room temperature, a C / S composite cathode material is obtained. A mixed solution of C / S composite cathode material, conductive agent (Ketjen Black), and binder (PVDF to NMP ratio of 0.75 g: 30 mL) is mixed at a weight ratio of 7:2:1 and ground to form a uniform and viscous slurry. The slurry is uniformly coated onto an aluminum foil with a thickness of 30 μm using a blade coating method, resulting in a coating thickness of 120 μm. The foil is then placed in a vacuum drying oven (vacuum degree -0.09 MPa) and dried at 60 ℃ for 10 h to obtain a cathode sheet. The cathode sheet is then punched into C / S circular electrode sheets with a diameter of 16 mm for later use. S2. In a glove box under an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm), using a C / S circular electrode as the positive electrode, Celgard 2500 as the separator, and a commercial lithium metal sheet (500 μm thick, wiped with anhydrous ethanol to remove the oxide layer before use) as the negative electrode; PDOL-MDA precursor solution is added dropwise to both sides of the separator to fill the gaps between the positive electrode and the separator, and between the negative electrode and the separator. The battery is then encapsulated under argon protection to obtain a semi-finished battery. S3. The battery semi-finished product is placed in a glove box (argon atmosphere, H2O < 0.1 ppm, O2 < 0.1 ppm) at room temperature for 24 h to allow the PDOL-MDA precursor solution to undergo in-situ polymerization, forming a PDOL electrolyte with a three-dimensional cross-linked network structure, and finally obtaining a quasi-solid-state lithium-sulfur battery.

[0018] Comparative Example 1 PDOL was added dropwise to both sides of the positive and negative electrodes and between the separator as the electrolyte: the initial capacity was 907 mAh / g, and the capacity remained at 595 mAh / g after 200 cycles (retention rate of 65.5%). Compared with Example 1, the capacity decreased significantly when only PDOL was added as the electrolyte, indicating that PDOL alone has a limited inhibitory effect on polysulfides.

[0019] Figure 1 A schematic diagram illustrating the ring-opening principle of solution in-situ polymerization of PDOL-MDA precursor was provided. Electrochemical performance tests were conducted on the lithium-sulfur batteries prepared in Example 1 and Comparative Example 1 under the following conditions: room temperature (25 °C), charge / discharge voltage range of 1.7-2.8 V, and rate testing range of 0.1C-2C (e.g., ...). Figure 2 As shown); cyclic test magnification 0.2C, number of cycles 200 (as shown). Figure 3 As shown); Symmetrical cell test (Li / PDOL-MDA / Li) (as shown) Figure 4 (As shown), the results are shown in Table 1-3 below: Table 1. Comparison of the performance of lithium-sulfur batteries prepared in Example 1 and Comparative Example 1 after 200 cycles. , Table 1 shows that, compared with the comparative PDOL electrolyte, the PDOL-MDA electrolyte of this invention with the introduction of MDA exhibits significantly improved electrochemical performance: The lithium-sulfur battery with the PDOL-MDA electrolyte prepared in Example 1 had an initial discharge specific capacity of 965 mAh / g, which was significantly higher than that of Comparative Example 1 (907 mAh / g). This indicates that the introduction of MDA is beneficial to improving the utilization rate of active materials and electrochemical reaction kinetics of the sulfur cathode. In terms of long-cycle performance, the battery in Example 1 still maintains a discharge specific capacity of 768 mAh / g after 200 cycles, with a capacity retention rate of 79.6%, while the comparative PDOL battery has a capacity of only 595 mAh / g under the same cycle conditions, with a capacity retention rate of 65.5%, showing obvious capacity decay.

[0020] Table 2 Comparison of rate performance of lithium-sulfur batteries prepared in Example 1 and Comparative Example 1 , Table 2 shows that, compared with the comparative PDOL electrolyte, the PDOL-MDA electrolyte of this invention with the introduction of MDA exhibits significantly improved rate performance.

[0021] The PDOL-MDA electrolyte prepared in Example 1 exhibited higher discharge specific capacity at different current densities and maintained high capacity output even at high rates. For example, at a high rate of 2C, its specific capacity was significantly better than that of the comparative PDOL electrolyte, indicating that the introduction of MDA effectively improved the Li- content of the system. + Transport capacity and electrochemical reaction kinetics.

[0022] Furthermore, when the current density recovers to a low rate, the capacity of the PDOL-MDA battery can essentially recover to its initial level, demonstrating excellent rate recovery capability, while the comparative PDOL battery exhibits significant capacity loss. This indicates that introducing MDA helps to build a stable electrolyte / electrode interface, reduce polarization, and promote Li... + Rapid migration enables excellent rate performance.

[0023] Table 3 Comparison of symmetry performance of lithium-sulfur batteries prepared in Example 1 and Comparative Example 1 , Table 3 shows that the PDOL-MDA electrolyte obtained after introducing MDA exhibits superior interfacial stability in symmetric cell tests. During long-term cycling, the system consistently maintains a low and stable polarization voltage, indicating good Li... + Transmission capability and interface compatibility.

[0024] Meanwhile, under the same current density conditions, the PDOL-MDA electrolyte maintained stable cycling behavior, while the comparative system exhibited significant increased polarization and cycling instability. This result indicates that the introduction of MDA effectively modulates lithium deposition behavior and promotes Li-200 lithium deposition. + Uniform deposition and suppression of dendrite growth result in excellent interface stability.

[0025] The above results show that the introduction of MDA can effectively suppress the shuttle effect of lithium polysulfides and improve the stability of the lithium anode interface, thereby significantly reducing the capacity decay rate of the battery during long-term cycling and achieving simultaneous improvement in the cycle stability and operational safety of lithium-sulfur batteries.

[0026] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a PDOL electrolyte based on cross-linking regulation, characterized in that, Includes the following steps: Step 1: In an argon-atmosphere glove box, 1,3-dioxapentane and ethylene glycol dimethyl ether are mixed evenly at a volume ratio of 2:1 to obtain a mixed solvent; lithium bis(trifluoromethanesulfonyl)imide is added to the mixed solvent, and the concentration of lithium bis(trifluoromethanesulfonyl)imide is controlled at 1 mol / L. The mixture is stirred for 15 min until completely dissolved to obtain mixed solution A. Step 2: Add 4,4'-methylenebis(N,N-diglycidylaniline) to mixed solution A, and stir for 15 min until 4,4'-methylenebis(N,N-diglycidylaniline) is completely and evenly dispersed to obtain mixed solution B; Step 3: Add lithium hexafluorophosphate to mixed solution B, control the concentration of lithium hexafluorophosphate to 1 mol / L, and stir continuously for 10 min to form a uniform blue precursor solution, denoted as PDOL-MDA; After in-situ polymerization of the precursor solution, a cross-linking-regulated PDOL electrolyte can be obtained.

2. The preparation method according to claim 1, characterized in that: The ambient concentrations in the glove box were H2O < 0.1 ppm and O2 < 0.1 ppm.

3. The preparation method according to claim 1, characterized in that: The mass of the 4,4'-methylenebis(N,N-diglycidylaniline) is 1% of the total mass of 1,3-dioxopentane and ethylene glycol dimethyl ether.

4. A PDOL electrolyte based on cross-linking regulation, characterized in that: It is prepared by the preparation method described in any one of claims 1-3.

5. The application of the cross-linked PDOL electrolyte as described in claim 4 in the preparation of lithium-sulfur batteries.

6. The application according to claim 5, characterized in that, Includes the following steps: S1. Preparation of the positive electrode: Carbon nanotubes and sulfur powder were mixed at a mass ratio of 1:3 and manually ground for 30 min until homogeneous. The mixture was then placed in a tube furnace under an argon atmosphere and heated at 155 °C for 12 h. After cooling to room temperature, a C / S composite cathode material was obtained. The C / S composite cathode material, conductive agent, and binder were mixed and ground to form a uniform and viscous slurry. The slurry was uniformly coated onto a 30 μm thick aluminum foil current collector using a blade coating method, with the coating thickness controlled at 120 μm. The coating was then dried in a vacuum drying oven at 60 °C for 10 h to remove the solvent. After drying, a cathode sheet was obtained and punched into 16 mm diameter C / S circular electrode sheets for later use. S2, Assembly of lithium-sulfur batteries: In a glove box under an argon atmosphere, the C / S circular electrode sheet prepared in step S1 is used as the positive electrode, Celgard 2500 polypropylene membrane is used as the separator, and commercial lithium metal sheet is used as the negative electrode. The PDOL-MDA precursor solution is uniformly dropped onto both sides of the separator to fill the gaps between the positive electrode and the separator, and between the negative electrode and the separator, serving as the electrolyte. Subsequently, the battery is encapsulated under argon protection to obtain an unpolymerized lithium-sulfur battery semi-finished product. S3, In-situ Polymerization and Battery Molding: The lithium-sulfur battery semi-finished product was placed in a glove box for 24 hours under an argon atmosphere to allow the PDOL-MDA precursor solution to undergo an in-situ polymerization reaction inside the battery, forming a PDOL electrolyte with a three-dimensional cross-linked network structure, and finally obtaining a quasi-solid-state lithium-sulfur battery.

7. The application according to claim 5, characterized in that, In step S1, the conductive agent is Ketjen Black, and the binder is composed of polyvinylidene fluoride and N-methylpyrrolidone, wherein the ratio of polyvinylidene fluoride to N-methylpyrrolidone is 0.75 g: 30 mL; the weight ratio of the C / S composite cathode material, conductive agent and binder is 7:2:1.

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