Electrolyte taking thioether compound as functional diluent

Abstract

The invention discloses an electrolyte taking a thioether compound as a functional diluent, and relates to the technical field of lithium ion batteries. The electrolyte comprises a lithium salt, a solvent for dissolving the lithium salt, a diluent and an additive, wherein the diluent is a thioether compound. By introducing a thioether compound as a functional diluent, a local high-concentration electrolyte system is constructed, and the ionic conductivity and the lithium ion transference number of the electrolyte are effectively improved. The diluent and the SPAN positive electrode have special affinity, and dissolution of polysulfide can be inhibited from physical and chemical levels; and meanwhile, the potential distribution and the ion desolvation process at the positive electrode interface are optimized, and a CEI interface which is rich in LiF and is beneficial to lithium ion transmission is formed. By introducing a thioether functional diluent, three functions of optimizing a solvation structure, anchoring an active substance and constructing a stable interface are simultaneously realized, and the rate capability and the cycling stability of the Li-SPAN battery are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to an electrolyte that uses sulfide compounds as functional diluents. Background Technology

[0002] Against the backdrop of global energy transition and the rapid development of the new energy vehicle industry, developing rechargeable batteries that combine high energy density, long cycle life, and fast charging capability has become a core challenge in the energy storage field. Traditional lithium-ion batteries face development bottlenecks due to limitations in the theoretical capacity of cathode materials and key metal resources. Sulphated polyacrylonitrile (SPAN) cathodes, with their unique "solid-solid" conversion mechanism, can effectively suppress polysulfide shuttle and are considered one of the ideal candidates for constructing high-energy lithium metal batteries. However, the intrinsically low electronic / ionic conductivity of SPAN materials leads to severely insufficient fast-charging performance. At high current densities, sluggish ion transport kinetics and unstable electrode / electrolyte interfaces induce severe polarization and capacity decay, which has become a key obstacle restricting its practical application.

[0003] Electrolytes are crucial for regulating ion transport and interfacial stability within batteries. Therefore, designing a high-performance, fast-charging electrolyte system is essential. Locally High Concentration Electrolyte (LHCE) strategies, by introducing a "diluent," improve macroscopic processing performance while maintaining the excellent interfacial properties of high-concentration electrolytes. The choice of diluent directly determines the overall performance of LHCE. Current research commonly uses fluorinated ethers as diluents, primarily utilizing their high oxidation stability and flame retardancy. However, the design philosophy of these traditional diluents focuses on "chemical inertness" and physical regulation, lacking active interfacial control functions for electrodes like SPANs with unique surface chemistry. Furthermore, high fluoride content typically leads to a significant increase in electrolyte density (>1.4 g mL⁻¹), which is detrimental to improving the overall energy density of the battery. More importantly, the operating voltage window of the SPAN system is relatively mild, and the extreme oxidation resistance requirement of the co-solvent is not necessary. Therefore, breaking through the limitations of traditional "inert" cosolvents and developing functional cosolvents that can actively participate in and optimize the chemical processes at the SPAN interface is of great significance for unleashing the fast-charging potential of Li||SPAN batteries. Summary of the Invention

[0004] The purpose of this invention is to provide an electrolyte that uses sulfide compounds as functional diluents to address the problems of slow lithium-ion transport kinetics and poor electrode / electrolyte interface stability in existing Li-SPAN battery systems.

[0005] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides an electrolyte using a thioether compound as a functional diluent, comprising a lithium salt, a solvent for dissolving the lithium salt, a diluent, and an additive.

[0006] The diluent is a thioether compound.

[0007] The thioether compounds include at least one of dimethyl sulfide, dipropyl sulfide, dipropyl disulfide, or dipropyl trisulfide.

[0008] The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, or lithium perchlorate.

[0009] The solvent for dissolving the lithium salt includes at least one of 1,2-diethoxyethane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, ethylene carbonate, propylene carbonate, dimethyl carbonate, or ethyl methyl carbonate.

[0010] The additive includes at least one of triethyl phosphate, fluoroethylene carbonate, or vinylene carbonate.

[0011] The concentration of the lithium salt is 0.5 ~ 3.0 mol / L; The volume ratio of the solvent to the thioether compound used to dissolve the lithium salt is 9:1 to 5:5. The amount of the additive used is 1-10% of the electrolyte mass fraction.

[0012] Preferably, the lithium salt is lithium bis(fluorosulfonyl)imide.

[0013] Preferably, the solvent for dissolving the lithium salt is ethylene glycol diethyl ether (DEE).

[0014] Preferably, the sulfide compound is dipropyl sulfide (DS).

[0015] Preferably, the additive is triethyl phosphate (TEP).

[0016] Secondly, the present invention provides a lithium metal battery, wherein the electrolyte is the electrolyte with sulfide compounds as functional diluents, the negative electrode is lithium metal, and the positive electrode is sulfided polyacrylonitrile (SPAN).

[0017] Thirdly, the present invention provides an application of the above-mentioned electrolyte in lithium metal batteries.

[0018] Technical principle of the invention: (1) Thioether diluents have weak solubility for lithium salts, but they are well miscible with the main solvent. In the electrolyte, they are not completely inert. By adjusting the solvation structure, they can promote a relative increase in the concentration of lithium salts in the local environment of the effective solvent (such as ethers).

[0019] (2) The sulfur atoms in thioethers (RSR) have lone pairs of electrons, which interact with the SPAN cathode and the polysulfides (Li2S) generated during cycling. x There are strong interactions between them, which anchors more polysulfides to the positive electrode side, thus weakening their dissolution and diffusion into the electrolyte from a chemical environment perspective.

[0020] (3) The locally high concentration of solvation structure alters the double layer structure and potential distribution at the cathode / electrolyte interface. This helps to lower the desolvation energy barrier of lithium ions at the interface, making it easier for lithium ions to escape the constraints of the solvent shell and enter the active material for reaction.

[0021] The beneficial effects of this invention are as follows: (1) Thioether-based diluents significantly reduce the overall viscosity of the electrolyte and improve ionic conductivity. At the same time, they optimize the solvation structure and increase the lithium-ion transference number.

[0022] (2) Thioether diluents significantly reduce the dissolution of polysulfides in the electrolyte and their shuttle to the negative electrode through the dual effects of physical dilution and chemical affinity. This directly alleviates the irreversible loss of positive electrode active material and the poisoning of lithium metal or the negative electrode interface.

[0023] (3) By introducing a thioether-based functional diluent, the three functions of optimizing the solvation structure, anchoring active substances, and building a stable interface are simultaneously achieved, simplifying the electrolyte formulation design. Attached Figure Description

[0024] Figure 1 These are the ionic conductivity test graphs and lithium-ion transference number test graphs for Example 1 and Comparative Example 1.

[0025] Figure 2 These are optical photographs of Example 1 and Comparative Example 1.

[0026] Figure 3 These are in-situ UV test images of Example 1 and Comparative Example 1.

[0027] Figure 4 The graphs show the coulombic efficiency of the lithium anode in Example 1 and Comparative Example 1.

[0028] Figure 5 These are the cycle performance graphs for Example 1 and Comparative Example 1.

[0029] Figure 6These are the rate performance diagrams for Example 1 and Comparative Example 1. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention. Example 1

[0031] This embodiment provides an electrolyte using thioether compounds as functional diluents, comprising the following steps: Step 1: In the glove box, weigh 0.561g of LiFSI and add it to a mixed solution of ethylene glycol diethyl ether (1mL) and dipropyl sulfide (1mL); add 10% of triethyl phosphate by mass of electrolyte to the above mixed solution and stir thoroughly until completely mixed.

[0032] Step 2: In the glove box, use a suitable filter membrane to filter the prepared electrolyte to remove any possible impurity particles and magnetic particles, and obtain a clear and transparent electrolyte.

[0033] Step 3: Assembly of the CR2032 button cell must be carried out in an argon-filled glove box, where the water content (w(H2O)) and oxygen content (w(O2)) must both be ≤0.01 ppm. The negative electrode uses a lithium metal sheet with dimensions of Φ14 mm × 500 μm, matched with Celgard. The positive electrode is prepared through the following steps: First, sulfurized polyacrylonitrile (SPAN, active material), superconducting carbon black (Super P, conductive agent), and sodium alginate (SA, binder) are weighed in a mass ratio of 8:1:1. Then, deionized water is used as a solvent to prepare a uniform slurry. The slurry is then uniformly coated onto the surface of an aluminum foil current collector. After coating, the aluminum foil is placed in a vacuum drying oven and dried at 90 ℃ and -0.1 MPa vacuum for 12 h to remove solvent and residual moisture. Finally, the dried positive electrode sheet is cut into Φ10 mm circular sheets. Example 2

[0034] The difference from Example 1 is that the volume ratio of ethylene glycol diethyl ether to dipropyl sulfide is 8:2. Example 3

[0035] The difference from Example 1 is that the thioether compound is dipropyl disulfide. Example 4

[0036] The difference from Example 1 is that the thioether compound is dipropyl trisulfide. Example 5

[0037] The difference compared to Example 1 is that the concentration of lithium salt is 1M. Example 6

[0038] The difference compared to Example 1 is that the concentration of lithium salt is 2M. Example 7

[0039] The difference compared to Example 1 is that the concentration of lithium salt is 3M.

[0040] Comparative Example 1 The difference from Example 1 is that the volume ratio of ethylene glycol diethyl ether to dipropyl sulfide is 10:0.

[0041] Performance testing The performance of the electrolytes prepared in Example 1 and Comparative Example 1, and the assembled lithium metal batteries, was tested: Ionic conductivity testing: Swagelok batteries were used for testing, with an applied frequency range of 1 MHz to 0.1 Hz. Impedance was measured using the Shanghai Chenhua electrochemical workstation, and ionic conductivity was calculated.

[0042] Ion transport number test: A lithium symmetric battery is used, and a small voltage (usually 10mV) is applied. The change of current over time and the interface impedance are observed and analyzed, and finally the lithium ion transport number is calculated.

[0043] In-situ UV testing: Assemble an in-situ UV electrolysis cell and observe the reaction.

[0044] Optical photographs: Observation of the color state of the electrolyte in the example containing 0.1M Li2S6.

[0045] Lithium anode coulombic efficiency test: The lithium compatibility of the electrolyte in the example was tested by assembling lithium copper half-cells.

[0046] The lithium foil is Φ12mm in size, the copper foil is Φ14mm in size, and the electrolyte volume is 40μL.

[0047] Rate performance testing: Assembled Li-SPAN batteries were tested at room temperature. A Blue Battery testing system was used, operating within a voltage range of 1–3V at 1C, 2C, 3C, 4C, and 5C (1C = 560 mAh g). -1 Charge and discharge tests were conducted using current density.

[0048] Cyclic performance testing: Assembled Li-SPAN batteries were subjected to room temperature cycle testing. A Blue Electricity testing system was used, operating at 3C (1C = 560 mAh g⁻¹) within a voltage range of 1–3V.-1 Charge and discharge tests were conducted using current density.

[0049] Results analysis: (1) such as Figure 1 As shown, Example 1 exhibits high ionic conductivity and lithium-ion transference number. The addition of dipropyl sulfide diluent significantly reduces the overall viscosity of the electrolyte and improves ionic conductivity. Simultaneously, the optimized solvation structure further enhances the lithium-ion transference number.

[0050] (2) For example Figure 2 and Figure 3 As shown, Example 1 can significantly inhibit the dissolution of polysulfides. Dipropyl sulfide adsorbs onto the SPAN surface with its central sulfur atom as an anchor point, and the propyl chains extending from both ends form a hydrophobic, nonpolar organic molecular layer at the interface, effectively repelling direct contact with polar ethylene glycol diethyl ether (DEE), thereby weakening the driving force for the solvation and dissolution of polysulfides from a physical and chemical perspective.

[0051] (3) such as Figure 4 As shown, Example 1 exhibits high coulombic efficiency. The localized high-concentration electrolyte at the interface on the negative electrode side, in conjunction with FSI⁻, constructs an ultra-stable, highly ionicly conductive, and uniformly lithium-enriched SEI layer on the lithium metal surface, significantly optimizing the deposition / stripping process of the lithium metal negative electrode.

[0052] (4) such as Figure 5 and Figure 6 As shown, Example 1 exhibits superior rate performance and cycle performance in a Li-SPAN battery. The bulk electrolyte of Example 1 possesses high ionic conductivity and lithium-ion transference number; during charge-discharge cycles, it can both bind polysulfides within the SPAN and form LiF-rich SEI and CEI at the positive and negative electrodes. Dipropyl sulfide, as a functional diluent, significantly enhances the rate performance and cycle performance of the Li-SPAN battery.

[0053] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. An electrolyte using sulfide compounds as functional diluents, comprising a lithium salt, a solvent for dissolving the lithium salt, a diluent, and additives, characterized in that, The diluent is a sulfide compound; The sulfide compounds include at least one of dimethyl sulfide, dipropyl sulfide, dipropyl disulfide, or dipropyl trisulfide. The lithium salts include at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium di(oxalate)borate, lithium di(oxalate)borate, or lithium perchlorate. The solvent for dissolving lithium salts includes at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, ethylene carbonate, propylene carbonate, dimethyl carbonate, or methyl ethyl carbonate. The additive includes at least one of triethyl phosphate, fluoroethylene carbonate, or vinylene carbonate. The concentration of the lithium salt is 0.5-3.0 mol / L; The volume ratio of the solvent to the thioether compound used to dissolve the lithium salt is 9:1 to 5:

5. The amount of the additive used is 1-10% of the electrolyte mass fraction.

2. The electrolyte using sulfide compounds as functional diluents according to claim 1, characterized in that, The lithium salt is lithium difluorosulfonylimide.

3. The electrolyte using sulfide compounds as functional diluents according to claim 1, characterized in that, The solvent for dissolving the lithium salt is ethylene glycol diethyl ether.

4. The electrolyte using sulfide compounds as functional diluents according to claim 1, characterized in that, The thioether compound is dipropyl thioether.

5. The electrolyte using sulfide compounds as functional diluents according to claim 1, characterized in that, The additive is triethyl phosphate.

6. The application of the electrolyte with thioether compounds as functional diluents as described in any one of claims 1-5 in lithium metal batteries.

7. A lithium metal battery, characterized in that, Includes the electrolyte according to any one of claims 1-5.

8. The lithium metal battery according to claim 7, characterized in that, The positive electrode of this lithium metal battery is sulfided polyacrylonitrile, and the negative electrode is lithium metal.

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