An electrolyte containing organic potassium salt, its preparation method and application

Abstract

This invention belongs to the field of lithium-sulfur battery technology, specifically relating to an electrolyte containing organic potassium salts, its preparation method, and its application. The electrolyte comprises a conductive lithium salt, an ether solvent, a primary additive, and secondary additives; the primary additive is an organic potassium salt. By adding a potassium-ion-containing additive to the electrolyte, this invention can form an electrostatic shielding effect at lithium protrusions, promoting uniform lithium ion deposition, improving lithium surface morphology, reducing lithium dendrite growth, and effectively protecting lithium at the resulting solid-electrolyte interface. This inhibits direct contact between the electrolyte and the negative electrode, prevents corrosion of the lithium negative electrode by soluble polysulfides, and reduces the loss of active sulfur.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery technology, specifically relating to an electrolyte containing organic potassium salts, its preparation method, and its application. Background Technology

[0002] Exploring environmentally friendly and sustainable energy sources and high-energy storage systems has always been our goal. Lithium-sulfur batteries have attracted considerable attention due to the low cost, readily available availability, and abundant quantity of sulfur as their cathode material, while lithium metal as their anode material boasts a high theoretical specific capacity (3860 mAh g⁻¹). -1 (and low potential (-3.040V vs standard hydrogen electrode)). Over the past decade or so, tremendous efforts have been made to develop high-performance lithium-sulfur batteries; however, due to some intractable problems, lithium-sulfur batteries have not yet reached the level of practical production applications.

[0003] This includes the so-called "shuttle effect," which refers to the series of intermediate products generated by sulfur in the positive electrode during discharge. These products are highly soluble in ether solvents and shuttle back and forth between the positive and negative electrodes, causing severe corrosion of the negative electrode, irreversible loss of active materials, and capacity decay. In addition, the high reactivity of lithium metal reacts with the liquid electrolyte to form an unstable solid electrolyte interphase (SEI). The SEI layer breaks down under large volume changes, and during repeated charge-discharge cycles, it continuously breaks down and reassembles, allowing the electrolyte to come into direct contact with fresh lithium, leading to the continuous consumption of active lithium and liquid electrolyte, ultimately causing battery failure. Currently, many efforts have been made to address the problems of sulfur cathodes, including using nanostructured carbon composite materials to physically limit the dissolution of polysulfides and utilizing the strong adsorption of polysulfides by polar metal oxides and transition metal disulfides. Although polysulfides can be captured to prevent shuttle travel, these intermediate species cannot be reused. To address the problems associated with lithium metal anodes, several methods have been proposed. One approach involves using glass fiber cloth with highly polar functional groups as an interlayer between the Li metal and the separator, ensuring uniform Li ion distribution and suppressing Li dendrite growth. Another method proposes using UV curing to introduce a polymer-based protective film onto the Li metal surface and forming a thin lithium-aluminum (LiAl) alloy layer on the lithium surface to mitigate the adverse effects of shuttle phenomenon. However, these methods are impractical for real-world manufacturing due to their high cost and complex processes. Therefore, introducing additives into the electrolyte to improve lithium morphology and protect the anode, thereby enhancing the rate performance and coulombic efficiency of lithium-sulfur batteries, presents a viable alternative strategy. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an electrolyte containing organic potassium salts, its preparation method, and its application. This electrolyte enables uniform deposition of lithium ions, avoids lithium dendrite growth, improves the negative electrode morphology, and promotes the formation of a stable SEI film, thereby enhancing the rate performance, coulombic efficiency, and cycle life of lithium-sulfur batteries.

[0005] To solve the above-mentioned technical problems of the present invention, the present invention provides the following technical solution:

[0006] The first objective of this invention is to provide an electrolyte containing an organic potassium salt, wherein the electrolyte is composed of a conductive lithium salt, an ether solvent, a main additive, and a secondary additive; wherein the main additive is an organic potassium salt.

[0007] This invention modifies the electrolyte to form a stable SEI layer on the negative electrode surface, thereby reducing the direct contact and reaction between exposed lithium metal and the electrolyte. Simultaneously, the formed SEI layer typically promotes uniform lithium-ion deposition, thus largely preventing the arbitrary growth of lithium dendrites. In this invention, organic potassium salts are used as electrolyte additives for lithium-sulfur batteries. Their function is to: at specific concentrations, potassium ions possess a lower effective reduction potential, forming a potassium-ion electrostatic shielding layer on the lithium protrusion surface, forcing uniform lithium-ion deposition. This simple and easy method of improving battery electrochemical performance through additives plays a positive role in negative electrode protection, thereby enhancing the electrochemical performance of lithium-sulfur batteries.

[0008] Furthermore, the organic potassium salt is one or more of potassium fluorosulfonate, potassium citrate, and potassium oxalate.

[0009] Furthermore, the potassium fluorosulfonate is potassium perfluorobutylsulfonate. Fluorine-rich anions are reduced on the lithium surface to form more LiF, resulting in a more stable SEI film.

[0010] Furthermore, based on the total volume of the electrolyte, the molar concentration of the organic potassium salt is 0.001–0.5 mol / L.

[0011] Furthermore, based on the total volume of the electrolyte, the molar concentration of the organic potassium salt is 0.005–0.03 mol / L. When the concentration of the organic potassium salt main additive is 0.005–0.03 mol / L, the rate performance and cycle stability of the battery reach their optimal levels.

[0012] Furthermore, the secondary additive is lithium nitrate; based on the total volume of the electrolyte, the molar concentration of the secondary additive is 0.01 to 0.5 mol / L, and when the concentration of the secondary additive is 0.1 to 0.2 mol / L, it will work with the primary additive to better improve the electrochemical performance.

[0013] Furthermore, the conductive lithium salt is one or more of lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(fluorophosphate), and the total molar concentration of the conductive lithium salt is 1 to 1.5 mol / L based on the total volume of the electrolyte.

[0014] Furthermore, the ether solvent is a mixed solvent of ethylene glycol dimethyl ether and 1,3-dioxolane, with a volume ratio of 1:1.

[0015] The second objective of this invention is to provide a method for preparing an electrolyte containing organic potassium salts, wherein conductive lithium salt, main additive, secondary additive, and ether solvent are mixed and stirred at 25–28°C for 12–16 h at a stirring speed of 600–1200 r / s to form a stable and homogeneous liquid, thereby obtaining the electrolyte.

[0016] A third objective of this invention is to provide an application of an electrolyte containing organic potassium salts in the assembly of a battery, the battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte containing organic potassium salts.

[0017] The beneficial effects of this invention are:

[0018] 1. This invention provides a novel electrolyte system for lithium-sulfur batteries. Its main function is to utilize the tip effect, where potassium ions adsorb at lithium protrusions to form an electrostatic shielding layer, thereby achieving uniform lithium ion deposition and inhibiting lithium dendrite growth. Secondly, when potassium fluorosulfonate is the main additive, the SEI formed at the negative electrode by reduction contains more LiF. LiF is a good electronic insulator, effectively eliminating electrons through the interface phase, preventing continuous electrolyte decomposition and dendrite formation. Compared with other Li compounds (such as Li₂O and LixS), LiF has a higher interfacial energy to Li metal, thus accelerating Li migration at the interface and forming a uniform Li deposition morphology. The LiF film has strong fracture resistance, and the Li metal anode protected by LiF exhibits good mechanical and morphological stability during Li deposition and volume expansion. The addition of potassium fluorosulfonate can form a robust SEI layer at the negative electrode, effectively mitigating the problem of polysulfides generated at the positive electrode shuttling to the negative electrode side, leading to lithium metal corrosion and irreversible loss of active materials.

[0019] 2. The present invention provides a method for protecting lithium metal anodes, which has advantages such as low operation difficulty, environmental friendliness, and high repeatability compared with other methods, and has good application value. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a comparison chart of the rate cycling performance of a lithium-sulfur battery with potassium perfluorobutyl sulfonate electrolyte prepared in Example 1 and a lithium-sulfur battery without potassium perfluorobutyl sulfonate electrolyte prepared in Comparative Example 1.

[0022] Figure 2 The image shows a comparison of the lithium-sulfur battery with potassium perfluorobutyl sulfonate electrolyte prepared in Example 1 and the lithium-sulfur battery with electrolyte without additives in Comparative Example 1, during 0.5C cycling.

[0023] Figure 3 The image shows a comparison of the lithium-sulfur battery with potassium perfluorobutyl sulfonate electrolyte prepared in Example 1 and the lithium-sulfur battery with electrolyte without additives in Comparative Example 1, at 1C cycling.

[0024] Figure 4 The lithium-lithium symmetric battery prepared in Comparative Example 2 without potassium perfluorobutylsulfonate electrolyte was tested at 1 mA cm⁻¹. -2 / 1mAh cm -2 SEM image after 50 cycles;

[0025] Figure 5 The lithium-lithium symmetric battery with potassium perfluorobutylsulfonate electrolyte prepared in Example 2 has a 1 mA capacity. -2 / 1mAhcm -2 SEM image after 50 cycles. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention relates to an electrolyte containing an organic potassium salt as a main additive and a battery containing the electrolyte. The battery electrolyte comprises: a conductive lithium salt, an ether solvent, a main additive, and a secondary additive. The main additive is an organic potassium salt, which is one or more of potassium fluorosulfonate, potassium citrate, and potassium oxalate; the potassium fluorosulfonate is potassium perfluorobutyl sulfonate; the secondary additive is lithium nitrate; the conductive lithium salt is one or more of lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate, and the total molar concentration of the conductive lithium salt is 1–1.5 mol / L based on the total volume of the electrolyte; the ether solvent is a mixed solvent of ethylene glycol dimethyl ether and 1,3-dioxolane in a volume ratio of 1:1.

[0028] Assembly of lithium-sulfur batteries. As an example, sublimed sulfur powder, carbon nanotubes, conductive carbon black, and PVDF binder were mixed in a mass ratio of 60:15:15:10, and N-methylpyrrolidone (NMP) solvent was added. After ball milling for 4–6 hours, a homogeneous slurry was formed. The slurry was coated onto carbon-containing aluminum foil using a scraper and then placed in a vacuum oven at 110°C for 10–12 hours to obtain the positive electrode. A coin-type lithium-sulfur battery was assembled in an argon glove box using a lithium metal sheet as the negative electrode, a polypropylene membrane as the separator, and a functional additive-containing electrolyte.

[0029] As described above, the present invention does not impose any particular restrictions on the cathode material used in lithium-sulfur batteries. For example, cathode materials containing elemental sulfur, such as sulfur / carbon composite materials, sulfur / polymer composite materials, and sulfur / metal oxide composite materials, can also be cathode materials containing sulfur, such as lithium sulfide / carbon composite materials, lithium sulfide / polymer composite materials, and lithium sulfide / metal oxide composite materials.

[0030] The lithium-sulfur battery of the present invention does not have any particular restrictions on the negative electrode material. It can be one or more of lithium metal, lithium foil, lithium metal sheet, and lithium alloy, or it can be carbon material, silicon material, silicon / carbon composite material, metal oxide or conductive polymer, etc.

[0031] The lithium-sulfur battery in this invention does not have any particular restrictions on the separator; it can be a polypropylene membrane.

[0032] The lithium-sulfur battery structure of the present invention is not particularly limited and can be a button cell, a tubular cell, or a pouch cell, etc.

[0033] Assembly of a lithium-ion symmetric battery. As an example, lithium metal sheets are used for the positive and negative electrodes, a polypropylene membrane is used as the separator, a prepared electrolyte containing functional additives is used as the electrolyte, and a CR2032 battery case is used for assembly.

[0034] As described above, the present invention does not impose any particular restrictions on the positive and negative electrode materials used in lithium-lithium symmetric batteries. The positive and negative electrodes can be one or more of lithium metal, lithium foil, lithium metal sheets, and lithium alloys.

[0035] The lithium-lithium symmetric battery in this invention does not have any particular limitations on the separator; it can be a polypropylene membrane.

[0036] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0037] Example 1: Preparation of a lithium-sulfur battery with an electrolyte containing potassium perfluorobutylsulfonate

[0038] Electrolyte preparation: In an argon-filled glove box (O2, H2O < 0.1 ppm), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to a mixture of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL), where DME:DOL (V:V) = 1:1. Potassium perfluorobutylsulfonate and lithium nitrate were added, and the mixture was stirred thoroughly at 25°C for 12 h to form a stable and homogeneous liquid, which is the electrolyte. The final concentration of lithium bis(trifluoromethanesulfonyl)imide was 1.0 mol / L, potassium perfluorobutylsulfonate was 0.01 mol / L, and lithium nitrate was 0.2 mol / L.

[0039] Preparation of the positive electrode: Sublimated sulfur powder, carbon nanotubes, conductive carbon black (conductive agent), binder (PVDF), and solvent NMP were mixed to form a slurry, which was then ball-milled, coated onto aluminum foil, dried, and cut into discs with a diameter of 12 mm. The sulfur loading was 1.2 mg / cm³. 2 .

[0040] Assembly of coin cell lithium-sulfur batteries: The batteries are assembled in a glove box filled with argon (O2, H2O < 0.1ppm), in the following order: positive electrode, polypropylene membrane separator, negative electrode lithium metal sheet. Electrolyte is added to both sides of the separator. The total amount of electrolyte is 60μL. The coin cell lithium-sulfur battery is then assembled.

[0041] Rate performance testing of lithium-sulfur batteries: at different rates (0.1C, 0.2C, 0.5C, 1C, 2C, 3C, 4C, 1C = 1675mAh g) -1 Tests were conducted under the following conditions, with a voltage window of 1.7–2.8V.

[0042] Long-cycle performance testing of lithium-sulfur batteries: Charge-discharge tests were conducted at 0.5C and 1C to compare capacity retention and coulombic efficiency with and without main additives.

[0043] Example 2: Preparation of a lithium-lithium symmetric battery with an electrolyte containing potassium perfluorobutylsulfonate

[0044] The electrolyte was prepared in the same manner as in Example 1.

[0045] Lithium-lithium symmetric battery assembly: The battery is assembled in a glove box filled with argon atmosphere. Both the positive and negative electrodes use metallic lithium sheets. Electrolyte needs to be added to both sides of the polypropylene membrane separator. The total amount of electrolyte is 80μL. CR2032 battery case is used for assembly.

[0046] At a current density of 1 mA cm -2 / 1mAh cm -2 Electrochemical performance was tested under the specified conditions.

[0047] Example 3: Preparation of a lithium-sulfur battery containing potassium perfluorobutylsulfonate electrolyte

[0048] Electrolyte preparation: In an argon-filled glove box (O2, H2O < 0.1 ppm), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to a mixture of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL), where DME:DOL (V:V) = 1:1. Potassium perfluorobutylsulfonate and lithium nitrate were added, and the mixture was stirred thoroughly at 25°C for 14 h to form a stable and homogeneous liquid, which is the electrolyte. The final concentration of lithium bis(trifluoromethanesulfonyl)imide was 1.0 mol / L, potassium perfluorobutylsulfonate was 0.02 mol / L, and lithium nitrate was 0.2 mol / L.

[0049] The preparation of the cathode material and the assembly of the battery are the same as in Example 1.

[0050] Example 4: Preparation of a lithium-sulfur battery with an electrolyte containing potassium perfluorobutylsulfonate

[0051] Electrolyte preparation: In an argon-filled glove box (O2, H2O < 0.1 ppm), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to a mixture of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL), where DME:DOL (V:V) = 1:1. Potassium perfluorobutylsulfonate and lithium nitrate were added, and the mixture was stirred thoroughly at 25°C for 16 h to form a stable and homogeneous liquid, which is the electrolyte. The final concentration of lithium bis(trifluoromethanesulfonyl)imide was 1.0 mol / L, potassium perfluorobutylsulfonate was 0.005 mol / L, and lithium nitrate was 0.2 mol / L.

[0052] The preparation of the cathode material and the assembly of the battery are the same as in Example 1.

[0053] Comparative Example 1

[0054] Electrolyte preparation: In an argon-filled glove box (O2, H2O < 0.1 ppm), lithium bis(trifluoromethanesulfonylimide) (LiTFSI) was added to a mixture of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL), where DME:DOL (V:V) = 1:1. Lithium nitrate was added, and the mixture was stirred thoroughly at 25°C for 12 h to form a stable and homogeneous liquid, which is the basic electrolyte. The final concentration of lithium bis(trifluoromethanesulfonylimide) was 1.0 mol / L, and the concentration of lithium nitrate was 0.2 mol / L.

[0055] The preparation of the cathode material and the assembly of the battery are the same as in Example 1.

[0056] Rate performance testing of lithium-sulfur batteries: at different rates (0.1C, 0.2C, 0.5C, 1C, 2C, 3C, 4C, 1C = 1675mAh g) -1 Tests were conducted under the following conditions, with a voltage window of 1.7–2.8V.

[0057] Long-cycle performance testing of lithium-sulfur batteries: Charge-discharge tests were conducted at 0.5C and 1C respectively to compare capacity retention and coulombic efficiency with and without additives.

[0058] Comparative Example 2

[0059] The electrolyte was prepared in the same manner as in Comparative Example 1.

[0060] Lithium-lithium symmetric battery assembly: The battery is assembled in a glove box filled with argon atmosphere. Both the positive and negative electrodes use lithium metal sheets. Electrolyte is added to both sides of the separator. The total amount of electrolyte is 80μL. CR2032 battery case is used for assembly.

[0061] At a current density of 1 mA cm -2 / 1mAh cm -2 Electrochemical performance was tested under the specified conditions.

[0062] The preparation of the cathode material and the assembly of the battery are the same as in Example 1.

[0063] Figure 1 This is a rate cycling comparison chart of the lithium-sulfur battery with potassium perfluorobutylsulfonate electrolyte prepared in Example 1 and the lithium-sulfur battery without potassium perfluorobutylsulfonate electrolyte prepared in Comparative Example 1. Figure 1 It can be seen that the battery containing potassium perfluorobutylsulfonate electrolyte exhibits more stable rate performance and achieves a higher discharge specific capacity, with an overall capacity approximately 200 mAh / g higher than the comparative sample. -1 .

[0064] Figure 2The image shows a comparison of the lithium-sulfur battery with potassium perfluorobutyl sulfonate electrolyte prepared in Example 1 and the lithium-sulfur battery with electrolyte without additives in Comparative Example 1, during 0.5C cycling. Figure 3 This is a comparison chart of the lithium-sulfur battery using the potassium perfluorobutyl sulfonate electrolyte prepared in Example 1 and the lithium-sulfur battery using the additive-free electrolyte in Comparative Example 1, at 1C cycling. Figure 2 , Figure 3 It can be seen that, compared to electrolytes that do not contain potassium perfluorobutylsulfonate, at a low rate of 0.5C, Figure 2 After 180 cycles, the discharge specific capacity remained unchanged (612mAh g). -1 The coulomb efficiency (~98%) is also higher, similarly at 1C high rate ( Figure 3 After 300 cycles, the electrolyte containing potassium perfluorobutylsulfonate maintained a higher discharge specific capacity (516 mAh g). -1 ) and Coulomb efficiency (~98%).

[0065] Figure 4 The lithium-lithium symmetric battery prepared in Comparative Example 2 without potassium perfluorobutylsulfonate electrolyte was tested at 1 mA cm⁻¹. -2 / 1mAh cm -2 SEM image after 50 cycles; Figure 5 The lithium-lithium symmetric battery with potassium perfluorobutylsulfonate electrolyte prepared in Example 2 has a 1 mA capacity. -2 / 1mAh cm -2 SEM image after 50 cycles. Figure 4 , Figure 5 It can be seen that, with the presence of potassium perfluorobutylsulfonate, the lithium metal anode SEI exhibits a uniform, flat, and dense surface morphology, while the lithium surface without potassium perfluorobutylsulfonate shows a large number of blocky dendrites and obvious pores. This indicates that the electrolyte containing potassium perfluorobutylsulfonate has the functions of uniform lithium deposition, inhibiting dendrite growth, and protecting the lithium anode.

[0066] The preferred embodiments of this patent have been described in detail above. However, this patent is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, other variations or modifications can be made. It is neither necessary nor possible to exhaustively list all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the protection scope of the claims of this invention.

Claims

1. A lithium-sulfur battery electrolyte containing an organic potassium salt, characterized in that, The electrolyte is composed of conductive lithium salt, ether solvent, main additive, and secondary additive; the main additive is an organic potassium salt. The organic potassium salt is potassium perfluorobutyl sulfonate; The secondary additive is lithium nitrate; based on the total volume of the electrolyte, the molar concentration of the secondary additive is 0.01–0.2 mol / L; The conductive lithium salt is lithium bis(trifluoromethanesulfonyl)imide, and the total molar concentration of the conductive lithium salt is 1–1.5 mol / L based on the total volume of the electrolyte. The ether solvent is a mixture of ethylene glycol dimethyl ether and 1,3-dioxolane in a volume ratio of 1:

1. Based on the total volume of the electrolyte, the molar concentration of the organic potassium salt is 0.005–0.03 mol / L.

2. The method for preparing the organic potassium salt-containing lithium-sulfur battery electrolyte according to claim 1, characterized by, The conductive lithium salt, main additive, secondary additive, and ether solvent are mixed and stirred at 25–28°C for 12–16 hours at a stirring speed of 600–1200 r / s to form a stable and homogeneous liquid, thus obtaining the electrolyte.

3. Use of the lithium-sulfur battery electrolyte containing organic potassium salt according to claim 1 in assembling lithium-sulfur battery cells, characterized by, The lithium-sulfur battery includes a positive electrode, a negative electrode, a separator, and an electrolyte containing organic potassium salts.

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