Lithium-sulfur battery electrolyte containing functional additive and lithium-sulfur battery thereof

Abstract

The application discloses a lithium-sulfur battery electrolyte containing a functional additive and a lithium-sulfur battery. The electrolyte contains a lithium salt, a solvent and an additive. The additive is one or more of the sulfur-containing compounds shown in formula (I). In formula (I), R1 and R2 are selected from H, C1-C15 alkyl and amino; and R3 is selected from cyano, fluoroalkyl, thioamide and thiol. The lithium-sulfur battery electrolyte has a simple formula. The addition of the additive in the electrolyte helps to form stable intermolecular chemical bonds with short-chain lithium polysulfides (Li2S and Li2S2), so as to realize the dissolution of more short-chain lithium polysulfides, reduce the reduction reaction barrier of the lithium-sulfur battery in the discharging process through liquid-phase reaction, reduce the shuttling of lithium polysulfides, and significantly improve the cycle stability of the lithium-sulfur battery.

Description

Technical Field

[0001] This invention relates to the field of lithium metal energy storage batteries, specifically to an electrolyte formulation that can suppress lithium polysulfide shuttle and enhance redox reaction kinetics and its lithium-sulfur battery. Background Technology

[0002] Over the past few decades, lithium-ion batteries (LIBs) have achieved tremendous success due to their portability, relatively high energy density, and long lifespan. However, LIBs based on intercalation reactions have approached the limit of theoretical energy density and cannot meet the demands of the ever-evolving electric vehicles, smart grids, and other fields. Therefore, developing a new generation of electrochemical energy storage systems with high specific capacity, high energy density, long cycle life, and low cost is a common goal pursued by researchers and industry. Among these numerous electrochemical energy storage systems, lithium-sulfur batteries are considered a highly promising next-generation lithium-ion rechargeable battery system. Lithium-sulfur batteries not only possess a high theoretical specific capacity of 1675 mAh / g and an energy density of 2600 Wh / kg, but sulfur is also environmentally friendly, abundant in the Earth's surface, and very inexpensive, making lithium-sulfur batteries an attractive and low-cost energy storage technology.

[0003] However, lithium-sulfur batteries suffer from problems such as rapid capacity decay, low conductivity of the sulfur cathode, "shuttle effect" of polysulfides as intermediate products of electrochemical reactions, lithium-ion deposition, and structural changes caused by sulfur volume changes during charging and discharging. These problems reduce the utilization rate of active materials and the cycle life of the battery, making it difficult to put lithium-sulfur batteries into large-scale commercial production.

[0004] To address issues such as the shuttle effect and lithium dendrite formation in lithium-sulfur batteries, researchers have undertaken extensive work. Improvement strategies mainly focus on several aspects, including enhancing the conductivity and stability of sulfur-based cathode materials, suppressing the loss of active sulfur components, preventing the dissolution of polysulfides in the electrolyte, and preventing the growth of lithium dendrites in the anode. These efforts include structural design of electrode materials, synthesis of many novel sulfur-containing cathode materials, separator materials, and electrolytes, as well as protection of the lithium anode.

[0005] Electrolyte regulation is the most convenient and simplest method. Electrolyte additives, due to their functional groups, can provide components for functional additives and suppress the shuttle effect of lithium polysulfides. Introducing organic functional groups is a feasible approach for the direct chemical modification of lithium polysulfides dissolved in the electrolyte. They provide tunable groups that can participate deeply in the electrochemical conversion of sulfur and its performance regulation.

[0006] CN202010751244.9 discloses a lithium-sulfur battery anode protection electrolyte, comprising a lithium salt, a mercapto-containing anode protection additive, and a solvent. This functional additive can generate a stable solid-state electrolyte interface in situ on the lithium anode surface, thereby inhibiting the reaction between lithium metal and lithium polysulfides, thus improving the cycle stability of the lithium-sulfur battery to some extent. However, this additive only provides a "passive" protection effect from the lithium anode direction, without "actively" addressing the problem from the perspective of the lithium-sulfur battery's reaction mechanism. Summary of the Invention

[0007] To address the problems of lithium-sulfur batteries, such as the loss of active materials and unsatisfactory electrochemical and cycling performance due to lithium polysulfide shuttle, this invention provides a lithium-sulfur battery electrolyte that mitigates the shuttle effect and enhances the cycling stability of lithium-sulfur batteries.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A lithium-sulfur battery electrolyte, wherein the electrolyte contains lithium salt, solvent and additives; wherein the additives are one or more sulfur-containing compounds having the formula (I);

[0010] (one);

[0012] R1 and R2 are selected from H, C1~C15 alkyl or amino groups; R3 is selected from cyano, fluoroalkyl, thioamide or thiol groups.

[0013] Furthermore, the additive accounts for 0.1-10% of the mass percentage of the lithium-sulfur battery electrolyte, preferably 3-5%.

[0014] Furthermore, the lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium nitrate, lithium difluorooxalateborate, lithium hexafluorophosphate, and lithium bis(oxalateborate).

[0015] Furthermore, the molar concentration of the lithium salt in the lithium-sulfur battery electrolyte is 0.1–7 mol / L, preferably 2–3 mol / L.

[0016] Furthermore, the solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,3-dioxolane, dimethyl sulfoxide, sulfolane, dimethylacetamide, and 1,3-dimethyl-2-imidazolinone.

[0017] This invention also provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, and the lithium-sulfur battery electrolyte described above. The electrolyte can improve the cycle stability of the lithium-sulfur battery. With a sulfur loading of 1 mg / cm³...2 The electrode was used as the positive electrode, the electrolyte was added at a rate of 40 μL, the charge-discharge rate was 0.5C, and a full-cell constant current charge-discharge test was conducted. The capacity reached 1268.8 mAh / g in the first cycle and the capacity retention rate reached 74.0% after 50 cycles.

[0018] The beneficial effects of this invention are as follows: The lithium-sulfur battery electrolyte formulation is simple. Adding such additives to the electrolyte helps form stable intermolecular chemical bonds with short-chain lithium polysulfides (Li₂S, Li₂S₂), thereby achieving the dissolution of more slightly soluble short-chain lithium polysulfides. This reduces the reduction reaction barrier during discharge through liquid-phase reaction, decreasing the shuttle effect of lithium polysulfides. Simultaneously, these additives can enhance the dissolution of non-conductive sulfides deposited on the positive electrode surface during charging and discharging, reducing the passivation of sulfur-carbon positive electrode materials during charging and discharging, exposing more conductive matrix to enhance redox reaction kinetics, and increasing the utilization rate of sulfur active materials. Furthermore, sulfur-containing additives can contribute to the overall capacity. Attached Figure Description

[0019] Figure 1 The cycling performance of Examples 1-6 and Comparative Example 1 is compared.

[0020] Figure 2 This is a comparison of the voltage platforms of Example 1 and Comparative Example 1. Detailed Implementation

[0021] The following is a detailed description of the preferred embodiments of the present invention, which does not constitute any limitation on the present invention. That is, the present invention is not limited to the above embodiments, and all common variations or alternative compounds in the art are included within the scope defined by the claims of this application.

[0022] In this embodiment of the invention, a 2025 type button cell was used for evaluation. The full cell test conditions are as follows: a sulfur-carbon composite electrode with a diameter of 12 mm was used as the positive electrode, and a lithium foil with a diameter of 15.6 mm and a thickness of 45 μm was used as the negative electrode; the electrochemical test charge-discharge rate was 0.5C.

[0023] Example 1

[0024] A lithium-sulfur battery electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate as lithium salts, ethylene glycol dimethyl ether as solvent, and 2,2,2-trimethylthioacetamide as additive. The preparation method is as follows: lithium salts (lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate in a molar ratio of 19:1) are added to ethylene glycol dimethyl ether to achieve a concentration of 2 mol / L. Then, additives are added to achieve a mass percentage of 3%.

[0025] With a sulfur loading of 1 mg / cm 2The electrode was used as the positive electrode, the electrolyte was added at a rate of 40 μL, and the charge / discharge rate was 0.5C. The full-cell constant current charge / discharge test was conducted.

[0026] Comparative Example 1

[0027] The difference between Example 1 and Comparative Example 1 is that no additives were added to the electrolyte. The test conditions for Example 1 and Comparative Example 1 were the same.

[0028] Test results show that electrolytes containing additives can achieve higher specific capacity and stronger cycle stability in lithium-sulfur batteries. Figure 1 Using the electrolyte of this invention, the lithium-sulfur battery achieved a specific capacity of approximately 1270 mAh / g in the first cycle, while the battery in Comparative Example 1 only achieved 1134 mAh / g. After 50 cycles, the capacity retention of the battery in Example 1 was 74.0%, while that of the battery in Comparative Example 1 was only 57.9%. Figure 1 As shown in Table 1, the capacity of Comparative Example 1 battery decreased extremely rapidly in the first five discharge cycles. This was due to the uneven distribution of non-conductive oxidized products at the positive electrode, leading to passivation of the positive electrode material. In contrast, Example 1 maintained its capacity well due to the presence of additives. Figure 2 The graph shows a comparison of the voltage-capacity plateaus of the button cells in Comparative Example 1 and Example 1 after activation by the first three cycles of low-current charge-discharge. It is clearly visible in the graph that compared to the 0.297V voltage hysteresis of the Comparative Example, the voltage hysteresis of the Example is only 0.266V, indicating a significant reduction in voltage hysteresis. This comparison also reveals that the Example's battery exhibits significantly less polarization, and its capacity performance is more stable.

[0029] Example 2

[0030] A lithium-sulfur battery electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate as lithium salts, ethylene glycol dimethyl ether and 1,3-dioxolane as solvents, and 2,2,2-trifluorothioacetamide as an additive. The preparation method is as follows: ethylene glycol dimethyl ether and 1,3-dioxolane are mixed at a volume ratio of 1:1, then the lithium salt (the molar ratio of lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate is 9:1) is added to achieve a concentration of 1 mol / L. Finally, the additive is added to achieve a mass percentage of 5%.

[0031] With a sulfur loading of 1 mg / cm 2 The electrode was used as the positive electrode, the electrolyte was added at a rate of 40 μL, and the charge / discharge rate was 0.5C. A full-cell constant current charge / discharge test was conducted. Figure 1 As shown in Table 1, the lithium-sulfur battery of Example 2 had a first-cycle capacity of 1258.0 mAh / g and a capacity retention rate of 67.1% after 50 cycles.

[0032] Example 3

[0033] A lithium-sulfur battery electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate as lithium salts, 1,3-dimethyl-2-imidazolinone as solvent, and N,N-dimethylthioacetamide as additive. The preparation method is as follows: the lithium salt (lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate in a molar ratio of 6:4) is added to the 1,3-dimethyl-2-imidazolinone solvent to achieve a concentration of 2 mol / L. Finally, the additive is added to achieve a mass percentage of 3%.

[0034] With a sulfur loading of 1 mg / cm 2 The electrode was used as the positive electrode, the electrolyte was added at a rate of 40 μL, and the charge / discharge rate was 0.5C. A full-cell constant current charge / discharge test was conducted. Figure 1 As shown in Table 1, the lithium-sulfur battery of Example 3 had a first-cycle capacity of 1266.8 mAh / g and a capacity retention rate of 72.1% after 50 cycles.

[0035] Example 4

[0036] A lithium-sulfur battery electrolyte comprises lithium difluorooxalate borate and lithium nitrate as lithium salts, dimethyl sulfoxide as solvent, and aminothiourea as additive. The preparation method is as follows: lithium salts (lithium difluorooxalate borate and lithium nitrate in a molar ratio of 9:1) are added to the solvent dimethyl sulfoxide to achieve a concentration of 6 mol / L. Finally, the additive is added to achieve a mass percentage of 10%.

[0037] With a sulfur loading of 1 mg / cm 2 The electrode was used as the positive electrode, the electrolyte was added at a rate of 40 μL, and a full-cell constant current charge-discharge test was conducted at a charge-discharge rate of 0.5C. The test revealed that, as... Figure 1 As shown in Table 1, the lithium-sulfur battery of Example 4 had a first-cycle capacity of 1225.4 mAh / g and a capacity retention rate of 71.7% after 50 cycles.

[0038] Example 5

[0039] A lithium-sulfur battery electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate as lithium salts, ethylene glycol dimethyl ether and 1,3-dioxolane as solvents, and 2-cyanothioacetamide as an additive. The preparation method is as follows: ethylene glycol dimethyl ether and 1,3-dioxolane are mixed at a volume ratio of 1:1, then the lithium salt (lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate in a molar ratio of 9:1) is added to achieve a concentration of 3 mol / L. Finally, the additive is added to achieve a mass percentage of 3%.

[0040] With a sulfur loading of 1 mg / cm 2 The electrode was used as the positive electrode, the electrolyte was added at a rate of 40 μL, and the charge / discharge rate was 0.5C. A full-cell constant current charge / discharge test was conducted. Figure 1As shown in Table 1, the lithium-sulfur battery of Example 5 had a first-cycle capacity of 1234.1 mAh / g and a capacity retention rate of 69.7% after 50 cycles.

[0041] Example 6

[0042] A lithium-sulfur battery electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate as lithium salts, ethylene glycol dimethyl ether and 1,3-dimethyl-2-imidazolinone as solvents, and ammonium thiocarboxylic acid as an additive. The preparation method is as follows: ethylene glycol dimethyl ether and 1,3-dimethyl-2-imidazolinone are mixed at a volume ratio of 1:1, then the lithium salt (the molar ratio of lithium bis(trifluoromethanesulfonyl)imide to lithium nitrate is 19:1) is added to achieve a concentration of 2 mol / L. Finally, the additive is added to achieve a mass percentage of 5%.

[0043] With a sulfur loading of 1 mg / cm 2 The electrode was used as the positive electrode, the electrolyte was added at a rate of 40 μL, and the charge / discharge rate was 0.5C. A full-cell constant current charge / discharge test was conducted. Figure 1 As shown in Table 1, the lithium-sulfur battery of Example 6 had a first-cycle capacity of 1257.5 mAh / g and a capacity retention rate of 70.4% after 50 cycles.

[0044] Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 First-run capacity (mAh / g) 1134.1 1268.8 1258.0 1266.8 1225.4 1234.1 1257.5 50-cycle capacity retention rate (%) 57.9 74.0 67.1 72.1 71.7 69.7 70.4

[0045] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A lithium-sulfur battery, comprising a positive electrode, a negative electrode, and a lithium-sulfur battery electrolyte; the lithium-sulfur battery electrolyte comprising a lithium salt, a solvent, and an additive, wherein the lithium salt is lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate, the solvent is ethylene glycol dimethyl ether, and the additive is 2,2,2-trimethylthioacetamide; the lithium-sulfur battery electrolyte is prepared by adding lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate to ethylene glycol dimethyl ether at a molar ratio of 19:1 to achieve a concentration of 2 mol / L, and then adding the additive to achieve a mass percentage of 3%; The lithium-sulfur battery electrolyte described above can improve the cycle stability of lithium-sulfur batteries, with a sulfur loading of 1 mg / cm³. 2 The electrode was used as the positive electrode, the electrolyte was added at a rate of 40 μL, the charge-discharge rate was 0.5C, and a full-cell constant current charge-discharge test was conducted. The capacity reached 1268.8 mAh / g in the first cycle and the capacity retention rate reached 74.0% after 50 cycles.

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