An inducible S3 ·- Radical-generating lithium-sulfur battery electrolyte, method of making and lithium-sulfur battery

Abstract

The present application relates to a kind of inducible S3 ·‑ Radical generation lithium-sulfur battery electrolyte and its preparation method and lithium-sulfur battery, by introducing an electrolyte additive-tetra-n-octylammonium chloride ((C8H 17 )4NCl) into electrolyte, promote S3 ·‑ Radical generation and stability, the lithium-sulfur battery electrolyte includes lithium salt, ether base solvent and additive;The additive is tetra-n-octylammonium chloride, the concentration of tetra-n-octylammonium chloride is 20-200mmol / L, this electrolyte can be used to assemble lithium-sulfur battery.Compared with prior art, the present application introduces tetra-n-octylammonium chloride to prepare lithium-sulfur battery electrolyte, changes the solvation structure of electrolyte, enhances the conversion kinetics of sulfur, promotes S3 ·‑ Radical formation and promote its stability, to promote its uniform growth in the process of lithium-sulfur battery charge and discharge solid electrolyte interface, improves ion transmission efficiency, in addition, the electrolyte synthesis path is simple, reduces the cost of battery manufacturing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery electrolyte additives, and relates to an electrolyte, a preparation method thereof and a battery, in particular to an electrolyte capable of inducing S3 ·- Lithium-sulfur battery electrolyte generated by free radicals, preparation method thereof and lithium-sulfur battery. BACKGROUND

[0002] Sulfur is abundant in the earth's crust and easy to exploit, so it has a relatively low price, and is environmentally friendly. In addition, elemental sulfur can be converted into the final discharge product Li2S, and has a high theoretical specific capacity, so it is a hot spot in the research of current battery cathode materials.

[0003] Lithium batteries with sulfur cathodes are a high-energy-density energy storage system, and their working principle is based on the chemical reaction between sulfur and lithium. The conversion process of the sulfur cathode directly affects the performance and efficiency of the battery. During discharge, S8 is first reduced to long-chain polysulfides (such as Li2S8), and then converted to short-chain polysulfides through a series of complex reaction steps, and finally generates solid lithium sulfide (Li2S). The intermediates in the sulfur conversion process have a direct impact on the discharge capacity, rate performance and cycle stability of the battery.

[0004] The specific process of S8 conversion can be represented by the following chemical reaction equations:

[0005]

[0006] During discharge, S8 is first reduced to S8 2- , and then converted to S6 2- ions. Next, S6 2- ions are further converted to two S3 ·- radical anions or 3 / 2 S4 2- ions. Then, S3 ·- radical anions accept an electron to be reduced to S3 2- , and finally S3 2- reacts with two lithium ions to generate Li2S.

[0007] In the above process, S3 ·- radicals are a key intermediate, and their formation and stability have a major impact on battery performance. Their stability is affected by factors such as solvation effect and discharge rate. If side reactions occur in the above reaction process and produce S4 2- ions, it may lead to a decrease in the utilization rate of active materials, and the formation of a stable solid-state electrolyte interface is affected, which affects ion transmission efficiency and causes dendrite growth, causing safety hazards. These problems seriously hinder the commercialization process of such batteries.

[0008] To solve the above problems, researchers have explored various strategies to improve S3 ·- radical stability. These strategies include designing new sulfur host materials, developing functional separators, or using electrolyte additives. Although these methods inhibit the generation of side reactions to some extent and improve the utilization of active materials, they are often complex in synthesis path, increasing the cost of battery manufacturing. SUMMARY

[0009] The purpose of the present application is to provide a kind of electrolyte that can induce S3 ·- Radical Generation and Its Preparation Method and Battery, Specifically by introducing an electrolyte additive into the battery electrolyte, i.e. tetra-n-octylammonium chloride ((C8H 17 )4NCl), to promote the generation and stability of S3 ·- Radical, thereby promoting the uniform growth of the solid electrolyte interface (SEI) during the charging and discharging process of the battery, improving ion transport efficiency, and improving the discharge capacity, cycle stability and charging rate of lithium-sulfur batteries, and also inhibiting dendrite growth and reducing safety hazards.

[0010] The purpose of the present application can be achieved by the following technical solutions:

[0011] The present application provides a kind of electrolyte that can induce S3 ·- Radical Generation, comprising lithium salt, ether-based solvent and additive; the additive is tetra-n-octylammonium chloride, the concentration of tetra-n-octylammonium chloride is 20-200 mmol / L, wherein the selected tetra-n-octylammonium chloride has the ability to generate and stabilize S3 ·- Radical.

[0012] Further, the lithium salt is a mixture of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate (LiNO3), the concentration of lithium bis(trifluoromethanesulfonyl)imide is 300-1500 mmol / L, and the amount of lithium nitrate used is 2-5 wt% of the mass of lithium bis(trifluoromethanesulfonyl)imide.

[0013] Further, the ether-based solvent is ethylene glycol dimethyl ether (DME).

[0014] Further, the ether-based solvent also includes 1,3-dioxane (1,3-DOX) or 1,4-dioxane (1,4-DOX).

[0015] Further, in the ether-based solvent, the volume ratio of ethylene glycol dimethyl ether and 1,3-dioxane is (1-5):1.

[0016] Further, in the ether-based solvent, the volume ratio of ethylene glycol dimethyl ether and 1,4-dioxane is (1-5):1.

[0017] The second aspect of the present application provides an electrolyte capable of inducing S3 ·- The preparation method of the electrolyte capable of generating free radicals comprises the following steps:

[0018] S1: a certain amount of lithium salt is weighed and added into the pre-mixed ether-based solvent to obtain a basic electrolyte;

[0019] S2: a proper amount of additive is added to the basic electrolyte in step S1 and then left to stand, so that the additive maintains a certain concentration in the electrolyte, thereby obtaining an electrolyte capable of inducing S3 ·- The electrolyte capable of generating free radicals can promote the generation and stability of S3 ·- free radicals, accelerate the reaction kinetics, and promote the growth of Li2S, thereby directly affecting the sulfur utilization rate and cycle stability of the lithium-sulfur battery.

[0020] Further, in step S1, the gas atmosphere is an inert gas.

[0021] Further, the inert gas is argon.

[0022] Further, in step S2, during the standing, the standing atmosphere is an argon atmosphere, the standing temperature is room temperature, and the standing time is 1-12 h, so as to ensure that the components in the electrolyte are fully miscible and form a uniform and stable electrolyte.

[0023] The third aspect of the present application provides a lithium-sulfur battery, which comprises a positive electrode, a separator, a negative electrode, and the above-mentioned electrolyte capable of inducing S3 ·- free radicals.

[0024] Further, the positive electrode is a sulfur-containing positive electrode sheet, the separator is a commercial separator known in the art, and the negative electrode is a lithium metal sheet. Preferably, the separator is Celgard-2500.

[0025] Further, the preparation process of the sulfur-containing positive electrode sheet is as follows:

[0026] S1: sulfur and carbon material are mixed and then heat-treated to obtain a mixture;

[0027] S2: the mixture in step S1 and a binder polyvinylidene fluoride (PVDF) are dispersed in N,N-dimethylformamide (DMF) to form a slurry;

[0028] S3: the slurry in step S2 is coated on an aluminum foil, and then heat-treated to obtain a sulfur-containing positive electrode sheet.

[0029] Further, in step S1, the mass ratio of the sulfur and the carbon material is 5:1.

[0030] Further, in step S1, the carbon material is selected from any one of acetylene black, ketjen black or carbon nanotube.

[0031] Further, in step S1, in the heat treatment, the heat treatment temperature is 155℃, and the heat treatment time is 12h.

[0032] Further, in step S2, the mass ratio of the mixture to PVDF is 9:1. Further, in step S2, in the coating, the areal density of elemental sulfur is 2mg / cm 2 .

[0033] Further, in step S2, in the heat treatment, the heat treatment temperature is 60℃, and the heat treatment time is 12h.

[0034] Further, the assembling process of the lithium-sulfur battery comprises: assembling the positive electrode, the separator and the negative electrode in an argon-filled glove box to assemble the battery, and injecting the electrolyte into a battery shell to ensure that the electrolyte is in full contact with the positive electrode and the negative electrode.

[0035] Further, the amount of the electrolyte is 40-80μL / mgS. Preferably, the amount of the electrolyte is 80μL / mgS.

[0036] Compared with the prior art, the present application has the following characteristics:

[0037] 1) The present application proposes a lithium-sulfur battery electrolyte with (C8H 17 )4NCl as an additive, changes the solvation structure of the electrolyte, thereby enhancing the conversion kinetics of sulfur, promoting the formation of S3 ·- radicals and improving their stability;

[0038] 2) The present application proposes a lithium-sulfur battery electrolyte with (C8H 17 )4NCl as an additive, which can promote the generation and stability of S3 ·- radicals, thereby promoting the uniform growth of the solid-state electrolyte interface in the charging and discharging process of the lithium-sulfur battery, improving the ion transmission efficiency, improving the discharge capacity, cycle stability and charging rate of the lithium battery based on the sulfur positive electrode, and also inhibiting the growth of lithium dendrites and reducing the safety hazard;

[0039] 3) The present application proposes a lithium-sulfur battery electrolyte with (C8H 17 )4NCl as an additive, which has a simple synthesis path and reduces the manufacturing cost of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 (C8H17 )4NCl electrolyte;

[0041] Figure 2 The UV-Vis absorption spectrum of the electrolyte prepared in Comparative Example 1 without (C8H 17 )4NCl electrolyte;

[0042] Figure 3 The cycle stability test chart of the button lithium-sulfur battery assembled with the electrolyte prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0043] The present application will be described in detail below with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical solution of the present application, and gives a detailed implementation and specific operation process, but the protection scope of the present application is not limited to the following examples.

[0044] In the following examples, unless otherwise specified, the raw reagents or processing techniques are all conventional commercially available products or conventional processing techniques in the art.

[0045] The preparation process of the sulfur positive electrode sheet in the example is as follows: 200 mg of sulfur and 40 mg of Ketjen black are weighed and mixed, and then heated in an oven at 155°C for 12 h. The mixed powder of sulfur and Ketjen black is dispersed in DMF with a mass ratio of 9:1 of sulfur to PVDF, and stirred thoroughly for 6 h to form a uniform slurry. Then, the slurry is uniformly coated on an aluminum foil, and dried in an oven at 60° for 12 h to obtain a sulfur positive electrode sheet. 2

[0046] Example 1:

[0047] A lithium-sulfur battery electrolyte containing an inducible S3 ·- radical generating additive ((C8H 17 )4NCl), and a preparation method thereof, comprises:

[0048] In an argon-filled glove box, LiTFSI is weighed according to a final concentration of 1000 mmol / L, and LiNO3 is weighed according to a mass amount of 3wt% relative to the mass of LiTFSI, and then dissolved in the pre-mixed ether-based solvent of DME and 1,3-DOX with a volume ratio of 2:1. Then, (C8H 17 )4NCl with a final concentration of 120 mmol / L is slowly added to the above solution, and completely dissolved under stirring, and then left to stand for 6 h under argon condition and room temperature, to ensure that the components in the electrolyte are fully miscible and form a stable electrolyte. After standing, sample is taken for UV-Vis absorption spectrum test, and S3 ·- ​The radical is located at the absorption peak of 632 nm.

[0049] The lithium-sulfur battery electrolyte containing (C8H 17 )4NCl prepared in this example was used to assemble button lithium-sulfur batteries and perform electrochemical performance tests, which were carried out according to the following method:

[0050] At room temperature, in an argon-filled glove box, button lithium-sulfur batteries were assembled using a sulfur-containing positive electrode sheet, a lithium negative electrode, and a separator (Celgard-2500). 40 μL of the electrolyte prepared in this example was added to the positive electrode sheet, and after covering the separator, 40 μL of electrolyte was added to the center of the separator, and then the lithium negative electrode was covered. After the battery was assembled, it was left to stand at room temperature for at least 12 h to allow the electrolyte to fully soak the battery components. Subsequently, a blue charge-discharge instrument was used to perform charge-discharge cycle tests at room temperature at a rate of 0.5C (1C = 1675 mA g -1 ) with a voltage range of 1.7 V to 2.8 V. The specific capacity at 50 cycles and the coulombic efficiency were tested and calculated.

[0051] Comparative Example 1:

[0052] A lithium-sulfur battery electrolyte not containing (C8H 17 )4NCl, the preparation method thereof comprising:

[0053] In an argon-filled glove box, LiTFSI was weighed according to a final concentration of 1000 mmol / L, and LiNO3 was weighed according to a mass amount of 3 wt% relative to the amount of LiTFSI. The two were dissolved together in the previously mixed ether-based solvent of DME and 1,3-DOX in a volume ratio of 2:1. Under argon conditions and at room temperature, the mixture was left to stand for 6 h to ensure that the components in the electrolyte were fully miscible and formed a stable electrolyte. After standing, a sample was taken for ultraviolet-visible light absorption spectrum testing to observe the S3 ·- The radical is located at the absorption peak of 632 nm.

[0054] The lithium-sulfur battery electrolyte not containing (C8H 17 )4NCl prepared in this comparative example was used to assemble button lithium-sulfur batteries and perform electrochemical performance tests, and the assembly method and test method were the same as in Example 1.

[0055] The test results of Example 1 and Comparative Example 1 are as follows:

[0056] Figure 1 and Figure 2 are the ultraviolet-visible light absorption spectra of the electrolyte containing (C8H 17 )4NCl prepared in Example 1 and the electrolyte not containing (C8H 17UV-Vis absorption spectrum of electrolyte of (C8H ·- Radicals. From the figure, it can be seen that the electrolyte containing (C8H 17 )4NCl has a higher intensity of absorption peak, and the intensity of other intermediates (S6 2- , S4 2- ) is lower. Therefore, the presence of (C8H 17 )4NCl improves the stability of S3 ·- radicals. Figure 3 The cycle stability test chart of the button lithium-sulfur battery assembled by the electrolyte prepared in Example 1 and Comparative Example 1 can be seen, and the button battery assembled by the electrolyte containing (C8H 17 )4NCl exhibits higher specific capacity and better coulombic efficiency after 50 cycles.

[0057] Example 2:

[0058] A lithium-sulfur battery electrolyte containing (C8H 17 )4NCl which can induce the generation of S3 ·- radicals, the preparation method comprising:

[0059] In an argon-filled glove box, LiTFSI was weighed according to a final concentration of 1500 mmol / L, LiNO3 was weighed according to 5wt% of the mass amount of LiTFSI, and was dissolved in the pre-mixed ether-based solvent of DME and 1,4-DOX with a volume ratio of 2:1. Then, (C8H 17 )4NCl with a final concentration of 100 mmol / L was slowly added to the above solution, and was completely dissolved under stirring. The electrolyte was placed in an argon condition and at room temperature for 4h to ensure that the components in the electrolyte were fully miscible and formed a stable electrolyte.

[0060] Example 3:

[0061] A lithium-sulfur battery electrolyte containing (C8H 17 )4NCl which can induce the generation of S3 ·- radicals, the preparation method comprising:

[0062] In an argon-filled glove box, LiTFSI was weighed according to a final concentration of 1000 mmol / L, LiNO3 was weighed according to 5wt% of the mass amount of LiTFSI, and was dissolved in the pre-mixed ether-based solvent of DME and 1,3-DOX with a volume ratio of 5:1. Then, (C8H 17)4NCl to the above solution, and completely dissolved under stirring, and left for 6h under argon condition and room temperature, to ensure that each component in the electrolyte is fully miscible and forms a stable electrolyte.

[0063] Example 4:

[0064] A lithium-sulfur battery electrolyte containing inducible S3 ·- radical-generating (C8H 17 )4NCl, the preparation method comprising:

[0065] In an argon-filled glove box, LiTFSI was weighed according to a final concentration of 1200mmol / L, LiNO3 was weighed according to 4wt% of the mass amount of LiTFSI, and both were dissolved in the ether-based solvent of DME and 1,3-DOX mixed in advance in a volume ratio of 3:1. Subsequently, (C8H 17 radical-generating (C8H ·- )4NCl was slowly added to the above solution in a final concentration of 150mmol / L, and completely dissolved under stirring, and left for 8h under argon condition and room temperature, to ensure that each component in the electrolyte is fully miscible and forms a stable electrolyte.

[0066] Example 5:

[0067] A lithium-sulfur battery electrolyte containing inducible S3 ·- radical-generating (C8H 17 )4NCl, the preparation method comprising:

[0068] In an argon-filled glove box, LiTFSI was weighed according to a final concentration of 1000mmol / L, LiNO3 was weighed according to 3wt% of the mass amount of LiTFSI, and both were dissolved in the ether-based solvent of DME and 1,4-DOX mixed in advance in a volume ratio of 1:1. Subsequently, (C8H 17 radical-generating (C8H 17 )4NCl was slowly added to the above solution in a final concentration of 50mmol / L, and completely dissolved under stirring, and left for 6h under argon condition and room temperature, to ensure that each component in the electrolyte is fully miscible and forms a stable electrolyte.

[0069] The above description of the embodiments is to facilitate the understanding and use of the invention by those of ordinary skill in the art. Those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described herein to other embodiments without having to go through creative labor. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. An inducible S3 •− A radical-generating lithium-sulfur battery electrolyte, characterized by, The lithium salt, the ether-based solvent and an additive; the additive is tetra-n-octylammonium chloride, and the concentration of the tetra-n-octylammonium chloride is 20-200 mmol / L; The lithium salt is a mixture of lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate, the concentration of the lithium bis(trifluoromethanesulfonyl)imide is 300-1500 mmol / L, and the amount of the lithium nitrate is 2-5 wt% of the mass of the lithium bis(trifluoromethanesulfonyl)imide.

2. The inducible S3 of claim 1 •− Radical-generating lithium-sulfur battery electrolyte, characterized in that The ether-based solvent comprises ethylene glycol dimethyl ether.

3. The inducible S3 of claim 2 •− Radical-generating lithium-sulfur battery electrolyte, characterized in that The ether-based solvent further comprises 1,3-dioxane or 1,4-dioxane.

4. The inducible S3 of claim 3 •− Radical-generating lithium-sulfur battery electrolyte, characterized in that In the ether-based solvent, the volume ratio of the ethylene glycol dimethyl ether to the 1,3-dioxane is (1-5):

1.

5. The inducible S3 of claim 3 •− Radical-generating lithium-sulfur battery electrolyte, characterized in that In the ether-based solvent, the volume ratio of the ethylene glycol dimethyl ether to the 1,4-dioxane is (1-5):

1.

6. An inducible S3 according to any one of claims 1 to 5 •− Process for the preparation of a radical-generating lithium-sulfur battery electrolyte, characterized in that, The method comprises the following steps: S1: adding a lithium salt into an ether-based solvent to obtain a basic electrolyte; S2: After adding the additive to the base electrolyte in step S1, standing to obtain an inducible S3 •− Radical-generating electrolyte.

7. The inducible S3 of claim 6 •− Process for the preparation of a radical-generating lithium-sulfur battery electrolyte, characterized in that, In step S1, the gas atmosphere is an inert gas.

8. The inducible S3 of claim 6 •− Process for the preparation of a radical-generating lithium-sulfur battery electrolyte, characterized in that, In step S2, in the standing, the standing atmosphere is an argon atmosphere, the standing temperature is room temperature, and the standing time is 1-12 h.

9. A lithium-sulfur battery, characterized by, The lithium-sulfur battery comprises a positive electrode, a separator, a negative electrode, and the inducible S3 according to any one of claims 1-5 •− Radical-generating lithium-sulfur battery electrolytes.

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