Application of trifluoromethyl phenyl thiourea in lithium-sulfur battery electrolyte, lithium-sulfur battery electrolyte, application of lithium-sulfur battery electrolyte and lithium-sulfur battery

Abstract

The invention belongs to the technical field of lithium-sulfur batteries, and provides application of trifluoromethyl phenyl thiourea in a lithium-sulfur battery electrolyte, the lithium-sulfur battery electrolyte, application of the lithium-sulfur battery electrolyte and a lithium-sulfur battery. According to the invention, trifluoromethyl phenyl thiourea, especially 3-(trifluoromethyl) phenyl thiourea (M-TFPT) as shown in a formula I, is used as an additive of the lithium-sulfur battery electrolyte. The M-TFPT can be used as an accelerant for optimizing a lithium polysulfide redox reaction path in a lithium-sulfur battery, and is also used as a building agent of a fluorinated SEI membrane. As the trifluoromethyl group in the M-TFPT molecule has lower dissociation energy, the M-TFPT can quickly form a dimer on the negative electrode side to be subjected to reductive decomposition and participate in construction of the fluorinated SEI membrane. The result shows that the initial specific discharge capacity is up to 1204.3 m.Ah.g <-1 > at the rate of 1C, and the specific discharge capacity is still up to 852.9 m.Ah.g <-1 > after 200 cycles.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-sulfur batteries, and in particular to the application of trifluoromethylphenylthiourea in the electrolyte of lithium-sulfur batteries, the electrolyte of lithium-sulfur batteries and its application, and lithium-sulfur batteries. Background Art

[0002] The theoretical energy density of lithium-sulfur batteries is 3 to 5 times higher than that of lithium-ion batteries, so it has received extensive attention in the scientific research community and the industrial community. However, there are still many unsolved problems in lithium-sulfur batteries, such as poor cycle stability of lithium-sulfur batteries. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide the application of trifluoromethylphenylthiourea in the electrolyte of lithium-sulfur batteries, the electrolyte of lithium-sulfur batteries and its application, and lithium-sulfur batteries. Applying trifluoromethylphenylthiourea to the electrolyte of lithium-sulfur batteries in the present invention can improve the cycle stability of lithium-sulfur batteries.

[0004] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides an application of trifluoromethylphenylthiourea in the electrolyte of lithium-sulfur batteries, and the trifluoromethylphenylthiourea has the structure shown in Formula I or Formula II:

[0006]

[0007] The present invention provides an electrolyte for lithium-sulfur batteries, which includes trifluoromethylphenylthiourea, lithium bis(trifluoromethanesulfonyl)imide, lithium nitrate, 1,3-dioxolane and ethylene glycol dimethyl ether;

[0008] The trifluoromethylphenylthiourea has the structure shown in Formula I or Formula II:

[0009]

[0010] Preferably, the concentration of trifluoromethylphenylthiourea in the electrolyte of lithium-sulfur batteries is 0.02 mol / L.

[0011] Preferably, the concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte of lithium-sulfur batteries is 1 mol / L.

[0012] Preferably, the concentration of lithium nitrate in the electrolyte of lithium-sulfur batteries is 0.01 mol / L.

[0013] Preferably, the volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether in the electrolyte of lithium-sulfur batteries is 1:1.

[0014] The present invention also provides the application of the electrolyte of lithium-sulfur batteries described in the above technical solution in lithium-sulfur batteries.

[0015] The present invention also provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the electrolyte is the lithium-sulfur battery electrolyte described in the above technical solution.

[0016] Preferably, the negative electrode is a lithium sheet.

[0017] Preferably, the positive electrode comprises a carrier and a sulfur element attached to the carrier; the surface loading of the sulfur element in the positive electrode is 1.5 to 4.3 mg / cm 2 .

[0018] The present invention provides application of trifluoromethylphenylthiourea in lithium-sulfur battery electrolyte.

[0019] Trifluoromethylphenylthiourea, especially 3-(trifluoromethyl)phenylthiourea (M-TFPT) shown in Formula I, is used as an additive to the electrolyte of lithium-sulfur batteries. Trifluoromethylphenylthiourea is an organic sulfide derivative with a chemical formula of C8H7F3N2S and has two isomeric structures, namely 3-(trifluoromethyl)phenylthiourea (M-TFPT) shown in Formula I and 4-(trifluoromethyl)phenylthiourea (P-TFPT) shown in Formula II. Among them, M-TFPT can be used as a promoter to optimize the redox reaction pathway of lithium polysulfide in lithium-sulfur batteries, and is also a builder of fluorinated SEI films. Because the trifluoromethyl group in the M-TFPT molecule has a lower dissociation energy, on the negative electrode side, M-TFPT can form dimers faster to undergo reductive decomposition and participate in the construction of a fluorinated SEI film. This SEI film not only promotes ion transport, but its LiF-rich properties also contribute to the uniform deposition of lithium ions, thereby effectively inhibiting the growth of lithium dendrites. Furthermore, when M-TFPT forms a dimer, the dissociation of the trifluoromethyl group causes the electron cloud density of the benzene ring to increase rapidly, making the dimer unstable and reducing it to a phenylthiourea radical. On the positive electrode side, the thiourea radical generated by M-TFPT directly changes the conversion pathway of polysulfides, enhances the electrochemical reaction kinetics, and effectively suppresses the shuttle effect. The results show that at a 1C rate, the initial discharge specific capacity is as high as 1204.3m·Ah·g -1 After 200 cycles, the discharge capacity is still as high as 852.9m·Ah·g -1 M-TFPT significantly improves the cycle life, safety and energy density of lithium-sulfur batteries, making it suitable for high-demand fields such as electric vehicles and energy storage systems, and has broad market prospects and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Lithium-sulfur batteries (surface loading 1.5 mg cm) assembled with blank electrolyte, M-TFPT electrolyte, and P-TFPT electrolyte -2 )’s first-cycle CV curve;

[0021] Figure 2 Initial charge-discharge test curves of lithium-sulfur batteries assembled with blank electrolyte, M-TFPT-containing electrolyte, and P-TFPT-containing electrolyte (areal loading 1.5 mg·cm -2 -2).

[0022] Figure 3 Cycling performance test results of lithium-sulfur batteries assembled with M-TFPT-containing electrolyte at 0.1C and 1.5 mg·cm -2 -2.

[0023] Figure 4 Constant current charge-discharge test of lithium-sulfur battery containing M-TFPT (areal loading 1.5 mg·cm -2 -2).

[0024] Figure 5 Cyclic voltammetry test chart of lithium-sulfur batteries containing M-TFPT and P-TFPT (areal loading 1.5 mg·cm -2 -2).

[0025] Figure 6 Cycling performance of high-loading lithium-sulfur batteries (areal loading of sulfur is 4.3 mg / cm 2 -2) assembled with M-TFPT-containing electrolyte and low electrolyte-sulfur ratio (E / S is 4.8 μL·mg -1 -1).

[0026] Figure 7 Rate performance chart of lithium-sulfur batteries assembled with blank electrolyte, M-TFPT-containing electrolyte, and P-TFPT-containing electrolyte (areal loading 1.5 mg·cm -2 -2).

[0027] Figure 8 Long cycling test of lithium-sulfur batteries assembled with blank electrolyte, M-TFPT-containing electrolyte, and P-TFPT-containing electrolyte (areal loading 1.5 mg·cm -2 -2).

[0028] Figure 9 CV test curves of lithium-sulfur batteries assembled with M-TFPT-containing electrolyte (areal loading 1.5 mg·cm -2 -2) in the scanning rate range of 0.1 to 0.5 mV·s -1 -1;

[0029] Figure 10 The oxidation-reduction peak current of lithium-sulfur batteries assembled with M-TFPT-containing electrolyte shows a linear relationship with the square root of the scanning rate v 1 / 2 -1;

[0030] Figure 11Li₂S deposition diagram of a lithium-sulfur battery assembled with an electrolyte containing M-TFPT;

[0031] Figure 12 Scanning electron microscope images of the lithium anode obtained after 200 cycles at a rate of 1C for lithium-sulfur batteries assembled with a blank electrolyte, an electrolyte containing M-TFPT, and an electrolyte containing P-TFPT;

[0032] Figure 13 Cycling performance diagrams of lithium-lithium symmetric batteries assembled with a blank electrolyte, an electrolyte containing M-TFPT, and an electrolyte containing P-TFPT at different current densities;

[0033] Figure 14 For the lithium-lithium symmetric battery assembled with M-TFPT at 1 mA·cm -2 SEM images of the lithium anode after cycling for 720 h;

[0034] Figure 15 For the lithium-lithium symmetric battery assembled with M-TFPT at 1 mA·cm -2 In-situ optical microscope photos of the lithium anode before and after cycling for 2 h;

[0035] Figure 16 For the lithium-lithium symmetric battery assembled with M-TFPT at 0.5 mA·cm -2 XPS spectra of the lithium anode after cycling 50 times. Specific embodiments

[0036] The present invention provides an application of trifluoromethylphenylthiourea in an electrolyte of a lithium-sulfur battery, and the trifluoromethylphenylthiourea has a structure shown in Formula I or Formula II:

[0037]

[0038] In the present invention, the trifluoromethylphenylthiourea shown in Formula I is 3-(trifluoromethyl)phenylthiourea (M-TFPT), and the trifluoromethylphenylthiourea shown in Formula II is 4-(trifluoromethyl)phenylthiourea (P-TFPT). M-TFPT and P-TFPT are isomers of trifluoromethylphenylthiourea.

[0039] The present invention provides an electrolyte for a lithium-sulfur battery, which includes trifluoromethylphenylthiourea, lithium bis(trifluoromethanesulfonyl)imide, lithium nitrate, 1,3-dioxolane, and ethylene glycol dimethyl ether;

[0040] The trifluoromethylphenylthiourea has a structure shown in Formula I or Formula II:

[0041]

[0042] Unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0043] The lithium-sulfur battery electrolyte provided by the present invention comprises trifluoromethylphenylthiourea, and the trifluoromethylphenylthiourea has the structure shown in Formula I or Formula II. In the present invention, the concentration of trifluoromethylphenylthiourea in the lithium-sulfur battery electrolyte is preferably 0.02 mol / L.

[0044] The lithium-sulfur battery electrolyte provided by the present invention comprises lithium bis(trifluoromethanesulfonyl)imide, and the concentration of lithium bis(trifluoromethanesulfonyl)imide in the lithium-sulfur battery electrolyte is preferably 1 mol / L.

[0045] The lithium-sulfur battery electrolyte provided by the present invention comprises lithium nitrate, and the concentration of lithium nitrate in the lithium-sulfur battery electrolyte is preferably 0.01 mol / L.

[0046] The lithium-sulfur battery electrolyte provided by the present invention comprises 1,3-dioxolane and ethylene glycol dimethyl ether, and the volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether in the lithium-sulfur battery electrolyte is preferably 1:1.

[0047] The present invention also provides an application of the lithium-sulfur battery electrolyte described in the above technical solution in a lithium-sulfur battery.

[0048] The present invention also provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the electrolyte is the lithium-sulfur battery electrolyte described in the above technical solution.

[0049] The lithium-sulfur battery provided by the present invention comprises a positive electrode, and the positive electrode preferably comprises a carrier and sulfur elemental attached to the carrier. In the present invention, the carrier preferably comprises ordered mesoporous carbon (CMK-3). In the present invention, the areal loading of sulfur elemental in the positive electrode is preferably 1.5 - 4.3 mg / cm 2 , specifically preferably 1.5 mg / cm 2 , 1.6 mg / cm 2 , 1.7 mg / cm 2 , 1.8 mg / cm 2 or 4.3 mg / cm 2 . In the present invention, the ratio of the volume of the electrolyte to the mass of sulfur elemental in the positive electrode is preferably 4.8 - 33.3 μL / mg, specifically preferably 4.8 μL / mg or 33.3 μL / mg.

[0050] The lithium-sulfur battery provided by the present invention comprises a negative electrode, and the negative electrode is preferably a lithium sheet.

[0051] The lithium-sulfur battery provided by the present invention comprises an electrolyte, and the electrolyte is the lithium-sulfur battery electrolyte described in the above technical solution.

[0052] The lithium-sulfur battery provided by the present invention comprises a separator, and the separator is preferably a Celgard separator.

[0053] The lithium-sulfur battery provided by the present invention preferably further includes an external circuit, and the present invention does not specifically limit the structure of the external circuit.

[0054] The lithium-sulfur battery provided by the present invention will be described in detail below in conjunction with embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0055] Example 1

[0056] M-TFPT and P-TFPT were respectively added to 10 mL of a commercial lithium-sulfur battery electrolyte (including LiTFSI, lithium nitrate, 1,3-dioxolane, and ethylene glycol dimethyl ether; wherein, the concentration of LiTFSI was 1 mol / L, the concentration of lithium nitrate was 0.01 mol / L, and the volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether was 1:1) to obtain a lithium-sulfur battery electrolyte, wherein the concentrations of M-TFPT and P-TFPT were both 0.02 mol / L; a commercially available lithium-sulfur battery electrolyte without additives was used as the blank group.

[0057] 75 μL of different electrolytes were respectively added to lithium-sulfur batteries (wherein, the negative electrode was a lithium sheet, the positive electrode included a carrier and sulfur, the carrier was ordered mesoporous carbon (CMK-3), and the areal loading of sulfur was 1.5 mg / cm 2 , and the separator was a Celgard separator), and the ratio of the volume of the electrolyte to the mass of sulfur in the positive electrode was 33.3 μL / mg.

[0058] Electrochemical tests were carried out using a land test system and a BioLogic electrochemical workstation, and the results were as Figure 1 shown, Figure 1 The first-cycle CV curves of lithium-sulfur batteries assembled with the blank electrolyte, the electrolyte containing M-TFPT, and the electrolyte containing P-TFPT. From Figure 1 it can be seen that: they have similar oxidation-reduction peaks, which are typical oxidation-reduction characteristic peaks of lithium-sulfur batteries. Compared with the lithium-sulfur battery assembled with the blank lithium-sulfur battery without additives and P-TFPT, the lithium-sulfur battery assembled with M-TFPT has a higher peak current, indicating its active electrochemical kinetics and fast charge transfer ability.

[0059] Figure 2 The first-cycle galvanostatic charge-discharge test curves of lithium-sulfur batteries assembled with the blank electrolyte, the electrolyte containing M-TFPT, and the electrolyte containing P-TFPT. From Figure 2It can be seen that: compared with the additive-free lithium-sulfur battery, the lithium-sulfur battery containing M-TFPT has a smaller plateau voltage gap (ΔE), indicating less polarization and better redox reversibility. At the same time, it is found that the Coulombic efficiency of the lithium-sulfur battery assembled with the M-TFPT-containing electrolyte is greater than 100%. This is mainly because during the electrochemical reaction process of M-TFPT, the thiourea groups form dimers connected by S-S bonds, and during the formation and breakage of the S-S bonds, capacity is provided for the extension of the low-voltage plateau.

[0060] Figure 3 The cycle performance test results of the lithium-sulfur battery assembled with the M-TFPT-containing electrolyte at 0.1C and 1.5 mg·cm -2 are as follows. It can be seen from Figure 3 that during the electrochemical reaction process of M-TFPT, the thiourea groups form dimers connected by S-S bonds, and during the formation and breakage of the S-S bonds, capacity is provided for the extension of the low-voltage plateau. However, the capacity provision only occurs in the initial stage of the electrochemical reaction. After three charge-discharge cycles, the Coulombic efficiency of the battery is lower than 100%, which may be due to the complete breakage of the S-S bonds.

[0061] To verify this hypothesis, a lithium-sulfur battery with M-TFPT as the positive electrode active material and lithium as the negative electrode was assembled, and constant current charge-discharge tests and cyclic voltammetry tests were carried out. The results are as shown in Figure 4 and Figure 5 respectively. Figure 4 Figure Figure 5 shows the constant current charge-discharge test of the lithium-sulfur battery containing M-TFPT, and Figure 4 Figure Figure 5 shows the cyclic voltammetry test diagrams of the lithium-sulfur batteries containing M-TFPT and P-TFPT. It can be seen from Figure 4 and Figure 5 that M-TFPT can undergo a redox reaction by itself to provide capacity for the battery. Although P-TFPT can also react, the effect of providing capacity is limited and no discharge plateau appears. This is because the group steric hindrance is different, resulting in different degrees of difficulty in undergoing redox reactions.

[0062] Figure 6 Figure 2 shows the cycle performance of the high-loading (the areal loading of sulfur is 4.3 mg / cm -1 ) and low electrolyte-sulfur ratio (E / S is 4.8 μL·mg -1 ) lithium-sulfur battery assembled with the M-TFPT-containing electrolyte. It can be seen from Figure 6 that under the condition of lean electrolyte (0.1C, 33 cycles, 674.2 m·Ah·g -1 , and the E / S is only 4.8 μL·mg -1 ), the lithium-sulfur battery assembled with M-TFPT can also achieve stable cycling, and the initial discharge specific capacity is as high as 1049.8 m·Ah·g -1, showing an extremely low capacity attenuation rate.

[0063] Figure 7 are the rate performance graphs of lithium-sulfur batteries assembled with blank electrolyte, M-TFPT-containing electrolyte, and P-TFPT-containing electrolyte. From Figure 7 it can be seen that: the rate performance of M-TFPT lithium-sulfur batteries has been significantly improved. For the lithium-sulfur batteries assembled with M-TFPT-containing electrolyte, at 0.1C, 0.2C, 0.5C, 1C, and 2C conditions, the discharge specific capacities are 1230.4, 967.2, 901.1, 787.8, 729.8 m·Ah·g -1 respectively, while the discharge specific capacities of the lithium-sulfur batteries assembled with blank electrolyte are only 1042.7, 838.6, 744.7, 690.1, 643.2 m·Ah·g -1 0. Moreover, when the current density reaches 0.1C, the capacity can recover to 957.3 m·Ah·g -1 .

[0064] Figure 8 are the long cycle tests of lithium-sulfur batteries assembled with blank electrolyte, M-TFPT-containing electrolyte, and P-TFPT-containing electrolyte. From Figure 8 it can be seen that the addition of M-TFPT significantly improves the discharge specific capacity and cycle stability of lithium-sulfur batteries. The initial discharge specific capacity of the lithium-sulfur battery with M-TFPT added is as high as 1204.3 m·Ah·g -1 , and after 200 cycles, the discharge specific capacity is still as high as 852.9 m·Ah·g -1 . In contrast, for the control group of lithium-sulfur batteries at 1C, the initial discharge specific capacity is only 735.9 m·Ah·g -1 4, and after 200 cycles, the capacity retention rate is only 66.5%.

[0065] Figure 9 are the CV test curves of the lithium-sulfur battery assembled with M-TFPT-containing electrolyte in the scanning rate range of 0.1 to 0.5 mV·s -1 . From Figure 9 it can be seen that: compared with the control battery, the redox peak currents of the batteries containing M-TFPR are enhanced at different scanning rates, and they are clearer and stronger even at a high scanning rate of 0.5 mV·s -1 .

[0066] Figure 10 is that the redox peak current of the lithium-sulfur battery assembled with M-TFPT-containing electrolyte has a linear relationship with the square root of the scanning rate v 1 / 2 .

[0067] To monitor the formation of discharge products, a Li2S deposition experiment was carried out. Specifically: First, the lithium-sulfur battery assembled with the M-TFPT-containing electrolyte was discharged to 2.06 V to convert most of the long-chain LiPSs into short-chain sulfur species, and then discharged at a constant voltage to induce Li2S nucleation and deposition. The whole process can be divided into two parts: the reduction of Li2S8 / Li2S6 and the deposition of Li2S. Figure 11 Figure for Li2S deposition of the lithium-sulfur battery assembled with the M-TFPT-containing electrolyte. According to Faraday's law, the deposition amount of Li2S after adding M-TFPT is much higher than that after adding P-TFPT and the control group lithium-sulfur battery, indicating that M-TFPT significantly promotes the transformation of long-chain LiPSs into Li2S.

[0068] After the lithium-sulfur batteries assembled with the blank electrolyte, the M-TFPT-containing electrolyte, and the P-TFPT-containing electrolyte were cycled 200 times at a 1C rate, the lithium anode of the cycled batteries was tested by scanning electron microscopy (SEM). The results are as Figure 12 shown. Figure 12 Scanning electron microscopy images of the lithium anodes obtained after the lithium-sulfur batteries assembled with the blank electrolyte, the M-TFPT-containing electrolyte, and the P-TFPT-containing electrolyte were cycled 200 times at a 1C rate. Among them, the upper row of photos are SEM photos of the lithium anode surface, and the lower row of photos are SEM images of the lithium anode cross-section. From Figure 12 it can be seen that after the lithium-sulfur battery with the M-TFPT-containing electrolyte was cycled 200 times at a 1C rate, a dense and smooth SEI was formed on the surface of metallic lithium, while dead lithium appeared on the surface of metallic lithium after the lithium-sulfur battery assembled with the control group electrolyte was cycled 200 times. In addition to the surface morphology, the SEM cross-section of the lithium anode also shows that M-TFPT helps to reduce the corrosion of lithium metal. It is inferred that because TFPT is a highly fluorinated molecule with poor thermodynamic stability on the surface of the metallic lithium anode, it promotes TFPT to react preferentially on the anode surface to form a stable fluorinated SEI on the surface of the metallic lithium anode. Due to the different steric hindrances of the substituents of M-TFPT and P-TFPT, the steric effect of the trifluoromethyl molecule in M-TFPT is greater than that of P-TFPT, resulting in M-TFPT being able to decompose preferentially on the anode surface, and the protection effect on metallic lithium is better than that of P-TFPT.

[0069] To further study the protective effects of M-TFPT and P-TFPT on the lithium anode, a lithium-lithium symmetric battery was assembled for electrochemical testing. The assembled lithium-lithium symmetric battery was cycled at different current densities. The results are as Figure 13 shown. Figure 13 Cycling performance graphs of the lithium-lithium symmetric batteries assembled with the blank electrolyte, the M-TFPT-containing electrolyte, and the P-TFPT-containing electrolyte at different current densities. From Figure 13It can be seen that the Li / Li symmetric battery assembled with M-TFPT can maintain cycling stability and has a small overpotential in the range of 0.25 - 2 mA·cm -2 while the Li / Li symmetric battery assembled with the control electrolyte can perform stable cycling at 0.25 - 0.5 mA·cm -2 but has a serious battery overpotential. When the current density reaches 1 mA·cm -2 the battery cannot perform stable cycling, and the battery shorts at 2 mA·cm -2 .

[0070] The lithium anode of the Li / Li symmetric battery assembled with M-TFPT was subjected to SEM testing after cycling at 1 mA·cm -2 for 720 h, and the results are as Figure 14 shown Figure 14 Figure 19 is the SEM image of the lithium anode of the Li / Li symmetric battery assembled with M-TFPT after cycling at 1 mA·cm -2 for 720 h. The upper figure is the surface SEM image, and the lower figure is the cross-section SEM image. It can be seen from Figure 14 this that the surface of the metallic lithium of the Li / Li symmetric battery after cycling is smooth and uniform, without the formation of dendrites and dead lithium.

[0071] The morphology of the lithium anode of the Li / Li symmetric battery assembled with M-TFPT was photographed using an in-situ optical microscope before and after cycling at 1 mA·cm -2 for 720 h, and the results are as Figure 15 shown Figure 15 Figure 20 is the in-situ optical microscope photos of the lithium anode of the Li / Li symmetric battery assembled with M-TFPT before and after cycling for 2 h at 1 mA·cm -2 . It can be seen from Figure 15 this that at a current density of 1 mA·cm -2 the surface of the metallic lithium of the Li / Li symmetric battery assembled with M-TFPT is smooth without dendrite formation at the initial stage of cycling, and a uniform and dense SEI can be observed on the surface of the metallic lithium at the later stage. This indicates that M-TFPT can inhibit dendrite growth and participate in the construction of SEI at the initial stage of the reaction.

[0072] To explore the composition of the SEI, XPS testing was performed on the metallic lithium anode of the Li / Li symmetric battery cycled 50 times at 0.5 mA·cm -2 , and the results are as Figure 16 shown Figure 16 Figure 21 is the XPS spectrum of the lithium anode of the Li / Li symmetric battery assembled with M-TFPT after cycling 50 times at 0.5 mA·cm -2 , as Figure 16As shown, the profile of the etching depth shows the chemical environment on the lithium metal surface of the lithium-lithium symmetric battery. In the lithium-lithium symmetric battery assembled with M-TFPT, Li-F mainly comes from the decomposition products of TFPT and LiTFSI, and Li-O and Li-N mainly come from the decomposition products of LiTFSI and LiNO3 in the electrolyte. The intensity of the Li-F peak does not decrease at all during the etching process, while the intensity of the Li-O peak gradually weakens with the increase of the etching depth. This is because the addition of M-TFPT in the electrolyte can participate in constructing the SEI mainly composed of LiF to protect metallic lithium.

[0073] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. Application of trifluoromethylphenylthiourea in electrolyte of lithium-sulfur battery, wherein the trifluoromethylphenylthiourea has a structure shown in Formula I or Formula II:

2. A lithium-sulfur battery electrolyte, characterized in that, Comprising trifluoromethylphenylthiourea, lithium bis(trifluoromethanesulfonyl)imide, lithium nitrate, 1,3-dioxolane and ethylene glycol dimethyl ether; The trifluoromethylphenylthiourea has a structure shown in Formula I or Formula II:

3. The lithium-sulfur battery electrolyte according to claim 2, wherein, The concentration of trifluoromethylphenylthiourea in the electrolyte of the lithium-sulfur battery is 0.02 mol / L.

4. The lithium-sulfur battery electrolyte according to claim 2, wherein, The concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte of the lithium-sulfur battery is 1 mol / L.

5. The lithium-sulfur battery electrolyte according to claim 2, wherein The concentration of lithium nitrate in the electrolyte of the lithium-sulfur battery is 0.01 mol / L.

6. The lithium-sulfur battery electrolyte according to claim 2, characterized in that, The volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether in the electrolyte of the lithium-sulfur battery is 1:

1.

7. Application of the electrolyte of the lithium-sulfur battery according to any one of claims 2 to 6 in a lithium-sulfur battery.

8. A lithium-sulfur battery, characterized in that, Comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the electrolyte is the electrolyte of the lithium-sulfur battery according to any one of claims 2 to 6.

9. The lithium-sulfur battery according to claim 8, characterized in that, The negative electrode is a lithium sheet.

10. The lithium-sulfur battery according to claim 8, characterized in that, The positive electrode includes a carrier and sulfur elemental attached to the carrier; the areal loading of sulfur elemental in the positive electrode is 1.5 to 4.3 mg / cm 2 .

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