Application of trifluoromethylbenzophenone imine as an electrolyte additive for lithium-sulfur batteries

Abstract

The present invention relates to the field of battery material technology, and more particularly to the use of p-trifluoromethylbenzophenone imine as an electrolyte additive for lithium-sulfur batteries. The present invention provides a use of p-trifluoromethylbenzophenone imine as an electrolyte additive for lithium-sulfur batteries. When used as an electrolyte additive for lithium-sulfur batteries, the p-trifluoromethylbenzophenone imine provided by the present invention can enhance the effect of van der Waals forces between p-trifluoromethylbenzophenone imine and polysulfides on reaction kinetics, and promote the release of fluoride ions from p-trifluoromethylbenzophenone imine during the cycle process, thereby constructing a dense, highly conductive solid electrolyte interface (SEI). This improves the utilization rate of active sulfur, effectively reduces the shuttling effect of polysulfides, and ensures the integrity of the lithium negative electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to p-trifluoromethylphenone imine, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium-sulfur batteries have received widespread attention from the scientific research and industrial communities because their theoretical energy density is 3-5 times higher than that of lithium-ion batteries. However, there are still many unresolved issues with lithium-sulfur batteries. Among them, the "shuttle effect" of lithium polysulfide will seriously consume the active materials inside the battery and cause irreversible corrosion to metallic lithium, which is the "high threshold" for the industrialization of lithium-sulfur batteries. Reasonable design of the electrolyte and the introduction of a small amount of additives can effectively improve the above problems. At this stage, commercial lithium-sulfur battery electrolytes use a small amount of lithium nitrate as an electrolyte additive, but it is still difficult to meet the demand for electrolyte during the lithium-sulfur battery cycle. Summary of the Invention

[0003] In view of this, the object of the present invention is to provide the use of trifluoromethylbenzophenone imine as a lithium-sulfur battery electrolyte additive. When the trifluoromethylbenzophenone imine provided by the present invention is used as an electrolyte additive, the electrolyte will not cause corrosion to the surface and interior of the lithium negative electrode.

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

[0005] The present invention provides an application of trifluoromethylbenzophenone imine as an additive for lithium-sulfur battery electrolyte.

[0006] The present invention also provides a lithium-sulfur battery electrolyte composition, comprising a lithium-sulfur battery electrolyte and p-trifluoromethylbenzophenone imine.

[0007] Preferably, the concentration of trifluoromethylbenzophenone imine in the lithium-sulfur battery electrolyte composition is 0.01 mol / mL.

[0008] Preferably, the lithium-sulfur battery electrolyte comprises LiTFSI, lithium nitrate, 1,3-dioxolane and ethylene glycol dimethyl ether.

[0009] Preferably, the concentration of LiTFSI in the lithium-sulfur battery electrolyte is 1 mol / L, and the concentration of lithium nitrate is 0.01 mol / L.

[0010] Preferably, the volume ratio of the 1,3-dioxolane to ethylene glycol dimethyl ether is 1:1.

[0011] The present invention provides a use of trifluoromethylbenzophenone imine as a lithium-sulfur battery electrolyte additive. When the trifluoromethylbenzophenone imine provided by the present invention is used as a lithium-sulfur battery electrolyte additive, the effect of the van der Waals force between trifluoromethylbenzophenone imine and polysulfides on the reaction kinetics can be enhanced, and the release of fluoride ions in trifluoromethylbenzophenone imine can be promoted during the cycle process, thereby constructing a dense and highly conductive solid electrolyte interface film (SEI), thereby improving the utilization rate of active sulfur, effectively reducing the shuttle effect of polysulfides, and ensuring the integrity of the lithium negative electrode.

[0012] The results showed that under the condition of lean electrolyte (E / S ratio of 8 μL mg -1 ), the PTPEI battery can still maintain 645.9mAhg after 50 cycles -1 High capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a test diagram of the effect of trifluoromethylbenzophenone imine on the electrochemical performance of lithium-sulfur batteries;

[0014] Figure 2 This is a test diagram of the effect of trifluoromethylbenzophenone imine on lithium negative electrode;

[0015] Figure 3 Electrochemical testing of lithium-lithium symmetric batteries and SEM and XPS testing of lithium negative electrodes after cycling;

[0016] Figure 4 The test results of basic electrochemical testing were performed by adding 0.05, 0.1, and 0.2 mol of trifluoromethylbenzophenone imine into 10 mL of commercial lithium-sulfur battery electrolyte. DETAILED DESCRIPTION

[0017] The present invention provides a use of trifluoromethylbenzophenone imine as a lithium-sulfur battery electrolyte additive, wherein the trifluoromethylbenzophenone imine has a structure shown in Formula I:

[0018]

[0019] In the present invention, unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0020] The present invention also provides a lithium-sulfur battery electrolyte, comprising the lithium-sulfur battery electrolyte and trifluoromethylbenzophenone imine.

[0021] In the present invention, the concentration of trifluoromethylphenone imine in the lithium-sulfur battery electrolyte composition is preferably 0.01 mol / mL.

[0022] In the present invention, the lithium-sulfur battery electrolyte comprises LiTFSI, lithium nitrate, 1,3-dioxolane and ethylene glycol dimethyl ether; the concentration of LiTFSI in the lithium-sulfur battery electrolyte is preferably 1 mol / L, and the concentration of lithium nitrate is preferably 0.01 mol / L.

[0023] In the present invention, the volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether is preferably 1:1.

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0025] Example 1

[0026] 0.05-0.2 mol of trifluoromethylbenzophenone imine was added to 10 mL of commercial lithium-sulfur battery electrolyte as the experimental group; 0.1 mol of trifluoromethylaniline was added to 10 mL of commercial lithium-sulfur battery electrolyte (including LiTFSI, lithium nitrate, 1,3-dioxolane and ethylene glycol dimethyl ether; the concentration of LiTFSI in the lithium-sulfur battery electrolyte was 1 mol / L, the concentration of lithium nitrate was 0.01 mol / L; the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether was 1:1) as the control group.

[0027] 70 μL of the electrolyte containing trifluoromethylbenzophenone imine was added to the lithium-sulfur battery;

[0028] The control group was composed of 70 μL of electrolyte containing trifluoromethylaniline added to the lithium-sulfur battery and 70 μL of commercial electrolyte for lithium-sulfur battery added to the lithium-sulfur battery.

[0029] The assembled battery was electrochemically tested using the Land test system and the BioLogic electrochemical workstation. The test results are shown in Figures 1 to 4 ; Figure 4 The test results of basic electrochemical tests were performed by adding 0.05, 0.1, and 0.2 mol of trifluoromethylbenzophenone imine to 10 mL of commercial lithium-sulfur battery electrolyte. Figure 4 It can be seen that: 0.1 mol of trifluoromethylbenzophenone imine added to 10 mL of commercial lithium-sulfur battery electrolyte has the best electrochemical performance in electrochemical testing.

[0030] Figure 1 This is a test diagram of the effect of trifluoromethylbenzophenone imine on the electrochemical performance of lithium-sulfur batteries; Figure 1(a) is a comparison of the second cycle CV curves of the battery without additives and with trifluoromethylaniline (TFMA, concentration in the electrolyte is 0.01 mol / mL) and trifluoromethylphenyl ketone imine (PTPEI, concentration in the electrolyte is 0.01 mol / mL). Figure 1 As shown in (a), the second cycle CV curves of the battery without additives and with trifluoromethylaniline (TFMA) and trifluoromethylphenyl ketone imine (PTPEI) all have similar redox peaks, which are typical redox peaks of Li-S batteries. However, compared with the battery without additives (2.48V) and TFMA battery (2.40V), the oxidation peak of the PTPEI battery at 2.38V is lower, while its reduction peaks (C1 and C2) are higher than the control battery at 2.31 and 2.03V, respectively (battery without additives: 2.26 and 1.97V; TFMA: 2.26 and 1.98V). Moreover, the PTPEI battery exhibits a higher peak current, indicating that it has active electrochemical kinetics and fast charge transfer capabilities.

[0031] Figure 1 (b) is the constant current charge and discharge test curve of the battery, which is consistent with the CV test results. The initial discharge capacity of the PTPEI battery at 0.1C is 1214mAhg -1 , and the polarization is small, which is 140mA, while the initial discharge specific capacities of the battery containing TFMA and without additives are 1089 and 1027mAhg, respectively. -1 .like Figure 1 As shown in (c), the PTPEI battery exhibits smaller polarization and higher capacity during the entire cycle compared to the control battery. Figure 1 As shown in (d), the rate performance of the PTPEI battery is significantly improved compared with the control battery. Specifically, at current densities of 0.1, 0.2, 0.5, 1, and 2C, the discharge specific capacities of the PTPEI battery are 1207, 957, 890, 786, and 669 mAh g, respectively. -1 In addition, when the current density reaches 0.1C, the capacity can be restored to 973mAhg -1 .like Figure 1 As shown in (e), even after 200 cycles at 1C rate, the discharge capacity of the PTPEI battery is still 580 mAh g -1 (49.2% of the initial capacity). In contrast, both the battery without the additive and the battery containing TFMA exhibited poor rate performance, characterized by significant capacity fluctuations with increasing current density and a rapid decay trend when cycling at a 1C rate. This phenomenon is mainly caused by the delayed conversion of lithium polysulfides during the charge and discharge process, resulting in sluggish reaction kinetics and corrosion of the lithium anode. Figure 1f depicts the cell with PTPEI at 0.1 to 0.9 mVs -1 CV test curves within the scan rate range. Compared with the control battery, the redox peak current of the battery containing PTPEI at different scan rates is enhanced, even at 0.9mVs -1 It also appears clearer and stronger at high scanning rates. Figure 1 As shown in (g), the redox peak current in the PTPEI battery is related to the scan rate v 1 / 2 The square root of the relationship is linear. -2 ) and lean electrolyte (E / S ratio of 8μLmg -1 ) conditions, the performance of PTPEI batteries was further evaluated. Benefiting from the enhanced D Li+ and electron transfer, the battery with PTPEI provided 1190.9 mAh g -1 The discharge capacity is 645.9 mAh g after 50 cycles at 0.1 C. -1 The capacity retention rate shows an extremely low capacity decay rate, which is only 0.9% per cycle. Figure 1 (h) in the figure.

[0032] Figure 2 This is a test diagram of the effect of trifluoromethylbenzophenone imine on lithium negative electrode. Figure 2 It can be seen that after 100 cycles at 0.1C, the surface of the lithium negative electrode in the battery without additives showed obvious moss characteristics, indicating that the degree of corrosion was relatively serious ( Figure 2 a). In contrast, the lithium anode in the battery using TFMA maintained a relatively intact morphology, indicating only minor corrosion ( Figure 2 b). It is worth noting that the surface of the lithium anode in the battery using PTPEI appears to be very flat without any obvious signs of corrosion ( Figure 2 c).

[0033] The present invention also used a scanning electron microscope to observe the cross section of the lithium negative electrode. Figure 2 As shown in Figure d, the surface and interior of the lithium negative electrode without additives are severely corroded. The battery containing TFMA shows that the lithium metal is corroded internally, but the corrosion is mainly concentrated on the surface of the lithium negative electrode and the degree is relatively mild ( Figure 2 e). Figure 2 In (f), a dense SEI is present on the anode surface of the PTPEI-containing cell, while no signs of corrosion are observed within the lithium anode.

[0034] The energy spectrum of the corresponding cross section of the lithium negative electrode is as follows Figure 2 As shown in hl, Figure 2It can be seen from hl that sulfur exists in the lithium negative electrode and shows a stronger and more obvious signal in the battery without additives. In contrast, in the battery containing TFMA, sulfur was found to be mainly concentrated on the surface. In the battery with PTPEI, the sulfur signal detected was very weak, and the presence of sulfur was almost unrecognizable deep in the lithium negative electrode. On the other hand, the fluorine signal intensity was weak and unevenly dispersed in the battery without additives. In contrast, in the battery with PTPEI, fluorine was evenly dispersed on the surface of the lithium negative electrode, and the signal was significantly stronger and denser than the signal observed in the battery with TFMA.

[0035] Figure 3 The electrochemical test of lithium-lithium symmetric battery and the SEM and XPS test images of lithium negative electrode after cycling, Figure 3 It can be seen that: at a current density of 1 mA cm -2 When the TFMA-containing battery and the PTPEI-containing battery showed stable overpotential after 190 h and 100 h of cycling, and maintained this stability for more than 1000 h ( Figure 3 a). In contrast, after 130h of cycling, the battery without additives experienced a short circuit due to the continuous growth of lithium dendrites. Figure 3 As shown in Figure b, the voltage polarization of the lithium-lithium symmetric battery containing TFMA and PTPEI changes regularly with the increase of current density. However, the battery without additives shows a significant fluctuation in voltage polarization. The present invention also conducted a scanning electron microscopy test on the lithium metal in the lithium-lithium symmetric battery after cycling. Compared with the phenomenon of uneven lithium metal surface deposition in the battery without additives ( Figure 3 c) The surface of lithium metal in TFMA battery is basically not corroded ( Figure 3 d). It is worth noting that a dense SEI can be observed on the lithium metal surface in the battery using PTPEI ( Figure 3 e). Whether before or after etching, the relative abundance of Li-F bonds in the Li1s spectrum of the cell containing PTPEI is significantly higher than that of the other two cells ( Figure 3 h). The addition of PTPEI to the electrolyte is conducive to the formation of a stable SEI mainly composed of LiF, which significantly enhances electronic conduction.

[0036] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A lithium-sulfur battery electrolyte composition, characterized in that: The invention comprises a lithium-sulfur battery electrolyte and p-trifluoromethylbenzophenone imine; the lithium-sulfur battery electrolyte comprises LiTFSI, lithium nitrate, 1,3-dioxolane and ethylene glycol dimethyl ether; the concentration of p-trifluoromethylbenzophenone imine in the lithium-sulfur battery electrolyte composition is 0.01 mol / mL; the concentration of LiTFSI in the lithium-sulfur battery electrolyte is 1 mol / L, and the concentration of lithium nitrate is 0.01 mol / L; the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether is 1:1.

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