A lithium-organic sulfur battery positive electrode material and its preparation method and application

Abstract

The present invention discloses a novel insoluble cyclic lithium-organic sulfur battery positive electrode material, its preparation method and application. The positive electrode material of the organosulfur battery is an insoluble cyclic organolithium, which is synthesized in a DMSO solution using TBBT as a raw material. The positive electrode material and a carbon nanotube substrate form a positive electrode, which circulates stably in a lithium metal battery and has a high coulombic efficiency. At the same time, since the discharge product Li2-TBBT formed during the discharge process can form a layer of organic / inorganic composite SEI at the negative electrode, it can exhibit excellent electrochemical performance in a full battery with lithiated carbon paper as the negative electrode; using Li-CP instead of lithium metal as the negative electrode greatly improves the safety of the battery and makes the lithium-organic sulfur battery have commercial application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-organic sulfur battery positive electrode materials, and in particular relates to a lithium-organic sulfur battery positive electrode material and a preparation method and application thereof. Background Art

[0002] With the development of portable electronic devices and electric vehicles, lithium-ion batteries have occupied a considerable market share due to their high energy density. The cathode materials of lithium-ion batteries are mainly transition metal oxides, such as lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium iron phosphate (LFP), etc. However, the further development of lithium-ion batteries is limited by the shortage of cobalt resources, poor cycle stability of LMO, and low energy density of LFP. Therefore, it is imperative to explore new cathode materials for lithium batteries. Compared with inorganic materials, organic electrodes have advantages such as high capacity, diverse structures, and low cost. Among them, carbonyl compounds, quinone compounds, and organic sulfur molecules are representative cathode materials. The charge storage mechanism in organic electrodes is based on the breaking and formation of chemical bonds, which is different from the ion embedding mechanism in transition metal oxides. Therefore, organic materials have a broad space for exploration as electrode materials and have interesting redox mechanisms.

[0003] Organic sulfur molecules containing sulfur-sulfur (SS) bonds are a class of organic electrode materials that exhibit electrochemical activity based on the breaking and forming of SS bonds. Numerous studies have reported that organic sulfur can exhibit excellent electrochemical performance in lithium batteries. However, most organic sulfur has only been studied in lithium metal half-cells, and most are easily soluble in electrolytes. The growth of lithium dendrites on lithium anodes can cause serious safety issues. In addition, the dissolution of organic sulfur can lead to rapid decay of battery capacity. Therefore, the development of insoluble organic sulfur materials and the replacement of lithium metal anodes with non-lithium metal anodes can greatly improve battery safety and promote the commercialization of organic sulfur cathodes. Summary of the Invention

[0004] The present invention aims to provide a lithium-organic sulfur battery cathode material, its preparation method, and its application. This cathode material, HTBCO, is poorly soluble in electrolyte, significantly reducing the loss of active material during battery cycling and extending the battery's cycle life. Its use in battery cathodes enables ultra-stable, long-term cycling.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] Provided is a lithium-organic sulfur battery cathode material, wherein the cathode material is HTBCO, and the HTBCO structure is as follows:

[0007] .

[0008] A preparation method of the positive electrode material HTBCO is provided, which comprises using 4,4'-thiobisthiophenol as a raw material, stirring and reacting the mixture in a dimethyl sulfoxide solution for 10 to 12 hours to obtain HTBCO.

[0009] Preferably, the product after the reaction is washed with acetone three times repeatedly and then dried at 50-60° C. for 10-12 hours to completely evaporate the solvent.

[0010] Provided is a lithium-organic sulfur battery positive electrode, comprising the above-mentioned HTBCO and a multi-walled carbon nanotube substrate loaded with the HTBCO.

[0011] According to the above scheme, the loading amount of HTBCO in the positive electrode is 1.3~1.5 mg cm -2 .

[0012] A method for preparing the above-mentioned positive electrode is provided, comprising the following steps:

[0013] Multi-walled carbon nanotubes and HTBCO are uniformly dispersed in anhydrous ethanol solvent by ultrasonication, and then post-treated to obtain a positive electrode material loaded with HTBCO.

[0014] According to the above scheme, the post-processing includes filtration, washing, vacuum drying, and cutting as needed. Preferably, the post-processing steps include: filtration, washing several times with anhydrous ethanol; then drying at 50-60°C under vacuum conditions for 10-12 hours; and finally cutting the dried composite material as needed.

[0015] According to the above scheme, the mass ratio of the multi-walled carbon nanotubes to HTBCO is 1.5-2.5:1.

[0016] Provided is a lithium-organic sulfur battery, comprising a lithium-sulfur electrolyte, a separator and a lithium negative electrode, and also comprising the above-mentioned positive electrode, wherein the lithium negative electrode is a lithium metal sheet or lithiated carbon paper.

[0017] According to the above solution, when the lithium-organic sulfur battery is a half-battery, the lithium negative electrode is a lithium metal sheet; when the lithium-organic sulfur battery is a full battery, the lithium negative electrode is lithiated carbon paper.

[0018] According to the above scheme, the lithium-sulfur electrolyte is a standard lithium-sulfur electrolyte, including lithium salt and ether solvent, wherein the lithium salt is lithium bistrifluoromethylsulfonyl imide (LiTFSI) and lithium nitrate (LiNO3), and the ether solvent is ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL).

[0019] Preferably, the concentration of LiTFSI is 1.0-1.5 mol / L, the concentration of LiNO3 is 0.15-0.25 mol / L, and the volume ratio of DME to DOL is (0.8-1.2):1.

[0020] According to the above scheme, the negative electrode material of the lithium-organic sulfur battery is lithium metal sheet or lithiated carbon paper (Li-CP).

[0021] Preferably, the Li-CP material is formed by assembling carbon paper and lithium metal into a half-cell in a carbonate electrolyte, and then completely discharging and inserting lithium to form Li-CP.

[0022] More preferably, in the carbonate electrolyte, the lithium salt is lithium hexafluorophosphate (LiPF6), and the ester solvents are ethylene carbonate (EC) and diethyl carbonate (DEC), wherein the concentration of LiPF6 is 1.0~1.5 mol / L, and the volume ratio of EC and DEC is (0.8~1.2):1.

[0023] According to the above scheme, the membrane is Celgard 2400.

[0024] Provided is an application of the above-mentioned annular lithium-organic sulfur battery positive electrode material in lithium battery positive electrode.

[0025] The present invention provides a lithium-organic sulfur battery positive electrode material HTBCO, which is poorly soluble in standard lithium-sulfur electrolyte and exhibits excellent electrochemical performance in lithium half-cells. The discharge product of HTBCO, Li2-TBBT, dissolves in the electrolyte in the initial cycle and then participates in the formation of an organic / inorganic composite SEI on the surface of the lithium negative electrode. In addition, Li2-TBBT also weakens the Li + The solvation structure of the electrolyte improves the stability of the electrode / electrolyte interface. The synergistic effect of the two effectively inhibits the + Solvent co-intercalation of DME enables highly reversible Li + Insertion and removal.

[0026] The beneficial effects of the present invention are:

[0027] 1. The organic sulfur cathode material provided by the present invention is poorly soluble in liquid electrolyte, which reduces the loss of active materials and exhibits excellent electrochemical performance in lithium half-cells with lithium metal sheets as lithium negative electrodes. At the same time, since the discharge product of HTBCO dissolves in the electrolyte during the initial cycle and then participates in the formation of an organic / inorganic composite SEI layer on the negative electrode surface; in addition, the discharge product Li2-TBBT also changes the Li + The solvation structure improves the stability of the electrode / electrolyte interface and effectively inhibits the Li + The solvent co-intercalation of -DME enables the full battery assembled with Li-CP negative electrode and HTBCO positive electrode to achieve ultra-stable long-term cycling in ether electrolyte.

[0028] 2. The lithium-organic sulfur battery provided by the present invention uses HTBCO as the positive electrode material, which is poorly soluble in the electrolyte. This reduces the loss of active material during battery cycling. The SEI formed by the discharge products can also improve the compatibility of the Li-CP negative electrode with ether electrolytes. Data show that the Li / HTBCO half-cell can stably cycle 1000 times at a rate of 1 C, with an average Coulombic efficiency of up to 99.9%. The Li-CP / HTBCO full cell exhibits a capacity retention rate of 65% after 1000 cycles at a rate of 1 C. The poorly soluble HTBCO positive electrode material provided by the present invention addresses two major challenges facing lithium-organic sulfur batteries, improving their cycling stability. Using Li-CP instead of lithium metal as the negative electrode significantly improves battery safety and makes lithium-organic sulfur batteries potentially commercially viable. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 IR spectra of HTBCO and raw material TBBT synthesized in Example 1 of the present invention.

[0030] Figure 2 The Raman spectra of HTBCO, raw material TBBT and S synthesized in Example 1 of the present invention are shown.

[0031] Figure 3 This is the mass spectrum of HTBCO synthesized in Example 1 of the present invention.

[0032] Figure 4 This is the mass spectrum of the discharge product Li2-TBBT after the Li / HTBCO battery in Example 1 of the present invention is cycled 10 times and replaced by proton hydrogen.

[0033] Figure 5 This is the mass spectrum of the corresponding charging product HTBCO after the Li / HTBCO battery in Example 1 of the present invention is cycled 10 times.

[0034] Figure 6 This is a charge-discharge cycle performance diagram of a lithium-organic sulfur battery (Li / HTBCO) assembled with HTBCO positive electrode material prepared in Example 1 of the present invention at a rate of 1 C.

[0035] Figure 7 The XRD spectra of the Toray carbon paper and the lithiated Toray carbon paper in Example 2 of the present invention are shown. The enlarged XRD pattern shows a (002) diffraction region between 21° and 31°.

[0036] Figure 8 In situ XRD patterns and corresponding voltage curves of Li-CP in the Li-CP / HTBCO full cell in Example 2 of the present invention during the third and fourth cycles.

[0037] Figure 9 This is a charge and discharge cycle performance diagram of the Li-CP / HTBCO battery in Example 2 of the present invention at a 1 C rate.

[0038] Figure 10 This is the SEM cross-sectional image of the Li-CP prepared in Example 2 of the present invention.

[0039] Figure 11 This is a cross-sectional SEM image of the Li-CP in the Li-CP / HTBCO battery after 6 cycles in Example 2 of the present invention.

[0040] Figure 12 This is the XPS spectrum of Li 1s of the Li-CP negative electrode of the Li / HTBCO battery prepared in Example 2 of the present invention after 10 cycles.

[0041] Figure 13 These are Raman spectra of the changes in free DME and coordinated DME in the blank Li-S electrolyte and the Li-S electrolyte containing Li2-TBBT in Example 2 of the present invention.

[0042] Figure 14 TFSI in the blank Li-S electrolyte and the Li-S electrolyte containing Li2-TBBT in Example 2 of the present invention - , CIP, and AGG changes in Raman spectra. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings.

[0044] Example 1

[0045] A method for preparing a positive electrode of a lithium-organic sulfur battery comprises the following steps:

[0046] 1) Preparation of HTBCO: Add 200 μL of DMSO to 50 mg of 4,4'-thiobisthiophenol (TBBT) and stir at room temperature for 12 hours. This yields a white solid, which is then washed three times with acetone. The precipitate is then dried in a vacuum oven at 60°C for 12 hours to yield a white HTBCO solid. The HTBCO structure is as follows:

[0047] .

[0048] Figure 1 This is the infrared (FTIR) spectrum of HTBCO and raw material TBBT prepared in Example 1 of the present invention. The infrared shift of SH in the TBBT molecule is at 2550 cm -1 HTBCO at 2550 cm -1The disappearance of the characteristic peak of SH bond at δ1+1 confirms that hydrogen is abstracted.

[0049] Figure 2 The Raman spectra of HTBCO, sulfur and TBBT prepared in Example 1 of the present invention are shown in Figure 1. The Raman shift of SS in the sulfur molecule is between 450-500 cm -1 The absence of characteristic absorption peaks of TBBT molecules in this region and the appearance of characteristic peaks of HTBCO molecules in this region confirm that hydrogen is abstracted and SS bonds are formed.

[0050] Figure 3 This is the mass spectrum of HTBCO prepared in Example 1 of the present invention, and product C is detected. 24 S6H 16 , its mass-to-charge ratio is 496.9658.

[0051] 2) Positive Electrode Preparation: Add 70 mg of CNTs and 30 mg of HTBCO obtained in step 1) to a beaker, followed by 350 mL of anhydrous ethanol. Ultrasonicate for 30 minutes, filter, and wash several times with anhydrous ethanol. Dry in a vacuum oven at 60°C for 12 hours. Cut the dried positive electrode into slices approximately 1.13 cm in area using a microtome. 2 The circular piece with a diameter of 12 mm is the organic sulfur positive electrode. The amount of HTBCO supported in the circular piece is 1.3 mg cm -2 .

[0052] Lithium-organic sulfur CR2032 button cells were assembled. The battery structure consisted of the organosulfur cathode obtained in this example, a lithium metal anode, a separator, and an electrolyte. The electrolyte consisted of 1 mol / L LiTFSI and 0.15 mol / L LiNO₃ dissolved in a 1:1 (volume ratio) DME / DOL solution. The lithium metal anode was 450 μm thick and 15.6 mm in diameter. The separator was Celgard 2400 with a diameter of 19 mm.

[0053] The electrochemical performance of the lithium-organic sulfur CR2032 button cell obtained in this example was tested, and the positive electrode after cycling was tested by liquid chromatography-mass spectrometry (LC-MS).

[0054] Figure 4 This is the mass spectrum of the positive electrode of the lithium-organic sulfur CR2032 button battery obtained in this example in the discharged state. The discharge product Li2-TBBT was detected. Since lithium ions were replaced by hydrogen protons during the detection process, the product is TBBT with a mass-to-charge ratio of 249.9908.

[0055] Figure 5This is the mass spectrum of the positive electrode of the lithium-organic sulfur CR2032 button battery obtained in this example under charging state, and the charging product C is detected. 24 S6H 16 , its mass-to-charge ratio is 495.9493.

[0056] Figure 6 This is a graph showing the cycling performance of the lithium-organic sulfur battery (Li / HTBCO) prepared in Example 1 of the present invention at a rate of 1 C. The graph shows that the battery can stably cycle 1000 times with an average coulombic efficiency of 99.9%.

[0057] Example 2

[0058] A method for preparing a lithium-organic sulfur battery positive electrode and a Li-CP negative electrode specifically comprises the following steps:

[0059] 1) Preparation of Li-CP: Toray carbon paper (CP) was cut into small circular pieces with a diameter of 12 mm and dried in an oven at 100°C for 24 hours. A lithium-to-carbon paper battery (Li / CP) was then assembled using a carbonate electrolyte. The battery was discharged at a rate of 0.025 C to 0.01 V to allow lithium to be intercalated into the graphite layer. After discharge, the battery was disassembled, and the Li-CP electrode was removed, cleaned with dimethylbenzene (DME), and dried.

[0060] A Li / CP battery was assembled, consisting of a Toray carbon paper positive electrode, a lithium metal anode, a separator, and an electrolyte. The electrolyte consisted of 1 mol / L LiPF₆ dissolved in a 1:1 (volume) solution of EC / DEC. The lithium metal anode was 450 μm thick and 15.6 mm in diameter. The separator was Celgard 2400 with a diameter of 19 mm.

[0061] 2) Positive Electrode Preparation: 70 mg of CNTs and 40 mg of HTBCO obtained in Example 1 were added to a beaker, followed by 350 mL of anhydrous ethanol. Ultrasonication was performed for 30 minutes, followed by filtration and washing with anhydrous ethanol several times. Drying was performed in a vacuum oven at 60°C for 12 hours. The dried positive electrode material was sliced ​​into approximately 1.13 cm sections using a microtome. 2 The circular piece with a diameter of 12 mm is the organic sulfur positive electrode. The amount of HTBCO supported in the circular piece is 1.5 mg cm -2 .

[0062] The HTBCO positive electrode obtained in this example was reassembled with Li-CP, a separator, and a nickel mesh into a CR2032 button-type Li-CP / HTBCO battery. The electrolyte was a standard lithium-sulfur electrolyte. Electrochemical performance tests were performed, and the negative electrode before and after cycling was subjected to X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Raman spectroscopy (Raman) testing was also performed on the electrolyte.

[0063] Figure 7 The XRD patterns of Li-CP and CP prepared in Example 2 of the present invention show the characteristic peaks of graphite. As shown in the figure, the signal peak of CP at 26.4° corresponds to the characteristic diffraction peak of graphite. After lithium is embedded in CP, the spacing between graphite layers increases, and the signal peak shifts to a lower angle of 24.1°.

[0064] Figure 8 The in-situ XRD patterns of the third and fourth cycles of the lithiated carbon paper-organic sulfur CR2032 button battery obtained in this example are as follows. In the third cycle of charging, lithium ions are embedded in the graphite layer, the graphite layer spacing increases, and the signal peak shifts to a low angle. During the discharge process, lithium ions gradually escape, the layer spacing gradually recovers, and the signal peak shifts to a high angle. This pattern is still observed in the fourth cycle, confirming that in the Li-CP / HTBCO battery, Li + Highly reversible deintercalation and intercalation can be performed in graphite layers.

[0065] Figure 9 This is a cycling performance diagram of the Li-CP / HTBCO battery prepared in Example 2 of the present invention at a rate of 1 C. The diagram shows that the battery can stably charge and discharge for 1000 cycles, and still has a capacity retention rate of 65% after 1000 cycles.

[0066] The cross-section of the Li-CP before and after cycling in the Li-CP / HTBCO battery was characterized. Figure 10 It can be seen from the SEM image that the SEI formed by Li-CP in carbonate electrolyte is relatively thin. Figure 11 This is the cross section of Li-CP after 6 cycles in Li-CP / HTBCO battery. From the SEM image, it can be seen that a thicker SEI layer is formed on the surface of Li-CP after cycling, which effectively prevents Li + -Solvent co-intercalation of DME.

[0067] Figure 12This is the Li 1s XPS spectrum of the Li-CP anode of the Li / HTBCO battery prepared in Example 2 after 10 cycles. The figure shows that after 10 cycles, in addition to LiF, the discharge product Li2-TBBT was also detected on the anode surface, indicating that during the initial cycling stage, the discharge products participated in forming an organic / inorganic composite SEI on the anode surface.

[0068] Raman spectroscopy was performed on the above-mentioned Li-S electrolyte and the Li-S electrolyte containing Li2-TBBT. Figure 13 Middle 820~870 cm -1 The weakening of the peaks between the two groups indicates that the free DME molecules decrease after adding Li2-TBBT, while the enhancement of the coordinated DME peak is due to the simultaneous reaction of DME with Li + Coordinated with Li2-TBBT. Figure 14 Shown at 725 to 760 cm -1 Freedom TFSI - , contact ion pairs (CIP) and aggregates (AGG). After adding Li2-TBBT, the proportion of CIP increased, accompanied by a decrease in free DME molecules and an increase in coordinated DME, indicating that Li + -DME ratio is reduced, and part of DME is coordinated with Li2-TBBT. Therefore, the discharge product of HTBCO can reduce Li + and DME, while the increase of CIP is beneficial to improving the compatibility of the electrode / electrolyte interface.

[0069] Obviously, the above embodiments are merely examples for illustrative purposes and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. However, any obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. Application of HTBCO as a cathode material for a lithium-organic sulfur battery, wherein the electrolyte of the lithium-organic sulfur battery comprises a lithium salt and an ether solvent, wherein the lithium salt is lithium bis(trifluoromethylsulfonyl)imide and lithium nitrate, and the ether solvent is ethylene glycol dimethyl ether and 1,3-dioxolane, characterized in that: The structure of HTBCO is as follows: 。 2. The use according to claim 1, characterized in that The preparation method of HTBCO comprises the following steps: Take 4,4'-thiobisthiophenol as the raw material and stir the reaction in dimethyl sulfoxide solution for 10-12 hours to obtain HTBCO.

3. A lithium-organic sulfur battery positive electrode, wherein the electrolyte of the lithium-organic sulfur battery comprises a lithium salt and an ether solvent, wherein the lithium salt is lithium bis(trifluoromethylsulfonyl)imide and lithium nitrate, and the ether solvent is ethylene glycol dimethyl ether and 1,3-dioxolane, characterized in that: It includes a positive electrode material HTBCO and a multi-walled carbon nanotube substrate loaded with the HTBCO; wherein the structure of the HTBCO is as follows: 。 4. The lithium-organic sulfur battery positive electrode according to claim 3, characterized in that The HTBCO loading is 1.3-1.5 mg cm -2 .

5. A method for preparing a positive electrode of a battery according to claim 3, characterized in that: The following steps are involved: Multi-walled carbon nanotubes and HTBCO are uniformly dispersed in anhydrous ethanol solvent by ultrasonication, and then post-treated to obtain a positive electrode material loaded with HTBCO.

6. The preparation method according to claim 5, characterized in that The mass ratio of the multi-walled carbon nanotubes to HTBCO is 1.5-2.5:

1.

7. A lithium-organic sulfur battery comprising a lithium-sulfur electrolyte, a separator and a lithium negative electrode, wherein the lithium-sulfur electrolyte comprises a lithium salt and an ether solvent, wherein the lithium salt is lithium bis(trifluoromethylsulfonyl)imide and lithium nitrate, and the ether solvent is ethylene glycol dimethyl ether and 1,3-dioxolane, characterized in that: It also includes the positive electrode according to claim 3; the lithium negative electrode is a lithium metal sheet or lithiated carbon paper; wherein: when the lithium-organic sulfur battery is a half-cell, the lithium negative electrode is a lithium metal sheet; when the lithium-organic sulfur battery is a full cell, the lithium negative electrode is lithiated carbon paper.

8. The lithium-organic sulfur battery according to claim 7, characterized in that Lithiated carbon paper is prepared by assembling carbon paper and lithium metal into a half-cell in a carbonate electrolyte, and then fully discharging and inserting lithium to form lithiated carbon paper.

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