Lithium-sulfur battery electrolyte containing additives, and preparation method and application thereof

Abstract

The application belongs to the technical field of batteries, and particularly relates to a lithium-sulfur battery electrolyte containing an additive, a preparation method and application thereof, which is composed of the following components: 0.5wt%-15wt% of an additive, 0.01-15mol / L of lithium salt and 1L of an ether solvent; the additive is one or more transition metal alkoxides. The transition metal alkoxide is introduced as the additive, the metal salt generated by the reaction of the additive and the sulfur positive electrode can effectively absorb polysulfides and simultaneously catalyze the conversion of the polysulfides, so that the capacity and long cycle stability of the lithium-sulfur battery are obviously improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a lithium-sulfur battery electrolyte containing an additive as well as a preparation method and application thereof. BACKGROUND

[0002] In a new energy storage system, a traditional lithium-sulfur battery with lithium metal as a negative electrode and elemental sulfur as a positive electrode has a theoretical energy density of 2600 Wh / kg and a theoretical volume energy density of 2800 Wh / L. Meanwhile, elemental sulfur has advantages of low price, rich resources and environmental friendliness, so that the system is extremely valuable in business and is considered as one of the most potential next-generation high-specific-energy secondary battery systems.

[0003] Although the lithium-sulfur battery has great advantages in energy density and cost, there are still many problems to be solved. The most important problem is that the soluble polysulfides are generated in the sulfur positive electrode during the charging and discharging process, and migrate under the action of the electric field and the concentration field to cause the shuttle effect. On the one hand, the shuttle effect reduces the utilization rate of the positive active material, and on the other hand, the polysulfides react with the lithium negative electrode to consume the metal lithium. These problems cause the rapid attenuation of the specific capacity and the reduction of the coulombic efficiency of the lithium-sulfur battery, resulting in the decline of the battery performance.

[0004] In view of the above problems, the current research progress is mainly focused on the positive electrode material. By introducing catalysts such as oxides, sulfides or nitrides into the positive electrode, the shuttle effect of the polysulfide ions can be inhibited to some extent, and the utilization rate of the active material can be improved. Or the structure of the sulfur positive electrode material is modified, for example, binary metal sulfides, organic sulfides, sulfur / metal oxide composite materials, sulfur / carbon composite materials, sulfur / polymer composite materials, etc. However, this method will greatly increase the cost, which is not conducive to the wide application and promotion of the lithium-sulfur battery. SUMMARY

[0005] In order to solve the above technical problems, the application provides a lithium-sulfur battery electrolyte containing an additive as well as a preparation method and application thereof. The additive can react with the sulfur positive electrode to generate a metal salt, and the metal salt can absorb the polysulfides and catalyze the conversion of the polysulfides at the same time, so that the capacity and long cycle stability of the lithium-sulfur battery are greatly improved.

[0006] The application is realized by the following technical solutions.

[0007] The first object of the application is to provide a lithium-sulfur battery electrolyte containing an additive, which is composed of the following components:

[0008] The additive is 0.5wt%-15wt%, the lithium salt is 0.01-15mol / L, and the ether solvent is 1L.

[0009] The additive is one or more transition metal alkoxides.

[0010] Preferably, the additive is one or more of aluminum isopropoxide, molybdenum isopropoxide, magnesium isopropoxide, indium isopropoxide, magnesium isopropoxide, sodium isopropoxide.

[0011] Preferably, the mass fraction of the additive is 0.5% to 5%.

[0012] Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate.

[0013] Preferably, the solvent is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran / dimethyltrisulfide, dimethyl disulfide, dimethyl sulfide, dipropylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,3-dioxolane.

[0014] A second object of the present application is to provide a preparation method of the additive-containing lithium-sulfur battery electrolyte, comprising the following steps:

[0015] Under a protective gas atmosphere, the lithium salt and the additive are added to the ether solvent and stirred and dissolved to obtain the electrolyte.

[0016] A third object of the present application is to provide the application of the additive-containing lithium-sulfur battery electrolyte in lithium-sulfur batteries.

[0017] Preferably, the composite sulfur / carbon material is used as the active material, a conductive agent, a binder and a solvent are added respectively and stirred sufficiently, and after being mixed uniformly, the mixture is coated on an aluminum foil, dried and cut into circular electrode pieces with a diameter of 12 mm; lithium metal is used as the negative electrode active material, a polypropylene separator is selected, and the positive and negative electrode pieces, the separator and the electrolyte are assembled in sequence to form a CR2032 lithium-sulfur battery.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] The present application introduces transition metal alkoxides as additives, the additive is a transition metal alkoxide, which can form a significant metal-organic compound on the surface of the sulfur positive electrode, the metal salt generated by the reaction of the additive and the sulfur positive electrode can effectively adsorb polysulfides, and at the same time catalyze the conversion of polysulfides, thereby significantly improving the capacity and long cycle stability of the lithium-sulfur battery.

[0020] The present application improves the performance of lithium-sulfur batteries by improving the composition of the electrolyte, the raw materials are easy to obtain, the cost is low, the method is simple and efficient, and is suitable for wide range of popularization and use. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The first charge-discharge process curve of Example 1 and Comparative Example 1 of the present application.

[0022] Figure 2 The cycle performance of Example 1 and Comparative Example 1 of the present application at a current density of 2C. DETAILED DESCRIPTION

[0023] In order to enable a person skilled in the art to better understand the technical solutions of the present application and to implement them, the present application will be further described below in conjunction with specific embodiments and drawings, but the embodiments are not limiting on the present application.

[0024] The experimental methods and detection methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0025] The present application provides a lithium-sulfur battery electrolyte, the components comprising:

[0026] 1) Additive: one or more transition metal alcoholates, the mass fraction of the additive being 0.5% to 15%.

[0027] 2) Lithium salt: one or more lithium salts, the concentration of the lithium salt being 0.01 to 15 mol / L.

[0028] 3) Solvent: one or more of ether compounds.

[0029] The additive is one or more of aluminum isopropoxide, molybdenum isopropoxide, magnesium isopropoxide, indium isopropoxide, magnesium isopropoxide, and sodium isopropoxide. Preferably, the mass fraction of the additive is 0.5% to 5%.

[0030] The lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluoro(oxalato)borate. Preferably, the concentration of the lithium salt is 0.1 to 3 mol / L.

[0031] The solvent is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran / dimethyl trisulfide, dimethyl disulfide, dimethyl sulfide, dipropylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane.

[0032] The additive-containing electrolyte is applied to a lithium-sulfur battery. The lithium-sulfur battery comprises a positive electrode, a negative electrode, a separator and the electrolyte; the positive electrode is one or more of elemental sulfur, a sulfur-containing composite material, lithium polysulfide and a composite material thereof; the negative electrode is one or more of metallic lithium, a lithium metal alloy, a lithium-containing composite material; the separator is one or more of polyethylene, polypropylene, polyvinylidene fluoride, polymethyl methacrylate and glass fiber.

[0033] The following is specifically illustrated by the following examples.

[0034] Example 1

[0035] 1) Preparation of the electrolyte

[0036] In an argon-filled glove box (moisture content <0.1 ppm, oxygen content <0.1 ppm), ethylene glycol dimethyl ether and 1,3-dioxolane were mixed uniformly at a volume ratio of 1:1 and continuously stirred, 1 mol / L lithium bis(trifluoromethanesulfonyl)imide was added to the mixed solvent, and then 2% by mass of molybdenum isopropoxide was added, and stirred until completely dissolved, thereby obtaining the electrolyte of the present example.

[0037] 2) Assembly of the lithium-sulfur battery

[0038] A composite sulfur / carbon material was used as the active material, and a conductive agent, a binder and a solvent were added and stirred thoroughly, and then coated on an aluminum foil, and cut into a circular electrode with a diameter of 12 mm after drying; metallic lithium was used as the negative electrode active material, and a polypropylene separator was selected, and the positive and negative electrode pieces, the separator and the electrolyte were assembled in sequence into a CR2032 lithium-sulfur battery. The specific raw material addition amount can use the parameters in the existing CR2032 lithium-sulfur battery, and will not be described in detail.

[0039] Example 2

[0040] 1) Preparation of the electrolyte

[0041] In an argon-filled glove box (moisture content <0.1 ppm, oxygen content <0.1 ppm), ethylene glycol dimethyl ether and 1,3-dioxolane were mixed uniformly at a volume ratio of 1:1 and continuously stirred, 1 mol / L lithium bis(trifluoromethanesulfonyl)imide was added to the mixed solvent, and then 1% by mass of molybdenum isopropoxide was added, and stirred until completely dissolved, thereby obtaining the electrolyte of the present example.

[0042] 2) The lithium-sulfur battery was assembled according to the method described in Example 1.

[0043] Example 3

[0044] 1) Preparation of the electrolyte

[0045] In an argon-filled glove box (moisture content <0.1ppm, oxygen content <0.1ppm), ethylene glycol dimethyl ether and 1,3-dioxolane are mixed evenly at a volume ratio of 1:1 and stirred continuously. 1 mol / L of lithium bis(trifluoromethanesulfonyl)imide is added to the mixed solvent, followed by 3% magnesium isopropoxide by mass. The mixture is stirred until completely dissolved to obtain the electrolyte of this embodiment.

[0046] 2) Assemble the lithium-sulfur battery as described in Example 1

[0047] Comparative Example 1

[0048] 1) Preparation of electrolyte

[0049] In an argon-filled glove box (moisture content <0.1ppm, oxygen content <0.1ppm), ethylene glycol dimethyl ether and 1,3-dioxolane are mixed evenly at a volume ratio of 1:1 and stirred continuously. 1 mol / L of lithium bis(trifluoromethanesulfonylimide) is added to the mixed solvent and stirred until completely dissolved to obtain the electrolyte of this comparative example.

[0050] 2) Assemble the lithium-sulfur battery as described in Example 1

[0051] Comparative Example 2

[0052] 1) Preparation of electrolyte

[0053] In an argon-filled glove box (moisture content <0.1ppm, oxygen content <0.1ppm), ethylene glycol dimethyl ether and 1,3-dioxolane are mixed evenly at a volume ratio of 1:1 and stirred continuously. 0.5mol / L lithium bis(trifluoromethanesulfonylimide) is added to the mixed solvent and stirred until completely dissolved to obtain the electrolyte of this comparative example.

[0054] 2) Assemble the lithium-sulfur battery as described in Example 1

[0055] Effect comparison

[0056] 1) After the batteries prepared in Example 1 and Comparative Example 1 were allowed to stand at room temperature for 12 hours, their electrochemical performance was tested on a blue electrode tester. The voltage range was 1.7-2.8V, and the current density was 0.2C (1C = 1672mAh / g). The initial charge-discharge curves are shown below. Figure 1 As shown. By Figure 1 It can be seen that the discharge specific capacity of Comparative Example 1 is 850 mAh / g, and the discharge specific capacity of Example 1 is 1136 mAh / g, which shows that the additive of the present invention can significantly improve the discharge specific capacity of lithium-sulfur batteries.

[0057] 2) After the battery prepared in Example 1 and Comparative Example 1 was left to stand at room temperature for 12 h, electrochemical performance test was carried out on a blue cell tester, the voltage interval was 1.7-2.8 V, the current density was 2 C (1 C = 1672 mAh / g), and the cycle performance was as shown in Figure 2 Figure 2 It can be seen that the initial discharge specific capacity of Comparative Example 1 was 650 mAh / g, the discharge specific capacity after 100 cycles was 530 mAh / g, and the cycle retention rate was 81.5%; the initial discharge specific capacity of Example 1 was 870 mAh / g, the discharge specific capacity after 100 cycles was 820 mAh / g, and the cycle retention rate was 94.3%. Due to the presence of the additive in Example 1, the additive can react with the sulfur positive electrode to form a metal salt, the metal salt can catalyze the conversion of polysulfides while adsorbing polysulfides, the dissolution and conversion of polysulfides are faster, the utilization rate of active substances is improved compared with Comparative Example 1, which is beneficial to the capacity release and long cycle stability of lithium-sulfur batteries. The performance of Example 2-Example 3 is similar to that of Example 1.

[0058] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, these modifications and variations are also intended to be included.​

Claims

1. A lithium-sulfur battery electrolyte containing additives, characterized in that, It consists of the following components: Additives 0.5~15wt%, lithium salt 0.01~15 mol / L, ether solvent 1L; The additive is one or more of aluminum isopropoxide, molybdenum isopropoxide, magnesium isopropoxide, indium isopropoxide, and sodium isopropoxide.

2. The lithium-sulfur battery electrolyte containing additives according to claim 1, characterized in that, The mass fraction of the additive is 0.5-5%.

3. The lithium-sulfur battery electrolyte containing additives according to claim 1, characterized in that, The lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalate)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalateborate.

4. The lithium-sulfur battery electrolyte containing additives according to claim 1, characterized in that, The ether solvent is one or more of the following: ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran / dimethyl trisulfide, dimethyl disulfide, dimethyl sulfide, dipropylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane.

5. The method for preparing the additive-containing lithium-sulfur battery electrolyte according to any one of claims 1-4, characterized in that, Includes the following steps: Under a protective gas atmosphere, lithium salt and additives are added to an ether solvent and stirred to dissolve, thus obtaining the electrolyte. The electrolyte contains 0.5-15 wt% additives, 0.01-15 mol / L lithium salt, and 1 L of ether solvent; the additives are one or more of aluminum isopropoxide, molybdenum isopropoxide, magnesium isopropoxide, indium isopropoxide, and sodium isopropoxide.

6. The application of the additive-containing lithium-sulfur battery electrolyte according to claim 1 in lithium-sulfur batteries.

7. The application according to claim 6, characterized in that, Using composite sulfur / carbon material as the active material, a conductive agent, binder and solvent are added and stirred thoroughly. After being mixed evenly, the mixture is coated on aluminum foil, dried and cut into circular electrode sheets. Using lithium metal as the negative electrode active material and a polypropylene separator, the positive and negative electrode sheets, separator and electrolyte are assembled in sequence to form a CR2032 lithium-sulfur battery.

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