阅读说明：本技术 一种锂硫电池电解液及其制备方法 (Lithium-sulfur battery electrolyte and preparation method thereof ) 是由 李西尧 张强 于 2021-07-07 设计创作，主要内容包括：本发明公开了属于能源化学技术领域的一种锂硫电池电解液及其制备方法。所述电解液包括有机溶剂、锂盐和高活性添加剂,高活性添加剂的结构为A-S-(n)-B、A-Se-(n)-B或A-Te-(n)-B的有机硫、硒、碲醚类中的一种或几种。通过引入含Se–Se、S–S或Te–Te键一种或几种的系列高活性添加剂,在电池充放电时发生可逆裂解和重组,与锂硫电池的中间产物多硫化物Li-(2)S-(x)作用,参与硫的氧化还原过程,生成反应性和扩散能力优异的有机多硫化物RS-(x+n)Li、RSe-(n)S-(x)Li或RTe-(n)S-(x)Li促进反应动力学,提升硫化锂的化学氧化活性物质的利用率,改善电化学反应的可逆性、循环性能和能量密度,提升电池整体性能。(The invention discloses a lithium-sulfur battery electrolyte and a preparation method thereof, belonging to the technical field of energy chemistry. The electrolyte comprises an organic solvent, lithium salt and a high-activity additive, wherein the structure of the high-activity additive is A-S n ‑B、A‑Se n -B or A-Te n One or more of organic sulfur, selenium and tellurium ether of-B. By introducing series of high-activity additives containing one or more of Se-Se, S-S or Te-Te bonds, reversible cracking and recombination occur during charging and discharging of the battery, and polysulfide Li, an intermediate product of the lithium-sulfur battery 2 S x Acts to participate in the redox process of sulfur to generate an organic polysulfide RS with excellent reactivity and diffusion capability x+n Li、RSe n S x Li or RTe n S x Li promotes reaction kinetics and promotes chemical oxygen of lithium sulfideThe utilization rate of the active substance is improved, the reversibility, the cycle performance and the energy density of the electrochemical reaction are improved, and the overall performance of the battery is improved.)

1. The lithium-sulfur battery electrolyte comprises an organic solvent and a lithium salt, and is characterized by further comprising a high-activity additive, wherein the structure of the high-activity additive is A-S_n-B、A-Se_n-B or A-Te_nOne or more of organic sulfur, selenium and tellurium ether of-B.

2. The lithium sulfur battery electrolyte as defined in claim 1 wherein n is a natural number of 1 to 10.

3. The lithium sulfur battery electrolyte as defined in claim 2 wherein n is a natural number of 3 to 10.

4. The lithium sulfur battery electrolyte of claim 1 wherein the number of carbon atoms in the a and B groups is from 1 to 8.

5. A lithium sulfur battery electrolyte according to claim 4 wherein the A and B group species comprise hydrocarbyl or phenyl; further, a halogenated hydrocarbon group or a halogenated aryl group is included.

6. The electrolyte for a lithium-sulfur battery according to claim 1, wherein the amount of the organic solvent is controlled so that the concentration of the highly active additive is 1 to 2000 mmol/L; the concentration of the lithium salt is 0.1-5 mol/L.

7. The lithium sulfur battery electrolyte as claimed in claim 1 wherein the organic solvent is 1, 3-Dioxolane (DOL), Ethylene Carbonate (EC), ethylene glycol dimethyl ether (DME), fluoroether (HFE), Propylene Carbonate (PC), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TEGDME), tetraethylene glycol dimethyl ether (TEGDME), dimethyl carbonate (DMC), carbon disulfide (CS)₂) Diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), dimethyl sulfoxide (DMSO)) One or more of Dimethylformamide (DMF) or fluoroethylene carbonate (FEC).

8. The lithium sulfur battery electrolyte as claimed in claim 1, wherein the lithium salt is lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium trifluoromethanesulfonate (LiTfO), lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (pentafluoroethanesulfonyl) imide (LiBETI), lithium bis (perfluoro-1-butanesulfonyl) imide (libbi), lithium tetrafluoroborate (LiBF)₄) Lithium iodide (LiI), lithium bromide (LiBr), lithium perchlorate (LiClO)₄) Lithium metaphosphate (LiPO)₃) Or lithium nitrate (LiNO)₃) One or more than one of (a).

9. A method of preparing a lithium sulphur battery electrolyte according to any of claims 1 to 8, characterised by the steps of: under the protection of inert gas, adding lithium salt into an organic solvent or a mixed organic solvent, then adding a high-activity additive, and fully and uniformly stirring to obtain a lithium-sulfur battery electrolyte; the inert gas is at least one of nitrogen, helium and argon; the water content in the inert gas is less than 0.1ppm, and the oxygen content is less than 0.1 ppm.

10. Use of the lithium sulphur battery electrolyte according to any of claims 1-8 in a lithium sulphur battery.

Technical Field

The invention belongs to the technical field of energy chemistry, and particularly relates to a lithium-sulfur battery electrolyte and a preparation method thereof.

Background

The continuous development of human society is accompanied by the increasing demand for energy, and the traditional fossil resources can not meet the increasing demand for energy, and the development and utilization of high-efficiency new energy become important means for relieving the pressure of environmental protection and guaranteeing the safety of energy structures. Battery systems play a crucial role in the conversion and storage of new energy.

In various energy consumption occasions including electric automobiles, consumer electronics and smart grids, commercial lithium ion batteries occupy the dominant position in an energy storage system, but the relevant performance indexes of the lithium ion batteries are close to the theoretical upper limit. Therefore, it is urgent to develop a next-generation rechargeable battery with high energy density. Lithium sulfur (Li-S) battery 2600Wh kg for it^-1Are receiving attention for extremely high theoretical energy density and low cost cathode materials.

However, the slow polysulfide conversion kinetics of the sulfur positive electrode seriously hinders the performance of the Li-S battery, and becomes one of the bottleneck problems of the practical application of the Li-S battery. In particular, lithium polysulfide (LiPS), an intermediate product of Li-S batteries, has a low diffusion capacity, limited solubility and poor surface reactivity, which severely inhibit the kinetics of conversion of sulfur species during discharge. In addition, due to the accumulation of LiPS in the electrolyte, solid Li having high activation energy and poor conductivity is unevenly precipitated on the surface of the positive electrode during discharge₂S, large particle Li₂S is difficult to recycle in subsequent processes, creating a huge barrier to the conversion of sulfur species in the charging process.

The electrolyte is an essential component in the Li-S battery, and has important prospect for solving the problems starting from the Li-S battery electrolyte. However, how to prepare the lithium-sulfur battery electrolyte with outstanding electrochemical performance and suitable for practical use becomes a great problem at present, and if the problem is successfully solved, a foundation is laid for the lithium-sulfur battery to be applied in a large scale.

Disclosure of Invention

In order to solve the problems, the invention provides an electrolyte for a lithium-sulfur battery, which has high specific discharge capacity and energy density, and can maintain high capacity retention rate and good cycle performance at the same time, in order to solve the problem of conversion kinetics faced by the lithium-sulfur battery.

A lithium-sulfur battery electrolyte comprises an organic solvent, a lithium salt and a high-activity additive, wherein the structure of the high-activity additive is A-S_n-B、A-Se_n-B or A-Te_nOne or more of organic sulfur, selenium and tellurium ether of-B.

N is a natural number of 1-10; further, n is a natural number of 3 to 10.

The number of carbon atoms of the A and B groups is 1-8.

The A and B group species include hydrocarbyl or phenyl; further, a halogenated hydrocarbon group or a halogenated aryl group; specifically, the alkyl group includes methyl, ethyl, propyl, isopropyl, tert-butyl, n-butyl, isobutyl, phenyl, benzyl, tolyl, fluoromethyl, chloromethyl, bromomethyl, and iodomethyl groups.

In the electrolyte, the dosage of the organic solvent is controlled to ensure that the concentration of the high-activity additive is 1-2000mmol/L, and further, the concentration of the high-activity additive is 1000-2000mmol L^-1Or 1-100mmol L^-1(ii) a The concentration of the lithium salt is 0.1-5 mol/L.

The organic solvent is 1, 3-Dioxolane (DOL), Ethylene Carbonate (EC), ethylene glycol dimethyl ether (DME), fluoroether (HFE), Propylene Carbonate (PC), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TEGDME), tetraethylene glycol dimethyl ether (TEGDME), dimethyl carbonate (DMC), carbon disulfide (CS)₂) Diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), dimethyl sulfoxide (DMSO), Dimethylformamide (DMF) or fluoroethylene carbonate (FEC).

The lithium salt is bis (trifluoromethanesulfonyl) lithium imide (LiTFSI), lithium trifluoromethanesulfonate (LiTfO), lithium difluorosulfonimide (LiFSI), lithium bis (pentafluoroethanesulfonyl) imide (LiBETI), lithium bis (perfluoro-1-butanesulfonyl) imide (LiBPBI), lithium tetrafluoroborate (LiBF)₄) Lithium iodide (LiI), lithium bromide (LiBr), lithium perchlorate (LiClO)₄) Lithium metaphosphate (LiPO)₃) Or lithium nitrate (LiNO)₃) One or more than one of (a).

A preparation method of a lithium-sulfur battery electrolyte comprises the following steps: under the protection of inert gas, adding lithium salt into an organic solvent or a mixed organic solvent, then adding a high-activity additive, and fully and uniformly stirring to obtain a lithium-sulfur battery electrolyte; the inert gas is at least one of nitrogen, helium and argon; the water content in the inert gas is less than 0.1ppm, and the oxygen content is less than 0.1 ppm.

The lithium-sulfur battery electrolyte is applied to a lithium-sulfur battery.

The lithium-sulfur battery comprises a positive plate, a negative plate, a diaphragm and the lithium-sulfur battery electrolyte; the positive plate comprises a positive active material, a conductive agent, a current collector and a binder; the negative electrode sheet includes a negative active material and a binder.

The positive active material includes lithium sulfide, elemental sulfur. The conductive agent in the positive active material comprises at least one of carbon nano tubes, carbon fibers, porous carbon spheres, carbon shells, graphene oxide, graphene, thin-layer graphite sheets, metal oxides, metal nitrides and metal sulfides. The current collector comprises an aluminum foil, a copper mesh or carbon paper. The negative active material includes a lithium foil, a lithium sheet, or a lithium alloy.

The invention has the beneficial effects that:

1. the lithium-sulfur battery electrolyte provided by the invention is added with the high-activity additive to perform spontaneous chemical reaction with polysulfide, namely, the original Se-Se, S-S or Te-Te in the additive is broken and recombined to generate RSeS_xLi、RSS_xLi or RTeS_xLi (where R is an organic functional group and x is polysulfide Li₂S_xNumber of S atoms in (a) series of species. These species have high reactivity and rapid diffusion capability, thus greatly improving the conversion kinetics of the positive electrode, in particular by reducing the internal resistance of the cell and increasing the degree of reaction of the sulfur species on the positive side.

2. The lithium-sulfur battery electrolyte chemically oxidizes lithium sulfide, so that the utilization rate of active substances is improved, the reversibility, the cycle performance and the energy density of electrochemical reaction are improved, and the overall performance of the battery is improved.

3. The high-activity additive added into the lithium-sulfur battery electrolyte provided by the invention can improve the intermediate species RSeS by regulating and controlling the central atom S, Se or Te_nLi、RSS_nLi and RTeS_nKinetic activity of Li.

Drawings

FIG. 1 is a specific capacity-cycling curve after addition of the lithium sulfur battery electrolyte;

FIG. 2 is a graph of the additive's self-contributed specific capacity versus cycle after addition of the various concentrations of the highly active additive.

Detailed Description

The invention is described in further detail below with reference to the following figures and specific examples:

the lithium-sulfur battery electrolyte comprises an organic solvent, a lithium salt and a high-activity additive, wherein the structure of the high-activity additive is A-S_n-B、A-Se_n-B or A-Te_nOne or more of organic sulfur, selenium and tellurium ether of-B. n is the atomic number of S, Se or Te in the additive.

The electrolyte of the invention is reversibly cracked and recombined during the discharge and charge of the battery by introducing a series of high-activity additives containing one or more of Se-Se, S-S or Te-Te bonds, and is reacted with an intermediate polysulfide Li in a lithium-sulfur battery₂S_xThe function of the catalyst is to participate in the oxidation-reduction process of sulfur to generate organic polysulfide RS with better reactivity and diffusion capacity_x+nLi (or RSe)_nS_xLi, or RTe_nS_xLi) (x is polysulfide Li)₂S_xNumber of S atoms in) to facilitate reaction kinetics. In addition, the chemical oxidation of the lithium sulfide improves the utilization rate of active substances, improves the reversibility, the cycle performance and the energy density of electrochemical reaction, and improves the overall performance of the battery.

Specifically, S, Se and Te are both in group VIA and cause changes in chemical and electrochemical properties of the compound due to increased atomic number and changes in the extra-nuclear electron cloud; that is, the diffusivity and the reactivity show a tendency that Se and Te are stronger than S, so as to further improve the overall performance of the battery.

Wherein n is a natural number of 1 to 10. Further, n is a natural number of 3-10. As Se-Se, S-S and Te-Te bonds are easier to break than C-Se, C-S and C-Te bonds (the bond energy of C-S breakage is far higher than that of S-S breakage), the polyselenium chains, the polysulphide chains and the polysulfomite chains in the intermediate species of the polyselenide, the polysulphide and the polytelluride are easier to graft in the additive, thereby improving the diffusivity and the reaction capability of the intermediate species and playing a role in improving the kinetics. Therefore, an additive containing a plurality of active centers S, Se or Te atoms (i.e., n is 3 to 10, n is a natural number) has a stronger effect of improving the performance than an electrolyte additive when n is 1 or 2.

The number of carbon atoms in the A and B groups is 1-8.

The A and B group species include hydrocarbyl or phenyl; further, a halogenated hydrocarbon group or a halogenated aryl group; specifically, the alkyl group includes methyl, ethyl, propyl, isopropyl, tert-butyl, n-butyl, isobutyl, phenyl, benzyl, tolyl, fluoromethyl, chloromethyl, bromomethyl, and iodomethyl groups.

In the electrolyte, the dosage of the organic solvent is controlled to ensure that the concentration of the high-activity additive is 0.1-2000 mmol/L; the concentration of the lithium salt is 0.1-5 mol/L.

High concentration (more than or equal to 1000mmol L)^-1) Containing Se-Se (or: the series of active additives of the S-S, Te-Te) bond can obviously improve the early-stage cycle specific capacity of the battery, but has some negative effects on the long cycle performance of the battery; low concentration (less than or equal to 100mmol L)^-1) The improvement effect of the additive on the specific capacity at the early stage of the battery is not as obvious as that of a high-concentration group, but the additive has remarkable advantages in the aspects of cycling stability and capacity retention rate.

The organic solvent is 1, 3-Dioxolane (DOL), Ethylene Carbonate (EC), ethylene glycol dimethyl ether (DME), fluoroether (HFE), Propylene Carbonate (PC), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TEGDME), tetraethylene glycol dimethyl ether (TEGDME), dimethyl carbonate (DMC), carbon disulfide (CS)₂) Diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), dimethyl sulfoxide (DMSO), Dimethylformamide (DMF) or fluoroethylene carbonate (FEC).

The lithium salt is bis (trifluoromethanesulfonyl) lithium imide (LiTFSI), lithium trifluoromethanesulfonate (LiTfO), lithium difluorosulfonimide (LiFSI), lithium bis (pentafluoroethanesulfonyl) imide (LiBETI), lithium bis (perfluoro-1-butanesulfonyl) imide (LiBPBI), lithium tetrafluoroborate (LiBF)₄) Lithium iodide (LiI), lithium bromide (LiBr), lithium perchlorate (LiClO)₄) Lithium metaphosphate (LiPO)₃) Or lithium nitrate (LiNO)₃) One or more than one of (a).

A preparation method of a lithium-sulfur battery electrolyte comprises the following steps: under the protection of inert gas, adding lithium salt into an organic solvent or a mixed organic solvent, then adding a high-activity additive, and fully and uniformly stirring to obtain a lithium-sulfur battery electrolyte; the inert gas is at least one of nitrogen, helium and argon; the water content in the inert gas is less than 0.1ppm, and the oxygen content is less than 0.1 ppm.

The lithium-sulfur battery electrolyte is applied to the lithium-sulfur battery. The lithium-sulfur battery comprises a positive plate, a negative plate, a diaphragm and the lithium-sulfur battery electrolyte; the positive plate comprises a positive active material, a conductive agent, a current collector and a binder; the negative electrode sheet includes a negative active material and a binder. The positive active material includes lithium sulfide, elemental sulfur. The conductive agent in the positive active material comprises at least one of carbon nano tubes, carbon fibers, porous carbon spheres, carbon shells, graphene oxide, graphene, thin-layer graphite sheets, metal oxides, metal nitrides and metal sulfides. The current collector comprises an aluminum foil, a copper mesh or carbon paper. The negative active material includes a lithium foil, a lithium sheet, or a lithium alloy.

The present invention is further illustrated by the following specific examples.

Example 1

1) Preparation of the electrolyte

Mixing DOL and DME according to the volume ratio of 1:1 to obtain an organic solvent;

adding LiTFSI and LiTfO into an organic solvent, wherein the concentrations of the LiTFSI and the LiTfO in a mixed solution of the organic solvent and an electrolyte salt are respectively 1 mol/L; adding additive LiNO₃，LiNO₃The mass fraction in the whole mixed system is 2 wt%;

and finally adding dimethyl diselenide, wherein the concentration of the dimethyl diselenide in the mixed solution is controlled to be 50mmol/L, and the lithium-sulfur battery electrolyte in the embodiment 1 is obtained.

2) Preparation of lithium-sulfur battery

And sequentially loading the positive plate, the electrolyte, the diaphragm and the negative plate into the battery, standing for 6h, discharging to 1.7V by using a 0.5C constant current, and then charging to 2.6V by using a constant current, thus finishing the preparation of the lithium-sulfur battery.

Example 2

Preparation of the electrolyte

Mixing DOL and DME according to the volume ratio of 1:1 to obtain an organic solvent;

adding LiBr and LiI into an organic solvent, wherein the concentrations of the LiBr and the LiI in a mixed solution of the organic solvent and an electrolyte salt are respectively 1 mol/L; adding additive LiNO₃，LiNO₃The mass fraction in the whole mixed system is 2 wt%;

and finally, adding diphenyl diselenide, wherein the concentration of the diphenyl diselenide in the mixed solution is controlled to be 0.1mmol/L, so that the lithium-sulfur battery electrolyte in the embodiment 2 is obtained.

Assembling a lithium-sulfur battery by using the electrolyte; the processes and parameters not specified in this example were the same as in example 1.

Example 3

Preparation of the electrolyte

DME is used as an organic solvent;

addition of LiBF to an organic solvent₄，LiBF₄The concentration in the mixed solution of the organic solvent and the electrolyte salt is 5 mol/L; adding additive LiNO₃，LiNO₃The mass fraction in the whole mixed system is 5 wt%;

and finally, adding diphenyl diselenide and dimethyl diselenide, wherein the concentration of the diphenyl diselenide and the dimethyl diselenide in the mixed solution is controlled to be 100mmol/L respectively, so that the lithium-sulfur battery electrolyte in the embodiment 3 is obtained.

Assembling a lithium-sulfur battery by using the electrolyte; the processes and parameters not specified in this example were the same as in example 1.

Example 4

Preparation of the electrolyte

DOL is used as an organic solvent;

adding LiTFSI and LiClO to an organic solvent₄LiTFSI and LiClO₄The concentrations in the mixed solution of the organic solvent and the electrolyte salt were 1mol/L and 0.1mol, respectively/L；

And finally adding di-tert-butyl disulfide and dimethyl trisulfide, wherein the concentrations of the di-tert-butyl disulfide and the dimethyl trisulfide in the mixed solution are both controlled to be 20mmol/L, and the electrolyte of the lithium-sulfur battery in the embodiment 4 is obtained.

Assembling a lithium-sulfur battery by using the electrolyte; the processes and parameters not specified in this example were the same as in example 1.

Example 5

Preparation of the electrolyte

Taking TEGDME as an organic solvent;

adding LiTFSI and LiFSI into the organic solvent, wherein the concentrations of the LiTFSI and the LiFSI in the mixed solution of the organic solvent and the electrolyte salt are respectively 0.1 mol/L; adding additive LiNO₃，LiNO₃The mass fraction in the whole mixed system is 2 wt%;

finally, dimethyl disulfide was added, and the concentration of which in the mixed solution was controlled to 2000mmol/L, which was the electrolyte for lithium sulfur battery of example 5.

Assembling a lithium-sulfur battery by using the electrolyte; the processes and parameters not specified in this example were the same as in example 1.

Example 6

Preparation of the electrolyte

Mixing EC and DEC according to the volume ratio of 1:1 to obtain an organic solvent;

adding LiPF to an organic solvent₆，LiPF₆The concentration in the mixed solution of the organic solvent and the electrolyte salt is 20 mol/L;

finally, diethyl diselenide and diethyl disulfide were added, and the concentrations thereof in the mixed solution were controlled to be 100mmol/L, which was the electrolyte for lithium-sulfur battery of example 6.

Assembling a lithium-sulfur battery by using the electrolyte; the processes and parameters not specified in this example were the same as in example 1.

Example 7

Preparation of the electrolyte

DMF and DMSO are used as organic solvents;

adding LiBETI and LiBPBI into the organic solvent, and dissolving LiBETI and LiBPBI in the organic solvent and electrolyte saltThe concentration of the mixed solution is 5 mol/L; adding additive LiNO₃，LiNO₃The mass fraction in the whole mixed system is 5 wt%;

finally, the benzhydryl diselenide is added, and the concentration of the benzhydryl diselenide in the mixed solution is controlled to be 50mmol/L, so that the lithium-sulfur battery electrolyte of the embodiment 7 is obtained.

Assembling a lithium-sulfur battery by using the electrolyte; the processes and parameters not specified in this example were the same as in example 1.

Example 8

Preparation of the electrolyte

Taking PC as an organic solvent;

adding LiI into the organic solvent, wherein the concentration of the LiI in the mixed solution of the organic solvent and the electrolyte salt is 5 mol/L; then adding the additive LiPO₃，LiPO₃The mass fraction in the whole mixed system is 10 wt%;

finally, diethyl ditelluroether is added, and the concentration of the diethyl ditelluroether in the mixed solution is controlled to be 50mmol/L, so that the lithium-sulfur battery electrolyte in the embodiment 8 is obtained.

Assembling a lithium-sulfur battery by using the electrolyte; the processes and parameters not specified in this example were the same as in example 1.

Example 9

Preparation of the electrolyte

Mixing DOL and DME according to the volume ratio of 1:1 to obtain an organic solvent;

adding LiI and LiTFSI into the organic solvent, wherein the concentrations of the LiI and the LiTFSI in the mixed solution of the organic solvent and the electrolyte salt are respectively 1 mol/L; adding additive LiNO₃，LiNO₃The mass fraction in the whole mixed system is 2 wt%;

and finally adding the diphenyl trisulfide and the diphenyl tetrasulfide, wherein the concentration of the diphenyl trisulfide and the diphenyl tetrasulfide in the mixed solution is controlled to be 100mmol/L, and the electrolyte of the lithium-sulfur battery in the embodiment 9 is obtained.

Assembling a lithium-sulfur battery by using the electrolyte; the processes and parameters not specified in this example were the same as in example 1.

Example 10

Preparation of the electrolyte

Mixing TEGDME, HFE and DOL according to a volume ratio of 4:2:4 to serve as an organic solvent;

adding LiBr and LiFSI into the organic solvent, wherein the concentrations of the LiBr and the LiFSI in the mixed solution of the organic solvent and the electrolyte salt are respectively 0.1 mol/L; adding additive LiNO₃，LiNO₃The mass fraction in the whole mixed system is 2 wt%;

and finally adding the dimethyl pentasulfide and the dimethyl hexasulfide, wherein the concentration of the dimethyl pentasulfide and the dimethyl hexasulfide in the mixed solution is controlled to be 200mmol/L, and the electrolyte of the lithium-sulfur battery is the electrolyte of the embodiment 10.

Assembling a lithium-sulfur battery by using the electrolyte; the processes and parameters not specified in this example were the same as in example 1.

Comparative example 1

1) Preparation of the electrolyte

Mixing 1,3 Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) according to a volume ratio of 1:1 to obtain an organic solvent, adding electrolyte salt LiTFSI into the organic solvent, wherein the concentration of LiTFSI in the mixed solution of the organic solvent and the electrolyte salt is 1mol/L, and adding an additive LiNO₃，LiNO₃The mass fraction in the whole mixed system was 2 wt%, which was the electrolyte used in the comparative example.

2) Preparation of lithium-sulfur battery

And sequentially loading the positive plate, the electrolyte, the diaphragm and the negative plate into the battery, standing for 6h, discharging to 1.7V at a constant current of 0.5C multiplying power, and then charging to 2.6V at a constant current of 0.5C multiplying power to complete the preparation of the lithium-sulfur battery.

TABLE 1 comparison of electrochemical properties of the examples and comparative examples

The lithium-sulfur battery electrolyte chemically oxidizes lithium sulfide, so that the utilization rate of active substances is improved, the reversibility, the cycle performance and the energy density of electrochemical reaction are improved, and the overall performance of the battery is improved.

The lithium sulfur battery was assembled using the lithium sulfur battery electrolyte of the inventive example, in combination with the performance results of table 1, in comparison with comparative example 1: the specific capacity can be improved by 150-250mAh/g (namely, 20-30 percent of the specific capacity of the comparison document 1); on the premise of improving the capacity retention rate by 5-15%, the cycle stability can be increased by 10-50 circles (namely, 15-25% of the cycle number of the comparison document 1); specific results of example 3 and comparative example 1 are shown in fig. 1, wherein the energy density of the Ah-grade soft package battery is increased by 50-100Wh/kg (namely, 15-25% of the energy density of comparative document 1).

As shown in Table 1, the Se-Se (or S-S, Te-Te) bonds in examples 1 and 2 only contain 1, while the Se-Se (or S-S, Te-Te) bonds in examples 9 and 10 contain 2 to 5, so that the specific capacities of the first circles of examples 1 and 2 are obviously lower than those of examples 9 and 10, which also indicates that the first circles of examples 1 and 2 contain more S, Se or Te atoms (i.e., n is 3 to 10, and n is an integer) to help the promotion of kinetics and the exertion of practical performance.

In summary, through the above experimental procedures and performance comparison, the following conclusions are drawn: additives containing multiple active centers S, Se or Te atoms (i.e., n is 3-10, n is an integer) have a stronger effect of enhancing performance than electrolyte additives containing only 1 or 2 atoms S, Se or Te (i.e., n is 1 or 2). In particular, Se-Se (or S-S, Te-Te) bonds are easier to break (the bond energy of C-S breakage is far higher than the bond energy of S-S breakage), so that polyselenium chains, polysulfide chains and polytelluride chains in polyselenide, polysulfide and polytelluride intermediate species are easier to graft in the additive, thereby improving the diffusivity and the reaction capability of the intermediate species and playing a role in improving the kinetics. The conclusion of this experiment is also fully documented by the first-turn specific capacity comparison of examples 1, 2 with examples 9, 10.

The three elements S, Se and Te are selected to have similar chemical properties because the three elements are in the same main group; however, due to the difference in atomic radius and arrangement of electrons outside the core, the chemical and electrochemical properties of the ethers are different after different atoms are introduced, and specifically, the diffusibility and the reaction capability of the ethers containing Se or Te are significantly higher than those of the ethers containing S. This is confirmed by the above examples, that is, in the capacity retention ratio and the specific capacity at the 100 th cycle, both example 3 using selenide and example 8 using telluride show higher values than example 4 using thioether, i.e., it is confirmed that the Se-or Te-containing ether has more excellent electrochemical properties.

The additive content range of the invention is wide and is 0.1-2000mmol L^-1. The series of active additives containing Se-Se (or S-S, Te-Te) bonds with high concentration can obviously improve the early-stage cycling specific capacity of the battery, but has some negative effects on the long cycling performance of the battery; the low-concentration additive has less obvious effect of improving the specific capacity at the early stage of the battery than a high-concentration additive, but has remarkable advantages in the aspects of cycling stability and capacity retention rate.

It is noted that the high concentration of additive itself contributes capacity in the discharge region of the lithium sulfur battery, and this additional capacity needs to be subtracted out in the evaluation of its kinetic promoting effect. Specifically, as shown in FIG. 2, we compared the active substances in examples 1, 2, 3 and 5 with their own contribution capacity, and the active substances in examples 1, 2 and 3 were all low in concentration (≦ 100mmol L)^-1) While the active substance in example 5 was at a high concentration (2000mmol L)^-1) Thus, the active substance in example 5 contributed much more capacity than in examples 1, 2, 3, and thus its own contributing capacity should be deducted when assessing kinetic enhancement.

In view of the above-mentioned characteristics, the electrolyte according to the invention is reversibly cleaved and reformed during discharge and charging of the cell by the introduction of series of highly active additives containing Se-Se (or: S-S, Te-Te) bonds, by reaction with the intermediate polysulfide Li in lithium-sulfur cells₂S_xThe function of the catalyst is to participate in the oxidation-reduction process of sulfur to generate organic polysulfide RS with better reactivity and diffusion capacity_{x+ n}Li (or RSe)_nS_xLi, or RTe_nS_xLi) to facilitate reaction kinetics. In addition, the chemical oxidation of the lithium sulfide improves the utilization rate of active substances, and improves the reversibility and circulation of electrochemical reactionThe performance and the energy density improve the overall performance of the battery.