CN110854437A - A lithium-sulfur battery electrolyte containing multifunctional additives and its application - Google Patents

Abstract

The invention discloses a lithium-sulfur battery electrolyte containing multifunctional additives and its application, belonging to the technical field of rechargeable high specific energy secondary batteries. The electrolyte of the present invention comprises an organic solvent, a lithium salt and a multifunctional additive, wherein the multifunctional additive is one or more of compounds having the chemical structural formula of R ₁ -O-R ₂ ; the R ₁ and R ₂ are the same or Different, R ₁ or R ₂ is selected from C1-C8 alkane, C2-C8 alkene, C3-C8 cycloalkyl, C3-C8 heterocycloalkyl or partially unsaturated C3-C8 cycloalkyl; the C3-C8 The ring structure of cycloalkyl, C3-C8 heterocycloalkyl or partially unsaturated C3-C8 cycloalkyl group may or may not be substituted. The invention reduces the loss of active material sulfur and lithium by introducing multifunctional ether additives, enhances the cycle stability of the battery, inhibits the chemical reaction between the polysulfide in the electrolyte and the metal lithium, and improves the coulomb of the battery. efficiency.

Description

A lithium-sulfur battery electrolyte containing multifunctional additives and its application

technical field

The invention belongs to the technical field of rechargeable high specific energy secondary batteries, and particularly relates to a lithium-sulfur battery electrolyte containing multifunctional additives and its application.

Background technique

With the continuous development of new energy technologies, especially with the urgent demand for high energy density secondary batteries in the fields of intelligent communication equipment and electric vehicles. The research on high energy density energy storage and conversion devices has practical significance. Compared with traditional lithium-ion batteries, which rely on the intercalation and deintercalation of lithium ions for energy storage, from an electrochemical point of view, multi-electron reactive material systems are the basis for building high specific energy secondary batteries. Among them, lithium-sulfur batteries have become the key research objects of next-generation new lithium secondary batteries because of their very high theoretical specific capacity (1672mAh/g) and theoretical energy density (2570Wh/kg), low price of sulfur and abundant reserves.

Although lithium-sulfur batteries have many advantages, they have not yet been commercialized. The main reason is that during the charging and discharging process of lithium-sulfur batteries, the intermediate product lithium polysulfide will dissolve in traditional ether electrolytes. The migration between the positive and negative electrodes under the action is the "shuttle effect". On the one hand, the shuttle effect will reduce the utilization rate of active materials; on the other hand, lithium polysulfides will also have irreversible chemical reactions with the metal lithium anode, corroding the metal lithium, causing serious lithium dendrite problems and rapid failure of the lithium anode. It seriously affects the coulombic efficiency and cycle life of lithium-sulfur batteries. At present, the research progress of lithium-sulfur batteries mainly focuses on the cathode material part. Through the design of the cathode structure and the introduction of chemical adsorption, the shuttle reaction of lithium polysulfides can be effectively inhibited. However, on the one hand, this will increase the cost, and on the other hand, it requires complex electrode material design, which is not conducive to the wide-scale application and promotion of lithium-sulfur batteries. The formation of stable SEI on the surface of metallic lithium by introducing functional additives is an effective method to protect metallic lithium anodes, but the poor long-term cycling stability is caused by the small amount of additives and the continuous consumption during cycling.

It is a simple, economical and long-term effective method to alleviate the corrosion of metal lithium and greatly improve the cycle stability and Coulomb efficiency of lithium-sulfur batteries by changing the solvent composition of the electrolyte. Therefore, the development of lithium-sulfur battery electrolytes that can significantly improve battery cycle life has become a current research hotspot. However, due to the complexity of the multi-electron conversion mechanism and the instability of polysulfides, the research and development of lithium-sulfur electrolytes faces great challenges.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a kind of lithium-sulfur battery electrolyte and application thereof containing multifunctional additive, and the concrete technical scheme is as follows:

A lithium-sulfur battery electrolyte containing a multifunctional additive, comprising an organic solvent, a lithium salt and a multifunctional additive, wherein the multifunctional additive is one or more of compounds with the chemical structural formula of R ₁ -OR ₂ ;

The R ₁ and R ₂ are the same or different, and R ₁ or R ₂ are selected from C1-C8 alkane, C2-C8 alkenyl, C3-C8 cycloalkyl, C3-C8 heterocycloalkyl or partially unsaturated C3- C8 cyclic hydrocarbon group;

The self-C1-C8 alkane group and C2-C8 alkene group described in the present invention are straight-chain or branched-chain hydrocarbon groups.

The ring structure of the C3-C8 cycloalkyl group, the C3-C8 heterocycloalkyl group or the partially unsaturated C3-C8 cycloalkyl group of the present invention contains or does not contain a substituent.

The heteroatom in the C3-C8 heterocycloalkyl group of the present invention is a nitrogen atom, a sulfur atom or an oxygen atom; the partially unsaturated C3-C8 cycloalkyl group includes a C3-C8 cycloalkenyl group, a phenyl group, and a substituted phenyl group.

The substituents on the C3-C8 cycloalkyl, C3-C8 heterocycloalkyl or partially unsaturated C3-C8 cyclohydrocarbyl ring structure are C1-C6 alkyl, C1-C6 alkenyl, amino, phenyl, halogen .

The organic solvent is 1,3-dioxane, 1,4-dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol One of dimethyl ether, tetrahydrofuran, ethyl methyl sulfone, sulfolane, isopropyl methyl sulfone, dimethyl sulfoxide, dimethyl trisulfide, dimethyl disulfide, dimethyl sulfide or more.

The lithium salt is lithium hexafluorophosphate, lithium bis-oxalate borate, lithium bis-trifluoromethanesulfonimide (LiTFSI), lithium bis-fluorosulfonimide, lithium perchlorate, lithium difluorooxalate borate, lithium nitrate and trifluoromethane One or more of lithium sulfonates.

The concentration of the lithium salt in the lithium-sulfur battery electrolyte is 0.1-4 mol/L, and the volume of the multifunctional additive is 5-80% of the volume of the lithium-sulfur battery electrolyte.

The lithium-sulfur battery electrolyte also contains auxiliary additives, and the auxiliary additives are one or more of lithium nitrate, lithium polysulfide, potassium nitrate, cesium nitrate, and lithium bromide.

The auxiliary additive is 0.1% to 5% of the mass of the lithium-sulfur battery electrolyte.

The lithium-sulfur battery electrolyte is used to prepare a lithium-sulfur battery. The lithium-sulfur battery includes a positive electrode, a negative electrode, a separator, and an electrolyte for the lithium-sulfur battery; the active material of the positive electrode is one or more of elemental sulfur, sulfur-containing polymer, lithium sulfide, and lithium polysulfide; The negative electrode is any one of metal lithium foil, lithium sheet, and lithium alloy.

The beneficial effects of the present invention are:

(1) The lithium-sulfur battery electrolyte containing multifunctional additives provided by the present invention, on the one hand, inhibits the chemical reaction between polysulfides in the electrolyte and metal lithium; on the other hand, changes the deposition morphology of metal lithium, Enhance the uniformity of metal lithium deposition, effectively avoid the rapid consumption of metal lithium anode, the generation of dead lithium and the growth of dendrites, etc. Regulate the deposition behavior of metal lithium, avoid the corrosion of lithium anode by high concentration of polysulfides, reduce electrolysis The concentration of polysulfides in the liquid. That is, the present invention reduces the loss of active substances—sulfur and lithium, by introducing multifunctional ether additives, improves the coulombic efficiency of the battery, and enhances the cycle stability of the battery.

(2) The lithium-sulfur battery electrolyte containing multifunctional additives provided by the present invention is simple in composition and low in cost, and can be applied to a sulfur positive electrode with high sulfur loading, and is a lithium-sulfur battery electrolyte with great research value and industrialization potential. liquid.

Description of drawings

Accompanying drawing 1 is the cycle performance and Coulomb efficiency of lithium-sulfur battery in Example 2 of the present invention;

Figure 2 shows the cycle performance and Coulomb efficiency of the lithium-sulfur battery in Comparative Example 2 of the present invention.

Detailed ways

The present invention provides a lithium-sulfur battery electrolyte containing multifunctional additives and its application. The present invention will be further described below with reference to the embodiments and accompanying drawings.

The lithium-sulfur battery of the present invention includes a positive electrode, a negative electrode, a separator and an electrolyte. The positive electrode of the present invention includes a positive electrode current collector and a positive electrode material compounded on the surface of the positive electrode current collector; the positive electrode current collector is a current collector with excellent conductivity in the field, such as aluminum foil.

The positive electrode material is obtained by solidifying the slurry of the positive electrode active material, a conductive agent, a binder and a solvent, wherein the conductive agent, the binder and the solvent are all commonly used materials in the art.

In the embodiment of the present invention, carbon nanotubes commonly used in lithium-sulfur batteries are used as the carrier of positive active material sulfur, and the positive electrode material is prepared with conductive agent acetylene black, binder polyvinylidene fluoride and solvent NMP, and the specific operations are as follows:

(1) Mix 30g of multi-walled carbon nanotubes (MWCNTs) with 70g of commercial sulfur powder, and ball-mill at 600rpm for 6h to obtain a uniformly mixed powder MWCNT/S; ball-mill the mixture of MWCNT/S, acetylene black and polyvinylidene fluoride Mix uniformly in N-methylpyrrolidone (NMP) solution according to the ratio of 8:1:1 to obtain the prepared slurry;

(2) The slurry was evenly coated on aluminum foil, dried at 60°C for 12h, cut into pole pieces with a diameter of 13mm, and put into a glove box to remove water for use.

In the embodiment of the present invention, a polypropylene microporous membrane of model Celgard 2400 is used as the diaphragm.

Example

Electrolyte configuration: in a glove box filled with argon (O ₂ , H ₂ O content are both < 0.1ppm), ethylene glycol dimethyl ether (DME), 1,3-dioxane (DOL), dioxane Ethylene glycol dimethyl ether (G2), triethylene glycol dimethyl ether (G3), tetraethylene glycol dimethyl ether (G4), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dimethyl trimethyl ether The mixed solution of two or more kinds of sulfide (DMTS) is used as the organic solvent. Add auxiliary additives of 0.1-5% of the total mass of the electrolyte, add multifunctional additives of 5-80% of the total volume of the electrolyte, add lithium salt, and make the concentration of lithium salt in the electrolyte to be 1.0mol/L (M), Fully stirring, the lithium-sulfur battery electrolyte is obtained.

In an argon atmosphere, a metal lithium sheet was used as the negative electrode, a polypropylene microporous membrane of type Celgard 2400 was used as the diaphragm, and the electrolyte dosage was 15 μL/mg S, and CR2025 lithium-sulfur batteries were assembled in sequence.

Lithium-sulfur batteries were assembled with electrolytes with different component contents to obtain Examples 1-10; Lithium-sulfur batteries were assembled with electrolytes without auxiliary additives to obtain Examples 11-15; composed of different organic solvents, added and implemented Examples 1-3 The same functional additives and auxiliary additives were used to assemble a lithium-sulfur battery, and Examples 16-18 were obtained.

Comparative Example 1

_The electrolyte prepared without adding multifunctional additives and auxiliary additives, namely the electrolyte containing organic solvent and lithium salt, was taken as Comparative Example ₁ . <0.1ppm), using the mixture of ethylene glycol dimethyl ether (DME) and 1,3-dioxane (DOL) with a volume ratio of 1:1 as an organic solvent, adding lithium salt, and making the lithium salt in The concentration of the electrolyte is 1.0M, and the electrolyte is fully stirred to obtain a lithium-sulfur battery electrolyte.

In an argon atmosphere, a lithium metal sheet was used as the negative electrode, a polypropylene microporous membrane of type Celgard 2400 was used as the diaphragm, and the electrolyte dosage was 15 μL/mg S, and the lithium-sulfur batteries were assembled in sequence.

Comparative Example 2

_The electrolyte prepared without adding multifunctional additives, that is, the electrolyte containing organic solvent, lithium salt and auxiliary additives, was taken as Comparative Example ₂ . <0.1ppm), the mixed solution of ethylene glycol dimethyl ether (DME) and 1,3-dioxane (DOL) with a volume ratio of 1:1 was used as the organic solvent; 2% anhydrous electrolyte was added to the total mass of the electrolyte Lithium nitrate (LiNO ₃ ) is used as an auxiliary additive; lithium salt is added, and the concentration of the lithium salt in the electrolyte is 1.0M, and the electrolyte is fully stirred to obtain a lithium-sulfur battery electrolyte.

In an argon atmosphere, a lithium metal sheet was used as the negative electrode, a polypropylene microporous membrane of type Celgard 2400 was used as the diaphragm, and the electrolyte dosage was 15 μL/mg S, and the lithium-sulfur batteries were assembled in sequence.

Examples 1-18, Comparative Example 1, Comparative Example 2 The types of components and their contents in the lithium-sulfur battery electrolyte are shown in Table 1:

Table 1

The batteries prepared in Examples 1-18, Comparative Example 1, and Comparative Example 2 were placed in a constant temperature room at 25°C for 12 hours, and then a charge-discharge cycle test was performed on a blue-electric test charge-discharge tester. The test conditions were constant. Flow 0.5C (1C=1672mAh/g) charge and discharge, the potential range is 1.7 ~ 2.6V, cycle 200 times.

The cycle performance and Coulomb efficiency of the batteries of Examples 1-18, Comparative Example 1 and Comparative Example 2 are shown in Table 2:

Table 2

Comparative analysis of Example 11-15 and Comparative Example 1 shows that the first cycle discharge specific capacity of the battery of Example 11-15 is not significantly different from that of Comparative Example 1, the 200-cycle cycle capacity retention rate reaches 72.6% to 75.2%, and the coulombic efficiency reaches 91.5% ~93.4%, much higher than the 200-cycle capacity retention rate of 40.5% and the Coulomb efficiency of 64.2% in Comparative Example 1. It shows that the single use of the multifunctional additive of the present invention can greatly improve the capacity retention rate and Coulomb efficiency of the battery.

Comparative analysis of Example 1-10 and Comparative Example 2, Example 1-10 at a discharge rate of 0.5C, the first cycle of discharge specific capacity and Comparative Example 2 have no significant difference, 200 cycles of capacity retention rate reached 78.6% ~ 90.3% , the Coulombic efficiency is 94.6% to 99.5%, which are much higher than the 200-cycle capacity retention rate of 57.5% in Comparative Example 2, and the Coulombic efficiency is 89.6%. It shows that the multifunctional additive of the present invention is also suitable for greatly improving the cycle performance and Coulombic efficiency of batteries containing non-solvent substances such as lithium nitrate and lithium bromide in the electrolyte.

Comparative analysis of Example 1-10 and Comparative Example 1, Example 1-10 at a discharge rate of 0.5C, the first cycle of discharge specific capacity and Comparative Example 1 have no significant difference, the 200-cycle cycle capacity retention rate reaches 78.6% ~ 90.3% , the Coulombic efficiency is 94.6%-99.5%, which are much higher than the 200-cycle capacity retention rate of 40.5% and the Coulombic efficiency of 64.2% in Comparative Example 1. It can be seen that adding the auxiliary additive and the multifunctional additive of the present invention at the same time can significantly improve the cycle capacity retention rate and the coulombic efficiency.

Comparing Examples 11-15 and Example 1-10, it can be found that the 200-cycle capacity retention rate and Coulomb efficiency of Example 1-10 are higher than those of Example 11-15. It shows that the auxiliary additive and the multifunctional additive of the present invention can produce synergistic effect, and can further improve the battery cycle performance and Coulomb efficiency.

Comparing Examples 1-3 and Examples 16-18, it can be found that there is no significant difference in the discharge capacity of the first cycle, the retention rate of the 200-cycle cycle capacity, and the average Coulomb efficiency. It is indicated that the multifunctional additive of the present invention is suitable for organic solvents of different systems.

Claims (10)

1. a lithium-sulfur battery electrolyte containing a multifunctional additive, is characterized in that, comprises organic solvent, lithium salt and multifunctional additive, and described multifunctional additive is a kind of in the compound with R ₁ -OR ₂ chemical structural formula or more; The R ₁ and R ₂ are the same or different, and R ₁ or R ₂ are selected from C1-C8 alkane, C2-C8 alkenyl, C3-C8 cycloalkyl, C3-C8 heterocycloalkyl or partially unsaturated C3- C8 cyclic hydrocarbon group; The ring structure of the C3-C8 cycloalkyl group, the C3-C8 heterocycloalkyl group or the partially unsaturated C3-C8 cycloalkyl group contains or does not contain a substituent. 2. The lithium-sulfur battery electrolyte according to claim 1, wherein the heteroatom in the C3-C8 heterocycloalkyl group is a nitrogen atom, a sulfur atom or an oxygen atom; the partially unsaturated C3-C8 ring Hydrocarbyl includes C3-C8 cycloalkenyl, phenyl, substituted phenyl. 3. The lithium-sulfur battery electrolyte according to claim 1, wherein the substituents on the C3-C8 cycloalkyl, C3-C8 heterocycloalkyl or partially unsaturated C3-C8 cyclohydrocarbyl ring structure For C1-C6 alkyl, C1-C6 alkenyl, amino, phenyl, halogen. 4. The lithium-sulfur battery electrolyte according to claim 1, wherein the organic solvent is 1,3-dioxane, 1,4-dioxane, ethylene glycol dimethyl ether, dioxane ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, ethyl methyl sulfone, sulfolane, isopropyl methyl sulfone, dimethyl sulfoxide, dimethyl trisulfoxide One or more of sulfide, dimethyl disulfide and dimethyl sulfide. 5. The lithium-sulfur battery electrolyte according to claim 1, wherein the lithium salt is lithium hexafluorophosphate, lithium dioxalate borate, lithium bistrifluoromethanesulfonimide, lithium bisfluorosulfonimide, lithium One or more of lithium chlorate, lithium difluorooxalate borate, lithium nitrate and lithium trifluoromethanesulfonate. 6 . The lithium-sulfur battery electrolyte according to claim 1 , wherein the concentration of the lithium salt in the lithium-sulfur battery electrolyte is 0.1 to 4 mol/L, and the volume of the multifunctional additive is the volume of the lithium-sulfur battery electrolyte. 7 . 5-80%. 7. The lithium-sulfur battery electrolyte according to claim 1, wherein the lithium-sulfur battery electrolyte also contains auxiliary additives, and the auxiliary additives are lithium nitrate, lithium polysulfide, potassium nitrate, cesium nitrate, lithium bromide one or more of. 8 . The lithium-sulfur battery electrolyte according to claim 7 , wherein the auxiliary additive is 0.1% to 5% of the mass of the lithium-sulfur battery electrolyte. 9 . 9 . The application of the lithium-sulfur battery electrolyte according to claim 1 , wherein the lithium-sulfur battery electrolyte is used to prepare a lithium-sulfur battery. 10 . 10. The application according to claim 9, wherein the lithium-sulfur battery comprises a positive electrode, a negative electrode, a separator and an electrolyte for the lithium-sulfur battery; the active material of the positive electrode is elemental sulfur, sulfur-containing polymer, One or more of lithium sulfide and lithium polysulfide; the negative electrode is any one of metal lithium foil, lithium sheet, and lithium alloy.

Images