RU2321104C2 - Electrolyte for lithium-sulfur batteries and lithium-sulfur batteries using this electrolyte - Google Patents

Abstract

FIELD: chemical power supplies using organic electrolytes.

SUBSTANCE: electrolytes proposed for use in lithium-sulfur batteries has electrolytic salt solutions mixed up with aprotic solvents (primarily sulfones) whose composition corresponds to or is close to eutectic one.

EFFECT: reduced low value of battery operating temperature range.

6 cl, 1 dwg, 1 tbl

Description

Technical field

The present invention relates to electrochemical energy and, in particular, to compositions of anhydrous aprotic electrolytes intended for use in chemical sources of electricity with negative electrodes made of active materials (lithium, sodium, etc.). The present invention also relates to chemical power sources containing such electrolytes. More specifically, the present invention relates to components of electrolyte systems containing anhydrous aprotic solvents, salts and other additives.

State of the art

The development of modern technology requires the creation of new types of batteries with, first of all, high specific energy, long cycle life and safety. The energy and operational characteristics of batteries are determined by the properties of the electrochemical system used. The main requirements for the characteristics of secondary lithium batteries and their components are described by US patent No. 5460905; 5,462,566; 5582623 and 5587253.

The highest specific energy is possessed by lithium-ion batteries with liquid and polymer electrolytes. However, at present they have achieved practically possible energy characteristics. Further progress in the development of batteries with high energy density may be with the use of new electrochemical systems.

The Li-S system is very promising, with a high energy density (2600 W * h / kg), low cost, accessibility and safety for nature and man. In the processes of charge and discharge of lithium-sulfur batteries, soluble compounds are formed - lithium polysulfides. Therefore, the characteristics of lithium-sulfur batteries (degree of sulfur utilization, duration of cycling, temperature range of working capacity, etc.) are largely determined by the physicochemical properties of electrolyte systems and components, their components, namely solvents and salts.

For electrolytes of lithium and lithium-ion batteries, it is proposed to use a large number of non-aqueous aprotic organic solvents of various classes, as well as their mixtures. For example, compositions of various electrolytes are described in US Pat. Nos. 3,185,590; 3,578,500; 3,778,310; 3,877,983; 4,163,829; 4,118,550; 4,252,876; 4,499,161; 4,740,436; 4,060,674; 4,104,451; 3,907,597; 6,030,720; 5079109 and Japan JP 08-298229; JP 09-147913 and JP 08-298230. As a rule, substituted and unsubstituted ethers, cyclic ethers, polyesters, linear and cyclic carbonates, organic sulfites and sulfates, organic nitriles and nitro compounds, etc. are used as solvents in lithium electrolytes.

Most electrolyte systems proposed for lithium-ion batteries are unsuitable for use in lithium-sulfur batteries. The best solvents for electrolyte systems of lithium-sulfur batteries are low molecular weight sulfones [1-4]. But low molecular weight sulfones have high melting points, which limits the lower temperature limit of their possible use. US Pat. No. 6,254,465 suggests using non-cyclic sulfones or fluorinated asymmetric non-cyclic sulfones having lower melting points, mixtures thereof, and also mixtures of asymmetric sulfones with other solvents such as carbonates, glymes, siloxanes, etc. as aprotic solvents for lithium-sulfur battery electrolytes. However, the melting points of the proposed sulfones are not low enough to produce electrolytes with the desired low temperature properties. In addition, the proposed sulfones are expensive, which limits the possibility of their large-scale use.

SUMMARY OF THE INVENTION

In the present invention, it is proposed to use solutions of electrolyte (mainly lithium) salts in eutectic and close to eutectic mixtures of aprotic solvents, mainly sulfones with a molecular weight of 94 to 150, as electrolytes for lithium-sulfur batteries.

The use of eutectic solvent mixtures significantly improves the low-temperature properties of electrolytes, which can significantly lower the lower temperature limit of the performance of lithium-sulfur batteries, improve their low-temperature capacitive and power characteristics, and also increase the duration of cycling at low temperatures.

The drawing shows a state diagram of the sulfolane-methylpropylsulfone system.

Examples of carrying out the invention

Example 1

The physicochemical properties of a number of low molecular weight sulfones were synthesized and studied. The data obtained are summarized in a table.

Name of sulfone Molecular mass Density 10 ³ * kg / m ³ Viscosity N * s / m ² , 10 ³ Molar volume, ^m3 / mol * June ¹⁰ t _stagnation. ° C n _D ε Methylethylsulfone * 108,2 1.1638 * 4.75 * 93.0 * 34.5 1,4453 57.5 Methylpropylsulfone 122,2 1,1081 5.22 110.3 32,5 1.4472 40,2 Methyl Butyl Sulfone 136.2 1,0686 6.58 127.5 30.3 1,4485 35.1 Sulfolane 120,2 1.2594 9.04 95.4 28,4 1.4820 42.9 2,4-dimethyl sulfolane 148.2 1,1263 6.74 131.6 -18.0 1.4708 30,0 • t = 40 ° C

Example 2

A mixture of 0.8 ml of methylpropylsulfone ( _mp = 32.5 ° C) and 0.2 ml of sulfolane ( _mp = 28.4 ° C) was prepared and the melting point of this mixture was determined. She was + 21 ° C.

Example 3

A mixture of 0.6 ml of methylpropylsulfone ( _mp = 32.5 ° C) and 0.4 ml of sulfolane ( _mp = 28.4 ° C) was prepared and the melting point of this mixture was determined. She was + 6 ° C.

Example 4

A mixture of 0.4 ml of methylpropylsulfone (t _PL = 32.5 ° C) and 0.6 ml of sulfolane (t _PL = 28.4 ° C) was prepared and the melting point of this mixture was determined. It amounted to 8.5 ° C.

Example 5

A mixture of 0.2 ml of methylpropylsulfone ( _mp = 32.5 ° C) and 0.8 ml of sulfolane ( _mp = 28.4 ° C) was prepared and the melting point of this mixture was determined. She was + 0.5 ° C.

Based on the melting points of pure sulfones and their mixtures, a state diagram of the sulfolane-methylpropylsulfone system was constructed, which is shown in the drawing. By extrapolating the branches of the temperature dependences, the composition of the eutectic and its melting temperature were found. From the data obtained it follows that the melting temperature of the eutectic mixture is approximately 45 ° C lower than the melting temperatures of the initial sulfones.

Example 6

A lithium-sulfur battery with an anode made of lithium metal foil, a Celgard separator and a sulfur cathode containing elemental sulfur (70% by weight), carbon conductive additive (Ketjenblack EC-600JD, -10% by weight) and a binder (polyethylene oxide with a molecular weight of 4,000,000 - 20% by weight.). The specific surface capacitance of the cathode was 2 mA · h / cm ² . The collected battery was charged with electrolyte, which is a 1 M solution of LiClO ₄ in sulfolane. The battery was quoted with a charge and discharge current density of 0.3 mA / cm ² at a temperature of 25 ° C. The capacity given by the battery for 1 cycle was 1.45 mA · h / cm ² . The degree of sulfur use is 72.5%.

Example 7

A lithium-sulfur battery was assembled in the same manner as in Example 6. The battery was cited with a charge and discharge current density of 0.3 mA / cm ² at a temperature of 0 ° C. The capacity given by the battery for 1 cycle was 0.42 mA · h / cm ² . The sulfur utilization is 21%.

Example 8

A lithium-sulfur battery was assembled in the same manner as in Example 7. The battery was cited with a charge and discharge current density of 0.3 mA / cm ² at a temperature of 10 ° C. The capacity given by the battery for 1 cycle was 0.02 mA · h / cm ² . The degree of use of sulfur is 1%.

Example 9

A lithium-sulfur battery was assembled in the same manner as in Example 7, but a 1 M solution of lithium perchlorate in an eutectic mixture of sulfolane (2 mol) and ethyl butyl sulfone (1 mol) was used as an electrolyte.

The battery was cited with a charge and discharge current density of 0.3 mA / cm ² at a temperature of 25 ° C. The capacity given by the battery for 1 cycle was 1.53 mA · h / cm ² . The degree of sulfur use is 76.5%.

Example 10

A lithium-sulfur battery was assembled in the same manner as in Example 7, but a 1 M solution of lithium perchlorate in an eutectic mixture of sulfolane (2 mol) and ethyl butyl sulfone (1 mol) was used as an electrolyte. The battery was cycled with a charge and discharge current density of 0.3 mA / cm ² at a temperature of 0 ° C. The capacity given by the battery for 1 cycle was 1.01 mA · h / cm ² . The degree of use of sulfur is 50.5%.

Example 11

A lithium sulfur battery was assembled in the same manner as in Example 6, but a 1 M solution of lithium perchlorate in 2,4-dimethyl sulfolane was used as the electrolyte. The battery was cycled with a charge and discharge current density of 0.3 mA / cm ² at a temperature of 10 ° C. The capacity given by the battery for 1 cycle was 0.13 mA · h / cm ² . The degree of use of sulfur is 6.5%.

The presented examples demonstrate the advantages of batteries with electrolyte in the form of solutions of electrolyte salts in eutectic mixtures of sulfones. At low temperatures (0 ° С-10 ° С), the given capacity and degree of sulfur utilization were higher for these batteries by 2.5 and 6 times, respectively.

Literary sources

1. Bikbaeva G.G., Gavrilova A.A., Kolosnitsyn B.C. Discharge characteristics of lithium cells with a solid sulfur cathode in the lithium sulfolane-perchlorate system. // Electrochemistry. - 1993. - T.29, No. 6. - S.716-720.

2. Kolosnitsyn B.C., Karaseva E.V., Amineva N.A., Batyrshina G.A. Quoting Li / S current sources. // Electrochemistry. - 2002. - T.38, No. 3. - S.368-371.

3. Kolosnitsyn V.S. Karaseva E.V. Li-S batteries: problems and prospects. Fundamental problems of energy conversion in lithium electrochemical systems. Materials of the VII International Conference. June 24-28. Saratov. - 2002, p.90

4. Kolosnitsyn B.C., Karaseva E.V., Seung D.Y., Cho M.D. The effect of the composition of the electrolyte system on the cycling efficiency of Li-S batteries. Fundamental problems of energy conversion in lithium electrochemical systems. Materials of the VII International Conference. June 24-28. Saratov - 2002, p. 91-93.

Claims (6)

1. The electrolyte for a lithium-sulfur battery, which is a solution of one or more electrolyte salts in a mixture of two or more aprotic organic solvents, characterized in that the mixture of aprotic solvents is eutectic or close to eutectic. 2. The electrolyte according to claim 1, characterized in that sulfones with a molecular weight of 94 to 150 are used as aprotic solvents. 3. A lithium-sulfur battery, including a negative electrode made of lithium-containing material, a positive electrode made of sulfur-containing material, and an electrolyte, characterized in that the electrolyte is a solution of one or more electrolyte salts in a eutectic or near eutectic mixture organic aprotic solvents. 4. The battery according to claim 3, characterized in that the lithium-containing material is selected from the group comprising metallic lithium, lithium-containing alloy, a compound capable of reversibly interpolating lithium ion. 5. The battery according to claim 3, characterized in that the sulfur-containing material is selected from the group comprising elemental sulfur and its compounds, in particular lithium polysulfides, organosulfur compounds and sulfur-containing polymers. 6. The battery according to any one of claims 3 to 5, characterized in that sulfones with a molecular weight of 94 to 150 are used as aprotic solvents.

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