DE102018007901A1 - Electrolyte for a lithium-sulfur cell for storing electrical energy and storage device for a motor vehicle - Google Patents

Abstract

The invention relates to an electrolyte for a lithium-sulfur cell (12) for storing electrical energy, with at least one ionic liquid, the electrolyte (20) having at least dimethyltrisulfide (DMTS).

Description

The invention relates to an electrolyte for a lithium-sulfur cell for storing electrical energy according to the preamble of claim 1. Furthermore, the invention relates to a storage device designed for storing electrical energy for a motor vehicle.

Such an electrolyte for a lithium-sulfur cell for storing electrical energy is, for example, already from the article "Effect of imidazolium cation on cycle life characteristics of secondary lithium-sulfur cells using liquid electrolytes", KIM et al., Electrochimica Acta 52 ( 2007) 2116-2122. The electrolyte has at least one ionic liquid.

The object of the present invention is to provide an electrolyte and a storage device designed for storing electrical energy for a motor vehicle, so that particularly safe operation and a particularly high energy density can be achieved.

This object is achieved by an electrolyte with the features of claim 1 and by a storage device with the features of claim 8. Advantageous refinements and expedient developments of the invention are specified in the remaining claims.

In order to develop an electrolyte of the type entered in the preamble of claim 1 in such a way that a particularly high level of safety, that is to say particularly safe operation and a particularly high energy density of the lithium-sulfur cell, can be achieved according to the invention that the electrolyte has at least dimethyltrisulfide (DMTS). The electrolyte according to the invention is preferably a liquid or liquid, in particular at a temperature of 24 degrees Celsius or at room temperature. In particular, it is preferably provided that the DMTS, in particular at least partially, at least predominantly or completely, is dissolved in the ionic liquid. The ionic liquid is therefore a, in particular liquid, solvent, in particular a, in particular liquid, co-solvent for the DMTS.

The invention is based on the knowledge that ionic liquids have no vapor pressure at all and are very difficult to ignite. Mixtures comprising at least one or more ionic liquids and at least one or more organic solvents are also very difficult to ignite. As a result, a particularly high level of safety or particularly safe operation can be achieved when using the electrolyte according to the invention. Furthermore, it was found that the additional use of DMTS ensures particularly high security and, at the same time, a particularly high energy density of the lithium-sulfur cell. Since the electrolyte according to the invention has both the ionic liquid and the DMTS, a combination of DMTS and ionic liquid is provided according to the invention. Compared to conventional solutions, this combination of DMTS and ionic liquid can increase safety and the energy density can also be increased compared to conventional electrolytes or compared to conventional lithium-sulfur cells. Particularly with respect to the use of volatile, flammable organic solvents in an electrolyte, a particularly high level of security and a high energy density can be achieved.

The electrolyte preferably has at least one component which is provided in addition to the DMTS and in addition to the ionic liquid and which is different from dimethyltrisulfide and from an ionic liquid, which is preferably a further liquid. In particular, the component can be an organic, in particular liquid, solvent. It can be provided that the DMTS, in particular at least partially, at least predominantly or completely, is dissolved in the further liquid. In other words, the electrolyte comprises, for example, a mixture or a mixture, the mixture or the mixture having the ionic liquid as the first solvent and for example the further liquid or in the further constituent as the second solvent. The DMTS is preferably at least partially, in particular at least largely completely, dissolved in the mixture or in the mixture. Here, for example, the ionic liquid acts as a co-solvent provided in addition to the second solvent.

In particular, the further constituent can be a conventional electrolyte, in particular a conventional electrolyte mixture. The further constituent can comprise, for example, dimethoxyethane (DME) and / or lithium bis (trifluoromethylsulfone) imide (LiTFSI) and / or dioxolane (DOL), in particular 1,3-dioxolane.

The ionic liquid is preferably 1-methyl-3-propylimidazoliumbis (trifluoromethylsufonyl) imide ([PMIM] [TFSO] / [PMIM] [MTf2]).

The dimethoxyethane is preferably 1,2-dimethoxyethane. The dioxolane is preferably 1,3-dioxolane. An imidazolium TFSI is preferably used, the imidazole kazion used preferably being [PMI] ⁺ .

The invention also includes a storage device for a motor vehicle, which is preferably designed as a motor vehicle, in particular as a motor vehicle. Electrical energy or electrical current can be stored by means of or in the storage device, which is also referred to as an energy store or electrical energy store. For this purpose, the storage device according to the invention has at least one lithium-sulfur accumulator (Li-S accumulator) for storing electrical energy or electrical current. The lithium-sulfur accumulator in this case comprises a plurality, in particular electrically connected, lithium-sulfur cells, each of which has an electrolyte according to the invention. Advantages and advantageous configurations of the electrolyte according to the invention are to be regarded as advantages and advantageous configurations of the storage device according to the invention and vice versa. The respective electrolyte is accommodated, for example, in the respective cell housing of the respective lithium-sulfur cell.

Further advantages, features and details of the invention result from the following description of a preferred exemplary embodiment and from the drawing. The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the combination indicated in each case, but also in other combinations or on their own, without the scope of Leaving invention.

• 1 ausschnittsweise eine schematische Seitenansicht einer erfindungsgemäßen Speichereinrichtung für ein Kraftfahrzeug;
• 2 die Summenformel und die Skelettformel einer ionischen Flüssigkeit eines Elektrolyten der Speichereinrichtung;
• 3 ein Diagramm zur Veranschaulichung einer Lithium-Schwefel-Zelle der Speichereinrichtung; und
• 4 ein weiteres Diagramm zur Veranschaulichung von Zellen der Speichereinrichtung.

The drawing shows in:

• 1 excerpts a schematic side view of a storage device according to the invention for a motor vehicle;
• 2nd the empirical formula and the skeletal formula of an ionic liquid of an electrolyte of the storage device;
• 3rd a diagram illustrating a lithium-sulfur cell of the storage device; and
• 4th another diagram illustrating cells of the memory device.

Identical or functionally identical elements are provided with the same reference symbols in the figures.

1 shows a detail in a schematic and sectional side view of a storage device designed to store electrical energy or electrical current 10th for a motor vehicle, which is preferably designed as a motor vehicle, in particular a passenger car. This means that the motor vehicle in its completely manufactured state has the storage device, which is also referred to as an energy store 10th having. In its completely manufactured state, the motor vehicle further comprises at least one electrical machine by means of which the motor vehicle can be driven electrically. The motor vehicle is thus designed as an electric vehicle or as a hybrid vehicle. In particular, the motor vehicle can be designed as a battery-electric vehicle (BEV). In order to drive the motor vehicle electrically, the electrical machine is operated in motor mode and thus as an electric motor. For this purpose, the electrical machine is included in the storage device 10th stored electrical energy. In order to be able to realize particularly large electrical outputs for electrically driving the motor vehicle, it is preferably provided that the storage device 10th and the electrical machine is designed as a high-voltage component whose respective electrical voltage, in particular electrical operating voltage, is greater than 12 V and is at least 48 V. The electrical voltage, in particular the electrical operating voltage, is preferably greater than 48 V, preferably greater than 50 V. The electrical voltage, in particular the electrical operating voltage, is particularly preferably several hundred volts in order to be able to realize particularly large electrical outputs for electrically driving the motor vehicle can.

The storage device 10th has a plurality of electrically connected memory cells, which are simply referred to as cells. By means of or in the storage cells, electrical energy or electrical current can be stored, with which the electrical machine can be supplied. Of the multiple memory cells of the memory device 10th is in 1 a memory cell designated by 12 is shown in a schematic and sectional side view. The previous and following comments on the memory cell 12th can also easily on the other memory cells of the memory device 10th be transferred and vice versa. To save space - a particularly large amount of electrical energy in the storage device in a weight-favorable manner 10th To be able to save is the memory cell 12th formed as a lithium-sulfur cell, so that the electrically interconnected lithium-sulfur cells a lithium-sulfur accumulator of the storage device 10th form.

The memory cell 12th has a cell housing 14 through which a recording room 16 is limited. In the recording room 16 is at least or exactly an electrode arrangement 18th added. It is also in the recording room 16 a, especially liquid, electrolyte 20th the memory cell 12th (Lithium-sulfur cell) added. Out 1 it can be seen that the electrode arrangement 18th at least partially, in particular at least predominantly completely, in the electrolyte 20th recorded or in the electrolyte 20th is immersed. By means of the electrode arrangement 18th and by means of the electrolyte 20th can electrical energy in the storage cell 12th get saved. The memory cell 12th also has connectors 22 and 24th which, for example, at least electrically with the electrode arrangement 18th are connected. Via the connections 22 and 24th can electrical energy into the storage cell 12th be saved. Furthermore, the memory cell 12th over the connections 22 and 24th in the memory cell 12th Provide stored electrical energy and thus transmit it to the electrical machine, for example.

The electrode arrangement 18th comprises, for example, at least or exactly one anode and at least or exactly one cathode. The cathode and the anode are also referred to collectively as electrodes. For example, one of the electrodes is electrical with one of the connections 22 and 24th connected, the other electrode being connected to the corresponding other connection 24th respectively 22 is electrically connected. The respective lithium-sulfur cell has, for example, only active material, in particular in the form of sulfur in the cathode.

In order to ensure particularly safe operation and a particularly high energy density of the respective lithium-sulfur cell and thus of the storage device 10th To be able to implement the electrolyte 20th at least or exactly one ionic liquid and dimethyltrisulfide (DMTS). In particular, the electrolyte 20th , which is preferably liquid at room temperature or at 24 degrees Celsius, a, in particular liquid, mixture of the ionic liquid and at least one further liquid constituent, so that the further liquid constituent is a further liquid. The mixture thus comprises at least the ionic liquid and the further liquid. The DMTS is at least partially, in particular at least largely completely, dissolved in the mixture, so that, for example, the further liquid is a solvent for the DMTS, and the ionic liquid is a co-solvent for the DMTS.

In particular, the electrolyte 20th be formed from a one-molar solution of lithium bis (trifluoromethylsulfone) imide (LiTFSI) in 1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL), dimethyltrisulfide (DMTS) and the ionic liquid (IL). Thus, for example, the aforementioned further liquid comprises LiTFSI, DME and DOL, so that the mixture as a whole comprises LiTFSI, DME, DOL and IL. The DMTS is dissolved in the mixture. DME, DOL, DMTS and IL are present in the mixture in the mixing ratio 1: 1: 2: 2.

The ionic liquid is preferably 1-methyl-3-propylimidazolium bis (trifluoromethylsufonyl) imide, its skeletal formula and valence formula in 2nd are shown. The electrolyte described was used in experiments 20th compared with another electrolyte, also referred to as a reference electrolyte, the further electrolyte being a standard electrolyte in the form of a three-molar solution of LiTFSI in ethylene carbonate (EC) and dimethyl carbonate (DMC).

3rd shows a diagram on the abscissa 26 a number of cycles is plotted where on the ordinate 28 the capacity of sulfur is plotted in mA / g. One in the in 3rd shown diagram entered course 30th illustrates a capacity curve of the memory cell 12th whose cathode is, for example, a SPAN-based cathode (SPAN) (sulphorized poly (acrylonitrile) - sulfurized polyacrylonitrile). The anode of the memory cell 12th is formed, for example, from elemental lithium.

4th shows another diagram on the abscissa 32 the capacity of sulfur is plotted in mAh / g. On the ordinate 34 the electrical voltage is plotted. Thus, in that 4th shown graph entered curves 36 and 38 Voltage-capacity curves, the course 36 a voltage-capacity curve of an initial discharge of two first cells and the curve 38 is a voltage-capacity curve of an initial discharge of two second cells. The first two cells are, for example, two of the lithium-sulfur cells described above, so that the respective first cell of the memory cell 12th or their structure corresponds. The respective second cell corresponds, for example, to the memory cell 12th , with the difference that instead of the described electrolyte 20th the standard electrolyte described above is provided. Out 4th it can be seen that the respective first cell or the memory cell 12th can provide a significantly higher discharge capacity than the respective second cell. Thus, by using the electrolyte 20th particularly safe operation and high energy density can be achieved.

Reference list

10th

Storage device

12th

Memory cell

14

Cell housing

16

Recording room

18th

Electrode arrangement

20th

electrolyte

22

connection

24th

connection

26

Abscesses

28

ordinate

30th

course

32

abscissa

34

ordinate

36

course

38

course

Claims (8)

Electrolyte (20) for a lithium-sulfur cell (12) for storing electrical energy, with at least one ionic liquid, characterized in that the electrolyte (20) has at least dimethyl trisulfide. Electrolyte (20) after Claim 1 , characterized in that the dimethyl trisulfide is at least partially, in particular at least predominantly or completely, dissolved in the ionic liquid. Electrolyte (20) after Claim 1 or 2nd , characterized in that the electrolyte (20) has at least one component which is provided in addition to the dimethyltrisulfide and in addition to the ionic liquid and which is different from dimethyltrisulfide and from an ionic liquid. Electrolyte (20) after Claim 3 , characterized in that the component is another liquid. Electrolyte (20) after Claim 4 , characterized in that the dimethyl trisulfide is at least partially, in particular at least predominantly or completely, dissolved in the further liquid. Electrolyte (20) according to one of the Claims 3 to 5 , characterized in that the further component comprises at least dimethoxyethane and / or lithium bis (trifluoromethylsulfone) imide and / or dioxolane. Electrolyte (20) according to one of the preceding claims, characterized in that the ionic liquid has 1-methyl-3-propylimidazoliumbis (trifluoromethylsufonyl) imide. Storage device (10) for a motor vehicle, with at least one lithium-sulfur battery for storing electrical energy, the lithium-sulfur battery having a plurality of lithium-sulfur cells (12), each of which has an electrolyte according to one of the preceding claims .

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