WO2013182360A1

WO2013182360A1 - Method for the production of a polyacrylonitrile-sulfur composite material

Info

Publication number: WO2013182360A1
Application number: PCT/EP2013/059302
Authority: WO
Inventors: Jean Fanous; Martin Tenzer
Original assignee: Robert Bosch Gmbh
Priority date: 2012-06-08
Filing date: 2013-05-03
Publication date: 2013-12-12
Also published as: DE102012209642A1

Abstract

The invention relates to a method for producing a polyacrylonitrile-sulfur composite material, comprising the step of: a) reacting sulfur with polyacrylonitrile with excess sulfur at a temperature of at least 300°C, in particular at least 550°C; the ratio between sulfur and polyacrylonitrile being selected according to the reaction temperature selected in step a). The invention further relates to a method for producing an active material for an electrode as well as to an energy accumulator.

Description

Description title

Process for producing a polyacrylonitrile-sulfur composite

The present invention relates to a method for producing a

Polyacrylonitrile-sulfur composite material, in particular as an active material for an alkali-sulfur battery, for example for a lithium-sulfur battery. The present invention further relates to a method for producing an active material for an electrode, in particular for a cathode of a lithium-sulfur battery. The invention further relates to an energy store.

State of the art

In order to produce batteries with a high energy density, research is currently being conducted on lithium-sulfur battery technology (Li / S for short). Inasmuch as the cathode of a lithium-sulfur cell would consist entirely of elemental sulfur, theoretically an energy content above 1,000 Wh / kg could be achieved.

However, elemental sulfur is neither ionic nor electrically conductive, so additives must be added to the cathode that significantly lower the theoretical value. In addition, elemental sulfur is conventionally reduced in the discharge of a lithium-sulfur cell to soluble polysulfides S _x ^{2 "} , which can diffuse into regions, for example the anode region, in which they participate in the electrochemical reaction of the following

Charging / discharging cycles can no longer participate. In addition, in the

Electrolytes polysulfides be dissolved, which can not be further reduced. In practice, therefore, currently the sulfur utilization and thus the

Energy density of lithium-sulfur cells significantly lower and is currently estimated between 400 Wh / kg and 600 Wh / kg. With respect to lithium-sulfur cells, Nazar et al. in Nature Materials, Vol. 8, June 2009, 500-506 that carbon tubes favor retention of polysulfides in the cathode compartment and at the same time for a

provide adequate electrical conductivity.

Wang et al. describe in Advanced Materials, 14, 2002, No. 13-14, pp. 963-965 and Advanced Functional Materials, 13, 2003, No. 6, pp. 487-492 and Yu et al. describe in Journal of Electroanalytical Chemistry, 573, 2004, 121-128 and Journal of Power Sources 146, 2005, 335-339 another technology in which polyacrylonitrile (PAN for short) is heated with an excess of elemental sulfur, wherein the sulfur to one is cyclized to form H ₂ S polyacrylonitrile to a polymer with conjugated ττ system and on the other hand in the cyclized matrix, in particular via a carbon-sulfur bond is bound.

Disclosure of the invention

The present invention is a process for producing a polyacrylonitrile-sulfur composite material, comprising the process step: a) reacting sulfur with polyacrylonitrile with an excess of sulfur at a temperature of greater than or equal to 300 ° C, in particular greater than or equal to 550 ° C;

wherein the ratio of sulfur to polyacrylonitrile is chosen depending on the reaction temperature selected in process step a).

Under a polyacrylonitrile-sulfur composite material (SPAN) can

in particular a composite material can be understood, which is prepared by a reaction of polyacrylonitrile (PAN) with sulfur (S).

The sulfur atoms in the polyacrylonitrile-sulfur composite may be bonded to a particular cyclized polyacrylonitrile backbone both directly by covalent sulfur-carbon bonds and indirectly by one or more covalent sulfur-sulfur bonds and one or more sulfur-carbon bonds. At least part of the sulfur atoms of the polyacrylonitrile-sulfur composite material, for example in the form of polysulfide chains, may be covalently bonded to a cyclized polyacrylonitrile strand.

With such composite materials, there is thus evidence of a sulfur-carbon bond, which thus binds the polysulfides firmly to the polymer matrix. Consequently, a sulfur-polyacrylonitrile composite with different functional groups and chemical bonds is formed, all of which may have different properties and contributions in terms of electrochemical performance and aging behavior.

By a method described above, a sulfur-polyacrylonitrile composite material having a particularly defined structure, high

Sulfur content and a good electrochemical cycle stability are produced, which is particularly suitable for producing an active material for a long-term stable cathode of a lithium-sulfur battery, wherein the largest possible proportion of the active material over a long period

can be used electrochemically.

In detail, sulfur is reacted with polyacrylonitrile in the process of the invention. For this purpose, an excess of sulfur is suitably used. Furthermore, advantageously temperatures are used for the production of composite materials, which are in a range of greater than or equal to 300 ° C, in particular greater than or equal to 550 ° C. This allows a conversion of sulfur and polyacrylonitrile proceed with particularly good turnovers and also a composite material can be achieved with a particularly good rate capability. In other words, for the purely exemplary case of use as active material in a lithium-sulfur battery, a particularly good charging or discharging behavior can be realized.

The reaction can be carried out in less than 12 hours, in particular less than 8 hours, for example 5 hours to 7 hours, for example in about 6 hours.

In particular, during the reaction, first a first temperature, for example in a range of greater than or equal to 300 ° C to less than or equal to 600 ° C, and then a second temperature, which is lower than the first Temperature is, for example, in a range of greater than or equal to 300 ° C to less than or equal to 400 ° C, can be set. In this case, the phase within which the second temperature is set, in particular, be longer than the phase in which the first temperature is set. By the first temperature phase, a cyclization of the polyacrylonitrile can be effected. During the second temperature phase, essentially the formation of covalent sulfur-carbon bonds can take place. As a result of the fact that a lower temperature is set here, longer polysulfide chains can, as already explained, be linked to the cyclized polyacrylonitrile skeleton.

Characterized in that according to the method described above, the ratio of sulfur to polyacrylonitrile is selected depending on in

Process step a) chosen reaction temperature, in particular the set during the reaction of the maximum temperature can be further ensured that the largest possible amount of sulfur can be incorporated into the formed matrix of the composite material. As a result, as in the purely exemplary use of the composite material as

Active material about a lithium-ion battery can be provided a particularly high capacity. In this case, this can be realized in particular without adversely affecting further reaction parameters, that is, for example, to extend the reaction time.

It can by a dependence of the ratio of sulfur to

Polyacrylonitrile to be counteracted in the reaction temperature chosen in process step a) in particular the effect that at a high

Reaction temperature of sulfur and polyacrylonitrile comparatively little sulfur is bound in the matrix of the composite material. A justification for this can be seen in particular in the fact that at higher

Temperatures, the chain lengths of the sulfur molecules are shorter and thus reduces the sulfur content in the matrix or in the framework. In particular, by always a suitable and sufficient

Excess of sulfur relative to the polyacrylonitrile, the polyacrylonitrile particles are sufficiently separated from each other, whereby each individual

Polyacrylonitrile particles a large amount of particular elemental

Sulfur may have in the immediate vicinity. This can for example improved crosslinking of the polyacrylonitrile particles with about

Lead sulfur bridges. In addition, a large amount of especially elemental sulfur in the immediate vicinity of the polyacrylonitrile particles also offers the possibility of realizing longer chain lengths, since further sulfur radicals are available.

Thus, in the method described above, the ratio of sulfur to polyacrylonitrile is chosen, in particular in such a dependence of the reaction temperature chosen in process step a), that at an increasing temperature, a larger amount of sulfur based on the amount of polyacrylonitrile used is used. By way of example only, at a temperature of about 330 ° C, for example, a

Ratio of sulfur to polyacrylonitrile in wt .-% in a range of 3: 1 to 5: 1 and at a temperature of 550 ° C, a ratio of sulfur to

Polyacrylonitrile in wt .-% in a range of 15: 1 can be adjusted.

Thus, by the process according to the invention, a reaction of sulfur with polyacrylonitrile can be improved such that an excess of sulfur with respect to polyacrylonitrile is always selected as a function of the temperature such that a sufficient amount of sulfur is incorporated into the polyacrylonitrile matrix to form the composite material In particular, the sulfur can be covalently bonded to the polyacrylonitrile matrix, but can still be reduced or prevented that excess sulfur remains as an unbound or free radical in the composite material. Such a sulfur radical can be disadvantageous, for example, because it can change the defined structure of the sulfur-polyacrylonitrile composite material.

In one embodiment, in process step a), a mixture of sulfur and polyacrylonitrile can be reacted in a range of greater than or equal to 7.5: 1 (% by weight).

In particular, by such an increased amount of sulfur in a

Temperature of greater than 350 ° C, a particularly good contact of each individual polyacrylonitrile particle can be achieved with the sulfur, which the

Sulfur content in the composite particles to be produced can further increase. As a result, a particularly high capacity can be achieved for the exemplary case of using such a composite material as active material in an electrode for a lithium-ion battery. Thus, in this embodiment, not only the rate capability is particularly improved in a particularly advantageous manner, but at the same time increases the capacity even at high temperatures.

For example, the weight ratio of sulfur to polyacrylonitrile may be greater than or equal to 7.5: 1 (wt .-%) and in particular less than or equal to 20: 1 wt .-%).

In an extreme case, and in particular at greatly elevated temperatures, for example, pure polyacrylonitrile or a polyacrylonitrile-sulfur mixture may be introduced into a sulfur melt initially introduced at 250.degree.

for example, by successive adding with stirring. Subsequently, the mixture can be stirred for some time at this temperature purely by way of example and the reaction then be continued at a temperature in a range of greater than or equal to 300 ° C to less than or equal to 550 ° C.

Within the scope of a further embodiment, the method may comprise the further method step:

b) purifying the composite material produced.

By purifying the polyacrylonitrile-sulfur composite material can be separated in particular from excess sulfur and thus can take a particularly defined structure without the risk of further changes. In addition, a composite material can serve directly as an active material after a cleaning. In this case, the composite material after the cleaning can be dried in particular. Purification can be performed, for example, by offsetting the composite material with an organic solvent such as toluene. This may conveniently be done after cooling the composite material produced at elevated temperature.

In this case, the purification according to process step b) can be carried out by a Soxhlet extraction, in particular wherein the Soxhlet extraction can be carried out using an organic solvent. In particular, the Soxhiet extraction can be carried out with an apolar solvent or solvent mixture, for example toluene, and the excess sulfur removed. Soxhiet extraction is a particularly simple and cost-effective method and is particularly gentle on the composite material produced, so that no structural change of the particles can take place during the purification. As a result, the rate capability can remain particularly stable. The Soxhiet extraction can also take place, for example, immediately after cooling of the composite material, or also after prior treatment of the composite material with an organic solvent, for example second

Purification step.

Within the scope of a further embodiment, at least the method step a) can be carried out under an inert gas atmosphere. Surprisingly, it has been found that an inert gas atmosphere can help to obtain a particularly homogeneous and defined structure of the polyacrylonitrile-sulfur composite material. In this context, an inert gas atmosphere can be understood as meaning in particular an atmosphere of an unreactive gas in the conditions prevailing in process step a).

For example, an inert gas atmosphere may be formed by argon or nitrogen.

In a further embodiment, a cyclized polyacrylonitrile can be reacted with sulfur in the process step a), wherein the cyclized polyacrylonitrile can be obtained by reacting polyacrylonitrile to cyclized polyacrylonitrile.

In a first method step, an electrically conductive base in the form of the electrically conductive, cyclized first, for example, can thus be used

Polyacrylonitrile (cPAN) are formed. In a further process step, the reaction can then be carried out with the electrochemically active sulfur, in particular wherein this can be covalently bonded to the electrically conductive skeleton of cyclized polyacrylonitrile to form a polyacrylonitrile-sulfur composite (ScPAN). By separating into two partial reactions, the reaction conditions can advantageously be optimized for the respective reaction. The first process step is similar a dehydrogenation reaction known from carbon fiber manufacture, the second process step being similar to a reaction from another completely different technical field, namely the vulcanization reaction of rubber.

The sulfur atoms may be cyclized in the polyacrylonitrile-sulfur composite both directly through covalent sulfur-carbon bonds and indirectly through one or more covalent sulfur-sulfur bonds and one or more sulfur-carbon bonds

Polyacrylnitrilgerüst be connected.

Alternatively or additionally, a portion of the sulfur atoms of the

Polyacrylonitrile-sulfur composite material, for example in the form of

Polysulfide chains, bilaterally intramolecular with a cyclized

Polyacrylonitrile, in particular with the formation of a cyclized to the

Polyacrylonitrile strand annelierten S-heterocycle, and / or intermolecularly with two cyclized polyacrylonitrile strands, in particular to form a bridge, in particular Polysulfidbrücke, between the cyclized polyacrylonitrile strands, covalently connected.

In this case, the cyclization in particular in an oxygen-containing

Atmosphere, for example, an air or oxygen atmosphere, take place. The cyclization may, for example, at a temperature in a range of greater than or equal to 150 ° C to less than or equal to 500 ° C,

in particular from greater than or equal to 150 ° C to less than or equal to 330 ° C or less than or equal to 300 ° C or less than or equal to 280 ° C, for example from greater than or equal to 230 ° C to less than or equal to 270 ° C.

Advantageously, the reaction time of the first process step may be less than 3 hours, in particular less than 2 hours, for example less than 1 hour. In particular, the first process step in the presence of a

Cyclization take place. As cyclization catalysts known catalysts can be used, for example, from the production of carbon fiber. By the addition of a Zyklisierungskatalysators can

advantageously the reaction temperature and / or the reaction time of the reaction of the polyacrylonitrile with the sulfur are reduced. Within the scope of a further embodiment, in method step a)

Polyacrylonitrile can be reacted with sulfur in the presence of a catalyst. By adding a catalyst can advantageously the

Reaction temperature and the reaction time can be reduced. By lowering the reaction temperature, moreover, the chain length of polysulfides covalently bonded to the cyclized polyacrylonitrile can be increased. This is because elemental sulfur is present at room temperature in the form of S8 rings. At temperatures above room temperature, sulfur is in the form of medium chain Sx chains, for example, from 6 to 26 sulfur atoms, or large chain length, for example, from 103 to 106

Sulfur atoms, before. Above 187 ° C, a thermal cracking process begins and the chain length decreases again. From 444, 6 ° C (boiling point) is gaseous sulfur with a chain length of 1-8 atoms. The use of a vulcanization catalyst has the advantage that at a lower temperature, longer inter- and / or intramolecular, covalently bonded to, in particular cyclized, polyacrylonitrile bound sulfur bridges can be introduced into the polyacrylonitrile-sulfur composite material. Thus, in turn, advantageously, a higher sulfur content of the polyacrylonitrile-sulfur composite and thus a higher capacity and energy density of auszustattenden with the cathode material alkali-sulfur cell, in particular

Lithium-sulfur cell, can be achieved.

Suitable catalysts are known in the technical field

Rubber vulcanization known. The reaction is therefore preferably carried out here at least temporarily in the presence of a vulcanization catalyst or vulcanization accelerator. In particular, the vulcanization catalyst or

Vulkanisationsbeschleuniger comprise or consist of at least one sulfidic radical initiator. In particular, the sulfidic

Radical starter may be selected from the group consisting of sulfidic

Metal complexes, for example obtainable by reaction of zinc oxide (ZnO) and tetramethylthiuramidisulfide or Ν, Ν-dimethylthiocarbamate, sulfenamides, for example 2-mercaptobenzothiazoylamine derivatives, and combinations thereof. For example, the reaction mixture may be greater than or equal to 3 wt% to less than or equal to 5 wt% zinc oxide and optionally greater than or equal to 0.5

Wt .-% to less than or equal to 1 wt .-% Tetramethylthiuramidisulfid. In order to reduce the reaction rate or terminate a reaction phase with, for example, by the catalyst, increased reaction rate, the reaction can be carried out at least temporarily in the presence of a vulcanization inhibitor. Suitable for this

Vulcanization inhibitors are also known in the rubber vulcanization art. For example, N- (cyclohexylthio) phthalamide can be used as a vulcanization inhibitor. Through the use and duration of the use of the catalyst, in particular of the vulcanization catalyst or vulcanization accelerator and / or vulcanization inhibitor, the properties of the polyacrylonitrile-sulfur composite material can be adjusted in a targeted manner. Optionally, the catalyst and optionally the inhibitor are partially or completely removed in a removal step.

With regard to further features and advantages of the inventive method for producing a polyacrylonitrile-sulfur composite material is hereby explicitly to the explanations in connection with the inventive method for producing an active material for an electrode, the

Use, the energy storage, the figure and the description of the figures referenced.

The invention further relates to a method for producing a

An active material for an electrode, in particular for a cathode of a lithium-sulfur battery, comprising a method configured as described above for producing a polyacrylonitrile-sulfur composite material. Here, in particular, it can be utilized that a polyacrylonitrile-sulfur composite material produced as described above can have advantageous properties, in particular a high rate capability, in particular as active material of an electrode, in particular a cathode, for a lithium-sulfur battery. As a result, for example, an energy store equipped with this can have a particularly preferred charging and / or discharging behavior.

As part of an embodiment, the method can continue the

Process step include: c) admixing at least one electrically conductive additive to the

Polyacrylonitrile-sulfur composite material, in particular selected from the group consisting of carbon black, graphite, carbon fibers, carbon nanotubes and mixtures thereof.

In this case, by way of example, greater than or equal to 0.1% by weight to less than or equal to 30% by weight, for example greater than or equal to 5% by weight to less than or equal to 20% by weight, can be admixed to electrically conductive additives. By adding an electrically conductive additive, the conductivity and thus the rate capability of the resulting mixture can be further improved, which makes use as an active material in an electrode particularly advantageous.

Within the scope of a further embodiment, the method may further comprise the method step:

d) admixing at least one binder, in particular of

Polyvinylidene fluoride and / or polytetrafluoroethylene, to which

Polyacrylonitrile-sulfur composite.

In this case, greater than or equal to 0.1% by weight to less than or equal to 30% by weight, for example greater than or equal to 5% by weight to less than or equal to 20% by weight, can be admixed to binders. In particular, the stability of the cathode material can be improved by adding binders, which can improve use in electrochemical energy stores. The binder may be added together with N-methyl-2-pyrrolidone as a solvent.

Within the scope of a further embodiment

in process step c) and / or in process step d) greater than or equal to 60% by weight to less than or equal to 90% by weight, in particular greater than or equal to 65% by weight to less than or equal to 75% by weight, for example 7% by weight be used on polyacrylonitrile-sulfur composite material, and / or

in process step c) greater than or equal to 0.1% by weight to less than or equal to 30% by weight, for example greater than or equal to 5% by weight to less than or equal to 20% by weight, are admixed to electrically conductive additives, and / or in process step d) greater than or equal to 0.1 wt% to less than or equal to 30 wt%, for example greater than or equal to 5 wt% to less than or equal to 20 wt%, are admixed to binders.

In this case, the sum of the percentages by weight of polyacrylonitrile-sulfur composite material, electrically conductive additives and binders, depending on the use, in particular a total of 100 percent by weight result.

With regard to further features and advantages of the method according to the invention for producing an active material for an electrode, reference is hereby explicitly made to the explanations in connection with the method according to the invention for producing a polyacrylonitrile-sulfur composite material, the use, the energy store, the figure and the description of the figures.

The invention further provides the use of a polyacrylonitrile-sulfur composite material, prepared according to a previously described

Method, as an active material in an electrode, in particular in a cathode of a lithium-ion battery. In particular, as an active material, a composite material thus produced can provide advantageous properties such as good capacity and rate capability.

With regard to further features and advantages of the use according to the invention is hereby explicitly to the explanations in connection with the

Inventive method for producing a polyacrylonitrile-sulfur composite, the method for producing an active material for an electrode, the energy storage, the figure and the figure description referenced.

The invention furthermore relates to an energy store, in particular a lithium-sulfur battery, comprising an electrode with an active material which has a polyacrylonitrile-sulfur composite material produced as described above.

To produce such an energy storage, an active material produced as described above, in particular in the form of a

Kathodenmatenalschlickers for producing a cathode, continue at least a solvent, for example N-methyl-2-pyrrolidone. Such a cathode metal slag can be applied, for example by doctoring, to a carrier material, for example an aluminum plate or foil. The solvents are preferably removed again after the application of the cathode material and before the assembly of the lithium-sulfur cell, preferably completely, in particular by a drying process.

The cathode material-carrier material arrangement can then be divided into several cathode material-carrier material units, for example by punching or cutting.

The cathode material-carrier material arrangement or units can be installed with a lithium metal anode, for example in the form of a plate or foil of metallic lithium, to form a lithium-sulfur cell.

In particular, a later-explained electrolyte can be added.

The anode may in particular be an alkali metal anode, in particular a lithium metal anode, for example in the form of a plate or foil, for example of metallic lithium.

In this case, the alkali-sulfur cell or battery may comprise an electrolyte, in particular of at least one electrolyte solvent and at least one conductive salt. Basically, the electrolyte solvent may be selected from the group consisting of carbonic acid esters,

in particular cyclic or acyclic carbonates, lactones, ethers, in particular cyclic or acyclic ethers, and combinations thereof. For example, the electrolyte solvent may be diethyl carbonate (DEC),

Dimethyl carbonate (DMC), propylene carbonate (PC), ethylene carbonate (EC), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), or a combination thereof, or consisting thereof. The salt can for example be selected from the group consisting of lithium hexafluorophosphate (LiPF _6), lithium bis (trifluormethylsulphonyl) imide (LiTFSI), lithium tetrafluoroborate (LiBF _4), lithium trifluoromethanesulfonate (LiCF ₃ S0 _3), lithium chlorate (LiCI0 ₄₎ Lithium bis (oxalato) borate (LiBOB), lithium fluoride (LiF), lithium nitrate (LiN0 ₃ ), lithium hexafluoroarsenate (LiAsF ₆ ), and combinations thereof.

Further, the electrolyte solvent may be selected from the group consisting of cyclic ethers, acyclic ethers, and combinations thereof, and / or may include the conductive salt lithium bis (trifluoromethylsulphonyl) imide (LiTFSI). These electrolyte solvents or this conductive salt have proved to be advantageous for cathode materials according to the invention, in particular to avoid reactions between the elemental sulfur and the electrolyte.

An energy store that can be produced in this way can be, in particular, a mobile or stationary energy store, which comprises an alkali-sulfur cell or battery according to the invention, in particular a lithium-sulfur cell or battery. For example, the energy storage device may be an energy storage device for a vehicle, for example an electric or electronic vehicle

Hybrid vehicle, or a power tool or device, such as a screwdriver or gardening tool, or an electronic device, such as a portable computer and / or a

Telecommunication device, such as a mobile phone, PDA, or a

High energy storage system for a home or a facility. Since the alkali-sulfur cells or batteries according to the invention have a very high energy density, they are particularly suitable for vehicles and stationary storage systems, such as high-energy storage systems for houses or installations.

With regard to further features and advantages of the invention

Energy storage is hereby explicitly to the explanations in connection with the inventive method for producing a polyacrylonitrile-sulfur composite material, the method for producing a

Active material for an electrode, the use, the figure and the

Figure description referenced. Examples and drawings

Further advantages and advantageous embodiments of the subject invention are illustrated by the examples and the drawings and explained in the following description. It should be noted that the examples and drawings are only descriptive and are not intended to limit the invention in any way. It shows

Fig. 1 is a diagram showing the capacity curve of test cells in

Dependence of sulfur concentration in the cathode.

The following is an example of the preparation of a polyacrylonitrile-sulfur composite material according to the invention or of an active material based thereon or an inventive material

Electrode for a lithium-sulfur battery with subsequent

electrochemical characterization. The dependence of the capacity of an energy store on the sulfur content in an active material comprising a sulfur-polyacrylonitrile composite material produced according to the invention is examined in detail.

The sulfur-containing, cyclized polyacrylonitrile, ie the finished composite, is processed to a cathode slurry for forming a cathode active material. For this, the active material (SPAN), carbon black (such as the carbon black available under the trade name Super P Li) as an electrically conductive additive and polyvinylidene fluoride (PVDF) as a binder or binder in a ratio of 70:15:15 (in wt .-%) in N-methyl-2-pyrrolidone (NMP) as

Solvent mixed and homogenized. The slurry will be on one

Lapped and dried aluminum foil. After complete drying, a cathode is punched out and installed in a test cell against a lithium-metal anode. Various cyclic and linear carbonates (DEC, DMC, EC) and mixtures thereof with a lithium-containing conducting salt (for example LiPF ₆ , lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) are used as the electrolyte.) Figure 1 shows a dependence on the capacity of test cells of the

Eduktmischung or the sulfur content. This shows the X-axis the number of cycles N and the Y-axis the specific capacity c _{s of} the cathode in mAh / g (cathode). In this case, different capacity curves are shown, of which curve A a ratio of 15: 1 (wt .-%) of sulfur to

Polyacrylonitrile during the preparation of the polyacrylonitrile composite and a sulfur content in the composite material of 31 wt .-% of which curve B a ratio of 10: 1 (wt .-%) of sulfur to polyacrylonitrile during the preparation of the polyacrylonitrile composite material and corresponds to a sulfur content in the composite material of 27 wt .-%, of which curve C to a ratio of 5: 1 (wt .-%) of sulfur to

Polyacrylonitrile during the preparation of the polyacrylonitrile composite and a sulfur content in the composite of 24 wt .-%, and of which curve D a ratio of 3: 1 (wt .-%) of sulfur to polyacrylonitrile during the preparation of the polyacrylonitrile composite and a sulfur content in the composite material of 22% by weight.

It can be clearly seen that with increasing sulfur-PAN ratio in the educt mixture, the sulfur content in the composite and thus also in the cathode increases. This can go completely into extra capacity. Thus, the output capacity of about 300mAh can be increased by about 50% and achieves a stable capacity of about 450mAh with a reactant mixture of 15: 1.

It can be seen that with respect to the theoretical capacity of the

Composite materials, an increase in the sulfur content in the composite by 5% to a capacity increase of about 60-70mAh / g _Ka Thode leads. This corresponds to a relative increase of 15-20% in relation to the actually achievable capacity.

Claims

claims

A process for producing a polyacrylonitrile-sulfur composite comprising the step of:

a) reacting sulfur with polyacrylonitrile with an excess of sulfur at a temperature greater than or equal to 300 ° C, in particular greater than or equal to 550 ° C;

wherein the ratio of sulfur to polyacrylonitrile is chosen in

Dependence of the reaction temperature selected in process step a).

2. The method of claim 1, wherein in step a) a mixture of sulfur and polyacrylonitrile in a range of greater than or equal to 7.5: 1 is reacted.

3. The method of claim 1 or 2, wherein the method further

Process step includes:

b) purifying the composite material produced.

4. The method of claim 3, wherein the purifying according to step b) is carried out by a Soxhlet extraction, in particular wherein the Soxhlet extraction is carried out using an organic

Solvent.

5. The method according to any one of claims 1 to 4, wherein at least the

Process step a) is carried out under an inert gas atmosphere.

6. The method according to any one of claims 1 to 5, wherein in the

Process step a) a cyclized polyacrylonitrile is reacted with sulfur, wherein the cyclized polyacrylonitrile is obtained by reacting polyacrylonitrile to cyclized polyacrylonitrile. Method according to one of claims 1 to 6, wherein in step a) polyacrylonitrile is reacted with sulfur in the presence of a catalyst

A method for producing an active material for an electrode, in particular for a cathode of a lithium-sulfur battery, comprising a method according to one of claims 1 to 7.

The method of claim 8, wherein the method further comprises

Process step includes:

c) admixing at least one electrically conductive additive to the

Polyacrylonitrile-sulfur composite material, in particular selected from the group consisting of carbon black, graphite, carbon fibers, carbon nanotubes and mixtures thereof. 10. The method according to any one of claims 8 or 9, wherein the method

further comprising the method step:

d) admixing at least one binder, in particular of

Polyvinylidene fluoride and / or polytetrafluoroethylene, to which

Polyacrylonitrile-sulfur composite.

1 1. A method according to any one of claims 8 to 10, wherein

in process step c) and / or in process step d) greater than or equal to 60% by weight to less than or equal to 90% by weight, in particular greater than or equal to 65% by weight to less than or equal to 75% by weight, further preferably 70% by weight be used on polyacrylonitrile-sulfur composite material, and / or

in process step c) greater than or equal to 0.1% by weight to less than or equal to 30% by weight, for example greater than or equal to 5% by weight to less than or equal to 20% by weight, are admixed to electrically conductive additives, and / or

in process step d) greater than or equal to 0.1 wt% to less than or equal to 30 wt%, for example greater than or equal to 5 wt% to less than or equal to 20 wt%, are admixed to binders.

12. Use of a polyacrylonitrile-sulfur composite material prepared by a process according to any one of claims 1 to 7 as an active material in an electrode, in particular in a cathode of a lithium-ion battery.

13. Energy storage device, in particular lithium-sulfur battery, comprising an electrode with an active material containing a polyacrylonitrile-sulfur

Composite material, which is prepared according to a method according to one of claims 1 to 7.