DE102012209642A1 - Process for producing a polyacrylonitrile-sulfur composite - Google Patents

Abstract

The present invention relates to 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). Moreover, the present invention relates to a method for producing an active material for an electrode and an energy store.

Description

The present invention relates to a process 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- . These can diffuse into regions, for example the anode region, in which they can no longer participate in the electrochemical reaction of the subsequent charge / discharge cycles. In addition, polysulfides can be dissolved in the electrolyte, which can not be further reduced. In practice, therefore, currently the sulfur utilization and thus the energy density of lithium-sulfur cells is significantly lower and is currently estimated between 400 Wh / kg and 600 Wh / kg.

Regarding lithium-sulfur cells Nazar et al. in Nature Materials, Vol. 8, June 2009, 500-506 in that carbon tubes promote retention of polysulfides in the cathode compartment while providing 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, the sulfur being cyclized to form H ₂ S polyacrylonitrile into a conjugated π-system polymer, and in the cyclized matrix, in particular is bound via a carbon-sulfur bond.

Disclosure of the invention

• a) Umsetzen von Schwefel mit Polyacrylnitril mit einem Überschuss an Schwefel bei einer Temperatur von größer oder gleich 300°C, insbesondere von größer oder gleich 550°C;

wobei das Verhältnis von Schwefel zu Polyacrylnitril gewählt wird in Abhängigkeit der in Verfahrensschritt a) gewählten Umsetzungstemperatur.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 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).

A polyacrylonitrile-sulfur composite material (SPAN) can be understood in particular to be a composite material which is produced by reacting 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.

In this case, 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 can be produced, which is particularly suitable for producing an active material for a long-term stable cathode of a lithium-sulfur battery, in which the largest possible proportion of the active material can be used electrochemically over a long period of time.

In detail, sulfur is reacted with polyacrylonitrile in the process of the invention. For this purpose, an excess of sulfur is suitably used. Continue to be Production of composite materials advantageously used temperatures 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, for example in a range of greater or equal to 300 ° C to less than or equal to 400 ° C, can be adjusted. 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.

The fact that according to the method described above, the ratio of sulfur to polyacrylonitrile is selected depending on the reaction temperature selected in step a), in particular the set during the reaction maximum temperature can be further ensured that the largest possible amount of sulfur in the matrix formed of the composite material can be installed. As a result, a particularly high capacity can be provided, for example, in the purely exemplary use of the composite material as active material, for example in a lithium-ion battery. 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 be counteracted by a dependence of the ratio of sulfur to polyacrylonitrile to the reaction temperature selected 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. One reason 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 an always suitable and sufficient excess of sulfur with respect to the polyacrylonitrile, the polyacrylonitrile particles are sufficiently separated from each other, whereby each individual polyacrylonitrile particles can have a large amount of particular elemental sulfur in the immediate vicinity. This can lead, for example, to improved crosslinking of the polyacrylonitrile particles, for example with 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. For example, 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 chosen 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 may be disadvantageous, for example, since it can change the defined structure of the sulfur-polyacrylonitrile composite material.

In one embodiment, in step a), a mixture of sulfur and polyacrylonitrile in a range of greater than or equal to 7.5: 1 (wt .-%) can be implemented.

In particular, by such an increased proportion of sulfur at a temperature of greater 350 ° C., a particularly good contact of each individual polyacrylonitrile particle with the sulfur can be achieved, which can further increase the sulfur content in the composite particles to be produced.

As a result, for the exemplary case of using such a composite material as active material in an electrode for a lithium-ion battery, a particularly high capacity can be achieved. 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 can be introduced into a sulfur melt initially introduced at 250 ° C., for example by successive addition 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.

• b) Aufreinigen des erzeugten Kompositwerkstoffs.

Durch ein Aufreinigen kann der Polyacrylnitril-Schwefel-Kompositwerkstoff insbesondere von überschüssigem Schwefel getrennt werden und kann somit eine besonders definierte Struktur ohne die Gefahr weiterer Veränderungen einnehmen. Darüber hinaus kann ein Kompositwerkstoff nach einem Aufreinigen unmittelbar als Aktivmaterial dienen. Dabei kann der Kompositwerkstoff nach dem Aufreinigen insbesondere getrocknet werden. Ein Aufreinigen kann beispielsweise durch ein Versetzen des Komposit-Werkstoffs mit einem organischen Lösungsmittel, wie beispielsweise Toluol, durchgeführt werden. Dies kann zweckmäßigerweise erfolgen nach einem Abkühlen des bei erhöhter Temperatur erzeugten Komposit-Werkstoffs.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 Soxhlet extraction can be carried out with an apolar solvent or solvent mixture, for example toluene, and the excess sulfur removed. A Soxhlet 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 Soxhlet 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 as a second purification stage.

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, for example, an electrically conductive base in the form of the electrically conductive, cyclized polyacrylonitrile (cPAN) can thus be initially formed. In a further process step, the reaction can then take place 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 material (ScPAN). By separating into two partial reactions, the reaction conditions can advantageously be optimized for the respective reaction. The first process step here resembles a dehydrogenation reaction known from carbon fiber production, the second process step being similar to a reaction from another completely different technical field, namely the vulcanization reaction of rubber.

The sulfur atoms can both directly in the polyacrylonitrile-sulfur composite by covalent sulfur-carbon bonds as well as indirectly by one or more covalent sulfur-sulfur bonds and one or more sulfur-carbon bonds to the cyclized polyacrylonitrile skeleton.

Alternatively or additionally, a portion of the sulfur atoms of the polyacrylonitrile-sulfur composite material, for example in the form of polysulfide, intramolecularly intramolecularly on both sides with a cyclized polyacrylonitrile, in particular forming an S-heterocycle fused to the cyclized polyacrylonitrile strand, and / or intermolecularly with two cyclized polyacrylonitrile strands , in particular with the formation of a bridge, in particular polysulfide bridge, between the cyclized polyacrylonitrile strands, be covalently bonded.

In this case, the cyclization can be carried out in particular in an oxygen-containing atmosphere, for example an air or oxygen atmosphere. In this case, 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 or equal to 280 ° C, for example from greater than or equal to 230 ° C to less than or equal to 270 ° C, take place. 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 can take place in the presence of a cyclization catalyst. As cyclization catalysts known catalysts can be used, for example, from the production of carbon fiber. By adding a cyclization catalyst it is advantageously possible to reduce the reaction temperature and / or the reaction time of the reaction of the polyacrylonitrile with the sulfur.

In a further embodiment, in process step a) polyacrylonitrile can be reacted with sulfur in the presence of a catalyst. By adding a catalyst, 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 long chain length, for example, from 103 to 106 sulfur atoms. 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, 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 material 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 rubber vulcanization art. 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 vulcanization accelerator may comprise or consist of at least one sulfidic radical initiator. In particular, the sulfidic radical initiator may be selected from the group consisting of sulfidic metal complexes, for example obtainable by reaction of zinc oxide (ZnO) and tetramethylthiuramidisulfide or N, N-dimethylthiocarbamate, sulfenamides, for example 2-mercaptobenzothiazoylamine derivatives, and combinations thereof. For example, the reaction mixture may comprise 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% tetramethylthiuramidisulfide.

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. Vulcanization inhibitors suitable for this purpose are likewise known from the technical field of rubber vulcanization. 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 the vulcanization catalyst or vulcanization accelerator and / or vulcanization inhibitor, the properties of the polyacrylonitrile-sulfur composite material can be adjusted specifically. 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 method according to the invention for producing a polyacrylonitrile-sulfur composite material, reference is explicitly made to the explanations in FIG Connection with the inventive method for producing an active material for an electrode, the use, the energy storage, the figure and the figure description referenced.

The invention further provides a method for producing 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. In particular, it can be utilized here 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.

• c) Zumischen mindestens eines elektrisch leitenden Additivs zu dem Polyacrylnitril-Schwefel-Kompositwerkstoff, insbesondere ausgewählt aus der Gruppe bestehend aus Ruß, Graphit, Kohlenstofffasern, Kohlenstoffnanoröhrchen und Mischungen davon.

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

• 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.

• d) Zumischen mindestens eines Bindemittels, insbesondere von Polyvinylidenfluorid und/oder Polytetrafluorethylen, zu dem Polyacrylnitril-Schwefel-Kompositwerkstoff.

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

• d) admixing at least one binder, in particular polyvinylidene fluoride and / or polytetrafluoroethylene, to the polyacrylonitrile-sulfur composite material.

In this case, 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 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.

• – in Verfahrensschritt c) und/oder in Verfahrensschritt d) größer oder gleich 60Gew.-% bis kleiner oder gleich 90Gew.-%, insbesondere größer oder gleich 65Gew.-% bis kleiner oder gleich 75Gew.-%, beispielsweise 7 Gew.-% an Polyacrylnitril-Schwefel-Kompositwerkstoff verwendet werden, und/oder
• – in Verfahrensschritt c) größer oder gleich 0,1Gew.-% bis kleiner oder gleich 30Gew.-%, beispielsweise größer oder gleich 5Gew.-% bis kleiner oder gleich 20Gew.-%, an elektrisch leitenden Additiven zugemischt werden, und/oder
• – in Verfahrensschritt d) größer oder gleich 0,1Gew.-% bis kleiner oder gleich 30Gew.-%, beispielsweise größer oder gleich 5Gew.-% bis kleiner oder gleich 20Gew.-%, an Bindemitteln zugemischt werden.

Within the scope of a further embodiment

• In process step c) and / or in process step d) greater than or equal to 60 wt% to less than or equal to 90 wt%, in particular greater than or equal to 65 wt% to less than or equal to 75 wt%, for example 7 wt% be used% of 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, of electrically conductive additives, and / or
• In process step d) 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, of binders are admixed.

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 total of 100 weight percent 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 by a previously described method, as 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, 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 method for producing an active material for an electrode, the energy store, the figure and the description of the figures.

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.

In order to produce such an energy store, an active material prepared as described above may comprise, in particular in the form of a cathode material slurry for producing a cathode, furthermore at least one solvent, for example N-methyl-2-pyrrolidone. Such a cathode metatarsal slurry 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. In principle, the electrolyte solvent can 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 include or consist of diethyl carbonate (DEC), dimethyl carbonate (DMC), propylene carbonate (PC), ethylene carbonate (EC), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), or a combination thereof , The conductive salt may, for example, be selected from the group consisting of lithium hexafluorophosphate (LiPF ₆ ), lithium bis (trifluoromethylsulphonyl) imide (LiTFSI), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium chlorate (LiClO ₄ ), lithium bis (oxalato) borate (LiBOB), lithium fluoride (LiF), lithium nitrate (LiNO 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 store may be an energy store for a vehicle, such as an electric or 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 telecommunications device as a cellphone, PDA, or a high energy storage system for a home or 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 energy storage device according to the invention, reference is hereby explicitly made to the explanations in connection with the inventive method for producing a polyacrylonitrile-sulfur composite material, the method for producing an active material for an electrode, the use of the figure and the description of the figures.

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

1 a diagram showing the capacity curve of test cells as a function of the sulfur concentration in the cathode.

In the following, an example of the production of a polyacrylonitrile-sulfur composite material according to the invention or an active material based thereon or an electrode according to the invention for a lithium-sulfur battery with subsequent electrochemical characterization is shown. In detail it examines the dependence of the capacity of a Energy storage of the sulfur content in an active material comprising a sulfur-polyacrylonitrile composite material according to the invention produced.

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 .-%) mixed in N-methyl-2-pyrrolidone (NMP) as a solvent and homogenized. The slurry is knife-coated on an aluminum foil and dried. After complete drying, a cathode is punched out and installed in a test cell against a lithium-metal anode. The electrolyte used are various cyclic and linear carbonates (DEC, DMC, EC) and mixtures thereof with a lithium-containing electrolyte salt (for example LiPF ₆ , lithium bis (trifluoromethanesulfonyl) imide (LiTFSI).

1 shows a capacity curve of test cells as a function of the educt mixture or the sulfur content. The X-axis shows the number of cycles N and the Y-axis the specific capacity c _{s of} the cathode in mAh / g (cathode). Different capacity curves are shown, of which curve A corresponds to a ratio of 15: 1 (wt.%) Of sulfur to polyacrylonitrile during the preparation of the polyacrylonitrile composite and a sulfur content in the composite of 31 wt.%, Of which curve B corresponds to a ratio of 10: 1 (wt.%) Of sulfur to polyacrylonitrile during the preparation of the polyacrylonitrile composite and a sulfur content in the composite of 27 wt.% Of which Curve C has 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% by weight, and of which curve D is a ratio of 3: 1 (wt%) of sulfur to polyacrylonitrile during production of the polyacrylonitrile composite and a sulfur content in the composite 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 composites, increasing the sulfur content in the composite by 5% results in a capacity increase of about 60-70mAh / g _cathode . This corresponds to a relative increase of 15-20% in relation to the actually achievable capacity.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Nazar et al. in Nature Materials, Vol. 8, June 2009, 500-506 [0003]
• Wang et al. describe in Advanced Materials, 14, 2002, No. 13-14, pp. 963-965 [0004]
• Advanced Functional Materials, 13, 2003, No. 6, pp. 487-492 [0004]
• Yu et al. describe in Journal of Electroanalytical Chemistry, 573, 2004, 121-128 [0004]
• Journal of Power Sources 146, 2005, 335-339 [0004]

Claims (13)

A method of 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 depending on the reaction temperature selected in process step a). 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. The method of claim 1 or 2, wherein the method comprises the further method step: b) purifying the composite material produced. 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. Method according to one of claims 1 to 4, wherein at least the method step a) is carried out under an inert gas atmosphere. A process according to any one of claims 1 to 5, wherein in step a) a cyclized polyacrylonitrile is reacted with sulfur, the cyclized polyacrylonitrile being 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 the step of: 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. Method according to one of claims 8 or 9, wherein the method further comprises the method step: d) admixing at least one binder, in particular polyvinylidene fluoride and / or polytetrafluoroethylene, to the polyacrylonitrile-sulfur composite material. 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 especially 70% by weight be used% of 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, of electrically conductive additives, and / or In process step d) 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, of binders are admixed. Use of a polyacrylonitrile-sulfur composite material produced 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. Energy storage, in particular lithium-sulfur battery, comprising an electrode with an active material comprising a polyacrylonitrile-sulfur composite, which is prepared according to a method according to any one of claims 1 to 7.

Images