Method of producing a positive electrode, positive electrode and battery

Abstract

A method of producing a positive electrode (10) having a collector (12) and a positive active material (18) applied to the collector (12) for a sodium ion battery or a potassium ion battery comprises a step in which the positive active material (18) in solution is provided with a coating (20) of a polythiophene. The invention also provides a positive electrode and a battery.

Description

[0001] Method for producing a positive electrode, positive electrode and battery

[0002] The invention relates to a method for producing a positive electrode for a sodium ion battery or a potassium ion battery, a positive electrode obtained according to such a method, and a battery comprising such a positive electrode.

[0003] Sodium and potassium ion batteries are promising battery types that offer an alternative to conventional lithium-ion batteries, for example, as energy storage devices in vehicles or stationary energy storage systems. A particular advantage is that these batteries do not require lithium, an element that is less common than sodium and potassium. Furthermore, cell chemistries are available for sodium and potassium ion batteries that also eliminate the need for other rare or difficult-to-obtain metals such as cobalt, nickel, and / or copper.

[0004] However, there is a need to further optimize the property profile of such sodium and potassium ion batteries in order to further improve their longevity, charging and discharging behavior, cell efficiency and specific capacity, in order to be more competitive in terms of performance and lifespan compared to known lithium ion batteries.

[0005] A sodium or potassium ion battery comprises a positive electrode (cathode) and a negative electrode (anode). Each of these electrodes contains an active material. In sodium or potassium ion batteries, both the positive and negative electrodes must be capable of absorbing and releasing sodium ions or potassium ions, respectively, during the battery's charge and discharge cycles. Of particular importance in this context is the formation of a CEI (cathode electrolyte interface) as the interface between the positive active material (a solid) and the liquid electrolyte.

[0006] To protect the sensitive positive active material from unwanted degradation, it is known to apply layers of an electrically conductive polymer to the active material using chemical vapor deposition. Chemical vapor deposition (CVD) offers the advantage that the layer thickness of the coating can be precisely controlled, achieving thicknesses of less than 50 nm. However, the effort involved in producing CVD-coated positive active materials is considerable, increasing costs to such an extent that the economical production of such positive active materials for sodium or potassium ion batteries is no longer feasible.

[0007] The object of the invention is therefore to provide a cost-effective method for manufacturing a positive electrode for sodium or potassium ion batteries, with which positive active materials can be coated. Furthermore, a cost-effective and high-performance positive electrode as well as a corresponding sodium or potassium ion battery are to be provided.

[0008] The object of the invention is solved by a method for producing a positive electrode with a current collector and a positive active material applied to the current collector for a sodium ion battery or a potassium ion battery, wherein the positive active material is provided in solution with a coating of polythiophene.

[0009] Polythiophenes are polymers that possess a delocalized TT electron system in their main chain, making them electrically conductive. This allows a polythiophene to be applied as a protective layer to the positive active material to counteract unwanted degradation of the active material, while simultaneously maintaining the electrical and ionic conductivity of the positive electrode. It has been found that polythiophenes are also suitable for this purpose in sodium and potassium ion batteries, as they restrict, but still fundamentally allow, the exchange of sodium and potassium ions between the positive active material and the electrolyte. In this way, the cycle stability and lifespan of the positive electrode, and thus of a sodium or potassium ion battery with such a positive electrode, can be improved.The invention is based on the fundamental concept of applying the polythiophene coating in solution, i.e., using a solvent such as an organic solvent and / or water. This eliminates the need for costly gas-phase processes that require a vacuum reaction. It has been found that positive active materials for sodium or potassium ion batteries can also be coated with polythiophene using wet-chemical processes, without requiring an excessive coating thickness.

[0010] In particular, the polythiophene coating has a layer thickness of less than 100 nm, preferably in the range of 10 nm to 70 nm, and especially preferably in the range of 15 nm to 25 nm.

[0011] A coating of polythiophene that is as thin as possible allows the ion mobility to be restricted as little as possible by the coating, while at the same time the positive active material is protected by the coating of polythiophene.

[0012] Preferably, the polythiophene coating has a layer thickness distribution that is as homogeneous as possible. This ensures that the ion mobility is as uniform as possible across the entire polythiophene coating. Furthermore, gaps in the coating can be avoided, where the positive active material would be unprotected or only less well protected than in areas with greater layer thickness.

[0013] Furthermore, the polythiophene coating reduces the thickness of the CEI when used as the positive electrode in a sodium or potassium ion battery, as the coating lowers the exchange rate of sodium or potassium ions between the positive active material and the electrolyte. Additionally, the electrical conductivity of the polythiophene coating reduces voltage spikes and overvoltages, thus preventing damage to the CEI or the underlying positive active material. This reduces the formation loss of available ion carriers in the sodium or potassium ion battery and increases the specific capacity. Moreover, due to its inherent electrical conductivity, the polythiophene coating can at least partially, and in some cases completely, function as a binder and / or conductivity modifier.This allows the amount of binder and / or conductivity modifier to be reduced or even completely omitted, further lowering manufacturing costs and increasing specific capacity.

[0014] The positive active material can comprise a variety of active material particles, which are coated with polythiophene. In this variant, it is possible for individual active material particles, also referred to as primary particles, to have the polythiophene coating, for primary particles to be cross-linked to form secondary particles via the coating, and / or for the entire mass of active material particles to be coated. This allows for flexible process control to produce a positive electrode with the desired property profile and optimized manufacturing costs.

[0015] The type of positive active material is not fundamentally restricted, as long as it is suitable for use in a sodium- or potassium-ion battery and chemically compatible with the polythiophene of the coating. Such compounds are capable of reversibly absorbing and releasing sodium or potassium ions, with the basic structure of the positive active material being essentially preserved. This reduces the stress on the positive active material during charge and discharge cycles and thus increases the lifespan of the positive electrode.

[0016] For example, the active material is selected from the group consisting of transition metal layer oxides, polyanionic active materials, Prussian blue analogues and combinations thereof, preferably from the group of Prussian blue analogues, particularly preferably from the group of manganese-containing Prussian blue analogues.

[0017] Transition metal layer oxides are compounds of the general formula Y X MO2, where Y is Na or K, M denotes one or more transition metals, and 1 > x > 0. In the case of a sodium-ion battery, the transition metal layer oxide is selected, for example, from the group of compounds Na. x NiyMn z O2 with y + z = 1 , 1 > y > 0, 1 > z > 0 and 1 > x > 2 / 3, Na x CaaNi y Mn z O2 with y + z = 1 , 1 > y > 0, 1 > z > 0, x > 2 / 3 and x + a / 2 = 1 , Na x A y TM z C>2 with A = Ca, Li, K, Mg, Zn and / or Al, TM = Ni, Mn, Fe, Cu, Al, Si, Co, Ti, Nb and / or B, and 1 > x > 0.33 as well as combinations thereof. In the case of a potassium ion battery, the transition metal layer oxide is selected in particular from the analogous potassium compounds.

[0018] The polyanionic active material can be selected from the group of phosphates, sulfates, silicates and combinations thereof, including appropriate polyphosphates, polysulfates and polysilicates.

[0019] For example, the polyanionic cathode active material can be selected from compounds with NASICON structure, tavorite structure, olivine structure, alluaudite structure and combinations thereof.

[0020] In the case of a sodium ion battery, the polyanionic cathode active material is selected, for example, from the group of compounds Na4Fe3(PO4)2P2O?, Na4Fe?(PO4)6, Na2CoPO4F, NasMnTi(PO4)3, Na3MnTi(PO4)2,83Fo,5, Na3Fe2(PO4)P2O?, Na3,85MnV(PO43,95Fo,o5)3, Na4MnV(PO4)s, Na3Fe2(PO4)3, Na3V2(PO4)3, Na3(VOPO4)2F, Na2Fe(SO4)2, Na2Fe2(SO4)3, Na2,sFei, 75(804)3 and combinations thereof, in the case of a potassium ion battery from the analogous potassium compounds.

[0021] The term "Prussian blue analogues" refers to compounds whose Krista II structure is identical or substantially similar to that of Prussian blue. Prussian blue analogues are characterized by excellent cycle stability and low volume expansion during charge and discharge cycles and are particularly well-suited for use in sodium-ion batteries.

[0022] In the case of a sodium-ion battery, the Prussian blue analogue is specifically selected from the group of compounds Na x E[G(CN)e], where G is Fe and / or Mn, and where E is selected from the group consisting of Zn, Ni, Cr, Cu, Mn, Fe, Co and combinations thereof, where one or more of these elements are used for a stoichiometric sum of 1, and where 2 > x > 0.66. In the case of a potassium ion battery, the Prussian blue analog is selected in particular from the analogous potassium compounds.

[0023] A manganese-containing Prussian blue analogue is particularly preferred. Manganese-containing Prussian blue analogues exhibit a higher specific capacitance compared to other Prussian blue analogues, especially compared to iron-based Prussian blue analogues such as Prussian white, but are more sensitive to undesirable decomposition effects and the leaching of manganese by the electrolyte. The combination with the polythiophene coating provided according to the invention at least partially compensates for the sensitivity of manganese-containing Prussian blue analogues, thus achieving an optimal compromise between higher specific capacitance and the longevity of the positive electrode.

[0024] The type of polythiophene is not fundamentally restricted, as long as it is chemically compatible with the positive active material. The coating's property profile can be tailored by selecting the polythiophene, and especially its substituents, for example, with regard to electrical conductivity, thickness, and / or stability.

[0025] The polythiophene can be a polythiophene with symmetrically, asymmetrically, and / or cyclically bridged substituted repeating units. If the polythiophene is asymmetrically substituted, it can exhibit a head-tail-head-tail, head-head-tail-head, head-head-tail-tail, or tail-tail-head-tail chain structure.

[0026] Preferably, the polythiophene is poly-3,4-ethylenedioxythiophene, also known as PEDOT. A coating made of PEDOT exhibits excellent electrical conductivity and is particularly easy to produce, as no regioregularity in the produced coating needs to be considered during the manufacturing process.

[0027] Preferably, the battery should be a sodium-ion battery.

[0028] To achieve particularly good adhesion of the positive active material within the positive electrode, especially between the active material particles themselves, the coated positive active material can be heated to a temperature above the glass transition temperature of the polythiophene after coating it with the polythiophene coating. This causes at least partial liquefaction of the coating, allowing it to flow and distribute itself particularly evenly over the active material. In particular, any voids between the active material particles can be reliably filled with the polythiophene in this way, and air inclusions can be removed.Furthermore, after exceeding the glass transition temperature, the polythiophene in the coating can rearrange itself into a "face on" configuration on the surface of the positive active material, which exhibits particularly high electrical conductivity.

[0029] It is understood that the temperature above the glass transition temperature is chosen such that neither the polythiophene nor any other components of the positive electrode are damaged at that temperature. For example, the temperature is in the range of 95 to 105 °C, especially if the polythiophene is a PEDOT.

[0030] Heating to a temperature above the glass transition temperature can be performed simultaneously with another process step in the production of the positive electrode, for example, in a drying step and / or a calendering process, or directly during application to the metallic conductor. This reduces the number of necessary process steps in the production of the positive electrode, thereby lowering production costs and time, while simultaneously producing a particularly uniform coating.

[0031] The positive active material coated with polythiophene can be dispersed in water, alone or in combination with a conductivity modifier and optionally with a binder, particularly a water-soluble one. The resulting dispersion is then applied to a metallic conductor and dried. Drying takes place under reduced pressure and / or elevated temperature.

[0032] The water-soluble binder comprises, for example, a carboxymethylcellulose, an alginate or a combination thereof, in particular each with a counterion that is tailored to the specific battery in which the positive electrode is to be used, i.e., in particular sodium in the case of a sodium ion battery and potassium in the case of a potassium ion battery.

[0033] In one variant, the positive active material is coated with the polythiophene by means of electropolymerization in an electrolyte solution, wherein the electrolyte solution comprises monomers for the production of the polythiophene, a conducting salt and at least one solvent.

[0034] In electropolymerization, a polymerization reaction of monomers contained in the electrolyte solution is triggered by applying an electrical potential and / or by electrolysis, with the polymerization taking place at a working electrode. Electropolymerization can be potentiostatic, galvanostatic, or potentiodynamic, particularly with cyclic polarization; cyclic or pulsed polarization with a constant potential is preferred.

[0035] The working electrode is a metallic conductor of the positive electrode, onto which the positive active material has been applied. The coating of the conductor with the positive active material is carried out, in particular, under exclusion of oxygen, in order to protect the still uncoated, and therefore unprotected, positive active material from oxidation.

[0036] The metallic surge arrester is made of aluminum, for example, and can optionally be coated with a plastic layer. This plastic layer is applied to sections of the arrester where the active material is not located. The plastic layer thus provides protection and / or insulation for the arrester. The plastic layer is typically made of polyimide, polyethylene terephthalate (PET), polyethylene (PE), and / or polypropylene (PP).

[0037] It is understood that further necessary processing steps may be carried out before immersion in the electrolyte solution, for example intermediate drying and / or a calendering step.

[0038] The positive active material can also be applied to the metallic conductor in the form of a slurry, which may contain additional components such as a conductivity modifier and a binder. In this case, the positive active material, along with the other components of the slurry, is coated with the polythiophene.

[0039] The drain, along with the positive active material, is then immersed in the electrolyte solution so that electrochemical polymerization takes place on the positive active material.

[0040] A counter electrode is typically an expanded metal sheet, for example, a titanium expanded metal sheet. The counter electrode can be coated with platinum, typically with a thickness of 20 to 80 pm. This increases the current efficiency and the service life of the counter electrode.

[0041] To achieve a more homogeneous layer thickness distribution of the thiophene coating, electropolymerization can be carried out in pulsed mode, specifically with voltage pulses. The pauses between pulses allow diffusion processes to occur between the polymerization phases, ensuring that monomers are readily available for further polymerization at the surface of the positive active material or the already formed coating layer at the start of the next pulse. This prevents layer thickness variations caused by diffusion limitations of the monomers present in the electrolyte solution.

[0042] The pulse shape of the pulses used can further influence the diffusion behavior and layer growth. Electropolymerization is particularly often carried out using rectangular pulses. The steep pulse edges of rectangular pulses achieve a particularly effective separation between time periods in which diffusion processes can occur and time periods in which layer growth takes place.

[0043] Electropolymerization can be carried out at a voltage greater than 800 mV, preferably at a voltage in the range of 800 to 850 mV. The voltage used for electropolymerization determines whether polymerization preferentially occurs on uncoated areas of the positive active material or on areas already coated, with a higher voltage favoring layer growth on uncoated areas. In other words, at a higher voltage of more than 800 mV, the equilibrium of the polymerization reactions shifts away from growth on existing layers towards the formation of new layers. This allows for particularly precise control of layer growth, enabling the achievement of very low layer thicknesses, especially less than 30 nm.

[0044] If electropolymerization is carried out using pulses, the voltage described above refers to the maximum voltage of the pulses used.

[0045] To further influence the layer growth of the polythiophene coating, the electrolyte solution can contain a solvent that is less polar than water, preferably acetonitrile. The polythiophene produced by polymerization tends to be more soluble in polar solvents than the monomers (thiophenes) contained in the electrolyte solution, since the polythiophene is generally more polar than the monomers. Therefore, by using a solvent in the electrolyte solution that is less polar than water, already formed polythiophene layers are less wetted by the electrolyte solution than uncoated areas of the positive active material. This further promotes the growth of new layers and weakens layer growth on existing layers.

[0046] The electrolyte solution can contain the solvent, which is less polar than water, and water in a volume ratio of 1:0.25 to 1:4. Accordingly, the term "solvent, which is less polar than water" in the context of the electrolyte solution is understood to mean an organic solvent, which is not water.

[0047] The electrolyte solution is reused, particularly for multiple coating processes. This means that the monomers present in the electrolyte solution are consumed or reduced to a minimum concentration, and then new monomers are added to the remaining electrolyte solution to initiate another polymerization process. This further reduces the cost of the process. The solvent contained in the electrolyte solution, which is less polar than water, can be recovered by distillation to achieve a closed-loop recycling process, for example, if the water content in the electrolyte solution becomes too high.

[0048] The monomers for the production of the polythiophene and / or the conducting salt are present in the electrolyte solution, preferably in concentrations of 0.02 to 0.2 mol / L, and most preferably in concentrations of 0.05 to 0.1 mol / L, and most preferably in concentrations of 0.7 to 0.8 mol / L. It is understood that the concentrations of the monomers for the production of the polythiophene and / or the conducting salt can be selected independently of one another within the aforementioned ranges.

[0049] The layer growth of the polythiophene coating can also be controlled via the pH value of the electrolyte solution. For this purpose, the electrolyte solution can contain a buffer, for example, a phosphate buffer.

[0050] The pH value of the electrolyte solution is particularly in the range of 6.6 to 7.0, preferably in the range of 6.7 to 6.9.

[0051] The conducting salt can be a polystyrene sulfonate, a chloride, and / or a sulfate. The counterion of the conducting salt is specifically tailored to the particular battery in which the positive electrode is to be used; in particular, sodium in the case of a sodium-ion battery and potassium in the case of a potassium-ion battery.

[0052] After coating by electropolymerization, the current collector, together with the coated positive active material, can be removed from the electrolyte solution, dried completely and, in particular, installed directly into a battery.

[0053] In another variant, the positive active material is suspended in an aqueous solution containing monomers for the production of polythiophene, and then an aqueous reaction solution containing an oxidizing agent is added dropwise, resulting in the positive active material coated with polythiophene. This variant is characterized by a particularly simple process starting from previously produced active material, especially active material particles, whereby the reaction progress and thus the coating thickness can be controlled by adjusting the dosing rate of the aqueous reaction solution. Furthermore, the coating thickness can be adjusted by changing the molar ratio between the monomer for the production of polythiophene and the oxidizing agent in the aqueous reaction solution.

[0054] The active material particles are dispersed or suspended in the aqueous solution, resulting in a dispersion or suspension after the positive active material has been absorbed into the aqueous solution.

[0055] In this variant, particularly when using active material particles, it is possible to ensure that primary particles on the active material itself are coated as completely as possible with the polythiophene coating before the coated primary particles are applied to a metallic conductor of the positive electrode, for example in the form of a slurry.

[0056] However, it is also possible to first apply the active material to the metallic conductor and then immerse the active material together with the metallic conductor in the aqueous reaction solution to create the coating.

[0057] The aqueous solution may contain an organic co-solvent, wherein the organic co-solvent is preferably selected from the group consisting of sulfoxides, formamides, polyethylene glycols, alcohols, and mixtures thereof. The sulfoxide is particularly preferably dimethyl sulfoxide (DMSO). The formamide is particularly preferably dimethylformamide (DMF). The alcohol is particularly preferably ethanol, isopropanol, propanol, or a mixture thereof. The use of the co-solvent increases the quinoid content of the polythiophene and thus its electrical and ionic conductivity, as a more linear structure is formed in the polythiophene.

[0058] The oxidizing agent of the aqueous reaction solution can be selected from the group consisting of persulfates, metal chlorides, and combinations thereof, preferably from the group consisting of sodium persulfate, ammonium persulfate, and iron trichloride. The choice of oxidizing agent can influence the reaction rate and thus the layer growth, and also provide counterions for the polythiophene in the aqueous reaction solution, i.e., sulfate ions and / or chloride ions, which can influence the conductivity and binder properties of the polythiophene coating.

[0059] The aqueous reaction solution can be added dropwise over a period of 1 to 8 hours, preferably over a period of 2 to 3 hours. A shorter addition time of the aqueous reaction solution can lead to a less uniform coating thickness, while a longer addition time increasingly and excessively increases the effort required to produce the positive electrode.

[0060] The aqueous reaction solution is added dropwise, especially at room temperature. Room temperature is defined here as a temperature of 23 ± 2 °C.

[0061] To influence the average chain length of the polythiophene, the aqueous solution can contain polystyrene sulfonate (PSS), resulting in a polythiophene coating that is a polythiophene-polystyrene sulfonate coating. This is achieved because the polystyrene sulfonate increases the water solubility of the polythiophene. In particular, the use of polystyrene sulfonate leads to a more complete coating of the active material's surface.

[0062] The polystyrene sulfonate in the polythiophene coating can be at least partially replaced with chloride ions in a post-treatment step. Replacing polystyrene sulfonate with chloride ions increases the coating's conductivity, as polystyrene sulfonate can have a partially insulating effect within the coating. Furthermore, incorporating chloride ions into the coating increases the linear component in the coiled structure of the polythiophene, which also positively impacts the coating's conductivity.

[0063] In the post-treatment step, the coated positive active material can be immersed in a hydrochloric acid treatment bath, wherein the hydrochloric acid treatment bath contains in particular an organic solvent and / or water, a polyethylene glycol and an acid mixture comprising hydrochloric acid.

[0064] The acid mixture is, in particular, a mixture of salt, phosphorus, and

[0065] Benzenesulfonic acid. The organic solvent is, in particular, a sulfoxide such as DMSO.

[0066] Alternatively, the exchange can be carried out electrochemically. For example, the potential of the positively charged active material coated with polythiophene is adjusted to neutral, causing the polystyrene sulfonate to detach from the polythiophene. Meanwhile, the aqueous solution is replaced with a slightly acidic saline solution, and finally, the original potential of the polythiophene is restored, so that the polythiophene has positive charges, with chloride ions from the aqueous solution being incorporated into the coating.

[0067] Optionally, the active material coated with the aqueous solution can be further coated with a polythiophene coating via electropolymerization. Specifically, primary particles of the positive active material can first be individually coated with the polythiophene in the aqueous solution, the coated primary particles applied to the current collector in slurry form, and then the current collector coated with an additional polythiophene coating produced by electropolymerization. It is understood that the coating on the primary particles can differ from the additional coating produced by electropolymerization, for example, with regard to layer thickness and / or the polythiophene used, or that both coatings can be identical, in particular using the same polythiophene.

[0068] The positive active material can be loaded with sulfur before the polythiophene coating is applied, a process also known as "sulfur preconditioning." By incorporating sulfur into the positive active material, an additional voltage plateau can be created in the charging and discharging curve of the positive active material, resulting in a more flexible positive electrode.

[0069] The amount of sulfur that can be incorporated into the positive active material depends primarily on the specific positive active material used. For example, if the positive active material is a Prussian blue analog, it can be loaded with up to 82 wt% sulfur, based on its total weight. The sulfur is incorporated particularly into the interstices of the respective crystal structure of the positive active material, such as the spaces within the crystal lattice of a Prussian blue analog.

[0070] Sulfur-containing active materials exhibit greater volume changes during subsequent charge and discharge cycles than would be the case for the same active materials without sulfur. According to the invention, by subsequently coating the sulfur-loaded positive active material with polythiophene, the extent of the volume changes is limited, as the coating counteracts any potential volume expansion. In this way, the advantage of the additional voltage plateau can be combined with a long lifetime and high electrical conductivity.

[0071] Similarly, the polythiophene coating counteracts other volume changes of the positive active material, for example caused by a change in the crystal structure of the positive active material such as a transition from a monoclinic to a rhombohedral Krista II structure in a Prussian blue analog, which has a positive effect on the longevity of the positive electrode.

[0072] To load the positive active material with sulfur, it can be suspended in a sulfur solution containing a nonpolar solvent and sulfur. The nonpolar solvent is then evaporated. The positive active material remains in the sulfur solution for a certain exposure time before the nonpolar solvent is completely evaporated. This exposure time can be selected depending on the desired sulfur content and the concentration of sulfur in the sulfur solution. In particular, the exposure time is less than 10 minutes.

[0073] To further reduce the cost of the process, the evaporated nonpolar solvent can be collected and recovered using a condenser. The nonpolar solvent is selected in particular from the group consisting of carbon disulfide, benzene, toluene, and mixtures thereof, preferably from the group consisting of benzene, toluene, and mixtures thereof.

[0074] Alternatively, the positive active material can be mixed with molten sulfur for loading. This eliminates the need for organic solvents, which require greater care and disposal and are associated with costs. Sulfur has a melting point of 115 °C, so the energy required and therefore the costs of melting the sulfur remain manageable.

[0075] For example, the positive active material and elemental sulfur are ground in a ball mill to melt the sulfur. In this variant, the energy input during grinding creates local hotspots in the ball mill, which are sufficient to liquefy the sulfur and introduce it into the positive active material, thus significantly minimizing the effort required to load the positive active material.

[0076] Furthermore, the positive active material can be placed in an autoclave and loaded with gaseous sulfur. The use of an autoclave allows for particularly controlled process management, as the addition of sulfur to the autoclave can be precisely controlled.

[0077] In particular, the positive active material is loaded with sulfur in the autoclave at a pressure of less than 0.1 mbar, for example at a pressure in the range of 0.01 to 0.1 mbar.

[0078] The positive active material can be loaded with sulfur in an autoclave at a temperature of at least 115 °C, preferably at a temperature of 115 to 130 °C. The pressure applied in the autoclave makes such a temperature sufficient to keep the sulfur in a gaseous state.

[0079] The sulfur-loaded positive active material can be coated with the thiophene coating as described above, for example by electropolymerization or in aqueous solution.

[0080] In yet another variant, the positive active material is coated with polythiophene during its synthesis by converting an active material precursor in an aqueous solution to form the positive active material. This aqueous solution contains monomers for generating the polythiophene. In this variant, the upstream preparation of the active material, such as active material particles, can be omitted, thus enabling a kind of one-pot synthesis in which both the active material and the coating are produced in situ.

[0081] In particular, in this variant the coated active material is obtained in the form of secondary particles that have primary particles of the positive active material which are connected or cross-linked together via the polythiophene coating.

[0082] In this variant, the active material precursor itself serves as an oxidizing agent, which reacts with the monomers contained in the aqueous solution to form the positive active material and the coating made of polythiophene.

[0083] In a preferred embodiment, the active material precursor is Na3[Fe(CN)e], K3[Fe(CN)e], or a mixture of these compounds, and the positive active material is Prussian white. In this embodiment, the respective Fe(llI) complex serves as the oxidizing agent, whereby the iron contained is reduced to Fe(ll) with the monomer, for example, 3,4-ethylenedioxythiophene (EDOT), and the sodium- and / or potassium-containing Prussian white is obtained.

[0084] The aqueous solution contains, in particular, an active material coreagent, wherein the active material coreagent contains manganese. Preferably, the active material coreagent is manganese(II) chloride. The active material coreagent is a compound that is at least partially incorporated into the positive active material during the reaction of the active material precursor without undergoing a redox reaction.

[0085] For example, when using Na3[Fe(CN)e], K3[Fe(CN)e] or a mixture thereof as the active material precursor and manganese(II) chloride as the active material coreagent, Na2Mn[Fe(CN)e], K2Mn[Fe(CN)e] or Na x K y Mn[Fe(CN)6] with x + y = 2, 2 > x > 0 and 2 > y > 0 as positive active material.

[0086] The choice of the active material coreagent makes it possible to influence the reaction equilibrium prevailing during the conversion of the active material precursor, for example the reaction rate, which in turn influences the crystal quality and the amount of water of crystallization contained in the positive active material.

[0087] The active material precursor and the monomers for the production of polythiophene can be present in equimolar concentrations in the aqueous solution. In particular, this results in an equimolar conversion of the active material precursor and the monomer to the active material precursor and the polythiophene.

[0088] To influence the grain size of the generated primary and secondary particles, reduce the number of crystal defects and / or minimize the proportion of water of crystallization bound in the positive active material, the aqueous solution can contain a complexing agent, wherein the complexing agent is preferably selected from the group consisting of ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetic acid,

[0089] Disodium ethylenediaminetetraacetic acid, trisodium citrate, disodium citrate, citric acid, sodium citrate, sodium alginate, sodium carboxymethylcellulose, tetrasodium pyrophosphate and combinations thereof.

[0090] It is also possible that the active material precursor is a compound containing at least one metal, wherein an active material modifier of the same compound type as the active material precursor and comprising a metal with a different oxidation state than the metal of the active material precursor is added to the aqueous solution, wherein, in particular, one metal of the active material precursor and one metal of the active material modifier are the same metal. The active material modifier thus serves to adjust the active material:polythiophene ratio, thereby allowing the property profile of the positive electrode to be tailored, for example, to optimize its longevity or specific capacitance.

[0091] The weight ratio between positive active material and polythiophene is in this case particularly in the range of 70:30 to 92:2, preferably from 80:20 to 95:5, and most preferably from 90:10 to 95:5. The molar ratio between positive active material and the polythiophene is in this case particularly in the range of 50:50 to 95:5, preferably from 60:40 to 90:10, and most preferably from 70:30 to 85:15.

[0092] In a preferred embodiment for a sodium ion battery, the active material precursor is Na3[Fe(CN)e], K3[Fe(CN)e] or a mixture of these compounds, the active material modifier is Na4[Fe(CN)e] and the positive active material is Prussian White.

[0093] The molar ratio of active material precursor to monomer for the production of polythiophene is in particular in the range of 1.2:1 to 1:1.2, especially in the ratio of 1.05:1 to 1:1.05.

[0094] The molar ratio of active material precursor to active material modifier can be in the range of 22:1 to 1:21, preferably in the range of 1:3 to 1:9.

[0095] The aqueous solution may contain one or more additives selected from the group consisting of sodium chloride, potassium chloride, polyvinylpyrrolidone, hydrochloric acid, sodium hydroxide, sodium L-ascorbate, potassium L-ascorbate, sulfoxides, polyethylene glycols, formamides, dialkyl esters, lactones, alcohols and combinations thereof.

[0096] Sodium chloride and / or potassium chloride are present in the aqueous solution, particularly in a proportion of 0 to 20 wt.%, preferably 0.1 to 20 wt.%, based on the total weight of the aqueous solution. The grain size of the primary and secondary particles produced can be influenced, the number of crystal defects reduced, and / or the proportion of water of crystallization bound in the positive active material, analogously to or in conjunction with the complexing agent, by adjusting the NaCl and / or KCl content.

[0097] A suitable polyvinylpyrrolidone is available under the designation K30.

[0098] The pH value of the aqueous solution can be optimized by adding hydrochloric acid and / or sodium hydroxide as additives.

[0099] The sulfoxide is in particular dimethyl sulfoxide (DMSO), the formamide is in particular dimethylformamide (DMF), and the dialkyl ester is in particular diethyl carbonate (DEC). The secondary particles produced in this variant can optionally be additionally coated with a further layer of polythiophene, in particular by electropolymerization or in aqueous solution with the addition of the aqueous reaction solution as described above. It is understood that the coating on the secondary particles may differ from the additional coating, for example, with regard to the layer thickness and / or the polythiophene used, or that both coatings may be identical, in particular using the same polythiophene.

[0100] Furthermore, the positive active material produced as secondary particles in this variant can also be loaded with sulfur, especially if the in situ generated coating does not completely cover the respective primary particles of the positive active material, so that the primary particles are at least partially accessible to sulfur.

[0101] Thus, analogous to the previously described alternatives for introducing sulfur before applying the coating, the already partially coated primary particles can be loaded with sulfur, for example by suspending them in a sulfur solution, mixing them with molten sulfur or loading them with gaseous sulfur in an autoclave, and reference is made to the explanations above.

[0102] Any gaps in the thiophene coating can then be closed, for example analogously to the variant described above, using an aqueous reaction solution containing an oxidizing agent, in combination with an aqueous solution comprising monomers for the production of the polythiophene, wherein the oxidizing agent is selected in particular from the group consisting of sodium persulfate, ammonium persulfate and iron trichloride, preferably iron trichloride.

[0103] The object of the invention is further achieved by a positive electrode for a sodium ion battery or a potassium ion battery, obtained by a method as described above.

[0104] The advantages and properties of the previously described method apply analogously to the positive electrode according to the invention, and vice versa. In particular, the same materials are used in the positive electrode as previously described in connection with the method according to the invention.

[0105] Furthermore, the object of the invention is solved by a battery comprising a positive electrode as described above, a negative electrode and a separator arranged between the positive electrode and the negative electrode, wherein the battery is a sodium ion battery or a potassium ion battery.

[0106] The battery is preferably a secondary battery.

[0107] The negative electrode has a negative active material, which may be selected in particular from the group consisting of hard carbon, for example in pure form, surface functionalized or doped with sulfur, phosphorus, nitrogen and / or oxygen, soft carbon, synthetic graphite, silicated graphite, natural graphite, graphene, mesocarbon, doped carbon, tin, tin oxide, phosphorus, antimony, antimony oxide, Prussian blue analogues and mixtures thereof.

[0108] If both the positive electrode and the negative electrode contain a Prussian blue analogue, the respective Prussian blue analogues must be different from each other.

[0109] Alternatively, it is also possible that in the case of a sodium ion battery, a sodium anode is used as the negative active material, and in the case of a potassium ion battery, a potassium anode is used as the negative active material, each of which can also act as a conductor of the negative electrode.

[0110] The separator is permeable to the ions to be cyclized, i.e. sodium ions or potassium ions, but is a non-conductor to electrons and serves to electrically isolate the positive and negative electrodes.

[0111] Polymers can be used as separators, in particular a polymer selected from the group consisting of polyesters, especially polyethylene terephthalate, polyolefins, especially polyethylene and / or polypropylene, polyacrylonitriles, polyvinylidene fluoride, polyvinylidene hexafluoropropylene, polyetherimide, polyimide, aramid, polyether, polyetherketone, or mixtures thereof. The separator can optionally be additionally coated with a ceramic material, for example, with Al₂O₃.

[0112] Furthermore, the battery contains an electrolyte that is conductive for sodium or potassium ions and can be either a solid electrolyte or a liquid comprising a solvent and at least one dissolved conducting salt, such as hexafluorophosphate or perchlorate. Other possible conducting salts include sodium or potassium triflate, tetraborate, trifluoromethylsulfonylamide, trifluoromethylsulfonylamide, and / or oxalatoborate.

[0113] Preferred conducting salts are salts that contain inert anions and are preferably non-toxic. Suitable conducting salts include, in particular, sodium or potassium hexafluorophosphate, sodium or potassium tetrafluoroborate, sodium or potassium perchlorate, and mixtures of the respective sodium or potassium salts.

[0114] The electrolyte solvent is preferably inert. Suitable solvents include, for example, organic solvents such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), sulfolanes, 2-methyltetrahydrofuran, acetonitrile, 1,3-dioxolane, 1,2-dimethoxyethane (DME), dipropyl ether (DPE), diethyl ether (DEE), and diethylene glycol dimethyl ether (diglyme).

[0115] In one variation, two or more of the above-mentioned liquids can be used.

[0116] If the electrolyte is liquid, the separator is particularly saturated or wetted with the electrolyte.

[0117] Further features and characteristics will become apparent from the following description of exemplary embodiments, which are not to be understood in a restrictive sense, as well as from the drawings. These show:

[0118] - Fig. 1 shows a schematic cross-section through a first embodiment of a positive electrode according to the invention, - Fig. 2 shows a schematic cross-section through a second embodiment of a positive electrode according to the invention,

[0119] - Fig. 3 shows a schematic cross-section through a third embodiment of a positive electrode according to the invention,

[0120] - Fig. 4 shows a block diagram of a first embodiment of a method according to the invention for producing a positive electrode,

[0121] - Fig. 5 shows a block diagram of a second embodiment of a method according to the invention for producing a positive electrode, and

[0122] - Fig. 6 shows a block diagram of a third embodiment of a method according to the invention for producing a positive electrode.

[0123] Fig. 1 shows a schematic cross-section through a first embodiment of a positive electrode 10 according to the invention.

[0124] In the embodiment shown, the positive electrode 10 is a positive electrode for a sodium ion battery.

[0125] In principle, the positive electrode 10 can also be a positive electrode for a potassium ion battery, whereby the sodium-containing components described below are used particularly in the form of the corresponding potassium compounds.

[0126] The positive electrode 10 comprises a metallic conductor 12, which is, for example, designed as aluminum foil. An electrode coating 16 is applied to one surface 14 of the metallic conductor.

[0127] On the reverse side 17 of the surge arrester 12, opposite the order side 14, a plastic coating (not shown) may be applied to protect the surge arrester 12; this coating may, for example, be a polyimide coating. It is also possible that all parts of the surge arrester 12 not covered by the electrode coating 16 are provided with the plastic coating.

[0128] The electrode coating 16 comprises a positive active material 18, which is in the form of a layer of active material particles, in the embodiment shown in Fig. 1 in the form of primary particles. In Fig. 1, the active material particles are shown as spherical particles. Naturally, the active material particles can also have a different shape.

[0129] The positive active material 18 is selected from the group consisting of transition metal layer oxides, polyanionic active materials, Prussian blue analogues and combinations thereof, preferably from the group of Prussian blue analogues, particularly preferably from the group of manganese-containing Prussian blue analogues.

[0130] On the side of the layer of active material particles facing away from the current collector 12, a coating 20 of polythiophene is applied to the positive active material 18. In other words, the positive active material 18 is covered with the coating 20 on the polythiophene, wherein, in the embodiment according to Fig. 1, not the individual primary particles, but the entire layer of active material particles is covered with the coating 20 of polythiophene.

[0131] It is understood that the representation in Fig. 1 is merely schematic and that the coating 20 made of polythiophene can also cover side surfaces of the layer of active material particles, the side surfaces connecting the top and bottom of the layer of active material particles.

[0132] The polythiophene coating 20 provides a protective coating for the positive active material 18, protecting it from unwanted degradation, for example, through oxidation or volume changes during subsequent operation of the positive electrode 10 in the sodium-ion battery. Furthermore, the polythiophene coating 20 is conductive for sodium ions and electrically conductive, allowing sodium ions to be incorporated into and removed from the positive active material 18.

[0133] The polythiophene in coating 20 is poly-3,4-ethylenedioxythiophene (PEDOT). However, other polythiophenes can also be used in coating 20, provided they are chemically compatible with the positive active material 18 and provide the desired conductivity.

[0134] Fig. 2 shows a schematic cross-section through a second embodiment of a positive electrode 10 according to the invention. The second embodiment corresponds essentially to the first embodiment, so only the differences will be discussed below. Identical reference numerals denote identical or functionally equivalent components, and reference is made to the above explanations.

[0135] In the second embodiment, the polythiophene coating 20 is not applied to the entire layer of active material particles. Instead, each individual primary particle of the positive active material 18 is coated with the polythiophene coating 20.

[0136] The individual coated primary particles can be stacked separately from one another to form a layer of active material particles or can be at least partially connected or cross-linked to form secondary particles via the coating 20 made of polythiophene.

[0137] In the second embodiment, the coating 20 made of polythiophene influences the mechanical properties as well as the conductivity property of the layer of active material particles.

[0138] In particular, it is possible to reduce or even completely eliminate the amount of additional conductivity modifier and / or binder in the positive electrode 10, since sufficient cohesion of the primary particles as well as sufficient ionic conductivity and electrical conductivity can already be provided via the coating 20 made of electrically conductive polythiophene.

[0139] Fig. 3 shows a schematic cross-section through a third embodiment of a positive electrode 10 according to the invention.

[0140] The third embodiment is essentially identical to the first and second embodiments, so only the differences will be discussed below. Identical reference numerals denote identical or functionally equivalent components, and reference is made to the explanations above.

[0141] In the third embodiment, the coating variants previously described for the first and second embodiments are combined. Thus, both the individual primary particles of the positive active material 18 are provided with the polythiophene coating 20, and the entire layer of active material particles is also provided with an additional polythiophene coating 20.

[0142] The coatings 20 differ from each other primarily in their thickness, but use the same polythiophene. However, it is also fundamentally possible that different polythiophenes are used in the coatings 20.

[0143] The positive electrode 10 can be installed in a battery according to the invention, together with a negative electrode with a negative active material and a separator that is arranged between the positive electrode 10 and the negative electrode.

[0144] In the following, a method according to the invention for producing the positive electrode 10 is described in more detail, from which further features and properties of the positive electrode 10 are also derived.

[0145] Fig. 4 shows a block diagram of a first embodiment of the method according to the invention.

[0146] First, the positive active material 18 is provided (see step S1 in Fig. 4).

[0147] The positive active material 18 is then applied to the drain 12 (see step S2 in Fig. 4). For this purpose, the positive active material 18 can first be mixed with a conductivity modifier such as conductive carbon black and a binder such as sodium carboxycellulose and / or sodium alginate to form a slurry, which is then applied to the drain 12 by wet coating. Subsequently, further processing steps can be carried out, for example, drying at a temperature in the range of 50 to 80 °C and / or a calendering process to compact the applied slurry.

[0148] As shown by the dashed box in Fig. 4, the positive active material 18 can optionally be loaded with sulfur before being applied to the drain 12 (see step S3 in Fig. 4). Loading with sulfur can be carried out in a sulfur solution, by mixing with molten sulfur, or in an autoclave with gaseous sulfur.

[0149] To load the positive active material 18 in a sulfur solution, the positive active material is suspended in the sulfur solution, which contains sulfur and a nonpolar solvent such as carbon disulfide, benzene and / or toluene, preferably benzene and / or toluene, and then the nonpolar solvent is evaporated.

[0150] Alternatively, the positive active material 18 can be ground with elemental sulfur in a ball mill, whereby the sulfur is melted during grinding and absorbed by the positive active material 18.

[0151] It is also possible to place the positive active material 18 in an autoclave and load it with gaseous sulfur at a pressure in the range of 0.01 to 0.1 mbar and a temperature of 115 to 130 °C.

[0152] The sulfur is deposited in interstices of the Krista II structure of the positive active material 18 and serves to generate an additional stress plateau in the charging and discharging curve of the positive active material 18.

[0153] The positive active material 18 applied to the drain 12 is subsequently coated with the polythiophene coating 20.

[0154] In one variant, the coating 20 is produced from the polythiophene by means of electropolymerization (see step S4 in Fig. 4).

[0155] For this purpose, the current collector 12, coated with the positive active material 18, is immersed in an electrolyte solution comprising monomers for generating the polythiophene, a conducting salt, and at least one solvent. A counter electrode is also immersed in the electrolyte solution and is electrically connected to the current collector 12 via a voltage source, allowing the current collector 12 to be used as a working electrode.

[0156] By applying a voltage via the voltage source, a polymerization of the monomers present in the electrolyte solution is induced on the surface of the working electrode, and thus on the surface of the positive active material 18, whereby the coating 20 is formed from the polythiophene.

[0157] The course of the polymerization reaction can be precisely controlled and regulated by the magnitude, type, and duration of the applied voltage.

[0158] Electropolymerization can be carried out using pulses, particularly rectangular pulses. Between each voltage pulse, additional monomer can diffuse to the interface where the polymerization reaction takes place.

[0159] The voltage pulses have a maximum voltage in the range of 800 to 850 mV in order to promote the formation of new layers of the coating 20 from the polythiophene compared to the growth of already formed layers, in order to achieve particularly low layer thicknesses of the coating 20.

[0160] The solvent for the electrolyte solution is, in particular, a solvent that is more polar than water, such as acetonitrile, and especially a mixture of water and the solvent is used. Sodium polystyrene sulfonate, sodium chloride, and / or sodium sulfate can be used as the conducting salt. Furthermore, the electrolyte solution may contain a phosphate buffer.

[0161] After the coating 20 has been produced from the polythiophene, the drain 12 together with the coated positive active material 18 is removed from the electrolyte solution and fed to further processing steps (see step S5 in Fig. 4).

[0162] Further processing steps include, in particular, a drying step and / or a calendering process in which the polythiophene coating 20 is heated to a temperature above the glass transition temperature of the polythiophene, for example, to a temperature in the range of 95 to 105 °C. Optionally, this drying step and / or calendering process is carried out under vacuum. This improves the coverage of the active material particles with the polythiophene coating 20. In another variant, the polythiophene coating 20 can be produced on the positive active material 18 in an aqueous solution by a wet chemical reaction instead of electropolymerization (see step S6 in Fig. 4).

[0163] For this purpose, the drain 12 together with the positive active material 18 applied to the drain 12 is immersed in the aqueous solution, wherein the aqueous solution contains monomers for the production of the polythiophene and optionally a co-solvene selected from the group consisting of sulfoxides, formamides, polyethylene glycols, alcohols and mixtures thereof, and the solution is stirred.

[0164] Subsequently, an aqueous reaction solution is added dropwise, which contains an oxidizing agent, in particular selected from the group consisting of persulfates, metal chlorides and combinations thereof, preferably from the group consisting of sodium sulfate, ammonium persulfate and iron trichloride.

[0165] The reaction solution is added dropwise over a period of 1 to 8 hours while maintaining the coating 20 of polythiophene on the positive active material 18.

[0166] It is also possible that the aqueous solution contains sodium polystyrene sulfonate, so that the coating 20 made from the polythiophene is a polythiophene:polystyrene sulfonate coating.

[0167] In this case, in an additional optional post-treatment step, the polystyrene sulfonate in the coating 20 can be at least partially exchanged for chloride ions, for example by immersing the coated positive active material 18 in a hydrochloric acid treatment bath containing an organic solvent, a polyethylene glycol and an acid mixture of hydrochloric, phosphoric and benzenesulfonic acid, or by electrochemical exchange in an acidic saline solution.

[0168] Subsequently, further processing steps can be carried out, as previously described in connection with electropolymerization, to obtain the positive electrode 10 (see step S5 in Fig. 4). In the first embodiment of the process according to the invention, a positive electrode 10 is obtained in particular as shown schematically in Fig. 1, that is, a positive electrode 10 in which the coating 20 made of polythiophene is applied to a layer of primary particles of the positive active material 10.

[0169] Fig. 5 shows a block diagram of a second embodiment of the method according to the invention.

[0170] The second embodiment essentially corresponds to the first embodiment of the method according to the invention described above. Identical process steps denote identical or functionally equivalent process steps, and reference is made to the above explanations.

[0171] In the second embodiment, the positive active material 18 is also first provided (see step S1 in Fig. 5) and the positive active material 18 can optionally be loaded with sulfur (see step S3 in Fig. 5).

[0172] However, the positive active material 18 is not applied directly to the current collector 12 and subsequently coated, as described in connection with the first embodiment. Instead, the positive active material 18 is directly coated with the polythiophene coating 20 using a wet chemical process, analogous to step S6 described for the first embodiment (see step S6 in Fig. 5).

[0173] In the second embodiment, the positive active material 18 itself is incorporated into the aqueous solution, and subsequently the aqueous reaction solution comprising the oxidizing agent is added dropwise.

[0174] In this way, the coating 20 made of polythiophene is produced on the individual primary particles of the positive active material 18, wherein the primary particles are in particular completely covered by the coating 20 made of polythiophene.

[0175] Subsequently, the coated primary particles are applied to the drain 12 (see step S2 in Fig. 5) and subjected to any further processing steps such as a drying step and / or a calendering process (see step S5 in Fig. 5), in particular the coating 20 made of the polythiophene is heated to a temperature above the glass transition temperature of the polythiophene.

[0176] Optionally, after applying the coated primary particles to the drain 12, an additional coating 20 made of polythiophene can be applied by electropolymerization, as indicated by a dashed box in Fig. 5 (see step S4 in Fig. 5).

[0177] In the second embodiment of the method according to the invention, positive electrodes 10 are particularly available, as shown schematically in Figs. 2 and 3, i.e. positive electrodes 10 in which the coating 20 made of polythiophene is applied to the individual primary particles, optionally provided with an additional coating 20 made of polythiophene (when using the additional electropolymerization).

[0178] Fig. 6 shows a block diagram of a third embodiment of the method according to the invention.

[0179] The third embodiment essentially corresponds to the first and second embodiments of the method according to the invention described above. Identical process steps denote identical or functionally equivalent process steps, and reference is made to the above explanations.

[0180] In the third embodiment, the positive active material 18 is provided with the coating 20 made of polythiophene in situ during its manufacture.

[0181] For this purpose, an active material precursor is converted to the positive active material in an aqueous solution containing monomers for the production of the polythiophene and, in particular, an active material coreagent (see step S7 in Fig. 6).

[0182] The active material precursor is, for example, Na3[Fe(CN)e], K3[Fe(CN)e], or a mixture thereof, which is reacted with 3,4-ethylenedioxythiophene (EDOT) as the monomer and manganese(II) chloride as the active material coreagent to give Prussian White as the positive active material 18, which is coated with a layer 20 of poly-3,4-ethylenedioxythiophene (PEDOT). Optionally, an active material modifier can be added, which is of the same compound type as the active material precursor and has a metal with a different oxidation state than a metal in the active material precursor. For example, the active material modifier is Na4[Fe(CN)6].

[0183] The aqueous solution may further comprise a complexing agent to influence the particle size of the coated primary particles. The complexing agent is preferably selected from the group consisting of ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetic acid,

[0184] Disodium ethylenediaminetetraacetic acid, trisodium citrate, disodium citrate, citric acid, sodium citrate, sodium alginate, sodium carboxymethylcellulose, tetrasodium pyrophosphate and combinations thereof.

[0185] The aqueous solution may also contain one or more additives selected from the group consisting of sodium chloride, potassium chloride, polyvinylpyrrolidone, hydrochloric acid, sodium hydroxide, sodium L-ascorbate, potassium L-ascorbate, sulfoxides, polyethylene glycols, formamides, dialkyl esters, lactones, alcohols and combinations thereof.

[0186] The positive active material 18 is present at the end of step S7, particularly in the form of primary particles, which are cross-linked to secondary particles via the coating 20 made of polythiophene.

[0187] Subsequently, the positive active material 18 coated with the polythiophene coating 20 is applied to the drain 12 (see step S2 in Fig. 6) and subjected to any further processing steps such as a drying step and / or a calendering process (see step S5 in Fig. 6), in particular the polythiophene coating 20 being heated to a temperature above the glass transition temperature of the polythiophene.

[0188] Optionally, after applying the coated positive active material 18 to the current collector 12, an additional coating 20 made of polythiophene can be applied by electropolymerization, as indicated by a dashed box in Fig. 6 (see step S4 in Fig. 6).

[0189] In the third embodiment of the process according to the invention, positive electrodes 10 are also obtained, as schematically depicted in Figures 2 and 3. These positive electrodes have a coating 20 of polythiophene applied to the individual primary particles, optionally provided with an additional coating 20 of polythiophene (when using the additional electropolymerization). The process according to the invention for producing the positive electrode 18 is thus characterized by flexible process control and low costs. A cost-effective positive electrode 18 is obtained that exhibits excellent performance characteristics and a long service life.

Claims

Patent claims 1. Method for producing a positive electrode (10) with a current collector (12) and a positive active material (18) applied to the current collector (12) for a sodium ion battery or a potassium ion battery, wherein the positive active material (18) is provided in solution with a coating (20) of a polythiophene.

2. Method according to claim 1, wherein the positive active material (18) comprises a plurality of active material particles, and wherein the active material particles are provided with the coating (20) of the polythiophene.

3. Method according to claim 1 or 2, wherein the positive active material (18) is selected from the group consisting of transition metal layer oxides, polyanionic active materials, Prussian blue analogues and combinations thereof, preferably from the group of Prussian blue analogues, particularly preferably from the group of manganese-containing Prussian blue analogues.

4. A method according to any of the preceding claims, wherein the polythiophene is a poly-3,4-ethylenedioxythiophene.

5. Method according to any of the preceding claims, wherein the battery is a sodium-ion battery.

6. Method according to one of the preceding claims, wherein after coating the positive active material (18) with the coating (20) of the polythiophene, the coated positive active material (18) is heated to a temperature above the glass transition temperature of the polythiophene.

7. Method according to one of the preceding claims, wherein the positive active material (18) is provided with the coating (20) of the polythiophene by electropolymerization in an electrolyte solution, wherein the electrolyte solution comprises monomers for generating the polythiophene, a conducting salt and at least one solvent.

8. The method of claim 7, wherein the electropolymerization is carried out in pulsed mode.

9. Method according to claim 7 or 8, wherein the electropolymerization is carried out at a voltage of more than 800 mV, preferably at a voltage in the range of 800 to 850 mV.

10. Method according to any one of claims 7 to 9, wherein the electrolyte solution contains a solvent that is more polar than water, preferably acetonitrile.

11. A method according to any one of claims 7 to 10, wherein the monomers for the production of the polythiophene and / or the conducting salt are present in the electrolyte solution at a concentration of 0.02 to 0.2 mol / L, preferably 0.05 to 0.1 mol / L, particularly preferably 0.7 to 0.8 mol / L.

12. Method according to any one of claims 7 to 11, wherein the electrolyte solution contains a buffer.

13. Method according to any one of claims 7 to 12, wherein the conducting salt is a polystyrene sulfonate, a chloride and / or a sulfate.

14. Method according to any one of claims 1 to 6, wherein the positive active material (18) is absorbed in an aqueous solution containing monomers for generating the polythiophene, and subsequently an aqueous reaction solution containing an oxidizing agent is added dropwise, obtaining the positive active material (18) coated with the polythiophene.

15. The method of claim 14, wherein the aqueous solution contains an organic co-solvent, and wherein the organic co-solvent is preferably selected from the group consisting of sulfoxides, formamides, polyethylene glycols, alcohols and mixtures thereof.

16. Method according to claim 14 or 15, wherein the oxidizing agent of the aqueous reaction solution is selected from the group consisting of persulfates, metal chlorides and combinations thereof, preferably from the group consisting of sodium persulfate, ammonium persulfate and iron trichloride.

17. Method according to any one of claims 14 to 16, wherein the aqueous reaction solution is added dropwise over a period of 1 to 8 hours, preferably over a period of 2 to 3 hours.

18. Method according to any one of claims 14 to 17, wherein the aqueous solution contains polystyrene sulfonate, such that the coating is obtained from a polythiophene as a polythiophene:polystyrene sulfonate coating.

19. Method according to claim 18, wherein the polystyrene sulfonate of the polythiophene:polystyrene sulfonate coating is at least partially exchanged for chloride ions in a post-treatment step.

20. Method according to claim 19, wherein the coated positive active material (18) is immersed in a hydrochloric acid treatment bath in the post-treatment step, and wherein the hydrochloric acid treatment bath contains in particular an organic solvent, a polyethylene glycol and an acid mixture comprising hydrochloric acid.

21. Method according to claim 19, wherein the exchange is carried out electrochemically.

22. Method according to one of the preceding claims, wherein the positive active material (18) is loaded with sulfur prior to the application of the coating (20) made of polythiophene.

23. Method according to claim 22, wherein for loading with sulfur the positive active material (18) is suspended in a sulfur solution, wherein the sulfur solution contains a nonpolar solvent and sulfur, and the nonpolar solvent is subsequently evaporated.

24. Method according to claim 23, wherein the nonpolar solvent is selected from the group consisting of carbon disulfide, benzene, toluene and mixtures thereof, preferably from the group consisting of benzene, toluene and mixtures thereof.

25. Method according to claim 22, wherein the positive active material (18) is mixed with molten sulfur for loading with sulfur.

26. Method according to claim 25, wherein the positive active material (18) and elemental sulfur are ground in a ball mill to melt the sulfur.

27. Method according to claim 22, wherein the positive active material (18) is placed in an autoclave and loaded with gaseous sulfur in the autoclave.

28. A method according to any one of claims 1 to 6, wherein the positive active material (18) is provided with the coating (20) of the polythiophene during the synthesis of the positive active material by reacting an active material precursor in an aqueous solution to form the positive active material (18), wherein the aqueous solution contains monomers for generating the polythiophene.

29. Method according to claim 28, wherein the aqueous solution further contains an active material coreagent, wherein the active material coreagent contains manganese, preferably manganese(II) chloride.

30. Method according to claim 28 or 29, wherein the active material precursor and the monomers for generating the polythiophene are present in equimolar proportions in the aqueous solution.

31. A method according to any one of claims 28 to 30, wherein the aqueous solution contains a complexing agent, and wherein the complexing agent is preferably selected from the group consisting of ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, trisodium citrate, disodium citrate, citric acid, sodium citrate, sodium alginate, sodium carboxymethylcellulose, tetrasodium pyrophosphate and combinations thereof.

32. A method according to any one of claims 28 to 31, wherein the active material precursor is a compound with at least one metal, and wherein an active material modifier is added to the aqueous solution, which is of the same compound type as the active material precursor and comprises a metal with a different oxidation state than the metal of the active material precursor.

33. The method of claim 32, wherein the molar ratio of active material modifier to active material precursor is in the range of 22:1 to 1:21, preferably in the range of 1:3 to 1:

9.

34. A method according to any one of claims 28 to 33, wherein the aqueous solution contains one or more additives selected from the group consisting of sodium chloride, potassium chloride, polyvinylpyrrolidone, hydrochloric acid, sodium hydroxide, sodium L-ascorbate, potassium L-ascorbate, sulfoxides, polyethylene glycols, formamides, dialkyl esters, lactones, alcohols and combinations thereof.

35. Positive electrode (10) for a sodium-ion battery or a potassium-ion battery, obtained according to a method according to any one of the preceding claims.

36. Battery comprising a positive electrode (10) according to claim 35, a negative electrode, and a separator arranged between the positive electrode and the negative electrode, wherein the battery is a sodium-ion battery or a potassium-ion battery.

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