Process for producing an aluminum ion-conducting polymer

Abstract

The invention relates to a method and its use for producing an aluminum ion-conducting polymer, comprising at least the steps: a) providing at least one aluminum salt; an organic compound capable of forming an ionic liquid with the at least one aluminum salt; and a polyacrylonitrile (PAN)-based polymer; b) producing an ionic liquid by mixing the at least one aluminum salt and the organic compound; c) adding the PAN-based polymer to the ionic liquid and subjecting it to a temperature treatment in the absence of air at a temperature in the range from 100°C to 230°C. The invention further relates to an aluminum ion-conducting polymer and its use.

Description

[0001] The invention relates to a method for producing an aluminum ion-conducting polymer.

[0002] In current technology, ionic liquids (ILs) and deep eutectic solutions (DESs) based on aluminum chloride (AlCl3) are used as electrolytes in aluminum batteries. These electrolytes contain chloroaluminate complexes, which are considered extremely corrosive due to their chemical properties. Because of this, there is a risk of leakage of the ionic liquids and the resulting corrosion. This risk can be reduced by polymerizing these liquids.

[0003] Currently, a gelling agent is added to liquid electrolytes (IL, DES) to create a gel electrolyte. Amide-based monomers or polymers such as acrylamide or polyamide have proven to be effective gelling agents [1, 2]. However, such gel electrolytes are usually still too liquid, making a separator essential, or the preparation of the polymer gel electrolyte requires the use of harmful solvents.

[0004] The production of a PAN-containing gel electrolyte membrane has been demonstrated in studies [3].

[0005] The object of the invention is therefore to provide a method for producing an aluminum ion-conducting polymer and an aluminum ion-conducting polymer which has sufficient stability for use in aluminum batteries without an additional separator and whose production does not require harmful solvents.

[0006] According to the invention, the problem is solved by a method according to independent claim 1 and an aluminum ion-conducting polymer according to independent claim 9. Advantageous embodiments of the invention are specified in the dependent claims.

[0007] A first aspect of the invention relates to a method for producing an aluminium ion-conducting polymer, comprising at least the steps of: a) Providing at least one aluminium salt; an organic compound capable of forming an ionic liquid with the at least one aluminium salt; and a polyacrylonitrile (PAN)-based polymer; b) Production of an ionic liquid by mixing the at least one aluminium salt and the organic compound; c) Addition of the PAN-based polymer to the ionic liquid and heat treatment under exclusion of air at a temperature in the range of 100 °C to 230 °C.

[0008] In embodiments, the method according to the invention is carried out in the sequence of steps a), b) and c).

[0009] The process according to the invention advantageously enables the simple and large-scale production of an aluminum ion-conducting polymer without the use of harmful solvents. It is also advantageous that the process allows the production of an aluminum ion-conducting polymer capable of electrochemically depositing aluminum, thus making it suitable for various applications. Furthermore, the production of the aluminum ion-conducting polymer can be easily integrated into existing manufacturing processes and technologies. The process also advantageously allows for the targeted adjustment of the properties of the aluminum ion-conducting polymer, such as ionic conductivity, elasticity, and / or strength, to suit the specific application of the polymer.Furthermore, an aluminium ion-conducting polymer produced in this way advantageously exhibits a higher viscosity compared to known gel electrolytes, so that the use of separators is obsolete.

[0010] In the following, the term "one" will always be understood to mean "at least one". Thus, an aluminum salt, an organic compound, a PAN-based polymer, etc., also means at least one aluminum salt, at least one organic compound, at least one PAN-based polymer, etc.

[0011] An aluminum salt according to the invention comprises aluminum halides, aluminum sulfonates, such as aluminum trifluoromethanesulfonate Al(OTf)3; aluminum nitrate Al(NO3)3, aluminum sulfate Al2(SO4)3 and aluminum phosphate AlPO4 and / or mixtures thereof. Preferably, the at least one aluminum salt is an aluminum halide, such as AlF3, AlCl3, AlBr3, All3 and / or a mixture of aluminum salts.

[0012] An organic compound may expediently include organic salts. Organic salts include pyridinium halides, ammonium halides, imidazolium halides, and / or mixtures thereof. The organic compound is further selected from ionic liquids such as 1-butylpyridinium chloride ([BP]Cl), trimethylphenylammonium chloride (TMPAC), 1-butyl-3-methylimidazolium halide ([BMIm]X), 1-ethyl-3-methylimidazolium halide ([EMIm]X), triethylamine hydrohalide ([Et3N]HX), 4-ethylpyridine, 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIm]OTf), and / or mixtures thereof. X is selected from the halogens F, Cl, Br, and I.

[0013] The organic compound is still selected from urea, acetamide, caprolactam and mixtures thereof.

[0014] In embodiments, the production of an ionic liquid in step b) is carried out by the stepwise addition of the at least one aluminum salt to the organic compound. Advantageously, this allows the exothermic reaction to be controlled.

[0015] In further embodiments, step b) is carried out in the absence of air. The term "absence of air" is understood to mean the use of an atmosphere with an oxygen content of no more than 10 ppm and / or a water content of no more than 10 ppm. In further embodiments, step b) and / or step c) is carried out in an inert gas atmosphere, in particular a nitrogen or argon atmosphere.

[0016] The ionic liquid produced in step b) may contain undissolved residues of at least one aluminum salt.

[0017] In step c), a PAN-based polymer is added to the ionic liquid produced in step b). This initially forms a suspension of ionic liquid and undissolved residues of at least one aluminum salt and the PAN-based polymer.

[0018] In some embodiments, the PAN-based polymer is added to the ionic liquid in step c) under anaerobic conditions. In other embodiments, the PAN-based polymer is added in powder form. It is advantageous if the powder of the PAN-based polymer has a particle size in the range of 50 µm to 100 µm.

[0019] Furthermore, in step c) a temperature treatment is carried out in the absence of air at a temperature in the range of 100 °C to 230 °C.

[0020] Advantageously, the heat treatment in step c) dissolves the solid components in the resulting suspension, such as any undissolved residues of the at least one aluminum salt and the PAN-based polymer. Furthermore, an aluminum ion-conducting polymer, particularly an elastomer, is advantageously formed, the degree of cross-linking and thus its strength of which can be adjusted by selecting the temperature and duration of the heat treatment. Higher temperatures and longer treatment times lead to an increase in the degree of cross-linking.

[0021] The degree of cross-linking refers to the ratio of the amount of cross-linked building blocks to the total number of building blocks present. Experimentally, the degree of swelling can be determined in a solvent, based on DIN ISO 1817, as a measure of the degree of cross-linking of a polymer.

[0022] The melt volume flow rate (or melt flow index) of the formed polymer can be determined in accordance with ISO 1133 and serves to characterize the flow behavior (molding compound testing) of a thermoplastic under certain pressure and temperature conditions, possibly under protective gas, and allows conclusions to be drawn about the degree of polymerization, i.e. the average number of monomer units in a molecule.

[0023] Temperatures above 230 °C should be avoided in step c), as these will lead to the decomposition of the polymer formed.

[0024] In various embodiments, the heat treatment is carried out for a duration of 1 to 120 minutes. The duration of the heat treatment depends on the thickness of the resulting aluminum ion-conducting polymer. For example, a duration of 30 to 120 minutes is advantageous if the aluminum ion-conducting polymer has a thickness of approximately 2 cm in order to achieve the desired degree of crosslinking. For thicknesses below 2 cm, e.g., for an aluminum ion-conducting polymer present as a coating, a duration of 1 to 10 minutes is advantageous.

[0025] In embodiments, the heat treatment in step c) is carried out at a temperature in the range of 120 °C to 140 °C for a duration of 10 to 60 minutes. Advantageously, this results in an aluminum ion-conducting polymer, which is present as a clear viscous solution and can be used as a starting material for the production of PAN nanofibers and thus carbon nanofibers.

[0026] In preferred embodiments, the PAN-based polymer is polyacrylonitrile (PAN) or a PAN-based copolymer with a PAN content in the range of 50 wt.% to 99 wt.%.

[0027] A PAN-based copolymer with a PAN content of 50 wt.% to 99 wt.% means a copolymer that contains the monomer acrylonitrile and at least one other monomer.

[0028] In embodiments, a PAN-based copolymer has a PAN content in the range of 60 wt.% to 99 wt.%, preferably in the range of 70 wt.% to 99 wt.%, particularly preferably in the range of 80 wt.% to 99 wt.% and most preferably in the range of 90 wt.% to 99 wt.%.

[0029] Advantageously, the ionic conductivity and strength of the aluminum ion-conducting polymer are adjusted by the PAN-based polymer and its proportion in the aluminum ion-conducting polymer, so that sufficient strength with good ionic conductivity can be achieved advantageously even with small proportions of the PAN-based polymer in the range of a few wt.% and at a suitable treatment temperature.

[0030] In preferred embodiments, in step b) the aluminum salt and the organic compound are mixed together in a molar ratio in the range of 1:1 to 4:1.

[0031] Advantageously, the acidity can be adjusted by varying the aluminum salt content, thus enabling the adaptation of the manufactured aluminum ion-conducting polymer for battery applications as an electrolyte.

[0032] In preferred embodiments, in step b) the aluminum salt and the organic compound are mixed in a molar ratio of 2:1 to 4:1.

[0033] This advantageously increases the solubility limit and reduces the loss of the negative dimer [Al2Cl7] - The reaction with the PAN-based polymer in the ionic liquid is balanced. This further advantageously increases the proportion of active complex ions in the formed polymer and thus the cell capacity, making such a polymer suitable for battery applications.

[0034] In preferred embodiments, in step c) the PAN-based polymer is added in a molar ratio of 0.1:1 to 2:1 relative to the organic compound.

[0035] This advantageously increases the solubility of at least one aluminum salt and adjusts the acidity of the mixture. The PAN-based polymer reacts with the negative dimer [Al2Cl7]- , whereby AlCl4 - which in turn reacts with the undissolved aluminum salt to form [Al2Cl7] - Reacts.

[0036] In embodiments, the proportion of the at least one aluminum salt in the suspension produced in step c) is at least 50 mol%. In further embodiments, the proportion of the at least one aluminum salt in the suspension produced in step c) is in the range of 50 mol% to 70 mol%.

[0037] In some embodiments, the proportion of the organic compound in the suspension produced in step c) is in the range of > 0 mol% to 50 mol%. In other embodiments, the proportion of the PAN-based polymer in the suspension produced in step c) is in the range of > 0 mol% to 50 mol%.

[0038] In embodiments, in step c), a mixture of a PAN-based polymer and at least one aluminum salt with a molar ratio in the mixture in the range of greater than 0:1 to 1:1 is added to the ionic liquid, and a temperature treatment is carried out in the absence of air at a temperature in the range of 100 °C to 230 °C. This is advantageous if, in step b), the aluminum salt and the organic compound are mixed in a molar ratio of 2:1.

[0039] In preferred embodiments, a forming process is carried out after step c) as step d).

[0040] Advantageously, this transforms the aluminium ion-conducting polymer produced in this way into a form that can be used for a variety of applications, preferably into a polymer film or a polymer layer.

[0041] In some embodiments, the forming process in step d) is carried out such that a polymer layer is formed. This can be achieved in some embodiments by extrusion, doctor blade forming, rolling, film casting, pressing, or nozzle application. The forming process must be selected depending on the degree of cross-linking and thus the viscosity, which is determined by the temperature treatment in step c). For example, polymers formed in step c) with a lower degree of cross-linking, which are viscous liquids, can be readily formed into a polymer layer by film casting, extrusion, doctor blade forming, etc. Polymers formed in step c) with higher degrees of cross-linking and thus increased viscosities can be formed into a polymer layer by, for example, rolling, calendering, or pressing. The possible forming processes and their selection depending on the viscosity of the material to be formed are generally known to those skilled in the art.

[0042] In further embodiments, the polymer formed in step c) can be applied to a film, nonwoven, or fabric. This is advantageous, for example, when forming is carried out by pressing or rolling and can prevent the polymer being formed from adhering to the pressing tools or rollers. In further embodiments, another film, nonwoven, or fabric can be applied to the polymer applied to the first film, nonwoven, or fabric, so that the polymer is embedded between the films, nonwovens, and / or fabrics.

[0043] In further embodiments, step d) is carried out in the absence of air.

[0044] In some embodiments, step d) is carried out at a temperature in the range of 80 °C to 130 °C. This is particularly advantageous if the heat treatment in step c) was performed at a temperature in the range of 150 °C to 230 °C. Such a heat treatment leads to an increased degree of cross-linking and, consequently, to increased viscosity and strength of the polymer formed, making subsequent forming more difficult. In such cases, it is advantageous to perform the forming at a temperature in the range of 80 °C to 130 °C in order to reduce the viscosity of the polymer and increase its formability.

[0045] In preferred embodiments, the temperature treatment in step c) takes place at a temperature in the range of 100 °C to 150 °C.

[0046] This advantageously facilitates the dissolution of solid components, such as any undissolved residues of the at least one aluminum salt and PAN-based polymer. Furthermore, it advantageously results in a partially or incompletely cross-linked, aluminum ion-conducting polymer, which exists in the form of a viscous liquid and is therefore flowable and easily formable.

[0047] In embodiments, a second temperature treatment is carried out as step e) at a temperature in the range of 150 °C to 230 °C.

[0048] This is particularly advantageous if the temperature treatment in step c) is carried out at a temperature in the range of 100 °C to 150 °C. In embodiments, the temperature treatment in step c) is carried out at a temperature in the range of 150 °C to 230 °C, and no second temperature treatment is performed as step e).

[0049] The second temperature treatment advantageously adjusts the final viscosity and strength of the aluminum ion-conducting polymer for the respective application.

[0050] In embodiments, step e) is performed after step d).

[0051] In further embodiments, step e) is carried out for a duration of 1 to 120 minutes. The duration of the heat treatment depends on the thickness of the resulting aluminum ion-conducting polymer. For example, a duration of 30 to 120 minutes is advantageous if the aluminum ion-conducting polymer has a thickness of approximately 2 cm in order to achieve a desired degree of crosslinking. For thicknesses below 2 cm, e.g., for an aluminum ion-conducting polymer present as a coating, a duration of 1 to 10 minutes is advantageous.

[0052] Another aspect concerns an aluminum ion-conducting polymer consisting of a covalently cross-linked PAN-based polymer and at least one aluminum salt dissolved therein and an organic compound, wherein the molar ratio of the aluminum salt to the organic compound is 1:1 to 4:1, and wherein the molar ratio of the PAN-based polymer to the organic compound is 0.1:1 to 2:1.

[0053] Advantageously, such an aluminum ion-conducting polymer exhibits a higher viscosity than known gel electrolytes, thus eliminating the need for separators. Furthermore, such a polymer advantageously contains no harmful solvents. As an electrolyte, such an aluminum ion-conducting polymer also advantageously exhibits significantly reduced chemical aggressiveness and corrosiveness compared to liquid electrolytes, enabling safe use. Additionally, such an aluminum ion-conducting polymer is less reactive towards water when used as a polymer electrolyte, meaning its stability upon contact with water or air is increased. It is also advantageous that the aluminum ion-conducting polymer is capable of electrochemically depositing aluminum and conducting aluminum ions or aluminum-containing complex ions, making it suitable for a variety of applications.Furthermore, such an aluminum ion-conducting polymer exhibits good mechanical properties and can be used as a solid electrolyte in the production of flexible and robust electrochemical energy storage devices. The properties of such an aluminum ion-conducting polymer, such as ionic conductivity, strength, and degree of cross-linking, are also advantageously adjustable over a wide range, making it adaptable to various applications.

[0054] In embodiments, the aluminium ion-conducting polymer exhibits an ionic conductivity in the range of 0.1 mS / cm to 10 mS / cm at a temperature in the range of 10 °C to 40 °C.

[0055] Such an aluminum ion-conducting polymer is advantageously usable as a polymer electrolyte in electrochemical energy storage devices, such as aluminum batteries, and in the electrochemical deposition of aluminum.

[0056] In embodiments, the molar ratio of the aluminum salt to the organic compound is 2:1 to 4:1.

[0057] Advantageously, by varying the aluminum salt content, the acidity of the aluminum ion-conducting polymer can be adjusted and the battery capacity increased in the case of application within an electrochemical energy storage system.

[0058] Another aspect concerns the use of an aluminum ion-conducting polymer produced according to the inventive method as an electrolyte in an aluminum battery, in a process for the electrochemical deposition of aluminum and / or in a process for the production of carbon fibers.

[0059] An aluminum ion-conducting polymer produced by the process according to the invention can be used in embodiments as an electrolyte, preferably as a polymer electrolyte, in electrochemical energy storage devices, e.g. aluminum batteries, in a process for the electrochemical deposition of aluminum and / or in a process for the production of carbon fibers, e.g. as a starting material in a process for the production of PAN nanofibers and thus carbon nanofibers.

[0060] Another aspect concerns the use of an aluminum ion-conducting polymer as an electrolyte in an aluminum battery, in a process for the electrochemical deposition of aluminum and / or in a process for the production of carbon fibers.

[0061] An aluminum ion-conducting polymer can be used in embodiments as an electrolyte, preferably as a polymer electrolyte, in electrochemical energy storage devices, e.g. aluminum batteries, in a process for the electrochemical deposition of aluminum and / or in a process for the production of carbon fibers, e.g. as a starting material in a process for the production of PAN nanofibers and thus carbon nanofibers.

[0062] For the realization of the invention, it is also advantageous to combine the aforementioned inventive configurations, embodiments and features of the claims. Examples of implementation

[0063] The invention will now be explained in more detail using an exemplary embodiment. The exemplary embodiments relate to a method for producing an aluminum ion-conducting polymer and to an aluminum ion-conducting polymer itself, and are intended to describe the invention without limiting it. Example 1

[0064] In one embodiment of the inventive process for producing an aluminum ion-conducting polymer, in step a) at least one aluminum salt, one organic compound, and one PAN-based polymer are provided as powders. The aluminum salt is AlCl3, the organic compound is 1-ethyl-3-methylimidazolium chloride [EMIM]Cl, and the PAN-based polymer is polyacrylonitrile (PAN). In step b) under anaerobic conditions in a glovebox, an ionic liquid containing undissolved AlCl3 residues is prepared from 2.5 mol of AlCl3 and 1 mol of 1-ethyl-3-methylimidazolium chloride [EMIM]Cl.

[0065] In step c), 0.5 mol of PAN is added to the prepared ionic liquid under anaerobic conditions. This creates a suspension of ionic liquid and undissolved AlCl3 and PAN residues. Furthermore, in step c), a heat treatment is carried out at 140 °C for 30 minutes under anaerobic conditions, which dissolves the undissolved components and forms an aluminum ion-conducting polymer in the form of a free-flowing, viscous liquid.

[0066] In step d), the formed polymer is then transformed by applying the flowable polymer as a polymer film to a surface, e.g., a nonwoven fabric, using doctor blades. Subsequently, in step e), a second heat treatment is carried out at a temperature of 180 °C for a duration of 2 to 10 minutes to achieve the final degree of cross-linking and strength. This results in a solid polymer film that can be used, for example, as a polymer electrolyte in electrochemical energy storage systems. Example 2

[0067] In a further embodiment of the method according to the invention, steps a) and b) are carried out analogously to embodiment 1. In step c), the heat treatment is performed at a temperature of 160 °C for a duration of 30 minutes. During this process, the undissolved components dissolve, and an aluminum ion-conducting polymer is formed that is no longer flowable. In a subsequent step d), the non-flowable polymer is formed by pressing it between heated plates at a temperature of 130 °C to form a polymer film. In one embodiment, the polymer is applied to a film before pressing, and another film is applied to the polymer to be formed, so that the polymer is arranged between two films, which prevents the polymer from adhering to the heated plates.

[0068] In another embodiment, the forming process in step d) is alternatively carried out by rolling at a temperature of 120°C (surface temperature of the rolls) in a calender. Here, too, direct contact and thus adhesion of the polymer to the heated rolls can be prevented by applying the polymer to a film before rolling and then applying another film to the polymer, so that the polymer is sandwiched between two films. Example 3

[0069] An aluminum ion-conducting polymer was produced by a process according to embodiments 1 and 2. The aluminum ion-conducting polymer consists of a covalently cross-linked PAN-based polymer and at least one dissolved aluminum salt and an organic compound, wherein the molar ratio of the aluminum salt to the organic compound is 1:1 to 4:1, and wherein the molar ratio of the PAN-based polymer to the organic compound is 0.1:1 to 2:1.

[0070] For comparison purposes, a polymer was produced using a similar process, but PA6 was added instead of PAN. The proportion of PAN and PA6 in the finished polymer is 3% by weight each.

[0071] The following properties of the produced polymers were observed in comparison: Characteristic PA6 PAN Flowability flows well does not flow Air contact Slow reaction Slow reaction Water contact Reaction violent Slow reaction

[0072] It is evident that the aluminum ion-conducting polymer produced with PAN according to the inventive process is non-flowable and can therefore be used as a solid electrolyte in battery applications. Due to the sluggish reactions occurring only upon contact with air and water, such a polymer electrolyte increases the safety of battery applications.

[0073] In comparison, a solid electrolyte with the desired properties and low polymer content cannot be produced using PA6, as the polymer still exhibits good flowability. Furthermore, the reaction upon contact with water is very vigorous, making it unsuitable for battery applications. Non-patent literature cited: [1] Liu, Zhidong, et al. “Low-cost gel polymer electrolyte for high-performance aluminum-ion batteries.” ACS Applied Materials & Interfaces 13.24 (2021): 28164-28170. [2] Mohammad, Amir, et al. „A Flexible Solid-State lonic Polymer Electrolyte for Application in Aluminum Batteries.“ ACS Applied Energy Materials 6.5 (2023): 2914-2923. [3] Elia, Giuseppe Antonio, et al. „A gel polymer electrolyte for aluminum batteries.“ Energy Technology 9.8 (2021): 2100208.

Claims

[1] Method for producing an aluminium ion-conducting polymer, comprising at least the steps of: a) Providing at least one aluminium salt; an organic compound capable of forming an ionic liquid with the at least one aluminium salt; and a polyacrylonitrile (PAN)-based polymer; b) Production of an ionic liquid by mixing the at least one aluminium salt and the organic compound; c) Addition of the PAN-based polymer to the ionic liquid and temperature treatment under exclusion of air at a temperature in the range of 100 °C to 230 °C, wherein the organic compound is selected from: - organic salts, and - Urea, acetamide, caprolactam and mixtures thereof. [2] Method according to claim 1, characterized bythat organic salts include pyridinium halides, ammonium halides, imidazolium halides and / or mixtures thereof. [3] Method according to claim 1, characterized by , that the organic compound is selected from: 1-Butylpyridinium chloride ([BP]CI), Trimethylphenylammonium chloride (TMPAC), 1-Butyl-3-Methylimidazolium halide ([BMIm]X), 1-Ethyl-3-Methylimidazolium halide ([EMIm]X), Triethylamine hydrohalide ([Et3N]HX), 4-Ethylpyridine, 1-Butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIm]OTf) and / or mixtures. [4] Method according to any one of claims 1 to 3, characterized by , that the PAN-based polymer is PAN or a PAN-based copolymer with a PAN content in the range of 50 wt.% to 99 wt.%. [5] Method according to any one of claims 1 to 4, characterized by , that in step b) the aluminum salt and the organic compound are mixed in a molar ratio in the range of 1:1 to 4:

1. [6] Method according to any one of claims 1 to 5, wherein in step b) the aluminium salt and the organic compound are mixed in a molar ratio of 2:1 to 4:

1. [7] Method according to any one of claims 1 to 6, characterized by , that in step c) the PAN-based polymer is added in a molar ratio of 0.1:1 to 2:1 relative to the organic compound. [8] Method according to any one of claims 1 to 7, characterized by , that in step c) a mixture of the PAN-based polymer and the at least one aluminium salt with a molar ratio in the range of greater than 0:1 to 1:1 is added to the ionic liquid and a temperature treatment is carried out in the absence of air at a temperature in the range of 100 °C to 230 °C. [9] Method according to any one of claims 1 to 8, characterized by , that after step c) a transformation takes place as step d). [10] Method according to any one of claims 1 to 9, characterized by, that the temperature treatment in step c) takes place at a temperature in the range of 100 °C to 150 °C. [11] Method according to any one of claims 1 to 10, characterized by , that a second temperature treatment as step e) takes place at a temperature in the range of 150 °C to 230 °C.