Method for producing a separator for a motor vehicle battery and separator

Abstract

In a method for producing a separator (6) for a motor vehicle battery (1), a powdered starting material (10) containing aluminum oxide (Al2O3), zirconium dioxide (ZrO2), titanium dioxide (TiO2) or manganese dioxide (MnO2) is provided, a powdered additive material (12) formed from lithium oxide (Li2O), lithium hydroxide (LiOH) and / or lithium carbonate (Li2CO3) is added to the starting material to form a powder mixture (14), and in the powder mixture (14) by a first heat supply (W1) of at least 700 degrees Celsius, preferably of 800 degrees Celsius, the starting material (10) and the additive material (12) are at least partially converted into lithium aluminum oxide (LiAlO2), lithium zirconium oxide (LiZrO2), lithium titanium oxide (Li2TiO3 or Li4Ti5O 12) or lithium manganese oxide (LiMn2O4). This powder mixture (14) is dispersed in a solvent after the first heat application (W1) and applied as a coating to a separator base element (18), and the separator base element (18) with the coating is subjected to a drying step (S7).

Description

[0001] The invention relates to a method for producing a separator for a motor vehicle battery. The invention also relates to a separator for a motor vehicle battery.

[0002] Separators are used in batteries to prevent galvanic contact between the different electrodes (cathode and anode). Depending on the battery design, the separator must exhibit different properties. While the separator should not be electrically conductive, it should allow the charge carriers present in the cell's chemistry to migrate between the electrodes (charge exchange). In widely used cells (single-cell batteries) that have a liquid electrolyte, charge exchange occurs via the transport of charge carriers (usually ions) through the separator or, if necessary, around it.

[0003] To achieve this, the separator must have a certain porosity to allow the electrolyte fluid to pass through it. This also requires the separator to be as wettable as possible, as a hydrophobic separator would prevent the electrolyte fluid from penetrating into and through the pores.

[0004] On the other hand, the separator must also be mechanically stable, especially in the case of lithium-ion cells. These cells can, under certain circumstances, be prone to the formation of so-called dendrites, which can lead to a short circuit between the electrodes. Common materials used to protect the separator and the electrodes are aluminum oxide and boehmite. However, these are not or only very slightly conductive to (lithium) ions, so the cell has a comparatively high impedance.

[0005] DE 10 2016 100 472 A1 describes a lithium-ion-conducting solid electrolyte deposited on a thin, flexible, porous aluminum oxide membrane arranged between coextensive, facing side surfaces of a porous, lithium-absorbing negative electrode and a positive electrode formed from a porous layer of particles of a compound of lithium, a transition metal element, and optionally another metal element. A liquid electrolyte, formed, for example, from LiPF6 dissolved in an organic solvent, permeates the electrode materials of the two porous electrodes to transport lithium ions during cell operation, but the solid electrolyte only permits the passage of lithium ions, and the negative electrode is protected from damage by transition metal ions or other chemical species generated in the positive electrode of the lithium-ion cell.

[0006] US 2021 / 0057702 A1 describes an electrode assembly and a rechargeable battery incorporating the same. The electrode assembly may comprise a negative electrode, a positive electrode, and a separator disposed between the negative electrode, the negative electrode, and the positive electrode, and having a first surface facing the negative electrode and a second surface facing the positive electrode. A first functional layer is disposed on the first surface and contains a fibrous polymer and a heat-resistant polymer, and a second functional layer is disposed on the second surface and contains an inorganic particle and an organic particle.

[0007] DE 10 2020 124 953 A1 describes a method for producing an electrode unit for a lithium-ion battery cell, comprising the steps of applying a ceramic layer to a separator film, arranging a first electrode layer on the ceramic layer, arranging a second electrode layer on a surface of the separator film facing away from the ceramic layer, and performing a pressure treatment and / or heat treatment during which the ceramic layer bonds to the first electrode layer. Furthermore, a lithium-ion battery cell with an electrode unit produced by the method is specified.

[0008] The invention is based on the object of enabling an improved separator.

[0009] This object is achieved according to the invention by a method for producing a separator for a motor vehicle battery having the features of claim 1. This object is also achieved according to the invention by a separator having the features of claim 6. Further advantageous and partly inventive embodiments and further developments of the invention are set out in the subclaims and the following description.

[0010] The method according to the invention is used to produce a separator for a motor vehicle battery. According to the method, a powdered starting material is first provided. This starting material contains (again in powder form) aluminum oxide (Al2O3), zirconium dioxide (ZrO2), titanium dioxide (TiO2) or manganese dioxide (MnO2). Subsequently, a powdered additive material is added (i.e., in particular, admixed) to the starting material to form a powder mixture. This starting material is formed from lithium oxide (Li2O), lithium hydroxide (LiOH) and / or lithium carbonate (Li2CO3). In this powder mixture, the starting material and the additive material are at least partially converted into lithium aluminum oxide (LiAlO2), lithium zirconium oxide (LiZrO2), lithium titanium oxide (Li2TiO3 or Li4Ti5O) by a first heat application of at least 700 degrees Celsius, preferably 800 degrees Celsius. 12) or lithium manganese oxide (LiMn2O4). In other words, in this step, the starting material reacts with the additive material in the powder mixture under the first heat application to form lithium aluminum oxide (LiAlO2), lithium zirconium oxide (LiZrO2), lithium titanium oxide (Li2TiO3 or Li4Ti5O 12 ) or lithium manganese oxide (LiMn2O4). In particular, the powder mixture is heated to a predetermined temperature, specifically the aforementioned at least 700, preferably 800 degrees Celsius. After the first heat application, i.e., preferably after the (first) reaction described above, the powder mixture is dispersed in a solvent and applied as a coating to a separator base element. In particular, the solvent is an alcohol, preferably ethanol. The separator base element with the coating is then subjected to a drying step.

[0011] The process described above has the advantage that, compared to conventional separator materials, the lithium plus X oxides described above (e.g., lithium aluminum oxide, etc.) are conductive to lithium ions. This has the advantage that ion transport processes occur significantly faster. Furthermore, sufficient wetting of the separator for sufficiently high ion transport is no longer necessary, thus reducing the complexity of cell production.

[0012] According to an advantageous process variant, phosphoric acid (H3PO4) is added to the powder mixture after the first heat application. A second heat application of at least 400 degrees Celsius, preferably 500 degrees Celsius, subsequently converts at least some of the residual lithium oxide (Li2O), lithium hydroxide (LiOH), and / or lithium carbonate (Li2CO3) in the powder mixture to lithium phosphate (Li3PO4). Preferably, the powder mixture is heated to a further predetermined temperature during the second heat application, in particular to at least 400, in particular 500 degrees Celsius. This lithium phosphate is a particularly good lithium ion conductor, so that the ionic conductivity through the separator can be further increased.

[0013] According to a suitable process variant, hydrogen fluoride (HF), in particular gaseous, is added to the coating during the drying step. This results in the formation of aluminum fluoride (AlF3) from aluminum oxide residues (AL2O3, optionally also other aluminum oxides, if present), particularly those present in the coating that did not react with the lithium compound(s) during the initial heat application. The aluminum fluoride provides protection against the effects of hydrogen fluoride during subsequent operation of the separator or the (motor vehicle) battery in which the separator is used. Likewise, any excess lithium hydroxide present in the coating can combine with the hydrogen fluoride and the aluminum fluoride to form lithium aluminum fluoride (Li3AlF6). This lithium compound is also a (further) lithium-ion conductor.Since usually not all of the particles present can react with their reactants, unreacted aluminum oxides may remain in the coating. These can "capture" hydrogen fluoride generated during normal battery operation by reacting with hydrogen fluoride to form aluminum fluoride. This provides a multiple protective effect, as the aluminum fluoride already present reduces the effects of acid attack by hydrogen fluoride, and the latter can also be "processed" in reactions, thereby building up an additional protective effect.

[0014] Preferably, a third heat input of 70 to 110 degrees Celsius, especially 80 to 100 degrees Celsius, is applied during the drying step. In other words, the coated separator base element is heated to this temperature.

[0015] The coating described above can preferably be applied to all sides of the separator base element. In this case, the separator base element is immersed, in particular, in the solution (mixture) of ethanol and the powder mixture. Alternatively, the coating can also be applied locally, for example, only to one side of the separator base element—particularly a film-like one. In the latter case, a conventional protective layer, e.g., made of aluminum oxide and / or boehmite, can also be applied to the other side of the separator base element.

[0016] According to an optional process variant, a further coating of polyvinylidene fluoride (PVDF) is applied to the coating. This further coating serves as a binder layer for the coating made from the powder mixture. After the drying step, the latter would be at least partially exposed on the separator base element. Preferably, the further coating is applied by powder spraying and optionally melted afterwards. In principle, however, the further coating can also be applied wet, i.e. dissolved in a solvent or in melt form. When the battery is in its intended use, polyvinylidene fluoride, under the influence of a liquid electrolyte, preferably forms a type of gel, which then encloses the particles of the coating made from the powder mixture or can at least flow around them.

[0017] In a particularly advantageous process variant, the respective lithium compound added to the starting material—i.e., lithium oxide (Li2O), lithium hydroxide (LiOH), and / or lithium carbonate (Li2CO3)—is extracted from process residues of a calcination process, particularly from battery production. This allows excess material to be advantageously reused and, in particular, process waste to be (at least partially) freed of valuable or problematic material.

[0018] According to a suitable process variant, a polyethylene film, a polypropylene film or optionally a multilayer film made of polyethylene and polypropylene is used as the separator base element.

[0019] The invention also relates to the separator for the motor vehicle battery. The separator comprises a separator base element and at least one coating applied to one side of the separator base element, which coating comprises lithium aluminum oxide (LiAlO2), lithium zirconium oxide (LiZrO2), lithium titanium oxide (Li2TiO3 or Li4Ti5O 12 ) or lithium manganese oxide (LiMn2O4). Additionally or alternatively, the separator base element comprises a film made of polyethylene or polypropylene filled with lithiated silicon. In other words, the separator is manufactured according to the method of the invention.

[0020] The separator therefore has the physical characteristics and advantages set out in the above description.

[0021] According to a practical embodiment, the coating comprises Li3PO4 and / or aluminum fluoride (AlF3).

[0022] To manufacture a battery, the separator base element, coated with the above-described coating, is placed between two electrodes as a separator. This assembly is then usually rolled ("jelly roll") and subsequently impregnated with electrolyte. This can further lithiate the silicon, causing the separator to "swell." This is advantageous because it forces the separator and electrodes more tightly against each other.

[0023] The conjunction “and / or” is to be understood here and in the following in particular in such a way that the features linked by means of this conjunction can be formed both together and as alternatives to one another.

[0024] In the following, exemplary embodiments of the invention are explained in more detail with reference to a drawing. In the drawings: Fig. 1 schematically shows a structure of a battery cell for a motor vehicle battery of a motor vehicle, and Fig. 2 shows a schematic representation of a manufacturing process for a battery cell separator.

[0025] Corresponding parts are always provided with the same reference symbols in all figures.

[0026] In Fig. Figure 1 schematically shows the structure of a battery cell 1 for a motor vehicle battery. The battery cell 1 has two electrodes, here an anode 2 and a cathode 4. These are plate- or foil-like. Furthermore, the battery cell 1 has a separator 6, which is placed between the cathode 4 and the anode 2. The separator 6 serves to prevent galvanic contact between the cathode 4 and the anode 6. Furthermore, the cathode 4 and the anode 2 are arranged in a housing filled with an electrolyte (not shown).

[0027] Based on Fig.2, a process variant for manufacturing the separator 6 is explained in more detail. Accordingly, in a first step S1, powdered aluminum oxide (Al2O3) is provided as starting material 10 and an additional material 12. The additional material 12 is also in powder form (i.e., a powder) and is formed from particles of lithium oxide (Li2O), lithium hydroxide (LiOH), and lithium carbonate (Li2CO3). The starting material 10 and the additional material 12 are mixed to form a powder mixture 14 and, in a second step S2, are subjected to a heat treatment with a heat input W1 of (i.e., heating to) 800 degrees Celsius. Due to this heat treatment, the aluminum oxide react with lithium oxide, lithium hydroxide, and lithium carbonate to form lithium aluminum oxide (LiAlO2). The powder mixture thus contains a lithium ion-conductive material.

[0028] In a further (fourth) step S4, phosphoric acid (H3PO4), indicated here by a can 15, is added to the powder mixture 14. The powder mixture 14, which has been mixed with the phosphoric acid, is heated to 500 degrees Celsius in a further heat treatment using a second heat supply W2. As a result, residues (or at least parts thereof) of lithium oxide, lithium hydroxide, and lithium carbonate contained in the powder mixture react with the phosphoric acid to form lithium phosphate (Li3PO4), which is also a lithium ion conductive material.

[0029] In a subsequent fifth step S5, the powder mixture 14 from step S4 is added to a container (tank 16) with ethanol and mixed. The particles are thus dispersed in the ethanol. Subsequently, in a sixth step S6, a separator base element 18—here a film, e.g., made of PE—is passed through the mixture of ethanol and the powder mixture 14 and thus coated on all sides with this mixture.

[0030] Subsequently, as the seventh step S7, a drying step is carried out, for example in a continuous furnace. Here, the coated separator base element 18 is heated to a temperature of 80 degrees Celsius by a third heat supply W3. The ethanol evaporates and the powder mixture 14 remains on the separator base element 18 as a coating. In addition, hydrogen fluoride (HF) is supplied in gaseous form (indicated by means of a nozzle 20). At the elevated temperature, the hydrogen fluoride reacts with residues of aluminum oxide that are still present in the powder mixture 14 on the separator base element 18 to form aluminum fluoride. Aluminum fluoride offers protection against further acid attacks by hydrogen fluoride during the ongoing operation of a battery in which the separator base element 18 coated in this way is used. In addition, excess, i.e.The lithium hydroxide still present in the powder mixture 12 on the separator base element 18 is reacted with hydrogen fluoride and aluminum fluoride to form lithium aluminum fluoride. This represents an additional lithium ion conductive material, so that the lithium ion conductivity of the coating made from the powder mixture 14 is gradually increased.

[0031] In a further (eighth) step S8, powdered polyvinylidene fluoride (PVDF) is sprayed onto the layer of powder mixture 14 using a nozzle 22. The polyvinylidene fluoride forms a binder layer 24, which holds the particles of powder mixture 14 among themselves and on the separator base element 18.

[0032] Subsequently, in a ninth step S9, the separator base element 18 coated with the powder mixture 14 and polyvinylidene fluoride is placed as separator 6 between the anode 2 and the cathode 4. In particular, an electrolyte is then introduced, thus forming the battery cell 1.

[0033] The subject matter of the invention is not limited to the exemplary embodiments described above. Rather, further embodiments of the invention can be derived by those skilled in the art from the above description. List of reference symbols 1 battery cell 2 anode 4 Cathode 6 Separator 10 Source material 12 Additional material 14 Powder mixture 15 cans 16 tanks 18 Separator base element 20 nozzle 22 nozzle 24 Binder course 50 extruders 52 powders 54 powder 56 Slide 58 Slide 60 foil laminate S1-S9 step W1-W3 heat supply F1-F5 manufacturing step WB heat treatment

Claims

[1] Method for producing a separator (6) for a motor vehicle battery (1), wherein - a powdered starting material (10) containing aluminum oxide Al2O3, zirconium dioxide ZrO2, titanium dioxide TiO2 or manganese dioxide MnO2 is provided, - a powdered additive material (12) formed from lithium oxide Li2O, lithium hydroxide LiOH and / or lithium carbonate Li2CO3 is added to the starting material to form a powder mixture (14), - in the powder mixture (14) by a first heat supply (W1) of at least 700 degrees Celsius, preferably of 800 degrees Celsius, the starting material (10) and the additional material (12) at least partially to lithium aluminum oxide LiAlO2, lithium zirconium oxide LiZrO2, lithium titanium oxide Li2TiO3, lithium titanium oxide Li4Ti5O 12 or lithium manganese oxide LiMn2O4 reacts, - the powder mixture (14) is distributed in a solvent after the first heat application (W1) and is distributed as a coating on a separator base element (18), and - the separator base element (18) with the coating is subjected to a drying step (S7) characterized by , that phosphoric acid H3PO4 is added to the powder mixture (14) after the first heat supply and by a second heat supply (W2) of at least 400 degrees Celsius, preferably 500 degrees Celsius, at least parts of residues of lithium oxide Li2O, lithium hydroxide LiOH and / or lithium carbonate Li2CO3 in the powder mixture (14) are converted to lithium phosphate Li3PO4, and / or that during the drying step (S7) of the coating, in particular gaseous hydrogen fluoride HF is added, so that aluminum fluoride AlF3 is formed from residues of aluminum oxide Al2O3. [2] Method according to claim 1, wherein during the drying step (S7) of the coating, in particular gaseous hydrogen fluoride HF is supplied so that aluminum fluoride AlF3 is formed from residues of aluminum oxide Al2O3, and wherein during the drying step (S7) a third heat supply (W3) of 70 to 110 degrees Celsius, in particular of 80 to 100 degrees Celsius, takes place. [3] Method according to claim 1 or 2, wherein a further coating of polyvinylidene fluoride (PVDF) is applied to the coating of the powder mixture (14), which serves as a binder layer (24). [4] Process according to one of claims 1 to 3, wherein the lithium oxide Li2O, lithium hydroxide LiOH and / or lithium carbonate Li2CO3 is taken from process residues of a calcination process. [5] Method according to one of claims 1 to 4, wherein a polyethylene film, a polypropylene film or a multilayer film made of polyethylene and polypropylene is used as the separator base element (18). [6] Separator (6) for a motor vehicle battery, comprising a separator base element (18) and at least one coating applied to one side of the separator base element (18), which comprises lithium aluminum oxide LiAlO2, lithium zirconium oxide LiZrO2, lithium titanium oxide Li2TiO3, lithium titanium oxide Li4Ti5O 12 or lithium manganese oxide LiMn2O4, and manufactured by a process according to any one of claims 1 to 5. [7] Separator (6) according to claim 6, wherein the coating comprises lithium phosphate Li3PO4 and / or aluminum fluoride AlF3.

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