Cathode and method for producing cathode

Abstract

The invention relates to a method (110) for producing a cathode (112), to a cathode (112) produced by such a method and to a battery comprising such a cathode (112). The method (110) comprises the steps of: a) supplying a current collector (114) wherein at least a surface (116) of the current collector has an electrically conductive material (118); b) coating a surface (116) of the current collector (114) with a carbon-containing layer (120), and c) applying a cathode active material (124) to the carbon-containing layer (120), the carbon-containing layer (120) comprising more than 60 wt% and less than 80 wt% of carbon and at least one polymer as binder, and at least step b) being carried out at a temperature of at least 30 DEG C to at most 70 DEG C.

Description

Field of the Invention

[0001] The present invention relates to a method for preparing a cathode, a cathode, and a battery including such a cathode. Background Art

[0002] For applications in the automotive industry, especially for electric drive vehicles and as stationary energy storage devices, energy storage devices with a long lifespan and as high an energy density and power density as possible are required. To achieve a high energy density, nickel-rich cathode active materials composed of lithium nickel manganese cobalt oxide (NMC) are increasingly used. On the anode side, graphite anodes or silicon-based anode materials are often used. These electrode materials are applied in the form of a slurry to a generally thin metal foil made of aluminum foil, which serves as a current collector, by means of a coating process, especially a slot die coating or a slurry casting process.

[0003] Conventional slurries for electrode preparation include a water-based treatment for coating the anode and an N-methyl-2-pyrrolidone (NMP)-based treatment for coating the cathode. Depending on the selected cathode active material, the weight ratio among the cathode active material, the carbon additive, and the binder, and according to the physicochemical properties of the cathode active material (especially its particle shape, particle size, particle size distribution, and molecular weight), the solid content of the anode slurry used is generally 40 wt% to 60 wt%, and the solid content of the cathode material used is generally 50 wt% to 70 wt%. In an extrusion process, a solid content as high as 90% can even be achieved. Even though the mixing process at an industrial scale is generally not known to the public, it is generally recognized that the complex mechanisms and process steps of slurry mixing (especially regarding wetting, dispersion, and stabilization) have a significant impact on the quality and stability of the finished electrode and the battery including such an electrode. Especially for high-viscosity slurries with a high solid content, the selection of the composition, binder, particle size, particle shape, and additives (if any) is crucial to obtain a uniform and reproducible cathode active material layer, which meets the high-quality requirements of lithium-ion batteries.

[0004] For cost and environmental reasons, especially in view of the government legislation in force and / or anticipated, the use of organic solvents, especially N-methyl-2-pyrrolidone (NMP), in cathode slurries is to be abandoned in the future. On the other hand, according to the currently known prior art, the preparation of cathode materials without NMP is a major technical challenge. Since the nickel-rich NMC cathode powder has a strong interaction with water, the stability of the slurry will decrease; especially due to the occurrence of a high pH value of pH≈12, the aluminum current collector will start to corrode. The corrosion of the aluminum current collector proceeds in the pH range above pH 9 and is accompanied by the formation of gaseous hydrogen, which can easily lead to damage to the surface of the aluminum current collector, especially due to the appearance of pores, cracks or delamination. To counteract this damage to the surface of the aluminum current collector, known measures include adding an acid, thereby typically reducing the pH value in this way to 7 to 11 (preferably to 8 to 10, especially to 9±0.5). However, adding an acid may have a negative impact on the rheological properties of the cathode slurry, its electrode conductivity or layer adhesion. Generally, battery degradation can be regarded as the result of adding an acid. Depending on the type of acid, a reaction layer can also form on the particles of the cathode active material, which causes an increase in the battery impedance and may generally lead to a decrease in the performance of the electrochemical cell. Alternatively or additionally, the coating of the cathode active material can be carried out especially by means of an artificial solid electrolyte interphase (SEI), for example by means of ZrO 2 coating is carried out to prevent water from reacting with the cathode active material, thereby avoiding an increase in the pH value.

[0005] DE102011077932A1 discloses a cathode unit for an alkali metal-sulfur battery, which comprises a cathode current collector including a carbon substrate, and an electrochemically active component selected from sulfur or an alkali metal sulfide and in conductive contact with the carbon substrate.

[0006] DE10251241Al discloses a method for producing a lithium polymer battery by means of a composite system including a current collector, an electrode and a separator, wherein the current collector foil is coated with a pasty electrode material and subsequently joined to the separator material such that the electrode substrate side coated with the electrode material is in contact with the separator material. The lithium polymer battery produced by this method has a smooth structure without surface roughness, and the cycle stability, long-term stability and suppression of interfering side reactions are improved.

[0007] EP1609878A1 discloses an aluminum material coated with carbon, which can improve the adhesion between the aluminum material and the active material layer. The aluminum material coated with carbon includes an aluminum material and a carbon-containing layer formed on the surface of the aluminum material, and also includes an intermediate layer formed between the aluminum material and the carbon-containing layer and containing aluminum and carbon. The method for preparing the aluminum material coated with carbon includes the steps of arranging the aluminum material in a space containing a hydrocarbon substance, and heating the aluminum material in a state where it is arranged in the space containing the hydrocarbon substance.

[0008] DE102014220964A1 discloses a method for preparing a lithium battery electrode or a capacitor electrode, including providing a graphite material containing at least one conductive carbon material; providing an active material mixture containing an electrochemically active material; supplying the graphite material and the active material mixture into a calendering device, so as to set a concentration gradient of the conductive carbon material through the width and height of the feed port, and shaping the supplied materials in the calendering device into a foil including at least a conductive carbon substrate and a layer containing the active material mixture.

[0009] WO2017 / 001118A1 discloses an anode for a lithium battery. In order to improve the coulombic efficiency and / or cycle resistance of the lithium battery, the lithium battery includes a porous silicon monolith with a graphite layer. In addition, the present invention relates to a preparation method, a lithium battery and a lithium battery.

[0010] Object of the Invention Starting from this, the object of the present invention is to provide a method for preparing a cathode, a cathode and a battery including such a cathode, which at least partially overcome the disadvantages and limitations known in the prior art.

[0011] The method and the cathode should be particularly capable of achieving that no acid needs to be added, so as to avoid damage to the surface of the aluminum current collector usually caused by the formation of small holes, cracks or layer separation, or other negative effects on the rheological properties of the cathode paste or the electrical conductivity and layer adhesion of the electrode, which may overall lead to an accelerated battery decay, so that the troublesome modification of the current collector and / or the cathode active material by means of an additional physical coating process can be omitted, and the specific capacitance of the cathode prepared by this method should not deteriorate compared with the cathodes known in the prior art. Summary of the Invention

[0012] This object is achieved by a method for preparing a cathode, a cathode and a battery including such a cathode according to the features of the independent claims. Advantageous improvement schemes that can be achieved alone or in any combination are shown in the following description of the specification and the dependent claims.

[0013] The present invention relates in a first aspect to a method for preparing a cathode, wherein the cathode has at least one current collector and cathode active material. The term "cathode" refers to an electrode, i.e., an object to which a voltage and / or current can be applied, and which undergoes a reduction process during battery discharge, generally a reduction reaction of the oxidation state of transition metal cations in the electrode active material. In contrast, the term "anode" refers to the other electrode, at which an oxidation process occurs during battery discharge. Additionally, the designations "cathode" and "anode" are traditionally maintained during battery charging, although the reduction and oxidation reactions occur in reverse. Further, the term "battery" refers to an electrochemical cell having at least one cathode, at least one anode electrically insulated from the cathode, and at least one electrolyte provided for charge exchange; other components may be present, such as electrical connectors and / or separators.

[0014] The method for preparing the cathode includes steps a) to c) described in detail below, where all steps a) to c) can preferably be carried out in the listed order, starting with step a), then first b) and then c). Alternatively, at least two of the listed steps can also be carried out partially simultaneously, especially in a continuous process, where step c) is carried out on a cathode section where step b) has already been carried out, while step b) is carried out on other sections of the cathode and step a) is carried out on yet other sections of the cathode.

[0015] The individual steps of the method are as follows: a) Providing a current collector, wherein at least the surface of the current collector has a conductive material; b) Coating a carbon-containing layer on the surface of the current collector; and c) Applying cathode active material to the carbon-containing layer, wherein the carbon-containing layer includes more than 60 wt% and less than 80 wt% carbon and at least one polymer as a binder, and wherein at least step b) is carried out at a temperature between at least 30 °C and a maximum of 70 °C.

[0016] According to step a) of the method, a current collector is provided. The term "current collector" refers to the part of the cathode that is provided for outputting the voltage and / or current generated by the cathode to an external conductive element, especially to at least one electrical connector. For this purpose, at least the surface of the current collector (preferably the entire body of the current collector) has a conductive material. In a particularly preferred embodiment, at least the surface of the current collector (preferably the entire body of the current collector) has: aluminum; nickel; at least one noble metal (especially gold or platinum) or 100% carbon, with aluminum being particularly preferred. However, it is also possible to use these materials or other materials (preferably ceramics, including Al 2 O 3 ) in the form of a thin layer, or semiconductors such as silicon (preferably in a doped form).

[0017] According to step b) of the present method, a carbon-containing layer is coated on the conductive surface of the current collector. The term "coating" herein refers to a process for applying at least one material onto a substrate to thereby produce a layer on the substrate. The term "layer" herein relates to an arrangement structure in which the planar extent of the layer exceeds the layer thickness by at least 5 times, preferably at least 10 times, and particularly preferably at least 50 times.

[0018] The term "carbon-containing layer" herein refers to a layer whose composition has a verifiable proportion of carbon (C), preferably a preponderant proportion of carbon (C). According to the present invention, the carbon-containing layer comprises more than 60 wt% (preferably at least 65 wt%, particularly preferably at least 67.5 wt%) and less than 80 wt% (preferably at most 75 wt%, particularly preferably at most 72.5 wt%) of carbon, particularly about 70 wt% of carbon, and at least one polymer as a binder, wherein the proportions of carbon and polymer in the carbon-containing layer particularly preferably total 100 wt%. Carbon black is preferably used as the carbon, wherein the term "carbon black" refers to a black powdery solid that comprises at least 80 wt% and at most 99.5 wt% of carbon. In principle, however, it is also possible to consider using at least one other type of carbon, in particular: conductive carbon black, which may have a particle size of up to several hundred nanometers; conductive graphite, such as KS6L, which has a particle size in the micron range or the submicron range; amorphous carbon, including soft carbon or hard carbon; and / or carbon material variants having impurities (e.g., in the form of impurity atoms).

[0019] "Binder" means being provided for producing a composite material by means of adhesion, cohesion, and / or adsorption force between particles and / or phase boundaries, which is substantially in the form of a physical connection, whereby the particles or the regions defined by the phase boundaries are adsorbed to each other within the composite material, causing them to polymerize, crosslink, or bond. According to the present invention, the binder comprised in the carbon-containing layer has at least one polymer. The term "polymer" herein relates to a compound that comprises a large number of molecules, which are arranged adjacent to each other and are the same or of the same kind and are called "monomers". In a particularly preferred embodiment, the polymer comprised in the binder is selected from: polyvinylidene fluoride (PVDF); polyamide (PA); polybutyl acrylate (PBA); polyacrylic acid (PAA); polymethyl methacrylate (PMA); cellulose, preferably carboxymethyl cellulose (CMC), particularly Na-CMC or succinylated carboxymethyl cellulose (SCMC); styrene-butadiene rubber (SBR), a mixture of SBR and SCMC; epoxy adhesives, particularly epoxy hardener systems; latex-hydride-polymers; biopolymers, preferably polysaccharide-based vegetable gums, particularly sodium alginate, guar gum, karaya gum, or xanthan gum. However, it is also possible to consider using at least one other polymer.

[0020] According to the present invention, the composition of the carbon-containing layer is thus set within the given narrow parameter range. An excessively high proportion of carbon (C), especially carbon black, will not effectively prevent the corrosion of the surface of the current collector, especially the corrosion of the conductive electrode material located on the surface of the current collector, due to the leaching of the carbon component (especially carbon black) from the composite material composed of carbon and binder, and especially preferably will not effectively prevent the corrosion of aluminum when applying the cathode active material to the carbon-containing layer according to step c) hereinafter. This effect can be verified by pre-tests on commercially available aluminum current collectors coated with graphite. Additionally, it can be observed that when the proportion of carbon (C), especially the proportion of carbon black, is very high, small holes are formed in the carbon-containing layer, which will expose the current collector, so that the current collector is no longer protected against corrosion. An excessively low proportion of carbon (C), especially the proportion of carbon black, will on the one hand deteriorate the electrical contact between the cathode and the current collector, and on the other hand, as can be proven by experiments, the hydrophobic wetting characteristics of the cathode paste may occur, which will make it significantly difficult or prevent the uniform coating of the carbon-containing layer as much as possible. For other details, reference can be made to the following description of the embodiments for this purpose.

[0021] Furthermore, according to step C) of the present invention, the carbon-containing layer is coated on the surface of the current collector at a temperature between at least 30 °C (preferably at least 35 °C, particularly preferably at least 40 °C) and a maximum of 70 °C (preferably a maximum of 65 °C, particularly preferably a maximum of 60 °C). For this purpose, the carbon-containing layer is coated on the surface of the current collector by means of the following coating processes, where the coating process is preferably selected from: roll coating process, spraying process, slot-die coating, extrusion process, spin coating process or printing process (especially aerogel jet printing); however, other types of coating processes can also be considered. The preferred coating process is particularly a simple process that is easy to implement at low cost; complex and expensive coating processes, especially physical vapour deposition (PVD) or atomic layer deposition (ALD), can be dispensed with.

[0022] The carbon-containing layer according to the present invention can thus particularly function as a passivation layer. The term "passivation layer" herein means a layer that can effectively prevent the corrosion of the surface of the current collector (particularly preferably the corrosion of aluminum) when applying the cathode active material to the carbon-containing layer.

[0023] The carbon-containing layer according to the present invention can have a layer thickness of at least 0.1 µm (preferably at least 0.25 µm, particularly preferably at least 0.5 µm) and a maximum of 20 µm (preferably a maximum of 10 µm, particularly preferably a maximum of 7.5 µm). For other details, reference can be made to the following description of the embodiments for this purpose.

[0024] Thus, according to the present invention, in addition to setting the composition of the carbon-containing layer within a given narrow parameter range, the carbon-containing layer is also prepared within another given narrow parameter range. For this purpose, it can be experimentally demonstrated that the drying of the carbon-containing layer, which may proceed very rapidly due to the very low layer thickness, should not be carried out at a temperature of 70 °C or higher, because within this temperature range, the texture of the carbon-containing layer changes in the micrometer range and / or the nanometer range compared to the selected temperature range, resulting in hydrophobic wetting properties or even superhydrophobic wetting properties for the layer coated thereon, which wetting properties are characterized by the occurrence of the so-called "lotus effect". For other details, reference may be made to the following description of the embodiments for this purpose.

[0025] According to step c) of the method, the cathode active material is applied to the carbon-containing layer. The term "applied" herein refers to the process used to coat at least one material onto a substrate, whereby the material remains on the substrate. The cathode material may include a lithium-containing material or a material having at least one additional cation, preferably a sodium ion. The lithium-containing material may preferably be selected from: lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O 4 , LNMO); a mixture of LNMO and an additional compound, the additional compound being selected from at least one of the elements Co, Al, and additional Li; lithium-rich NMC (x LiMn 2 O 3 •NMC); lithium nickel manganese cobalt oxide (LiNi x Mn y Co z , NMC) and lithium-rich lithium nickel manganese cobalt oxide (x LiMn 2 O 3 •NMC, x ≤ 0.4); lithium metal phosphide (LiMPO 4 ), wherein M is selected from at least one of the elements Fe, Mn, Co, or Ni, in particular lithium iron phosphate (LiFePO 4 , LFP), lithium manganese phosphate (LiMnPO 4 ), lithium cobalt phosphate (LiCoPO 4 ), and lithium nickel phosphate (LiNiPO 4 ); lithium cobalt oxide (LiCoO 2 ), LCO); lithium manganese oxide (LiMn 2 O 4 or Li 2 MnO 3 , LMO); or lithium nickel cobalt aluminum oxide (LiNi 1-x-y Co x Al y O 2, NCA). In addition, the cathode material may include other types of lithium-containing materials or sodium-containing materials. Additionally, a combination of at least two cathode materials may be suitable.

[0026] In a particularly preferred embodiment, it can be achieved by c1) applying an aqueous cathode slurry onto the carbon-containing layer; and c2) drying the aqueous cathode slurry on the carbon-containing layer to perform the application of the cathode active material onto the carbon-containing layer as described in step c). Preferably, the aqueous cathode slurry may include an aqueous solution of the cathode active material herein.

[0027] The term "cathode slurry" generally refers to a mixture of a cathode active material, at least one binder, optional additives (especially conductive carbon black or conductive graphite), and at least one solvent. By preferably using water as the solvent, different from the methods known in the prior art, the use of acid can be omitted in a particularly preferred manner. Thus, on the one hand, the current collector can be better protected from corrosion, and on the other hand, the capacitance of a battery including at least one electrode prepared by this method will not decrease.

[0028] The aqueous cathode slurry can be applied onto the carbon-containing layer according to step c1) by means of a coating process. Particularly preferably, the same coating process used for coating the carbon-containing layer on the surface of the current collector according to step b) can be used for this purpose. The coating process can preferably be selected from the coating processes described above; however, other types of coating processes can also be considered.

[0029] The drying of the aqueous cathode slurry on the carbon-containing layer can be carried out according to step c2) after step c1) or during the performance of step c1). The drying can be carried out in a passive or active manner. For active drying, a drying process selected from radiation drying (especially by means of laser radiation or infrared radiation) or convective drying (especially by means of a fluidized bed dryer) can be applied. In a particular embodiment, at least one temperature rise interval and / or at least one temperature zone can be used to dry the aqueous cathode slurry during step c2).

[0030] During step c), the same temperature can preferably be used as was used during the coating of the carbon-containing layer on the surface of the current collector according to step b); however, lower or higher temperatures can also be used. Thus, step c), in particular arrangement c2), can, in a particular embodiment, be carried out at a lower temperature, preferably already at room temperature (i.e., 15 °C to 25 °C, in particular approximately 20 °C), or after step b) has been completed at a temperature above 70 °C (in particular above 100 °C), but below the glass transition temperature of the polymer used as the binder and below the critical temperature at which a phase change or change in the state of matter occurs in the cathode active material, binder, and optionally additives (in particular conductive carbon black or conductive graphite) comprised in the cathode paste used.

[0031] In particular, as is shown in detail in the embodiments below, the selected composition of the carbon-containing layer within a narrow parameter range and the manner of preparation of the carbon-containing layer within a narrow parameter range enable the layer composed of the cathode active material to be shaped particularly preferably into a uniform layer on the surface of the carbon-containing layer. The term "uniform" here means a layer whose composition and spatial phase are largely independent of its position in the layer, in particular below a correspondingly selected threshold. The formation of a uniform layer from the cathode active material is promoted in particular by the fact that the carbon-containing layer exhibits wetting properties that enable uniform coating; hydrophobic wetting properties and even superhydrophobic wetting properties are excluded. For other details, reference can be made to the description of the embodiments below.

[0032] In a particularly preferred embodiment, applying the cathode active material to the carbon-containing layer according to step c) can additionally comprise the following steps: c3) Subsequently calendering at least partially dried cathode active material on the carbon-containing layer.

[0033] In particular, by using a calendering process, which can be carried out after applying an aqueous cathode paste to the carbon-containing layer and after the aqueous cathode paste on the carbon-containing layer has at least partially dried, as is detailed below in the description of the embodiments, the particles from the cathode active material are embedded or pressed into the carbon-containing layer. This process can be related in a particularly advantageous manner to improving the mechanical and / or electrical connection between the cathode active material and the current collector. In this way, on the one hand, the adhesion between the layer composed of the cathode active material and the current collector can be increased due to the presence of the carbon-containing layer in the cathode, and on the other hand, the contact resistance between the layer composed of the cathode active material and the current collector can also be reduced due to the presence of the carbon-containing layer in the cathode. However, other advantages are also conceivable.

[0034] The invention relates in another aspect to a cathode, which is preferably prepared by the method disclosed herein. The cathode comprises: - A current collector, the surface of which has a conductive material; - A carbon-containing layer located on the surface of the current collector; and - A cathode active material located on the carbon-containing layer, wherein the carbon-containing layer includes carbon in an amount higher than 60 wt% and lower than 80 wt% and at least one polymer as a binder, and wherein the layer composed of the cathode active material is formed as a uniform layer on the surface of the carbon-containing layer. For the term "uniform", reference is made to the definition of this term above.

[0035] In another aspect, the present invention relates to a battery that at least includes: - At least one cathode prepared by the method disclosed herein; - at least one anode; and - At least one electrolyte. In addition, the battery may have at least one additional component, in particular a separator for spatially separating at least one cathode from at least one anode. The battery can thus in particular be a lithium-ion battery, a lithium polymer battery or a so-called post-lithium battery (preferably a sodium battery). In addition, other types of batteries or energy storage devices can be considered, in particular solid-state batteries, which include hybrid polymer-ceramic solid batteries or supercapacitors.

[0036] The at least one anode may herein include at least one anode material, wherein the anode material may preferably be selected from: graphite, amorphous carbon (including soft carbon or hard carbon), silicon, silicon oxide, silicon / graphite composite, silicon oxide / carbon composite, silicon / carbon composite, metallic lithium, lithium titanate, an alloy of lithium with at least one element of tin, germanium, magnesium, aluminum and zinc or zinc oxide or tin oxide doped with a transition metal, tin, germanium, magnesium, aluminum or zinc; however, it is also possible to use other anode materials or a combination of at least two anode materials.

[0037] For other details regarding the cathode and the battery, reference is made to the description of the method disclosed herein and the examples.

[0038] The method for preparing a cathode, the cathode, and a battery including such a cathode disclosed in the present text have a series of advantages compared to the cathodes, the methods for preparing cathodes, and the batteries including the cathodes known in the prior art. In particular, when preparing the cathode, it is possible not to add an acid, and in this way, damage to the surface of the aluminum current collector in the cathode (usually due to the formation of small holes, cracks, or layer separation) and other disadvantages are avoided, especially those related to the rheological properties of the cathode paste, or the electrode conductivity and layer adhesion, which may overall cause accelerated decay of the battery. In addition, complex modification of the current collector and / or of the active material by an additional physical coating process can be omitted. Finally, the specific capacitance of the cathode prepared by this method can be maintained unchanged compared to the cathodes known in the prior art or even surprisingly improved.

[0039] The words "have", "has", "include", "comprise", or their grammatical variants are used in a non-exclusive manner in the present text. Correspondingly, these words can refer to both a situation where there are no additional features except those introduced by these words and a situation where there is one or more additional features. For example, the expressions "A has B", "A has B", "A includes B", or "A comprises B" can refer to both a situation where there are no other elements in A except B (i.e., the situation where A consists only of B) and a situation where there is one or more additional elements outside B, such as element C, elements C and D, or even more elements.

[0040] Furthermore, it should be noted that when the expressions "at least one" and "one or more" and their grammatical variants are used or are to express that an element or feature can be provided one or more times in relation to one or more elements or features, they are generally only used once, for example, when the feature or element is first introduced. When the feature or element is mentioned again subsequently, the corresponding expressions "at least one" or "one or more" are generally no longer used, without thereby restricting the possibility that the feature or element can be provided one or more times.

[0041] In addition, words such as "preferably", "specifically", "for example" or similar words are used herein in connection with optional features without thereby imposing a limitation on alternative embodiments. Accordingly, the features introduced by these words are optional features and are not intended to limit the scope of the claims, particularly the scope of the independent claims, by these features. Thus, the present invention, as will be apparent to those skilled in the art, can also be implemented using different solutions. Similarly, features introduced by "in one embodiment of the present invention" or by "in one example of the present invention" are understood to be optional features and should not thereby impose a limitation on the scope of protection of alternative solutions or independent claims. In addition, these introductory expressions do not affect all possibilities of combining the features introduced by them with other features, whether optional or non-optional features. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Other details and features of the present invention result from the following description of preferred embodiments, particularly those related to the dependent claims. Herein, the corresponding features can be implemented alone or in combination with each other. However, the present invention is not limited to the embodiments. The embodiments are schematically illustrated in the following drawings. Among them, the same reference numerals in the drawings represent the same or functionally identical elements or elements that correspond to each other functionally. Specifically, Figure 1 A schematic view of a preferred embodiment of the steps of a method for manufacturing a cathode according to the present invention is shown in a cross-sectional perspective; FIG. 2 shows the setting of the composition of the carbon-containing layer in a parameter range ( Figure 2a ) and the setting of preparing the carbon-containing layer in a temperature range ( Figure 2b ); Figure 3 A schematic view of a cathode according to the present invention is shown in a cross-sectional perspective; Figure 4 A comparison of curves of the specific capacitance of an NMC-622 half-cell as a function of the number of cycles at different C-rates is shown, where the NMC-622 half-cell is prepared using an aqueous slurry with and without adding acid; and Figure 5 A cyclic voltammogram of an example with a carbon-containing layer and a control example without a carbon-containing layer is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] Figure 1 Schematic views of preferred embodiments of steps a) to c) of a method 110 for preparing a cathode 112 according to the present invention are shown in a cross-sectional perspective, respectively.

[0044] According to step a) of method 110, a current collector 114 is provided, wherein at least the surface 116 of the current collector has a conductive material 118. Preferably, at least the surface 116 of the current collector 114 (preferably the entire body of the current collector 114) is made of aluminum; however, it is also feasible to use other conductive materials 118.

[0045] According to step b) of method 110, a carbon-containing layer 112 is coated on the surface 116 of the current collector 114, especially after step a). According to the invention, the carbon-containing layer comprises more than 60 wt% (preferably at least 65 wt%, particularly preferably at least 67.5 wt%) and less than 80 wt% (preferably at most 75 wt%, particularly preferably at most 72.5 wt%), especially approximately 70 wt% of carbon and at least one polymer as a binder, wherein the proportion of carbon and the binder in the carbon-containing layer preferably totals 100 wt%. Preferably, carbon black is used as the carbon.

[0046] According to step c) of method 110, a cathode active material 124 is applied to the surface 122 of the carbon-containing layer 120, especially after step b) or during the performance of step b). Step c) may preferably include: - According to step c1), an aqueous cathode slurry is applied to the surface 122 of the carbon-containing layer 120, and the aqueous cathode slurry comprises an aqueous solution of the cathode active material 124; and - According to step c2), the aqueous cathode slurry is dried on the surface 122 of the carbon-containing layer 120. After this step, it is possible to - According to step c3), the at least partially dried cathode active material 124 on the surface 122 of the carbon-containing layer 120 is calendered.

[0047] Optionally calendering the at least partially dried cathode active material on the surface 122 of the carbon-containing layer 120 after applying the cathode active material 124 to the carbon-containing layer 120 according to step c3) can be as described below with respect to Figure 3 such that both the adhesion between the layer composed of the cathode active material 124 and the current collector 114 is improved, and also the conductivity is improved due to the presence of the carbon-containing layer 120 in the cathode 112 and the contact resistance between the layer composed of the cathode active material 124 and the current collector 114 is reduced.

[0048] According to the invention, step b) is carried out at a temperature of at least 30 °C (preferably at least 35 °C, particularly preferably at least 40 °C) to a maximum of 70 °C (preferably at most 65 °C, particularly preferably at most 60 °C), especially at a temperature of approximately 50 °C. For step c), the same temperature can be used or even lower or higher temperatures as described in detail above can be used. In particular, as Figure 2a and 2bIt is known that within a narrow parameter range, the selected carbon-containing layer composition and the preparation method within the given narrow temperature range cause the layer composed of the cathode active material 124 to be formed into a uniform layer on the surface 122 of the carbon-containing layer 120.

[0049] The carbon-containing layer 120 according to the present invention can have a layer thickness of at least 0.1 µm (preferably at least 0.25 µm, particularly preferably at least 0.5 µm) and at most 20 µm (preferably at most 10 µm, particularly preferably at most 7.5 µm). In the embodiments shown below, a layer thickness between 0.5 µm and at most 6 µm is used for the carbon-containing layer. This low layer thickness of the carbon-containing layer according to the present invention means that the carbon-containing layer generally accounts for at most 1 wt% (preferably at most 0.5 wt%, particularly preferably at most 0.25 wt%) of the total weight of the cathode 112 and thus does not increase the total weight and material cost of the cathode 112. The carbon-containing layer 120 can particularly act as a passivation layer because it can effectively prevent the corrosion of the surface 116 of the current collector 114 during the application of the cathode active material 124 to the surface 122 of the carbon-containing layer 120, and this surface 116 particularly has aluminum.

[0050] Figure 2 shows the morphological variations of the layer composed of the cathode active material 124 on the surface of the carbon-containing layer 120 that are related to the composition of the carbon-containing layer 120 ( Figure 2a ), or related to the preparation method of the carbon-containing layer 120 ( Figure 2b ).

[0051] As Figure 2a is known, on the surface 122 of the carbon-containing layer 120, the desired uniform layer composed of the cathode active material 124 is formed only within the parameter range 130, within which the carbon-containing layer 120 has: - A carbon proportion 132 higher than 60 wt% and lower than 80 wt%, and - A binder proportion 134 of at least 20 wt% and at most 40 wt%, so that the proportions 132 and 134 together total 100 wt%. Here, the polymer polyvinylidene fluoride (PVDF) is exemplarily used as the binder; however, it is also feasible to use one or more other polymers.

[0052] In Figure 2a the additional parameter range 136 shown, in which the carbon-containing layer 120 has: - A carbon proportion 132 lower than 60 wt% and - A binder proportion 134 of at least 40 wt%, As a result, the proportions 132 and 134 both total 100 wt% here, and a hydrophobic wetting property or even a superhydrophobic wetting property appears on the surface 122 of the carbon-containing layer 120, which results in the layer composed of the cathode active material 124 not existing in the form of a desired uniform layer, but rather existing as an undesired droplet-like structure on the surface 122 of the carbon-containing layer 120.

[0053] In Figure 2a the further parameter range 138, also shown therein, in which the carbon-containing layer 120 has: - a carbon proportion 132 of at least 80 wt%, and - a binder proportion 134 of at most 20 wt%, As a result, the proportions 132 and 134 both total 100 wt% here, and pits or depressions 140 and / or capillary-like structures 142 are formed within the volume of the layer composed of the cathode active material 124, and these capillary-like structures extend to the surface 122 of the carbon-containing layer 120 or even to the surface 116 of the current collector 114. Due to these effects, the surface 116 of the current collector 114, which particularly has aluminum, is no longer protected against corrosion in an undesired manner.

[0054] As is Figure 2b known, on the surface 122 of the carbon-containing layer 120, a desired uniform layer composed of the cathode active material 124 is formed only within the temperature range 144, within which the carbon-containing layer 120 is coated on the surface 116 of the current collector 114 at a temperature 146 from a minimum of 30 °C to a maximum of 70 °C.

[0055] In Figure 2b the further temperature range 148, also shown therein, which has a temperature below 30 °C, pits or depressions 140 and / or capillary-like structures 142 are formed within the volume of the layer composed of the cathode active material 124, and these capillary-like structures extend to the surface 122 of the carbon-containing layer or even to the surface 116 of the current collector 114, and / or small holes 150 are formed, so that the surface 116 of the current collector 114, which particularly has aluminum, is no longer protected against corrosion here due to these effects.

[0056] In Figure 2b the further temperature range 152, also shown therein, which has a temperature above 70 °C, substantially the same effects as in the parameter range 136 occur, that is, here a hydrophobic wetting property or even a superhydrophobic wetting property appears on the surface 122 of the carbon-containing layer 120, which results in the layer composed of the cathode active material 124 not existing in the form of a desired uniform layer, but rather existing as an undesired droplet-like structure on the surface 122 of the carbon-containing layer 120.

[0057] Figure 3 A schematic view of the cathode 112 according to the present invention is shown in a cross-sectional view. It can be clearly observed how the particles composed of the cathode active material 124 are embedded or pressed into the carbon-containing layer 120, especially in order to improve the mechanical and electrical contact with the current collector 114 in this way.

[0058] Figure 4 The discharge specific capacitance in mAh / g of the NMC622 half-cell is shown as a function of the number of cycles n (>0 to <70) at different C-rates C dis Comparison of the curves 170, 172. Here, NMC622-00 represents a control sample not within the scope of the present invention, which has a cathode active material 124 lithium nickel manganese cobalt oxide (LiNi x Mn y Co z O 2 , NMC) that has been treated with phosphoric acid (H3PO4) during the preparation of the cathode 112 and has a layer thickness of 70 µm; while NMC622-01 represents a sample according to the present invention, which has a cathode active material 124 NMC that has not been acid-treated and has a layer thickness of 65 µm. Here, NMC622 represents Li(Ni 0.6 MnCo 0.2 )O 2 . The comparison between the curve 170 of the discharge specific capacitance of the sample NMC622-01 according to the present invention and the curve 172 of the discharge specific capacitance of the control sample NMC622-00 surprisingly shows that the discharge specific capacitance of the sample according to the present invention is improved compared to the control sample, especially above 1C.

[0059] Figure 5 The cyclic voltammogram 180 of an embodiment of a sample with a carbon-containing layer 120 according to the present invention and the cyclic voltammogram 182 of a control sample not within the scope of the present invention are shown. The control sample does not have a carbon-containing layer and is prepared with the addition of acid. The sample according to the present invention is prepared using a water-based NMC622 slurry without acid, while the control sample is prepared using a water-based NMC622 slurry with the addition of acid. Among them, the slurry without acid includes the following slurries, where the proportion of the slurry without the addition of acid does not affect the pH value. Through the reaction of NMC with water, a relatively high pH value appears, which may be in the range of 12 or higher. The absence of acid maintains this high pH value; the addition of acid can lower the pH value, generally to a pH value of 7 to 11 (preferably 8 to 10), and particularly to a pH value of 9 ± 0.5 in the current control sample.

[0060] For the two measurements, the cathode active material 124 NMC622 used was from the same batch. From the comparison of the cyclic voltammogram 180 of the sample according to the present invention with the cyclic voltammogram 182 of the control sample (available at https: / / doi.org / 10.3390 / nano11071840), it was found that redox peaks appeared at 3.9 V and 3.6 V in the control sample, while for the sample according to the present invention, the redox peaks located at 3.78 V and 3.71 V were significantly closer to each other, indicating a significantly lower degree of battery polarization. The reason for the increase in the degree of battery polarization when using an aqueous slurry with added acid may be due to the chemical reaction between the acid and the cathode active material 124 and the resulting increase in the contact resistance between the layer composed of the cathode active material 124 and the current collector 114. In addition, higher electrical conductivity can be achieved in the deeper region close to the current collector, which may be advantageous for a higher layer thickness. Other advantages are described above.

[0061] List of Reference Numerals 110 Method for preparing the cathode 112 Cathode 114 Current collector 116 Surface 118 Conductive material 120 Carbon-containing layer 122 Surface 124 Cathode active material 130 Parameter range 132 Carbon proportion 134 Binder proportion 136 Parameter range 138 Parameter range 140 Pit or depression 142 Capillary-like structure 144 Temperature range 146 Temperature 148 Temperature range 150 Small hole 152 Temperature range 160 Particle 170 Curve of the discharge specific capacitance of the sample according to the present invention 172 Curve of the discharge specific capacitance of the control sample 180 Cyclic voltammogram of the sample according to the present invention 182 Cyclic voltammogram of the control sample.

Claims

1. Method (110) for preparing a cathode (112), wherein, the cathode (112) has at least one current collector (114) and a cathode active material (124), and the method (110) comprises the following steps: a) providing a current collector (114), wherein at least the surface (116) of the current collector has a conductive material (118); b) coating a carbon-containing layer (120) on the surface (116) of the current collector (114); and c) applying a cathode active material (124) to the carbon-containing layer (120), wherein the carbon-containing layer (120) comprises more than 60% by weight and less than 80% by weight of carbon and at least one polymer as a binder, and at least step b) is carried out at a temperature of at least 30 °C to a maximum of 70 °C.

2. The method (110) according to the preceding claim, wherein, the carbon-containing layer (120) comprises carbon black, which is a black powdery solid, and the powdery solid comprises at least 80% by weight and at most 99.5% by weight of carbon.

3. The method (110) according to any one of the preceding claims, wherein, the cathode active material (124) is applied to the carbon-containing layer (120) according to step c) by: c1) applying an aqueous cathode slurry onto the carbon-containing layer (120); and c2) drying the aqueous cathode slurry on the carbon-containing layer (120), wherein the aqueous cathode slurry comprises an aqueous solution of the cathode active material (124).

4. The method according to any one of the preceding claims, wherein, the cathode active material (124) is formed into a uniform layer on the surface (122) of the carbon-containing layer (120).

5. The method (110) according to any one of the preceding claims, wherein, applying the cathode active material (124) to the carbon-containing layer (120) according to step c) comprises: c3) calendering at least a partially dried cathode active material (124) on the carbon-containing layer (120).

6. The method (110) according to any one of the preceding claims, wherein, at least step b) is carried out at a temperature of at least 40 °C to a maximum of 60 °C.

7. The method according to any one of the preceding claims, wherein, the carbon-containing layer (120) comprises at least 65% by weight and at most 75% by weight of carbon and the binder.

8. The method (110) according to any one of the preceding claims, wherein, the carbon-containing layer (120) is continuously coated on the surface (116) of the current collector (14) according to step b) until the carbon-containing layer (120) has a layer thickness of 0.1 µm to 20 µm.

9. The method (110) according to the preceding claim, wherein, the carbon-containing layer (120) is continuously coated on the surface (116) of the current collector (14) according to step b) until the carbon-containing layer (120) has a layer thickness of 0.1 µm to 10 µm.

10. The method (110) according to the preceding claim, wherein, the carbon-containing layer (120) is continuously applied to the surface (116) of the current collector (14) according to step b) until the carbon-containing layer (120) has a layer thickness of 0.1 µm to 7.5 µm.

11. The method (110) according to any one of the preceding claims, wherein, at least the surface (116) of the current collector (114) comprises aluminum, nickel, a noble metal, carbon, or comprises a thin layer composed of aluminum, nickel, a noble metal, carbon, or comprises a thin layer composed of a dielectric or a semiconductor.

12. The method (110) according to any one of the preceding claims, wherein, at least one of the polymers is selected from polyvinylidene fluoride, polybutyl acrylate, polyacrylic acid, styrene-butadiene rubber, a biopolymer, or a mixture of polyvinylidene fluoride, polybutyl acrylate, polyacrylic acid, styrene-butadiene rubber, and a biopolymer.

13. The method (110) according to any one of the preceding claims, wherein, the cathode active material is selected from (124) a lithium-containing material or a sodium-containing material.

14. A cathode (112), the cathode comprising: - a current collector (114), the surface (116) of the current collector having a conductive material (118); - a carbon-containing layer (120) located on the surface (116) of the current collector (114); and - a layer composed of a cathode active material (124) located on the carbon-containing layer (120), wherein the carbon-containing layer comprises more than 60% and less than 80% carbon by weight and at least one polymer as a binder, and the layer composed of the cathode active material (124) is formed as a uniform layer on the carbon-containing layer (120).

15. A battery, the battery comprising: - at least one cathode (112) according to the preceding claim; - at least one anode; and - at least one electrolyte.

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