Cathode and method for producing same

Abstract

The invention relates to a method (110) for producing a cathode (112), a cathode (112) which is produced using this method, and a battery which comprises such a cathode (112). The method (110) comprises the following steps: a) providing a current collector (114), wherein at least its surface (116) comprises an electrically conductive material (118); b) coating the surface (116) of the current collector (114) with a carbon-containing layer (120); and c) applying an active cathode material (124) to the carbon-containing layer layer (120), the carbon-containing layer layer (120) comprising 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 of at least 30°C to at most 70°C.

Description

[0001] Cathode and process for its manufacture

[0002] Field of the invention

[0003] The present invention relates to a method for producing a cathode, a cathode and a battery comprising such a cathode.

[0004] State of the art

[0005] For applications in the automotive industry, particularly for electrically powered vehicles and stationary storage systems, energy storage devices with a long service life and the highest possible energy and power density are desirable. To achieve high energy densities, nickel-rich active cathode material made of lithium nickel manganese cobalt oxide (NMC) is increasingly being used. Graphite anodes or silicon-based anode materials are frequently used on the anode side. These electrode materials are applied in the form of a slurry to a typically thin metallic aluminum foil, which serves as a current collector, using a coating process, particularly slot die coating or slip casting.

[0006] Conventional slurries for electrode production include a water-based process for coating the anodes and an N-methyl-2-pyrrolidone (NMP)-based process for coating the cathodes. The solids content is typically between 40 wt.% and 60 wt.% for the anode slurries used and between 50 wt.% and 70 wt.% for the cathode slurries used, depending on the active cathode material selected, the weight ratios between the active cathode material, the carbon additives, and the binder, as well as the physicochemical properties of the active cathode material, particularly its particle shape, particle size, particle size distribution, and molecular weight. Solids contents of up to 90% can be achieved with extrusion.Even though the mixing process on an industrial scale is generally not publicly known, it is generally understood that the complex mechanisms and process steps of slurry mixing, particularly with regard to wetting, dispersion, and stabilization, significantly influence the quality and stability of the finished electrodes and batteries containing such electrodes. Especially for highly viscous slurries with a high solids content, the choice of composition, binders, particle sizes, particle shapes, and, where present, additives are crucial to obtaining uniform and reproducible layers of active cathode material that meet the high quality requirements of lithium-ion batteries.

[0007] For both cost and environmental reasons, especially in light of current and / or anticipated government regulations, the use of organic solvents, particularly N-methyl-2-pyrrolidone (NMP), in cathode slurries will be eliminated in the future. However, based on the current state of the art, producing NMP-free cathode slurries is a major technical challenge. Due to the strong interaction of nickel-rich NMC cathode powder with water, the stability of the slurries is reduced; in particular, corrosion of the aluminum current collector begins due to the resulting high pH value of ~12.Corrosion of the aluminum current collector occurs in the pH range above pH > 9 and is associated with the formation of gaseous hydrogen, which can easily lead to damage to the surface of the aluminum current collector, particularly as a result of pore formation, cracking, or layer delamination. One known measure to counteract such damage to the surface of the aluminum current collector is the addition of an acid to thereby lower the pH, typically to 7 to 11, preferably to 8 to 10, in particular to 9 ± 0.5. However, the addition of acid can have a negative impact on the rheology of the cathode slurry, its electrode conductivity, or layer adhesion. Overall, increased cell degradation can be observed as a result of the addition of acid.Depending on the type of acid, reaction layers can also form on particles of the active cathode material, which can increase cell resistance and lead to an overall reduced performance of the electrochemical cell. Alternatively or additionally, the active cathode material can be coated, particularly using an artificial solid electrolyte interphase (SEI), e.g., by coating with ZrO2, to prevent water from reacting with the active cathode material and thus avoid an increase in the pH value.

[0008] DE 10 2011 077 932 A1 discloses a cathode unit for an alkali metal-sulfur battery, containing a cathode conductor comprising a carbon substrate and an electrochemically active component selected from sulfur or an alkali metal sulfide and in electrically conductive contact with the carbon substrate. DE 102 51 241 A1 discloses a method for producing Li-polymer batteries using a composite system comprising conductor, electrode masses, and separator. Conductor foils are coated with pasty electrode masses and subsequently joined with separator material such that the electrode substrate side coated with the electrode mass is in contact with the separator material. This method results in Li-polymer batteries with smooth structures without surface roughness, improved cycle stability, long-term stability, and the suppression of disruptive side reactions.

[0009] EP 1 609 878 A1 discloses a carbon-coated aluminum material capable of improving adhesion between an aluminum material and an active substance layer, and a manufacturing method. The carbon-coated aluminum material comprises an aluminum material and a carbonaceous layer formed on the surface of the aluminum material, and also comprises an intermediate layer formed between the aluminum material and the carbonaceous layer and containing aluminum and carbon. The manufacturing method for a carbon-coated aluminum material includes a step of placing an aluminum material in a space containing a hydrocarbon-containing substance, and a step of heating in the state where the aluminum material is placed in the space containing the hydrocarbon-containing substance.

[0010] DE 10 2014 220 964 A1 discloses a method for producing an electrode for a lithium-containing battery or a capacitor, comprising providing a graphite material containing at least one electrically conductive carbon material, providing an active material mixture containing electrochemically active material; feeding the graphite material and the active material mixture into a calendering device such that a concentration gradient of the electrically conductive carbon material is set across a gap width and a gap height, and forming the supplied materials in the calendering device into a film, at least comprising an electrically conductive carbon substrate and a layer containing the active material mixture.

[0011] WO 2017 / 001118 A1 discloses an anode for a lithium cell. To increase the coulomb efficiency and / or cycle stability of the lithium cell, the lithium cell comprises a porous silicon monolith with a graphite coating. The invention further relates to a manufacturing method, a lithium cell, and a lithium battery.

[0012] Object of the invention Based on this, the object of the present invention is to provide a method for producing a cathode, a cathode and a battery comprising such a cathode, which at least partially overcome the known disadvantages and limitations of the prior art.

[0013] The method and cathode are intended in particular to make it possible to omit the addition of acid in order to avoid damage to the surface of the aluminum current collector in the cathode, typically as a result of pore formation, cracking or layer detachment, or other negative influences on the rheology of the cathode slurry or the electrode conductivity and layer adhesion, which can overall lead to increased cell degradation, in order to be able to dispense with a complex modification of the current collector and / or the active cathode material by means of additional physical coating processes, wherein it would be desirable that the specific capacity of a cathode produced by this method does not deteriorate compared to the cathodes known from the prior art.

[0014] Disclosure of the invention

[0015] This object is achieved by a method for producing a cathode, a cathode, and a battery comprising such a cathode, according to the features of the independent claims. Advantageous further developments, which can be implemented individually or in any combination, are presented in the following description and in the dependent claims.

[0016] In a first aspect, the present invention relates to a method for producing a cathode, wherein the cathode has at least one current collector and an active cathode material. The term "cathode" refers to an electrode, i.e. a body to which an electrical voltage and / or an electrical current can be applied, which undergoes a reduction process during a battery discharge process, i.e. generally a reduction of an oxidation state of a transition metal cation in the active cathode material. In contrast, the term "anode" refers to a further electrode in which an oxidation process takes place during the battery discharge process. Furthermore, it is conventional that the terms "cathode" and "anode" are retained during a battery charging process, even though the reduction process and the oxidation process are interchanged.Furthermore, the term "battery" refers to an electrochemical cell having at least one cathode, at least one anode electrically isolated therefrom, and at least one electrolyte configured for electrical charge exchange; further components, e.g., electrical connections and / or a separator, are possible.

[0017] The present method for producing a cathode comprises steps a) to c) described in detail below, wherein all steps a) to c) can preferably be carried out consecutively in the specified order, beginning with step a), followed first by step b) and then by step c). Alternatively, at least two of the specified steps can also take place partially simultaneously, in particular in a continuous process, in which step c) is carried out on sections of the cathode on which step b) has already been carried out, while simultaneously step b) is carried out on other sections of the cathode and step a) is carried out on yet other sections of the cathode.

[0018] The individual steps of the present method are: a) providing a current collector, at least the surface of which comprises an electrically conductive material; b) coating the surface of the current collector with a carbon-containing layer; and c) applying an active cathode material to the carbon-containing layer, wherein the carbon-containing layer comprises 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 of at least 30°C to at most 70°C.

[0019] According to step a) of the present method, a current collector is provided. The term "current collector" refers to a part of the cathode that is configured to deliver an electrical voltage and / or electrical current generated by the cathode to an external electrically conductive element, in particular to at least one electrical terminal. For this purpose, at least the surface of the current collector, preferably the entire body of the current collector, comprises an electrically conductive material. In a particularly preferred embodiment, at least the surface of the current collector, preferably the entire body of the current collector, comprises aluminum; nickel; at least one precious metal, in particular gold or platinum, or 100% carbon, with aluminum being particularly preferred.However, the use of thin layers of these materials or other materials, preferably ceramic, including Al2O3, or a semiconductor such as Si, preferably in doped form, on any substrate is possible. According to step b) of the present method, the electrically conductive surface of the current conductor is coated with a carbon-containing layer. The term "coating" here refers to a process by which at least one material is applied to a substrate in such a way that a layer is created on the substrate. The term "layer" here refers to an arrangement in which a areal extent of the layer exceeds a layer thickness of the layer by a factor of at least 5, preferably at least 10, particularly preferably at least 50.

[0020] The term “carbon-containing layer” refers to a layer whose composition has a detectable proportion of carbon (C), preferably a predominant proportion of carbon (C). 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. % of carbon, preferably at most 75 wt. %, preferably at most 72.5 wt. %, in particular approximately 70 wt. % of carbon, as well as at least one polymer as a binder, wherein the proportions of carbon and polymer in the carbon-containing layer particularly preferably add up to 100 wt. %. Carbon black is preferably used as the carbon, wherein the term “carbon black” refers to a black powdery solid comprising at least 80 wt. % and at most 99.5 wt. % of carbon.In principle, however, the use of at least one other type of carbon is also conceivable, in particular conductive carbon black, which can have particle sizes of up to several 100 nm; conductive graphite, e.g. KS6L, which has particle sizes in the pm range or in the sub-pm range; amorphous carbon, including soft carbon or hard carbon; and / or carbon modifications that have an impurity, for example in the form of heteroatoms.

[0021] "Binders" or "binding agents" are substances designed to create a composite material in the form of a substantially physical bond between particles and / or phase boundaries by means of adhesion, cohesion, and / or adsorption, whereby the particles or the regions delimited by phase boundaries in the composite material are deposited on one another in such a way that they hold together, crosslink, or bond. According to the invention, the binder encompassed by the carbon-containing layer comprises at least one polymer. The term "polymer" refers to a chemical compound comprising a plurality of identical or similar molecules, referred to as "monomers," arranged side by side.In a particularly preferred embodiment, the at least one polymer comprised by the binder is selected from: polyvinylidene fluoride (PVDF); polyamide (PA); polybutyl acrylate (PBA); polyacrylic acid (PAA); poly(methyl acrylate) (PMA); a cellulose, preferably carboxymethyl cellulose (CMC), in particular Na-CMC or succinoyl carboxymethyl cellulose (SCMC); a styrene-butadiene rubber (SBR), a mixture of SBR+SCMC; an epoxy-based binder, in particular an epoxy hardener system; a latex hydride polymer; a biopolymer, preferably a polysaccharide-based plant gum, in particular alginate, guar gum, karaya, or xanthan. However, the use of at least one other polymer is conceivable.

[0022] According to the invention, the composition of the carbon-containing layer is thus adjusted within the specified narrow parameter range. An excessively high proportion of carbon (C), in particular of soot, would not adequately prevent corrosion of the surface of the current collector, in particular of the electrically conductive electrode material located on the surface of the current collector, particularly preferably the aluminum, during the subsequent application of the active cathode material to the carbon-containing layer in step c), due to a typically occurring dissolution of the carbon component, in particular of the soot, from the composite material of the carbon and the binder. This effect could be confirmed by preliminary tests on commercially available, graphite-coated aluminum current collectors.Additionally, it has been observed that with a very high proportion of carbon (C), particularly soot, pores form in the carbon-containing layer, which can expose the current collector to such an extent that the current collector is no longer protected against corrosion. A too low proportion of carbon (C), particularly soot, would, on the one hand, impair electrical contact between the cathode and the current collector, and, on the other hand, as confirmed by corresponding tests, would result in a hydrophobic wetting behavior of the cathode slurry, which would significantly complicate or even prevent the most homogeneous coating of the carbon-containing layer. For further details, please refer to the description of the exemplary embodiments below.

[0023] Furthermore, the coating of the surface of the current collector 1 with the carbon-containing layer according to step b) is carried out according to the invention at a temperature of at least 30 °C, preferably of at least 35 °C, particularly preferably of at least 40 °C, up to a maximum of 70 °C, preferably up to a maximum of 65 °C, particularly preferably up to a maximum of 60 °C. For this purpose, the coating of the surface of the current collector 1 with the carbon-containing layer is carried out by means of a coating process, wherein the coating process is preferably selected from a doctor blade process, spraying process, slot die coating, extrusion process, spin coating or printing process, in particular aerosol jet printing); however, the use of another type of coating process is conceivable.The preferred coating processes are, in particular, simple, cost-effective processes; the use of complex and costly coating processes, in particular physical vapor deposition (PVD) or atomic layer deposition (ALD), can be dispensed with.

[0024] The carbon-containing layer according to the invention can thus act in particular as a passivation layer. The term "passivation layer" refers to a layer that can sufficiently prevent corrosion of the surface of the current collector, particularly preferably the aluminum, during the application of the active cathode material to the carbon-containing layer.

[0025] The carbon-containing layer according to the invention can have a layer thickness of at least 0.1 pm, preferably at least 0.25 pm, particularly preferably at least 0.5 pm, and at most 20 pm, preferably at most 10 pm, particularly preferably at most 7.5 pm. For further details, please refer to the description of the exemplary embodiments below.

[0026] According to the invention, in addition to adjusting the composition of the carbon-containing layer within the specified narrow parameter range, the carbon-containing layer is also produced within the further specified narrow parameter range. Experimentally, it has been demonstrated that drying of the carbon-containing layer, which can proceed very quickly due to the very thin layer thickness, should not be carried out at a temperature of 70 °C or higher. In this temperature range, texturing of the carbon-containing layer on a micro- and / or nanoscale changes compared to drying at a temperature within the selected temperature range, resulting in a hydrophobic wetting behavior or even a superhydrophobic wetting behavior, characterized by the occurrence of the so-called "lotus effect," for a layer applied thereto.For further details, please refer to the description of the embodiments below.

[0027] According to step c) of the present method, an active cathode material is applied to the carbon-containing layer. The term "application" refers to a process by which at least one material is applied to a substrate in such a way that the material remains on the substrate. The cathode material can comprise lithium-containing materials or materials that have at least one other cation, preferably sodium. The lithium-containing materials can preferably be selected from lithium nickel manganese oxide (LiNiO, 5Mni, 5O4, LNMO); a mixture of LNMO with an additional compound selected from at least one of the elements Co, Al and additional Li; lithium-rich NMC (x LiMmCl • NMC); a lithium nickel manganese cobalt oxide (LiNi x Mn y Coz O2, NMC) and a lithium-rich lithium nickel manganese cobalt oxide (x LiMmCl NMC, x < 0.4); lithium metal phosphate (LiMPO4), where M is selected from at least one of the elements Fe, Mn, Co or Ni, in particular lithium iron phosphate (LiFePCU, LFP), lithium manganese phosphate (LiMnPCU), lithium cobalt phosphate (LiCoPCU, LCP) and lithium nickel phosphate (LiNiPCU); lithium cobalt oxide (LiCoCh, LCO); lithium manganese oxide (LiMmCU or Li2MnOs, LMO); or lithium nickel cobalt aluminum oxide (LiNii- x.y Co-xAlCl, NCA). Furthermore, the cathode material may comprise other types of lithium- or sodium-containing materials. Furthermore, a combination of at least two cathode materials may also be suitable.

[0028] In a particularly preferred embodiment, the application of the active cathode material to the carbon-containing layer according to step c) can be carried out by c1) applying an aqueous cathode slurry to the carbon-containing layer; and c2) drying the aqueous cathode slurry on the carbon-containing layer. The aqueous cathode slurry can preferably comprise an aqueous solution of the active cathode material.

[0029] The term "cathode slip" generally refers to a mixture of the active cathode material, at least one binder, optionally additives, in particular conductive carbon black or conductive graphite, and at least one solvent. By preferably using water as the solvent—in contrast to the processes known from the prior art—the use of an acid can be dispensed with in a particularly preferred manner. This allows, on the one hand, the current collector to be better protected against corrosion and, on the other hand, does not reduce the electrical capacity of a battery comprising at least one cathode produced using the present process.

[0030] The aqueous cathode slip can be applied to the carbon-containing layer according to step c1) by means of a coating process. Particularly preferably, the same coating process can be used for this purpose that is also used to coat the surface of the current collector with the carbon-containing layer according to step b). The coating process can preferably be selected from one of the above-mentioned coating processes; however, the use of a different type of coating process is conceivable.

[0031] Following step c1), or even during the implementation of step c1), the aqueous cathode slurry can be dried on the carbon-containing layer according to step c2). Drying can be passive or active, with a drying method selected from radiation drying, in particular by means of laser radiation or infrared radiation, or convection drying, in particular by means of a flotation dryer, being used for active drying. In a particular embodiment, at least one temperature ramp and / or at least one temperature zone can be used for drying the aqueous cathode slurry during step c2).

[0032] During step c), the same temperature can preferably be used as is used during the coating of the surface of the current collector with the carbon-containing layer according to step b); however, the use of a lower temperature or a higher temperature is possible. Step c), in particular step c2), can therefore also be carried out at a lower temperature, preferably already at room temperature, iefrom 15 °C to 25 °C, in particular at about 20 °C, or, after completion of step b), also at a temperature above 70 °C, in particular also above 100 °C, but below a glass transition temperature of the polymer used as binder and below a critical temperature at which a phase transition or an aggregate change occurs in the active cathode material, the binder, optionally the additive, in particular the conductive carbon black or conductive graphite, which are comprised by the cathode slip used in each case.

[0033] As will be particularly evident from the exemplary embodiments presented below, the selected composition of the carbon-containing layer within a narrow parameter range and the method of producing the carbon-containing layer within a narrow temperature range result in the layer of the active cathode material being particularly preferably formed as a homogeneous layer on the surface of the carbon-containing layer. The term "homogeneous" refers to a layer whose composition and spatial phase are largely independent of the location within the layer, in particular below a selected threshold value.The creation of a homogeneous layer of the active cathode material is particularly promoted by the fact that the carbon-containing layer exhibits wetting behavior that enables a homogeneous coating; hydrophobic wetting behavior or even superhydrophobic wetting behavior is excluded. For further details, please refer to the description of the exemplary embodiments below.

[0034] In a particularly preferred embodiment, the application of the active cathode material to the carbon-containing layer according to step c) may additionally comprise the following step: c3) subsequent calendering of the at least partially dried active cathode material on the carbon-containing layer.

[0035] In particular, by using a calendering process, which can be carried out after the aqueous cathode slurry has been applied to the carbon-containing layer and after the aqueous cathode slurry has at least partially, preferably completely, dried on the carbon-containing layer, particles of the active cathode material can be embedded or pressed into the carbon-containing layer, as explained in more detail below in the description of the exemplary embodiments. Such a process can be particularly advantageously combined with an increase in the mechanical and / or electrical connection of the active cathode material to the current collector.In this way, on the one hand, adhesion between the layer of active cathode 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, electrical contact resistance between the layer of active cathode material and the current collector can be reduced, also due to the presence of the carbon-containing layer in the cathode. However, further advantages are conceivable.

[0036] In a further aspect, the present invention relates to a cathode, which is preferably produced by the method disclosed herein. The cathode comprises

[0037] - a current collector whose surface has an electrically conductive material;

[0038] - a carbonaceous layer on the surface of the current collector; and

[0039] - an active cathode material on the carbon-containing layer, wherein the carbon-containing layer comprises more than 60 wt.% and less than 80 wt.% carbon and at least one polymer as a binder, and wherein the layer of the active cathode material is formed as a homogeneous layer on the surface of the carbon-containing layer. Regarding the term "homogeneous," reference is made to the above definition of this term.

[0040] In a further aspect, the present invention relates to a battery which comprises at least

[0041] - at least one cathode produced by the method disclosed herein; - at least one anode; and

[0042] - comprises at least one electrolyte. Furthermore, the battery may comprise at least one further component, in particular a separator for spatially separating the at least one cathode from the at least one anode. The battery may thus be, in particular, a lithium-ion battery, a lithium-polymer battery, or a so-called post-lithium battery, preferably a sodium battery. Furthermore, other types of batteries or energy storage devices are conceivable, in particular solid-state batteries, including hybrid polymer-ceramic solid-state batteries, or supercapacitors.

[0043] The at least one anode can comprise at least one anode material, wherein the anode material can preferably be selected from graphite, amorphous carbon, including soft carbon or hard carbon; silicon, silicon oxide, a silicon / graphite composite, a silicon oxide / carbon composite, a silicon / carbon composite, metallic lithium, lithium titanate, an alloy of lithium with at least one of the elements tin, germanium, magnesium, aluminum and zinc or a zinc oxide doped with a transition metal or tin oxide, tin, germanium, magnesium, aluminum or zinc; however, the use of another anode material or a combination of at least two cathode materials is possible.

[0044] For further details regarding both the cathode and the battery, reference is made to the description of the method disclosed herein and to the embodiments.

[0045] The method disclosed herein for producing a cathode, the cathode, and the battery comprising such a cathode have a number of advantages over cathodes, methods for producing cathodes, and batteries comprising such cathodes known from the prior art. In particular, the addition of an acid can be omitted during cathode production, thus avoiding damage to the surface of the aluminum current collector in the cathode, typically due to pore formation, cracking, or layer detachment, as well as other disadvantages, particularly those related to the rheology of the cathode slurry, the electrode conductivity, and the layer adhesion, which can overall cause increased cell degradation. Furthermore, complex modification of the current collector and / or the active material by means of additional physical coating processes can be dispensed with.Finally, the specific capacity of a cathode produced by the present method may remain unchanged compared to cathodes known from the prior art or may even be surprisingly improved. Herein, the terms "have," "have," "comprise," or "include," or any grammatical variations thereof, are used non-exclusively. Accordingly, these terms may refer to situations in which, besides the features introduced by these terms, no further features are present, or to situations in which one or more further features are present. For example, the expression "A has B," "A has B," "A comprises B," or "A includes B" may refer to the situation in which, apart from B, no further element is present in A (i.e.to a situation in which A consists exclusively of B), as well as to the situation in which, in addition to B, one or more further elements are present in A, for example element C, elements C and D, or even further elements.

[0046] Furthermore, it should be noted that the terms "at least one" and "one or more," as well as grammatical variations of these terms, when used in connection with one or more elements or features and intended to express that the element or feature may be provided singly or multiple times, are generally used only once, for example when the feature or element is first introduced. When the feature or element is subsequently mentioned again, the corresponding term "at least one" or "one or more" is generally no longer used, without this limiting the possibility that the feature or element may be provided singly or multiple times.

[0047] Furthermore, the terms “preferably,” “in particular,” “for example,” or similar terms are used herein in connection with optional features, without limiting alternative embodiments. Thus, features introduced by these terms are optional features, and these features are not intended to limit the scope of the claims, and in particular the independent claims. Thus, as those skilled in the art will recognize, the invention can also be carried out using other embodiments. Similarly, features introduced by “in one embodiment of the invention” or “in an embodiment of the invention” are understood to be optional features, without limiting alternative embodiments or the scope of the independent claims.Furthermore, these introductory expressions are intended to leave untouched all possibilities of combining the features introduced thereby with other features, be they optional or non-optional.

[0048] Brief Description of the Figures Further details and features of the present invention will become apparent from the following description of preferred embodiments, particularly in conjunction with the dependent claims. The respective features can be implemented individually or in combination with one another. However, the invention is not limited to the embodiments. The embodiments are schematically illustrated in the following figures. Like reference numerals in the figures denote like or functionally identical elements, or elements that correspond to one another in terms of their functions. In detail:

[0049] Figure 1 is a schematic representation of a preferred embodiment of the steps of the method according to the invention for producing a cathode with sketches in cross-sectional view;

[0050] Figure 2 is a schematic representation of the adjustment according to the invention of both the composition of the carbon-containing layer over a parameter range (Figure 2a) and the production of the carbon-containing layer over a temperature range (Figure 2b);

[0051] Figure 3 is a schematic representation of a cathode according to the invention in cross-sectional view;

[0052] Figure 4 shows a comparison of the specific capacity of NMC-622 half-cells as a function of the number of cycles for different C-rates, prepared using a water-based slurry with and without acid addition; and

[0053] Figure 5 Representation of cyclic voltammograms for an embodiment with a carbon-containing layer for a comparison example without a carbon-containing layer.

[0054] Description of the embodiments

[0055] Figure 1 shows, in cross-sectional view, a schematic representation of a preferred embodiment of steps a) to c) of the method 110 according to the invention for producing a cathode 112.

[0056] According to step a) of the present method 110, a current collector 114 is provided, wherein at least its surface 116 comprises an electrically conductive material 118. Preferably, at least the surface 116 of the current collector 114, preferably the entire body of the current collector 114, comprises aluminum; however, the use of another electrically conductive material 118 is possible. According to step b) of the present method 110, in particular following step a), the surface 116 of the current collector 114 is coated with a carbon-containing layer 120. 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.% of carbon, preferably at most 75 wt.%, preferably at most 72.5 wt.%, in particular approximately 70 wt.-% carbon, and at least one polymer as a binder, with the proportions of carbon and polymer in the carbon-containing layer particularly preferably adding up to 100 wt. Carbon black is preferably used as the carbon.

[0057] According to step c) of the present method 110, an active cathode material 124 is applied to the surface 122 of the carbon-containing layer 120, particularly after step b) or even during the execution of step b). Step c) can preferably

[0058] - applying an aqueous cathode slurry comprising an aqueous solution of the active cathode material 124 according to step c1) to the surface 122 of the carbon-containing layer 120; and

[0059] - drying the aqueous cathode slip according to step c2) on the surface 122 of the carbon-containing layer 120, wherein

[0060] - calendering of the at least partially dried active cathode material 124 on the surface 122 of the carbon-containing layer 120 according to step c3) can follow.

[0061] An optional calendering of the at least partially dried active cathode material 124 on the surface 122 of the carbon-containing layer 120 following the application of the active cathode material 124 to the carbon-containing layer 120 according to step c3) can, as described below with reference to Figure 3, lead both to improved adhesion between the layer of the active cathode material 124 and the current collector 114 and to an improvement in the electrical conductivity and to a reduction in an electrical contact resistance between the layer of the active cathode material 124 and the current collector 114 as a result of the presence of the carbon-containing layer 120 in the cathode 112.

[0062] 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, up to a maximum of 70°C, preferably up to a maximum of 65°C, particularly preferably up to a maximum of 60°C, in particular at approximately 50°C. For step c), the same temperature or, as described in more detail above, a lower or higher temperature can be used. As can be seen in particular from Figures 2a and 2b, the selected composition of the carbon-containing layer 120 within a narrow parameter range and the manner in which the carbon-containing layer 120 is produced within the specified narrow temperature range result in the layer of active cathode material 124 being formed as a homogeneous layer on the surface 122 of the carbon-containing layer 120.

[0063] The carbon-containing layer 120 according to the 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 of at most 20 μm, preferably at most 10 μm, particularly preferably at most 7.5 μm. In the exemplary embodiments presented below, a layer thickness of 0.5 μm to 6 μm was used for the carbon-containing layer. This small layer thickness of the carbon-containing layer 120 according to the invention means that it typically occupies at most 1 wt.%, preferably at most 0.5 wt.%, particularly preferably at most 0.25 wt.%, of a total weight of the cathode 112 and therefore increases neither the total weight nor the material costs of the cathode 112.The carbon-containing layer 120 can act in particular as a passivation layer in that it can sufficiently prevent the corrosion of the surface 116 of the current collector 114, which in particular comprises aluminum, during the application of the active cathode material 124 to the surface 122 of the carbon-containing layer 120.

[0064] Figure 2 shows variations in the shape of the layer of active cathode material 124 on the surface 122 of the carbonaceous layer 120 depending on the composition of the carbonaceous layer 120 (Figure 2a) or depending on the method of manufacturing the carbonaceous layer 120 (Figure 2b).

[0065] As can be seen from Figure 2a, the desired homogeneous layer of the active cathode material 124 is formed on the surface 122 of the carbon-containing layer 120 only within a parameter range 130 in which the carbon-containing layer 120

[0066] - a carbon content 132 of more than 60 wt% and less than 80 wt% and

[0067] - has a binder content of at least 20 wt.% and at most 40 wt.%, so that the contents of 132 and 134 each add up to 100 wt.%. The polymer polyvinylidene fluoride (PVDF) was used as an example here; however, the use of one or more other polymers is possible.

[0068] In a further parameter range 136 shown in Figure 2a, in which the carbon-containing layer 120 has a carbon content 132 of less than 60 wt.% and

[0069] - has a binder content 134 of at least 40 wt.%, so that the contents 132, 134 each add up to 100 wt.%, a hydrophobic wetting behavior or even a superhydrophobic wetting behavior occurs on the surface 122 of the carbon-containing layer 120, which leads to the layer of the active cathode material 124 not being in the form of the desired homogeneous layer, but as undesired droplets on the surface 122 of the carbon-containing layer 120.

[0070] In a further parameter range 138, also shown in Figure 2a, in which the carbon-containing layer 120

[0071] - a carbon content of at least 80% by weight and

[0072] - has a binder content 134 of at most 20 wt.%, so that here too the contents 132, 134 each add up to 100 wt.%, craters or cups 140 and / or capillaries 142 form in the volume of the layer of the active cathode material 124, which extend to the surface 122 of the carbon-containing layer 120 or even to the surface 116 of the current collector 114. As a result of these effects, the surface 116 of the current collector 114, which in particular comprises aluminum, is undesirably no longer protected against corrosion.

[0073] As can be seen from Figure 2b, the desired homogeneous layer of the active cathode material 124 forms on the surface 122 of the carbon-containing layer 120 only within a temperature range 144 in which the coating of the surface 116 of the current collector 114 with the carbon-containing layer 120 takes place at a temperature 146 of at least 30 °C to at most 70 °C.

[0074] In a further temperature range 148 shown in Figure 2b, which has a temperature below 30 °C, craters or cups 140 and / or capillaries 142, which extend to the surface 122 of the carbon-containing layer 120 or even to the surface 116 of the current collector 114, and / or pores 150 are formed in the volume of the layer of the active cathode material 124, so that here too the surface 116 of the current collector 114, which particularly comprises aluminum, is no longer protected against corrosion as a result of these effects.

[0075] In yet another temperature range 152, also shown in Figure 2b, which has a temperature above 70 °C, essentially the same effects occur as in the parameter range 136, ie here too, a hydrophobic wetting behavior or even a superhydrophobic wetting behavior occurs on the surface 122 of the carbon-containing layer 120, which leads to the layer of the active cathode material 124 not being present in the form of the desired homogeneous layer, but as undesired droplets on the surface 122 of the carbon-containing layer 120.

[0076] Figure 3 shows a schematic representation of the cathode 112 according to the invention in cross-sectional view. This clearly shows how particles 160 of the active cathode material 124 are embedded or pressed into the carbon-containing layer 120, in particular to improve the mechanical and electrical contact with the current collector 114.

[0077] Figure 4 shows a comparison of the curves 170, 172 of the specific discharge capacity Cats in mAh / g of NMC622 half-cells as a function of the number of cycles n for different C-rates from > 0 to < 70. NMC622-00 denotes a comparison sample not covered by the present invention with the active cathode material 124 lithium nickel manganese cobalt oxide (LiNi x Mn yCo2O2), NMC), which was treated with phosphoric acid (H3PO4) during the production of the cathode 112 and has a layer thickness of 70 pm, while NMC622-01 denotes a sample according to the invention with the active cathode material 124 NMC, which was not treated with acid and has a layer thickness of 65 pm. NMC622 here denotes Li(NiO,eMnCoo,2)O2. A comparison of the curve 170 of the specific discharge capacity of the inventive sample NMC622-01 with the curve 172 of the specific discharge capacity of the comparative sample NMC622-00 surprisingly even shows an increase in the specific discharge capacity in the inventive sample compared to the comparative sample, particularly above IC.

[0078] Figure 5 shows a representation of a cyclic voltammogram 180 for an embodiment with a sample according to the invention, which has a carbon-containing layer 120, as well as a further cyclic voltammogram 182 for a comparative sample not covered by the present invention, without a carbon-containing layer, which was produced with the addition of acid. The sample according to the invention was produced using an acid-free, water-based NMC622 slip, while the comparative sample was produced using a water-based NMC622 slip with the addition of acid. The acid-free slip comprises a slip to which no acid was added to influence the pH. The reaction of NMC with water results in a high pH, ​​which can be in the range of 12 or higher.Without acid, this high pH is maintained; with acid, the pH can be lowered, typically to a pH of 7 to 11, preferably 8 to 10, in particular 9 ± 0.5 in the present comparative example.

[0079] The active cathode materials 124 NMC622 used for both measurements come from the same batch. A comparison of the cyclic voltammogram 180 for the inventive sample with the cyclic voltammogram 182 for the comparative sample, available at https: / / doi.org / 10.3390 / nanol l071840, shows that the redox peaks in the comparative sample occur at 3.9 V and 3.6 V, while for the inventive sample, the redox peaks are much closer together at 3.78 and 3.71 V, indicating a significantly lower cell polarization. Increased cell polarization when using the water-based slurry with added acid may be due to a chemical reaction of the acid with the active cathode material 124 and a resulting increase in the electrical contact resistance between the layer of the active cathode material 124 and the current collector 114.Furthermore, this allows for higher electrical conductivity in deep regions near the downstream conductor, which can be particularly advantageous for thicker layers. Further advantages are listed above.

[0080] List of reference symbols

[0081] 110 Process for producing a cathode

[0082] 112 Cathode

[0083] 114 Stromab 1 eiter

[0084] 116 Surface

[0085] 118 electrically conductive material

[0086] 120 carbonaceous layer

[0087] 122 Surface

[0088] 124 active cathode material

[0089] 130 Parameter range

[0090] 132 Carbon content

[0091] 134 share in Binder

[0092] 136 Parameter range

[0093] 138 Parameter range

[0094] 140 craters or cups

[0095] 142 capillaries

[0096] 144 T emperature range

[0097] 146 Temperature

[0098] 148 T emperature range

[0099] 150 pores

[0100] 152 T emperature range

[0101] 160 particles

[0102] 170 Course of the specific discharge capacity of the sample according to the invention

[0103] 172 Course of the specific discharge capacity of the reference sample

[0104] 180 Cyclic voltammogram of the sample according to the invention

[0105] 182 Cyclic voltammogram of the reference sample

Claims

Patent claims Method (110) for producing a cathode (112), wherein the cathode (112) has at least one current collector (114) and an active cathode material (124), wherein the method (110) comprises the following steps: a) providing a current collector (114), wherein at least the surface (116) of said current collector (114) has an electrically conductive material (118); b) coating the surface (116) of the current collector (114) with a carbon-containing layer (120); and c) applying an active cathode 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 wherein at least step b) is carried out at a temperature of at least 30°C to at most 70°C.The method (110) according to the preceding claim, wherein the carbon-containing layer (120) comprises carbon black, the carbon black being a black powdered solid comprising at least 80 wt.% and at most 99.5 wt.% carbon. The method (110) according to any one of the preceding claims, wherein the application of the active cathode material (124) to the carbon-containing layer (120) according to step c) is carried out by c1) applying an aqueous cathode slurry to 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 active cathode material (124). Method according to one of the preceding claims, wherein the active cathode material (124) is formed as a homogeneous layer on a surface (122) of the carbon-containing layer (120).The method (110) of any preceding claim, wherein applying the active cathode material (124) to the carbonaceous layer (124) according to step c) comprises:. c3) calendering the at least partially dried active cathode 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 at most 60°C.

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

8. Method (110) according to one of the preceding claims, wherein the coating of the surface (116) of the current collector (14) with the carbon-containing layer (120) according to step b) is carried out until the carbon-containing layer (120) has a layer thickness of 0.1 pm to 20 pm.

9. Method (110) according to the preceding claim, wherein the coating of the surface (116) of the current collector (14) with the carbon-containing layer (120) according to step b) is carried out until the carbon-containing layer (120) has a layer thickness of 0.1 pm to 10 pm.

10. Method (110) according to the preceding claim, wherein the coating of the surface (116) of the current collector (14) with the carbon-containing layer (120) according to step b) is carried out until the carbon-containing layer (120) has a layer thickness of 0.1 pm to 7.5 pm.

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

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

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

14. Cathode (112), comprising - a current collector (114) whose surface (116) has an electrically conductive material (118); - a carbon-containing layer (120) on the surface (116) of the current collector (114); and - a layer of an active cathode material (124) on the carbon-containing layer (120), wherein the carbon-containing layer (120) comprises more than 60 wt.% and less than 80 wt.% carbon and at least one polymer as a binder, and wherein the layer of the active cathode material (124) is formed as a homogeneous layer on the carbon-containing layer (120). A 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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