Electrode and solvent-free process for the production of these

Abstract

The present invention relates to an electrode comprising a mixture of electrochemically active material and at least one fibrillable binder; wherein the electrode is produced by a solvent-free process and a solvent-free process for its production. Furthermore, the present invention relates to a battery comprising the electrode and to a vehicle comprising the battery.

Description

[0001] The present invention relates to an electrode and a solvent-free process for producing the same.

[0002] Conventional battery electrodes are manufactured using a wet-coating process. Different electrode porosities are achieved using wet-chemical electrode manufacturing. This results in a pore structure with winding diffusion paths and inhomogeneous pore size distribution (bottlenecks) that is detrimental to diffusion processes. Furthermore, conventional binder materials are used, which can form plugs during the wet coating process and thus block pores. This impairs the fast-charging capacity of batteries that use such electrodes. Particularly in motor vehicles that use such batteries for energy supply and / or propulsion, the fast-charging capacity of the vehicle battery is a key argument for increasing consumer acceptance of such vehicles and helping electric vehicles achieve their breakthrough.

[0003] Therefore, it would be desirable to provide anodes and / or cathodes for batteries that enable higher fast charging capability.

[0004] The aim of the invention is to propose a possibility which avoids or at least reduces at least some of the disadvantages known in the prior art.

[0005] The object is achieved according to the invention by means of an electrode according to the main claim, as well as by means of a method, a battery and a motor vehicle according to the independent claims.

[0006] The subject matter of the main claim relates to an electrode comprising mixture components comprising electrochemically active material and at least one fibrillatable binder. The electrode is manufactured using a solvent-free process.

[0007] The fast-charging capacity of battery cells is influenced by several factors, primarily the battery materials used (electrochemically active materials, binders, conductive additives, electrolyte, separators), electrode composition, cell format, thermal management, charging profiles, and electrode microstructure parameters (layer thickness, porosity / density, areal weight, tortuosity). For a given electrode composition, the electrode microstructure parameters represent the greatest degree of freedom for influencing fast-charging capacity. The parameters electrode thickness, porosity / density, and areal weight cannot be changed independently of one another to improve the fast-charging capacity of a battery cell. In principle, fast-charging capacity is improved by reducing layer thickness, increasing porosity, reducing areal loading, and reducing tortuosity.

[0008] The effective tortuosity is the only microstructure parameter that can be varied to some extent independently of the other parameters (layer thickness, porosity, surface loading).

[0009] The electrode according to the invention has a fast-charging-optimized microstructure characterized by particularly low tortuosity. A reduction in tortuosity is achieved by ensuring that the pore structure of the electrode minimizes any influence on mass transport in the electrolyte that fills the pore space. This advantageous microstructure of the electrode is achieved by a solvent-free electrode coating (dry coating). Furthermore, a battery cell with the fast-charging-optimized electrode described above achieves improved fast-charging performance, enabling higher current flow and thus a reduction in charging times.

[0010] An electrochemically active material within the meaning of the invention is a material in which electrical energy is stored in the cell in the form of chemical energy. The electrochemically active (battery) material undergoes a chemical reaction during the discharge and charge processes. Such electrochemically active materials are known to those skilled in the art.

[0011] The electrochemically active material may comprise an anode active material.

[0012] An anode active material in the sense of the invention is understood to mean a material which can be used in an anode.

[0013] An anode, as defined by the invention, is an electrode at which oxidation processes occur during the discharge process of the battery cell. This means that the oxidation state of the electrochemically active material increases, releasing electrons. If the anode and cathode are then connected to form an electrical circuit, electrons flow to the cathode via this external connection. In this external circuit, the anode then acts as the negative pole.

[0014] The anode active material can be selected from the group consisting of natural graphite, synthetic graphite, spherical graphite, silicon, silicon compounds and mixtures thereof.

[0015] Spherical graphite in the sense of the invention is also referred to as round graphite.

[0016] Silicon compounds within the meaning of the invention can include, for example, silicon oxide and silicon-carbon composites.

[0017] In a preferred embodiment, the anode active material may comprise synthetic graphite.

[0018] In a further preferred embodiment, the anode active material consists of synthetic graphite.

[0019] The fibrillatable binder may comprise fluoropolymers, fluorine-free polymers or mixtures thereof.

[0020] Fluoropolymers within the meaning of the invention are polymers based on fluorocarbons with multiple carbon-fluorine bonds, in which a large portion or even all of the hydrogen atoms otherwise present are usually replaced by fluorine. Fluoropolymers are known to those skilled in the art. Fluoropolymers can be, for example, polyvinylidene fluoride (PVDF), copolymers such as poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), and polytetrafluoropolyethylene (PTFE).

[0021] According to a preferred embodiment, the fluoropolymer comprises polytetrafluoropolyethylene (PTFE).

[0022] According to a preferred embodiment, the fluoropolymer comprises polyvinylidene fluoride (PVDF).

[0023] According to a preferred embodiment, the fluoropolymer comprises polytetrafluoropolyethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0024] Fluorine-free polymers within the meaning of the invention can include rubbers such as styrene-butadiene rubber (SBR), celluloses such as carboxymethylcellulose (CMC), or polyolefins.

[0025] Polyolefins within the meaning of the invention can include polypropylene (PP) and polyethylene (PE).

[0026] According to a preferred embodiment, the fluoropolymer comprises polytetrafluoropolyethylene (PTFE).

[0027] According to a further preferred embodiment, the fluoropolymer consists of polytetrafluoropolyethylene (PTFE).

[0028] The mixture components may further comprise at least one conductive additive. Conductive additives are used to improve electrical conductivity or to improve electrical transport. The conductive additive can be a known electrically conductive material. Conductive additives are known to those skilled in the art.

[0029] According to a preferred embodiment, the conductive additive is selected from the group consisting of conductive carbon black, carbon nanotubes (CNTs), graphene, graphite, and mixtures thereof. Conductive carbon blacks are known to those skilled in the art. Conductive carbon black can, for example, comprise (Super)C65, C45, or similar.

[0030] According to a preferred embodiment, the conductive carbon black comprises Super C65.

[0031] The mixture components may comprise 92.0 to 99.0 wt.% anode active material, preferably 94.0 to 99.0 wt.%, more preferably 96.0 to 98.2 wt.%, even more preferably 97.5 to 98.2 wt.%, further preferably 97.0 to 98.5 wt.% and in particular 96.5 to 98.8 wt.%.

[0032] The mixture components may comprise 0.0 to 5.0 wt.% conductive additive, preferably 0.5 to 2.5 wt.%, more preferably 0.6 to 2.0 wt.%, even more preferably 0.7 to 1.5 wt.% and in particular 0.8 to 1.2 wt.%.

[0033] The mixture components may comprise 0.5 to 3.0 wt.% binder, preferably 0.5 to 1.5 wt.%, more preferably 0.8 to 1.2 wt.%, even more preferably 0.7 to 1.2 wt.% and particularly preferably 0.8 to 1.2 wt.%.

[0034] According to a preferred embodiment, the mixture components comprise 92.0 to 99.0 wt.% anode active material, 0.0 to 5.0 wt.% conductive additive and 0.5 to 3.0 wt.% binder.

[0035] According to a preferred embodiment, the mixture components comprise 96.0 to 99.0 wt.% anode active material, 0.5 to 2.5 wt.% conductive additive and 0.5 to 1.5 wt.% binder.

[0036] According to a preferred embodiment, the mixture components comprise 97.5 to 98.2 wt.% anode active material, 0.8 to 1.2 wt.% conductive additive and 0.8 to 1.2 wt.% binder.

[0037] According to a preferred embodiment, the effective tortuosity of the electrode measured according to an electrochemical impedance spectroscopy measurement exceeds a value of E -1 * 1.6 not, where E is the porosity of the electrode.

[0038] Porosity, as defined in the invention, means (empty volume in the electrode) / (total volume of the electrode). The porous structure of the electrodes slows the mass transfer in the electrolyte according to: κeff=ε⋅κbulkτ

[0039] In general, geometric tortuosity is defined as: τgeo=deffd

[0040] This occurs due to detours in the transport path due to the geometry of porous structures. Where d is the material thickness in the transport direction and d eff the effective path, i.e., the path length, through the material thickness. This relationship is described in more detail in: B. Tjaden, DJL Brett, PR Shearing, International Materials Reviews 2018, 63, 47-67.

[0041] The effective tortuosity within the meaning of the invention can be described as follows: Effective tortuosity T: Includes ion flow-inhibiting effects of the pore surface (i.e., roughness) and different cross-sectional areas of the pores ("bottlenecks"). Required for the experimental determination of T: Porosity ε, volume conductivity κ bulk of the electrolyte, effective conductivity in the porous electrode κ eff : τ=ε⋅κbulkκeff=RIon⋅ε⋅A⋅κbulkd Where A is the surface area of ​​the electrode sample and d is its thickness.

[0042] For a given electrode composition, the electrode microstructure parameters represent the greatest degree of freedom for influencing fast-charging capability. The parameters electrode thickness, porosity / density, and areal weight cannot be changed independently of one another to improve the fast-charging capability of a battery cell. In principle, fast-charging capability is improved by: reducing layer thickness, increasing porosity, reducing areal loading, and reducing tortuosity.

[0043] The effective tortuosity is the microstructure parameter that can be varied to a certain extent independently of the other parameters. A reduction in tortuosity is achieved by ensuring that the pore structure of the electrode does not influence mass transport as much as possible. The reason for the reduced electrode tortuosity through dry coating is a pore structure that is advantageous for diffusion processes, with a pore size distribution that is as homogeneous as possible (no bottlenecks) and the complete absence of pore-blocking conventional binder materials that can form plugs during wet coating. The binder thread structure created during dry coating does not block any pores and allows a reduction in the binder content.

[0044] An electrochemical impedance spectroscopy measurement within the meaning of the invention can be a known electrochemical impedance spectroscopy measurement method. In particular, the electrochemical impedance spectroscopy measurement method can be a measurement method as described in "Turtuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy" (Johannes Landesfeind et al. 2016, Journal of the Electrochemical Society 163 (7) A1373-A1387).

[0045] The electrode according to the invention can be produced by a generally known solvent-free process. Accordingly, in a further aspect of the invention, a solvent-free process for producing an electrode is provided, the process comprising the following steps: - Providing the mixture components comprising electrochemically active material and at least one fibrillar binder, optionally conductive additive, for producing a coating material for an electrode of an energy storage cell, such as a lithium-ion cell, - processing the mixture components in a multi-screw extruder to produce the coating material or to manufacture the coating material, wherein the fibrillatable binder is at least partially fibrillated; - Applying the coating material to a carrier film.

[0046] By means of the present method, a satisfactory conductivity of the electrode can be achieved even without conductive additives.

[0047] The optional conductive additive can be used to further increase the conductivity of the electrode if required. Advantageously, a multi-screw extruder can be used to implement a continuous mixing process, which increases productivity and reduces costs and energy requirements compared to batch mixing processes or semi-continuous processes, such as those implemented in a jet mill. When using jet mills, for example, degradation of the electrochemically active components (particularly (intercalation) graphite, but also other materials such as oxides and silicon materials) can also occur, since the stress required to fibrillate the binder also causes grinding of the remaining components. The fibrillatable binder enables solvent-free electrode production.A particularly advantageous feature in this case is the ability to precisely adjust the degree of fibrillation using the multi-screw extruder. A number of parameters are available for this purpose, such as the process temperature, throughput, speed, and the configuration of the kneading and / or mixing elements used in the multi-screw extruder.

[0048] Following processing in the multi-screw extruder, the coating material is in powder form. Such a powder includes particles, granules, etc. The binder is in fibrillated form. The grain size of the aforementioned elements can also be conveniently adjusted via the multi-screw extruder.

[0049] The powder mixture with fibrillated binder can be processed into a free-standing electrode film using a rolling device (calender) in the first nip. This film is either laminated directly onto a metallic current collector foil (pre-coated / treated or untreated foil made of copper or aluminum, expanded metal, etc.) or pressed to the desired thickness and density using additional rollers (multi-roll mill). Different rotation speeds of the rollers in the first nip can also result in subsequent fibril formation and alignment, allowing the resulting layer to adhere to the faster-rotating roller and from there be transferred directly onto a current collector foil.

[0050] The method may further comprise the following step: - Preparation, in particular crushing, of the coating material before coating.

[0051] For further adjustment of the particle size, a comminutor (mixer, disperser, cutting tool, mill, or similar) can be used after extrusion of the powder mixture. Comminution can be achieved via a system directly connected to the extruder or via an external comminutor.

[0052] The method may further comprise the following step: - Introducing the mixture components into the multi-screw extruder as a mixture.

[0053] The mixture components can therefore already be premixed and introduced into the multi-screw extruder as a finished mixture.

[0054] The mixture can be produced in a tumble mixer.

[0055] Alternatively, the mixture components can be fed into the multi-screw extruder individually or separately. This means that mixing can only take place in the multi-screw extruder and not beforehand.

[0056] A mixture can be produced by homogenization in a tumble mixer. As already mentioned, direct dosing of the individual components into the multi-screw extruder is also possible. The mixture can be dosed into a multi-screw extruder with a screw diameter of, for example, 20 mm and a length-to-diameter ratio (L / D) of 40, with the process zone heated to, for example, 160°C. At a speed of 420 revolutions per minute and a mass throughput of 3.5 kg per hour, the binder, preferably a PTFE binder, can fibrillate, thus allowing further processing of the resulting dry mixture into free-standing electrodes / coating films and battery electrodes. The screw diameter can be adjusted according to the degree of scaling. For larger batches, a correspondingly larger screw diameter can be used.For larger series production, for example, screw diameters of at least 60 mm can be used.

[0057] In the process zone, both low temperatures, such as > 19°C, and higher temperatures, such as > 120°C, can prevail. Preferably, higher temperatures, such as > 120°C, and preferably 160°C, prevail in the process zone.

[0058] The electrode can be used in a battery. The present invention also relates to a battery comprising the electrode. Further components of a battery are known to those skilled in the art.

[0059] The battery can be used in a vehicle. The present invention further relates to a vehicle having the battery comprising the electrode according to the invention. The battery can function as a battery for providing electrical energy for an electric motor of the motor vehicle. The motor vehicle can thus be operated using the battery according to the invention. This means that the motor vehicle can use the battery according to the invention to provide electrical energy for the motor vehicle. Therefore, the battery according to the invention can supply electrical components of the motor vehicle with electrical energy. Thus, for example, the on-board system of the motor vehicle and / or other motor vehicle components and motor vehicle systems can be supplied with electrical energy by the battery according to the invention. In particular, the motor vehicle can be driven at least partially electrically using the battery according to the invention.The motor vehicle can also be driven fully electrically using the battery according to the invention. Special embodiments

[0060] [1] An electrode comprising mixture components comprising electrochemically active material and at least one fibrillatable binder; wherein the electrode is produced by a solvent-free process.

[0061] [2] Electrode according to paragraph [2], wherein the mixture components further comprise at least one conductive additive.

[0062] [3] An electrode according to paragraph [1] or [2], wherein the electrochemically active material comprises anode active material.

[0063] [4] Electrode according to paragraph [3], wherein the anode active material is selected from the group consisting of natural graphite, synthetic graphite, spherical graphite, silicon, silicon compounds and mixtures thereof.

[0064] [5] Electrode according to any one of paragraphs [2] to [4], wherein the conductive additive is selected from the group consisting of conductive carbon black, carbon nanotubes, graphene, graphite and mixtures thereof.

[0065] [6] An electrode according to any one of the preceding paragraphs, wherein the fibrillatable binder comprises fluoropolymers, fluorine-free polymers or mixtures thereof.

[0066] [7] An electrode according to paragraph [6], wherein the fluoropolymer comprises polytetrafluoroethylene.

[0067] [8] An electrode according to any one of paragraphs [2] to [7], wherein the anode active material comprises 92.0 to 99.0 wt%, the conductive additive comprises 0.0 to 5.0 wt% and the binder comprises 0.5 to 3.0 wt%.

[0068] [9] An electrode according to any one of the preceding paragraphs [2] to [8], wherein the electrochemically active material comprises 96.0 to 99.0 wt%, the conductive additive comprises 0.5 to 2.5 wt% and the binder comprises 0.5 to 1.5 wt%.

[0069]

[10] An electrode according to any one of the preceding paragraphs [2] to [9], wherein the electrochemically active material comprises 97.5 to 98.2 wt%, the conductive additive comprises 0.8 to 1.2 wt% and the binder comprises 0.8 to 1.2 wt%.

[0070]

[11] Electrode according to any one of the preceding paragraphs, wherein the effective tortuosity has a value of E -1 * does not exceed 1.6 and E represents the porosity of the electrode.

[0071]

[12] A solvent-free process for producing an electrode according to any one of the preceding paragraphs, the process comprising the following steps: - Providing the mixture components comprising electrochemically active material, optionally conductive additive, and at least one fibrillatable binder; - processing the mixture components in a multi-screw extruder to produce the coating material, wherein the fibrillatable binder is at least partially fibrillated; and - Applying the coating material to a carrier film.

[0072]

[13] A battery comprising an electrode according to any one of the preceding paragraphs [1] to

[12] .

[0073]

[14] Vehicle having a battery as defined in paragraph

[13] .

[0074] Further advantages and features will become apparent from the following description of an embodiment with reference to the attached figures. Fig. 1: a schematic view of an embodiment of the method. Fig. 2: a comparison of the effective tortuosity of a conventional wet-coated electrode with a dry-coated anode according to the invention.

[0075] Fig. Figure 1 schematically shows a multi-screw extruder 60 comprising a drive 62 and a process zone 64, which in this case comprises two screw elements. A mixture 10 comprising the mixture components is fed to the multi-screw extruder 60. The processing or mixing, or in particular the fibril formation, advantageously takes place in the present multi-screw extruder 60. In the region of the process zone 64, relatively high temperatures are preferably used, whereby relatively high temperatures of >120°C are meant, for example, according to a preferred embodiment, at 160°C.

[0076] Fibrillation of the binder in the mixture is favored by the elevated temperature. At such temperatures, lower shear forces are advantageously required for the same degree of fibril formation than at low temperatures. For a possible further adjustment of the grain or particle size of the coating material, a further device for processing the coating material can be used downstream of the multi-screw extruder 60, as also outlined here (see reference numeral 80). The processing device 80 can be, for example, a mixer, disperser, or a cutting tool, via which the (powdery) coating material is further comminuted.

[0077] The coating film is then produced in a corresponding rolling device 70. In this case, a carrier foil 40 is unwound from a first roll 72 and guided to two second rolls 74. There, a coating film 42 is immediately formed on the carrier foil 40. Schematically shown, the electrode thus produced is rewound on a third roll 76.

[0078] Alternatively, it is also possible to process the coating material 20 at a first roll gap, cf. for example the second rolls 74, into a free-standing coating film, which can be rolled up and processed at a later time.

[0079] Fig. Figure 2 shows a comparison of an electrode produced by the solvent-free process according to the invention and an electrode comprising carboxymethylcellulose (CMC) / styrene-butadiene rubber (SBR), which was produced by a conventional wet coating process. Fig.As can be seen in Figure 2, a reduction in electrode tortuosity is achieved through dry coating compared to conventional, wet-chemical electrode production for different electrode porosities. The reason for the reduced electrode tortuosity through dry coating is a pore structure that is advantageous for diffusion processes, with a pore size distribution that is as homogeneous as possible (no bottlenecks), as well as the complete absence of pore-blocking conventional binder materials that can form plugs during wet coating. The binder thread structure created during dry coating does not block pores and allows a reduction in the binder content.

[0080] The idea of ​​the invention can be summarized as follows: A method and a corresponding electrode are provided, which make it possible to electrically charge electric batteries even faster than conventional batteries.

[0081] Accordingly, an electric battery comprising the electrode according to the invention and a motor vehicle comprising such a battery are also provided.

[0082] The battery's particularly high fast-charging capacity results from the fact that the electrode acts as the battery's anode and is manufactured using a dry-coating process. Compared to wet-coating processes, a dry-coated anode has the advantage of a more homogeneous pore size distribution. This pore structure is particularly beneficial for diffusion processes. Furthermore, pore-blocking binder materials, such as those found in wet-coated anodes or in wet-chemical electrode production, are absent. These can form plugs.

[0083] The anode produced by dry coating according to the invention, on the other hand, allows for a reduction in the binder content. Furthermore, a binder thread structure is formed that does not block the pores, or at least not significantly so. This also has a positive effect on fast charging capability. Furthermore, a battery cell with the fast-charging-optimized electrode described above achieves improved fast charging performance. This allows for higher current delivery and thus a further reduction in charging times. List of reference symbols 10 Mixture 20 coating material 40 carrier film 42 coating film, electrode film 60 multi-screw extruders 62 drive 64 Process zone 70 rolling device 72 first role 74 second role 76 third role 80 Device for processing QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited non-patent literature

[0000] B. Tjaden, DJL Brett, PR Shearing, International Materials Reviews 2018, 63, 47-67

[0040] Turtuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy” (Johannes Landesfeind et al. 2016, Journal of the Electrochemical Society 163 (7) A1373-A1387

[0044]

Claims

[1] An electrode comprising mixture components comprising electrochemically active material and at least one fibrillatable binder; wherein the electrode is produced by a solvent-free process. [2] The electrode of claim 1, wherein the mixture components further comprise at least one conductive additive. [3] Electrode according to claim 1 or 2, wherein the electrochemically active material comprises anode active material, preferably selected from the group consisting of natural graphite, synthetic graphite, spherical graphite, silicon, silicon compounds and mixtures thereof. [4] The electrode according to claim 2 or 3, wherein the conductive additive is selected from the group consisting of conductive carbon black, carbon nanotubes, graphene, graphite and mixtures thereof. [5] Electrode according to any one of the preceding claims, wherein the fibrilizable binder comprises fluoropolymers, preferably polytertafluoroethylene, fluorine-free polymers or mixtures thereof. [6] Electrode according to any one of claims 2 to 5, wherein the anode active material comprises 92.0 to 99.0 wt%, the conductive additive 0.0 to 5.0 wt% and the binder 0.5 to 3.0 wt%, preferably the electrochemically active material comprises 96.0 to 99.0 wt%, the conductive additive 0.5 to 2.5 wt% and the binder 0.5 to 15 wt% and particularly preferably the electrochemically active material comprises 97.5 to 98.2 wt%, the conductive additive 0.8 to 1.2 wt% and the binder 0.8 to 1.2 wt%. [7] An electrode according to any one of the preceding claims, wherein the effective tortuosity has a value of E -1 * does not exceed 1.6 and E represents the porosity of the electrode. [8] A solvent-free process for producing an electrode according to any one of the preceding claims, the process comprising the following steps: - Providing the mixture components comprising electrochemically active material, optionally conductive additive and at least one fibrillatable binder; - processing the mixture components in a multi-screw extruder to produce the coating material, wherein the fibrillatable binder is at least partially fibrillated; and - Applying the coating material to a carrier film. [9] A battery comprising an electrode according to any one of the preceding claims 1 to 7. [10] A vehicle comprising a battery according to claim 9.

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