Method for manufacturing an electrode foil, electrode with electrode foil, and energy storage comprising the electrode

Abstract

The invention relates to a dry manufacturing method for manufacturing an electrode foil for an energy accumulator without adding a solvent, comprising the following method steps: A) providing raw materials, comprising: - a fluoropolymer dry binder having a particle size D 90 of not more than 1 pm, - an electrically conductive additive, and - an electrochemically active material, B) mixing the raw materials to form a mixture, and C) calendering the mixture to form an electrode foil, wherein in method step A) and / or B) an emulsifier is added to the raw materials or the mixture, the emulsifier being selected from the group consisting of perfluorocarboxylates, perfluorosulfonates, perfluoroethers and combinations thereof, and / or a redox stabilizer is added, the redox stabilizer being selected from the group consisting of europium compounds, cerium compounds and vanadium compounds and combinations thereof.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an electrode foil for an energy storage device, an electrode having the electrode foil, and an energy storage device having the electrode. Background Technology

[0002] In manufacturing electrodes for energy storage devices (such as lithium-ion or sodium-ion batteries), dry manufacturing methods are typically used, where no solvents are added. This has the advantage that the electrode material does not need to be dried for an extended period of time with significant costs after formation. Fluoropolymer dry binders, such as polytetrafluoroethylene (PTFE) with CF bonds, are preferred as dry binders. These fluoropolymer dry binders can be reduced in the energy storage device during electrode operation, where thermodynamically preferred CF bond breaking may occur to form CC double bonds. This CF bond breaking occurs particularly at locations in the fluoropolymer dry binder where there is a localized high concentration of fluorine. Due to this reduction, the capacity and cycle stability of the energy storage device may decrease. Summary of the Invention

[0003] The object of this invention is to provide a method for manufacturing electrode foil that improves upon the aforementioned disadvantages. Another object of this invention is to provide an electrode foil for an energy storage device that improves upon the aforementioned disadvantages. The subject matter of this invention also relates to providing emulsifiers and redox stabilizers for fluoropolymer dry adhesives.

[0004] One aspect of the present invention provides a dry manufacturing method for producing electrode foil for an energy storage device without adding solvents. The dry manufacturing method includes the following steps:

[0005] A) Provide raw materials, said raw materials including:

[0006] - With a particle size D not greater than 1 μm 90 Fluoropolymer dry adhesives,

[0007] - Additives that can conduct electricity, and

[0008] - Electrochemically active materials,

[0009] B) The raw materials are mixed to form a mixture, and

[0010] C) The mixture is rolled to form an electrode foil, wherein an emulsifier is added to the raw material or the mixture in method steps A) and / or B), the emulsifier being selected from the group consisting of perfluorocarboxylate, perfluorosulfonate, perfluoroether and combinations thereof, and / or a redox stabilizer is added, the redox stabilizer being selected from the group consisting of europium compounds, cerium compounds and vanadium compounds and combinations thereof.

[0011] The inventors discovered that a particle size D 90 Fluorinated dry binders smaller than 1 μm contain little or no agglomerates of dry binders with locally elevated fluorine concentrations. Therefore, such fluoropolymer dry binders are more stable relative to reduction during electrode operation in accumulators.

[0012] In particular, granularity D 90 The particle size can be determined by dynamic light scattering using the standard ISO 22412. In particular, fluorinated dry adhesives can also have a particle size D of less than 0.5 μm. 50 This particle size can also be determined, for example, by the ISO 22412 standard.

[0013] In the dry manufacturing method of the present invention, commercially available fluoropolymer dry adhesives having a particle size D of less than 1 μm can be used in particular. 90 For example, an aqueous PTFE dispersion sold by 3M under the trade name Dyneon™ PTFE Dispersion TF5060GZ 3M can be used. This dispersion has an average particle size of 210 nm. 50 .

[0014] Here, this dry manufacturing method is carried out without adding solvent. For this purpose, a dry binder that can be mixed without adding solvent is used. This avoids the time-consuming drying of the electrode material after mixing. The dry manufacturing method is also understood in the sense of the present invention as a manufacturing method in which raw materials, for example, containing an emulsifier or solvent, are added, wherein the emulsifier or solvent described in step B) of the method evaporates at a raised temperature at the beginning of the mixing process, and then the raw materials are dry-mixed without solvent. For example, the above-described aqueous PTFE dispersion can be used, wherein water, as a dispersion, is evaporated at the beginning of the mixing process in step B).

[0015] In particular, at the beginning of step B), the raw materials can be heated to an elevated temperature of 110°C up to below 150°C. This can be used to evaporate any residual solvent or dispersion remaining in the raw materials, and then the raw materials can be mixed in step B) without solvent.

[0016] Furthermore, the emulsifier added to the raw materials or mixture either in step A) or step B) enables better mixing of the fluoropolymer dry adhesive with other raw materials. This additionally ensures that the agglomerates of the fluoropolymer dry adhesive are dissolved in the resulting mixture, and thus reduces the probability of reductive decomposition of the dry adhesive during accumulator operation.

[0017] Additionally or alternatively, the redox stabilizer added to the raw materials or mixture in step A) or step B) can also stabilize the fluoropolymer dry binder in the mixture. In particular, the redox stabilizer can be selected from the group consisting of europium compounds, cerium compounds, and vanadium compounds, which can appear in different oxidation states of metallic europium, cerium, and vanadium. Therefore, the redox stabilizer is capable of capturing electrons. In particular, these metallic compounds can appear in oxidation states III, IV, and II, allowing the redox stabilizer to capture electrons and thus occupy different oxidation states. Advantageously, the redox stabilizer is capable of reversibly capturing and releasing electrons and therefore can also be regenerated, for example, during the charging of the energy storage device.

[0018] Cerium compounds can be selected from the group consisting of cerium(III), cerium(III,IV), and cerium(IV). Vanadium compounds can be selected from the group consisting of vanadium(V), vanadium(IV), and vanadium(III). Europium compounds can be selected from the group consisting of europium(III). These oxides of cerium, europium, or vanadium can particularly well exist in different oxidation states and are therefore suitable for capturing electrons during accumulator operation and, if necessary, releasing said electrons again, thus sufficient for the regeneration of redox stabilizers. In particular, cerium(III), cerium(III,IV), and cerium(IV) can be converted into cerium oxides with lower oxidation states, such as cerium(II), by capturing electrons. Vanadium(V), vanadium(IV), and vanadium(III) can be converted into corresponding oxides with lower oxidation states by capturing electrons, wherein vanadium(III) can be converted into vanadium(II).

[0019] The redox stabilizer can be added at a ratio of 0.3% to 1% by weight, preferably 0.4% to 0.8% by weight, of the total weight of the electrode foil. The redox stabilizer can be added, in particular, as a solid, for example, as a metal oxide.

[0020] In method steps A) and / or B), redox stabilizers or emulsifiers, or a combination of both, may be added.

[0021] Emulsifiers may include, in particular, perfluorocarboxylate salts. Specifically, perfluorocarboxylic acids may have the following general formula C1 nF (2n+1) COOH, wherein n can be between 5 and 12. Perfluorohexanoate to perfluorodecanoate are preferred, with perfluorooctanoate being particularly preferred. Alkali metal cations, for example, can be considered as cations. , , and ammonium cations or to Alkylammonium cations, such as tetramethylammonium cations.

[0022] As a perfluorosulfonate, it can be used with the general formula C n F (2n+1) SO3 - Salts, wherein n can be between 5 and 12. Perfluorooctane sulfonate is particularly preferred. The cations already listed above in the case of perfluorinated carboxylic acids can be considered as cations.

[0023] For example, perfluoro(2,5,8,11,14-pentamethyl-3,6,9,12,15-pentoxaoctadecanoate) or perfluoro-2,5-dimethyl-3,6-dioxanonanoate can be used as perfluoroethers.

[0024] The emulsifier can be added at a ratio of 0.5% to 5% by weight, preferably 1% to 3% by weight, of the total weight of the electrode foil. This weight percentage is particularly suitable for using the various compounds as emulsifiers in fluoropolymer dry adhesives.

[0025] The emulsifier can also be mixed with the electrochemically active material, for example, as an aqueous emulsion, and then dried. The electrochemically active material with the emulsifier can then be mixed with other raw materials and further processed. Alternatively, an aqueous emulsion of the emulsifier can be added to other raw materials, and then the emulsifier is immediately evaporated at an elevated temperature in step B), and the raw materials are then further mixed without solvent.

[0026] Fluoropolymer dry adhesives contain CF bonds. As mentioned above, these bonds are particularly prone to breakage during accumulator operation, leading to reduction of the dry adhesive. Fluoropolymer dry adhesives can be selected from the group consisting of: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polytetrafluoroethylene (PTFE). Preferably, the fluoropolymer comprises or is composed of PTFE.

[0027] In addition to fluoropolymer dry adhesives, other dry adhesives without CF bonds can also be provided as raw materials in step A). ​​For example, these polymeric dry adhesives can be polyolefins, polyethylene, or polypropylene. Poly(ethylene oxide) (PEO) can also be used.

[0028] It is preferable to use only fluoropolymer dry adhesives.

[0029] The total proportion of dry adhesives, especially fluoropolymer dry adhesives, can be 0.5% to 5% by weight, preferably 1% to 4% by weight, of the total weight of the electrode foil.

[0030] Conductive additives can be selected from the group consisting of: carbon powder, carbon nanotubes, carbon nanoparticles, and combinations thereof. Carbon powder can be, for example, activated carbon or carbon black.

[0031] The conductive additive can be added at a ratio of 0.2% to 5% by weight, preferably 0.8% to 3% by weight, of the total weight of the electrode foil.

[0032] Electrochemically active materials are particularly understood to be materials capable of capturing and releasing lithium ions if the energy storage device is a lithium-ion battery. Materials selected from the group consisting of graphite and oxides of lithium, nickel, and manganese can be used as active materials. If the electrode foil is to be used in the anode, the active material can be selected from the group consisting of: carbon-containing materials, silicon, nano-silicon, silicon composites, silicon low oxides, silicon alloys, lithium, lithium alloys, aluminum alloys, indium, indium alloys, tin, tin alloys, cobalt alloys, niobium pentoxide, titanium dioxide, titanates, and lithium titanate (Li₄Ti₅O₂). 12 Tin dioxide and mixtures thereof. Preferably, the active material is selected from the group consisting of: synthetic graphite, natural graphite, graphene, mesophase carbon, doped carbon, hard carbon, soft carbon, fullerene, silicon-carbon composites, silicon, surface-coated silicon, silicon low oxides, silicon alloys, lithium metal, aluminum alloys, indium, tin alloys, cobalt alloys, and mixtures thereof. If the electrode foil is to be used as the anode in a lithium-ion battery, the electrode foil may in particular include graphite as the active material.

[0033] Conversely, if the electrode foil is used in the cathode, the active material can be selected from the group consisting of: lithium transition metal oxides, such as lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese compounds (NCM or NMC), such as LiCoO2 and LiNi. 0.33 Co 0.33 Mn 0.33 O2; lithium nickel cobalt aluminum oxide (NCA); lithium olivine, such as lithium iron 25 phosphate (LFP); lithium spinel, such as lithium manganese spinel (LMO), or combinations thereof. So-called overlithiated layered oxides (OLO) may also be used.

[0034] In the case of sodium-ion batteries, electrochemically active materials are particularly understood to be materials capable of capturing and releasing sodium ions. For example, carbon, such as graphite, can be used as an anode material, which is capable of intercalating sodium ions during battery operation. For example, materials containing sodium ions, such as phosphates and diphosphates, such as sodium iron phosphate, can be used as a cathode material. For example, sodium salts (such as sodium hexafluorophosphate) can be used in conjunction with an organic solvent, such as organic carbonates, propylene carbonate, ethylene carbonate, or dimethyl carbonate.

[0035] Electrochemically active materials can be added at a ratio of 60% to 99% by weight, preferably 80% to 98% by weight, of the total weight of the electrode foil.

[0036] In step B), the raw materials can be mixed using a process with low shear force, for example, at 2000 to 22000 rpm. In a mixing method with a low velocity gradient, the different particle components can be mixed with each other at a low velocity gradient and therefore with low shear load. Under low shear load, the particles of different components can essentially maintain their shape and only experience abrasion on the walls of the mixing vessel. This process enables particularly economical mixing of raw materials. This can be achieved, for example, using a planetary centrifugal mixer, a blade mixer, or a paddle mixer.

[0037] Furthermore, to achieve complete mixing, in step B), the mixture can also be mixed at a high speed gradient, for example, after an initial mixing process with low shear force, by means of a mixing process with high shear load. In this high shear load mixing process, with a high speed gradient and no solvent, the different components of the electrode foil move relative to each other and thus mix, and in the case of PTFE as a fluoropolymer dry binder, they fiberize. Under high shear load, agglomerates of the dry binder, especially those still present, can be reduced or broken down, and fibrils of the polymeric dry binder PTFE are formed, particularly well. These fibrils can be used particularly well as binders for other raw materials of the electrode foil. This high shear load method can be implemented, for example, by jetting methods, such as by means of an impact jet mill, by a three-roll mill (Drei-Walzen-Stuhl), and by a twin-screw extruder, or a combination of these methods.

[0038] For example, in an impact jet mill, the mixture can be mixed with a pressurized gas in step B). Here, the pressure is preferably greater than 0.7 bar, and more preferably 5 to 8 bar.

[0039] The calendering in step C) can be carried out under a linear load of 100 N / mm to 3000 N / mm and / or at a temperature of 50°C to 280°C, preferably 80°C to 250°C. For example, a linear load of 330 N / mm can be used in a 14-roll calender.

[0040] The electrode foil can be, in particular, a self-supporting electrode foil, which is capable of supporting its own weight and, for example, can be rolled up. Such a roll can be stored for a long time and then unwound and processed into individual electrode foils for a single energy storage device.

[0041] In step C), the mixture can be rolled onto the current collector layer. Here, an electrode comprising the current collector layer and an electrode foil disposed thereon can be formed. The electrode can then either be rolled up and stored or can be installed in an accumulator.

[0042] The current collector layer or current collector foil is typically made of copper in the case of an anode foil and typically made of aluminum in the case of a cathode foil.

[0043] The subject of this invention also relates to a self-supporting electrode foil that can be manufactured according to the dry manufacturing method described herein.

[0044] The present invention also provides a self-supporting electrode foil. The self-supporting electrode foil comprises:

[0045] - Fluoropolymer dry adhesives with a particle size of no more than 1 μm.

[0046] - The first additive capable of conducting electricity

[0047] - Electrochemically active materials, and

[0048] - Emulsifiers, said emulsifiers being selected from the group consisting of: perfluorocarboxylate, perfluorosulfonate, perfluoroether, and combinations thereof, and / or

[0049] - A redox stabilizer, wherein the redox stabilizer is selected from the group consisting of europium compounds, cerium compounds and vanadium compounds and combinations thereof.

[0050] In this self-supporting electrode foil, the fluoropolymer dry binder has improved reduction stability due to the emulsifier and / or the redox stabilizer.

[0051] Particle size not exceeding 1 μm can be determined, particularly in the fabricated electrode foil, using scanning electron microscopy. For this purpose, the electrode foil sample can be measured using scanning electron microscopy by determining backscattered electrons. The accelerating voltage is 5 kV and the sample size is 1 cm. 2 Each sample was measured 5 times.

[0052] The subject of this invention also relates to an electrode for an energy storage device, the electrode comprising:

[0053] - As described above, a self-supporting electrode foil and a current collector foil, wherein the electrode foil is arranged on the current collector foil.

[0054] Preferably, the self-supporting electrode foil is rolled onto the current collector foil, and more preferably, the self-supporting electrode foil is arranged on the two main surfaces of the current collector foil.

[0055] The subject matter of this invention also relates to the use of perfluorocarboxylate, perfluorosulfonate, perfluoroether or combinations thereof as emulsifiers to improve the reduction stability of fluoropolymer dry binders in self-supporting electrode foils.

[0056] Another aspect of the invention is its use as a redox stabilizer for europium compounds, cerium compounds and vanadium compounds to improve the reduction stability of fluoropolymer dry binders in self-supporting electrode foils.

[0057] The invention will be described in detail below with the aid of an example: Example:

[0058] Anode active materials (such as graphite / silicon), carbon black, and PTFE dispersions (3M, PTFE5060GZ, Dyneon) are used directly in the manufacture of anodes.

[0059] To prepare the powder mixture, 95.2 wt% silicon as the electrochemical active material and 2 wt% carbon black were mixed in a planetary centrifugal mixer (ARE-250, Thinky Mixer, Japan) at 2000 rpm for 15 minutes. After mixing, 0.5 wt% ammonium perfluorooctanoate and 0.3 wt% vanadium oxide were added as solids. After further mixing for 10 minutes, 2 wt% polytetrafluoroethylene (PTFE) dispersion was added, and the raw materials were heated to an elevated temperature of 110°C up to below 150°C and finally mixed for 10 minutes.

[0060] High shear force was applied to the fibrous PTFE using a PM-100 ball mill (Rezstech, Germany). The electrode film was formed using this dried mixture through the gap of the calender rolls and then extruded at 150°C. The foil thickness was adjusted at a speed of 20 cm / min according to the roll gap of the calender. Finally, the self-standing foil was hot-rolled onto the current collector (current collector foil) at 150°C.

[0061] The electrodes were cut into 16mm diameter discs and dried in a vacuum furnace at 130°C for 12 hours.

[0062] The electrode exhibits improved cycle stability compared to electrodes without emulsifiers or redox stabilizers. In particular, it can achieve a 2 to 5-fold increase in service life.

[0063] This invention is not limited to the descriptions of the various embodiments. Rather, the invention includes each new feature and each combination of features, especially each combination of features in the claims, even if the feature or combination itself is not explicitly given in the claims or embodiments.

Claims

1. A dry manufacturing method for producing electrode foil for an energy storage device without adding solvent, the dry manufacturing method comprising the following steps: A) Provide raw materials, said raw materials including: - With a particle size D not greater than 1 μm 90 Fluoropolymer dry adhesives, - Additives that can conduct electricity, and - Electrochemically active materials, B) The raw materials are mixed to form a mixture, and C) The mixture is rolled to form an electrode foil, wherein an emulsifier is added to the raw material or the mixture in step A) and / or B), the emulsifier being selected from the group consisting of perfluorocarboxylate, perfluorosulfonate, perfluoroether and combinations thereof, and / or a redox stabilizer is added, the redox stabilizer being selected from the group consisting of europium compounds, cerium compounds and vanadium compounds and combinations thereof.

2. The dry manufacturing method according to the preceding claim, wherein, The emulsifier is added at a ratio of 0.5% to 5% by weight, preferably 1% to 3% by weight, of the total weight of the electrode foil.

3. The dry manufacturing method according to any one of the preceding claims, wherein, The redox stabilizer is added at a ratio of 0.3% to 1% by weight, preferably 0.4% to 0.8% by weight, of the total weight of the electrode foil.

4. A dry manufacturing method according to any one of the preceding claims, wherein, The fluoropolymer dry adhesive is selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polytetrafluoroethylene (PTFE). Preferably, the fluoropolymer dry adhesive comprises PTFE or is composed of PTFE.

5. A dry manufacturing method according to any one of the preceding claims, wherein, In step A), the emulsifier is mixed with the electrochemically active material as an emulsion and then dried.

6. The dry manufacturing method according to any one of the preceding claims, wherein, In step C), the calendering is performed under a line load of 100 N / mm to 3000 N / mm and / or at a temperature of 50°C to 280°C, preferably at a temperature of 80°C to 250°C.

7. The dry manufacturing method according to any one of the preceding claims, wherein, The cerium compound is selected from the group consisting of cerium oxide (III, IV) and cerium oxide (IV), and / or the vanadium compound is selected from the group consisting of vanadium oxide (V), vanadium oxide (IV) and vanadium oxide (III), and / or the europium compound is europium oxide (III).

8. The dry manufacturing method according to any one of the preceding claims, wherein, The electrode foil is a self-supporting electrode foil.

9. A self-supporting electrode foil, which can be manufactured according to the dry manufacturing method according to any one of the preceding claims.

10. A self-supporting electrode foil, comprising: - Fluoropolymer dry adhesives with a particle size of no more than 1 μm. - The first additive capable of conducting electricity - Electrochemically active materials, and - An emulsifier, said emulsifier being selected from the group consisting of: perfluorocarboxylate, perfluorosulfonate, perfluoroether, and combinations thereof, and / or - A redox stabilizer, wherein the redox stabilizer is selected from the group consisting of europium compounds, cerium compounds and vanadium compounds and combinations thereof.

11. An electrode for a storage device, the electrode comprising a self-supporting electrode foil and a current collector foil according to the preceding claim, wherein, The electrode foil is arranged, preferably rolled, on the current collector foil.

12. Use of an emulsifier for improving the reduction stability of fluoropolymer dry binders in self-supporting electrode foils and / or use of a redox stabilizer for improving the reduction stability of fluoropolymer dry binders in self-supporting electrode foils, wherein, The emulsifier is selected from the group consisting of: perfluorocarboxylate, perfluorosulfonate, perfluoroether or a combination thereof, and the redox stabilizer is selected from the group consisting of: europium compounds, cerium compounds and vanadium compounds.