Cathode unit and method of manufacturing cathode unit

Abstract

The invention relates to a cathode unit for a solid state battery and a method for manufacturing the same. The cathode unit has a layer made of a composite material 2 having an electrode material, a solid electrolyte material, a conductive additive and polytetrafluoroethylene as a binder. The composite material comprises less than 1% by weight of polytetrafluoroethylene, and the polytetrafluoroethylene is at least partially present in the form of fibrillated polytetrafluoroethylene.

Description

[0001] This application is a divisional application of the invention application with the application date of December 17, 2019, Chinese application number 201980083172.0, and invention name “Cathode unit and method for manufacturing cathode unit”. Technical Field

[0002] The present invention relates to a cathode unit and a method for manufacturing a cathode unit. Background Art

[0003] Solid-state batteries are a promising development direction for lithium-ion batteries. For solid-state batteries, a lithium-ion conductor (or sodium-ion conductor) that exists as a solid body is used as an electrolyte instead of a liquid electrolyte system. It acts as an ion conductor between the active material particles and an ion-conducting separator between the anode and the cathode. Important is the possibility of large-area processing of powdered electrode mixtures and the possibility of forming an intimate contact surface between the solid electrolyte and the active material, where the surface has as many contact points as possible and as few hollow spaces as possible.

[0004] Solid-state batteries can be classified according to the type of electrolyte used (oxide, sulfide and polymer-based). Oxide solid electrolytes have high chemical and mechanical stability. However, due to the high sintering temperature, the preparation of non-porous thin electrodes or solid electrolyte membranes is a huge challenge. Sulfide electrolyte materials are also difficult to deposit on large areas. Different binder-solvent mixtures are used for the anode, cathode and electrolyte layers for application by wet chemical processes, for example, as described in US2016 / 248120 A1, because if the layer is not applied, the underlying layer may dissolve. In this process, a relatively high binder content of several weight percent or mass percent and the resulting higher electrical resistance and ionic resistance are disadvantageous.

[0005] Therefore, the main object of the present invention is to provide a cathode unit and a manufacturing method thereof that overcome the above-mentioned disadvantages, that is, to be able to manufacture the cathode unit over a large area with the lowest possible electrical resistance and ionic resistance. Summary of the Invention

[0006] According to the invention, this object is achieved by a cathode unit according to claim 1 and a method for producing a cathode unit according to claim 11. Advantageous embodiments and further developments are described in the dependent claims.

[0007] A cathode cell for a solid-state battery, preferably an alkaline ion solid-state battery, a lithium battery, or a sodium battery, comprises a layer of a composite material. The composite material comprises an electrode material, a solid electrolyte material, a conductive additive, and polytetrafluoroethylene (PTFE) as a binder. The composite material comprises less than 1% by weight of PTFE, and the PTFE is at least partially in the form of fibrillated PTFE.

[0008] By using fibrillated PTFE as a binder, the amount of binder used can be reduced, requiring only a small amount of PTFE, less than 1% by weight of the cathode unit, and thus improving electrical performance. The composite material is typically solvent-free, enabling simpler processing and application, and forms a free-standing membrane.

[0009] The cathode unit may comprise a current collector made of a conductive material, onto which a layer of the composite material is applied. Here, the term "conductive" is understood to mean any material having a conductivity of more than 10 at room temperature, i.e., 25°C. 5 Alternatively, or in addition, the layers of the composite material can also be electrically conductive, since usually also electrically conductive conductive additives are selected in a correspondingly higher proportion.

[0010] The polytetrafluoroethylene in the composite material can be provided as at least partially uniaxially and / or biaxially oriented polytetrafluoroethylene to set the desired mechanical properties. Of course, the polytetrafluoroethylene can also be provided as fully uniaxially or fully biaxially oriented or aligned polytetrafluoroethylene.

[0011] The composite material may comprise an amount of 60 to 99 percent by weight, preferably up to 100 percent, of electrode material. The composite material typically comprises at least 0.1 percent by weight of polytetrafluoroethylene to provide sufficient available binder. The composite material preferably comprises less than 0.5 percent by weight of polytetrafluoroethylene, particularly preferably between 0.1 and 0.4 percent by weight.

[0012] The electrode material may include sulfur, lithium sulfide (Li2S), metal lithium oxide, metal sodium oxide or a mixture thereof to form, for example, a sulfide cathode. The conductive electrode material may include, in particular, a transition metal oxide, preferably LiCoO2, LiNiO2, LiNi 1_x Co x O2, LiFePO4, LiMnO2, LiMn2O4, Li2Mn3NiO8, LiNi x Co y Mn z O2、LiNi x Co y -Al zO2 (where x+y+z=1), Li4Ti5O 12 Or Li2FeSiO4 or mixtures thereof. Corresponding analogs containing sodium can also be used, preferably Na2S, Na x MnO2, Na3V2(PO4)3, NaFePO4, Na2FePO4F, NaNiMnO2, Na2TiO7, and / or NaTi2(PO4)3. Multilayer oxides of the AMO2 type, where A = Li, Na; and M = cobalt, manganese, nickel, can also be used as electrode materials. Different materials can also be combined to form electrodes.

[0013] Solid electrolyte materials may include materials composed of the following systems: Li2S-P2S5, Li2S-GeS2, Li2 S -B2S3Li2S-SiS2, Li5PS6CI, Li2S-P2S5-LiX (X=Cl, Br, l), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-Lil , Li2S-SiS2-Lil, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl1, Li2S-SiS2-B2S3-Lil, Li2S-SiS2-P2S5-Li l , Li2S-P2S5-Z m S n (wherein m and n are integers, m is selected from P, Si or Ge), Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (wherein P and q are integers, m is selected from P, Si or Ge), Na2S-P2S5, Na2S-GeS2, Na2S-B2S3, Na6PS5Cl, Na2S-SiS2, Na2S-P2S5-NaX (X=Cl, Br, l), Na2S-P2S5-Na2O, Na2S-P2S5-Na2O-Na, Na2S-SiS2-Nal, Na2S-SiS2-NaBr, Na2S-SiS2-NaCl, Na2S-SiS2-B2S3-Nal, Na2S-SiS2-P2S5-Nal, Na2S-P2S5-Z m S n (wherein m and n are integers, m is selected from P, Si or Ge), Na2S-SiS2-Na3PO4, Na2S-SiS2-Na p MO q(wherein P and q are integers and m is selected from P, Si or Ge) or a mixture thereof. In all compounds described in this application, lithium can generally be replaced by sodium. The solid electrolyte material is generally present in the powder mixture in a proportion of 1% to 35% by weight. Carbon nanotubes, black carbon, graphite, graphene and / or carbon nanofibers can be included in the composite material as a conductive additive in a proportion of 1% to 5% by weight. The solid electrolyte material is generally an electrochemically active material. The conductive additive can be an electrochemically inactive material.

[0014] The electrode material may include a protective layer applied to the particles of the material. The protective layer should prevent side reactions between the solid electrolyte material and the electrode material. For example, the protective layer may include Li2O-ZrO2 or other metal oxides. Each particle of the electrode material may typically have a protective layer having a thickness of 2-5 nm.

[0015] The conductive current collector typically comprises a conductive material, preferably aluminum, or is formed entirely of such a material. Alternatively, or in addition, a current collector layer, particularly a planar current collector, can be formed, preferably with a double-sided coating, as expanded metal, or as a current collector layer provided as a foam, fiber fabric, non-crimped fiber, or as a current collector having a primer layer. The primer layer can also be planar.

[0016] In a method for manufacturing a cathode unit for a solid-state battery, a powder mixture is manufactured from an electrode material, a solid electrolyte material, a conductive additive, and polytetrafluoroethylene as a binder. The weight percentage of the powder mixture here is less than 1% of the polytetrafluoroethylene. In the powder mixture, at least partially fibrillated polytetrafluoroethylene is formed by the action of shear forces on the powder mixture. The powder mixture is then formed into a flexible composite layer. The flexible composite layer is preferably applied to a conductive current collector to form the cathode unit. It may also be provided that the flexible composite layer and / or the current collector are subsequently compacted.

[0017] Simple processing is ensured by a powder mixture. A powder mixture is understood to be a material in granular form consisting of a plurality of small particles with a particle size of up to 15 μm, or a mixture or bulk material in granular or flake form. The powder mixture can be in dry form to simplify handling. Furthermore, according to DIN EN ISO 6186, the powder mixture cannot be cast. In the context of this document, "dry" is understood to mean that the components of the powder mixture are in solid form, free of liquid or liquid aggregates. The powder mixture can be solvent-free, i.e., free of solvent. A "flexible composite layer" is understood to be a composite layer that can be bent, folded, or unfolded through 180° at room temperature without breaking. In particular, the bending radius is 90 μm to 100 μm, with 100 μm being particularly preferred.

[0018] The at least partially fibrillated polytetrafluoroethylene can be formed by grinding, mixing, or a combination of these methods in a worm shaft or in a roller system, a kneading system, a pounding system, or by a combination of these methods to ensure effective fibrillation. The at least partially fibrillated polytetrafluoroethylene is typically formed at room temperature; however, to achieve a binder content of less than 0.5% by weight, it is preferably formed at an elevated temperature of 60°C to 100°C, particularly preferably 90°C to 100°C, in particular 100°C. However, the polytetrafluoroethylene can also be present in a completely fibrillated form.

[0019] The shaping of the powder mixture into a flexible composite layer is usually carried out by rolling, pressing or extrusion. However, combinations of the methods described can also be used.

[0020] Application of the flexible composite layer to the conductive current collector layer is typically performed at a temperature between 60°C and 120°C, preferably 80°C to 100°C.

[0021] The above-described method can be used to manufacture the cathode, ie the cathode can be produced by the above-described method.

[0022] The solid-state battery or lithium battery according to the present invention includes a cathode unit having the aforementioned characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the present invention are shown in the accompanying drawings and will be referred to below. Figures 1 to 10 To explain.

[0024] The accompanying drawings show:

[0025] Figure 1 It is a side view of a cathode;

[0026] Figure 2 To correspond to Figure 1 a cathode having a solid electrolyte membrane;

[0027] Figure 3 For Figure 1 a corresponding cathode having a solid electrolyte membrane and an anode;

[0028] Figure 4 This is a scanning electron micrograph of the dry film of the composite material;

[0029] Figure 5 is a discharge voltage profile of a test cell having a binder content of 0% by weight;

[0030] Figure 6 To correspond to Figure 5 Discharge voltage profile of a test cell having a binder content of 0.1% by weight;

[0031] Figure 7 To correspond to Figure 5 Discharge voltage profile of a test cell having a binder content of 0.3% by weight;

[0032] Figure 8 To correspond to Figure 5 Discharge voltage profile of a test cell having a binder content of 0.7% by weight;

[0033] Figure 9 To correspond to Figure 5 The discharge voltage profile of the test cell having a binder content of 1% by weight; and

[0034] Figure 10 Nyquist plot of the internal resistance of the test battery. DETAILED DESCRIPTION

[0035] exist Figure 1 The schematic side view of the shows a current collector layer 1 composed of aluminum as a base film or carrier film, which carries a first electrode 2 forming the cathode unit. In the illustrated embodiment, the first electrode 2 is formed from a composite material in powder form. This composite material comprises 85% by weight of lithium nickel manganese cobalt salt (NCM), 13% by weight of a solid electrolyte material (e.g., lithium Li2S-P2S5), 2% by weight of conductive carbon nanotubes (as a conductive additive), and 0.1% by weight of polytetrafluoroethylene (PTFE) (as a binder). The binder content is relative to the total mass, with a ratio of NCM:C:SE of 85::2:13 (SE designates the solid electrolyte as its abbreviation). The resulting composite material is powdery, dry, and solvent-free, but not castable. This composite material can be incorporated into a mortar. During this process, shear forces are applied to the mixture or powder mixture forming the composite material, influencing the formation of fibrils along the force vector. In a subsequent step, the composite material is rolled onto a sheet using rollers to the desired layer thickness and laminated onto the carrier film 1. The carrier film 1 has a thickness of less than 20 μm and may have a carbon primer. The cathode unit is finally formed by punching or laser cutting.

[0036] The composite material can also be added directly to the calender gap as a powder mixture or as a bulk material without solvent additives. As described in German patent application DE 10 2017 208 220, the two calender rollers use different rotational speeds, for example in a ratio of 10:9 to 10:4. A ratio of rotational speeds of 2:1, for example 10 mm / s:5 mm / s or 20 mm / s:10 mm / s, is advantageous. As a result, a shear force is exerted on the composite material in the gap, which influences the formation of the fibrils in the direction of travel of the rollers. A layer is formed on the rapidly rotating roller. In a subsequent step, this layer is laminated to the base film 1 and is finally shaped by punching or laser cutting. Furthermore, the formation of the film in the calender gap has made it possible to achieve a very high degree of compaction of the layers involved during film formation. It is important that the particle size distribution of the powder materials used for the composite material are coordinated with one another in order to fill the voids of the larger particles as efficiently as possible with smaller particles and to keep the porosity low. The density of the thin film before pressing is therefore 1.7-1.9 g / cm 3 , corresponding to a porosity of 50% to 55%. After pressing or compaction, the density is typically 3.5 g / cm 3 , with a porosity of a maximum of 10%, which can approach the ideal value of 0%.

[0037] The processing at high temperatures between 60°C and 100°C takes place in an advantageous manner, as a result of which the required binder content or adhesive content is significantly reduced. The cathode unit thus obtained has the layer sequence base film 1 - first electrode 2. The first electrode 2 typically has the following structure in its composition: cathode material 60% to 99% by weight, solid electrolyte material 13% to 35% by weight, conductive additive 2% to 5% by weight, with the adhesive (polytetrafluoroethylene) accounting for 0.1% to 1% of the total mass. The pressing mentioned at the outset is typically carried out as the last process step. The process described above is carried out at a pressure of 290 MPa to 450 MPa, preferably 300 MPa, in order to ensure the flow capability of the electrolyte. All process steps involving the solid electrolyte material are preferably carried out under a protective gas, for example an inert gas, preferably argon, nitrogen, or dry air with a dew point of less than -50°C.

[0038] The cathode unit of the carrier film 1 and the first electrode 2 is shown in Figure 1 corresponding to Figure 2 , the solid electrolyte film 3 is arranged in direct contact, i.e. touching contact, on the side or surface opposite the first electrode 2, the carrier film 1 being attached directly to the first electrode 2 as a current collector layer. When the carrier film 1 and the first electrode 2 are arranged on top of one another, i.e. have the same dimensions apart from their respective thicknesses, the solid electrolyte film 3 is wider than the first electrode 2. Identical reference numerals are used for repeated elements in the present and the following figures.

[0039] Figure 3 The solid-state battery is shown in the view corresponding to Figure 1 and Figure 2 In addition to the structure shown in Figure 2 , the anode unit is connected to the side arranged opposite to one side of the solid electrolyte film 3. The anode unit is formed by the second electrode 4 and the second substrate film 5 as the second current collector layer, which are in direct contact with each other in this order. The second electrode 4 is in direct contact with the solid electrolyte film. The solid electrolyte film, the second electrode 4 and the second carrier film 5 are arranged in a vertical alignment with each other, wherein the second carrier film 5 has the smallest thickness, the second electrode 4 has the largest thickness, and the thickness of the solid electrolyte film 3 is between the thicknesses of the second electrode 4 and the second carrier film 5. The capacitance is usually coordinated with each other, whereby the thicknesses are generated. For example, the thickness of the first electrode can be 100 pm, the second electrode as anode for lithium, for example, at most 10 pm. The thicknesses of the first carrier film 1 and the second carrier film 5 can also be the same. The thickness of the first electrode 2 is greater than the thickness of the solid electrolyte film 3, which in turn is greater than the thickness of the first carrier film 1. The battery electrodes for primary and secondary batteries can be manufactured with the described method, preferably with lithium-ion compounds or sodium-ion compounds, solid-state supercapacitor electrodes, or layer hygro- or sol-gel sensitive materials, i.e. various sulfide electrolytes.

[0040] Figure 4 A scanning electron microscope photograph (SEM photograph) of a dry film consisting of NCM, solid electrolyte (SE), carbon nanofiber (CNF) in a mass ratio of 85:13:2, 0.3% polytetrafluoroethylene (PTFE) of the total mass is shown.

[0041] Figures 5 to 9 The individual discharge voltage profiles of the test batteries of the solid-state batteries are shown. Here, the corresponding voltages are entered on the capacitance. In Figure 5 , the proportion of polytetrafluoroethylene is 0% by weight; in Figure 6 , the proportion is 0.1% by weight; in Figure 7 , the proportion is 0.3% by weight; in Figure 8 , the proportion is 0.7% by weight; in Figure 10 , the proportion is 1% by weight.

[0042] In Figure 10 , an impedance measurement is shown in a Nyquist plot, in which the imaginary part is entered on the real part. The measurement curves show that the internal resistance of a test battery with 0.1%, 0.3% and 1% polytetrafluoroethylene by weight of the binder fraction increases with increasing proportion of polytetrafluoroethylene.

[0043] Only the embodiments disclosed in the embodiments may be combined with one another and claimed individually.

Claims

1. A cathode unit for a solid-state battery, comprising a layer consisting of a composite material comprising an electrode material, a solid electrolyte material, a conductive additive and polytetrafluoroethylene as a binder, characterized in that The composite material is free of solvent and comprises less than 1% by weight of polytetrafluoroethylene; and The polytetrafluoroethylene is at least partially in the form of fibrillar polytetrafluoroethylene, wherein the layer composed of the composite material is a flexible composite layer, which refers to a composite layer that can be bent to a radius of 90 μm to 100 μm at room temperature and can be bent to 180° without breaking.

2. The cathode unit according to claim 1, wherein The electrode materials include sulfur, lithium sulfide, metal lithium oxide, metal sodium oxide, LiCoO2, LiNiO2, LiNi 1-x Co x O2, LiFePO4, LiMnO2, LiMn2O4, Li2Mn3NiO8, LiNi x Co y Mn z O2、LiNi x Co y Al z O2 (where x+y+z=1), Li4Ti5O 12 、Li2FeSiO4、Na2S、Na x MnO2, Na3V2(PO4)3, NaFePO4, Na2FePO4F, NaNiMnO2, Na2TiO7 and / or Na-Ti2(PO4)3 or mixtures thereof.

3. The cathode unit according to claim 1, wherein The solid electrolyte material includes materials composed of the following systems: Li2S-GeS2, Li2S-B2S3, Li6PS5CI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-Lil, Li2S-SiS2-LiBr, Li2S-SiS2-LiCI, Li2S-SiS2-B2S3-Lil, Li2S-SiS2-P2S5-Lil, Li2S-P2S5-Z m S n (where m and n are integers, M is P), Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (wherein p and q are integers, and M is selected from P, Si or Ge), Na2S-P2S5, Na2S-GeS2, Na2S-B2S3, Na6PS5CI, Na2S-SiS2, Na2S-P2S5-NaX (X=CI, Br, I), Na2S-P2S5-Na2O, Na2S-P2S5-Na2O-Nal, Na2S-SiS2-Nal, Na2S-SiS2-NaBr, Na2S-SiS2-NaCI, Na2S-SiS2-B2S3-Nal, Na2S-SiS2-P2S5-Nal, Na2S-P2S5-Z m S n (wherein m and n are integers, M is selected from P, Si or Ge), Na2S-SiS2-Na3PO4, Na2S-SiS2-Na p MO q (wherein, p and q are integers, and M is selected from P, Si or Ge) or a mixture thereof.

4. The cathode unit according to claim 1, wherein The solid electrolyte material includes Li6PS5CI-based and / or Na6PS5CI-based materials.

5. The cathode unit according to claim 1, wherein The flexible composite layer is formed by pressing a powder mixture consisting of a composite material under a pressure of 290 MPa to 450 MPa into the flexible composite layer.

6. The cathode unit according to claim 1, wherein: The cathode unit includes a current collector comprising or made of aluminum, the current collector having a primer layer.

7. The cathode unit according to claim 6, characterized in that The flexible composite layer is applied to the conductive current collector at a temperature of 60°C to 120°C.

8. The cathode unit according to claim 6, characterized in that The cathode unit includes a solid electrolyte membrane in close contact with a first surface of the flexible composite layer, the first surface being opposite to a second surface of the flexible composite layer, a conductive current collector being attached to the second surface of the flexible composite layer, the conductive current collector and the flexible composite layer having the same dimensions except for their respective thicknesses, and the solid electrolyte membrane being wider than the flexible composite layer and the conductive current collector.

9. A solid-state battery comprising the cathode unit according to claim 1.

10. A method of manufacturing a cathode unit for a solid-state battery, comprising: A powder mixture is prepared from an electrode material, a solid electrolyte material, a conductive additive, and polytetrafluoroethylene as a binder, wherein the powder mixture does not contain a solvent and includes less than 1% by weight of polytetrafluoroethylene; forming at least partially fibrillated polytetrafluoroethylene in the powder mixture by applying shear forces to the powder mixture; and The powder mixture is formed into a flexible composite layer, wherein the flexible composite layer refers to a composite layer that can be bent to a radius of 90 μm to 100 μm at room temperature and can be bent to 180° without cracking.

11. The method according to claim 10, characterized in that The solid electrolyte material includes Li6PS5CI-based and / or Na6PS5CI-based materials.

12. The method according to claim 10, characterized in that The powder mixture is formed into the flexible composite layer by pressing it at a pressure of 290 MPa to 450 MPa.

13. The method according to claim 10, characterized in that The flexible composite layer is applied to an electrically conductive current collector comprising or consisting of aluminum, wherein the current collector has a primer layer.

14. The method according to claim 13, characterized in that The flexible composite layer is applied to the conductive current collector at a temperature of 60°C to 120°C.

15. The method according to claim 13, characterized in that A solid electrolyte membrane is closely attached to the first surface of the flexible composite layer, the first surface is opposite to the second surface of the flexible composite layer, a conductive current collector is attached to the second surface of the flexible composite layer, the conductive current collector and the flexible composite layer have the same size except for their respective thicknesses, and the solid electrolyte membrane is wider than the flexible composite layer and the conductive current collector.

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