Electrode tabs and methods of making and using the same

Abstract

The present application relates to electrode sheet and its preparation method and application. The method comprises the following steps: mixing electrode active material, conductive agent and solid electrolyte, preparing at least two kinds of mixed dry materials, the D50 particle size of the solid electrolyte in the at least two kinds of mixed dry materials is different; on at least one surface of the current collector, sequentially carrying out multiple coating and hot roller rolling treatment, each coating comprises synchronously coating solvent and one kind of mixed dry material according to mass ratio 1:(20-40), wherein, in the direction away from the surface of the current collector side, the D50 particle size of the solid electrolyte in each coating mixed dry material is gradiently increased; after each coating, the solvent is removed by hot roller rolling treatment, the electrode active layer is formed on the surface of the current collector, and the current collector comprises at least two electrode active layers. The method can reduce the porosity of the electrode sheet, improve the compaction density, and when applied to the battery, the cycle performance of the battery can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to an electrode sheet, its preparation method, and its application. Background Technology

[0002] All-solid-state batteries use non-flammable solid electrolytes instead of the flammable organic liquid electrolytes found in traditional batteries, significantly improving the safety of rechargeable batteries. While enhancing safety, solid-state batteries can better accommodate high-energy positive and negative electrode materials and reduce system weight, thus achieving a simultaneous increase in energy density. All-solid-state batteries are the next-generation technology closest to industrialization, a consensus already reached by industry and the scientific community.

[0003] In traditional liquid lithium-ion batteries, the porosity of the electrodes is a crucial parameter in the design and manufacturing process, closely related to the battery's rate performance, cycle performance, internal resistance, and electrolyte injection volume. Excessive electrode porosity leads to a poor conductive network and increased internal resistance; conversely, insufficient porosity results in reduced electrolyte absorption, negatively impacting rate and cycle performance. Therefore, traditional liquid lithium-ion battery electrodes require a certain porosity (approximately 20%) to ensure electrolyte penetration and the formation of ion pathways.

[0004] Unlike liquid lithium-ion batteries, solid-state batteries utilize a solid electrolyte for ion transport. Therefore, the electrodes in all-solid-state batteries require the lowest possible porosity to ensure close contact between the active material and the solid electrolyte, reducing interfacial resistance. Furthermore, achieving low porosity also necessitates increasing the electrode's compaction density, thereby enhancing the energy density of the solid-state battery.

[0005] Currently, methods for reducing the porosity of solid-state battery electrodes typically involve using double-roller pressing equipment, isostatic pressing equipment, or other external pressure equipment. However, the pressure values ​​of these rolling pressing devices are limited and cannot significantly reduce the porosity of the electrodes. Furthermore, excessive pressure can cause problems such as electrode wrinkling or breakage of active material particles, thereby reducing the material's specific capacity. How to provide an electrode with low porosity and high compaction density to improve the cycle performance of solid-state batteries has been a persistent challenge for researchers. Summary of the Invention

[0006] Based on this, the present invention provides an electrode sheet with low porosity and high pressure density, which can be applied in the field of secondary batteries to improve the cycle performance of batteries, especially solid-state batteries.

[0007] The technical solution is as follows:

[0008] A method for preparing an electrode sheet includes the following steps:

[0009] A mixed electrode active material, a conductive agent, and a solid electrolyte are used to prepare at least two mixed dry materials, wherein the solid electrolyte in the at least two mixed dry materials has a different D50 particle size;

[0010] On at least one surface of the current collector, multiple coating and hot roller pressing processes are performed sequentially. Each coating process includes simultaneous coating of a solvent and a mixed dry material at a mass ratio of 1:(20-40), wherein the D50 particle size of the solid electrolyte in the mixed dry material of each coating increases in a gradient along the direction away from the surface of the current collector.

[0011] After each coating, the solvent is removed by hot roller pressing, and an electrode active layer is formed on the surface of the current collector. The current collector includes at least two electrode active layers.

[0012] In one embodiment, the particle size of the electrode active material in each mixed dry material is the same.

[0013] In one embodiment, in each mixed dry material, the particle size ratio of the electrode active material and the solid electrolyte is independently 1:(0.01~30), and none of them are 1:1.

[0014] In one embodiment, the electrode active material is a positive electrode active material.

[0015] In one embodiment, the positive electrode active material is selected from one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and lithium-rich manganese-based materials.

[0016] In one embodiment, the particle size of the positive electrode active material is 1 μm to 40 μm.

[0017] In one embodiment, the negative electrode active material is selected from one or more of graphite, silicon-carbon composite materials, and lithium titanate.

[0018] In one embodiment, the particle size of the negative electrode active material is 3 μm to 38 μm;

[0019] In one embodiment, the solid electrolyte is selected from one or more of sulfide solid electrolytes, oxide solid electrolytes, and polymer solid electrolytes.

[0020] In one embodiment, the particle size of the solid electrolyte is 0.01 μm to 30 μm.

[0021] In one embodiment, the conductive agent is selected from one or more of acetylene black, fumed carbon fiber, carbon nanotubes, carbon nanofibers, and graphene.

[0022] In one embodiment, the D50 particle size difference of the solid electrolytes in adjacent electrode active layers is 0.01 μm to 5 μm.

[0023] In one embodiment, the mass ratio of the electrode active material, the conductive agent and the solid electrolyte in each mixed dry material is independently (60-80):(0.1-2):(20-40).

[0024] In one embodiment, the solvent has a boiling point of 50°C to 200°C.

[0025] In one embodiment, the solvent is selected from one or a mixture of several of anhydrous ethanol, dichloromethane, anisole, cyclohexane, acrylonitrile, n-hexane, dimethyl disulfide, or solvent oils with a boiling point of 60°C to 200°C.

[0026] In one embodiment, the temperature of the hot roller pressing process is more than 5°C higher than the boiling point of the solvent.

[0027] In one embodiment, the pressure of the hot roller pressing process is 0.10 MPa to 0.50 MPa.

[0028] In one embodiment, in the multiple hot roll pressing processes, the pressure of the first hot roll pressing process is greater than the pressure of the subsequent hot roll pressing processes.

[0029] In one embodiment, the pressure of the first hot roll pressing treatment is 0.20 MPa to 0.50 MPa, and the pressure of the second and subsequent hot roll pressing treatments is 0.10 MPa to 0.40 MPa, each independently.

[0030] In one embodiment, the mixed dry material and solvent are simultaneously coated onto the surface of the current collector by spraying.

[0031] The present invention also provides an electrode sheet, which is prepared by the electrode sheet preparation method described above.

[0032] The present invention also provides a solid-state battery comprising the electrode plates described above.

[0033] The present invention has the following beneficial effects:

[0034] The method for preparing electrode sheets provided by the present invention mainly includes preparing at least two mixed dry materials containing electrode active materials, conductive agents and solid electrolytes, wherein the solid electrolytes contained in the different mixed dry materials have different D50 particle sizes, and then performing multiple coating and hot roller pressing treatments on at least one surface of a current collector. Each coating includes simultaneously coating a solvent and a mixed dry material at a mass ratio of 1:(20-40), wherein the D50 particle size of the solid electrolyte in each coated mixed dry material increases in a gradient along the direction away from the surface of the current collector, and removing the solvent by hot roller pressing after each coating, thereby forming at least two electrode active layers on the surface of the current collector.

[0035] This method ensures that the electrode active material (active substance), solid electrolyte, and conductive agent are uniformly dispersed, which is beneficial for the uniform and compact arrangement of particles of different sizes in the electrode sheet. Furthermore, with the aid of solvent lubrication, inter-particle friction is greatly reduced, making it easier to compact with the same external force, reducing porosity, lowering grain boundary resistance between particles, providing sufficient ion transport channels, and increasing the compaction density of the electrode sheet. At the same thickness, this increases the active material content and improves battery cycle performance. Moreover, along the direction away from the current collector, the D50 particle size of the solid electrolyte in the electrode active layer increases in a gradient, giving the all-solid-state battery electrode sheet prepared by this method a gradient ionic conductivity characteristic. That is, the ionic conductivity of the electrode material layer near the current collector is lower than that away from the current collector. This structure has good ion transport capability and can improve the cycle life of the all-solid-state battery. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of an electrode sheet prepared according to one embodiment of the present invention;

[0037] Figure 2 This is a diagram of the apparatus used in one embodiment of the present invention. Detailed Implementation

[0038] To facilitate understanding of the present invention, a more comprehensive description is provided below, along with preferred embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] In this invention, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0041] This invention only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range that is not explicitly stated; and any lower limit can be combined with other lower limits to form a range that is not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range that is not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower limit or upper limit and can be combined with any other point or single value or with other lower limits or upper limits to form a range that is not explicitly stated.

[0042] In this invention, unless otherwise specified, all steps can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. For example, the multiple coating and hot roller pressing treatment in this invention may involve coating once and hot roller pressing once, or multiple coatings followed by hot roller pressing.

[0043] In this invention, if the unit of a data range is only followed by the right endpoint, it indicates that the units of the left and right endpoints are the same. For example, 0.5~1.0μm means that the units of the left endpoint "0.5" and the right endpoint "1.0" are both μm (micrometers), and 15~30℃ means that the units of the left endpoint "15" and the right endpoint "30" are both ℃ (degrees Celsius).

[0044] In this invention, "several" means at least two, such as two, three, etc., unless otherwise explicitly specified. "Multiple" means at least twice, such as twice, three, etc., unless otherwise explicitly specified. In this invention, "a number" means at least one, such as one, two, etc.

[0045] Unless otherwise stated, a singular term may include a plural term and should not be understood as having a quantity of one.

[0046] Furthermore, the accompanying drawings are not drawn to a 1:1 scale, and the relative dimensions of the elements are shown in the drawings only as examples to facilitate understanding of the invention, but are not necessarily drawn to actual scale. The scales in the drawings do not constitute a limitation on the invention.

[0047] This invention provides an electrode sheet with low porosity and high compaction density, which can be applied to the field of secondary batteries, especially solid-state batteries.

[0048] The technical solution is as follows:

[0049] This invention provides an electrode sheet (see reference). Figure 1 The preparation method of ) includes the following steps:

[0050] A mixed electrode active material, a conductive agent, and a solid electrolyte are used to prepare at least two mixed dry materials, wherein the solid electrolyte in the at least two mixed dry materials has a different D50 particle size;

[0051] On at least one surface of the current collector, multiple coating and hot roller pressing processes are performed sequentially. Each coating involves simultaneously coating a solvent and a mixed dry material at a mass ratio of 1:(20-40), wherein the coating is performed in a direction away from the surface of the current collector (e.g., ...). Figure 1 (Arrow direction) The D50 particle size of the solid electrolyte in each coated dry mixture increases in a gradient.

[0052] After each coating, the solvent is removed by hot roller pressing, and an electrode active layer is formed on the surface of the current collector. The current collector includes at least two electrode active layers.

[0053] This method ensures uniform dispersion of active materials, solid electrolytes, and conductive agents, facilitating a uniform and compact arrangement of particles of varying sizes within the electrode. Furthermore, solvent lubrication significantly reduces inter-particle friction, making compaction easier with the same external force, reducing porosity, lowering grain boundary resistance, providing ample ion transport channels, and increasing the compaction density of the electrode sheet. At the same thickness, this increases the active material content and improves battery cycle performance. Simultaneously, the all-solid-state battery electrode sheet prepared by this method exhibits gradient ionic conductivity, meaning the ionic conductivity of the electrode material layer closer to the current collector is lower than that further away from the current collector. This structure provides excellent ion transport capabilities, improving the cycle life of the all-solid-state battery.

[0054] Figure 1 This is a schematic diagram of the structure of an electrode sheet obtained according to one embodiment of the present invention, wherein C0 is a current collector, C1 is a first electrode active layer, C2 is a second electrode active layer, and C3 is a third electrode active layer. C1, C2, and C3 are all on the same side surface of the current collector and are arranged along the direction away from the side surface of the current collector, i.e. Figure 1 The direction indicated by the middle arrow shows that the D50 particle size of the solid electrolyte in the electrode active layer increases in a gradient, that is, the D50 of the solid electrolyte in C1 is the smallest, the D50 of the solid electrolyte in C2 is larger, and the D50 of the solid electrolyte in C3 is the largest.

[0055] The following is a detailed description of the electrode sheet provided by the present invention:

[0056] S10 mixes electrode active material, conductive agent and solid electrolyte to prepare at least two mixed dry materials, wherein the solid electrolyte in the at least two mixed dry materials has a different D50 particle size.

[0057] In one embodiment, the electrode active material is a positive electrode active material.

[0058] In one embodiment, the positive electrode active material is selected from one or more of lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese aluminum oxide (NCMA), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium iron phosphate (LFP), or lithium-rich manganese-based materials. Preferably, the positive electrode active material is lithium nickel cobalt manganese oxide (NCM).

[0059] In one embodiment, the particle size of the positive electrode active material is 1 μm to 40 μm, including but not limited to 1 μm, 2 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 36 μm, 38 μm and 40 μm, preferably 3 μm to 15 μm.

[0060] In one embodiment, the electrode active material is a negative electrode active material.

[0061] In one embodiment, the negative electrode active material is selected from one or more of graphite, silicon-carbon composite materials, and lithium titanate. Preferably, the negative electrode active material is graphite.

[0062] In one embodiment, the particle size of the negative electrode active material is 3μm to 38μm, including but not limited to 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 25μm, 30μm, 35μm, 36μm and 38μm, preferably 10μm to 25μm.

[0063] In one embodiment, the conductive agent is selected from one or more of acetylene black, fumed carbon fiber (VGCF), carbon nanotubes, carbon nanofibers, and graphene.

[0064] In one embodiment, the solid electrolyte is selected from one or more of sulfide solid electrolytes, oxide solid electrolytes, and polymer solid electrolytes. Preferably, the solid electrolyte is a sulfide solid electrolyte, selected from one or two of lithium germanium phosphorus sulfide (LGPS) and lithium phosphorus sulfide chlorine (LPSC).

[0065] In one embodiment, the particle size of the solid electrolyte is 0.01 μm to 30 μm, including but not limited to 0.01 μm, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 25 μm, 26 μm, 28 μm and 30 μm, preferably 0.5 μm to 15 μm.

[0066] In one embodiment, the D50 particle size difference of the solid electrolyte in adjacent electrode active layers is 0.01 μm to 5 μm, which is beneficial for establishing low porosity or high compaction of the electrode sheet. Understandably, the D50 particle size difference of the solid electrolyte in adjacent electrode active layers includes, but is not limited to, 0.01 μm, 0.02 μm, 0.04 μm, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, and 5 μm.

[0067] Understandably, sulfide solid electrolytes of different particle sizes can be obtained by sieving.

[0068] In one embodiment, the electrode active material in each mixed dry material has the same particle size, while the solid electrolyte in different mixed dry materials has different D50 particle sizes. After coating and hot rolling treatment, the particles are aligned along the direction away from the surface of the current collector (e.g., ...). Figure 1 (Arrow direction) The D50 particle size of the solid electrolyte in the electrode active layer increases in a gradient. (1) The solid electrolyte particles near the current collector are small and can form a dense layer on the surface of the current collector. The particle size increases sequentially along the direction away from the current collector. Under the action of external pressure, a high-pressure solid electrode can be formed based on the bottom dense layer. (2) The smaller the solid electrolyte particle size, the smaller the ionic conductivity. That is, the ionic conductivity of the mixture near the current collector is lower than that of the mixture away from the current collector. As the bottom ions gradually migrate upward, the upper ions increase. Higher and higher ionic conductivity is required to migrate as many ions as possible, thus improving the electrode performance.

[0069] In one embodiment, the particle size ratio of the electrode active material and the solid electrolyte in each mixed dry material is independently 1:(0.01~30), and none of them are 1:1, so that the electrode sheet is more likely to form a high-pressure solid electrode sheet under the action of external force. Understandably, the particle size ratio of the electrode active material to the solid electrolyte is 1:0.01, 1:0.02, 1:0.04, 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.1, 1:1.2, 1:1.5, 1:1.6, 1:2, 1:2.4, 1:3, 1:4, 1:5, 1:6, 1:8, 1:10, 1:15, 1:20, 1:25, 1:28, and 1:30, preferably 1:(0.04 to 2).

[0070] In one embodiment, the mass ratio of the electrode active material, the conductive agent and the solid electrolyte in each mixed dry material is independently (60-80):(0.1-2):(20-40).

[0071] Preferably, in this invention, the electrode active material, conductive agent, and solid electrolyte are mixed as dry powder. Compared to the wet homogenization process, this method is simpler, requires no solvents, reduces solvent involvement during electrode processing, avoids the decrease in ionic conductivity caused by solvent evaporation, and shortens the drying process, thus improving production efficiency and safety. Optionally, the mixing method includes high-speed shearing, ball milling, or high-energy roller milling, all of which can achieve uniform mixing.

[0072] S20 involves sequentially coating and hot roller pressing on at least one surface of the current collector, wherein each coating includes simultaneously coating a solvent and a mixed dry material at a mass ratio of 1:(20-40), wherein the D50 particle size of the solid electrolyte in the mixed dry material coated in each coating increases in a gradient along the direction away from the surface of the current collector.

[0073] After each coating, the solvent is removed by hot roller pressing, and an electrode active layer is formed on the surface of the current collector. The current collector includes at least two electrode active layers.

[0074] Understandably, the current collector has two surfaces. The present invention coats the mixed dry material and solvent onto at least one surface of the current collector, including coating onto one side surface of the current collector and preparing an electrode active layer only on one side surface of the current collector, and coating onto both sides surface of the current collector and preparing an electrode active layer on both sides surface of the current collector.

[0075] In this invention, the mixed dry material and solvent are simultaneously coated onto the surface of the current collector (i.e., starting and ending simultaneously). Simultaneous coating of the mixed dry material and solvent has two advantages: firstly, it promotes micro-wetting of the solvent within the mixed dry material, ensuring that the mixed dry material achieves high density under the lubricating effect of the solvent during rolling, thereby obtaining a low-porosity, high-compact electrode sheet; secondly, coating the mixed dry material first and then the solvent, or vice versa, may result in agglomeration of the mixed dry material upon contact with the solvent.

[0076] In one embodiment, the mixed dry material is coated onto the same side surface of the current collector by spraying. Spraying the mixed dry material evenly onto the electrode surface not only achieves tight bonding between particles, greatly improving interfacial contact and reducing interfacial impedance, but also, through multiple layer-by-layer spraying, ensures close contact between particles, enhances density, and improves ionic conductivity. Furthermore, in this invention, the mixed dry materials are sprayed onto the current collector layer by layer according to the solid electrolyte D50 particle size from small to large. This spraying method has the following advantages: (1) The solid electrolyte particles close to the current collector are small, which can form a dense layer on the surface of the current collector. The particle size increases in the direction away from the current collector, and a high-pressure solid electrode can be formed based on the bottom dense layer under the action of external pressure; (2) The smaller the solid electrolyte particle size, the lower the ionic conductivity. That is, the ionic conductivity of the mixed materials close to the current collector is lower than that of the mixed materials away from the current collector. As the bottom ions gradually migrate upward, the upper ions increase, and higher and higher ionic conductivity is required to migrate as many ions as possible. This method of increasing ionic conductivity layer by layer can meet such requirements, ensure smooth and efficient ion migration, and achieve the same discharge effect, thereby improving the battery energy density.

[0077] In one embodiment, the solvent is applied to the same side surface of the current collector by spraying. Spraying the solvent ensures sufficient contact between the solvent and the particles in the mixture, achieving a micro-wetting effect. Under the lubrication of the solvent, the mixed dry materials are compacted by external force, resulting in electrode sheets with lower porosity. Furthermore, spraying allows for control of the solvent flow rate. Based on these advantages, the cycle life of solid-state batteries (especially sulfide solid-state batteries) can be optimized. Understandably, the number of spraying times N depends on the type of mixed dry materials.

[0078] In this invention, the spraying of the mixed dry material and the solvent are preferably performed simultaneously. This ensures that the mixed dry material is completely wetted by the solvent, which greatly reduces the friction between particles. The resulting electrode sheet, under the lubrication of the solvent and under external rolling pressure, can approach the minimum porosity to a greater extent, improving compaction, reducing grain boundary resistance, and thus improving battery cycle performance. Understandably, the spraying speed depends on the mass of the mixed dry material and the solvent.

[0079] Understandably, in preparing each electrode active layer, the mass ratio of the mixed dry material and solvent is independently (20-40):1. A small amount of solvent is added, which does not react with the electrode active material, conductive agent, and solid electrolyte. During coating, the solvent adheres to the surface of the solid particles, acting as a lubricant between them, greatly reducing the "solid-solid" friction between particles. Furthermore, the solvent does not form additional pores during the hot roller evaporation process, and its evaporation during rolling has almost no impact on electrode compaction. In addition, the solvent can be directly removed after hot roller pressing, eliminating the need for electrode drying, making the operation safe, simple, and efficient. However, the amount of solvent in this invention cannot be too small. If too little is used, the solvent only acts as a lubricant between a small portion of the electrode particles; if too much solvent is used, the mixture of the dry material and solvent during spraying will create a slurry effect, causing sticking to the rollers during rolling, thus affecting the electrode porosity and battery cycle performance. Understandably, the mass ratio of the mixed dry material and solvent used in this invention includes, but is not limited to, 20:1, 25:1, 30:1, 35:1 or 40:1, preferably (25-30):1.

[0080] In one embodiment, the solvent has a boiling point of 50°C to 200°C.

[0081] Furthermore, the solvent is selected from one or a mixture of several of the following: anhydrous ethanol, dichloromethane, anisole, cyclohexane, acrylonitrile, n-hexane, dimethyl disulfide, or solvent oil with a boiling point of 60°C to 200°C. The solvent oil is a mixture of hydrocarbons with various structures and a boiling point of 60°C to 200°C.

[0082] Preferably, the solvent is a solvent oil with a boiling point of 80°C to 120°C. On the one hand, the solvent oil does not react with the electrode active material, solid electrolyte, or conductive agent. On the other hand, a reasonable boiling point range helps the solvent to micro-wet the surface of the electrode layer particles and play a lubricating role between the particles. If the boiling point is too low, the solvent will evaporate during the coating (such as spraying) process, resulting in insufficient solvent usage. If the boiling point is too high, it will affect the temperature of the hot roller and the solvent cannot be completely removed by the hot roller alone, reducing production efficiency.

[0083] In particular, this invention employs a hot roller pressing method, which can directly remove the solvent without the need for electrode drying. That is, hot roller pressing can both compact the electrode and remove the solvent. Understandably, in this invention, the temperature of the hot roller needs to be matched with the boiling point of the solvent. Too high a temperature is detrimental to operational safety and increases production costs, while too low a temperature will not achieve the desired solvent removal effect.

[0084] In one embodiment, the solvent has a boiling point of 50°C to 200°C, the temperature of the hot roller pressing process is at least 5°C higher than the boiling point of the solvent, and the pressure is 0.10 MPa to 0.50 MPa. This effectively compacts the electrode, reduces porosity, and improves battery performance, while also directly removing the solvent.

[0085] Understandably, the temperature of the hot roller pressing process is 5°C or higher than the boiling point of the solvent, including but not limited to 5°C, 5.5°C, 6°C, 6.5°C, 7°C, 7.5°C, 8°C, 8.5°C, 9°C, 9.5°C, 10°C, 15°C, 20°C, and 25°C higher. Optionally, for a specific solvent, the temperature of the hot roller pressing process includes but is not limited to 55°C, 65°C, 70°C, 75°C, 85°C, 90°C, 95°C, 100°C, 105°C, 115°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 205°C, 210°C, and 220°C. The pressure of the hot roller pressing process is 0.10 MPa to 0.50 MPa, including but not limited to 0.10 MPa, 0.15 MPa, 0.20 MPa, 0.25 MPa, 0.30 MPa, 0.35 MPa, 0.40 MPa, 0.45 MPa and 0.50 MPa.

[0086] Specifically, the hot roller pressing process described in this invention is a single-coat pressing followed by a single-coat pressing. In this invention, "single-coat pressing followed by a single-coat pressing" refers to applying a mixed dry material to the surface of the current collector, then pressing it, and then applying and pressing the next mixed dry material; that is, pressing and curing are performed after each coating. "Multiple-coat pressing followed by a single-coat pressing," on the other hand, refers to spraying and coating multiple mixtures layer by layer, and then pressing them all at once; that is, pressing is performed only after all coatings are completed. Compared to multiple coatings followed by pressing, single-coat pressing followed by a single-coat pressing is more beneficial for reducing electrode porosity and improving battery cycle performance.

[0087] In one embodiment, the hot roller pressing process is a single-coating followed by roller pressing. Furthermore, a single-coating followed by roller pressing and curing method is adopted, meaning that roller pressing and curing are performed after each coating process. This ensures that each single-layer active electrode in the electrode sheet is sufficiently dense, resulting in an electrode sheet with low porosity and high compaction characteristics. This provides abundant and sufficient channels for ion transport, greatly improving the cycle performance of the battery.

[0088] Understandably, in this invention, after each coating process, a hot roller pressing treatment is performed, forming at least two electrode active layers on the surface of the current collector. Therefore, the hot roller pressing treatment is performed more than twice, including but not limited to two, three, four, five, or six times. Further, in these multiple hot roller pressing treatments, the pressure of the first hot roller pressing treatment is greater than the pressure of subsequent hot roller pressing treatments. Even further, the pressure of the first hot roller pressing treatment is 0.20 MPa to 0.50 MPa, and the pressure of the second and subsequent hot roller pressing treatments is independently 0.10 MPa to 0.40 MPa. Generally, during the rolling process of the electrode sheet, the surface and bottom layers of the electrode sheet experience the largest stress areas. Therefore, this invention selects appropriate pressures for the first and subsequent rolling pressings to prevent excessive stress on the bottom layer of the electrode sheet during non-first rolling pressings, while ensuring the electrode sheet porosity and compaction performance. This further reduces the porosity of the all-solid-state battery electrode sheet and improves its compaction and cycle performance.

[0089] Understandably, the pressure of the first hot roll pressing treatment includes, but is not limited to, 0.20 MPa, 0.25 MPa, 0.30 MPa, 0.35 MPa, 0.40 MPa, 0.45 MPa and 0.50 MPa, and the pressure of the second and subsequent hot roll pressing treatments includes, but is not limited to, 0.10 MPa, 0.15 MPa, 0.20 MPa, 0.25 MPa, 0.30 MPa, 0.35 MPa and 0.40 MPa.

[0090] The present invention also provides an electrode sheet, which is prepared by the electrode sheet preparation method described above. Testing shows that the porosity of the electrode sheet prepared by the present invention is 0.5% to 30%, and the porosity of the electrode sheet prepared in the best-performing embodiment is only 0.5% to 5%, demonstrating excellent performance.

[0091] Figure 2 This is a diagram of an apparatus used in one embodiment of the present invention, including an unwinding device 1, a guiding device 2, a first spraying device 3 (mixed dry material spraying device 3a; solvent spraying device 3b), a first rolling device 4, a thickness measuring device 5, a second spraying device 6 (mixed dry material spraying device 6a; solvent spraying device 6b), a second rolling device 7, a thickness measuring device 8, a guiding device 9, and a winding device 10. It can be understood that the first spraying device 3 and the second spraying device 6 are configured according to the types of mixed dry materials. When there are three types of mixed materials, a third spraying device and a third rolling device are also required between the second thickness measuring device 8 and the winding device 10 to perform layer-by-layer spraying and rolling of multiple mixed dry materials.

[0092] The present invention also provides a solid-state battery comprising the electrode plates described above.

[0093] The present invention will be further described in detail below with reference to specific embodiments.

[0094] Example 1

[0095] This embodiment provides an electrode sheet and its preparation method. Details are as follows:

[0096] Preparation of the positive electrode sheet: The positive electrode material is NCM811 (D50 is 5μm), and the solid electrolyte is LPSC (D50 is 2 / 6 / 10μm respectively). The positive electrode material and solid electrolyte are weighed at a mass ratio of 8:2. The conductive agent is VGCF, which accounts for 1% of the total mass of dry materials. The positive electrode mixture (Z1 / Z2 / Z3) is prepared by ball milling (mass ratio of milling beads to total dry materials is 5:1). The mass ratio of single-layer positive electrode mixture dry materials to solvent (solvent oil with a boiling point of 120℃) is 25:1. The mixture is uniformly sprayed onto aluminum foil in the order of Z1, Z2, Z3. The mass of each layer of mixture is basically consistent. The rolling curing pressure is 0.50MPa, 0.40MPa, and 0.30MPa respectively, and the hot roller temperature is 125℃. The prepared positive electrode sheet has a surface capacity of 3mAh / cm². 2 .

[0097] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet prepared according to Embodiment 1 of the present invention, wherein C0 is the current collector, C1 is the first electrode active layer, C2 is the second electrode active layer, and C3 is the third electrode active layer. C1, C2, and C3 are all on the same side surface of the current collector, and are arranged along the direction away from the side surface of the current collector, i.e. Figure 1 The direction indicated by the middle arrow shows that the D50 particle size of the solid electrolyte in the electrode active layer increases in a gradient, that is, the D50 of the solid electrolyte in C1 is the smallest, the D50 of the solid electrolyte in C2 is larger, and the D50 of the solid electrolyte in C3 is the largest.

[0098] Examples 1-13 and Comparative Examples 1-9 also provide battery electrode sheets and their preparation methods. The battery electrode sheet includes a current collector and an electrode layer located on the surface of the current collector. The electrode layer includes at least two layers. Each electrode layer includes an active material, a solid electrolyte, and a conductive agent. The specific types of materials in the electrode sheet, as well as the D50 of the active material and the solid electrolyte and the solvent ratio, are shown in Table 1. It should be noted that in Comparative Example 5, the mixed dry material is sprayed first and then the solvent is sprayed.

[0099] Table 1

[0100]

[0101]

[0102]

[0103] Battery assembly and testing

[0104] (1) Preparation of electrolyte layer: The sulfide solid electrolyte LPSC and the binder polytetrafluoroethylene PTFE were mixed at a mass ratio of 99.5:0.5 to form a film with an electrolyte layer thickness of 150 μm.

[0105] (2) Battery assembly: Assemble the electrode sheets, electrolyte membrane and lithium indium anode (or cathode) prepared above into a coin cell all-solid-state battery;

[0106] (3) Electrode porosity test: The porosity of the electrode sheet is tested at room temperature using a fully automatic mercury porosimetry pore size analyzer.

[0107] (4) Electrochemical performance test: Cyclic performance test of coin cell all-solid-state battery was carried out; the voltage window for testing positive electrode was 2.4 to 3.65V, and the voltage window for testing negative electrode was -0.595 to 0.9V; the charge and discharge rate conditions were 0.1C / 0.1C; the results of the above test are shown in Table 2.

[0108] Table 2

[0109]

[0110]

[0111] Based on Tables 1 and 2, compared with Comparative Examples 1 to 9, Examples 1 to 13 have lower porosity and better battery cycle performance.

[0112] By comparing Examples 1, 2 and 3, it can be seen that the solvent should preferably be a solvent that does not easily evaporate at room temperature. This can avoid the problem that a large amount of solvent (such as anhydrous ethanol) has evaporated during the spraying process, resulting in a weak lubricating effect on the mixed dry material and making it difficult to further reduce the porosity of the electrode.

[0113] By comparing Examples 1 and 4, Examples 5 and 6, Examples 7 and 8, it can be seen that a reasonable particle size ratio is beneficial to reducing porosity (improving compaction). In particular, if there is a particle size ratio of 1:1 in the mixture, the porosity will increase under the same conditions. The increase in porosity directly affects the cycle life of the battery. Therefore, in order to further improve the compaction of the electrode sheet, the present invention preferably uses a particle size ratio of the electrode active material and the solid electrolyte that is not 1:1.

[0114] By comparing Examples 1 and 9, it can be seen that controlling the D50 particle size difference of the solid electrolyte in the adjacent electrode active layers is beneficial to controlling the electrode porosity and battery cycle performance.

[0115] By comparing Example 1 with Examples 10 and 11, it can be seen that increasing the first curing pressure can avoid the problems of incomplete compaction and high porosity.

[0116] By comparing Example 1 and Comparative Example 1, it can be seen that omitting the use of solvent will result in a larger porosity, which is not conducive to battery cycle performance.

[0117] By comparing Example 1 and Comparative Example 2, it can be seen that using solid electrolytes with the same particle size as the active material and only one particle size will result in a large porosity, which is not conducive to battery cycle performance.

[0118] By comparing Example 1 and Comparative Example 3, it can be seen that it is difficult to achieve low porosity by using only one particle size of solid electrolyte and by obtaining electrode sheets through a single rolling process.

[0119] By comparing Example 1 and Comparative Example 4, it can be seen that using a large-particle-size solid electrolyte near the current collector is not conducive to the formation of a low-porosity electrode, and the smaller ionic conductivity is also not conducive to the migration of the underlying active material, thus affecting the battery energy density.

[0120] By comparing Example 1 and Comparative Example 5, it can be seen that spraying the mixed dry material and solvent separately will cause some active material particles to agglomerate, which will affect the battery cycle performance.

[0121] By comparing Example 1 and Comparative Example 6, it can be seen that if the amount of solvent is too large, a slurry effect will be formed when the dry material is mixed with the solvent. If the solvent does not evaporate in time during rolling, it will cause the roller to stick.

[0122] By comparing Example 1 and Comparative Example 7, it can be seen that when the amount of solvent is too small, the solvent only plays a lubricating role between a small number of electrode particles, and most of the particles still cannot achieve optimal compaction due to inter-particle friction.

[0123] By comparing Example 1 and Comparative Example 8, and Comparative Example 13 and Comparative Example 9, it can be seen that when all the mixed dry materials and solvents are sprayed and then rolled and cured, the porosity is large and the cycle performance is poor.

[0124] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0125] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method of making an electrode tab, characterized by, The method comprises the following steps: mixing an electrode active material, a conductive agent and a solid-state electrolyte to prepare at least two mixed dry materials, the D50 particle size of the solid-state electrolyte in the at least two mixed dry materials being different; on at least one surface of a current collector, sequentially performing multiple coating and hot roller pressing processes, each coating comprising synchronously coating a solvent and one mixed dry material at a mass ratio of 1:(20-40), wherein the D50 particle size of the solid-state electrolyte in the mixed dry material of each coating increases in a gradient in a direction away from the surface of the current collector; after each coating, removing the solvent by hot roller pressing to form an electrode active layer on the surface of the current collector, the current collector comprising at least two electrode active layers.

2. The method of producing an electrode tab according to claim 1, characterized by, The particle size of the electrode active material in each mixed dry material is the same.

3. The method of making an electrode patch of claim 1, wherein, In each mixed dry material, the particle size ratio of the electrode active material to the solid-state electrolyte is independently 1:(0.01-30) and neither is 1:

1.

4. The method of making an electrode panel of claim 3, wherein, The electrode active material is a positive electrode active material or a negative electrode active material.

5. The method of making an electrode patch of claim 4, wherein, The positive electrode active material is selected from one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate and lithium-rich manganese-based materials.

6. The method of making an electrode patch of claim 4, wherein, The negative electrode active material is selected from one or more of graphite, silicon-carbon composite material and lithium titanate.

7. The method of making an electrode patch of claim 4, wherein, The particle size of the positive electrode active material is 1-40 μm.

8. The method of making an electrode patch of claim 4, wherein, The particle size of the negative electrode active material is 3-38 μm.

9. The method of making an electrode patch of claim 3, wherein, The particle size of the solid-state electrolyte is 0.01-30 μm.

10. The method of making an electrode patch of claim 4, wherein, The difference in the D50 particle size of the solid-state electrolyte in adjacent electrode active layers is 0.01-5 μm.

11. The method of making an electrode patch of claim 1, wherein, In each mixed dry material, the mass ratio of the electrode active material, conductive agent and solid-state electrolyte is independently (60-80):(0.1-2):(20-40).

12. The method of producing an electrode sheet according to any one of claims 1 to 11, characterized by, The boiling point of the solvent is 50-200 ℃.

13. The method of producing an electrode sheet according to any one of claims 1 to 11, characterized by, The temperature of the hot roller pressing is higher than the boiling point of the solvent by 5 ℃ or more.

14. The method of producing an electrode sheet according to any one of claims 1 to 11, characterized by, The pressure of the hot roller pressing is 0.10-0.50 MPa.

15. The method of producing an electrode sheet according to any one of claims 1 to 11, characterized by, The solvent is selected from one or more of anhydrous ethanol, dichloromethane, anisole, cyclohexane, acrylonitrile, n-hexane, dimethyl disulfide or solvent oil with a boiling point of 60-200 ℃.

16. The method of producing an electrode sheet according to any one of claims 1 to 11, characterized by, The solid-state electrolyte is selected from one or more of sulfide solid-state electrolyte, oxide solid-state electrolyte and polymer solid-state electrolyte.

17. The method of producing an electrode sheet according to any one of claims 1 to 11, characterized by, The conductive agent is selected from one or more of acetylene black, vapor-phase carbon fiber, carbon nanotube, nano-carbon fiber and graphene.

18. The method of producing an electrode sheet according to any one of claims 1 to 11, characterized by, In the multiple hot roller pressing processes, the pressure of the first hot roller pressing is greater than the pressure of the subsequent hot roller pressing.

19. The method of producing an electrode sheet according to any one of claims 1 to 11, characterized by, The pressure of the first hot roller pressing is 0.20-0.50 MPa, and the pressure of the second and subsequent hot roller pressings is independently 0.10-0.40 MPa.

20. The method of producing an electrode sheet according to any one of claims 1 to 11, characterized by, The mixed dry material and the solvent are synchronously coated on the surface of the current collector by spraying.

21. An electrode, characterized by The electrode sheet is prepared by the method of any one of claims 1-20.

22. A solid state battery, characterized by The electrode sheet comprises the electrode sheet of claim 21.

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