A positive electrode sheet, a method for manufacturing the same, and a solid-state battery

Abstract

The present application relates to the technical field of solid-state batteries, and provides a positive electrode sheet, a preparation method thereof and a solid-state battery.The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode active material, a solid-state electrolyte, a first conductive agent and a binder; the binder comprises polymer fibers, the surface of the polymer fibers is negatively charged; the length of the polymer fibers is 50-200 mu m, and the diameter is 5-15 mu m; and the surface of the polymer fibers is further provided with nano grooves.The present application can effectively inhibit the agglomeration of polymer fibers by multidimensional regulation of the geometric size, surface charge and nano structure of the polymer fiber binder, the uniform dispersibility of the polymer fibers is better, and the adhesion and flexibility of the positive electrode sheet are improved.

Description

Technical Field

[0001] This invention relates to the technical field of solid-state batteries, specifically to a positive electrode sheet, its preparation method, and a solid-state battery. Background Technology

[0002] In the field of solid-state batteries, dry electrode technology has become a highly promising electrode fabrication process due to its advantages such as solvent-free processing, environmental friendliness, and high energy density. However, current dry processes still face many technical bottlenecks in cathode preparation, severely restricting their industrial application. In the dry mixing stage, the fiber materials used for bonding are prone to agglomeration due to significant van der Waals forces on their surface. To achieve uniform dispersion of the fiber materials, the mixing time often exceeds 30 minutes, which not only significantly reduces production efficiency but also increases energy consumption and equipment wear. In addition, the smooth surface of the fiber materials makes it difficult to form an effective mechanical interlocking structure with the active material particles, resulting in highly brittle electrode films with generally low tensile strength. They are prone to cracking and delamination during rolling, cutting, and battery charging and discharging, seriously affecting the stability of the electrode structure. At the same time, due to uneven fiber dispersion, the conductive agent exhibits local enrichment or sparseness in the cathode, making it impossible to build a continuous and stable electron transport network. This results in high fluctuations in the surface resistance of the cathode, significantly reducing battery charge-discharge performance and cycle life. The aforementioned problems make it difficult for dry-process cathode sheets to meet the high performance and high reliability requirements of solid-state batteries in practical applications, and they urgently need to be solved through innovative technical means. Summary of the Invention

[0003] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a positive electrode sheet, its preparation method, and a solid-state battery. This invention effectively suppresses polymer fiber agglomeration by multi-dimensionally controlling the geometric dimensions, surface charge, and nanostructure of the polymer fiber binder, resulting in better uniform dispersion of the polymer fibers and improved bonding performance and flexibility of the positive electrode sheet.

[0004] To achieve the above objectives, the first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector;

[0005] The positive electrode active material layer includes a positive electrode active material, a solid electrolyte, a first conductive agent, and a binder; the binder includes polymer fibers, and the polymer fibers have a negative charge on their surface.

[0006] The polymer fibers have a length of 50μm-200μm and a diameter of 5μm-15μm;

[0007] The surface of the polymer fiber is also provided with nanogrooves.

[0008] A second aspect of the present invention provides a method for preparing the positive electrode sheet described in the first aspect, comprising the following steps:

[0009] Step S1: The polymer fiber and the first conductive agent are mixed for the first time to obtain the first mixture.

[0010] Step S2: The first mixture, the positive electrode active material, and the solid electrolyte are mixed a second time to obtain the second mixture;

[0011] Step S3: The second mixture obtained in step S2 is applied to the surface of the positive electrode current collector and then subjected to hot pressing.

[0012] A third aspect of the present invention provides a solid-state battery comprising the positive electrode sheet described in the first aspect of the present invention, or the positive electrode sheet obtained by the preparation method described in the second aspect of the present invention.

[0013] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0014] (1) In the positive electrode sheet provided by the present invention, by multi-dimensionally controlling the geometric size, surface charge and nanostructure of the polymer fiber binder, the aggregation of polymer fibers can be effectively suppressed, and its uniform dispersion in the positive electrode active material layer can be achieved, thereby improving the interfacial bonding energy of polymer fiber-positive electrode active material and improving the bonding performance of the positive electrode sheet.

[0015] (2) In the positive electrode sheet provided by the present invention, the nanogrooves on the surface of the polymer fiber can increase the specific surface area of ​​the binder, enhance the mechanical interlocking force between the binder and the positive electrode active material and other components, improve the tensile strength of the positive electrode sheet, and significantly improve the flexibility of the positive electrode sheet.

[0016] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to those ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In this document, unless otherwise specified, data ranges include endpoints. Detailed Implementation

[0017] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0018] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0019] The first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector;

[0020] The positive electrode active material layer includes a positive electrode active material, a solid electrolyte, a first conductive agent, and a binder; the binder includes polymer fibers, and the polymer fibers have a negative charge on their surface.

[0021] The polymer fibers have a length of 50μm-200μm and a diameter of 5μm-15μm;

[0022] The surface of the polymer fiber is also provided with nanogrooves.

[0023] In this invention, polymer fibers are used as a binder in the positive electrode sheet, and the diameter and length of the polymer fibers are limited to the aforementioned ranges. The polymer fibers also have a negative charge on their surface and are provided with nanogrooves. On one hand, the electrostatic repulsion effect of the negative charge and a suitable aspect ratio can effectively suppress the aggregation of polymer fibers due to van der Waals forces, achieving uniform dispersion of the polymer fibers in the positive electrode active material layer, improving the interfacial bonding energy between the polymer fibers and the positive electrode active material, and enhancing the bonding performance of the positive electrode sheet. On the other hand, the nanogrooves on the surface of the polymer fibers can increase the specific surface area of ​​the binder, enhance the mechanical interlocking force between the binder and components such as the positive electrode active material, improve the tensile strength of the positive electrode sheet, and significantly improve its flexibility. This simultaneously achieves multi-dimensional optimization of the binder's dispersibility, the bonding strength of the positive electrode sheet, and its flexibility.

[0024] In some embodiments, the length of the polymer fiber is 50μm-200μm, for example, it can be any point value in the range of 50μm, 60μm, 80μm, 100μm, 120μm, 150μm, 160μm, 180μm, 200μm or a combination of two point values, preferably 130μm-170μm.

[0025] In some embodiments, the diameter of the polymer fiber is 5μm-15μm, for example, it can be any point value in the range of 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm or a combination of two point values, preferably 8μm-12μm.

[0026] In some embodiments, the polymer fiber mass percentage, based on the total mass of the positive electrode active material layer, is 1%-3%, for example, it can be any value within a range of 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any combination of these values. When the polymer fiber mass percentage is within the above range, it avoids the situation where the polymer fiber binder cannot form a continuous network, leading to insufficient interfacial adhesion and broken conductive pathways, if the polymer fiber mass percentage is too low. Simultaneously, it avoids the situation where the polymer fiber mass percentage is too high, which would reduce the active material loading and decrease the electrode volumetric energy density. This mass percentage range effectively balances the synergistic optimization of adhesion strength, conductivity, and energy density.

[0027] It should be noted that the mass percentage of polymer fibers in the positive electrode active material layer of the positive electrode sheet refers to the percentage of the mass of polymer fibers in the total mass of all components (such as positive electrode active material, solid electrolyte, conductive agent, binder, etc.) in the positive electrode active material layer when preparing the positive electrode sheet.

[0028] In some embodiments, the polymer fiber includes at least one of polytetrafluoroethylene fiber, cellulose, polyvinylidene fluoride fiber, and polyetheretherketone fiber.

[0029] In some embodiments, the polymer fiber is preferably polytetrafluoroethylene fiber (PTFE fiber).

[0030] Furthermore, this application also found that in existing dry-process positive electrode sheets, uneven distribution of binder fibers leads to localized enrichment of conductive agents (such as carbon black), resulting in discontinuous electron transport paths and significant fluctuations in the sheet resistance. To further reduce the sheet resistance of the positive electrode sheet and decrease sheet resistance fluctuations, this invention proposes the following optimization scheme:

[0031] In some embodiments, the surface of the polymer fiber is coated with a second conductive agent, the second conductive agent including a linear conductive agent.

[0032] Linear conductive agents can form covalent bonds such as COC with nanogrooves on the surface of polymer fibers through chemical vapor deposition (XPS characterization can confirm this) to form a core-shell structure. Utilizing the one-dimensional interconnectivity of the linear conductive agent and the effect of covalent bonding, a synergistic enhancement system of "fiber skeleton-conductive network" can be constructed: on the one hand, it can connect the conductive pathways between positive electrode active materials, improve the uniformity of conductive agent distribution, and reduce electron transport impedance; on the other hand, the interfacial covalent bonds between polymer fibers and linear conductive agents in the core-shell structure can maintain the stability of the conductive network and reduce the sheet resistance of the positive electrode.

[0033] In some embodiments, the mass percentage of the second conductive agent in the polymer fiber is 0.2%-1%, for example, it can be any value within a range of 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination of two values. This invention further adjusts the mass percentage of the second conductive agent in the polymer fiber to avoid insufficient addition of the linear conductive agent, which would prevent the formation of an effective conductive network and result in low electron transport efficiency; it also avoids excessive addition of the linear conductive agent, which would cause the linear conductive agent to agglomerate, disrupting the continuity of the conductive network and failing to effectively reduce the surface resistivity of the positive electrode.

[0034] The mass percentage of the second conductive agent in the polymer fiber refers to the percentage of the mass of the second conductive agent added during the preparation process of coating the polymer fiber surface with the second conductive agent, relative to the mass of the polymer fiber.

[0035] In some embodiments, the diameter of the linear conductive agent is 3nm-10nm (e.g., it can be any point value within the range of 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, or any combination of two values), and the length is 0.5μm-5μm (e.g., it can be any point value within the range of 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, or any combination of two values). By further adjusting the diameter and length of the linear conductive agent within the above ranges, the present invention can further improve the continuity of the conductive network, increase electron transport efficiency, and reduce the sheet resistance of the positive electrode.

[0036] In some embodiments, the linear conductive agent includes at least one of carbon nanotubes, carbon fibers (e.g., vapor-grown carbon fibers VGCF), and graphene nanoribbons.

[0037] In some embodiments, the linear conductive agent is a carbon nanotube with a diameter of 3nm-8nm and a length of 0.5μm-3μm.

[0038] In some embodiments, the depth of the nanogroove is 50 nm to 100 nm; and / or, the length of the nanogroove is 50 μm to 100 μm.

[0039] This invention employs processes such as plasma jetting to create nanogrooves on the surface of polymer fibers. By further limiting the depth and length of the nanogrooves to the aforementioned range, on the one hand, the appropriately deep grooves provide physical anchoring points for the linear conductive agent, increasing the amount of linear conductive agent embedded. Through the dual effects of mechanical locking and covalent bonding, the continuity of the conductive network is ensured. On the other hand, the nanogrooves increase the specific surface area of ​​the polymer fibers, promoting the uniform dispersion of the linear conductive agent, avoiding stress concentration caused by agglomeration, and improving the tensile strength of the positive electrode, thus significantly enhancing the electrode's conductivity, mechanical strength, and cycle stability.

[0040] To provide a more detailed and complete description of the components in the positive electrode, this invention further specifies the selection of components such as the positive electrode active material, the solid electrolyte, and the first conductive agent, as follows:

[0041] In some embodiments, the positive electrode active material includes a ternary material, the chemical formula of which is Li. a Ni x Co y Mn z O2, where 0.9≤a≤1.1, 0.7≤x<1, 0≤y≤1, 0≤z≤1.

[0042] In some embodiments, the solid electrolyte includes at least one of sulfide solid electrolyte, halide solid electrolyte, oxide solid electrolyte and polymer solid electrolyte.

[0043] In some embodiments, the solid electrolyte is preferably a sulfide solid electrolyte. Sulfide solid electrolytes exhibit good chemical compatibility with the aforementioned ternary cathode active materials. Furthermore, the soft nature of sulfide electrolytes allows them to maintain close contact with the cathode active material particles, reducing interfacial voids, lowering interfacial impedance, and improving the cycle stability of the battery.

[0044] In some embodiments, the sulfide solid electrolyte includes glassy 20Li2S-80P2S5 and glass-ceramic Li7P3S. 11 , Crystalline Li6PS6Cl, Li 10 GeP2S 12 At least one of them.

[0045] In some embodiments, the first conductive agent includes at least one of Ketjen black, graphene, acetylene black, conductive graphite, and conductive carbon black.

[0046] In some embodiments, based on the total mass of the positive electrode active material layer, the positive electrode active material accounts for 85%-95% of the mass, the solid electrolyte accounts for 3%-10% of the mass, the polymer fiber (binder) accounts for 1%-3% of the mass, and the first conductive agent accounts for 0.5%-5% of the mass.

[0047] In some embodiments, the thickness of the positive electrode is 300 μm-330 μm.

[0048] The positive electrode sheet provided by the first aspect of the present invention has advantages such as good adhesion performance, good flexibility and small surface resistance fluctuation.

[0049] A second aspect of the present invention provides a method for preparing the positive electrode sheet described in the first aspect of the present invention, comprising the following steps:

[0050] Step S1: The polymer fiber and the first conductive agent are mixed for the first time to obtain the first mixture.

[0051] Step S2: The first mixture, the positive electrode active material, and the solid electrolyte are mixed a second time to obtain the second mixture;

[0052] Step S3: The second mixture obtained in step S2 is applied to the surface of the positive electrode current collector and then subjected to hot pressing.

[0053] Step S1

[0054] In step S1, the polymer fiber used is the polymer fiber mentioned in the first aspect of the present invention, which has a negatively charged surface and is provided with nanogrooves with a length of 50μm-200μm and a diameter of 5μm-15μm. In addition, the surface of the polymer fiber may optionally be coated with a second conductive agent (linear conductive agent).

[0055] In step S1, the polymer fiber and the first conductive agent are mixed for the first time. The electrostatic-mechanical synergistic anchoring effect formed by the negative charge on the fiber surface and the nanogrooves can form a primary conductive framework and improve electron transport efficiency.

[0056] In step S1, the conditions for the first mixing include: a vibration mixing frequency of 25Hz-30Hz and a mixing time of 3min-10min (for example, it can be any point value within the range of 3min, 5min, 6min, 8min, 10min or two points).

[0057] Step S2

[0058] In step S2, the conditions for the second mixing include: a vibration mixing frequency of 10Hz-25Hz (e.g., any value within the range of 10Hz, 15Hz, 20Hz, 25Hz, or any combination of values), and a mixing time of 8min-15min (e.g., any value within the range of 8min, 10min, 12min, 14min, 15min, or any combination of values). These mixing conditions can also be adjusted based on the mass of the mixture.

[0059] In step S2, the first mixture of materials, positive electrode active material and solid electrolyte are mixed by low-frequency vibration. This ensures that the materials are fully dispersed while effectively preventing the polymer fibers from breaking due to high-frequency shear force, thus ensuring the mechanical support function of the polymer fibers and the stability of the conductive network. At the same time, low-frequency vibration mixing promotes the uniform wetting of the positive electrode active material by the solid electrolyte, resulting in a shorter ion diffusion path and reduced interfacial impedance.

[0060] Step S2 also includes vibrating sieving (100 mesh) of the second mixture, which sieves the mixed second material (the material with more clumps after mixing) into more uniform granular material. On the one hand, hot pressing film processing is good, and on the other hand, the mixture is relatively more uniform, and the overall consistency of the film is relatively high.

[0061] Step S3

[0062] In step S3, the conditions for the hot pressing treatment include: a pressure of 10 MPa-20 MPa (for example, it can be any point within the range of 10 MPa, 12 MPa, 15 MPa, 18 MPa, 20 MPa, or any two points); a temperature of 80℃-150℃ (for example, it can be any point within the range of 80℃, 100℃, 120℃, 150℃, or any two points); and a speed of 1 m / min-5 m / min (for example, it can be any point within the range of 1 m / min, 2 m / min, 3 m / min, 4 m / min, 5 m / min, or any two points).

[0063] In this invention, the polymer fibers used as binders are pretreated. Untreated polymer fiber raw materials have a length of 450μm-600μm and a diameter of 5μm-15μm. Untreated polymer fiber raw materials are prone to agglomeration and have insufficient mechanical bonding force with the positive electrode active material particles.

[0064] This invention further proposes a pretreatment process for polymer fiber raw materials, as detailed below:

[0065] In some embodiments, before step S1, a step of pretreating the polymer fiber raw material to obtain polymer fibers is included; the pretreatment includes a primary shear treatment, a secondary electrostatic dispersion treatment, and a tertiary plasma activation treatment.

[0066] Primary shearing

[0067] In some embodiments, the conditions for the first-stage shearing treatment include: a shearing speed of 8000 rpm to 12000 rpm (e.g., any value within a range of 8000 rpm, 9000 rpm, 10000 rpm, 11000 rpm, 12000 rpm, or any combination of these values), and a shearing time of 1 min to 3 min (e.g., any value within a range of 1 min, 2 min, 3 min, or any combination of these values). These conditions can also be adjusted based on the length and agglomeration of the polymer fiber raw material.

[0068] In the first-stage shearing process, a high-speed shearing machine with a rotation speed of 8000rpm-12000rpm and a sawtooth stator and rotor is used to generate high-frequency strong shearing force that can instantly destroy the van der Waals forces between polymer fiber bundles, efficiently breaking the fiber bundles into single filaments with a length of 50μm-200μm, laying the foundation for the uniform dispersion of polymer fibers in the subsequent process.

[0069] Secondary electrostatic dispersion treatment

[0070] In some embodiments, the conditions for the secondary electrostatic dispersion treatment include: an electrostatic field voltage of -8kV to -12kV (e.g., the voltage can be any value within the range of -8kV, -9kV, -10kV, -11kV, -12kV, or any combination of two values), an inert gas flow rate of 8L / min to 12L / min (e.g., the flow rate can be any value within the range of 8L / min, 9L / min, 10L / min, 11L / min, 12L / min, or any combination of two values), and a treatment time of 3min to 10min (e.g., the voltage can be any value within the range of 3min, 4min, 5min, 6min, 8min, 10min, or any combination of two values).

[0071] In some implementations, the inert gas includes nitrogen, argon, helium, etc.

[0072] The secondary electrostatic dispersion treatment applies a high-voltage electrostatic field under an inert gas protective atmosphere, causing the surface of the polymer fiber monofilaments after the primary shearing treatment to uniformly carry a negative charge, forming an electrostatic repulsion barrier, which effectively inhibits the secondary aggregation between polymer fiber monofilaments.

[0073] Three-stage plasma activation treatment

[0074] In some embodiments, the three-stage plasma activation treatment includes treatment using a plasma jet. The plasma jet comprises: a mixed gas jet of inert and oxidizing gases, with a gas pressure of 2 MPa-4 MPa (e.g., the pressure can be any value within the range of 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, or any combination of these values); a plasma jet generator with a power of 300W-800W (e.g., it can be any value within the range of 300W, 400W, 500W, 600W, 700W, 800W, or any combination of these values); and a treatment time of 1 min-6 min (e.g., the voltage can be any value within the range of 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, or any combination of these values).

[0075] In some embodiments, the inert gas includes at least one of argon, helium, and neon.

[0076] In some embodiments, the oxidizing gas includes at least one of oxygen, nitrous oxide, and carbon dioxide.

[0077] In some embodiments, the volume ratio of inert gas to oxidizing gas is (3-7):1.

[0078] In the three-stage plasma activation process, a mixed gas plasma jet of inert and oxidizing gases is used to precisely etch nanogrooves on the surface of polymer fibers through the synergistic effect of physical bombardment and chemical etching. This increases the specific surface area of ​​the polymer fibers, significantly enhances the mechanical bonding and chemical bonding between the polymer fibers and the positive electrode active material and conductive agent, and improves the flexibility of the positive electrode sheet.

[0079] In some embodiments, the pretreated polymer fibers further include a step of coating with a second conductive agent. Preferably, the coating is performed using a chemical vapor deposition process.

[0080] In some embodiments, the chemical vapor deposition conditions include: a gas system comprising a carbon source gas / reducing gas, a deposition temperature of 500°C-800°C (e.g., any value within a range of 500°C, 600°C, 700°C, 800°C, or any value within a range of pairs of values), and a deposition time of 8 min-15 min (e.g., any value within a range of 8 min, 10 min, 11 min, 12 min, 14 min, 15 min, or any value within a range of pairs of values).

[0081] In some embodiments, the volume ratio of the carbon source gas to the reducing gas is 2:1 to 8:1, for example, any point value within the range of 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or a combination of two point values.

[0082] In some embodiments, the carbon source gas includes at least one of ethylene, propylene, and acetylene.

[0083] In some embodiments, the reducing gas includes hydrogen.

[0084] Linear conductive agents are deposited in nanogrooves on the surface of polymer fibers via chemical vapor deposition, which can connect the conductive pathways between positive electrode active materials, improve the uniformity of conductive agent distribution, reduce electron transport impedance, and reduce the surface resistance fluctuation of the positive electrode sheet.

[0085] The dry process for preparing positive electrode sheets used in this invention employs a completely dry process with no solvent emissions, which can effectively reduce energy consumption.

[0086] A third aspect of the present invention provides a solid-state battery comprising the positive electrode sheet described in the first aspect of the present invention, or the positive electrode sheet obtained by the preparation method described in the second aspect of the present invention.

[0087] Applying the positive electrode sheet provided by this invention to solid-state batteries can improve the cycle performance, energy density, and flexibility of solid-state batteries.

[0088] The solid-state battery provided by this invention can be applied to high-consistency power batteries (e.g., electric vehicles, energy storage power stations), ultra-thick electrode systems (>200μm, improving energy density), and flexible and stretchable battery application scenarios (e.g., wearable devices, electronic skin).

[0089] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0090] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0091] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0092] Example 1a

[0093] 1. Pretreatment of polymer fiber raw materials

[0094] (1) First-stage shearing treatment: PTFE fiber raw material (500μm in length and 8μm in diameter) is sheared in a high-speed shearing machine with a sawtooth stator and rotor. The shearing speed is 10000rpm and the shearing time is 2min. The length of PTFE fiber is reduced to about 150μm and the diameter is 8μm.

[0095] (2) Secondary electrostatic dispersion treatment: A -10kV high voltage electrostatic field was applied to the PTFE fibers after the primary shearing treatment in a nitrogen atmosphere, with a nitrogen flow rate of 10L / min, for 5min.

[0096] (3) Three-stage plasma activation treatment: Nanogrooves were etched on the surface of PTFE fiber by plasma jet (Ar / O2 mixed gas, volume ratio of 5:1), air pressure of 3 MPa, power of 500 W for 3 min. The surface grooves were 80 nm deep and 80 μm long.

[0097] (4) Chemical vapor deposition of carbon nanotubes (CNTs): Carbon nanotubes (5 nm in diameter, 1 μm-2 μm in length) were chemically vapor deposited on the surface of pretreated PTFE fibers. The mass input of CNTs accounted for 0.5% of the pretreated PTFE fiber material. Ethylene / hydrogen gas (volume ratio 4:1) was introduced at 650℃ and the deposition time was 10 min.

[0098] 2. Preparation of the positive electrode:

[0099] Step S1: Dry mix the pretreated PTFE fibers and the first conductive agent Ketjen black for 5 minutes to obtain the first mixture.

[0100] Step S2: Add the first mixture and the positive electrode active material (LiNi) 0.92 Co 0.03 Mn 0.05 O2 (NCM9235) and solid electrolyte (Li6PS5Cl) were mixed by low-frequency vibration (20Hz, 10min) to obtain a second mixture.

[0101] The second mixture contains the following formulation by mass ratio: NCM9235 (92%) + Li6PS5Cl (5%) + pretreated PTFE fiber (2%) + Ketjen Black (1%).

[0102] Step S3: The second mixture obtained in step S2 is applied to the surface of the positive electrode current collector and rolled into a film. Rolling parameters: pressure 15MPa, temperature 100℃, speed 2m / min, to obtain a positive electrode sheet with a thickness of 80μm.

[0103] 2. Preparation of the negative electrode:

[0104] Nano Ag powder, nano carbon black, and PVDF binder are dispersed and slurried in a double planetary mixer at a mass ratio of 72:24:4, with NMP as the solvent. The slurry is then sprayed onto the surface of copper foil to form a sheet, which is then rolled and slit to obtain the negative electrode sheet of the target specification.

[0105] 3. Solid electrolyte film: Solid electrolyte Li6PS5Cl powder and PTFE powder are mixed at a mass ratio of 3:1, dispersed and mixed evenly at high speed, and then film-forming and rolled to obtain a solid electrolyte film with a thickness of 40μm.

[0106] 4. Battery assembly

[0107] After the negative electrode (welded tab), solid electrolyte film, and positive electrode (welded tab) are stacked in sequence, they are encapsulated with aluminum-plastic film and then compacted by an isostatic pressing device to achieve close contact between the electrode and the electrolyte film; low-current formation is performed, and constant current and constant voltage charging is carried out at 0.1C to 40% SOC.

[0108] The same example was carried out as in Example 1a. The main differences between the other examples and comparative examples are shown in Tables 1-3.

[0109] The positive electrode plates or batteries obtained in the above embodiments and comparative examples were subjected to the following performance tests:

[0110] (1) Adhesion of the positive electrode

[0111] Test method for adhesion of positive electrode: According to the method standard GB / T 2792-2014 "Test method for peel strength of adhesive tape", the peel strength between the tape sample and the stainless steel plate is tested.

[0112] ① Place the adhesive tape sample in an environment of 23±1℃ and 50±5%RH for 24 hours to condition it. ② Wipe the surface of the stainless steel plate four times with acetone and let it air dry for 10 minutes. ③ Remove the four layers of adhesive tape from the surface of the sample and cut a specimen with a width of 24mm and a length of 300mm from the remaining sample using a cutter. ④ Fold one end of the cut specimen in half to form a folded layer of about 12mm in length. Attach the other end of the specimen to one end of the steel plate and roll it twice with an adhesive tape roller at a speed of 600mm / min. ⑤ Peel about 25mm of adhesive tape from the steel plate at the folded end of the specimen and clamp the steel plate and the free end of the specimen in the upper and lower clamps of the equipment, respectively. ⑥ Set the test speed (300mm / min), specimen width (24mm), and other parameters, click the test option, and the test will begin. The equipment will automatically record the force value during the peeling process and report the peel strength of the specimen accordingly. ⑦ Repeat the sample cutting, preparation, and testing procedures in (3) to (6) and test the peel strength values ​​of the three samples.

[0113] (2) Surface resistance test

[0114] The single-probe method uses a resistor meter fixed at one end and a moving terminal at the other end to test the sample resistance. The controllable-pressure single-probe device fixes one end to a controllable-pressure device and places the other end at the edge of the sample. At the same time, parameters such as test pressure and holding time are set on the MRMS software, and the test is started. The software automatically reads the resistance data.

[0115] (3) Flexibility test

[0116] Flexibility test: Cut a positive electrode sheet 15mm long and 10mm wide, fold the electrode sheet 180° in half, and fold it back and forth 3 times. If the result is that it is not transparent and does not break, the flexibility test is passed; otherwise, it is not passed.

[0117] (4) Tensile strength test:

[0118] 1. Positive electrode sampling: Avoid the coating edge (>10mm from the edge) and take samples along the coating direction (MD) and transverse direction (TD) respectively (to evaluate anisotropy); the total length of the sample is ≥100mm, the gauge length is 25mm (width) × 80mm (length), and the clamping end is ≥15mm (widened for anti-slip).

[0119] 2. Sample loading: Set the fixture spacing to 50mm; the coating surface should face inwards, and the current collector should face outwards (to reduce fixture damage to the coating); pretension 0.1N (to eliminate wrinkles);

[0120] 3. Test conditions: Tensile speed: 10 mm / min (simulating actual winding speed); Termination condition: specimen fracture or strain > 100%;

[0121] 4. Calculation formula: Electrode tensile strength σ = F max / (W×T); W: width; T: thickness.

[0122] Examples 1-3 and Comparative Examples 1-7 were performed according to Example 1a, with the main differences shown in Table 1. In Example 1, the length of the PTFE fibers was changed by adjusting the time in the primary shearing process (4.5 min in Example 1b; 2.5 min in Example 1c). In Example 2, PTFE fiber raw materials with different diameters were directly selected. In Example 3, the depth and length of the nanogrooves were changed by adjusting the plasma jet process parameters (350 W in Example 3a; 6 min in Example 3b). In Comparative Example 1, the PTFE fiber raw material was not pretreated. In Comparative Example 2, the shearing time was 1 min, and the length of the PTFE fibers was outside the protection range. In Comparative Example 3, the shearing time was 6 min, and the length of the PTFE fibers was outside the protection range. In Comparative Examples 4 and 5, PTFE fiber raw materials with diameters outside the protection range were selected. In Comparative Example 6, the PTFE fiber raw material was not subjected to electrostatic dispersion treatment (and therefore did not carry a negative charge). In Comparative Example 7, the PTFE fiber raw material was not subjected to three-stage plasma activation treatment, nor was carbon nanotube (CNT) deposited by chemical vapor deposition (without nanogrooves, no CNTs were deposited).

[0123] Table 1

[0124]

[0125] Note: " / " indicates that the corresponding parameter was not tested.

[0126] As can be seen from Table 1, in the positive electrode provided by the embodiments of the present invention, by controlling the geometric dimensions, surface charge and nano-groove dimensions of the polymer fiber binder within the protection range of the present invention, the bonding performance of the positive electrode can be effectively improved, the tensile strength of the positive electrode can be improved, the flexibility of the positive electrode can be significantly improved, and the surface resistance of the positive electrode can be reduced.

[0127] Example 4 was performed in accordance with Example 1a, with the main differences shown in Table 2. In Example 4a, polyvinylidene fluoride fiber was used instead of PTFE; in Example 4b, carbon fiber (VGCF) was used instead of CNT; and in Example 4c, cellulose was used instead of PTFE, and graphene nanoribbons were used instead of CNT.

[0128] Table 2

[0129]

[0130] As shown in Table 2, both the type of polymer fiber binder and the type of second conductive agent coated on the polymer fiber binder surface affect the performance of the positive electrode. When polytetrafluoroethylene (PTFE) fiber is preferred as the polymer fiber, and CNT is chosen as the second conductive agent, the overall performance of the positive electrode is better.

[0131] Examples 5-7 were performed in accordance with Example 1a, with the main differences shown in Table 3. Specifically, in Example 5, the process parameters for the primary shearing treatment were adjusted; in Example 6, the process parameters for the secondary electrostatic dispersion treatment were adjusted; and in Example 7, the process parameters for the tertiary plasma activation treatment were adjusted.

[0132] Table 3

[0133]

[0134] The performance data of test groups 5-7 in Example 1 are shown in Table 4.

[0135] Table 4

[0136]

[0137]

[0138] As can be seen from Table 4, changes in the process parameters of polymer fiber raw material pretreatment can affect the length of polymer fibers, the surface negative charge, and the size of nanogrooves, which in turn affect the bonding performance, tensile strength, flexibility, and surface resistivity of the positive electrode sheet.

[0139] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0140] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector; The positive electrode active material layer includes a positive electrode active material, a solid electrolyte, a first conductive agent, and a binder; the binder includes polymer fibers, the polymer fibers having a negative charge on their surface; the polymer fibers include at least one of polytetrafluoroethylene fibers, cellulose, polyvinylidene fluoride fibers, and polyetheretherketone fibers; The polymer fibers have a length of 50 μm-200 μm and a diameter of 5 μm-15 μm; The surface of the polymer fiber is also provided with nanogrooves, the depth of which is 50 nm-100 nm and the length of which is 50 μm-100 μm.

2. The positive electrode sheet according to claim 1, characterized in that, The surface of the polymer fiber is coated with a second conductive agent, the second conductive agent including a linear conductive agent; The second conductive agent accounts for 0.2%-1% of the mass of the polymer fiber.

3. The positive electrode sheet according to claim 2, characterized in that, The linear conductive agent has a diameter of 3 nm-10 nm and a length of 0.5 μm-5 μm.

4. The positive electrode sheet according to claim 2, characterized in that, The linear conductive agent includes at least one of carbon nanotubes, carbon fibers, and graphene nanoribbons.

5. The positive electrode sheet according to claim 1, characterized in that, The polymer fiber accounts for 1%-3% of the total mass of the positive electrode active material layer. And / or, the polymer fiber is polytetrafluoroethylene fiber.

6. The positive electrode sheet according to any one of claims 1-5, characterized in that, The positive electrode active material includes a ternary material, the chemical formula of which is Li. a Ni x Co y Mn z O2, where 0.9≤a≤1.1, 0.7≤x<1, 0≤y≤1, 0≤z≤1; And / or, the solid electrolyte includes at least one of sulfide solid electrolyte, halide solid electrolyte, oxide solid electrolyte and polymer-based solid electrolyte; And / or, the first conductive agent includes at least one of graphene, conductive graphite, and conductive carbon black.

7. The positive electrode sheet according to any one of claims 1-5, characterized in that, The solid electrolyte is a sulfide solid electrolyte.

8. A method for preparing the positive electrode sheet according to any one of claims 1-7, characterized in that, Includes the following steps: Step S1: The polymer fiber and the first conductive agent are mixed for the first time to obtain the first mixture. Step S2: The first mixture, the positive electrode active material, and the solid electrolyte are mixed a second time to obtain the second mixture; Step S3: The second mixture obtained in step S2 is applied to the surface of the positive electrode current collector and then subjected to hot pressing.

9. The method according to claim 8, characterized in that, Before step S1, the process also includes a step of pretreating the polymer fiber raw material to obtain polymer fibers; The pretreatment includes a first-stage shearing treatment, a second-stage electrostatic dispersion treatment, and a third-stage plasma activation treatment. The polymer fiber raw material has a length of 450 μm-600 μm and a diameter of 5 μm-15 μm.

10. The method according to claim 9, characterized in that, The conditions for the first-stage shearing process include: a shearing speed of 8000 rpm-12000 rpm and a shearing time of 1 min-3 min.

11. The method according to claim 9, characterized in that, The conditions for the secondary electrostatic dispersion treatment include: an electrostatic field voltage of -8kV to -12kV, an inert gas flow rate of 8 L / min to 12 L / min, and a treatment time of 3 min to 10 min.

12. The method according to claim 9, characterized in that, The three-stage plasma activation treatment includes treatment using a plasma jet; the plasma jet includes a mixed gas jet of inert gas and oxidizing gas, with a gas pressure of 2 MPa-4 MPa, a power of 300W-800W, and a treatment time of 1min-6min.

13. The method according to claim 9, characterized in that, The pretreatment also includes the step of coating the surface of the polymer fiber with a second conductive agent.

14. The method according to claim 13, characterized in that, The coating is applied using a chemical vapor deposition process.

15. The method according to claim 14, characterized in that, The conditions for chemical vapor deposition include: a gas system consisting of a carbon source gas and a reducing gas, with a volume ratio of 2:1 to 8:1 between the carbon source gas and the reducing gas; a deposition temperature of 500℃ to 800℃; and a deposition time of 8 min to 15 min.

16. The method according to claim 8, characterized in that, In step S1, the conditions for the first mixing include: a vibration mixing frequency of 25 Hz-30 Hz and a mixing time of 3-10 min; And / or, in step S2, the conditions for the second mixing include: a vibration mixing frequency of 10 Hz-25 Hz and a mixing time of 8-15 min.

17. The method according to claim 8, characterized in that, In step S3, the conditions for hot pressing include: pressure of 10 MPa-20 MPa, temperature of 80℃-150℃, and speed of 1 m / min-5 m / min.

18. A solid-state battery, characterized in that, This includes the positive electrode sheet according to any one of claims 1-7, or the positive electrode sheet obtained by the preparation method according to any one of claims 8-17.

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