Positive plate, preparation method thereof and solid-state battery

Abstract

The invention relates to the technical field of solid-state batteries, and provides a positive plate, a preparation method thereof and a solid-state battery. The positive plate comprises a positive current collector and a positive active material layer arranged on at least one side surface of the positive current collector; the positive electrode active material layer comprises a nickel-containing positive electrode active material, a solid electrolyte, a conductive agent and a binder; the binder comprises a first binder and a second binder; the first binder comprises polymer nanofibers, and the length-diameter ratio of the polymer nanofibers is 30-90; the mass ratio of the first binder in the positive active material layer is 0.8%-5%; the second binder includes a catechol group-containing polymer. According to the invention, the first binder and the second binder are combined for use to form a tough composite adhesion system, so that the adhesion of the positive plate is remarkably improved, and the high and low temperature performance and flexibility of the solid-state battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid-state batteries, in particular to a positive electrode sheet, a preparation method thereof and a solid-state battery. BACKGROUND

[0002] With the rapid development of new energy technology, solid-state batteries have become the core development direction of the next generation of power battery technology due to their high energy density and high safety. In the preparation process of solid-state batteries, dry process is attracting much attention because it does not require solvents, is environmentally friendly, and can achieve high surface density coating. However, this process still faces significant technical bottlenecks in the positive electrode system.

[0003] Existing solutions focus on optimizing a single factor, which is difficult to fundamentally solve the problem of insufficient interface adhesion, seriously restricting the improvement of the cycle life and safety of solid-state batteries, and becoming a key obstacle to their large-scale application. Therefore, it is urgent to develop a new technology that has strong interface bonding force and high adhesion stability to break through the technical bottleneck of solid-state battery industrialization. SUMMARY

[0004] Insufficient adhesion of solid-state dry positive electrode film is a core technical bottleneck in the preparation process of solid-state batteries. The present application found that the main reasons for insufficient adhesion of the positive electrode film include the following three aspects: first, the mechanical interlocking between the positive active material, the solid-state electrolyte and the current collector is insufficient, which leads to a high risk of delamination of the positive electrode film and greatly weakens the stability of the battery structure; second, traditional polytetrafluoroethylene-based binders mainly rely on physical entanglement to achieve adhesion, which is prone to creep during high-temperature or long-term cycling, leading to adhesion failure; third, the alkaline substances remaining on the surface of the positive electrode material have chemical inertia, which hinders the chemical bonding between the positive active material and the binder and the solid-state electrolyte, further reducing the interface adhesion strength.

[0005] The purpose of the present application is to overcome the above-mentioned problems existing in the prior art, and to provide a positive electrode sheet, a preparation method thereof and a solid-state battery. The first binder and the second binder are used in combination to form a strong and tough composite adhesion system, which significantly improves the adhesion of the positive electrode sheet and thus improves the cycle performance, high and low temperature performance and flexibility of the solid-state battery.

[0006] To achieve the above-mentioned purpose, the present application provides a positive electrode sheet in the first aspect, which comprises a positive electrode current collector and a positive active material layer arranged on at least one side surface of the positive electrode current collector; the positive active material layer comprises a nickel-containing positive active material, a solid-state electrolyte, a conductive agent and a binder; the binder comprises a first binder and a second binder; The first binder comprises polymer nanofibers, and the aspect ratio of the polymer nanofibers is 30-90; the mass fraction of the first binder in the positive active material layer is 0.8%-5%; The second binder comprises a polymer containing a pyrocatechol group.

[0007] The second aspect of the present application provides a method for preparing the positive electrode sheet of the first aspect, comprising the following steps: Step S1: dry mixing the nickel-containing positive electrode active material, solid-state electrolyte, conductive agent, first binder and second binder to obtain a mixture; Step S2: covering the mixture obtained in step S1 on the surface of the positive electrode current collector, and then performing hot pressing treatment; The hot pressing treatment comprises a first hot pressing stage, a second hot pressing stage and a third hot pressing stage in sequence. The temperature of the first hot pressing stage is 70-100℃, and the pressure is 8-15Mpa. The temperature of the second hot pressing stage is 110-140℃, and the pressure is 12-20Mpa. The temperature of the third hot pressing stage is 50-80℃, and the pressure is 18-25Mpa.

[0008] The third aspect of the present application provides a solid-state battery comprising the positive electrode sheet of the first aspect of the present application.

[0009] The present application has the following beneficial effects by adopting the above technical solutions: (1) The positive electrode sheet provided by the present application uses the first binder and the second binder in combination, the first binder constructs a preliminary physical adhesion framework, and the second binder and the first binder interweave with each other to jointly form a strong and tough composite adhesion system, which significantly improves the adhesion of the positive electrode sheet.

[0010] (2) The solid-state battery provided by the present application comprises the positive electrode sheet with better adhesion, and has the advantages of good cycle performance, stable high-low temperature performance and good flexibility.

[0011] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the present application. Any numeric range recited is intended to include all values from the lower value to the upper value. For values that are less than one, one part in 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 parts per hundred are also specifically intended to be disclosed. The endpoints of the ranges and any value are not limited to the precise value stated. These endpoints and any value between the recited values are included in the range unless otherwise indicated. Thus, any numerical range recited is intended to include all sub-ranges and combinations of integers falling within the recited ranges. In the present specification, data ranges are inclusive of the endpoints unless otherwise specifically indicated. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The structure of the positive electrode current collector in an example is shown.

[0013] Figure 2The diagram shown is a schematic representation of the internal structure of a solid-state battery in an example.

[0014] Figure 3 The diagram shows the external structure of a solid-state battery in an example. Detailed Implementation

[0015] 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.

[0016] 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.

[0017] 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; the positive active material layer comprises a nickel-containing positive active material, a solid electrolyte, a conductive agent and a binder; the binder comprises a first binder and a second binder; The first binder comprises polymer nanofibers with an aspect ratio of 30-90; the first binder accounts for 0.8%-5% of the mass of the positive electrode active material layer; The second adhesive comprises a polymer containing catechol groups.

[0018] In this invention, the polymer nanofibers in the first binder have an aspect ratio of 30-90. This unique nanoscale elongated structure gives them extremely strong winding and filling capabilities, allowing them to fully penetrate and wind into the structural pores of the positive electrode active material layer, forming a mechanical interlocking structure between the positive electrode active material, the solid electrolyte, and the positive electrode current collector. When the membrane is subjected to external force, this mechanical interlocking can effectively disperse stress and prevent the positive electrode active material layer from separating from the current collector. Moreover, the content of the first binder is limited to a suitable range, which can fully exert the role of the first binder and maintain the adhesion performance of the positive electrode sheet. Meanwhile, the second binder is a polymer containing catechol groups. Catechol groups have strong chemical activity and can react with Ni in the nickel-containing positive electrode active material. 3+ A catechol-metal coordination reaction occurs, forming stable coordination bonds, which tightly anchors the positive electrode active material to the surface of the positive electrode current collector, further enhancing the adhesion of the positive electrode sheet. This invention utilizes a combination of a first adhesive and a second adhesive. The first adhesive extends and fills the positive electrode active material, constructing a preliminary physical adhesion framework. The second adhesive forms a chemical connection network with the nickel-containing positive electrode active material, filling the weak points in the physical structure formed by the first adhesive, and intertwines with polymer nanofibers, organically integrating physical entanglement and chemical bonding to jointly constitute a strong and tough composite adhesion system, significantly improving the adhesion of the positive electrode sheet.

[0019] In some embodiments, the aspect ratio of the polymer nanofibers is 30-90, for example, it can be any value within the range of 30, 40, 45, 50, 55, 60, 70, 80, 90, or any combination of these values, preferably 45-55. A larger aspect ratio of the polymer nanofibers results in longer fiber length, smaller diameter, and a longer conductive path. Linear conductivity is long-range conductivity, and its conductivity is relatively poorer than short-range conductivity. By adjusting the aspect ratio of the polymer nanofibers within the above range and adjusting the mass ratio of the first binder within a suitable range, the present invention can improve the electronic conductivity of the electrode.

[0020] In some embodiments, the first binder accounts for 0.8%-5% of the mass of the positive electrode active material layer; for example, the mass percentage can be any value within the range of 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within any pairwise range. When the mass percentage of the first binder is less than 0.8%, the polymer nanofibers are difficult to form an effective physical entanglement network in the positive electrode active material layer, resulting in insufficient mechanical support. When the membrane is subjected to external force or changes in battery charge / discharge volume, it is prone to structural loosening and active material shedding. Moreover, the formed fiber network structure is insufficient, the porosity inside the electrode is larger, the electronic conduction path is tortuous and long, resulting in poor electronic conductivity of the positive electrode. When the mass percentage of the first binder exceeds 5%, the excessive amount of the first binder will increase the rigidity of the membrane and reduce its flexibility, making the membrane prone to cracking when bent or subjected to thermal stress. Moreover, the binder itself is not conductive, and excessive addition will weaken the single-electron conductivity of the positive electrode.

[0021] In some embodiments, the diameter of the polymer nanofiber is 200 nm-400 nm, for example, it can be any value within the range of 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, or any combination of these values. When the aspect ratio of the polymer nanofiber is ≥100, further adjusting the diameter of the polymer nanofiber to meet the above range can avoid the following: if the diameter of the polymer nanofiber is too small (e.g., <200 nm), the polymer nanofiber is prone to agglomeration, and the mechanical support of a single polymer nanofiber is insufficient, making it difficult to effectively embed into the porous structure of the positive electrode active material; and if the diameter is too large (e.g., >400 nm), it is not conducive to the extension and filling of the polymer nanofiber in the positive electrode active material, making it difficult to form a stable mechanical interlocking structure.

[0022] In some embodiments, the length of the polymer nanofibers is 10,000 nm to 20,000 nm, for example, it can be any value within the range of 10,000 nm, 12,000 nm, 14,000 nm, 15,000 nm, 16,000 nm, 18,000 nm, 20,000 nm, or any combination of these values. This invention further limits the fiber length to a suitable range, making the polymer nanofibers less prone to entanglement and agglomeration during mixing, and more easily and uniformly dispersed in the active material. This ensures the stability of the electrode structure, and the contact area between the nanofibers and the active material is more uniform. This effectively avoids problems such as low electron transport efficiency and structural instability caused by long-range conductivity of long fibers, achieving synergistic optimization of the conductivity and mechanical properties of the electrode material.

[0023] In some embodiments, the polymer nanofibers include at least one of polyetheretherketone nanofibers, polytetrafluoroethylene, and polyacrylic acid fibers.

[0024] In some embodiments, the glass transition temperature of the polymer nanofibers is 140-160°C. When the glass transition temperature of the polymer nanofibers is limited to the above range, the polymer nanofibers exhibit excellent high-temperature stability, are not prone to creep and failure during high-temperature cycling, and can maintain a stable physical morphology, further improving the adhesion performance of the positive electrode.

[0025] In some embodiments, the polymer nanofibers are polyetheretherketone (PEEK) nanofibers. PEEK nanofibers have a glass transition temperature in the range of 140-160°C, which allows them to better perform their primary bonding function and improve the adhesion performance of the positive electrode.

[0026] In some embodiments, the polymer containing catechol groups includes at least one of polydopamine, polycatecholamine, tannic acid-based polymers, and polycatechol vinyl ether.

[0027] In some embodiments, the polymer containing catechol groups is polydopamine (polyDOPA). Polydopamine molecules contain a large number of catechol groups, as well as amine and imine groups. The catechol groups endow polyDOPA with relatively active chemical properties. In cathode material systems, for high-nickel materials, the Ni present on their surface... 3+ It can undergo a catechol-metal coordination reaction with the catechol groups of polyDOPA to form stable and strong coordination bonds. These coordination bonds tightly fix the positive electrode active material to the current collector surface, greatly enhancing the bonding force between the two and effectively preventing the positive electrode active material from falling off the current collector surface during battery charge and discharge cycles, thus ensuring the stability and integrity of the electrode structure.

[0028] To further optimize and improve the adhesion of the dry-process positive electrode, the present invention further adjusts the content of the second binder, specifically as follows: In some embodiments, the second binder constitutes 0.3%-4% of the positive electrode active material layer by mass; for example, the mass percentage can be any value within a range of 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3.0%, 3.3%, 3.5%, 3.8%, 4%, or any value within a pairwise range. If the mass percentage of the second binder is less than 0.3%, it contains insufficient catechol groups, which cannot bind with the Ni on the surface of the high-nickel material. 3+ Even with sufficient coordination, it is difficult to form a sufficiently dense covalent network during hot pressing, resulting in weak interfacial adhesion. When the proportion exceeds 4%, excessive cross-linking of the second binder can make the film hard and brittle, and may hinder lithium-ion transport.

[0029] The present invention further controls the content of the first binder and the second binder within the above-mentioned range, which can enhance the adhesion of the membrane and ensure that the membrane has a certain degree of flexibility to adapt to the deformation of the battery under different operating conditions and maintain the integrity of the electrode structure.

[0030] It should be noted that the mass ratio of the first binder and the second binder in the positive electrode active material layer refers to the percentage of the mass of the first binder and the second binder relative to the total mass of each component (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.

[0031] Furthermore, in some embodiments, the positive electrode active material layer also includes a silane coupling agent.

[0032] Silane coupling agents possess a unique bifunctional structure, where the amino (-NH2) end can react with S in the solid electrolyte. 2- A hydrogen bond network is formed, tightly connecting the positive electrode active material layer and the solid electrolyte, effectively enhancing the interfacial bonding force between the two. Simultaneously, the silanol groups (-Si(OH)3) generated after the hydrolysis of the silane coupling agent can undergo a condensation reaction with the hydroxyl groups on the electrode current collector or the surface of the active material, forming stable Si-O-Si covalent bonds. This establishes a robust chemical bridge between the active material layer and the current collector, further improving the overall structural stability. The physical entanglement of the silane coupling agent and the first binder, along with the chemical coordination of the second binder, synergistically construct a strong and tough composite interface from the current collector to the solid electrolyte.

[0033] In some embodiments, the silane coupling agent has a mass percentage of 0.1%-1% in the positive electrode active material layer; for example, the mass percentage can be any point value within the range of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any point value in a pairwise range.

[0034] In some embodiments, the silane coupling agent includes at least one of γ-aminopropyltriethoxysilane (KH-550), N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (KH-792), N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane (KH-602), and diethylenetriaminopropyltrimethoxysilane.

[0035] In some embodiments, the silane coupling agent is γ-aminopropyltriethoxysilane (KH-550).

[0036] When the content and type of silane coupling agent are further limited to the above range, the silane coupling agent can achieve optimal synergy with the first binder and the second binder, enhance the interfacial bonding force, and provide a more stable basis for the physical entanglement of the first binder and the chemical bonding of the second binder. At the same time, the three work together to optimize the ion transport channel, improve the overall performance of the positive electrode active material layer, and thus improve the cycle performance of the solid-state battery.

[0037] For example, the mass percentage of silane coupling agent in the positive electrode active material layer refers to the percentage of the mass of silane coupling agent in the total mass of each component (e.g., positive electrode active material, solid electrolyte, conductive agent, binder, etc.) in the positive electrode active material layer when preparing the positive electrode sheet.

[0038] To further optimize and improve the adhesion of the dry-process positive electrode sheet, the present invention further improves the structure of the positive electrode current collector, specifically as follows: In some embodiments, the surface of the positive current collector on one side of the positive active material layer is provided with a protrusion.

[0039] When protrusions are provided on the surface of the current collector, the surface roughness of the current collector is increased, and the contact area between the current collector and the positive electrode active material layer is greatly increased. The first binder and positive electrode active material in the positive electrode active material layer can be more fully embedded in the gaps of the protrusions, forming a mechanical interlocking structure to ensure the long-term stable bonding between the positive electrode active material layer and the current collector, improve the adhesion of the positive electrode sheet, and effectively prevent the positive electrode active material layer from falling off due to volume changes during battery charging and discharging.

[0040] In some embodiments, the protrusions are arranged in an array at intervals; the arrangement of the protrusions can be uniformly spaced, or the arrangement can be adjusted according to actual needs, such as partially uniformly spaced and partially non-uniformly spaced.

[0041] In some embodiments, the diameter of the protrusion is 5 μm-10 μm; and / or, the height of the protrusion is 3 μm-5 μm; and / or, the spacing between adjacent protrusions is 2 μm-5 μm.

[0042] When the diameter, height, and spacing of the protrusions are further limited to the above-mentioned ranges, the present invention can provide sufficient adhesion sites for the first and second adhesives, and facilitate the filling of solid electrolytes therein. The first adhesive can tightly wrap around the protrusion structure, and the positive electrode active material particles can be fully embedded in the gaps between the protrusions to form a continuous mechanical interlocking network. This effectively improves the bonding force between the positive electrode active material layer and the current collector, effectively resists the stress caused by volume changes during battery charging and discharging, prevents the positive electrode active material layer from falling off, and improves the cycle stability and capacity retention of the solid-state battery.

[0043] In some embodiments, the protrusions are at least one of the following: mushroom-shaped, gecko-foot-shaped, or octopus-foot-like sucker-like. The protrusions employ a biomimetic structure, significantly increasing the specific surface area of ​​the current collector through complex micromorphology. This greatly increases the contact area between the current collector and the positive electrode active material layer, enhancing interfacial chemical bonding and further improving the adhesion of the positive electrode sheet.

[0044] For example, such as Figure 1 As shown, protrusions 111 are distributed at intervals on one side surface of the positive current collector 11. The shape of the protrusions 111 is similar to that of a gecko's foot (this figure is only a schematic diagram, and the actual height of the protrusions is less than the thickness of the current collector).

[0045] In some embodiments, a nanoporous layer is provided at the end of the protrusion furthest from the positive electrode current collector. The nanoporous layer has a high specific surface area, providing abundant adsorption sites for the binder. The first binder can penetrate into the nanoporous layer, forming a mechanical interlock between the fiber and the pores, improving the bonding strength between the binder and the positive electrode current collector, and effectively resisting the shedding of the positive electrode active material during battery cycling.

[0046] In some embodiments, the pore size of the nanoporous layer is 50 nm to 200 nm. The pore size of the nanoporous layer matches the size of the nanoscale binder molecules and solid electrolyte particles, and its pores can serve as stress buffer units. When the electrode undergoes volume changes, the elastic deformation of the pores in the nanoporous layer can absorb stress, avoid structural damage caused by stress concentration, and extend the electrode's service life.

[0047] 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 nickel-containing positive electrode active material and the solid electrolyte, as follows: In some embodiments, the chemical formula of the nickel-containing positive electrode active material 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.

[0048] In some embodiments, the Dv50 of the nickel-containing positive electrode active material is 4 μm-12 μm, for example, any value within the range of 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any combination of these values. When the Dv50 of the nickel-containing positive electrode active material is within the above range, the nickel-containing positive electrode active material forms a good size match with the first binder, the second binder, and the silane coupling agent. The nickel-containing positive electrode active material can be fully encapsulated by the binder, while simultaneously embedding micron-scale biomimetic protrusions and nanoporous layers of the current collector, forming a stable mechanochemical composite interface, effectively improving the overall bonding strength of the electrode.

[0049] In some embodiments, the solid electrolyte includes at least one of a sulfide solid electrolyte, an oxide solid electrolyte, and a polymer-based solid electrolyte.

[0050] In some embodiments, the solid electrolyte is preferably a sulfide solid electrolyte. Sulfide solid electrolytes have good chemical compatibility with nickel-containing cathode active materials, and their S content... 2-It can form a hydrogen bond network with the amino groups of silane coupling agents, enhancing the adhesion of the positive electrode. At the same time, the soft properties of the sulfide electrolyte allow it to make close contact with the positive electrode active material particles, reducing interfacial voids, lowering interfacial impedance, and improving the cycle stability of the battery.

[0051] In some embodiments, the sulfide solid electrolyte includes glassy 20Li2S-80P2S5 and glass-ceramic Li7P3S. 11 crystalline Li 10 GeP2S 12 At least one of Li6PS5Cl.

[0052] In some embodiments, the mass ratio of the nickel-containing positive electrode active material to the solid electrolyte is (3-5):1, for example, it can be any value within the range of 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any value within the range of any two values. When the mass ratio of the nickel-containing positive electrode active material to the solid electrolyte is within the above range, the positive electrode active material and the solid electrolyte form a compact and uniform composite structure, which works synergistically with the biomimetic microstructure of the current collector (such as mushroom-shaped protrusions or nanoporous layers) to enhance the mechanical strength of the electrode. During battery charging and discharging, the volume change of the positive electrode active material can be effectively buffered, reducing damage to the electrode structure and shedding of the active material, thereby improving the structural stability of the battery.

[0053] The conductive agent in the positive electrode active material layer of the present invention is not particularly limited, and can be selected from conventional conductive agents in solid-state batteries, such as conductive carbon black or one or more mixed conductive agents from carbon nanotubes, graphene, and carbon fibers.

[0054] 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: Step S1: Dry-mix the nickel-containing positive electrode active material, solid electrolyte, conductive agent, first binder and second binder to obtain a mixture. Step S2: The mixture obtained in step S1 is applied to the surface of the positive electrode current collector and then subjected to hot pressing. The hot pressing process includes a first hot pressing stage, a second hot pressing stage, and a third hot pressing stage that occur sequentially. The temperature of the first hot pressing stage is 70℃-100℃, and the pressure is 8Mpa-15Mpa. The temperature of the second hot pressing stage is 110℃-140℃, and the pressure is 12Mpa-20Mpa; The temperature of the third hot-pressing stage is 50℃-80℃, and the pressure is 18Mpa-25Mpa.

[0055] In some embodiments, the dry mixing conditions in step S1 include: ultrasonic-assisted mixing with an ultrasonic frequency of 30-50 kHz and an ultrasonic time of 8-15 min. These ultrasonic conditions can also be adjusted based on the quality of the mixture.

[0056] In some implementations, step S2 involves three consecutive hot-pressing processes. The entire dynamic hot-pressing process is controlled by temperature-pressure coupling, allowing the first and second adhesives to leverage their respective advantages and work synergistically at different stages.

[0057] For example, the temperature of the first hot pressing stage is 70°C-100°C (e.g., it can be any point in the range of 70°C, 80°C, 90°C, 100°C or any point in the range of two pairs of values), and the pressure is 8 MPa-15 MPa (e.g., it can be any point in the range of 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa or any point in the range of two pairs of values).

[0058] For example, the temperature of the second hot-pressing stage is 110°C-140°C (e.g., it can be any point in the range of 110°C, 120°C, 130°C, 140°C or any point in the range of two pairs of values), and the pressure is 12 MPa-20 MPa (e.g., it can be any point in the range of 12 MPa, 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, 20 MPa or any point in the range of two pairs of values).

[0059] For example, the temperature of the third hot pressing stage is 50°C-80°C (e.g., it can be any point in the range of 50°C, 60°C, 70°C, 80°C or any point in the range of two pairs of values), and the pressure is 18 MPa-25 MPa (e.g., it can be any point in the range of 18 MPa, 19 MPa, 20 MPa, 21 MPa, 22 MPa, 23 MPa, 24 MPa, 25 MPa or any point in the range of two pairs of values).

[0060] There are no special restrictions on the temperatures of the first, second, and third hot-pressing stages; they can be adjusted according to factors such as the compaction density of the electrode sheets.

[0061] In the first hot-pressing stage, the glass transition of the first binder (polymer nanofibers) is activated, allowing it to stretch and fill pores under pressure and lower temperature, constructing a preliminary physical adhesion framework. In the second hot-pressing stage, the second binder undergoes a cross-linking reaction at higher temperature and pressure, forming a covalent network that fills weak points in the physical structure of the polymer nanofibers and intertwines with them, organically fusing physical entanglement and covalent bonds to form a strong and robust composite adhesion system. The third hot-pressing stage is a second pressing treatment, using high pressure to stabilize the previously formed microstructure and chemical bonding state, preventing excessive rebound of the electrode sheet after the first two hot presses. This ensures stable and high-strength adhesion between the positive electrode film and the current collector, active material, and solid electrolyte, thereby improving the overall performance and stability of the dry-process positive electrode sheet for solid-state batteries.

[0062] In some embodiments, prior to step S1, the method for preparing the positive electrode sheet further includes a step of pre-treating the positive electrode current collector: treating the positive electrode current collector with a laser process to form a protrusion on at least the surface of the positive electrode current collector on the side where the positive electrode active material layer is disposed.

[0063] In some embodiments, a protrusion array structure is generated on the surface of the positive electrode current collector on the side where the positive electrode active material layer is disposed by laser induction.

[0064] In some implementations, a pulsed laser is used to form a nanoporous layer at the end of the protrusion away from the positive current collector.

[0065] In some embodiments, the parameters of the laser process include: wavelength of 1000 nm-1500 nm, power of 40W-60W, and frequency of 80kHz-150kHz.

[0066] In some embodiments, a pretreatment step of removing residual alkali from the nickel-containing positive electrode active material is included before step S1. Specifically, an acidic solution can be used to clean the nickel-containing positive electrode active material to remove surface residual alkali; for example, a 2wt% citric acid solution can be used as the acidic solution. Optionally, after cleaning with the acidic solution, the nickel-containing positive electrode active material needs to be washed to prevent residual substances from forming an impurity layer on the surface of the nickel-containing positive electrode active material.

[0067] This invention overcomes the core technical bottleneck of insufficient adhesion of high-nickel solid-state dry cathode films through interdisciplinary innovation of bionics and materials chemistry, providing key process assurance for the large-scale application of high-reliability solid-state batteries, while also possessing the advantages of green manufacturing and low cost.

[0068] 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.

[0069] Applying the positive electrode sheet provided by this invention to solid-state batteries can improve the cycle performance, high and low temperature performance, and flexibility of solid-state batteries.

[0070] For example, a schematic diagram of the internal structure of a solid-state battery is shown below. Figure 2 As shown.

[0071] For example, a schematic diagram of the external structure of a solid-state battery is shown below. Figure 3 As shown.

[0072] The solid-state battery provided by this invention can be applied in high-vibration environments (e.g., engineering machinery, aerospace), wide-temperature-range energy storage systems (e.g., polar / desert regions), and ultra-thin and flexible application scenarios (e.g., foldable electronic devices).

[0073] 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.

[0074] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0075] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0076] Example 1a 1. Preparation of the positive electrode: (1) Current collector pretreatment: After cleaning with acetone, the aluminum foil (thickness of 12μm) is processed with a femtosecond laser (wavelength 1030nm) to form a mushroom-shaped array of protrusions (diameter 5-10μmm, height 3-5μm, spacing 2-5μm) on one side surface of the aluminum foil; and a nanoporous layer (pore size 100-150nm) is formed on the top of the protrusions by a pulsed laser (power 50W, frequency 100kHz). (2) Residual alkali removal from high-nickel materials: The high-nickel material NCM9235 (Dv50=6μm) was cleaned with 2wt% citric acid solution to remove residual alkali from the surface; then it was washed with deionized water and dried. (3) Material composite: The high-nickel material NCM9235 after removing residual alkali, solid electrolyte Li6PS5Cl, PEEK fiber, polyDOPA, and KH-550 were dry-mixed in a mass ratio of 80:20:2:1:0.5. Ultrasonic-assisted mixing was used with an ultrasonic frequency of 40kHz and an ultrasonic time of 10min. Among them, the average diameter of PEEK fiber is about 300nm, the aspect ratio is 39, and the glass transition temperature is 149℃; (4) Dynamic hot pressing: The mixture obtained in step (3) is spread on the surface of the pretreated aluminum foil and hot pressing is carried out in three stages; the temperature of the first hot pressing stage is 80℃, the pressure is 10MPa, and the hot pressing time is 20s; the temperature of the second hot pressing stage is 120℃, the pressure is 15MPa, and the hot pressing time is 30s; the temperature of the third hot pressing stage is 60℃, the pressure is 20MPa, and the hot pressing time is 25s; dry positive electrode sheet is obtained.

[0077] 2. Preparation of the negative electrode: 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.

[0078] 3. Solid electrolyte film: Solid electrolyte Li6PS5Cl powder and PTFE powder are mixed at a mass ratio of 3:1, dispersed and mixed uniformly at high speed, and then film-forming and rolled to obtain a solid electrolyte film with a thickness of 40μm.

[0079] 4. Battery assembly 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 and 0.1C constant current and constant voltage charging to 40% SOC.

[0080] The following examples were performed according to Example 1a. The main differences between the remaining examples and comparative examples are shown in Table 1. Specifically, the aspect ratio of the PEEK fibers was changed primarily by shearing the PEEK fibers to alter their length, thereby adjusting their aspect ratio. The mass percentage of the first binder was adjusted during the mixing process in step (3). In Examples 1a-1e, both the aspect ratio of the polymer nanofibers and the mass percentage of the first binder were within the scope of protection of this invention. In Comparative Examples 1 and 2, neither the aspect ratio of the polymer nanofibers nor the mass percentage of the first binder were within the scope of protection of this invention. In Comparative Example 3, the mass percentage of the first binder was not within the scope of protection of this invention. In Comparative Example 4, the aspect ratio of the polymer nanofibers was not within the scope of protection of this invention. In Comparative Example 5, no second binder was added.

[0081] Table 1 As can be seen from Table 1, the present invention improves the adhesion, high and low temperature performance and flexibility of the positive electrode by using a combination of the first binder and the second binder, and by adjusting the aspect ratio and content of the first binder within a suitable range.

[0082] The positive electrode plates or batteries obtained in the above embodiments and comparative examples were subjected to the following performance tests: (1) Adhesion of the positive electrode The test method for the adhesion of the positive electrode includes: 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.

[0083] 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 with acetone four times 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 24 mm and a length of 300 mm from the remaining sample. ④ Fold one end of the cut specimen in half to form a folded layer of about 12 mm 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 600 mm / min. ⑤ Peel about 25 mm 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 (300 mm / min), specimen width (24 mm), and other parameters, click the test option, the test starts, the equipment automatically records the force value during the peeling process, and reports the peel strength of the specimen accordingly. ⑦ Repeat steps (3) to (6) regarding the sample cutting, preparation, and testing procedures, and test the peel strength of 3 samples. If the peel strength is ≥6 N / m, it is qualified; if the peel strength is <6 N / m, it is unqualified.

[0084] (2) High and low temperature performance test Set the high / low temperature chamber temperature to 60℃ / -20℃, place the battery in the chamber for 2 hours, and set the charge / discharge steps as follows: 0.1C constant current constant voltage charging to 4.25V, 0.1C constant current discharging to 2.5V; repeat 3 times. Compare the charge / discharge capacity at 60℃ / -20℃ with the charge / discharge capacity at room temperature (25℃), and determine if the value is ≥80%. If the ratio of the charge / discharge capacity at 60℃ / -20℃ to that at room temperature (25℃) is ≥80%, the battery is qualified; if it is <80%, the battery is unqualified.

[0085] (3) Flexibility test Cut the positive electrode sheet to 15mm in length and 10mm in width. Fold the electrode sheet 180° in half and back and forth 3 times. If the result is that it is not transparent and does not break, it passes the flexibility test (marked as qualified). Otherwise, it fails (marked as unqualified).

[0086] 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.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications or equivalent substitutions 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 nickel-containing positive electrode active material, a conductive agent, a binder, and a silane coupling agent; The adhesive includes a first adhesive and a second adhesive; The first binder comprises polymer nanofibers, wherein the glass transition temperature of the polymer nanofibers is 140-160°C, and the aspect ratio of the polymer nanofibers is 30-90. The second adhesive comprises a polymer containing catechol groups.

2. The positive electrode sheet according to claim 1, characterized in that, The silane coupling agent includes at least one of γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, and diethylenetriaminopropyltrimethoxysilane.

3. The positive electrode sheet according to claim 1, characterized in that, The first binder accounts for 0.8%-5% of the mass of the positive electrode active material layer; And / or, the second binder accounts for 0.3%-4% of the mass of the positive electrode active material layer.

4. The positive electrode sheet according to claim 1, characterized in that, The polymer nanofibers are polyetheretherketone nanofibers.

5. The positive electrode sheet according to claim 1, characterized in that, The polymer containing catechol groups is polydopamine.

6. The positive electrode sheet according to any one of claims 1-5, characterized in that, The chemical formula of the nickel-containing positive electrode active material 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 Dv50 of the nickel-containing positive electrode active material is 4 μm-12 μm.

7. The positive electrode sheet according to any one of claims 1-5, characterized in that, The positive electrode active material layer includes a solid electrolyte; The solid electrolyte includes at least one of sulfide solid electrolyte, oxide solid electrolyte and polymer-based solid electrolyte; The sulfide solid electrolyte includes glassy 20Li2S-80P2S5 and glass-ceramic Li7P3S. 11 , Crystalline Li6PS5Cl, Li 10 GeP2S 12 At least one of them.

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: Dry-mix the nickel-containing positive electrode active material, conductive agent, first binder and second binder to obtain a mixture. Step S2: The mixture obtained in step S1 is applied to the surface of the positive electrode current collector and then subjected to hot pressing. The hot pressing process includes a first hot pressing stage, a second hot pressing stage, and a third hot pressing stage that occur sequentially. The temperature of the first hot pressing stage is 70℃-100℃, and the pressure is 8Mpa-15Mpa. The temperature of the second hot pressing stage is 110℃-140℃, and the pressure is 12Mpa-20Mpa; The temperature of the third hot-pressing stage is 50℃-80℃, and the pressure is 18Mpa-25Mpa.

9. The method according to claim 8, characterized in that, Before step S1, there is also a step of pre-treatment of the positive current collector: the positive current collector is treated with laser technology to form a protrusion on at least the surface of the positive current collector on the side where the positive active material layer is set. The parameters of the laser process include: wavelength 1000 nm-1500 nm, power 40W-60W, and frequency 80kHz-150kHz.

10. A solid-state battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1-7.

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