Preparation method of integrated positive electrode and solid-state battery

Abstract

The invention provides a preparation method of an integrated positive electrode and a solid-state battery, and belongs to the technical field of solid-state batteries. The method comprises the following steps: mixing a positive active material precursor, a solid electrolyte material, a stress buffer material and a solvent to obtain composite slurry; putting a metal-based porous current collector into the composite slurry, and carrying out vacuum impregnation treatment to obtain a filled current collector; placing the filled current collector in a magnetic field of which the magnetic field direction is along the thickness direction of the filled current collector, and performing magnetic field treatment to obtain an intermediate product; sintering the intermediate product to obtain an integrated positive electrode; wherein the stress buffer material comprises an inner core and a shell layer coating the surface of the inner core, the inner core is magnetic nanoparticles, and the material of the shell layer comprises a polyvinylidene fluoride-hexafluoropropylene copolymer. The invention aims to solve the technical problems that an existing positive electrode layer is low in interface bonding strength, and interface degradation is aggravated due to stress accumulation generated in the battery charging and discharging process.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, specifically to a method for preparing an integrated positive electrode and a solid-state battery. Background Technology

[0002] Solid-state batteries, as a next-generation energy storage technology, have attracted widespread attention due to their high safety and high energy density. The positive electrode layer is a key component of the solid-state battery system, and its structural design directly affects the overall performance of the battery.

[0003] In existing technologies, the positive electrode layer of solid-state batteries is typically prepared using a mechanical mixing method. This involves mixing the positive electrode active material, solid electrolyte, and conductive agent through mechanical means such as ball milling, and then directly coating the mixture onto the surface of the current collector to form the positive electrode layer. However, positive electrode layers prepared using this method suffer from problems such as low interfacial bonding strength between the positive electrode layer and the current collector, and stress accumulation during battery charging and discharging easily exacerbating interfacial degradation. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a method for preparing an integrated positive electrode and a solid-state battery, which aims to solve the technical problems of low interfacial bonding strength and accelerated interface degradation caused by stress accumulation during battery charging and discharging in the existing positive electrode layer.

[0005] In a first aspect, embodiments of this application provide a method for preparing an integrated positive electrode, comprising the following steps:

[0006] A composite slurry is obtained by mixing a positive electrode active material precursor, a solid electrolyte material, a stress buffer material, and a solvent. The metal-based porous current collector is immersed in the composite slurry for vacuum impregnation to obtain a filled current collector. The filling current collector is placed in a magnetic field with the magnetic field direction along the thickness direction of the filling current collector, and magnetic field treatment is performed to obtain an intermediate product; The intermediate product is sintered to obtain an integrated positive electrode. The stress-buffering material includes a core and a shell covering the surface of the core. The core is a magnetic nanoparticle, and the shell is made of polyvinylidene fluoride-hexafluoropropylene copolymer.

[0007] Secondly, embodiments of this application also provide a solid-state battery, including an integrated positive electrode prepared by the preparation method described above.

[0008] The technical solution proposed in this application has the following beneficial effects: The preparation method provided in this application employs a composite slurry-impregnation-sintering process. On one hand, this effectively increases the loading of the positive electrode active material, while simultaneously ensuring the uniform distribution of the positive electrode active material precursor, solid electrolyte material, and stress buffer material on the surface and within the pore structure of the metal-based porous current collector. This allows the positive electrode active material and solid electrolyte material to be uniformly distributed within the three-dimensional pore structure, forming a continuous ion-electron conduction pathway, thereby effectively improving the conductivity of the positive electrode network. On the other hand, by introducing the stress buffer material, the volume change stress of the positive electrode active material is effectively absorbed, helping to reduce the generation of interfacial microcracks while maintaining the integrity of the ion transport channels, thus improving the cycle stability and interfacial durability of the electrode structure. Furthermore, this application applies a magnetic field to the stress buffer material while introducing it. Through the magnetic core and magnetic field guidance, the stress buffer material is oriented along its thickness direction within the positive electrode, constructing an oriented stress buffer network, further enhancing its stress buffering and absorption capabilities.

[0009] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0011] Figure 1 This is a schematic diagram of the orientation distribution of the stress-buffering material before it is treated with a gradient magnetic field. Figure 2 This is a schematic diagram of the orientation distribution of a stress-buffering material after treatment with a gradient magnetic field. Figure 3 A comparison graph showing the 1C discharge performance of batteries prepared using the integrated positive electrode of Example 1 and the positive electrode of Comparative Example 1. Figure 4 A comparison graph showing the cycle life of batteries made using the integrated positive electrode of Example 1 and the positive electrode of Comparative Example 1; Figure 5 The DCR comparison graphs are shown for batteries prepared using the integrated positive electrode of Example 1 and the positive electrode of Comparative Example 1 at 100% SOC, 3C, and 5s. Detailed Implementation

[0012] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0013] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0014] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, and therefore applies regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0015] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0016] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0017] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0018] In the description of the embodiments of this application, the term "at least one" refers to one or more, "more than one" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces). "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0019] In existing technologies, the positive electrode layer of solid-state batteries is typically prepared using a mechanical mixing method. This involves mixing the positive electrode active material, solid electrolyte, and conductive agent through mechanical means such as ball milling, and then directly coating the mixture onto the surface of the current collector to form the positive electrode layer. However, positive electrode layers prepared using this method suffer from problems such as low interfacial bonding strength between the positive electrode layer and the current collector, and stress accumulation during battery charging and discharging easily exacerbating interfacial degradation.

[0020] In view of this, embodiments of this application propose a method for preparing an integrated positive electrode, the method comprising the following steps: S10, a positive electrode active material precursor, a solid electrolyte material, a stress buffer material, and a solvent are mixed to obtain a composite slurry; wherein, the stress buffer material includes a core and a shell covering the surface of the core, wherein the core is a magnetic nanoparticle, and the material of the shell includes polyvinylidene fluoride-hexafluoropropylene copolymer.

[0021] S20, the metal-based porous current collector is placed into the composite slurry for vacuum impregnation treatment to obtain a filled current collector.

[0022] S30, the filling current collector is placed in a magnetic field with the magnetic field direction along the thickness direction of the filling current collector, and magnetic field treatment is performed to obtain an intermediate product.

[0023] S40, the intermediate product is sintered to obtain an integrated positive electrode.

[0024] Research has revealed that the main reasons for the shortcomings of the cathode layer prepared by existing technologies are: (1) The positive electrode active material and the current collector mainly have face-to-face physical contact, resulting in low interfacial bonding strength. As a result, as the working time of the solid-state battery increases, interfacial peeling is very likely to occur, which will increase the internal resistance and affect the cycle life and discharge performance of the battery; (2) During the charging and discharging process, the positive electrode active material will undergo volume changes, which will generate stress. If it cannot be effectively released, the accumulated stress will easily damage the interface, aggravate the interface degradation, and thus affect the battery performance. At the same time, the coating method also has the problems of the positive electrode active material loading being limited by the coating area of ​​the current collector and the uneven distribution of solid electrolyte material in the cathode layer. The limited loading will easily affect the battery capacity and cycle performance, and the uneven distribution will cause the ion transport channels to be discontinuous, thus affecting the battery performance; In addition, the electron and ion transport paths in the cathode layer prepared by existing methods often compete with each other, making it difficult to form a cooperative conduction network, which will affect the conductivity. These defects restrict the further improvement of solid-state battery performance.

[0025] The preparation method provided in this application can produce a positive electrode with an integrated structure that combines a positive electrode active material, a solid electrolyte, and a current collector. The integrated positive electrode includes a metal-based porous current collector and a positive electrode active material precursor, a solid electrolyte material, and a stress buffer material uniformly dispersed on the surface and in the pore structure of the metal-based porous current collector. By employing a process that first disperses the positive electrode active material precursor, solid electrolyte material, and stress buffer material in a solvent to form a fluid composite slurry, then fills the pore structure of a metal-based porous current collector through an impregnation method, and finally sintersects, the process effectively improves the loading capacity and utilization rate of the positive electrode active material by leveraging the well-developed and continuous three-dimensional pore structure of the metal-based porous current collector. Simultaneously, it ensures the uniform distribution of the positive electrode active material precursor, solid electrolyte material, and stress buffer material on the surface and within the pore structure of the metal-based porous current collector, solving the problem of uniform distribution of these components in the positive electrode. This allows the positive electrode active material and solid electrolyte material to be uniformly distributed within the three-dimensional pore structure to form a continuous ion-electron conduction pathway, thereby effectively improving the conductivity of the positive electrode network. Furthermore, the stress buffer material's shell is elastic and deformable. By introducing the stress buffer material, it can effectively absorb the volume change stress of the positive electrode active material, reduce the generation of interfacial microcracks, and maintain the integrity of the ion transport channels, thereby improving the cycle stability and interfacial durability of the electrode structure. Furthermore, this application introduces a stress-absorbing material while applying a magnetic field to it. Through the magnetic core and magnetic field guidance, the stress-absorbing material is oriented along its thickness direction within the positive electrode, constructing an oriented stress-absorbing network, which further enhances its stress-absorbing and stress-absorbing capabilities. In addition, the method of this application avoids the use of binders, reduces inactive components, and increases energy density.

[0026] In addition, the self-supporting properties of the integrated positive electrode obtained in this application avoid the alignment and bonding problems of traditional coating processes, simplifying the battery assembly process. At the same time, the robust structural design helps to improve the mechanical strength of the electrode, which is beneficial to the large-scale production and application of the battery.

[0027] In some embodiments, before step S10, a step of preparing a stress-buffering material is included. Specifically, the preparation of the stress-buffering material includes the following steps: S1, Magnetic nanoparticles are dispersed in water, an emulsifier is added, and the mixture is ultrasonically suspended to form a suspension; S2, vinylidene fluoride monomer, hexafluoropropylene monomer and potassium persulfate are added to the suspension, heated and stirred to polymerize, and a reaction mixture is obtained; S3, the reaction mixture is separated into solid and liquid phases and the solid phase is collected. The solid phase is then dried to obtain a stress-absorbing material.

[0028] Specifically, in step S1, the magnetic nanoparticles include, but are not limited to, any one of iron(III) oxide nanoparticles (Fe3O4), cobalt ferrite nanoparticles (CoFe2O4), and nickel ferrite nanoparticles (NiFe2O4). The average particle size of the magnetic nanoparticles is 20-50 nm, for example, 20 nm, 30 nm, 40 nm, 50 nm, or any value between two of the above. Controlling the size of the nanoparticles within the above range helps to regulate the size of the stress-absorbing material. The water used can be deionized water. By first dispersing the nanoparticles in deionized water and adding an emulsifier, a stable suspension with active groups such as hydroxyl groups adsorbed on the surface is formed. Then, a monomer is introduced to form a polyvinylidene fluoride-hexafluoropropylene copolymer on the surface of the nanoparticles, thereby directionally forming a core-shell structured particulate material and avoiding abnormal morphologies such as magnetic nanoparticles being loaded on the polymer surface or nanoparticles being independently distributed from the polymer. In addition, the emulsifier can include, but is not limited to, at least one of sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS).

[0029] The amount of nanoparticles and emulsifier added can meet the following conditions: the mass ratio of the magnetic nanoparticles to the emulsifier is 1:0.03~0.15; for example, 1:0.03, 1:0.05, 1:0.08, 1:0.10, 1:0.13, 1:0.15 and any two of the above values.

[0030] The amount of nanoparticles and water added can meet the following conditions: the mass ratio of the magnetic nanoparticles to water is 1:100~150; for example, 1:100, 1:110, 1:120, 1:130, 1:140, 1:150 and any two of the above values.

[0031] Ultrasound can promote the uniform dispersion of magnetic nanoparticles and emulsifiers in water. In some embodiments, the frequency of ultrasound is 20-40 kHz, the power is 40-60 W / L, and the duration is 30-60 min.

[0032] In step S2, the ratio of the total mass of the vinylidene fluoride monomer and the hexafluoropropylene monomer to the mass of the magnetic nanoparticles is 1:2 to 5; for example, it can be 1:2, 1:3, 1:4, 1:5, or any value between the above two. By controlling the ratio of the total monomer content to the mass of the nanoparticles within the above range, the shell thickness can be adjusted, thereby controlling the stress absorption capacity of the stress-absorbing material. In some embodiments, the shell thickness of the stress-absorbing material is approximately 5 to 20 nm.

[0033] In some specific embodiments, the mass ratio of vinylidene fluoride monomer to hexafluoropropylene monomer can be 90:10.

[0034] In step S2, the heating and stirring temperature is 50~80℃, for example, it can be 50℃, 60℃, 70℃, 80℃ and any two of the above values; the heating and stirring time is 3~8h, for example, it can be 3h, 4h, 5h, 6h, 7h, 8h and any two of the above values.

[0035] In some embodiments, in step S3, the reaction mixture can be separated into a solid phase and a liquid phase through solid-liquid separation. After washing the solid phase multiple times and then drying it, a core-shell structured stress-absorbing material can be obtained. Specifically, solid-liquid separation can be performed by centrifugation at a speed of 7000-9000 r / min for 8-12 min; the washing can be repeated 3-5 times. The drying temperature is 50-70℃, for example, 50℃, 60℃, 70℃, or any value between two of these values; the drying time is 8-12 h, for example, 8h, 9h, 10h, 11h, 12h, or any value between two of these values.

[0036] In step S10, the solid electrolyte material is a sulfide solid electrolyte, which includes Li2S-P2S5, Li2S-SiS2, or Li 10 GeP2S 12 At least one of the following; the particle size distribution of the solid electrolyte material is in the range of 0.1 μm to 1 μm. It can be understood that Li2S-P2S5 refers to a mixture of Li2S and P2S5, and Li2S-SiS2 refers to a mixture of Li2S and SiS2. In specific implementation, the two components can be mixed and ball-milled.

[0037] In step S10, the positive electrode active material precursor includes a mixture of a transition metal source and a lithium source. The transition metal source may include, but is not limited to, nickel compounds, cobalt compounds, manganese compounds, etc., specifically carbonates or hydroxides, such as nickel cobalt manganese carbonate. The lithium source may include, but is not limited to, lithium carbonate or lithium hydroxide. The molar ratio of the lithium source to the transition metal source can be 1.05~1.10:1. In specific implementation, the transition metal source and the lithium source can be mixed and dried to prepare the positive electrode active material precursor. Taking nickel cobalt manganese carbonate as an example, the transition metal source can be obtained through the following steps: mixing nickel sulfate, cobalt sulfate, manganese sulfate, sodium carbonate, and water, and reacting to obtain nickel cobalt manganese carbonate.

[0038] The particle size of the positive electrode active material precursor can be 3~5μm.

[0039] In step S10, the solvent may include, but is not limited to, at least one of N-methylpyrrolidone (NMP) and acetonitrile.

[0040] The viscosity of the composite slurry is 3000~5000 mPa·s; for example, it can be 3000 mPa·s, 4000 mPa·s, 5000 mPa·s, or any value between two of the above. In specific implementation, the viscosity of the composite slurry can be adjusted by controlling the amount of solvent added.

[0041] Furthermore, the addition amounts of the positive electrode active material precursor, solid electrolyte material, and stress buffer material can refer to the following conditions: In the mixed system composed of the positive electrode active material precursor, the solid electrolyte material, and the stress buffer material, the mass percentage of the stress buffer material is 1-3%; for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, or any value between any two of the above. In the mixed system composed of the positive electrode active material precursor and the solid electrolyte material, the mass percentage of the solid electrolyte material is 20-30%; for example, it can be 20%, 22%, 25%, 28%, 30%, or any value between any two of the above.

[0042] By controlling the component ratio and viscosity within the above range, the fluidity and dispersion of the composite slurry can be adjusted, the filling effect of the slurry can be improved, the uniformity of the distribution of positive electrode active material, solid electrolyte material and stress buffer material in the positive electrode can be enhanced, a complete ion-electron conduction pathway can be constructed, and the ion conductivity and electronic conductivity can be balanced.

[0043] In step S20, the metal-based porous current collector has multiple pores; furthermore, in some embodiments, the multiple pores are interconnected to form a three-dimensional channel structure. This three-dimensional channel structure provides ideal accommodating space for the subsequent filling of composite slurry, its continuous network skeleton ensures rapid electron conduction within the current collector, and the uniformly distributed channels provide ample space for the loading of the positive electrode active material. Furthermore, the metal material of the metal-based porous current collector can be, but is not limited to, at least one of nickel and aluminum. Specifically, the metal-based porous current collector can be nickel foam, aluminum foam, nickel fiber felt, aluminum fiber felt, etc.

[0044] As a preferred embodiment, a metal-based porous current collector meeting the following conditions can be used: a porosity of 60% to 80%, an average pore size of 5 μm to 15 μm, and a thickness of 50 μm to 200 μm. By adjusting the pore characteristics of the current collector, the loading of the positive electrode active material can be adjusted, and this can be modified according to the loading requirements during application. In practice, it can be purchased commercially or commissioned from a manufacturer, or it can be prepared in-house. For example, it can be prepared by following these steps: placing a pure nickel block in a foaming furnace and heating it to approximately 50 to 100°C above the melting point of nickel under a protective atmosphere, then adding a foaming agent and maintaining the temperature, and finally cooling it at a certain cooling rate to obtain a foamed nickel matrix with a porous structure. In actual operation, the porosity, average pore size, and thickness of the product can be adjusted by regulating the foaming temperature, holding time, and cooling rate.

[0045] In some embodiments, step S20 may specifically include: placing the metal-based porous current collector into the composite slurry, and under ultrasonic conditions of 25-35 kHz, first impregnating it under a vacuum of 0.01-0.03 MPa for 10-20 min, and then impregnating it under a vacuum of 0.06-0.08 MPa for 20-40 min to obtain a filled current collector. It can be understood that in this embodiment, the metal-based porous current collector is placed in the composite slurry, and the metal-based porous current collector undergoes two-step vacuum impregnation, with continuous ultrasonic oscillation treatment of the impregnation system during the vacuum impregnation process. Compared with the prior art, this invention achieves uniform filling of the composite slurry in the metal-based porous current collector through the synergistic effect of stepwise vacuum impregnation and ultrasonic oscillation. First, preliminary impregnation is completed under a low vacuum. The composite slurry penetrates the surface pores of the metal-based porous current collector under capillary action, reducing residual air bubbles. Then, deep impregnation is carried out under a higher vacuum, which promotes the composite slurry to penetrate deep into the pores. At the same time, ultrasonic oscillation at a specific frequency breaks up the agglomeration of the composite slurry and traps air bubbles, promoting the entry of nanoscale components into micron-scale pores. This ensures the uniform distribution of positive electrode active material, solid electrolyte material, and stress buffer material in the three-dimensional porous network, forming a continuous interpenetrating ion-electron conduction pathway, effectively improving the conductivity network connectivity and active material utilization of the positive electrode.

[0046] The vacuum degree for preliminary impregnation is 0.01~0.3MPa, specifically 0.01MPa, 0.02MPa, 0.03MPa, or any two of these values; the preliminary impregnation time is 10~20min, specifically 10min, 12min, 15min, 17min, 20min, or any two of these values; the vacuum degree for deep impregnation is 0.06~0.08MPa, specifically 0.060MPa, 0.07MPa, 0.08MPa, or any two of these values; the deep impregnation time is 20~40min, specifically 20min, 25min, 30min, 35min, 40min, or any two of these values. In practice, an impregnation tank can be used for the above impregnation steps.

[0047] The frequency of the ultrasound is 25~40kHz, for example, it can be 25kHz, 30kHz, 35kHz, 37kHz, 40kHz, or any value between the two above; in specific implementation, a piezoelectric ceramic transducer can be set at the bottom of the impregnation tank to generate ultrasonic oscillation.

[0048] In some embodiments, an excessive amount of composite slurry is used during vacuum impregnation to ensure complete filling of the pores. Specifically, the amount of composite slurry used is calculated based on the effective pore volume of the current collector: for a metal-based porous current collector with a thickness of 50~200μm, 0.05~0.2mL of composite slurry is used per square centimeter of metal-based porous current collector. This not only ensures complete filling of the pores but also avoids excessive residue.

[0049] In some embodiments, after the vacuum impregnation step is completed, the filling current collector can be lifted at a constant speed to ensure that excess slurry on the surface of the current collector is removed evenly.

[0050] In some embodiments, before step S20, the metal-based porous current collector may be pretreated. Specifically, the pretreatment step may include: performing plasma activation treatment on the metal-based porous current collector using a mixed gas of argon and oxygen. The power of the plasma activation treatment is 500W~1000W, for example, 500W, 600W, 700W, 800W, 900W, 1000W, or any value between any two of the above; the treatment time is 5~15min, for example, 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min, 15min, or any value between any two of the above; the volume fraction of oxygen in the mixed gas is 5~10%, for example, 5%, 6%, 7%, 8%, 9%, 10%, or any value between any two of the above. During plasma treatment, high-energy particles bombard the surface of the current collector, which can introduce oxygen-containing functional groups and form nanoscale pits, increasing the surface roughness and reducing the contact angle. This improves the wettability of the current collector surface to the composite slurry and enhances the filling effect during subsequent vacuum impregnation.

[0051] Furthermore, in some embodiments, during pretreatment, the metal-based porous current collector can be rotated at a constant speed to ensure uniform contact between the current collector and the mixed gas, thereby improving the uniformity of plasma treatment.

[0052] In some embodiments, step S30 may specifically include: placing the filling current collector in a gradient magnetic field for magnetic field treatment, while simultaneously applying mechanical vibration to the filling current collector to obtain an intermediate product; wherein the magnetic field direction of the gradient magnetic field is consistent with the thickness direction of the filling current collector, and the magnetic field strength of the gradient magnetic field increases along the thickness direction of the filling current collector, and the vibration direction of the mechanical vibration is along the thickness direction of the filling current collector. The stress-absorbing material has magnetic particles as its core and is therefore magnetic. Figure 1 and Figure 2As shown, under the action of a gradient magnetic field, the stress buffer material can move and align in an orderly manner along the direction of the magnetic field. Simultaneously, mechanical vibration can break up particle agglomeration, ensuring uniformity of arrangement. This directional arrangement forms a continuous directional stress buffer network in the composite slurry, with its orientation consistent with the stress direction during subsequent charging and discharging, thus buffering stress. Specifically, the directional stress buffer network can be understood as follows: the long axis of each core-shell structured stress buffer material particle (the alignment direction formed by the magnetic field orientation) is parallel to the thickness direction of the current collector (from the weak magnetic field side 0.5T to the strong magnetic field side 1.5T). The particles are interconnected but not agglomerated, forming a network structure similar to "directional fiber bundles," wrapping the surface of the positive electrode active material and the solid electrolyte material. This network is uniformly interwoven within three-dimensional channels, ensuring that volume change stress in any region during charging and discharging can be effectively absorbed.

[0053] The magnetic field strength of the gradient magnetic field is distributed in the range of 0.5~1.5T, that is, along the thickness direction of the filling current collector (set as follows). Figure 1 As shown in the bottom-up direction, a gradient magnetic field is formed on the filling current collector, gradually increasing from bottom to top, with the magnetic field strength increasing from 0.5T to 1.5T. Based on this, this application does not limit the rate of change of the magnetic field strength. In one specific embodiment, magnetic fields with strengths of 0.5T, 1T, and 1.5T can be provided at the lower, middle, and upper parts of the filling current collector, respectively.

[0054] The magnetic field treatment time is 10 to 30 minutes; for example, it can be 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or any value between any two of the above.

[0055] The frequency of the mechanical vibration is 20~30kHz, for example, it can be 20kHz, 22kHz, 25kHz, 27kHz, 30kHz and any two of the above values; the vibration amplitude of the mechanical vibration is 0.1~0.5mm, for example, it can be 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm and any two of the above values.

[0056] In some embodiments, before placing the filling current collector in a gradient magnetic field for magnetic field treatment, the process may further include: pre-treating the filling current collector in a uniform magnetic field with a magnetic field strength of 0.1~0.3T for 5~15 minutes. The direction of the uniform magnetic field is consistent with the thickness direction of the filling current collector; the magnetic field strength is 0.1~0.3T, for example, it can be 0.1T, 0.15T, 0.2T, 0.25T, 0.3T, or any value between two of the above; the pre-treatment time is 5~15 minutes, for example, it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, or any value between two of the above. That is, a pre-orientation treatment is first performed using a uniform magnetic field to induce initial movement and orientation of the stress buffer material, laying the foundation for subsequent magnetic field treatment. Then, a gradient magnetic field is used for assisted orientation to construct a stress buffer network.

[0057] The pretreatment step can be carried out in the range of 25°C to 50°C.

[0058] Furthermore, during the pretreatment process, the filling current collector is rotated at a constant speed with the thickness direction of the filling current collector as the central axis, thus ensuring the uniformity of the magnetic field effect. The rotation speed can be 5~15 r / min.

[0059] In some embodiments, step S40 may be implemented as follows: in an air atmosphere, the intermediate product is heat-treated at 250~350°C for 1~3 hours to obtain a carbide; in a protective atmosphere, the carbide is heat-treated at 600~800°C for 4~8 hours to obtain an integrated positive electrode. The first heat treatment temperature is 250~350℃, for example, it can be 250℃, 270℃, 300℃, 330℃, 350℃, or any value between any two of the above; the first heat treatment time is 1~3h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, or any value between any two of the above; the second heat treatment temperature is 600~800℃, for example, it can be 600℃, 650℃, 700℃, 750℃, 800℃, or any value between any two of the above; the second heat treatment time is 4~8h, for example, it can be 4h, 5h, 6h, 7h, 8h, or any value between any two of the above. First, heat treatment is performed at a lower temperature and in an air atmosphere to promote the gentle decomposition and carbonization of the organic components in the composite slurry. Then, heat treatment is performed under a protective atmosphere and at high temperature to induce a solid-state reaction in the positive electrode active material precursor, generating the positive electrode active material and forming a strong interfacial chemical bond with the metal-based porous current collector. During this process, not only does the positive electrode active material form a continuous network structure within the solid electrolyte material matrix, but the stress-buffered network also provides buffer space for volume changes. Furthermore, the stepwise heat treatment design avoids sudden impacts of high temperatures on the material structure and promotes the chemical bonding between the active material and the current collector.

[0060] In some embodiments, the intermediate product is heated from room temperature to 250-350°C at a heating rate of 1-3°C / min. This avoids the rapid and large-scale decomposition of organic components due to excessive heating, which would lead to the rapid generation of a large amount of gas and cause cracking. It also avoids the problem of insufficient carbonization due to excessively slow heating.

[0061] In some embodiments, the intermediate product is heated from 250-350°C to 600-800°C at a heating rate of 1-3°C / min. This can improve production efficiency and avoid large particle agglomeration caused by excessively rapid heating, resulting in uneven particle growth.

[0062] The air flow rate can be from 0.5L / min to 2L / min.

[0063] The protective atmosphere can be formed by a mixture of argon and hydrogen. The hydrogen component in the mixture is controlled within the range of 3% to 5%, and the gas flow rate is 1 to 3 L / min.

[0064] In some embodiments, after step S40, the process may further include: depositing a protective layer on the exposed surface of the integrated positive electrode using atomic layer deposition (ALD) technology. The exposed surface includes at least one of the following: the outer surface of the integrated positive electrode, the inner wall of the pores of the metal-based porous current collector, the surface of the positive electrode active material precursor, the surface of the solid electrolyte material, and the surface of the stress buffer material. This nanoscale protective layer can effectively isolate the positive electrode active material from direct contact with the solid electrolyte material while maintaining lithium-ion transmission capability, effectively suppressing interfacial side reactions between them, and helping to enhance the interfacial compatibility between the positive electrode active material and the solid electrolyte material to form a stable and low-resistance interfacial structure.

[0065] The thickness of the protective layer is 5~20nm; for example, it can be 5nm, 10nm, 15nm, 20nm, or any value between two of the above.

[0066] The protective layer is made of lithium lanthanum zirconium oxide or lithium lanthanum tantalum oxide. When the material is lithium lanthanum zirconium oxide, bis(trimethylsilyl)aminolithium and tetra(diethylamino)zirconium can be used as precursors, and atomic layer deposition is performed at 250~350℃. The number of deposition cycles can be adjusted according to the thickness of the protective layer to be formed, for example, 50 to 200 cycles. When the material is lithium lanthanum tantalum oxide, bis(trimethylsilyl)aminolithium and penta(diethylamino)tantalum can be used as precursors, and atomic layer deposition is performed at 300~350℃. The number of deposition cycles can be adjusted according to the thickness of the protective layer to be formed, for example, 50 to 200 cycles.

[0067] In addition, this application also provides a solid-state battery, including an integrated positive electrode prepared by the preparation method described above.

[0068] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0069] Example 1 (1) Commercially available nickel foam was cut to the required size (10cm × 10cm) and then ultrasonically cleaned with anhydrous ethanol and deionized water for 15 min in sequence. Subsequently, the cleaned nickel foam was placed on the sample stage of the plasma reaction chamber. The reaction chamber was evacuated to 10 Pa, and then a mixture of argon and oxygen (oxygen volume fraction of 8 vol%) was introduced and the pressure was maintained at 50 Pa. Subsequently, the nickel foam was plasma treated at a radio frequency power of 800 W for 10 min. During the treatment, the sample stage rotated at a constant speed of 10 r / min.

[0070] (2) A mixed solution of nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 8:1:1 was prepared and added to a reactor in parallel with a sodium carbonate solution. The reaction temperature was controlled at 55℃ and the pH value at 8.0. The mixture was stirred continuously for 12 hours. After filtration, washing, and drying, a nickel cobalt manganese carbonate precursor was obtained. The nickel cobalt manganese carbonate precursor was mixed with lithium carbonate in a molar ratio of 1.08:1 and deionized water was added to prepare a slurry with a solid-liquid ratio of 1:0.8. The spherical positive electrode active material precursor with a particle size distribution in the range of 3~5μm was prepared by spray drying.

[0071] (3) Take Li2S and P2S5 in a molar ratio of 70:30, put Li2S and P2S5 into a planetary ball mill jar, add zirconia ball milling beads, and ball mill at a speed of 400 r / min for 20 h under argon protection. After sieving, solid electrolyte material with a particle size distribution of 0.1~1 μm is obtained.

[0072] (4) At a mass ratio of 1:120:0.1 for iron oxide nanoparticles to water and sodium dodecyl sulfate, iron oxide nanoparticles with an average particle size of approximately 20 nm were dispersed in deionized water. Sodium dodecyl sulfate was added, and the mixture was sonicated at 30 kHz and 50 W / L for 45 min to form a uniform suspension. Then, at a mass ratio of 1:3 for the total mass of vinylidene fluoride monomer and hexafluoropropylene monomer to the mass of iron oxide nanoparticles, and a mass ratio of 90:10 for the vinylidene fluoride monomer and hexafluoropropylene monomer, vinylidene fluoride monomer and hexafluoropropylene monomer were added to the suspension. Potassium persulfate was added as an initiator, and the mixture was stirred in a water bath at 70 °C for 5 h to obtain a reaction mixture. The reaction mixture was centrifuged at 8000 r / min for 10 min to obtain a solid phase. The solid phase was then washed three times with deionized water and then vacuum dried at 60 °C for 10 h to obtain a stress-absorbing material with a core-shell structure.

[0073] (5) Mix the positive electrode active material precursor, solid electrolyte and stress buffer in a mass ratio of 70:28:2, add an appropriate amount of N-methylpyrrolidone as a solvent, and stir and mix for 2 hours at a speed of 200 r / min using a planetary mixer to form a composite slurry with a solid content of 60% and a viscosity of about 4000 mPa·s.

[0074] (6) Add composite slurry to the impregnation tank, and then fix the foamed nickel obtained in step (2) onto the sample holder and place it into the impregnation tank. First, evacuate the impregnation tank until its vacuum degree is 0.02MPa, and maintain it for 15min for preliminary impregnation. Then, increase the vacuum degree to 0.07MPa and maintain it for 30min for deep impregnation to obtain the filling current collector. During the entire impregnation process, 30kHz ultrasonic oscillation is generated by the piezoelectric ceramic transducer set at the bottom of the impregnation tank, and the ultrasonic power density is controlled at 50W / L. After impregnation, the filling current collector is lifted at a uniform speed of 0.5mm / s.

[0075] (7) The filling current collector obtained in step (6) is placed in a uniform magnetic field with a magnetic field strength of 0.2T and a magnetic field direction parallel to the thickness direction of the filling current collector for magnetic field pretreatment. The treatment temperature is controlled at 40℃ and the treatment time is 10min. During the treatment, the sample holder rotates uniformly around its thickness direction at a speed of 10r / min.

[0076] (8) Place the filled current collector processed in step (7) on the sample stage. Take three independently controlled electromagnetic coils and arrange them at intervals from bottom to top along the direction away from the sample stage to construct a gradient magnetic field with the magnetic field direction parallel to the thickness direction of the filled current collector. The magnetic field strength at the lower, middle and upper positions of the filled current collector is 0.5T, 1T and 1.5T respectively. Place the filled current collector in this gradient magnetic field for 20min. During this period, apply axial mechanical vibration of 25kHz with the vibration direction parallel to the thickness direction through a vibration platform. The vibration amplitude is 0.3mm to obtain the intermediate product.

[0077] (9) The intermediate product obtained in step (8) is placed in a temperature-controlled tube furnace. First, the temperature is increased from room temperature to 300°C at a heating rate of 2°C / min. The temperature is maintained for 2 hours in a dry air atmosphere with a gas flow rate of 1L / min. Then, the atmosphere is switched to a mixture of argon and hydrogen (hydrogen integral is 4%). The temperature is increased to 700°C at a heating rate of 2°C / min and maintained for 6 hours with a gas flow rate of 2L / min to obtain an integrated positive electrode semi-finished product.

[0078] (10) The integrated cathode semi-finished product was placed in the deposition chamber of a thermal atomic layer deposition system. Using bis(trimethylsilyl)aminolithium and tetra(diethylamino)zirconium as precursors, and high-purity nitrogen as carrier gas and purge gas, atomic layer deposition was performed at 300°C to form a dense lithium lanthanum zirconium oxide protective layer with a thickness of about 12 nm on the exposed surface of the integrated cathode semi-finished product, thus obtaining the integrated cathode. During each deposition cycle, bis(trimethylsilyl)aminolithium was introduced for 0.1 s, purge gas for 20 s, tetra(diethylamino)zirconium for 0.1 s, and purge gas for 20 s; the cycle was repeated 150 times.

[0079] Comparative Example 1 This comparative example uses a traditional coating method to prepare the positive electrode. The specific steps are as follows: Current collector pretreatment: Commercial aluminum foil with a thickness of 15μm was selected as the positive electrode current collector and cut into 10cm×10cm sizes. It was ultrasonically cleaned with anhydrous ethanol and deionized water for 15min in sequence to remove surface oil and impurities, and then dried in an 80℃ oven for 2h for later use.

[0080] Positive electrode slurry preparation: The NCM811 active material, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were added sequentially to a mixing tank in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was gradually added to the system as a solvent, controlling the slurry solid content to be 45%–50%. The mixture was first premixed by stirring at 300 rpm for 1 hour using a planetary mixer, then transferred to a ball mill jar. Zirconia balls were used as the grinding medium at a ball-to-material ratio of 5:1, and ball milling was performed at 200 rpm for 2 hours to ensure uniform dispersion of all components.

[0081] Coating and forming: The above slurry is evenly coated onto the pretreated aluminum foil surface using a doctor blade coater, controlling the wet film thickness to be 100μm~120μm. During the coating process, the doctor blade moving speed is maintained at 50mm / s to avoid slurry dripping or uneven coating.

[0082] Segmented drying: Place the coated aluminum foil in a hot air drying oven and dry it at 80°C for 1 hour to remove most of the solvent; then raise the temperature to 120°C and dry it for 2 hours to completely remove residual NMP and prevent coating cracking during subsequent rolling.

[0083] Roller pressing densification: The dried electrode sheet is placed in a roller press and subjected to single-roll pressing under a pressure of 5MPa~8MPa.

[0084] Cutting and setting aside: Cut the rolled electrode sheet into circular positive electrode sheets with a diameter of 14 mm. After vacuum drying (100℃, 2h) to remove trace moisture, the positive electrode product prepared by the traditional coating method is obtained and set aside.

[0085] (ii) Battery performance testing The integrated positive electrode prepared in Example 1 and the positive electrode prepared in Comparative Example 1 were assembled into a battery according to the following steps and conditions, and the battery performance was tested: Example 1 Battery: Using graphite as the negative electrode, the integrated positive and negative electrode sheets are cut into circular positive electrode sheets with a diameter of 14mm, and stacked together to obtain a secondary battery.

[0086] Comparative Example 1 Battery: A secondary battery was obtained by stacking graphite as the negative electrode and NCM811 as the positive electrode.

[0087] The battery was tested using an electrochemical workstation as follows: (1) At 25℃, 1C discharge performance was tested at an initial 100% SOC, such as... Figure 3 As shown in the figure, Comparative Example 1 is the same as the control example 1.

[0088] (2) The cycle life of the battery was tested at 25°C and 1C rate, as follows: Figure 4 As shown in the figure, the vertical axis SOH represents the capacity retention rate; Comparative Example 1 is also known as Comparative Example 1.

[0089] (3) At 25℃ and 100% SOC, a 3C / 5s discharge pulse was applied to the battery, and its DCR value was measured. The results are as follows: Figure 5 As shown.

[0090] Results Analysis: Compared with Comparative Example 1, the battery of Example 1 showed significantly better discharge performance, cycle life and lower DCR, indicating that the integrated positive electrode provided by this application has better interfacial bonding strength and stress buffering effect, which can solve the problems of increased internal resistance and decreased cycle life caused by interfacial degradation due to low interfacial bonding strength and stress accumulation. In addition, the integrated positive electrode has a high positive electrode active material loading and distribution uniformity, and has a continuous and non-interfering electron-ion dual conduction network, thus exhibiting good discharge performance.

[0091] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing an integrated positive electrode, characterized in that, Includes the following steps: A composite slurry is obtained by mixing a positive electrode active material precursor, a solid electrolyte material, a stress buffer material, and a solvent. The metal-based porous current collector is immersed in the composite slurry for vacuum impregnation to obtain a filled current collector. The filling current collector is placed in a magnetic field with the magnetic field direction along the thickness direction of the filling current collector, and magnetic field treatment is performed to obtain an intermediate product; The intermediate product is sintered to obtain an integrated positive electrode. The stress-buffering material includes a core and a shell covering the surface of the core. The core is a magnetic nanoparticle, and the shell is made of polyvinylidene fluoride-hexafluoropropylene copolymer.

2. The preparation method according to claim 1, characterized in that, Before the step of mixing the positive electrode active material precursor, solid electrolyte material, stress buffer material, and solvent to obtain the composite slurry, the following steps are also included: Magnetic nanoparticles are dispersed in water, an emulsifier is added, and the mixture is ultrasonically suspended. Vinylidene fluoride monomer, hexafluoropropylene monomer and potassium persulfate were added to the suspension, and the mixture was heated and stirred to polymerize, thus obtaining a reaction mixture. The reaction mixture is separated into solid and liquid phases and the solid phase is collected. The solid phase is then dried to obtain a stress-absorbing material.

3. The preparation method according to claim 2, characterized in that, The magnetic nanoparticles have an average particle size of 20-50 nm; and / or, The magnetic nanoparticles include any one of magnetite nanoparticles, cobalt ferrite nanoparticles, and nickel ferrite nanoparticles; and / or, The emulsifier includes at least one of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate; and / or, The mass ratio of the magnetic nanoparticles to the emulsifier is 1:0.03~0.15; and / or, The ratio of the total mass of the vinylidene fluoride monomer and the hexafluoropropylene monomer to the mass of the magnetic nanoparticles is 1:2~5; and / or, The heating and stirring temperature is 50~80℃, and the heating and stirring time is 3~8h; and / or, The drying process is carried out at a temperature of 50-70°C for 8-12 hours.

4. The preparation method according to claim 1, characterized in that, The metal-based porous current collector has multiple pores; and / or, The metal material of the metal-based porous current collector includes at least one of nickel and aluminum; and / or, The solid electrolyte material is a sulfide solid electrolyte, including Li₂S-P₂S₅, Li₂S-SiS₂, or Li₂S-P₂S₅. 10 GeP2S 12 At least one of them; and / or, The particle size distribution of the solid electrolyte material is in the range of 0.1 μm to 1 μm; and / or, The positive electrode active material precursor includes a mixture of a transition metal source and a lithium source; and / or, The solvent includes at least one of N-methylpyrrolidone and acetonitrile; and / or, The viscosity of the composite slurry is 3000~5000 mPa·s; and / or, In the mixed system composed of the positive electrode active material precursor, the solid electrolyte material, and the stress buffer material, the mass percentage of the stress buffer material is 1-3%; and / or, In the mixed system composed of the positive electrode active material precursor and the solid electrolyte material, the mass percentage of the solid electrolyte material is 20-30%.

5. The preparation method according to claim 1, characterized in that, The step of immersing the metal-based porous current collector in the composite slurry under vacuum impregnation to obtain a filled current collector includes: immersing the metal-based porous current collector in the composite slurry under ultrasonic conditions of 25-35 kHz, first impregnating it under a vacuum of 0.01-0.03 MPa for 10-20 min, and then impregnating it under a vacuum of 0.06-0.08 MPa for 20-40 min to obtain a filled current collector; and / or, The step of sintering the intermediate product to obtain an integrated cathode includes: heat-treating the intermediate product at 250~350℃ for 1~3h in an air atmosphere to obtain a carbide; and heat-treating the carbide at 600~800℃ for 4~8h in a protective atmosphere to obtain an integrated cathode.

6. The preparation method according to claim 1, characterized in that, The step of placing the filling current collector in a magnetic field with the magnetic field direction along the thickness direction of the filling current collector and performing magnetic field treatment to obtain an intermediate product includes: placing the filling current collector in a gradient magnetic field for magnetic field treatment, and simultaneously applying mechanical vibration to the filling current collector to obtain an intermediate product; wherein, the magnetic field direction of the gradient magnetic field is consistent with the thickness direction of the filling current collector, and the magnetic field strength of the gradient magnetic field increases along the thickness direction of the filling current collector, and the vibration direction of the mechanical vibration is along the thickness direction of the filling current collector.

7. The preparation method according to claim 6, characterized in that, The magnetic field strength of the gradient magnetic field is distributed in the range of 0.5~1.5T, and the magnetic field treatment time is 10~30min; and / or, The frequency of the mechanical vibration is 20~30kHz, and the amplitude is 0.1~0.5mm; and / or, Before placing the filling current collector in a gradient magnetic field for magnetic field treatment, the method further includes: pre-treating the filling current collector in a uniform magnetic field with a magnetic field strength of 0.1~0.3T for 5~15 minutes; wherein the magnetic field direction of the uniform magnetic field is consistent with the thickness direction of the filling current collector, and during the pre-treatment process, the filling current collector is rotated at a uniform speed with the thickness direction of the filling current collector as the central axis.

8. The preparation method according to claim 1, characterized in that, After sintering the intermediate product to obtain an integrated positive electrode, the method further includes: depositing a protective layer on the exposed surface of the integrated positive electrode using atomic layer deposition (ALD) technology. The exposed surface includes at least one of the following: the outer surface of the integrated positive electrode, the inner wall surface of the pores of the metal-based porous current collector, the surface of the positive electrode active material precursor, the surface of the solid electrolyte material, and the surface of the stress-buffering material; and / or, Before the step of immersing the metal-based porous current collector in the composite slurry for vacuum impregnation to obtain the filled current collector, the process further includes: performing plasma activation treatment on the metal-based porous current collector using a mixed gas of argon and oxygen; wherein the power of the plasma activation treatment is 500W~1000W, the treatment time is 5~15min, and the volume fraction of oxygen in the mixed gas is 5~10%.

9. The preparation method according to claim 8, characterized in that, The protective layer is made of lithium lanthanum zirconium oxide or lithium lanthanum tantalum oxide.

10. A solid-state battery, characterized in that, Including the integrated positive electrode prepared by the preparation method according to any one of claims 1 to 9.

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