Composite positive electrode, method for manufacturing the same, solid-state battery, battery pack, and electric device

Abstract

This disclosure relates to a composite cathode and its preparation method, a solid-state battery, a battery pack, and an electrical device. The composite cathode includes a cathode current collector and a composite active material layer disposed on at least one surface of the cathode current collector. The composite active material layer includes a first cathode layer and a second cathode layer. The second cathode layer is located on a side away from the cathode current collector. The first cathode layer includes a monocrystalline cathode active material and a first solid electrolyte, and the second cathode layer includes a polycrystalline cathode active material and a second solid electrolyte. The composite cathode of this disclosure improves the rate performance and interface stability of the battery, and increases the overall energy density of the electrode.

Description

Technical Field

[0001] This disclosure relates to the field of solid-state batteries, specifically to a composite cathode and its preparation method, a solid-state battery, a battery pack, and an electrical device. Background Technology

[0002] Solid-state batteries, characterized by high safety, high energy density potential, and wide temperature adaptability, have garnered widespread attention from the industry. The positive electrode of a solid-state battery typically comprises a positive electrode active material and a solid electrolyte. Compared to traditional liquid lithium batteries, solid-state batteries use a solid electrolyte instead of an organic electrolyte, significantly reducing the risk of thermal runaway and enabling the use of high-voltage positive electrode materials and lithium metal anodes.

[0003] Currently, the cathode material widely studied in solid-state battery systems is lithium-nickel-cobalt-manganese-oxygen ternary layered material, which has the characteristics of high operating voltage, large theoretical specific capacity, good cell consistency, and small capacity loss at low temperature.

[0004] However, the rate performance, energy density, and cycle stability of existing solid-state batteries still need further improvement. Summary of the Invention

[0005] The purpose of this disclosure is to provide a composite cathode to improve the energy density and rate performance of solid-state batteries, while also enhancing the cycle stability of solid-state batteries.

[0006] To achieve the above objectives, a first aspect of this disclosure provides a composite positive electrode, the composite positive electrode comprising a positive current collector and a composite active material layer disposed on at least one surface of the positive current collector; the composite active material layer comprising a first positive electrode layer and a second positive electrode layer; the second positive electrode layer being located on a side away from the positive current collector; The first positive electrode layer comprises a monocrystalline positive electrode active material and a first solid electrolyte, and the second positive electrode layer comprises a polycrystalline positive electrode active material and a second solid electrolyte.

[0007] Optionally, the volumetric particle size Dv50 of the single-crystal positive electrode active material is 1~10 μm, preferably 1.5~4 μm.

[0008] Optionally, the polycrystalline positive electrode active material particles are spherical or near-spherical in shape; the volumetric particle size Dv50 of the polycrystalline positive electrode active material is 1.5~15 μm, preferably 2~5 μm.

[0009] Optionally, the monocrystalline positive electrode active material and the polycrystalline positive electrode active material are each independently selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0010] Optionally, the volume fraction of the monocrystalline positive electrode active material in the first positive electrode layer is 50-85%; and / or, the volume fraction of the polycrystalline positive electrode active material in the second positive electrode layer is 50-85%.

[0011] Optionally, the thickness of the first positive electrode layer is 20~80 μm, preferably 40~70 μm; and / or, the thickness of the second positive electrode layer is 20~80 μm, preferably 30~60 μm.

[0012] Optionally, the thickness of the composite active material layer is 70~160 μm.

[0013] Optionally, the composite active material layer further includes a transition layer located between the first positive electrode layer and the second positive electrode layer; the transition layer includes the monocrystalline positive electrode active material and the polycrystalline positive electrode active material.

[0014] Optionally, the first solid electrolyte and the second solid electrolyte are each independently selected from the chemical formula Li. 7-m+a-c-d M m / n P 1-a AaS 5-b D b Cl c X d At least one of the sulfide electrolytes; wherein M is selected from one or more of Na, Mg, Ca, Zn and Al; A is selected from one or more of Si, Sn and Ge; D is selected from O and / or Se; X is selected from Br and / or I; 0≤m≤1, 1≤n≤3, 0≤a≤1, 0≤b<2, 0≤c<2, 0≤d<2, 1≤c+d<2.

[0015] A second aspect of this disclosure provides a method for preparing the composite cathode described in the first aspect of this disclosure, comprising: A single-crystal positive electrode active material, a first solid electrolyte, and a first solvent are mixed evenly to form a first positive electrode slurry; a polycrystalline positive electrode active material, a second solid electrolyte, and a second solvent are mixed evenly to form a second positive electrode slurry. The first positive electrode slurry and the second positive electrode slurry are sequentially coated onto at least one side of the positive electrode current collector and dried to obtain a composite positive electrode.

[0016] Optionally, the first positive electrode slurry and the second positive electrode slurry are coated onto at least one side surface of the positive electrode current collector, such that the first positive electrode slurry is located on the surface of the positive electrode current collector and the second positive electrode slurry is located on the side of the first positive electrode slurry away from the positive electrode current collector, and then dried to form the first positive electrode layer and the second positive electrode layer.

[0017] Optionally, the first positive electrode slurry is coated onto at least one side of the positive electrode current collector and dried to form a first positive electrode layer; the second positive electrode slurry is coated onto the surface of the first positive electrode layer away from the positive electrode current collector and dried to form a second positive electrode layer.

[0018] In a third aspect, this disclosure provides a solid-state battery, the solid-state battery comprising the composite positive electrode described in the first aspect of this disclosure or the composite positive electrode prepared by the method described in the second aspect of this disclosure.

[0019] In a fourth aspect, this disclosure provides a battery pack comprising a plurality of solid-state batteries as described in the third aspect of this disclosure.

[0020] In a fifth aspect, this disclosure provides an electrical device, the electrical device comprising the solid-state battery described in the third aspect of this disclosure or the battery pack described in the fourth aspect of this disclosure.

[0021] Through the above technical solution, the composite cathode of this disclosure adopts a polycrystalline cathode active material on the side away from the cathode current collector, which effectively alleviates interfacial polarization and enhances the uniformity of electrochemical reaction; at the same time, it adopts a monocrystalline cathode active material on the side close to the cathode current collector, which effectively suppresses the expansion of grain boundary fracture and interfacial side reactions, improves the structural integrity of the material, thereby improving the rate performance and interfacial stability of the battery, and increasing the overall energy density of the electrode.

[0022] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the composite positive electrode structure in some embodiments of this disclosure.

[0024] Figure 2 These are SEM images of single-crystal positive electrode active material particles of composite positive electrodes in some embodiments of this disclosure.

[0025] Figure 3 These are SEM images of polycrystalline cathode active material particles in some embodiments of the composite cathode of this disclosure.

[0026] Explanation of reference numerals in the attached figures 110. Positive current collector; 121. First positive electrode layer; 122. Second positive electrode layer. Detailed Implementation

[0027] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0028] In this disclosure, the concepts of "first" and "second" are used only to distinguish different devices, modules or units, and are not used to limit the order of functions performed by these devices, modules or units or their interdependencies. They should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0029] It should be noted that the terms "a" and "a plurality of" used in this disclosure are illustrative rather than restrictive, and those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0030] The first aspect of this disclosure provides a composite positive electrode, such as Figure 1 As shown, the composite positive electrode includes a positive current collector 110 and a composite active material layer disposed on at least one surface of the positive current collector 110; the composite active material layer includes a first positive electrode layer 121 and a second positive electrode layer 122; the second positive electrode layer 122 is located on the side away from the positive current collector 110; wherein, the first positive electrode layer 121 includes a single-crystal positive electrode active material and a first solid electrolyte, and the second positive electrode layer 122 includes a polycrystalline positive electrode active material and a second solid electrolyte.

[0031] In sulfide-based all-solid-state batteries, the positive electrode and the sulfide electrolyte form a solid-solid interface, and ion transport relies on continuous ion conduction pathways within the electrode and at the interface. Due to the limited ion diffusion capacity of solid electrolytes, and the susceptibility of the physical contact between the positive electrode active material and the sulfide electrolyte to factors such as pressing processes, volume changes, and interface stability, traditional views typically attribute the performance degradation on the positive electrode side of all-solid-state batteries to interfacial chemical instability or mechanical contact deterioration, while paying less attention to the non-uniformity of ion transport in the thickness direction within the electrode. This invention, through analysis of solid-state batteries using microstructure analysis (high-resolution tomography), spatially resolved electrochemical testing (synchrotron radiation), local impedance mapping, and multi-scale simulation, suggests that in the positive electrode surface region near the sulfide electrolyte, there are relatively few effective ion conduction pathways, limiting lithium-ion migration and causing a decrease in local ion conductivity, forming a "bottleneck region" for lithium-ion transport. Especially at high current densities, this region is prone to problems such as uneven lithium-ion insertion / extraction and intensified interfacial polarization, leading to capacity decay and cycle performance degradation.

[0032] This disclosure proposes a gradient functionalized active material distribution structure in the cathode sheet. Specifically, a monocrystalline cathode active material is used in the first cathode layer near the cathode current collector to improve the overall energy density and cycle life of the cathode sheet, while a polycrystalline cathode active material is used in the second cathode layer away from the cathode current collector to improve interfacial reaction kinetics, ensure fast charge and discharge capability, and improve the physical contact between the cathode active material and the solid electrolyte. This achieves functional zoning and functional complementarity of the composite cathode, significantly improves the rate performance of the battery, maintains the high energy density of the battery, and improves the cycle stability of the battery.

[0033] In this disclosure, "monocrystalline positive electrode active material" refers to positive electrode particles that have been treated with CP (argon ion polishing) and observed in BSD mode of scanning electron microscopy or characterized by EBSD, and analyzed by contrast or crystal orientation. Individual particles have no obvious grain boundaries or only contain grain agglomeration caused by insufficient dispersion due to the preparation process (a single positive electrode particle consists of n < 7 grains), and the whole has a single crystal morphology.

[0034] In this disclosure, the "polycrystalline positive electrode active material" is formed by the accumulation of particles in one step. This means that after CP (argon ion polishing) treatment, the positive electrode particles are observed in the BSD mode of a scanning electron microscope or characterized by EBSD. The analysis is performed by contrast or crystal orientation. There are clear grain boundaries between the grains, and a single positive electrode particle is composed of n (n≥7) grains.

[0035] According to this disclosure, the region near the positive electrode current collector can provide a relatively sufficient ion transport environment, resulting in high ion transport capacity. Based on this, using a single-crystal positive electrode active material in the first positive electrode layer can fully leverage its advantages such as excellent structural stability, low tendency for microcrack formation during cycling, and high compaction density. Single-crystal particles can effectively suppress grain boundary fracture and the propagation of interfacial side reactions during long-term charge-discharge processes, improving the structural integrity of the material while achieving a higher volumetric specific capacity, thereby increasing the overall capacity density of the electrode.

[0036] In some embodiments, the volumetric particle size Dv50 of the single-crystal positive electrode active material can be 1~10 μm. For example, the volumetric particle size Dv50 of the single-crystal positive electrode active material can be 1 μm, 1.5 μm, 2 μm, 2.8 μm, 3.0 μm, 3.2 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or values ​​within the aforementioned range, or any range between the two. Using a single-crystal positive electrode active material with a volumetric particle size Dv50 in the range of 1~10 μm ensures sufficient contact between the single-crystal positive electrode active material and the first solid electrolyte, which is beneficial for improving the lithium-ion transport rate and the conductivity of the positive electrode active material layer. When the volumetric particle size Dv50 of the single-crystal positive electrode active material is too small, for example, less than 1 μm, although it can shorten the lithium-ion diffusion path and better adapt to volume changes during charge and discharge, which is beneficial for significantly improving the material's reactivity and rate performance, the material's structural stability and cycle life are poor, and it is prone to agglomeration. When the volumetric particle size Dv50 of the single-crystal cathode active material is large, for example, greater than 10 μm, although it is beneficial to improve the structural stability and cycle life of the material, it also slows down the diffusion of lithium ions inside the particles, resulting in a decrease in the rate performance of the material and affecting the uniformity of the coating. In order to balance the rate performance, structural stability and cycle life of the material near the cathode current collector region, the volumetric particle size Dv50 of the single-crystal cathode active material is preferably 1.5~4 μm.

[0037] The volumetric particle size Dv50 of the monocrystalline positive electrode active material in the first positive electrode layer and the volumetric particle size Dv50 of the polycrystalline positive electrode active material in the second positive electrode layer can be detected by a method including the following steps: S1. Obtain a three-dimensional image of the composite positive electrode sheet; S2. Analyze the obtained three-dimensional image using three-dimensional image processing software, identify and segment the positive electrode active material particles in the three-dimensional image, measure the maximum diameter, minimum diameter and average diameter of each positive electrode active material particle, and then obtain the Dv50 of the positive electrode active material.

[0038] Specifically, step S2 includes: preprocessing the three-dimensional image, identifying and segmenting the positive electrode active material and solid electrolyte; measuring the maximum diameter, minimum diameter and average diameter of each positive electrode active material particle; and generating a particle size distribution map or probability density curve after summarizing the particle size data of all positive electrode active material particles to obtain the volumetric particle size Dv50 of the positive electrode active material.

[0039] One approach is to use computed tomography (CT) to scan the composite cathode sheet, obtaining images of each cross-section, and then reconstructing them to obtain a three-dimensional image of the composite cathode sheet. Alternatively, in some other embodiments, focused ion beam scanning electron microscopy (FIB-SEM) can be used to obtain a three-dimensional image of the composite cathode sheet through a combination of layer-by-layer milling and simultaneous imaging. Using FIB-SEM technology for deep etching and three-dimensional reconstruction of the composite cathode sheet can yield a series of high-resolution two-dimensional cross-sectional images (three-dimensional image data).

[0040] In step S2 above, image processing software such as Dragonfly can be used to preprocess the obtained 3D image. For example, in some specific processing methods, the voxel size is first determined, and then image preprocessing is performed, including using non-local means filtering to reduce noise introduced during etching and imaging; using homogenization tools to correct brightness differences between different layers; and calibrating possible sample drift.

[0041] It is understood that the monocrystalline and polycrystalline positive electrode active materials in this disclosure can also be modified, for example by coating, doping or other surface modification techniques, to slow down the reaction between the active material and the electrolyte material and to improve the ion transport capability of the positive electrode active material.

[0042] According to this disclosure, polycrystalline materials are composed of a large number of micron-sized primary particles, possessing a high specific surface area and abundant grain boundary structures. This provides more lithium-ion insertion / extraction reaction sites and significantly shortens the lithium-ion diffusion path. By placing the polycrystalline cathode active material on the side away from the cathode current collector, local ion insertion / extraction kinetics are effectively improved, interfacial polarization is alleviated, the uniformity of the chemical reaction is enhanced, and the rate performance and interfacial stability of the battery are improved.

[0043] In the embodiments of this disclosure, the shapes of the single-crystal positive electrode active material and the polycrystalline positive electrode active material particles are not specifically limited; for example, they can be spherical, square, or sheet-like. Preferably, the polycrystalline positive electrode active material particles are spherical or near-spherical in shape to reduce porosity between material particles, increase the compaction density of the positive electrode sheet, and thus improve energy density. Simultaneously, spherical particles can also reduce the tortuosity of lithium ions in the transport path, further improving the diffusion rate of lithium ions.

[0044] In some embodiments, the volumetric particle size Dv50 of the polycrystalline cathode active material is 1.5~15 μm. For example, the volumetric particle size Dv50 of the polycrystalline cathode active material can be 1.5 μm, 2 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4 μm, 4.2 μm, 5 μm, 5.2 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or values ​​within the aforementioned range, or any range between the two. A volumetric particle size Dv50 of 1.5~15 μm for the polycrystalline cathode active material is beneficial for improving the rate performance and interface stability of the battery. When the volumetric particle size Dv50 of the polycrystalline cathode active material is too small, for example, less than 1.5 μm, although the lithium-ion transport rate can be improved, the particle size is too small, and grain boundary side effects dominate. When the volumetric particle size Dv50 of the polycrystalline cathode active material is large, for example, greater than 15 μm, although the volumetric energy density of the material can be improved and side reactions can be reduced, intergranular cracks become severe and grain boundary diffusion paths become longer. In order to balance the rate performance and structural stability of the polycrystalline cathode active material, the volumetric particle size Dv50 of the polycrystalline cathode active material is preferably 2~5 μm.

[0045] In this disclosure, the specific types of monocrystalline and polycrystalline positive electrode active materials are not particularly limited, and those skilled in the art can choose according to actual needs. In some embodiments, the monocrystalline and polycrystalline positive electrode active materials can each be independently selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide, and other conventionally known materials that can be used as positive electrode active materials for lithium-ion batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more materials.

[0046] As some preferred embodiments, the single-crystal positive electrode active material and the polycrystalline positive electrode active material can each be independently selected from at least one of ternary positive electrode materials, LiMnO2, lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), and lithium cobalt oxide (LiCoO2), with ternary positive electrode materials being preferred. The ternary positive electrode materials include lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), nickel cobalt manganese aluminum composite ternary positive electrode materials, lithium nickel cobalt titanate (NCT), lithium nickel cobalt vanadium oxide (NCV), lithium nickel cobalt zirconate (NCZ), lithium nickel cobalt stannate (NCS), etc. Among them, lithium nickel cobalt manganese oxide (NCM) has the chemical formula Li... 1+m Ni x Co y Mn 1-x-yO2X, 0≤x≤1, 0≤y≤1, 0≤m≤0.1, where X can be one or more of the elements Zr, Al, S, Sr, Zn, Fe, Cu, Na, Y, Ti, Mg, B, and W.

[0047] Particularly preferably, the monocrystalline positive electrode active material and the polycrystalline positive electrode active material can each be independently selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.95 Co 0.025 Mn 0.025 O2 (NCM9505) and LiNi 0.8 Co 0.15 Al 0.05 One or more of the following: O2. The active material particles with different nickel contents are related to the battery's energy density, cycle life, and rate performance. Increasing the nickel content usually increases the material's specific capacity, thereby improving energy density, but may sacrifice some cycle stability and rate performance.

[0048] In some embodiments, the volume fraction of the monocrystalline positive electrode active material in the first positive electrode layer can be 50-85%, for example, 50%, 52%, 54%, 55%, 56%, 58%, 60%, 62%, 63%, 65%, 68%, 70%, 71%, 72%, 73%, 74%, 75%, 76.5%, 77%, 77%, 78%, 80%, 82%, 84%, 85%, or any value within the aforementioned range. The first positive electrode layer has an appropriate content of monocrystalline positive electrode active material. The monocrystalline particles have fewer grain boundaries, can withstand higher rolling pressure, and achieve higher compaction density. However, if the content is too high, it leads to a reduction in lithium-ion transport paths, restricted migration, and the formation of a "bottleneck region" for lithium-ion transport.

[0049] In some embodiments, the volume fraction of the polycrystalline cathode active material in the second cathode layer can be 50-85%. For example, it can be 50%, 52%, 54%, 55%, 56%, 58%, 60%, 62%, 63%, 65%, 68%, 70%, 71%, 72%, 73%, 74%, 75%, 76.5%, 77%, 77%, 78%, 80%, 82%, 84%, 85%, or any value within the aforementioned range. A volume fraction of 50-85% of the polycrystalline cathode material in the second cathode layer is beneficial for improving local ion insertion / extraction kinetics, alleviating interfacial polarization, and enhancing the uniformity of electrochemical reactions, thereby improving the rate performance and interfacial stability of the battery. However, when the content of polycrystalline cathode material is too high, intergranular cracks become severe, and side reactions increase.

[0050] The volume fraction of monocrystalline positive electrode active material in the first positive electrode layer and the volume fraction of polycrystalline positive electrode active material in the second positive electrode layer can be detected by a method including the following steps: S1. Obtain a three-dimensional image of the composite positive electrode sheet; S2. Analyze the obtained three-dimensional image using three-dimensional image processing software to separate the positive electrode active material and the solid electrolyte from the background, and calculate the volume fraction of the positive electrode active material and the solid electrolyte respectively.

[0051] Specifically, in step S2, the three-dimensional image is preprocessed and segmented in sequence to separate the positive electrode active material and the solid electrolyte from the background. After the segmentation results are verified to be correct, the volume of each phase is calculated and the volume fraction of the phase in the overall structure is statistically analyzed to obtain the percentage of the positive electrode active material in the total volume of the positive electrode active material and the solid electrolyte.

[0052] One approach is to use computed tomography (CT) to scan the composite cathode sheet, obtaining images of each cross-section, and then reconstructing them to obtain a three-dimensional image of the composite cathode sheet. Alternatively, in some other embodiments, focused ion beam scanning electron microscopy (FIB-SEM) can be used to obtain a three-dimensional image of the composite cathode sheet through a combination of layer-by-layer milling and simultaneous imaging. Using FIB-SEM technology for deep etching and three-dimensional reconstruction of the composite cathode sheet can yield a series of high-resolution two-dimensional cross-sectional images (three-dimensional image data).

[0053] In step S2 above, image processing software such as Dragonfly can be used to preprocess the obtained 3D image. For example, in some specific processing methods, the voxel size is first determined, followed by image preprocessing, including using non-local means filtering to reduce noise introduced during etching and imaging; using homogenization tools to correct brightness differences between different layers; and calibrating possible sample drift. Since the positive electrode active material and the solid electrolyte usually have different grayscale or morphological characteristics in the image, a multi-threshold segmentation method can be used to separate the positive electrode active material and the solid electrolyte from the background according to the grayscale range. For areas with indistinct grayscale differences or blurred boundaries, more accurate identification and segmentation can be performed, which will not be elaborated here. After segmenting the positive electrode active material and the solid electrolyte, morphological operations can be used to optimize the segmentation effect to ensure that the extracted positive electrode active material and solid electrolyte regions have structural continuity and physical rationality. The volume of each phase can be calculated according to the functions of the image processing software.

[0054] In some embodiments, the thickness of the first positive electrode layer is 20-80 μm, for example, it can be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, or any value within the aforementioned range. Providing a first positive electrode layer with a thickness of 20-80 μm containing single-crystal positive electrode active material near the positive electrode current collector can, on the one hand, withstand higher rolling pressure and increase the content of active material per unit volume. To further improve the rate performance of the battery, the thickness of the first positive electrode layer is preferably 40-70 μm.

[0055] In some embodiments, the thickness of the second positive electrode layer is 20~80 μm, for example, it can be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm or any value within the aforementioned range. To further improve the structural integrity and cycle stability of the material, the thickness of the second positive electrode layer is preferably 30~60 μm.

[0056] The thickness of the first positive electrode layer and / or the second positive electrode layer can be observed and measured under a scanning electron microscope (SEM). For example, in some specific embodiments, the cross-section of the composite positive electrode sheet can be first subjected to argon ion polishing (CP) treatment, and then the thickness of the first positive electrode layer and the second positive electrode layer in the electrode sheet can be observed and measured under a scanning electron microscope after argon ion polishing treatment.

[0057] In the above embodiments, the thickness of the composite active material layer can be 70~160 μm, for example, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, or any value within the aforementioned range. This reduces interfacial impedance and constructs continuous ion and electron transport channels.

[0058] In some embodiments, the composite active material layer further includes a transition layer located between the first positive electrode layer and the second positive electrode layer; the transition layer includes the monocrystalline positive electrode active material and the polycrystalline positive electrode active material. For example, in a dual-layer synchronous wet coating process, the slurries used to form the first positive electrode layer and the second positive electrode layer interpenetrate to form the transition layer.

[0059] In some embodiments, the first solid electrolyte and the second solid electrolyte are each independently selected from the chemical formula Li. 7-m+a-c-d M m / n P 1-a AaS 5-b D b Cl c X d At least one of the sulfide electrolytes; wherein M is selected from one or more of Na, Mg, Ca, Zn and Al; A is selected from one or more of Si, Sn and Ge; D is selected from O and / or Se; X is selected from Br and / or I; 0≤m≤1, 1≤n≤3, 0≤a≤1, 0≤b<2, 0≤c<2, 0≤d<2, 1≤c+d<2.

[0060] In some specific embodiments of this disclosure, in the first positive electrode layer, the mass ratio of the monocrystalline positive electrode active material to the first solid electrolyte can be 100:(10~40); in the second positive electrode layer, the mass ratio of the polycrystalline positive electrode active material to the second solid electrolyte can be 100:(10~40). By limiting the mass ratio of the positive electrode active material and the solid electrolyte in the first and second positive electrode layers to the above range, the contact between the solid electrolyte and the positive electrode active material can be enhanced, lithium-ion transport can be guaranteed, and the energy density and power density of the battery can be further balanced.

[0061] In some embodiments of this disclosure, the first positive electrode layer further includes a first positive electrode conductive agent, and the second positive electrode layer further includes a second positive electrode conductive agent. The first positive electrode conductive agent and the second positive electrode conductive agent may be independently selected from one or more of carbon black, vapor-grown carbon fiber (VGCF), activated carbon, carbon nanotubes, Ketjen black, acetylene black and graphene, preferably conductive carbon black and / or VGCF.

[0062] In some embodiments of this disclosure, the first positive electrode layer further includes a first positive electrode binder, and the second positive electrode layer further includes a second positive electrode binder. The first positive electrode binder and the second positive electrode binder are each independently selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyisobutylene (PIB), styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene-butene-styrene block copolymer (SEBS), styrene-butadiene rubber (SBR), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), polyimide (PI), and polyacrylic acid (PAA), preferably one or more of SBR, NBR, and HNBR.

[0063] A second aspect of this disclosure provides a method for preparing the composite cathode described in the first aspect of this disclosure, comprising: A single-crystal positive electrode active material, a first solid electrolyte, and a first solvent are mixed evenly to form a first positive electrode slurry; a polycrystalline positive electrode active material, a second solid electrolyte, and a second solvent are mixed evenly to form a second positive electrode slurry. The first positive electrode slurry and the second positive electrode slurry are sequentially coated onto at least one side of the positive electrode current collector and dried to obtain a composite positive electrode.

[0064] In the composite cathode constructed in this disclosure, the monocrystalline cathode active material in the first cathode layer near the cathode current collector can withstand higher rolling pressure, achieving a higher compaction density (>3.6 g / cm³) and increasing the content of active material per unit volume. The polycrystalline cathode active material in the second cathode layer has a larger specific surface area, enhancing the contact area with the solid electrolyte, reducing interfacial impedance, and promoting rapid lithium-ion migration.

[0065] Furthermore, this disclosure achieves local optimization and overall coordination of ion / electron transport characteristics and electrochemical performance through the spatial gradient arrangement of positive electrode active materials without introducing additional interface modification layers or complex processes, demonstrating good manufacturability and industrialization prospects.

[0066] In some embodiments, the first positive electrode slurry and the second positive electrode slurry are coated onto at least one side of the surface of the positive electrode current collector, such that the first positive electrode slurry is located on the surface of the positive electrode current collector, and the second positive electrode slurry is located on the side of the first positive electrode slurry away from the positive electrode current collector, and then dried to form the first positive electrode layer and the second positive electrode layer. Specifically, a dual-die synchronous wet coating process can be used, in which case an interpenetrating transition layer may appear between the first positive electrode layer and the second positive electrode layer of the resulting composite positive electrode, which also falls within the protection scope of this disclosure.

[0067] In some embodiments, the first positive electrode slurry is coated onto at least one surface of the positive electrode current collector and dried to form a first positive electrode layer; the second positive electrode slurry is coated onto the surface of the first positive electrode layer away from the positive electrode current collector and dried to form a second positive electrode layer. This allows for separate control of the thickness and shape of the first and second positive electrode layers.

[0068] In this disclosure, the electrode obtained by coating the first positive electrode slurry or coating the first positive electrode slurry and the second positive electrode slurry can be dried using methods commonly found in the art. In this disclosure, the first solvent and the second solvent can be common organic solvents found in the art. For example, in some embodiments, the first solvent and the second solvent are each independently selected from at least one of toluene, xylene, acetone, cyclohexane, anisole, and butyl butyrate.

[0069] A third aspect of this disclosure provides a solid-state battery, comprising the composite positive electrode described in the first aspect of this disclosure or the composite positive electrode prepared by the method described in the second aspect of this disclosure. The specific structure of the solid-state battery is not particularly limited, and it may include other structures commonly found in the art, such as a negative electrode and a solid electrolyte layer.

[0070] In a fourth aspect, this disclosure provides a battery pack comprising a plurality of solid-state batteries as described in the third aspect of this disclosure. The solid-state batteries in the battery pack are connected in parallel or in series.

[0071] In a fifth aspect, this disclosure provides an electrical device, the electrical device comprising the solid-state battery described in the third aspect of this disclosure or the battery pack described in the fourth aspect of this disclosure.

[0072] The electrical equipment used in the embodiments of this disclosure can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), automobile chassis, electronic devices (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations on this.

[0073] The present disclosure will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present disclosure and are not intended to limit the present disclosure.

[0074] All raw materials and reagents used in the examples and comparative examples are commercially available products.

[0075] Example 1 This embodiment illustrates the preparation method of the composite positive electrode disclosed herein, including the following steps: (1) Preparation of cathode slurry: The single-crystal cathode active material LiNi 0.8 Co 0.1Mn 0.1 O2 (NCM811, with a volumetric particle size Dv50 of 2.8 μm and a particle size range of 1.5~4.0 μm), the first solid electrolyte Li6PS5Cl (LPSCl), the first conductive agent SuperP, and the first binder NBR (with a solid content of 10 wt%) are mixed uniformly in the first solvent toluene at a mass ratio of 85:12:2:1 to form the first positive electrode slurry; Polycrystalline cathode active material LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622, volume Dv50 of 3.5 μm, particle size range of 2.0~5.0 μm), second solid electrolyte Li 5.6 PS 4.6 Cl 0.7 Br 0.7 The second conductive agent VGCF and the second binder NBR are mixed evenly in the second solvent xylene at a mass ratio of 80:17:1:2 to form the second positive electrode slurry.

[0076] (2) The first positive electrode slurry is coated onto both sides of the positive electrode current collector and dried to form the first positive electrode layer; the second positive electrode slurry is coated onto the surface of the first electrode layer and dried to form the second positive electrode layer.

[0077] (3) The unformed electrode sheet obtained in step (2) is heated at 100°C. o After drying at C, the material is compacted and cut to obtain the positive electrode sheet.

[0078] According to the test and analysis, the volume fraction of monocrystalline positive electrode active material in the first positive electrode layer is 76.5%; the volume fraction of polycrystalline positive electrode active material in the second positive electrode layer is 72%; the thickness of the first positive electrode layer is 70 μm and the thickness of the second positive electrode layer is 30 μm.

[0079] Example 2 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the volumetric particle size Dv50 of the single-crystal cathode active material NCM811 is 1.5 μm, and the particle size range is 1~3.5 μm.

[0080] Example 3 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1. The difference is that the volumetric particle size Dv50 of the single-crystal cathode active material NCM811 is 3.2 μm, and the particle size range is 2.0~4.5 μm.

[0081] Example 4 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the volumetric particle size Dv50 of the single-crystal cathode active material NCM811 is 4.0 μm, and the particle size range is 3.0~6.0 μm.

[0082] Example 5 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1. The difference is that the volumetric particle size Dv50 of the single-crystal cathode active material NCM811 is 10 μm, and the particle size range is 7~12 μm.

[0083] Example 6 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the volumetric particle size Dv50 of the polycrystalline cathode active material NCM622 is 2 μm, and the particle size range is 1~4.5 μm.

[0084] Example 7 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the volumetric particle size Dv50 of the polycrystalline cathode active material NCM622 is 4.0 μm, and the particle size range is 2~6 μm.

[0085] Example 8 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the volumetric particle size Dv50 of the polycrystalline cathode active material NCM622 is 5.2 μm, and the particle size range is 2~7 μm.

[0086] Example 9 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the volumetric particle size Dv50 of the polycrystalline cathode active material NCM622 is 15 μm, and the particle size range is 12~17 μm.

[0087] Example 10 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the thickness of the first cathode layer is 80 μm.

[0088] Example 11 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the thickness of the first cathode layer is 40 μm.

[0089] Example 12 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the thickness of the first cathode layer is 30 μm.

[0090] Example 13 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the thickness of the second cathode layer is 20 μm.

[0091] Example 14 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the thickness of the second cathode layer is 50 μm.

[0092] Example 15 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the thickness of the second cathode layer is 60 μm.

[0093] Example 16 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the thickness of the second cathode layer is 80 μm.

[0094] Example 17 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the volume fraction of the single-crystal cathode active material in the first cathode layer is 63%.

[0095] Example 18 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the volume fraction of the single-crystal cathode active material in the first cathode layer is 72%.

[0096] Example 19 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the volume fraction of the polycrystalline cathode active material in the second cathode layer is 72%.

[0097] Example 20 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that the volume fraction of the polycrystalline cathode active material in the second cathode layer is 76.5%.

[0098] Example 21 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that: In the first positive electrode slurry, the mass ratio of the single-crystal positive electrode active material NCM811, the first solid electrolyte Li3PS4, the first conductive agent CNT, and the first binder NBR is 80:16:2:2. In the second positive electrode slurry, the mass ratio of polycrystalline positive electrode active material NCM622, second solid electrolyte Li6PS5Cl, second conductive agent VGCF, and second binder NBR is 80:18:1:1; the second solvent is toluene. The thickness of the first cathode layer is 40 μm, and the thickness of the second cathode layer is 60 μm.

[0099] Example 22 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that: In the first cathode slurry, the single-crystal cathode active material is LiNi0.8Co0. 15 Al0. 05 The mass ratio of O2 (NCA, with a volumetric particle size Dv50 of 3.0 μm and a particle size range of 2.0~4.5 μm), the first solid electrolyte Li6PS5Cl, the first conductive agent CNT, and the first binder HNBR is 85:12:2:1. In the second positive electrode slurry, the polycrystalline positive electrode active material LiNi0.5Co0.2Mn0.3O2 (NCM523, with a volumetric particle size Dv50 of 4.2 μm and a particle size range of 3.0~6.5 μm) and the second solid electrolyte Li6PS5Cl are present. 0.5 Br 0.5 The mass ratio of the second conductive agent SuperP to the second binder NBR is 80:18.5:0.5:1; the second solvent is acetone. The thickness of the first cathode layer is 80 μm, and the thickness of the second cathode layer is 20 μm.

[0100] Example 23 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that: In the first positive electrode slurry, the mass ratio of the single-crystal positive electrode active material NCM811, the first solid electrolyte Li6PS5Cl, the first conductive agent Super P, and the first binder NBR is 80:17:2:1; the first solvent is xylene. In the second positive electrode slurry, the polycrystalline positive electrode active material NCM622 and the second solid electrolyte Li 10 GeP2S 12 The mass ratio of the second conductive agent VGCF to the second binder NBR is 80:17:2:1; the second solvent is cyclohexane. The thickness of the first cathode layer is 20 μm, and the thickness of the second cathode layer is 80 μm.

[0101] Example 24 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that: In the first positive electrode slurry, the mass ratio of the single-crystal positive electrode active material NCM811, the first solid electrolyte Li6PS5Cl, the first conductive agent Super P, and the first binder NBR is 85:12:2:1; the first solvent is cyclohexane. In the second positive electrode slurry, the polycrystalline positive electrode active material LiNi0.8Co0.1Mn0.1O2 (NCM811, with a volumetric particle size Dv50 of 5.2 μm and a particle size range of 4.0~7.0 μm) and the second solid electrolyte Li 5.6 PS 4.6 Cl 0.4 The mass ratio of Br, the second conductive agent VGCF, and the second binder NBR is 85:12:2:1; the second solvent is cyclohexane. The thickness of the first cathode layer is 40 μm, and the thickness of the second cathode layer is 30 μm.

[0102] Example 25 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that: In the first cathode slurry, the single-crystal cathode active material is LiNi0. 95 Co0. 025 Mn0. 025 The mass ratio of O2 (NCM9505, volumetric particle size Dv50 of 3.2 μm, particle size range of 2.0~4.5 μm), the first solid electrolyte Li6PS5Cl, the first conductive agent CNT and the first binder NBR is 85:12:2:1; the first solvent is anisole. In the second positive electrode slurry, the polycrystalline positive electrode active material LiNi0.8Co0.1Mn0.1O2 (NCM811, with a volumetric particle size Dv50 of 4.0 μm and a particle size range of 3.0~6.0 μm) and the second solid electrolyte Li 5.4 PS 4.4 Cl 0.2 Br 1.4 The mass ratio of the second conductive agent VGCF to the second binder NBR is 80:17:2:1; the second solvent is anisole. The thickness of the first cathode layer is 80 μm, and the thickness of the second cathode layer is 80 μm.

[0103] Example 26 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that: In the first positive electrode slurry, the mass ratio of the single-crystal positive electrode active material NCM811, the first solid electrolyte Li6PS5Cl, the first conductive agent Super P, and the first binder NBR is 85:13:1:1; the first solvent is butyl butyrate. In the second positive electrode slurry, the mass ratio of polycrystalline positive electrode active material NCM622, second solid electrolyte Li6PS5Cl, second conductive agent VGCF, and second binder NBR is 80:18:1:1; the second solvent is toluene. The thickness of the first cathode layer is 70 μm, and the thickness of the second cathode layer is 60 μm.

[0104] Example 27 The method for preparing the composite cathode in this embodiment is basically the same as that in Example 1, except that: In the first positive electrode slurry, the mass ratio of the single-crystal positive electrode active material NCM811, the first solid electrolyte Li3PS4, the first conductive agent CNT, and the first binder NBR is 80:16:3:1; the first solvent is anhydrous acetone. In the second positive electrode slurry, the mass ratio of the polycrystalline positive electrode active material polycrystalline LiNi0.8Co0.1Mn0.1O2 (NCM811, with a volumetric particle size Dv50 of 4.0 μm and a particle size range of 3.0~6.0 μm), the second solid electrolyte Li6PS5Cl, the second conductive agent VGCF, and the second binder NBR is 80:16:3:1; the second solvent is anhydrous acetone. The thickness of the first cathode layer is 50 μm, and the thickness of the second cathode layer is 50 μm.

[0105] Example 28 The method for preparing the composite cathode in this embodiment is the same as in Example 1, except that: (2) The first positive electrode slurry and the second positive electrode slurry are sequentially coated onto the two sides of the positive electrode current collector using a dual-head synchronous wet coating process, and then dried to form a first positive electrode layer, a second positive electrode layer and a transition layer between the first positive electrode layer and the second positive electrode layer on the positive electrode current collector. The thickness of the first cathode layer is 60 μm, the thickness of the second cathode layer is 20 μm, and the thickness of the transition layer is 20 μm.

[0106] Comparative Example 1 The preparation method of the positive electrode in this comparative example includes: (1) Preparation of cathode slurry: The single-crystal cathode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811, with a volumetric particle size Dv50 of 2.8 μm and a particle size range of 1.5~4.0 μm), solid electrolyte Li6PS5Cl (LPSCl), conductive agent Super P, and binder NBR (solid content of 10 wt%) are mixed evenly in xylene solvent at a mass ratio of 85:13:1:1 to form a positive electrode slurry. (2) The positive electrode slurry is coated onto both sides of the positive electrode current collector and dried to form a positive electrode layer; the thickness of the positive electrode layer is 100 μm.

[0107] (3) The unformed electrode sheet obtained in step (2) is heated at 100°C. o After drying at C, the material is compacted and cut to obtain the positive electrode sheet.

[0108] Comparative Example 2 The method for preparing the positive electrode in this comparative example is the same as that in Comparative Example 1, except that: (1) Preparation of positive electrode slurry: Polycrystalline positive electrode active material LiNi0.8Co0.1Mn0.1O2 (NCM811, volumetric particle size Dv50 of 5.2 μm, particle size range of 4.0~7.0 μm), solid electrolyte Li6PS5Cl (LPSCl), conductive agent VGCF and binder NBR (solid content of 10 wt%) are mixed evenly in solvent toluene at a mass ratio of 80:17:2:1 to form positive electrode slurry.

[0109] Comparative Example 3 The method for preparing the positive electrode in this comparative example is the same as in Example 1, except that: In step (1), the solvent for the first positive electrode slurry is butyl butyrate; In step (2), a second positive electrode slurry containing polycrystalline positive electrode active material is coated onto both sides of the positive electrode current collector and dried to form a first positive electrode layer; a first positive electrode slurry containing monocrystalline positive electrode active material is coated onto the surface of the first electrode layer and dried to form a second positive electrode layer; wherein, the thickness of the first positive electrode layer is 70 μm and the thickness of the second positive electrode layer is 30 μm.

[0110] Preparation of negative electrode sheet: The negative electrode silicon-carbon (Si / C) active material nano-silicon, the negative electrode conductive agent carbon nanotube, and the negative electrode binder SBR (solid content of 10 wt%) are dispersed in xylene solvent at a mass ratio of 90:5:5 to form a uniform negative electrode slurry by high-speed shearing. The negative electrode slurry is sieved and coated onto a copper foil substrate and dried at 100℃ to obtain the negative electrode sheet.

[0111] Preparation of electrolyte layer: Li6PS5Cl, a sulfide solid electrolyte of silver-germanium sulfide, and styrene-butadiene rubber (solid content 10 wt%) as binder are mixed at a mass ratio of 97:3. Xylene solvent is added and the mixture is stirred under vacuum until the system is homogeneous to obtain electrolyte slurry. The electrolyte slurry is uniformly coated on the surface of the aluminum foil substrate, dried at room temperature, and then transferred to an oven for further drying to obtain electrolyte layer.

[0112] Fabrication of the all-solid-state battery: The electrolyte layer described above was transferred to both sides of a silicon-carbon (Si / C) negative electrode sheet (11×21 cm) and rolled to bond the electrolyte layer to the negative electrode sheet. The transferred negative electrode sheet was then stacked with the composite positive electrode sheet described above, resulting in a total of 10 positive electrode sheets and 11 silicon-carbon negative electrode sheets with transferred electrolyte. The stacked sheets were then encapsulated with an aluminum-plastic film and subjected to isostatic pressing at 60°C and 500 MPa to obtain the all-solid-state battery.

[0113] 1. Acquisition and observation of the composite cathode interface: The all-solid-state battery prepared using the composite cathode obtained in Example 1 was disassembled, the cathode sheet was peeled off, and the cross-section of the cathode sheet was polished using a vacuum cryogenic argon-ion polishing machine. The conditions for argon-ion polishing included: an accelerating voltage of 4.5 kV and a freezing temperature of -40°C. o C. Polishing time was 5 h. The positive electrode was transferred to the scanning electron microscope (SEM) sample chamber under vacuum. Under the conditions of SEM accelerating voltage of 5 kV and beam current of 10 μA, the differences and distribution of the crystal structure of the positive electrode material in the thickness direction of the electrode were observed using BSD mode.

[0114] Specifically, the positive electrode layer was selected in two regions: the region closest to the positive electrode current collector (20 μm) and the region closest to the electrolyte layer (i.e., the region furthest from the positive electrode current collector). The difference in the lining density of single particles of positive electrode material within these regions was analyzed. Figure 2 It can be observed that in the positive electrode layer within a 20 μm region near the positive electrode current collector, individual particles have no obvious grain boundaries or only contain grain agglomerations caused by insufficient dispersion due to the preparation process (a single positive electrode particle consists of n < 7 grains), exhibiting a single crystal morphology overall, and are single-crystal particles. According to Figure 2 It can be observed that in the positive electrode layer within 20 μm of the electrolyte layer, there are clear grain boundaries between the grains, and a single positive electrode particle is composed of n grains (n≥7), which are polycrystalline particles.

[0115] 2. Battery performance test (1) First-cycle discharge capacity test A 20 MPa restraint force was applied to the all-solid-state battery, which was then charged at 0.1C to 3.7V at room temperature (25℃), and then charged at a constant voltage of 3.7V until the charging current was less than or equal to 0.05C. After standing for 10 minutes, it was discharged at 0.1C to 2.0V. Its discharge specific capacity was recorded. The test results are shown in Table 1.

[0116] (2) Ratio performance test A 20 MPa restraint force was applied to the all-solid-state battery. At room temperature (25°C), the battery was charged at 0.1C to 3.7V, and then charged at a constant voltage of 3.7V until the current was less than or equal to 0.05C. It was then discharged at 0.1C to 2.0V. The charging capacity was recorded as C0. The battery was charged at 0.2C to 3.7V, and then discharged at 0.1C to 2.0V. It was charged at 0.33C to 3.7V, and then discharged at 0.1C to 2.0V. Finally, it was charged at 1C to 3.7V, and then discharged at 0.1C to 2.0V. The charging capacity was recorded as C1. The 1C charging capacity retention rate is C1 / C0. The test results are shown in Table 1.

[0117] (3) Cyclic performance test Within a voltage range of 2.0 V to 4.2 V, the battery was charged and discharged at a constant current of 1 C for 500 cycles. The percentage of discharge capacity at the 500th cycle relative to the discharge capacity at the first cycle was recorded, i.e., the cycle retention rate. The test results are shown in Table 1.

[0118] Table 1

[0119] According to the data in the table above, compared with Comparative Examples 1-3, the 1C discharge capacity and 500-cycle capacity retention of the all-solid-state batteries prepared using the composite cathodes prepared in Examples 1-28 have been significantly improved.

[0120] Compared to the single-layer active material layer in Comparative Example 1 or Comparative Example 2, the composite cathode of this disclosure exhibits better rate performance and battery capacity. Compared to the cathode structure in Comparative Example 3, the present disclosure, by employing a polycrystalline cathode active material on the side away from the cathode current collector, effectively alleviates interfacial polarization, enhances the uniformity of the electrochemical reaction, and improves the battery's rate performance. Simultaneously, by employing a monocrystalline cathode active material on the side closer to the cathode current collector, it effectively suppresses grain boundary fracture and the propagation of interfacial side reactions, improves compaction density and structural integrity, and is beneficial for balancing the battery's energy density and rate performance.

[0121] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0122] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0123] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A composite positive electrode, characterized in that, The composite positive electrode includes a positive electrode current collector and a composite active material layer disposed on at least one surface of the positive electrode current collector; the composite active material layer includes a first positive electrode layer and a second positive electrode layer; the second positive electrode layer is located on the side away from the positive electrode current collector; The first positive electrode layer comprises a monocrystalline positive electrode active material and a first solid electrolyte, and the second positive electrode layer comprises a polycrystalline positive electrode active material and a second solid electrolyte.

2. The composite positive electrode according to claim 1, wherein, The volumetric particle size Dv50 of the single-crystal positive electrode active material is 1~10 μm, preferably 1.5~4 μm.

3. The composite positive electrode according to claim 1, wherein, The polycrystalline positive electrode active material particles are spherical or nearly spherical in shape. The volumetric particle size Dv50 of the polycrystalline positive electrode active material is 1.5~15 μm, preferably 2~5 μm.

4. The composite cathode according to any one of claims 1 to 3, wherein, The monocrystalline positive electrode active material and the polycrystalline positive electrode active material are each independently selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

5. The composite positive electrode according to claim 1, wherein, The volume fraction of the single-crystal positive electrode active material in the first positive electrode layer is 50-85%; and / or, The volume fraction of the polycrystalline positive electrode active material in the second positive electrode layer is 50-85%.

6. The composite positive electrode according to claim 1, wherein, The thickness of the first positive electrode layer is 20~80 μm, preferably 40~70 μm; and / or, The thickness of the second positive electrode layer is 20~80 μm, preferably 30~60 μm.

7. The composite positive electrode according to claim 6, wherein, The thickness of the composite active material layer is 70~160 μm.

8. The composite positive electrode according to claim 1, wherein, The composite active material layer further includes a transition layer located between the first positive electrode layer and the second positive electrode layer; the transition layer includes the monocrystalline positive electrode active material and the polycrystalline positive electrode active material.

9. The composite positive electrode according to claim 1, wherein, The first solid electrolyte and the second solid electrolyte are each independently selected from the chemical formula Li 7-m+a-c-d M m / n P 1-a AaS 5-b D b Cl c X d At least one of the sulfide electrolytes; wherein M is selected from one or more of Na, Mg, Ca, Zn and Al; A is selected from one or more of Si, Sn and Ge; D is selected from O and / or Se; X is selected from Br and / or I; 0≤m≤1, 1≤n≤3, 0≤a≤1, 0≤b<2, 0≤c<2, 0≤d<2, 1≤c+d<2.

10. A method for preparing the composite positive electrode according to any one of claims 1 to 9, characterized in that, include: A single-crystal positive electrode active material, a first solid electrolyte, and a first solvent are mixed evenly to form a first positive electrode slurry; a polycrystalline positive electrode active material, a second solid electrolyte, and a second solvent are mixed evenly to form a second positive electrode slurry. The first positive electrode slurry and the second positive electrode slurry are sequentially coated onto at least one side of the positive electrode current collector and dried to obtain a composite positive electrode.

11. The method according to claim 10, wherein, The first positive electrode slurry and the second positive electrode slurry are coated onto at least one side of the surface of the positive electrode current collector, such that the first positive electrode slurry is located on the surface of the positive electrode current collector and the second positive electrode slurry is located on the side of the first positive electrode slurry away from the positive electrode current collector, and then dried to form the first positive electrode layer and the second positive electrode layer.

12. The method according to claim 10, wherein, The first positive electrode slurry is coated onto at least one side surface of the positive electrode current collector and dried to form a first positive electrode layer; The second positive electrode slurry is coated on the surface of the first positive electrode layer away from the positive electrode current collector, and then dried to form the second positive electrode layer.

13. A solid-state battery, characterized in that, The solid-state battery includes the composite cathode as described in any one of claims 1 to 9 or the composite cathode prepared by the method described in any one of claims 10 to 12.

14. A battery pack, characterized in that, The battery pack includes a plurality of solid-state batteries as described in claim 13.

15. An electrical appliance, characterized in that, The electrical device includes the solid-state battery of claim 13 or the battery pack of claim 14.

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