Dry-method all-solid-state positive pole piece, preparation method thereof and all-solid-state battery

Abstract

The invention provides a dry-method all-solid-state positive pole piece, a preparation method thereof and an all-solid-state battery, and particularly relates to the field of batteries. The dry-method all-solid-state positive electrode plate comprises a positive electrode current collector, a first dry-method positive electrode layer and a second dry-method positive electrode layer, the first dry-method positive electrode layer is arranged on at least one side of the positive electrode current collector; the second dry-method positive electrode layer is arranged on one side, deviating from the positive electrode current collector, of the first dry-method positive electrode layer; wherein the first dry-method positive electrode layer comprises a positive electrode active material, a solid electrolyte, a conductive agent and a first binder, and the crystallinity of the first binder is 96%-99%; the second dry-method positive electrode layer comprises a positive electrode active material, a solid electrolyte, a conductive agent and a second binder, and the crystallinity of the second binder is 70%-90%. According to the double-layer positive electrode structure, the long-term cycle performance and the rate capability of the all-solid-state battery are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a dry-process all-solid-state positive electrode sheet, its preparation method, and an all-solid-state battery. Background Technology

[0002] Solid-state batteries are considered one of the ultimate forms of commercial lithium-ion batteries. Compared to traditional liquid lithium-ion batteries, solid-state batteries fundamentally solve the safety hazards such as leakage and combustion caused by liquid electrolytes by using solid electrolytes instead of flammable liquid electrolytes. At the same time, they have higher energy density and better long-term cycle performance, showing great application potential in scenarios such as power batteries where safety and range requirements are stringent.

[0003] Currently, the positive electrode is one of the core components of all-solid-state batteries, and its typical structure includes a dry-process positive electrode layer and a current collector. During battery charge-discharge cycles, stress is generated between the current collector and the dry-process positive electrode layer: the first type of stress originates from the interfacial shear force caused by the volume expansion and contraction of the positive electrode active material during charge and discharge; the second type of stress occurs under conditions such as fast charging, where the internal temperature of the battery rises rapidly, and due to the significant difference in the thermal expansion coefficients between the current collector and the dry-process positive electrode layer, thermomechanical stress is generated at the interface. These two types of stress accumulate continuously during long-term battery cycling, eventually leading to interfacial delamination between the dry-process positive electrode layer and the current collector. Interfacial delamination disrupts the electron and ion conduction pathways within the battery, directly causing a sharp decline in the capacity of the all-solid-state battery (i.e., a capacity drop), and also significantly increasing the internal resistance of the battery, severely restricting the cycle life and industrial application of all-solid-state batteries.

[0004] Therefore, how to alleviate stress accumulation between the current collector and the dry cathode layer and improve the stability of the interface bonding has become a key technical problem that urgently needs to be solved in the field of all-solid-state batteries. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a dry all-solid-state positive electrode sheet, a method for preparing the same, and an all-solid-state battery, which improves the problem of interface delamination caused by stress accumulation between the positive electrode current collector and the dry positive electrode layer.

[0006] To achieve the above and other related objectives, the present invention provides a dry-process all-solid-state positive electrode sheet, comprising a positive current collector, a first dry-process positive electrode layer, and a second dry-process positive electrode layer; the first dry-process positive electrode layer is disposed on at least one side of the positive current collector; the second dry-process positive electrode layer is disposed on the side of the first dry-process positive electrode layer opposite to the positive current collector; wherein, the first dry-process positive electrode layer comprises a positive active material, a solid electrolyte, a conductive agent, and a first binder, the first binder having a crystallinity of 96%~99%; the second dry-process positive electrode layer comprises a positive active material, a solid electrolyte, a conductive agent, and a second binder, the second binder having a crystallinity of 70%~90%.

[0007] In one embodiment of the present invention, the first adhesive and the second adhesive are each independently selected from polytetrafluoroethylene and ethylene. Tetrafluoroethylene copolymer, ethylene-vinyl acetate copolymer, polypropylene, polyethylene, ethylene One or more of octene copolymers and polyimides.

[0008] In one embodiment of the present invention, the content of the first binder in the first dry cathode layer is 0.5wt%~1wt%; and the content of the second binder in the second dry cathode layer is 1wt%~2wt%.

[0009] In one embodiment of the present invention, the thickness ratio of the first dry cathode layer to the second dry cathode layer is 1:(3~5).

[0010] In one embodiment of the present invention, the first adhesive is prepared by the following method: firstly, an adhesive with a crystallinity of 70% to 90% is heated to 340°C to 355°C at a rate of 5°C / min to 10°C / min under an inert atmosphere and held at that temperature for 1 to 2 hours; then, it is cooled to below 300°C at a rate of 0.2°C / min to 1°C / min; finally, it is quenched with liquid nitrogen to obtain a first adhesive with high crystallinity.

[0011] In one embodiment of the present invention, the conductive agent is selected from at least one of graphite, graphene, carbon black, carbon fiber, and carbon nanotubes.

[0012] In one embodiment of the present invention, the positive electrode active material is selected from at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based oxide.

[0013] In one embodiment of the present invention, the solid electrolyte is selected from at least one of oxide solid electrolytes, sulfide solid electrolytes, and halide solid electrolytes.

[0014] In one embodiment of the present invention, the conductive agent is selected from one-dimensional conductive agents, and the aspect ratio of the one-dimensional conductive agent is greater than or equal to 200.

[0015] This invention also provides a method for preparing a dry-process all-solid-state positive electrode, comprising the following steps: Premixing: The positive electrode active material, solid electrolyte, and conductive agent are mixed according to the component ratios of the first and second dry-process positive electrode layers to obtain the first premix and the second premix. Mixing: The first premix is ​​mixed with the first binder to obtain a first mixture; the second premix is ​​mixed with the second binder to obtain a second mixture; fibrillation: The first mixture and the second mixture are subjected to fibrillation treatment respectively to obtain the first fibrillated material and the second fibrillated material; Crushing and granulation: The first fibrillated material and the second fibrillated material are crushed and granulated respectively to obtain the first dry cathode material and the second dry cathode material; Thinning: The first dry cathode material and the second dry cathode material are respectively formed into films and thinned to a preset thickness to obtain a first dry cathode layer and a second dry cathode layer; the first dry cathode layer and the second dry cathode layer are horizontally stacked and then thinned together to the target areal capacity to obtain a dry cathode layer; Composite current collector: The first dry-process positive electrode layer side of the dry-process positive electrode layer is combined with the positive electrode current collector to obtain a dry-process all-solid-state positive electrode sheet; Hot pressing: The dry-process all-solid-state positive electrode sheet is subjected to hot pressing treatment to fuse the interface between the first dry-process positive electrode layer and the second dry-process positive electrode layer.

[0016] In one embodiment of the present invention, in the premixing step, the linear velocity of the stirring paddle is 20m / s to 40m / s, the stirring time is 20min to 60min, and the processing temperature is 20℃ to 30℃.

[0017] In one embodiment of the present invention, in the mixing step, the linear velocity of the stirring paddle is 5 m / s to 20 m / s, the stirring time is 20 min to 60 min, and the processing temperature is 5 °C to 20 °C.

[0018] In one embodiment of the present invention, in the fibrillation step, the processing temperature is 60℃~80℃, the linear velocity of the stirring paddle is 40m / s~60m / s, and the stirring time is 10min~30min.

[0019] In one embodiment of the present invention, the temperature used for thinning in the thinning step is 80°C to 120°C.

[0020] In one embodiment of the present invention, in the hot pressing step, the hot pressing temperature is 120℃~150℃, the pressure is 5MPa~8MPa, and the hot pressing time is 30s~60s.

[0021] The present invention also provides an all-solid-state battery, wherein the all-solid-state battery includes any of the above-described dry-process all-solid-state positive electrode sheets, or a dry-process all-solid-state positive electrode sheet prepared by the above-described preparation method.

[0022] The beneficial effects of this invention are as follows: This invention employs a double-layer dry-process all-solid-state positive electrode sheet: In the first dry-process positive electrode layer near the positive electrode current collector, a high-modulus binder is used to construct a rigid support layer, which can eliminate the interface abrupt change between the positive electrode current collector and the dry-process positive electrode layer to achieve a smooth stress transfer and avoid interface delamination, and also form a microcrack barrier to inhibit the extension of microcracks caused by the cyclic expansion of the active material layer into the current collector; In the second dry-process positive electrode layer near the electrolyte layer, a medium-modulus binder is used to form a flexible and tough protective layer, whose deformation capacity is consistent with the cyclic volume expansion characteristics of the active material. With a high degree of matching, it can absorb expansion stress through elastic deformation, avoiding separation of the electrolyte layer and active material layer due to deformation differences. This synergistic design of "rigid support-flexible buffer" not only solves the defects of "easy cracking and poor deformation adaptability" of single high modulus binders, but also makes up for the shortcomings of "insufficient support and weak stress dispersion ability" of single medium modulus binders. It can effectively improve the problems of interfacial stress concentration, microcrack propagation, electron conduction failure and insufficient deformation adaptability faced by existing dry all-solid-state cathodes during cycling, and greatly improve the long-term cycle performance and rate performance of all-solid-state batteries.

[0023] This invention can regulate the crystallinity of the binder by controlling the process conditions, thereby regulating the modulus of the binder. This process control method does not require the introduction of multiple binders, which reduces the difficulty and cost of raw material compatibility, improves the compatibility of the double-layer electrode interface, and avoids compatibility problems between different binders. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the dry-process all-solid-state positive electrode sheet of the present invention in one embodiment; Figure 2 This is a flowchart of one embodiment of the dry-process all-solid-state positive electrode preparation method of the present invention.

[0026] Component designation explanation: 100. Dry-process all-solid-state positive electrode sheet; 110. Positive current collector; 120. First dry-process positive electrode layer; 130. Second dry-process positive electrode layer. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0029] In this article, the terms "multiple" and "various kinds" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more kinds.

[0030] In this document, "preferred" refers only to a better implementation method or embodiment, and should be understood as not constituting a limitation on the scope of protection of this invention. If multiple "preferred" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" option is independent.

[0031] In this document, terms such as "further" and "even further" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0032] In this document, when referring to numerical ranges, unless otherwise specified, the distribution of selectable values ​​within a numerical range is considered continuous, including the two endpoints of the range (i.e., the minimum and maximum values), and every value between these two endpoints. When multiple numerical ranges are provided to describe a feature or property, these numerical ranges can be combined.

[0033] Dry-process all-solid-state positive electrode sheets are prepared using a dry process. The dry process does not require liquid solvents, which can avoid the risks of hydrolysis / solventization of electrolytes such as sulfides from the source, ensure close contact between the electrode and the electrolyte to reduce interfacial impedance, adapt to thick electrode designs and maintain a continuous conductive / ion transport network, and the process is simplified, environmentally friendly and more suitable for large-scale production.

[0034] However, the binders commonly used in dry-process technology have low modulus. When applied to dry-process all-solid-state cathode sheets, stress is generated between the cathode current collector and the dry-process cathode layer. During battery cycling, the accumulation of stress can cause the dry-process cathode layer and the cathode current collector to delaminate, leading to a sharp drop in all-solid-state battery capacity and an increase in internal resistance. The reasons are twofold: First, the cathode current collector and the dry-process cathode layer have vastly different materials and mechanical properties. The former is a rigid metal (such as aluminum foil), while the latter is a composite system containing active materials and conductive agents, making them prone to interfacial delamination due to stress concentration during charge-discharge cycles. Second, the volume expansion and contraction of the dry-process cathode layer during charge-discharge processes can easily lead to interfacial cracking, and the resulting microcracks can easily extend towards the cathode current collector. Therefore, the dry-process cathode layer near the cathode current collector needs a highly rigid structure for constraint and protection. Furthermore, the interfacial contact quality between the electrolyte layer and the dry-process cathode layer directly determines the ion transport efficiency. The volume expansion of the active material during cycling can easily lead to interfacial cracking, necessitating a highly resilient structure to adapt to deformation and maintain a tight fit.

[0035] The applicant's research revealed that: low-crystallinity binders have a high proportion of amorphous regions and a large degree of freedom in molecular chain movement, corresponding to low modulus and high toughness, and can absorb stress through elastic deformation and adapt to interfacial deformation; high-crystallinity binders have regular and compact molecular chains and a high proportion of crystalline regions, corresponding to high modulus and high rigidity, and can provide stable mechanical support and inhibit structural failure.

[0036] Based on this, the present invention provides a dry all-solid-state positive electrode sheet, its preparation method and an all-solid-state battery. By adopting a double-layer structure dry all-solid-state positive electrode sheet, a rigid support bottom layer is constructed on the side near the positive electrode current collector, and a flexible and tough protective layer is constructed on the side near the electrolyte layer. The double-layer structure of rigid support and flexible buffering synergistically improves the peeling problem between the positive electrode current collector and the dry positive electrode layer.

[0037] Please see Figure 1 The first aspect of this invention provides a dry-process all-solid-state positive electrode 100, which includes a positive current collector 110, a first dry-process positive electrode layer 120, and a second dry-process positive electrode layer 130. The positive current collector 110 can be made of any conductive material capable of carrying and supporting the first dry-process positive electrode layer 120 and the second dry-process positive electrode layer 130, such as aluminum foil, carbon-coated aluminum foil, etc. The first dry-process positive electrode layer 120 is disposed on at least one side of the positive current collector 110. Figure 1(Only the case of single-sided arrangement is shown). For example, the positive electrode current collector 110 has a first surface and a second surface arranged opposite to each other along its thickness direction. The first dry positive electrode layer 120 can be disposed on one of the first surface and the second surface, or it can be disposed on both the first surface and the second surface. The second dry positive electrode layer 130 is disposed on the side of the first dry positive electrode layer 120 away from the positive electrode current collector 110, that is, the first dry positive electrode layer 120 and the second dry positive electrode layer 130 are arranged sequentially in the direction away from the positive electrode current collector 110.

[0038] The first dry-process positive electrode layer 120 and the second dry-process positive electrode layer 130 together constitute the active material layer of the dry-process all-solid-state positive electrode sheet 100. Both include positive electrode active material, solid electrolyte, conductive agent and binder. The positive electrode active material, solid electrolyte and conductive agent are not specifically limited and can be conventional materials in the art, but the crystallinity of the binder is different. Here, the binder in the first dry-process positive electrode layer 120 is referred to as the first binder, and the binder in the second dry-process positive electrode layer 130 is referred to as the second binder. The crystallinity of the first binder is 96%~99%, for example, it can be 96%, 97%, 98% or 99%, etc. The molecular chains of the highly crystallized binder are regular and compact, with a high proportion of crystalline regions, corresponding to high modulus and high rigidity. It can serve as a rigid substrate for the active material layer, firmly fixing the connection between the positive electrode active material, the conductive agent and the positive electrode current collector 110, eliminating the interface abrupt change between the positive electrode current collector 110 and the dry-process positive electrode layer to achieve smooth stress transmission and avoid interface delamination. At the same time, after compaction, the particles of the highly crystallized binder undergo plastic deformation, and the fragments composed of lamellar bundles are tightly attached, embedded and entangled, forming a dense physical network structure, thereby preventing the microcracks generated by the cyclic expansion of the dry-process positive electrode layer from extending to the positive electrode current collector 110. The crystallinity of the second binder is 70%~90%, for example, it can be 70%, 80% or 90%, etc.; the low crystallinity binder has a high proportion of amorphous regions and a large degree of freedom of molecular chain movement, corresponding to low modulus and high toughness. It can absorb expansion stress through elastic deformation and avoid separation of the electrolyte layer and dry cathode layer due to deformation differences. The rigid support of the first dry cathode layer 120 and the flexible buffer of the second dry cathode layer 130 synergistically solve the problems of interface stress concentration, microcrack propagation, electron conduction failure and insufficient deformation adaptation faced by existing dry all-solid-state cathodes during cycling, which greatly improves the long-term cycle performance and rate performance of all-solid-state batteries.

[0039] In this invention, the crystallinity of the binder refers to the percentage of the mass of the crystalline region in which the molecular chains are arranged in a regular manner to the total mass of the binder. It essentially reflects the degree of ordered packing of the molecular chains and is calculated by peak fitting using X-ray diffraction (XRD) analysis.

[0040] In some alternative embodiments, the first adhesive and the second adhesive are each independently selected from polytetrafluoroethylene (PTFE), ethylene ETFE (ethylene tetrafluoroethylene copolymer), EVA (ethylene-vinyl acetate copolymer), PP (polypropylene), PE (ethylene), ethylene One or more of octene copolymer (POE) and polyimide (PI). That is, the first and second adhesives are independent and do not interfere with each other. They can both be of the same type of adhesive, such as both being polytetrafluoroethylene (PTFE) or ethylene-tetrafluoroethylene copolymer, etc.; they can also be of different types of adhesives, such as the first adhesive being PTFE and the second adhesive being ethylene-vinyl acetate copolymer, etc. Preferably, the first and second adhesives are of the same type, differing only in crystallinity, thus avoiding compatibility issues between different adhesives.

[0041] In an optional embodiment, the crystallinity of the binder can be controlled by adjusting the process conditions, transforming it from a low-crystallinity binder to a high-crystallinity binder. For example: (1) Melt reconstitution: First, place the commercially available binder with a crystallinity of 70%~90% in an inert atmosphere and heat it to 340℃~355℃ at a heating rate of 5℃ / min~10℃ / min, and keep it at that temperature for 1h~2h.

[0042] Melting and recombining low-crystallinity binders at a certain temperature can disrupt their original crystal structure, allowing molecular chains to fully untangle. If the melting and recombining temperature is too low, the binder may not completely melt, and the residual crystals act as heterogeneous nucleation sites, inducing rapid and disordered stacking of molecular chains, resulting in low crystallinity. If the melting and recombining temperature is too high, the melt viscosity decreases sharply, making it difficult for the molecular chains to arrange themselves in an orderly manner during cooling, thus hindering the improvement of crystallinity. In some embodiments, the crystallinity of the binder raw material for melting and recombining can be 70%, 80%, or 90%, etc.; the melting temperature can be 340℃, 345℃, 350℃, or 355℃, etc.; the heating rate can be 5℃ / min, 8℃ / min, or 10℃ / min, etc.; and the holding time can be 1h, 1.5h, or 2h, etc. The parameters for the melting and recombining step can be selected based on the crystallinity of the selected raw material and the desired crystallinity of the binder.

[0043] (2) Gradient cooling: After the melting and reorganization is completed, the temperature is first cooled to below 300°C, and then quenched with liquid nitrogen to obtain the first binder with high crystallinity.

[0044] A suitable gradient cooling rate can provide the molecular chains with time for slow, ordered alignment, which is beneficial for forming highly regular crystals and thus improving crystallinity. In some embodiments, the cooling rate is controlled at 0.2℃ / min to 1℃ / min during the cooling to 300℃ process, for example, it can be 0.2℃ / min, 0.5℃ / min, 0.8℃ / min, or 1℃ / min, etc. When the temperature is below 300℃, liquid nitrogen is used for quenching to obtain a highly crystalline binder.

[0045] The standard specific gravity of the aforementioned first adhesive (high crystallinity adhesive) is 2.18~2.20 g / cm³. 3 The bulk density is 450~550g / L, and the extrusion pressure is 80~120MPa (380℃).

[0046] The binder plays the following roles in the dry-process cathode layer: on the one hand, it tightly bonds and solidifies the cathode active material, solid electrolyte, and conductive agent into a continuous film layer with a certain mechanical strength in a solvent-free dry molding environment; on the other hand, it establishes stable adhesion between different interfaces, including the interfacial bonding between components within the film layer, between the film layer and the current collector, and between the film layer and the solid electrolyte layer. Therefore, the binder content in the dry-process cathode layer is a key parameter for controlling electrode performance. Excessive or insufficient binder content will lead to performance defects: if the binder content is insufficient, it cannot form a complete bonding network, making it difficult to ensure the self-support of the dry-process cathode layer and providing sufficient interfacial adhesion, easily leading to problems such as interlayer delamination and active material shedding during processing or cycling; if the binder content is too high, it will reduce the effective proportion of the cathode active material, solid electrolyte, and conductive agent, directly reducing the energy density of the electrode and increasing the resistance to electron and ion transport, resulting in a decrease in battery rate performance and charge / discharge efficiency.

[0047] In some embodiments, the content of the first binder in the first dry cathode layer 120 is 0.5wt% to 1wt%, for example, it can be 0.5wt%, 0.8wt%, or 1wt%, etc. The content of the second binder in the second dry cathode layer 130 is 1wt% to 2wt%, for example, it can be 1wt%, 1.5wt%, or 2wt%, etc.

[0048] In this invention, the first dry-process positive electrode layer 120 serves as a rigid support layer, forming a synergistic effect of rigid support and flexible buffer with the second dry-process positive electrode layer 130, which serves as a tough protective layer. The thicknesses of the two layers must be matched. If the thickness of either layer deviates from the matching range with the other, it will break the synergistic balance of rigid support and flexible buffer, leading to performance defects. If the thickness of the first dry-process positive electrode layer 120 is too large and the thickness of the second dry-process positive electrode layer 130 is insufficient, the rigidity of the entire electrode sheet will be too high. The stress generated by the battery charge and discharge cycle cannot be effectively unloaded and absorbed by the second dry-process positive electrode layer 130, and the interlayer interface will crack due to the increased stress concentration. Conversely, if the thickness of the first dry-process positive electrode layer 120 is normal but the thickness of the second dry-process positive electrode layer 130 is too large, it will lead to excessive flexibility of the entire electrode sheet. The rigid support effect of the first dry-process positive electrode layer 120 will be weakened, and the electrode structure will be prone to deformation during pressing or cycling.

[0049] If the thickness of the first dry cathode layer 120 is too thin, even if the thickness of the second dry cathode layer 130 is suitable, it will not be able to form an effective crack blocking barrier due to insufficient rigid support at the bottom layer. The microcracks generated by the active material layer can easily penetrate the first dry cathode layer 120 and extend to the cathode current collector 110. At the same time, the electron conduction network carried by the first dry cathode layer 120 will collapse due to the lack of support, resulting in the interruption of the electron transmission path. The second dry cathode layer 130 cannot replace it to achieve a stable conductive support function.

[0050] In some embodiments, the thickness ratio of the first dry cathode layer 120 to the second dry cathode layer 130 is 1:(3~5), for example, it can be 1:3, or 1:4, or 1:5, etc.

[0051] The positive electrode active material, conductive agent, and solid electrolyte in the dry-process positive electrode layer can be selected according to actual application requirements. For example, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based oxides. In other words, the positive electrode active material can be a single material, such as lithium cobalt oxide, or lithium nickel cobalt manganese oxide, or lithium nickel manganese oxide, etc.; the positive electrode active material can also be a combination of multiple materials, such as a combination of lithium cobalt oxide and lithium nickel oxide, a combination of lithium nickel cobalt aluminum oxide, lithium-rich oxide, and lithium nickel cobalt manganese oxide, etc. The types of positive electrode active materials are not limited to those listed above.

[0052] Conductive agents themselves possess excellent electrical conductivity. Adding conductive agents to the dry-process positive electrode layer can effectively improve the conductivity of the electrode, reduce its resistance, and thus improve the battery's rate performance and charge / discharge rate. For example, the conductive agent includes at least one of graphite, graphene, carbon black (Superp), carbon fiber (VGCF), and carbon nanotubes, such as graphite, carbon black, or a combination of carbon black and carbon fiber. Preferably, the conductive agent is a one-dimensional conductive agent with an aspect ratio ≥ 200, such as carbon fiber or carbon nanotubes. One-dimensional conductive agents, with their unique aspect ratio structure, can construct a continuous "point-line-surface" interconnected electron conduction network inside the electrode. Compared to traditional zero-dimensional conductive agents (such as carbon black), their conduction path is more direct, effectively reducing the jumping resistance during electron transport. This advantage is particularly prominent in thick electrodes, reducing the amount of conductive agent used inside the electrode while avoiding the problem of reduced active material content due to excessive conductive agent. Furthermore, the highly crystalline first binder in the first dry-process positive electrode layer 120 provides a rigid support framework for the one-dimensional conductive agent, firmly fixing its spatial position and constraining its displacement and aggregation during electrode pressing and cyclic deformation, ensuring that the continuous conduction pathway it constructs is not disrupted. This combination of the one-dimensional conductive agent and the high-modulus binder significantly reduces the electron transport resistance of the thick electrode. At the same time, the long-chain structure of the one-dimensional conductive agent can also form multi-point anchoring with the active material particles, helping to disperse stress and further suppressing the generation and propagation of microcracks.

[0053] Solid-state electrolytes provide migration pathways for lithium ions, allowing them to shuttle smoothly between the positive and negative electrodes, thus facilitating the battery's charge and discharge processes. Furthermore, solid-state electrolytes can bond tightly with the positive electrode active material, reducing side reactions at the interface, lowering interfacial resistance, and consequently improving the overall battery performance and cycle life. As examples, solid-state electrolytes include at least one of oxide solid-state electrolytes, sulfide solid-state electrolytes, and halide solid-state electrolytes; for instance, they can be oxide solid-state electrolytes, sulfide solid-state electrolytes, or a combination of oxide solid-state electrolytes and halide solid-state electrolytes, etc.

[0054] In this invention, the proportions of the components in the first dry cathode layer and the second dry cathode layer can be adjusted according to actual needs, and are not limited here.

[0055] Please see Figure 2 The second aspect of the present invention provides a method for preparing the above-mentioned dry-process all-solid-state positive electrode sheet, the method comprising the following steps: S1. Mix the positive electrode active material, solid electrolyte, and conductive agent according to the component ratios of the first and second dry-process positive electrode layers respectively to obtain the first premix and the second premix. S2. The first premix and the first binder are mixed to obtain a first mixture; the second premix and the second binder are mixed to obtain a second mixture; S3. The first mixture and the second mixture are subjected to fiberization treatment to obtain the first fibrillated material and the second fibrillated material; S4. The first fibrillated material and the second fibrillated material are crushed and granulated respectively to obtain the first dry cathode material and the second dry cathode material; S5. The first dry cathode material and the second dry cathode material are respectively formed into films and thinned to a preset thickness to obtain the first dry cathode layer and the second dry cathode layer; the first dry cathode layer and the second dry cathode layer are horizontally stacked and then thinned together to the target areal capacity to obtain the dry cathode layer. S6. Combine the first dry-process positive electrode layer with the positive electrode current collector to obtain a dry-process all-solid-state positive electrode sheet. S7. Perform hot pressing on the dry-process all-solid-state positive electrode sheet to fuse the interface between the first dry-process positive electrode layer and the second dry-process positive electrode layer.

[0056] Specifically, step S1 is room temperature premixing, in which the positive electrode active material, solid electrolyte and conductive agent are premixed according to the component ratio of the first dry positive electrode layer 120 and the second dry positive electrode layer 130 to be prepared, so as to obtain a uniformly mixed first premix and second premix.

[0057] In one embodiment, during the premixing step, the linear velocity of the stirring paddle is 20 m / s to 40 m / s, the stirring time is 20 min to 60 min, and the processing temperature is 20°C to 30°C. Exemplarily, the linear velocity of the stirring paddle can be 20 m / s, 30 m / s, or 40 m / s, the stirring time can be 20 min, 40 min, or 60 min, and the processing temperature can be 20°C, 25°C, or 30°C. The parameters in the premixing step can be set according to the actual processing conditions; it is sufficient to ensure that the positive electrode active material, conductive agent, and solid electrolyte are thoroughly and uniformly mixed.

[0058] After premixing is completed, step S2 is performed to mix the first premix with the first binder to obtain the first mixture, and the second premix with the second binder to obtain the second mixture.

[0059] The second binder can be purchased directly through general commercial means. The first binder is obtained by controlling the process conditions to increase the crystallinity of the second binder to 96%~99%. The specific process is as follows: First, the second binder with a crystallinity of 70%~90% is heated to 340℃~355℃ at a rate of 5℃ / min~10℃ / min under an inert atmosphere and held for 1h~2h; then it is cooled to below 300℃ at a rate of 0.2℃ / min~1℃ / min; finally, it is quenched with liquid nitrogen to obtain the first binder with high crystallinity.

[0060] In the mixing step, the linear velocity of the agitator is 5 m / s to 20 m / s, the mixing time is 20 min to 60 min, and the processing temperature is 5℃ to 20℃. For example, the linear velocity of the agitator can be 5 m / s, 10 m / s, 15 m / s, or 20 m / s, the mixing time can be 20 min, 40 min, or 60 min, and the processing temperature can be 5℃, 10℃, 15℃, or 20℃. During the binder mixing process, the linear velocity and processing temperature should not be too high. If the linear velocity is too high, it may cause the binder to agglomerate or break; if the processing temperature is too high, it may cause some of the binder to prematurely fibrillate, resulting in uneven binder dispersion. The positive electrode active material, conductive agent, and solid electrolyte are pre-mixed before being mixed with the binder because: during the mixing process, the collision and friction between materials generate heat. The longer the mixing time, the higher the heat generated, and the higher the internal temperature of the material. If the binder is mixed with other materials, it may cause some of the binder to prematurely fibrillate, affecting the uniformity of binder dispersion.

[0061] Step S3, or fibrillation, involves treating the first and second mixtures with fibrillation to fully fibrillate the binder into a fiber network structure, and then fixing the positive electrode active material, conductive agent, and solid electrolyte within the fiber network structure.

[0062] In one embodiment, the fiberization treatment temperature is 60°C to 80°C, the linear velocity of the agitator is 40 m / s to 60 m / s, and the stirring time is 10 min to 30 min. Exemplarily, the treatment temperature can be 60°C, 70°C, or 80°C, the linear velocity can be 40 m / s, 50 m / s, or 60 m / s, and the stirring time can be 10 min, 20 min, or 30 min.

[0063] Step S4 involves crushing and granulating the first and second fibrillated materials respectively to obtain the first and second dry-process cathode materials that meet processing requirements. The binder, after high-intensity shearing, forms an entangled fiber network that encapsulates the cathode active material, conductive agent, and solid electrolyte, forming fiber clumps. These fiber clumps have a large particle size and poor flowability, making them unable to spread uniformly on the cathode current collector. Crushing the fibrillated materials breaks down the fiber clumps into microparticles, achieving uniform mixing of the components. Granulation spherizes irregular particles, and these spherical particles undergo plastic deformation under pressure to form dense electrode sheets. Crushing and granulation can be performed using mechanical crushers and granulators. The particle size after crushing and granulation can be selected according to actual needs and is not limited here.

[0064] Step S5 involves rolling the first and second dry-process cathode materials into films using multi-roll rolling and thinning them to a preset thickness to obtain a first dry-process cathode layer and a second dry-process cathode layer. Then, the first and second dry-process cathode layers are horizontally stacked and thinned together to the target areal capacity to obtain the dry-process cathode layer. The target areal capacity refers to the designed or desired charge (capacity) stored per unit area of ​​the electrode, measured in mAh / cm², and can be set according to actual needs without limitation. The temperature used during the thinning process is 80℃~120℃, for example, 80℃, 100℃, or 120℃, etc.

[0065] Step S6 involves combining the first dry cathode layer 120 obtained in step S5 with the cathode current collector 110 through roll forming to obtain a dry all-solid cathode sheet.

[0066] Step S7 is the hot pressing step: the dry-process all-solid-state positive electrode sheet obtained in step S6 is subjected to hot pressing treatment to fuse the interface between the first dry-process positive electrode layer 120 and the second dry-process positive electrode layer 130.

[0067] In one embodiment, during the hot pressing step, the hot pressing temperature is 120°C to 150°C, the pressure is 5MPa to 8MPa, and the hot pressing time is 30s to 60s. For example, the hot pressing temperature can be 120°C, 130°C, 140°C, or 150°C, etc.; the pressure can be 5MPa, 6MPa, 7MPa, or 8MPa, etc.; and the hot pressing time can be 30s, 40s, 50s, or 60s, etc.

[0068] This invention controls the crystallinity of the binder by adjusting process conditions, thereby controlling the binder's modulus. Simultaneously, a highly crystallinity binder is used in the first dry-process cathode layer on the current collector side to avoid abrupt interface changes and stress concentration. Furthermore, the high crystallinity causes plastic deformation of the particles after compaction, resulting in tightly packed and entangled fragments composed of lamellar bundles, forming a dense physical network structure. This prevents microcracks in the active material layer caused by cyclic expansion from extending to the current collector. A conventionally available medium-modulus binder is used in the second dry-process cathode layer on the electrolyte layer side to form a tough protective layer that adapts to the deformation of the active material. This dual-layer composite design significantly improves the battery's long-cycle performance and rate performance.

[0069] A third aspect of the present invention provides an all-solid-state battery, the battery comprising the above-described dry-process all-solid-state positive electrode sheet, or the dry-process all-solid-state positive electrode sheet prepared by the above-described preparation method.

[0070] The all-solid-state battery also includes necessary components such as a negative electrode and a solid electrolyte layer. The solid electrolyte layer is placed between the all-solid-state dry-process positive electrode and the negative electrode to provide a channel for ion transport between the positive and negative electrodes, while blocking electron transport, thereby avoiding short circuits.

[0071] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector. The negative current collector is, for example, copper foil or carbon-coated copper foil. The negative active material layer can be disposed on one surface of the negative current collector or simultaneously on both surfaces. The negative active material layer includes a negative active material, a conductive agent, and a binder. The negative active material includes graphite-based materials and / or silicon materials. Graphite-based materials can be natural graphite, artificial graphite, or a composite material of natural and artificial graphite. Natural graphite includes, but is not limited to, block graphite, flake graphite, and amorphous graphite. Artificial graphite includes, but is not limited to, single-crystal graphite, polycrystalline graphite, pyrolytic graphite, and graphite fiber. Silicon materials include, but are not limited to, crystalline silicon, amorphous silicon, organosilicon, silicon-carbon materials, and silicon-oxygen materials. Conductive agents include, but are not limited to, one or more of graphite, graphene, carbon black, carbon fibers, and carbon nanotubes. The binder varies depending on the manufacturing process of the negative electrode sheet. When the negative electrode sheet is manufactured using a wet process, the binder is selected from at least one of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), styrene-acrylate, and acrylic multi-component copolymers. For example, the negative electrode binder may be polyvinylidene fluoride, or a combination of styrene-butadiene rubber and carboxymethyl cellulose, etc. When the negative electrode sheet is manufactured using a dry process, the binder is selected from polytetrafluoroethylene (PTFE), ethylene... Tetrafluoroethylene copolymer, ethylene-vinyl acetate copolymer, polypropylene, polyethylene, ethylene One or more of octene copolymers and polyimides.

[0072] In other embodiments, the negative electrode may also be an alloy composed of indium, lithium, aluminum, or at least two of the above metals.

[0073] The solid electrolyte layer includes a solid electrolyte, which includes, but is not limited to, oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, and polymer solid electrolytes. It can be a single material or a mixture of multiple materials.

[0074] All-solid-state battery assembly: The prepared dry-process all-solid-state positive and negative electrode sheets are placed on both sides of the solid electrolyte layer for assembly to obtain an all-solid-state battery.

[0075] It should be noted that the structures not described in detail in the above batteries can be set up with reference to conventional techniques in this field, and will not be elaborated here.

[0076] The all-solid-state battery of this invention can be used in the form of individual cells, battery modules, or battery packs to power electronic devices. Electronic devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, electric vehicles, new energy vehicles, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.

[0077] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the embodiments are all commercially available.

[0078] Example 1 This embodiment provides a dry-process all-solid-state positive electrode sheet, which includes a positive electrode current collector, a first dry-process positive electrode layer disposed on the positive electrode current collector, and a second dry-process positive electrode layer disposed on the first dry-process positive electrode layer. The positive electrode current collector is a carbon-coated aluminum foil, and the first dry-process positive electrode layer contains a positive electrode active material (LiNi). 0.92 Co 0.04 Mn 0.04 O2), solid electrolyte (Li6PS5Cl), conductive agent (VGCF), first binder (PTFE) with 96% crystallinity, and second dry-process positive electrode layer containing positive electrode active material (LiNi). 0.92 Co 0.04 Mn 0.04O2), solid electrolyte (Li6PS5Cl), conductive agent (VGCF), and a second binder (PTFE) with 90% crystallinity.

[0079] The above LiNi 0.92 Co 0.04 Mn 0.04 O2 is sourced from Xiamen Tungsten Co., Ltd., model XW109; Li6PS5Cl is sourced from Zhongke GuNeng New Energy Technology Co., Ltd., model SHICB-S; VGCF is sourced from Showa Denko Co., Ltd., model VGCF-H; PTFE with 90% crystallinity is sourced from Daikin, model F104; PTFE with 96% crystallinity is obtained through the following method: (1) Melt reconstitution: F104 PTFE was placed in an inert atmosphere and heated to 350℃ at a heating rate of 10℃ / min, and held at that temperature for 1h; (2) Gradient cooling: Subsequently, the temperature is cooled to below 300°C at a cooling rate of 1°C / min. When the temperature is below 300°C, liquid nitrogen is used for quenching to obtain PTFE with a crystallinity of 96%, which is the first binder.

[0080] LiNi in the first dry process cathode layer 0.92 Co 0.04 Mn 0.04 The mass ratio of O2, Li6PS5Cl, VGCF, and highly crystalline binder PTFE is 70:28:1:1; LiNi in the second dry cathode layer... 0.92 Co 0.04 Mn 0.04 The mass ratio of O2, Li6PS5Cl, VGCF and PTFE with 90% crystallinity is 70:28:1:1; the thickness ratio of the first dry cathode layer to the second dry cathode layer is 1:4.

[0081] This embodiment also provides a method for preparing the above-mentioned dry-process all-solid-state positive electrode sheet, which includes the following steps: (1) Room temperature premixing: LiNi 0.92 Co 0.04 Mn 0.04 O2, Li6PS5Cl, and VGCF are mixed to obtain the first premix, and LiNi is then added. 0.92 Co 0.04 Mn 0.04 O2, Li6PS5Cl, and VGCF were mixed to obtain a second premix; during the premixing process, the linear velocity of the stirring paddle was 30 m / s, the stirring time was 30 min, and the processing temperature was 25℃. (2) Low-temperature mixing: The first premix and the second premix are respectively mixed with the first binder (PTFE with a crystallinity of 96%) and the second binder (F104 PTFE) at low temperature to obtain the first mixture and the second mixture; during the mixing process, the linear velocity of the stirring paddle is 15m / s, the stirring time is 30min, and the processing temperature is 10℃; (3) Fibration: The first mixture and the second mixture are subjected to fibrillation treatment to obtain the first fibrillated material and the second fibrillated material respectively; the treatment temperature is 80℃, the linear velocity of the stirring paddle is 40m / s, and the stirring time is 10min; (4) Crushing and granulation: The first and second raw fiber materials are crushed and granulated respectively to obtain the first dry cathode material and the second dry cathode material; (5) Thinning: At 100°C, the first dry-process positive electrode material is rolled into a film and thinned to 50 μm to obtain the first dry-process positive electrode layer; the second dry-process positive electrode material is rolled into a film and thinned to 200 μm to obtain the second dry-process positive electrode layer; the first dry-process positive electrode layer and the second dry-process all-solid-state positive electrode layer are horizontally stacked and then thinned to 4 mAh / cm. 2 The surface capacity is used to obtain the dry-process positive electrode layer; (6) Composite current collector: The first dry-process all-solid-state positive electrode layer in the dry-process positive electrode layer is combined with carbon-coated aluminum foil to obtain a dry-process all-solid-state positive electrode sheet; (7) Hot pressing interface treatment: Hot pressing dry solid-state positive electrode sheet at 120℃ and 5MPa for 60s.

[0082] This embodiment also provides an all-solid-state lithium-ion battery, which includes the aforementioned all-solid-state positive electrode, negative electrode, and solid electrolyte layer. The solid electrolyte layer is composed of Li6PS5Cl; the negative electrode is a lithium-indium alloy sheet (diameter φ=10mm).

[0083] The preparation steps of an all-solid-state lithium-ion battery are as follows: Step 1: Place 1000mg of Li6PS5Cl powder into a mold with a diameter of 10mm and pressurize it to 100MPa to obtain a solid electrolyte layer; Step 2: Place the dry-process all-solid-state positive electrode sheet and the lithium indium alloy sheet on both sides of the solid electrolyte layer for assembly; after assembly, pressurize to 100MPa and tighten the nut at the top of the column to maintain constant pressure, thus obtaining an all-solid-state lithium-ion battery.

[0084] Note: The assembly process was completed in a glove box under an argon atmosphere. The diameter of the above-mentioned dry-process all-solid-state positive electrode sheet and lithium-indium alloy sheet is 10mm.

[0085] Example 2 The difference between this embodiment and Embodiment 1 is that the crystallinity of the first adhesive is 98%, and its preparation process is as follows: (1) Melt reconstitution: F104 PTFE was placed in an inert atmosphere and heated to 350℃ at a heating rate of 10℃ / min, and held at that temperature for 1h; (2) Gradient cooling: Subsequently, the temperature was cooled to below 300°C at a cooling rate of 0.5°C / min. When the temperature was below 300°C, liquid nitrogen was used for quenching to obtain PTFE with a crystallinity of 98%.

[0086] Example 3 The difference between this embodiment and Embodiment 1 is that the thickness ratio of the first dry cathode layer to the second dry cathode layer is 1:3.

[0087] Example 4 The difference between this embodiment and Embodiment 1 is that the thickness ratio of the first dry cathode layer to the second dry cathode layer is 1:5.

[0088] Example 5 The difference between this embodiment and Embodiment 1 is that the crystallinity of the first adhesive is 99%, and its preparation process is as follows: (1) Melt reconstitution: F104 PTFE was placed in an inert atmosphere and heated to 355℃ at a heating rate of 10℃ / min, and held at that temperature for 2h; (2) Gradient cooling: Cool to 320°C at a cooling rate of 0.3°C / min, then cool to 300°C at a cooling rate of 0.2°C, and then quench with liquid nitrogen to obtain PTFE with a crystallinity of 99%.

[0089] Example 6 The difference between this embodiment and Embodiment 1 is that the content of the first binder in the first dry cathode layer is 0.5 wt%, i.e., LiNi 0.92 Co 0.04 Mn 0.04 The mass ratio of O2, Li6PS5Cl, VGCF and the first binder is 70.5:28:1:0.5.

[0090] Example 7 The difference between this embodiment and Embodiment 1 is that the content of the first binder in the first dry cathode layer is 0.8 wt%, i.e., LiNi 0.92 Co 0.04 Mn 0.04 The mass ratio of O2, Li6PS5Cl, VGCF and the first binder is 70.2:28:1:0.8.

[0091] Example 8 The difference between this embodiment and Embodiment 1 is that the content of the first binder in the first dry cathode layer is 1.5 wt%, i.e., LiNi0.92 Co 0.04 Mn 0.04 The mass ratio of O2, Li6PS5Cl, VGCF and the first binder is 69.5:28:1:1.5.

[0092] Example 9 The difference between this embodiment and Embodiment 1 is that the content of the second binder in the second dry cathode layer is 2wt%, i.e., LiNi 0.92 Co 0.04 Mn 0.04 The mass ratio of O2, Li6PS5Cl, VGCF, and the second binder is 69:28:1:2.

[0093] Example 10 The difference between this embodiment and Embodiment 1 is that the content of the second binder in the second dry cathode layer is 1.5 wt%, i.e., LiNi 0.92 Co 0.04 Mn 0.04 The mass ratio of O2, Li6PS5Cl, VGCF, and the second binder is 69.5:28:1:1.5.

[0094] Example 11 The difference between this embodiment and Embodiment 1 is that the PTFE in the second adhesive has a crystallinity of 70%, and the preparation process of the first adhesive is as follows: (1) Melt reconstitution: Place PTFE with 70% crystallinity in an inert atmosphere and heat it to 355°C at a heating rate of 5°C / min, and hold it for 2 hours.

[0095] (2) Gradient cooling: The temperature is reduced from 355℃ to 300℃, and the cooling rate is controlled at 0.5℃ / min. After the temperature drops below 300℃, liquid nitrogen is used for quenching to obtain PTFE with a crystallinity of 96%.

[0096] Example 12 The difference between this embodiment and Embodiment 1 is that the PTFE in the second adhesive has a crystallinity of 80%, and the preparation process of the first adhesive is as follows: (1) Melt reconstitution: Place PTFE with 80% crystallinity in an inert atmosphere and heat it to 355°C at a heating rate of 8°C / min, and hold it for 1.5 hours.

[0097] (2) Gradient cooling: the temperature is reduced from 355℃ to 300℃, the cooling rate is controlled at 0.7℃ / min, and liquid nitrogen is used to quench the temperature below 300℃ to obtain PTFE with a crystallinity of 96%.

[0098] Example 13 The difference between this embodiment and Embodiment 1 is that the second adhesive uses a commercially available ethylene-tetrafluoroethylene copolymer with a crystallinity of 90%. The ethylene-tetrafluoroethylene copolymer with a crystallinity of 90% is sourced from Chemours and is model HT-2180. The preparation process of the first adhesive is as follows: (1) Melt recombination: Place the ethylene-tetrafluoroethylene copolymer with 90% crystallinity in an inert atmosphere and heat it to 355°C at a heating rate of 10°C / min, and keep it at that temperature for 2 hours.

[0099] (2) Gradient cooling: the temperature was reduced from 355℃ to 300℃, and the cooling rate was controlled at 0.3℃ / min. After the temperature dropped below 300℃, liquid nitrogen was used for quenching to obtain ethylene-tetrafluoroethylene copolymer with a crystallinity of 96%.

[0100] Comparative Example 1 The difference between this comparative example and Example 1 is that F104 PTFE was directly used to prepare the dry-process all-solid-state positive electrode.

[0101] Comparative Example 2 The difference between this comparative example and Example 1 is that the crystallinity of the first adhesive is 92%, and its preparation method is as follows: (1) Melt reconstitution: F104 PTFE was placed in an inert atmosphere and heated to 372℃ at a heating rate of 10℃ / min, and held at that temperature for 1h; (2) Cooling: 372℃ to room temperature, with the cooling rate controlled at 1℃ / min, to obtain PTFE with a crystallinity of 92%.

[0102] Comparative Example 3 The difference between this comparative example and Example 1 is that the thickness ratio of the first dry cathode layer to the second dry cathode layer is 1:2.

[0103] Comparative Example 4 The difference between this comparative example and Example 1 is that the thickness ratio of the first dry cathode layer to the second dry cathode layer is 1:6.

[0104] To verify the performance of the dry-process all-solid-state positive electrode sheet of the present invention, the applicant conducted performance tests on the dry-process all-solid-state positive electrode sheet and all-solid-state lithium-ion battery of Examples 1-13 and Comparative Examples 1-4, respectively. The test methods are as follows, and the test results are shown in Table 1.

[0105] (1) X-ray diffraction (XRD) was used to test the crystallinity of the adhesive: First, the dry-process all-solid-state positive electrode sheet was immersed in a mixed solvent of 1,2-ethylenediamine (EDA) and 1,2-ethylenedithiol (EDT) in a mass ratio of 1:1 for 24 hours. The immersion process was repeated three times after changing the solvent to remove the sulfide electrolyte components in the dry-process all-solid-state positive electrode sheet. Then, the dry-process all-solid-state positive electrode sheet was vacuum dried at 120℃ for 24 hours to remove the solvent. Subsequently, the crystallinity of the binder in the dry-process all-solid-state positive electrode sheet was tested by XRD using Cu Kα rays with a scanning range of 2θ=10°-60°. The crystallinity was calculated by the Segal method, and the ratio of the integrated area of ​​the crystal diffraction peak to the sum of the integrated area of ​​the crystal diffraction peak and the amorphous scattering area was the crystallinity of the binder.

[0106] (2) Battery performance testing: The all-solid-state lithium-ion battery was subjected to long-cycle charge-discharge and rate performance testing after being capacitated at 25℃. The capacitation condition was a 0.6mA current. The test conditions were: long-cycle charge-discharge testing was conducted after capacitation, with a test rate of 0.3C. During the test, the first-cycle discharge specific capacity and the number of cycles at room temperature when the State of Health (SOH) was 80% were recorded. Under a rate of 2C, the first-cycle discharge specific capacity was measured as the rate performance. During the test, the battery's charge-discharge range was 1.9V~3.7V.

[0107] Table 1: Parameters and performance of Examples 1-13 and Comparative Examples 1-4

[0108] As shown in Table 1, Examples 1, 2, 5, and Comparative Example 2, with other conditions kept the same, adjusted the crystallinity of the first binder in the first dry-process positive electrode layer by controlling the process conditions. The test results show that when the crystallinity of the first binder is controlled within the range of 96% to 99%, the battery exhibits better first-cycle discharge specific capacity, high-rate discharge performance, and long-cycle stability. In contrast, the crystallinity of the first binder in Comparative Example 2 is 92% (below 96%), and its various electrochemical performances are significantly lower than those of the examples. However, compared to the conventional structure of Comparative Example 1, it still achieves a substantial improvement in battery performance. This phenomenon indicates that the synergistic design of a high-crystallinity binder stabilizing the current collector side and a medium-modulus binder adapting to deformation on the electrolyte side achieves dual optimization of battery structural stability and interface compatibility, ultimately significantly improving the long-cycle performance and rate performance of the all-solid-state lithium-ion battery.

[0109] Examples 1, 3, 4 and Comparative Examples 3 and 4, keeping other conditions the same, adjusted the thickness ratio of the first dry-process positive electrode layer to the second dry-process positive electrode layer. The test results showed that when the thickness ratio of the first dry-process positive electrode layer to the second dry-process positive electrode layer was in the range of 1:(3~5), the battery's first-cycle discharge specific capacity, high-rate discharge performance, and long-cycle stability all reached optimal levels. When deviating from this ratio range, the electrochemical performance showed significant degradation. When the thickness ratio was higher than this range (Comparative Example 3), the first dry-process positive electrode layer was relatively thick, and the second dry-process positive electrode layer was relatively thin, resulting in an excessively high rigidity ratio of the entire electrode sheet, and compromising the flexible buffer constructed by the medium-modulus binder. Insufficient layer thickness cannot effectively unload and absorb the volume expansion stress generated during battery charge and discharge cycles. The interlayer interface cracks due to increased stress concentration, which in turn leads to interface peeling and breakage of electron conduction pathways, ultimately resulting in a sharp drop in rate performance and accelerated cycle decay. When the thickness ratio is below this range (Comparative Example 4), the first dry cathode layer is too thin, resulting in insufficient rigid support and an inability to form an effective microcrack barrier. Cyclic stress directly drives the cracks to propagate to the current collector. At the same time, the second dry cathode layer is too thick, which significantly prolongs the ion transport path inside the electrode, causing severe concentration polarization, resulting in a decrease in the first discharge specific capacity and deterioration of high-rate performance.

[0110] In Examples 1, 6-8, keeping other conditions the same, the content of the first binder in the first dry-process positive electrode layer was adjusted. The test results showed that: moderately increasing the content of the first binder (as in Examples 1 and 7) resulted in a more uniform distribution inside the electrode, which could fully encapsulate the active material and conductive agent particles, further strengthening the density of the physical support network, reducing the risk of active material shedding during cycling, and significantly improving the cycle stability and rate performance of the battery compared to the group with a lower binder content; however, when the content of the first binder was too high (as in Example 8), the excessive binder would crowd out the effective proportion of the active material, resulting in a reduction in the number of active sites participating in the electrochemical reaction within the unit volume of the electrode, directly causing a significant decrease in the specific capacity of the battery during the first discharge cycle, which in turn offset the structural stability advantage brought by the binder.

[0111] Examples 1, 9, and 10, keeping other conditions the same, adjusted the content of the second binder in the second dry-process positive electrode layer. The results showed that an appropriate amount of second binder can improve the overall performance of the battery. However, when the content of the second binder is too high, excessive second binder will crowd out the effective proportion of the positive electrode active material, leading to a reduction in electrochemical reaction active sites per unit volume of electrode. This not only directly causes a significant decrease in the battery's first-cycle discharge specific capacity but also further degrades the battery's cycle performance and rate performance. The reason for this is that the insulating second binder has a dual regulatory effect on the battery's cycle performance: firstly, excessive second binder reduces the ion transport efficiency inside the electrode, exacerbating the battery's cycle capacity decay; secondly, the second binder can improve the electrode's cohesion, effectively mitigating electrode structure damage during cycling and thus improving cycle performance. These two effects are antagonistic. When the second binder content is 2%, the positive improvement effect brought by cohesion dominates. Therefore, the cycle performance of Example 9 shows a slight improvement compared to Example 10; the rate performance variation also follows this principle.

[0112] Examples 1, 11, and 12, keeping other conditions the same, adjusted the crystallinity of the second binder in the second dry-process cathode layer, while simultaneously ensuring the first binder maintained high crystallinity by controlling process conditions. Test results showed that even using a low-crystallinity binder (70%~80%) could be converted to a high-crystallinity binder through process optimization. However, due to differences in the crystallinity of the second binder itself, the electrochemical performance of the battery exhibited significant differences: the crystallinity of the second binder used in Examples 11 and 12 was lower than that in Example 1, resulting in relatively poor stability of the fiber network structure in its second dry-process cathode layer. Consequently, the cycle performance and rate performance of the battery showed a downward trend compared to Example 1.

[0113] In Examples 1 and 13, keeping other conditions the same, only the types of the first and second binders were changed. The first-cycle discharge specific capacity, high-rate performance and long-cycle stability of the battery still reached similar levels, indicating that different binders can achieve the technical effects of the present invention.

[0114] This invention employs a dual-layer dry-process all-solid-state cathode sheet: In the first dry-process cathode layer on the current collector side, a high-modulus binder is used to construct a rigid support layer. This eliminates abrupt interface changes between the current collector and the dry-process cathode layer, achieving smooth stress transfer and preventing interface delamination. It also forms a microcrack barrier to inhibit the extension of microcracks caused by cyclic expansion of the active material layer towards the current collector. In the second dry-process cathode layer near the electrolyte layer, a medium-modulus binder is used to form a flexible and tough protective layer. Its deformation capability is highly matched to the cyclic volume expansion characteristics of the active material, absorbing expansion stress through elastic deformation and preventing separation between the electrolyte layer and the dry-process cathode layer due to deformation differences. This synergistic design of rigid support and flexible buffer effectively improves the problems of interface stress concentration, microcrack propagation, electron conduction failure, and insufficient deformation adaptation faced by existing dry-process all-solid-state cathodes during cycling, greatly enhancing the long-term cycle performance and rate performance of all-solid-state batteries. Therefore, this invention effectively overcomes some practical problems in the prior art, thus possessing high utilization value and practical significance.

[0115] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A dry-process all-solid-state positive electrode, characterized in that, include: Positive current collector; A first dry-process positive electrode layer is disposed on at least one side of the positive electrode current collector; The second dry cathode layer is disposed on the side of the first dry cathode layer away from the cathode current collector; The first dry-process positive electrode layer includes a positive electrode active material, a solid electrolyte, a conductive agent, and a first binder, wherein the crystallinity of the first binder is 96% to 99%; the second dry-process positive electrode layer includes a positive electrode active material, a solid electrolyte, a conductive agent, and a second binder, wherein the crystallinity of the second binder is 70% to 90%.

2. The dry-process all-solid-state positive electrode sheet according to claim 1, characterized in that, The first adhesive and the second adhesive are each independently selected from polytetrafluoroethylene and ethylene. Tetrafluoroethylene copolymer, ethylene-vinyl acetate copolymer, polypropylene, polyethylene, ethylene One or more of octene copolymers and polyimides.

3. The dry-process all-solid-state positive electrode sheet according to claim 1, characterized in that, The content of the first binder in the first dry cathode layer is 0.5wt%~1wt%; the content of the second binder in the second dry cathode layer is 1wt%~2wt%.

4. The dry-process all-solid-state positive electrode sheet according to claim 1, characterized in that, The thickness ratio of the first dry cathode layer to the second dry cathode layer is 1:(3~5).

5. The dry-process all-solid-state positive electrode according to claim 1, characterized in that, The first binder is prepared by the following method: First, the binder with a crystallinity of 70% to 90% is heated to 340°C to 355°C at a rate of 5°C / min to 10°C / min under an inert atmosphere and held at that temperature for 1 to 2 hours; then, it is cooled to below 300°C at a rate of 0.2°C / min to 1°C / min; finally, it is quenched with liquid nitrogen to obtain the first binder with high crystallinity.

6. The dry-process all-solid-state positive electrode according to claim 1, characterized in that, Includes one or more of the following: The conductive agent is selected from at least one of graphite, graphene, carbon black, carbon fiber, and carbon nanotubes. The positive electrode active material is selected from at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based oxide. The solid electrolyte is selected from at least one of oxide solid electrolytes, sulfide solid electrolytes, and halide solid electrolytes.

7. The dry-process all-solid-state positive electrode sheet according to claim 1, characterized in that, The conductive agent is selected from one-dimensional conductive agents, and the aspect ratio of the one-dimensional conductive agent is greater than or equal to 200.

8. A method for preparing a dry-process all-solid-state positive electrode sheet according to any one of claims 1 to 7, characterized in that, Includes the following steps: Premixing: The positive electrode active material, solid electrolyte, and conductive agent are mixed according to the component ratios of the first and second dry-process positive electrode layers to obtain the first premix and the second premix. Mixing: The first premix is ​​mixed with the first binder to obtain a first mixture; the second premix is ​​mixed with the second binder to obtain a second mixture; fibrillation: The first mixture and the second mixture are subjected to fibrillation treatment respectively to obtain the first fibrillated material and the second fibrillated material; Crushing and granulation: The first fibrillated material and the second fibrillated material are crushed and granulated respectively to obtain the first dry cathode material and the second dry cathode material; Thinning: The first dry cathode material and the second dry cathode material are respectively formed into films and thinned to a preset thickness to obtain the first dry cathode layer and the second dry cathode layer; The first dry cathode layer and the second dry cathode layer are horizontally stacked and then thinned together to the target surface capacity to obtain the dry cathode layer. Composite current collector: The first dry-process positive electrode layer side of the dry-process positive electrode layer is combined with the positive electrode current collector to obtain a dry-process all-solid-state positive electrode sheet; Hot pressing: The dry-process all-solid-state positive electrode sheet is subjected to hot pressing treatment to fuse the interface between the first dry-process positive electrode layer and the second dry-process positive electrode layer.

9. The preparation method according to claim 8, characterized in that, In the premixing step, the linear velocity of the stirring paddle is 20m / s to 40m / s, the stirring time is 20min to 60min, and the processing temperature is 20℃ to 30℃. In the mixing step, the linear velocity of the stirring paddle is 5m / s to 20m / s, the stirring time is 20min to 60min, and the processing temperature is 5℃ to 20℃. In the fibrillation step, the processing temperature is 60℃~80℃, the linear velocity of the stirring paddle is 40m / s~60m / s, and the stirring time is 10min~30min. In the thinning step, the temperature used for thinning is 80℃~120℃; In the hot pressing step, the hot pressing temperature is 120℃~150℃, the pressure is 5MPa~8MPa, and the hot pressing time is 30s~60s.

10. An all-solid-state battery, characterized in that, Includes the dry-process all-solid-state positive electrode sheet according to any one of claims 1 to 7, or the dry-process all-solid-state positive electrode sheet prepared by the preparation method according to claim 8 or 9.

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