A dry bonding method for positive electrode material and solid electrolyte layer in solid-state batteries

Abstract

This invention discloses a dry bonding method for positive electrode materials and solid electrolyte layers in solid-state batteries. The method first involves dry mixing and pre-pressing positive electrode active material powder, solid electrolyte powder, and conductive agent powder to form a positive electrode composite material preform. Subsequently, the surface of the solid electrolyte layer is activated to increase its surface energy. A key step is to apply longitudinal vibration at a specific frequency and amplitude to the preform and the activated solid electrolyte layer for resonant acoustic interface coupling treatment, causing microscopic rearrangement and initial meshing of interface particles. This invention is solvent-free throughout the process. Through the synergistic effect of vibration and hot pressing, a stable interface with tight contact, strong bonding, and low impedance is constructed at the microscale, effectively solving problems such as poor interface contact, easy peeling, or performance degradation caused by solvent residue in existing dry and wet processes. It is particularly suitable for high-activity solid-state battery systems.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery manufacturing technology, and in particular to a dry bonding method for a positive electrode material and a solid electrolyte layer for a solid-state battery. Background Technology

[0002] All-solid-state lithium batteries are considered an important direction for the development of next-generation energy storage technology due to their high energy density, high safety, and long cycle life. However, their industrialization process faces a key bottleneck: how to construct a stable and low-impedance cathode / solid electrolyte interface.

[0003] Currently, mainstream interface preparation technologies are mainly divided into two categories: wet processes and dry processes. Wet processes borrow from mature technologies used in liquid lithium-ion batteries. They involve dispersing the positive electrode active material, solid electrolyte powder, conductive agent, and binder in an organic solvent (such as N-methylpyrrolidone) to form a slurry, which is then coated onto a current collector and followed by drying and rolling to form the electrode sheet. This method has inherent technical drawbacks: First, the organic solvent may react with highly active solid electrolytes (especially sulfide electrolytes), leading to electrolyte decomposition or performance degradation. Second, solvent evaporation during drying inevitably creates pores and microcracks inside the electrode and at the interface, increasing the tortuosity of the ion transport path and resulting in increased interfacial contact resistance. Third, removing residual solvent or curing polymer binders often requires high heat treatment temperatures, which can trigger more severe interfacial side reactions and interdiffusion between the positive electrode material and the electrolyte, impairing electrochemical stability.

[0004] To avoid the problems caused by solvents, solvent-free dry processes have attracted widespread attention. Existing dry processes typically rely on fibrous binders such as polytetrafluoroethylene (PTFE). High-shear mixing causes the binder to form a fibrous network that encapsulates the active material, which is then densified by roll forming to directly create the electrode. However, this type of process faces new challenges in constructing an integrated cathode / solid electrolyte interface. First, the ionic conductivity of insulating polymer binders such as PTFE is extremely low. The resulting fibrous network severely hinders lithium-ion transport within the cathode composite material, leading to a decline in battery performance. Second, simple physical-mechanical bonding is insufficient to achieve tight, conformal contact between the cathode material and the solid electrolyte layer at the nanoscale. Since both are rigid solid particles, the number of contact points is limited, resulting in numerous "point contacts" and voids at the interface, leading to a small actual contact area and still high interfacial resistance. Third, the strength of mechanical bonding is limited. During battery cycling, the electrode material undergoes volume expansion and contraction, making this fragile physical contact prone to failure or even peeling, causing a continuous increase in interfacial resistance and rapid capacity decay.

[0005] Therefore, developing a dry bonding method that can achieve a tight and firm bond between the cathode and the solid electrolyte at the microscale without introducing ion transport barriers is crucial for promoting the commercialization of all-solid-state batteries. Summary of the Invention

[0006] To achieve the above objectives, the present invention provides a dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery, comprising the following steps:

[0007] Step 1: Dry mix the positive electrode active material powder, solid electrolyte powder and conductive agent powder to obtain dry positive electrode composite powder, and press the dry positive electrode composite powder for the first time to form a positive electrode composite material preform.

[0008] Step 2: Perform surface activation treatment on the surface of the solid electrolyte layer to be bonded;

[0009] Step 3: The bonding surface of the positive electrode composite material preform is brought into contact with the bonding surface of the surface-activated solid electrolyte layer to form a laminated assembly. Longitudinal vibration is applied to the laminated assembly to perform resonant acoustic interface coupling treatment.

[0010] Step 4: The laminated assembly that has undergone resonant acoustic interface coupling treatment is heated and subjected to a second pressing to achieve hot-press densification and interface fusion;

[0011] Step 5: Maintain pressure to cool the stacked assembly, resulting in a composite electrode sheet integrating the positive electrode material and the solid electrolyte layer.

[0012] Preferably, in step one, the dry mixing is carried out under an inert atmosphere, and the rotation speed and time of the dry mixing are determined according to the type and ratio of the positive electrode active material powder, the solid electrolyte powder and the conductive agent powder.

[0013] The pressure of the first pressing is the pressure that allows the positive electrode composite material preform to be completely demolded from the mold without breaking. This pressure is determined by preparing multiple preforms molded under different pressures and conducting demolding and breaking tests.

[0014] Preferably, in step two, the surface activation treatment is performed by low-energy argon ion beam bombardment or low-temperature plasma treatment;

[0015] Before performing surface activation treatment, the initial water contact angle of the solid electrolyte layer to be bonded is measured.

[0016] The process parameters for surface activation treatment are determined through the following process: a set of gradually increasing processing power or processing time is used to test the solid electrolyte layer sample. The water contact angle of the solid electrolyte layer sample surface is measured immediately after each test treatment. The set of processing power range or processing time range corresponding to the water contact angle decreasing to the lowest stable value is selected as the final process parameters for surface activation treatment.

[0017] Preferably, in step three, the specific process of applying longitudinal vibration to the laminated assembly for resonant acoustic interface coupling treatment includes: placing the laminated assembly on a vibration device, applying broadband micro-amplitude scanning vibration to the laminated assembly through an exciter, simultaneously measuring the vibration response of the laminated assembly using a sensor, plotting a frequency response curve based on the vibration response signal, identifying one or more inherent resonant frequencies or main modal frequencies of the laminated assembly from the frequency response curve, and selecting one of the inherent resonant frequencies or main modal frequencies as the working frequency of the longitudinal vibration.

[0018] Preferably, in step three, the amplitude of the longitudinal vibration is determined based on the particle size distribution of the dry positive electrode composite powder;

[0019] The process of determining the amplitude includes: measuring the particle size distribution of the dry positive electrode composite powder to obtain the maximum particle size value and the characteristic particle size value;

[0020] The initial amplitude of the longitudinal vibration is set to a proportional value of the characteristic particle size.

[0021] By preparing multiple samples with resonant acoustic interface coupling treatment at different amplitudes, observing the macroscopic integrity of the cathode composite preform and testing the interface contact resistance, the amplitude value that can significantly reduce the interface contact resistance while ensuring that the preform has no macroscopic fragmentation is selected as the final working amplitude.

[0022] Preferably, in step four, the pressure of the second pressing is higher than the pressure of the first pressing;

[0023] The pressure value for the second pressing is determined through the following process: multiple test samples with the same structure as the stacked component are prepared, and the test samples are hot-pressed and densified under different pressures. After the processing is completed, the thickness and density of the interface region in each test sample are measured and the porosity is calculated. The correspondence between pressure and interface region porosity is established, and the pressure value that makes the interface region porosity lower than a preset threshold is selected as the pressure for the second pressing.

[0024] Preferably, in step four, the heating temperature during hot pressing densification and interface fusion is lower than the temperature at which the positive electrode active material and the solid electrolyte material undergo significant solid-phase reaction.

[0025] The heating temperature is determined by the following process: thermal analysis curves of positive electrode active material powder and solid electrolyte material powder are tested respectively using thermal analysis methods; the glass transition temperature or softening point temperature of the solid electrolyte material is determined from the thermal analysis curve; and the starting temperature at which the positive electrode active material begins to decompose or undergo phase change is determined from the thermal analysis curve.

[0026] A temperature range higher than the glass transition temperature or softening point of the solid electrolyte material but lower than the onset temperature of decomposition or phase change of the positive electrode active material is selected as the range of heating temperature.

[0027] Preferably, in step four, the process of determining the specific heating temperature value from the selected range of heating temperatures includes: selecting multiple different temperature points within the selected temperature range, preparing multiple samples for hot pressing at different temperature points under the same second pressing pressure, testing the interfacial bonding strength and interfacial ion transport impedance of each sample, and selecting the temperature point that optimizes the overall performance of interfacial bonding strength and interfacial ion transport impedance as the final heating temperature.

[0028] Preferably, in step five, the cooling is rate-controlled cooling;

[0029] The rate of controlled cooling was optimized and determined through the following process: multiple stacked component samples were prepared under the same hot pressing process parameters. Under the condition of keeping the pressure constant, the multiple stacked component samples were cooled to room temperature at multiple different cooling rates. The interfacial shear strength of each composite electrode after cooling was tested, and the relationship curve between cooling rate and interfacial shear strength was plotted. The cooling rate range that makes the interfacial shear strength reach the peak value was selected as the final controlled cooling rate.

[0030] Preferably, between step three and step four, a step of preheating the stacked assembly that has undergone resonant acoustic interface coupling treatment is also included;

[0031] Preheating is carried out below the temperature of hot pressing densification and interface fusion. The preheating temperature is set to a temperature value below the glass transition temperature or softening point temperature of the solid electrolyte material. The purpose of preheating is to homogenize the overall temperature of the laminated assembly and eliminate residual stress.

[0032] The beneficial effects of this invention are:

[0033] 1. This invention provides a completely solvent-free dry bonding process, fundamentally eliminating interface problems caused by solvents. From raw material dry mixing to final molding, this method requires no introduction of any organic solvents or liquid media, avoiding chemical corrosion and side reactions of the highly active solid electrolyte by solvents. Simultaneously, it eliminates the risk of porosity and microcracks generated inside the electrode and at the interface due to solvent evaporation. This ensures the intrinsic chemical stability and structural integrity of the interface material, laying a reliable foundation for constructing low-impedance, long-life solid-state battery interfaces.

[0034] 2. This invention achieves high-strength, low-impedance interfacial bonding at the microscale through the synergistic effect of "resonant acoustic interface coupling" and "hot-press densification." The resonant treatment causes microscopic rearrangement and initial meshing of interfacial particles, significantly increasing the effective contact area. The subsequent hot-pressing process, under precise temperature and pressure control, softens the micro-regions on the surface of the solid electrolyte and forms a physical interlock and thermal fusion with the cathode particles. This bonding mechanism transcends simple physical pressing or polymer bonding, achieving excellent interfacial bonding strength and extremely low ion transport impedance, significantly improving the battery's rate performance and cycle stability.

[0035] 3. The method described in this invention features a mild process and scientifically determined parameters, exhibiting good controllability and repeatability. The core steps are all performed at relatively low temperatures, avoiding damage to the material structure caused by high-temperature sintering. Each key process parameter is determined through systematic material testing and performance optimization processes, rather than empirical values. This parameter determination method, based on feedback from the intrinsic properties of the material and target performance, ensures a clear process window, strong process controllability, and facilitates product consistency, making it easy to implement and promote in large-scale production. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart of the steps of the method of the present invention. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0039] Please seeFigure 1 This invention provides a dry bonding method for a positive electrode material and a solid electrolyte layer for solid-state batteries. The method begins with the preparation of a positive electrode composite material preform. The specific steps are as follows: Positive electrode active material powder, solid electrolyte powder, and conductive agent powder in a predetermined mass ratio are placed together in a dry mixing device and mixed at a specific speed for a specific time under an inert atmosphere until a uniformly composed dry composite powder is obtained.

[0040] Subsequently, the composite powder is filled into a mold and pressed under a first pressure to form a self-supporting preform. The value of this first pressure is obtained through a series of tests, namely testing the demolding integrity and fracture resistance of the molded preform under different pressures, and selecting the lowest pressure value that can satisfy demolding without fracture. The preform has a certain mechanical strength, which facilitates subsequent operations, while dry mixing avoids the introduction of solvents, eliminating the risk of side reactions from the source.

[0041] In one possible implementation, inert atmosphere protection is achieved by introducing high-purity argon or nitrogen into the mixing equipment chamber and maintaining positive pressure. The determination of the dry mixing speed and time depends on the characteristics of the powder system. This is achieved by first conducting small-batch tests, mixing at different combinations of speed and time, then observing the microstructure of the mixed powder using a scanning electron microscope, and analyzing the uniformity of component distribution using elemental surface methodology. The final process parameters are selected based on the combination of speed and time that achieves optimal dispersion of the different powder components without excessive shearing of the conductive agent fibers.

[0042] The specific process for determining the initial pressing pressure included: preparing multiple samples pressed under different preset pressures, observing and recording the edge integrity of each sample upon ejection from the mold, and then applying a slight bending force to the demolded samples using a quantitative mechanical testing instrument to detect whether cracks occurred. Combining the results of these two tests, the minimum pressure threshold required for the preform to meet the mechanical requirements of subsequent operations was determined. Through scientifically determined process parameters, the compositional uniformity and structural reliability of the preform were ensured, laying a solid foundation for subsequent interface treatment.

[0043] In one possible implementation, firstly, a contact angle meter is used to measure the water contact angle of the original surface of the solid electrolyte layer in an inert atmosphere to obtain a reference value. Subsequently, the solid electrolyte layer is placed in a plasma processing chamber or an ion beam processing chamber. Taking low-energy argon ion beam bombardment as an example, in specific implementation, the chamber is first evacuated to a high vacuum, and then argon gas is introduced as the working gas. The ion beam energy is controlled by adjusting the ion source current and accelerating voltage to maintain the ion energy within a range sufficient to clean surface adsorbates without causing bulk sputtering damage.

[0044] The optimization process for process parameters is as follows: keeping other conditions constant, the bombardment time or beam density is systematically changed to prepare a series of treated samples. The water contact angle of each sample is measured immediately after treatment, and a curve showing the relationship between the treatment parameters and the change in water contact angle is plotted. The parameter range corresponding to the lowest plateau region of the water contact angle in the curve is selected as the final process window.

[0045] Controllable surface activation significantly improves the surface energy of the solid electrolyte layer and introduces active sites, thereby greatly enhancing its wettability and chemical bonding potential with the cathode composite material.

[0046] In one possible implementation, an assembly formed by stacking a positive electrode composite preform and a solid electrolyte layer is securely mounted on the sample stage of a vibration generator. This device includes an exciter capable of generating wideband micro-amplitude vibrations and a high-precision vibration response sensor. First, a sweep frequency signal with a linear frequency variation from low to high frequency is generated by a signal generator to drive the exciter, applying a steady-state sinusoidal sweep frequency excitation with a very small amplitude to the stacked assembly. During this process, the sensor monitors the vibration response amplitude at specific points on the assembly in real time. The response amplitudes corresponding to all frequency points are recorded, and a frequency response curve is plotted with frequency on the x-axis and response amplitude on the y-axis.

[0047] Analyze the curve and identify the peak points. The frequencies corresponding to these peak points are the natural resonant frequencies or principal modal frequencies of the laminated component under the constraint conditions. From the identified frequencies, select a suitable frequency as the fixed operating frequency for subsequent vibration application.

[0048] By capturing the resonant frequency of the system for driving, significant microscopic relative motion can be generated inside the stacked components with a small input energy, which is highly efficient and targeted.

[0049] In one possible implementation, the dry cathode composite powder is first tested using a laser particle size analyzer to obtain its volumetric particle size distribution data, from which characteristic parameters such as the median particle size and the maximum particle size are extracted. The initial amplitude setting can be based on the median particle size multiplied by an empirical coefficient less than 1.

[0050] The final optimization of the amplitude was achieved experimentally: multiple identical stacked components were prepared, and a series of vibrations with different amplitudes were applied at a determined resonant frequency for a fixed duration. After treatment, the surface and edges of the cathode composite preform were first visually inspected or microscopically for macroscopic damage such as cracks or peeling. Subsequently, electrochemical impedance spectroscopy was used to test each treated sample, and the interfacial contact resistance value was obtained through equivalent circuit fitting. By comprehensively analyzing the macroscopic structural integrity and interfacial contact resistance data, the minimum amplitude that significantly reduced the interfacial contact resistance while ensuring the preform structure remained intact was selected as the final working amplitude.

[0051] The embodiments of the present invention ensure that the vibration energy is sufficient to break up weak agglomeration between particles and promote close contact at the interface, while avoiding excessive energy that could damage the preform structure, thus achieving precise control of the process window.

[0052] In one possible implementation, these test samples are grouped and subjected to hot-pressing treatment under the same preheating and hot-pressing temperatures, with multiple different preset pressures applied. After treatment, the physical properties of the interface region of each sample are measured using precision instruments. Specifically, focused ion beam cutting technology can be used to prepare the cross-section of the sample, and then the cross-sectional image can be captured using a high-resolution scanning electron microscope.

[0053] Using image analysis software, a region extending a certain width from the interface line to both sides was selected as the analysis area. Pores were identified using grayscale thresholding, and the proportion of pore area to the total area of ​​the analysis region was calculated to obtain the porosity of that region. The porosities of the interface region measured under different pressures were summarized, and a pressure-porosity relationship curve was plotted. Based on the interface density requirements of all-solid-state batteries, an acceptable porosity threshold was set. The minimum pressure value required to lower the porosity below this threshold was found from the relationship curve; this pressure value was determined as the pressure for the second pressing.

[0054] By quantifying the relationship between interface density and pressure, the optimal pressure required to achieve a low-impedance interface was scientifically determined, avoiding problems caused by insufficient or excessive pressure.

[0055] In one possible implementation, firstly, small amounts of positive electrode active material powder and solid electrolyte material powder are taken separately and tested using a differential scanning calorimeter or a thermogravimetric-differential thermal analyzer. The tests are conducted under an inert atmosphere, with the temperature increased at a constant rate, and the heat flow or mass change curves of the samples during the heating process are recorded.

[0056] Analyzing the heat flow curves of solid electrolyte materials reveals the temperature range where a step change in heat flow occurs; the starting point of this change can be identified as the glass transition temperature or softening point of the material. Similarly, analyzing the heat flow or thermogravimetric curves of positive electrode active materials identifies the temperature at which the first significant endothermic peak or the temperature at which a sudden change in mass begins; this temperature is considered the starting temperature for significant decomposition or phase transition of the material.

[0057] The heating temperature is limited to a range higher than the glass transition temperature or softening point of the solid electrolyte material, while remaining below the initiation temperature of decomposition or phase transition of the positive electrode active material. This effectively avoids damage to the positive electrode material structure and the generation of harmful interfacial reactions caused by high temperatures, while ensuring controllable softening of the solid electrolyte surface to promote interfacial fusion.

[0058] In one possible implementation, at least three different temperature points are uniformly selected as candidate temperatures within a defined temperature range. Multiple identical multilayer module samples are prepared and hot-pressed at these candidate temperatures under the same second pressing pressure and holding time. After processing, two key performance tests are performed on the samples. The first is an interfacial bonding strength test, which can be performed using a 180-degree peel test to measure the force required per unit width to peel the positive electrode layer from the electrolyte layer.

[0059] The second step is the interfacial ion transport impedance test, typically using a blocked electrode configuration. Electrochemical impedance spectroscopy is used to measure and fit the resistance values ​​related to interfacial ion transport. The interfacial bonding strength and interfacial ion transport impedance values ​​at each temperature point are then tabulated or plotted for analysis. By comprehensively evaluating both indicators, the temperature point that achieves high interfacial bonding strength while maintaining low interfacial ion transport impedance—the temperature point with the optimal overall performance—is identified and determined as the final heating temperature. Through comprehensive optimization of multiple performance indicators, the optimal hot-pressing temperature balance point for achieving a high-strength and low-impedance interface is found.

[0060] In one possible implementation, this technical feature requires preparing multiple laminated component samples under identical hot-pressing process parameters. After the hot-pressing process is completed, while maintaining a constant pressure, different cooling methods are used for different samples to achieve different cooling rates.

[0061] For example, a series of average cooling rates, from slow to fast, can be obtained by controlling the natural heat dissipation, forced air cooling, or circulating water cooling of the hot press heating plate after power failure. All samples are removed after cooling to room temperature and the pressure is released. The interfacial bonding strength is quantified using a push-shear test: the composite electrode is fixed, and a punch of a specific size is used to apply a pushing force to the interface, recording the maximum shear stress at which interface separation occurs. The interfacial shear strength values ​​measured at different cooling rates are summarized, and a cooling rate-interfacial shear strength relationship curve is plotted. Analyzing this curve, a peak value is usually found in the shear strength as a function of the cooling rate. The cooling rate range corresponding to the peak strength is selected as the final target rate range for controlled cooling in the process.

[0062] By controlling the cooling process, the microstructure of the interface region caused by thermal stress was optimized, thereby maximizing the interfacial mechanical bonding strength of the final composite electrode.

[0063] In one possible implementation, the preheating step is carried out as follows: after the resonant acoustic interface coupling treatment, the laminated assembly is transferred to a temperature-controlled preheating platform or placed directly in a hot press. The preheating temperature is set to a value clearly lower than the subsequent hot pressing densification and interface fusion temperature, typically set to a specific temperature between 20 and 50 degrees Celsius lower than the glass transition temperature or softening point temperature of the solid electrolyte material.

[0064] The laminated assembly is held at this preheated temperature for a period of time, the holding time of which is determined based on the assembly thickness and thermal conductivity, to ensure that the overall temperature of the assembly reaches a uniform level. After the holding period, the temperature is raised to the hot-pressing temperature according to the preset heating program for step four. The beneficial effect of this preheating step is that it ensures that the laminated assembly is heated uniformly, reduces the internal temperature gradient and thermal stress that may be generated during direct high-temperature hot pressing, helps to eliminate micro-stress concentration that may occur in the previous steps, and promotes a more uniform and stable fusion of the interface during the subsequent hot pressing process.

[0065] Example: Dry bonding of an NCM811 cathode to a silver-germanium sulfide solid electrolyte membrane for a sulfide all-solid-state battery;

[0066] It should be noted that the sulfide-germanium ore-type solid electrolyte involved in this embodiment has the general chemical formula Li6PS5X (where X represents a halogen). When the halogen X is chlorine (Cl), its standard chemical formula should be written as Li6PS5Cl. This material often exhibits certain non-stoichiometric characteristics in actual preparation and application. For ease of description and to conform to the general expression habits in the research field of this material, the simplified empirical formula Li6PS5Cl will be used uniformly in the following text to refer to this type of sulfide-germanium ore-type solid electrolyte material mainly composed of lithium, phosphorus, sulfur, and chlorine. Similarly, the positive electrode active material LiNi0.8Co0.1Mn0.1O2 is abbreviated as NCM811.

[0067] This embodiment focuses on the manufacturing of high-energy-density sulfide all-solid-state lithium batteries. The method of this invention is used to integrate the high-nickel ternary cathode material NCM811 with the silver-sulfur germanium mineral type Li6PS5Cl solid electrolyte membrane.

[0068] Step 1: Preparation of the positive electrode composite material preform;

[0069] First, the raw materials are provided: the positive electrode active material powder is NCM811, with an average particle size of 5 micrometers; the solid electrolyte powder is Li6PS5Cl, with an average particle size of 1 micrometer; and the conductive agent powder is vapor-grown carbon fiber, with an average diameter of 150 nanometers and an average length of 10 micrometers. The mass ratio of the three is NCM811:Li6PS5Cl:vapor-grown carbon fiber = 70:28:2.

[0070] The three powders were transferred to the mixing jar of a planetary ball mill. Before loading the powder into the mixing jar, it was purged and purged with argon gas three times in an argon-atmosphere protected glove box to ensure that the oxygen and water content were both below 0.1 ppm. The dry mixing process was carried out in the glove box, with the ball mill speed set to 200 rpm and the milling time set to 30 minutes. This speed and time were determined based on previous experiments: the microstructure and elemental distribution of the powder were tested after mixing at 100 rpm, 200 rpm, and 300 rpm for 15, 30, and 60 minutes, respectively. Scanning electron microscopy and energy dispersive spectroscopy analysis confirmed that mixing at 200 rpm for 30 minutes resulted in uniform dispersion of the powder without hard agglomeration, and the vapor-grown carbon fibers were not excessively sheared.

[0071] After thorough mixing, a dry positive electrode composite powder is obtained. A certain amount of the dry positive electrode composite powder is filled into a circular stainless steel mold with a diameter of 20 mm. The surface of the mold is coated with a release agent. The first pressing is performed using a tablet press. The pressure value for the first pressing needs to be precisely determined. The specific determination process is as follows: Under the same filling amount, five samples are pressed using pressures of 50 MPa, 100 MPa, 150 MPa, and 200 MPa respectively. After pressing, the samples are ejected from the mold, and their integrity after demolding is observed. Under a pressure of 50 MPa, the sample's edges are loose after demolding, and it crumbles easily upon slight contact; under a pressure of 100 MPa, the sample can be demolded intact, but pressing the surface with a finger will produce cracks; under pressures of 150 MPa and 200 MPa, the samples can be demolded intact and have a certain degree of toughness, with no cracks appearing when pressed with a finger. Therefore, 100 MPa was chosen as the pressure for the first pressing. This pressure is the minimum effective pressure that allows the preform to be completely demolded from the mold without breaking, which is beneficial for the rearrangement of particles in subsequent steps. After pressing, a cathode composite material preform with a thickness of approximately 300 micrometers was obtained.

[0072] Step 2: Surface activation of the solid electrolyte layer;

[0073] The provided solid electrolyte layer is a 150-micrometer-thick Li6PS5Cl self-supporting film prepared by cold pressing.

[0074] First, the initial water contact angle of the Li6PS5Cl film surface was measured inside a glove box using a contact angle meter, and the measured value was 75 degrees. This indicates that the surface still has some hydrophobicity or has adsorbed trace impurities.

[0075] Low-temperature plasma treatment was selected for surface activation. The Li6PS5Cl thin film was placed in the sample chamber of the plasma treatment equipment. The chamber was pre-evacuated and then refilled with high-purity argon gas to a working pressure of 50 Pa. To determine the optimal treatment parameters, parameter optimization experiments were conducted: A fixed treatment time of 60 seconds was used to treat four groups of samples with radio frequency (RF) powers of 50 W, 100 W, 150 W, and 200 W respectively; another fixed RF power of 100 W was used to treat four groups of samples for 30 seconds, 60 seconds, 90 seconds, and 120 seconds respectively. Immediately after each treatment, the water contact angle of the sample surface was measured inside a glove box.

[0076] Test results showed that under a fixed 60-second condition, as the power increased from 50 watts to 150 watts, the water contact angle rapidly decreased from 75 degrees to 28 degrees. When the power increased to 200 watts, the water contact angle slightly increased back to 32 degrees. Under a fixed 100-watt condition, as the time increased from 30 seconds to 90 seconds, the water contact angle decreased from 70 degrees to 26 degrees. After 120 seconds of processing, the water contact angle was 25 degrees, and the change was no longer significant. The decrease in the water contact angle indicates an increase in surface energy, but when the power is too high or the time is too long, it may cause slight surface damage or overheating leading to changes in composition, which may cause the contact angle to slightly increase or no longer improve. Therefore, the parameter range corresponding to the lowest stable value of water contact angle (approximately 26 degrees), namely RF power of 100 watts to 150 watts and processing time of 60 seconds to 90 seconds, was selected as the final process parameter range. In this embodiment, a specific parameter of 120 watts of RF power and 75 seconds was used to activate the surface of the film to be bonded.

[0077] Step 3: Coupling of resonant acoustic interfaces;

[0078] Align the bonding surface (the relatively flat side) of the positive electrode composite material preform prepared in step one with the bonding surface of the Li6PS5Cl solid electrolyte membrane that has undergone surface activation treatment in step two, and gently stack them to make them contact each other to form a stacked assembly.

[0079] The laminated assembly was carefully transferred and fixed onto the sample stage of the resonant acoustic processing equipment, which was connected to a piezoelectric ceramic exciter. First, a frequency scan was performed to determine the operating frequency. The equipment's signal generator was activated, producing a linear sweep sine wave signal from 100 Hz to 5000 Hz, driving the piezoelectric ceramic exciter to apply micro-amplitude vibrations (amplitude much less than 1 micrometer) to the laminated assembly. Simultaneously, a laser vibrometer was used to measure the vibration velocity response at the center point of the upper surface of the laminated assembly. The response amplitudes at different frequencies were recorded, and frequency response curves were plotted. Two distinct resonance peaks were observed near 1250 Hz and 3100 Hz on the curves. Analysis suggests that the 1250 Hz resonance peak corresponds to the overall bending mode of the laminated assembly, while the 3100 Hz resonance peak may correspond to local resonance or higher-order modes within the assembly's internal structure. To avoid excessive amplitude leading to macroscopic structural deformation, 1250 Hz was selected as the operating frequency for longitudinal vibration.

[0080] Next, the working amplitude was determined. The volume average particle size (D50) of the dry cathode composite powder was measured to be 3.5 μm using a laser particle size analyzer. The initial amplitude was set to 10% of the D50 value, i.e., 0.35 μm. An amplitude optimization experiment was conducted: at a frequency of 1250 Hz, amplitudes of 0.2 μm, 0.35 μm, 0.5 μm, and 0.7 μm were set, and four identical stacked component samples were vibrated for 60 seconds each. After the treatment, the sample with an amplitude of 0.2 μm showed no change on the surface of the preform; the samples with amplitudes of 0.35 μm and 0.5 μm showed a denser particle arrangement and a slightly darker color on the surface of the preform, but no cracks overall; the sample with an amplitude of 0.7 μm showed slight peeling at the edge of the preform. Subsequently, an impedance analyzer was used to test the interfacial contact resistance between the cathode preform and the electrolyte membrane in the four groups of samples at a frequency of 1 MHz. The results showed that the contact resistance of the sample with an amplitude of 0.2 μm was 850 ohms·cm²; the contact resistance of the sample with an amplitude of 0.35 μm decreased to 320 ohms·cm²; the contact resistance of the sample with an amplitude of 0.5 μm was 310 ohms·cm²; and although the contact resistance of the sample with an amplitude of 0.7 μm was 300 ohms·cm², the sample was already damaged. Therefore, 0.35 μm was selected as the final working amplitude, which is sufficient to induce microscopic slippage and rearrangement of particles to reduce resistance while ensuring the integrity of the preform structure.

[0081] Finally, the stacked assembly was subjected to resonant acoustic interface coupling treatment for 120 seconds at a frequency of 1250 Hz and an amplitude of 0.35 μm.

[0082] Step 4: Hot pressing densification and interface fusion;

[0083] The resonant-treated laminated assembly is transferred to a hot press with a heating plate located inside a glove box.

[0084] First, the pressure for the second pressing was determined. Several simplified samples were prepared by stacking a preform consisting only of cathode composite powder pre-pressed at 100 MPa with a Li6PS5Cl film. Under the same preheating conditions (described later), hot pressing was performed at pressures of 200 MPa, 300 MPa, 400 MPa, and 500 MPa (temperatures tentatively set to the midpoint of the temperature range described later). After hot pressing, a cross-section was prepared at the sample interface using focused ion beam cutting technology, and the porosity of the interface region (extending approximately 10 μm from the interface line to both sides) was calculated using scanning electron microscopy and image analysis software. The results showed that the porosity was approximately 12% at 200 MPa; decreased to approximately 5% at 300 MPa; approximately 3.5% at 400 MPa; and approximately 3.2% at 500 MPa, but some NCM811 particles showed signs of cracking. To ensure a dense interface without damaging the active material, a target porosity threshold of 5% was set. Therefore, 300 MPa was chosen as the pressure for the second pressing.

[0085] Next, the heating temperature was determined. Differential scanning calorimetry (DSC) was used to test NCM811 powder and Li6PS5Cl powder under an argon atmosphere. The curve for Li6PS5Cl showed a glass transition temperature of approximately 210°C. The curve for NCM811 showed a significant endothermic peak above approximately 300°C, possibly related to lattice oxygen release or phase transition. Therefore, theoretically, the heating temperature range should be between 210°C and 300°C. To determine the specific temperature, hot-pressing tests were conducted at 220°C, 240°C, 260°C, and 280°C, using a pressure of 300 MPa to prepare four sets of samples. The interfacial bonding strength (using a 180°C peel test) and interfacial ion transport impedance were tested (by measuring the impedance spectrum of a blocked electrode, and fitting the sum of the bulk resistance and interfacial resistance). The results are shown in the table below:

[0086]

[0087] Data shows that the binding strength increases continuously with increasing temperature, but the ion transport resistance is lowest at 260 degrees Celsius and increases at 280 degrees Celsius, possibly due to slight interfacial side reactions triggered by excessively high temperatures. Therefore, the optimal temperature for overall performance is 260 degrees Celsius. Ultimately, this embodiment determined the heating temperature to be 260 degrees Celsius, the pressure to be 300 MPa, and the hot-pressing holding time to be 30 minutes.

[0088] Step 5: Cooling and setting;

[0089] After hot pressing, the heating power was turned off, and the pressure was kept constant at 300 MPa, allowing the hot pressing device to cool naturally with the furnace. The average cooling rate of this natural cooling process was approximately 5 degrees Celsius per minute. Once the temperature dropped below 50 degrees Celsius, the pressure was released, the sample was removed, and the final composite electrode sheet integrating the positive electrode material and the solid electrolyte layer was obtained. After the composite electrode sheet was left to stand at room temperature for 24 hours, its interfacial shear strength (measured by push-shear test) reached 3.5 MPa.

[0090] To demonstrate the effectiveness of the method of the present invention, the following two comparative examples are set up for comparison:

[0091] Comparative Example 1 (Wet Coating Process): NCM811, Li6PS5Cl, and vapor-grown carbon fibers of equal mass ratio were dispersed in anhydrous N-methylpyrrolidone solvent, and PVDF binder was added. The mixture was ball-milled to form a slurry. The slurry was coated onto the surface of a Li6PS5Cl solid electrolyte membrane and dried at 80°C for 12 hours to completely remove the solvent. Then, it was cold-pressed at 100 MPa.

[0092] Comparative Example 2 (Traditional Dry Pressing Process): Dry cathode composite powder with the same mass ratio was directly spread on Li6PS5Cl solid electrolyte membrane and pressed in one step at 300 MPa pressure and room temperature without surface activation or resonance treatment.

[0093] Four key performance indicators of the composite electrodes prepared in the embodiments of the present invention, Comparative Example 1, and Comparative Example 2 were tested respectively, and the results are shown in the table below:

[0094]

[0095] Effect Analysis:

[0096] Interface contact resistance: The interface contact resistance of this embodiment is much lower than that of the two comparative examples. This is directly attributed to the fact that "resonant acoustic interface coupling" promotes close particle-level contact, and "thermal pressing densification" achieves interface fusion, which greatly increases the effective contact area.

[0097] Interfacial shear strength: The interfacial bonding strength of the embodiments of the present invention is the highest. This proves that "surface activation" enhances the bonding basis, and the mechanical interlocking and thermal fusion effect formed by the synergy of "resonance" and "thermal pressing" create a stronger bonding force.

[0098] Ionic conductivity: The composite electrode in this embodiment of the invention exhibits the highest overall ionic conductivity. This is because the absence of solvents avoids electrolyte decomposition, and the tight, low-resistance interface reduces overall transport resistance.

[0099] Cycle stability: A symmetrical battery was assembled with a composite electrode as the positive electrode and a lithium-indium negative electrode and subjected to lithium deposition / stripping cycling. After 100 cycles, the battery of the present invention showed the smallest overpotential increase, indicating that its interface was the most stable during cycling and less prone to degradation. In contrast, Comparative Example 1 may be affected by residual solvents or binders, while Comparative Example 2 is prone to failure during cycling due to poor interface contact.

[0100] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery, characterized in that, Includes the following steps: Step 1: Dry mix the positive electrode active material powder, solid electrolyte powder and conductive agent powder to obtain dry positive electrode composite powder, and press the dry positive electrode composite powder for the first time to form a positive electrode composite material preform. Step 2: Perform surface activation treatment on the surface of the solid electrolyte layer to be bonded; Step 3: The bonding surface of the positive electrode composite material preform is brought into contact with the bonding surface of the surface-activated solid electrolyte layer to form a laminated assembly. Longitudinal vibration is applied to the laminated assembly to perform resonant acoustic interface coupling treatment. Step 4: The laminated assembly that has undergone resonant acoustic interface coupling treatment is heated and subjected to a second pressing to achieve hot-press densification and interface fusion; Step 5: Maintain pressure to cool the stacked assembly, resulting in a composite electrode sheet integrating the positive electrode material and the solid electrolyte layer.

2. The dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery according to claim 1, characterized in that, In step one, the dry mixing is carried out under an inert atmosphere. The rotation speed and time of the dry mixing are determined according to the type and ratio of the positive electrode active material powder, the solid electrolyte powder and the conductive agent powder. The pressure of the first pressing is the pressure that allows the positive electrode composite material preform to be completely demolded from the mold without breaking. This pressure is determined by preparing multiple preforms molded under different pressures and conducting demolding and breaking tests.

3. The dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery according to claim 1, characterized in that, In step two, the surface activation treatment is performed by low-energy argon ion beam bombardment or low-temperature plasma treatment; Before performing surface activation treatment, the initial water contact angle of the solid electrolyte layer to be bonded is measured. The process parameters for surface activation treatment are determined through the following process: a set of gradually increasing processing power or processing time is used to test the solid electrolyte layer sample. The water contact angle of the solid electrolyte layer sample surface is measured immediately after each test treatment. The set of processing power range or processing time range corresponding to the water contact angle decreasing to the lowest stable value is selected as the final process parameters for surface activation treatment.

4. The dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery according to claim 1, characterized in that, In step three, the specific process of applying longitudinal vibration to the laminated assembly for resonant acoustic interface coupling treatment includes: placing the laminated assembly on a vibration device, applying broadband micro-amplitude scanning vibration to the laminated assembly through an exciter, simultaneously measuring the vibration response of the laminated assembly using a sensor, plotting a frequency response curve based on the vibration response signal, identifying one or more natural resonant frequencies or main modal frequencies of the laminated assembly from the frequency response curve, and selecting one of the natural resonant frequencies or main modal frequencies as the working frequency of the longitudinal vibration.

5. A dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery according to claim 4, characterized in that, In step three, the amplitude of the longitudinal vibration is determined based on the particle size distribution of the dry cathode composite powder; The process of determining the amplitude includes: measuring the particle size distribution of the dry positive electrode composite powder to obtain the maximum particle size value and the characteristic particle size value; The initial amplitude of the longitudinal vibration is set to a proportional value of the characteristic particle size. By preparing multiple samples with resonant acoustic interface coupling treatment at different amplitudes, observing the macroscopic integrity of the cathode composite preform and testing the interface contact resistance, the amplitude value that can significantly reduce the interface contact resistance while ensuring that the preform has no macroscopic fragmentation is selected as the final working amplitude.

6. The dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery according to claim 1, characterized in that, In step four, the pressure of the second pressing is higher than the pressure of the first pressing; The pressure value for the second pressing is determined through the following process: multiple test samples with the same structure as the stacked component are prepared, and the test samples are hot-pressed and densified under different pressures. After the processing is completed, the thickness and density of the interface region in each test sample are measured and the porosity is calculated. The correspondence between pressure and interface region porosity is established, and the pressure value that makes the interface region porosity lower than a preset threshold is selected as the pressure for the second pressing.

7. The dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery according to claim 1, characterized in that, In step four, the heating temperature during hot pressing densification and interface fusion is lower than the temperature at which the positive electrode active material and the solid electrolyte material undergo significant solid-phase reaction. The heating temperature is determined by the following process: thermal analysis curves of positive electrode active material powder and solid electrolyte material powder are tested respectively using thermal analysis methods; the glass transition temperature or softening point temperature of the solid electrolyte material is determined from the thermal analysis curve; and the starting temperature at which the positive electrode active material begins to decompose or undergo phase change is determined from the thermal analysis curve. A temperature range higher than the glass transition temperature or softening point of the solid electrolyte material but lower than the onset temperature of decomposition or phase change of the positive electrode active material is selected as the range of heating temperature.

8. A dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery according to claim 7, characterized in that, In step four, the process of determining the specific heating temperature value from the selected heating temperature range includes: selecting multiple different temperature points within the selected temperature range, preparing multiple samples for hot pressing at different temperature points under the same second pressing pressure, testing the interfacial bonding strength and interfacial ion transport impedance of each sample, and selecting the temperature point that optimizes the overall performance of interfacial bonding strength and interfacial ion transport impedance as the final heating temperature.

9. A dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery according to claim 1, characterized in that, In step five, the cooling is rate-controlled cooling; The rate of controlled cooling was optimized and determined through the following process: multiple stacked component samples were prepared under the same hot pressing process parameters. Under the condition of keeping the pressure constant, the multiple stacked component samples were cooled to room temperature at multiple different cooling rates. The interfacial shear strength of each composite electrode after cooling was tested, and the relationship curve between cooling rate and interfacial shear strength was plotted. The cooling rate range that makes the interfacial shear strength reach the peak value was selected as the final controlled cooling rate.

10. A dry bonding method for a positive electrode material and a solid electrolyte layer in a solid-state battery according to claim 1, characterized in that, Between steps three and four, there is also a step of preheating the stacked assembly that has undergone resonant acoustic interface coupling treatment; Preheating is carried out below the temperature of hot pressing densification and interface fusion. The preheating temperature is set to a temperature value below the glass transition temperature or softening point temperature of the solid electrolyte material. The purpose of preheating is to homogenize the overall temperature of the laminated assembly and eliminate residual stress.

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