A continuous preparation method of a multistage sulfide solid electrolyte film based on grain boundary engineering

Abstract

This invention discloses a continuous preparation method for multi-level sulfide solid electrolyte membranes based on grain boundary engineering, belonging to the field of solid-state lithium battery electrolyte material preparation technology. The method involves constructing an initial concentration gradient along the film thickness direction using a double-layer co-casting process: one layer containing amorphous lithium thiophosphate glass powder, and another layer without the glass powder. Degreasing is performed below the initial crystallization temperature of the glass powder to maintain its amorphous state. Subsequently, the temperature is rapidly increased to the sintering temperature in a sulfur-containing isostatic atmosphere at a rate higher than the critical crystallization rate of the glass powder, causing the glass powder to directly melt into a glass melt. Under capillary action, the melt permeates along grain boundaries and pores from the upper cast layer side to the lower cast layer side, forming a gradient distribution with the glass phase content continuously decreasing along the thickness direction. After cooling, a continuous amorphous fast ion conductor interface phase is formed at the grain boundaries.

Description

Technical Field

[0001] This invention relates to the field of solid-state lithium battery electrolyte material preparation technology, and in particular to a method for continuous preparation of multi-level sulfide solid electrolyte membranes based on grain boundary engineering. Background Technology

[0002] Sulfide solid electrolytes are considered key materials for realizing high-energy-density all-solid-state lithium batteries due to their extremely high room-temperature lithium-ion conductivity. The intrinsic ionic conductivity of sulforaphane-germanium crystalline electrolytes, represented by this type, can reach [amount missing]. The scale is significant. However, there are three closely related technical challenges in processing powdered sulfide electrolytes into dense, usable films.

[0003] The first challenge is the excessively high grain boundary impedance. In polycrystalline electrolyte films formed by powder pressing or casting, factors such as the space charge layer effect at grain boundaries, impurity segregation, local crystal orientation mismatch, and amorphous phase encapsulation make the migration barrier for lithium ions across grain boundaries much higher than that within the grains. Measured electrochemical impedance spectroscopy shows that grain boundary impedance often accounts for more than 50% of the total impedance, resulting in a macroscopic ionic conductivity of the film that is much lower than the intrinsic crystal value. To reduce grain boundary impedance, some studies have attempted to mechanically mix a second-phase fast ion conductor into the electrolyte powder, such as... Glass powder, but mechanical mixing cannot accurately guide the glass phase to the grain boundary region. Instead, a large number of glass particles are embedded inside the grain, which not only dilutes the high ionic conductivity channels of the grain body, but also makes it difficult to form a continuous low impedance path at the grain boundary.

[0004] The second challenge is the lack of continuous manufacturing capabilities. Sulfide electrolytes are extremely sensitive to moisture and oxygen, requiring all operations to be performed in a high-purity inert atmosphere. Traditional dry pressing and annealing processes are only suitable for batch production and cannot produce large-area, uniformly thick continuous films. While wet casting has the potential for continuous production, the cast film must undergo high-pressure sintering after drying and degreasing to achieve acceptable density. Under pressureless or low-pressure conditions, the film is prone to retaining a large number of grain boundary pores, resulting in high grain boundary impedance and poor mechanical integrity. How to achieve low-pressure densification of sulfide electrolyte films on a continuous production line without compromising their ion conductivity remains a core obstacle to industrialization.

[0005] The third challenge is the inherent contradiction between a homogeneous electrolyte membrane with a single composition and the differentiated requirements of the positive and negative electrode interfaces. In all-solid-state batteries, the electrolyte membrane is in contact with a high-voltage positive electrode on one side and a low-potential lithium metal negative electrode on the other. The positive electrode side requires the electrolyte to have sufficient oxidation stability, while the negative electrode side needs to be chemically compatible with lithium metal and able to suppress lithium dendrite growth. A homogeneous electrolyte membrane with a single composition cannot simultaneously meet the different requirements of the two interfaces for ion conduction and chemical stability. Previous studies have prepared bilayer or trilayer electrolyte membranes through layer-by-layer cold pressing, but macroscopic bonding defects exist at the stacked interfaces, which are prone to delamination due to volume changes during long-term cycling, leading to interruption of ion transport.

[0006] Therefore, there is an urgent need for a method that can simultaneously complete the targeted elimination of grain boundary impedance, the construction of multi-level structures in the film thickness direction, and the preparation of high-density continuous films in a continuous manufacturing process. Summary of the Invention

[0007] To achieve the above objectives, this invention provides a method for the continuous preparation of multi-level sulfide solid electrolyte membranes based on grain boundary engineering, comprising the following steps: Step 1: Prepare a first precursor slurry and a second precursor slurry in an inert atmosphere; the first precursor slurry contains a matrix sulfide electrolyte powder, a binder, a plasticizer, and an organic solvent; the second precursor slurry contains the matrix sulfide electrolyte powder, amorphous lithium thiophosphate glass powder, a binder, a plasticizer, and an organic solvent. Step 2: The first precursor slurry and the second precursor slurry are simultaneously cast on the carrier film in a multilayer co-casting manner to form a lower casting layer and an upper casting layer. The lower casting layer is composed of the first precursor slurry, and the upper casting layer is composed of the second precursor slurry. Step 3: Dry the formed double-layer wet film to obtain a double-layer green film; Step 4: Roll-press the double-layer green film; Step 5: Degrease the rolled double-layer green film at a temperature lower than the crystallization initiation temperature of the amorphous lithium thiophosphate glass powder to remove the binder and plasticizer, and keep the amorphous lithium thiophosphate glass powder in an amorphous state. Step 6: Sinter the degreased membrane under a sulfur-containing atmosphere and isostatic pressure. The sulfur partial pressure of the sulfur-containing atmosphere shall not be lower than [value missing]. During the sintering heating process, the temperature should be no lower than The heating rate increases from the crystallization initiation temperature of the amorphous lithium thiophosphate glass powder to... The sintering temperature is set and held at the temperature so that the amorphous lithium thiophosphate glass powder melts into a glass melt when the sintering temperature is reached. Under the action of capillary force, the glass melt penetrates from the upper casting layer side to the lower casting layer side along the grain boundaries and pores, forming a gradient distribution in which the glass phase content continuously decreases along the film thickness direction. Step 7: at a level not lower than The cooling rate drops to This process solidifies the permeated glass melt into an amorphous interface phase, resulting in a multi-level sulfide solid electrolyte membrane with one side surface enriched with the amorphous glass phase, the opposite side surface depleted with the amorphous glass phase, and a continuous transition in between.

[0008] Preferably, the matrix sulfide electrolyte powder in step 1 is... Crystal powder, the Average particle size of crystalline powder for The amorphous lithium thiophosphate glass powder is Amorphous glass, wherein the average particle size of the amorphous lithium thiophosphate glass powder is... for The glass transition temperature of the amorphous lithium thiophosphate glass powder for Crystallization initiation temperature for .

[0009] Preferably, the preparation process of the first precursor slurry in step 1 is as follows: [The text abruptly ends here, so the translation stops.] weight Crystal powder, Parts by weight of polyvinyl butyral binder Parts by weight of dibutyl phthalate plasticizer and Anhydrous toluene organic solvent of a certain weight was placed in a sealed ball mill jar and milled on a planetary ball mill. ball mill rotation speed Hours; the preparation process of the second precursor slurry is as follows: ... weight Crystal powder, weight Amorphous glass powder, Parts by weight of polyvinyl butyral binder Parts by weight of dibutyl phthalate plasticizer and Anhydrous toluene organic solvent of a certain weight was placed in a sealed ball mill jar and milled on a planetary ball mill. ball mill rotation speed Hours; all weighing and sealing operations are performed while controlling the water content to be less than And the oxygen content is less than The process is completed inside the inert atmosphere glove box.

[0010] Preferably, the carrier film in step 2 is a polyethylene terephthalate film with a surface coated with an organosilicon release layer, and the conveyor speed is set to... The multilayer co-casting is achieved using a co-casting machine equipped with a first die and a second die. The first die extrudes the first precursor slurry to form a wet film with a thickness of [missing information]. The lower casting layer, the second die head extrudes the second precursor slurry to form a wet film with a thickness of The upper casting layer; the gap between the first die head lip is The gap between the lips of the second mold head is The temperature of the slurry inside the first and second mold heads is controlled at... The co-casting operation is carried out in a closed cavity, and a dew point not higher than [a certain value] is continuously introduced into the cavity. The dry air is collected in real time by an online dew point meter to measure the dew point value in the sealed cavity. The total thickness of the wet film is continuously collected by a laser displacement sensor and the feedback is used to control the speed of the slurry metering pump.

[0011] Preferably, the drying in step 3 is accomplished by continuously conveying the double-layer wet film along with the carrier film through a three-section drying duct, wherein the hot air temperature in the first section of the drying duct is [temperature missing]. Wind speed Duration of stay minutes; the hot air temperature in the second drying duct is... Wind speed Duration of stay minutes; the hot air temperature in the third drying duct is... Wind speed Duration of stay Minutes; the atmosphere in each section of the dry air duct has a dew point not exceeding [missing information]. The air is dried; after drying, the total thickness of the double-layer green film and the individual thicknesses of the lower and upper cast layers are continuously scanned using an online laser thickness gauge. The scan data is fed back to step 2 to adjust the extrusion rates of the first and second dies, so that the total thickness of the double-layer green film is maintained at a certain level. .

[0012] Preferably, the rolling process in step 4 is carried out in an inert atmosphere glove box, where the water content and oxygen content are both less than [amount missing]. After the double-layer green film is peeled off from the carrier film, it is subjected to double-sided rolling pressing by a pair of precision steel rollers. The heating temperature of the precision steel rollers is [temperature missing]. The linear pressure between the precision steel rollers is collected and controlled in real time by a piezoelectric force sensor. After rolling, the relative density of the double-layer green film reaches The relative density is determined by a combination of an online weighing system and a laser thickness gauge. The online weighing system collects the mass of a fixed-length film sample using a precision electronic analytical balance, while the laser thickness gauge collects thickness data at the corresponding position. The acquisition time and position of both are synchronized by an encoder.

[0013] Preferably, the degreasing in step 5 is carried out in a tubular atmosphere furnace, with an injection flow rate of [missing information]. The high-purity argon gas, degreasing and heating procedure is as follows: The rate of temperature increase from room temperature to ,exist Insulation Hours; then with The rate of heating up to ,exist Insulation Hours; then The rate of degreasing is as the furnace cools to room temperature; the maximum degreasing temperature Below the crystallization initiation temperature of the amorphous lithium thiophosphate glass powder This ensures that the amorphous lithium thiophosphate glass powder remains amorphous after degreasing.

[0014] Preferably, the specific process of sintering the degreased membrane in step 6 is as follows: the degreased membrane is placed on a dense graphite sintering plate, covered with flexible graphite paper, and then wrapped and folded with Hastelloy C-276 nickel-based alloy foil, leaving a width not exceeding The openings and gaps serve as atmosphere exchange channels; the package is moved into a pressure sintering furnace, where sulfur powder is pre-placed, with the mass of the sulfur powder equal to the mass of the degreased film. Double; after closing the furnace door, evacuate the furnace chamber to a vacuum level of [number missing]. Next, fill with high-purity argon gas until the gauge pressure is [value missing]. ;by The heating rate is increased to Insulation Minutes; during the heating process, sulfur powder gradually sublimates to produce sulfur vapor, maintaining the partial pressure of sulfur vapor in the furnace at [value missing]. .

[0015] Preferably, in step 7, The cooling rate decreases from the sintering temperature to This causes the permeated glass melt to solidify into an amorphous interface phase; the pressure inside the furnace is below the temperature. The pressure was then released to normal atmospheric pressure; the membrane material was removed from the furnace, and the graphite paper and Hastelloy C-276 nickel-based alloy foil were removed to obtain the multi-stage sulfide solid electrolyte membrane.

[0016] Preferably, the thickness of the multi-stage sulfide solid electrolyte membrane obtained in step 7 is [missing information]. The relative density is not less than ; in the thickness direction of the multi-stage sulfide solid electrolyte film, from one surface to the other, it is amorphous. The volume fraction of the glass phase is not less than Decrease continuously until no higher than Furthermore, there is no interlayer interface between the two sides.

[0017] The beneficial effects of this invention are: 1. This invention utilizes a double-layer co-casting technique to pre-construct an initial concentration gradient of grain boundary modifier glass powder along the film thickness direction. During the degreasing stage, the temperature is strictly controlled below the initial crystallization temperature of the glass powder to maintain its amorphous activity. Combined with a rapid heating strategy during the sintering stage, the glass powder reaches the sintering temperature and melts into a low-viscosity glass melt before significant crystallization occurs. Driven by capillary force, this glass melt continuously penetrates along grain boundaries and pore networks from the high-concentration side to the low-concentration side, ultimately forming a continuous amorphous fast-ion conductor interface phase chemically bonded to the surface of the matrix grains at the grain boundaries. This interface phase transforms the originally high-barrier grain boundary region into a low-impedance fast conduction pathway, significantly increasing the total ionic conductivity of the electrolyte membrane. The proportion of grain boundary impedance to total impedance is suppressed to below 15%, fundamentally solving the core technical problem of excessively high grain boundary impedance in polycrystalline sulfide electrolyte membranes. 2. This invention organically integrates casting, low-temperature degreasing, and sulfur-containing isostatic pressing sintering into a continuous manufacturing process. By introducing a rolling process before degreasing to increase the green body density, and then utilizing the liquid-phase-assisted densification effect generated by the capillary penetration of the glass melt during sintering, a high degree of densification with a relative density exceeding 98.5% can be achieved under mild conditions with only isostatic pressure applied. This avoids the dependence on high uniaxial pressure in traditional dry pressing sintering and the resulting problems of film cracking and warping, making the continuous production of large-area, uniformly thick sulfide solid electrolyte membranes possible, and providing an engineerable process path for the large-scale manufacturing of all-solid-state batteries. 3. The multi-level sulfide solid electrolyte membrane prepared by this invention exhibits a gradient distribution characteristic in the thickness direction, with the content of amorphous glass phase continuously decreasing from one surface to the other, and no macroscopic interlayer interface between the two sides. The side enriched in glass phase has a lower elastic modulus and higher plastic rheological ability, which can effectively release the stress generated by lithium deposition and inhibit dendrite penetration when in contact with the lithium metal anode, while the interfacial impedance on this side is significantly reduced. The other side, which is depleted in glass phase, basically retains the rigid framework characteristics of the matrix grains, and has a more matched chemical potential with the high-voltage cathode material, reducing the occurrence of interfacial side reactions. This multi-level structure with continuous transition of composition and mechanical properties on both sides achieves differentiated compatibility of the positive and negative electrode interfaces simultaneously in a single continuous manufacturing process, fundamentally avoiding the risk of delamination failure due to volume changes in traditional multilayer electrolyte membranes during long cycles. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this 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 for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of the steps of the method of the present invention. Detailed Implementation

[0020] 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.

[0021] Please see Figure 1 This invention provides a method for the continuous preparation of multi-level sulfide solid electrolyte membranes based on grain boundary engineering, aiming to solve the technical problems of high grain boundary impedance, inability to achieve continuous production, and the inability of a single homogeneous membrane to meet the differentiated interface requirements of the positive and negative electrodes. The technical approach of this invention achieves the above objectives through the organic coupling of three core process steps: First, a double-layer co-casting technique is used to pre-construct an initial concentration difference structure in the thickness direction of the electrolyte membrane, consisting of one layer containing grain boundary modifier glass powder and another layer without grain boundary modifier glass powder; Second, during the degreasing stage, the maximum temperature is strictly limited below the crystallization initiation temperature of the grain boundary modifier glass powder, ensuring that the glass powder retains its original amorphous activity after degreasing; Third, during the sulfur-containing atmosphere pressure sintering stage, a specific rapid heating strategy is employed to allow the amorphous glass powder to pass through its dangerous temperature range where crystallization easily occurs in a very short time, thereby transforming it into a low-viscosity glassy state or supercooled liquid state that can be capillarily permeated when the preset sintering temperature is reached.

[0022] It should be noted that the term "grain boundary engineering" used in this article refers to a set of operable and measurable process steps, specifically including: the selection of amorphous lithium thiophosphate glass powder in step 1 and the spatial distribution design of it and the matrix sulfide electrolyte powder in a specific layer; the preservation of the amorphous state of the amorphous lithium thiophosphate glass powder by controlling the degreasing temperature to be lower than the crystallization initiation temperature of the amorphous lithium thiophosphate glass powder in step 5; and the control of the heating rate to allow the amorphous lithium thiophosphate glass powder to reach the sintering temperature before significant crystallization occurs, and the formation of continuous amorphous ion conduction pathways at the grain boundaries through subsequent capillary penetration and cooling solidification in step 6.

[0023] Without being bound by any particular theory, the applicant discovered through experiments that using a higher heating rate through the temperature range between the crystallization initiation temperature and the melting temperature of the amorphous lithium thiophosphate glass powder helps to reduce the crystallization tendency of the powder. This allows the glass powder to participate in grain boundary filling mainly in a flowable glassy state or a supercooled liquid state during this stage, rather than being dominated by a clearly crystalline phase. This is beneficial for obtaining a low-viscosity glass melt in the subsequent heat preservation stage and ultimately forming a continuous amorphous interface phase.

[0024] The term "crystallization onset temperature" in this article specifically refers to the temperature at which an amorphous substance begins its crystallization transformation during heating, as determined by differential scanning calorimetry. The standard for this measurement is based on... The extrapolated onset temperature is obtained by measuring the heating rate. "Glass transition temperature" specifically refers to the midpoint of the temperature range corresponding to the transition of an amorphous substance from a rubbery state to a glassy state or vice versa. For the preferred embodiment of this invention... The crystallization initiation temperature of amorphous lithium thiophosphate glass Approximately Glass transition temperature Approximately .

[0025] Regarding the effect of the sulfur-containing atmosphere in step 6, the applicant found that by matching and controlling the amount of sulfur powder added, the free volume of the furnace, and the sintering temperature, the partial pressure of sulfur vapor in the furnace can be maintained within a specific range, which is beneficial for suppressing sulfur vapor concentration. The surface desulfurization and phase decomposition of the matrix grains at high temperatures also help reduce the condensation of free sulfur on the film surface. The applicant confirmed through a series of calibration experiments that... At the sintering temperature, when the partial pressure of sulfur vapor in the furnace is at to Within the specified range, no obvious decomposition phase characteristic peaks were observed in the X-ray diffraction pattern of the matrix grains of the obtained electrolyte membrane, and the residual sulfur content on the membrane surface was acceptable. The aforementioned sulfur partial pressure can be monitored online by mass spectrometry or gas sensors, or indirectly calibrated and controlled by precisely controlling the amount of sulfur powder added, the free volume of the furnace, and temperature and pressure parameters, combined with a thermodynamic calculation model.

[0026] Regarding the structural characteristics of the finally obtained multi-level sulfide solid electrolyte membrane, the descriptions of "one side surface enriched with amorphous glass phase," "the opposite side surface depleted of amorphous glass phase," and "continuous transition in the middle" in this paper can be characterized and defined in the following operable way: Prepare cross-sectional samples along the thickness direction of the membrane material, and perform elemental line scanning analysis using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy to obtain the continuous variation curve of the characteristic X-ray intensity ratio of sulfur and phosphorus along the thickness direction; when this curve shows a monotonous and continuous decreasing trend from one side surface to the other, and no abrupt intensity steps or plateaus characterizing the interlayer interface appear, the multi-level sulfide solid electrolyte membrane is considered to have a continuous transition structural characteristic. Alternatively, at least along the membrane thickness direction... Nanoindentation tests were performed at equidistant sampling points. The measured reduced elastic modulus showed a monotonically varying trend along the thickness direction, and the modulus difference between adjacent points did not exceed the higher value among adjacent points. In this case, it can also be determined that the membrane material has achieved a continuous transition in mechanical properties and there is no macroscopic interlayer interface.

[0027] The technical solution of the present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0028] Example 1 (1) Slurry preparation; In a water content and oxygen content both less than In an argon glove box, a precision electronic balance was used to weigh... of Crystal powder, whose average particle size was measured by a laser particle size analyzer for Weigh again Polyvinyl butyral adhesive and Dibutyl phthalate plasticizer. The weighed powder, binder, and plasticizer are placed together in a container with a volume of... Add to the ball mill jar and add Anhydrous toluene was used as the organic solvent. After sealing the milling jar inside the glove box, it was removed from the glove box and placed on the planetary ball mill. The milling parameters were set to [speed value missing]. ,time After hours, a uniformly dispersed first precursor slurry is obtained.

[0029] In the same glove box, the second precursor slurry was prepared using the same steps. Weigh... of Crystal powder, of Amorphous lithium thiophosphate glass powder, Polyvinyl butyral adhesive and The dibutyl phthalate plasticizer. Average particle size of glass powder for It is achieved through differential scanning calorimetry in Glass transition temperature measured at heating rate for Crystallization initiation temperature for All materials together Anhydrous toluene was sealed together with the ball mill jar inside the glove box, to... ball mill rotation speed After hours, the second precursor slurry was obtained.

[0030] (2) Double-layer co-cast molding; The two prepared slurries are transferred to a co-casting molding device with a dual-die head. The device is located in a sealed cavity, which is continuously circulated with water at a dew point of [missing information]. Dry air. The carrier membrane is a polyethylene terephthalate membrane with a silicone release layer coated on its surface, and the conveyor speed is precisely set to... The first die extrudes the first precursor slurry onto the carrier membrane, forming a layer with a thickness of [missing information]. The wet film serves as the lower casting layer; then, the second die precisely extrudes and coats the second precursor slurry onto the upper surface of the lower casting layer, forming a layer with a thickness of [missing information]. The wet film is used as the upper casting layer. The lip gaps of the two die heads are respectively set to... and The temperature inside the mold head is precisely controlled by a circulating water bath. During the casting process, a laser displacement sensor located behind the die head monitors the total thickness of the wet film in real time. This data is fed back to the control system, which uses a closed-loop adjustment to regulate the speed of the slurry metering pump, ensuring that the total thickness of the double-layer wet film remains stable. .

[0031] (3) Drying; The formed double-layer wet film, along with the carrier film, directly enters the three-stage drying duct for drying. The hot air temperature in the first stage duct... Wind speed , stay Minutes; Second section air duct temperature Wind speed , stay Minutes; Temperature of the third air duct Wind speed , stay Minutes. All duct atmosphere dew points were maintained at [value missing]. After the membrane material leaves the drying duct, it passes through an online laser thickness gauge to scan and confirm the total thickness of the resulting double-layer green membrane. The lower layer of green body is thick The upper layer of green body is thick .

[0032] (4) Roller pressing; The dried green film, along with the carrier film, enters a rolling unit connected to a glove box. The glove box is in a high-purity argon atmosphere (water and oxygen content are both below a certain level). The membrane is peeled off from the carrier membrane and fed into a pair of preheated membranes. Double-sided rolling is performed between precision steel rollers. The rolling pressure is controlled by feedback from a force sensor and kept constant at a constant value. After rolling, an online detection system integrating a precision electronic balance and a laser thickness gauge is used. Employing a fixed-length cutting and synchronous data acquisition method, the relative density of the membrane material is measured by jointly calculating the geometric dimensions and weighing mass of the membrane sample. .

[0033] (5) Degreasing; The rolled membrane is placed in a tubular atmosphere furnace for degreasing. A continuous flow rate of [flow rate missing] is applied. Under a high-purity argon atmosphere, the following heating procedure was performed: First, with... Heat up to And keep warm Hours to remove plasticizers; then with Heat up to And keep warm The process takes several hours to fully pyrolyze and remove the polyvinyl butyral binder. The highest processing temperature during the entire degreasing process is [temperature value missing]. Always lower Crystallization initiation temperature of glass powder This ensures that the glass powder retains its amorphous state after degreasing. After degreasing, the membrane was tested using a mercury porosimeter, and its porosity was [value missing]. The porosity is basically consistent with that of the green blank after roll pressing.

[0034] (6) Sulfur-containing isostatic pressing sintering; The degreased porous membrane was placed on a sintering plate made of dense graphite, and a sheet of flexible graphite paper was placed on its upper surface. Then, a sheet of paper with a thickness of [missing information] was used. The entire piece is wrapped in Hastelloy C-276 nickel-based alloy foil, with a strip approximately [width missing] wide left. The gaps serve as atmosphere exchange channels. The inclusions are moved into the furnace chamber of the pressure sintering furnace, and pre-added to a separate crucible inside the furnace. High-purity sulfur powder, the quality of which is the same as the quality of the degreased film. After closing the furnace door, use a vacuum pump system to evacuate the furnace to [a certain temperature]. The vacuum was then filled. The high-purity argon gas caused the gauge pressure inside the furnace to reach [a certain value]. Start the heating program to... The rapid heating rate raises the furnace temperature to and keep warm at this temperature. Minutes. During this heating process, the temperature rises from... Rise to Only when Minutes. The applicant confirmed through preliminary experiments that the traversal time was shorter than stated. During the isothermal crystallization incubation period of the glass powder in this temperature range, the glass powder tends to remain in an amorphous or supercooled liquid state throughout the heating process until it reaches the desired temperature. It transforms into a low-viscosity glass melt. Simultaneously, the sulfur powder gradually sublimates. Through calculations using pre-calibrated sulfur powder mass and furnace free volume, combined with verification using an online mass spectrometer, the partial pressure of sulfur vapor within the furnace was maintained at approximately [value missing]. This sulfur partial pressure level is conducive to inhibiting The matrix undergoes surface desulfurization and decomposition at high temperatures. During the heat preservation stage, the molten glass melt, driven by capillary force, continuously penetrates along the pores and grain boundary network of the porous membrane from the upper casting layer region with high concentration to the lower casting layer region with low concentration, forming a glass phase concentration gradient along the thickness direction.

[0035] (7) Cooling and post-treatment; After the insulation is completed, The rate at which the furnace temperature decreases is controlled is higher than the critical cooling rate of the glass melt (determined by differential scanning calorimetry). This ensures that the glass melt penetrating into the grain boundaries solidifies into an amorphous interface phase. When the furnace temperature drops... Then, stop the forced cooling and allow it to cool naturally. When the temperature is below... At this time, the high-pressure gas in the furnace is slowly released to atmospheric pressure. After the furnace temperature has completely cooled to room temperature, the furnace door is opened and the package is removed. The outer Hastelloy C-276 alloy foil and graphite paper are removed to obtain a complete, non-warped multi-stage sulfide solid electrolyte membrane.

[0036] Comparative Example 1 (conventional homogeneous film, without grain boundary modifier gradient) A single-component slurry was prepared using the exact same matrix material and slurry formulation as in Example 1, i.e., only the first precursor slurry from Example 1 was used. A conventional single-layer casting process was employed, with other steps such as drying, rolling, and debinding parameters identical to those in Example 1. After debinding, the film was placed in the same pneumatic sintering furnace and subjected to the same conditions. Argon isostatic pressure and Under-insulation Sintering is performed over a period of minutes, but without introducing sulfur powder or any grain boundary modifier glass powder. After sintering and cooling, a homogeneous monolayer is obtained. Solid electrolyte membrane.

[0037] Comparative Example 2 (Mechanical Mixing Modifier, Homogeneous Membrane) The same matrix material and grain boundary modifier glass powder as in Example 1 were used, but the mixing method was a one-time mechanical mixing of all powders. Specifically, the powders were mixed in a glove box. of Crystal powder and of Amorphous glass powder is premixed and then added. Polyvinyl butyral, Dibutyl phthalate and Anhydrous toluene was ball-milled to prepare a single-type slurry. Subsequently, a homogeneous film with a uniformly distributed modifier was obtained using single-layer casting and the same drying, rolling, degreasing, and sintering processes as in Example 1.

[0038] Performance testing and comparative analysis: The electrolyte membranes obtained in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to the following performance tests. All electrochemical tests were conducted within [time period missing]. The procedure is carried out in a glove box with a high-purity argon atmosphere.

[0039] Total ionic conductivity and grain boundary impedance were determined by electrochemical impedance spectroscopy. The membrane material was punched to a diameter of... A circular disc, with carbon-coated aluminum foil on both sides serving as blocking electrodes, was assembled into a symmetrical blocking cell. Testing was conducted using an electrochemical workstation. to Within the frequency range, apply The sinusoidal AC disturbance signal was used. The obtained impedance spectrum was fitted using ZView software, and the equivalent circuit was adopted. Model, in which Grain impedance, Grain boundary impedance, It is a constant phase angle element. The proportion of grain boundary impedance to total impedance is determined by the formula... Calculations were performed. The critical current density was determined using a lithium-electrolyte-lithium symmetric cell with constant current step testing, where each current step was continuously polarized with constant current. Minutes later, when the polarization voltage suddenly drops sharply and cannot be recovered, a lithium dendrite short circuit is determined to have occurred, and the current density value of the previous step is recorded as the critical current density. The interfacial impedance of the positive and negative electrodes is also obtained by electrochemical impedance spectroscopy testing after assembling the corresponding semi-blocked electrodes and symmetrical cells.

[0040] Thermal stability was evaluated through thermal cycling tests, the specific procedure of which involved placing the assembled symmetrical cells in... and Loop between Each cycle maintains constant temperature at both high and low temperatures. The temperature change rate is 1 hour. The increase in resistance after thermal cycling was determined by comparing the electrochemical impedance spectroscopy before and after cycling. Total ohmic resistance below To calculate, the formula is: The cross-sectional structure was determined by observing the membrane material in backscattered electron mode using a scanning electron microscope after brittle fracture in liquid nitrogen, combined with energy-dispersive X-ray spectroscopy for sulfur and phosphorus elemental line scans along the thickness direction to confirm the presence of gradient transitions or interlayer interfaces.

[0041] The table below summarizes the comparison results of various performance indicators.

[0042]

[0043] The test results show that, compared with Comparative Example 1, the total ionic conductivity of the film obtained in Example 1 is significantly improved, and the proportion of grain boundary impedance is significantly reduced. This is attributed to the continuous distribution of the amorphous glass phase at the grain boundaries, which provides a fast transport channel for lithium ions. Simultaneously, the film of Example 1 exhibits the smallest increase in resistance after thermal cycling, indicating that the filling of the amorphous glass phase at the interface helps release the stress caused by volume changes. Compared with Comparative Example 2, Example 1 maintains a similarly high density while exhibiting lower grain boundary impedance and higher critical current density. Furthermore, its cross-sectional energy-dispersive X-ray spectroscopy line scan shows that the sulfur signal intensity decreases monotonically from the glass-rich side to the glass-poor side, without any abrupt intensity plateau, indicating that the film of Example 1 possesses a continuous gradient multi-level structure not found in Comparative Example 2. This structural difference results in Example 1 exhibiting significantly lower interface impedance than both comparative examples when facing high-voltage positive electrodes and metallic lithium negative electrodes, demonstrating the synergistic advantages of the present invention in multi-level structure construction and grain boundary engineering. 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.

[0044] 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 method for continuous preparation of multi-level sulfide solid electrolyte membranes based on grain boundary engineering, characterized in that, Includes the following steps: Step 1: Prepare a first precursor slurry and a second precursor slurry in an inert atmosphere; the first precursor slurry contains a matrix sulfide electrolyte powder, a binder, a plasticizer, and an organic solvent; the second precursor slurry contains the matrix sulfide electrolyte powder, amorphous lithium thiophosphate glass powder, a binder, a plasticizer, and an organic solvent. Step 2: The first precursor slurry and the second precursor slurry are simultaneously cast on the carrier film in a multilayer co-casting manner to form a lower casting layer and an upper casting layer. The lower casting layer is composed of the first precursor slurry, and the upper casting layer is composed of the second precursor slurry. Step 3: Dry the formed double-layer wet film to obtain a double-layer green film; Step 4: Roll-press the double-layer green film; Step 5: Degrease the rolled double-layer green film at a temperature lower than the crystallization initiation temperature of the amorphous lithium thiophosphate glass powder to remove the binder and plasticizer, and keep the amorphous lithium thiophosphate glass powder in an amorphous state. Step 6: Sinter the degreased membrane under a sulfur-containing atmosphere and isostatic pressure. The sulfur partial pressure of the sulfur-containing atmosphere shall not be lower than [value missing]. During the sintering heating process, the temperature should be no lower than The heating rate increases from the crystallization initiation temperature of the amorphous lithium thiophosphate glass powder to... The sintering temperature is set and held at the temperature so that the amorphous lithium thiophosphate glass powder melts into a glass melt when the sintering temperature is reached. Under the action of capillary force, the glass melt penetrates from the upper casting layer side to the lower casting layer side along the grain boundaries and pores, forming a gradient distribution in which the glass phase content continuously decreases along the film thickness direction. Step 7: at a level not lower than The cooling rate drops to This process solidifies the permeated glass melt into an amorphous interface phase, resulting in a multi-level sulfide solid electrolyte membrane with one side surface enriched with the amorphous glass phase, the opposite side surface depleted with the amorphous glass phase, and a continuous transition in between.

2. The method for continuous preparation of a multi-level sulfide solid electrolyte membrane based on grain boundary engineering according to claim 1, characterized in that, The matrix sulfide electrolyte powder mentioned in step 1 is Crystal powder, the Average particle size of crystalline powder for ; The amorphous lithium thiophosphate glass powder is Amorphous glass, wherein the average particle size of the amorphous lithium thiophosphate glass powder is... for The glass transition temperature of the amorphous lithium thiophosphate glass powder for Crystallization initiation temperature for .

3. The method for continuous preparation of a multi-level sulfide solid electrolyte membrane based on grain boundary engineering according to claim 2, characterized in that, The preparation process of the first precursor slurry in step 1 is as follows: ... weight Crystal powder, Parts by weight of polyvinyl butyral binder Parts by weight of dibutyl phthalate plasticizer and Anhydrous toluene organic solvent of a certain weight was placed in a sealed ball mill jar and milled on a planetary ball mill. ball mill rotation speed Hours; the preparation process of the second precursor slurry is as follows: ... weight Crystal powder, weight Amorphous glass powder, Parts by weight of polyvinyl butyral binder Parts by weight of dibutyl phthalate plasticizer and Anhydrous toluene organic solvent of a certain weight was placed in a sealed ball mill jar and milled on a planetary ball mill. ball mill rotation speed Hours; all weighing and sealing operations are performed while controlling the water content to be less than And the oxygen content is less than The process is completed inside the inert atmosphere glove box.

4. The method for continuous preparation of a multi-level sulfide solid electrolyte membrane based on grain boundary engineering according to claim 1, characterized in that, The carrier film mentioned in step 2 is a polyethylene terephthalate film with an organosilicon release layer coated on its surface, and the belt conveyor speed is set to... The multilayer co-casting is achieved using a co-casting machine equipped with a first die and a second die. The first die extrudes the first precursor slurry to form a wet film with a thickness of [missing information]. The lower casting layer, the second die head extrudes the second precursor slurry to form a wet film with a thickness of The upper casting layer; the gap between the first die head lip is The gap between the lips of the second mold head is The temperature of the slurry inside the first and second mold heads is controlled at... The co-casting operation is carried out in a closed cavity, and a dew point not higher than [a certain value] is continuously introduced into the cavity. The dry air is collected in real time by an online dew point meter to measure the dew point value in the sealed cavity. The total thickness of the wet film is continuously collected by a laser displacement sensor and the feedback is used to control the speed of the slurry metering pump.

5. The method for continuous preparation of a multi-level sulfide solid electrolyte membrane based on grain boundary engineering according to claim 4, characterized in that, The drying process described in step 3 is accomplished by continuously conveying the double-layer wet film along with the carrier film through a three-section drying duct. The hot air temperature in the first section of the drying duct is... Wind speed Duration of stay minutes; the hot air temperature in the second drying duct is... Wind speed Duration of stay minutes; the hot air temperature in the third drying duct is... Wind speed Duration of stay Minutes; the atmosphere in each section of the dry air duct has a dew point not exceeding [missing information]. The air is dried; after drying, the total thickness of the double-layer green film and the individual thicknesses of the lower and upper cast layers are continuously scanned using an online laser thickness gauge. The scan data is fed back to step 2 to adjust the extrusion rates of the first and second dies, so that the total thickness of the double-layer green film is maintained at a certain level. .

6. The method for continuous preparation of a multi-level sulfide solid electrolyte membrane based on grain boundary engineering according to claim 1, characterized in that, The rolling process described in step 4 is carried out in an inert atmosphere glove box, where the water content and oxygen content are both less than [amount missing]. After the double-layer green film is peeled off from the carrier film, it is subjected to double-sided rolling pressing by a pair of precision steel rollers. The heating temperature of the precision steel rollers is [temperature missing]. The linear pressure between the precision steel rollers is collected and controlled in real time by a piezoelectric force sensor. After rolling, the relative density of the double-layer green film reaches The relative density is determined by a combination of an online weighing system and a laser thickness gauge. The online weighing system collects the mass of a fixed-length cut film sample using a precision electronic analytical balance, while the laser thickness gauge collects thickness data at the corresponding position. The acquisition time and position of both are synchronized by an encoder.

7. The method for continuous preparation of a multi-level sulfide solid electrolyte membrane based on grain boundary engineering according to claim 1, characterized in that, The degreasing process described in step 5 is carried out in a tubular atmosphere furnace with a flow rate of [missing information]. The high-purity argon gas, degreasing and heating procedure is as follows: The rate of temperature increase from room temperature to ,exist Insulation Hours; then with The rate of heating up to ,exist Insulation Hours; then The rate of degreasing is as the furnace cools to room temperature; the maximum degreasing temperature Below the crystallization initiation temperature of the amorphous lithium thiophosphate glass powder This ensures that the amorphous lithium thiophosphate glass powder remains amorphous after degreasing.

8. The method for continuous preparation of a multi-level sulfide solid electrolyte membrane based on grain boundary engineering according to claim 7, characterized in that, The specific process of sintering the degreased membrane in step 6 is as follows: Place the degreased membrane on a dense graphite sintering plate, cover it with flexible graphite paper, then wrap and fold it with Hastelloy C-276 nickel-based alloy foil, leaving a width not exceeding The openings and gaps serve as channels for air exchange. The encapsulated body is transferred into a pressure sintering furnace, where sulfur powder is pre-placed. The mass of the sulfur powder is equal to the mass of the degreased film. Double; after closing the furnace door, evacuate the furnace chamber to a vacuum level of [number missing]. Next, fill with high-purity argon gas until the gauge pressure is [value missing]. ;by The heating rate is increased to Insulation Minutes; during the heating process, sulfur powder gradually sublimates to produce sulfur vapor, maintaining the partial pressure of sulfur vapor in the furnace at [value missing]. .

9. The method for continuous preparation of a multi-level sulfide solid electrolyte membrane based on grain boundary engineering according to claim 8, characterized in that, In step 7, The cooling rate decreases from the sintering temperature to This causes the permeated glass melt to solidify into an amorphous interface phase; the pressure inside the furnace is below the temperature. The pressure was then released to normal atmospheric pressure; the membrane material was removed from the furnace, and the graphite paper and Hastelloy C-276 nickel-based alloy foil were removed to obtain the multi-stage sulfide solid electrolyte membrane.

10. The method for continuous preparation of a multi-level sulfide solid electrolyte membrane based on grain boundary engineering according to claim 9, characterized in that, The thickness of the multi-stage sulfide solid electrolyte membrane obtained in step 7 is The relative density is not less than In the thickness direction of the multi-stage sulfide solid electrolyte film, from one surface to the other, it is amorphous. The volume fraction of the glass phase is not less than Decrease continuously until no higher than Furthermore, there is no interlayer interface between the two sides.

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