High-performance all-solid-state secondary battery equipped with stabilized positive electrode sheet

Abstract

This invention relates to the field of all-solid-state secondary battery technology and discloses a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode, comprising a positive electrode, a negative electrode layer, and a solid electrolyte layer. The positive electrode is manufactured by coating and drying a slurry containing 80%-88% positive electrode active material, 10%-16% sulfide solid electrolyte, 1%-2% conductive agent, and 1%-2% binder, followed by a heat-pressurization treatment at 100℃-250℃ and 10MPa-100MPa. This invention constructs a dense interface stabilization layer in situ between the positive electrode active material and the sulfide electrolyte by applying a thermo-pressure coupling treatment to the positive electrode precursor. This stabilization layer improves the physical contact between the solid and solid interfaces and reduces interfacial impedance. Simultaneously, this stabilization layer acts as a physical barrier, inhibiting the oxidative decomposition of the electrolyte under high voltage, slowing capacity decay, and improving the battery's cycle life and structural stability.

Description

Technical Field

[0001] This invention relates to the field of all-solid-state secondary battery technology, specifically to a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode. Background Technology

[0002] All-solid-state rechargeable batteries, by using solid electrolytes instead of traditional liquid electrolytes, hold the promise of fundamentally solving battery safety issues and possessing the potential to improve energy density, making them an important direction for next-generation energy storage technology. Among various solid electrolyte systems, sulfide solid electrolytes, represented by Argyrodite-type sulfides, have attracted much attention due to their high room-temperature ionic conductivity, comparable to that of liquid electrolytes.

[0003] However, in the actual development of applying sulfide solid electrolytes to all-solid-state batteries, researchers have discovered interfacial compatibility issues between them and high-voltage cathode materials. Firstly, in traditional electrode fabrication processes, the cathode active material and solid electrolyte particles are simply mixed and compacted, making it difficult to form ideal solid-to-solid interfacial contact, resulting in numerous pores and gaps. This poor physical contact directly leads to high interfacial ion transport impedance, limiting the battery's rate performance.

[0004] Secondly, sulfide solid electrolytes have limited thermodynamic stability, resulting in a typically narrow electrochemical window. When paired with high-energy-density layered oxide cathodes (such as lithium nickel manganese cobalt oxide (NMC) or lithium cobalt oxide (LCO), continuous electrochemical side reactions occur at the cathode-electrolyte interface when the battery is charged to high voltage. Sulfide electrolytes are easily oxidized and decomposed by the high-potential cathode, generating a high-resistivity byproduct layer, such as elemental sulfur or polysulfides. This accumulated decomposition layer continuously increases the interfacial impedance, causing rapid capacity decay and severely impacting the battery's cycle life.

[0005] Furthermore, the positive electrode active material undergoes lattice volume contraction and expansion during repeated charge and discharge processes. In the rigid system of a solid-state electrode, this volume change is sensitive to stress, easily leading to the destruction of the microstructure of the active material particles or the loss of contact with the surrounding solid electrolyte particles. This interface degradation process driven by mechanical stress is also a factor contributing to the long-term performance degradation of the battery and affecting its reliability. Therefore, how to construct a positive electrode / electrolyte interface with low impedance, high electrochemical stability, and a robust structure is a pressing technical challenge that needs to be solved in the development of high-performance all-solid-state rechargeable batteries. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode. This solves the problems in existing all-solid-state secondary batteries where there is poor physical contact and electrochemical incompatibility at the interface between the positive electrode and the sulfide solid electrolyte. Poor physical contact leads to high interface impedance, and the oxidative decomposition of the sulfide electrolyte under high voltage generates high-impedance byproducts, resulting in a decline in battery cycle performance.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of the present invention provides a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode, comprising a positive electrode, a negative electrode layer, and a solid electrolyte layer located between the positive electrode and the negative electrode layer; the positive electrode is made by coating a positive electrode slurry onto a current collector and then drying and heating / pressurizing it, wherein the positive electrode slurry contains the following raw materials by weight percentage: positive electrode active material accounting for 80%-88%; sulfide solid electrolyte accounting for 10%-16%; conductive agent accounting for 1%-2%; binder accounting for 1%-2%; the sum of the weight percentages of the raw materials is 100%.

[0008] By employing the above technical solution, this invention applies specific heating and pressurization treatments to the coated and dried positive electrode precursor during the preparation of the positive electrode sheet. The temperature-pressure coupling process constructs an interface stabilizing layer in situ between the positive electrode active material and the sulfide solid electrolyte. This stabilizing layer has two functions:

[0009] First, the pressure promotes physical densification between particles, allowing solid electrolyte particles to fill the gaps between positive electrode active material particles, increasing the effective contact area and reducing interfacial contact resistance.

[0010] Second, a suitable temperature induces a controllable shallow reaction at the interface, consuming the most unstable component at the interface and generating a new, thermodynamically and electrochemically more stable phase, such as a composite interface layer rich in Li, P, O, and S elements (e.g., (Similar structure), and the average thickness of the interface stabilizing layer is controlled between 1 nm and 100 nm. This ultrathin nanoscale thickness is sufficient to block electron transport without increasing the transport path length of lithium ions.

[0011] The in-situ generated stabilizing layer has high lithium-ion conductivity. At the same time, as an electronic insulator, the stabilizing layer acts as a physical barrier during high-voltage charging, isolating the highly oxidizable positive electrode surface from the electrolyte body and inhibiting the continuous oxidative decomposition of the electrolyte.

[0012] Therefore, the growth rate of interface impedance is reduced, thereby improving the cycle life and capacity retention of the battery.

[0013] Preferably, the positive electrode active material is selected from layered lithium nickel cobalt manganese oxide or lithium cobalt oxide; the sulfide solid electrolyte is an Argyrodite type sulfide solid electrolyte; the conductive agent is acetylene black; and the binder is selected from styrene-butadiene rubber or hydrogenated nitrile rubber.

[0014] By adopting the above technical solutions, the selected NMC or LCO cathode materials have high energy density, the Argyrodite-type solid electrolyte has high room temperature ionic conductivity, and the SBR or H-NBR binder exhibits good solubility and adhesion to electrode materials in specific solvent systems. These preferred material combinations provide a foundation for constructing high-performance all-solid-state batteries.

[0015] Preferably, the Argyrodite-type sulfide solid electrolyte has an average particle size D50 of 0.8 μm to 5.0 μm; the sulfide solid electrolyte is prepared by reacting Li2S, P2S5 and LiCl in a molar ratio of 2.0:0.5:1.5.

[0016] By employing the above technical solution, the particle size of the solid electrolyte is controlled within the range of 0.8 μm to 5.0 μm. This ensures that the electrolyte particles can effectively fill the gaps between the positive electrode active material particles, forming a continuous ionic conductive network, while avoiding the problems of excessively high surface energy and exacerbated side reactions caused by excessively small particle size. The limited molar ratio of raw materials ensures that the synthesized Argyrodite-type solid electrolyte has a pure phase and high ionic conductivity.

[0017] The second aspect of this invention provides a method for preparing a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode, comprising the following steps: dispersing a positive electrode active material, a sulfide solid electrolyte, a conductive agent, and a binder in a solvent to obtain a positive electrode slurry; coating the positive electrode slurry onto the surface of a current collector, and drying it to remove the solvent to obtain a positive electrode precursor; subjecting the positive electrode precursor to heating and pressurizing treatment under an inert atmosphere to obtain a positive electrode, wherein the heat treatment temperature of the heating and pressurizing treatment is 100℃-250℃, and the applied pressure is 10MPa-100MPa; assembling the positive electrode, the solid electrolyte layer, and the negative electrode layer to obtain a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode.

[0018] By adopting the above technical solution, the core of the method of this invention lies in the introduction of a stable positive electrode preparation step. This step, through the synergistic effect of precisely controlling temperature and pressure, modifies the positive electrode / electrolyte interface in situ.

[0019] The pressure applied (10MPa-100MPa) overcomes the repulsive forces between particles, causing the positive electrode active material, solid electrolyte, and conductive agent particles to rearrange and undergo plastic deformation, eliminating pores at the solid-solid interface and forming a physically tight contact. If the pressure is below 10MPa, effective particle rearrangement cannot be achieved; if the pressure is above 100MPa, mechanical damage will occur to the crystal structure of the positive electrode active material.

[0020] The temperature effect (100℃-250℃) provides adequate activation energy for shallow interfacial reactions and softens the binder to aid densification. Below 100℃, interfacial reaction kinetics are insufficient; above 250℃, it can trigger bulk decomposition of the sulfide solid electrolyte or uncontrolled side reactions with the positive electrode.

[0021] Through the aforementioned temperature-pressure coupling treatment, within a precise process window, an interfacial reaction is induced between the positive electrode active material and the sulfide solid electrolyte, generating in situ a thin and dense interfacial stabilizing layer with high ionic conductivity and electronic insulation properties, thereby improving the electrochemical stability of the interface at its source.

[0022] Preferably, in the preparation step of the stabilized positive electrode, the holding time of the heating and pressurizing treatment is 10 minutes to 120 minutes.

[0023] By adopting the above technical solution, setting the holding time can ensure that the interface reaction proceeds more fully and uniformly, while ensuring that the effects of pressure and temperature can be transmitted to the entire electrode thickness range, forming a uniform interface structure.

[0024] Preferably, in the preparation step of the positive electrode slurry, the binder is added in the form of a binder solution; when the binder is styrene-butadiene rubber, the solvent is anhydrous xylene; when the binder is hydrogenated nitrile butadiene rubber, the solvent is anhydrous anisole.

[0025] By adopting the above technical solutions, suitable and excellent solvents were selected for different polymeric binders. Styrene-butadiene rubber in xylene and hydrogenated nitrile rubber in anisole can form uniform and stable solutions, ensuring that the binder can uniformly coat the surface of the active material and electrolyte particles during slurry preparation, forming an effective bonding network, thereby ensuring the mechanical integrity of the positive electrode sheet.

[0026] Preferably, in the forming step of the positive electrode precursor, the drying is carried out under vacuum conditions, the drying temperature is 90℃-110℃, and the drying time is 3 hours-6 hours.

[0027] By employing the above technical solution and using mild vacuum drying conditions, residual solvents in the slurry can be completely removed without damaging the material structure. Complete solvent removal is beneficial for subsequent hot-pressing steps and the electrochemical performance of the battery, and can prevent side reactions caused by solvent residue.

[0028] Preferably, in the battery assembly step, the negative electrode layer is selected from lithium indium alloy foil or metallic lithium foil; the assembly process also includes applying a cold isostatic pressing treatment of 500 MPa to the three-layer structure of the positive electrode sheet, solid electrolyte layer and negative electrode layer.

[0029] By adopting the above technical solution and using lithium-indium alloy or lithium metal foil as the negative electrode, high capacity and suitable potential are provided. Applying high-pressure cold isostatic pressing in the final stage of assembly ensures that a seamless and tight solid-solid interface is formed between the positive electrode, the solid electrolyte layer, and the negative electrode layer, thereby reducing the overall internal resistance of the battery.

[0030] This invention provides a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode. It has the following beneficial effects:

[0031] 1. This invention synergistically treats the positive electrode precursor by applying a pressure of 10MPa-100MPa and a temperature of 100℃-250℃, thereby forming a dense interfacial stabilizing layer in situ between the positive electrode active material and the sulfide solid electrolyte. This stabilizing layer improves the physical contact between the solid and solid interfaces, effectively reducing the initial interfacial impedance of the battery and lowering the initial resistivity per unit area to a minimum. The following provides the foundation for achieving high-rate performance.

[0032] 2. The interface stabilizing layer generated in situ in this invention has the characteristics of ion conduction and electronic insulation. During high-voltage cycling, it can act as a physical barrier to effectively suppress the continuous side reactions between the positive electrode active material and the sulfide solid electrolyte. In particular, it suppresses the oxidative decomposition of the sulfide electrolyte at high potential, slows down the capacity decay rate of the battery during long cycles, and enables the capacity retention rate to reach more than 90% after 500 cycles under high voltage (4.3V) operating conditions, thereby improving cycle life.

[0033] 3. This invention constructs a stable electrochemical interface and, through pressure, causes the particles inside the electrode to pack tightly, thereby enhancing the mechanical structural strength of the positive electrode itself. This helps to buffer the volume change of the positive electrode active material during repeated lithium ion insertion and extraction, slowing down the electrode failure process caused by particle pulverization or interface peeling, thus ensuring the long-term reliability of the battery. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the interface microstructure of the present invention;

[0035] Figure 2 This is a graph showing the AC impedance variation of the present invention;

[0036] Figure 3 This is a comparison chart of the cycle performance retention rate of the present invention. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] Preparation Examples 1-4:

[0039] Preparation Example 1:

[0040] This preparation example provides an Argyrodite-type sulfide solid electrolyte with an average particle size D50 controlled in the range of 0.8 μm to 1.2 μm, comprising the following steps:

[0041] In an argon glove box with a dew point below -60°C and an oxygen content below 0.1 ppm; according to , Accurately weigh the raw material powder according to the molar ratio (this ratio corresponds to the synthesis of the chlorine-rich phase). ).

[0042] The weighed raw materials are loaded into a zirconia ball mill jar equipped with zirconia balls, with the ball-to-material mass ratio set at 15:1.

[0043] After sealing the milling jar, the powder was removed and subjected to high-energy ball milling at 500 rpm for 20 hours using a planetary ball mill to obtain amorphous precursor powder. The precursor powder was placed in a carbon-coated quartz tube, sealed under vacuum conditions (vacuum degree better than 1 Pa), and then placed in a tube furnace.

[0044] The sintered block was heated to 500℃ at a heating rate of 2℃ / min and held for 8 hours. It was then allowed to cool naturally to room temperature in the furnace to obtain a well-crystallized sintered block. The sintered block was initially pulverized using an agate mortar in a glove box, followed by refining using an air jet mill under 0.4MPa nitrogen pressure. The powder was then sieved through an 800-mesh sieve to obtain Argyrodite-type sulfide solid electrolyte powder with an average particle size D50 of approximately 1.0μm.

[0045] Preparation Example 2:

[0046] This preparation example provides an Argyrodite-type sulfide solid electrolyte with an average particle size D50 controlled in the range of 4.0 μm to 5.0 μm, comprising the following steps:

[0047] The molar ratio and weighing procedures of the raw materials are exactly the same as those in Preparation Example 1.

[0048] ( The raw materials are loaded into the ball mill jar. To reduce mechanical energy input and retain some structure, the ball-to-material mass ratio is set to 10:1.

[0049] The ball milling speed was set to 350 rpm, and the milling time was 12 hours to obtain precursor powder. The sintering process was the same as in Preparation Example 1, and the powder was held at 500°C for 8 hours.

[0050] After sintering, the block was mechanically ground in a glove box and sieved through a 400-mesh sieve. The sieve-undersized material was collected, and finally Argyrodite-type sulfide solid electrolyte powder with an average particle size D50 of about 4.5 μm was obtained.

[0051] Preparation Example 3:

[0052] This preparation example provides a modified polymer binder solution for a positive electrode, comprising the following steps:

[0053] Solvent-based styrene-butadiene rubber (SBR) was selected as the solute and cut into small pieces with a side length of less than 5 mm. Anhydrous xylene was weighed and added to the reactor as the solvent in a dry room with a dew point below -50°C. The stirrer was turned on and the speed was set to 300 rpm. The SBR pieces were slowly added to the xylene, maintaining a mass ratio of SBR to xylene of 5:95.

[0054] The temperature of the reactor was raised to 50°C and stirred continuously for 24 hours until the SBR was completely dissolved. The solution was transparent or microemulsion and free of visible particles. After filtration through a 200-mesh filter, an SBR binder solution with a solid content of 5 wt% was obtained.

[0055] Preparation Example 4:

[0056] This preparation example provides a modified polymer binder solution for positive electrodes, comprising the following steps: Hydrogenated nitrile butadiene rubber (H-NBR) is selected as the solute and chopped. Anhydrous anisole is weighed as the solvent in a dry room environment with a dew point below -50°C. H-NBR blocks are added to the anisole, controlling the mass ratio of H-NBR to anisole to be 4:96. The mixture is magnetically stirred at 500 rpm for 48 hours under a 60°C water bath heating condition to ensure the polymer chains are fully extended and dissolved. After cooling to room temperature, the solution is filtered through a 200-mesh filter to obtain an H-NBR binder solution with a solid content of 4 wt%.

[0057] Examples 1-4:

[0058] Example 1:

[0059] This embodiment provides a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode, including the following steps:

[0060] Preparation of positive electrode slurry:

[0061] In an argon-filled glove box, the positive electrode active material NMC811, the Argyrodite-type sulfide solid electrolyte obtained in Preparation Example 1, the conductive agent acetylene black, and the SBR binder solution obtained in Preparation Example 3 were weighed. The mass ratio of each component (on a dry weight basis) was: NMC811: solid electrolyte: acetylene black: SBR = 85:12:1.5:1.5. An appropriate amount of anhydrous xylene was added to adjust the solid content of the slurry to 60 wt%. The mixture was dispersed at 2000 rpm for 20 minutes using a planetary mixer to obtain a uniform positive electrode slurry.

[0062] Forming of the positive electrode: The positive electrode slurry prepared above was coated onto the surface of a carbon-coated aluminum foil with a thickness of 15 μm using an automatic coating machine. The wet film coating thickness was set to 150 μm. The coated electrode was placed in a vacuum oven and dried at 100°C for 4 hours to remove the solvent, thus obtaining the positive electrode precursor.

[0063] Preparation of stabilized positive electrode (in-situ interface formation): The dried positive electrode precursor was placed in a precision flatbed hot press. Under an argon atmosphere, the heat treatment temperature was set to 180℃, the applied pressure was 30MPa, and the holding time was 30 minutes. After the treatment, the electrode was cooled to room temperature in the furnace to obtain a positive electrode with an in-situ formed stable layer.

[0064] Preparation of solid electrolyte layer: Weigh 80 mg of Argyrodite type sulfide solid electrolyte powder obtained in Preparation Example 1, place it in a mold with a diameter of 10 mm, apply a pressure of 30 MPa for cold pressing, and form an electrolyte layer with a thickness of about 100 μm.

[0065] Battery Assembly: The prepared positive electrode sheet was punched into a 10mm diameter disc and placed on one side of the electrolyte layer. A 10mm diameter, 100μm thick lithium-indium alloy foil was placed on the other side of the electrolyte layer as the negative electrode. The three-layer structure was subjected to cold isostatic pressing (CIP) at 500MPa for 3 minutes to ensure tight contact. Finally, the compacted cell was placed in a 2032 coin cell casing and sealed to obtain an all-solid-state secondary battery.

[0066] Example 2:

[0067] This embodiment provides a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode, including the following steps:

[0068] Preparation of positive electrode slurry: The types and proportions of raw materials are the same as in Example 1.

[0069] The forming of the positive electrode sheet: the coating and drying process is the same as in Example 1.

[0070] Preparation of stabilized positive electrode sheet: The dried positive electrode sheet precursor was placed in a flatbed hot press. The heat treatment temperature was set to 250℃, the applied pressure was 10MPa, and the holding time was 10 minutes. After the treatment, the sheet was cooled to room temperature in the furnace to obtain the stabilized positive electrode sheet.

[0071] Preparation of the solid electrolyte layer: Same as in Example 1.

[0072] Battery assembly: Same as in Example 1.

[0073] Example 3:

[0074] This embodiment provides a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode, including the following steps:

[0075] Preparation of the positive electrode slurry: The large-particle-size Argyrodite type sulfide solid electrolyte obtained in Preparation Example 2 and the H-NBR binder solution obtained in Preparation Example 4 were selected. The solvent was replaced with anhydrous anisole. The mass ratio of each component (on a dry weight basis) was: NMC811: solid electrolyte: acetylene black: H-NBR = 80:16:2:2. The mixture was dispersed at 2500 rpm for 15 minutes using a high-speed disperser.

[0076] Forming of the positive electrode: The slurry is coated onto the surface of carbon-coated aluminum foil, with a wet film thickness of 200 μm. It is then dried under vacuum at 90 °C for 6 hours.

[0077] Preparation of stabilized positive electrode sheet: The dried positive electrode sheet precursor was placed in a flatbed hot press. The heat treatment temperature was set to 100℃, the applied pressure to 100MPa, and the holding time to 120 minutes. After the treatment, the sheet was cooled to room temperature in the furnace to obtain the stabilized positive electrode sheet.

[0078] Preparation of the solid electrolyte layer: The solid electrolyte powder obtained in Preparation Example 2 was used, and the remaining steps were the same as in Example 1.

[0079] Battery assembly: A 100μm thick lithium metal foil was used as the negative electrode, and the remaining assembly steps were the same as in Example 1.

[0080] Example 4:

[0081] This embodiment provides a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode, including the following steps:

[0082] Preparation of positive electrode slurry: Lithium cobalt oxide (LiCO) was selected. As the positive electrode active material, the remaining raw materials were the solid electrolyte from Preparation Example 1 and the H-NBR binder solution from Preparation Example 4. The mass ratio of each component (on a dry weight basis) was: LiCoO2: solid electrolyte: acetylene black: H-NBR = 88:10:1:1.

[0083] Forming of the positive electrode: The wet film thickness is 120μm, and it is dried under vacuum at 110℃ for 3 hours.

[0084] Preparation of stabilized positive electrode: The dried positive electrode precursor was placed in a flatbed hot press. The heat treatment temperature was set to 150℃, the applied pressure to 50MPa, and the holding time to 60 minutes. After treatment, the electrode was cooled to room temperature in the furnace.

[0085] Preparation of the solid electrolyte layer: Same as in Example 1.

[0086] Battery assembly: Same as in Example 1.

[0087] Comparative Examples 1-4:

[0088] Comparative Example 1:

[0089] This comparative example provides an all-solid-state secondary battery as a blank control to demonstrate the battery performance without in-situ interface stabilization treatment, including the following steps:

[0090] The preparation process of the positive electrode slurry and the forming process of the positive electrode sheet are exactly the same as in Example 1.

[0091] Treatment of positive electrode sheet: The dried positive electrode sheet precursor is stored at room temperature (25℃) and normal pressure (0.1MPa) without any additional heating or pressurization.

[0092] The preparation of the solid electrolyte layer and the battery assembly steps are the same as in Example 1.

[0093] Comparative Example 2:

[0094] This comparative example provides an all-solid-state secondary battery, including the following steps:

[0095] The preparation process of the positive electrode slurry and the forming process of the positive electrode sheet are exactly the same as in Example 1.

[0096] Positive electrode processing: The dried positive electrode precursor is placed in a flatbed hot press. The heat treatment temperature is set to 180°C, but the applied pressure is adjusted to 350 MPa, and the holding time is 30 minutes. This pressure is higher than the protection range of this invention, simulating the traditional high-pressure densification process. After processing, it is cooled to room temperature in the furnace.

[0097] The preparation of the solid electrolyte layer and the battery assembly steps are the same as in Example 1.

[0098] Comparative Example 3:

[0099] This comparative example provides an all-solid-state secondary battery, including the following steps:

[0100] The preparation process of the positive electrode slurry and the forming process of the positive electrode sheet are exactly the same as in Example 1.

[0101] Positive electrode processing: The dried positive electrode precursor was placed in a flatbed hot press. The applied pressure was set to 30 MPa, but the heat treatment temperature was adjusted to 350°C, and the holding time was 30 minutes. This temperature exceeded the thermal stability window of the sulfide solid electrolyte. After processing, the electrode was cooled to room temperature in the furnace.

[0102] The preparation of the solid electrolyte layer and the battery assembly steps are the same as in Example 1.

[0103] Comparative Example 4:

[0104] This comparative example provides an all-solid-state secondary battery, including the following steps:

[0105] The preparation process of the positive electrode slurry and the forming process of the positive electrode sheet are exactly the same as in Example 1.

[0106] Positive electrode processing: The dried positive electrode precursor is placed in a flatbed hot press. The heat treatment temperature is set to 180℃, but the applied pressure is adjusted to 5MPa, and the holding time is 30 minutes. This pressure is insufficient to form a tight physical contact between the solid particles. After processing, the sample is cooled to room temperature in the furnace.

[0107] The preparation of the solid electrolyte layer and the battery assembly steps are the same as in Example 1.

[0108] Test Example 1-2:

[0109] Test Example 1: Initial Internal Resistance Test of Battery;

[0110] For the all-solid-state secondary batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 4, their initial resistivity per unit area was determined by electrochemical impedance spectroscopy (EIS) to evaluate the interfacial charge transport characteristics. Measurements were performed using a Solartron 1260A impedance analyzer combined with a 1287A electrochemical interface analyzer. The assembled batteries were placed in a 25°C incubator for 4 hours to reach thermal equilibrium before testing was initiated. The test frequency range was set from 10 MHz to 0.1 Hz, the applied AC voltage amplitude was 10 mV, and the DC bias voltage was set to the open-circuit voltage (OCV). The obtained electrochemical impedance spectra (Nyquist plots) are shown below. Figure 2As shown. The acquired impedance data was fitted using ZView software, based on... Figure 2 Calculate the total resistance value by taking the intercept of the semicircle with the real axis and the diameter of the semicircle in the high-frequency region, and combine this with the electrode geometry ( The resistance per unit area (ASR) is obtained by conversion.

[0111] The test results are shown in the table below:

[0112] Table 1. Initial sheet resistance test results of all-solid-state batteries in each embodiment and comparative example.

[0113]

[0114] Conclusions and Analysis:

[0115] Table 1 shows that the initial surface resistivity values ​​of Examples 1 to 4 are distributed as follows: to Between them, all were lower than that of comparative example 1. This confirms that the specific temperature and pressure treatment process (10-100MPa pressure and 100-250℃ temperature) described in this invention promotes the formation of an ion-conducting phase at the interface between the positive electrode active material and the sulfide solid electrolyte, thereby reducing the interfacial charge transfer resistance.

[0116] The test results verified that... Figure 1 The interface modification mechanism is shown. For example... Figure 1 As shown in ② (of the present invention), through the process of the present invention, a stable layer (reference numeral 4) is formed in situ between the positive electrode active material layer (reference numeral 1) and the solid electrolyte layer (reference numeral 3). This stable layer not only establishes a physical tight connection, but also constructs an effective lithium-ion conduction pathway. Figure 1 (as shown by the dashed arrow in the middle) and electron conduction pathways ( Figure 1 (As indicated by the solid arrow in the middle), thus achieving a lower interface resistance in the embodiment.

[0117] The resistance value of Comparative Example 1 is Its interface state corresponds to Figure 1 In section ① (Prior Art), due to the lack of specific temperature and pressure induction, an uncontrolled spontaneous reaction occurred between the positive electrode active material layer (labeled 1) and the solid electrolyte layer (labeled 3), generating a reaction layer (labeled 2) mainly composed of decomposition products. For example... Figure 1 As shown, the reaction layer blocks or hinders the effective transport of lithium ions and electrons, resulting in an interface impedance higher than that of the example.

[0118] Comparative Example 2 showed a high resistance after treatment under 350 MPa pressure. Data shows that high voltage exceeding the protection limit causes mechanical damage and lattice distortion in layered oxide cathode particles, disrupting the internal conductive network. Although the high voltage physically compresses the interface, the newly formed surface caused by particle breakage triggers side reactions in the electrolyte, which in turn exacerbates the problem. Figure 1 The tendency to form a reaction layer, as shown in ①, increases the interfacial impedance.

[0119] Comparative Example 3, after treatment at 350℃, has a resistance value of The impedance is higher than in the example because the processing temperature exceeded the upper limit of the thermal stability of the Argyrodite-type sulfide electrolyte, resulting in phase transition decomposition of the electrolyte and loss of sulfur, generating a decomposition product layer with low ionic conductivity.

[0120] Comparative Example 4, after treatment under 5 MPa pressure, has a resistance value of Although lower than Comparative Example 1, it is still higher than Example 1. (Combined) Figure 1 Mechanism analysis revealed that the low-pressure treatment failed to create sufficient physical contact area between the positive electrode particles and the electrolyte particles, leading to... Figure 1 The stable layer shown in ② cannot be formed continuously, the lithium-ion conduction pathway (dashed arrow) is blocked, and the contact resistance is large.

[0121] Based on the above data and Figure 1 Mechanism model Figure 2 Based on measured data, this invention achieves minimal interfacial resistance by synergistic processing within a range of 10MPa to 100MPa and 100℃ to 250℃, while ensuring the integrity of the material structure. The process parameters of Example 1 (30MPa / 180℃) correspond to the lowest resistance value. This indicates that a stable layer is formed under these conditions. Figure 1 The structure labeled 4) is most favorable for the interfacial transport of lithium ions.

[0122] Figure 2 Initial internal resistance ( () indicates the initial surface resistance; Example indicates an embodiment; Comparison Example indicates a comparative example.

[0123] Test Example 2: High Voltage Cyclic Performance Test;

[0124] Long-cycle performance tests under high-voltage conditions were conducted on the all-solid-state secondary batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 4. A Neware battery testing system (CT-4008) was used, and the assembled coin cells were placed in a 25°C constant-temperature chamber. The test voltage window was set from 3.0V to 4.3V (relative to...). The charge / discharge regime adopted a constant current charge-constant current discharge (CC-CC) mode, with both charge and discharge rates set to 0.1C. The change in the battery's discharge specific capacity during cycling was recorded, and a typical cycle performance curve is shown below. Figure 3 As shown. The specific discharge capacity of each battery in the first cycle and the specific discharge capacity after 500 cycles are statistically analyzed, and the capacity retention rate after 500 cycles is calculated.

[0125] The test data is shown in the table below:

[0126] Table 2. High-voltage cycling performance test results of all-solid-state batteries in each embodiment and comparative example.

[0127]

[0128] Conclusions and Analysis:

[0129] Table 2 data and Figure 3 The cycling curves show that the capacity retention rates of Examples 1 to 4 after 500 cycles are all between 88% and 94%, with Example 1 reaching 94%, which is superior to the comparative examples. This indicates that under the limited temperature and pressure process, a stable buffer layer is formed in situ at the interface between the positive electrode active material and the solid electrolyte. This interface layer blocks the direct contact between the positive electrode surface and the sulfide electrolyte during charge and discharge, effectively inhibiting the oxidative decomposition of the sulfide electrolyte at high potentials.

[0130] Figure 3 The "After 500 cycles" capacity retention rate (%) represents the capacity retention rate after 500 cycles; "Example" indicates a specific example; "Comparison Example" indicates a comparative example.

[0131] The capacity retention of Comparative Example 1 (untreated) was only 65%. Due to the lack of an in-situ generated stabilizing layer, the cathode material was directly exposed to the sulfide electrolyte, and side reactions continued to occur at the interface during cycling, resulting in increased interfacial impedance and loss of active lithium.

[0132] The capacity retention of Comparative Example 2 (ultra-high voltage 350 MPa) was 70%, lower than that of Example 1 and Comparative Example 4 (low voltage 75%). The data confirms that while high voltage provides initial contact, excessive pressure causes mechanical breakage of the layered cathode particles. Figure 3 Analysis of the degradation trend shows that the newly formed surfaces generated by particle breakage continuously exacerbate electrolyte decomposition during cycling, and internal cracks in the particles lead to electrical isolation of active materials. This indicates that the negative impact of structural damage caused by ultra-high pressure on cycle life far outweighs the positive benefits brought by densification.

[0133] Comparative Example 3 (high temperature 350℃) showed a capacity retention of 78%. Although the high temperature promoted interfacial fusion, 350℃ exceeded the thermal stability limit of the sulfide electrolyte, causing some electrolyte to undergo thermal decomposition during the preparation stage. Although the resulting decomposition products covered the cathode surface to some extent, they had low ionic conductivity and unstable structure, making them unable to support long-term lithium-ion insertion / extraction.

[0134] Comparative Example 4 (low pressure 5 MPa) maintained a capacity of 75%. Due to insufficient pressure, a tight physical contact could not be formed between the cathode particles and the electrolyte. During long-term cycling, with the repeated expansion and contraction of the cathode material's lattice volume, physical delamination easily occurred at the interface, leading to contact failure.

[0135] In summary, the temperature-pressure coupling process (10-100 MPa and 100-250 °C) employed in this invention balances interfacial physical contact with electrochemical stability. Data from Example 1 (94%) confirms that these process conditions can construct an optimal interfacial structure that is both adaptable to volume changes and resistant to high-voltage oxidation, thereby maximizing the cycle life of all-solid-state batteries.

Claims

1. A high-performance all-solid-state secondary battery equipped with a stabilized positive electrode, characterized in that, include: Positive electrode, negative electrode layer, and solid electrolyte layer located between the positive electrode and negative electrode layer; The positive electrode sheet is made by coating a positive electrode slurry onto a current collector, followed by drying and heating / pressurization. The positive electrode slurry contains the following raw materials by weight percentage: Positive electrode active material: 80%-88%; Sulfide solid electrolyte: 10%-16%; Conductive agent: 1%-2%; Adhesive: 1%-2%.

2. A high-performance all-solid-state secondary battery equipped with a stabilized positive electrode according to claim 1, characterized in that, The positive electrode active material is selected from layered lithium nickel cobalt manganese oxide or lithium cobalt oxide; the sulfide solid electrolyte is an Argyrodite type sulfide solid electrolyte; the conductive agent is acetylene black; and the binder is selected from styrene-butadiene rubber or hydrogenated nitrile rubber.

3. A high-performance all-solid-state secondary battery equipped with a stabilized positive electrode according to claim 1, characterized in that, The Argyrodite-type sulfide solid electrolyte has an average particle size D50 of 0.8 μm to 5.0 μm; the sulfide solid electrolyte is composed of... , It was prepared by reacting with LiCl in a molar ratio of 2.0:0.5:1.

5.

4. A method for preparing a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode, characterized in that, The application of a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode as described in any one of claims 1-3 includes the following steps: A positive electrode slurry is prepared by dispersing the positive electrode active material, sulfide solid electrolyte, conductive agent and binder in a solvent. The positive electrode slurry is coated onto the surface of the current collector, and the solvent is removed by drying to obtain the positive electrode precursor; The positive electrode precursor is heated and pressurized under an inert atmosphere to obtain the positive electrode. The heat treatment temperature for the heating and pressurizing process is 100℃-250℃, and the applied pressure is 10MPa-100MPa. The positive electrode, solid electrolyte layer and negative electrode layer are assembled to obtain a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode.

5. The method for preparing a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode according to claim 4, characterized in that, The holding time for the heating and pressurizing treatment is 10 minutes to 120 minutes.

6. The method for preparing a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode according to claim 4, characterized in that, The adhesive is added in the form of an adhesive solution; When the binder is styrene-butadiene rubber, the solvent is anhydrous xylene; When the binder is hydrogenated nitrile rubber, the solvent is anhydrous anisole.

7. The method for preparing a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode according to claim 6, characterized in that, The adhesive solution is prepared by the following steps: The shredded adhesive solute is added to the solvent and stirred at 50℃-60℃ for 24-48 hours. After filtration, an adhesive solution with a solid content of 4wt%-5wt% is obtained.

8. The method for preparing a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode according to claim 4, characterized in that, The sulfide solid electrolyte is prepared by the following steps: The raw material powder was ball-milled to obtain an amorphous precursor, which was then sintered at 500°C for 8 hours under vacuum conditions. After cooling, it was pulverized and sieved to obtain the final product.

9. The method for preparing a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode according to claim 4, characterized in that, The drying is carried out under vacuum conditions, at a temperature of 90℃-110℃, for a time of 3-6 hours.

10. A method for preparing a high-performance all-solid-state secondary battery equipped with a stabilized positive electrode according to claim 4, characterized in that, The negative electrode layer is selected from lithium indium alloy foil or metallic lithium foil; The assembly process also includes applying a cold isostatic pressing treatment of 500 MPa to the three-layer structure of the positive electrode, solid electrolyte layer and negative electrode layer.

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