Method for testing thermal stability of composite positive electrode layer of solid-state battery

Abstract

The invention provides a method for testing the thermal stability of a composite positive electrode layer of a solid-state battery. The test method comprises the following steps: charging a mold battery to a target voltage under a constant current-constant voltage to reach a preset electric quantity state; disassembling the mold battery under a preset electric quantity state, stripping the composite positive electrode layer to obtain a composite positive electrode material, and manufacturing the composite positive electrode material into a plurality of first to-be-tested samples; performing thermal analysis on the first to-be-detected sample by using a thermal analysis and mass spectrometer to obtain a main exothermic peak temperature of the composite positive electrode material; the first to-be-tested sample is heated to a first preset temperature and then cooled, a second to-be-tested sample is obtained, the second to-be-tested sample is tested through a scanning electron microscope-energy disperse spectroscopy, and the first preset temperature is the main exothermic peak temperature + / -10 DEG C. According to the method, the thermal stability of the composite positive electrode of the solid-state battery in different electric quantity working states can be truly simulated, and the thermal response characteristic of the composite positive electrode under the heating condition can be more accurately evaluated.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and more specifically, to a test method for the thermal stability of composite cathode layers in solid-state batteries. Background Technology

[0002] With the increasing demand for high energy density and high safety from electric vehicles and energy storage systems, traditional liquid lithium-ion batteries, which use flammable organic electrolytes, pose a risk of fire and explosion under high temperature or abuse conditions, making them unsuitable for the future development requirements of power batteries. All-Solid-State Batteries (ASSBs), using non-flammable solid electrolytes instead of liquid electrolytes, possess excellent thermal stability and mechanical strength, and are considered an important development direction for next-generation high-safety energy storage devices. Among them, sulfide solid electrolytes (such as Li6PS5Cl) have high ionic conductivity (>10). -3 With its good S / cm, excellent ductility, and moderate processing performance, it has become one of the current research hotspots.

[0003] However, under actual operating conditions, especially at full charge, highly delithiated cathode materials (such as NCM) exhibit strong oxidizing properties and are prone to violent interfacial side reactions with reducing sulfide electrolytes, leading to heat generation, gas generation, structural damage, and even thermal runaway. Therefore, accurately assessing the thermal response characteristics of composite cathodes during heating is crucial for revealing their failure mechanisms, guiding material modification, and battery design. Currently, commonly used thermal stability testing methods mainly involve physically mixing the cathode active material with the solid electrolyte and then directly performing DSC or TG-DSC analysis. However, while these methods are simple to operate, they cannot accurately reflect the thermal response characteristics of the composite cathode layer during heating. Summary of the Invention This invention aims to at least partially solve one of the technical problems in related technologies. To this end, one objective of this invention is to propose a test method for the thermal stability of a solid-state battery composite cathode layer. This method can realistically simulate the thermal stability of the solid-state battery composite cathode under different charge levels, and can more accurately evaluate its thermal response characteristics such as exothermic behavior, gas release characteristics, morphological evolution, and element migration patterns under heated conditions.

[0004] In one aspect of the present invention, a method for testing the thermal stability of a composite cathode layer in a solid-state battery is provided. According to an embodiment of the present invention, the method for testing the thermal stability of the composite cathode layer in a solid-state battery includes: charging a mold battery to a target voltage under constant current-constant voltage conditions to reach a predetermined charge state, wherein the composite cathode layer of the mold battery comprises a cathode active material and a solid electrolyte material; disassembling the mold battery under the predetermined charge state, peeling off the composite cathode layer to obtain a composite cathode material, and fabricating the composite cathode material into multiple first test samples; performing thermal analysis on one of the first test samples using a thermal analysis and mass spectrometry (TMS) instrument to obtain the main exothermic peak temperature of the composite cathode material; taking another first test sample, heating it to a first predetermined temperature and then cooling it to obtain a second test sample, and testing the second test sample using a scanning electron microscope-energy dispersive spectroscopy (SEM) instrument, wherein the first predetermined temperature is the main exothermic peak temperature ±10°C. Therefore, this method can realistically simulate the thermal stability of solid-state battery composite cathodes under different charge levels, and can more accurately evaluate their thermal response characteristics such as exothermic behavior, gas release characteristics, morphological evolution and element migration patterns under heated conditions.

[0005] According to an embodiment of the present invention, the method for testing the thermal stability of the composite cathode layer of the solid-state battery further includes: heating the first test sample to different temperatures and then cooling it to perform XPS and / or XRD tests respectively.

[0006] According to an embodiment of the present invention, the method for preparing the composite positive electrode layer includes: uniformly mixing the positive electrode active material and the solid electrolyte material and pressing them under a first pressure to obtain the composite positive electrode layer; the method for preparing the composite positive electrode material into a plurality of first test samples includes: pressing the composite positive electrode material under a second pressure to obtain the first test sample, wherein the first pressure and the second pressure are the same.

[0007] According to an embodiment of the present invention, the first pressure and the second pressure are 300~600 MPa, respectively.

[0008] According to an embodiment of the present invention, the charging amount of the predetermined power state is greater than or equal to 50%, preferably, the predetermined power state is a fully charged state.

[0009] According to an embodiment of the present invention, the composite cathode material has multiple main exothermic peak temperatures. The first test sample is heated to different second predetermined temperatures and then cooled, and XPS and / or XRD tests are performed respectively. The second predetermined temperature is set to the main exothermic temperature ±10℃.

[0010] According to an embodiment of the present invention, the mass mixing ratio of the positive electrode active material and the solid electrolyte material is (6~8):(4~2).

[0011] According to an embodiment of the present invention, the heating rate during the thermal analysis is 3~8℃ / min.

[0012] According to an embodiment of the present invention, the heating rate during the process of heating the first sample to be tested to a first predetermined temperature and then cooling it to obtain the second sample to be tested is consistent with the heating rate during the thermal analysis process.

[0013] According to an embodiment of the present invention, the heating rate during the process of heating the first sample to be tested to different temperatures and then cooling it to perform XPS and / or XRD tests is consistent with the heating rate during the thermal analysis process.

[0014] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0015] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 and Figure 2 These are the TG-DSC curves of the composite cathode layer in Examples 1-3; Figure 3 These are SEM-EDS test images of the composite cathode layer in Example 1 at different temperatures.

[0016] Figure 4 These are XPS test images of the composite cathode layer in Example 1 at different temperatures.

[0017] Figure 5 These are XRD test images of the composite cathode layer in Example 1 at different temperatures. Detailed Implementation

[0018] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0019] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0020] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0021] The terms "first" and "second" used in this document are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature marked "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0022] In one aspect, the present invention provides a method for testing the thermal stability of a composite cathode layer in a solid-state battery. According to an embodiment of the present invention, the method for testing the thermal stability of the composite cathode layer in a solid-state battery includes: S100: Charge the mold battery to the target voltage under constant current and constant voltage to reach the predetermined charge state. The composite positive electrode layer of the mold battery includes positive electrode active material and solid electrolyte material.

[0023] According to some embodiments of the present invention, the mass mixing ratio of the positive electrode active material and the solid electrolyte material is (6~8):(4~2), such as 6:4, 7:3, 8:2, etc. The above ratio can accurately reflect the material state of the composite positive electrode layer in the solid-state battery.

[0024] According to some embodiments of the present invention, a method for preparing a composite positive electrode layer includes: uniformly mixing a positive electrode active material and a solid electrolyte material in a certain proportion, and then pressing them under a first pressure to obtain a composite positive electrode layer. In some embodiments, the first pressure is 300~600 MPa, such as 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, 550 MPa, 600 MPa, etc. Therefore, under the above pressure, the positive electrode active material and the solid electrolyte material can be in closer contact, the capacity of the materials can be fully utilized, and the thermal response characteristics of the composite positive electrode layer can be tested more accurately. In some specific embodiments, the first pressure is 450 MPa.

[0025] According to some embodiments of the present invention, there are no specific requirements for the materials of the positive active material and the solid electrolyte material. Those skilled in the art can flexibly select suitable negative electrode materials according to actual needs. For example, the positive active material includes, but is not limited to, layered oxide positive electrode materials (such as LiCoO2 (LCO), LiNi). x Co y Mn 1-x-y O2 (NCM, such as NCM811 / 622), LiNi x Co y Al 1-x-y O2 (NCA), where x is 0~1, y is 0~1, and 1-xy is 0~1; polyanionic cathode materials; spinel cathode materials; and solid electrolyte materials including sulfide solid electrolytes (such as Li7P3S). 11 (LPS), Li6PS5Cl (LPSC), Li3PS4 (LPS), Li 10 GeP2S 12 (LGPS)), oxide solid electrolytes and halide solid electrolytes, at least one of them.

[0026] According to some embodiments of the present invention, there are no limitations on the negative electrode material of the mold battery, and those skilled in the art can flexibly select a suitable negative electrode material according to actual needs.

[0027] According to some embodiments of the present invention, the charge level of the predetermined charge state is greater than or equal to 50%. In some specific embodiments, the predetermined charge state is a fully charged state. In this way, the thermal stability of the solid-state battery composite cathode in the working state can be simulated more realistically, and its thermal response characteristics such as exothermic behavior, gas release characteristics, morphological evolution and element migration laws under heated conditions can be evaluated more accurately.

[0028] In some specific embodiments, the preparation method of the mold battery may include: uniformly mixing the positive active material and the solid electrolyte at a predetermined mass ratio, and hand-milling to ensure uniform dispersion; then pressing the mixed material into a disc of predetermined diameter (e.g., 10 mm) as the positive electrode layer under a first pressure in a high-pressure mold; assembling the mold battery with lithium indium alloy as the negative electrode. The assembled mold battery is then placed in an inert atmosphere (argon) for a certain time (e.g., 10 h), and charged to the target voltage using a constant current-constant voltage (CC-CV) mode, with a cutoff current of 0.02C, to ensure that the predetermined state of charge is reached.

[0029] S200: Disassemble the mold battery under a predetermined charge state, peel off the composite positive electrode layer to obtain the composite positive electrode material, and make multiple first test samples from the composite positive electrode material.

[0030] According to some embodiments of the present invention, a method for preparing multiple first test samples from composite cathode materials includes: pressing the composite cathode material under a second pressure of 300-600 MPa to obtain the first test samples; further, the first pressure and the second pressure are the same. This effectively preserves the original interfacial chemical state and microstructure of the composite cathode material after electrochemical cycling.

[0031] According to some embodiments of the present invention, the first sample to be tested can be a small disc with a diameter of 3-4 mm, the disc diameter being less than the diameter of a 70 μL alumina crucible (5 mm).

[0032] S300: Take a first sample to be tested and perform thermal analysis using a thermo-analytical mass spectrometer (TG-DSC-MS) to obtain the main exothermic peak temperature of the composite cathode material.

[0033] According to some embodiments of the present invention, during the thermal analysis, the heating rate is 3~8℃ / min, such as 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, etc. A suitable heating rate can improve the resolution of the testing process, reduce thermal hysteresis, and improve baseline stability. According to some embodiments of the present invention, the composite cathode material has multiple main exothermic peak temperatures.

[0034] According to some embodiments of the present invention, the specific steps of thermal analysis may include: placing the first sample to be tested in a 70 μL alumina crucible and performing TG-DSC-MS coupled testing under an inert atmosphere (such as high-purity argon, flow rate 50 mL / min). In some embodiments, the heating rate is 5 °C / min, the temperature range is room temperature to 500 °C, and the following data are recorded in real time: the initial exothermic temperature in the DSC curve, the total heat release, the mass change corresponding to TG, and the mass-to-charge ratio signal of key gaseous products monitored in real time by MS, including: m / z = 32 (O2), m / z = 48 (SO), and m / z = 64 (SO2).

[0035] S400: Take another first test sample, heat the first test sample to a first predetermined temperature and then cool it to obtain a second test sample, and use a scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) to test the second test sample. The first predetermined temperature is the main exothermic peak temperature ±10℃.

[0036] According to some embodiments of the present invention, the composite cathode material has multiple main exothermic peak temperatures. Thus, a second test sample can be tested at at least one main exothermic peak temperature using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Specifically, the first test sample can be heated to different predetermined temperatures and then cooled to obtain second test samples treated at different temperatures. These second test samples obtained at different temperatures are then tested using SEM-EDS. This allows for better analysis and comparison of the thermal stability of the composite cathode material at different temperatures.

[0037] According to some embodiments of the present invention, the heating rate during the process of heating the first test sample to a first predetermined temperature and then cooling it to obtain the second test sample is consistent with the heating rate during the thermal analysis process. Therefore, the consistency of the heating state of the composite cathode material can be maintained, improving the consistency of the test results.

[0038] S500: The first test sample (or another first test sample) is heated to different temperatures and then cooled for XPS and / or XRD tests. This allows for accurate identification of decomposition paths, phase transition mechanisms, and interfacial reaction processes through multi-dimensional data correlation, providing a more comprehensive theoretical basis for the optimization of composite cathode materials.

[0039] According to some embodiments of the present invention, the composite cathode material has multiple main exothermic peak temperatures. A first test sample is heated to different second predetermined temperatures and then cooled, followed by XPS and / or XRD tests. The second predetermined temperature is set to the main exothermic temperature ±10°C. Thus, testing the XPS and / or XRD of the composite cathode material after heating to different temperatures allows for better analysis and comparison of the thermal stability of the composite cathode material at different temperatures.

[0040] In some embodiments, in addition to the second predetermined temperature mentioned above, XPS and / or XRD tests can be performed at other temperature points, so that the thermal stability of the composite cathode material at different temperatures can be analyzed and compared more comprehensively and better. For example, a temperature greater than the maximum main exothermic peak temperature can be selected.

[0041] According to some embodiments of the present invention, the heating rate during the process of heating the first sample to be tested to different temperatures and then cooling it for XPS and / or XRD tests is consistent with the heating rate during the thermal analysis process. This maintains the consistency of the heating state of the composite cathode material and improves the consistency of the test results.

[0042] According to embodiments of the present invention, the above-described testing method allows the composite cathode material to undergo real electrochemical cycling, reflecting the real chemical environment (such as lithium vacancy concentration, lattice distortion, interface phase transition, etc.) under different charge states. It can reproduce the dense contact and local stress distribution formed during battery assembly, taking into account the influence of interface passivation layers or by-reaction products that may be formed during charging and discharging. Thus, this method can realistically simulate the thermal stability of the composite cathode of solid-state batteries under different charge states, and can more accurately evaluate its thermal response characteristics such as exothermic behavior, gas release characteristics, morphological evolution, and element migration patterns under heated conditions. It can even perform microstructure, elemental composition, and valence state analysis by pinpointing the macroscopic heat generation location. The obtained data can provide theoretical basis and technical support for the design of high-safety solid-state batteries, and assist in material screening and interface modification strategy development.

[0043] In the above-mentioned testing method of this invention, data from four dimensions—heat generation, gas generation, morphology, and composition—can be integrated to establish a multi-parameter evaluation system for the thermal stability of composite cathodes, comprehensively revealing the thermal runaway mechanism: "heat generation" reflects the overall thermal risk level of the system; "gas generation" identifies potential explosion hazards and side reaction pathways; "morphology" reveals the degree of structural damage and crack propagation behavior; and "composition" elucidates the mechanism of element migration and new phase formation. In other words, the above-mentioned testing method of this invention achieves closed-loop analysis from macroscopic thermal behavior to microscopic mechanisms, and can be used for comparative studies of thermal stability under different cathode materials, electrolyte ratios, and charging strategies.

[0044] Furthermore, the testing method of this invention employs standardized pressing, assembly, and testing procedures, thereby ensuring experimental repeatability and data comparability. Additionally, the testing method of this invention is applicable to various composite cathode systems based on solid-state electrolytes (such as NCM, NCA, LFP, LMFP, etc.).

[0045] According to embodiments of the present invention, the method uses TG-DSC-MS to determine the temperature point corresponding to the thermal reaction and performs fixed-point sampling characterization using the exothermic peak temperature, jointly revealing the thermal reaction failure mechanism of the composite cathode layer, including LiNi x Co y Mn 1-x-y Taking the composite cathode layer of O2 and sulfide solid electrolyte LPSC as an example, TG-DSC-MS testing of this composite cathode layer yields three main exothermic peak temperatures: the first exothermic peak temperature K1, the second exothermic peak temperature K2, and the third exothermic peak temperature K3. The specific reaction mechanism is as follows: Firstly, at the first exothermic peak temperature (K1), gaseous oxygen and sulfur dioxide are generated, corresponding to the transformation of the layered structure to a spinel structure, accompanied by the release of lattice oxygen (O2). The sample was heated to K1±10℃, cooled, and then subjected to XPS and XRD tests. The XPS results further confirmed the presence of P2S in the S 2p spectrum within this temperature range. x and (SO3) 2- Characteristic peaks, P2S appears in the P2p spectrum x The characteristic peaks of the radical indicate that the released oxygen undergoes a mild redox reaction with LPSC, and LPSC is oxidized to P2S. x And sulfite species. Combining XRD and SEM results, no new phases were formed in the system at this stage, and no elements diffused, indicating that the interfacial reaction was weak. The heat release mainly came from the superposition of phase transformation and mild interfacial reaction, and the microstructure and phases remained intact.

[0046] The second exothermic peak temperature (K2) indicates intense interfacial reaction and product formation. The sample was heated to K2±10℃, cooled, and then subjected to XPS and XRD tests. XPS data showed that at this temperature, the S 2p spectrum exhibited characteristic peaks for NiS / CoS, and the P 2p spectrum showed (PO4) peaks. 3- Characteristic peaks indicate that LPSC undergoes significant decomposition, S 2- Ni produced after oxidation and decomposition of NCM 2+ Co 2+ Mn 2+ Metal sulfides are formed by the combination of phosphorus and oxygen, while phosphorus combines with oxygen to form phosphates. XRD data simultaneously verified this process, with characteristic peaks for LiCl and NiO appearing at 320℃, confirming the Cl- produced by the decomposition of LPSC. - With Li + The reaction combines to form LiCl, while NCM decomposes to produce NiO. This stage of the reaction is intense, releasing a large amount of heat, corresponding to the second exothermic peak temperature in TG-DSC, and the phase and microstructure begin to show significant damage.

[0047] The third exothermic peak (K3) indicates complete reaction and structural disintegration. The sample was heated to K3 ± 10℃, cooled, and then subjected to XPS and XRD tests. XPS characterization showed the appearance of the S 2p spectrum (SO4). 2- Characteristic peaks indicate that the oxidation reaction further deepens, generating sulfate species. XRD data confirms that at this temperature, the original characteristic peaks of NCM and LPSC completely disappear, transforming entirely into final products such as LiCl, NiO, Li3PO4, MnS, CoS, and sulfates. SEM images show that particle boundaries completely disappear, and elements undergo comprehensive mixing and diffusion, indicating that the system has undergone complete reaction. This stage involves a sustained exothermic reaction, completely destroying the crystal structure and microstructure of the system, and resulting in a complete loss of thermal stability.

[0048] As can be seen from the above, the high-temperature reaction between solid electrolyte materials (such as sulfides, halides, and oxides) and positive electrode active materials (such as NCM and LCO) may produce gaseous products such as O2, S, and P. The generation mechanism of these gases is crucial to battery safety, but TG-DSC cannot provide this information. Furthermore, during TG-DSC testing, the evolution of the material's microstructure (such as grain boundary cracks, interface delamination, and surface reconstruction of positive electrode particles) cannot be observed in situ. Therefore, simply performing TG-DSC testing on the composite positive electrode layer cannot provide a mechanistic explanation for the specific thermal reactions. In this invention, the stability testing method, based on TG-DSC, combines MS, XPS, and XRD testing techniques to fully and comprehensively analyze the reactions of composite positive electrode materials at different temperatures, as well as the changes in materials and reaction products. This provides a more sufficient theoretical basis and technical support for the design of high-safety solid-state batteries, and assists in material screening and the development of interface modification strategies.

[0049] Example Example 1 Lithium nickel cobalt manganese oxide (LiNi) x Co y Mn 1-x-yO2, where x=0.92, y=0.2 (92SN), was uniformly mixed with sulfide solid electrolyte LPSC at a predetermined mass ratio of 7:3. The mixture was then pressed into 10mm diameter discs in a high-pressure mold under a pressure of 450 MPa to serve as the positive electrode layer. A lithium-indium alloy was used as the negative electrode to assemble a mold battery. After standing at 100 MPa for 10 h, the mold battery was charged to the cutoff voltage using a 0.1C constant current-constant voltage (CC-CV) mode. The cutoff current was 0.02C, and the cutoff voltage was 3.78V. The mold battery was disassembled under full charge, and 10 mg of the composite positive electrode layer was scraped off and pressed again into 4mm diameter discs under 450 MPa. TG-DSC-MS was used for testing: heating rate 5℃ / min, final temperature 500℃, argon atmosphere (50 mL / min), using a 70μL Al2O3 crucible. The main exothermic peak temperatures K1, K2, and K3 were obtained through testing. The test results are shown in [reference missing]. Figure 1 and Figure 2 Simultaneously, MS was used to monitor the signals at m / z=32 (O2), m / z=48 (SO), and m / z=64 (SO2). Small discs were also taken and sampled at room temperature, heated to the main exothermic peak temperature K1±10℃, and K3±10℃, respectively, and then cooled for SEM-EDS analysis. Small discs were also heated to different temperatures and then tested for XPS and XRD.

[0050] The TG-DSC-MS test results in Examples 1-3 can be found in Table 1.

[0051] Table 1

[0052] In Example 1, the composite cathode layer of LPSC and 92SN was characterized by SEM-EDS at room temperature and after heating to 220°C and 460°C, respectively. Figure 3 As shown in the figure, 220 ℃ (within the range of K1±10 ℃) represents the temperature after the 92SN phase transition, and 460 ℃ is taken from a temperature point after the mixed system has fully reacted. Under the condition of 220 ℃, SEM and EDS analysis showed that the smaller, brighter parts in the figure are 92SN particles, and the larger, darker parts are LPSC particles. EDS analysis showed that at 220 ℃, there was basically no diffusion of O, P, and S. When the temperature was further increased to 460 ℃, S element diffusion into the Co and Ni rich regions was observed, while P and O elements aggregated. This indicates that O and S exchanged with each other at high temperature, generating CoS and phosphate and sulfate products.

[0053] In Example 1, for the composite cathode layer of LPSC and 92SN, XPS testing was performed as follows: Figure 4 As shown, the test results indicate that the P2S spectrum appeared in the S 2p spectrum at 195℃. x and (SO3) 2- The characteristic peaks of P2S were observed, and the P2p spectrum also indicated that P2S... x The presence of functional groups. Combined with DSC test results, it was shown that a slight interfacial reaction occurred between LPSC and 92SN at 220℃, with the sulfide electrolyte being oxidized to P2Sx; at 320℃, the S 2p spectrum showed characteristic peaks for NiS / CoS, and the P 2p spectrum showed (PO4). 3- SO4 appeared at 460℃. 2- Spectroscopic findings indicate that a violent chemical reaction occurs between LPSC and 92SN at 320°C, generating a large amount of heat and producing substances such as metal sulfides, metal oxides, and phosphates. At 460°C, substances such as sulfites and phosphates are produced.

[0054] In Example 1, for the composite cathode layer of LPSC and 92SN, XRD tests were performed as follows: Figure 5 As shown, the test results indicate that the composite cathode layer was sintered in an atmosphere furnace to different temperatures and then characterized by XRD. Figure 5 It can be seen that the XRD phases at 25 ℃, 195 ℃, and 220 ℃ are the same as the phases of the raw materials added to prepare the mixture. When the temperature rises to 320 ℃, the LiCl peak and NiO peak appear. As the temperature continues to rise to 460 ℃, the lithium nickel cobalt manganese oxide peak and the Li6PS5Cl peak completely disappear, accompanied by the appearance of the LiCl peak, NiO peak, Li3PO4 peak, MnS peak, and CoS peak.

[0055] In summary, the first exothermic peak shows a decreasing peak temperature with increasing nickel content, accompanied by significant weight loss, corresponding to the release of lattice oxygen. The second exothermic peak shows the formation of lithium chloride, NiS, and CoS, indicating a solid-solid reaction between the solid electrolyte and the metal oxide. The third exothermic peak releases a large amount of heat without significant weight loss; this process generates lithium phosphate, lithium sulfate, and metal sulfides.

[0056] Therefore, the stability testing method of the present invention can accurately test the thermal stability of cathode materials.

[0057] Example 2 Lithium nickel cobalt manganese oxide (LiNi) xCoyMn1-x-yO2, where x=0.6, y=0.2 (6SN), was uniformly mixed with sulfide solid electrolyte LPSC at a predetermined mass ratio of 7:3. Then, it was pressed into a 10mm diameter disc in a high-pressure mold under a pressure of 450 MPa to serve as the positive electrode layer. A lithium indium alloy was used as the negative electrode to assemble a mold battery. After the mold battery was left to stand at 100 MPa for 10 h, it was charged to the cutoff voltage using a 0.1C constant current-constant voltage (CC-CV) mode. The cutoff current was 0.02C, and the cutoff voltage was 3.78V. The mold battery was disassembled under full charge, and 10 mg of the composite positive electrode layer was scraped off and pressed again into a 4mm diameter disc under 450 MPa. The results were measured using a TG-DSC-MS system, and the TG-DSC curves were obtained (e.g., [image of TG-DSC-MS]). Figure 1 (As shown): Heating rate 5℃ / min, final temperature 500℃, argon atmosphere (50 mL / min), using a 70 μL Al2O3 crucible, simultaneously obtaining the main exothermic peak temperatures K1, K2, and K3. See the test results below. Figure 1 and Figure 2 And Table 1, MS simultaneously monitored the signals at m / z=32 (O2), m / z=48 (SO), and m / z=64 (SO2); small discs were also taken and sampled at room temperature, heated to the main exothermic peak temperature K1±10℃, and K3±10℃, respectively, and then subjected to SEM-EDS analysis; small discs were also taken and heated to different temperatures for XPS and XRD tests.

[0058] Example 3 Lithium nickel cobalt manganese oxide (LiNi) x CoyMn1-x-yO2, where x=0.86, y=0.1 (86SN), was uniformly mixed with sulfide solid electrolyte LPSC at a predetermined mass ratio of 7:3. Then, it was pressed into a 10mm diameter disc in a high-pressure mold under a pressure of 450 MPa to serve as the positive electrode layer. A lithium indium alloy was used as the negative electrode to assemble a mold battery. After the mold battery was left to stand at 100 MPa for 10 h, it was charged to the cutoff voltage using a 0.1C constant current-constant voltage (CC-CV) mode. The cutoff current was 0.02C, and the cutoff voltage was 3.78V. The mold battery was disassembled under full charge, and 10 mg of the composite positive electrode layer was scraped off and pressed again into a 4mm diameter disc under 450 MPa. The TG-DSC curve was obtained using a TG-DSC-MS instrument (e.g., TG-DSC-MS). Figure 1 (As shown): Heating rate 5℃ / min, final temperature 500℃, argon atmosphere (50 mL / min), using a 70 μL Al2O3 crucible. The main exothermic peak temperatures K1, K2, and K3 were obtained through testing. The test results are shown in [reference]. Figure 1 and Figure 2And Table 1, MS simultaneously monitored the signals at m / z=32 (O2), m / z=48 (SO), and m / z=64 (SO2); small discs were also taken and sampled at room temperature, heated to the main exothermic peak temperature K1±10℃, and K3±10℃, respectively, and then subjected to SEM-EDS analysis; small discs were also taken and heated to different temperatures for XPS and XRD tests.

[0059] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0060] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for testing the thermal stability of a composite cathode layer in a solid-state battery, characterized in that, include: The mold battery is charged to the target voltage under constant current and constant voltage to reach the predetermined charge state. The composite positive electrode layer of the mold battery includes a positive electrode active material and a solid electrolyte material. The mold battery is disassembled under the predetermined power state, the composite positive electrode layer is peeled off to obtain the composite positive electrode material, and the composite positive electrode material is made into multiple first test samples; A sample of the first test was taken and thermally analyzed using a thermal analysis and mass spectrometry instrument to obtain the main exothermic peak temperature of the composite cathode material. Take another sample of the first test, heat it to a first predetermined temperature and then cool it to obtain a second test sample. Use a scanning electron microscope-energy dispersive spectroscopy (EDS) instrument to test the second test sample. The first predetermined temperature is the temperature of the main exothermic peak ±10℃.

2. The test method according to claim 1, characterized in that, Also includes: The first sample to be tested was heated to different temperatures and then cooled for XPS and / or XRD tests.

3. The test method according to claim 2, characterized in that, The method for preparing the composite positive electrode layer includes: uniformly mixing the positive electrode active material and the solid electrolyte material, and then pressing them under a first pressure to obtain the composite positive electrode layer. A method for fabricating multiple first test samples from the composite cathode material includes: pressing the composite cathode material under a second pressure to obtain the first test samples. Wherein, the first pressure and the second pressure are the same.

4. The test method according to claim 3, characterized in that, The first pressure and the second pressure are 300~600 MPa, respectively.

5. The test method according to any one of claims 1 to 4, characterized in that, The predetermined charge level is greater than or equal to 50%, preferably, the predetermined charge level is a fully charged state.

6. The test method according to any one of claims 2 to 4, characterized in that, The composite cathode material has multiple main exothermic peak temperatures. The first test sample is heated to different second predetermined temperatures and then cooled, and XPS and / or XRD tests are performed respectively. The second predetermined temperature is set to the main exothermic temperature ±10℃.

7. The test method according to any one of claims 1 to 4, characterized in that, The mass mixing ratio of the positive electrode active material and the solid electrolyte material is (6~8):(4~2).

8. The test method according to any one of claims 2 to 4, characterized in that, During the thermal analysis, the heating rate is 3~8℃ / min.

9. The test method according to claim 8, characterized in that, The heating rate during the process of heating the first sample to be tested to a first predetermined temperature and then cooling it to obtain the second sample to be tested is consistent with the heating rate during the thermal analysis process.

10. The test method according to claim 8, characterized in that, The heating rate during the process of heating the first sample to be tested to different temperatures and then cooling it for XPS and / or XRD tests is consistent with the heating rate during the thermal analysis process.

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