A method and system for testing stability of a battery solid-state electrolyte

Abstract

The present application belongs to the technical field of battery detection, and in particular to a method and system for testing the stability of a battery solid-state electrolyte. The method comprises: obtaining a target composite positive electrode formula, a charge-discharge potential, a test temperature, a stacking pressure, and a charging system, determining a candidate composite microzone test potential window after unifying the potential reference; preparing and screening the same batch of solid-state electrolyte samples, establishing a blank microzone control system to determine the composite microzone test window and background criteria; obtaining a single reference oxidation starting point and a composite microzone oxidation candidate starting point, respectively, and after confirmation by a parallel termination sample, outputting a stability test result according to the advance amount of the two; the present application improves the accuracy and application relevance of the stability evaluation of solid-state electrolytes for high-voltage all-solid-state batteries.

Description

Technical Field

[0001] This invention belongs to the field of battery testing technology, and in particular relates to a method and system for testing the stability of solid electrolytes in batteries. Background Technology

[0002] All-solid-state batteries typically use solid electrolytes instead of liquid electrolytes to improve the safety and structural stability of the battery system. In high-energy-density all-solid-state batteries, to increase output voltage and capacity, high-voltage positive electrode active materials are often used on the positive electrode side, and the positive electrode active material, solid electrolyte powder, conductive agent, and binder are combined to form a composite positive electrode. The solid electrolyte not only undertakes ion conduction but also forms numerous contact interfaces with the positive electrode active material and conductive agent in the vicinity of the composite positive electrode. Therefore, evaluating the oxidation stability of solid electrolytes is a crucial basis for determining their suitability for high-voltage all-solid-state batteries.

[0003] Current methods for testing the oxidation stability of solid-state electrolytes (SSEs) primarily employ single-piece testing. This involves placing a solid-state electrolyte sample in contact with an inert or blocking electrode and obtaining the oxidation initiation potential using linear sweep voltammetry, potentiostatic holding, or similar electrochemical testing techniques. This method allows for evaluation of the high-potential tolerance of the solid-state electrolyte material under relatively simplified and repeatable interfacial conditions, and also facilitates cross-sectional comparisons between different batches of SSEs. However, in actual high-voltage all-solid-state battery composite cathodes, the solid-state electrolyte does not simply form a single contact with an inert electrode. Instead, it simultaneously exists within a local interfacial environment comprised of the high potential of the cathode active material, the electronic conduction pathway formed by the conductive agent, and the ion conduction pathway formed by the solid-state electrolyte. This local interfacial environment simultaneously provides the solid-state electrolyte surface with both electron accessibility and ion migration conditions, while also subjecting it to the localized high potential generated by the cathode active material. Consequently, the solid-state electrolyte may undergo interfacial oxidation reactions at potentials lower than the oxidation initiation potential obtained from single-piece testing. Especially in the small area where the positive electrode active material, conductive agent and solid electrolyte are adjacent to each other, the local potential distribution, electronic accessibility and interfacial side reaction conditions are different from the inert electrode contact state in the single-piece test. This may cause the oxidation current response in the composite positive electrode to appear earlier, so that the oxidation initiation potential obtained by the single-piece test is higher than the actual oxidation initiation potential of the solid electrolyte under the local contact conditions of the composite positive electrode. This leads to an overestimation of the high potential stability of the solid electrolyte and failure to detect the early oxidation risk within the target application potential range.

[0004] Existing single-cell testing typically assumes that the oxidation initiation point exhibited by the solid electrolyte under inert electrode contact conditions represents its oxidation stability in composite cathodes. However, this assumption may fail in high-voltage composite cathode applications. Specifically, when a high-potential cathode active material, a continuous conductive agent pathway, and a solid electrolyte contact interface are simultaneously present in a localized high-potential micro-region of the composite cathode, premature oxidation may occur on the solid electrolyte surface before the oxidation initiation point shown in single-cell testing. Because conventional single-cell testing does not reflect this localized three-phase contact environment within the composite cathode, test results easily lead to the assessment that the solid electrolyte is stable within the target application potential range, thus missing the potential risk of premature oxidation that may already exist at the actual composite cathode interface. This missed detection cannot be completely eliminated by simply reducing the scan rate, increasing the test temperature, or extending the holding time, because its root cause lies in the inconsistency between the interface conditions of single-cell testing and the interface conditions of the localized micro-region of the composite cathode, resulting in the failure to effectively expose the premature oxidation behavior of the solid electrolyte in actual high-voltage composite cathode applications. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention provides a method and system for testing the stability of solid-state electrolytes for batteries. This invention improves the accuracy and application relevance of stability evaluation for solid-state electrolytes used in high-voltage all-solid-state batteries.

[0006] To achieve one of the above objectives, the present invention adopts the following technical solution: A method for testing the stability of a battery solid electrolyte, comprising the following steps: S1. Obtain the target composite cathode formulation, and obtain the target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime; unify the target cathode charge cut-off potential and target cathode discharge lower limit potential to the same potential reference system, and determine the candidate composite micro-region test potential window based on the unified target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime; wherein, the target composite cathode formulation is used for subsequent construction of blank micro-region layer, composite cathode micro-region simulation layer, and active material background reference layer; S2. Samples are prepared using the same batch of solid electrolyte raw materials. Samples are screened and grouped equally according to their thickness, effective test area and initial area resistance to obtain a uniform solid electrolyte sample group. S3. Establish a blank micro-region control system based on a standardized solid electrolyte sample group. Collect the current density curve of the blank micro-region within the test potential window of the candidate composite micro-region. Determine the test potential window of the composite micro-region, the upper limit of the background current of the micro-region, and the threshold of the number of consecutive points of oxidation response of the micro-region based on the current density curve of the blank micro-region. S4. Perform single-chip reference testing within the test potential window of the composite micro-region to obtain the single-chip reference oxidation start point; S5. Construct a composite cathode micro-region simulation layer and perform potential scanning and recording within the composite micro-region test potential window at the same scanning rate as the single-chip benchmark test to obtain the full-process micro-region current density curve; construct an active material background reference structure to obtain the active material background current density curve; analyze the full-process micro-region correction current density curve based on the full-process micro-region current density curve and the active material background current density curve, and combine the upper limit of the micro-region background current and the threshold of the number of consecutive points of micro-region oxidation response to obtain the candidate starting point of composite micro-region oxidation; S6. Confirm the candidate starting point of composite micro-region oxidation by parallel termination of the sample, obtain the starting point of composite micro-region oxidation, and output the stability test results based on the advance of the starting point of composite micro-region oxidation relative to the single-piece reference oxidation starting point.

[0007] Preferably, in step S1, the method for determining the test potential window of the candidate composite micro-region is as follows: The target positive electrode discharge lower limit potential and the target positive electrode potential when it reaches the charging cutoff state under the target test temperature, target stacking pressure and target charging regime are uniformly converted to the same potential reference system; the uniformly converted target positive electrode discharge lower limit potential is used as the composite micro-region starting test potential, the uniformly converted positive electrode potential when it reaches the charging cutoff state is used as the candidate upper limit test potential, and the potential range formed by the composite micro-region starting test potential to the candidate upper limit test potential is used as the candidate composite micro-region test potential window.

[0008] Preferably, in step S2, the initial area resistivity of each sample is measured under the same target test temperature and the same target stacking pressure. The upper limit of the clamping repeatability error is determined based on the deviation of the initial area resistivity measured by repeated clamping of the same sample. Samples whose deviation of initial area resistivity relative to the median of initial area resistivity of the same batch of samples is ≤ the upper limit of the clamping repeatability error are determined as qualified samples. Qualified samples are then evenly grouped according to initial area resistivity and sample thickness to obtain a uniform solid electrolyte sample group.

[0009] Preferably, in step S3, the method for determining the composite micro-area test potential window, the upper limit of the micro-area background current, and the threshold for the number of consecutive points of micro-area oxidation response is as follows: Background scanning of the blank micro-region control system was performed within the test potential window of the candidate composite micro-region to obtain the current density curve of the blank micro-region. The highest usable potential of the fixture was determined based on the current density curve of the blank micro-region. The lower of the candidate upper limit test potential and the highest usable potential of the fixture was taken as the upper limit test potential of the composite micro-region. The potential interval formed from the initial test potential of the composite micro-region to the upper limit test potential of the composite micro-region was taken as the test potential window of the composite micro-region. The average current density and standard deviation are calculated based on the blank low potential baseline segment within the test potential window of the composite micro-region in the blank micro-region current density curve, and the average current density plus three times the standard deviation is taken as the upper limit of the background current of the micro-region. Identify each consecutive over-limit interval in the blank micro-region current density curve where the current density exceeds the upper limit of the micro-region background current, count the number of sampling points contained in each consecutive over-limit interval, and add one to the maximum number of sampling points as the threshold for the number of consecutive points in the micro-region oxidation response; when there are no sampling points in the blank micro-region current density curve where the current density exceeds the upper limit of the micro-region background current, record the maximum number of sampling points as zero, and set the threshold for the number of consecutive points in the micro-region oxidation response to one.

[0010] Preferably, the composite cathode micro-region simulation layer includes the target cathode active material, the solid electrolyte powder to be evaluated, the conductive agent and the binder, and the types and mass ratios of each component are determined according to the target composite cathode formulation. The method for constructing a composite cathode micro-region simulation layer is as follows: Several candidate composite micro-region simulation layers were prepared on the surface of the same batch of solid electrolyte samples, arranged in order of increasing areal loading. In-plane electron conduction tests were performed on each candidate composite micro-region simulation layer, and the candidate composite micro-region simulation layer with the lowest areal loading that meets the continuous electron conduction condition was selected as the composite positive electrode micro-region simulation layer. The continuous electron conduction condition means that the in-plane electron resistance test between the center and edge positions of the candidate composite micro-region simulation layer and between adjacent edge positions did not show an open circuit state outside the instrument range.

[0011] Preferably, the method for constructing the background reference structure of the active material is as follows: Based on the mass ratio of the target positive electrode active material, conductive agent and binder in the target composite positive electrode formulation, the mass ratio is normalized after removing the solid electrolyte powder to be evaluated, and an active material background reference layer is prepared. Multiple candidate ion-conducting layers different from the solid electrolyte material to be evaluated were prepared. The initial area resistivity of each candidate ion-conducting layer was measured at the target test temperature and target stacking pressure. The candidate ion-conducting layer whose initial area resistivity was not greater than the sum of the median initial area resistivity of the solid electrolyte sample to be evaluated and the upper limit of the clamping repeatability error was determined as the conductive candidate layer. Within the test potential window of the composite micro-region, the potential of the candidate conductive layer is scanned at the same scan rate as that of the monolithic benchmark test, and the background curve of the corresponding inert electrode is subtracted to obtain the corrected current density curve of the candidate ion conduction layer. The upper limit of the background current of the isolation layer is determined based on the low potential baseline segment near the initial test potential of the composite micro-region. When the corrected current density curve of the candidate ion conduction layer does not have a continuous interval within the test potential window of the composite micro-region where the number of continuous sampling points is not less than the threshold of the number of continuous points of the monolithic oxidation response and the current density of each sampling point is higher than the upper limit of the background current of the isolation layer, the corresponding candidate conductive layer is determined as the inert ion conduction isolation layer. An active material background reference layer is set on the surface of an inert ion conduction isolation layer, and the areal loading of the target positive electrode active material in the active material background reference layer is matched with the areal loading of the target positive electrode active material in the composite positive electrode micro-region simulation layer to obtain an active material background reference structure.

[0012] Preferably, in step S5, the method for obtaining candidate starting points for oxidation in composite micro-regions is as follows: In the micro-area correction current density curve of the whole process, the continuous intervals that first meet the following conditions are identified: the number of continuous sampling points ≥ the threshold of the number of continuous points of micro-area oxidation response, the current density of each sampling point is higher than the upper limit of the micro-area background current, and the current density at the end of the interval is greater than the current density at the beginning of the interval. The first potential point of the continuous interval is taken as the candidate starting point of composite micro-area oxidation.

[0013] Preferably, in step S6, the method for obtaining the oxidation starting point of the composite micro-region is as follows: The test was set at the first type of parallel termination confirmation sample, the test was stopped at the pre-confirmation potential, the test was stopped at the candidate oxidation starting point of the composite micro-region, and the test was stopped at the upper limit test potential of the composite micro-region. When the representative value of the target oxidation product of the second type of parallel termination confirmation sample is higher than that of the target oxidation product of the first type of parallel termination confirmation sample and reaches the oxidation product confirmation threshold, and the representative value of the target oxidation product of the third type of parallel termination confirmation sample is higher than that of the second type of parallel termination confirmation sample, the candidate starting point of composite micro-region oxidation is confirmed as the starting point of composite micro-region oxidation. The target oxidation product representative value is the median of the target oxidation product ratios among all samples in the same class of parallel termination confirmation samples. The target oxidation product ratio is the ratio of the characteristic peak area of ​​the target oxidation product to the characteristic peak area of ​​the matrix.

[0014] Preferably, in step S6, the method for outputting the stability test results is as follows: When the oxidation starting point of the composite micro-region is lower than the oxidation starting point of the single-electrode reference, the difference between the two is greater than the deviation judgment threshold, and the oxidation starting point of the composite micro-region is confirmed by the parallel termination confirmation sample, the risk of early oxidation failure under the contact condition of the composite positive electrode micro-region will be output as the stability test result; wherein, the deviation judgment threshold is determined based on at least one of the repeatability of the oxidation starting point of the single-electrode reference, the repeatability of the oxidation starting point of the composite micro-region, and the repeatability of the false trigger potential point of the blank micro-region.

[0015] To achieve the second objective mentioned above, the present invention provides a stability testing system for battery solid electrolytes. The system is used to implement a stability testing method for battery solid electrolytes. The system includes a data acquisition and analysis module, a preparation and grouping module, a control analysis module, a benchmark testing module, a composite analysis module, and a stability analysis module. The data acquisition and analysis module is used to obtain the target composite cathode formulation, and to acquire the target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime. The target cathode charge cut-off potential and target cathode discharge lower limit potential are unified to the same potential reference system. Based on the unified target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime, the test potential window for candidate composite micro-regions is determined. The target composite cathode formulation is used for subsequent construction of the blank micro-region layer, the composite cathode micro-region simulation layer, and the active material background reference layer. The preparation and grouping module is used to prepare samples using the same batch of solid electrolyte raw materials. It screens and groups the samples according to their thickness, effective test area and initial area resistivity to obtain a uniform solid electrolyte sample group. The comparative analysis module is used to establish a blank micro-region control system based on a uniform solid electrolyte sample group. It collects the current density curve of the blank micro-region within the test potential window of the candidate composite micro-region and determines the test potential window of the composite micro-region, the upper limit of the background current of the micro-region, and the threshold of the number of consecutive points of the oxidation response of the micro-region based on the current density curve of the blank micro-region. The benchmark module is used to perform monolithic benchmark testing within the test potential window of the composite micro-region to obtain the monolithic benchmark oxidation start point; The composite analysis module is used to construct a composite cathode micro-region simulation layer and perform potential scanning and recording within the composite micro-region test potential window at the same scanning rate as the single-chip benchmark test to obtain the full-process micro-region current density curve; construct an active material background reference structure to obtain the active material background current density curve; analyze the full-process micro-region correction current density curve based on the full-process micro-region current density curve and the active material background current density curve, and combine the upper limit of the micro-region background current and the threshold of the number of consecutive points of micro-region oxidation response to obtain the candidate starting point of composite micro-region oxidation; The stability analysis module is used to confirm the candidate starting point of oxidation in the composite micro-region by confirming the sample through parallel termination, obtain the oxidation starting point of the composite micro-region, and output the stability test results based on the advance of the oxidation starting point of the composite micro-region relative to the single-piece reference oxidation starting point.

[0016] The advantages of this invention are: (1) The present invention determines the test potential window of candidate composite micro-regions under the same potential reference system, and further obtains the test potential window of composite micro-regions, the upper limit of micro-region background current and the threshold of the number of consecutive points of micro-region oxidation response by using the blank micro-region control system, so that the subsequent single-piece benchmark test and composite micro-region test are under comparable potential windows and background judgment benchmarks, avoiding the distortion of the comparison of oxidation starting point due to different test windows or background current apertures.

[0017] (2) By using solid electrolyte samples from the same batch and screening and balancing them according to sample thickness, effective test area and initial area resistance, this invention ensures that there is a basis for sample consistency among single-piece benchmark test, blank micro-area control test, composite micro-area simulation test, active material background reference test and parallel termination confirmation test, thereby reducing the interference of sample batch differences, thickness differences and impedance differences on the determination of oxidation start point.

[0018] (3) This invention constructs a composite positive electrode micro-region simulation layer containing the target positive electrode active material, solid electrolyte powder, conductive agent and binder on the surface of the solid electrolyte sample, so that the solid electrolyte is in a test environment close to the local contact area of ​​the target composite positive electrode, which can expose the local high potential micro-region effect that is difficult to be reflected in the test of a single inert electrode, thereby improving the correspondence between the oxidation stability test of solid electrolyte and the actual application environment of high voltage all-solid-state battery.

[0019] (4) By establishing a background reference structure for active materials, the present invention obtains the background current density curve of active materials and subtracts it from the current density curve of the whole process micro-region to obtain the corrected current density curve of the whole process micro-region. This can reduce the interference of the target positive electrode active material’s own delithiation, capacitance response or surface side reaction on the oxidation response of solid electrolyte and improve the attribution accuracy of the candidate starting point identification of composite micro-region oxidation.

[0020] (5) By combining the upper limit of the micro-area background current and the threshold of the number of consecutive points of the micro-area oxidation response, the present invention obtains the candidate starting point of the composite micro-area oxidation from the micro-area correction current density curve of the whole process, which can avoid misjudging single-point noise or short-term background fluctuations as the oxidation starting point and improve the repeatability and stability of the composite micro-area oxidation response identification.

[0021] (6) The present invention confirms the surface oxidation products of the candidate oxidation starting point of the composite micro-region by confirming the sample through parallel termination. It corresponds the candidate oxidation starting point in the electrochemical curve with the generation result of the oxidation product on the surface of the solid electrolyte, which can reduce the risk of misjudgment caused by judging the oxidation behavior based solely on the current rise and improve the evidence integrity of the early oxidation judgment.

[0022] (7) In addition to conventional single-cell benchmark testing, the present invention can identify the situation where the solid electrolyte is oxidized prematurely under the condition of local high potential micro-region of composite cathode, solve the problem that existing single-cell testing is prone to missing the risk of early oxidation in the actual interface of composite cathode, and improve the accuracy and application relevance of the stability evaluation of solid electrolyte for high-voltage all-solid-state batteries. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the method for determining the test potential window of the composite micro-region, the upper limit of the background current of the micro-region, and the threshold of the number of consecutive points of oxidation response in the micro-region according to the present invention.

[0024] Figure 2 This is a schematic diagram of the method for obtaining candidate oxidation starting points in composite micro-regions according to the present invention.

[0025] Figure 3 This is a schematic diagram of the system of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] A method for testing the stability of a battery solid electrolyte, comprising: S1. Obtain the target composite cathode formulation, and obtain the target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime; unify the target cathode charge cut-off potential and target cathode discharge lower limit potential to the same potential reference system, and determine the candidate composite micro-region test potential window based on the unified target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime; wherein, the target composite cathode formulation is used for subsequent construction of the blank micro-region layer, the composite cathode micro-region simulation layer, and the active material background reference layer; as detailed below: Obtain information on the target all-solid-state battery for which the solid electrolyte to be evaluated is intended to be applied, and form a target application condition record table. The target application condition record table includes the target composite cathode formulation, the target cathode charging cut-off potential, the target cathode discharge lower limit potential, the target test temperature, the target stacking pressure, the target charging regime, and the potential reference system.

[0028] The target composite cathode formulation includes the types and mass ratios of the target cathode active material, solid electrolyte powder, conductive agent, and binder; the target composite cathode formulation is obtained from the target all-solid-state battery design documents, target composite cathode preparation records, or target cathode verification sheet preparation records; if the above documents only record the mass of each component, the mass ratio is the proportion of the mass of each solid component to the total mass of the solid components; if there are drying, sintering, or curing steps, the mass of the solid components before entering the film formation, pressing, or coating steps is used as the basis for calculating the mass ratio.

[0029] Both the target positive electrode charging cutoff potential and the target positive electrode discharging lower limit potential are uniformly expressed as relative to Li / Li + The positive electrode potential; if the target all-solid-state battery design document has given the target positive electrode potential relative to Li / Li + The charging cutoff potential and discharge lower limit potential are determined by the target positive electrode relative to Li / Li. + The charging cutoff potential; the target positive electrode charging cutoff potential and the target positive electrode discharge lower limit potential are derived from the positive electrode potential file, the actual measurement of a full cell with reference, or the actual measurement of a half cell for target positive electrode verification.

[0030] Li / Li + This refers to the electrochemical equilibrium reference system between lithium metal and lithium ions; relative to Li / Li + The potential refers to the potential of the electrode under test relative to the lithium metal reference electrode. If a lithium indium reference electrode is used, the potential of the lithium indium reference electrode relative to the lithium metal electrode should first be calibrated, and then the test potential should be converted to a value relative to Li / Li. + A unified potential system.

[0031] If the target all-solid-state battery design document only provides the full-cell charge cut-off voltage and the full-cell discharge lower limit voltage, but does not provide the positive electrode relative to Li / Li + The potential is obtained primarily through testing the target all-solid-state battery with a reference electrode. Specifically, a lithium metal reference electrode or a calibrated lithium indium reference electrode is set in the target all-solid-state battery, and the positive electrode potential, negative electrode potential, and full cell voltage are recorded under the target charging regime. The full cell voltage is the difference between the positive electrode potential and the negative electrode potential, i.e., the full cell voltage equals the positive electrode potential minus the negative electrode potential. Therefore, when the target all-solid-state battery reaches the charging cutoff state, the full cell charging cutoff voltage at that moment is compared with the negative electrode potential relative to Li / Li. +The potentials are added together to obtain the target positive electrode charging cutoff potential; when the target all-solid-state battery reaches the discharge lower limit state, the discharge lower limit voltage of the full battery at that moment is compared with the negative electrode relative to Li / Li + The potentials are added together to obtain the target positive electrode discharge lower limit potential; the charging cut-off state is determined by the target all-solid-state battery reaching the full battery charging cut-off voltage, cut-off current condition, or the stop condition specified by the target charging regime; the discharge lower limit state is determined by the target all-solid-state battery reaching the full battery discharge lower limit voltage or the stop condition specified by the target discharge regime.

[0032] If the target all-solid-state battery cannot have a reference electrode set, or if the negative electrode relative to Li / Li cannot be obtained, + Instead of using the full-cell voltage to calculate the positive electrode potential, the target positive electrode potential is directly measured using the target positive electrode verification half-cell. Specifically, a target positive electrode verification sheet is prepared using the target positive electrode active material, the solid electrolyte powder in the target composite positive electrode formulation, the conductive agent, and the binder. The target positive electrode verification sheet, a solid electrolyte layer of the same type as the target all-solid-state battery, and a lithium metal electrode or a lithium indium electrode are assembled into a target positive electrode verification half-cell. Under the target test temperature and target stacking pressure, charge and discharge tests corresponding to the target charging regime are performed on the target positive electrode verification half-cell, and the potential of the target positive electrode verification sheet relative to the reference electrode is recorded and converted to Li / Li + Reference system: The positive electrode potential when the target positive electrode verification half cell reaches the charging cut-off state is taken as the charging cut-off potential of the target positive electrode, and the positive electrode potential when the target positive electrode verification half cell reaches the discharge lower limit state is taken as the discharge lower limit potential of the target positive electrode.

[0033] If a lithium metal reference electrode is used, the measured potential of the electrode under test relative to the lithium metal reference electrode is directly taken as the potential relative to Li / Li + The potential of the lithium indium electrode relative to the lithium metal electrode is determined. If a lithium indium reference electrode is used, the lithium indium electrode / solid electrolyte / lithium metal electrode calibration structure is assembled under the same test temperature, stacking pressure, and solid electrolyte contact conditions as in subsequent tests. The potential difference between the lithium indium electrode and the lithium metal electrode is measured, and this potential difference is used as the lithium indium reference calibration potential. In subsequent tests, if the potential of the working electrode relative to the lithium indium reference electrode recorded by the tester is the measured potential of the working electrode, then the potential of the working electrode relative to Li / Li + The unified potential is the sum of the measured potential of the working electrode and the reference calibration potential of lithium indium. If the tester outputs with opposite polarity, the sign is corrected according to the definition of the working electrode potential in the tester's manual, and the same conversion direction is maintained in the same batch of tests.

[0034] The target test temperature is determined in the following order: If the target all-solid-state battery design document or test schedule provides a charging stability evaluation temperature, then that temperature is used as the target test temperature; if only the operating temperature range is given, then the temperature point used for charging testing or high-voltage stability evaluation within that operating temperature range is used as the target test temperature, and the source of that temperature point is recorded in the target application condition record table; if the target all-solid-state battery does not yet have application temperature requirements, then the target test temperature is determined through preliminary testing of the target cathode verification half-cell; the preliminary test includes: placing the target cathode verification half-cell in an environmental chamber and performing the target test at the candidate test temperature. For standard charging regimes or low-rate charging regimes, select the temperature that allows the target positive electrode verification half-cell to complete the charging test without any temperature control interruption records as the target test temperature; temperature control interruption records refer to records where the ambient temperature deviates from the set temperature, causing the tester to pause or terminate the test; if multiple candidate temperatures meet the above conditions, then the temperature closest to the actual charging environment in the intended application scenario of the target all-solid-state battery shall be used as the target test temperature, and the selection basis shall be recorded in the record table; the temperature closest to the actual charging environment refers to the candidate temperature with the smallest difference from the charging environment temperature in the target all-solid-state battery design documents, test task book, or application scenario temperature record.

[0035] The target stacking pressure is determined in the following order: if the cell working clamping pressure is given in the target all-solid-state battery design document or assembly process document, then the working clamping pressure is taken as the target stacking pressure; if only the assembly pressure range is given, then the clamping pressure recorded in the actual charging test of the target all-solid-state battery is taken as the target stacking pressure; if the target stacking pressure is not given, it is determined by a pressure-area resistance pre-test of the same solid electrolyte sample; the pressure-area resistance pre-test includes: applying clamping pressure to the same solid electrolyte sample at the target test temperature in stages, and measuring the initial area resistance at each pressure level; when the difference in initial area resistance between two adjacent pressure levels is not greater than the upper limit of the area resistance error for repeated clamping under the same pressure, the lower pressure level is taken as the target stacking pressure; the upper limit of the area resistance error for repeated clamping is obtained by repeatedly clamping the same sample under the same pressure and measuring the initial area resistance.

[0036] The target charging regime is determined in the following order: If the target all-solid-state battery design document, BMS charging strategy document, or test task book provides the charging current, charging rate, constant current / constant voltage conversion conditions, cutoff current, or charging termination conditions, then these conditions are used as the target charging regime; if only the target charging time is given, the charging current is determined based on the reversible capacity of the target cathode verification sheet and the target charging time, i.e., the reversible capacity of the target cathode verification sheet is divided by the target charging time to obtain the charging current; if the target charging time is not given, the target charging regime is determined through the pre-charge test of the target cathode verification half-cell; the pre-charge test includes: using the target cathode verification sheet, at the target test temperature and target stacking pressure... The charging process proceeds with charging current levels from low to high, recording the voltage curves and charging completion status at each current level. The highest charging current level that allows the target positive electrode verification chip to reach the target positive electrode charging cutoff potential without triggering overvoltage, overcurrent, or temperature control interruptions on the tester is selected as the charging current in the target charging regime. Each charging current level is derived from the current levels that can be set on the tester or the standard current levels of the target positive electrode verification test equipment, without setting any additional arbitrary current values. If the target charging regime is a stepped current or pulse charging regime, the cumulative charging time from the target positive electrode reaching the target positive electrode charging cutoff potential from the first time from the lower discharge limit potential is used as the charging time used for subsequent scan rate calculations.

[0037] The target positive electrode discharge lower limit potential and the target positive electrode potential when it reaches the charging cutoff state under the target test temperature, target stacking pressure and target charging regime are uniformly converted to the same potential reference system; the uniformly converted target positive electrode discharge lower limit potential is used as the composite micro-region starting test potential, the uniformly converted positive electrode potential when it reaches the charging cutoff state is used as the candidate upper limit test potential, and the potential range formed by the composite micro-region starting test potential to the candidate upper limit test potential is used as the candidate composite micro-region test potential window.

[0038] S2. Samples are prepared using the same batch of solid electrolyte raw materials. Based on sample thickness, effective test area, and initial area resistivity, samples are screened and grouped uniformly to obtain a consistent solid electrolyte sample group; details are as follows: Multiple solid electrolyte samples are prepared using the same batch of solid electrolyte raw materials; the sample preparation method is consistent with the preparation method of the solid electrolyte layer in the target all-solid-state battery; if the final preparation method of the target all-solid-state battery has not yet been determined, a pressing sheet, sintered sheet, cast film or composite film that can form a continuous sheet-like ion conductor is used.

[0039] For each solid electrolyte sample, record the sample number, sample thickness, effective test area, and initial area resistance.

[0040] The sample thickness is obtained by measuring with a thickness gauge; the measurement positions include a center position and multiple edge positions; the center position refers to the geometric center of the effective test area; the edge positions are determined according to the boundary of the effective test area: first, determine the effective test area formed by the actual overlap of the subsequent electrode, current collector, or micro-layer with the solid electrolyte sample; select several boundary reference points on the boundary of the corresponding effective test area, and then move the thickness gauge indenter inward along the direction pointing from each boundary reference point to the geometric center of the effective test area by one contact radius of the thickness gauge indenter, and take the moved point as the edge measurement position; if the contact radius of the thickness gauge indenter is unknown, the position where the thickness gauge indenter can completely fall into the effective test area without crossing the boundary is taken as the edge. Edge measurement positions: When the effective test area is circular or approximately circular, the edge positions are uniformly selected along the circumference; when the effective test area is rectangular or approximately rectangular, the edge positions correspond to the areas near the four sides respectively; when the effective test area is irregular in shape, the edge positions are obtained after dividing the outer contour of the effective test area into equal arc lengths; the thickness is measured at the center position and each edge position to obtain multiple thickness measurements, and the median of the multiple thickness measurements is taken as the sample thickness of the corresponding solid electrolyte sample; if there are abnormal readings caused by the indenter not being able to make stable contact, the sample edge notch, or obvious warping at a certain measurement position, the position is discarded and a new position where the indenter can make stable contact is selected in the same boundary direction for measurement.

[0041] The effective test area refers to the surface area of ​​the solid electrolyte sample that actually participates in current transmission during subsequent electrochemical testing, and is not directly based on the sample's external area. In single-piece benchmark testing, the effective test area is determined by the overlapping area between the inert electronic conductive layer and the solid electrolyte sample. In blank micro-area control testing and composite micro-area simulation testing, the effective test area is determined by the overlapping area of ​​the current collector layer, the micro-area layer, and the solid electrolyte sample. In active material background reference testing, the effective test area is determined by the overlapping area of ​​the active material background reference layer, the current collector layer, and the inert ion conduction isolation layer. Specifically, the effective test area is obtained by recording the electrical data before assembly. The geometric dimensions and positioning of the electrode layer, current collector layer, micro-area layer, or reference layer are specified. After assembly, the actual overlapping area is confirmed by using the fixture positioning holes, indentation boundaries, current collector layer coverage boundaries, or by taking a calibration image. If the fixture limits the electrode exposure window, the intersection of the fixture exposure window and the functional layer coverage area is taken as the effective test area. If there are uncovered areas, the uncovered areas are deducted from the effective test area. If the effective test area is different for the same sample in different test structures, it is recorded as the single-piece reference effective test area, the blank micro-area effective test area, the composite micro-area effective test area, and the active material background effective test area, respectively.

[0042] The initial area resistivity is obtained through AC impedance testing; the AC impedance test temperature and stacking pressure adopt the target test temperature and target stacking pressure; during the test, inert electrodes with ion blocking and electron conduction are set on both sides of the solid electrolyte sample to form an inert electrode / solid electrolyte sample / inert electrode structure; this structure is placed in the same fixture as the subsequent test, and kept at the target test temperature until the sample temperature recorded by the tester reaches the target test temperature, and the AC impedance test is performed after the fixture pressure is kept stable under the target stacking pressure.

[0043] During impedance spectrum acquisition, the test frequency is scanned from the high-frequency end where the tester can stably output to the low-frequency end until the solid electrolyte bulk phase response and electrode blocking response can be observed in the impedance spectrum. If the high-frequency intercept cannot be observed in the first scan, the high-frequency scanning range allowed by the tester is expanded or the sampling density at the high-frequency end is increased and the scan is repeated. If a clear high-frequency intercept still cannot be obtained, the bulk resistance is obtained by equivalent circuit fitting.

[0044] Bulk resistance is obtained according to the following rules: When the Nyquist plot of the impedance spectrum has a clear intersection with the real axis at the high-frequency end, the real impedance corresponding to the intersection with the real axis at the high-frequency end is taken as the bulk resistance; when the high-frequency end does not directly form a clear intersection with the real axis but there is a high-frequency semicircle or high-frequency arc, an equivalent circuit is fitted to the high-frequency semicircle or high-frequency arc, and the resistive element representing the bulk conduction of the solid electrolyte in the fitted circuit is taken as the bulk resistance; when the impedance spectrum shows both bulk response and grain boundary response, the resistance corresponding to the highest frequency arc is taken as the bulk resistance, and the resistance corresponding to the mid- and low-frequency arcs is taken as the grain boundary or interface contribution and is not included in the bulk resistance; when it is impossible to distinguish between the bulk arc and the grain boundary arc, it is recorded as unable to extract the bulk resistance alone, and this sample is not used for consistency screening.

[0045] The equivalent circuit fitting uses a circuit model that can distinguish between ohmic resistance, bulk conduction, and interface barrier response. The circuit model includes at least a series ohmic resistor, a resistive element representing bulk conduction, and a capacitive element or constant-phase element representing interface barrier response. Before fitting, the fixture background impedance is obtained by testing with an empty fixture or a short-circuited fixture. If the fixture background impedance is not negligible relative to the sample impedance, the fixture background impedance is subtracted before fitting. If the bulk resistive element in the fitting result cannot converge stably, or if the difference in bulk resistance obtained by repeated fitting of the same sample is greater than the upper limit of repeated clamping error under the same test conditions, the fitting result is not used as the initial area resistance data.

[0046] The initial area resistance of the sample is obtained by multiplying the bulk resistance by the effective test area of ​​the corresponding test structure. The initial area resistance is only used for consistency screening of samples in the same batch and is not used to directly represent the area resistance of the finished battery.

[0047] Sample consistency is determined by the repeated clamping error of the same test fixture. The repeated clamping test uses the target test temperature and target stacking pressure, and adopts the same inert electrode, fixture, effective test area, and AC impedance test method as the initial area resistance test. Specifically, a sample with intact appearance, no cracks, and initial area resistance close to the median of the samples in the same batch is selected as the repeated clamping sample. At least three independent clamping measurements are performed on the repeated clamping sample. Each independent clamping includes: unloading the fixture pressure, removing the sample, repositioning the sample, reapplying the target stacking pressure, restoring thermal equilibrium at the target test temperature, reacquiring the AC impedance spectrum, and calculating the initial area resistance. If there is an abnormal record in the three measurements due to poor contact, sample displacement, fixture pressure not reaching the target stacking pressure, or temperature not reaching the target test temperature, the record is discarded and an additional independent clamping measurement is performed.

[0048] After obtaining multiple repeated clamping area resistance values, calculate the median of these repeated clamping area resistance values; then calculate the absolute deviation of each repeated clamping area resistance value relative to the median; and take the maximum absolute deviation as the upper limit of clamping repetition error.

[0049] The initial resistivity of all solid electrolyte samples was measured using the same test method, and the median of the initial resistivity of all samples was calculated. If the absolute deviation of the initial resistivity of a sample relative to the median of the initial resistivity of all samples is not greater than the upper limit of the clamping repeatability error, the corresponding sample is determined to be a qualified sample. If the corresponding absolute deviation is greater than the upper limit of the clamping repeatability error, the sample is considered to be inconsistent with the samples in the same batch and will not be included in subsequent comparative tests. If a sample has cracks, through holes, edge defects that enter the effective test area, unstable contact at the thickness measurement position, or the inability to obtain bulk resistance or determine the effective test area by AC impedance testing, it will not be considered a qualified sample even if its initial resistivity meets the above deviation conditions.

[0050] Qualified samples are not arbitrarily divided, but are grouped evenly according to sample thickness and initial area resistivity. Specifically, all qualified samples are first sorted in ascending order of initial area resistivity. If the difference in initial area resistivity between two samples is not greater than the upper limit of clamping repeatability error, they are then sorted in ascending order of sample thickness. After sorting, the samples are sequentially assigned to the single-sample benchmark test group, blank micro-area control test group, composite micro-area simulation test group, active material background reference test group, and parallel termination confirmation test group using a rotating allocation method.

[0051] After the rotation and allocation are completed, the initial median area resistivity and median sample thickness of each test group are calculated respectively. If the deviation of the initial median area resistivity of any test group relative to the initial median area resistivity of all qualified samples is greater than the upper limit of clamping repeatability error, the grouping is readjusted so that the deviation of the initial median area resistivity of each group is not greater than the upper limit of clamping repeatability error. For sample thickness, the repeatability measurement error of the same thickness gauge is used as the equalization threshold. This repeatability measurement error is obtained by repeatedly measuring the thickness of the same sample at the same measurement position, and the maximum absolute deviation of each measurement value relative to the median is taken as the upper limit of thickness repeatability measurement error. If the deviation of the median sample thickness of any test group relative to the median thickness of all qualified samples is greater than the upper limit of thickness repeatability measurement error, the grouping is readjusted so that the median thickness of each group meets the deviation condition.

[0052] Each of the single-piece benchmark test group, blank micro-region control test group, composite micro-region simulation test group, and active material background reference test group should include at least three qualified samples; the parallel termination confirmation test group should include at least nine qualified samples, so as to subsequently form pre-confirmation potential termination samples, composite micro-region oxidation candidate start point termination samples, and composite micro-region upper limit test potential termination samples, with each type of termination sample including at least three qualified samples; if the number of qualified samples is insufficient to meet the above requirements, or if the initial area resistivity and sample thickness equalization conditions cannot be met simultaneously, then the same batch of solid electrolyte samples should be re-prepared and this step should be repeated.

[0053] After the above screening and grouping, a standardized solid electrolyte sample group is formed. The standardized solid electrolyte sample group includes a single-piece benchmark test group, a blank micro-area control test group, a composite micro-area simulation test group, an active material background reference test group, and a parallel termination confirmation test group. Each test group meets the same batch comparability conditions in terms of initial area resistivity and sample thickness.

[0054] S3, such as Figure 1 As shown, a blank micro-region control system was established based on a standardized solid electrolyte sample group. Current density curves of the blank micro-region were collected within the test potential window of the candidate composite micro-region. Based on the blank micro-region current density curves, the test potential window of the composite micro-region, the upper limit of the micro-region background current, and the threshold for the number of consecutive points of the micro-region oxidation response were determined; specifically as follows: Samples were selected from the blank micro-region control test group in the standardized solid electrolyte sample group, and a blank micro-region layer was formed on the surface of the sample. The blank micro-region layer included solid electrolyte powder, conductive agent and binder of the same type as the target composite cathode formulation, but without the addition of the target cathode active material.

[0055] The areal loading of the blank micro-region layer is determined by candidate layer screening. Specifically, on the surface of qualified solid electrolyte samples in the same batch, at least two, preferably at least three, candidate blank micro-region layers are prepared according to the feeding quality level, coating gap level, or tableting feeding level that can be achieved by the same preparation equipment, arranged from low to high areal loading. The actual areal loading of each candidate blank micro-region layer is obtained by weighing the sample mass difference before and after preparation and dividing it by the effective test area of ​​the blank micro-region.

[0056] In-plane electronic continuity testing is performed on each candidate blank micro-area layer. The contact points for the in-plane electronic continuity test include the center and edge positions of the effective test area. The center position is the geometric center of the effective test area. The edge positions are obtained according to the rules for determining the boundary of the effective test area and correspond to the areas where the actual current collector and the blank micro-area layer may contact. The distance between adjacent contact points is not greater than the contact width of the actual current collector. The in-plane electronic resistance between the center position and each edge position, as well as between adjacent edge positions, is measured using an electronic resistance meter. If no open circuit state outside the instrument range is found in the above paths, the candidate blank micro-area layer is determined to form a continuous electronic continuity layer. The open circuit state outside the instrument range is determined by the open circuit reading displayed by the electronic resistance meter when the two test probes are disconnected, without setting an empirical resistance threshold. The candidate blank micro-area layer that meets the continuous electronic continuity condition and has the lowest actual areal load is selected as the blank micro-area control layer.

[0057] The blank micro-region control layer, the same batch of solid electrolyte sample, the current collector, and the lithium metal electrode or lithium indium electrode are assembled into a blank micro-region control system; the test temperature, stacking pressure, and potential reference system of the blank micro-region control system adopt the target test temperature, target stacking pressure, and unified reference system.

[0058] Background scanning was performed on the blank micro-region control system within the test potential window of the candidate composite micro-region to obtain the current density curve of the blank micro-region. The scan rate was determined by the target charging regime: the charging time required for the target cathode to charge from the lower discharge limit state to the charging cutoff state was obtained according to the target charging regime, and the potential span of the test potential window of the candidate composite micro-region was divided by the charging time to obtain the background scan rate. If the target charging regime is a constant current charging regime, the charging time is the time required for the target cathode to reach the charging cutoff potential from the lower discharge limit state of the target cathode. If the target charging regime is a constant current and constant voltage charging regime, the charging time is the time required from the constant current stage of the test potential window of the candidate composite micro-region to the charging cutoff potential of the target cathode. The time required for the target positive electrode discharge lower limit potential to reach the target positive electrode charging cutoff potential is taken as the charging time. The constant voltage stage is not used to calculate the background scan rate, but only to define the target charging termination condition. If the target charging regime is a stepped current charging regime or a pulse charging regime, the cumulative charging time from the target positive electrode discharge lower limit potential to the target positive electrode charging cutoff potential for the first time is taken as the charging time. The cumulative charging time of the stepped current charging regime is the sum of the durations of each stepped current, and the cumulative charging time of the pulse charging regime is the sum of the durations of each charging pulse, excluding rest time, intermittent time, and constant voltage holding time.

[0059] The highest usable potential of the fixture is determined based on the blank micro-area current density curve; the blank low-potential baseline segment is first determined; the blank low-potential baseline segment is taken from the interval near the initial test potential of the composite micro-area and where no continuous current rise has occurred; the number of continuous sampling points required for continuous rise is determined by the open-circuit noise current curve of the tester: under the open-circuit state without connecting the electrochemical test cell, the open-circuit noise current curve is collected according to the same sampling period as the blank micro-area background scan, and the effective test area of ​​the blank micro-area is converted into the open-circuit noise current density curve; the maximum number of sampling points with continuous unidirectional fluctuation in the open-circuit noise current density curve is counted, and this maximum number of sampling points is added by one as the number of continuous rise confirmation points; according to this number of continuous rise confirmation points, the interval before the first continuous rise in the blank micro-area current density curve is identified from the scan start point, and this interval is taken as the blank low-potential baseline segment.

[0060] The average and standard deviation of the current density in the blank low-potential baseline segment are calculated, and the average plus three times the standard deviation is taken as the upper limit of the fixture background current. In the blank micro-area current density curve, if an interval appears after a certain potential point where the number of consecutive sampling points is not less than the threshold of the number of consecutive points of fixture abnormality and the current density is higher than the upper limit of the fixture background current, then the first potential point in the interval is taken as the starting point of the fixture background abnormality. The threshold of the number of consecutive points of fixture abnormality is obtained by adding one to the longest number of consecutive sampling points in the circuit noise current density curve that exceeds the upper limit of the fixture background current. If no starting point of fixture background abnormality appears, the candidate upper limit test potential is taken as the highest potential available to the fixture. If a starting point of fixture background abnormality appears, the sampling potential before the starting point of fixture background abnormality is taken as the highest potential available to the fixture.

[0061] The lower of the candidate upper limit test potential and the highest available potential of the fixture is used as the upper limit test potential of the composite micro-region. If the highest available potential of the fixture is less than or equal to the starting test potential of the composite micro-region, it is determined that the current fixture or blank micro-region control system is not suitable for this composite micro-region test. The composite micro-region test potential window is not generated, and the fixture is replaced, the blank background response is reduced, or a blank micro-region control system is re-prepared and the background scan is re-executed. The final composite micro-region test potential window is formed from the starting test potential of the composite micro-region to the upper limit test potential of the composite micro-region.

[0062] Simultaneously, based on the blank low-potential baseline segment in the blank micro-region current density curve that is located within the final composite micro-region test potential window, the average current density and standard deviation of the corresponding baseline segment are calculated, and the average value plus three times the standard deviation is used as the upper limit of the micro-region background current; the number of the longest continuous sampling points in the blank micro-region current density curve that exceeds the upper limit of the micro-region background current plus one is used as the threshold for the number of continuous points of micro-region oxidation response; the upper limit of micro-region background current and the threshold for the number of continuous points of micro-region oxidation response are used for subsequent identification of candidate starting points for composite micro-region oxidation.

[0063] S4. Perform single-chip reference testing within the test potential window of the composite micro-region to obtain the single-chip reference oxidation start point; details are as follows: Samples are selected from the monolithic benchmark test group in the standardized solid electrolyte sample set. An inert electronic conductive layer is set on one side of the sample as the working electrode, and a lithium metal electrode or lithium indium electrode is set on the other side as the reference / counter electrode, and assembled into a monolithic benchmark test cell.

[0064] The inert electronic conductive layer uses a platform material that does not contain the target positive electrode active material and does not provide the target positive electrode lithium insertion / extraction reaction within the composite micro-region test potential window, including gold, platinum, stainless steel, or carbon layers. When using a carbon layer, a blank carbon layer battery is set up using qualified samples from the same batch, and scanned within the same composite micro-region test potential window, with its current density curve used as the carbon layer background curve. If gold, platinum, or stainless steel is used, the inert electrode background curve is obtained through the corresponding inert electrode blank battery. The test temperature, stacking pressure, scan rate, reference system, and effective test area of ​​the inert electrode background curve are consistent with those of the single-cell reference test battery.

[0065] Under the target test temperature and target stacking pressure, a single reference test cell is scanned according to the composite micro-region test potential window. The scan start potential is the composite micro-region start test potential, and the scan end potential is the composite micro-region upper limit test potential. The scan rate is consistent with the background scan rate. The original current density curve of the single reference test cell is subtracted from the corresponding inert electrode background curve to obtain the single-cell corrected current density curve. Subtraction is performed at the same potential point. If the sampling potential points of the two curves are not completely consistent, the sampling potential point of the single reference test cell is used as the reference. The adjacent sampling points on both sides of the potential point in the inert electrode background curve are taken, and the corresponding background current density is obtained by linear interpolation before subtraction.

[0066] The upper limit of the background current of a single chip is determined based on the single-chip calibration current density curve. Specifically, the interval near the initial test potential of the composite micro-region where no continuous current rise occurs is taken as the low potential baseline segment of the single chip. The number of continuous sampling points required for continuous rise is determined by the number of continuous rise confirmation points determined by the circuit breaker noise current density curve. The average value and standard deviation of the current density of the low potential baseline segment of the single chip are calculated, and the average value plus three times the standard deviation is taken as the upper limit of the background current of the single chip.

[0067] The threshold for the number of consecutive points in the single-chip oxidation response is determined by the corresponding inert electrode background curve. Specifically, the number of consecutive sampling points in the inert electrode background curve where the current density exceeds the upper limit of the single-chip background current is counted to obtain the maximum value of the number of consecutive points of false triggering of the inert electrode background. This maximum value is then added to one as the threshold for the number of consecutive points in the single-chip oxidation response.

[0068] In the monolithic calibration current density curve, if for the first time a continuous sampling point number is not less than the threshold for the continuous sampling point number of monolithic oxidation response, and the current density of all sampling points in the continuous interval is higher than the upper limit of the monolithic background current, and the current density at the end of the continuous interval is greater than the current density at the beginning, then the first potential point of the continuous interval is determined as the monolithic reference oxidation start point; if no interval conforming to the above rules is identified in the composite micro-area test potential window, then the monolithic reference oxidation start point is recorded as a test potential higher than the upper limit of the composite micro-area; this record only indicates that the monolithic oxidation start point was not observed in the test window determined in this embodiment.

[0069] S5. Construct a composite cathode micro-region simulation layer and perform potential scanning and recording within the composite micro-region test potential window at the same scanning rate as the single-chip benchmark test to obtain the full-process micro-region current density curve; construct an active material background reference structure to obtain the active material background current density curve; analyze the full-process micro-region current density curve and the active material background current density curve to obtain the full-process micro-region correction current density curve, and combine the upper limit of the micro-region background current and the threshold of the number of consecutive points of micro-region oxidation response to obtain the candidate starting point of composite micro-region oxidation; as detailed below: Samples were selected from the composite micro-region simulation test group in the standardized solid electrolyte sample group, and a composite cathode micro-region simulation layer was formed on one side of the sample. The composite cathode micro-region simulation layer includes the target cathode active material, solid electrolyte powder, conductive agent and binder, and the types and mass ratios of each component are all derived from the target composite cathode formulation.

[0070] The areal loading of the composite cathode micro-region simulation layer is determined through candidate layer screening. Specifically, on the surface of qualified solid electrolyte samples from the same batch, at least two, preferably at least three, candidate composite micro-region simulation layers are prepared according to the feeding quality level, coating gap level, or tableting feeding level achievable by the same preparation equipment. The actual areal loading of each candidate composite micro-region simulation layer is obtained by weighing the sample mass difference before and after preparation and dividing it by the effective test area of ​​the composite micro-region. The candidate composite micro-region simulation layers are subjected to in-plane electronic conductivity tests according to the contact point arrangement rules, contact distance rules, and open circuit judgment rules for in-plane electronic conductivity tests. The candidate composite micro-region simulation layer that meets the continuous electronic conductivity condition and has the lowest actual areal loading is selected as the composite cathode micro-region simulation layer. This composite cathode micro-region simulation layer is used to simulate the three-phase contact area of ​​the target composite cathode near the solid electrolyte layer and is not used as a complete capacity cathode.

[0071] A current collector layer is set outside the composite cathode micro-region simulation layer and assembled with the solid electrolyte sample to be evaluated, lithium metal electrode or lithium indium electrode to form a composite micro-region test structure; the effective test area, test temperature, stacking pressure, reference system and scan rate of the composite micro-region test structure are consistent with those of the single-piece benchmark test.

[0072] Simultaneously, samples were selected from the active material background reference test group in the standardized solid electrolyte sample group to establish an active material background reference test structure. The active material background reference layer includes the target positive electrode active material, conductive agent, and binder, without adding the solid electrolyte powder to be evaluated, and is set on the surface of the inert ion conduction isolation layer. The inert ion conduction isolation layer was confirmed by single-piece potential scanning of the candidate ion conduction layer: a single-piece potential scan was performed on the candidate ion conduction layer within the test potential window of the composite micro-region to obtain the corrected current density curve of the candidate ion conduction layer. The corrected current density curve of the candidate ion conduction layer was obtained by subtracting the corresponding inert electrode background curve. The interval near the initial test potential of the composite micro-region in the corrected current density curve of the candidate ion conduction layer without a continuous rise in current was taken as the low potential baseline segment of the isolation layer. The average current density and standard deviation of the low potential baseline segment of the isolation layer were calculated, and the average current density plus three times the standard deviation was taken as the upper limit of the background current of the isolation layer. Candidate ion-conducting layers with a number of sampling points not less than the threshold for continuous points in a single-layer oxidation response and a current density higher than the upper limit of the background current of the isolation layer are selected as inert ion-conducting isolation layers. The areal loading of the target positive electrode active material in the active material background reference layer is consistent with that in the composite positive electrode micro-region simulation layer. The closest target positive electrode active material areal loading means that the absolute difference between the target positive electrode active material areal loading of the candidate active material background reference layer and that in the composite positive electrode micro-region simulation layer is the smallest. If the layer continuity is insufficient due to the absence of the solid electrolyte powder to be evaluated, the same candidate layer screening method as the composite micro-region simulation layer is used to select the candidate layer that meets the continuous electron conduction condition and whose target positive electrode active material areal loading is closest to that in the composite positive electrode micro-region simulation layer as the active material background reference layer. If there are two or more candidate layers with the same absolute difference, the candidate layer with the lower actual areal loading is selected as the active material background reference layer.

[0073] A potential scan is performed on the active material background reference test structure within the test potential window of the composite micro-region to obtain the background current density curve of the active material. A full-process potential scan is performed on the composite micro-region test structure, starting from the initial test potential of the composite micro-region and scanning to the upper limit test potential of the composite micro-region. Potential, current and time are continuously recorded to form the full-process micro-region current density curve. When the upper limit test potential of the composite micro-region is lower than the target positive electrode charging cutoff potential, it is recorded as the test window not covering the entire target application potential range. Therefore, no conclusion is drawn that no early oxidation risk is found within the target application potential range.

[0074] The entire process micro-area current density curve is subtracted from the active material background current density curve to obtain the entire process micro-area corrected current density curve. Before subtraction, the entire process micro-area current and the active material background current are converted into current density according to the corresponding effective test area. During subtraction, the same potential point is used as the correspondence. If the sampling potential points of the two curves are not completely consistent, the sampling potential point of the entire process micro-area current density curve is used as the reference. The adjacent sampling points on both sides of the potential point in the active material background current density curve are taken, and the corresponding background current density is obtained by linear interpolation before subtraction.

[0075] In the full-process micro-area calibration current density curve, if for the first time a continuous sampling point number is not less than the threshold of the continuous sampling point number of micro-area oxidation response, and the current density of all sampling points in the continuous interval is higher than the upper limit of the micro-area background current, and the current density at the end of the continuous interval is greater than the current density at the beginning, then the first potential point of the continuous interval is determined as the candidate starting point of composite micro-area oxidation; if no interval that meets the above rules is identified in the composite micro-area test potential window, it is recorded as no candidate starting point of composite micro-area oxidation has been obtained.

[0076] S6, such as Figure 2 As shown, the candidate oxidation starting point of the composite micro-region is confirmed by parallel termination of the sample, the oxidation starting point of the composite micro-region is obtained, and the stability test results are output according to the advance of the oxidation starting point of the composite micro-region relative to the single-piece reference oxidation starting point; the details are as follows: When a candidate starting point for oxidation of the composite micro-region is obtained, a sample is selected from the parallel termination confirmation test group in the uniform solid electrolyte sample group, and the parallel termination confirmation sample is prepared according to the same formulation, areal load screening rules, effective test area, current collector setting method and assembly method as the composite cathode micro-region simulation layer.

[0077] The preliminary confirmation potential is determined based on the candidate starting point of the composite micro-area oxidation. The confirmation potential interval is determined by the test scan rate, the tester sampling period, and the threshold for the number of consecutive points of the micro-area oxidation response. Specifically, it is the test scan rate multiplied by the tester sampling period and then multiplied by the threshold for the number of consecutive points of the micro-area oxidation response. The preliminary confirmation potential is obtained by subtracting the confirmation potential interval from the candidate starting point of the composite micro-area oxidation. If the preliminary confirmation potential is lower than the starting test potential of the composite micro-area, the starting test potential of the composite micro-area is used as the preliminary confirmation potential, and the source of this adjustment is recorded.

[0078] Three types of parallel termination confirmation samples were set up: the first type of sample was scanned to the pre-confirmation potential and then the test was stopped; the second type of sample was scanned to the candidate starting point of oxidation in the composite micro-region and then the test was stopped; the third type of sample was scanned to the upper limit test potential of the composite micro-region and then the test was stopped. Each type of parallel termination confirmation sample included at least three samples prepared in the same batch. After the test was stopped for the three types of samples, the interface products were detected under the same disassembly environment, the same transfer container, the same transfer time control rules, and the same surface detection method.

[0079] The transfer time control rules were determined through a preliminary experiment on the exposure stability of untested solid electrolyte samples in the same batch. Specifically, the ratio of target oxidation products was detected after exposing the untested solid electrolyte samples to different candidate transfer times. The longest candidate transfer time that ensured the increase in the ratio of target oxidation products relative to the zero-exposure sample was no greater than the standard deviation of repeated detections was selected as the upper limit of the transfer time. The time from disassembly and exposure to entering the detection chamber or sealed transfer container for the three types of parallel termination confirmation samples did not exceed this upper limit of the transfer time.

[0080] For each type of sample, the ratio of target oxidation products at the composite micro-region contact interface and the non-contact interface was detected. The composite micro-region contact interface refers to the surface area of ​​the solid electrolyte sample that is in direct contact with the composite cathode micro-region simulation layer. The non-contact interface refers to the surface area on the same sample that is not covered by the composite cathode micro-region simulation layer but has undergone the same disassembly and transfer process. For oxide solid electrolytes, new or enhanced peroxide characteristic peaks, oxygen vacancy characteristic peaks, metal valence state increase characteristic peaks, or corresponding binding energy shift characteristic peaks were detected compared with the sample before oxidation. For polymer solid electrolytes, carbonyl groups, ether bond cleavage products, fluorinated salt decomposition products, or polymer oxidation crosslinking related species were detected. The actual target oxidation products were determined by the characteristic peaks that could distinguish the background and the post-oxidation response in the surface detection spectra of the untested sample, the blank micro-region control sample, and the composite micro-region termination sample.

[0081] The oxidation product confirmation threshold is determined by the background samples in the same batch. Specifically, samples that were not tested for solid electrolyte, samples that did not reach the single-piece reference oxidation starting point in the single-piece reference test, and samples after blank micro-area control test are tested to obtain the ratio of the target oxidation product peak area to the matrix characteristic peak area. The maximum value of the above ratio is added to three times the standard deviation of repeated detections as the oxidation product confirmation threshold. The standard deviation of repeated detections is calculated from the ratio of target oxidation products at multiple detection points in the same area of ​​the same sample.

[0082] The median of the target oxidation product ratios for parallel termination confirmation samples of the same type is taken as the representative value of the target oxidation product for that type of sample. When the representative value of the target oxidation product of the second type of sample is higher than that of the first type of sample, and the representative value of the target oxidation product of the second type of sample reaches the oxidation product confirmation threshold, and the representative value of the target oxidation product of the third type of sample is higher than that of the second type of sample, it is determined that there is a corresponding relationship between the candidate starting point of oxidation in the composite micro-region and the generation of oxidation products on the surface of the solid electrolyte, and the candidate starting point of oxidation in the composite micro-region is confirmed as the starting point of oxidation in the composite micro-region. If the representative value of the target oxidation product at the non-contact interface also reaches the oxidation product confirmation threshold, it is determined to be overall sample contamination, disassembly contamination, or transfer contamination, and this result is not used as the oxidation confirmation result caused by composite micro-region contact.

[0083] Subsequently, deviations were determined based on the single-cell baseline oxidation initiation point and the composite micro-region oxidation initiation point. The deviation determination threshold was determined by the repeatability of the same batch of samples: the single-cell baseline oxidation initiation point was obtained and the standard deviation was calculated for multiple qualified samples in the single-cell baseline test group; the composite micro-region oxidation initiation point was obtained and the standard deviation was calculated for multiple qualified samples in the composite micro-region simulation test group; the standard deviation was calculated for the blank false trigger potential points that appeared in the blank micro-region control test group; the maximum value of the above standard deviations was multiplied by three to obtain the deviation determination threshold. If no oxidation initiation point or false trigger potential point appeared in a certain group, that group was not included in the standard deviation calculation. If only one group could calculate the standard deviation, the standard deviation of that group was multiplied by three to obtain the deviation determination threshold. If no standard deviation could be calculated for any group, the background abnormal initiation point or test termination potential deviation obtained by scanning after repeated mounting of the same blank battery was used as the source of potential test repeatability, and the deviation determination threshold was determined accordingly.

[0084] When the oxidation starting point of the composite micro-region is lower than the single-electrode reference oxidation starting point, and the difference between the two is greater than the deviation judgment threshold, and the parallel termination sample confirms that the candidate oxidation starting point of the composite micro-region corresponds to the generation of oxidation products on the surface of the solid electrolyte, the stability test result is output indicating a risk of missed detection of early oxidation under composite cathode micro-region contact conditions. When the single-electrode reference oxidation starting point is recorded as higher than the upper limit test potential of the composite micro-region, the difference between the upper limit test potential of the composite micro-region and the oxidation starting point of the composite micro-region is used as a conservative difference for judgment. In the corresponding case, the single-electrode reference oxidation starting point does not appear within the test potential window of the composite micro-region, so the upper limit test potential of the composite micro-region is used as the conservative lower limit of the single-electrode reference oxidation starting point for difference calculation. If the difference between the upper limit test potential of the composite micro-region and the oxidation starting point of the composite micro-region is still greater than the deviation judgment threshold, it is determined that the judgment requirement of the oxidation starting point of the composite micro-region being earlier than the single-electrode reference oxidation starting point is met.

[0085] If the oxidation initiation point of the composite micro-region is below the target positive electrode charging cutoff potential, the result of the risk of missed early oxidation within the target application potential range will be output. If, provided that the upper limit test potential of the composite micro-region is not lower than the target positive electrode charging cutoff potential, no candidate oxidation initiation point of the composite micro-region is obtained, or the candidate oxidation initiation point of the composite micro-region is not confirmed by surface oxidation products, or the advance of the oxidation initiation point of the composite micro-region relative to the single-piece reference oxidation initiation point is not greater than the deviation judgment threshold, the stability test result indicating that no risk of missed early oxidation under the contact condition of the composite positive electrode micro-region will be output. If the upper limit test potential of the composite micro-region is lower than the target positive electrode charging cutoff potential, the result of insufficient test window will be output, and the conclusion that no risk of missed early oxidation will be output will not be output.

[0086] Example 1

[0087] I. Experimental Materials and Target Application Conditions

[0088] The solid electrolyte to be evaluated is a Li6PS5Cl sulfide solid electrolyte with a purity of not less than 99.5% and a median particle size of 3.2 μm. The target positive electrode active material is LiNi0.8Co0.1Mn0.1O2, abbreviated as NCM811; the conductive agent is conductive carbon black, and the binder is polytetrafluoroethylene.

[0089] The mass ratio of NCM811, Li6PS5Cl, conductive carbon black, and polytetrafluoroethylene in the target composite cathode is 70:27:2:1. The target cathode has a discharge lower limit potential of 3.00 V and a charge cutoff potential of 4.10 V, both relative to Li / Li + The target test temperature is 25 ℃, the target voltage is 10 MPa, and the target charging regime is constant current charging at 0.2 C to 4.10 V followed by constant voltage charging until the current decreases to 0.05 C.

[0090] The constant current phase time for charging the target positive electrode half-cell from 3.00 V to 4.10 V was 4.25 h. Therefore, the potential scan rate was determined according to the following formula: ; In the formula, The potential scan rate is denoted by . The test potential window for candidate recombination microregions is 3.00–4.10 V.

[0091] All operations involving the preparation, tableting, assembly, disassembly, and transfer of Li6PS5Cl are carried out in an argon-filled glove box, where the water and oxygen content are respectively not more than 0.1 ppm.

[0092] II. Solid Electrolyte Sample Preparation and Consistency Screening

[0093] Li6PS5Cl powder was added to a tableting mold with a diameter of 10 mm and held at a pressure of 350 MPa for 3 min to obtain a solid electrolyte sample. The effective exposure window diameter of the subsequent testing fixture was 8 mm, corresponding to an effective testing area of ​​0.503 cm².

[0094] A total of 75 solid electrolyte samples were prepared. Thickness measurements were taken at the center and four edge positions of each sample, and the median of the five thickness measurements was used as the sample thickness. To determine the upper limit of the repeatability error of the thickness gauge, a solid electrolyte sample with intact appearance was selected, and five consecutive measurements were taken at the same center position, yielding thickness measurements of 0.804 mm, 0.812 mm, 0.796 mm, 0.803 mm, and 0.806 mm. The median of the five measurements was 0.804 mm, and the absolute deviations of each measurement relative to this median were 0 mm, 0.008 mm, 0.008 mm, 0.001 mm, and 0.002 mm, respectively. Therefore, the maximum absolute deviation of 0.008 mm was taken as the upper limit of the repeatability error of the thickness gauge. AC impedance spectroscopy was measured using a stainless steel blocking electrode under conditions of 25 ℃ and 10 MPa, and the initial area resistivity was obtained by multiplying the bulk resistance at the high-frequency end with the effective test area.

[0095] The initial resistivity obtained by five repeated clamping of the same wafer was 31.2 Ω·cm², 31.8 Ω·cm², 31.5 Ω·cm², 31.9 Ω·cm² and 31.4 Ω·cm², respectively. The median was 31.5 Ω·cm² and the maximum absolute deviation was 0.4 Ω·cm². Therefore, the upper limit of the clamping repeatability error was determined to be 0.4 Ω·cm².

[0096] The median initial area resistivity of the 75 samples was 31.6 Ω·cm². Samples with an initial area resistivity between 31.2 and 32.0 Ω·cm², no cracks, and a measurable effective test area were considered qualified samples. A total of 72 qualified samples were obtained. These 72 qualified samples were divided into core test samples and comparison and reference test samples. Among them, 33 samples were used for the core tests of this invention, including 6 samples in the single-cell benchmark test group, 6 samples in the blank micro-region control group, 6 samples in the composite micro-region simulation group, 6 samples in the active material background reference group, and 9 samples in the parallel termination confirmation group; the remaining 39 samples were used for comparison and reference tests, including 6 samples in the conventional single-cell test group, 6 samples in the full-cell comparison test group, and 27 samples in the stepped termination reference group.

[0097] The sample data for each test group are shown in Table 1.

[0098] Table 1. Consistency data of samples from each test group

[0099] The initial area resistivity in Table 1 is only used to evaluate the consistency of each solid electrolyte sample; the area resistivity before and after charging in Comparative Example 2 is the area resistivity of the full-cell test structure. The two test structures and uses are different, so they are not directly compared.

[0100] The deviation of the median of the initial area resistivity of each group from the median of all qualified samples does not exceed 0.2 Ω·cm², which is less than the upper limit of the clamping repeatability error of 0.4 Ω·cm²; the maximum difference of the median thickness of each group is 0.005 mm, which is less than the upper limit of the thickness gauge repeatability error of 0.008 mm. Therefore, each test group meets the consistency requirements.

[0101] III. Blank Micro-region Comparison and Criterion Determination

[0102] A blank microlayer without NCM811 was prepared using Li6PS5Cl, conductive carbon black, and polytetrafluoroethylene in a mass ratio of 90:6.7:3.3. Candidate blank microlayers with areal loadings of 0.6 mg / cm², 0.9 mg / cm², and 1.2 mg / cm² were prepared. The candidate layer with an areal loading of 0.6 mg / cm² showed an open circuit at the edge test point, while the candidate layers with areal loadings of 0.9 mg / cm² and 1.2 mg / cm² met the continuous electron conduction condition. Therefore, the candidate layer with an areal loading of 0.9 mg / cm² was selected as the blank microlayer.

[0103] Background scanning was performed on the blank micro-area control system within the range of 3.00–4.30 V to determine the highest usable potential of the test fixture. A continuous abnormal response meeting the fixture background anomaly judgment criteria first appeared at 4.26 V; therefore, 4.26 V was determined as the starting point of the fixture background anomaly. Since the candidate upper limit test potential was 4.10 V, which is lower than the usable potential range corresponding to the starting point of the fixture background anomaly, 4.10 V was taken as the upper limit test potential of the composite micro-area. The final composite micro-area test potential window was determined to be 3.00–4.10 V.

[0104] The average current density in the blank low-potential baseline segment is 0.021 μA / cm², with a standard deviation of 0.006 μA / cm². Therefore, the upper limit of the micro-region background current is... for: ; In six blank micro-area scans, the longest consecutive sampling point with a current density exceeding 0.039 μA / cm² was 4. Therefore, the threshold for the number of consecutive sampling points in the micro-area oxidation response was determined. for: ; That is, only when the current density of at least 5 consecutive sampling points is higher than 0.039 μA / cm², and the current density at the end of the corresponding continuous interval is higher than the current density at the beginning, is the continuous interval considered as the micro-area oxidation response interval.

[0105] IV. Single-chip benchmark test results

[0106] A gold electrode was placed on one side of a solid electrolyte sample, and a lithium indium reference / counter electrode was placed on the other side. Single-piece benchmark tests were performed under the conditions of 25 °C, 10 MPa, and 0.0719 mV / s.

[0107] Within the target application potential window of 3.00 to 4.10 V, none of the six samples showed a continuous range that met the single-chip oxidation response criterion. Therefore, the single-chip reference oxidation start point recorded in this invention is higher than 4.10 V.

[0108] To obtain the actual oxidation starting point of the conventional single-chip linear scan voltammetry method, the conventional single-chip test group was scanned to 4.30 V. The oxidation starting points obtained for the six samples were 4.16 V, 4.17 V, 4.17 V, 4.18 V, 4.17 V, and 4.16 V, respectively, with an average value of 4.168 V and a standard deviation of 0.008 V. The oxidation starting point obtained from the conventional single-chip test was taken as 4.17 V.

[0109] In the low-potential baseline range of 3.20–3.80 V for six single-chip reference test samples, the average corrected current density was 0.018 μA / cm², with a standard deviation of 0.005 μA / cm². Therefore, the upper limit of the background current for a single chip is: .

[0110] Analysis of the circuit breaker noise current density curve revealed that the maximum number of continuous sampling points with sustained unidirectional fluctuations was 3, and the number of points with continuous rise was 4. In the inert electrode background curve, the longest number of continuous sampling points with current density exceeding 0.033 μA / cm² was 4, and the threshold for the number of continuous points in the single-piece oxidation response was 5.

[0111] V. Composite Micro-area Test and Background Subtraction Results

[0112] A composite cathode micro-region simulation layer was prepared using NCM811, Li6PS5Cl, conductive carbon black, and polytetrafluoroethylene in a mass ratio of 70:27:2:1. Candidate layers with actual areal loadings of 1.2 mg / cm², 1.8 mg / cm², and 2.4 mg / cm² were prepared. The candidate layer with an areal loading of 1.2 mg / cm² did not meet the edge-position electron conduction condition, while the candidate layers with areal loadings of 1.8 mg / cm² and 2.4 mg / cm² met the continuous electron conduction condition. Therefore, the candidate layer with an areal loading of 1.8 mg / cm² was selected as the composite cathode micro-region simulation layer. The actual areal loading of NCM811 was 1.26 mg / cm².

[0113] The active material background reference layer, without the addition of Li6PS5Cl, was prepared using NCM811, conductive carbon black, and polytetrafluoroethylene, and was placed on the surface of an inert ion-conducting isolation layer that, as confirmed by monolithic potential scanning, exhibited no oxidation response in the range of 3.00–4.10 V. The actual areal loading of NCM811 in the active material background reference layer was 1.25 mg / cm², which differed from the areal loading of NCM811 in the composite cathode micro-region simulation layer by 0.01 mg / cm².

[0114] In this embodiment, the relative deviation of the areal loading of the target positive electrode active material in the background reference layer and the composite positive electrode micro-region simulation layer is no more than 2% as the areal loading matching condition; the areal loading of NCM811 in the composite positive electrode micro-region simulation layer is 1.26 mg / cm², and the areal loading of NCM811 in the background reference layer is 1.25 mg / cm², with a relative deviation of: ; The load factor is less than 2%, therefore the surface load matching condition is met.

[0115] The full-process micro-area current density, the background current density of the active material, and the full-process micro-area corrected current density obtained after subtracting both are shown in Table 2.

[0116] Table 2 Current density data during composite micro-area testing

[0117] The original current density in the micro-region throughout the entire process is higher than the upper limit of the micro-region background current starting from 3.40 V. However, after deducting the background current of the active material, the micro-region corrected current density in the range of 3.40 to 3.95 V does not reach 0.039 μA / cm², indicating that the original current response in this range mainly comes from the lithium insertion / extraction reaction of NCM811.

[0118] Starting from 3.980 V, the micro-area correction current densities at five consecutive sampling points are 0.043 μA / cm², 0.048 μA / cm², 0.055 μA / cm², 0.061 μA / cm², and 0.069 μA / cm², respectively. All of these are higher than 0.039 μA / cm², and the current density at the end of the interval is higher than that at the beginning of the interval. Therefore, 3.980 V is determined as the candidate starting point for composite micro-area oxidation.

[0119] The candidate starting points for oxidation of the composite micro-regions obtained from the six composite micro-region simulation samples were 3.97 V, 3.98 V, 3.98 V, 3.99 V, 3.98 V and 3.97 V, respectively, with an average value of 3.978 V and a standard deviation of 0.008 V.

[0120] VI. Parallel Termination Sample Confirmation

[0121] To determine the upper limit of transfer time during surface detection, untested Li6PS5Cl solid electrolyte samples from the same batch were selected and exposed for 0 min, 1 min, 3 min, 5 min, 10 min, and 20 min, respectively, and the target oxidation product ratio was measured. The target oxidation product ratio for the zero-exposure sample was 0.020, and the ratios for 1 min, 3 min, 5 min, 10 min, and 20 min were 0.021, 0.022, 0.023, 0.027, and 0.041, respectively; the standard deviation of repeated detections was 0.003. The increments of each candidate transfer time relative to the zero-exposure sample were 0.001, 0.002, 0.003, 0.007, and 0.021, respectively. The increment of 0.003 corresponding to 5 min was not greater than the standard deviation of repeated detections of 0.003, while the increment of 0.007 corresponding to 10 min was greater than 0.003. Therefore, 5 min was taken as the upper limit of transfer time. The time from disassembly and exposure of the three types of parallel termination confirmation samples to their entry into the testing chamber or sealed transfer container is controlled within 5 minutes.

[0122] The testing instrument has a sampling period of 30 s, a scan rate of 0.0719 mV / s, and a threshold of 5 consecutive points for micro-area oxidation response. Therefore, the potential interval is confirmed. for: ; The candidate starting point for oxidation of the composite micro-region is 3.980 V, therefore the preliminary confirmation potential is... for: ; The pre-test potential was set to 3.97 V. The first type of parallel termination test sample stopped testing at 3.97 V, the second type of parallel termination test sample stopped testing at 3.98 V, and the third type of parallel termination test sample stopped testing at 4.10 V. Each type included three samples.

[0123] X-ray photoelectron spectroscopy was used to detect the characteristic peaks of newly added high-binding-energy sulfur-containing decomposition components on the surface of the solid electrolyte compared with the untested sample, and the ratio of the area of ​​this characteristic peak to the area of ​​sulfur characteristic peaks in the Li6PS5Cl matrix was used as the target oxidation product ratio.

[0124] Five untested solid electrolyte samples, five samples that did not reach the single-piece baseline oxidation starting point in the single-piece benchmark test, and five samples after the blank micro-area control test were selected. Five detection points were set on the same surface area of ​​each sample, resulting in 75 sets of target oxidation product ratios; the maximum value was 0.028. Ten additional detection areas were selected for repeated testing, with each area tested five times, yielding a repeat detection standard deviation of 0.003. Therefore, the oxidation product confirmation threshold was determined. for: .

[0125] The test results of the three types of parallel termination confirmation samples are shown in Table 3.

[0126] Table 3. Target oxidation product ratios of parallel termination confirmation samples

[0127] The representative value of the target oxidation product in the second type of sample (0.055) is higher than that in the first type of sample (0.029), and reaches the oxidation product confirmation threshold of 0.037. The representative value of the third type of sample (0.188) is higher than that in the second type of sample (0.055). Meanwhile, the representative values ​​of the non-contact interfaces in all three types of samples are below 0.037, ruling out overall sample contamination, disassembly contamination, and transfer contamination. Therefore, 3.98 V is confirmed as the starting point for oxidation in the composite micro-area.

[0128] The standard deviations of the oxidation initiation points of both the single-chip reference and the composite micro-region were 0.008 V. No false trigger potentials were found in the blank micro-region control group that could be used to calculate the standard deviation; therefore, the deviation judgment threshold was [not specified]. for: ; Using a conservative difference of 4.10-3.98=0.12V, and since 0.12V>0.024V, it is already possible to output the risk of missed detection in the early oxidation stage.

[0129] The oxidation initiation point obtained from conventional single-chip testing is 4.17 V, while the oxidation initiation point of the composite micro-region is 3.98 V. The lead time for both is: .

[0130] The lead time of 0.19 V is greater than the deviation judgment threshold of 0.024 V, and the oxidation start point of the composite micro-region of 3.98 V is lower than the target positive electrode charging cutoff potential of 4.10 V. Therefore, the output is: there is a risk of missed detection of early oxidation of the solid electrolyte under the contact conditions of the composite positive electrode micro-region.

[0131] VII. Determining the Reference Oxidation Start Point through Stepped Termination Test

[0132] To independently evaluate the oxidation starting point obtained by each test method, 27 qualified samples from the same batch were used to prepare the same composite cathode micro-region structure. The test was stopped at 3.90 V, 3.92 V, 3.94 V, 3.96 V, 3.98 V, 4.00 V, 4.02 V, 4.04 V and 4.06 V, respectively. Three samples were set at each termination potential, and the median of the target oxidation product ratio was obtained by the same X-ray photoelectron spectroscopy detection method.

[0133] Table 4 Results of the Stepped Termination Test

[0134] 3.98 V is the first termination potential that causes the target oxidation product ratio to reach the oxidation product confirmation threshold, and the target oxidation product ratio corresponding to each subsequent termination potential increases sequentially. Therefore, 3.98 V is taken as the true value of the reference oxidation starting point for this group of samples.

[0135] 8. Proportional Setting

[0136] Comparative Example 1 is a conventional single-chip linear scan voltammetry test. This method uses a gold electrode in direct contact with the solid electrolyte sample, without setting a target composite cathode micro-region simulation layer, and scans at a scan rate of 0.0719 mV / s up to 4.25 V. The oxidation initiation point is determined based on the position where the calibration current density first continuously exceeds the upper limit of the single-chip background current.

[0137] Comparative Example 2 shows the full-cell charging and impedance testing. A capacity-type composite cathode was prepared using the target composite cathode formulation, and a full cell was formed with the same batch of Li6PS5Cl solid electrolyte and lithium indium anode. The cell was charged to 4.10 V according to the target charging regime. The oxidation of the solid electrolyte was determined based on whether abnormal voltage response appeared in the charging curve and the change in area resistivity before and after charging.

[0138] Comparative Example 3 focuses on the detection of surface products at the endpoint. After charging the full battery to 4.10 V, it was disassembled, and the ratio of the target oxidation products at the interface between the solid electrolyte and the composite cathode was detected only at the end of charging. Multiple termination potentials were not set.

[0139] Comparative Example 4 uses a composite micro-region test structure, but does not subtract the background current density curve of the active material. Instead, it directly uses the position where the original current density of the micro-region first exceeds 0.039 μA / cm² as the oxidation starting point.

[0140] Comparative Example 5 analyzes the micro-area correction current density curves throughout the process, but does not use a continuous point threshold. As long as the current density at any sampling point exceeds 0.039 μA / cm², the corresponding potential is taken as the oxidation starting point.

[0141] Comparative Example 6 uses active material background subtraction and consecutive point threshold to obtain candidate starting points for oxidation in composite micro-regions, but does not set parallel termination confirmation samples, nor does it detect surface oxidation products at the corresponding potential.

[0142] IX. Final Results of Examples and Comparative Examples

[0143] In the full-cell comparison test group, no voltage response capable of independently determining the oxidation initiation point was observed on the charging curve during the charging process to 4.10 V. The average area resistivity before charging was 52.1 Ω·cm², and the average area resistivity after charging was 72.4 Ω·cm², representing an increase of: In the formula, This represents the percentage increase in resistivity before and after charging.

[0144] This impedance change only indicates an increase in interface impedance after charging is complete; it cannot determine the potential at the start of the oxidation reaction.

[0145] The target oxidation product ratio measured at 4.10 V was 0.164, which is higher than the oxidation product confirmation threshold of 0.037. This can prove that there are oxidation decomposition products at the charging endpoint, but the oxidation start point cannot be located at 3.98 V.

[0146] In the data processing of Comparative Example 5, an isolated sampling point with a current density of 0.051 μA / cm² appeared at 3.76 V. The two sampling points following this point decreased to 0.028 μA / cm² and 0.026 μA / cm², respectively, without forming a continuously rising range. When using single-point determination, this isolated sampling point was identified as the oxidation starting point; when using the continuous point threshold of this invention, this sampling point was excluded.

[0147] The final results of each test method are shown in Table 5.

[0148] Table 5 Test results of the present invention and various comparative examples

[0149] 10. Comparison Results Analysis

[0150] As shown in Table 5, the oxidation starting point obtained by conventional single-cell testing is 4.17 V, which is 0.19 V higher than the reference oxidation starting point of 3.98 V determined by the step termination test. Furthermore, no oxidation response was detected within the target application potential window of 3.00 to 4.10 V. Therefore, premature oxidation of the solid electrolyte under the contact conditions of the composite positive electrode micro-region cannot be identified.

[0151] Full-cell charging and impedance testing yielded a 39.0% increase in area resistivity after charging, and endpoint surface product detection confirmed the presence of oxidation products at 4.10 V. However, neither method could determine whether the oxidation reaction started at 3.98 V.

[0152] The oxidation starting point obtained without deducting the background of the active material is 3.40 V, which differs from the true reference value by 0.58 V, indicating that the lithium insertion / extraction current of the target cathode active material interferes with the attribution of the oxidation current of the solid electrolyte. The oxidation starting point obtained without using the consecutive point threshold is 3.76 V, which differs from the true reference value by 0.22 V, indicating that isolated current fluctuations can cause premature determination of the oxidation starting point.

[0153] This invention forms a contact environment in which the target positive electrode active material, solid electrolyte, and conductive agent coexist by simulating a composite positive electrode micro-region layer; it eliminates the current contribution of the lithium insertion / extraction reaction of the target positive electrode by subtracting the background current of the active material; it eliminates single-point fluctuations by using the upper limit of the micro-region background current and the threshold of the number of consecutive points; and it correlates the candidate electrochemical response with the oxidation products on the surface of the solid electrolyte by using parallel termination samples.

[0154] The oxidation starting point of the composite micro-region obtained by this invention is 3.98 V, which is consistent with the reference true value obtained by the step termination test, and the oxidation behavior is identified as being 0.19 V earlier than that of conventional monolithic testing.

[0155] Example 2

[0156] like Figure 3 As shown, a stability testing system for battery solid electrolytes includes: The system includes a data acquisition and analysis module, a preparation and grouping module, a control analysis module, a benchmark testing module, a composite analysis module, and a stability analysis module. The data acquisition and analysis module is used to obtain the target composite cathode formulation, and to acquire the target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime. The target cathode charge cut-off potential and target cathode discharge lower limit potential are unified to the same potential reference system. Based on the unified target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime, the test potential window for candidate composite micro-regions is determined. The target composite cathode formulation is used for subsequent construction of the blank micro-region layer, the composite cathode micro-region simulation layer, and the active material background reference layer. The preparation and grouping module is used to prepare samples using the same batch of solid electrolyte raw materials. It screens and groups the samples according to their thickness, effective test area and initial area resistivity to obtain a uniform solid electrolyte sample group. The comparative analysis module is used to establish a blank micro-region control system based on a uniform solid electrolyte sample group. It collects the current density curve of the blank micro-region within the test potential window of the candidate composite micro-region and determines the test potential window of the composite micro-region, the upper limit of the background current of the micro-region, and the threshold of the number of consecutive points of the oxidation response of the micro-region based on the current density curve of the blank micro-region. The benchmark module is used to perform monolithic benchmark testing within the test potential window of the composite micro-region to obtain the monolithic benchmark oxidation start point; The composite analysis module is used to construct a composite cathode micro-region simulation layer and perform potential scanning and recording within the composite micro-region test potential window at the same scanning rate as the single-chip benchmark test to obtain the full-process micro-region current density curve; construct an active material background reference structure to obtain the active material background current density curve; analyze the full-process micro-region correction current density curve based on the full-process micro-region current density curve and the active material background current density curve, and combine the upper limit of the micro-region background current and the threshold of the number of consecutive points of micro-region oxidation response to obtain the candidate starting point of composite micro-region oxidation; The stability analysis module is used to confirm the candidate starting point of oxidation in the composite micro-region by confirming the sample through parallel termination, obtain the oxidation starting point of the composite micro-region, and output the stability test results based on the advance of the oxidation starting point of the composite micro-region relative to the single-piece reference oxidation starting point.

[0157] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing the stability of a battery solid electrolyte, characterized in that, The specific steps are as follows: S1. Obtain the target composite cathode formulation, and obtain the target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime; unify the target cathode charge cut-off potential and target cathode discharge lower limit potential to the same potential reference system, and determine the candidate composite micro-region test potential window based on the unified target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime; wherein, the target composite cathode formulation is used for subsequent construction of blank micro-region layer, composite cathode micro-region simulation layer, and active material background reference layer; S2. Samples are prepared using the same batch of solid electrolyte raw materials. Samples are screened and grouped equally according to their thickness, effective test area and initial area resistance to obtain a uniform solid electrolyte sample group. S3. Establish a blank micro-region control system based on a standardized solid electrolyte sample group. Collect the current density curve of the blank micro-region within the test potential window of the candidate composite micro-region. Determine the test potential window of the composite micro-region, the upper limit of the background current of the micro-region, and the threshold of the number of consecutive points of oxidation response of the micro-region based on the current density curve of the blank micro-region. S4. Perform single-chip reference testing within the test potential window of the composite micro-region to obtain the single-chip reference oxidation start point; S5. Construct a composite cathode micro-region simulation layer and perform potential scanning and recording within the composite micro-region test potential window at the same scanning rate as the single-chip benchmark test to obtain the full-process micro-region current density curve; construct an active material background reference structure to obtain the active material background current density curve; analyze the full-process micro-region correction current density curve based on the full-process micro-region current density curve and the active material background current density curve, and combine the upper limit of the micro-region background current and the threshold of the number of consecutive points of micro-region oxidation response to obtain the candidate starting point of composite micro-region oxidation; S6. Confirm the candidate starting point of composite micro-region oxidation by parallel termination of the sample, obtain the starting point of composite micro-region oxidation, and output the stability test results based on the advance of the starting point of composite micro-region oxidation relative to the single-piece reference oxidation starting point.

2. The method for testing the stability of a battery solid electrolyte according to claim 1, characterized in that, In step S1, the method for determining the test potential window for the candidate composite micro-region is as follows: The target positive electrode discharge lower limit potential and the target positive electrode potential when it reaches the charging cutoff state under the target test temperature, target stacking pressure and target charging regime are uniformly converted to the same potential reference system; the uniformly converted target positive electrode discharge lower limit potential is used as the composite micro-region starting test potential, the uniformly converted positive electrode potential when it reaches the charging cutoff state is used as the candidate upper limit test potential, and the potential interval formed by the composite micro-region starting test potential to the candidate upper limit test potential is used as the candidate composite micro-region test potential window.

3. The method for testing the stability of a battery solid electrolyte according to claim 1, characterized in that, In step S2, the initial area resistivity of each sample is measured under the same target test temperature and the same target stacking pressure. The upper limit of the clamping repeatability error is determined based on the deviation of the initial area resistivity measured by repeated clamping of the same sample. Samples whose initial area resistivity deviation relative to the median initial area resistivity of the same batch of samples is ≤ the upper limit of the clamping repeatability error are determined as qualified samples. Qualified samples are then evenly grouped according to initial area resistivity and sample thickness to obtain a uniform solid electrolyte sample group.

4. The method for testing the stability of a battery solid electrolyte according to claim 1, characterized in that, In step S3, the method for determining the composite micro-area test potential window, the upper limit of the micro-area background current, and the threshold for the number of consecutive points of micro-area oxidation response is as follows: Background scanning of the blank micro-region control system was performed within the test potential window of the candidate composite micro-region to obtain the current density curve of the blank micro-region. The highest usable potential of the fixture was determined based on the current density curve of the blank micro-region. The lower of the candidate upper limit test potential and the highest usable potential of the fixture was taken as the upper limit test potential of the composite micro-region. The potential interval formed from the initial test potential of the composite micro-region to the upper limit test potential of the composite micro-region was taken as the test potential window of the composite micro-region. The average current density and standard deviation are calculated based on the blank low potential baseline segment within the test potential window of the composite micro-region in the blank micro-region current density curve, and the average current density plus three times the standard deviation is taken as the upper limit of the background current of the micro-region. Identify each consecutive over-limit interval in the blank micro-region current density curve where the current density exceeds the upper limit of the micro-region background current, count the number of sampling points contained in each consecutive over-limit interval, and add one to the maximum number of sampling points as the threshold for the number of consecutive points of micro-region oxidation response; when there are no sampling points in the blank micro-region current density curve where the current density exceeds the upper limit of the micro-region background current, record the maximum number of sampling points as zero, and set the threshold for the number of consecutive points of micro-region oxidation response to one.

5. The method for testing the stability of a battery solid electrolyte according to claim 1, characterized in that: The composite cathode micro-region simulation layer includes the target cathode active material, the solid electrolyte powder to be evaluated, the conductive agent and the binder. The types and mass ratios of each component are determined according to the target composite cathode formulation. The method for constructing a composite cathode micro-region simulation layer is as follows: Several candidate composite micro-region simulation layers were prepared on the surface of the same batch of solid electrolyte samples, arranged in order of increasing areal loading. In-plane electron conduction tests were performed on each candidate composite micro-region simulation layer, and the candidate composite micro-region simulation layer with the lowest areal loading that meets the continuous electron conduction condition was selected as the composite positive electrode micro-region simulation layer. The continuous electron conduction condition means that the in-plane electron resistance test between the center and edge positions of the candidate composite micro-region simulation layer and between adjacent edge positions did not show an open circuit state outside the instrument range.

6. The method for testing the stability of a battery solid electrolyte according to claim 1, characterized in that, The method for constructing the background reference structure of the active material is as follows: Based on the mass ratio between the target positive electrode active material, conductive agent and binder in the target composite positive electrode formulation, after removing the solid electrolyte powder to be evaluated, the mass ratio is normalized to prepare the active material background reference layer. Multiple candidate ion-conducting layers different from the solid electrolyte material to be evaluated were prepared. The initial area resistivity of each candidate ion-conducting layer was measured at the target test temperature and target stacking pressure. The candidate ion-conducting layer whose initial area resistivity was not greater than the sum of the median initial area resistivity of the solid electrolyte sample to be evaluated and the upper limit of the clamping repeatability error was determined as the conductive candidate layer. Within the test potential window of the composite micro-region, the potential of the candidate conductive layer is scanned at the same scan rate as that of the monolithic benchmark test, and the background curve of the corresponding inert electrode is subtracted to obtain the corrected current density curve of the candidate ion conduction layer. The upper limit of the background current of the isolation layer is determined based on the low potential baseline segment near the initial test potential of the composite micro-region. When the corrected current density curve of the candidate ion conduction layer does not have a continuous interval within the test potential window of the composite micro-region where the number of continuous sampling points is not less than the threshold of the number of continuous points of the monolithic oxidation response and the current density of each sampling point is higher than the upper limit of the background current of the isolation layer, the corresponding candidate conductive layer is determined as the inert ion conduction isolation layer. An active material background reference layer is set on the surface of an inert ion conduction isolation layer, and the areal loading of the target positive electrode active material in the active material background reference layer is matched with the areal loading of the target positive electrode active material in the composite positive electrode micro-region simulation layer to obtain an active material background reference structure.

7. The method for testing the stability of a battery solid electrolyte according to claim 1, characterized in that, In step S5, the method for obtaining candidate starting points for oxidation in composite micro-regions is as follows: In the micro-area correction current density curve of the whole process, the continuous intervals that first meet the following conditions are identified: the number of continuous sampling points ≥ the threshold of the number of continuous points of micro-area oxidation response, the current density of each sampling point is higher than the upper limit of the micro-area background current, and the current density at the end of the interval is greater than the current density at the beginning of the interval. The first potential point of the continuous interval is taken as the candidate starting point of composite micro-area oxidation.

8. The method for testing the stability of a battery solid electrolyte according to claim 1, characterized in that, In step S6, the method for obtaining the oxidation starting point of the composite micro-region is as follows: The test was set at the first type of parallel termination confirmation sample, the test was stopped at the pre-confirmation potential, the test was stopped at the candidate oxidation starting point of the composite micro-region, and the test was stopped at the upper limit test potential of the composite micro-region. When the representative value of the target oxidation product of the second type of parallel termination confirmation sample is higher than that of the target oxidation product of the first type of parallel termination confirmation sample and reaches the oxidation product confirmation threshold, and the representative value of the target oxidation product of the third type of parallel termination confirmation sample is higher than that of the second type of parallel termination confirmation sample, the candidate starting point of composite micro-region oxidation is confirmed as the starting point of composite micro-region oxidation. The target oxidation product representative value is the median of the target oxidation product ratios among all samples in the same class of parallel termination confirmation samples, and the target oxidation product ratio is the ratio of the characteristic peak area of ​​the target oxidation product to the characteristic peak area of ​​the matrix.

9. The method and system for testing the stability of a battery solid electrolyte according to claim 1, characterized in that, In step S6, the method for outputting the stability test results is as follows: When the oxidation starting point of the composite micro-region is lower than the oxidation starting point of the single-electrode reference, the difference between the two is greater than the deviation judgment threshold, and the oxidation starting point of the composite micro-region is confirmed by the parallel termination confirmation sample, the risk of early oxidation failure under the contact condition of the composite positive electrode micro-region will be output as the stability test result; wherein, the deviation judgment threshold is determined based on at least one of the repeatability of the oxidation starting point of the single-electrode reference, the repeatability of the oxidation starting point of the composite micro-region, and the repeatability of the false trigger potential point of the blank micro-region.

10. A stability testing system for battery solid electrolytes, characterized in that, The system is used to implement the stability testing method for a battery solid electrolyte according to any one of claims 1-9. The system includes a data acquisition and analysis module, a preparation and grouping module, a control analysis module, a benchmark testing module, a composite analysis module, and a stability analysis module. The acquisition and analysis module is used to obtain the target composite cathode formulation, and to obtain the target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime. The target cathode charge cut-off potential and target cathode discharge lower limit potential are unified to the same potential reference system. Based on the unified target cathode charge cut-off potential, target cathode discharge lower limit potential, target test temperature, target stacking pressure, and target charging regime, the test potential window for candidate composite micro-regions is determined. The target composite cathode formulation is used for subsequent construction of a blank micro-region layer, a composite cathode micro-region simulation layer, and an active material background reference layer. The preparation and grouping module is used to prepare samples using the same batch of solid electrolyte raw materials, and to screen and group them equally according to the sample thickness, effective test area and initial area resistance to obtain a uniform solid electrolyte sample group. The control analysis module is used to establish a blank micro-region control system based on a uniform solid electrolyte sample group, collect the blank micro-region current density curve within the test potential window of the candidate composite micro-region, and determine the composite micro-region test potential window, the upper limit of the micro-region background current, and the threshold of the number of consecutive points of micro-region oxidation response based on the blank micro-region current density curve. The benchmark testing module is used to perform single-chip benchmark testing within the composite micro-region test potential window to obtain the single-chip benchmark oxidation start point; The composite analysis module is used to construct a composite cathode micro-region simulation layer and perform potential scanning and recording within the composite micro-region test potential window at the same scanning rate as the single-chip benchmark test to obtain the full-process micro-region current density curve; construct an active material background reference structure to obtain the active material background current density curve; analyze the full-process micro-region correction current density curve based on the full-process micro-region current density curve and the active material background current density curve, and combine the upper limit of the micro-region background current and the threshold of the number of consecutive points of micro-region oxidation response to obtain the candidate starting point of composite micro-region oxidation; The stability analysis module is used to confirm the candidate starting point of oxidation in the composite micro-region by confirming the sample through parallel termination, obtain the oxidation starting point of the composite micro-region, and output the stability test results based on the advance of the oxidation starting point of the composite micro-region relative to the single-piece reference oxidation starting point.

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