Method for selecting battery separator and application thereof

Abstract

This invention discloses a method for selecting battery separators and its application. The selection method includes the following steps: constructing a battery model I containing a standard separator based on the battery system to be tested; performing an adiabatic thermal runaway test on battery model I to obtain test data for battery model I, and then obtaining the self-heating initiation temperature T0 and the thermal runaway initiation temperature T0. c Based on the temperature T within the temperature range of T0 to Tc, and the time t required for battery model I to heat up from temperature T to Tc in the adiabatic thermal runaway test, a relationship graph between T and t is obtained, which serves as the response temperature-response time dynamic range graph applicable to the thermally broken separator of the battery system under test. The thermally broken temperature T' and response time t' of the thermally broken separator under test are determined. Based on the response temperature-response time dynamic range graph, the longest response time corresponding to T' in the dynamic range graph is obtained, denoted as t. ’ max Choose T0 < T' < Tc, and t' < t ’ max The thermally fusible separator is used as a thermally fusible separator applicable to the battery system under test. This detection method is based on the battery thermal runaway mechanism and can accurately and quickly determine whether the thermally fusible separator is suitable for a specific battery material system.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a method for selecting battery separators and their application. Background Technology

[0002] Lithium-ion batteries (LIBs), as a new generation of rechargeable battery systems, boast advantages such as high energy density and light weight, making them one of the most advanced energy storage devices currently available. Among these, lithium-ion battery safety is a major concern, with thermal runaway caused by internal short circuits being a primary contributing factor. Since the battery separator is typically located between the positive and negative electrodes, controlling the electrolyte's wetting and transport of lithium ions plays a crucial role in reducing or preventing thermal runaway. To address lithium-ion battery safety issues, numerous measures have been taken from the perspective of the battery separator, such as adding flame retardants or highly stable ceramic materials to the traditional separator manufacturing process; developing novel separators with high thermal stability; and developing lithium-ion separators with thermal shutdown capabilities. Currently published thermally shut-off separators exhibit a wide range of response temperatures and times, varying considerably. For example, response temperatures can range from 80-230℃, and response times from 30s-120min, representing orders of magnitude differences. This makes it difficult to accurately and quickly determine whether a thermally shut-off separator is suitable for a specific battery material system. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a new method for selecting battery separators. This detection method is based on the battery thermal runaway mechanism and can accurately and quickly determine whether a thermally melted separator is suitable for a specific battery material system. It has the characteristics of simple operation and good detection effect.

[0004] The present invention also proposes the application of the above-mentioned method for selecting battery separators.

[0005] A first aspect of the present invention provides a method for selecting a battery separator, comprising the following steps:

[0006] Based on the battery system under test, a battery model I containing a standard separator was constructed. Adiabatic thermal runaway tests were conducted on battery model I to obtain test data, from which the self-heating initiation temperature T0 and the thermal runaway initiation temperature T0 were obtained. c ;

[0007] Based on the temperature T located in the temperature range of T0 to Tc, and the time t required for battery model I to heat up from temperature T to Tc in the adiabatic thermal runaway test, a graph showing the relationship between T and t is obtained, which can be used as a dynamic range graph of response temperature-response time for the thermally melted separator of the battery system under test.

[0008] Determine the thermal break temperature T' and response time t' of the thermally broken diaphragm to be tested. Based on the dynamic range diagram of response temperature and response time, obtain the longest response time corresponding to T' in the dynamic range diagram, and denote it as t'. max Choose T0 < T' < Tc, and t' < t' max The thermally fused separator is used as a thermally fused separator that can be applied to the battery system under test.

[0009] The method for selecting a battery separator according to embodiments of the present invention has at least the following beneficial effects:

[0010] The battery separator selection method in this invention is based on the battery thermal runaway mechanism and effectively evaluates the suitability and safety of the separator through the response temperature-response time range. It can accurately and quickly determine whether a thermally shut-off separator is suitable for a specific battery material system (such as existing commercially available cathode materials, anode materials, and electrolyte combinations). It features simple operation and good testing results, providing a theoretical basis for exploring the commercial application of thermally shut-off separators (also known as thermal shutdown separators). It can be used to determine whether a thermally shut-off separator can be used commercially in commercial lithium-ion batteries. Simultaneously, the safety performance of the thermally shut-off separator under test can be judged based on the aforementioned response temperature-response time dynamic range diagram, verifying whether the thermally shut-off separator can be applied to commercial batteries and control battery thermal runaway at the response temperature, thereby effectively evaluating the separator's safety.

[0011] The response temperature of the thermally fused diaphragm is usually the melting point of the thermally fused layer (response material) in the thermally fused diaphragm. It can be measured by differential scanning calorimetry and is called the response material.

[0012] The response time of a thermally fused separator: This usually refers to the time required for the thermally fused layer in the separator to change from a high-porosity state to a dense state that hinders lithium-ion transport at the response temperature of the thermally fused separator.

[0013] In this invention, the dynamic range graph of response temperature-response time shows the response temperature on the horizontal axis and the response time on the vertical axis. It is formed by the relationship between temperature T (located in the T0 to Tc temperature range) and the time t required for battery model I to heat up from temperature T to Tc during the adiabatic thermal runaway test. This relationship, along with the horizontal axis, encloses the dynamic range region. When the thermal breakage temperature T' and response time t' of the thermal breakage separator under test are within the dynamic range region, the thermal breakage separator under test can be used as a thermal breakage separator applicable to the battery system under test.

[0014] The standard separator is the same type of separator used in conventional commercial lithium-ion batteries.

[0015] In some embodiments of the present invention, based on the test data, a thermal runaway temperature-time curve of battery model I is obtained, thereby obtaining the self-heating initiation temperature T0 and the thermal runaway initiation temperature T0. c .

[0016] Optionally, the test data can be analyzed in stages according to the battery thermal runaway stage (such as before the self-heating stage, the self-heating stage, and the thermal runaway stage) to obtain a thermal runaway temperature-time curve.

[0017] The thermal runaway temperature-time curve of battery model I was filtered for temperature range and mathematically processed to obtain a dynamic range of response temperature-response time for the thermally melted separator applicable to the battery system under test. The horizontal axis represents the response temperature, and the selection of the response temperature range is based on the analysis of the changes in specific internal components at different stages of thermal runaway. The resulting response temperature range is from the self-exothermic initiation temperature T0 to the thermal runaway initiation temperature T... c The vertical axis represents the response time t. The longest response time is determined based on the accumulation of heat in the battery during the self-heating process at the response temperature T, causing the overall battery temperature to rise to T. c The time required.

[0018] Preferably, in this invention, the characteristic temperature points of the thermal runaway behavior of the measured battery model I are analyzed (to obtain the self-heating initiation temperature T0, the thermal runaway initiation temperature T...). c The rate of temperature rise from T0 to Tc is obtained from adiabatic thermal runaway tests. c The times are t0 and t1 respectively. c For T0 to T c The time difference is calculated for each temperature point T within the response temperature range (the time difference is the time t required for battery model I to rise from temperature T to Tc in the adiabatic thermal runaway test), and the relationship between the response temperature T and the response time t is calculated. From this, the dynamic range diagram of the response temperature-response time of the thermally melted separator can be obtained.

[0019] In this invention, the candidate response materials can be selected first from the dynamic range diagram of the response temperature-response time of the thermally meltable diaphragm. The selected material is the response temperature range (T0 to T10) where the melting point (response temperature) falls within the dynamic range region of the dynamic range diagram. c Response material within the response temperature range.

[0020] In some embodiments of the present invention, differential scanning calorimetry is used to obtain the response temperature of the thermally fused diaphragm under test. Preferably, differential scanning calorimetry is used to obtain the melting point of the thermally fused fracture layer (response material) in the thermally fused diaphragm under test, and this is used as the response temperature of the thermally fused diaphragm.

[0021] In some embodiments of the present invention, the response time of the thermally broken diaphragm under test is obtained by scanning electron microscopy or by charge-discharge testing; wherein the charge-discharge testing method includes the following steps:

[0022] Battery Model I was used as the battery system, and the standard separator was replaced with the thermally melt-through separator to be tested, to construct Battery Model II.

[0023] At room temperature, after charging battery model II to achieve a state of charge of 95-100%, battery model II is placed at the response temperature of the thermally broken separator under test and then discharged to obtain the actual response time t' of the thermally broken separator under test.

[0024] Except for the separator, the positive and negative electrode materials of battery model II are the same as those of battery model I. Preferably, except for the separator, the positive electrode material, negative electrode material, and electrolyte of battery model II are the same as those of battery model I. After battery model II is placed at the response temperature of the thermally melted separator under test, it begins to discharge. The actual response time t' of the thermally melted separator under test is obtained by combining its voltage, current, and capacity changes.

[0025] In some preferred embodiments of the present invention, the response time of the thermally fused diaphragm under test is obtained by observing the surface state of the thermally fused diaphragm at different times using a scanning electron microscope.

[0026] In some preferred embodiments of the present invention, battery model II is charged and discharged using a constant current and constant voltage charging and discharging method, that is, a constant current and constant voltage charging-constant current discharging mode is used for charging and discharging tests.

[0027] In some preferred embodiments of the present invention, the standard separator in battery model I is replaced with the thermally melt-through separator to be tested, thereby obtaining battery model II.

[0028] In some preferred embodiments of the present invention, the battery model II is a coin cell. Typically, verifying that the thermally fused separator can prevent thermal runaway requires characterizing the thermal behavior using an accelerating rate calorimeter (ARC). However, firstly, ARC testing usually uses 18650 cylindrical or pouch cells, but the basic equipment requirements for preparing pouch cells and 18650 cells are high, and the preparation cost is also high. Therefore, preparing 18650 cylindrical or pouch cells with the thermally fused separator to be tested is costly and difficult. Even if a contract manufacturer is chosen for preparation, the cycle is long and expensive, and contract manufacturing generates too many useless batteries due to mass production, resulting in resource waste and environmental pollution. Secondly, ARC testing equipment is expensive, has high requirements for the experimental environment, and the cost of sending samples to testing institutions for testing is also relatively high. To maintain experimental accuracy, at least three identical battery samples need to be tested, which is time-consuming and costly.

[0029] In this invention, by obtaining the response temperature-response time dynamic range diagram of the thermo-melt-break separator, only the thermal behavior of battery model I needs to be tested using ARC. Subsequently, any thermo-melt-break separator fabricated can be incorporated into the dynamic range diagram for exploring its commercial potential and battery material matching. This process only requires fabricating the thermo-melt-break separator into a button cell model and testing its actual response time using a simple battery charge-discharge cycle device. The entire testing process is simple and easy to perform, and once the response temperature-response time dynamic range diagram corresponding to battery model I is established, it can be used long-term with stability and wide applicability, enabling a relatively accurate analysis of the commercial potential of the thermo-melt-break separator.

[0030] Since the positive electrode material, negative electrode material, and electrolyte of battery model II are the same as those of battery model I, the test results of battery model II are suitable for judging the compatibility between the thermally fused separator to be tested and the battery material system contained in battery model I. It can be used to judge whether the thermally fused separator to be tested can effectively block battery thermal runaway when used in battery model I.

[0031] In some preferred embodiments of the present invention, the charge-discharge test method includes the following operations: preparing a battery model II, determining the voltage range according to the positive and negative electrode materials, charging the battery model II at room temperature with constant current and constant voltage until its state of charge reaches 100%, placing the battery model II at the response temperature of the thermally broken separator to be tested and starting to discharge, and obtaining the actual response time t' of the thermally broken separator to be tested.

[0032] In some preferred embodiments of the present invention, battery model II is a coin cell battery, and a constant current and constant voltage charging-constant current discharging mode is adopted. The main observation is of the voltage and current changes during the battery discharge stage and the time taken for the voltage to drop to the minimum voltage to complete the discharge process is recorded. This time is the actual response time of the thermally melted separator.

[0033] In some embodiments of the present invention, an adiabatic thermal runaway test is performed on battery model I, and a thermal runaway temperature-time curve of battery model I is obtained based on the obtained test data; from the thermal runaway temperature-time curve, the self-heating initiation temperature T0 and the thermal runaway initiation temperature T of the battery model containing the standard separator are obtained. c .

[0034] In some embodiments of the present invention, the standard separator includes, but is not limited to, various commercially available separators, which conform to the GB / T36363-2018 "Polyolefin Separators for Lithium-ion Batteries" test standard.

[0035] Given the wide variety of commercially available batteries, batteries can be selected for testing based on actual needs. For example, a more suitable commercial separator can be chosen as the standard separator, or more suitable commercial battery components other than the separator can be selected as the constituent components of Battery Model I. Battery Model I can select commercial lithium-ion batteries of different capacities, types, and positive and negative electrodes.

[0036] In some embodiments of the present invention, the standard diaphragm is made of polyolefin.

[0037] In some embodiments of the present invention, the material of the standard diaphragm includes at least one of polyethylene (PE) or polypropylene (PP).

[0038] In some preferred embodiments of the present invention, the standard diaphragm may be a single-layer membrane or a multi-layer membrane. A multi-layer membrane may be a composite membrane.

[0039] In some preferred embodiments of the present invention, the standard diaphragm is a polyethylene membrane, a polypropylene membrane, or a composite membrane.

[0040] In some preferred embodiments of the present invention, the composite film comprises a PP layer, a PE layer and a PP layer stacked sequentially.

[0041] In some embodiments of the present invention, the thickness of the standard diaphragm is preferably 15-40 μm.

[0042] In some embodiments of the present invention, the positive electrode of the battery model I includes at least one of ternary nickel-cobalt-manganese material, lithium iron phosphate, or lithium cobalt oxide material.

[0043] In some embodiments of the present invention, the negative electrode of battery model I comprises at least one of graphite, graphene, carbon nanotubes, or silicon-based materials. Those skilled in the art will know that battery model I also includes an electrolyte, which may be a commercially available electrolyte composition.

[0044] In some embodiments of the present invention, T0 is the temperature at which the battery model I has a self-heating rate ≥ 0.02℃ / min under adiabatic thermal runaway test conditions.

[0045] In some preferred embodiments of the present invention, T0 is the temperature at which the self-heating rate of the battery model I is 0.02℃ / min under adiabatic thermal runaway test conditions.

[0046] In some embodiments of the present invention, the T c The temperature at which the self-heating rate of the battery model I is ≥1℃ / min under adiabatic thermal runaway test conditions.

[0047] Optionally, based on the adiabatic thermal runaway test data, a thermal runaway temperature-time curve can be obtained, and the thermal runaway temperature rise rate can be obtained. Along the positive direction of the horizontal axis of the thermal runaway temperature-time curve, the temperature point where the temperature rise rate first reaches ≥0.02℃ / min is selected as the self-heating temperature T0, and the temperature point where the temperature rise rate first reaches ≥1℃ / min is selected as the thermal runaway initiation temperature T. c .

[0048] In some embodiments of the present invention, the state of charge (SOC) of battery model I is 0-100%, and then an adiabatic thermal runaway test is performed. Preferably, this includes, but is not limited to, a fully charged state or a half-charged state. Optionally, the battery is processed to a certain SOC using a charge-discharge apparatus.

[0049] In some preferred embodiments of the present invention, the state of charge of battery model I is 50-100%, and then an adiabatic thermal runaway test is performed.

[0050] In some embodiments of the present invention, the test temperature range in the adiabatic thermal runaway test step is 50-400℃.

[0051] In some preferred embodiments of the present invention, the test temperature range in the adiabatic thermal runaway test step is 80-400℃.

[0052] In some preferred embodiments of the present invention, the heating gradient of the adiabatic thermal runaway test is 4-6°C, and the isothermal time under each heating gradient is 10-20 min.

[0053] In some embodiments of the present invention, an adiabatic accelerated calorimeter is used to conduct adiabatic thermal runaway tests on battery model I.

[0054] ARC (Acoustic Calorimetry) precisely tracks temperature to bring the sample temperature close to the ambient temperature, reducing heat exchange and providing a near-adiabatic environment for testing and analyzing the exothermic behavior of samples. It typically includes a calorimetric chamber and a control system. Its purpose is to assess the thermal hazard of substances and obtain the reaction kinetics and thermodynamic parameters of the samples. ARC can simulate the thermal characteristics of exothermic reaction processes when heat inside a battery cannot dissipate in time, making the reaction closer to the actual reaction process inside a lithium-ion battery, thus obtaining the kinetics of apparent exothermic reactions under thermal runaway conditions.

[0055] In some preferred embodiments of the present invention, the adiabatic thermal runaway test includes the following operations:

[0056] The battery model is placed in the calorimetric chamber (experimental area) of an adiabatic accelerated calorimeter, with the temperature-controlled thermocouple of the adiabatic accelerated calorimeter fixed to the center of the outer surface of the battery model. Optionally, three external thermocouples are added to test the temperature of the top, bottom, and sides of the battery model, respectively. The use of external thermocouples facilitates timely observation of the location of self-heating or thermal runaway within the battery.

[0057] In some preferred embodiments of the present invention, the program settings parameters of the adiabatic accelerated calorimeter (ARC) in the adiabatic thermal runaway test include: heating from room temperature to 50±2℃, holding for 10-20 min, performing gradient heating with a heating gradient of 5℃ and a sensitivity α of 0.02℃ / min; preferably, the ARC test temperature range is 50-400℃. The ARC uses a "Heat-Wait-Seek" mode to detect the exothermic behavior of the battery model. Specifically, through the above implementation, the battery is heated in steps starting from the initial temperature. When the temperature rises to each step, the system enters a wait mode to allow the sample, container, and calorimetric chamber to reach thermal equilibrium, enabling the system to more accurately search for the sample's exothermic behavior. After the wait phase, the system enters a seek mode to detect the sample's release temperature. The system determines that if the heating rate is less than the sensitivity (typically 0.02℃ / min), the system will return to the heating state. However, if the heating rate exceeds the detection sensitivity, it will be identified as a spontaneously exothermic system entering adiabatic mode. Accelerated calorimetry can simulate the thermal characteristics of exothermic reactions when internal battery heat cannot dissipate in time, making the reaction closer to the real reaction process, thus obtaining the kinetics of the apparent exothermic reaction under thermal runaway conditions. The data can be analyzed to obtain thermal performance parameters (such as the self-exothermic initiation temperature T0, the thermal runaway initiation temperature Tc, the maximum thermal runaway temperature, the heating rate, etc.).

[0058] In a second aspect, the present invention proposes the application of the above-described method for selecting battery separators in battery separator testing.

[0059] In this invention, an adiabatic thermal runaway test is conducted on battery model I to obtain its thermal runaway temperature-time curve. This allows for the generation of a dynamic range diagram (dynamic temperature-response time) for the thermally fused separator, which is matched to the battery system under test. Only the thermal behavior of the target battery model needs to be tested using ARC (Anaerobic Arc Testing). Subsequently, any thermally fused separator fabricated can be incorporated into the dynamic range diagram for commercial potential exploration and battery material matching. This process only requires fabricating the thermally fused separator into a test battery model (such as a coin cell model) and testing its actual response time using a simple battery charge-discharge cycle device. The entire testing process is simple and easy to perform. Furthermore, once the dynamic range diagram of the target battery model is established, it can be used long-term with stability and wide applicability, enabling a relatively accurate analysis of the commercial potential of the thermally fused separator. Attached Figure Description

[0060] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0061] Figure 1 This is a thermal runaway temperature-time curve of the pouch cell in Embodiment 1 of the present invention;

[0062] Figure 2 This is a dynamic range diagram of the response temperature-response time of the thermally meltable diaphragm in Embodiment 1 of the present invention;

[0063] Figure 3 This is a graph showing the charge and discharge test results of the battery model under test in Embodiment 1 of the present invention;

[0064] Figure 4 The SEM image shows the response time of the PBS / PI composite membrane in Example 1 of this invention.

[0065] Figure 5 This is a graph showing the response temperature-response time test results of the PBS / PI composite membrane in Example 1 of the present invention;

[0066] Figure 6 This is a graph showing the response temperature-response time test results of the diaphragm disclosed in Embodiment 1 of the present invention;

[0067] Figure 7 This is a thermal runaway temperature-time curve of the cylindrical battery in Embodiment 2 of the present invention;

[0068] Figure 8 This is a dynamic range diagram of the response temperature-response time of the thermally meltable diaphragm in Embodiment 2 of the present invention;

[0069] Figure 9 This is a graph showing the response temperature-response time test results of the PBS / PI composite membrane in Example 2 of the present invention;

[0070] Figure 10This is a comparative diagram showing the thermal runaway temperature-time curve of the cylindrical battery and the dynamic range of the response temperature-response time of the thermally melted separator in Embodiment 2 of the present invention.

[0071] Figure 11 This is a thermal runaway temperature-time curve of the cylindrical battery in Embodiment 3 of the present invention;

[0072] Figure 12 This is a dynamic range diagram of the response temperature-response time of the thermally meltable diaphragm in Embodiment 3 of the present invention;

[0073] Figure 13 The graph shows the response temperature-response time test results of the PBS / PI composite membrane in Example 3 of this invention. Detailed Implementation

[0074] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0075] Unless otherwise specified, the experimental methods described in the following examples are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used are all commercially available from the conventional market unless otherwise specified.

[0076] The preparation method of the PBS / PI composite membrane includes the following steps:

[0077] 1) Preparation of PBS spinning solution: Dissolve PBS in hexafluoroisopropanol and stir thoroughly to obtain spinning solution; wherein, the mass ratio of PBS to solvent hexafluoroisopropanol is 1:9, the stirring speed is 1000 rpm, and the time is 2h.

[0078] 2) Electrospun PBS nanofiber membrane: The spinning solution obtained in step 1) was subjected to high voltage to form a Taylor cone and received oriented onto a roller, followed by drying to obtain a PBS nanofiber membrane. The syringe capacity was 5 mL, with a 22# stainless steel needle; the electrospinning conditions were: temperature controlled at 20℃; positive voltage of 13 kV and negative voltage of -2 kV; injection speed of 0.7 mm / min; receiving distance of 10 cm; and spinning time of 30 min. The spun membrane was dried at 60℃ for 8 h.

[0079] 3) Preparation of polyamic acid (PAA) spinning solution: 4,4'-diaminodiphenyl ether (ODA) and pyromellitic anhydride (PMDA) were dissolved in N,N-dimethylamide (DMF) and stirred thoroughly to obtain the spinning solution. The mass ratio of ODA to PMDA was 1:1, and the mass ratio of the total mass of ODA and PMDA to the solvent DMF was 1:8. The stirring environment was an ice bath. ODA was first dissolved in DMF, and then PMDA was added successively. The stirring speed was 1000 rpm, and the stirring time was 10 h.

[0080] 4) Electrospun PAA nanofiber membrane: The spinning solution obtained in step 3) was subjected to high voltage to form a Taylor cone and received oriented onto a roller, followed by drying to obtain a PAA nanofiber membrane; the syringe capacity was 5 mL, and a 22# stainless steel needle was used. The electrospinning conditions were: temperature controlled at 60℃; positive spinning voltage of 16 kV, negative voltage of -2 kV; injection speed of 0.18 mm / min; receiving distance of 10 cm; spinning time of 20 min. The spun membrane was dried at 60℃ for 8 h.

[0081] 5) Preparation of PI nanofiber membrane by amidation of PAA nanofiber membrane: The prepared PAA membrane was placed in a muffle furnace and subjected to a stepped heat treatment program to obtain a yellow PI nanofiber membrane. The muffle furnace used stepped heating: the temperature was increased from 20℃ to 100℃ and held for 30 min, then increased to 200℃ and held for 30 min, then increased to 300℃ and held for 30 min, and finally increased to 400℃ and held for 30 min, with a heating rate of 5℃ / min.

[0082] 6) Preparation of PBS / PI composite membrane: The prepared PBS membrane and PI membrane were hot-pressed to obtain the PBS / PI composite membrane. The hot-pressing pressure was 1 MPa and the time was 30 min.

[0083] Electrolyte I: 1M LiPF6 solution, the solvent of which is a mixture of EC:DEC:DMC in a mass ratio of 1:1:1;

[0084] Example 1

[0085] This embodiment discloses a method for selecting a battery separator, which specifically includes the following steps:

[0086] (I) Take a soft-pack battery (battery model I), which is 96mm long, 42mm wide, and 7.2mm thick, and is softly packaged in an aluminum-plastic composite film shell. The positive electrode material is ternary nickel-cobalt-manganese (NCM), the negative electrode is graphite, the electrolyte is electrolyte I, the rated capacity is 3400mAh, and the voltage range is 3V-4.2V. The separator is a KELU 2325 separator made of PP / PE / PP three-layer separator, set as standard commercial separator I.

[0087] (II) Pre-treatment of the pouch battery: Discharge at a constant current of 0.5C to the cutoff voltage of 3V, let stand for 20 minutes, then charge at a constant current of 0.5C to 4.2V to the cutoff voltage, then switch to constant voltage charging until the current is less than 0.05C, let stand for 20 minutes. Repeat the above steps 3 times. The final state of charge of the pre-treated pouch battery is 100%.

[0088] (III) The pouch cell is fixed in the ARC experimental area, and the temperature-controlled thermocouple of the adiabatic accelerated calorimeter is fixed in the middle of the outer surface of the cell model. Optionally, three external thermocouples are added close to the cell surface and distributed at three positions along the longitudinal direction of the cylindrical cell (top, middle, and bottom) to observe the location of self-heating or thermal runaway in the cell. ARC test program parameters: The test sample is heated from room temperature to 50±2℃ in the chamber, rested for 15 min, and then subjected to gradient heating with a heating gradient of 5℃, resting for 10 min under each heating gradient; sensitivity 0.02℃ / min; ARC test temperature range 50-400℃. ARC uses a "Heat-Wait-Seek" mode to detect the exothermic behavior of the sample. The battery is heated in steps starting from the initial temperature. As the temperature rises to each step, the system enters a wait mode (optional 10 minutes) to allow the sample, container, and calorimetric chamber to reach thermal equilibrium. This allows for more precise detection of the sample's exothermic behavior. After the wait phase, the system enters a seek mode to detect the sample's release temperature. If the heating rate is less than 0.02℃ / min... -1 The system will return to the heating state, but if the rate of temperature increase exceeds the detection sensitivity, it will be identified as a spontaneously exothermic system entering adiabatic mode. Based on ARC test data, precise thermal reaction process parameters for the entire process are obtained, and thermal runaway temperature-time curves are plotted, such as... Figure 1 As shown.

[0089] (IV) Data Processing: Export the ARC test data, combine it with the thermal runaway temperature-time curve, differentiate it to obtain the thermal runaway temperature rise rate parameter, and select the point where the temperature rise rate first ≥ 0.02℃ / min as the self-heating initiation temperature T0 along the positive direction of the horizontal axis of the thermal runaway temperature-time curve, and the point where the temperature rise rate first ≥ 1℃ / min as the thermal runaway initiation temperature T0. c Select the temperature range T0 to T c This refers to the thermal runaway temperature range that can be controlled using a thermally fused diaphragm. T0 and T... were obtained from ARC experiments. c The times are t0 and t1 respectively. c For T0 to T cFor each temperature point T within the response temperature range, the time difference t (the time t required for battery model I to heat up from temperature T to Tc in an adiabatic thermal runaway test) is calculated. The relationship between the response temperature T and the response time t is then obtained, thus yielding the dynamic range diagram of the thermally broken separator's response temperature versus response time, as shown below. Figure 2 ( Figure 2 The shaded area represents the dynamic range region. The thermal runaway temperature range controlled by the thermally fused diaphragm is from the exothermic initiation temperature T0 to the thermal runaway initiation temperature T. c That is, 93.38℃-192.49℃. The response time dynamically changes according to different response temperatures. When the response temperature is 93.38℃, the dynamic response time is the longest, at 2189.82 min. For the specific response time corresponding to each response temperature, please refer to [link / reference]. Figure 2 .

[0090] (V) The positive electrode material, negative electrode material, electrolyte, and PBS / PI composite separator (with PI nanofibers as the substrate and PBS nanofibers as the thermally fused layer) are assembled to obtain a coin cell model of the battery under test (wherein, the positive electrode material, negative electrode material, and electrolyte of the coin cell are the same as those of the pouch cell in step I). The response temperature of the PBS / PI composite separator was measured to be 115℃ using DSC, which is between 93.38℃ and 192.49℃.

[0091] A coin cell battery model was subjected to charge-discharge tests using a constant current / constant voltage charge-discharge mode (the battery voltage range can be determined by the positive and negative electrode materials). The process included: charging the coin cell battery model at room temperature with constant current and constant voltage until its state of charge reached 100%; then placing it at 115℃ to reach thermal equilibrium with the environment before starting discharge. The main observation was during the battery discharge phase, specifically when the voltage began to drop from 4.2V. The coin cell battery model's voltage rapidly dropped to 3V. The duration of this discharge process, which corresponds to the actual response time of the thermally melted separator, was approximately 1.47 minutes. Figure 3 .

[0092] Alternatively, the response time of the PBS / PI composite membrane can be obtained by observing the state of the PBS / PI composite membrane in a coin cell at 115°C using a scanning electron microscope: (e.g., ...) Figure 5 As shown, the response time of the PBS / PI composite membrane at 115℃ is about 2 minutes, which is similar to the test results of the charge and discharge test mentioned above. The reason for the difference is that the response time of the SEM test is an integer time (the membrane is tested at integer minute time points).

[0093] Combining the actual response time obtained by charging and discharging the battery voltage as described above, the measured response temperature-response time of the PBS / PI composite separator is located at... Figure 2 Within the dynamic range of response temperature-response time (e.g.) Figure 4As shown), its response temperature is 115℃, and the actual response time is 1.47 min, which is less than... Figure 2 The maximum response time at 115℃ can be used as a thermally fused separator for the soft-pack battery system in step (Ⅰ), and has great potential for application in the preparation of commercial batteries. It is suitable for battery material systems where the positive electrode material is ternary nickel-cobalt-manganese material and the negative electrode is graphite.

[0094] Furthermore, in step (V) of this embodiment, the standard commercial separator I in the pouch cell in step (I) can be replaced with a PBS / PI composite separator to obtain the battery model under test (pouch cell), and then a charge-discharge test is performed. The charge-discharge test method is the same as that of the coin cell battery model under test in this embodiment. The charge-discharge test results of the battery model under test (pouch cell) are comparable to those of the coin cell battery used in this embodiment.

[0095] Furthermore, for other types of thermoplastic diaphragms that have been disclosed, based on their specific response temperature and response time, the following methods are adopted: Figure 2 The response temperature-response time dynamic range diagram of the thermally fused diaphragm is used to evaluate the performance of the publicly disclosed thermally fused diaphragm. Table 1 shows the publicly disclosed diaphragm information, and the comparison results with the response temperature-response time dynamic range of the thermally fused diaphragm are as follows: Figure 6 As shown. Among the reported heat-sealable separators, 7 types, namely PAN@PBS separator [2], PLA@PBS separator [3], PE@PI separator [4], PAI-PE separator [5], PBI / PE / PBI separator [7], LDPE / PET separator [8] and PI / PVDF / PI separator

[10] , fall within the dynamic range of response temperature-response time of the heat-sealable separator determined in Example 1. This indicates that they have commercial potential for application in the battery material system of battery model I shown in Example 1. Specifically, the response temperature of PAI-PE separator [5] is 1. At 30℃, the longest dynamic response time is 719.82 min, while the actual response time of PAI-PE separator [5] is 30 min, which is much lower than the longest response time; for example, the response temperature of PI / PVDF / PI separator

[10] is 170℃, which corresponds to the longest dynamic response time of 31.06 min, while the actual response time of PI / PVDF / PI separator

[10] is 10 min, which is lower than the longest response time. This shows that this thermally melt-off separator can shut off the separator in time within the response temperature, thereby hindering lithium-ion transmission and preventing battery thermal runaway.

[0096] PAN / PEO / PAN separator [1], CNF / PE / CNF separator [6], PMIA@PVDF separator [9], PVDF / PET / PVDF separator

[11] , PSA / PAN / PSA separator

[12] and PBI@PL / PEI separator

[13] are located outside the dynamic range of response temperature-response time, but are close to the boundary of the dynamic range. The following is a detailed analysis of these separators: Among them, PAN / PEO / PAN separator [1] is not suitable for commercial production because its response temperature is too low, because the battery is in operation The temperature may rise briefly by 80°C, but there is no risk of thermal runaway in actual applications. However, the separator has already begun to respond and hinder lithium-ion transport. Since the thermal melting process is irreversible, the battery can only be scrapped at this time, which will undoubtedly cause a huge waste of resources. Among them, the PMIA@PVDF separator [9] and the PI / PVDF / PI separator

[10] have similar temperatures. The longest dynamic response time corresponding to the response temperature of 170°C is 31.06 min, and the longest dynamic response time corresponding to the response time of 174°C is 21.85 min. The PI / PVDF / PI separator

[10] The actual response time is 10 min, which is within the longest dynamic response time of 31.06 min. However, the actual response time of the PMIA@PVDF separator [9] is as high as 120 min, which is far beyond the longest dynamic response time of 21.85 min. At this time, the battery has already thermally runaway, causing battery safety problems. Among them, the PSA / PAN / PSA separator

[12] is the same as the PMIA@PVDF separator [9], which also meets the response temperature conditions in the dynamic response range diagram. However, the longest dynamic response time at the response temperature of 180℃ is 12.14 min. The actual response time of the SA separator

[12] is 60 min, which cannot achieve thermal shutdown of the battery; among them, CNF / PE / CNF separator [6], PVDF / PET / PVDF separator

[11] and PBI@PL / PEI separator

[13] do not meet the response temperature conditions in the dynamic response range diagram. At this time, the battery has reached the critical value of thermal runaway and the temperature rises rapidly. At this time, it is futile to control the battery temperature. Even if the actual response time is 1 min, such as that of CNF / PE / CNF separator [6], which is a relatively fast response speed, it is still impossible to prevent the battery from thermal runaway.

[0097] Table 1

[0098]

[0099]

[0100] References:

[0101] [1]GONG W,ZHANG Z,WEI S,et al.Thermosensitive polyacrylonitrile / polyethylene oxide / polyacrylonitrile membrane separators for prompt and saferthermal lithium-ion battery shutdown[J].Journal of The ElectrochemicalSociety,2020,167(2):020509.

[0102] DOI:10.1149 / 1945-7111 / ab615f

[0103] [2]WEI Z,GU J,ZHANG F,et al.Core–shell structured nanofibers forlithium ion battery separator with wide shutdown temperature window andstable electrochemical performance[J].ACS Applied Polymer Materials,2020,2(5):1989-1996.

[0104] DOI:10.1021 / acsapm.0c00164

[0105] [3]JIANG X,XIAO L,AI X,et al.A novel bifunctional thermo-sensitivepoly(lactic acid)@poly(butylene succinate)core–shell fibrous separatorprepared by a coaxial electrospinning route for safe lithium-ion batteries[J].Journal of Materials Chemistry A,2017,5(44):23238-23242.

[0106] DOI:10.1039 / C7TA08063H

[0107] [4]HSIEH C T,LIN S C,LEE C H,et al.Designing multifunctionalpolyethylene-polyimide composite separators for rechargeable lithium-ionbatteries[J].Journal of The Electrochemical Society,2019,166(14):A3132.

[0108] DOI:10.1149 / 2.0071914jes

[0109] [5]WANG Z,CHEN J,YE B,et al.A pore-controllable polyamine(PAI)layer-coated polyolefin(PE)separator for pouch lithium-ion batteries with enhancedsafety[J].Journal of Solid State Electrochemistry,2020,24:843-853.

[0110] DOI:10.1007 / s10008-019-04488-y

[0111] [6]PAN R,XU X,SUN R,et al.Nanocellulose modified polyethyleneseparators for lithium metal batteries[J].Small,2018,14(21):1704371.

[0112] DOI:10.1002 / smll.201704371

[0113] [7]LI D,SHI D,YUAN Z,et al.A low cost shutdown sandwich-likecomposite membrane with superior thermo-stability for lithium-ion battery[J].Journal of Membrane Science,2017,542:1-7

[0114] DOI:10.1016 / j.memsci.2017.07.051

[0115] [8]KIM Y,LEE W Y,KIM K J,et al.Shutdown-functionalized nonwovenseparator with improved thermal and electrochemical properties for lithium-ion batteries[J].Journal of Power Sources,2016,305:225-232.DOI:10.1016 / j.jpowsour.2015.11.106

[0116] [9]WANG L,DENG N,JU J,et al.A novel core-shell structured poly-mphenyleneisophthalamide@polyvinylidene fluoride nanofiber membrane forlithium ion batteries with high-safety and stable electrochemical performance[J].Electrochimica Acta,2019,300:263-273.

[0117] DOI:10.1016 / j.electacta.2019.01.115

[0118]

[10] WU D,SHI C,HUANG S,et al.Electrospun nanofibers for sandwichedpolyimide / poly(vinylidene fluoride) / polyimide separators with the thermalshutdown function[J].Electrochimica Acta,2015,176:727-734.

[0119] DOI:10.1016 / j.electacta.2015.07.072

[0120]

[11] ZHOU Y T,YANG J,LIANG H Q,et al.Sandwich-structured compositeseparators with an anisotropic pore architecture for highly safe Li-ionbatteries[J].Composites Communications,2018,8:46-51.

[0121] DOI:10.1016 / j.coco.2018.03.009

[0122]

[12] TIAN X,XIN B,LU Z,et al.Electrospun sandwich polysulfonamide / polyacrylonitrile / polysulfonamide composite nanofibrous membranes forlithium-ion batteries[J].RSC advances,2019,9(20):11220-11229.

[0123] DOI:10.1039 / c8ra10229e

[0124]

[13] SUN G,LIU B,NIU H,et al.In situ welding:Superb strength,goodwettability and fire resistance tri-layer separator with shutdown functionfor high-safety lithium ion battery[J].Journal of Membrane Science,2020,595:117509.

[0125] DOI:10.1016 / j.memsci.2019.117509

[0126] As shown above, comparing with publicly available separators allows for accurate and rapid determination of whether a separator can be used in commercial lithium-ion batteries, demonstrating good testing results. From the perspective of commercial lithium-ion batteries, selecting a separator capable of controlling thermal runaway truly improves battery safety and stability. The separator selection method in this invention is based on the battery thermal runaway mechanism. Through the response temperature-response time dynamic range diagram, the selectivity for thermally melt-breaking separators can be fully demonstrated, providing a theoretical basis for future separator preparation and testing.

[0127] Example 2

[0128] This embodiment discloses a method for selecting a battery separator, which specifically includes the following steps:

[0129] (I) Take an 18650 cylindrical battery with a diameter of 18mm and a height of 65mm, packaged in a metal casing. The positive electrode material is lithium cobalt oxide (LCO), the negative electrode is graphite, the electrolyte is electrolyte I, the rated capacity is 3400mAh, and the voltage range is 2.5V-3.65V. The separator is a KELU 2325 separator made of PP / PE / PP three-layer material, designated as standard commercial separator II.

[0130] (II) Pretreatment of the 18650 cylindrical battery: Discharge at a constant current of 0.5C to the cutoff voltage of 2.5V, let stand for 20 minutes, then charge at a constant current of 0.5C to the cutoff voltage of 3.65V, then switch to constant voltage charging until the current is less than 0.05C, and let stand for 20 minutes. Repeat the above steps 3 times. The final state of charge of the pretreated 18650 cylindrical battery is 100%.

[0131] (III) Fix the 18650 cylindrical battery in the ARC test area and conduct the ARC adiabatic thermal runaway test: The test method is the same as step (III) in Example 1;

[0132] (IV) Using ARC test data, obtain the thermal runaway temperature-time curve and the dynamic range diagram of the thermally melted diaphragm's response temperature-response time, such as... Figure 7-8 As shown, the data processing method is the same as step (IV) in Example 1. In this example, the thermal runaway temperature range controlled by the thermally fused diaphragm is from the exothermic initiation temperature T0 to the thermal runaway initiation temperature T. c That is, 106.13℃-163.63℃. The response time changes dynamically according to different response temperatures. When the response temperature is 106.13℃, the dynamic response time is the longest, which is 682.43min.

[0133] (V) The positive electrode material, negative electrode material, electrolyte, and PBS / PI composite separator from Example 1 were assembled to obtain a coin cell model of the battery under test (wherein, the positive electrode material, negative electrode material, and electrolyte of the coin cell are the same as those of the 18650 cylindrical battery in Step I). The coin cell model was subjected to charge-discharge tests using a constant current / constant voltage charge-discharge mode (the battery voltage range can be determined by the positive and negative electrode materials). This included: after the coin cell model was charged at room temperature with constant current and constant voltage until its state of charge reached 100%, it was placed at 115°C to reach thermal equilibrium with the environment before discharge. The actual response time was obtained by combining the test results and the battery voltage (the battery voltage range can be determined by the positive and negative electrode materials). The measured response temperature-response time of the PBS / PI composite separator was within the range of... Figure 8 Within the dynamic range of response temperature-response time (e.g.) Figure 9 As shown in the figure, the response time of the PBS / PI composite membrane was measured to be less than [amount missing]. Figure 8 The maximum response time at 115℃ can be used as a thermally fused separator for the battery system of the 18650 cylindrical battery in step (Ⅰ). It has great potential for application in the preparation of commercial batteries and is suitable for battery material systems with lithium cobalt oxide (LCO) as the positive electrode and graphite as the negative electrode.

[0134] Alternatively, the state of the PBS / PI composite membrane in the coin cell at 115°C can be observed using a scanning electron microscope, and the response time of the PBS / PI composite membrane is the same as the test results of the charge-discharge test mentioned above.

[0135] Furthermore, in step (V) of this embodiment, the standard commercial separator II in the 18650 cylindrical battery in step (I) can be replaced with a PBS / PI composite separator to obtain the battery model to be tested (cylindrical battery). Then, charge-discharge tests are performed, using the same method as the coin cell battery model in this embodiment. The charge-discharge test results of the battery model to be tested (cylindrical battery) are comparable to those of the coin cell battery model used in this embodiment.

[0136] Unlike the pouch cell in Example 1, Example 2 uses an 18650 cylindrical battery, resulting in a significant structural difference. Figure 10 (Left image) The thermal runaway temperature-time curve shows a plateau during the continuous temperature rise, where the temperature suddenly drops and then rises again. This is due to the unique design of the 18650 cylindrical battery – the safety valve. This temperature is called the pressure relief temperature, as the safety valve opens and releases a large amount of material, thus cooling the battery. The safety valve of the 18650 cylindrical battery can initially prevent internal explosions. When the internal pressure reaches a specific threshold, the safety valve automatically opens, preventing circuit overload and avoiding danger. (Corresponding to the dynamic range of response temperature-response time) Figure 10(Right figure) There is also a range where the response temperature corresponds to two longest response times. It is uniformly stipulated that the response time after depressurization is the longest response time.

[0137] Example 3

[0138] This embodiment discloses a method for selecting a battery separator, which specifically includes the following steps:

[0139] (I) Take an 18650 cylindrical battery with a diameter of 18mm and a height of 65mm, packaged in a metal casing. The positive electrode material is ternary nickel-cobalt-manganese (NCM), the negative electrode is graphite, the electrolyte is electrolyte I, the rated capacity is 3400mAh, and the voltage range is 3V-4.2V. The separator is a KELU 2500 separator with a 25μm PP material, designated as standard commercial separator II.

[0140] (II) Pretreatment of the 18650 cylindrical battery: Discharge at a constant current of 0.5C to the cutoff voltage of 3V, let stand for 20 minutes, then charge at a constant current of 0.5C to the cutoff voltage of 4.2V, then switch to constant voltage charging until the current is less than 0.05C, let stand for 20 minutes. Repeat the above steps 3 times. The final state of charge of the pretreated 18650 cylindrical battery is 100%.

[0141] (III) Fix the 18650 cylindrical battery in the ARC test area and conduct the ARC adiabatic thermal runaway test: The test method is the same as step (III) in Example 1.

[0142] (IV) Using RC test data, obtain the thermal runaway temperature-time curve and the dynamic range diagram of the thermally melted diaphragm's response temperature-response time, such as... Figure 11-12 As shown, the data processing method is the same as step (IV) in Example 1. In this example, the thermal runaway temperature range controlled by the thermally fused diaphragm is from the exothermic initiation temperature T0 to the thermal runaway initiation temperature T. c That is, 106.09℃-157.41℃. The response time changes dynamically according to different response temperatures. When the response temperature is 106.09℃, the actual response time is the longest at 558.60 min.

[0143] (V) The positive electrode material, negative electrode material, electrolyte, and PBS / PI composite separator from Example 1 were assembled to obtain a coin cell model of the battery under test (wherein, the positive electrode material, negative electrode material, and electrolyte of the coin cell are the same as those of the 18650 cylindrical battery in Step I). The coin cell model was subjected to charge-discharge tests using a constant current / constant voltage charge-discharge mode (the battery voltage range can be determined by the positive and negative electrode materials). This included: after the coin cell model was charged at room temperature with constant current and constant voltage until its state of charge reached 100%, it was placed at 115°C to reach thermal equilibrium with the environment before discharge. The actual response time was obtained by combining the test results and the battery voltage (the battery voltage range can be determined by the positive and negative electrode materials). The measured response temperature-response time of the PBS / PI composite separator was within the range of... Figure 12 Within the dynamic range of response temperature-response time (e.g.) Figure 13 As shown in the figure, the response time of the PBS / PI composite membrane was measured to be less than [amount missing]. Figure 12 The maximum response time at 115℃ can be used as a thermally fused separator for the battery system of the 18650 cylindrical battery in step (Ⅰ), and has great potential for application in the preparation of commercial batteries.

[0144] Alternatively, the state of the PBS / PI composite membrane in the coin cell at 115°C can be observed using a scanning electron microscope, and the response time of the PBS / PI composite membrane is the same as the test results of the charge-discharge test mentioned above.

[0145] Furthermore, in step (V) of this embodiment, the standard commercial separator II in the 18650 cylindrical battery in step (I) can be replaced with a PBS / PI composite separator to obtain the battery model to be tested (cylindrical battery). Then, charge-discharge tests are performed, using the same method as the coin cell battery model in this embodiment. The charge-discharge test results of the battery model to be tested (cylindrical battery) are comparable to those of the coin cell battery model used in this embodiment.

[0146] Table 2 shows some data from the dynamic range graph of the response temperature-response time of the thermally fused diaphragm measured in Examples 1-3:

[0147] Table 2

[0148] Example 1 Example 2 Example 3 <![CDATA[T0(℃)]]> 93.38 106.13 106.09 <![CDATA[T c (℃)]]> 192.49 163.63 157.41 <![CDATA[t c -t0(min)]]> 2189.82 682.43 558.60

[0149] A comprehensive analysis of the commercial application potential of the PBS / PI composite separator in Examples 1-3 was conducted. Examples 1-3 varied the battery type, cathode material, and separator type, respectively. All battery models prepared with the PBS / PI composite separator achieved thermal shutdown. In Example 1, a soft-pack battery model prepared using NCM|PBS / PI composite separator@electrolyte|graphite showed a maximum response time of 1075.83 min at a response temperature of 115°C, while the actual response time of the PBS / PI composite separator was only 2 min, significantly lower than its maximum response time. In Example 2, an 18650 cylindrical battery was prepared using an LCO|PBS / PI composite separator@electrolyte|graphite. At a response temperature of 115°C, its longest response time was 322.87 min, while the actual response time of the PBS / PI composite separator was shorter than the longest response time. In Example 3, an 18650 cylindrical battery was prepared using an NCM|PBS / PI composite separator@electrolyte|graphite. At a response temperature of 115°C, its longest response time was 328.60 min, again with the actual response time of the PBS / PI composite separator being shorter than the longest response time. This indicates that the process of developing the dynamic range diagram of the thermally fused separator response temperature-response time based on different battery models is simple and easy to implement, possessing good practicality. Furthermore, it facilitates the initial selection of thermally fused materials for the thermally fused separator, preliminarily removing response materials outside the dynamic range diagram's response temperature, simplifying the subsequent experimental process for preparing the thermally fused separator. It also helps in the preliminary assessment of whether the prepared thermally fused separator has commercial potential, saving time and money costs in subsequent commercialization verification experiments.

[0150] In summary, this invention proposes a novel method for selecting battery separators. Based on the battery thermal runaway mechanism, it innovatively proposes to effectively evaluate separator safety by analyzing the response temperature-response time range of the thermally melted separator and plotting a dynamic range diagram. This method accurately and quickly determines whether a thermally melted separator is suitable for existing commercial battery material systems. It features simple operation, good detection results, time and money savings, and wide applicability. It provides a theoretical basis for exploring the commercial application of thermally melted separators and can be used to determine whether thermally shut-off separators can be used commercially in commercial lithium-ion batteries. From the perspective of commercial lithium-ion batteries, it allows for the selection of separators that can control thermal runaway, thereby truly improving battery safety and stability.

[0151] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for selecting a battery separator, characterized in that, Includes the following steps: Based on the battery system under test, a battery model I with a standard separator was constructed. Adiabatic thermal runaway tests were conducted on battery model I to obtain test data, from which the self-heating initiation temperature was determined. T 0 and thermal runaway initiation temperature T c ; According to the location T 0 to Tc Temperature T in the temperature range, and the temperature rise of battery model I from temperature T to [temperature value missing] during the adiabatic thermal runaway test. Tc The required time t is used to obtain the relationship between T and t, which can be used as a dynamic range diagram of response temperature-response time for the thermally melted separator of the battery system under test. Determine the thermal break temperature T' and response time t' of the thermally broken diaphragm under test. Based on the dynamic range diagram of response temperature and response time, obtain the longest response time corresponding to T' in the dynamic range diagram, denoted as t. ’ max ,choose T 0 < T' < Tc And t' < t ’ max The thermally fused separator is used as a thermally fused separator that can be applied to the battery system under test.

2. The method for selecting a battery separator according to claim 1, characterized in that, The response temperature of the thermally broken diaphragm under test was obtained by differential scanning calorimetry.

3. The method for selecting a battery separator according to claim 1, characterized in that, The response time of the thermally broken diaphragm under test is obtained by scanning electron microscopy or by charge-discharge testing; wherein the charge-discharge testing method includes the following steps: Battery Model I was used as the battery system, and the standard separator was replaced with the thermally melt-through separator to be tested, to construct Battery Model II. At room temperature, after charging battery model II to achieve a state of charge of 95-100%, battery model II is placed at the response temperature of the thermally broken separator under test and then discharged to obtain the actual response time t' of the thermally broken separator under test.

4. The method for selecting a battery separator according to claim 1, characterized in that, The standard diaphragm is made of polyolefin.

5. The method for selecting a battery separator according to claim 4, characterized in that, The standard diaphragm is made of at least one of polyethylene or polypropylene.

6. The method for selecting a battery separator according to claim 1, characterized in that, The positive electrode of battery model I includes at least one of ternary nickel-cobalt-manganese materials, lithium iron phosphate, or lithium cobalt oxide materials.

7. The method for selecting a battery separator according to claim 1, characterized in that, The negative electrode of battery model I includes at least one of graphite, graphene, carbon nanotubes, or silicon-based materials.

8. The method for selecting a battery separator according to claim 1, characterized in that, Battery model I was charged at 50-100% before undergoing adiabatic thermal runaway testing.

9. The method for selecting a battery separator according to claim 1, characterized in that, The T 0 represents the temperature at which the self-heating rate of the battery model I is ≥0.02℃ / min under adiabatic thermal runaway test conditions.

10. The method for selecting a battery separator according to claim 9, characterized in that, The T c The temperature at which the self-heating rate of the battery model I is ≥1℃ / min under adiabatic thermal runaway test conditions.

11. The method for selecting a battery separator according to claim 1, characterized in that, In the aforementioned adiabatic thermal runaway test procedure, the test temperature range is 50-400℃.

12. The method for selecting a battery separator according to claim 11, characterized in that, The heating gradient for the adiabatic thermal runaway test is 4-6℃, and the isothermal time at each heating gradient is 10-20 min.

13. The application of the battery separator selection method according to any one of claims 1-12 in battery separator testing.

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