Method for pre-judging mechanical safety of battery based on pole piece parameters

Abstract

The present application relates to a kind of methods for judging battery mechanical safety based on pole piece parameters, comprising the following steps: preparing positive pole piece to be evaluated;Test the following parameters of positive pole piece: the peel strength P of positive coating and positive current collector, the contact resistance R of positive coating under simple simulation needle puncture and micron scratch critical load F;When any of the following conditions is met, then it is judged that the battery assembled by the positive pole piece can pass the standard needle puncture safety test: 1) the detection values of the three parameters meet the respective lower threshold requirements, and the three parameters are not in critical state at the same time;2) the detection values of two of the three parameters far exceed the corresponding lower threshold requirements, and the remaining one parameter does not meet the corresponding lower threshold requirements.The present application can quickly, low-cost and non-destructively screen and judge the safety performance of the positive pole piece before battery assembly, greatly improving the product development efficiency and the quality control ability of manufacturing process.

Description

Technical Field

[0001] This invention relates to the field of battery safety assessment technology, and in particular to a method for predicting battery mechanical safety based on electrode parameters. Background Technology

[0002] With the widespread use of batteries, people have increasingly higher requirements for battery performance, and excellent safety performance is a prerequisite for battery use. To measure battery safety performance, the following tests are commonly used: internal and external short circuits, overcharging, nail penetration, flat plate impact, and heating. These methods play an important role in verifying battery safety.

[0003] In current production, in order to evaluate the safety performance of batteries under extreme internal short circuit conditions, it is often necessary to conduct nail penetration tests on battery packs. Nail penetration tests are usually conducted using complete battery packs, and nail penetration tests can cause fires or explosions. They need to be carried out in specific testing equipment, which is complex and costly.

[0004] Therefore, a new method for testing the mechanical safety of batteries is needed. Summary of the Invention

[0005] Therefore, it is necessary to provide a method for predicting the mechanical safety of a battery based on electrode parameters to address the aforementioned technical problems in the existing technology. By testing the parameters of the positive electrode, namely the peel strength between the positive electrode coating and the positive electrode current collector, the contact resistance of the positive electrode coating under a simplified simulated needle penetration test, and the critical load of micron scratches, it is possible to accurately predict whether the battery made from the positive electrode can pass the needle penetration test. This allows for rapid, low-cost, and non-destructive screening and prediction of the safety performance of the positive electrode before battery assembly, greatly improving product development efficiency and quality control capabilities in the manufacturing process.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for predicting battery mechanical safety based on electrode parameters includes the following steps:

[0008] Prepare a positive electrode sheet to be evaluated. The positive electrode sheet includes a positive current collector and a positive coating disposed on the positive current collector.

[0009] The following parameters of the positive electrode were tested: the peel strength P between the positive electrode coating and the positive electrode current collector, the contact resistance R of the positive electrode coating under a simple simulated needle penetration, and the critical load F of micron scratches.

[0010] A battery assembled from positive electrode sheets is predicted to pass the standard nail penetration safety test if any of the following conditions are met:

[0011] 1) The detection values ​​of the three parameters all meet their respective lower limit threshold requirements, and the three parameters are not simultaneously in a critical state;

[0012] 2) Two of the three parameters have detection values ​​that far exceed the corresponding lower threshold requirements, while the remaining parameter does not meet the corresponding lower threshold requirements;

[0013] Among them, the lower threshold of peel strength P is 70 N / m, the lower threshold of contact resistance R is 20 mΩ, and the lower threshold of critical load F for micron scratches is 15 N.

[0014] Preferably, the critical state refers to the ratio of the detected value of the parameter to the lower limit threshold of the parameter satisfying: 1 ≤ detected value / lower limit threshold ≤ 1.1;

[0015] A parameter's detected value far exceeding the corresponding lower threshold requirement means that the ratio of the parameter's detected value to the lower threshold is ≥1.3.

[0016] Preferably, the peel strength P between the positive electrode coating and the positive electrode current collector is measured using a 180° peel test, specifically including the following steps:

[0017] Sample preparation: Cut the positive electrode sheet into samples with a width of 25 mm and a length of 10 cm to 30 cm;

[0018] Clamping: The positive electrode coating and the positive electrode current collector are pre-peeled to form the positive electrode coating end and the positive electrode current collector end, and the positive electrode coating end and the positive electrode current collector end are clamped in the upper and lower clamps of the testing machine respectively to ensure accurate peeling angle;

[0019] Setting parameters: Set the peeling speed to 50 mm / min~300 mm / min;

[0020] Test: Start the testing machine, peel the specimen at a constant speed, and record the force and displacement data in real time.

[0021] Preferably, the contact resistance R of the positive electrode coating under simplified simulated needle puncture is tested by the following test method: multiple positions are randomly selected on the positive electrode sheet, and pressure is applied with a probe to puncture the positive electrode coating, and the contact resistance R at different positions of the positive electrode coating is tested;

[0022] This includes at least one positive electrode at its center.

[0023] Preferably, the pressure range is 5 N to 20 N;

[0024] The number of selected locations is greater than 5.

[0025] Preferably, it also includes testing the contact resistance of the positive electrode under a simple simulated needle penetration test, with a contact resistance ≥28 Ω;

[0026] The method for testing the contact resistance of the positive electrode under a simple simulated needle puncture is as follows: randomly select multiple positions on the positive electrode, apply pressure with a probe to puncture the entire electrode, and test the contact resistance at different positions on the positive electrode.

[0027] This includes at least one positive electrode at its center;

[0028] Pressure range: 5 N to 25 N;

[0029] The number of selected locations is greater than 5.

[0030] Preferably, the test method for the critical load F of micron scratches is as follows: using a nanoindenter, the positive electrode coating in the test area is completely peeled off from the positive electrode current collector, and the load on the exposed surface of the positive electrode current collector is determined as the critical load F.

[0031] Preferably, the specific test for the critical load F of micron scratching includes the following steps:

[0032] Sample preparation: Cut the positive electrode sheet into small pieces, fix them on the substrate, and wipe off the surface dust with anhydrous ethanol;

[0033] Parameter settings: Select incremental load mode, scratch length is 1 mm to 5 mm, scratch speed is 1 mm / min to 5 mm / min;

[0034] Equipment calibration: Calibrate the equipment using standard samples;

[0035] Test positioning: Select the test area on the positive electrode coating;

[0036] Scratch execution: Start scratching according to preset parameters. After the indenter contacts the sample surface, it begins linear loading and synchronous sliding.

[0037] The positive electrode coating in the test area was completely peeled off from the positive electrode current collector, and the load on the exposed surface of the positive electrode current collector was determined as the critical load F.

[0038] Preferably, the thickness of the positive electrode sheet is 50 μm to 200 μm.

[0039] Preferably, the parameter tests are performed at room temperature.

[0040] Due to the adoption of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0041] 1. The method of the present invention can accurately predict whether the battery made from the positive electrode sheet can pass the needle penetration test by testing the parameters of the positive electrode sheet, namely the peel strength between the positive electrode coating and the positive electrode current collector, the contact resistance of the positive electrode coating under a simple simulated needle penetration test, and the critical load of micron scratches. This allows for rapid, low-cost, and non-destructive screening and prediction of the safety performance of the positive electrode sheet before battery assembly, greatly improving product development efficiency and quality control capabilities in the manufacturing process.

[0042] 2. The method of this invention is compatible with a variety of cathode materials and has a wide range of applications;

[0043] 3. The three parameters selected in the method of this invention are simple and easy to obtain through testing. Attached Figure Description

[0044] Figure 1 The graph shows the test curve of the critical load LC for micron scratches in Example 1. Detailed Implementation

[0045] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0047] In current production, in order to evaluate the safety performance of batteries under extreme internal short circuit conditions, it is often necessary to conduct nail penetration tests on battery packs. Nail penetration tests are usually conducted using complete battery packs, and nail penetration tests can cause fires or explosions. They need to be carried out in specific testing equipment, which is complex and costly.

[0048] Therefore, a new method for testing the mechanical safety of batteries is needed.

[0049] During actual operation, the applicant found that the positive electrode material easily releases oxygen during the needle penetration test, which causes a side reaction with the electrolyte and leads to thermal runaway of the battery. Therefore, this application uses a positive electrode sheet for testing, which can simplify the testing process and ensure the accuracy of the test results.

[0050] Based on this, the present invention provides a method for predicting the mechanical safety of a battery based on electrode parameters, comprising the following steps:

[0051] Prepare a positive electrode sheet to be evaluated. The positive electrode sheet includes a positive current collector and a positive coating disposed on the positive current collector.

[0052] The following parameters of the positive electrode were tested: peel strength P between the positive electrode coating and the positive electrode current collector (unit: N / m), contact resistance R of the positive electrode coating under a simple simulated needle penetration (unit: mΩ), and critical load (LC) F of micron scratch (unit: N).

[0053] A battery assembled from positive electrode sheets is predicted to pass the standard nail penetration safety test if any of the following conditions are met:

[0054] 1) The detection values ​​of the three parameters all meet their respective lower limit threshold requirements, and the three parameters are not simultaneously in a critical state;

[0055] 2) Two of the three parameters have detection values ​​that far exceed the corresponding lower threshold requirements, while the remaining parameter does not meet the corresponding lower threshold requirements;

[0056] The lower threshold values ​​for peel strength P are 70 N / m, resistance R is 20 mΩ, and the critical load for micron scratches F is 15 N. In other words, all three parameters must meet their respective lower threshold requirements: peel strength P ≥ 70 N / m, resistance R ≥ 20 mΩ, and critical load for micron scratches F ≥ 15 N.

[0057] This invention, by testing the parameters of the positive electrode sheet, namely the peel strength between the positive electrode coating and the positive electrode current collector, the contact resistance of the positive electrode coating under a simplified simulated needle penetration test, and the critical load of micron scratches, can accurately predict whether the battery made from the positive electrode sheet can pass the needle penetration test. It can quickly, cost-effectively, and non-destructively screen and predict the safety performance of the positive electrode sheet before battery assembly, greatly improving product development efficiency and quality control capabilities in the manufacturing process.

[0058] In a specific embodiment, the critical state refers to the ratio of the detected value of the parameter to the lower limit threshold of the parameter satisfying: 1 ≤ detected value / lower limit threshold ≤ 1.1;

[0059] A parameter's detected value far exceeding the corresponding lower threshold requirement means that the ratio of the parameter's detected value to the lower threshold is ≥1.3.

[0060] The applicant discovered that the mechanical integrity of the positive electrode coating, particularly its bonding strength with the positive electrode current collector and its failure sequence under stress, is crucial in determining the short-circuit mode. Research revealed that the "contact resistance" during an internal short circuit and the bonding strength between the positive electrode coating and the positive electrode current collector are two key parameters determining whether thermal runaway occurs.

[0061] If the bonding force between the positive electrode coating and the positive current collector is weak, the coating is easily detached upon impact, exposing the current collector. In this case, a sharp object (such as a nail) can directly form a short circuit with extremely low contact resistance with the aluminum foil, instantly generating enormous Joule heat and directly triggering thermal runaway. Conversely, if the positive electrode coating is firmly bonded and the electrode material itself has high contact resistance, the short circuit process is mild, and the temperature rise is controllable.

[0062] Therefore, the present invention selects parameters of the positive electrode sheet, including the contact resistance of the positive electrode coating under simplified simulated needle penetration, the peel strength between the positive electrode coating and the positive electrode current collector, and the critical load test of micron scratches as predictive parameters for evaluating whether the battery can pass the needle penetration test.

[0063] The evaluation method of this application uses a positive electrode sheet instead of the entire battery for testing, which simplifies the testing process and ensures the accuracy of the test results.

[0064] In a specific embodiment, the peel strength P between the positive electrode coating and the positive electrode current collector was measured using a 180° peel test.

[0065] The core failure scenario of the needle penetration test is that when a steel needle punctures the battery cell, it exerts a complex force on the electrode sheet—both a compressive / pushing force perpendicular to the surface of the positive electrode current collector and a shear / frictional tensile force parallel to the surface of the positive electrode current collector. This ultimately leads to the separation of the positive electrode coating from the positive electrode current collector interface, cracking and peeling of the positive electrode coating, and consequently, an internal short circuit. In the 180° peel test, after the tape adheres to the positive electrode coating, it is stretched in the opposite direction at a 180° angle. The force on the positive electrode coating is a complex force of tensile force perpendicular to the interface and shear force parallel to the interface. This is highly consistent with the actual stress state of the positive electrode coating-positive electrode current collector interface during needle penetration, and can accurately characterize the interface's resistance to separation under the combined action of "compression + shear". In the 90° peel test, the positive electrode coating is pulled upward by a force perpendicular to the surface of the positive electrode current collector. The force direction is singular, reflecting only the vertical bonding force of the interface, and cannot simulate the shear force parallel to the positive electrode current collector during needle penetration, resulting in a low degree of matching with the actual failure mechanism.

[0066] The 180° peel test includes the following steps:

[0067] Sample preparation: Cut the positive electrode sheet into a sample with a width of 25 mm and a length of 10 cm to 30 cm.

[0068] Clamping: Adhesive tape is applied to the upper and lower surfaces of the positive electrode sample, i.e., adhesive tape is applied to the lower surface of the positive current collector and the upper surface of the positive electrode coating. The positive current collector is then attached to the working table of the testing machine using the adhesive tape. The positive electrode coating and the positive current collector are pre-peeled to form the positive electrode coating end and the positive current collector end. The positive electrode coating end and the positive current collector end are then clamped in the upper and lower clamps of the testing machine, respectively. The adhesive tape, along with the positive electrode coating, is stretched in the opposite direction at a 180° positioning angle to ensure accurate peeling angle.

[0069] Setting parameters: Set the peeling speed to 50 mm / min-300 mm / min, and you can also set the data acquisition frequency, etc.

[0070] Test: Start the testing machine, the instrument peels the sample at a constant speed and records the force and displacement data in real time.

[0071] In a specific embodiment, the contact resistance R of the positive electrode coating under simplified simulated needle puncture is tested using the following method: multiple positions are randomly selected on the positive electrode sheet, and pressure is applied using a probe to puncture the positive electrode coating, and the contact resistance R1 at different positions of the positive electrode coating is tested.

[0072] In a specific embodiment, the selection of the location includes at least the center position of one positive electrode.

[0073] The probe pierces only the positive electrode coating, not the positive electrode current collector. By testing the contact resistance of the positive electrode coating, the structural stability of the coating can be characterized. The higher the structural stability of the positive electrode coating, the easier it is to maintain its shape during the needle penetration test, reducing the risk of short circuit.

[0074] In a specific embodiment, the pressure range is 5 N to 20 N.

[0075] In a specific embodiment, the number of selected locations is greater than 5.

[0076] In a specific embodiment, the method further includes testing the contact resistance R2 of the positive electrode under a simple simulated needle penetration test. The contact resistance R2 must satisfy: R2≥28 Ω.

[0077] The method for testing the contact resistance of the positive electrode under a simple simulated needle puncture is as follows: randomly select multiple positions on the positive electrode, apply pressure with a probe to puncture the entire electrode, and test the contact resistance at different positions on the positive electrode.

[0078] In a specific embodiment, at least one positive electrode is located at the center.

[0079] In one specific embodiment, the pressure range is 5 N to 25 N.

[0080] In a specific embodiment, the number of selected locations is greater than 5.

[0081] By testing the resistance of the positive electrode coating and the resistance of the entire electrode, the accuracy of the evaluation method can be further improved. It can also be further analyzed whether the failure due to needle penetration is due to poor quality of the positive electrode coating, an interfacial bonding problem between the positive electrode coating and the positive electrode current collector, or an excessively thin positive electrode current collector, which facilitates subsequent process optimization.

[0082] In a specific embodiment, the test method for the micron scratch critical load (LC) F is as follows: using a nanoindenter, the positive electrode coating in the test area is completely peeled off from the positive electrode current collector, and the load on the exposed surface of the positive electrode current collector is determined as the critical load F.

[0083] In a specific embodiment, the specific test of the critical load F for micron-level scratches includes the following steps:

[0084] Sample preparation: Cut the positive electrode sheet into small pieces, fix them on the substrate, and wipe off the surface dust with anhydrous ethanol.

[0085] Specifically, the positive electrode sheet is cut into 30 mm × 30 mm size and fixed on the metal / glass substrate with conductive adhesive or vacuum adsorption to ensure that there is no warping or loosening and to avoid sample displacement during the scratching process;

[0086] Then, surface pretreatment is performed: wipe away surface dust with anhydrous ethanol. No polishing is required; retain the surface condition under actual working conditions. If there are obvious protrusions on the surface, the test area should be removed in advance.

[0087] Parameter settings: Select incremental load mode, scratch length is 1 mm to 5 mm, scratch speed is 1 mm / min to 5 mm / min.

[0088] Specifically, a Rockwell C indenter with a tip radius of 200 μm is selected, which is suitable for linear scratches and reduces local crushing.

[0089] Increment the load gradually, from 1 mN to 5 N, to find the critical load.

[0090] Scratch parameters: Scratch length is 1 mm to 5 mm, covering the typical area of ​​the positive electrode coating of the positive electrode sheet; scratch speed is 1 mm / min to 5 mm / min, balancing test efficiency and data accuracy; in some scenarios, multiple parallel scratches can be set with a spacing of ≥1 mm to avoid mutual interference; the number of scratches is generally 3 or more.

[0091] Equipment calibration: Calibrate the equipment using standard samples. Specifically, calibrate the indenter tip radius, load accuracy, and scratch length accuracy using materials such as single-crystal silicon or alumina ceramic.

[0092] Test location: Select a test area on the positive electrode coating; for example, to improve the accuracy of the test, 3 to 5 test locations can be randomly selected in the positive electrode coating area of ​​the positive electrode sheet, avoiding the exposed positive electrode current collector and particle agglomeration area.

[0093] Scratch execution: Start scratching according to preset parameters. After the indenter contacts the sample surface, it begins linear loading and synchronous sliding, records real-time data, and completely peels the positive electrode coating of the test area from the positive electrode current collector. The load on the exposed surface of the positive electrode current collector is determined as the critical load F.

[0094] After the scratching is completed, the peeling, cracks, and detachment of the positive electrode coating can be observed using an optical microscope or SEM.

[0095] In a specific embodiment, the thickness of the positive electrode sheet is 50 μm to 200 μm. For example, the thickness of the positive electrode sheet is 50 μm, 75 μm, 90 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm or 200 μm, etc.

[0096] In one specific embodiment, the parameter test was performed at room temperature.

[0097] In a specific embodiment, the preparation method of the positive electrode sheet to be evaluated is as follows: the components of the positive electrode slurry are mixed, diluted with an appropriate solvent and stirred until all components are completely mixed to form a stable positive electrode slurry, which is then coated on an aluminum foil to obtain the positive electrode sheet.

[0098] The positive electrode slurry includes the following components: positive electrode active material, conductive agent, and binder.

[0099] In a specific embodiment, with the total mass of the positive electrode active material, conductive agent, and binder being 100%, the mass percentage of the positive electrode active material is 80% to 99%; the mass percentage of the conductive agent is 0.1% to 15%; and the mass percentage of the binder is 0.1% to 15%.

[0100] In one specific embodiment, the positive electrode slurry also includes a functional enhancement material to improve the safety performance of the positive electrode sheet.

[0101] In a specific embodiment, the functional enhancement material includes at least one of lithium iron phosphate and lithium titanium aluminum phosphate.

[0102] In a specific embodiment, with the total mass of the positive electrode active material, conductive agent, binder, and functional reinforcement material being 100%, the mass percentage of the positive electrode active material is 81% to 97%; the mass percentage of the conductive agent is 0.8% to 2.0%; the mass percentage of the binder is 0.8% to 2.5%; and the mass percentage of the functional reinforcement material is 1% to 15%.

[0103] In a specific embodiment, the positive electrode slurry also includes additives to reduce particle agglomeration, increase solid content, improve rheology, and enhance electrode uniformity and electrochemical performance.

[0104] In a specific embodiment, the additive includes a surfactant, which, exemplarily, may be one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, fatty alcohol polyoxyethylene ether, or polyvinylpyrrolidone.

[0105] In a particular embodiment, the additive includes a dispersant, which, for example, may be ammonium polyacrylate, ammonium polymethacrylate, etc.

[0106] In a specific embodiment, the positive electrode active material is a layered high-nickel ternary material LiNi. x Co y Mn z O2, x+y+z=1, and x≥0.6;

[0107] Or lithium-rich manganese-based materials xLi2MnO3·(1-x)LiMO2, M=Mn,Ni,Co, x>0;

[0108] Or spinel-structured lithium manganese oxide material LiMn2O4.

[0109] In a specific embodiment, the primary particle size D50 of the positive electrode active material is 2 μm to 10 μm, including but not limited to 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm.

[0110] In a specific embodiment, conductive carbon black is selected as the conductive agent, polyvinylidene fluoride (PVDF) is selected as the binder, and N-methylpyrrolidone (NMP) is selected as the solvent.

[0111] The following is a detailed description with reference to specific embodiments.

[0112] Example 1

[0113] The positive electrode active material is the ternary positive electrode material LiNi. 0.6 Co 0.1 Mn 0.3 O2 (NCM613), functional enhancement material lithium iron phosphate (LiFePO4) (LFP), conductive agent superP, and binder PVDF are mixed in a mass ratio of 86.4:9.6:2:2 and diluted with an appropriate solvent nmp and stirred until all components are completely mixed to form a stable positive electrode slurry, which is then coated on aluminum foil to obtain the positive electrode sheet.

[0114] Example 2

[0115] The only difference between this embodiment and Embodiment 1 is that lithium iron phosphate (LFP) is replaced with Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP), the mass ratio of positive electrode active material to LATP is 95:5.

[0116] Example 3

[0117] The only difference between this embodiment and Embodiment 2 is that the mass ratio of NCM613 to LATP is 97:3.

[0118] Example 4

[0119] The only difference between this embodiment and Embodiment 1 is that the positive electrode active material is replaced with LiMn2O4 (LMO).

[0120] Example 5

[0121] The difference between this embodiment and Embodiment 1 is that lithium iron phosphate is not added, and only the ternary cathode material NCM613 is used as the positive electrode active material.

[0122] Example 6

[0123] The only difference between this embodiment and Embodiment 2 is that the positive electrode active material is replaced with lithium-rich manganese-based material xLi2MnO3·(1-x)LiMO2(LR), and the mass ratio of the positive electrode active material phase to LATP is 85:15.

[0124] Performance testing:

[0125] 1) 180° peel strength test:

[0126] Sample preparation: Cut the positive electrode sheet into a sample with a width of 25 mm and a length of 15 cm.

[0127] Clamping: The positive electrode coating and the positive electrode current collector are pre-peeled to form the positive electrode coating end and the positive electrode current collector end, and the positive electrode coating end and the positive electrode current collector end are clamped in the upper and lower clamps of the testing machine respectively to ensure accurate peeling angle.

[0128] Setting parameters: Set the peeling speed to 100 mm / min.

[0129] Test: Start the testing machine, the instrument peels the sample at a constant speed and records the force and displacement data in real time.

[0130] 2) Simple simulation of contact resistance R1 test of positive electrode coating under needle penetration:

[0131] Ten locations, including the center, were selected on the positive electrode. A probe was used to pierce the positive electrode coating, the resistance value was tested, and the average value R1 was calculated. A pressure of 5 N was applied.

[0132] 3) Simple simulation of contact resistance R2 test of positive electrode under needle penetration:

[0133] Ten locations, including the center, are selected on the positive electrode. A probe is used to pierce the entire electrode to test the resistance value and calculate the average value R2. A pressure of 5 N is applied.

[0134] 4) Testing of the critical load LC for micron-sized scratches:

[0135] Sample preparation

[0136] Cut the positive electrode sheet to a size of 30 mm × 30 mm, fix it to the metal / glass substrate with conductive adhesive or vacuum adsorption, wipe off the surface dust with anhydrous ethanol, select the test area in the positive electrode coating area of ​​the positive electrode sheet, the test area is the center of the electrode sheet, and avoid the exposed positive electrode current collector and the particle agglomeration area.

[0137] The preset parameters are: Rockwell C indenter, tip radius of 200 μm, scratch length of 1.5 mm, scratch speed of 1 mm / min, and incremental load mode.

[0138] Equipment calibration: Use monocrystalline silicon or alumina ceramic to calibrate the tip radius, load accuracy, and scratch length accuracy of the indenter.

[0139] The scratching process is initiated according to preset parameters. After the indenter contacts the sample surface, linear loading begins and synchronous sliding commences, recording real-time data. The positive electrode coating in the test area is completely peeled off from the positive electrode current collector, and the load exposing the surface of the positive electrode current collector is determined as the critical load F. After the scratching is completed, the peeling, cracks, and detachment of the positive electrode coating can be observed using an optical microscope or SEM.

[0140] The test results are shown in Table 1. (Appendix) Figure 1 The test curve for the critical load LC of micron scratch in Example 1 is shown.

[0141] 4) Needle prick test

[0142] The positive electrode sheets prepared in Examples 1-6 were used to fabricate batteries. The preparation methods are as follows:

[0143] The obtained positive electrode sheet is rolled and thermally combined, and then assembled with the negative electrode sheet, separator and electrolyte to form a lithium-ion soft pack battery.

[0144] The negative electrode sheet includes a copper foil current collector and a negative electrode layer disposed on the current collector. The negative electrode layer includes graphite as the negative electrode active material, SuperP as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and CMC as the water-soluble thickener, with a mass ratio of 92:3:3:2.

[0145] Preparation method of negative electrode sheet: Mix graphite, conductive agent SuperP, styrene-butadiene rubber (SBR) binder, and water-soluble thickener CMC, add deionized water to prepare a negative electrode slurry, coat it on copper foil, and dry it to obtain the negative electrode.

[0146] The diaphragm is a PE diaphragm.

[0147] The electrolyte is a mixed solution of lithium electrolyte salt and carbonate organic solvent. The lithium electrolyte salt is lithium hexafluorophosphate (LiPF6), and the mass percentage of the electrolyte salt in the electrolyte is 13%. The solvent is ethylene carbonate EC: dimethyl carbonate DMC: ethyl methyl carbonate EMC, with a mass ratio of 1:1:1.

[0148] Needle penetration test: The battery is fully charged to 4.4 V (NCM and LR systems) or 4.2 V (LMO system). According to GB / T31485 standard, a steel needle with a diameter of 3 mm is used to pierce the center of the battery at a speed of 25 mm / s. The test is monitored for fire and explosion. The result is recorded as "Y" (pass) or "N" (fail). The test results are shown in Table 1.

[0149] Table 1 Test Result Data Table of Examples 1 to 6

[0150]

[0151] This invention establishes a quantifiable safety prediction method: it establishes a direct correlation model between three quantifiable parameters—peel strength (P), contact resistance (R), and scratch critical load (F)—at the positive electrode layer and the needle penetration safety results at the cell layer, and provides clear prediction thresholds (P≥70 N / m, R1≥25 mΩ, and F≥15 N). This method can quickly, cost-effectively, and non-destructively screen and predict electrode safety performance before battery assembly, greatly improving product development efficiency and quality control capabilities in the manufacturing process.

[0152] This invention offers good process compatibility and provides a rapid and accurate quantitative method for predicting battery mechanical safety at the electrode stage. The embodiments of this invention demonstrate the universality of this approach in cathode materials through verification with NCM, LR, and LMO systems. This approach, from material design to safety assessment, forms a complete technical system with significant theoretical and practical value for developing high-safety lithium-ion batteries.

[0153] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0154] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for predicting battery mechanical safety based on electrode parameters, characterized in that, Includes the following steps: Prepare a positive electrode sheet to be evaluated, the positive electrode sheet comprising a positive current collector and a positive coating disposed on the positive current collector; The following parameters of the positive electrode sheet were tested: the peel strength P between the positive electrode coating and the positive electrode current collector, the contact resistance R of the positive electrode coating under a simplified simulated needle penetration test, and the critical load F of micron scratches. A battery assembled from the positive electrode sheet is predicted to pass the standard nail penetration safety test if any of the following conditions are met: 1) The detection values ​​of the three parameters all meet their respective lower limit threshold requirements, and the three parameters are not simultaneously in a critical state; 2) Two of the three parameters have detection values ​​that far exceed the corresponding lower threshold requirements, while the remaining parameter does not meet the corresponding lower threshold requirements; Wherein, the lower threshold of the peel strength P is 70 N / m, the lower threshold of the contact resistance R is 20 mΩ, and the lower threshold of the micron scratch critical load F is 15 N. The critical state refers to the ratio of the detected value of the parameter to the lower limit threshold of the parameter satisfying: 1 ≤ detected value / lower limit threshold ≤ 1.1; The detection value of the parameter far exceeds the corresponding lower threshold requirement, which means that the detection value of the parameter / the lower threshold is ≥1.

3.

2. The method for predicting battery mechanical safety based on electrode parameters according to claim 1, characterized in that, The peel strength P between the positive electrode coating and the positive electrode current collector was measured using a 180° peel test, specifically including the following steps: Sample preparation: Cut the positive electrode sheet into a sample with a width of 25 mm and a length of 10 cm to 30 cm; Clamping: The positive electrode coating and the positive electrode current collector are pre-peeled to form the positive electrode coating end and the positive electrode current collector end, and the positive electrode coating end and the positive electrode current collector end are clamped in the upper and lower clamps of the testing machine respectively to ensure accurate peeling angle; Setting parameters: Set the peeling speed to 50 mm / min~300 mm / min; Test: Start the testing machine, peel the specimen at a constant speed, and record the force and displacement data in real time.

3. The method for predicting battery mechanical safety based on electrode parameters according to claim 1, characterized in that, The contact resistance R of the positive electrode coating under a simplified simulated needle puncture was tested using the following method: multiple locations were randomly selected on the positive electrode sheet, and pressure was applied with a probe to puncture the positive electrode coating. The contact resistance R at different locations of the positive electrode coating was then tested. This includes at least one of the center positions of the positive electrode sheet.

4. The method for predicting battery mechanical safety based on electrode parameters according to claim 3, characterized in that, The pressure range is 5 N to 20 N; The number of selected locations is greater than 5.

5. The method for predicting battery mechanical safety based on electrode parameters according to claim 1, characterized in that, It also includes testing the contact resistance of the positive electrode under a simple simulated needle penetration test, wherein the contact resistance is ≥28 Ω; The method for testing the contact resistance of the positive electrode under a simplified simulated needle puncture is as follows: multiple positions are randomly selected on the positive electrode, pressure is applied using a probe to puncture the entire electrode, and the contact resistance at different positions of the positive electrode is tested. This includes at least one of the center positions of the positive electrode sheet; The pressure range is 5 N to 25 N; The number of selected locations is greater than 5.

6. The method for predicting battery mechanical safety based on electrode parameters according to claim 1, characterized in that, The test method for the critical load F of the micron scratch is as follows: using a nanoindenter, the positive electrode coating in the test area is completely peeled off from the positive electrode current collector, and the load on the surface of the exposed positive electrode current collector is determined as the critical load F.

7. The method for predicting battery mechanical safety based on electrode parameters according to claim 6, characterized in that, The specific testing of the critical load F for micron-level scratches includes the following steps: Sample preparation: Cut the positive electrode sheet into small pieces, fix them on the substrate, and wipe off the surface dust with anhydrous ethanol; Parameter settings: Select incremental load mode, scratch length is 1 mm to 5 mm, scratch speed is 1 mm / min to 5 mm / min; Equipment calibration: Calibrate the equipment using standard samples; Test positioning: Select a test area on the positive electrode coating; Scratch execution: Start scratching according to preset parameters. After the indenter contacts the sample surface, it begins linear loading and synchronous sliding. The positive electrode coating in the test area is completely peeled off from the positive electrode current collector, and the load on the surface of the exposed positive electrode current collector is determined as the critical load F.

8. The method for predicting battery mechanical safety based on electrode parameters according to claim 1, characterized in that, The thickness of the positive electrode sheet is 50 μm to 200 μm.

9. The method for predicting battery mechanical safety based on electrode parameters according to claim 1, characterized in that, The parameter tests were conducted at room temperature.

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