Method for evaluating performance of lithium ion battery cathode material based on single particle strength

Abstract

This invention relates to a method for evaluating the performance of lithium-ion battery cathode materials based on single-particle strength, belonging to the field of lithium-ion battery technology. By conducting single-particle strength tests on cathode materials under different operating conditions and electrochemical states, this invention can evaluate the intrinsic properties of the grains, the degree of stress concentration, and the structural integrity of individual particles, providing a multi-dimensional evaluation method. Furthermore, this invention assesses the degree of mechanical failure by combining quantitative mechanical performance indicators with electrochemical performance tests, which can be used to select cathode materials that maintain particle integrity even under extreme conditions. This provides a scientific basis for the optimized design of lithium-ion battery cathode materials and helps improve the cycle life and safety performance of lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to a method for evaluating the performance of lithium-ion battery cathode materials based on single-particle strength. Background Technology

[0002] Lithium-ion batteries, characterized by high energy density, long cycle life, and environmental friendliness, have been widely used in electronics, electric vehicles, and other fields. However, the energy density and cycle life of a battery largely depend on the structural stability and mechanical integrity of the cathode material. In recent years, with the rapid development of high-energy-density materials such as high-nickel cathodes and lithium-rich manganese-based materials, research has revealed that stress changes experienced by cathode particles during charging and discharging lead to mechanical failure. This mechanical failure has become a key factor restricting the improvement of electrochemical performance in lithium-ion batteries.

[0003] During cycling, the delithiation and lithiation of cathode materials are accompanied by changes in lattice volume, leading to localized stress concentration, crack propagation, and even particle breakage. This is especially true for single-crystal or secondary particle materials, where the internal stress distribution and mechanical strength directly affect structural integrity and the reversibility of the electrochemical process. Therefore, testing the mechanical strength of single particles is crucial for assessing the structural stability of materials and predicting electrochemical performance degradation. Common methods for characterizing the mechanical properties of single particles include nanoindentation, in-situ SEM, or AFM testing. However, these methods mostly only measure the surface of the cathode material and cannot reflect the internal structure or the entire particle, lacking a direct correlation with the structural changes and performance degradation of cathode materials under actual electrochemical cycling conditions. In other words, current technologies cannot directly verify or predict the electrochemical performance of single particles in a battery system using their mechanical data. Furthermore, different preparation processes (such as doping, coating, and particle size control) significantly affect the mechanical strength of particles and their stress release mechanisms, properties closely related to electrochemical performance.

[0004] Therefore, there is an urgent need to propose a method for evaluating the performance of lithium-ion battery cathode materials through single-particle strength testing, so as to better reflect the degree of material failure, guide battery design and material optimization, and improve the performance and lifespan of lithium-ion batteries. Summary of the Invention

[0005] In view of the above problems, this invention proposes a method for evaluating the performance of lithium-ion battery cathode materials based on single-particle strength. By characterizing the mechanical properties of single particles of cathode materials after experiencing different electrochemical states, and combining this with their electrochemical performance data, the degree of mechanical failure of single particles during cycling can be quantitatively assessed. This provides a scientific basis for the optimized design of cathode materials and helps improve the cycle life and safety performance of lithium-ion batteries. This invention solves the technical problem of the difficulty in assessing the mechanical failure of lithium-ion battery cathodes, achieving the technical effect of accurately assessing grain integrity and grain boundary cracking processes after cycling.

[0006] This invention provides a method for evaluating the performance of lithium-ion battery cathode materials based on single-particle strength, comprising: Step 1: Provide multiple lithium-ion batteries with specific electrochemical states; extract the positive electrode material of each lithium-ion battery in the specific electrochemical state, dry and store it; Step 2: Pre-treat each dried cathode material to obtain single-particle samples of each cathode material; Step 3: Use a single-particle strength tester to test the single-particle samples of each cathode material to obtain the fracture toughness and fracture stress of the single-particle samples of each cathode material, which are characterized as the fracture strength of the single-particle samples of each cathode material. Step 4: Obtain the electrochemical performance data of each lithium-ion battery during cycling under different operating conditions, and use this data as the electrochemical data of each corresponding cathode material. Based on the fracture strength of single-particle samples of each cathode material, combined with the corresponding electrochemical data, the mechanical failure degree of the cathode material and its impact on battery performance are evaluated by comparing the evolution of mechanical properties of different materials under different conditions and their correspondence with electrochemical decay.

[0007] Optionally, the cathode material for lithium-ion batteries can be selected from layered oxide materials, spinel-type materials, or olivine-type materials.

[0008] Optionally, the operating conditions include temperature, voltage window, charge / discharge rate, and / or charge / discharge cycle count.

[0009] Optionally, the electrochemical performance data includes capacity retention, discharge specific capacity, coulombic efficiency, and / or dQ / dV curves.

[0010] Optionally, step 4 also includes: Based on the fracture strength of single-particle samples of each cathode material, combined with the corresponding electrochemical data, the effect of different doping elements on improving the cathode material's resistance to anisotropic expansion stress or the accelerating effect of high-temperature cycling on the mechanical damage of the cathode material are evaluated; further, cathode materials that can maintain structural integrity to the greatest extent during long-range cycling are screened out.

[0011] Optionally, step 4 further includes: based on the fracture strength of the single-particle samples of each cathode material, combined with the corresponding electrochemical data, evaluating the stress concentration and volume change resistance of different cathode materials under different working conditions, and obtaining the grain integrity and grain boundary cracking process of each cathode material.

[0012] Optionally, the particle size of the single-particle sample is 1-20 μm.

[0013] Optionally, step 3 may include the following specific steps: Step 31: Select a single particle sample with an approximately spherical shape from each positive electrode material single particle sample using an optical microscope as the particle to be tested; Step 32: Using a nanomechanical testing instrument equipped with a flat plate indenter, move the flat plate indenter toward the particle to be tested at a constant rate and compress it until the particle to be tested breaks, and obtain the force-displacement curve during the compression process. Step 33: Obtain the fracture stress and fracture toughness of the particle under test based on the force-displacement curve; Optionally, the fracture force of the particle under test can be determined from the highest point of the force-displacement curve, and the corresponding fracture stress can be obtained based on the contact area of ​​the particle, further reflecting the fracture strength of the particle.

[0014] Step 34: For each single-particle sample of the cathode material, select and test at least 50 test particles and repeat steps 31-33 to obtain the final fracture stress and fracture toughness of each cathode material particle, which are characterized as the fracture strength of each single-particle sample of the cathode material.

[0015] Optionally, step 3 further includes: using a high-speed camera to record the particle fracture process and analyzing the fracture mode; the fracture mode includes radial cracking or shear failure.

[0016] Optionally, step 4 further includes: based on the grain integrity and grain boundary cracking process of each cathode material, obtaining the cathode material corresponding to a single particle that can maintain structural integrity to the greatest extent after multiple charge-discharge cycles.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The present invention can effectively evaluate the mechanical failure of the positive electrode of lithium-ion battery, overcoming the deficiency of the lack of effective evaluation methods in the prior art; (2) This invention can accurately assess the grain integrity and grain boundary cracking process after cycling; it provides a scientific basis for the optimized design of lithium-ion battery cathode materials and helps to improve the cycle life and safety performance of lithium-ion batteries. Attached Figure Description

[0018] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0019] Figure 1 This is a schematic diagram of the apparatus for testing the fracture stress of a single particle strength tester in an embodiment of the present invention; Figure 2 This is a schematic diagram of single-particle intensity statistics under different charging states of two positive electrodes in an embodiment of the present invention; Figure 3 This is a schematic diagram of the single-particle strength statistics for four samples with different number of cycles in an embodiment of the present invention; Figure 4 This is a schematic diagram of the cycling performance curves of four samples in the embodiments of the present invention at a 1C rate and a voltage window of 2.8V-4.3V. Detailed Implementation

[0020] To better understand the above-described objectives, features, and advantages of the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other. Furthermore, the present invention can be implemented in other ways different from those described herein; therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0021] A specific embodiment of the present invention, such as Figure 1-4 A method for evaluating the performance of lithium-ion battery cathode materials based on single-particle strength is disclosed, including: Step 1: Provide multiple lithium-ion batteries with specific electrochemical states; extract the positive electrode material of each lithium-ion battery in the specific electrochemical state, dry and store it; Alternatively, the cathode material for lithium-ion batteries can be selected from layered oxide materials, spinel-type materials, or olivine-type materials.

[0022] The layered oxide material includes lithium nickel cobalt manganese oxide (NCM) or lithium-rich manganese-based oxide.

[0023] The chemical formula of lithium nickel cobalt manganese oxide is LiNi 0.8 Co 0.1 Mn 0.1 O 2。

[0024] The chemical formula for lithium-rich manganese-based lithium is Li. 1.2 Mn 0.5 N 0.2 Co 0.1 O 2。

[0025] The spinel-type material includes: lithium manganese oxide (LiMn2O4) and nickel manganese spinel (LiNi). 0.5 Mn 1.5 O4.

[0026] Olivine-type materials include: lithium iron phosphate (LiFePO4), lithium manganese iron phosphate (LiMnPO4), lithium nickel phosphate (LiNiPO4), or materials that have undergone doping or coating treatments. The material after doping and coating treatments can be a high-nickel ternary cathode material with Al and Zr dual doping, with the chemical formula NCM-Al-Zr.

[0027] Alternatively, the lithium-ion battery can be in the form of a button cell, pouch cell, cylindrical cell, or prismatic cell.

[0028] It is understood that the specific electrochemical state can be selected based on the evaluation purpose; For example, a specific electrochemical state refers to the electrochemical behavior characteristics under different operating conditions, state of charge (SOC), cycling stages, or environmental factors.

[0029] Optionally, the specific electrochemical state can be a pre-cycle state, a charged state, a cycle decay state, or a cycle process under different operating conditions.

[0030] For example, the pre-cycle state can be positive electrode material not assembled into a lithium-ion battery, positive electrode sheet, or positive electrode sheet after being soaked in electrolyte.

[0031] For example, the state of charge includes a fully uncharged state (SOC 0%), a low-charge state (SOC 30%), a half-charged state (SOC 60%), a high-charged state (SOC 80%), and a fully charged state (SOC 100%).

[0032] Furthermore, the state of charge is suitable for evaluating the particle's resistance to anisotropic expansion or contraction; Cyclic decay status is used to evaluate the ability of cathode particles to maintain structural integrity after long-term cycling.

[0033] Optionally, the specific steps for drying and preservation include: transferring the extracted cathode material to a vacuum drying oven for storage, with the temperature controlled at 20-30℃.

[0034] Step 2: Pre-treat each dried cathode material to obtain single-particle samples of each cathode material; For example, the single-particle sample is a single positive electrode particle sample.

[0035] Optionally, the pretreatment method is ultrasonic dispersion of the positive electrode powder in a solvent, and the specific steps include: The same weight of active material powder was scraped off each of the dried cathode materials to obtain a variety of active material powders; Each active material powder was placed in a centrifuge tube containing an organic solvent, and the suspension in the centrifuge tube was ultrasonically dispersed using an ultrasonic cleaner to obtain various treated suspensions. Use a pipette to extract each treated suspension onto a clean glass slide or silicon wafer, and dry at room temperature to obtain single-particle samples of each cathode material dispersion, ensuring sufficient spacing between particles for subsequent single-particle testing.

[0036] Optionally, the active material powder weighs 5-10 mg.

[0037] Optionally, the ultrasonic power is 50-2000W, and the processing time is 1-30 minutes.

[0038] Alternatively, the organic solvent may be anhydrous ethanol, N-methylpyrrolidone, or acetone; The volume of the organic solvent is 3-5 ml.

[0039] Optionally, the room temperature drying temperature is 20-30°C.

[0040] Optionally, the particle size of the single-particle sample is 1-20 μm. The spacing between individual particle samples is smaller than the probe diameter; Optionally, the diameter of the probe is 50μm-100μm.

[0041] Step 3: Use a single-particle strength tester to test the single-particle samples of each cathode material to obtain the fracture toughness and fracture stress of the single-particle samples of each cathode material, which are characterized as the fracture strength of the single-particle samples of each cathode material. Optionally, step 3 may include the following specific steps: Step 31: Select a single particle sample with an approximately spherical shape from each positive electrode material single particle sample using an optical microscope as the particle to be tested; Step 32: Using a nanomechanical testing instrument equipped with a flat plate indenter, move the flat plate indenter toward the particle to be tested at a constant rate and compress it until the particle to be tested breaks, and obtain the force-displacement curve during the compression process. Step 33: Obtain the fracture stress and fracture toughness of the particle under test based on the force-displacement curve; Optionally, the fracture force of the particle under test can be determined from the highest point of the force-displacement curve, and the corresponding fracture stress can be obtained based on the contact area of ​​the particle, further reflecting the fracture strength of the particle.

[0042] Step 34: For each single-particle sample of the cathode material, select and test at least 50 test particles and repeat steps 31-33 to obtain the final fracture stress and fracture toughness of each cathode material particle, which are characterized as the fracture strength of each single-particle sample of the cathode material.

[0043] Optionally, the moving speed of the flat plate indenter is 0.02-1 μm / s.

[0044] Optionally, step 3 further includes: using a high-speed camera to record the particle fracture process and analyzing the fracture mode; the fracture mode includes radial cracking or shear failure.

[0045] Step 4: Obtain the electrochemical performance data of each lithium-ion battery during cycling under different operating conditions, and use this data as the electrochemical data of each corresponding cathode material. Based on the fracture strength of single-particle samples of each cathode material, combined with the corresponding electrochemical data, the mechanical failure degree of the cathode material and its impact on battery performance are evaluated by comparing the evolution of mechanical properties of different materials under different conditions and their correspondence with electrochemical decay.

[0046] For example, the effect of different doping elements on improving the resistance of cathode materials to anisotropic expansion stress can be evaluated, or the accelerating effect of high-temperature cycling on the mechanical damage of cathode materials can be evaluated; based on this evaluation, cathode materials that can maintain structural integrity to the greatest extent during long-range cycling can be screened.

[0047] For example, based on the fracture strength of single-particle samples of each cathode material and combined with the corresponding electrochemical data, the stress concentration and volume change resistance of different cathode materials under different working conditions are evaluated, thereby obtaining the grain integrity and grain boundary cracking process of each cathode material.

[0048] Optionally, the operating conditions can be set as needed; For example, the operating conditions include temperature, voltage window, charge / discharge rate, and / or charge / discharge cycle count; The temperature can be 25℃, 45℃, or 60℃; The voltage window can be 2.8-4.3V or 2-4.8V; The charge / discharge rate can be 0.1C, 0.5C, or 1C; The number of charge / discharge cycles can be 1, 50, or 100.

[0049] Optionally, the electrochemical performance data includes capacity retention, discharge specific capacity, coulombic efficiency, and / or dQ / dV curves.

[0050] Optionally, the method also includes step 5, obtaining a single-particle cathode material that can maintain structural integrity to the greatest extent after multiple charge-discharge cycles, based on the grain integrity and grain boundary cracking process of each cathode material.

[0051] Based on the grain integrity and grain boundary cracking process of each cathode material, this invention further reveals that a cathode material can better maintain the structural integrity of a single cathode particle even after more than 100 charge-discharge cycles.

[0052] Optionally, by controlling different operating conditions, electrochemical cycle tests can be performed on the Blue Electric Test Cabinet or the Newway Test Cabinet to obtain the target state battery and its electrochemical performance data.

[0053] Example 1 This embodiment applies the method of the present invention to evaluate the effect of Al and Zr dual doping on the structural stability of high-nickel ternary cathode material (NCM) under different charge states.

[0054] A method for evaluating the performance of lithium-ion battery cathode materials using single-particle strength testing is used to assess the ability of lithium-ion battery cathode particles to maintain grain integrity and withstand stress concentration during charge-discharge cycles. The method includes the following steps: Step 1: Obtain a positive electrode sheet in a specific electrochemical state from a lithium-ion battery; In this embodiment, two button-type lithium-ion batteries with different cathodes are selected. The cathode material is high-nickel ternary cathode material NCM, labeled as battery A; and the high-nickel ternary cathode material NCM-Al-Zr, which is double-doped with Al and Zr under specific synthesis conditions, is labeled as battery B. Battery A and Battery B each took five lithium-ion batteries of different models in the first charging cycle, with the charging states including: SOC 0% before charging, SOC 30% in the low charging state, SOC 60% in the half charging state, SOC 80% in the high charging state, and SOC 100% in the fully charged state. Each lithium-ion battery was placed in a glove box protected by inert gas for disassembly, and the positive electrode of each lithium-ion battery was extracted. To prevent changes in material condition, the disassembled positive electrode sheet was immediately transferred to a vacuum drying oven for storage, with the temperature controlled at 25℃. Step 2: Scrape 3mg of active material powder from the positive electrode of each lithium-ion battery; Each powder was placed in a centrifuge tube containing 3 ml of ethanol, and the centrifuge tubes were ultrasonically dispersed using an ultrasonic cleaner with an ultrasonic power of 400 W for 10 minutes. After ultrasonic treatment, use a dropper to take an appropriate amount of suspension and drop it onto a clean glass slide. Allow it to dry naturally to obtain a well-dispersed single positive electrode particle sample of each positive electrode sheet, which can be used as a sample for single particle strength testing. Ensure that there is sufficient spacing between the particles to facilitate subsequent single particle testing. Step 3: The single-particle strength test technology is used to test the individual positive electrode particle samples of each positive electrode sheet. A nanomechanical tester equipped with a flat plate indenter is used to perform a compression test on the individual positive electrode particles dispersed on the glass slide. A single particle with a near-spherical shape is observed and selected using an optical microscope, and then the indenter is moved downward at a constant rate of 0.2 μm / s until the particle breaks. Record the force-displacement curves throughout the compression process, and determine the fracture force and fracture stress of the particles from the curves; For each positive electrode sheet under each charging state, at least 50 particles are tested to obtain statistically significant results, which are used as the nominal fracture strength of the sample particles. Meanwhile, high-speed cameras were used to record the particle fracture process and analyze fracture modes such as radial cracking and shear failure. Step 4: Based on the mechanical property indicators of the fracture force and fracture stress of the particles, evaluate the ability of particles of different positive electrode sheets to alleviate lattice shrinkage and stress during the lithium insertion / extraction process. The single-particle strength test results for different states of charge (SOC) of batteries A and B are as follows: Figure 2 As shown: The results indicate that, under the same conditions, the doped NCM-Al-Zr exhibits a higher nominal fracture strength than the undoped NCM, indicating that it can withstand greater stress concentration. As the state of charge increases, the fracture stress of a single positive electrode particle first decreases, then increases, and finally decreases again, reaching its lowest value at 60SOC. This is due to the decrease in the mechanical properties of the positive electrode material caused by anisotropic expansion stress. Compared to 0 SOC, the nominal fracture strength of NCM-Al-Zr decreased by only 14.57 MPa at 60 SOC, while the strength of NCM decreased by 29.83 MPa, indicating that the doped sample has a significantly improved ability to resist anisotropic expansion. The results show that Al and Zr co-doping significantly enhances the material's ability to resist anisotropic expansion stress, indicating that it can better maintain structural integrity during long-term cycling, thus achieving better electrochemical performance.

[0055] Based on the mechanical properties of different charging states, it can be predicted that NCM-Al-Zr can maintain higher particle integrity after long-range cycling, which can specifically manifest as better electrochemical performance. The long-range cycle process is a process of more than 100 cycles in the charge and discharge state.

[0056] These results provide important insights into the mechanical behavior of lithium-ion battery cathodes under different charging states, and can be used to optimize the synthesis strategy of cathode materials to obtain cathode materials with high electrochemical performance.

[0057] Example 2 This embodiment applies the method of the present invention to quantitatively compare and evaluate the effect of W doping on the mechanical integrity of LNO cathode materials after cycling at different temperatures.

[0058] This embodiment aims to apply the evaluation method of the present invention to quantitatively compare and evaluate the mechanical integrity of cathode materials at different cycling temperatures, including the following steps: Step 1: Obtain the positive electrode from a lithium-ion battery under specific operating conditions; In this embodiment, LNO and LNO-doped W are selected respectively. 6+ (LNO-W) cathode material is used to assemble button-type lithium-ion batteries; the two types of batteries are treated at different cycling temperatures as follows: Sample 1 (25℃): Three batteries with LNO as the positive electrode were uniformly assembled and subjected to a standard formation process of three charge-discharge cycles at a low rate. Then, they were charged at a constant current rate of 1C to 4.3V at a constant temperature of 25℃, and then discharged at a constant current rate of 1C to 2.8V for 0, 50, and 100 cycles respectively.

[0059] Sample 2 (45℃): Three batteries with LNO as the positive electrode were charged at a constant current rate of 1C to 4.3V at 45℃, and then discharged at a constant current rate of 1C to 2.8V, and cycled for 0 cycles, 50 cycles and 100 cycles respectively.

[0060] Sample 3 (25℃): Three batteries that were uniformly assembled with LNO-W as the positive electrode were taken, and after formation treatment, they were charged at a constant current rate of 1C to 4.3V at 25℃, and then discharged at a constant current rate of 1C to 2.8V. They were cycled for 0 cycles, 50 cycles and 100 cycles respectively.

[0061] Sample 4 (45℃): Three batteries with LNO-W as the positive electrode were charged at a constant current rate of 1C to 4.3V at 45℃, and then discharged at a constant current rate of 1C to 2.8V, and cycled for 0 cycles, 50 cycles and 100 cycles respectively.

[0062] After processing, to ensure consistency of testing conditions, all batteries were fully discharged to 2.8V. Subsequently, the batteries were disassembled in an inert atmosphere glove box filled with argon, and their respective positive electrode plates were carefully extracted. Step 2: Perform the same pretreatment operation on the positive electrode sheets from Sample 1, Sample 2, Sample 3, and Sample 4 with different number of cycles: clean and dry the positive electrode sheets removed from the battery with dimethyl carbonate (DMC), and scrape about 5mg of positive active material powder from each positive electrode sheet. The positive electrode active material powder was placed in centrifuge tubes containing 3 ml of ethanol solvent. The suspension was ultrasonically dispersed using an ultrasonic cleaner with a power setting of 400 W and a treatment time of 10 minutes to ensure that the aggregated particles were effectively dispersed. After ultrasonic treatment, use a dropper to take an appropriate amount of suspension and drop it onto a clean glass slide. Allow it to dry naturally to obtain well-dispersed individual positive electrode particles of each positive electrode sheet, which can be used as samples for single particle strength testing. Ensure that there is sufficient spacing between the particles to facilitate subsequent single particle testing. Step 3: Use a single-particle strength tester equipped with a flat-head indenter with a diameter of 60 μm to perform single-particle strength tests on individual positive electrode particles from Sample 1, Sample 2, Sample 3, and Sample 4. Using the optical microscope built into the tester, we searched for and located individual positive electrode particles with regular shapes, approximately spherical shapes, and particle sizes in the range of 10±2μm on the silicon wafer substrate. The pressure head is driven at a constant loading rate of 0.4 mN / s to compress the selected particles until the particles break significantly. High-precision sensors record the force-displacement curves in real time during this process, and determine the fracture force and fracture stress of the particles from the curves; For each sample, repeat the above steps and test at least 50 effective particles to ensure that the results are statistically representative. The fracture force of the particle is determined from the highest point of each load-displacement curve, and its fracture stress is calculated based on the contact area of ​​the particle. This index directly reflects the fracture strength of the particle. Step 4: Based on the particle fracture strength and the cycle capacity diagram at different temperatures, evaluate the ability of different cathode materials to maintain structural integrity under high-temperature cycling. Statistical results of average fracture stress from single-particle strength testing of cathode materials and electrochemical performance testing results are as follows: Figure 3 and Figure 4 As shown: The specific statistical results are summarized in the table below:

[0063] Results Analysis and Evaluation: Benchmark strength established: The fracture stresses of samples 1 and 2 before cycling were 51.4 and 50.6 MPa, respectively, while the fracture stresses of samples 3 and 4 before cycling were 60.3 and 63.2 MPa, respectively. These values ​​represent the initial mechanical strength of this batch of LNO materials under almost no cyclic stress and serve as the baseline for subsequent evaluation. Comparative analysis shows that W-doped LNO materials can withstand stronger mechanical stress.

[0064] Quantification of Cyclic Damage and Electrochemical Cycling: The continuous decrease in capacity retention with increasing cycle count is closely related to the single-particle strength of the cathode material. At 25°C, the capacity retention of LNO after 100 cycles is 79.3%, with an average fracture stress decrease of 40.8 MPa, while the capacity retention of LNO-W after 100 cycles is 88.7%, with an average fracture stress decrease of only 30.7 MPa. Similarly, at 45°C, the capacity retention of LNO after 100 cycles is 67.3%, with an average fracture stress decrease of 44.1 MPa, while the capacity retention of LNO-W after 100 cycles is 77.2%, with an average fracture stress decrease of only 36.6 MPa. Precise mechanical data quantitatively reveal the degree of mechanical damage accumulated by lattice anisotropic strain caused by repeated lithium-ion insertion / extraction during conventional charge-discharge cycles.

[0065] Accelerated damage effect of high-temperature cycling: The capacity retention rate of samples 3 (25℃ cycling) and 4 (45℃ cycling) after 100 cycles showed that the capacity retention rate decreased by 11.5% under high-temperature cycling. Compared to the baseline strength, the average fracture stress decreased by 36.6 MPa under high-temperature cycling and by 29.8 MPa under room-temperature cycling, indicating that high-temperature cycling exacerbates the mechanical damage to the cathode particles. Similarly, the capacity retention rate of samples 1 (25℃ cycling) and 2 (45℃ cycling) after 100 cycles showed that the capacity retention rate decreased by 12% under high-temperature cycling. Compared to the baseline strength, the average fracture stress decreased by 44.1 MPa under high-temperature cycling and by 40.8 MPa under room-temperature cycling. This result strongly demonstrates that, through the quantitative correlation between single-particle strength and high-temperature cycling, W doping can alleviate the mechanical failure of LNO cathode particles at high temperatures.

[0066] Evaluation of Doping Modification: Comparing Sample 1 and Sample 3, the fracture stress of LNO-W was significantly higher than that of LNO both before and after cycling, indicating that W doping improved the intrinsic strength and resistance to cyclic damage of the material. After 100 cycles, the strength decrease of Sample 3 (29.8 MPa) was much lower than that of Sample 1 (40.8 MPa), which is completely consistent with the trend of better capacity retention (Sample 3 88.7% vs Sample 1 79.3%).

[0067] High-Temperature Accelerated Damage Assessment: Comparing Samples 3 and 4, high-temperature cycling exacerbated the mechanical damage of the materials. After 100 cycles, the strength decrease of LNO-W at high temperature (36.6 MPa) was greater than that at room temperature (29.8 MPa), and its capacity retention (77.2%) was also significantly lower than that after room temperature cycling (88.7%). The same phenomenon of high-temperature accelerated mechanical damage and capacity decay was observed in LNO materials (Samples 1 and 2).

[0068] This embodiment demonstrates, through quantitative data on single-particle strength, that W doping can effectively mitigate the mechanical failure of LNO cathode materials during cycling (especially at high temperatures), and establishes a direct and quantitative link with the degradation of electrochemical performance.

[0069] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for evaluating the performance of a lithium-ion battery cathode material based on single particle strength, characterized in that, include: Step 1: Provide multiple lithium-ion batteries with specific electrochemical states; Extract the positive electrode material of each lithium-ion battery in a specific electrochemical state, and dry and store it. Step 2: Pre-treat each dried cathode material to obtain single-particle samples of each cathode material; Step 3: Use a single-particle strength tester to test the single-particle samples of each cathode material to obtain the fracture toughness and fracture stress of the single-particle samples of each cathode material, which are characterized as the fracture strength of the single-particle samples of each cathode material. Step 4: Obtain the electrochemical performance data of each lithium-ion battery during cycling under different operating conditions, and use this data as the electrochemical data of each corresponding cathode material. Based on the fracture strength of single-particle samples of each cathode material, combined with the corresponding electrochemical data, the mechanical failure degree of the cathode material and its impact on battery performance are evaluated by comparing the evolution of mechanical properties of different materials under different conditions and their correspondence with electrochemical decay.

2. The method for evaluating the performance of a lithium-ion battery cathode material based on single particle strength according to claim 1, characterized in that, The cathode material for lithium-ion batteries can be selected from layered oxide materials, spinel-type materials, or olivine-type materials.

3. The method for evaluating the performance of a lithium-ion battery cathode material based on single particle strength according to claim 1, characterized in that, The operating conditions include temperature, voltage window, charge / discharge rate, and / or charge / discharge cycle count.

4. The method for evaluating the performance of a lithium-ion battery cathode material based on single particle strength according to claim 1, characterized in that, The electrochemical performance data include capacity retention, discharge specific capacity, coulombic efficiency, and / or dQ / dV curves.

5. The method for evaluating the performance of a lithium-ion battery cathode material based on single particle strength according to claim 1, characterized in that, Step 4 also includes: Based on the fracture strength of single-particle samples of each cathode material, combined with the corresponding electrochemical data, the effect of different doping elements on improving the cathode material's resistance to anisotropic expansion stress or the accelerating effect of high-temperature cycling on the mechanical damage of the cathode material are evaluated; further, cathode materials that can maintain structural integrity to the greatest extent during long-range cycling are screened out.

6. The method for evaluating the performance of a lithium-ion battery cathode material based on single particle strength according to claim 1, characterized in that, Step 4 also includes: based on the fracture strength of the single-particle samples of each cathode material, combined with the corresponding electrochemical data, evaluating the stress concentration and volume change resistance of different cathode materials under different working conditions, and obtaining the grain integrity and grain boundary cracking process of each cathode material.

7. The method for evaluating the performance of a lithium-ion battery cathode material based on single particle strength according to claim 1, characterized in that, The particle size of the single-particle sample is 1-20 μm.

8. The method for evaluating the performance of lithium-ion battery cathode materials based on single-particle strength according to claim 1, characterized in that, Step 3 includes the following specific steps: Step 31: Select a single particle sample with an approximately spherical shape from each positive electrode material single particle sample using an optical microscope as the particle to be tested; Step 32: Using a nanomechanical testing instrument equipped with a flat plate indenter, move the flat plate indenter toward the particle to be tested at a constant rate and compress it until the particle to be tested breaks, and obtain the force-displacement curve during the compression process. Step 33: Obtain the fracture stress and fracture toughness of the particle under test based on the force-displacement curve; Optionally, the fracture force of the particle under test can be determined from the highest point of the force-displacement curve, and the corresponding fracture stress can be obtained based on the contact area of ​​the particle, further reflecting the fracture strength of the particle. Step 34: For each single-particle sample of the cathode material, select and test at least 50 test particles and repeat steps 31-33 to obtain the final fracture stress and fracture toughness of each cathode material particle, which are characterized as the fracture strength of each single-particle sample of the cathode material.

9. The method for evaluating the performance of lithium-ion battery cathode materials based on single-particle strength according to claim 8, characterized in that, Step 3 also includes: using a high-speed camera to record the particle fracture process and analyzing the fracture mode; the fracture mode includes radial cracking or shear failure.

10. The method for evaluating the performance of lithium-ion battery cathode materials based on single-particle strength according to claim 6, characterized in that, Step 4 also includes: based on the grain integrity and grain boundary cracking process of each cathode material, obtaining the cathode material corresponding to a single particle that can maintain structural integrity to the greatest extent after multiple charge-discharge cycles.

Images