A method for rapid evaluation of lithium-ion battery system stability

Abstract

The present application relates to a kind of method for rapidly evaluating lithium ion battery system stability, it is characterized in that: in preset temperature environment, the lithium ion battery of different system is carried out charge-discharge test to actual cycle mode, the voltage variation rate Ux% after discharge hibernation of different system cycle x times is compared, if the voltage variation rate after discharge hibernation is greater in the same cycle number, it is more that lithium ion accumulated in the vicinity of anode in lithium ion battery, the resistance that lithium ion diffusion in liquid phase is greater, simultaneously accompanied by the occurrence of side reaction, it is greater that the polarization of system, the available lithium ion in internal reduces, system is more unstable.The present application has feasibility according to the voltage variation rate after discharge hibernation of lithium battery to judge lithium ion battery system stability;It is suitable for the judgment of various lithium ion battery system stability, effectively shortens test time, battery system and product development cycle, improves research and development efficiency.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, and in particular relates to a method for rapidly evaluating the stability of lithium-ion battery systems. Background Technology

[0002] In the development of lithium-ion battery products, it is often necessary to conduct a large number of experiments and long-term tests to comprehensively evaluate the stability of the system. The lithium-ion battery system is not only closely related to key components such as positive electrode, negative electrode, electrolyte, and separator, but is also affected by structural design and process.

[0003] Existing methods for evaluating the stability of lithium-ion battery systems mainly involve accelerating the cycle testing of the battery by changing conditions such as battery temperature, pressure, charging and discharging voltage, and current. Patent document CN115656849A discloses a method for testing the stability of a lithium-ion battery system, including: S10, at a preset temperature, charging the lithium-ion battery with a first preset current until the lithium-ion battery reaches the charging termination voltage, and then charging the lithium-ion battery with a constant voltage. The preset temperature range is 45℃~60℃, and the first preset current is a small current.

[0004] S11. Allow the lithium-ion battery to stand for a first preset time. S12. Repeat steps S10 and S11, recording the charging termination voltage of the lithium-ion battery for each charge in real time until the recorded charging termination voltage reaches or falls below a preset voltage value. Record the number of repetitions. The preset voltage value is lower than the specified upper limit voltage of the lithium-ion battery. The above-mentioned patented technology mainly involves intermittent charging of the lithium-ion battery with a small current within the high-voltage range at a preset high temperature. This method avoids overcharging the battery, which could lead to lithium plating and affect the system stability assessment. However, changes in these conditions may cause the chemical reactions occurring within the lithium-ion battery system to differ from the degradation reactions occurring under actual cycling conditions, resulting in a significant deviation from the actual system stability of the battery.

[0005] How to quickly assess the stability of battery systems and find accurate and effective evaluation methods has become a key technical problem that urgently needs to be solved in the industry. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the above-mentioned technologies and provide a method for rapidly evaluating the stability of lithium-ion battery systems. By comparing the voltage change rate after discharge dormancy for the same number of cycles in different lithium-ion battery systems under actual cycling conditions, the stability performance of the lithium battery system can be quickly determined.

[0007] To achieve the above objectives, this invention employs the following technical solution: A method for rapidly evaluating the stability of a lithium-ion battery system. Under a preset temperature environment, charge-discharge tests are conducted on lithium-ion batteries of different systems using actual cycling conditions. The voltage change rate Ux% after x cycles of discharge dormancy is compared between different systems. If the voltage change rate after discharge dormancy is greater for the same number of cycles, it indicates that more lithium ions accumulate near the negative electrode inside the lithium-ion battery, resulting in greater resistance to lithium ion diffusion in the liquid phase. Simultaneously, the occurrence of side reactions indicates greater polarization of the system, reduced available lithium ions, and a more unstable system. The specific steps are as follows:

[0008] Step 1: Obtain lithium-ion batteries of different systems according to the lithium-ion battery manufacturing process;

[0009] Step 2: Under a preset temperature environment, charge the lithium-ion batteries of different systems obtained in Step 1 using the actual charging cycle mode. The charging sleep time is T1. Then, discharge the batteries using the actual discharge cycle mode. The discharge sleep time is T2. This is one complete cycle. The voltage after the first discharge sleep is recorded as U1.

[0010] Step 3: Repeat step 2 for x times, export the loop data and collect the voltage Ux corresponding to each discharge sleep T2;

[0011] Step 4: Subtract the voltage U1 after the first discharge and dormancy in Step 2 from the Ux obtained in Step 3 to get the voltage change value ΔUx after x cycles. Then divide ΔUx by the number of cycles x to get the voltage change rate Ux% after x cycles, i.e., Ux-U1=ΔUx; ΔUx / x=Ux%;

[0012] Step 5: Plot the U%-x curve with the cell cycle number x as the x-axis and the Ux% obtained in Step 4 as the y-axis;

[0013] Step 6: Compare the voltage change rate Ux% after x cycles of discharge dormancy for different systems. The voltage change rate for system 1 is Ux%1, and the voltage change rate for system 2 is Ux%2.

[0014] If Ux%1 > Ux%2, then the stability of system 1 is inferior to that of system 2.

[0015] If Ux%1 < Ux%2, then the stability of system 1 is better than that of system 2.

[0016] If Ux%1 = Ux%2, then the stability of system 1 is similar to that of system 2.

[0017] Preferably, the lithium-ion batteries with different systems mentioned in step 1 include lithium-ion batteries composed of different positive electrode materials, different negative electrode materials, different separators, different electrolytes, different foils, different auxiliary materials, different material formulations, different manufacturing processes, or different structural designs. The variables can be one or more of the above.

[0018] Preferably, the preset temperature in step 2 is 25-60℃; the actual cycle system refers to the charging and discharging cycle system formulated during battery development to meet the needs of different customers, including the charging cut-off voltage, discharging cut-off voltage, charging current and discharging current, as well as the charging and discharging sleep time T1 and T2.

[0019] Preferably, the actual charging cycle in step 2 is as follows: constant current charging at 0.8C to 4.2V, then switching to constant voltage charging. When the current drops to 0.5C, constant current charging at 0.5C is resumed to 4.45V, with an upper limit voltage of 4.45V. Then, constant voltage charging is resumed, stopping when the current drops to 0.05C. The charging sleep time is 5 minutes. Then, constant current discharge at 0.5C is performed until the lower limit voltage of 3.0V is reached, with a discharge sleep time of 5 minutes.

[0020] Preferably, the number of cycles x in step 6 is greater than or equal to 10% of the total number of cycles, and does not exceed 50% of the total number of cycles.

[0021] Preferably, the positive electrode material includes one or more of lithium cobalt oxide, ternary materials, lithium iron phosphate, or lithium manganese oxide; the negative electrode material includes one or more of graphite or silicon negative electrodes.

[0022] Beneficial effects: Compared with existing technologies, this invention is feasible for judging the stability of lithium-ion battery systems based on the voltage change rate after the lithium battery discharge dormancy period; the recording and subsequent processing of the voltage after the lithium battery discharge dormancy period are simple and convenient, with strong feasibility, and are applicable to the judgment of the stability of various lithium-ion battery systems. It can guide R&D personnel to optimize battery system design, effectively shorten the testing time, battery system and product development cycle, and improve R&D efficiency; the use of actual cycle system overcomes the defect of existing technologies that cannot achieve performance consistent with actual use. Attached Figure Description

[0023] Figure 1 This is a flowchart of the present invention;

[0024] Figure 2 This is the voltage change rate curve after cyclic discharge dormancy in Example 1;

[0025] Figure 3 This is the cycle capacity retention curve of Example 1;

[0026] Figure 4This is the voltage change rate curve after cyclic discharge dormancy in Example 2;

[0027] Figure 5 This is the cycle capacity retention curve of Example 2. Detailed Implementation

[0028] To better understand the above-mentioned objects, features, and advantages of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention.

[0029] In the various embodiments of the present invention, for ease of description and not limitation of the invention, the term "connection" used in the present invention patent application specification and claims is not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Above," "below," "underneath," "left," "right," etc., are only used to indicate relative positional relationships, and when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0030] See appendix for details Figure 1-5 This invention provides a method for rapidly evaluating the stability of lithium-ion battery systems. Under a preset temperature environment, charge-discharge tests are conducted on lithium-ion batteries of different systems using actual cycling conditions. The voltage change rate Ux% after x cycles of discharge dormancy is compared between different systems. A larger voltage change rate after discharge dormancy for the same number of cycles indicates that more lithium ions accumulate near the negative electrode inside the lithium-ion battery, resulting in greater resistance to lithium ion diffusion in the liquid phase. Simultaneously, the occurrence of side reactions indicates greater polarization of the system, reduced available lithium ions, and a more unstable system. The specific steps are as follows:

[0031] Step 1: Obtain lithium-ion batteries of different systems according to the lithium-ion battery manufacturing process;

[0032] Step 2: Under a preset temperature environment, charge the lithium-ion batteries of different systems obtained in Step 1 using the actual charging cycle mode. The charging sleep time is T1. Then, discharge the batteries using the actual discharge cycle mode. The discharge sleep time is T2. This is one complete cycle. The voltage after the first discharge sleep is recorded as U1.

[0033] Step 3: Repeat step 2 for x times, export the loop data and collect the voltage Ux corresponding to each discharge sleep T2;

[0034] Step 4: Subtract the voltage U1 after the first discharge and dormancy in Step 2 from the Ux obtained in Step 3 to get the voltage change value ΔUx after x cycles. Then divide ΔUx by the number of cycles x to get the voltage change rate Ux% after x cycles, i.e., Ux-U1=ΔUx; ΔUx / x=Ux%;

[0035] Step 5: Plot the U%-x curve with the cell cycle number x as the x-axis and the Ux% obtained in Step 4 as the y-axis;

[0036] Step 6: Compare the voltage change rate Ux% after x cycles of discharge dormancy for different systems. The voltage change rate for system 1 is Ux%1, and the voltage change rate for system 2 is Ux%2.

[0037] If Ux%1 > Ux%2, then the stability of system 1 is inferior to that of system 2.

[0038] If Ux%1 < Ux%2, then the stability of system 1 is better than that of system 2.

[0039] If Ux%1 = Ux%2, then the stability of system 1 is similar to that of system 2.

[0040] Preferably, the lithium-ion batteries with different systems mentioned in step 1 include lithium-ion batteries composed of different positive electrode materials, different negative electrode materials, different separators, different electrolytes, different foils, different auxiliary materials, different material formulations, different manufacturing processes, or different structural designs.

[0041] The positive electrode material includes one or more of lithium cobalt oxide, ternary materials, lithium iron phosphate, or lithium manganese oxide; the negative electrode material includes one or more of graphite or silicon negative electrodes.

[0042] The lithium-ion batteries of different systems described in this invention are examples of such batteries, where the variables can be one or more of the above-mentioned variables. The separator includes one or more variables related to separator thickness, material, manufacturer, and manufacturing process; the foil includes one or more variables related to foil thickness, material, manufacturer, and manufacturing process; the auxiliary materials include one or more variables related to the thickness, material, manufacturer, and manufacturing process of the tabs and tapes; the material formulation includes one or more variables related to the proportions of positive and negative electrode materials, the proportions of conductive agents and binders, their manufacturers, and manufacturing process; the manufacturing process includes one or more changes in the parameters of the homogenization, coating, rolling, shearing, assembly, drying, liquid injection, formation, and aging processes during battery production; and different structural designs include one or more variables related to coating amount, compaction density, N / P ratio (negative electrode capacity / positive electrode capacity), and tab position.

[0043] Preferably, the preset temperature in step 2 is 25-60℃; the actual cycle system refers to the charging and discharging cycle system formulated during battery development to meet the needs of different customers, including the charging cut-off voltage, discharging cut-off voltage, charging current and discharging current, as well as the charging and discharging sleep time T1 and T2.

[0044] Preferably, the actual charging cycle in step 2 is as follows: constant current charging at 0.8C to 4.2V, then switching to constant voltage charging. When the current drops to 0.5C, constant current charging at 0.5C is resumed to 4.45V, with an upper limit voltage of 4.45V. Then, constant voltage charging is resumed, stopping when the current drops to 0.05C. The charging sleep time is 5 minutes. Then, constant current discharge at 0.5C is performed until the lower limit voltage of 3.0V is reached, with a discharge sleep time of 5 minutes.

[0045] Preferably, the number of cycles x in step 6 is greater than or equal to 10% of the total number of cycles, and does not exceed 50% of the total number of cycles.

[0046] Example 1

[0047] In Example 1, the test sample was a 554892 soft-pack lithium-ion battery with a capacity of 4.3 Ah. The positive electrode active material of the battery was high-voltage lithium cobalt oxide, and the negative electrode active material was high-pressure solid graphite. The positive and negative electrode materials, separators, electrolytes, and models were the same for different systems, only the fixture formation process was different. The formation process 1 system conditions were: formation temperature 60℃, surface pressure 1.0 MPa, and state of charge 60%; the formation process 2 system conditions were: formation temperature 85℃, surface pressure 1.0 MPa, and state of charge 85%.

[0048] The battery testing equipment is a conventional charge and discharge testing equipment. In this embodiment, the equipment used is the Arbin charge and discharge testing system.

[0049] In Example 1, a method for rapidly evaluating the stability of a lithium-ion battery system specifically includes the following steps:

[0050] The first step is to obtain lithium-ion batteries of formation process 1 and formation process 2 systems according to the lithium-ion battery production process.

[0051] The second step involves charging at a constant current of 0.8C to 4.2V at 45℃, then switching to constant voltage charging. When the current drops to 0.5C, it is charged at a constant current of 0.5C to 4.45V, with an upper limit voltage of 4.45V. Then, constant voltage charging is performed, stopping when the current drops to 0.05C. The charging sleep time is 5 minutes. Then, constant current discharge is performed at 0.5C until the lower limit voltage of 3.0V is reached, with a discharge sleep time of 5 minutes. The voltage after the first discharge sleep is recorded as U1. The customer requires a capacity retention rate of ≥80% after 600 cycles at 45℃.

[0052] The third step is to cycle the cycle 150 times according to the cycle pattern of the second step, export the cycle data and collect the voltage Ux corresponding to each discharge sleep 5 minutes later;

[0053] The fourth step is to subtract the voltage U1 after the first discharge and hibernation in the second step from the Ux obtained in the third step to get the voltage change value ΔUx after x cycles. Then, divide ΔUx by the number of cycles x to get the voltage change rate Ux% after x cycles.

[0054] Fifth, plot the U%-x curve with the cell cycle count x as the x-axis and the Ux% obtained in step four as the y-axis, as shown below. Figure 2 As shown, the U%-x curves for different formation process systems were obtained;

[0055] Step 6: Compare the voltage change rate Ux% after discharge dormancy of the formation process 1 and formation process 2 systems after x cycles. The number of cycles is calculated as 10% of the total number of cycles required by the customer, and the number of cycles should be ≥60.

[0056] Therefore from Figure 2 It can be seen that after 60-150 cycles, Ux%1 > Ux%2, indicating that the voltage change rate is large after the formation process 1 is in a dormant state, the polarization of the system is large, the number of available lithium ions inside is reduced, and the system is more unstable. Therefore, the stability performance of formation process 1 is inferior to that of formation process 2. Figure 3 Table 1 shows the capacity retention curves for formation processes 1 and 2 after different number of cycles. It can be seen that the capacity retention rates of formation processes 1 and 2 are basically the same after 60 cycles, and the capacity difference is not significant after 150 cycles. As the cycles continue, the difference in cycle trends between the two processes becomes more pronounced. After 500 cycles, the capacity retention rates of formation processes 1 and 2 are 87.7% and 88.5%, respectively. The actual cycle trend after 500 cycles is consistent with the system stability obtained by comparing the voltage change rate after discharge dormancy using the method of this invention.

[0057] Table 1

[0058] Chemical formation process 1 98.2％ 95.8％ 87.7％ Chemical formation process 2 98.3％ 96.1％ 88.5％

[0059] Example 2

[0060] In Example 2, the test sample was a 376080 soft-pack lithium-ion battery with a capacity of 3.7 Ah. The positive electrode active material of the battery was high-voltage lithium cobalt oxide, and the negative electrode active material was high-pressure compact graphite. The only difference between the two systems was the positive electrode material; all other materials and formulation processes were the same. The two systems were referred to as positive electrode material system 1 and positive electrode material system 2, respectively.

[0061] The battery testing equipment is a conventional charge and discharge testing equipment. In this embodiment, the equipment used is the Arbin charge and discharge testing system.

[0062] In Example 2, the present invention provides a method for rapidly evaluating the stability of a lithium-ion battery system, which specifically includes the following steps:

[0063] The first step is to obtain lithium-ion batteries with cathode material 1 system and cathode material 2 system according to the lithium-ion battery production process;

[0064] The second step involves cycling 1-23 times at 45℃, charging at a constant current of 0.7C to the upper limit voltage of 4.48V, then charging at a constant voltage until the current drops to 0.05C, with a charging sleep time of 20 hours. Then, discharging at a constant current of 0.5C until the lower limit voltage of 3.0V is reached, with a discharge sleep time of 10 minutes. This cycle is repeated 23-136 times, charging at a constant current of 0.7C to 4.43V, the upper limit voltage of 4.43V, then charging at a constant voltage until the current drops to 0.05C, with a charging sleep time of 20 hours. Then, discharging at a constant current of 0.5C until the lower limit voltage of 3.0V is reached, with a discharge sleep time of 10 minutes. This cycle is a 45℃ interval cycle, where the customer requires a discharge capacity retention rate of ≥70% after 136 45℃ interval cycles.

[0065] The third step is to repeat the cycle 20 times according to the cycle pattern of the second step, export the cycle data and collect the voltage Ux corresponding to each discharge sleep 10 minutes;

[0066] The fourth step is to subtract the voltage U1 after the first discharge and hibernation in the second step from the Ux obtained in the third step to get the voltage change value ΔUx after x cycles. Then, divide ΔUx by the number of cycles x to get the voltage change rate Ux% after x cycles.

[0067] Fifth, plot the U%-x curve with the cell cycle count x as the x-axis and the Ux% obtained in step four as the y-axis, as shown below. Figure 4 As shown, the U%-x curves for different cathode material systems were obtained;

[0068] Step 6: Compare the voltage change rate Ux% after discharge dormancy of the cathode material 1 and cathode material 2 systems after x cycles. The number of cycles is calculated as 10% of the total number of cycles required by the customer, and the number of cycles should be ≥14.

[0069] Figure 4 Table 2 shows the voltage change rate curves after cyclic discharge dormancy for different cathode material systems. The voltage change rate of cathode material 1 system after 14-20 cycles is greater than that of cathode material 2 system. The specific values ​​are shown in Table 2. This indicates that cathode material 1 system has greater polarization, resulting in more lithium ions accumulating near the negative electrode inside the lithium-ion battery. This leads to greater resistance to the diffusion of lithium ions in the liquid phase, reduced available lithium ions, and system instability. Therefore, the stability of cathode material 1 system is inferior to that of cathode material 2 system. Figure 5 The curves show the energy retention rates of different cathode material systems during cyclic discharge. The curves indicate that the energy retention rates of cathode material 1 and cathode material 2 are essentially the same before the voltage reduction in the first 23 cycles. After the voltage reduction, the energy difference is not significant from 23 to 50 cycles. After 50 cycles, the energy retention rate of cathode material 1 is significantly higher than that of cathode material 2. The actual cycle trend after 136 cycles is consistent with the system stability obtained by comparing the voltage change rate after discharge dormancy using the method of this invention. This interval test requires one day per cycle, and the entire test takes 136 days to complete. Using the evaluation method of this invention, system stability can be determined after only 14 cycles, which can greatly shorten the testing cycle and improve R&D efficiency.

[0070] Table 2

[0071]

[0072] Key technical features of the present invention

[0073] (1) Under a preset temperature environment, charge and discharge tests were conducted on lithium-ion batteries of different systems using actual cycle conditions, overcoming the shortcomings of existing technologies that cannot achieve the same performance as in actual use.

[0074] (2) Compare the voltage change rate Ux% after discharge dormancy for different systems after x cycles. The voltage change rate for system 1 is Ux%1, and the voltage change rate for system 2 is Ux%2. Among them, the number of cycles x is greater than or equal to 10% of the total number of cycles required by the customer and does not exceed 50% of the total number of cycles required by the customer. This can shorten the testing cycle and the battery system and product development cycle, and improve R&D efficiency.

[0075] If Ux%1 > Ux%2, then the stability of system 1 is inferior to that of system 2.

[0076] If Ux%1 < Ux%2, then the stability of system 1 is better than that of system 2.

[0077] If Ux%1 = Ux%2, then the stability of system 1 is similar to that of system 2.

[0078] If the voltage change rate is greater after the same number of discharge cycles, it indicates that more lithium ions have accumulated near the negative electrode inside the lithium-ion battery, the diffusion of lithium ions in the liquid phase is more difficult, and the occurrence of side reactions is also more likely. This indicates that the polarization of the system is greater, the number of available lithium ions inside is reduced, and the system is more unstable.

[0079] (3) The method of the present invention is simple and convenient for recording and subsequent processing of the voltage after the lithium battery discharge dormancy, and has strong implementation capability. It is applicable to the determination of the stability of various lithium-ion battery systems.

[0080] The principle of this method:

[0081] During charge-discharge cycles, it's difficult to monitor the complex and ever-changing chemical reactions within a lithium-ion battery in real time while current flows through it. After discharge, during the resting period, lithium ions slowly diffuse to the positive electrode surface, consuming the accumulated negative charge and restoring the electrode surface to equilibrium. This results in an increase in the positive electrode potential and a decrease in the negative electrode potential, a process that eliminates concentration polarization and electrochemical polarization. As cycling continues, various side reactions occur, causing the voltage after discharge dormancy to gradually increase. For different lithium-ion battery systems, a greater rate of voltage change after discharge dormancy within the same number of cycles indicates a greater accumulation of lithium ions near the negative electrode, resulting in greater resistance to lithium ion diffusion in the liquid phase. The accompanying side reactions indicate greater polarization of the system, reduced available lithium ions, and increased system instability.

[0082] The aforementioned method for rapidly assessing the stability of a lithium-ion battery system, including the equipment and method for collecting and recording the voltage Ux of the lithium battery after discharge dormancy, as well as the graphing and calculation methods involved, are all techniques that can be mastered by those skilled in the art.

[0083] The above detailed description of a method for rapidly evaluating the stability of a lithium-ion battery system, with reference to the embodiments, is illustrative rather than limiting. Several embodiments may be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method for rapidly evaluating the stability of a lithium-ion battery system, characterized in that: Under a preset temperature environment, charge-discharge tests were conducted on lithium-ion batteries of different systems using actual cycle conditions. The voltage change rate Ux% after discharge dormancy was compared for different systems after x cycles. If the voltage change rate after discharge dormancy is larger for the same number of cycles, it indicates that more lithium ions accumulate near the negative electrode inside the lithium-ion battery, the diffusion of lithium ions in the liquid phase is more difficult, and side reactions occur simultaneously, indicating that the polarization of the system is greater, the number of available lithium ions inside is reduced, and the system is more unstable. The specific steps are as follows: Step 1: Obtain lithium-ion batteries of different systems according to the lithium-ion battery manufacturing process; Step 2: Under a preset temperature environment, charge the lithium-ion batteries of different systems obtained in Step 1 using the actual charging cycle mode. The charging sleep time is T1. Then, discharge the batteries using the actual discharge cycle mode. The discharge sleep time is T2. This is one complete cycle. The voltage after the first discharge sleep is recorded as U1. Step 3: Repeat step 2 for x times, export the loop data and collect the voltage Ux corresponding to each discharge sleep T2; Step 4: Subtract the voltage U1 after the first discharge and dormancy in Step 2 from the Ux obtained in Step 3 to get the voltage change value ΔUx after x cycles. Then divide ΔUx by the number of cycles x to get the voltage change rate Ux% after x cycles, i.e., Ux-U1=ΔUx; ΔUx / x=Ux%; Step 5: Plot the Ux%-x curve with the cell cycle number x as the x-axis and the Ux% obtained in Step 4 as the y-axis; Step 6: Compare the voltage change rate Ux% after x cycles of discharge dormancy for different systems. The voltage change rate for system 1 is Ux%1, and the voltage change rate for system 2 is Ux%2. If Ux%1 > Ux%2, then the stability of system 1 is inferior to that of system 2. If Ux%1 < Ux%2, then the stability of system 1 is better than that of system 2. If Ux%1 = Ux%2, then the stability of system 1 is similar to that of system 2.

2. The method for rapidly evaluating the stability of a lithium-ion battery system according to claim 1, characterized in that: The lithium-ion batteries with different systems mentioned in step 1 include lithium-ion batteries composed of different positive electrode materials, different negative electrode materials, different separators, different electrolytes, different foils, different auxiliary materials, different material formulations, different manufacturing processes, or different structural designs. The variables can be one or more of the above.

3. The method for rapidly evaluating the stability of a lithium-ion battery system according to claim 1, characterized in that: The preset temperature mentioned in step 2 is 25-60℃; the actual cycle system refers to the charging and discharging cycle system formulated during battery development to meet the needs of different customers, including the charging cut-off voltage, discharging cut-off voltage, charging current and discharging current, as well as the charging and discharging sleep time T1 and T2.

4. The method for rapidly evaluating the stability of a lithium-ion battery system according to claim 1 or 2, characterized in that: The actual charging cycle described in step 2 is as follows: constant current charging at 0.8C to 4.2V, then switching to constant voltage charging. When the current drops to 0.5C, constant current charging at 0.5C is resumed to 4.45V, with an upper limit voltage of 4.45V. Then, constant voltage charging is resumed, stopping when the current drops to 0.05C. The charging sleep time is 5 minutes. Then, constant current discharge at 0.5C is performed until the lower limit voltage of 3.0V is reached, with a discharge sleep time of 5 minutes.

5. The method for rapidly evaluating the stability of a lithium-ion battery system according to claim 1, characterized in that: The number of iterations x in step 6 is greater than or equal to 10% of the total number of iterations, but does not exceed 50% of the total number of iterations.

6. The method for rapidly evaluating the stability of a lithium-ion battery system according to claim 2, characterized in that: The positive electrode material includes one or more of lithium cobalt oxide, ternary materials, lithium iron phosphate, or lithium manganese oxide; the negative electrode material includes one or more of graphite or silicon negative electrodes.

Images