An accelerated evaluation method for the cycling performance of lithium-ion battery electrode materials

Abstract

The present invention discloses an accelerated evaluation method for the cycling performance of a lithium-ion battery electrode material, comprising: Step S1, analyzing to obtain the characteristic SOC range where the electrode material of the battery system of the electrode material to be tested undergoes cycling decay, and determining the accelerated test SOC range; Step S2, respectively performing accelerated cycling tests on the battery of the electrode material to be tested and the battery of the reference electrode material within the accelerated test SOC range to obtain the accelerated cycling capacity retention rate curve of the battery; Step S3, comparing the accelerated cycling capacity retention rate curves of the battery of the electrode material to be tested and the battery of the reference electrode material to judge the superiority and inferiority of the cycling performance of the battery of the electrode material to be tested relative to the battery of the reference electrode material and the cycling performance of the electrode material to be tested relative to the reference electrode material. The present invention is used for accelerating the evaluation of the cycling performance of different electrode materials, and can accurately, reliably and quickly screen out electrode materials with excellent performance for battery system design, thereby improving the R & D efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery performance testing, and in particular to an accelerated evaluation method for the cycle performance of a lithium ion battery electrode material. Background Art

[0002] At present, lithium-ion batteries have been widely used in digital products, electric vehicles and energy storage fields due to their advantages such as high energy density, good cycle performance, and green and pollution-free.

[0003] In the process of lithium-ion battery product development, a large number of experiments are usually required to screen out the battery material system that can meet customer needs. The battery material system includes key components such as positive electrode, negative electrode, electrolyte, and separator. When comparing and analyzing the performance of different materials, it is usually necessary to make batteries first, and then test and characterize the corresponding projects. Among them, the material cycle performance test is the most time-consuming test project, which seriously affects the overall progress of lithium-ion battery system and battery product development.

[0004] Therefore, how to speed up the evaluation of battery cycle performance and find reasonable and effective cycle evaluation methods have become key technical issues that need to be urgently solved in the lithium-ion battery industry.

[0005] At present, in the field of accelerated evaluation of the cycle performance of electrode materials (including positive electrode materials or negative electrode materials) of lithium-ion batteries, the battery cycle performance is mainly accelerated by changing stress conditions such as battery temperature, pressure, voltage, and current. However, changes in these stresses may cause the chemical and electrochemical reactions occurring in the lithium-ion battery material system to be inconsistent with the attenuation reactions occurring under the actual cycle format, which in turn leads to a large deviation between the results of the accelerated test and the actual cycle performance of the battery. Summary of the invention

[0006] The purpose of the present invention is to provide a method for accelerating the evaluation of the cycle performance of lithium-ion battery electrode materials in view of the technical defects in the prior art.

[0007] To this end, the present invention provides a method for accelerating the evaluation of the cycle performance of a lithium-ion battery electrode material, which comprises the following steps:

[0008] Step S1, for a battery with an electrode material to be tested having an electrode material to be tested, preselect a battery with good cycle electrode material and a battery with poor cycle electrode material of the same battery system as the battery with the electrode material to be tested, analyze and obtain a characteristic SOC interval in which the electrode material of the battery system with the electrode material to be tested undergoes cycle attenuation, and determine an accelerated test SOC interval;

[0009] Step S2: Using the battery with the optimized electrode material in the cycle as the reference electrode material battery, then respectively conduct accelerated cycle tests on the battery with the electrode material to be tested and the reference electrode material battery within the accelerated test SOC range obtained in the first step, and correspondingly obtain the accelerated cycle capacity retention rate curves of the battery with the electrode material to be tested and the reference electrode material battery.

[0010] Step S3: By comparing the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested and the accelerated cycle capacity retention rate curve of the reference electrode material battery, judge the superiority or inferiority of the cycle performance of the battery with the electrode material to be tested relative to the cycle performance of the reference electrode material battery, and the superiority or inferiority of the cycle performance of the electrode material to be tested relative to the cycle performance of the reference electrode material.

[0011] As can be seen from the technical solutions provided by the present invention above, compared with the prior art, the present invention provides an accelerated evaluation method for the cycle performance of lithium-ion battery electrode materials. Its design is scientific and applicable to the development of lithium-ion battery products. It is used to accelerate the evaluation of the cycle performance of different electrode materials (including positive electrode materials or negative electrode materials), can accurately and reliably screen out electrode materials with excellent performance for battery system design, can effectively shorten the development cycle of battery systems and products, improve the R & D efficiency, and has good application prospects and popularization value.

[0012] For the present invention, first analyze the characteristic SOC range where the electrode material to be tested undergoes cycle attenuation to determine the accelerated test SOC range, conduct accelerated cycle tests on the battery with the electrode material to be tested and the reference electrode material battery in the actual cycle mode, and measure the charging and discharging capacities of the batteries in the actual cycle mode at different stages of the accelerated cycle for calculating the capacity retention rate. Further, by comparing the capacity retention rate versus cycle number curves of the battery with the electrode material to be tested and the reference electrode material battery, judge the superiority or inferiority of the cycle performance of the battery with the electrode material to be tested relative to the reference electrode material battery.

[0013] In the method provided by the present invention, since the accelerated cycle analysis is limited within the characteristic attenuation range of the electrode material, compared with the cycle test of the full SOC, the evaluation period of the cycle performance of the electrode material can be greatly shortened, and the R & D efficiency can be improved. Brief Description of the Drawings

[0014] Figure 1 It is a flowchart of an accelerated evaluation method for the cycle performance of lithium-ion battery electrode materials provided by the present invention;

[0015] Figure 2 It is a schematic diagram of the analysis curve of the characteristic SOC range of the cycle attenuation of the negative electrode material in the negative electrode material battery system to be tested in Example 1 for the accelerated evaluation method of the cycle performance of lithium-ion battery electrode materials provided by the present invention;

[0016] Figure 3 An accelerated evaluation method for the cycling performance of a lithium-ion battery electrode material provided by the present invention. Schematic diagram of the accelerated cycling capacity retention rate curves of the battery with the negative electrode material to be tested and the battery with the reference negative electrode material in Example 1;

[0017] Figure 4 An accelerated evaluation method for the cycling performance of a lithium-ion battery electrode material provided by the present invention. Schematic diagram of the comparison of the actual cycling results (i.e., the actual cycling performance curves) between the battery with the negative electrode material to be tested and the battery with the reference negative electrode material in Example 1;

[0018] Figure 5 An accelerated evaluation method for the cycling performance of a lithium-ion battery electrode material provided by the present invention. Schematic diagram of the characteristic SOC interval analysis curve of the cycling decay of the positive electrode material in the battery system of the positive electrode material to be tested in Example 2;

[0019] Figure 6 An accelerated evaluation method for the cycling performance of a lithium-ion battery electrode material provided by the present invention. Schematic diagram of the accelerated cycling capacity retention rate curves of the battery with the positive electrode material to be tested and the battery with the reference positive electrode material in Example 2;

[0020] Figure 7 An accelerated evaluation method for the cycling performance of a lithium-ion battery electrode material provided by the present invention. Schematic diagram of the comparison of the actual cycling results (i.e., the actual cycling performance curves) between the battery with the positive electrode material to be tested and the battery with the reference positive electrode material in Example 2. Detailed implementation manners

[0021] In order to enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below with reference to the drawings and embodiments.

[0022] See Figures 1 to 7 , the present invention provides an accelerated evaluation method for the cycling performance of a lithium-ion battery electrode material, including the following steps:

[0023] Step S1: For the battery with the electrode material to be tested, a battery with a cycling-optimal electrode material and a battery with a cycling-poor electrode material in the same battery system as the battery with the electrode material to be tested are pre-selected, the characteristic SOC (i.e., the capacity retention rate, also called the state of charge) interval in which the electrode material in the battery system of the electrode material to be tested undergoes cycling decay is analyzed, and the accelerated test SOC interval is determined;

[0024] Step S2: Using the battery with the cycling-optimal electrode material as the reference electrode material battery, then the battery with the electrode material to be tested and the reference electrode material battery are respectively subjected to accelerated cycling tests within the accelerated test SOC interval obtained in the first step, and the accelerated cycling capacity retention rate curves of the battery with the electrode material to be tested and the reference electrode material battery are correspondingly obtained;

[0025] Step S3: By comparing the accelerated cycle capacity retention rate curves of the battery with the test electrode material and the battery with the reference electrode material, determine the superiority or inferiority of the cycle performance of the battery with the test electrode material relative to that of the battery with the reference electrode material, and the superiority or inferiority of the cycle performance of the test electrode material relative to that of the reference electrode material.

[0026] In the present invention, specifically, the test electrode material includes a test positive electrode material or a test negative electrode material;

[0027] In the present invention, specifically, the battery with the test electrode material includes a battery with a test positive electrode material or a battery with a test negative electrode material;

[0028] The battery with the reference electrode material includes a battery with a reference positive electrode material or a battery with a reference negative electrode material;

[0029] When the battery with the test electrode material is a battery with a test positive electrode material, the corresponding battery with the reference electrode material is a battery with a reference positive electrode material;

[0030] When the battery with the test electrode material is a battery with a test negative electrode material, the corresponding battery with the reference electrode material is a battery with a reference negative electrode material.

[0031] For the present invention, the working principle of step S1 is as follows: Step S1 is to perform a comparative analysis by means of batteries with positive or negative electrode materials having significantly different known cycle performances, so as to obtain the characteristic SOC intervals of the corresponding positive or negative electrode decay.

[0032] In the present invention, specifically, step S1 specifically includes the following operations

[0033] Step S11: Conduct a comparative test on two batteries with electrode materials having known cycle performance advantages and disadvantages (a battery with a cycle-advantaged electrode material and a battery with a cycle-disadvantaged electrode material): Select a battery with a cycle-advantaged electrode material and a battery with a cycle-disadvantaged electrode material (i.e., two batteries with electrode materials having known cycle performance advantages and disadvantages) of the same battery system as the battery with the test electrode material, and perform a preset charge and discharge cycle operation on each of them, and collect the battery voltage V and the charge capacity Q of the battery with the cycle-advantaged electrode material and the battery with the cycle-disadvantaged electrode material in real time;

[0034] In step S11, the battery with the cycle-advantaged electrode material is preferably a battery that has not undergone capacity decay;

[0035] In the present invention, the battery with the cycle-advantaged electrode material, the battery with the cycle-disadvantaged electrode material, and the battery with the test electrode material are batteries belonging to the same battery system, but different negative electrode materials are used;

[0036] In the present invention, batteries of the same battery system refer to: battery cells of the same specification model, that is, battery cells having the same specification dimensions and the same chemical system. For example, lithium iron phosphate system batteries of the 18650 size (which are cylindrical lithium iron phosphate battery cells). Of course, according to the needs of users, it can also be: batteries of the same other size and having a comparable chemical system (such as lithium cobaltate system or NCM ternary system, etc.) that are the same.

[0037] In step S2, the battery with the electrode material to be tested and the battery with the reference electrode material are two batteries that are exactly the same in all other battery components except that one electrode material is different (the negative electrode material is different or the positive electrode material is different). That is to say, they are two batteries that only differ in one negative electrode material (negative electrode material or positive electrode material). That is, it can be two batteries of the same system with two different negative electrode materials, or two batteries of the same system with two different positive electrode materials. For example, it can be two 21700 cylindrical lithium-ion batteries with different negative electrode materials, or two 21700 cylindrical lithium-ion batteries with different positive electrode materials.

[0038] In step S2, the battery with the electrode material to be tested is a battery prepared using the electrode material to be tested;

[0039] In step S11, the difference in the battery capacity retention rate between the battery with the excellent cycling electrode material and the battery with the poor cycling electrode material is greater than a preset value (for example, greater than 5%). That is to say, it is required that the battery with the excellent cycling electrode material and the battery with the poor cycling electrode material have obvious performance differences in the actual cycling test.

[0040] In step S11, the preset charge and discharge cycling operation includes one discharge operation and one charge operation. Specifically: first, charge at a constant current with a preset charging current (0.05C to 0.5C) until the preset charging upper limit voltage, and then discharge at a constant current with a preset discharging current (0.05C to 0.5C) until the preset discharging lower limit voltage;

[0041] It should be noted that for each specification model of battery product, during development, in combination with customer needs and based on a fixed chemical system design, the charging upper limit voltage and the preset discharging lower limit voltage of the developed battery can be determined, that is, the operating voltage range of the product, and the charging upper limit voltage and the discharging lower limit voltage of the battery will be clearly given in the specification of the battery product.

[0042] In step S12, for the battery with the excellent cycling electrode material and the battery with the poor cycling electrode material, respectively, differentiate the charging capacity Q with respect to the battery voltage V (specifically the charging voltage of the battery) to obtain dQ / dV of the battery with the excellent cycling electrode material and the battery with the poor cycling electrode material;

[0043] Step S13: For the battery with the electrode material having good cycling performance and the battery with the electrode material having poor cycling performance, respectively, taking dQ / dV as the ordinate and the state of charge SOC in real time during the charging process of the battery (i.e., the state of charge SOC corresponding to the charging capacity Q of the battery) as the abscissa, plot the incremental capacity (IC) curves of both in one graph;

[0044] Step S14: Taking the incremental capacity (IC) curve of the battery with the electrode material having good cycling performance as the reference curve, compare the incremental capacity (IC) curve of the battery with the electrode material having poor cycling performance with the reference curve, and determine the operation according to the preset characteristic SOC interval. Among the incremental capacity (IC) curves of the two batteries, namely the battery with the electrode material having good cycling performance and the battery with the electrode material having poor cycling performance, determine the characteristic SOC interval in which the electrode material of the battery system with the electrode material having poor cycling performance (which is equal to the battery system of the electrode material to be tested because the battery systems of the electrode material having poor cycling performance, the battery systems of the electrode material having poor cycling performance, and the battery system of the electrode material to be tested are the same) undergoes cycling decay;

[0045] The battery system of the electrode material having poor cycling performance is equivalent to the battery system of the electrode material to be tested (and is also equivalent to the fresh battery system);

[0046] The characteristic SOC interval in which the electrode material of the battery system of the electrode material having poor cycling performance undergoes cycling decay is the characteristic SOC interval in which the electrode material of the battery system of the electrode material to be tested undergoes cycling decay;

[0047] The characteristic SOC interval in which the electrode material of the battery system of the electrode material having poor cycling performance undergoes cycling decay includes the lower limit value SOC L and the upper limit value SOC U ;

[0048] In the present invention, the characteristic SOC interval is, on the curves of the fresh battery and the reference battery (such as the incremental capacity IC curve, i.e., the dQ / dV - SOC curve), by comparing the peaks of the two curves one by one, determining the starting position and ending position of the peak whose peak value is significantly reduced, or the peak whose peak value is significantly reduced and the peak position is significantly shifted corresponding to the SOC interval; that is, the characteristic SOC interval must satisfy the condition that the peak value is significantly reduced, and the peak position shift may or may not occur. If the peak position shift occurs, it is preferably the SOC interval corresponding to the peak whose peak value is significantly reduced and the peak position is shifted.

[0049] In the present invention, in step S14, the operation for determining the preset characteristic SOC interval includes the following steps:

[0050] First, on the incremental capacity (IC) curves (dQ / dV-SOC curves) of the battery with excellent cycling electrode material and the battery with poor cycling electrode material, by comparing the peaks of the two curves one by one, determine the peak whose peak value is significantly reduced, or the peak whose peak value is significantly reduced and the peak position is significantly shifted. Then, use it as the characteristic peak of cycle attenuation;

[0051] The significant reduction in the peak value of the peak means that the reduction ratio of the peak value of the peak is greater than or equal to the preset peak value reduction;

[0052] The significant shift in the peak position of the peak means that the SOC shift amplitude corresponding to the peak position of the peak is greater than or equal to the preset peak position shift value;

[0053] Then, take the SOC interval corresponding to the starting position and the ending position of the characteristic peak of cycle attenuation as the characteristic SOC interval.

[0054] Specifically, the operation of determining the preset characteristic SOC interval specifically includes the following steps:

[0055] When the battery capacity decays by 5%, on the incremental capacity (IC) curves (dQ / dV-SOC curves) of the battery with excellent cycling electrode material and the battery with poor cycling electrode material, compare the peaks of the two curves one by one (that is, the first, second... Nth peaks of the fresh battery curve are compared with the first, second... Nth peaks of the reference battery curve, and N is a natural number greater than 2). Determine the peak whose peak value reduction ratio ≥ 10%, or the peak whose peak value reduction ratio ≥ 10% and the SOC shift amplitude corresponding to the peak position ≥ 3% as the characteristic peak of cycle attenuation. Preferably, the peak whose peak value reduction ratio ≥ 10% and the SOC shift amplitude corresponding to the peak position ≥ 3% is used as the characteristic peak of cycle attenuation;

[0056] The abscissa corresponding to the starting position of this peak (i.e., the characteristic peak of cycle attenuation) is the lower limit value SOC of the characteristic SOC interval L The abscissa corresponding to the ending position of this peak is the upper limit value SOC of the characteristic SOC interval U That is to say: in the electrochemical reaction corresponding to this peak, the battery not only experiences the attenuation of the activity of the active material (peak value reduction), but also may experience the increase of polarization (the voltage or SOC corresponding to the peak position shifts).

[0057] In Example 1, the peak height of the second peak in the dQ / dV-SOC curve of the anode battery with good cycling performance is 5.97 Ah / V, and the peak height of the second peak in the anode battery with poor cycling performance is 5.36 Ah / V. Then the reduction ratio of the peak value of the second peak reaches (5.97 - 5.36) / 5.97 = 10.2%. Then this second peak is the characteristic peak of the battery's cycling degradation. The abscissa SOC corresponding to the starting position of this peak is 12%, which is the lower limit value of SOC L , and the abscissa SOC corresponding to the ending position of this peak is 24%, which is the upper limit value of SOC U .

[0058] It should be noted that in the present invention, during the test in the characteristic SOC interval, the selected batteries are two batteries of electrode materials with significantly different cycling performances (i.e., the battery of electrode material with good cycling performance and the battery of electrode material with poor cycling performance), and they belong to the same system as the battery of the electrode material to be tested. During the test, the battery of electrode material with good cycling performance and the battery of electrode material with poor cycling performance are selected for comparative testing. The test results of the two batteries are compared in one graph. As the capacity decays, the peak with a reduced peak value or the peak with a reduced peak value and a shifted peak position is selected as the characteristic peak of cycling degradation, so as to determine the characteristic SOC interval according to the starting and ending positions of this peak

[0059] In step S14, specifically, according to the operation of determining the preset characteristic SOC interval, in the incremental capacity (IC) curves of the battery of electrode material with good cycling performance and the battery of electrode material with poor cycling performance, the characteristic SOC interval in which the electrode material of the battery system of the electrode material with poor cycling performance undergoes cycling degradation is determined. Specifically: in the incremental capacity (IC) curves of the battery of electrode material with good cycling performance and the battery of electrode material with poor cycling performance, the state of charge (SOC) interval corresponding to the significant reduction of the peak value (i.e., the value at the highest point) of the peak where the curve has a peak and the significant shift of the peak position of the peak is determined as the characteristic SOC interval in which the electrode material of the battery (i.e., the battery as the reference electrode material) system of the electrode material with poor cycling performance undergoes cycling degradation

[0060] It should be noted that in the present invention, the peak value of the peak on the incremental capacity (IC) curve is the highest value of each peak. The abscissas corresponding to the starting position and the ending position of this peak indicate its position, that is, the peak position

[0061] It should be noted that the reduction of the peak value of the peak indicates that: the reaction activity of the active substance (positive electrode or negative electrode) of the battery undergoing this electrochemical reaction decreases. When the battery capacity decays by 5%, on the corresponding dQ / dV-SOC curve (incremental capacity IC curve), if the reduction ratio of the peak value ≥ 10%, the influence caused by test errors can be excluded, and it can be determined that the peak value of the peak of the curve is significantly reduced

[0062] It should be noted that for the incremental capacity (IC) curves of the battery with a cycling-optimized electrode material and the battery with a cycling-poor electrode material, the peak positions of the peaks on the two curves shift. This is usually caused by an increase in battery polarization. When the battery capacity decays by 5%, on the dQ / dV-SOC curve, if the SOC shift corresponding to the starting position or the ending position of the characteristic peak is ≥ 3%, the influence caused by test errors can be excluded, and it can be determined that the peak position of the curve significantly shifts.

[0063] Step S15: Determine the accelerated test SOC interval according to the characteristic SOC interval where the electrode material of the battery system with the electrode material to be tested undergoes cyclic decay. The accelerated test SOC interval includes the lower limit value SOC CL and the upper limit value SOC CU ;

[0064] Among them, the accelerated test SOC interval includes all the characteristic SOC intervals where the electrode material of the battery system with the electrode material to be tested undergoes cyclic decay, or includes some of the characteristic SOC intervals where the electrode material of the battery system with the electrode material to be tested undergoes cyclic decay.

[0065] In step S15, specifically, to fully shorten the test cycle, the lower limit value SOC of the accelerated test SOC interval CL = SOC L ± 10%, and the upper limit value SOC of the accelerated test SOC interval CU = SOC U ± 10%; specifically, it is preferably SOC CL = SOC L ± 5%, SOC CU = SOC U ± 5%.

[0066] In step S2, use the battery with a cycling-optimized electrode material as the reference electrode material battery, and then perform an accelerated cycling test on the battery with the electrode material to be tested within the accelerated test SOC interval obtained in the first step, and correspondingly obtain the accelerated cycling capacity retention rate curve of the battery with the electrode material to be tested, which specifically includes the following steps:

[0067] Step S21A: Perform a preset number of (for example, 3 times) charge and discharge cycle operations (each charge and discharge cycle operation includes one discharge operation and one charge operation) on the battery with the electrode material to be tested in accordance with the actual cycling regime of the reference electrode material battery, and use the battery charging capacity and discharge capacity obtained during the last charge and discharge cycle operation as the initial charging capacity C0 and the initial discharge capacity D0 of the battery with the electrode material to be tested;

[0068] It should be noted that the actual cycling regime refers to the charging and discharging cycling regime established for life evaluation according to customer requirements during battery development, including the upper charging voltage, lower discharging voltage, charging current, discharging current, and rest duration, etc. For example, in the embodiment, for a 21700 cylindrical battery with a capacity of 4.7 Ah, its cycling regime is: constant current charging at 1C until its upper voltage reaches 4.2V, then changing to constant voltage charging, and cutting off when the current drops to 0.05C, resting for 15 minutes, discharging at 1C until the lower voltage of 2.5V is reached, resting for 15 minutes, and then continuing the charging and discharging cycle.

[0069] For the actual cycling regime, it is the cycling regime used for life evaluation formulated by product developers according to customer requirements during battery development and agreed by the customer, and the specific regime content is clearly specified in the specification.

[0070] It should be noted that in the present invention, since the battery with the electrode material to be tested is an experimental battery (R & D experimental battery) made by diversifying the electrode material (replacing the same type of material due to performance improvement or cost reduction requirements) or optimizing the process on the basis of the battery with the reference electrode material, the battery with the electrode material to be tested is a successful (i.e., the performance of the battery with the electrode material to be tested is better than or equivalent to that of the battery with the reference electrode material) or failed (i.e., the performance of the battery with the electrode material to be tested is inferior to that of the battery with the reference electrode material) same type of battery intended to replace the battery with the reference electrode material, and the actual cycling regimes of the battery with the electrode material to be tested and the battery with the reference electrode material are the same. The actual cycling regime of the battery with the electrode material to be tested can be obtained from the specification of the battery with the reference electrode material.

[0071] Step S22A: Using the actual cycling regime of the battery with the reference electrode material as the accelerated cycling regime, perform accelerated cycling tests on the battery with the electrode material to be tested in multiple (for example, n, where n is a natural number greater than 1) stages (i.e., repeatedly perform accelerated cycling tests in multiple stages), and after each stage of the accelerated cycling test, obtain the charging capacity and discharging capacity of the battery with the electrode material to be tested, and record the total number of accelerated cycles corresponding to the end of each stage of the accelerated cycling test (i.e., starting from the first stage of the accelerated cycling test and up to the end of this stage of the accelerated cycling test, the total number of accelerated cycles executed).

[0072] In step S22A, the test content of the accelerated cycling tests in multiple stages is the same.

[0073] Each stage of the accelerated cycling test specifically includes the following operations:

[0074] The first step: Charge the battery to the lower limit value SOC of the accelerated test SOC interval with a pre-set charging current (for example, a small current of 0.05 - 0.5C). CL, and then let it stand for a preset duration (e.g., 10 - 30 minutes);

[0075] In the second step, perform the same accelerated cycle test operation on the battery for a preset number of times (e.g., N times, where N is a natural number greater than 1, e.g., N is 50 times);

[0076] The specific operation of each accelerated cycle test is as follows: Select the charging current Ic and the discharging current Id corresponding to the accelerated test SOC interval in the actual cycle regime of the battery with the electrode material to be tested. Then, first perform a charging operation on the battery with the electrode material to be tested for a preset charging duration tc with the charging current Ic, and then perform a discharging operation on the battery for a preset discharging duration td with the discharging current Id, so that the charging and discharging capacities of the battery within the accelerated test SOC interval (from the lower limit value SOC CL to the upper limit value SOC CU ) are the same; that is, Ic * tc = Id * td;

[0077] The actual cycle regime of the battery with the electrode material to be tested is the same as that of the battery with the reference electrode material;

[0078] It should be noted that the charging current Ic and the discharging current Id corresponding to the accelerated test SOC interval in the actual cycle regime of the battery with the electrode material to be tested can be obtained from the actual cycle regime specified in the specification of the battery with the reference electrode material belonging to the same battery system. For example, in the embodiment, its actual cycle regime is to charge at a constant current of 1C to the upper limit voltage of 4.2V, then switch to constant voltage charging, and stop when the current drops to 0.05C, let it stand for 15 minutes, and then discharge at a constant current of 1C until the lower limit voltage of 2.5V is reached. Therefore, the charging current and the discharging current of the battery with the electrode material to be tested within the accelerated test SOC interval are both 1C.

[0079] In the third step, continue to perform charge and discharge cycle operations of fully charging and fully discharging the battery with the electrode material to be tested for a preset number of times (e.g., 2 to 5 times) in the actual cycle regime;

[0080] In the fourth step, take the battery charging capacity and the discharging capacity obtained during the last fully charging and fully discharging charge and discharge cycle operation as the charging capacity and the discharging capacity of the battery with the electrode material to be tested after each stage of the accelerated cycle test;

[0081] In the third step, as mentioned above, the actual cycling regime refers to the charging and discharging cycling regime established for life evaluation according to customer requirements during battery development, including the upper charging voltage, lower discharging voltage, charging current, discharging current, and rest duration, etc. For example, for the battery with the electrode material to be tested, as in the embodiment, its actual cycling regime is to charge at a constant current of 1C to the upper voltage of 4.2V, then switch to constant voltage charging, stop when the current drops to 0.05C, rest for 15 minutes, and then discharge at a constant current of 1C until the lower voltage of 2.5V is reached.

[0082] It should be noted that in the third step, full charge and full discharge means charging and discharging according to the actual cycling regime, that is, charging to the upper charging voltage of the battery and discharging to the lower discharging voltage of the battery. For example, it can be: charging at a constant current of 1C to the upper voltage of 4.2V, then switching to constant voltage charging at 4.2V, stopping when the current drops to 0.05C, resting for 15 minutes, and then discharging at a constant current of 1C until the lower voltage of 2.5V is reached. Then rest for 15 minutes and perform the same charging and discharging cycle again.

[0083] In the present invention, full charge and full discharge is relative to accelerated cycling. Accelerated cycling is carried out within a certain SOC range, while full charge and full discharge is to charge and discharge within the entire SOC range. The purpose of performing full charge and full discharge here is: after evaluating the accelerated cycling for a certain period, to determine how much of the charging and discharging capacity of the tested battery remains when tested according to the actual cycling regime, so as to calculate and evaluate the capacity retention rate.

[0084] It should be noted that when the number of charging and discharging cycles reaches N times, perform 2 - 5 full charge and full discharge cycles on the battery according to the actual cycling regime to be investigated, and record the charging and discharging capacity of the last cycle as the charging capacity C N and discharging capacity D N of the battery after N - time accelerated cycling. At this time, the corresponding battery charging capacity retention rate is C N / C0, and the discharging capacity retention rate is D N / D0.

[0085] Step S23A: Calculate the battery charging capacity retention rate and battery discharging capacity retention rate of the battery with the electrode material to be tested in each stage of the accelerated cycling test based on the charging capacity and discharging capacity in each stage of the accelerated cycling test of the battery with the electrode material to be tested, and the initial charging capacity C0 and initial discharging capacity D0 obtained in step S21A;

[0086] In step S23A, the battery charging capacity retention rate of the battery with the electrode material to be tested in each stage of the accelerated cycling test is equal to the charging capacity C of the battery with the electrode material to be tested in each stage of the accelerated cycling test待测 The quotient obtained by dividing by the initial charge capacity C0; that is, it is equal to C 待测 / C0;

[0087] In step S23A, the battery discharge capacity retention rate of the battery with the electrode material to be tested in the accelerated cycle test at each stage is equal to the discharge capacity D of the battery with the electrode material to be tested in the accelerated cycle test at each stage 待测 The quotient obtained by dividing by the initial discharge capacity D0; that is, it is equal to D 待测 / D0.

[0088] Step S24A: Using the battery charge capacity retention rate and the battery discharge capacity retention rate of the battery with the electrode material to be tested in the accelerated cycle test at each stage as the ordinate, and using the total number of accelerated cycles corresponding to the end of the accelerated cycle test at each stage as the abscissa, plot to obtain the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested.

[0089] In step S2, using the battery with the cyclic excellent electrode material as the reference electrode material battery, and then performing an accelerated cycle test on the reference electrode material battery within the accelerated test SOC range obtained in the first step, and correspondingly obtaining the accelerated cycle capacity retention rate curve of the reference electrode material battery, specifically including the following steps:

[0090] Step S21B: Using the actual cycle regime of the reference electrode material battery, perform a preset number of (for example, 3 times) charge and discharge cycle operations on the reference electrode material battery (each charge and discharge cycle operation includes one discharge operation and one charge operation), and use the battery charge capacity and discharge capacity obtained during the last charge and discharge cycle operation as the initial charge capacity C1 and the initial discharge capacity D1 of the reference electrode material battery;

[0091] It should be noted that the actual cycle regime is determined according to the battery model and is clearly stated in the specification. When evaluating the battery with the electrode material to be tested and the reference electrode material battery in this battery model, their actual cycle regimes are the same.

[0092] Step S22B: Using the actual cycle regime of the reference electrode material battery as the accelerated cycle regime, perform multiple (for example, n, where n is a natural number greater than 1) stages of accelerated cycle tests on the reference electrode material battery in sequence (that is, repeat multiple stages of accelerated cycle tests), and in each stage of the accelerated cycle test, obtain the charge capacity and discharge capacity of the reference electrode material battery, and record the total number of accelerated cycles corresponding to the end of each stage of the accelerated cycle test (that is, starting from the first stage of the accelerated cycle test until the end of this stage of the accelerated cycle test, the total number of accelerated cycles executed);

[0093] In step S22B, the test content of multiple stages of accelerated cycle tests is the same;

[0094] The accelerated cycle test for each stage specifically includes the following operations:

[0095] In the first step, the battery is charged to the lower limit value SOC of the accelerated test SOC range with a pre-sized charging current (for example, a small current of 0.05 - 0.5C), CL and then left to stand for a preset duration (for example, 10 - 30 minutes);

[0096] In the second step, the battery is subjected to the same accelerated cycle test operation a preset number of times (for example, N times, where N is a natural number greater than 1);

[0097] Each accelerated cycle test operation specifically involves: selecting the charging current Ic and discharging current Id corresponding to the accelerated test SOC range in the actual cycle regime of the reference electrode material battery, and then, successively, performing a charging operation on the reference electrode material battery with the charging current Ic for a preset charging duration tc and a discharging operation on the battery with the discharging current Id for a preset discharging duration td, such that the charging and discharging capacities of the battery within the accelerated test SOC range (from the lower limit value SOC CL to the upper limit value SOC CU ) are the same; that is, Ic * tc = Id * td;

[0098] The actual cycle regime of the battery with the electrode material to be tested is the same as that of the reference electrode material battery;

[0099] It should be noted that the charging current Ic and discharging current Id corresponding to the accelerated test SOC range in the actual cycle regime of the reference electrode material battery can be obtained from the actual cycle regime specified in the specification of the reference electrode material battery. For example, in the embodiment, its actual cycle regime is constant current charging at 1C to the upper limit voltage of 4.2V, then switching to constant voltage charging and stopping when the current drops to 0.05C, standing for 15 minutes, and then performing constant current discharging at 1C until the lower limit voltage of 2.5V is reached. Therefore, the charging current and discharging current of the reference electrode material battery within the accelerated test SOC range are both 1C.

[0100] In the third step, the reference electrode material battery is continued to be subjected to a preset number of (for example, 2 to 5 times) full charge and full discharge charge and discharge cycle operations in the actual cycle regime;

[0101] In the fourth step, the battery charging capacity and discharging capacity obtained during the last full charge and full discharge charge and discharge cycle operation are used as the charging capacity and discharging capacity of the reference electrode material battery after the accelerated cycle test for each stage;

[0102] It should be noted that in the third step, full charge and discharge means charging and discharging according to the actual cycle mode, that is, charging to the upper limit voltage of the battery for charging and discharging to the lower limit voltage of the battery for discharging.

[0103] In the present invention, full charge and discharge is relative to accelerated cycling. Accelerated cycling is carried out within a certain SOC range, while full charge and discharge is carried out for charging and discharging within the entire SOC range. The purpose of performing full charge and discharge here is: after evaluating the accelerated cycling for a certain period, to determine how much of the charging and discharging capacity remains when the reference battery is tested according to the actual cycle mode, so as to calculate and evaluate the capacity retention rate.

[0104] Step S23 B: According to the charging capacity and discharging capacity of the reference electrode material battery in the accelerated cycling test at each stage, as well as the initial charging capacity C1 and the initial discharging capacity D1 obtained in step S21B, calculate the battery charging capacity retention rate and the battery discharging capacity retention rate of the reference electrode material battery in the accelerated cycling test at each stage;

[0105] In step S23 B, the battery charging capacity retention rate of the reference electrode material battery in the accelerated cycling test at each stage is equal to the quotient of the charging capacity C of the reference electrode material battery in the accelerated cycling test at each stage 参比 divided by the initial charging capacity C1; that is, equal to C 参比 / C1;

[0106] In step S23 B, the battery discharging capacity retention rate of the reference electrode material battery in the accelerated cycling test at each stage is equal to the quotient of the discharging capacity D of the reference electrode material battery in the accelerated cycling test at each stage 参比 divided by the initial discharging capacity D1, that is, equal to D 参比 / D1.

[0107] Step S24 B: Using the battery charging capacity retention rate and the battery discharging capacity retention rate of the reference electrode material battery in the accelerated cycling test at each stage as the vertical coordinates, and the total number of accelerated cycles corresponding to the end of the accelerated cycling test at each stage as the horizontal coordinates, plot the accelerated cycling capacity retention rate curve of the reference electrode material battery.

[0108] In step S3, specifically, if the accelerated cycling capacity retention rate curve (i.e., the charging and discharging capacity retention rate curve) of the battery with the electrode material to be tested is above the accelerated cycling capacity retention rate curve (i.e., the charging and discharging capacity retention rate curve) of the reference electrode material battery, it is determined that the cycling performance of the battery with the electrode material to be tested is superior to that of the reference electrode material battery, and it is determined that the cycling performance of the electrode material to be tested is superior to that of the reference electrode material.

[0109] In step S3, specifically, if the accelerated cycle capacity retention rate curve (i.e., the charge and discharge capacity retention rate curve) of the battery with the electrode material to be tested is below the accelerated cycle capacity retention rate curve (i.e., the charge and discharge capacity retention rate curve) of the battery with the reference electrode material, it is determined that the cycle performance of the battery with the electrode material to be tested is inferior to that of the battery with the reference electrode material, and it is determined that the cycle performance of the electrode material to be tested is inferior to that of the reference electrode material.

[0110] In the present invention, in step S3, specifically, if the accelerated cycle capacity retention rate curve (i.e., the charge and discharge capacity retention rate curve) of the battery with the electrode material to be tested during the accelerated cycle is substantially coincident with the accelerated cycle capacity retention rate curve (i.e., the charge and discharge capacity retention rate curve) of the battery with the reference electrode material, it is necessary to repeatedly perform the accelerated cycle test in step S2 to repeatedly obtain the accelerated cycle capacity retention rate curves of the battery with the electrode material to be tested and the battery with the reference electrode material until the accelerated cycle capacity retention rate curves of the battery with the electrode material to be tested and the battery with the reference electrode material are completely separated. Then, according to the relative position (i.e., above or below) of the accelerated cycle capacity retention rate curves of the battery with the electrode material to be tested and the battery with the reference electrode material, the superiority or inferiority of the cycle performance of the electrode material to be tested compared to the cycle performance of the reference electrode material is determined.

[0111] Among them, when the coincidence degree between the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested and the accelerated cycle capacity retention rate curve of the battery with the reference electrode material is greater than or equal to a preset first ratio (e.g., 85%), it is determined that the two are substantially coincident.

[0112] Among them, when the coincidence degree between the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested and the accelerated cycle capacity retention rate curve of the battery with the reference electrode material is less than or equal to a preset second ratio (e.g., 5%), it is determined that the two are completely separated.

[0113] The preset first ratio is greater than the preset second ratio.

[0114] Among them, it should be noted that when the accelerated cycle test in step S2 is repeatedly performed currently, among the accelerated cycle tests in multiple stages included in the accelerated cycle test in step S2, the total number of accelerated cycles corresponding to the end of the last stage of the accelerated cycle test is greater than the total number of accelerated cycles corresponding to the end of the last stage of the accelerated cycle test in the accelerated cycle test in step S2 when step S2 was previously performed. For example, if the previous total number was 200 times, then the total number of accelerated cycles required when repeatedly performing step S2 is greater than 200 times, such as 300 times.

[0115] In the present invention, in step S3, the accelerated cycle capacity retention rate curve of the reference electrode material battery can be used as reference data to establish a database. When screening and evaluating the electrode materials of the same system battery later, it can be directly used as a reference curve for comparative analysis.

[0116] Based on the above technical solutions, for the present invention, first, the cyclic attenuation characteristic interval of the electrode material to be tested is analyzed to determine the accelerated test interval. Then, the accelerated cycle test is carried out on the battery of the negative electrode to be tested and the reference electrode material battery in the actual cycle mode. At different stages of the accelerated cycle test, the charging and discharging capacities of the battery are measured in the actual cycle mode for calculating the capacity retention rate of the battery of the electrode material to be tested. Then, further by comparing with the battery of the reference electrode material in terms of the curve of the capacity retention rate versus the number of cycles, the superiority or inferiority of the cyclic performance of the battery of the electrode material to be tested relative to the reference battery (i.e., the battery of the reference electrode material) is judged.

[0117] Compared with the prior art, the accelerated evaluation method for the cyclic performance of the lithium-ion battery electrode material provided by the present invention has the following beneficial technical effects:

[0118] 1. For the method provided by the present invention, first, the characteristic SOC interval where the electrode material to be tested undergoes cyclic attenuation and the accelerated test SOC interval are determined. Then, the accelerated cycle test is carried out within the accelerated test SOC interval, and by analyzing the capacity retention rate after the accelerated cycle, the superiority or inferiority of the cyclic performance of the electrode material to be tested is judged. Compared with the traditional full-SOC cycle test, the evaluation time can be significantly shortened.

[0119] 2. The present invention first determines the characteristic SOC interval where the electrode material to be tested undergoes cyclic attenuation. Within this SOC interval, the cyclic attenuation characteristics of the electrode material to be tested are significant, so it can be used as the accelerated test SOC interval for the cycle to shorten the cycle evaluation time.

[0120] 3. For the present invention, within the selected accelerated test SOC interval, the battery of the electrode material to be tested and the battery of the reference electrode material are subjected to the accelerated cycle test according to the charging current Ic and the discharging current Id in the actual cycle mode, and the charging and discharging time is stopped when the charging and discharging capacities of the battery within the accelerated test SOC interval (from the lower limit value SOC CL to the upper limit value SOC CU ) are the same, that is, Ic*tc = Id*td. This accelerated cycle mode is taken from the actual cycle mode. Therefore, no additional influencing factors (such as temperature, rate, etc.) are introduced, ensuring the reliability of the accelerated cycle test for the electrode material to be tested.

[0121] 4. For the present invention, in the rapid evaluation of the battery cycling performance of the electrode material to be tested, taking the measured battery charge and discharge capacity retention rates as the ordinate and the corresponding total number of accelerated cycles as the abscissa, the accelerated cycle capacity retention rate curves of the battery with the electrode material to be tested and the battery with the reference electrode material are obtained respectively; the cycling performance of the electrode material to be tested is evaluated by comparing the positions of the curves. Instead of analyzing only based on the comparison of the capacity retention rates at one or several times under the same number of accelerated cycles, the present invention ensures the accuracy and comprehensiveness of the analysis results. Especially when the capacity retention rate curves of the battery with the electrode material to be tested and the battery with the reference electrode material cross, the results of the curve analysis can maintain accuracy, while if only analyzing based on the capacity retention rate points in the previous several times, misjudgment may occur.

[0122] To more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described below through specific embodiments.

[0123] Example 1.

[0124] Below, taking the test of a commercial cylindrical lithium-ion battery as an example, the present invention will be described in detail with reference to the accompanying drawings to further elaborate on the substantial features and remarkable progress of the present invention.

[0125] In this Example 1, the test sample is a 21700 cylindrical lithium-ion experimental battery with a 1C capacity of 4.7 Ah. The batteries with the negative electrode material to be tested and the reference negative electrode material have the same model, except for the different negative electrode materials.

[0126] The battery test equipment is a conventional charge and discharge instrument. In this example, the equipment used is the Arbin BT2000 charge and discharge test system.

[0127] In Example 1, the accelerated evaluation method for the cycling performance of the lithium-ion battery electrode material provided by the present invention specifically includes the following steps:

[0128] Step 1: For the battery with the negative electrode material to be tested having the negative electrode material to be tested, a battery with a cycling-optimal electrode material and a battery with a cycling-poor electrode material in the same battery system as the battery with the negative electrode material to be tested are pre-selected, and the characteristic SOC (i.e., capacity retention rate, also called state of charge) interval in which the negative electrode material in the battery system of the negative electrode material to be tested undergoes cycling decay is analyzed, and the accelerated test SOC interval is determined;

[0129] The specific operation is as follows: First, take two batteries of the same system with different anode materials (i.e., the battery with excellent cycling anode material and the battery with poor cycling anode material), and these two batteries have significant performance differences in actual cycling tests: the capacity retention rate of the battery with the excellent cycling anode is 99.04%, and the capacity retention rate of the battery with the poor cycling anode is 93.38%. Use these two cycled batteries to analyze the characteristic SOC range of the cycling decay of the anode material of this battery system.

[0130] Then, perform small current charge and discharge at 0.1C on these two cycled batteries. Differentiate the battery voltage with respect to the charge capacity to obtain dQ / dV. Take dQ / dV as the ordinate and the real-time state of charge SOC of the battery as the abscissa to plot the incremental capacity IC curve, as shown in the appendix Figure 2 . From the appendix Figure 2 , it can be seen that the characteristic range where the anode material decays significantly is the range from 12% SOC to 24% SOC. As the capacity retention rate of the battery decreases, the peak height of the lithium insertion peak of its IC curve decreases significantly, and the peak position shifts towards lower SOC. This range includes the lower limit value SOC L (12% SOC) and the upper limit value SOC U (24% SOC).

[0131] Then, based on the characteristic SOC range of the cycling decay of the above anode material, determine the accelerated test SOC range. The accelerated test SOC range is the range that includes or partially includes the characteristic SOC range of the cycling decay. This range includes the lower limit value SOC CL and the upper limit value SOC CU . To fully shorten the test cycle, generally preferably SOC CL = SOC L ±10%, SOC CU = SOC U ±10%. Further preferably, it is SOC CL = SOC L ±5%, SOC CU = SOC U ±5%. In this example, the accelerated test range is selected as 10% - 20% SOC, that is, SOC CL is 10%, and SOC CU is 20%.

[0132] Second step: Take the battery with the excellent cycling anode material as the reference anode material battery. Then, perform accelerated cycling tests on the battery with the anode material to be evaluated and the reference anode material battery within the accelerated test SOC range, and obtain the accelerated cycling capacity retention rate curves of the battery with the anode material to be evaluated and the reference anode material battery respectively. The specific operations include the following:

[0133] Step 1: Take the battery made of the negative electrode material to be evaluated, perform 3 charge-discharge cycles in the actual cycling regime to be investigated, and record the charging and discharging capacities of the 3rd cycle as the initial charging capacity C0 and the initial discharging capacity D0 of the battery.

[0134] Charge and discharge the battery at 1C = 4.7A. The constant current charging cut-off voltage is 4.2V, and the constant voltage charging stops when the current drops to 0.05C = 0.235A. The discharging cut-off voltage is 2.5V. Record the initial charging capacity C0 and the initial discharging capacity D0 of the battery with the negative electrode material to be evaluated in the 3rd cycle in Table 1, and the initial charging capacity C 0S and the initial discharging capacity D 0S of the reference negative electrode material battery.

[0135] Step 2: Charge the battery with the negative electrode material to be evaluated and the reference negative electrode material battery at a small current of 0.2C to the lower limit value of the accelerated test interval (10% SOC - 20% SOC), that is, 10% SOC, and let it stand for 10 - 30 minutes.

[0136] Step 3: Select the charging current Ic and the discharging current Id corresponding to the accelerated test interval (10% - 20% SOC) in the actual cycling regime of the battery in this system, and use the charging and discharging time as the cut-off to make the charging and discharging capacities of the battery in the characteristic SOC interval (10% - 20% SOC) the same, that is, Ic*tc = Id*td. Ic = 4.7A, tc = 360s, Id = 4.7A, td = 360s, and the number of charge-discharge cycles of the battery in the accelerated test interval (10% - 20% SOC) is set to 50 times.

[0137] Step 4: When the number of the above charge-discharge cycles reaches 50 times (i.e., N is 50), perform 2 full charge and full discharge cycles on the battery with the negative electrode material to be evaluated and the reference negative electrode material battery in the actual cycling regime of 1C charge and discharge, and record the charging and discharging capacities of the last cycle as the charging capacity C N and the discharging capacity D N of the battery after 50 accelerated cycles. At this time, the corresponding battery charging capacity retention rate is C N / C0, and the discharging capacity retention rate is D N / D0.

[0138] Step 5: Repeat the acceleration cycle process of Step 2 to Step 4 for n times (n equals 3) (the acceleration cycle process of Step 2 to Step 4 is the acceleration cycle test for one stage), and end when the number of acceleration cycles of the battery reaches 150 (equal to n*N, that is, 3*50). Then, obtain the charge capacity retention rate and discharge capacity retention rate of the battery after 50, 100, and 150 acceleration cycles (that is, obtain the battery charge capacity retention rate and battery discharge capacity retention rate for these 3 stages), and record them in Table 1.

[0139] Table 1: Schematic table of charge and discharge capacities and retention rates of the reference anode material battery and the battery with the anode material to be tested during the acceleration cycle.

[0140]

[0141] Step 6: Use the charge and discharge capacity retention rates of the battery measured in the above steps as the ordinate and the corresponding total number of acceleration cycles as the abscissa to plot graphs, and respectively obtain the acceleration cycle capacity retention rate curves of the battery with the anode material to be tested and the reference anode material battery, as shown in the appendix Figure 3 as follows.

[0142] Step 3: Quick evaluation of the cycle performance of the anode material to be evaluated: By comparing the acceleration cycle capacity retention rate curve of the battery with the anode material to be tested and the acceleration cycle capacity retention rate curve of the reference anode material battery, judge the superiority or inferiority of the cycle performance of the battery with the anode material to be tested relative to the cycle performance of the reference anode material battery, and the superiority or inferiority of the cycle performance of the anode material to be tested relative to the cycle performance of the reference anode material.

[0143] In this Example 1, it can be seen from Figure 3 that during 150 acceleration cycles, the acceleration cycle capacity retention rate curve of the battery with the anode material to be tested is above the acceleration cycle capacity retention rate curve of the reference anode material battery, and the distance between the two curves is getting larger and larger, and it is impossible to cross again. Therefore, it is determined that the cycle performance of the battery with the anode material to be tested is better than that of the reference anode material battery, that is, the cycle performance of the anode material to be tested is better than that of the reference anode material.

[0144] In this Example 1, by performing acceleration cycle tests on the battery with the anode material to be tested and the reference anode material battery, it can be known that the cycle performance of the anode material to be tested is better than that of the reference anode material, and it is consistent with the Figure 4 actual cycle test results shown as follows.

[0145] After inspection, for this Example 1, the acceleration cycle test for the cycle performance of the anode material to be tested only takes 6 days, that is, the evaluation results consistent with the actual cycle test are obtained, significantly shortening the cycle evaluation period of the anode material, effectively improving the R & D efficiency, and further shortening the R & D cycle of battery products and systems.

[0146] Example 2

[0147] Taking the test of commercial cylindrical lithium-ion batteries as an example, the present invention will be described in detail with reference to the accompanying drawings to further illustrate the substantial features and remarkable progress of the present invention.

[0148] In this Example 2, the test sample is a 21700 cylindrical lithium-ion experimental battery, and the 1C capacity is 4.7 Ah. The battery with the positive electrode material to be tested and the battery with the reference positive electrode material have the same model, except for the different positive electrode materials.

[0149] The battery test equipment is a conventional charge and discharge instrument. In this example, the equipment used is the Arbin BT2000 charge and discharge test system.

[0150] In Example 1, the method for accelerating the evaluation of the cycling performance of the lithium-ion battery electrode material provided by the present invention specifically includes the following steps:

[0151] The first step: For the battery with the positive electrode material to be tested having the positive electrode material to be tested, a battery with a good cycling positive electrode material and a battery with a poor cycling positive electrode material in the same battery system as the battery with the positive electrode material to be tested are pre-selected, and the characteristic SOC (i.e., the capacity retention rate, also called the state of charge) range in which the positive electrode material of the battery system with the positive electrode material to be tested undergoes cycling decay is analyzed, and the accelerated test SOC range is determined;

[0152] The specific operation is as follows: First, take two batteries of the same system with different positive electrode materials (i.e., the battery with a good cycling positive electrode material and the battery with a poor cycling positive electrode material), and there are significant performance differences between these two batteries in the actual cycling test: the capacity retention rate of the battery with the good cycling positive electrode is 99.04%, and the capacity retention rate of the battery with the poor cycling positive electrode is 85.90%. Use these two cycled batteries to analyze the characteristic SOC range of the cycling decay of the positive electrode material of this battery system.

[0153] Then, perform small current charge and discharge of 0.1C on these two cycled batteries. Differentiate the battery voltage with respect to the charging capacity to obtain dQ / dV. Take dQ / dV as the ordinate and the real-time state of charge SOC of the battery as the abscissa to plot the incremental capacity IC curve, as shown in the appendix Figure 5 From the appendix Figure 5It can be seen that there are two relatively significant characteristic intervals in the attenuation of the positive electrode material. One is the interval from 8% SOC to 23% SOC. As the battery capacity retention rate decreases, the peak height of the lithium intercalation peak in the IC curve decreases significantly, and the peak position shifts towards a lower SOC, which is the most significant SOC interval for attenuation. The other is the interval from 78% SOC to 100% SOC, where the peak height of the battery with poor cycling performance decreases significantly. Therefore, the characteristic SOC intervals for the cyclic attenuation of the positive electrode material in this system are the two intervals from 8% SOC to 23% SOC and from 78% SOC to 100% SOC. As is well known, a decrease in the peak height of the IC curve indicates a decrease in the lithium deintercalation and intercalation ability of the active material, that is, the reversible capacity decreases, while the peak position shift indicates an increase in the polarization of this reaction. Therefore, considering these two factors comprehensively, the most significant characteristic SOC interval for the cyclic attenuation of the positive electrode material is from 8% SOC to 23% SOC, and this interval includes the lower limit value SOC L and the upper limit value SOC U .

[0154] Based on the characteristic SOC intervals of the cyclic attenuation of the positive electrode material described above, the accelerated test SOC interval is determined. The accelerated test SOC interval includes or partially includes the characteristic SOC intervals of the cyclic attenuation, and this interval includes the lower limit value SOC CL and the upper limit value SOC CU . To fully shorten the test cycle, it is generally preferred that SOC CL = SOC L ±10%, SOC CU = SOC U ±10%. Further preferably, SOC CL = SOC L ±5%, SOC CU = SOC U ±5%. In Example 2 of this embodiment, considering the test cycle and the excessive polarization of the battery in the low state of charge interval comprehensively, the accelerated test SOC interval is selected as 10% - 20% SOC, that is, SOC CL is 10%, and SOC CU is 20%.

[0155] Step 2: Use the battery with the positive electrode material with excellent cycling performance as the reference positive electrode material battery, and then perform accelerated cycling tests on the battery with the positive electrode material to be evaluated and the reference positive electrode material battery within the accelerated test SOC interval, and obtain the accelerated cycling capacity retention rate curves of the battery with the positive electrode material to be evaluated and the reference positive electrode material battery correspondingly. The specific operations include the following:

[0156] Step 1, Take the battery made of the positive electrode material to be evaluated, perform 3 charge-discharge cycles with the actual cycling regime to be investigated, and record the charging and discharging capacities of the 3rd cycle as the initial charging capacity C0 and the initial discharging capacity D0 of the battery.

[0157] Charge and discharge the battery at 1C = 4.7A. The constant current charging cut-off voltage is 4.2V. Charge at constant voltage until the current drops to 0.05C = 0.235A and then discharge the battery at 1C = 4.7A with the cut-off voltage of 2.5V. Record the initial charging capacity C0 and the initial discharging capacity D0 of the battery with the positive electrode material to be evaluated in the 3rd cycle in Table 2. The initial charging capacity C 0S and the initial discharging capacity D 0S of the reference positive electrode material battery

[0158] Step 2: Charge the battery with the positive electrode material to be evaluated and the reference positive electrode material battery at a small current of 0.2C to the lower limit value of the accelerated test interval (10% SOC - 20% SOC), i.e., 10% SOC, and let it stand for 10 - 30 minutes.

[0159] Step 3: Select the charging current Ic and the discharging current Id corresponding to the accelerated test interval (10% - 20% SOC) in the actual cycling regime of the battery in this system, and cut off the charging and discharging by time, so that the charging and discharging capacities of the battery in the characteristic SOC interval (10% - 20% SOC) are the same, i.e., Ic * tc = Id * td. Ic = 4.7A, tc = 360s, Id = 4.7A, td = 360s. Set the number of charging and discharging cycles of the battery in the accelerated test interval (10% - 20% SOC) to 50 times.

[0160] Step 4: When the number of the above charge-discharge cycles reaches 50 times (i.e., N is 50), perform 2 full charge and discharge cycles on the battery with the positive electrode material to be tested and the reference positive electrode material battery in the actual cycling regime of 1C charge and discharge, and record the charging and discharging capacities of the last cycle as the charging capacity C N and the discharging capacity D N of the battery after 50 accelerated cycles. At this time, the corresponding battery charging capacity retention rate is C N / C0, and the discharging capacity retention rate is D N / D0.

[0161] Step 5: Repeat the accelerated cycling process of the second to fourth steps n times (n is equal to 3) (the accelerated cycling process of the second to fourth steps is an accelerated cycling test of one stage), and end when the accelerated cycling times of the battery reach 150 (equal to n * N, i.e., 3 * 50) times. Then obtain the charging capacity retention rate and the discharging capacity retention rate of the battery after 50, 100, and 150 accelerated cycles (i.e., obtain the battery charging capacity retention rates and battery discharging capacity retention rates of these 3 stages), and record them in Table 2.

[0162] Table 2: Schematic table of the charge-discharge capacities and retention rates of the reference positive electrode material battery and the battery with the positive electrode material to be tested during the accelerated cycling process

[0163]

[0164] Step 6: Taking the retention rates of the battery charge and discharge capacities measured in the above steps as the ordinate and the corresponding total number of accelerated cycles as the abscissa, plot graphs respectively to obtain the accelerated cycle capacity retention rate curves of the battery with the positive electrode material to be tested and the battery with the reference positive electrode material, as shown in the appendix Figure 6 as follows.

[0165] Step 3: Rapid evaluation of the cycling performance of the positive electrode material to be tested: By comparing the accelerated cycle capacity retention rate curve of the battery with the positive electrode material to be tested and the accelerated cycle capacity retention rate curve of the battery with the reference positive electrode material, judge the superiority or inferiority of the cycling performance of the battery with the positive electrode material to be tested relative to the cycling performance of the battery with the reference positive electrode material, and the superiority or inferiority of the cycling performance of the positive electrode material to be tested relative to the cycling performance of the reference positive electrode material.

[0166] In Example 2 of the present invention, it can be seen from Figure 6 that during 150 accelerated cycles, the accelerated cycle capacity retention rate curve of the battery with the positive electrode material to be tested is below the accelerated cycle capacity retention rate curve of the battery with the reference positive electrode material, and the distance between the two curves is getting larger and larger, and it is impossible to cross again. Therefore, it is determined that the cycling performance of the battery with the positive electrode material to be tested is inferior to the cycling performance of the battery with the reference positive electrode material, that is, the cycling performance of the positive electrode material to be tested is inferior to the cycling performance of the reference positive electrode material.

[0167] In Example 2 of the present invention, by performing accelerated cycle tests on the battery with the positive electrode material to be tested and the battery with the reference positive electrode material, it can be known that the cycling performance of the positive electrode material to be tested is inferior to the cycling performance of the reference positive electrode material, and it is consistent with the Figure 7 actual cycle test results shown.

[0168] After inspection, for Example 2, the accelerated cycle test for the cycling performance of the positive electrode material to be tested only takes 6 days, that is, the evaluation results consistent with the actual cycle test are obtained, significantly shortening the cycle evaluation period of the positive electrode material, effectively improving the R & D efficiency, and further shortening the R & D cycle of the battery product and system.

[0169] In summary, compared with the prior art, an accelerated evaluation method for the cycling performance of a lithium-ion battery electrode material provided by the present invention is scientifically designed, applicable to the development of lithium-ion battery products, used to accelerate the evaluation of the cycling performance of different electrode materials (positive electrode materials or negative electrode materials), can accurately and reliably and quickly screen out excellent electrode materials for battery system design, effectively shorten the development cycle of the battery system and products, improve the R & D efficiency, and has good application prospects and promotion value.

[0170] For the present invention, first, the characteristic SOC interval in which the test electrode material undergoes cyclic attenuation is analyzed to determine the accelerated test SOC interval. The test electrode material battery and the reference electrode material battery are subjected to accelerated cycle testing in the actual cycle mode, and the charge and discharge capacities of the battery are measured in the actual cycle mode at different stages of the accelerated cycle for the calculation of the capacity retention rate. Further, by comparing the capacity retention rate versus cycle number curves of the test electrode material battery and the reference electrode material battery, the superiority or inferiority of the cycle performance of the test electrode material battery relative to the reference electrode material battery is determined.

[0171] In the method provided by the present invention, since the accelerated cycle analysis is limited within the characteristic attenuation interval of the electrode material, compared with the cycle test of the full SOC, the evaluation period of the cycle performance of the electrode material can be greatly shortened, and the R & D efficiency can be improved.

[0172] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An accelerated evaluation method for the cycling performance of a lithium-ion battery electrode material, characterized in that, Including the following steps: Step S1: For a battery with a test electrode material to be measured, a cycling-optimal electrode material battery and a cycling-poor electrode material battery of the same battery system as the battery with the test electrode material to be measured are pre-selected. Taking the capacity increment curve of the cycling-optimal electrode material battery as a reference curve, the capacity increment curve of the cycling-poor electrode material battery is compared with the reference curve, and an operation is determined according to a preset characteristic SOC interval. In the capacity increment curves of the cycling-optimal electrode material battery and the cycling-poor electrode material battery, the characteristic SOC interval in which the electrode material of the cycling-poor electrode material battery system undergoes cycling decay is determined; Among them, the cycling-poor electrode material battery system is equivalent to the battery system of the battery with the test electrode material to be measured; the characteristic SOC interval in which the electrode material of the cycling-poor electrode material battery system undergoes cycling decay is the characteristic SOC interval in which the electrode material of the battery system of the battery with the test electrode material to be measured undergoes cycling decay; According to the characteristic SOC interval in which the electrode material of the battery system of the battery with the test electrode material to be measured undergoes cycling decay, an accelerated test SOC interval is determined; Step S2: Using the cycling-optimal electrode material battery as a reference electrode material battery, then the battery with the test electrode material to be measured and the reference electrode material battery are respectively subjected to an accelerated cycling test within the accelerated test SOC interval obtained in the first step, and the accelerated cycling capacity retention rate curves of the battery with the test electrode material to be measured and the reference electrode material battery are obtained correspondingly; Step S3: By comparing the accelerated cycling capacity retention rate curve of the battery with the test electrode material to be measured and the accelerated cycling capacity retention rate curve of the reference electrode material battery, the superiority or inferiority of the cycling performance of the battery with the test electrode material to be measured relative to the cycling performance of the reference electrode material battery, and the superiority or inferiority of the cycling performance of the test electrode material relative to the cycling performance of the reference electrode material are judged.

2. The accelerated evaluation method for the cycling performance of the lithium-ion battery electrode material according to claim 1, wherein, The said Step S1 specifically includes the following operations Step S11: Comparative tests are carried out on two electrode material batteries with known cycling performance advantages or disadvantages: One cycling-optimal electrode material battery and one cycling-poor electrode material battery of the same battery system as the battery with the test electrode material to be measured are selected, and preset charge and discharge cycling operations are respectively carried out, and the battery voltage V and the charging capacity Q of the cycling-optimal electrode material battery and the cycling-poor electrode material battery are collected in real time; Step S12: For the cycling-optimal electrode material battery and the cycling-poor electrode material battery, the charging capacity Q is respectively differentiated with respect to the charging voltage V of the battery to obtain dQ / dV of the cycling-optimal electrode material battery and the cycling-poor electrode material battery; Step S13: For the cycling-optimal electrode material battery and the cycling-poor electrode material battery, with dQ / dV as the ordinate and the state of charge SOC in real time during the charging process of the battery as the abscissa, the capacity increment curves of both are plotted and obtained in one graph; Among them, the characteristic SOC interval of the electrode material of the battery system with poor cycle electrode material cycle attenuation, including the lower limit SOC L And upper limit SOC U ; The accelerated test SOC range includes the lower limit SOC CL and the upper limit SOC CU ; Among them, the accelerated test SOC interval includes all of the characteristic SOC intervals in which the electrode material of the battery system of the battery with the test electrode material to be measured undergoes cycling decay, or includes part of the characteristic SOC intervals in which the electrode material of the battery system of the battery with the test electrode material to be measured undergoes cycling decay; The operation for determining the preset characteristic SOC interval includes the following steps: First, on the incremental capacity (IC) curves of the battery with the electrode material having good cycle performance and the battery with the electrode material having poor cycle performance, by comparing the peaks of the two curves one by one, determine the peak whose peak value of the peak significantly decreases, or the peak where both the peak value of the peak significantly decreases and the peak position of the peak significantly shifts, and then use it as the characteristic peak of cycle attenuation; The significant decrease in the peak value of the peak means that the decrease ratio of the peak value of the peak is greater than or equal to the preset peak value decrease; The significant shift in the peak position of the peak means that the offset amplitude of the peak position corresponding to the SOC is greater than or equal to the preset peak position offset value; Then, use the SOC interval corresponding to the start position and the end position of the characteristic peak of cycle attenuation as the characteristic SOC interval.

3. The accelerated evaluation method for the cycle performance of the lithium-ion battery electrode material according to claim 2, wherein, In step S11, the battery with the electrode material to be tested is a battery prepared with the electrode material to be tested; The battery with the electrode material to be tested includes the battery with the positive electrode material to be tested or the battery with the negative electrode material to be tested; The battery with the reference electrode material includes the battery with the reference positive electrode material or the battery with the reference negative electrode material; When the battery with the electrode material to be tested is the battery with the positive electrode material to be tested, the corresponding battery with the reference electrode material is the battery with the reference positive electrode material; When the battery with the electrode material to be tested is the battery with the negative electrode material to be tested, the corresponding battery with the reference electrode material is the battery with the reference negative electrode material; In step S11, the battery with the electrode material to be tested and the battery with the reference electrode material are two batteries with exactly the same other battery components except that the negative electrode material or the positive electrode material is different; In step S11, the difference in the battery capacity retention rates of the battery with the electrode material having good cycle performance and the battery with the electrode material having poor cycle performance is greater than the preset value; In step S15, the lower limit value SOC of the SOC interval for the accelerated test CL = SOC L ± 10%, and the upper limit value SOC of the SOC interval for the accelerated test CU = SOC U ± 10%; In step S11, the preset charge-discharge cycle operation includes one discharge operation and one charge operation. Specifically: first, charge at a constant current with a preset charging current to the preset charging upper limit voltage, and then discharge at a constant current with a preset discharging current to the preset discharging lower limit voltage.

4. The accelerated evaluation method for the cycle performance of the lithium-ion battery electrode material according to claim 1, wherein In step S2, use the battery with the electrode material having good cycle performance as the battery with the reference electrode material, and then perform an accelerated cycle test on the battery with the electrode material to be tested within the accelerated test SOC interval obtained in the first step, and correspondingly obtain the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested, which specifically includes the following steps: Step S21A, perform a preset number of charge-discharge cycle operations on the battery with the electrode material to be tested with the actual cycle regime of the battery with the reference electrode material, and use the battery charging capacity and discharging capacity obtained during the last charge-discharge cycle operation as the initial charging capacity C0 and the initial discharging capacity D0 of the battery with the electrode material to be tested; Step S22A, use the actual cycle regime of the battery with the reference electrode material as the accelerated cycle regime, perform multiple stages of accelerated cycle tests on the battery with the electrode material to be tested in sequence, and after each stage of the accelerated cycle test, obtain the charging capacity and discharging capacity of the battery with the electrode material to be tested, and record the total number of accelerated cycles corresponding to the end of each stage of the accelerated cycle test; Step S23A: Calculate the battery charge capacity retention rate and the battery discharge capacity retention rate of the battery with the electrode material to be tested in the accelerated cycle test at each stage based on the charge capacity and the discharge capacity in the accelerated cycle test at each stage of the battery with the electrode material to be tested, as well as the initial charge capacity C0 and the initial discharge capacity D0 obtained in Step S21A. Step S24A: Use the battery charge capacity retention rate and the battery discharge capacity retention rate of the battery with the electrode material to be tested in the accelerated cycle test at each stage as the ordinate, and use the total number of accelerated cycles corresponding to the end of the accelerated cycle test at each stage as the abscissa to plot the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested.

5. The accelerated evaluation method for the cycle performance of the lithium-ion battery electrode material according to claim 4, wherein In Step S22A, the accelerated cycle test at each stage specifically includes the following operations: First step, charge the battery to the lower limit value SOC of the accelerated test SOC range with a pre-sized charging current CL , and then let it stand for a preset duration; The second step: Perform the same accelerated cycle test operation a preset number of times on the battery. Each accelerated cycle test operation is specifically as follows: Select the charging current Ic and the discharging current Id corresponding to the accelerated test SOC interval in the actual cycle regime of the battery with the electrode material to be tested. Then, first perform a charging operation on the battery with the electrode material to be tested for a preset charging duration tc with the charging current Ic, and then perform a discharging operation on the battery for a preset discharging duration td with the discharging current Id, so that the charge and discharge capacities of the battery in the accelerated test SOC interval are the same; that is, Ic * tc = Id * td. The actual cycle regime of the battery with the electrode material to be tested is the same as the actual cycle regime of the reference electrode material battery. The third step: Continue to perform a preset number of full charge and full discharge charge and discharge cycle operations on the battery with the electrode material to be tested in the actual cycle regime. The fourth step: Use the battery charge capacity and the discharge capacity obtained during the last full charge and full discharge charge and discharge cycle operation as the charge capacity and the discharge capacity of the battery with the electrode material to be tested after the accelerated cycle test at each stage.

6. The accelerated evaluation method for the cycle performance of the lithium-ion battery electrode material according to claim 1, wherein, In Step S2, use the battery with the cyclic excellent electrode material as the reference electrode material battery, and then perform an accelerated cycle test on the reference electrode material battery within the accelerated test SOC interval obtained in the first step, and correspondingly obtain the accelerated cycle capacity retention rate curve of the reference electrode material battery, which specifically includes the following steps: Step S21B: Perform a preset number of charge and discharge cycle operations on the reference electrode material battery in the actual cycle regime of the reference electrode material battery, and use the battery charge capacity and the discharge capacity obtained during the last charge and discharge cycle operation as the initial charge capacity C1 and the initial discharge capacity D1 of the reference electrode material battery. Step S22B: Use the actual cycle regime of the reference electrode material battery as the accelerated cycle regime, and perform multiple stages of accelerated cycle tests on the reference electrode material battery in sequence. And in the accelerated cycle test at each stage, obtain the charge capacity and the discharge capacity of the reference electrode material battery, and record the total number of accelerated cycles corresponding to the end of the accelerated cycle test at each stage. Step S23B: Calculate the battery charge capacity retention rate and the battery discharge capacity retention rate of the reference electrode material battery in the accelerated cycle test at each stage based on the charge capacity and the discharge capacity of the battery in the accelerated cycle test at each stage, as well as the initial charge capacity C1 and the initial discharge capacity D1 obtained in Step S21B. Step S24B: Plot the accelerated cycle capacity retention rate curve of the reference electrode material battery with the battery charge capacity retention rate and the battery discharge capacity retention rate of the reference electrode material battery in the accelerated cycle test at each stage as the vertical coordinates and the total number of accelerated cycles corresponding to the end of the accelerated cycle test at each stage as the horizontal coordinates.

7. The accelerated evaluation method for the cycle performance of the lithium-ion battery electrode material according to claim 6, characterized in that, In Step S22B, the accelerated cycle test at each stage specifically includes the following operations: In the first step, charge the battery to the lower limit value SOC of the accelerated test SOC range with a pre-sized charging current CL , and then let it stand for a preset duration; The second step: Perform the same accelerated cycle test operation a preset number of times on the battery. Each accelerated cycle test operation is specifically as follows: Select the charging current Ic and the discharging current Id corresponding to the accelerated test SOC range in the actual cycle regime of the reference electrode material battery. Then, first charge the reference electrode material battery with the charging current Ic for a preset charging duration tc, and then discharge the battery with the discharging current Id for a preset discharging duration td, so that the charge and discharge capacities of the battery in the accelerated test SOC range are the same; that is, Ic*tc = Id*td. The actual cycle regime of the battery with the electrode material to be tested is the same as the actual cycle regime of the reference electrode material battery. The third step: Continue to perform a preset number of full charge and full discharge charge and discharge cycle operations on the reference electrode material battery in the actual cycle regime. The fourth step: Use the battery charge capacity and the discharge capacity obtained during the last full charge and full discharge charge and discharge cycle operation as the charge capacity and the discharge capacity of the reference electrode material battery after the accelerated cycle test at each stage.

8. The accelerated evaluation method for the cycle performance of the lithium-ion battery electrode material according to claim 1, wherein In Step S3, if the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested is above the accelerated cycle capacity retention rate curve of the reference electrode material battery, it is determined that the cycle performance of the battery with the electrode material to be tested is better than that of the reference electrode material battery, and it is determined that the cycle performance of the electrode material to be tested is better than that of the reference electrode material. In Step S3, if the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested is below the accelerated cycle capacity retention rate curve of the reference electrode material battery, it is determined that the cycle performance of the battery with the electrode material to be tested is worse than that of the reference electrode material battery, and it is determined that the cycle performance of the electrode material to be tested is worse than that of the reference electrode material.

9. The accelerated evaluation method for the cycle performance of the lithium-ion battery electrode material according to claim 1, wherein, In step S3, if the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested is basically coincident with the accelerated cycle capacity retention rate curve of the battery with the reference electrode material, it is necessary to repeat the accelerated cycle test in step S2 to repeatedly obtain the accelerated cycle capacity retention rate curves of the battery with the electrode material to be tested and the battery with the reference electrode material until the accelerated cycle capacity retention rate curves of the battery with the electrode material to be tested and the battery with the reference electrode material are completely separated. Then, according to the relative positions of the accelerated cycle capacity retention rate curves of the battery with the electrode material to be tested and the battery with the reference electrode material, the pros and cons of the cycle performance of the electrode material to be tested compared to the cycle performance of the reference electrode material are judged; Among them, when the coincidence degree between the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested and the accelerated cycle capacity retention rate curve of the battery with the reference electrode material is greater than or equal to a preset first ratio, it is judged that the two are basically coincident; Among them, when the coincidence degree between the accelerated cycle capacity retention rate curve of the battery with the electrode material to be tested and the accelerated cycle capacity retention rate curve of the battery with the reference electrode material is less than or equal to a preset second ratio, it is judged that the two are completely separated; The preset first ratio is greater than the preset second ratio.

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