Method for testing rate capability of negative electrode material and application

Abstract

The invention discloses a negative electrode material rate capability testing method and application, and the negative electrode material rate capability testing method comprises the steps: taking a negative electrode material to be tested, and assembling the negative electrode material into a button type half cell; activating the button type half cell; the activated button type half cell is subjected to n times of cyclic charging and discharging, and n is a natural number and is larger than or equal to 2; the multiplying power X adopted in the discharging stage of each cycle charging and discharging is different; the state of charge SOC (i) when the potential is the preset value PV in each charging and discharging is calculated, the higher the state of charge SOC (i) is, the better the rate capability of the negative electrode material to be tested is, i is a natural number, and n > = i > = 2. According to the test method provided by the embodiment of the invention, the negative electrode material meeting the quick charge requirement can be quickly screened out, the difference between the multiplying power and the quick charge performance of different materials can be accurately compared, the evaluation efficiency of the lithium ion battery is accelerated, and the test method also plays an important role in improving the efficiency of the process development and optimization process of the negative electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of testing negative electrode materials, and more specifically, to a testing method and application for the rate performance of negative electrode materials. Background Art

[0002] With the rapid development of electric vehicles, people's requirements for the driving range and fast charging of electric vehicles are getting higher and higher. Among them, the negative electrode material is one of the decisive factors for the fast charging performance of the battery. If the used negative electrode material cannot meet the requirements of fast charging, lithium plating is very likely to occur under inappropriate charging conditions, causing serious safety problems. Therefore, the current demand for fast-charging negative electrode materials is becoming more urgent and strict, but the existing testing methods for fast charging performance are relatively cumbersome and have a long testing cycle. For example, CN115097341A discloses a method for detecting the lithium plating performance of graphite-based materials, which mainly distinguishes the differences in fast charging performance by comparing the rate lithium plating intervals of different materials. When processing data, it is necessary to first make a voltage-time curve and then perform differential processing; in the case where the distinction fails for the first time, it is necessary to optimize the rate interval again for testing to distinguish the rate differences between materials. If the rate interval is set too small, the testing cycle will be long.

[0003] In view of this, a testing method for the rate performance of negative electrode materials with a short testing time and convenient data processing is particularly important. Summary of the Invention

[0004] The purpose of the present invention is to provide a testing method and application for the rate performance of negative electrode materials, which overcome the problems of long testing cycles, difficult data processing, and low discrimination accuracy or accuracy of existing methods.

[0005] The present invention is implemented as follows:

[0006] In a first aspect, the present invention provides a testing method for the rate performance of negative electrode materials, including:

[0007] Taking the negative electrode material to be tested and assembling it into a button-type half-cell;

[0008] Activating the button-type half-cell;

[0009] Performing n cycles of charge and discharge on the activated button-type half-cell, where n is a natural number and n≥2; the rate X used in the discharge stage of each cycle of charge and discharge is different;

[0010] Calculating the state of charge SOC(i) when the potential is the preset value PV during each charge and discharge. The higher the state of charge SOC(i), the better the rate performance of the negative electrode material to be tested, where i is a natural number and n≥i≥2.

[0011] In an alternative embodiment, the state of charge SOC(i) = Q0(i) / Q t (i)*100, where Q0(i) is the capacity at the preset value PV during the i-th cycle charge and discharge; Q t (i) is the discharge capacity at the preset value PV during the i-th cycle charge and discharge.

[0012] In an alternative embodiment, a single cycle process of the cyclic charge and discharge includes discharging, standing after discharging, charging, and standing after charging in sequence;

[0013] Preferably, 2 ≤ n ≤ 15.

[0014] In an alternative embodiment, the standing time after discharging is 45 - 90 min;

[0015] And / or, the standing time after charging is 20 - 40 min.

[0016] In an alternative embodiment, discharging in the i-th cycle is performed at a rate of X(i), and the discharging time is t, where t = [C / X(i)]*60 min, C is the rated capacity of the battery; and X(i) > X(i - 1).

[0017] In an alternative embodiment, the charging rates and cut-off voltages are the same during the n-cycle charge and discharge;

[0018] And / or, the charging rates and cut-off voltages during the n-cycle charge and discharge are the same as those during the charging in the activation stage.

[0019] In an alternative embodiment, the rate used in the discharging stage of the i-th cycle charge and discharge is X(i), and 0.1C ≤ X(i) ≤ 3C.

[0020] In an alternative embodiment, the negative electrode material includes natural graphite, artificial graphite, silicon carbide, and graphite doping materials.

[0021] In a second aspect, the present invention provides a rapid screening method for a high-rate performance negative electrode material, including: testing m kinds of negative electrode materials to be tested by using the testing method for the rate performance of the negative electrode material according to any one of the foregoing embodiments, numbering them from 1 to m in sequence to obtain m groups of test data; each group of the test data contains n SOC(i) values, where m is a positive integer ≥ 2;

[0022] Selecting the x-th group and the y-th group from the m groups of negative electrode materials to be tested for comparison:

[0023] If T1 > T2, the rate performance of the x-th group of negative electrode materials is superior to that of the y-th group of negative electrode materials;

[0024] If T1 < T2, the rate performance of the x-group anode material is worse than that of the y-group anode material;

[0025] If T1 = T2, the rate performance of the x-group anode material is comparable to that of the y-group anode material;

[0026] Among them, T1 is the number of times of SOC x (i) > SOC y (i); T2 is the number of times of SOC x (i) < SOC y (i); 1 ≤ x ≤ m, 1 ≤ y ≤ m, and x ≠ y.

[0027] In a third aspect, the present invention provides a method for predicting the rate performance of an anode material by using the method described in any one of the foregoing embodiments, including:

[0028] When predicting the rate performance of the anode material to be tested:

[0029] When X(i) ≤ 0.75C, for every 1% increase in SOC 较大 (i) compared to SOC 较小 (i), the lithium plating rate of the full cell corresponding to the high-rate performance anode material is increased by ΔX compared to the lithium plating rate of the full cell corresponding to the low-rate performance anode material 析锂 , 0.03C ≤ ΔX 析锂 ≤ 0.3C;

[0030] When X(i) > 0.75C, for every 1% increase in SOC 较大 (i) compared to SOC 较小 (i), the lithium plating rate of the full cell corresponding to the high-rate performance anode material is increased by ΔX compared to the lithium plating rate of the full cell corresponding to the low-rate performance anode material 析锂 , 0.08C ≤ ΔX 析锂 ≤ 0.2C;

[0031] Among them, SOC 较大 (i) refers to the larger one of the SOC(i) values corresponding to the x-group and y-group anode materials, and SOC 较小 (i) refers to the smaller one of the SOC(i) values corresponding to the x-group and y-group anode materials;

[0032] And / or, select any one of the anode materials with better rate performance or the two groups of anode materials with comparable rate performance among the x-group and y-group anode materials, and repeat the comparison step with any one of the remaining (m - 2) groups of anode materials until all m groups of data are compared to screen out the high-rate performance anode materials.

[0033] The present invention has the following beneficial effects:

[0034] The test method of the embodiment of the present invention makes a button-type half-cell with the negative electrode material, tests its SOC(i) value at different rates, and evaluates the rate performance of the negative electrode material intuitively, simply, quickly and accurately by comparing the magnitudes of the SOC(i) values at multiple different rates. Thus, the negative electrode materials meeting the fast charging requirements can be quickly screened out, the cycle test period can be greatly shortened, the differences in the rates and fast charging performances of different materials can be more accurately compared, the discrimination is high, the evaluation efficiency of lithium-ion batteries can be effectively accelerated, and it also plays an important role in improving the efficiency of the process development and optimization of the negative electrode material. In addition, the test method of the embodiment of the present invention is less affected by the production of the button-type half-cell, eliminates the measurement error caused by poor consistency of the button cell, is beneficial to improving the accuracy of the results, and this test method has universality, is not only applicable to the performance tests of various negative electrode materials, but also the test results can be applied to various battery structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0036] Figure 1 SOC(%) values at 0V of the negative electrode materials to be tested in each embodiment at different rates;

[0037] Figure 2 EIS test results of the negative electrode materials to be tested in each embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0039] The embodiment of the present invention provides a test method for the rate performance of a negative electrode material, including:

[0040] Taking the negative electrode material to be tested and assembling it into a button-type half-cell;

[0041] Activating the button-type half-cell;

[0042] Performing n times of cyclic charge and discharge on the activated button-type half-cell, where n is a natural number and n≥2; the rate X used in the discharge stage of each cyclic charge and discharge is different;

[0043] Calculate the state of charge SOC(i) when the potential is the preset value PV during each charge and discharge process. The higher the state of charge SOC(i), the better the rate performance of the negative electrode material to be measured, where i is a natural number and n≥i≥2.

[0044] Further, it should be noted that during the assembly process of the coin-type half-cell, a lithium sheet is used in combination with the negative electrode material to be measured.

[0045] In the embodiment of the present invention, a coin-type half-cell evaluation system is adopted. The production cycle of the coin-type half-cell is short, and the overall test cycle is also shorter than that of the full cell test cycle. At the same time, in the coin-type half-cell, a lithium sheet is used in combination with the negative electrode material to be measured. Compared with the full cell system, it can exclude the influence of the positive electrode material and better reflect the kinetic performance differences of the negative electrode material itself to be measured. By comparing the state of charge SOC(i) of different negative electrode materials at different rates and when the potential is the preset value PV, the fast charging performance between materials can be distinguished. If the SOC(i) under PV is higher, it indicates that the polarization internal resistance of this material is lower, and more capacity can be obtained under the same rate and cut-off conditions. It should be noted that the preset potential value PV can be selected according to needs. For example, in some embodiments, it can be 0V or 1V, etc. In some embodiments, considering that the negative electrode potential of 0V is the thermodynamic condition for lithium ions to precipitate into lithium metal, the SOC% at 0V is taken as the standard for comparison.

[0046] The embodiment of the present invention does not require making voltage-time intervals at different rates, and further processing such as differential processing is not required. By calculating the state of charge SOC(i) when the potential is the preset value PV, the fast charging performance of different materials can be distinguished. And for materials with little difference in fast charging performance, when using the rate lithium stripping interval to distinguish the difference in fast charging performance, if the rate interval is not appropriate, the lithium stripping peaks of the two materials will appear in the same interval, making it impossible to accurately distinguish. The discrimination and accuracy of the embodiment of the present application are higher.

[0047] In summary, the test method of the embodiment of the present invention makes the negative electrode material into a button-type half-cell, tests the SOC(i) value at different rates, and evaluates the rate performance of the negative electrode material intuitively, simply, quickly and accurately by comparing the magnitudes of the SOC(i) values at multiple different rates. Thus, the negative electrode material meeting the fast charging requirements can be quickly screened out, the cycle test period can be greatly shortened, the differences in the rates and fast charging performances of different materials can be more accurately compared, the discrimination degree is high, the evaluation efficiency of lithium-ion batteries can be effectively accelerated, and it also plays an important role in improving the efficiency of the process development and optimization of the negative electrode material. In addition, the test method of the embodiment of the present invention is less affected by the production of the button-type half-cell, eliminates the measurement error caused by poor consistency of the button cell, is beneficial to improving the accuracy of the result, and the test method has universality, is not only applicable to the performance test of various negative electrode materials, but also the test results can be applied to various battery structures.

[0048] In an alternative embodiment, the state of charge SOC(i) = Q0(i) / Q t (i)*100, where Q0(i) is the capacity at the potential of the preset value PV during the i-th charge and discharge cycle; Q t (i) is the discharge capacity at the potential of the preset value PV during the i-th charge and discharge cycle.

[0049] Directly read the capacity at the potential of the preset value PV; Q t (i) is the discharge capacity at the potential of the preset value PV during the i-th charge and discharge cycle, and the SOC at PV is obtained by simple calculation.

[0050] In an alternative embodiment, the single cycle process of the charge and discharge cycle includes discharging, standing after discharging, charging, and standing after charging in sequence;

[0051] Preferably, 2 ≤ n ≤ 15.

[0052] The rate performances of two negative electrode materials can be compared with a minimum of 2 cycles; the number of cycles is greatly shortened, and both the accuracy and discrimination accuracy of the test results are relatively high, which is beneficial to improving the screening speed of the negative electrode material, providing a basis for material selection, and at the same time reducing the cost.

[0053] It should be noted that increasing the number of cycles is beneficial to improving the accuracy of the test results, but it will also cause a decrease in the test efficiency. Therefore, the number of charge and discharge cycles is not as large as possible.

[0054] It should be noted that the discharge in each cycle is a constant current discharge.

[0055] In an alternative embodiment, the rest time after discharging is 45 - 90 min, specifically it can be 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min or any value within the range;

[0056] And / or, the rest time after charging is 20 - 40 min, specifically it can be 20 min, 24 min, 28 min, 32 min, 36 min, 40 min or any value within the range.

[0057] The purpose of resting is to stabilize the voltage. In some embodiments, during the rest period after charging or after discharging, sampling can be performed at intervals of 5 s and 1 mV voltage to determine whether the voltage is stable.

[0058] It should be noted that usually, the entire testing process is carried out at room temperature, for example, at 18°C - 25°C.

[0059] In an alternative embodiment, the discharging in the i-th cycle is carried out at a rate of X(i), and the discharging time is t, where t = [C / X(i)] * 60 min, and C is the rated capacity of the battery; and X(i) > X(i - 1).

[0060] During the charge-discharge process of n cycles, the rate gradually increases, which is beneficial to ensuring the stability of the initial state of the battery, avoiding irreversible damage to the battery caused by high rates at the initial stage; it is beneficial to reducing the influence of the cumulative effect, controlling the temperature rise and polarization phenomenon, optimizing the test sequence to obtain more accurate data; it is beneficial to improving the test safety and reliability and preventing early failure.

[0061] In some embodiments, the rates X adopted in the discharging stage of each cycle of charge-discharge can be 0.5C, 0.75C, 1C, 1.25C, and 1.5C respectively, and the discharging cut-off times are 120 min, 80 min, 60 min, 48 min, and 40 min respectively. The rate is not limited to changing in the range from 0.5C to 1.5C at intervals of 0.25C, and other rate intervals and rate ranges are also possible. The rate interval is generally ≥ 0.1C.

[0062] In an alternative embodiment, the rate adopted in the discharging stage of the i-th cycle of charge-discharge is X(i), and 0.1C ≤ X(i) ≤ 3C.

[0063] If the rate is too small, it is not conducive to improving the test efficiency. At too high rates, it may cause damage to the battery, resulting in a decrease in the accuracy of the test results. Therefore, the discharging rate needs to be reasonably selected.

[0064] In an alternative embodiment, the rates and cut-off voltages during charging in the n-cycle charge-discharge are the same;

[0065] And / or, in the n-cycle charge and discharge, both the charging rate and the cut-off voltage are the same as those in the charging stage of the activation stage.

[0066] In an alternative embodiment, the activation treatment of the coin half-cell is a conventional operation understood by those skilled in the art. Specifically, it can be: using a charge and discharge rate of 0.1C and a voltage range of 0.005V - 1.5V, charging and discharging the battery for 1 - 3 cycles.

[0067] In some embodiments, the specific conditions for activation are to charge and discharge at a rate of 0.1C for two weeks, with a voltage range of 0.005 - 1.5V. After activation, almost all the lithium on the graphite material is removed; the specific steps for one week of activation are: charging at 0.1C to 1.5V, and then discharging at 0.1C to 0.005V; in the charging stage of the n-cycle charge and discharge, it is charged at a constant rate of 0.1C to 1.5V, and then left standing for 30 minutes.

[0068] In an alternative embodiment, the negative electrode material includes natural graphite, artificial graphite, silicon carbide, and graphite doping materials, with a wide range of applications and universality.

[0069] The embodiments of the present invention also provide a rapid screening method for a negative electrode material with high rate performance, including using the test method for the rate performance of the negative electrode material described in any one of the foregoing embodiments

[0070] Testing m kinds of negative electrode materials to be tested, numbered from 1 to m in sequence, to obtain m groups of test data; each group of the test data contains n SOC(i) values, where m is a positive integer ≥ 2;

[0071] Selecting the x-th group and the y-th group from the m groups of negative electrode materials to be tested for comparison:

[0072] If T1 > T2, the rate performance of the x-th group of negative electrode materials is better than that of the y-th group of negative electrode materials;

[0073] If T1 < T2, the rate performance of the x-th group of negative electrode materials is worse than that of the y-th group of negative electrode materials;

[0074] If T1 = T2, the rate performance of the x-th group of negative electrode materials is equivalent to that of the y-th group of negative electrode materials;

[0075] Wherein, T1 is the number of times of SOC x (i) > SOC y (i); T2 is the number of times of SOC x (i) < SOC y (i); 1 ≤ x ≤ m, 1 ≤ y ≤ m, and x ≠ y.

[0076] In theory, all n SOC(i) values corresponding to the anode material with excellent rate performance will be better than those of the anode material with poor rate performance. However, in actual operation, there may be certain errors, resulting in some individual SOC(i) values of the anode material with relatively poor rate performance being better than those of the anode material with relatively excellent rate performance. Especially when the difference in rate performance between the two materials is small, therefore, the majority of the data shall prevail.

[0077] The embodiment of the present invention further provides a method for predicting the rate performance of an anode material by using the method described in any one of the foregoing embodiments, including: when predicting the rate performance of the anode material to be tested:

[0078] When X(i) ≤ 0.75C, the SOC at 0V 较大 (i) compared with SOC 较小 (i), for every 1% increase, the lithium precipitation rate of the full cell corresponding to the anode material with high rate performance is increased by △X compared with the lithium precipitation rate of the full cell corresponding to the anode material with low rate performance 析锂 , 0.03C ≤ △X 析锂 ≤ 0.3C;

[0079] When X(i) > 0.75C, the SOC at 0V 较大 (i) compared with SOC 较小 (i), for every 1% increase, the lithium precipitation rate of the full cell corresponding to the anode material with high rate performance is increased by △X compared with the lithium precipitation rate of the full cell corresponding to the anode material with low rate performance 析锂 , 0.08C ≤ △X 析锂 ≤ 0.2C;

[0080] Among them, SOC 较大 (i) refers to the larger one of the SOC(i) values corresponding to the anode materials of the x-th group and the y-th group, and SOC 较小 (i) refers to the smaller one of the SOC(i) values corresponding to the anode materials of the x-th group and the y-th group;

[0081] And / or, select any one of the anode materials with better rate performance or the anode materials of two groups with comparable rate performance among the anode materials of the x-th group and the y-th group, and repeat the comparison step with any one of the remaining (m - 2) groups of anode materials until all m groups of data are compared, and screen out the anode materials with high rate performance.

[0082] During each charge-discharge cycle, there is a certain relationship between the state of charge SOC(i) at the preset potential PV and the lithium plating rate of the corresponding material. By observing the variation of the PV SOC(i) value at any rate, the improvement of the rate performance of the corresponding material can be quantitatively estimated. In this way, the lithium plating rate can be estimated. When comparing the rate performance of multiple negative electrode materials to be tested, the lithium plating rate of each material can be estimated to compare and rank the rate performance of multiple negative electrode materials to be tested. There is no need to compare every two groups, and the process is simple and the result is intuitive, with extremely high application value.

[0083] The features and performance of the present invention will be further described in detail below in conjunction with embodiments.

[0084] Example 1

[0085] This example provides a method for testing the rate performance of a negative electrode material, including the following steps:

[0086] S1. Under normal temperature conditions of 25°C, use needle coke secondary particle (NS) graphite as the graphite to be tested. Assemble the graphite to be tested and a lithium sheet into a battery. The battery model is a CR2016 coin-type half-cell (the diameter of the electrode sheet is 14 mm) and activate it at 0.1C for two weeks (voltage range: 0.005 - 1.5V). After activation, all the lithium on the graphite material is removed, and the battery voltage is 1.5V at this time. Prepare 4 parallel sample batteries for each graphite material to be tested and conduct parallel experiments synchronously to reduce errors. In the four groups of parallel experiments, abnormal data need to be excluded. If there are more than two abnormal data, re-detection is required.

[0087] S2. After activation, perform cyclic charge-discharge and record the voltage change during the static stage after each discharge cycle.

[0088] The first cycle: Perform constant current discharge at 0.5C for 120 min, then let it stand for 1 h, record the capacity at 0V and the discharge capacity, calculate the SOC(%) at 0.5C, then charge at 0.1C to 1.5V, and let it stand for 30 min until the voltage is stable.

[0089] The second cycle: Perform constant current discharge at 0.75C for 80 min, let it stand for 1 h, record the capacity at 0V and the discharge capacity, calculate the SOC(%) at 0.75C, then charge at 0.1C to 1.5V, and let it stand for 30 min until the voltage is stable.

[0090] Third to fifth cycles: Continue to sequentially obtain the 0V potential point SOC(%) under constant current discharges of 1C, 1.25C, and 1.5C according to the steps of the first and second times. The cut-off times (discharge times) for the constant current discharges of 1C, 1.25C, and 1.5C are 60 min, 48 min, and 40 min respectively. During the charging stage of each cycle, the charging rate is 0.1C, the charging cut-off voltage is 1.5V, and the rest time after charging is 30 min.

[0091] S3. Plot the curve of the 0V potential point SOC(%) varying with the rate under different rate discharges, as Figure 1 shown.

[0092] S4. Additionally, take the button cell of NS for the test of AC impedance. For the battery after activation, discharge it to 50% SOC at 0.1C and conduct the EIS test (the test condition is that the perturbation voltage is 0.5 mv and the frequency range is 10 5 -0.03 Hz). The test results are as Figure 2 shown.

[0093] Example 2

[0094] This example provides a method for testing the rate performance of a negative electrode material. The main difference from Example 1 is that the tested graphite model is replaced with needle coke secondary particles mixed with needle coke single particles (NSD). Repeat the above steps the same as in Experimental Example 1 to obtain the SOC(%) values at 0V of NSD at different rates, as Figure 1 shown. The EIS test results are as Figure 2 shown.

[0095] Example 3

[0096] This example provides a method for testing the rate performance of a negative electrode material. The main difference from Example 1 is that the tested graphite model is replaced with the carbonized product of needle coke secondary particles (NST). Repeat the above steps the same as in Experimental Example 1 to obtain the SOC(%) values at 0V of NSD at different rates, as Figure 1 shown. The EIS test results are as Figure 2 shown.

[0097] Example 4

[0098] This example provides a method for testing the rate performance of a negative electrode material. The main difference from Example 1 is that the tested graphite model is replaced with the carbonized product of needle coke secondary particles mixed with needle coke secondary particles (NSTS). Repeat the above steps the same as in Experimental Example 1 to obtain the SOC(%) values at 0V of NSD at different rates, as Figure 1 shown. The EIS test results are as Figure 2 shown.

[0099] Comparative Example 1

[0100] This comparative example provides a method for testing the rate performance of a negative electrode material. According to the method disclosed in Example 1 of CN115097341A, the critical lithium plating rate range of NS is obtained, as shown in Table 1.

[0101] Comparative Example 2

[0102] This comparative example provides a method for testing the rate performance of a negative electrode material. According to the method disclosed in Example 1 of CN115097341A, the critical lithium plating rate range of NSD is obtained, as shown in Table 1.

[0103] Comparative Example 3

[0104] This comparative example provides a method for testing the rate performance of a negative electrode material. According to the method disclosed in Example 1 of CN115097341A, the critical lithium plating rate range of NST is obtained, as shown in Table 1.

[0105] Comparative Example 4

[0106] This comparative example provides a method for testing the rate performance of a negative electrode material. According to the method disclosed in Example 1 of CN115097341A, the critical lithium plating rate range of NSTS is obtained, as shown in Table 1.

[0107] Table 1 Critical lithium plating ranges of graphite materials in Examples 1 - 4

[0108] Model Critical lithium plating range NS 0.75-1C NSD 0.75-1C NST 1.25-1.5C NSTS 1.25-1.5C

[0109] Verification Example 1

[0110] Soft-pack battery test:

[0111] Using the graphite materials in Examples 1 - 4 as the negative electrode respectively, an LFP material as the positive electrode material, LiTFSI as the electrolyte, a mixed solvent of EC and DEC with a volume ratio of 1:1 as the electrolyte solvent, and a Celgard 2400 membrane as the separator, soft-pack lithium-ion batteries are prepared. 40 batteries of each type of graphite are reserved for standby, and a fast charging experiment is carried out. The test conditions are: voltage range: 2.5V - 3.65V, charging at a Y C rate (Y = 1 + 0.05X, X is a natural number, 0 ≤ X ≤ 40). After each charging is completed, the battery needs to be disassembled. If no lithium plating occurs, the next rate test will be carried out. The test results are shown in Table 2.

[0112] Table 2

[0113]

[0114] Analysis of Comparative Examples 1-4 in combination with Table 1 shows that the critical lithium plating intervals of NST and NSTS are significantly higher than those of NS and NSD, indicating better kinetic performance of NST and NSTS. However, the critical lithium plating intervals of NST and NSTS are the same, and the kinetic differences between the two cannot be further distinguished.

[0115] Combined with Figure 1 Analysis of Examples 1-4 shows that the rate performance curve of NST is higher than that of NSTS, indicating that the polarization internal resistance of NST is smaller and its kinetic performance is better. Combined with Figure 2 the results of EIS, the overall difference between the two is not significant, and the impedance of NST is slightly smaller, which is in line with the rule. At the same time, NS and NSD can also be clearly distinguished by the difference in the rate performance curve. The kinetic performance of NS is significantly better than that of NSD. Combined with the results of EIS, the impedance of NS is slightly smaller, indicating that NS has better kinetic performance than NSD.

[0116] The above comparison shows that the test method for the rate performance of the graphite class of the present invention has higher discrimination and is simpler to operate compared to the method shown in the comparative examples disclosed in CN115097341A.

[0117] The lithium plating rate (C) of the full cell obtained in the verification example was compared with the SOC (%) at 0V under different rates obtained in Examples 1-4, and the results are shown in Table 3.

[0118] Table 3 SOC (%) at 0V and lithium plating rate (C) of the full cell under different rates

[0119]

[0120] Comparing the 0V SOC% and lithium plating rate of different anode materials in Table 3, when the rate ≤ 0.75C, when the 0V SOC% increases by 1%, the corresponding lithium plating rate of the full cell increases by about 0.03C - 0.3C. At the rate of 0.75C - 1.5C, when the 0V SOC% increases by 1%, the corresponding lithium plating rate of the full cell increases by 0.08C - 0.2C.

[0121] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for testing the rate performance of negative electrode materials, characterized in that: include: Take the negative electrode material to be tested and assemble it into a button-type half-cell; Activating the button half-cell; The activated button-type half-cell is charged and discharged for n cycles, wherein n is a natural number and n≥2; The rate X used in the discharge phase of each cycle of charge and discharge is different; The state of charge SOC(i) when the potential is the preset value PV in each charge and discharge is calculated. The higher the state of charge SOC(i), the better the rate performance of the negative electrode material to be tested, wherein i is a natural number and n≥i≥2.

2. The method for testing the rate performance of negative electrode materials according to claim 1, characterized in that: State of charge SOC(i) = Q0(i) / Q t (i)*100, where Q0(i) is the capacity when the potential is at the preset value PV in the i-th cycle of charge and discharge; Q t (i) is the discharge capacity when the potential is at the preset value PV in the i-th charge and discharge cycle.

3. The method for testing the rate performance of negative electrode materials according to claim 1, characterized in that: The single cycle process of the cyclic charge and discharge comprises discharge, rest after discharge, charge and rest after charge in sequence; Preferably, 2≤n≤15.

4. The method for testing the rate performance of negative electrode materials according to claim 3, characterized in that: The standing time after discharge is 45-90min; And / or, the rest time after charging is 20-40 minutes.

5. The method for testing the rate performance of negative electrode materials according to any one of claims 1 to 4, characterized in that: In the i-th cycle, the discharge is performed at a rate of X(i), and the discharge time is t, wherein t=[C / X(i)]*60 min, wherein C is the rated capacity of the battery; and X(i) is greater than X(i-1).

6. The method for testing the rate performance of negative electrode materials according to any one of claims 1 to 4, characterized in that: The charging rate and cut-off voltage are the same in n cycles of charge and discharge; And / or, the charging rate and cut-off voltage in the n-cycle charge and discharge are the same as the charging rate and cut-off voltage in the activation stage.

7. The method for testing the rate performance of negative electrode materials according to any one of claims 1 to 4, characterized in that: The discharge rate used in the discharge phase of the i-th cycle charge and discharge is X(i), and 0.1C≤X(i)≤3C.

8. The method for testing the rate performance of negative electrode materials according to claim 1, characterized in that: The negative electrode material includes natural graphite, artificial graphite, silicon carbon and graphite doped material.

9. A rapid screening method for high rate performance negative electrode materials, characterized in that: The method comprises testing m kinds of negative electrode materials to be tested by using the negative electrode material rate performance test method according to any one of claims 1 to 8, numbering them from 1 to m in sequence, and obtaining m groups of test data; each group of the test data comprises n SOC(i) values, wherein m is a positive integer ≥ 2; Select group x and group y from m groups of negative electrode materials to be tested for comparison: If T1>T2, the rate performance of the negative electrode material of group x is better than that of the negative electrode material of group y; If T1<T2, the rate performance of the negative electrode material of group x is worse than that of the negative electrode material of group y; If T1 = T2, the rate performance of the negative electrode material of group x is equivalent to that of the negative electrode material of group y; Among them, T1 is SOC x (i)>SOC y (i) times; T2 is SOC x (i)<SOC y (i) Degree; 1≤x≤m, 1≤y≤m, and x≠y; And / or, select the negative electrode material with better rate performance in the xth group and the yth group of negative electrode materials or any group of negative electrode materials with equivalent rate performance, and repeat the comparison step with any group of negative electrode materials in the remaining (m-2) groups of negative electrode materials until all m groups of data are compared, and the negative electrode material with high rate performance is screened out.

10. A method for predicting the rate performance of negative electrode materials using the method of claim 9, characterized in that: include: When estimating the rate performance of the negative electrode material to be tested: When X(i)≤0.75C, SOC at 0V 较大 (i) Compared with SOC 较小 (i) For every 1% increase, the lithium deposition rate of the whole battery corresponding to the high-rate performance negative electrode material is increased by △X compared to the lithium deposition rate of the whole battery corresponding to the low-rate performance negative electrode material 析锂 , 0.03C≤△X 析锂 ≤0.3C; When X(i)>0.75C, SOC at 0V 较大 (i) Compared with SOC 较小 (i) For every 1% increase, the lithium deposition rate of the whole battery corresponding to the high-rate performance negative electrode material is increased by △X compared to the lithium deposition rate of the whole battery corresponding to the low-rate performance negative electrode material 析锂 , 0.08C≤△X 析锂 ≤0.2C; Among them, SOC 较大 (i) refers to the larger of the SOC(i) values ​​corresponding to the negative electrode materials of group x and group y. 较小 (i) refers to the smaller of the SOC(i) values ​​corresponding to the negative electrode materials of group x and group y.

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