Electrode material dynamics performance evaluation method

Abstract

The invention discloses a method for evaluating the dynamic performance of an electrode material, and belongs to the technical field of battery material performance evaluation. The method comprises the following steps: measuring a differential voltage curve of an electrode material, and extracting characteristic parameters of the differential voltage curve; measuring the constant current ratio of the electrode material by a conventional constant current and constant voltage method; and establishing a dynamic performance standard curve according to the characteristic parameters and the constant current ratio. Therefore, the dynamic performance of the electrode material can be judged based on the characteristic parameters of the differential voltage curve. Compared with the prior art, the standard curve is established based on statistical data and a conventional detection method, the detection result is reliable, and meanwhile the method has the advantages of being high in sensitivity, simple and rapid.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery material performance evaluation, and particularly relates to a method for evaluating the kinetic performance of electrode materials. Background Art

[0002] With the rapid development of electric vehicles, the lithium-ion battery as its power source has also faced major challenges. Among them, the fast charging performance is one of the most prominent performance indicators at present. And the lithium insertion / extraction kinetics of electrode materials is the main reason restricting the fast charging performance of batteries. If a negative electrode material with poor lithium insertion kinetics is used, it will cause lithium plating on the surface of the negative electrode, which will not only cause a significant drop in battery capacity, but also cause safety problems due to the continuous growth of lithium dendrites and internal short circuits. Therefore, evaluating the kinetic performance of electrode materials is crucial for the development of lithium-ion batteries.

[0003] At present, there are many methods for detecting the kinetic performance of electrode materials. The vast majority are based on electrochemical methods, which are generally divided into the capacity comparison method and the diffusion coefficient comparison method. The capacity comparison methods mainly include: 1) The rate charge-discharge method. After multiple rate charge-discharges of the battery, the capacity retention rate at each rate is analyzed, and then the kinetic performance of the electrode material is judged. 2) The constant current-constant voltage method. Through the constant current-constant voltage (CC-CV) charging method, the constant current (CC) capacity and the constant voltage (CV) capacity are measured respectively, and the constant current ratio CC / (CC + CV) is calculated. By comparing the magnitudes of the constant current ratios, the kinetic performance of the electrode material is judged. The advantage of the capacity comparison method is that it is relatively simple, but its disadvantage is that after the battery is activated, the test needs to be carried out for a certain number of cycles, which takes a long time; at the same time, the sensitivity of this type of method is low, and it is difficult to effectively distinguish when the kinetic performances of two materials are close.

[0004] The diffusion coefficient comparison methods include: 1) The galvanostatic intermittent titration technique (GITT) / the potentiostatic intermittent titration technique (PITT). By periodically applying a small current (short duration) and a relaxation process (long duration), the diffusion coefficient (D Li+ ) of lithium ions in the material is calculated according to the corresponding formula, and then the kinetic performance of the electrode material is judged. 2) Electrochemical impedance spectroscopy. Select the diffusion control part from the Nyquist plot, calculate the Warburg coefficient, and then calculate D Li+ . 3) Cyclic voltammetry. Under the set voltage window, by setting different scan rates and cycling for a certain number of cycles, the diffusion coefficient is calculated according to the Randles-Sercik equation, and then the kinetic performance of the electrode material is judged. The advantage of the diffusion coefficient comparison method is that the sensitivity is relatively high, but its disadvantage is that the battery needs to be activated, and the test takes a long time; the data processing is complex, and in the actual use process, it is difficult to measure various parameters in the formula, and only the apparent diffusion coefficient can be obtained. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies and drawbacks mentioned in the above background art, and to provide a method for evaluating the kinetic performance of electrode materials based on differential voltage curves, which can simply and quickly identify the kinetic performance of electrode materials.

[0006] The object of the present invention can be achieved by the following technical solutions: A method for evaluating the kinetic performance of electrode materials, comprising the following steps:

[0007] Firstly, the establishment of the standard curve of the kinetic performance of battery materials:

[0008] ① Assemble three or more electrode materials into a battery, perform constant current charge and discharge tests at a low current density, obtain differential voltage curves, fit the peaks therein or directly read the peak intensities, and use them as the characteristic parameters of the kinetic performance of the electrode materials;

[0009] ② Continue to perform the constant current and constant voltage method test on the battery in step ①, and calculate the constant current ratio;

[0010] ③ Establish a standard curve, with the characteristic parameters in step ① as the abscissa and the constant current ratio in step ② as the ordinate to establish the standard curve of kinetic performance;

[0011] Secondly, the evaluation of the kinetic performance of the sample to be tested:

[0012] Assemble the sample to be tested into a battery according to step ①, perform constant current charge and discharge tests at the same low current density, obtain differential voltage curves, fit the peaks therein or directly read the peak intensities, obtain the characteristic parameters of the kinetic performance of the sample to be tested, and use the standard curve in step ③ to evaluate the kinetic performance of the sample to be tested.

[0013] Preferably, the value range of the low current density in step ① is 0.05C - 1C.

[0014] Preferably, the electrode materials in step ① are one or more of many electrode materials such as graphite negative electrode, amorphous carbon negative electrode, titanium dioxide negative electrode, lithium iron phosphate positive electrode, and ternary positive electrode.

[0015] Preferably, the electrode materials in step ① are applied to one of lithium ion batteries, sodium ion batteries, and potassium ion batteries.

[0016] Preferably, the method for obtaining the differential voltage curve in step ① is to directly export it from the test instrument, or to obtain the initial differential voltage curve according to the constant current charge and discharge curve, and filter the initial differential voltage curve to obtain the corresponding differential voltage curve.

[0017] Preferably, the filtering method of the differential voltage curve includes, but is not limited to, Savitzky-Golay, adjacent averaging method, or binomial function.

[0018] Preferably, the peak fitting function in step ① includes, but is not limited to, Gauss, Lorentz, PsdVoigt1, and PearsonIV functions.

[0019] Preferably, the kinetic performance test mainly includes the following steps:

[0020] (1) Preparation of the electrode sheet:

[0021] Mix the electrode material with a conductive agent and a binder in a certain proportion, where the content of the active substance shall not be less than 80%. After homogenization, coat it on the current collector with a certain thickness, and after vacuum drying at 60 - 120 °C for 4 - 12 h, cut it into small round pieces with a diameter of 12 mm, which is the electrode sheet. The loading amount of the active substance in the electrode sheet is 1.5 - 12 mg cm -2 ;

[0022] (2) Battery assembly and kinetic performance test:

[0023] In the glove box, use the electrode sheet as the working electrode to assemble one of a half-cell, a full-cell, or a three-electrode cell. Let the battery stand for 6 - 48 h, and perform the kinetic performance test on the battery test system.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] First, the present invention establishes a standard curve based on statistical data, which can make the results more reliable and improve the accuracy of detection.

[0026] Second, when evaluating the kinetic performance of the electrode material, the present invention can convert the conventional capacity comparison method into comparing the characteristic parameters of the differential voltage curve through the establishment of the standard curve. Since the slope of the standard curve (Δ constant current ratio) / (Δ characteristic parameter) is less than 1, it can be considered that the characteristic parameter has higher sensitivity for evaluating the kinetic performance, and since the differential voltage curve can be obtained in the activation stage of the battery, the detection efficiency is also higher. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1Schematic diagram of differential voltage curve in Embodiment 1 of the present invention;;

[0029] Figure 2 Peak in Embodiment 1 of the present invention S2 Standard kinetic performance curve of peak value and constant current ratio;

[0030] Figure 3 Peak in Embodiment 2 of the present invention S2 Graph of the relationship between peak value and constant current discharge capacity;

[0031] Figure 4 ΔPeak in Embodiment 3 of the present invention S2 Graph of the relationship between peak value and constant current ratio;

[0032] Figure 5 ΔPeak in Embodiment 3 of the present invention S2 Schematic diagram of peak value;

[0033] Figure 6 ΔPeak in Comparative Example 2 of the present invention S1 Graph of the relationship between peak value and constant current ratio.

[0034] Figure 7 ΔPeak in Comparative Example 3 of the present invention S3 Graph of the relationship between peak value and constant current ratio;

[0035] Figure 8 ΔPeak in Comparative Example 4 of the present invention S4 Graph of the relationship between peak value and constant current ratio. Detailed implementation manners

[0036] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and meticulously in conjunction with the accompanying drawings of the specification and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0037] Unless otherwise defined, all the professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. The preferred implementation methods and materials described herein are only for demonstration purposes. Without departing from the principles of the embodiments of the present invention, several improvements and modifications can be made, and these improvements and modifications are also regarded as the protection scope of the present invention.

[0038] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0039] Embodiment 1

[0040] In this embodiment, by analyzing the differential voltage curve of the graphite anode material and extracting key characteristic parameters, it can be used to evaluate the kinetic performance of the graphite anode material. The specific steps are as follows:

[0041] I. Establish a standard curve for evaluating kinetic performance using the differential voltage curve

[0042] 1. Preparation of electrode sheets and assembly of batteries:

[0043] (1) Preparation of electrode sheets:

[0044] Mix the graphite anode sample, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber with a concentration of 48% in a mass ratio of 94%:1%:3%:2%. Drop an appropriate amount of deionized water and stir evenly to prepare a slurry. Coat the slurry on a copper foil current collector with a certain thickness. After vacuum drying at 80°C for 12 h, the electrode sheet is roll-pressed under appropriate pressure and cut into small round pieces with a diameter of 12 mm to obtain the electrode sheet. The active material loading in the electrode sheet is ~9 mg cm -2 ;

[0045] (2) Assembly of CR2032 coin cells:

[0046] Place the graphite electrode sheet in the middle of the positive electrode case in a glove box with the active material side facing up, and drop 40 μL of electrolyte (1 mol L -1 ethylene carbonate / dimethyl carbonate solution of sodium hexafluorophosphate, with a solvent volume ratio of 3:7). Then place a Celgard 2400 separator, drop another 40 μL of electrolyte, and sequentially place a lithium sheet, gasket, spring piece, and negative electrode case. Finally, press the battery with a pressure of 10 GPa to complete the assembly of the battery. Assemble 3 or more batteries for each sample;

[0047] 2. Extract characteristic parameters of the differential voltage curve:

[0048] Let the batteries assembled in step 1 stand for 8 h. On a Novonix UHPC test system, perform constant current charge-discharge tests at a low current density to obtain the differential voltage curve of the graphite anode material. The naming of the characteristic peaks is as Figure 1 shown. The current density is set to 0.1 C, where 1 C = 372 mA g -1 , the number of cycles is set to 3, and the voltage window is set to 0.005 - 1.5 V. Read the peak intensities of each characteristic peak in the differential voltage curve, as shown in Table 1.

[0049] 3. Extract the constant current ratio

[0050] Continue to test the battery in Step 2 using the constant current and constant voltage method, and calculate the constant current ratio. Discharge stage: The current density in the constant current stage is set to 1C, the cut-off voltage is 5mV, the constant voltage in the constant voltage stage is set to 5mV, and the cut-off current is set to: 0.1C. Charge stage: Set the current density to 1C and the cut-off voltage to 1.5V. One charge and discharge cycle is defined as one cycle, and set the number of cycles to 15. Extract the 1C constant current discharge capacity of the 5th cycle, as shown in Table 2. Extract the constant current ratio of the 5th cycle, as shown in Table 2. Constant current ratio = 1C constant current discharge capacity / (1C constant current discharge capacity + 5mV constant voltage discharge capacity).

[0051] 4. Establish the kinetic performance standard curve

[0052] Use the Peak in Step 2 S2 peak value as the abscissa and the constant current ratio in Step 3 as the ordinate to establish a linear relationship. The Pearson correlation coefficient is 0.95, indicating that the Peak S2 peak value and the constant current ratio are highly positively correlated. The results are as Figure 2 shown.

[0053] II. Kinetic performance test of the sample to be measured

[0054] 1. Perform constant current charge and discharge tests on the samples to be measured, A and B, at a low current density in Step 1 to obtain the differential voltage curve of the electrode material. Read the peak intensity of the Peak S2 peak in the differential voltage curve, as shown in Table 3;

[0055] 2. Calculate the constant current ratios of Sample A and Sample B using the kinetic performance standard curve in Step 1, as shown in Table 3.

[0056] Example 2

[0057] Use the same method as in Example 1 to fabricate the electrode sheet, assemble the button battery, and extract the characteristic parameters of the differential voltage curve and the 1C constant current discharge capacity of the 5th cycle under the same conditions. Use the Peak S2 peak value as the abscissa and the 1C constant current discharge capacity as the ordinate to establish a linear relationship. The Pearson correlation coefficient is 0.97, indicating that the Peak S2 peak value and the 1C constant current discharge capacity are highly positively correlated. The results are as Figure 3 shown.

[0058] Example 3

[0059] Use the same method as in Example 1 to fabricate the electrode sheet, assemble the button battery, and extract the characteristic parameters of the differential voltage curve and the constant current ratio under the same conditions. Use the ΔPeak S2 peak value as the abscissa and the constant current ratio as the ordinate to establish a linear relationship. The Pearson correlation coefficient is 0.94, indicating that the ΔPeak S2The peak value is highly positively correlated with the constant current ratio, and the results are as Figure 4 shown. Among them, ΔPeak S2 peak value is obtained by subtracting the background from Peak S2 peak value, as Figure 5 shown.

[0060] Comparative Example 1

[0061] In this comparative example, the test samples A and B were made into electrode sheets, assembled into button cells respectively, and tested by the constant current and constant voltage method to extract the constant current ratio. The test results are shown in Table 4.

[0062] Comparative Example 2

[0063] In this comparative example, the electrode sheets were made and the button cells were assembled by the same method as in Example 1, and the characteristic parameters of the differential voltage curve and the constant current ratio were extracted under the same conditions. Using ΔPeak S1 peak value as the abscissa and the constant current ratio as the ordinate, a linear relationship was established, and the Pearson correlation coefficient was 0.56. The results are as Figure 6 shown.

[0064] Comparative Example 3

[0065] In this comparative example, the electrode sheets were made and the button cells were assembled by the same method as in Example 1, and the characteristic parameters of the differential voltage curve and the constant current ratio were extracted under the same conditions. Using ΔPeak S3 peak value as the abscissa and the constant current ratio as the ordinate, a linear relationship was established, and the Pearson correlation coefficient was 0.91. The results are as Figure 7 shown.

[0066] [[ID=`37]]Comparative Example 4

[0067] In this comparative example, the electrode sheets were made and the button cells were assembled by the same method as in Example 1, and the characteristic parameters of the differential voltage curve and the constant current ratio were extracted under the same conditions. Using ΔPeak S4 peak value as the abscissa and the constant current ratio as the ordinate, a linear relationship was established, and the Pearson correlation coefficient was 0.898. The results are as Figure 8 shown.

[0068] Table 1 Characteristic parameters of the differential voltage curve of the graphite electrode material

[0069]

[0070] Table 2 Constant current ratio of the graphite electrode material

[0071]

[0072] Table 3 Characteristic parameters of the differential voltage curve of the test sample, constant current ratio calculated from the kinetic performance standard curve

[0073]

[0074] Table 4 Constant current ratio obtained from the test of the sample to be tested

[0075]

[0076] In summary, the present technical solution provides a new method for evaluating the kinetic performance of electrode materials. This method can simply and quickly evaluate the kinetic performance of electrode materials by obtaining characteristic parameters in the differential voltage curve during the battery activation stage.

[0077] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for evaluating the kinetic performance of an electrode material, characterized in that, It includes the following steps: (1) Establishing the standard curve of the kinetic performance of battery materials, which mainly includes the following steps: ① Assembling batteries with 3 or more electrode materials, performing constant current charge-discharge tests at a low current density, obtaining differential voltage curves, fitting the peaks therein or directly reading the peak intensities, and taking them as the characteristic parameters of the kinetic performance of the electrode materials; ② Continuing to perform the constant current and constant voltage method test on the batteries in step ①, and calculating the constant current ratio; ③ Establishing a standard curve, using the characteristic parameters in step ① as the abscissa and the constant current ratio in step ② as the ordinate to establish the standard curve of kinetic performance; (2) Evaluating the kinetic performance of the sample to be tested: Assembling the sample to be tested into a battery according to step (1)①, performing constant current charge-discharge tests at the same low current density, obtaining differential voltage curves, fitting the peaks therein or directly reading the peak intensities, obtaining the characteristic parameters of the kinetic performance of the sample to be tested, and using the standard curve in step (1)③ to evaluate the kinetic performance of the sample to be tested.

2. The method for evaluating the kinetic performance of an electrode material according to claim 1, characterized in that, The numerical range of the low current density is 0.05C - 1C.

3. The method for evaluating the kinetic performance of an electrode material according to claim 1 or 2, characterized in that, The electrode material is one or more of many electrode materials such as graphite negative electrode, amorphous carbon negative electrode, titanium dioxide negative electrode, lithium iron phosphate positive electrode, and ternary positive electrode.

4. The method for evaluating the kinetic performance of an electrode material according to claim 1 or 2, characterized in that The electrode material is applied to one of lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries.

5. The method for evaluating the kinetic performance of an electrode material according to claim 1 or 2, characterized in that, The method for obtaining the differential voltage curve is to directly export it from the test instrument, or to obtain the initial differential voltage curve according to the constant current charge-discharge curve through the constant current charge-discharge curve, and then obtain the corresponding differential voltage curve after filtering the initial differential voltage curve.

6. The kinetic performance evaluation method of an electrode material according to claim 5, characterized in that The filtering method of the differential voltage curve includes but is not limited to Savitzky-Golay, adjacent averaging method, or binomial function.

7. The method for evaluating the kinetic performance of an electrode material according to claim 1 or 2, characterized in that, The peak fitting function includes but is not limited to Gauss, Lorentz, PsdVoigt1, and PearsonIV functions.

8. The method for evaluating the kinetic performance of an electrode material according to claim 1 or 2, characterized in that The kinetic performance test mainly includes the following steps: (1) Preparation of electrode sheets: Mix the electrode material with a conductive agent and a binder in a certain proportion, where the content of the active substance shall not be less than 80%. After homogenization, coat it on the current collector with a certain thickness. After vacuum drying at 60-120 °C for 4-12 h, cut it into small round pieces with a diameter of 12 mm, namely the electrode sheets. The loading of the active substance in the electrode sheets is 1.5-12 mg cm -2 ; (2) Battery assembly and kinetic performance test: In the glove box, using the electrode sheet as the working electrode, assembling it into one of a half-cell, a full-cell, or a three-electrode cell, allowing the battery to stand for 6 - 48h, and performing kinetic performance tests on the battery test system.

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