Evaluation method and screening method of lithium ion battery cathode material coating agent

Abstract

The present application belongs to the field of battery, and particularly relates to a kind of lithium ion battery positive electrode material coating agent evaluation method and screening method, the evaluation method provided by the present application includes the following steps: different components of positive electrode material coating agent are mixed with conductive agent, binder and solvent respectively, to obtain slurry;Slurry is coated on current collector, dried to obtain pole piece;Pole piece is assembled into button half battery;Cyclic voltammetry test is carried out on button half battery, the maximum oxidation-reduction peak value of cyclic voltammogram corresponding to different components of positive electrode material coating agent is compared, and the relative height of the electrochemical activity of different components of positive electrode material coating agent is judged according to the comparison result.The evaluation method provided by the present application can exclude the influence of positive electrode material coating process and other interference factors, more accurately evaluate the height of the electrochemical activity of positive electrode material coating agent itself, and provide reliable experimental basis for the optimization and screening of lithium ion battery positive electrode material coating agent.

Description

Technical Field

[0001] This invention belongs to the field of batteries, and particularly relates to an evaluation method and a screening method for coating agents of lithium-ion battery cathode materials. Background Technology

[0002] Lithium-ion battery cathode materials, such as ternary lithium, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate, have high surface activity and are prone to side reactions when in direct contact with the electrolyte, leading to a decrease in cycle life. Therefore, it is necessary to coat the particle surface with an inert material to protect the stability of the material structure, reduce the occurrence of side reactions, ensure the stability of the cathode, and thus extend the lifespan of the lithium-ion battery. This inert coating material is called the cathode material coating agent.

[0003] The electrochemical activity of cathode material coating agents in lithium-ion batteries directly impacts battery lifespan. Using materials with low electrochemical activity as cathode material coating agents helps ensure the stability of the cathode sheet. Therefore, accurately evaluating the electrochemical activity of cathode material coating agents is of significant guiding importance for lithium-ion battery manufacturing. Currently, the evaluation and screening of cathode material coating agents involves directly coating the agent onto the cathode material and then judging the quality of the coating agent by testing the electrochemical properties of the finished electrode. While this method can evaluate and screen cathode material coating agents, the coating process itself directly affects the battery's electrochemical performance, thus posing a significant risk of misjudgment. It is not only time-consuming but also lacks accuracy. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide an evaluation method and a screening method for cathode material coating agents of lithium-ion batteries. The evaluation method provided by this invention can eliminate the influence of interfering factors such as cathode material coating process, and more accurately evaluate the electrochemical activity of the cathode material coating agent itself, thereby providing a reliable experimental basis for the optimization and screening of cathode material coating agents of lithium-ion batteries.

[0005] This invention provides a method for evaluating coating agents for lithium-ion battery cathode materials, comprising the following steps:

[0006] a) Mix the positive electrode material coating agent, conductive agent, binder and solvent to obtain a slurry;

[0007] b) Coat the slurry onto the current collector and dry it to obtain the electrode sheet;

[0008] c) Assemble a button cell; the positive electrode material of the button cell is the electrode sheet, and the negative electrode material is lithium;

[0009] d) Following steps a) to c), change the composition of the positive electrode material coating agent to prepare coin cells corresponding to positive electrode material coating agents with different compositions;

[0010] e) Cyclic voltammetry tests were performed on the coin half-cells corresponding to the cathode material coating agents with different compositions to obtain the cyclic voltammetry curves corresponding to the cathode material coating agents with different compositions.

[0011] f) Compare the peak values ​​of the maximum redox peaks of the cyclic voltammetry curves corresponding to the different components of the cathode material coating agent, and determine the relative electrochemical activity of the different components of the cathode material coating agent based on the comparison results.

[0012] Preferably, in step f), the determination method is as follows: if the peak value of the maximum redox peak is relatively large, the electrochemical activity of the corresponding cathode material coating agent is relatively high; if the peak value of the maximum redox peak is relatively small, the electrochemical activity of the corresponding cathode material coating agent is low.

[0013] Preferably, in step a), the mass ratio of the positive electrode material coating agent, conductive agent, binder and solvent is (5-10):(1-5):0.1:(0.5-1.5).

[0014] Preferably, in step b), the thickness of the current collector is 5–30 μm; and the drying temperature is 80–200 °C.

[0015] Preferably, in step c), the electrode is rolled and punched before being used to assemble a button cell.

[0016] Preferably, in step e), before performing cyclic voltammetry testing on the coin cell, its open-circuit voltage is tested first; coin cells with an open-circuit voltage above 0V are selected for cyclic voltammetry testing.

[0017] Preferably, in step f), the cyclic voltammetry curve obtained in the third or subsequent cycles is used as the basis for comparing the peak value.

[0018] This invention provides a method for screening coating agents for lithium-ion battery cathode materials, comprising the following steps:

[0019] a) Mix the positive electrode material coating agent, conductive agent, binder and solvent to obtain a slurry;

[0020] b) Coat the slurry onto the current collector and dry it to obtain the electrode sheet;

[0021] c) Assemble a button cell; the positive electrode material of the button cell is the electrode sheet, and the negative electrode material is lithium;

[0022] d) Following steps a) to c), change the composition of the positive electrode material coating agent to prepare coin cells corresponding to positive electrode material coating agents with different compositions;

[0023] e) Cyclic voltammetry tests were performed on the coin half-cells corresponding to the cathode material coating agents with different compositions to obtain the cyclic voltammetry curves corresponding to the cathode material coating agents with different compositions.

[0024] f') Based on the peak value of the maximum redox peak of the cyclic voltammetry curve corresponding to the different components of the cathode material coating agent, determine whether the corresponding component can be used as a cathode material coating agent for lithium-ion batteries.

[0025] Preferably, in step e), the voltage range of the cyclic voltammetry test is 0–5V; the scan rate of the cyclic voltammetry test is 1–5mV / s.

[0026] Preferably, in step f'), the determination method is as follows: if the peak value of the maximum oxidation peak of the cyclic voltammetry curve is ≤0.001A and the peak value of the maximum reduction peak is ≥-0.002A, then the corresponding component is used as a coating agent for the positive electrode material of a lithium-ion battery.

[0027] Compared with existing technologies, this invention provides an evaluation and screening method for positive electrode material coating agents in lithium-ion batteries. The evaluation method provided by this invention includes the following steps: a) mixing a positive electrode material coating agent, a conductive agent, a binder, and a solvent to obtain a slurry; b) coating the slurry onto a current collector and drying it to obtain an electrode sheet; c) assembling a coin cell; the positive electrode material of the coin cell is the electrode sheet, and the negative electrode material is lithium; d) following steps a) to c), changing the composition of the positive electrode material coating agent to prepare coin cells corresponding to positive electrode material coating agents with different compositions; e) performing cyclic voltammetry tests on the coin cells corresponding to the different compositions of positive electrode material coating agents to obtain cyclic voltammetry curves corresponding to the different compositions of positive electrode material coating agents; f) comparing the peak values ​​of the maximum redox peaks of the cyclic voltammetry curves corresponding to the different compositions of positive electrode material coating agents, and judging the relative electrochemical activity of the different compositions of positive electrode material coating agents based on the comparison results. The evaluation method provided by this invention first prepares coin-type lithium-ion half-cells using cathode material coating agents with different compositions. Then, cyclic voltammetry is used to examine their electrochemical behavior during charge and discharge. Finally, the relative electrochemical activity of different cathode material coating agents is determined based on the elution of the maximum redox peak in the cyclic voltammetry curves. In this invention, the appearance of redox peaks in the cyclic voltammetry curves corresponds to the occurrence of electrochemical reactions; the more pronounced the peak, the stronger the reaction. The maximum redox peak represents the upper limit of the reaction of the corresponding test material in the cyclic voltammetry test. Therefore, by directly comparing the relative sizes of the maximum redox peaks in the cyclic voltammetry test of coin-type half-cells prepared with different cathode material coating agents, the relative electrochemical activity of the corresponding cathode material coating agents can be determined. The evaluation method provided by this invention eliminates the need to coat the cathode material with a cathode material coating agent, thus removing the influence of interference factors such as the coating process on the evaluation results. Furthermore, compared to methods that test the finished product after coating the cathode material, this method is simpler, effectively saving material, labor, and time costs, resulting in better economic efficiency. The evaluation method provided by this invention can be used to evaluate the electrochemical activity of different types of lithium-ion battery cathode material coating agents, providing reliable experimental evidence for the optimization and screening of lithium-ion battery cathode material coating agents.The screening method provided by this invention includes the following steps: a) mixing a positive electrode material coating agent, a conductive agent, a binder, and a solvent to obtain a slurry; b) coating the slurry onto a current collector and drying it to obtain an electrode sheet; c) assembling a coin cell; the positive electrode material of the coin cell is the electrode sheet, and the negative electrode material is lithium; d) changing the composition of the positive electrode material coating agent according to steps a) to c) to prepare coin cells corresponding to positive electrode material coating agents with different compositions; e) performing cyclic voltammetry tests on the coin cells corresponding to the positive electrode material coating agents with different compositions to obtain cyclic voltammetry curves corresponding to the positive electrode material coating agents with different compositions; f') determining whether the corresponding composition can be used as a positive electrode material coating agent for lithium-ion batteries based on the peak value of the maximum redox peak of the cyclic voltammetry curves corresponding to the positive electrode material coating agents with different compositions. The screening method and evaluation method provided by this invention are based on the same technical concept. This method can eliminate the influence of interfering factors such as the coating process of positive electrode materials, and more accurately determine the electrochemical activity of different components. This allows for the screening of which components are more suitable as coating agents for lithium-ion battery positive electrode materials, providing certain technical guidance for the optimization and screening of coating agents for lithium-ion battery positive electrode materials. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1 This is a CV curve of different coating agents under test conditions of 0-5V and 2mV / s provided in Example 1 of the present invention;

[0030] Figure 2 This is a capacity retention diagram of NCM ternary materials with different coating agents provided in Comparative Example 1 of this invention;

[0031] Figure 3 This is a CV curve of different coating agents under test conditions of 0-5V and 2mV / s provided in Example 2 of the present invention;

[0032] Figure 4 This is a capacity retention diagram of NCM ternary materials with different coating agents provided in Comparative Example 2 of this invention. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention provides a method for evaluating coating agents for lithium-ion battery cathode materials, comprising the following steps:

[0035] a) Mix the positive electrode material coating agent, conductive agent, binder and solvent to obtain a slurry;

[0036] b) Coat the slurry onto the current collector and dry it to obtain the electrode sheet;

[0037] c) Assemble a button cell; the positive electrode material of the button cell is the electrode sheet, and the negative electrode material is lithium;

[0038] d) Following steps a) to c), change the composition of the positive electrode material coating agent to prepare coin cells corresponding to positive electrode material coating agents with different compositions;

[0039] e) Cyclic voltammetry tests were performed on the coin half-cells corresponding to the cathode material coating agents with different compositions to obtain the cyclic voltammetry curves corresponding to the cathode material coating agents with different compositions.

[0040] f) Compare the peak values ​​of the maximum redox peaks of the cyclic voltammetry curves corresponding to the different components of the cathode material coating agent, and determine the relative electrochemical activity of the different components of the cathode material coating agent based on the comparison results.

[0041] In the evaluation method provided by the present invention, in step a), the components of the positive electrode material coating agent include, but are not limited to, one or more of aluminum oxide (Al2O3), niobium pentoxide (Nb2O5), strontium oxide (CeO2), and tungsten oxide (W2O5); the conductive agent includes, but is not limited to, conductive carbon black (SP); the binder includes, but is not limited to, polyvinylidene fluoride (PVDF); and the solvent includes, but is not limited to, N-methylpyrrolidone (NMP).

[0042] In the evaluation method provided by this invention, in step a), the preferred mass ratio of the positive electrode material coating agent to the binder is (5-10):0.1, specifically 5:0.1, 5.5:0.1, 6:0.1, 6.5:0.1, 7:0.1, 7.5:0.1, 8:0.1, 8.5:0.1, 9:0.1, 9.5:0.1, or 10:0.1; the preferred mass ratio of the conductive agent to the binder is (1-5):0.1, specifically 1:0.1, 1.5:0.1, or 10:0.1. The solvent-to-binder mass ratio is preferably (0.5-1.5):0.1, specifically 0.5:0.1, 0.6:0.1, 0.7:0.1, 0.8:0.1, 0.9:0.1, 1:0.1, 1.1:0.1, 1.2:0.1, 1.3:0.1, 1.4:0.1, or 1.5:0.1.

[0043] In the evaluation method provided by the present invention, in step a), the mixing method is preferably high-speed dispersion; the rotation speed of the high-speed dispersion is preferably 1000 to 3000 rpm, specifically 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm or 3000 rpm.

[0044] In the evaluation method provided by the present invention, in step b), the current collector includes, but is not limited to, aluminum foil; the thickness of the current collector is preferably 5 to 30 μm, specifically 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm or 30 μm.

[0045] In the evaluation method provided by the present invention, in step b), the coating thickness of the slurry is preferably 100-300 μm, specifically 100 μm, 120 μm, 150 μm, 170 μm, 200 μm, 230 μm, 250 μm, 270 μm or 300 μm.

[0046] In the evaluation method provided by the present invention, in step b), the coating method is preferably scraping.

[0047] In the evaluation method provided by the present invention, in step b), the drying method is preferably oven drying; the drying temperature is preferably 80-200℃, specifically 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃ or 200℃; the drying time is not particularly limited, as long as it is completely dried.

[0048] In the evaluation method provided by this invention, in step c), the electrode sheet is first rolled and punched before being used to assemble a coin cell. The rolling pressure is preferably 10–30t, specifically 10t, 11t, 12t, 13t, 14t, 15t, 16t, 17t, 18t, 19t, 20t, 21t, 22t, 23t, 24t, 25t, 26t, 27t, 28t, 29t, or 30t. The punched shape is preferably a circular sheet. The diameter (Φ) of the circular sheet is preferably 6–20mm, specifically 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm.

[0049] In the evaluation method provided by this invention, in step e), preferably, the open-circuit voltage of the coin cell is tested before performing the cyclic voltammetry test; coin cells with an open-circuit voltage above 0V are selected for cyclic voltammetry testing, i.e., abnormal coin cells are eliminated. In this invention, when the coin cell voltage is ≥0V, it indicates that its assembly is normal; if the open-circuit voltage is <0V, it indicates that the components in the half-cell are installed backwards or have other problems.

[0050] In the evaluation method provided by this invention, in step e), the voltage range of the cyclic voltammetry test is preferably 0–5V; the scan speed of the cyclic voltammetry test is preferably 1–5mV / s, specifically 1mV / s, 1.5mV / s, 2mV / s, 2.5mV / s, 3mV / s, 3.5mV / s, 4mV / s, 4.5mV / s, or 5mV / s; the number of cycles of the cyclic voltammetry test is preferably 1–10 times, specifically 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 times.

[0051] In the evaluation method provided by the present invention, in step f), since side reactions may occur during the first two test cycles of the coin half-cell, resulting in unstable test results, it is preferable to use the cyclic voltammetry curve obtained in the third or subsequent cycles as the basis for comparing the redox peak size.

[0052] In the evaluation method provided by this invention, in step f), if the maximum redox peak value in the cyclic voltammetry curve is relatively large, it indicates that the electrochemical activity of the corresponding cathode material coating agent is relatively high. The greater the negative impact of coating the cathode material with this agent, the less suitable it is for use as a cathode material coating agent, and vice versa. Therefore, the specific judgment method in step f) is: if the maximum redox peak value is relatively large, the electrochemical activity of the corresponding cathode material coating agent is relatively high; if the maximum redox peak value is relatively small, the electrochemical activity of the corresponding cathode material coating agent is relatively low.

[0053] In the evaluation method provided by this invention, in step f), since lithium-ion batteries rarely operate within the 0-1V voltage range, the redox peaks occurring within the 0-1V test voltage range can be disregarded when comparing the peak values ​​of the maximum redox peaks in the cyclic voltammetry curves corresponding to different cathode material coating agents. In other words, in step f), it is preferable to compare the peak values ​​of the maximum redox peaks in the cyclic voltammetry curves corresponding to the different cathode material coating agents within the range of 1V to the right-hand side of the test voltage.

[0054] The evaluation method provided by this invention first prepares coin-type lithium-ion half-cells using cathode material coating agents of different compositions. Then, cyclic voltammetry is used to examine their electrochemical behavior during charge and discharge. Finally, the relative electrochemical activity of the cathode material coating agent is determined based on the elution of the maximum redox peak in the cyclic voltammetry test curves. This evaluation method eliminates the need to coat the cathode material coating agent onto the lithium-ion battery cathode material, thus removing the influence of interference factors such as the coating process on the evaluation results. Moreover, compared to methods that test the finished product after coating the cathode material, this method is simpler and can effectively save material, labor, and time costs, resulting in better economic efficiency. The evaluation method provided by this invention can be used to evaluate the electrochemical activity of different types of lithium-ion battery cathode material coating agents, providing reliable experimental evidence for the optimization and screening of lithium-ion battery cathode material coating agents.

[0055] This invention also provides a method for screening coating agents for lithium-ion battery cathode materials, comprising the following steps:

[0056] a) Mix the positive electrode material coating agent, conductive agent, binder and solvent to obtain a slurry;

[0057] b) Coat the slurry onto the current collector and dry it to obtain the electrode sheet;

[0058] c) Assemble a button cell; the positive electrode material of the button cell is the electrode sheet, and the negative electrode material is lithium;

[0059] d) Following steps a) to c), change the composition of the positive electrode material coating agent to prepare coin cells corresponding to positive electrode material coating agents with different compositions;

[0060] e) Cyclic voltammetry tests were performed on the coin half-cells corresponding to the cathode material coating agents with different compositions to obtain the cyclic voltammetry curves corresponding to the cathode material coating agents with different compositions.

[0061] f') Based on the peak value of the maximum redox peak of the cyclic voltammetry curve corresponding to the different components of the cathode material coating agent, determine whether the corresponding component can be used as a cathode material coating agent for lithium-ion batteries.

[0062] In the screening method provided by this invention, the specific implementation process of steps a) to e) is consistent with that described in the evaluation method above, and will not be repeated here.

[0063] In the screening method provided by this invention, when the voltage range of the cyclic voltammetry test in step e) is 0–5V and the scan rate is 1–5mV / s, the preferred method for judgment in step f') is: if the peak value of the maximum oxidation peak of the cyclic voltammetry curve is ≤0.001A and the peak value of the maximum reduction peak is ≥-0.002A, then the corresponding component is used as a coating agent for the positive electrode material of a lithium-ion battery. Preferably, the closer the peak values ​​of the maximum oxidation peak and the maximum reduction peak of the cyclic voltammetry curve are to 0A, the more suitable the corresponding component is as a coating agent for the positive electrode material of a lithium-ion battery.

[0064] The screening method and evaluation method provided by this invention are based on the same technical concept. This method can eliminate the influence of interfering factors such as the coating process of positive electrode materials, and more accurately determine the electrochemical activity of different components. This allows for the screening of which components are more suitable as coating agents for lithium-ion battery positive electrode materials, providing certain technical guidance for the optimization and screening of coating agents for lithium-ion battery positive electrode materials.

[0065] For clarity, the following examples will be used to provide a detailed description.

[0066] Example 1

[0067] Alumina (Al2O3) and niobium pentoxide (Nb2O5) were selected as coating agents for the cathode material. The slurry preparation process was as follows (all operations below must be carried out at 23±2℃ and dew point ≤-40℃): First, PVDF and NMP were prepared in a beaker at a mass ratio of 1:9 to form a clear and transparent slurry, which was then transferred to an aluminum bottle for storage. Then, according to the mass ratio of cathode material coating agent: SP: slurry = 7:2:1, the cathode material coating agent, SP and slurry were dispersed at a speed of 2000 rpm to form a uniform slurry.

[0068] The calculated slurry is coated onto an aluminum foil (10-18 μm thick) to a thickness of 200 μm by a scraping method. The coated electrode is then baked at 110-120°C for 0.5-1 h, and then rolled under a pressure of 20-30 t. After rolling, the electrode is punched into small round pieces of Φ15 mm. 30 μL of 1 M LiPF6 electrolyte with EC:EMC:DMC = 1:1:1 (volume ratio) is dropped onto the punched electrode. After placing a separator, the electrode is assembled with a lithium metal anode to form a coin cell and sealed under a pressure of 0.7 MPa.

[0069] The open-circuit voltage of the coin cell was tested, and coin cells with an open-circuit voltage ≥ 0V were selected as normal operating cells. The normal operating cells were then subjected to cyclic voltammetry testing on an electrochemical workstation under the following conditions: 0–5V, 2mV / s, to obtain cyclic voltammetry curves. The redox peaks of the cyclic voltammetry curves corresponding to different cathode material coatings in the voltage range of 1–4V were compared, and the relative electrochemical activity of different cathode material coatings was determined based on the comparison results.

[0070] In this embodiment, the cyclic voltammetry (CV) curves of the cathode material coated with Al2O3 and Nb2O5 were tested simultaneously (test conditions: 0–5V, 2mV / s). The CV curve test results of the 5th test cycle are as follows. Figure 1 As shown, Figure 1 This is a CV curve diagram of different coating agents under test conditions of 0-5V and 2mV / s provided in Example 1 of the present invention. Figure 1 As can be seen, the CV curves of Nb2O5 show oxidation peaks at 0.2852V, 1.5550V, and 1.9712V, with corresponding peak values ​​of 0.000607A, 0.001165A, and 0.002184A (max), respectively, and reduction peaks at 0.5122V and 1.4774V, with corresponding peak values ​​of -0.002162A and -0.002425A (max), respectively. The CV curves of Al2O3 show oxidation peaks at 0.3251V and 1.1041V, with corresponding peak values ​​of 0.000282A and 0.000355A (max), respectively, and reduction peaks at 0.4318V and 1.3566V, with corresponding peak values ​​of -0.001300A (max) and -0.000342A, respectively. It is evident that the peak value of the maximum redox peak in the CV curve of Nb2O5 is much larger than that of Al2O3. This indicates that Nb2O5 has higher electrochemical activity than Al2O3. Coating the cathode material with Nb2O5 will affect the electrical performance of the cathode material, resulting in poorer performance.

[0071] Comparative Example 1

[0072] The coating materials (Al2O3 and Nb2O5) from Example 1 were used to coat the positive electrode material, and the positive electrode active material precursor [Ni 0.82 Co 0.1 Mn 0.08 (OH)₂ and LiOH·H₂O are mixed evenly to obtain a mixture. This mixture is then sintered in an atmosphere sintering furnace at 600–700℃ in an oxygen-containing atmosphere with 90% O₂ concentration for 13–16 hours. After natural cooling, the cathode material is obtained. The cathode material is then pulverized, sieved, and mixed separately with Al₂O₃ or Nb₂O₅ in a high-speed mixer for 1 hour to obtain a mixture. This mixture is then sintered. The sintered product is crushed and sieved to obtain Al₂O₃-coated modified cathode material and Nb₂O₅-coated modified cathode material, respectively.

[0073] A high-nickel NCM ternary cathode active material (NCM), a conductive agent (SP+KS-6), and a binder (PVDF) were mixed with a solvent (NMP) at a mass ratio of 94.5:3:2.5 to form a cathode slurry. This slurry was then coated on both sides of an aluminum foil with a thickness of 10–18 μm, resulting in a coating density of 20 g / cm³. 2 After drying and rolling, the positive electrode sheet and the surface density are 10 g / cm³. 2 A 503048 battery with a capacity of approximately 800mAh was assembled using a negative electrode and a separator with a thickness of 10–25 μm. This battery was then used for testing. Charge-discharge cycles were performed in a constant-temperature charge-discharge cabinet using a 1C charge-discharge cycle and a cutoff current of 0.05C. The voltage range was 2.8V–4.25V. The capacity retention rate after 100 cycles was calculated as the ratio of the discharge capacity in the 100th cycle to the discharge capacity in the 2nd cycle. The ambient temperature was 45℃ ± 2℃. The capacity retention rate of the high-nickel NCM ternary material at 45℃ was tested. To ensure the accuracy of the test results, a set of parallel experiments was set up.

[0074] Test results are as follows Figure 2 As shown, Figure 2 This is a capacity retention diagram of the NCM ternary materials with different coating agents provided in Comparative Example 1 of this invention. Figure 2 It can be seen that Al2O3 is selected as the coating material, which has the best positive electrode performance. This is the same experimental conclusion as in Example 1, thus verifying the accuracy of the method in Example 1.

[0075] Example 2

[0076] Strontium oxide (CeO2) and tungsten oxide (W2O5) were selected as coating agents for the positive electrode material. The slurry preparation process and the button half-cell fabrication were the same as those in Example 1, and will not be repeated here.

[0077] In this embodiment, the CV curves of the cathode material coating agents CeO2 and W2O5 were tested simultaneously (test conditions: 0-5V, 2mV / s). The CV curve test results of the 5th test cycle are as follows. Figure 3 As shown, Figure 3 This is a CV curve diagram of different coating agents under test conditions of 0-5V and 2mV / s provided in Example 2 of the present invention. Figure 3 As can be seen, the CV curve of W2O5 shows oxidation peaks at 0.5705V, 1.2710V, and 2.0724V, with corresponding peak values ​​of 0.001328A, 0.001545A, and 0.001675A(max), respectively, and a reduction peak at 1.2823V, with a corresponding peak value of -0.002528A. The CV curve of CeO2 shows oxidation peaks at 0.5193V and 1.1710V, with corresponding peak values ​​of 0.000724A(max) and 0.000646A, respectively, and a reduction peak at 0.4309V, with a corresponding peak value of -0.001599A. It is evident that the peak value of the maximum redox peak in the CV curve of W2O5 is much larger than that of CeO2. This indicates that the electrochemical activity of W2O5 is higher than that of CeO2. Coating W2O5 onto the cathode material will affect the electrical performance of the cathode material, resulting in poor performance.

[0078] Comparative Example 2

[0079] The coating materials (CeO2 and W2O5) from Example 2 were used to coat the positive electrode material, and the positive electrode active material precursor [Ni] was coated onto it. 0.6 Co 0.1 Mn 0.3 (OH)₂ and LiOH are mixed evenly to obtain a mixture. This mixture is then sintered in an atmosphere sintering furnace at 900–1000℃ in an oxygen-containing atmosphere with 90% O₂ concentration for 13–16 hours. After natural cooling, the cathode material is obtained. The cathode material is then pulverized, sieved, and mixed with either CeO₂ or W₂O₅ in a high-speed mixer for 1 hour to obtain a mixture. This mixture is then sintered. The sintered product is crushed and sieved to obtain CeO₂-coated modified cathode material and W₂O₅-coated modified cathode material, respectively.

[0080] Medium-low nickel NCM ternary cathode active material (NCM), conductive agent (SP+KS-6), and binder (PVDF) were mixed with solvent (NMP) at a mass ratio of 94.5:3:2.5 to form a cathode slurry. This slurry was then coated on both sides of an aluminum foil with a thickness of 10–18 μm, resulting in a coating density of 20 g / cm³. 2 After drying and rolling, the positive electrode sheet and the surface density are 10 g / cm³. 2A 503048 battery with a capacity of approximately 800mAh was assembled using a negative electrode and a separator with a thickness of 10–25 μm. This battery was then used for testing. Charge-discharge cycles were performed in a constant-temperature charge-discharge cabinet using a 1C charge-discharge cycle and a cutoff current of 0.05C. The voltage range was 2.8V–4.25V. Capacity retention after 100 cycles was calculated as the ratio of the discharge capacity in the 100th cycle to the discharge capacity in the 2nd cycle. The ambient temperature was 45℃ ± 2℃. The capacity retention of the low-nickel NCM ternary material at 45℃ was tested. To ensure the accuracy of the test results, a set of parallel experiments was set up.

[0081] Test results are as follows Figure 4 As shown, Figure 4 This is a capacity retention diagram of the NCM ternary materials with different coating agents provided in Comparative Example 2 of this invention. Figure 4 It can be seen that CeO2 is selected as the coating material, which has the best positive electrode performance. This is the same experimental conclusion as in Example 2, thus verifying the accuracy of the method in Example 2.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An evaluation method for a coating agent of a lithium-ion battery cathode material, comprising the following steps: a) Mix the positive electrode material coating agent, conductive agent, binder and solvent to obtain a slurry; b) Coat the slurry onto the current collector and dry it to obtain the electrode sheet; c) Assemble a button cell; the positive electrode material of the button cell is the electrode sheet, and the negative electrode material is lithium; d) Following steps a) to c), change the composition of the positive electrode material coating agent to prepare coin cells corresponding to positive electrode material coating agents with different compositions; e) Cyclic voltammetry tests were performed on the coin half-cells corresponding to the cathode material coating agents with different compositions to obtain the cyclic voltammetry curves corresponding to the cathode material coating agents with different compositions. f) Compare the peak values ​​of the maximum redox peaks of the cyclic voltammetry curves corresponding to the different components of the cathode material coating agent, and determine the relative electrochemical activity of the different components of the cathode material coating agent based on the comparison results; In step f), the determination method is as follows: if the peak value of the maximum redox peak is relatively large, the electrochemical activity of the corresponding cathode material coating agent is relatively high; if the peak value of the maximum redox peak is relatively small, the electrochemical activity of the corresponding cathode material coating agent is relatively low.

2. The evaluation method according to claim 1, characterized in that, In step a), the mass ratio of the positive electrode material coating agent, conductive agent, binder and solvent is (5~10):(1~5):0.1:(0.5~1.5).

3. The evaluation method according to claim 1, characterized in that, In step b), the thickness of the current collector is 5~30μm; the drying temperature is 80~200℃.

4. The evaluation method according to claim 1, characterized in that, In step c), the electrode is rolled and punched before it is used to assemble a button cell.

5. The evaluation method according to claim 1, characterized in that, In step e), before performing cyclic voltammetry testing on the coin cell, its open-circuit voltage is tested first; coin cells with an open-circuit voltage above 0V are selected for cyclic voltammetry testing.

6. The evaluation method according to claim 1, characterized in that, In step f), the cyclic voltammetry curve obtained in the third or subsequent cycles is used as the basis for comparing the magnitude of the peak value.

7. A method for screening coating agents for lithium-ion battery cathode materials, comprising the following steps: a) Mix the positive electrode material coating agent, conductive agent, binder and solvent to obtain a slurry; b) Coat the slurry onto the current collector and dry it to obtain the electrode sheet; c) Assemble a button cell; the positive electrode material of the button cell is the electrode sheet, and the negative electrode material is lithium; d) Following steps a) to c), change the composition of the positive electrode material coating agent to prepare coin cells corresponding to positive electrode material coating agents with different compositions; e) Cyclic voltammetry tests were performed on the coin half-cells corresponding to the cathode material coating agents with different compositions to obtain the cyclic voltammetry curves corresponding to the cathode material coating agents with different compositions. In step e), the voltage range of the cyclic voltammetry test is 0~5V; the scan rate of the cyclic voltammetry test is 1~5mV / s; f') Based on the peak value of the maximum redox peak of the cyclic voltammetry curve corresponding to the different components of the cathode material coating agent, determine whether the corresponding component can be used as a cathode material coating agent for lithium-ion batteries; In step f'), the determination method is as follows: if the peak value of the maximum oxidation peak of the cyclic voltammetry curve is ≤0.001A and the peak value of the maximum reduction peak is ≥-0.002A, then the corresponding component is used as a coating agent for the positive electrode material of lithium-ion batteries.

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