A method for evaluating the performance of a soft-pack lithium ion full cell with a button-type half cell

Abstract

The present application relates to the field of lithium ion battery, disclose a kind of with button type half-cell evaluation soft package lithium ion full battery performance method, steps include making positive plate, making negative plate, combination compaction is respectively made into two systems and three systems button type half-cell, battery performance test is carried out to button type half-cell made, button type half-cell made by setting electrolyte injection ratio, coating surface density and selecting different size negative electrode material and copper foil negative combination can accurately reflect the battery performance of lithium ion full battery, improve the reliability of button type half-cell data, and a series of different positive electrode coating amount full battery can be evaluated, a large number of test resources are saved, the test method in the present application has good applicability in three electrode system, shorten the difference between button type half-cell lithium ion full battery evaluation result.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a method for evaluating the performance of soft package lithium ion full battery by using button half battery. BACKGROUND

[0002] Button half battery with lithium metal as the counter electrode has attracted widespread interest in the research of lithium ion batteries, and has become an important research means in the development of lithium ion power battery products. However, due to the obvious differences between the components of button half battery and full battery, including the counter electrode of button half battery being pure lithium sheet (the main material in full battery being graphite and the like), and the ratio of electrolyte additive being higher than that of full battery, etc., these factors will significantly affect the performance of soft package lithium ion full battery. Therefore, it is a certain technical challenge to use button half battery to verify the characteristics of new materials and estimate the performance of large-size soft package lithium ion full battery. Therefore, establishing a bridge between button half battery and soft package full battery can effectively reduce the performance evaluation difference between the two batteries, reduce the risk of material evaluation and performance verification, and accelerate the development of new lithium ion battery products.

[0003] For example, a method for testing the specific capacity of lithium battery material is disclosed in Chinese patent document "Method for testing specific capacity of lithium battery material", application number CN109375113A. The technical solution includes making a positive electrode sheet, making a negative electrode sheet, punching and weighing, selecting the mass of the positive and negative electrode sheets according to the types of positive and negative electrode materials for corresponding pairing, and then placing them in a glove box for 2h; glove box point assembly, the completed button cell is held on an electrochemical test cabinet, the charge and discharge current is calculated according to the test rate (0.2C, 1C, 3C, 5C), current = rate x theoretical specific capacity x (M2-M1) x w. The invention replaces the traditional metal lithium sheet negative electrode with a conventional negative electrode sheet. When cutting and assembling the button half battery, the negative electrode coating is easy to fall off from the current collector, resulting in a decrease in the accuracy of the test results. The battery is easy to short circuit during continuous charge and discharge. For thick electrodes, this problem is more prominent. The reason is that the thicker the coating layer, the easier it is to peel off, which has certain technical limitations.

[0004] A method for evaluating lithium battery electrode materials after cycling using button cell is disclosed in Chinese patent document "A method for evaluating lithium battery electrode materials after cycling using button cell", application number CN110927593A, which mainly includes the following steps: S1 disassembling lithium ion full battery, taking out the battery electrode sheet; S2 wiping off one side of the sheet obtained in step S1, baking in bulk; S3 punching the sheet obtained in step S2 and assembling into a button cell; S4 electrochemical performance test of the button cell obtained in step S3; S5 evaluating the capacity of the electrode material according to the electrical performance test of step S4. The invention uses button cell to evaluate the performance of lithium ion battery material after cycling, the purpose is to analyze the battery material attenuation behavior and mechanism before and after cycling, without considering and evaluating the difference between button cell and full cell, which has technical limitations.

[0005] Commercialized lithium ion full battery uses graphite layer coated on copper foil as counter electrode, and when the same negative electrode material is used to make button cell, the process is complicated, the operation time is long, and when the positive electrode coating changes more than 5g / m 2 The optimal size of graphite combined with copper foil is different from the negative electrode of the half cell, and the composition of the negative electrode sheet needs to be redesigned and tested.

[0006] To solve the above problems, a method for evaluating the performance of soft package lithium ion full battery by button cell half battery is needed. By confirming the main experimental parameters affecting the button cell half battery, a button cell test standard related to soft package lithium ion full battery is established, which ensures that the evaluation results of button cell half battery are consistent with the results of soft package lithium ion full battery, and verifies the accuracy of the test standard in the comparison of the evaluation results of three-electrode button cell half battery and soft package lithium ion full battery. SUMMARY

[0007] The present application is to overcome the lack of limited connection between button cell and soft package lithium ion full battery in the prior art, which causes technical deviation and risk in the performance evaluation results of button cell, reduces the reliability of data, and delays the efficiency of product development. A method for evaluating the performance of soft package lithium ion full battery by button cell half battery is provided, which uses negative electrode sheets made of negative electrode materials and copper foils of different sizes instead of traditional pure lithium sheet negative electrode, and combines with positive electrode sheets of a certain coating amount to form button cells. The battery performance of lithium ion full battery is evaluated by the battery performance of button cell, which has high accuracy; the button cell can also test and evaluate a series of full cells with different positive electrode coating amounts, which saves a lot of test resources.

[0008] To achieve the above purpose, the present application adopts the following technical scheme:

[0009] A method for evaluating the performance of soft package lithium ion full battery by button cell half battery, comprising the following steps:

[0010] A) Preparation of positive electrode sheet: the positive electrode material, positive electrode conductive agent and positive electrode binder are mixed uniformly and coated on aluminum foil, the coating amount is 75-125 g / m 2 or 130-180 g / m 2 , and the coated and dried positive electrode sheet is prepared by compaction;

[0011] B) Preparation of negative electrode sheet: the positive electrode coating amount is 75-125 g / m 2 , and the lithium sheet layer with a thickness of 45-55 μm is selected as the negative electrode material and the copper foil with a thickness of 195-205 μm is pressed to prepare the negative electrode sheet in an inert gas atmosphere at 20-100 standard atmospheres;

[0012] or the positive electrode coating amount is 130-180 g / m 2 , and the lithium sheet layer with a thickness of 60-70 μm is selected as the negative electrode material and the copper foil with a thickness of 180-190 μm is pressed to prepare the negative electrode sheet in an inert gas atmosphere at 20-100 standard atmospheres;

[0013] C) Assembling the two-electrode system button-type half-cell in the order of negative electrode sheet, separator, positive electrode sheet, and injecting electrolyte into the button-type half-cell; or assembling the three-electrode system button-type half-cell in the order of negative electrode sheet, separator, reference electrode, separator, negative electrode sheet, and injecting electrolyte into the button-type half-cell;

[0014] D) The battery prepared in step C) is placed at room temperature for 2-4 weeks, and the standard capacity of the battery is recorded, and then the battery is cycled at room temperature for 200-400 times, and the capacity retention rate of the battery is recorded.

[0015] The conventional method often does not consider the essential difference between the button-type battery and the full battery, directly uses the button-type battery to evaluate the material performance, including the capacity, rate and cycle life, etc., and then directly uses it for the evaluation of the full battery. In fact, there is a big difference between the two, and the performance of the lithium ion button-type half-cell is closely related to its use conditions, and the test results are often significantly different from the lithium ion full battery using the same material system. The main reasons are as follows: first, the pure lithium sheet layer is used as the counter electrode in the button-type half-cell, while the graphite layer coated on the copper foil is used as the counter electrode in the lithium ion full battery. The conductivity of the pure lithium sheet layer is much lower than that of the copper foil, which can easily cause uneven potential distribution in the lithium sheet layer, and the pure lithium sheet layer can provide an approximate infinite "lithium" source, and the theoretical cycle life is higher than that of the graphite counter electrode; second, the positive electrode coating amount of the button-type half-cell is generally lower than that of the full battery, and the electrolyte addition amount is much higher than that of the lithium ion full battery, which can cause the performance test results of the button-type half-cell to be significantly different from the full battery.

[0016] The application replaces the combination of the graphite layer in the negative sheet and the copper foil with the combination of the lithium sheet layer and the copper foil, and has the technical advantages that, on the one hand, the problem of the falling of the graphite layer edge and the decrease in the test accuracy is avoided, and on the other hand, when the positive coating amount is changed within a certain range (±30 g / m 2 ), the corresponding best size combination of the lithium sheet layer and the copper foil still has good accuracy, that is, one combination of the negative round sheet can be used to test and evaluate a series of full batteries with different positive coating amounts, so that the accuracy is improved and a large amount of test resources is saved.

[0017] The three-electrode battery with the reference electrode is one of the most commonly used battery systems for evaluating the voltage performance of the full battery, and the test and evaluation method of the application also has applicability to the evaluation of the performance of the three-electrode battery, and has high accuracy.

[0018] Preferably, in step A), the positive electrode material is selected from NCM ternary layered materials, the positive electrode conductive agent is carbon nanotubes or graphene, and the positive electrode binder is polyvinylidene fluoride.

[0019] Preferably, in step A), the mass ratio of the positive electrode material, the positive electrode conductive agent and the positive electrode binder is 80-90:5-10:5-10. Preferably, in step A), the thickness of the aluminum foil is 15-20 μm.

[0020] Preferably, in step C), the thickness of the separator is 12-20 μm.

[0021] Preferably, in step C), the electrolyte is a 0.8-1.2 mmol / L LiPF6 solution, the solvent of the electrolyte includes a mixed solution of ethylene carbonate / methyl ethyl carbonate in a volume ratio of 2-4:6-8 and 0.1-0.2 mmol / L of vinylene carbonate.

[0022] Preferably, in step C), the reference electrode is a lithium wire wrapped into an electrode sheet with the same shape as the positive sheet.

[0023] Preferably, in step D), the N / P of the assembled battery is set to 1.1-1.17.

[0024] Preferably, in step D), after the button-type half battery is prepared, it is placed at room temperature for 3-6 hours, and is charged and discharged at a rate of 0.08-0.12 C and a voltage of 2.8-4.3 V.

[0025] Preferably, in step D), the battery is cycled at a rate of 0.4-0.6 C and a voltage of 2.8-4.3 V at room temperature.

[0026] Therefore, the application has the following beneficial effects:

[0027] (1) The application provides a method for evaluating performance difference of button-type half cells and soft package lithium ion full cells, test standards of button-type half cells are established through experiments, and the test accuracy is high;

[0028] (2) The test method can be used to evaluate a series of full cells with different positive electrode coating amounts through a combined negative electrode wafer, so that the accuracy is improved and a large amount of test resources is saved;

[0029] (3) The test method has good practicability in a three-electrode system, and the difference between evaluation results of button-type half cells and lithium ion full cells is shortened. DETAILED DESCRIPTION

[0030] The application will be further described in combination with specific embodiments.

[0031] In the examples and comparative examples, the electrolyte is a 1.0 mmol / L LiPF6 solution, the volume ratio of ethylene carbonate / methyl ethyl carbonate in the electrolyte is 3:7, and the electrolyte contains 0.15 mmol / L of vinylene carbonate; the reference electrode is a lithium wire with a diameter of 0.2 mm, which is wound into a lithium wire wafer with the same diameter as the positive electrode wafer; the separator is a 16 μm thick lithium ion battery porous polymer separator; the purity of the copper foil is greater than 99.5%; and the purity of the lithium wafer layer is 99.9%.

[0032] Example 1:

[0033] A) Preparation of the positive electrode wafer: NCM811 ternary layered material: carbon nanotube: polyvinylidene fluoride are uniformly mixed in a ratio of 85:7.5:7.5, and then coated on an 18 μm aluminum foil, with a coating amount of 100 g / m 2 , and after drying, the coating is compacted at a compaction density of 3.2 g / cm 3 , to form a positive electrode wafer with a diameter of 1.2 cm;

[0034] B) Preparation of the negative electrode wafer: a 50 μm thick lithium wafer layer and a 200 μm thick copper foil are pressed under an argon atmosphere at 40 standard atmospheres to form a negative electrode wafer with a diameter of 1.4 cm, which is used as a counter electrode;

[0035] C) Assemble the button-type half cell into a two-electrode system in the order of negative electrode wafer, separator, positive electrode wafer, and inject 110 μL of electrolyte into the button-type half cell; assemble the button-type half cell into a three-electrode system in the order of negative electrode wafer, separator, reference electrode, separator, negative electrode wafer, and inject 110 μL of electrolyte into the button-type half cell;

[0036] D) The battery prepared in step C) is left at room temperature for 4.5 hours, set N / P to 1.14, charged and discharged at 0.1C rate at 3.6V voltage for 3 weeks, record the third week discharge capacity as the standard capacity of the battery, then cycle at 0.5C rate at 3.6V voltage for 300 weeks at room temperature, record the capacity retention rate of the battery = the 300th week discharge capacity / the first week discharge capacity.

[0037] Example 2:

[0038] A) Preparation of positive electrode sheet: NCM811 ternary layered material: carbon nanotube: polyvinylidene fluoride are mixed in a ratio of 80:10:10 and uniformly coated on a 20μm aluminum foil, the coating amount is 75g / m 2 , after coating and drying, compacted at a compaction density of 3.0g / cm 3 , to make a positive electrode sheet with a diameter of 1.0cm;

[0039] B) Preparation of negative electrode sheet: 55μm thick lithium sheet layer and 195μm thick copper foil are pressed under an argon atmosphere at 100 standard atmospheres to make a negative electrode sheet with a diameter of 1.2cm, which is used as a counter electrode;

[0040] C) Assemble a two-electrode system button cell in the order of negative electrode sheet, separator, positive electrode sheet, and inject 110μL of electrolyte into the button cell; assemble a three-electrode system button cell in the order of negative electrode sheet, separator, reference electrode, separator, negative electrode sheet, and inject 110μL of electrolyte into the button cell;

[0041] D) The battery prepared in step C) is left at room temperature for 3 hours, set N / P to 1.1, charged and discharged at 0.08C rate at 2.8V voltage for 3 weeks, record the third week discharge capacity as the standard capacity of the battery, then cycle at 0.4C rate at 2.8V voltage for 300 weeks at room temperature, record the capacity retention rate of the battery = the 300th week discharge capacity / the first week discharge capacity.

[0042] Example 3:

[0043] A) Preparation of positive electrode sheet: NCM811 ternary layered material: carbon nanotube: polyvinylidene fluoride are mixed in a ratio of 90:5:5 and uniformly coated on a 15μm aluminum foil, the coating amount is 125g / m 2 , after coating and drying, compacted at a compaction density of 3.3g / cm 3 , to make a positive electrode sheet with a diameter of 1.4cm;

[0044] B) Preparation of negative electrode sheet: 45μm thick lithium sheet layer and 205μm thick copper foil are pressed under an argon atmosphere at 20 standard atmospheres to make a negative electrode sheet with a diameter of 1.6cm, which is used as a counter electrode;

[0045] C) Assemble the battery into a two-electrode system button cell in the order of negative electrode sheet, separator, positive electrode sheet, and inject 110 μL of electrolyte into the button cell; assemble the battery into a three-electrode system button cell in the order of negative electrode sheet, separator, reference electrode, separator, negative electrode sheet, and inject 110 μL of electrolyte into the button cell;

[0046] D) Place the battery prepared in step C) at room temperature for 6 hours, set N / P to 1.17, and charge and discharge at a voltage of 4.3 V at a rate of 0.12 C for 3 weeks, record the discharge capacity in the third week as the standard capacity of the battery, and then cycle at a rate of 0.6 C at a voltage of 4.3 V for 300 weeks at room temperature, record the capacity retention rate of the battery = discharge capacity in the 300th week / discharge capacity in the first week.

[0047] Example 4:

[0048] The coating amount on the aluminum foil is 155 g / m 2 , the negative electrode material is selected to be a lithium sheet layer with a thickness of 65 μm; the copper foil has a thickness of 185 μm, the amount of injected electrolyte is 120 μL, and other conditions are the same as in Example 1, finally, record the standard capacity of the battery and the capacity retention rate of the battery.

[0049] Example 5:

[0050] The coating amount on the aluminum foil is 130 g / m 2 , the negative electrode material is selected to be a lithium sheet layer with a thickness of 60 μm; the copper foil has a thickness of 190 μm, the amount of injected electrolyte is 120 μL, and other conditions are the same as in Example 1, finally, record the standard capacity of the battery and the capacity retention rate of the battery.

[0051] Example 6:

[0052] The coating amount on the aluminum foil is 180 g / m 2 , the negative electrode material is selected to be a lithium sheet layer with a thickness of 70 μm; the copper foil has a thickness of 180 μm, the amount of injected electrolyte is 120 μL, and other conditions are the same as in Example 1, finally, record the standard capacity of the battery and the capacity retention rate of the battery.

[0053] Comparative Example 1:

[0054] The negative electrode material is a lithium sheet layer with a thickness of 250 μm, the negative electrode material, negative electrode conductive agent and negative electrode binder are mixed uniformly and directly pressed into a negative electrode sheet, and other conditions are the same as in Example 1; finally, record the standard capacity of the battery and the capacity retention rate of the battery.

[0055] Comparative Example 2:

[0056] The amount of electrolyte injected is 70 μL, and other conditions are the same as in Example 1; finally, record the standard capacity of the battery and the capacity retention rate of the battery.

[0057] Comparative Example 3:

[0058] The negative material was a 90 pm lithium sheet layer, the copper foil thickness was 160 pm, and the other conditions were the same as in Example 1; finally, the standard capacity of the battery and the battery capacity retention rate were recorded.

[0059] Comparative Example 4:

[0060] The negative material was a 10 pm lithium sheet layer, the copper foil thickness was 240 pm, and the other conditions were the same as in Example 1; finally, the standard capacity of the battery and the battery capacity retention rate were recorded.

[0061] Comparative Example 5:

[0062] The negative material was a 50 pm lithium sheet layer, the copper foil thickness was 100 pm, and the other conditions were the same as in Example 1; finally, the standard capacity of the battery and the battery capacity retention rate were recorded.

[0063] Comparative Example 6:

[0064] The negative material was a 100 pm lithium sheet layer, the copper foil thickness was 200 pm, and the other conditions were the same as in Example 1; finally, the standard capacity of the battery and the battery capacity retention rate were recorded.

[0065] Comparative Example 7:

[0066] The negative material was a 90 pm graphite layer, the copper foil was 160 pm, and the other conditions were the same as in Example 1; finally, the standard capacity of the battery and the battery capacity retention rate were recorded.

[0067] Comparative Example 8:

[0068] The negative material was a 140 pm graphite layer, the copper foil was 110 pm, and the other conditions were the same as in Example 1; finally, the standard capacity of the battery and the battery capacity retention rate were recorded.

[0069] Comparative Example 9:

[0070] The negative material was a 90 pm lithium sheet layer, the copper foil thickness was 160 pm, and the other conditions were the same as in Example 4; finally, the standard capacity of the battery and the battery capacity retention rate were recorded.

[0071] Comparative Example 10:

[0072] The negative material was a 10 pm lithium sheet layer, the copper foil thickness was 240 pm, and the other conditions were the same as in Example 4; finally, the standard capacity of the battery and the battery capacity retention rate were recorded.

[0073] Comparative Example 11:

[0074] The negative material is a 50-μm lithium flake layer, the copper foil thickness is 100 μm, and other conditions are the same as in Example 4; finally, the standard capacity of the battery and the battery capacity retention rate are recorded.

[0075] Comparative Example 12:

[0076] The negative material is a 100-μm lithium flake layer, the copper foil thickness is 200 μm, and other conditions are the same as in Example 4; finally, the standard capacity of the battery and the battery capacity retention rate are recorded.

[0077] In order to better illustrate the accuracy of the test method of the present application, two groups of commercial batteries are selected for comparison of typical negative coating amounts as reference examples. The closer the data of the examples to the reference examples, the higher the accuracy of the test method of the present application.

[0078] Reference Example 1:

[0079] A soft-pack lithium ion full battery with a battery capacity of 35 Ah and a size of 308*102*8.0 is selected, the positive electrode sheet composition is NCM811: carbon nanotube: PVDF binder mixed uniformly at a mass ratio of 89:5:6, coated on an 18-μm aluminum foil, and the positive coating amount is 100 g / m 2 The negative electrode sheet composition is artificial graphite: conductive carbon black: carboxymethyl cellulose / styrene-butadiene rubber mixed uniformly at a ratio of 92:3.5:4.5, coated on the surface of a 160-μm copper foil, and the negative graphite layer thickness is 90 μm. The lithium ion full battery is tested and the battery capacity retention rate is recorded.

[0080] Reference Example 2:

[0081] A soft-pack lithium ion full battery with a battery capacity of 50 Ah and a size of 308*102*11 is selected, the positive electrode sheet composition is NCM811: carbon nanotube: PVDF binder mixed uniformly at a mass ratio of 90:5:5, coated on an 18-μm aluminum foil, and the positive coating amount is 155 g / m 2 The negative electrode sheet composition is artificial graphite: conductive carbon black: carboxymethyl cellulose / styrene-butadiene rubber mixed uniformly at a ratio of 88:4.5:7.5, coated on the surface of a 110-μm copper foil, and the negative graphite layer thickness is 140 μm. The lithium ion full battery is tested and the battery capacity retention rate is recorded.

[0082] The above data is summarized in a table.

[0083] Table 1.1 Test conditions of different button-type half-batteries and test results of two-electrode and three-electrode system batteries prepared therefrom.

[0084]

[0085] Table 1.2 Test conditions of different coin-type half-cells and test results of two-electrode and three-electrode system batteries made therefrom.

[0086]

[0087]

[0088] Table 1.3 Test conditions of different coin-type half-cells and test results of two-electrode and three-electrode system batteries made therefrom.

[0089]

[0090] Table 1.4 Test conditions of different coin-type half-cells and test results of two-electrode and three-electrode system batteries made therefrom.

[0091]

[0092] In order to better illustrate the accuracy of the test method of the present application, first, the battery performance of two soft pack lithium ion full batteries (Reference Example 1 and Reference Example 2) was tested, then the battery performance of the coin-type half-cells corresponding to the two reference examples (Comparative Example 7 and Comparative Example 8) was tested, and the test results showed that the experimental data of Comparative Example 7 and Comparative Example 8 can completely represent the battery performance of the corresponding soft pack lithium ion full batteries.

[0093] From the comparison of Example 1 and Comparative Example 7 and Comparative Example 1, it can be seen that when the positive electrode coating amount is 100 g / m 2 , Example 1 has higher accuracy than Comparative Example 1, the battery capacity retention rates of the two-electrode system and the three-electrode system of Example 1 are 87.8% and 87.7% respectively, the battery capacity retention rates of the two-electrode system battery and the three-electrode system battery are 0.3% and 0.4% different from those of Comparative Example 7 respectively, while the battery capacity retention rates of the two-electrode system battery and the three-electrode system battery measured by Comparative Example 1 are 86.7% and 86.4% respectively, the battery capacity retention rates of the two-electrode system battery and the three-electrode system battery are 0.8% and 0.9% different from those of Comparative Example 7 respectively.

[0094] From the comparison of Comparative Example 7, Example 1, Example 2, Example 3, it can be seen that when the positive electrode coating amount is 75-125 g / m 2In this case, a coin cell half-cell made using a combination of a 50μm thick lithium sheet and a 200μm thick copper foil as the negative electrode showed performance closest to that of Comparative Example 7. Comparisons of Comparative Examples 7, 8, and 1 show that replacing the lithium sheet in conventional testing with a graphite layer and copper foil negative electrode combination for the full cell results in no significant impact on cycle performance when the graphite layer thickness is low (Comparative Example 7). However, when the graphite layer thickness increases to 140μm (Comparative Example 8), the battery cycle capacity retention rate is significantly lower than that of Comparative Example 1. This indicates that using a coin cell half-cell made with a pure lithium sheet as the negative electrode to characterize the performance of a lithium-ion full cell, especially when the coating density of the positive and negative electrodes is high, results in larger errors and lower reliability in cycle tests. Comparisons of Comparative Example 8, Example 4, Example 5, and 6 show that when the positive electrode coating amount is 130-180 g / m², the cycle performance is significantly better. 2 At that time, the coin cell made by using a combination of a 65μm thick lithium sheet and a 185μm thick copper foil as the negative electrode was closest in performance to the battery of Comparative Example 8.

[0095] As can be seen from the comparison between Example 1 and Comparative Example 2, in addition to the composition of the negative electrode, the amount of electrolyte injected is another important factor affecting the accuracy. When the amount of electrolyte injected is too low, the transport performance of liquid lithium ions is limited due to insufficient interface wetting, which leads to a decrease in the accuracy of the evaluation.

[0096] The comparison between Example 1 and Comparative Examples 3, 4, 5, and 6 shows that when the positive electrode coating amount is 75-125 g / m², 2 When a coin cell with a 45-55 μm thick lithium sheet and a 195-205 μm thick copper foil as the negative electrode was used, its performance was close to that of Comparative Example 7. Among them, the coin cell with a 50 μm thick lithium sheet and a 200 μm thick copper foil as the negative electrode had the closest performance to that of Comparative Example 7. Similarly, from the comparison between Example 2 and Comparative Examples 9, 10, 11, and 12, it can be seen that when the positive electrode coating amount is 130-180 g / m 2 At that time, the coin cell made by combining a 65μm thick lithium sheet and a 185μm thick copper foil as the negative electrode was closest in performance to the battery of Comparative Example 8.

[0097] In the testing method of this invention, for a positive electrode material with a certain coating amount, a negative electrode material of corresponding size and copper foil are selected to form a coin cell. The test results of the coin cell can accurately reflect the battery performance of the lithium-ion full battery. The testing method of this invention can be applied to both two-electrode and three-electrode systems for testing and evaluating the battery performance of lithium-ion full batteries.

Claims

1. A method for evaluating the performance of a pouch lithium-ion full battery using a coin cell half-cell, wherein the lithium-ion full battery uses a graphite layer coated on copper foil as the counter electrode, characterized in that... The steps include the following: A) Fabrication of the positive electrode sheet: After uniformly mixing the positive electrode material, positive electrode conductive agent, and positive electrode binder, the mixture is coated onto aluminum foil with a coating amount of 75-125 g / m². 2 Or 130-180g / m 2 After coating and drying, the material is pressed to form a positive electrode sheet. B) Fabrication of the negative electrode: The positive electrode coating amount is 75-125g / m 2 A lithium sheet with a thickness of 45-55μm is selected as the negative electrode material and pressed with a copper foil with a thickness of 195-205μm in an inert gas atmosphere at 20-100 standard atmospheres to form a negative electrode sheet. Or the positive electrode coating amount is 130-180g / m 2 A lithium sheet with a thickness of 60-70μm is selected as the negative electrode material and pressed with a copper foil with a thickness of 180-190μm in an inert gas atmosphere under a pressure of 20-100 standard atmospheres to form a negative electrode sheet. C) Assemble a coin cell into a two-electrode system by following the order of negative electrode, separator, and positive electrode, and inject electrolyte into the coin cell; or assemble a coin cell into a three-electrode system by following the order of negative electrode, separator, reference electrode, separator, and negative electrode, and inject electrolyte into the coin cell. D) Place the battery obtained in step C) at room temperature and charge and discharge it for 2-4 weeks, record the standard capacity of the battery, and then cycle it at room temperature for 200-400 cycles, and record the battery capacity retention rate.

2. The method according to claim 1, characterized in that, In step A), the positive electrode material is selected from NCM ternary layered materials, the positive electrode conductive agent is carbon nanotubes or graphene, and the positive electrode binder is polyvinylidene fluoride.

3. The method according to claim 1, characterized in that, In step A), the mass ratio of positive electrode material: positive electrode conductive agent: positive electrode binder is 80-90: 5-10: 5-10.

4. The method according to claim 1, characterized in that, In step A), the thickness of the aluminum foil is 15-20 μm.

5. The method according to claim 1, characterized in that, In step C), the thickness of the diaphragm is 12-20 μm.

6. The method according to claim 1, characterized in that, In step C), the electrolyte is a 0.8-1.2 mol / L LiPF6 solution, and the solvent of the electrolyte includes a mixture of ethylene carbonate / ethyl methyl carbonate in a volume ratio of 2-4:6-8 and 0.1-0.2 mmol / L vinylene carbonate.

7. The method according to claim 1, characterized in that, In step C), the reference electrode is an electrode sheet in which lithium wire is wound to the same shape as the positive electrode sheet.

8. The method according to claim 1, characterized in that, In step D), the N / P value of the assembled battery is set to 1.1-1.

17.

9. The method according to claim 1, characterized in that, In step D), after the button cell is made, it is placed at room temperature for 3-6 hours and charged and discharged at a rate of 0.08-0.12C and a voltage of 2.8-4.3V.

10. The method according to claim 1, characterized in that, In step D), the battery is cycled at room temperature at a rate of 0.4-0.6C and a voltage of 2.8-4.3V.

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