Electrochemically active specific surface area test method

Abstract

The application discloses an electrochemical active specific surface area test method, and relates to the technical field of battery testing. The electrochemical active specific surface area test method comprises the following steps: providing a battery with an electrode sheet to be tested; determining a voltage range in which the battery performs double-layer behavior and a plurality of scanning speeds corresponding to the voltage range; obtaining CV curves of the plurality of scanning speeds in the voltage range; obtaining a plurality of integral areas corresponding to the plurality of scanning speeds according to the plurality of CV curves; one-to-one corresponding the plurality of scanning speeds and the plurality of integral areas to form a plurality of coordinate points, linearly fitting the plurality of coordinate points, and obtaining the slope of a fitted straight line; and determining the electrochemical active specific surface area of the electrode sheet to be tested according to the slope. The application can improve the accuracy of the electrochemical active specific surface area test of the electrode sheet.

Description

Technical Field

[0001] This application relates to the field of battery testing technology, specifically to a method for testing the electrochemically active specific surface area. Background Technology

[0002] Electrochemically active specific surface area refers to the effective area of ​​an electrode material's surface that participates in electrochemical reactions; it is one of the important parameters for evaluating electrode material performance. In lithium-ion batteries, the electrochemically active specific surface area is directly related to processes such as lithium insertion / extraction, deintercalation, and side reactions in the electrode material, significantly impacting the battery's kinetics and lifespan. Therefore, improving the accuracy of electrode electrochemically active specific surface area testing is of great significance for optimizing battery performance. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems, and its purpose is to provide a method for testing the electrochemical active specific surface area, which can improve the accuracy of testing the electrochemical active specific surface area of ​​electrodes.

[0004] To achieve the above objectives, this application proposes a method for testing electrochemically active specific surface area.

[0005] This application provides a method for testing the specific surface area of ​​electrochemical activity, including the following steps:

[0006] Provide a battery with the electrode to be tested;

[0007] Determine the voltage range in which the battery exhibits double-layer behavior, and the multiple scan rates corresponding to the voltage range;

[0008] Obtain CV curves for multiple scan rates within the voltage range;

[0009] Based on multiple CV curves, obtain multiple integral areas corresponding to the multiple scanning velocities;

[0010] Multiple scanning speeds and their corresponding integral areas are matched one-to-one to form multiple coordinate points. Linear fitting is performed through multiple coordinate points to obtain the slope of the fitted line.

[0011] The electrochemically active specific surface area of ​​the electrode under test is determined based on the slope.

[0012] Therefore, in the technical solution of this application, the CV curves of the battery's double-layer behavior at multiple scan rates within the voltage range are first obtained. Then, the integrated area of ​​the CV curves at different scan rates is obtained. The electrochemical active specific surface area of ​​the electrode under test is determined by the slope obtained by fitting the integrated area with the scan rate linearly. Based on the principle of double-layer capacitance, the electrochemical active specific surface area of ​​the electrode is tested. Ions respond rapidly to potential, and when the voltage of the external circuit is changed, the potential at the electroactive sites of the electrode under test changes, the potential of the non-electroactive sites is generally unaffected. The adsorption of ions near the corresponding electroactive sites will change. The test results basically only include electroactive sites, which can improve the accuracy of the test of the electrochemical active specific surface area of ​​the electrode. Moreover, the test method is simple and easy to operate.

[0013] In any embodiment, during the step of providing a battery with the electrode to be tested, the battery is in a fully discharged state. Using a fully discharged battery to test the electrochemically active specific surface area can improve the accuracy of the electrode electrochemically active specific surface area test.

[0014] In any embodiment, the step of providing a battery with the electrode to be tested includes a coin cell, a stacked cell, or a pouch cell. Using these battery types facilitates testing operations and can also improve the accuracy of electrode electrochemical activity specific surface area testing.

[0015] In any embodiment, in the step of providing a battery with an electrode to be tested, the electrode to be tested is a positive electrode. Testing the electrochemically active specific surface area of ​​the positive electrode can improve the accuracy of the electrochemically active specific surface area test.

[0016] In any embodiment, in the step of providing a battery with an electrode to be tested, the electrode to be tested is a porous electrode. Testing the electrochemically active specific surface area of ​​the porous electrode allows ions to penetrate deep into the interior of the porous electrode, largely unaffected by the micropores and mesopores present within the porous electrode, thus improving the accuracy of the electrochemically active specific surface area test.

[0017] In any embodiment, in the step of determining the voltage range for the battery to exhibit double-layer behavior and the multiple scan speeds corresponding to the voltage range, the number of test points for the CV curve scan at each scan speed is greater than or equal to 20. Using the above-mentioned range for the number of test points can improve the accuracy of electrochemically active surface area testing.

[0018] In any embodiment, in the step of determining the voltage range for the battery to exhibit double-layer behavior and the plurality of scan rates corresponding to the voltage range, the number of scan rates is greater than or equal to 4. Using the above-mentioned range for the number of scan rates can improve the accuracy of electrochemically active surface area testing.

[0019] In any embodiment, in the step of determining the electrochemically active specific surface area of ​​the electrode under test based on the slope, the electrochemically active specific surface area of ​​the electrode under test is calculated using the following formula:

[0020]

[0021] Among them, S A The specific surface area of ​​the electrode under test is the electrochemically active surface area, in m². 2 / g;

[0022] k a The slope;

[0023] k is the electrostatic constant;

[0024] d represents the thickness of the electric double layer, in meters (m).

[0025] ε is the relative permittivity of the electrolyte in the battery;

[0026] m is the mass of the active material of the electrode to be tested, in grams;

[0027] ΔU is the difference in voltage range, in units of V.

[0028] Get the slope (k) a After that, the electrochemical active specific surface area of ​​the electrode under test can be calculated using the above formula, which can improve the accuracy of the electrochemical active specific surface area test.

[0029] In any embodiment, after the step of determining the electrochemically active specific surface area of ​​the electrode under test based on the slope, the method further includes: determining the electrochemically active surface area of ​​the electrode under test based on the electrochemically active specific surface area. The electrochemically active surface area of ​​the electrode under test can be further obtained from the electrochemically active specific surface area.

[0030] In any embodiment, in the step of determining the electrochemical active surface area of ​​the electrode under test based on the electrochemical active specific surface area, the electrochemical active surface area of ​​the electrode under test is calculated using the following formula:

[0031] S = mS A (2)

[0032] Where S is the electrochemical active surface area of ​​the electrode under test, in m².2 ;

[0033] m is the mass of the active material of the electrode to be tested, in grams;

[0034] S A The specific surface area of ​​the electrode under test is the electrochemically active surface area, in m². 2 / g.

[0035] Obtain the electrochemical active surface area (S A After that, the electrochemical active surface area of ​​the electrode to be tested can be further obtained by using the above formula. Attached Figure Description

[0036] Figure 1 This is a schematic flowchart of an embodiment of the electrochemically active specific surface area testing method of this application.

[0037] Figure 2 This is an exploded view of a button battery according to one embodiment of this application.

[0038] Figure 3 This is a CV curve diagram of Embodiment 1 of this application.

[0039] Figure 4 This is a CV curve diagram of Embodiment 2 of this application.

[0040] Figure 5 This is the CV curve diagram of Embodiment 3 of this application.

[0041] Figure 6 This is the CV curve diagram of Embodiment 4 of this application.

[0042] Figure 7 This is a linear fitting graph of the integral area versus scanning speed for embodiments 1 to 4 of this application.

[0043] Figure 8 This is a graph showing the relationship between the electrochemically active surface area of ​​the positive electrode sheet to be tested and the coating weight of the positive electrode sheet to be tested obtained in Examples 1 to 4 of this application.

[0044] Figure 9 This is a comparison diagram of the electrochemically active specific surface area of ​​the positive electrode sheets to be tested obtained in Examples 1 to 4 and Comparative Examples 1 to 4 of this application.

[0045] Figure 10 The specific surface area of ​​the positive electrode to be tested obtained from Comparative Examples 5 to 8 of this application is the electrochemically active surface area.

[0046] Figure 11 This is the CV curve diagram of Embodiment 5 of this application.

[0047] Figure 12 This is a CV curve diagram of Embodiment 6 of this application.

[0048] Figure 13 This is a CV curve diagram of Embodiment 7 of this application.

[0049] Figure 14 This is the CV curve diagram of Embodiment 8 of this application.

[0050] Figure 15 This is a linear fitting graph of the integral area versus scanning speed for embodiments 5 to 8 of this application.

[0051] Figure 16 This is a graph showing the relationship between the electrochemically active surface area of ​​the negative electrode sheet to be tested and the coating weight of the negative electrode sheet to be tested, obtained in Examples 5 to 8 of this application.

[0052] Figure 17 This is a comparison diagram of the electrochemically active specific surface area of ​​the negative electrode sheets to be tested obtained in Examples 5 to 8 and Comparative Examples 9 to 12 of this application.

[0053] Figure 18 The specific surface area of ​​the negative electrode sheet to be tested obtained from comparative examples 13 to 16 of this application is the electrochemically active surface area. Detailed Implementation

[0054] The embodiments of the electrochemically active surface area testing method of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0055] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0057] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0058] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0059] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0060] Electrochemically active specific surface area refers to the effective area of ​​an electrode material's surface that participates in electrochemical reactions; it is one of the important parameters for evaluating electrode material performance. In lithium-ion batteries, the electrochemically active specific surface area is directly related to processes such as lithium insertion / extraction, deintercalation, and side reactions in the electrode material, significantly impacting the battery's kinetics and lifespan. Therefore, improving the accuracy of electrode electrochemically active specific surface area testing is of great significance for optimizing battery performance.

[0061] Based on this, this application proposes a method for testing the electrochemically active specific surface area.

[0062] Please see Figure 1 This application provides a method for testing the electrochemically active specific surface area, comprising the following steps:

[0063] Provide a battery with the electrode to be tested;

[0064] Determine the voltage range in which the battery exhibits double-layer behavior, and the multiple scan rates corresponding to the voltage range;

[0065] Obtain CV curves for multiple scan rates within the voltage range;

[0066] Based on multiple CV curves, obtain multiple integral areas corresponding to the multiple scanning velocities;

[0067] Multiple scanning speeds and their corresponding integral areas are matched one-to-one to form multiple coordinate points. Linear fitting is performed through multiple coordinate points to obtain the slope of the fitted line.

[0068] The electrochemically active specific surface area of ​​the electrode under test is determined based on the slope.

[0069] Therefore, in the technical solution of this application, the CV curves (cyclic voltammetry curves) of the battery's double-layer behavior at multiple scan rates within the voltage range are first obtained. Then, the integrated area of ​​the CV curves at different scan rates is obtained. Finally, the electrochemical active specific surface area of ​​the electrode under test is determined by the slope obtained by fitting the integrated area with the scan rate linearly. Based on the principle of double-layer capacitance, the electrochemical active specific surface area of ​​the electrode is tested. Ions respond rapidly to potential, and when the voltage of the external circuit is changed, the potential at the electroactive sites of the electrode under test changes, the potential of the non-electroactive sites is generally unaffected. The adsorption of ions near the corresponding electroactive sites will change. The test results basically only include electroactive sites, which can improve the accuracy of the test of the electrochemical active specific surface area of ​​the electrode. Moreover, the test method is simple and easy to operate.

[0070] It should be noted that the electric double layer refers to the ion adsorption layer that occurs on the solution side of the interface due to the potential at the electrode-electrolyte interface. In this application, the standard for determining the voltage range for the battery to exhibit electric double layer behavior is that the shape of the CV curves at each scan rate is approximately rectangular within the voltage range. If the shape of the CV curve is not approximately rectangular or obvious electrochemical redox peaks appear, it is not applicable, and the voltage range needs to be reselected. It can be understood that in the steps of determining the voltage range for the battery to exhibit electric double layer behavior and the multiple scan rates corresponding to the voltage range, the CV curves that meet the requirements can be screened out to obtain the CV curves of multiple scan rates within the voltage range. The electrode to be tested can be a negative electrode or a positive electrode.

[0071] In any embodiment, during the step of providing a battery with the electrode to be tested, the battery is in a fully discharged state. Using a battery in a fully discharged state to test the electrochemically active surface area can improve the accuracy of the electrode electrochemically active surface area test. It is understood that the battery can be a newly assembled battery or a battery that has been used for a period of time and is in a fully discharged state; a fully discharged state refers to a battery with a state of charge (SOC) of 0%.

[0072] In any embodiment, the step of providing a battery with the electrode to be tested includes a coin cell, a stacked cell, or a pouch cell. Using these battery types facilitates testing operations and can also improve the accuracy of electrode electrochemical activity specific surface area testing.

[0073] In any embodiment, in the step of providing a battery with an electrode to be tested, the electrode to be tested is a positive electrode. Testing the electrochemically active specific surface area of ​​the positive electrode can improve the accuracy of the electrochemically active specific surface area test.

[0074] In any embodiment, in the step of providing a battery with an electrode to be tested, the electrode to be tested is a porous electrode. Testing the electrochemically active specific surface area of ​​the porous electrode allows ions to penetrate deep into the interior of the porous electrode, largely unaffected by the micropores and mesopores present within the porous electrode, thus improving the accuracy of the electrochemically active specific surface area test.

[0075] In any embodiment, in the step of determining the voltage range for the battery to exhibit double-layer behavior and the multiple scan speeds corresponding to the voltage range, the number of test points for the CV curve scan at each scan speed is greater than or equal to 20. Using the above-mentioned range for the number of test points can improve the accuracy of the electrochemically active surface area test. At each scan speed, the number of test points for the CV curve scan can be 20, 30, 40, 50, 60, 70, 80, 90, or 100; it should be noted that the number of test points for the CV curve scan is the ratio of the voltage range difference to the scan speed.

[0076] In any embodiment, in the step of determining the voltage range for the battery to exhibit double-layer behavior and the multiple scan rates corresponding to the voltage range, the number of scan rates is greater than or equal to 4. Using the above-mentioned range for the number of scan rates can improve the accuracy of the electrochemically active surface area test. The number of scan rates can be 4, 5, 6, 7, 8, 9, or 10; it is understood that "greater than or equal to 4 scan rates" means selecting more than 4 different scan rates within the voltage range.

[0077] In any embodiment, in the step of determining the electrochemically active specific surface area of ​​the electrode under test based on the slope, the electrochemically active specific surface area of ​​the electrode under test is calculated using the following formula:

[0078]

[0079] Among them, S A The specific surface area of ​​the electrode under test is the electrochemically active surface area, in m². 2 / g;

[0080] k a The slope;

[0081] k is the electrostatic constant;

[0082] d represents the thickness of the electric double layer, in meters (m).

[0083] ε is the relative permittivity of the electrolyte in the battery;

[0084] m is the mass of the active material of the electrode to be tested, in grams;

[0085] ΔU is the difference in voltage range, in units of V.

[0086] Get the slope (k) a Afterwards, the electrochemically active specific surface area of ​​the electrode under test can be calculated using the above formula, which can improve the accuracy of the electrochemically active specific surface area test. It should be noted that the electrostatic constant (k) is 9.0 × 10⁻⁶. 9 Nm2 / C 2 The double layer thickness (d) can be obtained based on the Stern double layer model (IHP layer and OHP layer) and the radius of the solvated ions, or it can be obtained based on the Debye length. The relative permittivity (ε) of the electrolyte can be obtained by consulting books (such as the Gaussian Handbook, the Langevin Chemical Handbook, etc.). If the electrolyte of some mixed solvents cannot be found, it can be obtained experimentally (such as the two methods provided in the following literature, DOI:10.3969 / j.issn.1672-0679.2013.02.001). The active material mass (m) of the electrode to be tested can be obtained by weighing the electrode or by coating weight. The voltage range difference (ΔU) is the difference between the two endpoints of the voltage range.

[0087] In any embodiment, after the step of determining the electrochemically active specific surface area of ​​the electrode under test based on the slope, the method further includes: determining the electrochemically active surface area of ​​the electrode under test based on the electrochemically active specific surface area. The electrochemically active surface area of ​​the electrode under test can be further obtained from the electrochemically active specific surface area.

[0088] In any embodiment, in the step of determining the electrochemical active surface area of ​​the electrode under test based on the electrochemical active specific surface area, the electrochemical active surface area of ​​the electrode under test is calculated using the following formula:

[0089] S = mS A (2)

[0090] Where S is the electrochemical active surface area of ​​the electrode under test, in m². 2 ;

[0091] m is the mass of the active material of the electrode to be tested, in grams;

[0092] S A The specific surface area of ​​the electrode under test is the electrochemically active surface area, in m². 2 / g.

[0093] Obtain the electrochemical active surface area (S A After that, the electrochemical active surface area of ​​the electrode to be tested can be further obtained by using the above formula.

[0094] Example

[0095] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0096] Example 1

[0097] A method for measuring the specific surface area of ​​electrochemical activity includes the following steps:

[0098] Preparation of the electrode to be tested: LFP system electrode was used as the electrode to be tested, with a coating weight of 0.147g / 1540.25mm. 2 Cut the electrode to be tested into small circular pieces with a radius of 7 mm, weigh them and calculate the mass (m) of the active material in the small circular pieces;

[0099] Assemble a button cell: Combine the positive electrode steel casing, the electrode to be tested, the separator, the lithium electrode, the nickel mesh, and the negative electrode steel casing according to... Figure 2 The cells were assembled and injected with electrolyte to obtain the battery under test; the electrolyte used was LFP commercial electrolyte.

[0100] CV testing: The test cell was CV scanned using an electrochemical workstation. CV curves were selected with a voltage range of 2.0V to 2.2V and scan rates of 1.0mV / s, 1.5mV / s, 2.0mV / s, 2.5mV / s, and 3.0mV / s.

[0101] Linear fitting: Integrate the CV curve for each scan rate to obtain the area of ​​integration, then linearly fit the area of ​​integration to the scan rate to obtain the slope (k). a );

[0102] Calculate the electroactive specific surface area: (k) a Substituting the mass (m) of the active material into formula (1), the electroactive specific surface area (S) of the electrode to be tested is calculated. A ); where k is 9.0 × 10 9 Nm 2 / C 2 ;d is 1.0 × 10 -9 m; ε is 50; ΔU is 0.2V.

[0103] Example 2

[0104] Referring to Example 1, the difference is that the coating weight of the electrode under test is 0.220 g / 1540.25 mm. 2 .

[0105] Example 3

[0106] Referring to Example 1, the difference is that the coating weight of the electrode under test is 0.293 g / 1540.25 mm. 2 .

[0107] Example 4

[0108] Referring to Example 1, the difference is that the coating weight of the electrode under test is 0.366 g / 1540.25 mm. 2 .

[0109] Example 5

[0110] A method for measuring the specific surface area of ​​electrochemical activity includes the following steps:

[0111] Preparation of the electrode to be tested: Graphite electrode was used as the electrode to be tested, with a coating weight of 0.071 g / 1540.25 mm. 2 Cut the electrode to be tested into small circular pieces with a radius of 7 mm, weigh them and calculate the mass (m) of the active material in the small circular pieces;

[0112] Assemble a button cell: Combine the positive electrode steel casing, the electrode to be tested, the separator, the lithium electrode, the nickel mesh, and the negative electrode steel casing according to... Figure 2 The cells were assembled and injected with electrolyte to obtain the battery under test; the electrolyte used was LFP commercial electrolyte.

[0113] CV testing: The cell under test was CV scanned using an electrochemical workstation. CV curves were selected with a voltage range of 1.5V to 1.6V and scan rates of 0.3mV / s, 0.5mV / s, 0.7mV / s, and 1.0mV / s.

[0114] Linear fitting: Integrate the CV curve for each scan rate to obtain the area of ​​integration, then linearly fit the area of ​​integration to the scan rate to obtain the slope (k). a );

[0115] Calculate the electroactive specific surface area: (k) a Substituting the mass (m) of the active material into formula (1), the electroactive specific surface area (S) of the electrode to be tested is calculated. A ); where k is 9.0 × 10 9 Nm 2 / C 2 ;d is 1.0 × 10 -9 m; ε is 50; ΔU is 0.1V.

[0116] Example 6

[0117] Referring to Example 5, the difference is that the coating weight of the electrode under test is 0.141 g / 1540.25 mm. 2 .

[0118] Example 7

[0119] Referring to Example 5, the difference is that the coating weight of the electrode under test is 0.176 g / 1540.25 mm. 2 .

[0120] Example 8

[0121] Referring to Example 5, the difference is that the coating weight of the electrode under test is 0.220 g / 1540.25 mm. 2 .

[0122] Comparative Example 1

[0123] The specific surface area of ​​the electrode under test is determined by the BET method, which is the electroactive specific surface area (S) of the electrode under test. A The electrode used is the same as that used in Example 1.

[0124] Comparative Example 2

[0125] Referring to Comparative Example 1, the electrode used was the same as that used in Example 2.

[0126] Comparative Example 3

[0127] Referring to Comparative Example 1, the electrode used was the same as that used in Example 3.

[0128] Comparative Example 4

[0129] Referring to Comparative Example 1, the electrode used was the same as that used in Example 4.

[0130] Comparative Example 5

[0131] The electroactive specific surface area (Sa) of the electrode under test was measured by the ferrocene CV method. A This includes the following steps:

[0132] Preparation of the electrode to be tested: LFP system electrode was used as the electrode to be tested, with a coating weight of 0.147g / 1540.25mm. 2 Cut the electrode to be tested into small circular pieces with a radius of 7 mm, weigh them and calculate the mass (m) of the active material in the small circular pieces;

[0133] Assemble a button cell: Combine the positive electrode steel casing, the electrode to be tested, the separator, the lithium electrode, the nickel mesh, and the negative electrode steel casing according to... Figure 2 The cells were assembled and injected with electrolyte to obtain the battery to be tested. The electrolyte was obtained by adding ferrocene to LFP commercial electrolyte, and the molar concentration of ferrocene in the obtained electrolyte was 50 mmol / L.

[0134] CV testing: The cell under test was CV scanned using an electrochemical workstation, with a voltage range of 3.0V to 3.4V and scan rates of 0.1mV / s, 0.3mV / s, 0.5mV / s and 1mV / s.

[0135] Peak current extraction and linear fitting: Extract the peak current at each scan rate, and perform linear fitting between the peak current and the scan rate. The fitting formula is the randles-sevcik equation. Obtain the slope and then calculate the electroactive specific surface area based on the slope.

[0136] Comparative Example 6

[0137] Referring to Comparative Example 5, the difference is that the electrode used is the same as the electrode used in Example 2.

[0138] Comparative Example 7

[0139] Referring to Comparative Example 5, the difference is that the electrode used is the same as that used in Example 3.

[0140] Comparative Example 8

[0141] Referring to Comparative Example 5, the difference is that the electrode used is the same as that used in Example 4.

[0142] Comparative Example 9

[0143] Referring to Comparative Example 1, the electrode used was the same as that used in Example 5.

[0144] Comparative Example 10

[0145] Referring to Comparative Example 1, the electrode used was the same as that used in Example 6.

[0146] Comparative Example 11

[0147] Referring to Comparative Example 1, the electrode used was the same as that used in Example 7.

[0148] Comparative Example 12

[0149] Referring to Comparative Example 1, the electrode used was the same as that used in Example 8.

[0150] Comparative Example 13

[0151] Referring to Comparative Example 5, the difference is that the electrode used is the same as that used in Example 5.

[0152] Comparative Example 14

[0153] Referring to Comparative Example 13, the difference is that the electrode used is the same as the electrode used in Example 6.

[0154] Comparative Example 15

[0155] Referring to Comparative Example 14, the difference is that the electrode used is the same as the electrode used in Example 7.

[0156] Comparative Example 16

[0157] Referring to Comparative Example 15, the difference is that the electrode used is the same as the electrode used in Example 8.

[0158] The electrode sheets to be tested in Examples 1 to 4, Comparative Examples 1 to 4, and Comparative Examples 9 to 12 were LFP system electrode sheets, which were the positive electrode sheets to be tested. The electrode sheets to be tested in Examples 5 to 8, Comparative Examples 5 to 8, and Comparative Examples 13 to 16 were graphite electrode sheets, which were the negative electrode sheets to be tested. Examples 1 to 4 were tested four times, Examples 5 to 8 were tested three times, Comparative Examples 1 to 4 and Comparative Examples 9 to 12 were tested with more than ten electrode sheets at the same time, and Comparative Examples 5 to 8 and Comparative Examples 13 to 16 were tested twice.

[0159] The CV curves of Examples 1 to 4 are shown below. Figures 3 to 6 The linear fitting of the integral area and scanning speed in Examples 1 to 4 is shown in [reference needed]. Figure 7 The electrochemical active surface area of ​​the positive electrode sheets to be tested in Examples 1 to 4 was calculated using formula (2). The relationship between the electrochemical active surface area of ​​the positive electrode sheets to be tested obtained in Examples 1 to 4 and the coating weight of the positive electrode sheets to be tested is shown in [reference needed]. Figure 8 (Where, the dashed line represents the average of four repetitions); the electrochemically active specific surface areas of the positive electrode sheets obtained in Examples 1 to 4 and Comparative Examples 1 to 4 are shown in [reference needed]. Figure 9 In this application, the electrochemical active specific surface area (average of four replicates) of Examples 1 to 4 is used; the BET method is used for the electrochemical active specific surface area of ​​Comparative Examples 1 to 4 (equivalent to the average of multiple positive electrode sheets tested simultaneously); the electrochemical active specific surface area of ​​the positive electrode sheets obtained in Comparative Examples 5 to 8 is shown in [reference needed]. Figure 10 Among them, the ferrocene CV method is the electrochemically active specific surface area of ​​comparative examples 5 to 8 (average of two replicates);

[0160] The CV curves of Examples 5 to 8 are shown below. Figures 11 to 14 The linear fitting of the integral area and scanning speed in Examples 5 to 8 is shown in [reference needed]. Figure 15The electrochemical active surface area of ​​the negative electrode sheets to be tested in Examples 5 to 8 was calculated using formula (2). The relationship between the electrochemical active surface area of ​​the negative electrode sheets to be tested obtained in Examples 5 to 8 and the coating weight of the negative electrode sheets to be tested is shown in [reference needed]. Figure 16 (Where, the dashed line represents the average of three repetitions); the electrochemically active specific surface area of ​​the negative electrode sheets obtained in Examples 5 to 8 and Comparative Examples 9 to 12 is shown in the figure. Figure 17 In this application, the electrochemically active specific surface area (average of three replicates) of Examples 5 to 8 is used; the BET method is used for the electrochemically active specific surface area of ​​Comparative Examples 9 to 12 (equivalent to the average of multiple negative electrode sheets tested simultaneously); the electrochemically active specific surface area of ​​the negative electrode sheets obtained in Comparative Examples 13 to 16 is shown in [reference needed]. Figure 18 Among them, the electrochemically active specific surface area of ​​ferrocene CV method is the average of two replicates of comparative examples 13 to 16.

[0161] Depend on Figures 3 to 6 It can be seen that the shape of each CV curve selected in Examples 1 to 4 is approximately rectangular, indicating that double-layer behavior mainly occurs and no electrochemical redox reaction occurs. Furthermore, the consistency of the four replicates of each example at each scan rate is good. Figure 7 It can be seen that the integral area in Examples 1 to 4 has a good correlation with the scanning speed, and the consistency of the four repetitions in each example is good; Figure 8 It can be seen that the electrochemically active surface area of ​​the positive electrode obtained in Examples 1 to 4 shows a good linear relationship with the coating weight of the positive electrode, and the consistency of the four replicates in each example is good; Figure 9 It can be seen that the specific surface area of ​​the positive electrode obtained in Examples 1 to 4 is smaller than that obtained in Comparative Examples 1 to 4. This is mainly because the BET method results include both electroactive and non-electroactive sites, while the results of this application primarily include only electroactive sites. Furthermore, compared to Comparative Examples 1 to 4, the specific surface area of ​​the positive electrode obtained in Examples 1 to 4 fluctuates more smoothly under the coating weight of the positive electrode, essentially remaining on a horizontal line. That is, under the same design, as the mass of the active material of the electrode increases, the specific surface area of ​​the tested electrode remains essentially unchanged. Figure 9 and Figure 10 It can be seen that the electrochemically active specific surface area of ​​the positive electrode sheets obtained in Examples 1 to 4 is on the order of magnitude (m²). 2 The surface area of ​​the positive electrode obtained in Comparative Examples 5 to 8 ( / g) is orders of magnitude larger than the specific surface area of ​​the electrochemically active electrode (cm²) of the positive electrode obtained in Comparative Examples 5 to 8. 2 / g), mainly because the ferrocene CV method can only test the electroactive sites on the surface of porous positive electrode sheets and cannot quickly penetrate into the interior of porous positive electrode sheets; indicating that this application can improve the accuracy of the electrochemical activity specific surface area test of positive electrode sheets.

[0162] Depend on Figures 11 to 14 It can be seen that the shape of each CV curve selected in Examples 5 to 8 is approximately rectangular, indicating that double-layer behavior mainly occurs and no electrochemical redox reaction occurs. Furthermore, the consistency of the three repetitions of each example at each scan rate is good. Figure 15 It can be seen that the integral area in Examples 5 to 8 has a good correlation with the scanning speed, and the consistency of the three repetitions of each example is good; Figure 16 It can be seen that the electrochemically active surface area of ​​the negative electrode obtained in Examples 5 to 8 increases with the increase of the coating weight of the negative electrode, which basically conforms to the rule, and the consistency of the three repetitions of each example is good; Figure 17 It can be seen that the specific surface area of ​​the electrochemically active negative electrode obtained in Examples 5 to 8 is smaller than that obtained in Comparative Examples 9 to 12. This is mainly because the results of the BET method include both electroactive and non-electroactive sites, while the results of this application primarily include only electroactive sites. Figure 17 and Figure 18 It can be seen that the electrochemically active specific surface area of ​​the negative electrode sheets obtained in Examples 5 to 8 is on the order of magnitude (m²). 2 The surface area of ​​the negative electrode obtained in Comparative Examples 13 to 16 ( / g) is orders of magnitude larger than the electrochemically active specific surface area of ​​the negative electrode obtained in Comparative Examples 13 to 16 (cm²). 2 / g), mainly because the ferrocene CV method can only test the electroactive sites on the surface of porous negative electrode sheets and cannot quickly penetrate into the interior of porous negative electrode sheets; indicating that this application can improve the accuracy of the electrochemical activity specific surface area test of negative electrode sheets.

[0163] In summary, this application can improve the accuracy of electrode electrochemical activity specific surface area testing. Furthermore, from Figure 9 and Figure 17 It can be seen that this application, when used for positive electrode sheets, can further improve the accuracy of the electrochemical activity specific surface area test of the electrode sheets.

[0164] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for testing electrochemically active specific surface area, characterized in that, Includes the following steps: Provide a battery with the electrode to be tested; Determine the voltage range in which the battery exhibits double-layer behavior, and the multiple scan rates corresponding to the voltage range; Obtain CV curves for multiple scan rates within the voltage range; Based on multiple CV curves, obtain multiple integral areas corresponding to the multiple scanning velocities; Multiple scanning speeds and their corresponding integral areas are matched one-to-one to form multiple coordinate points. Linear fitting is performed through multiple coordinate points to obtain the slope of the fitted line. The electrochemically active specific surface area of ​​the electrode under test is determined based on the slope.

2. The method for testing electrochemically active specific surface area as described in claim 1, characterized in that, In the step of providing a battery with an electrode to be tested, the battery is in a fully discharged state.

3. The method for testing electrochemically active specific surface area as described in claim 1 or 2, characterized in that, In the step of providing a battery with an electrode to be tested, the battery includes a button cell, a stacked cell, or a pouch cell.

4. The method for testing electrochemically active specific surface area as described in any one of claims 1 to 3, characterized in that, In the step of providing a battery with an electrode to be tested, the electrode to be tested is a positive electrode.

5. The method for testing electrochemically active specific surface area according to any one of claims 1 to 4, characterized in that, In the step of providing a battery with an electrode to be tested, the electrode to be tested is a porous electrode.

6. The method for testing electrochemically active specific surface area according to any one of claims 1 to 5, characterized in that, In the step of determining the voltage range for the battery to perform double-layer behavior and the multiple scan speeds corresponding to the voltage range, the number of test points for CV curve scanning at each scan speed is greater than or equal to 20.

7. The method for testing electrochemically active specific surface area according to any one of claims 1 to 6, characterized in that, In the step of determining the voltage range for the battery to perform double-layer behavior and the multiple scan speeds corresponding to the voltage range, the number of scan speeds is greater than or equal to 4.

8. The method for testing electrochemically active specific surface area according to any one of claims 1 to 7, characterized in that, In the step of determining the electrochemically active specific surface area of ​​the electrode under test based on the slope, the electrochemically active specific surface area of ​​the electrode under test is calculated using the following formula: Among them, S A The specific surface area of ​​the electrode under test is the electrochemically active surface area, in m². 2 / g; k a The slope; k is the electrostatic constant; d represents the thickness of the electric double layer, in meters (m). ε is the relative permittivity of the electrolyte in the battery; m is the mass of the active material of the electrode to be tested, in grams; ΔU is the difference in voltage range, in units of V.

9. The method for testing electrochemically active specific surface area according to any one of claims 1 to 8, characterized in that, After determining the electrochemically active specific surface area of ​​the electrode under test based on the slope, the method further includes: The electrochemical active surface area of ​​the electrode under test is determined based on the electrochemical active specific surface area.

10. The method for testing electrochemically active specific surface area as described in claim 9, characterized in that, In the step of determining the electrochemical active surface area of ​​the electrode under test based on the electrochemical active specific surface area, the electrochemical active surface area of ​​the electrode under test is calculated using the following formula: S=mS A (2) Where S is the electrochemical active surface area of ​​the electrode under test, in m². m is the mass of the active material of the electrode to be tested, in grams; S A The specific surface area of ​​the electrode under test is the electrochemically active surface area, in m². 2 / g.

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