Method for detecting lithium intercalation content of negative electrode sheet

Abstract

An embodiment of the present application discloses a method for detecting the lithium intercalation content of a negative electrode sheet. The detection method does not require the production of a button cell. After the battery cell is charged or discharged, the battery cell is disassembled to take the negative electrode sheet for XRD testing, avoiding the problem of large deviation in the detection result caused by the loss of material during the cutting of the negative electrode sheet for the production of the button cell. Through the XRD spectrum information, from the LiC6 stage of the negative electrode sheet to the peak intensity change of the LiC 12 stage, combined with the theoretical specific capacity per gram of the carbon material, the graphitization degree of the carbon material, and the N / P value of the battery cell, the actual specific capacity of the carbon material is calculated. The lithium intercalation content of the negative electrode sheet is calculated based on the actual specific capacity of the carbon material. It is not affected by the polarization during the charge and discharge of the battery cell, and the result deviation is within the range of 0-5%. The test method is simple to operate, removing the unstable factors in the button cell test. By utilizing the phase change that occurs during the lithium intercalation process of graphite, the intrinsic change of the crystal structure is characterized by XRD testing, the test result is more intuitive, the detection accuracy is high, the detection time is short, and the detection efficiency is high.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a method for detecting the lithium intercalation content of a negative electrode sheet. Background Art

[0002] X-ray diffraction (XRD) testing has been widely used in the study of the microscopic crystal structure of materials, and it can reflect structural information such as the crystal plane spacing, unit cell size, and phase of crystals. The carbon material in the negative electrode sheet of a lithium battery, such as graphite crystals, will undergo regular changes during the charge and discharge of the battery.

[0003] In the failure analysis of batteries, the detection and calculation of the capacity loss of the positive and negative electrodes are generally involved. Among them, in the evaluation of the negative electrode capacity loss, it is often evaluated by making a coin cell to test the specific capacity. This requires cutting a negative electrode sheet of a certain size from the negative electrode sheet of the failed battery, making it into a coin cell, and performing a low-rate test to calculate the lithium intercalation state of the negative electrode sheet. However, for this coin cell production, a negative electrode sheet of a certain size needs to be cut, generally with a diameter greater than 10 mm. When cutting the disassembled negative electrode sheet, the electrode sheet is brittle and prone to material loss, resulting in a large deviation in the test. Due to the many processes in making the coin cell, it is extremely easy to cause unstable testing, and the test requires a low-rate test, which takes a long time. Summary of the Invention

[0004] The embodiments of this application provide a method for detecting the lithium intercalation content of a negative electrode sheet, which can solve the problems of large deviation, poor stability, and long time consumption in the existing coin cell test for negative electrode capacity loss.

[0005] The embodiments of this application provide a method for detecting the lithium intercalation content of a negative electrode sheet, including the following steps:

[0006] Take an electric core, the electric core includes a positive electrode sheet and a negative electrode sheet. After charging or discharging the electric core, disassemble the electric core and take the negative electrode sheet. The negative electrode sheet includes a carbon material;

[0007] Process the negative electrode sheet to obtain a test sample;

[0008] XRD test: Perform an XRD test on the test sample, with the scanning range of 24° to 28°, obtain the XRD pattern of the test sample, find the characteristic peak of LiC6 in the XRD pattern and record the peak intensity H6 of the characteristic peak of LiC6, and find the characteristic peak of LiC 12 and record the peak intensity H of the characteristic peak of LiC 12 ; 12 ;

[0009] Calculate the actual specific capacity Q of the carbon material according to formula (1) real :

[0010] Qreal = Theoretical specific capacity per gram of carbon material × G / A... Equation (1); in Equation (1), G is the graphitization degree of the carbon material, A is the N / P value of the battery cell, N is the capacity of the negative electrode sheet per unit area, and P is the capacity of the positive electrode sheet per unit area;

[0011] Calculate the lithium intercalation content Q of the negative electrode sheet according to Equation (2) C :

[0012] Q C = Q real × B6 + (Q real / 2) × B 12 ... Equation (2); in Equation (2), B6 is the content of LiC6 in the negative electrode sheet, B6 = H6 / (H6 + H 12 )), B 12 is the content of LiC 12 in the negative electrode sheet, B 12 = 1 - B6.

[0013] Optionally, it further includes: calculating the content M of the carbon material in the negative electrode sheet according to Equation (3):

[0014] M = S × F × K × E... Equation (3); in Equation (3), S is the product of the length and width of the battery cell, F is the areal density of the battery cell, K is the number of negative electrode sheets in the battery cell, and E is the mass content of the carbon material in the negative electrode sheet; calculate the remaining specific capacity Q of the negative electrode sheet after the battery cell is fully charged or discharged according to Equation (4) 余 :

[0015] Q 余 = D / M... Equation (4); in Equation (4), D is the capacity of the battery cell after full charge, or D is the remaining capacity of the battery cell after full discharge.

[0016] Optionally, calculate the deviation value Q C between the lithium intercalation content Q of the negative electrode sheet and the remaining specific capacity Q 余 of the negative electrode sheet according to Equation (5) 偏 :

[0017] Q 偏 = ∣Q C - Q 余 ∣ / Q 余 ... Equation (5).

[0018] Optionally, 0 ≤ Q 偏 ≤ 5%.

[0019] Optionally, the carbon material is selected from any one of graphite, soft carbon, and hard carbon.

[0020] Optionally, 0.9 < G < 0.98.

[0021] Optionally, in the XRD test step, the wavelength of the X-ray is 1.540593 angstroms, and the scanning speed is 2° / min.

[0022] Optionally, in the XRD test step, the characteristic peak of LiC6 is searched in the range of 24° to 25°, and the characteristic peak of LiC6 is searched in the range of 25° to 26°.

[0023] Optionally, 1.1 < A < 1.5.

[0024] Optionally, the negative electrode sheet includes a negative electrode current collector and negative electrode active material layers provided on two surfaces of the negative electrode current collector, and the negative electrode active material layers include the carbon material; the step of processing the negative electrode sheet to obtain a test sample further includes: after cleaning the negative electrode sheet, removing the negative electrode active material layer on one surface of the negative electrode current collector to expose one surface of the negative electrode current collector; the XRD test step further includes: attaching the exposed surface of the negative electrode current collector to the test bench of the XRD diffractometer, and pasting a protective film on the side of the negative electrode active material layer facing away from the negative electrode current collector.

[0025] The beneficial effect of the present application is to provide a method for detecting the lithium intercalation content of a negative electrode sheet. The detection method does not require the production of a button cell. After the battery cell is charged or discharged, the battery cell is disassembled to take the negative electrode sheet for XRD testing, avoiding the problem of large deviation in the detection result caused by the loss of materials during the cutting of the negative electrode sheet for making the button cell. Through the XRD pattern information, from the LiC6 stage to LiC 12 stage, the change in the peak intensity, combined with the theoretical specific capacity per gram of the carbon material, the graphitization degree of the carbon material, and the N / P value of the battery cell, calculates the actual specific capacity of the carbon material, and calculates the lithium intercalation content of the negative electrode sheet based on the actual specific capacity of the carbon material. It is not affected by the polarization during the charge and discharge of the battery cell, and the result deviation is within the range of 0 to 5%. The test method is simple to operate, removes the unstable factors in the button cell test, utilizes the phase change occurring during the lithium intercalation process of graphite, and characterizes the intrinsic change of the crystal structure through XRD testing. The test result is more intuitive, the detection accuracy is high, the detection time is short, and the detection efficiency is high. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0027] Figure 1It is the XRD pattern of the negative electrode sheet in the method for detecting the lithium intercalation content of the negative electrode sheet provided in Embodiment 1 of the present application;

[0028] Figure 2 It is the XRD pattern of the negative electrode sheet in the method for detecting the lithium intercalation content of the negative electrode sheet provided in Embodiment 2 of the present application. Specific embodiments

[0029] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0030] In the specific embodiments and the claims, a list of items connected by the term "at least one of" may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements. The term "at least one of" has the same meaning as the term "at least one of".

[0031] In this specification, a numerical range indicated by using "~" means a range including the values recited before and after "~" as the minimum value and the maximum value, respectively.

[0032] The embodiments of the present application provide a method for detecting the lithium intercalation content of a negative electrode sheet. The detection method does not require making a button cell. After the battery cell is charged or discharged, the battery cell is disassembled to take the negative electrode sheet for XRD testing, avoiding the problem of large deviation in the detection result caused by the loss of the negative electrode sheet during the cutting of the button cell. Through the XRD pattern information, from the LiC6 stage to LiC of the negative electrode sheet 12The change in the peak intensity of the stage, combined with the theoretical specific capacity per gram of the carbon material, the graphitization degree of the carbon material, and the N / P value of the battery cell, is used to calculate the actual specific capacity per gram of the carbon material. Based on the actual specific capacity per gram of the carbon material, the lithium intercalation content of the negative electrode sheet is calculated. It is not affected by the polarization during the charge and discharge of the battery cell, and the result deviation is within the range of 0-5%. The test method is simple to operate, eliminates the unstable factors in the coin cell test, and utilizes the phase change that occurs during the lithium intercalation process of graphite. Through XRD testing, the intrinsic changes in the crystal structure are characterized. The test results are more intuitive, the detection accuracy is high, the detection time is short, and the detection efficiency is high.

[0033] A secondary battery, such as a lithium-ion battery, includes a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and a casing. Among them, the positive electrode sheet, the separator, and the negative electrode sheet constitute the battery cell. The battery cell is formed by winding or stacking the positive electrode sheet and the negative electrode sheet, and the separator is disposed between the positive electrode sheet and the negative electrode sheet. Among them, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a carbon material, such as graphite, soft carbon, or hard carbon, preferably graphite.

[0034] Taking graphite as an example, when lithium intercalation / deintercalation (Li) occurs in graphite, the interlayer spacing of the graphite crystal will change. Generally, it is considered that there are four stages of changes from fully lithiated graphite to completely de-lithiated graphite: the four stages of changes are LiC6→LiC 12 →LiC 24 →C. LiC6 represents fully lithiated graphite, and C represents completely de-lithiated graphite.

[0035] The interlayer spacings corresponding to the changes in these four stages are also different. Therefore, when performing XRD testing on the negative electrode sheet, specific characteristic peaks will appear at specific stages. Among them, there is a change in the peak intensity of the characteristic peak corresponding to the stage of LiC6→LiC 12 This peak intensity can represent the amount of lithium present in the negative electrode active material (such as graphite) at this stage. By comparing the content of LiC6 and LiC 12 at this stage, combined with the theoretical specific capacity per gram of the carbon material, the graphitization degree of the carbon material, and the N / P value of the battery cell, the actual specific capacity per gram of the carbon material is calculated. Based on the actual specific capacity per gram of the carbon material, the lithium intercalation content of the negative electrode sheet is calculated.

[0036] In some embodiments, the method for detecting the lithium intercalation content of the negative electrode sheet includes the following steps:

[0037] 110) Disassemble the battery cell and take the negative electrode sheet

[0038] Take the battery cell to be disassembled and put it into a glove box for disassembly. The glove box has an argon environment with a water content <1 ppm and an oxygen content <1 ppm. The disassembled negative electrode sheet is washed and soaked in dimethyl carbonate for 5 min and then dried.

[0039] Among them, the negative electrode sheet includes a negative electrode current collector and negative electrode active material layers provided on two surfaces of the negative electrode current collector. The negative electrode active material layer includes a carbon material, and the carbon material includes any one of graphite, soft carbon, and hard carbon, preferably graphite. The negative electrode current collector is aluminum foil or copper foil, preferably copper foil.

[0040] 120) Process the negative electrode sheet to obtain a test sample

[0041] Place the negative electrode sheet on a glass plate slightly larger than the negative electrode sheet, stick the periphery of the negative electrode sheet firmly with tape, take it out of the glove box, let it stand for 1 h, gently wipe one surface of the negative electrode sheet with deionized water, and erase the negative electrode active material layer on one surface of the negative electrode current collector (copper foil) until the negative electrode current collector is completely exposed (at this time, only one surface of the negative electrode current collector is provided with the negative electrode active material layer), then place it in the glove box, cut it along the tape with a cutter, take an appropriate size, make the exposed surface of the negative electrode current collector fit the test bench of the XRD diffractometer, and paste a protective film on the side of the negative electrode active material layer facing away from the negative electrode current collector to isolate the negative electrode active material layer from the outside world, thus obtaining a test sample.

[0042] In some embodiments, the protective film is a kapton film, and the Kapton film is a polyimide (PI) thin film material produced by DuPont Company in the United States.

[0043] 130) XRD test:

[0044] Perform an XRD test on the test sample. The XRD diffractometer uses a copper target, the wavelength is 1.540593 Å, the tube voltage is 40 kV, the current is 50 mA, the slit is 1 / 2, the step size is 0.01°, the scanning range is 24° to 28°, the scanning speed is 2° / min. After the test, search for the characteristic peak of LiC6 near 24° to 25° and record the peak intensity H6 of the characteristic peak of LiC6. Search for the characteristic peak of LiC 12 and record the characteristic peak of LiC 12 and record the peak intensity H 12 .

[0045] Among them, during the XRD test, it is necessary to remove the influence of the test background generated by the XRD diffractometer itself.

[0046] 140) Calculate the actual specific capacity Q of the carbon material according to formula (1) real :

[0047] Q real = theoretical specific capacity of carbon material × G / A... formula (1);

[0048] In formula (1), G is the graphitization degree of the carbon material, where 0.9 < G < 0.98, A is the N / P value of the battery cell, where 1.1 < A < 1.5, N is the negative electrode sheet capacity per unit area, and P is the positive electrode sheet capacity per unit area.

[0049] For the negative electrode sheet after charging or discharging, due to factors such as the graphitization degree G, the formation of the SEI film, and other side reactions, the actual specific capacity of the carbon material will be lower than its theoretical specific capacity.

[0050] In some embodiments, the carbon material is graphite, and the theoretical specific capacity of graphite is 372 mAh / g.

[0051] 150) Calculate the lithium intercalation content Q of the negative electrode sheet according to formula (2) C :

[0052] Q C = Q real × B6 + (Q real / 2) × B 12 …… formula (2);

[0053] In formula (2), B6 is the content of LiC6 in the negative electrode sheet, B6 = H6 / (H6 + H 12 ), B 12 is the content of LiC 12 in the negative electrode sheet, B 12 = 1 - B6.

[0054] Among them, when there is a two-phase change of LiC6 → LiC 12 , two characteristic peaks at different positions will appear in the XRD pattern. The proportion of the two phases B6 and B 12 is determined by comparing the peak intensities of the two-phase characteristic peaks.

[0055] In some embodiments, the method for detecting the lithium intercalation content of the negative electrode sheet further includes a step of confirming the accuracy of the detection result of the lithium intercalation content of the negative electrode sheet. Specifically, it includes:

[0056] Calculate the content M of the carbon material in the negative electrode sheet according to formula (3):

[0057] M = S × F × K × E... formula (3);

[0058] In formula (3), S is the product of the length and width of the battery cell, F is the areal density of the battery cell, K is the number of negative electrode sheets in the battery cell, and E is the mass content of the carbon material in the negative electrode sheet.

[0059] Calculate the remaining specific capacity Q 余 of the negative electrode sheet after the battery cell is fully charged or discharged according to formula (4):

[0060] Q 余= D / M... Equation (4);

[0061] In Equation (4), D is the capacity of the battery cell after charging is completed, or D is the remaining capacity of the battery cell after discharging is completed.

[0062] Calculate the lithium intercalation content Q of the negative electrode sheet according to Equation (5) C and the remaining specific capacity Q of the negative electrode sheet 余 The deviation value Q between them 偏 :

[0063] Q 偏 = ∣Q C - Q 余 ∣ / Q 余 ... Equation (5).

[0064] That is, Q 偏 is the ratio of the absolute value of the difference between Q C and Q 余 to Q 余 .

[0065] In some embodiments, 0 ≤ Q 偏 ≤ 5%.

[0066] The following is an explanation of the method for detecting the lithium intercalation content of the negative electrode sheet provided by the present application with reference to specific embodiments:

[0067] Embodiment 1

[0068] 110) Disassemble a failed battery cell and take the negative electrode sheet:

[0069] Take the battery cell to be disassembled and charge the battery cell to a capacity D of 136 mAh. The battery cell includes one positive electrode sheet and two negative electrode sheets, that is, the number of negative electrode sheets K is 2. The length of the battery cell is 5.4 cm and the width is 4.4 cm. That is, S = 5.4 cm × 4.4 cm. The N / P value A of the battery cell is 1.12. The negative electrode active material in the negative electrode sheet is graphite, the graphitization degree G is 0.95, and the mass content of graphite in the negative electrode sheet is 96%, that is, E is 0.96. The areal density F of the battery cell is 11.32 mg / cm 2 , put the battery cell to be disassembled into the glove box. The glove box has an argon environment with a water content < 1 ppm and an oxygen content < 1 ppm. Disassemble the battery cell to obtain the negative electrode sheet, soak the disassembled negative electrode sheet in dimethyl carbonate for 5 min, and dry it.

[0070] 120) Prepare test samples:

[0071] Place the negative electrode sheet on a glass plate slightly larger than the size of the negative electrode sheet, tape the four sides firmly, take it out of the glove box, let it stand for 1 h, gently wipe one surface of the negative electrode sheet with deionized water, and erase the negative electrode active material layer on one surface of the copper foil until the copper foil is completely exposed (at this time, only one surface of the copper foil is provided with the negative electrode active material layer), then place it in the glove box, cut it along the tape with a cutter, take an appropriate size, make the exposed surface of the negative electrode current collector fit the test bench of the XRD diffractometer, and paste the kapton film on the side of the negative electrode active material layer facing away from the negative electrode current collector to the test bench to seal it from the outside world.

[0072] 130) XRD sample test:

[0073] The XRD diffractometer uses a copper target, the wavelength is 1.540593 Å, the tube voltage is 40 kV, the current is 50 mA, the slit is 1 / 2, the step size is 0.01°, the scanning range is 24° to 28°, and the scanning speed is 2° / min. After the test, the XRD pattern as shown is obtained. Search for the characteristic peak of LiC6 near 24.5° and record the peak intensity H6 of the characteristic peak of LiC6 as 1185 a.u., search for the LiC12 characteristic peak near 25.7° and record the peak intensity H6 of the characteristic peak of LiC6 as 568 a.u. Figure 1 Then, the content B6 of LiC6 in the negative electrode sheet = 1185 / (1185 + 568) = 67.6%, and the content B of LiC in the negative electrode sheet

[0074] = 1 - 67.6% = 32.4%. 12 of 12 is

[0075] 140) Calculate the actual specific capacity Q of graphite real :

[0076] Q real = theoretical specific capacity of graphite × G / A = 372 mAh / g × 0.95 / 1.12 = 315.5 mAh / g.

[0077] 150) Calculate the lithium intercalation content Q of the negative electrode sheet C :

[0078] Q C = Q real × B6 + (Q real / 2) × B 12 = 315.5 × 67.6% + (315.5 / 2) × 32.4% = 264.4 mAh / g.

[0079] Accuracy confirmation of the detection result Q of the lithium intercalation content of the negative electrode sheet C :

[0080] Calculate the content M of carbon material in the negative electrode sheet:

[0081] M = S × F × K × E = 5.4 cm × 4.4 cm × 11.32 mg / cm 2 × 2 × 0.96 = 516 mg = 0.516 g.

[0082] Calculate the remaining specific capacity Q of the negative electrode sheet after the battery cell is fully charged 余 :

[0083] Q 余 = D / M = 136 mAh / 0.516 g = 263.6 mAh / g.

[0084] Calculate the lithium intercalation content Q of the negative electrode sheet C and the deviation value Q 余 between the remaining specific capacity Q of the negative electrode sheet 偏 :

[0085] Q 偏 = |Q C - Q 余 | / Q 余 = |264.4 - 263.6| / 263.6 = 0.3%, indicating that the accuracy of the lithium intercalation content Q of the negative electrode sheet measured by the lithium intercalation content detection method of the negative electrode provided in the embodiments of the present application is relatively high. C The accuracy is relatively high.

[0086] Example 2

[0087] 110) Disassemble a failed battery cell and take the negative electrode sheet:

[0088] Take the battery cell to be disassembled, discharge the battery cell to be disassembled by 21 mAh. After discharging, the capacity of the battery cell is 136 mAh, that is, D = 136 mAh - 21 mAh = 115 mAh. The battery cell includes one positive electrode sheet and two negative electrode sheets, that is, the number K of negative electrode sheets is 2. The length of the battery cell is 5.4 cm and the width is 4.4 cm, that is, S = 5.4 cm × 4.4 cm. The N / P value A of the battery cell is 1.12. The negative electrode active material in the negative electrode sheet is graphite, the graphitization degree G is 0.95, and the mass content of graphite in the negative electrode sheet is 96%, that is, E is 0.96. The areal density F of the battery cell is 11.32 mg / cm 2 , put the battery cell to be disassembled into a glove box. The glove box has an argon environment, the water content < 1 ppm, and the oxygen content < 1 ppm. Disassemble the battery cell to obtain the negative electrode sheet. Immerse the disassembled negative electrode sheet in dimethyl carbonate and clean it for 5 min, and then dry it.

[0089] 120) Prepare test samples:

[0090] Place the negative electrode sheet on a glass plate slightly larger than the size of the negative electrode sheet, tape the four sides firmly, take it out of the glove box, let it stand for 1 h, gently wipe one surface of the negative electrode sheet with deionized water, and erase the negative electrode active material layer on one surface of the copper foil until the copper foil is completely exposed (at this time, only one surface of the copper foil is provided with the negative electrode active material layer), then place it in the glove box, cut it along the tape with a cutter, take an appropriate size, make the exposed surface of the negative electrode current collector fit the test bench of the XRD diffractometer, and paste the kapton film on the side of the negative electrode active material layer facing away from the negative electrode current collector to the test bench to seal it from the outside.

[0091] 130) XRD sample test:

[0092] The XRD diffractometer uses a copper target, the wavelength is 1.540593 Å, the tube voltage is 40 kV, the current is 50 mA, the slit is 1 / 2, the step size is 0.01°, the scanning range is 24° to 28°, and the scanning speed is 2° / min. After the test, the XRD pattern as shown in Figure 2 is obtained. Search for the characteristic peak of LiC6 near 24.5° and record the peak intensity H6 of the characteristic peak of LiC6 as 1126 a.u., and search for the LiC12 characteristic peak near 25.7° and record the peak intensity H6 of the characteristic peak of LiC6 as 1520 a.u.

[0093] Then, the content B6 of LiC6 in the negative electrode sheet = 1126 / (1126 + 1520) = 42.6%, and the content B 12 of 12 in the negative electrode sheet = 1 - 42.6% = 57.4%.

[0094] 140) Calculate the actual specific capacity Q real of graphite:

[0095] Q real = graphite theoretical specific capacity × G / A = 372 mAh / g × 0.95 / 1.12 = 315.5 mAh / g.

[0096] 150) Calculate the lithium intercalation content Q C of the negative electrode sheet:

[0097] Q C = Q real × B6 + (Q real / 2) × B 12 = 315.5 × 42.6% + (315.5 / 2) × 57.4% = 225.0 mAh / g.

[0098] Accuracy confirmation of the detection result Q C of the lithium intercalation content of the negative electrode sheet:

[0099] Calculate the content M of carbon material in the negative electrode sheet:

[0100] M=S×F×K×E=5.4cm×4.4cm×11.32mg / cm 2 ×2×0.96=516mg=0.516g.

[0101] Calculate the remaining gram capacity Q of the negative electrode after the battery is fully charged 余 :

[0102] Q 余 =D / M=(136mAh-21mAh) / 0.516g=222.9mAh / g.

[0103] Calculate the lithium content Q of the negative electrode C The remaining gram capacity Q of the negative electrode 余 The deviation value Q 偏 :

[0104] Q 偏 =|Q C -Q 余 ∣ / Q 余 =|225.0-222.9| / 222.9=0.9%, indicating that the negative electrode lithium insertion content Q measured by the negative electrode lithium insertion content detection method provided in the embodiment of the present application is C The accuracy is higher.

[0105] The above is a detailed introduction to a method for detecting the lithium content of a negative electrode sheet provided in an embodiment of the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for technical personnel in this field, according to the idea of the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for detecting the lithium intercalation content of a negative electrode sheet, characterized in that, It includes the following steps: Take an electrode cell, the electrode cell includes a positive electrode sheet and a negative electrode sheet. After charging or discharging the electrode cell, disassemble the electrode cell, take the negative electrode sheet, and the negative electrode sheet includes a carbon material; Process the negative electrode sheet to obtain a test sample; XRD test: Perform XRD test on the test sample, with the scanning range of 24° to 28°, obtain the XRD pattern of the test sample, search for the characteristic peak of LiC6 in the XRD pattern and record the peak intensity H6 of the characteristic peak of LiC6, search for the characteristic peak of LiC 12 in the XRD pattern and record LiC 12 of the characteristic peak and record the peak intensity H 12 ; Calculate the actual specific capacity Q of the carbon material according to Equation (1). real : Q real = Theoretical specific capacity of carbon material × G / A... Equation (1); In formula (1), G is the graphitization degree of the carbon material, A is the N / P value of the electrode cell, N is the capacity of the negative electrode sheet per unit area, and P is the capacity of the positive electrode sheet per unit area; Calculate the lithium intercalation content Q of the negative electrode sheet according to formula (2). C : Q C = Q real ×B6 + (Q real / 2)×B 12 …… Equation (2); In formula (2), B6 is the content of LiC6 in the negative electrode sheet, B6 = H6 / (H6 + H 12 ), B 12 is the content of LiC 12 in the negative electrode sheet, B 12 = 1 - B6; Calculate the content M of the carbon material in the negative electrode sheet according to formula (3): M = S×F×K×E... formula (3); In formula (3), S is the product of the length and width of the electrode cell, F is the areal density of the electrode cell, K is the number of negative electrode sheets in the electrode cell, and E is the mass content of the carbon material in the negative electrode sheet; After charging or discharging of the battery cell is completed, the remaining specific capacity Q of the negative electrode plate is calculated according to formula (4). 余 :[[]]END]] Q 余 = D / M……Equation (4); In formula (4), D is the capacity of the electrode cell after charging is completed, or D is the remaining capacity of the electrode cell after discharging is completed; 0.9＜G＜0.98； In the XRD test step, the wavelength of the X-ray is 1.540593 angstroms, and the scanning speed is 2° / min; 1.1＜A＜1.5。 2. The method for detecting the lithium intercalation content of the negative electrode sheet according to claim 1, wherein, Calculate the lithium intercalation content Q of the negative electrode sheet according to formula (5). C And the remaining specific capacity Q of the negative electrode sheet 余 The deviation value Q between them 偏 : Q 偏 = |Q C -Q 余 | / Q 余 …… Equation (5).

3. The method for detecting the lithium intercalation content of the negative electrode sheet according to claim 2, wherein 0≤Q 偏 ≤5%。 4. The method for detecting the lithium intercalation content of the negative electrode sheet according to claim 1, wherein, The carbon material is selected from any one of graphite, soft carbon, and hard carbon.

5. The method for detecting the lithium intercalation content of the negative electrode sheet according to claim 1, wherein In the XRD test procedure, search for the characteristic peak of LiC6 in the range of 24° to 25°, and search for the characteristic peak of LiC 12 in the range of 25° to 26°.

6. The method for detecting the lithium intercalation content of the negative electrode sheet according to claim 1, wherein, The negative electrode sheet includes a negative electrode current collector and negative electrode active material layers provided on two surfaces of the negative electrode current collector, and the negative electrode active material layers include the carbon material; The step of processing the negative electrode sheet to obtain a test sample further includes: cleaning the negative electrode sheet and then removing the negative electrode active material layer on one surface of the negative electrode current collector to expose one surface of the negative electrode current collector; The XRD test step further includes: attaching the exposed surface of the negative electrode current collector to the test bench of the XRD diffractometer and pasting a protective film on the side of the negative electrode active material layer facing away from the negative electrode current collector.

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