A method for measuring thickness or thickness change rate of an electric core during charging and discharging

Abstract

The present application relates to the technical field of battery manufacturing, in particular to a kind of determination method of the thickness or thickness change rate of battery cell in charging and discharging process, including sample preparation step, charging and discharging and XRD test step and calculating thickness step, first battery cell is handled by charging and discharging, while in situ XRD test is carried out to battery cell, respectively, the diffraction angle of SOC, negative electrode characteristic peak and the diffraction angle of positive electrode characteristic peak are obtained, and the following formula is substituted into, the thickness of battery cell in charging and discharging process can be calculated: Di=3*λ / [2*sin(X a / 2)]+a*λ / [2*sin(X b / 2)], method is simple and fast, and the accuracy of conventional method is obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery manufacturing, in particular to a method for measuring the thickness or thickness change rate of an electric core in a charging and discharging process. BACKGROUND

[0002] When an electric core is assembled into a module or a package, its thickness will change with the charging and discharging, and because of the restraint force of the module or the package, the constraint force of the electric core will also change. In order to exert the excellent performance of the electric core, the selection of the constraint force of the electric core becomes particularly important. Generally, an initial force is given to the electric core, and the change of the thickness or the force of the electric core in the charging and discharging process is tested to predict the optimal constraint force of the electric core. The soft package is mapped to the square battery, thereby providing a basis for the selection of the constraint force of the electric core.

[0003] At present, the change of the thickness of the electric core in the charging and discharging cycle process is mainly measured by a vernier caliper. This testing method is complex to operate and has a large safety hazard. Therefore, the prior art also discloses a in-situ expansion force testing system for testing the thickness of the electric core. However, this kind of testing the thickness change of the electric core from the soft package experiment requires certain precise testing equipment, and the testing is relatively complex. The thickness change of the pole group of the square shell electric core is also generally mapped from the thickness change of the soft package electric core, thereby increasing the error sources.

[0004] Therefore, there is an urgent need for a method for simply and accurately measuring the thickness or thickness change of the electric core in the charging and discharging process. SUMMARY

[0005] Therefore, the technical problem to be solved by the present application is to overcome the defect that the thickness or thickness change of the electric core in the charging and discharging process of the battery cannot be accurately measured in the prior art, thereby providing a method for measuring the thickness or thickness change rate of the electric core in the charging and discharging process.

[0006] The present application provides a method for testing the thickness of an electric core in a charging and discharging process, comprising the following steps:

[0007] A sample preparation step: assembling a positive electrode sheet containing a positive electrode active material and a negative electrode sheet containing a negative electrode active material into a full battery as an electric core; and / or, assembling a positive electrode sheet containing a positive electrode active material and a negative electrode sheet containing a negative electrode active material with a lithium sheet into a positive electrode material half-cell and a negative electrode material half-cell, respectively, as an electric core.

[0008] A charging and discharging and XRD testing step: performing in-situ XRD testing while performing charging and discharging treatment on the electric core, collecting the diffraction angle of the negative electrode active material characteristic peak and the diffraction angle of the positive electrode active material characteristic peak of the electric core in the charging and discharging process;

[0009] The calculation step: according to the diffraction angle and the ratio of the molar number of active material per unit area of the negative plate to the molar number of active material per unit area of the positive plate, the thickness of the battery is calculated according to the following formula:

[0010] Thickness Di=3*λ / [2*sin(X a / 2)]+a*λ / [2*sin(X b / 2)], wherein a is the ratio of the molar number of active material per unit area of the negative plate to the molar number of active material per unit area of the positive plate, Xa and Xb are the diffraction angles corresponding to the characteristic peaks of the positive active material (003) and the negative active material (002) respectively, and λ is the wavelength.

[0011] In the present application, the thickness of the battery is the thickness corresponding to a pair of positive and negative electrode unit molecules, Di is the real-time thickness corresponding to a pair of positive and negative electrode unit molecules during the charging and discharging process, which is referred to as real-time thickness. D0 is Di when SOC is 0%, which is referred to as initial thickness. D1 is Di when SOC is 100%, which is referred to as terminal thickness.

[0012] The diffraction angle has two units, degrees and radians. In all formulas in the present application, the unit of the diffraction angle is radian.

[0013] The term SOC, state of charge, also called remaining capacity, is used to reflect the remaining capacity of the battery, and its value is defined as the percentage of the actual capacity to the rated capacity.

[0014] In the present application, the diffraction angle during charging can be collected, and the diffraction angle during discharging can also be collected to calculate the thickness or thickness change rate during charging or discharging.

[0015] In the present application, the positive plate or the negative plate can be obtained after the tested battery is disassembled, or it can be prepared by using the same type of positive active material and negative active material as the raw material of the tested battery through a conventional process.

[0016] In the present application, a full battery can be used as a battery, and a half battery can also be used to test the thickness of the tested battery.

[0017] Further, it further includes the steps of calculating the initial thickness and / or the terminal thickness:

[0018] Further, the diffraction angles of the characteristic peaks of the negative active material and / or the positive active material at SOC of 0% or SOC of 100% are collected, and the steps of calculating the initial thickness and / or the terminal thickness are calculated according to the following formula:

[0019] Terminal thickness D0=3*λ / [2*sin(X3 / 2)]+a*λ / [2*sin(X4 / 2)];

[0020] Initial thickness D1 = 3*λ / [2*sin(X1 / 2)] + a*λ / [2*sin(X2 / 2)];

[0021] Wherein, X1 is the diffraction angle corresponding to the characteristic peak of the positive electrode active material (003) when the SOC is 0%, X2 is the diffraction angle corresponding to the characteristic peak of the negative electrode active material (002) when the SOC is 0%, X3 is the diffraction angle corresponding to the characteristic peak of the positive electrode active material (003) when the SOC is 100%, and X4 is the diffraction angle corresponding to the characteristic peak of the negative electrode active material (002) when the SOC is 100%.

[0022] The present invention also provides a method for measuring the cell thickness change rate during charging and discharging, comprising the cell thickness measurement method during charging and discharging as described above, and further comprising calculating the cell thickness change rate according to one or more of the following formulas. Di's steps:

[0023] Di = (Di - D1) / D1 * 100% (I); or, Di = (D0 - Di) / D0 * 100%.

[0024] Furthermore, this also includes using SOC as the x-axis, and... The steps to generate the SOC-thickness change rate relationship curve with Di as the ordinate.

[0025] Furthermore, the number of moles of active material per unit area of ​​the negative electrode sheet is calculated according to the following formula: Number of moles of active material per unit area of ​​the negative electrode sheet = Areal density of the negative electrode sheet * Content of the negative electrode active material / Molar mass of the negative electrode active material; The number of moles of active material per unit area of ​​the positive electrode sheet is calculated according to the following formula: Number of moles of active material per unit area of ​​the positive electrode sheet = Areal density of the positive electrode sheet * Content of the positive electrode active material / Molar mass of the positive electrode active material.

[0026] Furthermore, the voltage range during the charge-discharge process of the positive electrode material half-cell is 3-4.4V, the voltage range during the charge-discharge process of the negative electrode material half-cell is 0.005-2V, and the voltage range during the charge-discharge process of the full cell is 2.8-4.35V.

[0027] Furthermore, the step size during XRD diffraction is controlled to be 0.005-0.02°, preferably 0.009-0.011°.

[0028] Furthermore, X a Within the range of 17.5° to 19°, X b Within the range of 24° to 29°.

[0029] Further, the XRD diffractometer adopts a copper target, the slit is 1 / 4-1 / 2, and the scanning speed is 2°-5° / min.

[0030] In some preferred embodiments, the positive electrode active material is selected from one or more of layered positive electrode active materials, preferably ternary positive electrode active materials, cobalt-free binary positive electrode active materials. It can be combined with the current collector by using conventional processes such as coating and cold pressing. Specifically, the positive electrode active material, the conductive agent, and the binder are mixed uniformly according to the conventional proportion and added to the solvent to prepare a positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, dried and cold pressed, and then cut and striped to prepare a positive electrode sheet. The solid content of the positive electrode slurry can be 70-75%, the conductive agent can be a conventional conductive agent such as acetylene black, the binder can be a conventional binder such as styrene-butadiene rubber or polyvinylidene fluoride PVDF, and the solvent can be a conventional organic solvent such as N-methyl pyrrolidone NMP.

[0031] In some preferred embodiments, the negative electrode active material is selected from at least one of graphite, hard carbon, soft carbon, and mesocarbon microbeads. It can be combined with the current collector by using conventional processes such as coating and cold pressing. Specifically, the negative electrode active material, the conductive agent, and the binder are mixed according to the conventional proportion, added to the solvent water, mixed uniformly, and prepared into a negative electrode slurry; the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, dried, and cold pressed to prepare a negative electrode sheet. The solid content of the negative electrode slurry can be 50-55%, the conductive agent can be a conventional conductive agent such as acetylene black, and the binder can be a conventional binder such as styrene-butadiene rubber or polyvinylidene fluoride PVDF.

[0032] The electrode liquid of the present application can use a conventional commercially available lithium ion electrolyte, or can be self-made from existing conventional materials, for example, an electrolyte including a solvent, a lithium salt, and an additive, the solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate. The lithium salt is selected from lithium hexafluorophosphate and / or lithium tetrafluoroborate; the additive is selected from at least one of vinylene carbonate, propylene carbonate, ethylene sulfate, and lithium difluorophosphate. The molar concentration of the lithium salt is 0.8-1.2 mol / L, and a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1-1:2 can be used as the solvent. The present application can use existing conventional separators, such as PE separators, PP separators, PP / PE composite films, or other commercially available separators.

[0033] The technical scheme of the present application has the following advantages:

[0034] 1. The main part of the electrode group of the battery cell is generally composed of positive electrode sheets, negative electrode sheets, electrolyte and separators in the longitudinal direction, wherein the positive electrode sheets and the negative electrode sheets participate in the reaction during the charging and discharging process, the separators do not participate in the reaction, and the electrolyte belongs to the liquid phase, so the thickness change of the electrode group is mainly caused by the positive electrode sheets and the negative electrode sheets. For the positive electrode sheets and the negative electrode sheets, the active material accounts for more than 90%, which is the main reason for the thickness change.

[0035] The positive active material includes a layered structure of ternary positive active material, cobalt-free binary positive material, etc. During the charging and discharging process, lithium ions are deintercalated, and the crystal c-axis direction is contracted and expanded. Because of the preferred orientation of the positive electrode sheet active material, the thickness change direction is basically the same as the c-axis change direction, and the (003) peak is the characteristic peak of the reaction active material c-axis change, so the characteristic peak (003) of the positive electrode sheet can be tested by in-situ XRD. Similarly, the graphite negative electrode is also a layered structure, and the (002) peak is tested to calculate the change in the longitudinal direction of the electrode sheet.

[0036] The method for measuring the thickness of the battery cell during the charging and discharging process provided by the application comprises a sample preparation step, a charging and discharging and XRD testing step, and a thickness calculation step. The battery cell is first subjected to charging and discharging treatment, and in-situ XRD testing is performed on the battery cell at the same time. The diffraction angles of the SOC, the negative electrode characteristic peak and the positive electrode characteristic peak are obtained respectively, and are substituted into the following formula to calculate the thickness of the battery cell during the charging and discharging process: Di=3*lambda / [2*sin(X a / 2)]+a*lambda / [2*sin(X b / 2)], which is simple and fast, and the accuracy is obviously improved compared with the conventional method.

[0037] 2. The method for measuring the thickness of the battery cell during the charging and discharging process provided by the application can obtain a small polarization and a test result closer to the intrinsic state of the battery through small-rate testing.

[0038] 3. The method for measuring the thickness of the battery cell during the charging and discharging process provided by the application is simple to operate, does not need to be made into a large battery cell, finds the reason for the thickness change from the material level, can calculate the trend and change rule, saves time and cost, and provides a basis for the design of the battery cell, the module and the pack. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0040] Figure 1The change of the (003) characteristic peak in the charging process of the positive electrode material half battery in Example 1 of the present application;

[0041] Figure 2 The relationship curve between the positive electrode layer spacing and the SOC in the charging process of the positive electrode material half battery in Example 1 of the present application;

[0042] Figure 3 The change of the (002) characteristic peak in the charging process of the negative electrode material half battery in Example 1 of the present application;

[0043] Figure 4 The relationship curve between the negative electrode layer spacing and the SOC in the charging process of the negative electrode material half battery in Example 1 of the present application;

[0044] Figure 5 The relationship curve between the thickness change rate and the SOC in the charging process of the battery cell in Example 1 of the present application;

[0045] Figure 6 The change of the (003) characteristic peak in the charging process of the positive electrode material half battery in Example 2 of the present application;

[0046] Figure 7 The relationship curve between the positive electrode layer spacing and the SOC in the charging process of the positive electrode material half battery in Example 2 of the present application;

[0047] Figure 8 The change of the (002) characteristic peak in the charging process of the negative electrode material half battery in Example 2 of the present application;

[0048] Figure 9 The relationship curve between the negative electrode layer spacing and the SOC in the charging process of the negative electrode material half battery in Example 2 of the present application;

[0049] Figure 10 The relationship curve between the thickness change rate and the SOC in the charging process of the battery cell in Example 2 of the present application;

[0050] Figure 11 The comparison chart of the relationship curve between the thickness change rate and the SOC in the charging process of the battery cell in Example 1 and Example 2 of the present application, the upper curve is Example 1, and the lower curve is Example 2;

[0051] Figure 12 The comparison chart of the relationship curve between the thickness change rate and the SOC in the charging process of the battery cell in Comparative Example 1 and Comparative Example 2, the upper curve is Comparative Example 1, and the lower curve is Comparative Example 2. DETAILED DESCRIPTION

[0052] The following examples are provided to better enable those skilled in the art to further understand and practice the present application, and are not intended to limit the scope of the present application, and are not intended to limit the scope of the present application, and are not intended to limit the content and scope of protection of the present application, and any person who is inspired by the present application or combines the present application with other prior art features to obtain any product which is the same or similar to the present application falls within the scope of protection of the present application.

[0053] If the specific experimental steps or conditions are not indicated in the examples, the operation or conditions can be carried out according to the conventional experimental steps described in the literature in the art. If the reagents or instruments are not indicated by the manufacturer, they are conventional reagent products that can be obtained by purchase.

[0054] Example 1

[0055] The present embodiment provides a method for measuring the thickness of the battery cell and the thickness change rate during the charging and discharging process of the medium nickel-graphite system, comprising the following steps:

[0056] S1, sample preparation step, comprising the following steps:

[0057] I. Obtaining positive and negative electrode sheets

[0058] Take the existing battery cell, disassemble it in a glove box environment, the glove box is in an argon environment, the water content is <1 ppm, the oxygen content is <1 ppm, carefully take out the positive and negative electrode sheets, put them into DMC (dimethyl carbonate) for thorough cleaning, dry them, and place the positive and negative electrode sheets on glass plates, paste them tightly around the edges with tape, take them out of the glove box, wipe the positive electrode with NMP (nitrogen methyl pyrrolidone) on one side, wipe the negative electrode with deionized water on one side, put them into the glove box, cut them into positive and negative electrode sheets with a diameter of 12 mm. The positive electrode sheet includes an aluminum foil and a positive electrode material combined on the aluminum foil, the positive electrode material contains conductive agent acetylene black, binder polyvinylidene fluoride and positive electrode active material, the mass ratio is 2.2:1.2:96.6, the molecular formula of the positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 O2, the molar mass is 96.93 g / mol, and the positive electrode surface density is 19 mg / cm 2 The negative electrode sheet includes a copper foil and a negative electrode material combined on the copper foil, the negative electrode material contains conductive agent acetylene black, binder styrene-butadiene rubber and negative electrode active material, the mass ratio is 1:3:96, the negative electrode active material is graphite, the molecular formula is C, the molar mass is 12 g / mol, and the negative electrode surface density is 11.31 mg / cm 2The ratio a of the number of moles of active material per unit area of the negative electrode sheet to the number of moles of active material per unit area of the positive electrode sheet is a = (the surface density of the negative electrode sheet * the content of the negative electrode active material / the molar mass of the negative electrode active material) / (the surface density of the positive electrode sheet * the content of the positive electrode active material / the molar mass of the positive electrode active material) = (11.31 * 96% / 12) / (19 * 96.6% / 96.93) = 4.78.

[0059] II. Half-cell preparation step

[0060] In an argon environment in a glove box, the water content is <1 ppm, and the oxygen content is <1 ppm. The positive electrode sheet, the separator (purchased from Shanghai Enjie, model 9+3+1+1), and the lithium sheet are assembled in the in-situ XRD test tool in a stacked manner. The electrolyte (1 mol / L lithium hexafluorophosphate solution (the solvent is a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:2)) is injected, and the opening is sealed, thereby obtaining the positive electrode material half-cell. The negative electrode sheet, the separator (purchased from Shanghai Enjie, model 9+3+1+1), and the lithium sheet are assembled in the in-situ XRD test tool in a stacked manner. The electrolyte (1 mol / L lithium hexafluorophosphate solution (the solvent is a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:2)) is injected, and the opening is sealed, thereby obtaining the negative electrode material half-cell.

[0061] S2, charge-discharge and XRD test step: the positive electrode material half-cell and the negative electrode material half-cell are simultaneously subjected to charge-discharge treatment and in-situ XRD test at 25°C. The in-situ XRD mold is taken, the positive electrode material half-cell uses an aluminum foil window film, and the negative electrode material half-cell uses a single-side copper foil window film.

[0062] In the tester, the charge-discharge device is connected. During the charge-discharge process of the positive electrode material half-cell, the rate is 0.1C, the positive electrode material half-cell is first completely discharged to 3V (cut-off voltage), and then charged to 4.4V (cut-off voltage).

[0063] During the charge-discharge process of the negative electrode material half-cell, the rate is 0.1C, the negative electrode material half-cell is first charged to 2V (cut-off voltage), and then discharged to 0.005V (cut-off voltage).

[0064] The XRD diffractometer uses a copper target, the wavelength is 1.540593 angstrom, the light tube voltage is 40 kV, the current is 50 mA, the slit is 1 / 2, the step is 0.01°, and the scanning speed is 2° / min. The angle range of the positive electrode characteristic peak is set to 17.5°-19°, the angle range of the negative electrode characteristic peak is set to 24°-28°, and slow scanning is performed. The changes in the characteristic peak positions of the positive electrode active material and the negative electrode active material during the charging process are shown in FIGS. 1 and 2. Figure 1 and 3

[0065] ​The capacity data in real-time corresponding to the charging and discharging process and the diffraction angle of the characteristic peak of the negative active material and the diffraction angle of the characteristic peak of the positive active material are collected. The SOC is calculated according to the following formula: SOC = Qi / Q0*100%, Qi is the capacity of the positive material half cell or the negative material half cell when the XRD scanning is performed once, and the rated capacity is Q0. The corresponding interlayer spacing is calculated according to the Bragg formula λ = 2dsinθ. Specifically, the positive interlayer spacing = 3*λ / [2*sin(X a / 2)], and the negative interlayer spacing = λ / [2*sin(X b / 2)], X a is the diffraction angle corresponding to the characteristic peak of the positive active material (003) of the positive material half cell to be measured, X b is the diffraction angle corresponding to the characteristic peak of the negative active material (002) in the negative material half cell with the same SOC as the positive material half cell, and λ is the wavelength. The relationship curve between the SOC and the interlayer spacing is prepared with the SOC as the horizontal coordinate and the interlayer spacing as the vertical coordinate, as shown in Figure 2 and 4 .

[0066] S3, thickness calculation step

[0067] The thickness is calculated according to the following formula: thickness Di = 3*λ / [2*sin(X a / 2)]+a*λ / [2*sin(X b / 2)].

[0068] Wherein, a is the ratio of the number of moles of active material per unit area of the negative plate to the number of moles of active material per unit area of the positive plate, X a is the diffraction angle corresponding to the characteristic peak of the positive active material (003) of the positive material half cell to be measured, X b is the diffraction angle corresponding to the characteristic peak of the negative active material (002) in the negative material half cell with the same SOC as the positive material half cell, and λ is the wavelength.

[0069] S4, thickness change rate calculation step:

[0070] The thickness change rate is calculated according to the following formula: Di = (Di-D1) / D1*100%; D1 = 3*λ / [2*sin(X1 / 2)]+a*λ / [2*sin(X2 / 2)].

[0071] Wherein, X1 is the diffraction angle corresponding to the characteristic peak of the positive active material (003) when SOC is 0%, X2 is the diffraction angle corresponding to the characteristic peak of the negative active material (002) when SOC is 0%, a is the ratio of the molar number of the active material per unit area of the negative plate to the molar number of the active material per unit area of the positive plate, Di is the real-time thickness in the charging and discharging process, and D1 is the initial thickness.

[0072] S5, making a relationship curve of SOC and thickness change rate

[0073] Taking SOC as the horizontal coordinate and the thickness change rate as the vertical coordinate, a relationship curve of SOC and thickness change rate is made, as shown in FIG. 1. Figure 5

[0074] (1) Taking the positive material half-cell and the negative material half-cell both charged to SOC of 4.32% as an example, the thickness change rate is calculated. The diffraction angles corresponding to the characteristic peaks of the positive active material (003) in the positive material half-cell and the negative active material (002) in the negative material half-cell when SOC is 4.32% or 0% are shown in the following table.

[0075] Table 1: Diffraction angle / degree

[0076]

[0077] The above diffraction angles are converted into radians, and the real-time thickness, the initial thickness and the thickness change rate when SOC is 4.32% are calculated as shown in the following table:

[0078] Table 2: Test and calculation results

[0079]

[0080] (2) Taking the positive material half-cell and the negative material half-cell both discharged to SOC of 4.32% as an example, the thickness change rate is calculated. The diffraction angles corresponding to the characteristic peaks of the positive active material (003) in the positive material half-cell and the negative active material (002) in the negative material half-cell when SOC is 4.32% or 0% are shown in the following table.

[0081] Table 3: Diffraction angle / degree

[0082]

[0083] The above diffraction angles are converted into radians, and the real-time thickness, the initial thickness and the thickness change rate when SOC is 4.32% are calculated as shown in the following table:

[0084] Table 4: Test and calculation results

[0085] ​

[0086] Example 2

[0087] This example provides a method for measuring the thickness and thickness change rate of the battery cell during the charging and discharging process of the cobalt-free graphite system, which is basically the same as Example 1, the difference is only that the types and mass ratios of the positive active materials in the positive electrode sheet and the negative electrode sheet obtained by disassembling the existing battery cell are different, wherein the positive electrode material in the present application contains conductive agent acetylene black, binder polyvinylidene fluoride and positive active material, and the mass ratio is 2.2:1.8:96, the molecular formula of the positive active material is LiNi 0.75 Mn 0.25 O2, the molar mass is 96.69 g / mol, and the positive surface density is 18.68 mg / cm 2 . The negative electrode material contains conductive agent acetylene black, binder styrene-butadiene rubber and active material, and the mass ratio is 1:3:96, the negative active material is graphite, the molecular formula is C, the molar mass is 12 g / mol, and the negative surface density is 11.31 mg / cm 2 . The ratio a of the molar number of active material per unit area of the negative electrode sheet to the molar number of active material per unit area of the positive electrode sheet = (negative electrode surface density * negative active material content / molar mass of negative active material) / (positive electrode surface density * positive active material content / molar mass of positive active material) = (11.31 * 96% / 12) / (18.68 * 96% / 96.69) = 4.88.

[0088] The characteristic peak position changes of the positive active material and the negative active material during the charging process are shown in Figure 6 and 8 . The relationship curve between SOC and interlayer spacing is shown in Figure 7 and 9 . The relationship curve between SOC and thickness change rate is shown in Figure 10 .

[0089] Taking the positive electrode material half-cell and the negative electrode material half-cell charged to SOC of 4.32% as an example, the thickness change rate was calculated. The diffraction angle of the positive active material (003) characteristic peak in the positive electrode material half-cell and the diffraction angle of the negative active material (002) characteristic peak in the negative electrode material half-cell at SOC of 4.32% or 0% are shown in the following table.

[0090] Table 5 Diffraction angle / degree

[0091]

[0092] The above diffraction angle is converted into radian unit, and the real-time thickness, initial thickness and thickness change rate of SOC 4.32% are calculated as shown in the following table: The diffraction angle obtained by the test according to the above method, the calculated real-time thickness, initial thickness and thickness change rate are shown in Table 6 as follows:

[0093] Table 6 Test and calculation results

[0094]

[0095] Example 3

[0096] This embodiment provides a method for measuring the thickness and thickness change rate of the battery during the charging and discharging process of the medium nickel-graphite system, which is basically the same as Example 1, the only difference is that the XRD test step is 0.005°. The remaining steps and parameters are the same as those in Example 1.

[0097] Taking the positive electrode material half-cell and the negative electrode material half-cell both charged to SOC 4.32% as an example, the thickness change rate is calculated. The diffraction angle corresponding to the positive electrode active material (003) characteristic peak in the positive electrode material half-cell and the diffraction angle corresponding to the negative electrode active material (002) characteristic peak in the negative electrode material half-cell when SOC is 4.32% or 0% are shown in the following table.

[0098] Table 7 Diffraction angle / degree

[0099]

[0100] The above diffraction angle is converted into radian unit, and the real-time thickness, initial thickness and thickness change rate of SOC 4.32% are calculated as shown in the following table:

[0101] Table 8 Test and calculation results

[0102]

[0103] Example 4

[0104] This embodiment provides a method for measuring the thickness and thickness change rate of the battery during the charging and discharging process of the medium nickel-graphite system, which is basically the same as Example 1, the only difference is that the XRD test step is 0.015°. The remaining steps and parameters are the same as those in Example 1.

[0105] Taking the positive electrode material half-cell and the negative electrode material half-cell both charged to SOC 4.32% as an example, the thickness change rate is calculated. The diffraction angle corresponding to the positive electrode active material (003) characteristic peak in the positive electrode material half-cell and the diffraction angle corresponding to the negative electrode active material (002) characteristic peak in the negative electrode material half-cell when SOC is 4.32% or 0% are shown in the following table.

[0106] Table 9 Diffraction angle / degree

[0107]

[0108] The above diffraction angle is converted into radian unit, and the real-time thickness, initial thickness and thickness change rate of SOC of 4.32% are calculated as shown in the following table:

[0109] Table 10 Test and calculation results

[0110]

[0111] Comparative Example 1 Actual test

[0112] The in-situ expansion force test system is used to test the battery cells (not disassembled) of the same batch as Example 1, and the method is as follows: the battery cell is placed on the test plate, the pressure plate with thickness sensor is placed on the battery cell, and after fixing, the positive and negative electrodes of the battery cell are connected to the charge-discharge system, the charge-discharge steps are set, the rate is 0.1C, first fully discharged to 2.8V (cut-off voltage), then charged to 4.35V (cut-off voltage), and the charge-discharge and thickness test system are started at the same time. After the test is completed, the charge-discharge data and thickness change data are extracted. The relationship curve of SOC and thickness change rate is drawn with SOC as the horizontal coordinate and thickness change rate as the vertical coordinate, as shown in Figure 12 .

[0113] Comparative Example 2

[0114] The positive electrode sheet and the negative electrode sheet of the same batch as Example 2 are used, the positive electrode sheet, the separator (purchased from Shanghai Enjie, model 9+3+1+1), and the negative electrode sheet are assembled in a laminated manner to obtain a battery pole group, the battery pole group is placed in an aluminum plastic film for assembly, electrolyte (1 mol / L lithium hexafluorophosphate solution (solvent is a mixture of volume ratio 1:2 ethylene carbonate and diethyl carbonate)) is injected, and then sealed to obtain a soft package battery cell. The soft package battery cell is tested by the same method as Comparative Example 1, wherein the charge-discharge steps are: the rate is 0.1C, first fully discharged to 2.8V (cut-off voltage), then charged to 4.3V (cut-off voltage), and the relationship curve of SOC and thickness change rate is drawn with SOC as the horizontal coordinate and thickness change rate as the vertical coordinate, as shown in Figure 12 .

[0115] The relative deviation of the thickness change rate of Examples 1, 3-5 compared to Comparative Example 1 at SOC of 4.32%, and the relative deviation of the thickness change rate of Example 2 compared to Comparative Example 2 at SOC of 4.32% are calculated, and the results are shown in the following table.

[0116] Table 11 Relative deviation results

[0117]

[0118] From the above table and the figures, it can be seen that the experimental results of the actual test of Comparative Example 1 and Comparative Example 2 are consistent with the results calculated by the method of the present application, i.e. the change rate of the battery of the medium nickel system is greater than that of the cobalt-free system, and the change rate occurs in three stages, 0%-30% SOC, 30%-60% SOC, and 60%-100% SOC. It can be seen from the comparison of Example 1 and Examples 3-4 that by controlling the step length of XRD within the preferred range, the relative deviation can be further reduced and the accuracy can be improved.

[0119] Obviously, the above examples are only examples for the sake of clarity, and are not limitations on the embodiments. Based on the above description, other different forms of changes or variations can also be made by those of ordinary skill in the art. It is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for measuring the thickness of an electrode during charging and discharging, characterized by, The method comprises the following steps: A sample preparation step: assembling a positive electrode sheet containing a positive electrode active material and a negative electrode sheet containing a negative electrode active material into a full battery as an electric core; and / or, assembling the positive electrode sheet containing a positive electrode active material and the negative electrode sheet containing a negative electrode active material with lithium sheets into a positive electrode material half battery and a negative electrode material half battery respectively, which are collectively used as the electric core; A charging and discharging and XRD testing step: performing in-situ XRD testing on the electric core while performing charging and discharging treatment on the electric core, and collecting diffraction angles of a negative electrode active material characteristic peak and diffraction angles of a positive electrode active material characteristic peak during the charging and discharging process of the electric core; A thickness calculation step: calculating the thickness of the electric core according to the diffraction angles, the wavelength of the XRD testing, and the ratio of the molar number of the active material per unit area of the negative electrode sheet to the molar number of the active material per unit area of the positive electrode sheet according to the following formula: Thickness Di = 3 * λ / [2 * sin (X a / 2)] + a * λ / [2 * sin (X b / 2)], where a is the ratio of the number of moles of active material per unit area of the negative electrode sheet to the number of moles of active material per unit area of the positive electrode sheet, X a and X b are the diffraction angles corresponding to the characteristic peaks of the positive electrode active material (003) and the negative electrode active material (002) respectively at the same SOC, and λ is the wavelength.

2. The method of claim 1, wherein the method is characterized by, Further comprising a step of calculating an initial thickness and / or a final thickness: collecting diffraction angles of the negative electrode active material and the positive electrode active material characteristic peak at SOC of 0% and / or SOC of 100%, and calculating the initial thickness and / or the final thickness according to the following formula respectively: Final thickness D0=3*λ / [2*sin(X3 / 2)]+a*λ / [2*sin(X4 / 2)]; Initial thickness D1=3*λ / [2*sin(X1 / 2)]+a*λ / [2*sin(X2 / 2)]; Wherein, X1 is the diffraction angle corresponding to the (003) characteristic peak of the positive electrode active material at SOC of 0%, X2 is the diffraction angle corresponding to the (002) characteristic peak of the negative electrode active material at SOC of 0%, X3 is the diffraction angle corresponding to the (003) characteristic peak of the positive electrode active material at SOC of 100%, and X4 is the diffraction angle corresponding to the (002) characteristic peak of the negative electrode active material at SOC of 100%.

3. The method of claim 2, wherein the method further comprises: Also included is calculating the rate of change of thickness of the cell according to one or more of the following equations Di's steps: Di = (Di - Dl) / Dl * 100%; Di = (Do - Di) / Do * 100%.

4. The method of claim 3, wherein the method further comprises: Also included is a step of generating a relationship curve of SOC-thickness change rate with SOC as the abscissa and Di as the ordinate. Di as the ordinate.

5. The method of claim 4, wherein the method further comprises: The molar number of the active material per unit area of the negative electrode sheet is calculated according to the following formula: molar number of the active material per unit area of the negative electrode sheet = face density of the negative electrode sheet * content of the negative electrode active material / molar mass of the negative electrode active material; and the molar number of the active material per unit area of the positive electrode sheet is calculated according to the following formula: molar number of the active material per unit area of the positive electrode sheet = face density of the positive electrode sheet * content of the positive electrode active material / molar mass of the positive electrode active material.

6. The method of claim 1-5, wherein, The voltage range of the positive electrode material half battery during the charging and discharging process is 3-4.4V, the voltage range of the negative electrode material half battery during the charging and discharging process is 0.005-2V, and the voltage range of the full battery during the charging and discharging process is 2.8-4.35V.

7. The method of claim 1-5, wherein, The step length is controlled to be 0.005-0.02° during the XRD diffraction process. 8.The method of claim 7, wherein, The step length is controlled to be 0.009-0.011° during the XRD diffraction process.

9. The method of claim 1-5, wherein, X a X in the range of 17.5° to 19° b X in the range of 24° to 29°.

10. The method of claim 1-5, wherein, The XRD diffractometer uses a copper target, the slit is 1 / 4-1 / 2, and the scanning speed is 2-5° / min.

11. The method of claim 1-5, wherein, The positive electrode active material is a layered positive electrode active material; and the negative electrode active material is selected from at least one of graphite, hard carbon, soft carbon, and mesocarbon microbeads.

12. The method of claim 11, wherein the method further comprises: The positive electrode active material is one or more of a ternary positive electrode active material and a cobalt-free binary positive electrode active material.

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