A method for preparing a lithium battery pole piece cross-section sample

Abstract

The present invention relates to a method for preparing cross-sectional samples of lithium battery pole pieces, and belongs to the technical field of cross-sectional sample preparation. The method comprises: drying the disassembled pole piece, heating and plastic-sealing it, and then cutting it into samples; pasting a silicon wafer on a sample table, and pasting the sample on the silicon wafer; using a conductive medium to connect the plastic film on the pole piece surface and the silicon wafer at multiple points to improve the conductivity of the pole piece; and ion milling the sample to obtain it. This method solves the problem of pole piece material falling off by reinforcing the lithium battery pole piece through plastic sealing. It is simple to operate, takes less time, improves the success rate of ion milling, and reduces the preparation cost. At the same time, scanning electron microscopy and energy spectrum analysis can be directly performed without gold or carbon spraying.

Description

Technical Field

[0001] The present invention belongs to the technical field of cross-section sample preparation, and in particular relates to a method for preparing a cross-section sample of a lithium battery pole piece. Background Art

[0002] Lithium-ion batteries offer advantages such as no memory effect, environmental friendliness, and high energy density. After decades of development, they are widely used in portable electronic devices such as laptops, mobile phones, and cameras, bringing great convenience to people's lives. However, to meet the current demand for electric vehicles, lithium-ion batteries still need much improvement. For example, the battery's poor cycling stability under high temperature and high voltage conditions has become one of the key factors restricting the large-scale application of lithium-ion batteries in electric vehicles. Lithium battery positive electrode materials can improve their high-temperature and high-voltage performance by modifying the material structure through processes such as doping and coating. The improved positive electrode materials need to be prepared into batteries and their electrical properties tested. The electrical properties are analyzed to evaluate the quality of the doping and coating processes.

[0003] During the charge and discharge cycles of lithium batteries, the internal structure and porosity of the electrode material plates change, shortening the cycle life of the lithium battery materials. This requires cross-sectional polishing of lithium battery material plates to observe and analyze the internal structure and porosity of the plate samples. Currently, several methods are used to prepare cross-sectional samples of lithium battery material plates. One is metallographic grinding and polishing using resin embedding techniques. This involves complex sample preparation steps, is time-consuming, and easily contaminates and damages the surface structure, resulting in poor conductivity and unsatisfactory preparation results. The second method is FIB (focused ion beam). While FIB is suitable for preparing small samples, lithium battery material plates are typically around 200μm thick. Using FIB for sample preparation is unscientific, costly, and ineffective for observing large areas. The third method is direct argon ion cross-sectional polishing, but this can lead to plate collapse and poor polishing results. This is especially true for test cycle battery plates, where poor adhesion between the active material and the current collector due to electrolyte immersion. Therefore, a new method for preparing cross-sectional samples of plate plates is needed to address these issues. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a method for preparing a lithium battery electrode cross-section sample, and its technical solution is as follows:

[0005] A method for preparing cross-sectional samples of lithium battery pole pieces includes: drying and heat-sealing the disassembled pole pieces, and then cutting them into samples; attaching a silicon wafer to a sample stage, and attaching the sample to the silicon wafer; using a conductive medium to connect the plastic film on the pole piece surface and the silicon wafer at multiple points to improve the pole piece's conductivity; and ion milling the sample. The resulting cross-sectional sample is vacuum-transferred to a scanning electron microscope sample stage. The pole piece does not require carbon spraying or metal conductive layer conductivity treatment and can be directly subjected to scanning electron microscopy and energy spectrum analysis.

[0006] Furthermore, the disassembly environment is: temperature is 20-25°C, humidity is below 1%.

[0007] Preferably, the drying process is an air-drying process; more preferably, the residual electrolyte after the air-drying process does not affect the vacuum degree of the scanning electron microscope; further preferably, the air-drying time is 30-60 minutes.

[0008] Preferably, before the heating and plastic sealing, the electrode is flattened and placed in the plastic sealing film.

[0009] Preferably, the thickness of the heat-sealed plastic film is less than 0.10 mm; more preferably, the thickness of the heat-sealed plastic film is 0.03-0.10 mm.

[0010] Preferably, the temperature of the heating and plastic sealing is 90-110°C.

[0011] Optionally, the heat-sealed plastic film is PET and / or EVA, preferably a composite material of PET and EVA.

[0012] Furthermore, the area of ​​the sample is smaller than the area of ​​the silicon wafer.

[0013] Preferably, the cutting direction is perpendicular to the surface of the pole piece.

[0014] Optionally, the conductive medium is a conductive liquid or a liquid conductive glue.

[0015] Furthermore, the maximum operating voltage of the ion milling is 6 kV, and the operating time is between 0.5-1 h.

[0016] Preferably, the upper surface of the sample is 1.5-2.5 mm higher than the upper surface of the silicon wafer to prevent the argon ion beam from penetrating the sample and bouncing off the silicon wafer, causing sample contamination.

[0017] Furthermore, the lithium battery includes one of a button battery, a cylindrical battery, a soft-pack battery or a square aluminum shell battery.

[0018] The lithium battery pole piece cross-section sample preparation method of the present invention solves the problem of pole piece material falling off by reinforcing the lithium battery pole piece through plastic sealing. The operation is simple, time-saving, and the success rate of ion milling is improved, and the preparation cost is reduced. At the same time, scanning electron microscopy and energy spectrum analysis can be directly performed without gold spraying or carbon spraying. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a low-magnification scanning electron microscope image of the cross section of the cylindrical lithium-ion battery positive electrode material piece prepared in Example 1 of the present invention, wherein: Figure 1 Part a is the positive electrode material, and part b is the aluminum foil;

[0021] Figure 2 This is a high-magnification scanning electron microscope image of the cross section of the cylindrical lithium-ion battery positive electrode material piece prepared in Example 1 of the present invention, wherein: Figure 2 Part c is the positive electrode material, and part d is the aluminum foil;

[0022] Figure 3 This is a low-magnification scanning electron microscope image of a cross-section of a positive electrode material piece for a button lithium-ion battery prepared in Example 2 of the present invention, wherein: Figure 3 Part e is the positive electrode material, and part f is the aluminum foil;

[0023] Figure 4 This is a high-magnification scanning electron microscope image of the cross section of the positive electrode material for a button lithium-ion battery prepared in Example 2 of the present invention, wherein: Figure 4 Part g is the positive electrode material, and part h is the aluminum foil;

[0024] Figure 5 This is a scanning electron microscope image of the cross section of the positive electrode material of the button lithium ion battery prepared in Comparative Example 1, wherein: Figure 5 Part i is the positive electrode material, and part j is the aluminum foil;

[0025] Figure 6 This is a scanning electron microscope image of the cross section of the cylindrical lithium-ion battery positive electrode material prepared in Comparative Example 2, wherein: Figure 6 The k part is the positive electrode material, and the l part is the aluminum foil. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0027] Example 1

[0028] A method for preparing a lithium battery electrode cross-section sample is as follows:

[0029] (1) Use diagonal pliers to tear the edge of the cylindrical battery cap outward, then lift the cap, cut off the tabs, and then use diagonal pliers to slowly tear open the steel shell and take out the battery cell.

[0030] (2) Slowly unfold the wound battery cell and separate the positive electrode, negative electrode and diaphragm. Pay attention to the alignment of the diaphragm and the positive and negative electrodes during the process. Use heavy objects to press the ends of the electrode and diaphragm so that the entire electrode and diaphragm are flat on the table.

[0031] (3) Use a hair dryer to air dry the disassembled lithium battery electrodes for at least 30 minutes to ensure that the residual electrolyte does not affect the scanning electron microscope test.

[0032] (4) Flatten the air-dried positive (negative) electrode and place it in a 0.05 mm thick plastic film. Set the temperature of the plastic sealing machine to 90°C and heat-seal the electrode. Ensure that the electrode is not wrinkled during the plastic sealing process, and the plastic sealing cooling time is not less than 10 minutes. The plastic sealing film is a composite material of PET and EVA.

[0033] (5) Use a paper cutter to cut the electrode perpendicular to the surface of the plastic-sealed electrode to obtain a sample with a length of 1.2 cm and a width of 1.2 cm. Glue the silicon wafer with a length of 1.5 cm and a width of 1.5 cm to the sample stage with glue, ensuring that the silicon wafer is about 3-5 mm higher than the sample stage after bonding.

[0034] (6) Paste the cut sample on the silicon wafer, ensuring that the upper surface of the sample is about 2 mm higher than the upper surface of the silicon wafer.

[0035] (7) Use liquid conductive glue to connect the plastic film and silicon wafer at multiple points to improve the conductivity of the electrode.

[0036] (8) Place the sample stage under a microscope and select a suitable area for positioning so that the sample is approximately 50 μm above the sample stage baffle. Place the positioned sample in an ion mill for thinning. Use cross-section milling with a working voltage of 6 kV and a working time of 50 min to obtain a smooth and contamination-free cross-section sample.

[0037] The prepared cross-section sample is vacuum-transferred to the scanning electron microscope sample stage, and the electrode is directly subjected to scanning electron microscopy and energy spectrum analysis without the need for carbon spraying or metal conductive layer conductive treatment.

[0038] Figure 1 A low-magnification scanning electron microscope image of a cross section of a cylindrical lithium-ion battery positive electrode material electrode piece prepared in this embodiment is shown. Figure 1 Part a is the positive electrode active material, and part b is the aluminum foil. It can be seen that the positive electrode active material is evenly distributed above and below the aluminum foil, among which the positive electrode active material is evenly dispersed and some particles are broken. Figure 2 for Figure 1 The scanning electron microscope image shown is an enlarged cross-sectional view of the positive electrode sheet of a lithium-ion battery. Part c is the positive electrode active material and part d is the aluminum foil. It can be seen that although cracks appear in the positive electrode material after cycling and the secondary particles gradually pulverize into single particles, during the sample preparation process, based on the plastic sealing step, the cross-section of the sample does not collapse and is not contaminated by the plastic sealing film. This shows that the sample prepared by the method of the present application is conducive to characterization and observation.

[0039] Example 2

[0040] A method for preparing a lithium battery electrode cross-section sample is as follows:

[0041] (1) Use diagonal pliers to tear the edge of the button battery cap outward, then lift the cap and remove the positive electrode, diaphragm, lithium sheet and gasket (nickel foam).

[0042] (2) Place the disassembled positive electrode of the lithium-ion battery flat on the table and use a hair dryer to air dry it for at least 30 minutes to ensure that the residual electrolyte does not affect the scanning electron microscope test.

[0043] (3) Flatten the air-dried positive (negative) electrode and place it in a 0.05 mm thick plastic film. Set the laminating machine temperature to 90°C and heat-laminate. Ensure that the electrode is wrinkle-free during laminating. Cool down for at least 10 minutes after laminating. The plastic film is made of PET.

[0044] (4) Use a paper cutter to cut the electrode perpendicular to the surface of the plastic-sealed electrode to obtain a sample with a length of 1.2 cm and a width of 1.2 cm. Glue the silicon wafer with a length of 1.5 cm and a width of 1.5 cm to the sample stage, ensuring that the silicon wafer is about 3-5 mm higher than the sample stage after bonding.

[0045] (5) Paste the cut sample on the silicon wafer, ensuring that the upper surface of the sample after bonding is about 2 mm higher than the upper surface of the silicon wafer.

[0046] (6) Use liquid conductive glue to connect the plastic film and silicon wafer at multiple points to improve the conductivity of the electrode.

[0047] (7) Place the sample stage under the microscope and select a suitable area for positioning so that the sample is approximately 50 μm above the sample stage baffle. Place the positioned sample in an ion mill for thinning. Use cross-section milling with a working voltage of 6 kV and a working time of 35 min to obtain a smooth and contamination-free cross-section sample.

[0048] The prepared cross-section sample is vacuum-transferred to the scanning electron microscope sample stage, and the electrode is directly subjected to scanning electron microscopy and energy spectrum analysis without the need for carbon spraying or metal conductive layer conductive treatment.

[0049] Figure 3 A low-magnification scanning electron microscope image of the cross-section of the positive electrode sheet of the button lithium battery prepared in this embodiment is shown, wherein part e is the positive electrode active material and part f is the aluminum foil. It can be seen that the positive electrode active material and the conductive agent are evenly distributed on the aluminum foil, wherein the positive electrode active material is evenly dispersed and some particles are broken. Figure 4 for Figure 3 The scanning electron microscope image shown is an enlarged cross-sectional view of the positive electrode of a lithium-ion battery, where part g is the positive electrode active material and part h is the aluminum foil. Figure 4 It can be seen that the positive electrode particles gradually break from the spherical edge to the inside, and the particle edges are severely damaged.

[0050] Comparative Example 1

[0051] A method for preparing a lithium battery electrode cross-section sample is as follows:

[0052] (1) Use diagonal pliers to tear the edge of the button battery cap outward, then lift the cap and remove the positive electrode, diaphragm, lithium sheet and gasket (nickel foam).

[0053] (2) Place the disassembled positive electrode of the lithium-ion battery flat on the table and use a hair dryer to air dry it for at least 30 minutes to ensure that the residual electrolyte does not affect the scanning electron microscope test.

[0054] (3) Use a paper cutter to cut perpendicularly to the surface of the electrode to obtain a sample with a length of 1.2 cm and a width of 1.2 cm. Use glue to stick the silicon wafer with a length of 1.5 cm and a width of 1.5 cm on the sample stage, ensuring that the silicon wafer is about 3-5 mm higher than the sample stage after bonding.

[0055] (4) Paste the cut sample on the silicon wafer, ensuring that the upper surface of the sample after bonding is about 2 mm higher than the upper surface of the silicon wafer.

[0056] (5) Use liquid conductive glue to connect the electrode and silicon wafer at multiple points to improve the conductivity of the electrode.

[0057] (6) Place the sample stage under the microscope and select a suitable area for positioning so that the sample is approximately 50 μm above the sample stage baffle. Place the positioned sample in an ion mill for thinning using a cross-section milling method with a working voltage of 6 kV and a working time of 35 min.

[0058] The prepared cross-section sample was vacuum transferred to the scanning electron microscope sample stage for scanning electron microscopy and energy spectrum analysis.

[0059] Figure 5 The scanning electron microscope image of the sample cross section after argon ion milling in this comparative example is shown, wherein part i is the positive electrode active material and part j is the aluminum foil. Figure 3 and 5 A comparison shows that direct use of argon ion beam grinding causes the active material to crack and fall off, resulting in surface contamination of the sample and inability to characterize the sample well.

[0060] Comparative Example 2

[0061] A method for preparing a lithium battery electrode cross-section sample is as follows:

[0062] (1) Use diagonal pliers to tear the edge of the cylindrical battery cap outward, then lift the cap, cut off the tabs, and then use diagonal pliers to slowly tear open the steel shell and take out the battery cell.

[0063] (2) Slowly unfold the wound battery cell and separate the positive electrode, negative electrode and diaphragm. Pay attention to the alignment of the diaphragm and the positive and negative electrodes during the process. Use heavy objects to press the ends of the electrode and diaphragm so that the entire electrode and diaphragm are flat on the table.

[0064] (3) Use a hair dryer to air dry the disassembled lithium battery electrodes for at least 30 minutes to ensure that the residual electrolyte does not affect the scanning electron microscope test.

[0065] (4) Flatten the air-dried positive electrode and place it in a 0.2 mm thick plastic film. Set the laminating machine temperature to 150°C and heat-laminate. Ensure that the electrode is wrinkle-free during laminating. Cool down for at least 10 minutes after laminating. The plastic film is made of PET.

[0066] (5) Use a paper cutter to cut perpendicularly to the surface of the electrode to obtain a sample with a length of 1.2 cm and a width of 1.2 cm. Use glue to stick the silicon wafer with a length of 1.5 cm and a width of 1.5 cm on the sample table, ensuring that the silicon wafer is about 3-5 mm higher than the sample table after bonding.

[0067] (6) Paste the cut sample on the silicon wafer, ensuring that the upper surface of the sample is about 2 mm higher than the upper surface of the silicon wafer.

[0068] (7) Use liquid conductive glue to connect the plastic film and silicon wafer at multiple points to improve the conductivity of the electrode.

[0069] (8) Place the sample stage under the microscope and select a suitable area to position the sample so that it is approximately 50 μm above the sample stage baffle. Place the positioned sample in an ion mill for thinning using a cross-section milling method with a working voltage of 6 kV and a working time of 50 min.

[0070] The prepared cross-section sample was vacuum transferred to the scanning electron microscope sample stage for scanning electron microscopy and energy spectrum analysis.

[0071] Figure 6 The scanning electron microscope low-magnification image of the cross section of the cylindrical lithium-ion battery positive electrode material of this comparative example is shown, wherein the k part is the positive electrode active material, the l part is the aluminum foil, Figure 6 It can be seen that when the thickness of the aluminum-plastic film is thicker, there is more pollution on the electrode, which affects the test observation of the electrode. The edge of the sample particles is seriously contaminated, and the charging phenomenon is more serious, causing image deformation and poor test results.

[0072] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of this application, several variations and improvements can be made, which all fall within the scope of protection of this application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A method for preparing a lithium battery pole piece cross-section sample, characterized in that: include: The disassembled electrode pieces are dried, heated and plastic-sealed, and then cut into samples; Pasting a silicon wafer on a sample stage, and pasting the sample on the silicon wafer; Use conductive medium to connect the plastic film on the surface of the electrode and the silicon wafer at multiple points to improve the conductivity of the electrode; The sample is subjected to ion milling to obtain the electrode sheet selected from a cycle battery electrode sheet; The thickness of the heat-sealed plastic film is 0.03-0.10 mm; The temperature of the heating and plastic sealing is 90-110°C; The plastic sealing film for heat sealing is PET and / or EVA.

2. The method for preparing a lithium battery pole piece cross-section sample according to claim 1, characterized in that: The plastic sealing film is a composite material of PET and EVA.

3. The method for preparing a lithium battery pole piece cross-section sample according to claim 1, wherein: The drying process is air drying; The residual electrolyte after air drying does not affect the vacuum degree of the scanning electron microscope; The air-drying time is 30-60 minutes.

4. The method for preparing a lithium battery pole piece cross-section sample according to claim 1, characterized in that: The area of ​​the cut sample is smaller than the area of ​​the silicon wafer; The cutting direction is perpendicular to the surface of the pole piece.

5. The method for preparing a lithium battery pole piece cross-section sample according to claim 1, characterized in that: The conductive medium is liquid conductive glue.

6. The method for preparing a lithium battery pole piece cross-section sample according to claim 1, characterized in that: The maximum operating voltage of the ion milling is 6 kV, and the operating time is between 0.5 and 1 hour.

7. The method for preparing a lithium battery pole piece cross-section sample according to claim 1, characterized in that: The upper surface of the sample is 1.5-2.5 mm higher than the upper surface of the silicon wafer.

8. The method for preparing a lithium battery pole piece cross-section sample according to claim 1, characterized in that: The lithium battery includes one of a button battery, a cylindrical battery, a soft pack battery or a square aluminum shell battery.

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