Transmission electron microscope sample preparation method for battery positive electrode secondary particle pellets

Abstract

The invention relates to a transmission electron microscope sample preparation method for battery positive electrode secondary particle pellets, and belongs to the field of transmission electron microscopes. The method comprises the following specific operation steps: (1) immersing an electrode plate into a dimethyl carbonate solvent, ultrasonically dispersing and dripping the electrode plate onto a silicon wafer, and drying; (2) a complete secondary particle small ball is found under an electron beam of a concentrated ion beam system, and a protective layer is deposited on a target area on the surface of the complete secondary particle small ball; (3) fixedly welding the top end of the nano manipulator with the secondary particle small ball; (4) controlling the nanometer control hand to carry the secondary particle small balls to be separated from the silicon wafer; (5) grooves are etched in the grid columns, a second metal layer is deposited through ion beams, and the secondary particle small balls are welded to the grooves; (6) etching and separating the nano manipulator from the secondary particle spheres; and (7) carrying out thinning cleaning on the secondary particle pellets to obtain the secondary particle pellet slice for transmission electron microscope characterization. The operation steps of rough cutting, fine cutting and U-shaped cutting are omitted, and the sample preparation time is greatly shortened.

Description

Technical Field

[0001] The present invention belongs to the field of transmission electron microscopy, and specifically relates to transmission electron microscopy sample preparation using a focused ion beam system. The technical terms in the present invention refer to JY / T0583-2020 "General Rules for Analysis Methods of Focused Ion Beam Systems". Background Art

[0002] As a core component of novel energy storage systems, the electrochemical performance of lithium-ion (Na-ion) batteries (LIBs) is determined by the synergistic effects of key components, including cathode materials, anode materials, electrolytes, separators, and current collectors. The cathode material, as the primary carrier of Li-ion intercalation and deintercalation and the key driver of energy density, directly influences the battery's specific capacity, cycling stability, and thermal safety margin. While significant progress has been made in mainstream layered oxide cathode systems (such as Li / Na(Ni x Co y Mn z)O 2 ) through the coordination and manipulation of transition metals, the practical performance of LIBs remains constrained by the intrinsic structural stability and surface-interface evolution mechanisms of the materials. Crystalline anisotropy can lead to lattice distortion during cycling. The complex grain boundary network within the micron-sized secondary agglomerated particles (composed of single-crystal primary particles measuring hundreds of nanometers) of LIB cathode materials exacerbates ion diffusion kinetics, while valence fluctuations of transition metals can easily trigger irreversible phase transitions and interfacial side reactions.

[0003] In this context, transmission electron microscopy (TEM) characterization, with its atomic-level spatial resolution and multimodal analysis capabilities, has become a key breakthrough in revealing the structure-activity relationship of cathode materials. High-resolution TEM characterization allows intuitive analysis of the crystal plane arrangement of single-crystal particles, accurately capturing the dynamic evolution of defects such as lattice distortion and dislocation slip during cycling. Combined with selected-area electron diffraction and geometric phase analysis, it can quantitatively characterize the internal grain boundary misorientation and stress distribution characteristics of secondary pellets in lithium (sodium)-ion batteries, elucidating the structural failure mechanism of polycrystalline secondary pellets during ion insertion and extraction. Furthermore, chemical microanalysis techniques based on electron energy loss spectroscopy and energy-dispersive X-ray spectroscopy enable the simultaneous in situ detection of transition metal element valence gradient distributions, grain boundary element segregation, and electrode-electrolyte interface reaction products. This multi-scale, multi-dimensional microstructural information provides an irreplaceable theoretical basis for overcoming the capacity fading bottleneck of layered oxide cathode materials and optimizing the structural design of secondary pellets, and is of great guiding significance for the development of advanced battery systems with high energy density and long cycle life.

[0004] Due to the limited penetration of the electron beam, transmission electron microscopy (TEM) samples are generally required to be less than 100 nm thick. The thinner the sample, the higher the imaging quality. Ultrasonic dispersion or focused ion beam systems are currently commonly used to prepare samples for TEM of secondary particles in battery cathodes. However, ultrasonic dispersion is limited by the randomness of mechanical fragmentation, making it difficult to precisely control the sample thinning scale. Furthermore, due to the destruction of the topological structure of the secondary particles in lithium (sodium) ion batteries, cross-scale spatial correlation information is lost, hindering the analysis of key features such as grain boundary evolution and inter-particle stress distribution.

[0005] Therefore, people are now more likely to prepare transmission electron microscopy samples of secondary particle pellets of battery positive electrode materials according to the standard method of GB / T 45459-2025 "Microbeam analysis focused ion beam transmission electron microscopy sample preparation method". It is divided into 6 steps in total: (1) Deposition of protective layer: find a secondary particle spherical cap on the surface of a 200μm thick substrate composed of positive electrode material (secondary particle pellets), binder, and conductive agent, and then use electron beam and ion beam to deposit a metal layer on the spherical cap as a protective layer; (2) Rough cutting: use a large beam current to etch two wedge-shaped grooves on both sides of the protective layer area. For secondary particles with a diameter of 10μm, the dimensions of the wedge grooves on both sides need to be at least 15μm deep, 20μm wide, and 12μm long. μm; (3) Fine cutting: Use a small beam to continue cutting the side of the sample on both sides of the protective layer area; (4) U-shaped cutting: Use a small beam to etch a penetrating asymmetric U-shaped groove in the sample, and only a small area on the right side of the sample is connected to the substrate; (5) Extraction: Insert the nanomanipulator, weld the tip of the nanomanipulator to the left side of the sample, use a small beam to etch the area on the right side of the sample connected to the substrate, lift the manipulator, extract the sample from the substrate, and manipulate the manipulator to weld the sample to the TEM grid column; (6) Thinning and cleaning: Tilt the sample stage so that the grid column is parallel to the incident direction of the ion beam, select the appropriate ion beam, alternately tilt the sample stage ±0.5 to ±6.5°, and use a small beam to alternately thin the side of the sample until the sample thickness reaches the target thickness.

[0006] However, there are certain limitations when using this traditional transmission electron microscopy sample preparation method to prepare samples of secondary particle pellets of battery positive electrodes. First, since most secondary particle pellets of lithium (sodium) ion batteries are partially embedded in the electrode substrate, it is impossible to confirm whether they maintain a complete spherical structure before extraction. The morphological integrity of the particles is crucial to accurately revealing the three-dimensional distribution of pores inside the particles, the uniformity of the lattice structure, the local distribution of doping elements, the gradient change of oxygen vacancy concentration and other internal key features. Secondly, considering that the typical particle size range of secondary particle pellets of lithium (sodium) ion batteries is about 10 μm, in order to completely extract a single particle, the depth of the grooves on both sides needs to exceed 10 μm and the width needs to be greater than 10 μm during the rough cutting process of the sample preparation using the standard method, and a subsequent U-cutting step is also required, which takes a lot of time. Finally, since the base material of the positive electrode sheet is mainly composed of loose carbon black and other conductive agents, it has low mechanical strength. As a result, during the series of operations of ion thinning, sample transfer, storage, and finally loading into the transmission electron microscope sample rod, the thinned particle flakes are very easy to fall off the supporting grid, resulting in a significant reduction in the success rate of sample preparation. Summary of the Invention

[0007] In order to efficiently and stably obtain thin slices of positive electrode secondary particle beads of lithium (sodium) ion batteries for transmission electron microscopy characterization, and provide reliable technical support for accurately characterizing the microstructure of positive electrode secondary particle beads of lithium (sodium) ion batteries, the present invention provides a transmission electron microscopy sample preparation method for battery positive electrode secondary particle beads.

[0008] The steps for preparing a sample for a transmission electron microscope for secondary particles of a battery positive electrode are as follows: (1) Immerse the cut battery electrode in dimethyl carbonate solvent and ultrasonicate for 20-30 minutes to obtain solution 1; drop solution 1 onto a clean silicon wafer and wait for 2-3 minutes for the solution to dry to obtain silicon wafer 2 with the sample dropped on it.

[0009] (2) Place the silicon wafer 2 with the sample and the transmission electron microscope grid into the cavity of the focused ion beam system (FIB). Under the electron beam, find a complete spherical secondary particle ball 3 in the sample on the silicon wafer 2. Insert a gas injection system into the cavity of the focused ion beam system, and deposit a protective layer 4 on the target area on the secondary particle ball 3 by electron beam induced deposition and ion beam induced deposition respectively. The protective layer 4 consists of an inner layer and an outer layer. The material of the inner layer is carbon, and the material of the outer layer is tungsten metal or platinum metal.

[0010] (3) inserting a nanomanipulator 5 into the cavity of the focused ion beam system; manipulating the nanomanipulator 5 to move so that the tip of the nanomanipulator 5 contacts the protective layer 4 of the secondary particle ball 3, and inducing the deposition of a first metal layer 6 at the contact position by ion beam, so that the nanomanipulator 5 and the secondary particle ball 3 are welded together; The material of the first metal layer 6 is tungsten metal or platinum metal.

[0011] (4) Manipulate the nanomanipulator 5 to lift the secondary particle ball 3 upward, so that the secondary particle ball 3 is separated from the silicon wafer 2; and withdraw the gas injection system and the nanomanipulator 5 from the cavity of the focused ion beam system.

[0012] (5) Etching a groove 8 on the grid column 7 of the transmission electron microscope grid, wherein the groove width of the groove 8 is slightly smaller than the diameter of the secondary particle ball 3; inserting the gas injection system and the nanomanipulator 5 into the cavity of the focused ion beam system, manipulating the nanomanipulator 5, placing the secondary particle ball 3 on the upper part of the groove 8, so that the two sides of the secondary particle ball 3 are in contact with the two side groove edges of the groove 8, and depositing the second metal layer 9 by ion beam induction, so that the secondary particle ball 3 is welded to the upper part of the groove 8; The second metal layer 9 is made of tungsten or platinum.

[0013] (6) Ion beam etching is performed at the position where the first metal layer 6 of the nanomanipulator 5 is welded to the secondary particle ball 3 to etch away the first metal layer 6 at the welding point, so that the nanomanipulator 5 and the secondary particle ball 3 are separated, and the nanomanipulator 5 and the gas injection system are withdrawn from the cavity of the focused ion beam system.

[0014] (7) According to the standard process of GB / T 45459-2025 "Microbeam analysis focused ion beam transmission electron microscopy sample preparation method", the secondary particle beads 3 are thinned and cleaned to obtain a thin slice 10. The thickness of the thin slice 10 is less than 100 nm, and a sample of the secondary particle beads of the battery positive electrode for transmission electron microscopy characterization is obtained.

[0015] Further technical solutions are as follows: In step (1), the cut battery electrode sheet should be a positive electrode sheet with a thickness of 200 μm, which is composed of battery positive electrode secondary particle pellets, a binder, and a conductive agent.

[0016] In step (1), the transmission electron microscope grid is a half-copper grid or a half-molybdenum grid specially used for focused ion beam (FIB) system sample preparation.

[0017] In step (2), the target area is a rectangular area with a center of the secondary particle ball 3 as its center, a length equal to the diameter of the secondary particle ball, and a width of 1.5 μm.

[0018] In step (2), the protective layer 4 is first deposited by electron beam induction to form a carbon layer with a thickness of 0.4-0.5 μm, and then deposited by ion beam induction to form a tungsten metal or platinum metal layer with a thickness of 1.5-2 μm on the carbon layer.

[0019] In step (3), the metal source of the gas injection system is a platinum (Pt) source or a tungsten source.

[0020] In step (3), the thickness of the first metal layer 6 is 0.4-0.5 μm.

[0021] In step (5), the thickness of the second metal layer 9 is 0.4-0.5 μm.

[0022] In step (6), the etching conditions are: ion beam current 0.23A, acceleration voltage 30kV.

[0023] In step (7), the thinning and cleaning operation according to GB / T 45459-2025 "Microbeam Analysis Focused Ion Beam Transmission Electron Microscope Sample Preparation Method" is as follows: first, the sample stage is tilted so that the copper column where the secondary particle ball is located is parallel to the incident direction of the ion beam, and the sample stage is tilted alternately in the positive and negative directions by ±0.5° to ±6.5°, and an ion beam with an acceleration voltage of 30 kV and a suitable ion beam current is selected to thin the secondary particle ball to a suitable thickness; finally, the ion beam acceleration voltage is reduced to a low voltage of no more than 5 kV, and the small beam current is scanned on the sample surface to remove the damaged layer on the sample surface.

[0024] The beneficial technical effects of the present invention are embodied in the following aspects: 1. The present invention combines the ultrasonic dispersion method and the focused ion beam system sample preparation to prepare the secondary particle pellets for transmission electron microscopy. The ultrasonic dispersion method in the prior art is to place the electrode sheet in a dimethyl carbonate solvent for ultrasonic dispersion, and the dispersed solution is directly dripped onto the transmission electron microscope grid to find some secondary particle fragments for direct transmission electron microscopy characterization. This method requires long-term ultrasound and consumes a large amount of transmission electron microscope machine time to find samples. Moreover, this method destroys the spherical structure of the secondary particles and cannot obtain relevant spatial distribution information. The standard focused ion beam method in the prior art prepares samples directly on the electrode sheet. Since the secondary particles are deeply buried in the electrode sheet, only the spherical cap of the secondary particle pellet can be seen in the focused ion beam system. Therefore, it cannot be guaranteed that a complete secondary particle pellet is found during sample preparation. In addition, since the secondary particles are large in size, the conventional focused ion beam method takes a long time to prepare samples. Finally, the electrode substrate is mainly composed of loose carbon black conductive agents. Therefore, when the standard focused ion beam method in the prior art is used for sample preparation, these loose carbon black conductive agents are welded to the carrier mesh. During the transfer process of the carrier mesh, the loose carbon black conductive agents are easily detached, thereby causing the prepared thin slice to detach from the carrier mesh, resulting in sample preparation failure. Step (1) of the present invention is to drop the solution containing secondary particle beads after ultrasonic dispersion onto the silicon wafer. After the solution dries, the secondary particle beads are exposed on the surface of the silicon wafer. It is easy to find a complete spherical secondary particle bead using electron beam scanning imaging in the focused ion beam system. Compared with the standard focused ion beam method in the prior art that directly finds the crown of the secondary particle bead on the electrode sheet to prepare the sample, the present invention can efficiently and stably find a complete spherical secondary particle bead for sample preparation.

[0025] 2. The operating steps (3) to (5) of the present invention utilize a manipulator to directly transfer the secondary particle pellets from the silicon wafer to the carrier grid, thereby omitting the three operating steps of rough cutting, fine cutting, and U-shaped cutting in GB / T 45459-2025 "Microbeam Analysis Focused Ion Beam Transmission Electron Microscope Sample Preparation Method", thereby shortening the sample preparation time. At the same time, the operating step (5) of the present invention directly welds the secondary particle pellets to the transmission electron microscope carrier grid. The strong welding avoids the risk of the secondary particle pellets falling off the carrier grid. This solves the problem of secondary particle pellets often falling off the carrier grid in the prior art sample preparation. The transmission electron microscope sample preparation method of the present invention is also applicable to the transmission electron microscope sample preparation of other micron-sized pellets. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is an operational flow chart of the present invention.

[0027] Figure 2 Lithium nickel cobalt manganese oxide (LiNi 1 / 3 Fe 1 / 3 Mn 1 / 3Scanning electron microscope photographs of the O2 secondary particle ball before (a) and after (b) protective coating, and the control hand welded to the secondary particle ball (c).

[0028] Figure 3 To control the lithium nickel cobalt manganese oxide (LiNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Scanning electron microscope photos of the O2 secondary particle balls before (a), after (b) welding to the copper column slot of the carrier grid, and after disconnecting the control hand (c).

[0029] Figure 4 To prepare lithium nickel cobalt manganese oxide (LiNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) Scanning electron microscope photograph of secondary particle spherical flakes.

[0030] Figure 5 shows the prepared Na nickel cobalt manganese oxide (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) Scanning electron microscope photograph of secondary particle spherical flakes. DETAILED DESCRIPTION

[0031] The present invention will be further described below by way of embodiments with reference to the accompanying drawings.

[0032] The equipment used in the following examples is described as follows: the model of the focused ion beam system is Thermo Fisher Helios G5X. Example 1

[0033] This embodiment 1 is for lithium nickel cobalt manganese oxide (LiNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) Preparation of secondary particle pellets of ternary layered battery cathode material for transmission electron microscopy. The specific sample preparation steps are as follows: (1) Immerse the cut battery positive electrode slices in dimethyl carbonate solvent and ultrasonicate for 20 minutes to obtain solution 1; see Figure 1 In step (1), solution 1 is dropped onto the prepared clean silicon wafer, and the solution 1 is allowed to dry for 2 minutes to obtain silicon wafer 2 with the sample dropped thereon.

[0034] The cut battery pole piece is a positive pole piece with a thickness of 200 μm, which is composed of battery positive electrode secondary particle beads, a binder, and a conductive agent.

[0035] (2) Place the silicon wafer 2 with the sample and the transmission electron microscope grid into the cavity of the focused ion beam system, see Figure 2(a) in the figure, find a complete spherical secondary particle 3 in the sample on the silicon wafer 2 under the electron beam; see Figure 1 In step (2), a gas injection system is inserted into the cavity of the focused ion beam system to deposit a protective layer 4 on the target area of the secondary particle pellet 3 by electron beam and ion beam induction, see Figure 2 In (b), the middle white rectangular area is the deposited protective layer 4.

[0036] The transmission electron microscope grid in this embodiment 1 is a half-copper grid specially used for sample preparation in a focused ion beam system.

[0037] The diameter of the secondary particle ball 3 in this embodiment 1 is 10 μm; the target area is a rectangular area with a length of 10 μm and a width of 1.5 μm centered on the ball center.

[0038] The protective layer 4 consists of an inner layer and an outer layer. The inner layer is made of carbon, and the outer layer is made of tungsten metal.

[0039] The specific manufacturing operation of the protective layer 4 is: first, a carbon layer with a thickness of 0.5 μm is deposited by electron beam induction, and then a tungsten metal layer with a thickness of 2 μm is deposited on the carbon layer by ion beam induction.

[0040] (3) Insert the nanomanipulator 5 into the cavity of the focused ion beam system. The metal source of the gas injection system is a tungsten source. Manipulate the nanomanipulator 5 to move so that the tip of the nanomanipulator 5 contacts the protective layer 4 of the secondary particle ball 3; see Figure 1 In step (3), a first metal layer 6 is deposited at the contact position by ion beam induction. The material of the first metal layer 6 is tungsten metal with a thickness of 0.5 μm. Figure 2 In (c), the nanomanipulator 5 and the secondary particle ball 3 are welded together.

[0041] (4) Manipulate the nanomanipulator 5 to lift the secondary particle ball 3 upward. When lifting the nanomanipulator 5, first move the nanomanipulator 5 back and forth and left and right to ensure that the nanomanipulator 5 is firmly welded to the secondary particle ball 3 and can drive the secondary particle ball 3, then lift it up. Figure 1 In step (4), the secondary particle ball 3 is separated from the silicon wafer 2. The gas injection system and the nanomanipulator 5 are withdrawn from the cavity of the focused ion beam system.

[0042] Compared with the existing standard method process of GB / T 45459-2025 "Microbeam analysis focused ion beam transmission electron microscopy sample preparation method", step (4) of the present invention omits the operating steps of rough cutting, fine cutting and U-shaped cutting.

[0043] (5) Find the copper column of the transmission electron microscope grid under the electron beam, that is, grid column 7 (if the sample contains copper, grids with other chemical compositions can be used), see Figure 3 In (a), a groove 8 is etched on the grid column 7; the gas injection system and the nanomanipulator 5 are inserted into the cavity of the focused ion beam system, and the nanomanipulator 5 is manipulated. Figure 1 In step (5), the secondary particle ball 3 is placed on the upper part of the groove 8 so that both sides of the secondary particle ball 3 are in contact with the groove edges on both sides of the groove, and the second metal layer 9 is deposited by ion beam induction, see Figure 3 In step (b), the secondary particle ball 3 is welded to the upper part of the groove 8.

[0044] The width of the groove 8 is 9 μm and the depth is 15 μm; the material of the deposited second metal layer 9 is a tungsten metal layer with a thickness of 0.5 μm.

[0045] (6) See Figure 1 Step (6) and Figure 3 In (c), ion beam etching with an ion beam current of 0.23A and an acceleration voltage of 30kV is used to etch away the first metal layer 6 at the welding point, so that the nanomanipulator 5 is separated from the secondary particle ball 3, and the nanomanipulator 5 and the gas injection system are withdrawn from the cavity of the focused ion beam system.

[0046] (7) See Figure 1 Step (7) in the process is to perform a thinning and cleaning treatment of the secondary particle beads. The specific operation is as follows: first, the sample stage is tilted so that the grid column 7 where the secondary particle beads 3 are located is parallel to the incident direction of the ion beam. The sample stage is tilted alternately in both positive and negative directions by ±1°. An acceleration voltage of 30 kV is used. The ion beam currents of 0.23nA, 80 pA, and 40pA are selected in sequence to thin the secondary particle beads. At the same time, the electron beam is used to observe the change in the thickness of the secondary particle beads 3. When the contrast of the secondary particle beads 3 is observed to become lighter, it indicates that the particle thickness is already relatively thin. Then, the sample stage is tilted alternately in both positive and negative directions by ±3.5° to reduce the ion beam acceleration voltage to 5kV, and a beam current of 39pA is selected to further thin the secondary particle beads. At the same time, the sample condition is observed at any time under the electron beam, see Figure 4 When a portion of the thin slice of the secondary particle beads under the electron beam turns white, the thickness of the thin slice of secondary particle beads 3 is suitable for transmission electron microscopy. Finally, the sample stage is tilted alternately by ±5° in both forward and reverse directions, the ion beam acceleration voltage is reduced to 2kV, and the small beam current is scanned across the sample surface for 30 seconds to remove the damaged layer on the surface of the secondary particle beads 3 thin slice, thus obtaining a thin slice of secondary particle beads suitable for transmission electron microscopy. Example 2

[0047] This embodiment 2 is for sodium nickel cobalt manganate (NaNi 1 / 3 Fe1 / 3 Mn 1 / 3 O2) Preparation of secondary particle beads of ternary layered battery cathode material for transmission electron microscopy. The specific sample preparation steps are the same as those in Example 1. Figure 5 Finally, secondary particle spherical flakes that can be used for transmission electron microscopy characterization are obtained.

Claims

1. A method for preparing samples for transmission electron microscopy of secondary particles of battery positive electrode, characterized in that: The steps are as follows: (1) Immerse the cut battery electrode in dimethyl carbonate solvent and ultrasonicate for 20-30 minutes to obtain solution (1); drip solution (1) onto a clean silicon wafer and wait for 2-3 minutes for the solution to dry to obtain a silicon wafer with the sample (2); (2) Place the silicon wafer (2) with the sample and the transmission electron microscope grid into the cavity of a focused ion beam system (FIB), find a complete spherical secondary particle ball (3) in the sample on the silicon wafer (2) under the electron beam, insert a gas injection system into the cavity of the focused ion beam system, and deposit a protective layer (4) on the target area on the secondary particle ball (3) by electron beam induced deposition and ion beam induced deposition respectively; The protective layer (4) is composed of an inner layer and an outer layer, the material of the inner layer is carbon, and the material of the outer layer is tungsten metal or platinum metal; (3) inserting a nanomanipulator (5) into the cavity of the focused ion beam system; manipulating the nanomanipulator (5) to move so that the tip of the nanomanipulator (5) contacts the protective layer (4) of the secondary particle ball (3); and inducing the deposition of a first metal layer (6) at the contact position by ion beam, so that the nanomanipulator (5) and the secondary particle ball (3) are welded together; The material of the first metal layer (6) is tungsten metal or platinum metal; (4) manipulating the nanomanipulator (5) to lift the secondary particle ball (3) upward, so that the secondary particle ball (3) is separated from the silicon wafer (2); and withdrawing the gas injection system and the nanomanipulator (5) from the cavity of the focused ion beam system; (5) etching a groove (8) on a grid column (7) of a transmission electron microscope grid, wherein the width of the groove (8) is slightly smaller than the diameter of the secondary particle ball (3); inserting the gas injection system and the nanomanipulator (5) into the cavity of the focused ion beam system, manipulating the nanomanipulator (5) to place the secondary particle ball (3) on the upper part of the groove (8), so that both sides of the secondary particle ball (3) are in contact with the groove edges on both sides of the groove (8), and depositing a second metal layer (9) by ion beam induction, so that the secondary particle ball (3) is welded to the upper part of the groove (8); the material of the second metal layer (9) is tungsten metal or platinum metal; (6) etching the first metal layer (6) where the nanomanipulator (5) and the secondary particle ball (3) are welded by ion beam etching to remove the first metal layer (6) at the welding position, thereby separating the nanomanipulator (5) and the secondary particle ball (3), and withdrawing the nanomanipulator (5) and the gas injection system from the cavity of the focused ion beam system; (7) According to the standard process of GB / T 45459-2025 "Microbeam analysis focused ion beam transmission electron microscopy sample preparation method", the secondary particle beads (3) are thinned and cleaned to obtain a thin slice (10). The thickness of the thin slice (10) is less than 100 nm, and a sample of the battery positive electrode secondary particle beads for transmission electron microscopy characterization is obtained.

2. The method for preparing samples for a transmission electron microscope of secondary particles of a positive electrode of a battery according to claim 1, characterized in that: In step (1), the cut battery electrode sheet should be a positive electrode sheet with a thickness of 200 μm, which is composed of battery positive electrode secondary particle pellets, a binder, and a conductive agent.

3. The method for preparing samples for a transmission electron microscope of secondary particles of a battery positive electrode according to claim 1, characterized in that: In step (1), the transmission electron microscope grid is a grid specifically used for focused ion beam (FIB) sample preparation.

4. The method for preparing samples for a transmission electron microscope of secondary particles of a battery positive electrode according to claim 1, characterized in that: In step (2), the target area is a rectangular area with a length equal to the diameter of the secondary particle ball and a width of 1.5 μm, centered at the center of the secondary particle ball (3).

5. The method for preparing samples for a transmission electron microscope of secondary particles of a positive electrode of a battery according to claim 1, characterized in that: In step (2), the protective layer (4) is first deposited by electron beam induction to form a carbon layer with a thickness of 0.4-0.5 μm, and then deposited by ion beam induction to form a tungsten metal or platinum metal layer with a thickness of 1.5-2 μm on the carbon layer.

6. The method for preparing samples for a transmission electron microscope of secondary particles of a battery positive electrode according to claim 1, characterized in that: In step (3), the metal source of the gas injection system is a platinum (Pt) source or a tungsten source.

7. The method for preparing samples for a transmission electron microscope of secondary particles of a battery positive electrode according to claim 1, characterized in that: In step (3), the thickness of the first metal layer (6) is 0.4-0.5 μm.

8. The method for preparing samples for a transmission electron microscope of secondary particles of a battery positive electrode according to claim 1, characterized in that: In step (5), the thickness of the second metal layer (9) is 0.4-0.5 μm.

9. The method for preparing samples for a transmission electron microscope of secondary particles of a battery positive electrode according to claim 1, characterized in that: In step (6), the etching conditions are: ion beam current 0.23A, acceleration voltage 30kV.

10. The method for preparing samples for a transmission electron microscope of secondary particles of a battery positive electrode according to claim 1, characterized in that: In step (7), the thinning and cleaning operation according to GB / T 45459-2025 "Microbeam Analysis Focused Ion Beam Transmission Electron Microscope Sample Preparation Method" is as follows: first, the sample stage is tilted so that the copper column where the secondary particle ball is located is parallel to the incident direction of the ion beam, and the sample stage is tilted alternately in the positive and negative directions by ±0.5° to ±6.5°, and an ion beam with an acceleration voltage of 30 kV and a suitable ion beam current is selected to thin the secondary particle ball to a suitable thickness; finally, the ion beam acceleration voltage is reduced to a low voltage of no more than 5 kV, and the small beam current is scanned on the sample surface to remove the damaged layer on the sample surface.

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