A method for preparing a cross-sectional sample of powder particles

Abstract

The present invention provides a method for preparing a cross-section sample of powder particles, in particular a method for preparing a cross-section sample of micron-sized powder particles for a scanning electron microscope. The preparation method is as follows: Prepare a modulation solvent with CMC and water; fully mix a carbon conductive agent, a test material, and a dispersant to form a powder mixture; add the powder mixture into the modulation solvent, stir evenly at 40-50 °C, and drop SBR for viscosity modulation to form a test sample; finally, place the test sample in a mold, after heating and curing, perform grinding and / or thinning to obtain the sample. The present invention uses a new slurry system to extend the curing time, enabling the sample to be fully mixed with the embedding agent; uses spherical alumina as a dispersant to uniformly disperse small particles in the embedding agent; at the same time, reduces the interference of aluminum and copper foils through a special sample preparation mold, and quickly provides a cross-section sample with good conductivity and no pollution.

Description

Technical Field

[0001] The present invention relates to a method for preparing a cross-sectional sample of powder particles, and particularly to a method for preparing a cross-sectional sample of micron-sized powder particles of a scanning electron microscope. Background Art

[0002] With the continuous development of the new energy industry, people's requirements for power batteries are getting higher and higher. As a result, the nickel content in ternary materials is also increasing. However, the problems of cathode material stability, electrolyte matching, and high temperature rise during high-current charging that lead to battery failure have also attracted more and more attention. Single-crystal cathode materials have emerged as the times require. Single-crystal cathode materials not only enhance stability and improve battery safety, but also can raise the voltage of the entire system to a new level. Single-crystal cathode materials are obtained by doping different elements, different stoichiometric ratios, and different sintering processes. The particle size of the sintered single-crystal particles is usually small, generally remaining at 3-5 μm. Compared with agglomerated cathode materials, they have strong hardness, poor sphericity, and are not easy to process cross-sections.

[0003] The development of lithium battery materials is inseparable from testing and analysis by a scanning electron microscope. With the development of doping technology, material cross-section analysis is imminent. For the preparation of a scanning electron microscope cross-sectional sample of a cathode material, traditional methods use epoxy resin embedding and mechanical polishing. This method takes a long time to make, and epoxy resin is not conductive, resulting in poor test results. With the popularization and development of ion milling technology, liquid conductive glue and aluminum foil (copper foil) are now commonly used for embedding and sample preparation. This method solves the disadvantages of long sample preparation time and non-conductivity of epoxy resin. However, for samples embedded with liquid conductive glue and aluminum foil (copper foil), due to the fast curing time of the liquid conductive glue, the material is prone to uneven dispersion. Another method is to use NMP as a solvent for embedding. This method shortens the time compared with epoxy resin preparation, but has poor conductivity and cannot perform energy spectrum testing. The above two sample preparation methods have problems with single-crystal materials. First, the single-crystal cathode material particles have poor sphericity. Due to structural differences, they are more difficult to disperse evenly than agglomerates. In addition, in energy spectrum analysis, for the aluminum foil (copper foil) embedding technology, due to the fast curing of the liquid conductive glue, voids are easily formed in the middle of the sample, resulting in poor embedding effect. Moreover, aluminum foil (copper foil) contaminates the material during the grinding process, affecting the energy spectrum test results; the NMP embedding technology also affects the energy spectrum test results due to poor conductivity.

[0004] Below, the advantages and disadvantages of the existing technology can be seen through Table 1.

[0005] Table 1 Analysis of the Advantages and Disadvantages of the Technology

[0006]

[0007] In addition, through Figure 1 it can be seen that in the optical microscope, due to the fast curing of the liquid conductive glue in the aluminum foil embedding process, voids are formed in the sample; through Figure 2and Figure 3 It can be seen that due to the structural differences, single crystal small particle materials cannot be dispersed as uniformly as aggregates.

[0008] In view of this, the present invention is specifically proposed. Summary of the Invention

[0009] To solve the above technical problems, the present invention provides a method for preparing a cross-sectional sample of powder particles. A new slurry system is adopted to extend the curing time, so that the sample and the embedding agent are fully mixed; spherical alumina is used as a dispersant to uniformly disperse small particles in the embedding agent; at the same time, a special sample preparation mold is used to reduce the interference of aluminum and copper foils, and a cross-sectional sample with good conductivity and no pollution is quickly provided.

[0010] To achieve the above object, the technical solution of the present invention is as follows:

[0011] A method for preparing a cross-sectional sample of powder particles, comprising the following steps:

[0012] S1: Prepare a modulation solvent with CMC and water for later use.

[0013] Further, the mass ratio of CMC to water is (2 - 3):(97 - 98).

[0014] S2: Fully mix a carbon conductive agent, a test material, and a dispersant to form a powder mixture.

[0015] Further, the mass ratio of the carbon conductive agent to the sum of the test material and the dispersant is (20 - 50):(50 - 80).

[0016] The dispersant is spherical alumina with a particle size of 3 - 10 microns, which can play the role of dispersing the sample and fixing the material.

[0017] Optionally, when the size of the test material is less than 5 microns, the particle size of the spherical alumina is 3 - 4 microns; the mass ratio of the test material to the spherical alumina is (2.95 - 3.15):1.

[0018] Optionally, when the size of the test material is 6 - 8 microns, the particle size of the spherical alumina is 5 - 8 microns; the mass ratio of the test material to the spherical alumina is (3.85 - 4.25):1.

[0019] Optionally, when the size of the test material is 9 - 15 microns, the particle size of the spherical alumina is 9 - 10 microns; the mass ratio of the test material to the spherical alumina is (4.80 - 5.25):1.

[0020] S3: Add the powder mixture described in step S2 into the modulation solvent described in step S1, stir evenly at 40 - 50 °C, and drop SBR for viscosity modulation to form a test sample. The temperature of 40 - 50 °C can increase the fluidity of the solvent and accelerate the full fusion of the powder.

[0021] Furthermore, the mass ratio of the modulation solvent, the powder mixture, and SBR is: (45 - 55):(23 - 44):(1 - 2).

[0022] S4: Place the test sample described in step S3 in a mold, after heating and curing, conduct grinding and / or thinning to obtain the product.

[0023] Furthermore, the temperature of the heating and curing is 80 - 120 °C, and the heating and curing time is 30 - 60 minutes.

[0024] The present invention also provides a mold described in step S4, which is a cubic mold with at least one sample slot. Preferably, the mold has two sample slots.

[0025] Preferably, the sample slot is cubic in shape.

[0026] Preferably, the inner surface of the sample slot is a frosted surface;

[0027] Preferably, at least one surface of the mold is provided with a scale ruler for auxiliary positioning of the test sample.

[0028] Compared with the prior art, for test materials with different particle sizes, the present invention adopts targeted conductive agents, binders, dispersants, and modulators for step - by - step combination, prolongs the curing time, fully disperses the sample, and solves the problems of difficult dispersion of single - crystal small particles and poor embedding effect; the preparation time is short, and it can quickly obtain cross - section samples of single - crystal materials and meet the analysis of the internal structure and doping elements of single - crystal materials; at the same time, a special mold is designed to replace the aluminum foil (copper foil) as a carrier for ion milling, reducing the pollution of aluminum foil (copper foil). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the background art and embodiments of the present invention, the following will briefly introduce the drawings required for the background art and embodiments. It should be understood that the following drawings may only show some embodiments of the present invention, so they should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0030] Figure 1 It is a sample of the aluminum foil embedding process under an optical microscope in the prior art;

[0031] Figure 2It is a low-magnification electron microscope image of single-crystal small-particle materials in the prior art;

[0032] Figure 3 It is a low-magnification electron microscope image of agglomerated particle materials in the prior art;

[0033] Figure 4 It is a front view structural schematic diagram of the mold of the present invention;

[0034] Figure 5 It is a low-magnification scanning electron microscope image of the cross-section of the ternary single-crystal material of the lithium-ion battery cathode material powder prepared in Example 1;

[0035] Figure 6 It is a high-magnification scanning electron microscope image of the cross-section of the ternary single-crystal material of the lithium-ion battery cathode material powder prepared in Example 1;

[0036] Figure 7 It is the Mapping data of the cross-section of the ternary single-crystal material of the lithium-ion battery cathode material powder obtained in Example 2;

[0037] Figure 8 It is the EDS data of the cross-section of the ternary single-crystal material of the lithium-ion battery cathode material obtained in Example 2;

[0038] Figure 9 It is the test sample diagram obtained in step S3 of Example 1;

[0039] Figure 10 It is the test sample diagram obtained in step S3 of Comparative Example 1;

[0040] Figure 11 It is a comparison diagram of two groups of test samples obtained in step S3 of Example 5 and Comparative Example 2; the slurry in the beaker on the left is the test sample diagram of Example 5; the beaker on the right is the test sample diagram of Comparative Example 2;

[0041] Figure 12 It is the test sample diagram obtained in step S3 of Example 6;

[0042] Figure 13 It is the test sample diagram obtained in step S3 of Comparative Example 3.

[0043] Main element symbol description:

[0044] 1 - Mold body; 2 - Sample groove; 3 - Scale ruler; 4 - Fixed wire hole. Detailed implementation manners

[0045] The embodiments of the present invention will be described in detail below. As used herein, the terms:

[0046] "Prepared by" is synonymous with "comprising". As used herein, the terms "comprising", "including", "having", "containing" or any other variation thereof are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or apparatus comprising the listed elements need not be limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article or apparatus.

[0047] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value, whether or not the ranges are separately disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0048] In these examples, unless otherwise specified, the parts and percentages are by mass.

[0049] Examples of the embodiments are shown in the drawings, wherein like or similar reference numerals designate like or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

[0050] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention.

[0051] In addition, in the description of the present invention, the meanings of "a plurality of" and "several" are two or more, unless otherwise clearly and specifically defined. In the present invention, unless otherwise clearly stipulated and defined, terms such as "installation", "connection", "connection", "fixation" and other terms should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0052] Example 1

[0053] A preparation method for a scanning electron microscope cross-section sample of a 3-5 micron ternary single-crystal lithium-ion battery cathode material powder particle includes the following steps:

[0054] S1: Take CMC (sodium carboxymethyl cellulose) and water in a mass ratio of 2:98, mix and stir as a solvent for standby, and the stirring time is not less than 10 minutes.

[0055] S2: Fully mix 2.5 g of carbon conductive agent acetylene black, 5.6 g of 3-5 micron positive electrode material to be tested, and 1.9 g of 3-4 micron spherical alumina to form a powder mixture.

[0056] S3: Add 10 g of the powder mixture prepared in step S2 to 15 g of the solvent in step S1, stir evenly at 45 °C, and the stirring time is not less than 10 minutes. While stirring, drop 0.5 g of SBR (styrene-butadiene rubber) for viscosity modulation to form a test sample. As Figure 9 shown, the test sample is evenly dispersed and the slurry has good fluidity.

[0057] S4: Place the test sample in step S3 in a horizontally placed mold, ensure sufficient sample, scrape off the excess sample, then put it into an oven, heat and cure at 90 °C for 40 minutes, cut the cured sample with a blade to make the sample flush with the edge of the sample slot, put it into the sample stage bracket of the ion milling instrument, observe and adjust the position of the sample to be tested in the optical microscope, and then put it into the ion milling instrument for thinning to obtain a cross-section sample of the ion-milled particles.

[0058] Fix the prepared cross-section sample to the scanning electron microscope sample stage, and the powder can be directly analyzed by scanning electron microscope without spray-coating a carbon or metal conductive layer for conductivity treatment. As Figure 5 shown, the powder particles with a flat and smooth cross-section are evenly dispersed in the sample, and the cross-section is smooth without visible scratches; Figure 6 For Figure 5The scanning electron microscope image shown is an enlarged cross-sectional view of the powder particles of the ternary single crystal lithium-ion battery positive electrode material. It can be seen from the figure that the secondary particles are composed of 2-3 small grains, the particles are evenly dispersed, and are fully integrated with the embedding agent.

[0059] The mold in this embodiment, such as Figure 4 As shown, the mold body 1 has a cubic shape, with a length of 2 cm, a height of 1 cm, and a width of 0.5 cm. Two parallel cubic sample slots 2 are provided on the upper part between the main viewing surface and the top viewing surface. Each sample slot 2 is 0.8 cm long, 0.5 cm high, and 0.1 cm wide, and has a frosted surface inside. Two fixing wire holes 4 are provided below the sample slots 2 at the lower part of the mold body 1.

[0060] A scale ruler 3 is provided on the top of the mold body 1 to assist in positioning the sample.

[0061] Example 2

[0062] A method for preparing a scanning electron microscope cross-section sample for preparing 3-5 micron ternary single crystal lithium ion battery positive electrode material powder particles, comprising the following steps:

[0063] S1: Mix CMC and water in a mass ratio of 3:97 and stir as a solvent for standby use. The stirring time is not less than 10 minutes.

[0064] S2: 3g of carbon conductive agent acetylene black, 5.1g of 3-5 micron positive electrode material to be tested and 1.69g of 3-4 micron spherical alumina are fully mixed to form a powder mixture.

[0065] S3: Add 5 g of the powder mixture obtained in step S2 to 11 g of the solvent in step S1, stir evenly at 40° C. for not less than 10 minutes, and while stirring, drop 0.1 g of SBR into the mixture to modulate the viscosity to form a test sample.

[0066] S4: Place the test sample described in step S3 in a flat mold to ensure that the sample is sufficient, scrape off the excess sample, and then put it into an oven. After heating and curing at 80°C for 60 minutes, use a blade to cut the cured sample so that the sample and the edge of the sample slot are flush, and put it into the sample stage bracket of the ion milling instrument. After observing and adjusting the position of the sample to be tested under an optical microscope, put it into the ion milling instrument for thinning to obtain the ion-milled particle cross-section sample.

[0067] The prepared cross-section sample is fixed on the sample stage of the scanning electron microscope, and the powder can be directly subjected to energy spectrum analysis without the need for carbon spraying or metal conductive layer conductive treatment. Figure 7It is the Mapping data of the cross-section of the micron-sized powder particles of the ternary single-crystal lithium-ion battery cathode material prepared in this embodiment. It can be seen from the figure that a certain doping element is unevenly dispersed in the inner part of the single-crystal material; Figure 8 is Figure 7 The enlarged EDS data of the cross-section edge of the ternary single-crystal lithium-ion battery cathode material powder particles shown in the scanning electron microscope image, and the thickness and composition of the coating layer can be clearly observed.

[0068] The mold in this embodiment is the same as that in Embodiment 1.

[0069] Embodiment 3

[0070] A method for preparing a scanning electron microscope cross-section sample of ternary single-crystal lithium-ion battery cathode material powder particles with a size of 6-8 microns, comprising the following steps:

[0071] S1: Take CMC and water in a mass ratio of 2:98, mix and stir as a solvent for standby, and the stirring time is not less than 10 minutes.

[0072] S2: Fully mix 2 g of carbon conductive agent acetylene black, 6.4 g of 3-5 micron cathode material to be tested, and 1.6 g of 5-8 micron spherical alumina to form a powder mixture.

[0073] S3: Add the 10 g of powder mixture prepared in step S2 into 22 g of the solvent in step S1, stir evenly at 50 °C, and the stirring time is not less than 10 minutes. While stirring, drop 0.5 g of SBR for viscosity modulation to form a test sample.

[0074] S4: Place the test sample in step S3 in a flat mold, ensure sufficient sample, scrape off the excess sample, then put it into an oven, heat and cure at 100 °C for 30 minutes, and the subsequent operation process is the same as that in Embodiment 1.

[0075] The mold in this embodiment is the same as that in Embodiment 1.

[0076] Embodiment 4

[0077] A method for preparing a scanning electron microscope cross-section sample of ternary single-crystal lithium-ion battery cathode material powder particles with a size of 9-15 microns, comprising the following steps:

[0078] S1: Take CMC and water in a mass ratio of 2:98, mix and stir as a solvent for standby, and the stirring time is not less than 10 minutes.

[0079] S2: Fully mix 4.0 g of carbon conductive agent SUPER-P, 5.0 g of 3-5 micron cathode material to be tested, and 1.0 g of 9-10 micron spherical alumina to form a powder mixture.

[0080] S3: Add the 10 g of powder mixture prepared in step S2 into 15 g of the solvent in step S1, stir evenly at 40 °C for no less than 10 minutes. While stirring, drop 0.7 g of SBR for viscosity modulation to form a test sample.

[0081] S4: Place the test sample in step S3 in a flat mold, ensure sufficient sample, scrape off the excess sample, then put it into an oven and heat and cure at 120 °C for 30 minutes. After that, the operation process is the same as that in Example 1.

[0082] The mold in this example is the same as that in Example 1.

[0083] Example 5

[0084] Except that the mass ratio of the solvent, powder mixture and SBR is 55:23:2, the other technical features are the same as those in Example 1. As Figure 11 shown by the test sample in the beaker on the left, the test sample is evenly dispersed and the slurry has good fluidity.

[0085] Example 6

[0086] Except that the mass ratio of the solvent, powder mixture and SBR is 50:28:2, the other technical features are the same as those in Example 1. As Figure 12 shown, the test sample is evenly dispersed and the slurry has good fluidity.

[0087] Comparative Example 1

[0088] Except that the mass ratio of CMC and water is 6:94, the other technical features are the same as those in Example 1. As Figure 10 shown, the slurry has poor fluidity, the sample is dispersed, and there are gel-like substances locally, affecting the grinding effect.

[0089] Comparative Example 2

[0090] Except that the mass ratio of the solvent, powder mixture and SBR is 40:58:2, the other technical features are the same as those in Example 1. As Figure 11 shown by the test sample in the beaker on the right, the test sample is not evenly dispersed, and there is an enrichment of part of the powder mixture, affecting the grinding effect.

[0091] Comparative Example 3

[0092] Except that the mass ratio of the solvent, powder mixture and SBR is 50:24:6, the other technical features are the same as those in Example 1. As Figure 13 shown, the test sample is not evenly dispersed and there are gel-like substances in the slurry.

[0093] In the description of this specification, the descriptions referring to terms such as "one embodiment", "one example", "some embodiments", "preferred embodiment", "specific embodiment", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0094] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a cross-sectional sample of powder particles, comprising the following steps: S1: Prepare a modulation solvent with CMC and water for later use; S2: Thoroughly mix a carbon conductive agent, a test material, and a dispersant to form a powder mixture; The mass ratio of the carbon conductive agent to the sum of the test material and the dispersant is (20 - 50):(50 - 80); The dispersant is spherical alumina with a particle size of 3 - 10 microns; S3: Add the powder mixture in step S2 into the modulation solvent in step S1, stir evenly at 40 - 50 °C, and drop in SBR for viscosity modulation to form a test sample; S4: Place the test sample in step S3 in a mold, after heating and curing, perform grinding and / or thinning to obtain the sample; The test material is powder particles of a ternary single-crystal lithium-ion battery cathode material.

2. The method for preparing a powder particle cross-sectional sample according to claim 1, characterized in that, In step S1, the mass ratio of CMC to water is (2 - 3):(97 - 98).

3. The method for preparing a powder particle cross-sectional sample according to claim 1, wherein, The spherical alumina satisfies one of the following conditions: a. When the size of the test material is less than 5 microns, the particle size of the spherical alumina is 3 - 4 microns; b. When the size of the test material is 6 - 8 microns, the particle size of the spherical alumina is 5 - 8 microns; c. When the size of the test material is 9 - 15 microns, the particle size of the spherical alumina is 9 - 10 microns.

4. The method for preparing a powder particle cross-sectional sample according to claim 3, characterized in that, In condition a, the mass ratio of the test material to the spherical alumina is (2.95 - 3.15):1; In condition b, the mass ratio of the test material to the spherical alumina is (3.85 - 4.25):1; In condition c, the mass ratio of the test material to the spherical alumina is (4.80 - 5.25):

1.

5. The method for preparing a powder particle cross-section sample according to claim 1, wherein In step S3, the mass ratio of the modulation solvent, the powder mixture, and SBR is: (45 - 55):(23 - 44):(1 - 2).

6. The method for preparing a powder particle cross-section sample according to claim 1, wherein In step S4, the temperature for heating and curing is 80 - 120 °C, and the heating and curing time is 30 - 60 minutes.

7. The method for preparing a powder particle cross-sectional sample according to claim 1, wherein The mold in step S4 is a cube mold with at least one sample groove.

8. The method for preparing a cross-sectional sample of powder particles according to claim 7, wherein The sample groove is cube-shaped.

9. The method for preparing a powder particle cross-sectional sample according to claim 7 or 8, characterized in that The inner surface of the sample groove is a frosted surface.

10. The method for preparing a powder particle cross-sectional sample according to claim 7, wherein At least one surface of the mold is provided with a scale ruler for auxiliary positioning of the test sample.

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