A method for detecting a coating layer on a material surface

Abstract

The application discloses a material surface coating layer detection method, which comprises the following steps: calendering a base material with a surface coating layer to be detected into a calendered film, etching the calendered film by using an Ar ion beam after coating, and then performing secondary ion mass spectrometry, collecting the number of secondary ions of the coating layer material and the number of secondary ions of the coated base material in the secondary ion mass spectrometry, and calculating the coating rate and the thickness of the coating layer. The material surface coating layer detection method can be used for measuring a thin coating layer (1-3 nm in thickness) and a thick coating layer (greater than 10 nm in thickness), and solves the problem that surface pollution elements in the sample preparation and test transfer process interfere with the measurement results.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of materials, in particular to a method for detecting a surface coating layer of a material. BACKGROUND

[0002] At present, when modifying a material, other substances are usually selected to coat the material or the material is made to pass through a gas phase or liquid phase reaction so as to form a coating layer on the surface of the material. The uniformity and thickness of the coating layer have important influences on the modification quality. Since the detection depth of the commonly used surface testing means is about 3-10 nm, the existing means cannot accurately detect and evaluate the coating effect for the coating layer with a thickness less than 3 nm or greater than 10 nm. In addition, when the surface coating layer is prepared by a gas phase or liquid phase reaction, since the coating layer substance and the coated substance contain the same elements, the coating rate and the thickness of the coating layer are often difficult to detect. Furthermore, in the preparation process of the test sample, the surface of the material sample is easily contaminated, thereby greatly influencing the accuracy of the test result.

[0003] Therefore, the present application is proposed to solve the existing problems. SUMMARY

[0004] The present application provides a method for detecting a surface coating layer of a material, which realizes the accurate detection of the coating rate and thickness of the material surface coating layer (1-3 nm) and thicker coating layer (>10 nm), and solves the problem of surface contamination of the sample in the preparation process, thereby effectively improving the accuracy of the test result.

[0005] To achieve the above object, the present application provides a method for detecting a surface coating layer of a material, which is performed in the following steps in sequence:

[0006] (1) a substrate material with a surface coating layer to be detected is calendered into a film to obtain a calendered film sample;

[0007] (2) the calendered film prepared in step (1) is coated to obtain a coated calendered film sample;

[0008] (3) the coated calendered film prepared in step (2) is etched by an ion beam, and secondary ion mass spectrometry is performed on the etched coated calendered film to collect the number of secondary ions of the coating layer substance A1 and the number of secondary ions of the coated substrate substance B1;

[0009] (4) the etched area of the etched coated calendered film in step (3) is gradient etched by an ion beam, and secondary ion mass spectrometry is performed on the coated calendered film after each etching to collect the number of secondary ions of the coating layer substance and the number of secondary ions of the coated substrate substance in each secondary ion mass spectrometry, wherein the number of secondary ions of the coating layer substance in the mth secondary ion mass spectrometry is A mThe number of secondary ions of the coated substrate material is B m ;

[0010] (5) Continue etching and after each etching, conduct secondary ion mass spectrometry test on the coated film, until the absolute value of the change rate of A m or B m is ≤1%, then stop etching;

[0011] (6) Calculate the coating rate and the thickness of the coating layer according to the number of times n that the absolute value of the change rate of A1, B1, the total number of etching times m and A m or B m is ≤1%, wherein:

[0012] The coating rate is A1 / (A1+B1)×100%, and the thickness of the coating layer is (m-n)×1nm.

[0013] Preferably or optionally, step (1) is conducted in an inert gas environment, which is any one of argon, helium, nitrogen environment, and most preferably argon environment.

[0014] Preferably or optionally, the material of the surface coating layer in step (1) is one or a combination of Li, C, Al, Ag, Zr, Sr, Mo, Sn, Mg, Ti, Zn, La, Au, and oxides or fluorides thereof.

[0015] Preferably or optionally, the thickness of the film in step (2) is 10-500nm.

[0016] Preferably or optionally, the material used for film coating in step (2) is different from the substrate material, and further, the material used for film coating is one of Ag, Sn, Au, SiO2.

[0017] Preferably or optionally, the method used for film coating in step (2) is any one of atomic layer deposition, vapor deposition, magnetron sputtering, evaporation film coating, and sputtering.

[0018] Preferably or optionally, the etching area in step (2) is a square with a side length of 1-500μm.

[0019] Preferably or optionally, the etching depth in step (3) is the thickness of the film minus the maximum detection depth of secondary ion mass spectrometry, plus 1nm.

[0020] Preferably or optionally, in step (4), the etching area of the coated film in step (3) is gradient etched with a gradient of 1nm by using an ion beam.

[0021] Preferably or optionally, in step (5), n is any integer value between 3 and 7.

[0022] Preferably or optionally, in step (6), the coating rate is A1 / (A1+B1) x 100%, and the coating layer thickness is (m-n) x 1 nm.

[0023] The application provides a detection method for a material surface coating layer, which effectively prevents the coating layer from being unable to be detected due to the detection depth of SIMS being greater than the coating layer thickness, and thus can be applied to the determination of a material shallow surface coating layer (thickness 1-3 nm);

[0024] In combination with ion beam etching, the determination of a thicker coating layer (>10 nm) is also achieved, and the accurate determination of the coating layer thickness is also achieved.

[0025] The plating film also solves the problem that surface pollution elements of the sample during the preparation and test transfer process interfere with the determination result, and improves the accuracy of the detection.

[0026] In addition, the method in the application can also be used for the determination of the coating rate and thickness of the coating layer of a material containing the same elements as the coated material, and has better adaptability than the traditional method. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of the change trend of the number of secondary ions of carbon / silicon in Example 1 with the etching times;

[0028] Figure 2 is a three-dimensional Mapping diagram of carbon in the thickness direction in Example 1;

[0029] Figure 3 is a three-dimensional Mapping diagram of silicon in the thickness direction in Example 1;

[0030] Figure 4 is a schematic diagram of the change trend of the number of secondary ions of lithium fluoride / silicon in Example 2 with the etching times;

[0031] Figure 5 is a schematic diagram of the change trend of the number of secondary ions of lithium oxide / lithium in Example 3 with the etching times. DETAILED DESCRIPTION

[0032] In order to further illustrate the technical means and results adopted by the application to achieve the predetermined object, the following preferred embodiments are used to specifically and in detail explain the specific implementation manners, technical schemes and features according to the application. The specific features, structures or characteristics in the following embodiments can be combined in any suitable form.

[0033] The conditions of the SIMS test in the following embodiments are shown as follows:

[0034] Ion source: Bi ion;

[0035] Energy: 30 KeV;

[0036] Ion current: 2 nA;

[0037] Maximum probing depth: 10 nm.

[0038] Example One

[0039] This example determines the carbon coating layer coverage rate and thickness of a carbon-coated silicon-based material for a lithium ion battery negative electrode, and the specific steps are as follows:

[0040] Under an argon environment, the silicon negative electrode material to be determined with a carbon coating layer is calendered into a calendered film.

[0041] A gas deposition method is used to add a silicon dioxide coating layer to the surface of the calendered film, and the coating layer thickness is 15 nm.

[0042] An Ar ion beam with an energy of 1 kV is used to etch the surface of the coated calendered film, the etching area is a square of 400x400 μm, and the etching depth is 15 nm-10 nm+1 nm=6 nm.

[0043] After etching is completed, the etching area is subjected to SIMS testing.

[0044] In positive ion mode, the number of returned carbon and silicon secondary ions is collected; and a 100x100 μm square area in the etching area is selected to draw a two-dimensional Mapping graph of carbon and silicon in the area.

[0045] After this etching, the number of carbon secondary ions collected by SIMS detection is 60723, and the number of silicon secondary ions is 1379 (i.e. the result of the first etching).

[0046] The same Ar ion beam is continued to be used to gradient etch the etched area on the surface of the coated calendered film, the etching gradient is 1 nm, SIMS testing is performed after each etching, the conditions of each SIMS testing are the same as before, the number of returned carbon and silicon secondary ions is collected at the same time, and the two-dimensional Mapping graph of carbon and silicon elements in the same area is continued to be drawn, and the change rate of the number of carbon and silicon secondary ions with the number of etchings is calculated.

[0047] When the absolute value of the change rate of the number of secondary ions of either of the two elements carbon and silicon is ≤1% after continuous etching for 7 times, etching is stopped.

[0048] The results of gradient etching are shown in Table 1, and the trend line of the number of carbon / silicon secondary ions with the number of etchings is shown in Figure 1 .

[0049] Table 1: Carbon / Silicon Secondary Ion Counting Table and Its Change Rate After Different Etching Times

[0050] Etching times Carbon secondary ions Variation rate / % Silicon secondary ions Variation rate / % 1 60723 0％ 1379 0％ 2 64170 5.68％ 1698 23.13％ 3 65950 2.77％ 1812 6.71％ 4 66471 0.79％ 1875 3.48％ 5 66506 0.05％ 2040 8.80％ 6 66702 0.29％ 2184 7.06％ 7 65950 -1.13％ 2212 1.28％ 8 65828 -0.18％ 2301 4.02％ …… …… …… …… …… 70 26269 -1.55％ 35303 -0.03％ 71 25863 -2.14％ 35532 0.65％ 72 25309 -2.47％ 35200 -0.93％ 73 24683 -3.59％ 35304 0.30％ 74 23798 -0.92％ 35591 0.81％ 75 23578 -3.86％ 35487 -0.29％ 76 22669 35466 -0.06％

[0051] According to the experimental results, the carbon coating rate of the silicon negative electrode material with a carbon coating layer to be determined is 60723 / (60723+1379)≈98%, and the carbon coating is complete. At the same time, from Table 1 and Figure 1 It can be seen that the total etching times is 76 times, and the absolute value of the change rate of the number of silicon element ions is less than 1% for 7 consecutive times from the beginning of the 70th etching and thereafter, that is, the change trend is close to horizontal. Therefore, the thickness of the carbon coating layer of the silicon negative electrode material with a carbon coating layer to be determined is (76-7) x 1 nm = 69 nm.

[0052] Example Two

[0053] In this example, the coating rate and thickness of the solid electrolyte interface (SEI) film on the surface of the silicon negative electrode in the formed lithium ion battery are determined, and the specific steps are as follows:

[0054] Under an argon environment, the formed lithium ion battery is disassembled and the silicon negative electrode is taken out. After scraping the negative active material layer from the current collector, the film is calendered.

[0055] An Au plating layer with a thickness of 12 nm is added to the surface of the calendered film by atomic layer deposition.

[0056] The surface of the calendered film is etched by an Ar ion beam with an energy of 1 kV. The etching area is a square of 400x400 μm, and the etching depth is 12 nm-10 nm+1 nm=3 nm.

[0057] After etching, the etching area is tested by SIMS.

[0058] In positive ion mode, the number of returned lithium fluoride and silicon secondary ions is collected; and a 100x100 μm square area in the etching area is selected to draw a two-dimensional Mapping graph of lithium fluoride and silicon in the area.

[0059] After this etching, the number of lithium fluoride secondary ions collected by SIMS detection is 27234, and the number of carbon secondary ions is 1458 (i.e. the result of the first etching).

[0060] The same Ar ion beam is continuously used to perform gradient etching on the etched area of the above-mentioned calendered film surface, the etching gradient is 1 nm, and SIMS testing is performed after each etching. The conditions of each SIMS test are the same as before, and the number of lithium fluoride and silicon secondary ions returned each time is collected, and the two-dimensional Mapping diagram of lithium fluoride and silicon of the same area is continuously drawn, and the change rate of the number of lithium fluoride and silicon secondary ions with the number of etching times is calculated.

[0061] When the change rate of the number of secondary ions of either lithium fluoride or silicon is ≤1% after 5 consecutive etchings, stop etching.

[0062] The results of gradient etching are shown in Table 2, and the trend line of the number of lithium fluoride / silicon secondary ions with the number of etching times is shown in Figure 2 .

[0063] Table 2 Statistics of the number of lithium fluoride / silicon secondary ions after different etching times and their change rates

[0064]

[0065]

[0066] The SEI film is an important product formed by the first week of small current charging (formation process) of the battery cell, which prevents the side reaction of the negative material and the electrolyte, effectively alleviates the aging of the battery cell caused by the loss of the negative material and the active lithium, and has a great and important influence on the subsequent cycle performance and storage performance of the battery cell. The formation process is usually the longest step in the preparation process of the battery cell, so judging the effectiveness of the formation of the SEI film is an effective means to optimize the formation process.

[0067] In this embodiment, according to the experimental results, the coating rate of the SEI film formed on the surface of the silicon negative electrode of the lithium ion battery under this formation system is 27234 / (27234+1458)≈94.82%, which is almost completely coated, so there is no need to further reduce the formation current, otherwise it will cause unnecessary extension of the preparation cycle. At the same time, from Table 2 and Figure 4 it can be seen that the total etching times is 8 times, among which from the 4th etching and after that, the absolute value of the change rate of the number of silicon element ions is less than 1% for 5 consecutive times, that is, the change trend is close to horizontal. Therefore, the carbon coating layer thickness of the silicon negative electrode material to be determined is (8-5) x 1 nm = 3 nm, and the SEI film with this thickness has a relatively small influence on the internal resistance of the battery cell, which is beneficial to the rate performance of the battery cell.

[0068] Example Three

[0069] The present embodiment determines the coating effect of the lithium oxide inert coating layer on the surface of the lithium powder particles, which is formed by the surface layer of the lithium powder being oxidized in an inert argon environment containing trace oxygen;

[0070] The prepared lithium powder with the coating layer is calendered into a film under an argon environment.

[0071] An Au plating layer with a thickness of 20 nm is added to the surface of the calendered film by using an atomic layer deposition method.

[0072] The surface of the calendered film is etched by using an Ar ion beam with an energy of 1 kV, the etching area is a square of 400x400 μm, and the etching depth is 20 nm-10 nm+1 nm=11 nm.

[0073] After the etching is completed, the etching area is subjected to SIMS testing.

[0074] In the positive ion mode, the returned secondary ion number information of lithium oxide and lithium is collected; and a 100x100 μm square area in the etching area is selected to draw a two-dimensional Mapping graph of lithium oxide and lithium in the area.

[0075] After the etching, the SIMS detection collects 4532.17 secondary ions of lithium oxide and 1112.56 secondary ions of lithium (i.e. the result of the first etching).

[0076] The etched area on the surface of the above calendered film is continuously subjected to gradient etching by using the same Ar ion beam, the etching gradient is 1 nm, the SIMS testing is performed after each etching, the conditions of each SIMS testing are the same as before, the returned secondary ion number information of lithium oxide and lithium is collected, and the two-dimensional Mapping graph of lithium fluoride and carbon in the same area is continuously drawn, and the change rate of the secondary ion number of lithium oxide and lithium with the etching times is calculated.

[0077] When the change rate of the secondary ion number of either of lithium oxide and lithium is ≤1% after continuous etching for 6 times, the etching is stopped.

[0078] The results of the gradient etching are shown in Table 3, and the trend line of the change of the secondary ion number of lithium oxide / lithium with the etching times is shown in Figure 3 .

[0079] Table 3 Secondary ion number statistics of lithium oxide / lithium after different etching times and the change rate thereof

[0080]

[0081]

[0082] In this example, the coating layer is formed after the coated substance is oxidized, and the element composition of the coated substance and the coating layer is almost the same, so if not in the form of substance molecules for qualitative analysis, the coating layer and the coated substance cannot be distinguished, and the product qualification of the metal lithium powder cannot be judged naturally.

[0083] In this example, according to the experimental results, the coating rate of the inert lithium oxide coating layer on the surface of the metal lithium powder is 4532.17 / (4532.17+1112.56)=80.29%, which indicates that about 20% of the larger surface area is not coated by the inert layer, so the metal lithium powder is easy to fail in use. From Table 3 and Figure 5 It can be seen that the total etching times is 127 times, and from the 122th etching, the absolute value of the change rate of the lithium element ion number is less than 1% for 6 times in succession, that is, the change trend is close to horizontal. Therefore, the thickness of the lithium oxide coating layer of the metal lithium powder to be determined with the inert coating layer is (127-6) x 1 nm = 121 nm.

[0084] The detection method of the coating layer on the surface of a material provided by the application can effectively prevent the coating layer from being unable to be detected due to the detection depth of SIMS being greater than the thickness of the coating layer, so the method can be applied to the determination of the shallow surface coating layer (thickness 1-3 nm) of the material;

[0085] The determination of the thicker coating layer (>10 nm) is also realized by combining ion beam etching, and the accurate determination of the thickness of the coating layer is also realized;

[0086] The plating film also solves the problem that the surface pollution elements of the sample during the preparation and transfer process of the test interfere with the determination results, and improves the accuracy of the detection.

[0087] Through the two-dimensional element Mapping diagram collected multiple times during the determination, a three-dimensional element Mapping diagram can be synthesized in the later stage, and the uniformity of the coating layer can be judged intuitively and quickly through the three-dimensional element Mapping diagram.

[0088] In addition, the method in the application can also be used for the determination of the coating rate and thickness of the coating layer of the material containing the same elements of the coated substance and the coated substance, and has better adaptability compared with the traditional method.

[0089] The above description is only the preferred specific implementation of the application; however, the protection scope of the application is not limited to this. Any person skilled in the art can make equivalent replacement or change according to the technical solution and the improvement concept of the application within the technical range disclosed by the application, which should be covered in the protection scope of the application.

Claims

1. A method for detecting the surface coating of a material, characterized in that, The following steps are performed in sequence: (1) calendering the substrate material to be detected with a surface coating layer into a film to obtain a calendered film sample; (2) coating the calendered film obtained in step (1) to obtain a coated calendered film sample; (3) etching the coated calendered film obtained in step (2) using an ion beam, the etching depth being: the thickness of the coating minus the maximum detection depth of secondary ion mass spectrometry, plus 1 nm; and performing secondary ion mass spectrometry on the etched coated calendered film to collect the number of secondary ions of the coating layer material A1 and the number of secondary ions of the coated substrate material B1; (4) using an ion beam to gradient etch the etched area of the plated calendered film in step (3), and after each etching, performing secondary ion mass spectrometry on the plated calendered film, collecting the secondary ion number of the cladding layer material and the secondary ion number of the cladded substrate material in each secondary ion mass spectrometry, wherein the secondary ion number of the cladding layer material in the mth time is A m , and the secondary ion number of the cladded substrate material is B m ; (5) continue etching and after each etching, conduct secondary ion mass spectrometry test on the plated calendered film, until A m or B m After the absolute value of the change rate is less than or equal to 1%, stop etching; (6) according to A1, B1, the total etching number k, and A m or B m The number n of the duration of the absolute value of the change rate ≤ 1% is calculated to calculate the coating rate and the coating layer thickness of the coating layer.

2. The method of claim 1, wherein The step (1) is performed in an inert gas environment, which is any one of argon, helium, nitrogen environment.

3. The method of claim 1, wherein In step (4), the etched area of the coated calendered film in step (3) is gradient etched with a gradient of 1 nm.

4. The method of claim 1, wherein The coating thickness in step (2) is 10-500 nm.

5. The method of claim 1, wherein In step (5), n is any integer value between 3 and 7.

6. The method of claim 1, wherein In step (6), the coating rate is A1 / (A1+B1)×100%, and the coating layer thickness is (k-n)×1 nm.

7. The method of claim 1, wherein The material of the surface coating layer in step (1) is one or a combination of Li, C, Al, Ag, Zr, Sr, Mo, Sn, Mg, Ti, Zn, La, Au, and oxides or fluorides thereof.

8. The method of claim 1, wherein, The material used for coating in step (2) is different from the substrate material. The material used for coating in step (2) is one of Ag, Sn, Au, and SiO2.

9. The method of claim 1, wherein, The method used for coating in step (2) is any one of atomic layer deposition, vapor deposition, magnetron sputtering, evaporation coating, and sputtering.

10. The method of claim 1, wherein The etched area in step (2) is a square with a side length of 1-500 μm.

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