Method for detecting the change of the electric contact state and the swelling stress during the charging and discharging of an electrode

Abstract

The application provides a detection method for the change of the electric contact state and the expansion stress in the electrode charging and discharging process, which uses single-walled carbon nanotubes as sensitive mechanical probes to form an in-situ half battery in contact with the electrode material. Due to the strong van der Waals interaction between the single-walled carbon nanotubes and the electrode material, even if the electrode material has a large volume expansion in the charging and discharging process, the electrode material still maintains good electric contact with the single-walled carbon nanotubes. The Raman signal is highly sensitive to the stress change of the reticular single-walled carbon nanotubes. Therefore, the in-situ Raman test is carried out on the half battery, the Raman spectrum is obtained, the stress of the single-walled carbon nanotubes is measured by analyzing the G peak shift of the Raman spectrum, and the stress change of the electrode material in contact with the single-walled carbon nanotubes is calculated. The whole detection process does not need to add extra solvent, has no toxic gas emission, belongs to nondestructive testing, and is suitable for all battery materials.

Description

Technical Field

[0001] This invention relates to the field of new energy materials and their preparation technology, and in particular to a method for detecting changes in electrical contact state and expansion stress during electrode charging and discharging. Background Technology

[0002] With global energy shortages and increased environmental awareness, new energy sources have become an important development direction. Lithium-ion batteries, with their advantages such as high operating voltage, no memory effect, low self-discharge, and long cycle life, have become a hot topic in the energy industry and are widely used in mobile electronic products such as mobile phones and computers.

[0003] Electrode materials, such as silicon anode electrode materials, are valued for their high theoretical energy density (4200 mAh g⁻¹). -1 Due to its advantages of low environmental impact, it is widely used in lithium-ion batteries. However, its huge volume change (400%) hinders its commercialization. Therefore, efforts have been made to develop and improve electrode materials to mitigate the negative impact of mechanical stress on battery performance.

[0004] Various in-situ diffraction and spectroscopy techniques, including X-ray diffraction, Raman spectroscopy, and optical sensors, have been developed to detect volume changes and electrode strain under lithium-driven conditions during charging and discharging. However, there are few techniques for characterizing electrical contact states and detecting stress changes. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a method for detecting changes in electrical contact state and expansion stress during electrode charging and discharging. This method uses reticulated single-walled carbon nanotubes (SWCNTs) as sensitive mechanical probes to form an in-situ half-cell in contact with the electrode material. During the charging and discharging process of the half-cell, Raman laser signals are collected in situ to form Raman spectra. The shift of the G peak in the Raman spectrum is used to accurately evaluate the changes in electrical contact state and stress caused by the expansion of the electrode material during the charging and discharging process.

[0006] The specific details of the invention are as follows:

[0007] In a first aspect, the present invention provides a method for detecting changes in electrical contact state and expansion stress during electrode charging and discharging, the detection method comprising the following steps:

[0008] S1. A network of single-walled carbon nanotubes is formed by self-assembly of single-walled carbon nanotubes relying on van der Waals forces.

[0009] S2. The electrode material, the mesh single-walled carbon nanotube structure and the current collector are rolled together to prepare the electrode, and then assembled in the in-situ cell to form an in-situ half cell.

[0010] S3. Connect the in-situ half-cell to the electrochemical workstation to perform in-situ charge-discharge tests and in-situ Raman tests to obtain the Raman spectrum of the single-walled carbon nanotubes.

[0011] S4. Calculate the stress generated by the single-walled carbon nanotube based on the shift of the G peak in the Raman spectrum, and deduce the electrical contact state and expansion stress changes during the charging and discharging process of the electrode based on the stress changes.

[0012] Optionally, the electrode material includes silicon-based active materials or silicon carbide active materials.

[0013] Optionally, the thickness of the network single-walled carbon nanotube structure is 3-10000 nm.

[0014] Optionally, the sheet resistance of the network single-walled carbon nanotube structure is 10-50Ω.

[0015] Optionally, in the in-situ Raman test, the Raman laser emitted by the Raman spectrometer has a wavelength of 532 nm.

[0016] Optionally, the in-situ charge-discharge process includes a discharge process and a charging process;

[0017] The discharge process includes: the in-situ half-cell discharging from 1.5V to 0.01V;

[0018] The charging process includes charging the in-situ half-cell from 0.01V to 1.5V.

[0019] Optionally, the stress generated by the network of single-walled carbon nanotubes is derived from the following formula:

[0020] F = -ΔG / 8 * 1.1 = -1.375 * ΔG

[0021] Where ΔG represents the G-peak offset.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] This invention provides a method for detecting the electrical contact state and expansion stress changes during electrode charging and discharging. The method uses a network of single-walled carbon nanotubes (SUVs) as a sensitive mechanical probe to form an in-situ half-cell in contact with the electrode material. Due to strong van der Waals interactions, the electrode material maintains good electrical contact with the SUVs even during significant volume expansion during charging and discharging. Furthermore, the Raman signal is highly sensitive to stress changes in the SUVs. Therefore, in-situ Raman testing is performed during the half-cell charging and discharging process to generate a Raman spectrum. By analyzing the G peak shift in the Raman spectrum, the stress on the SUVs can be measured, thereby calculating the stress change in the contacting electrode material. The entire detection process requires no additional solvents, emits no toxic gases, is non-destructive testing, is applicable to all battery materials, and provides accurate, simple, and practical results. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A flowchart of the detection method for electrical contact state and expansion stress changes during electrode charging and discharging provided in an embodiment of the present invention is shown. Detailed Implementation

[0026] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0027] Specific experimental steps or conditions are not specified in the examples; however, they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products.

[0028] Single-walled carbon nanotubes (SWCNTs) are highly sensitive to strain and structural integrity due to their excellent electrical and thermal conductivity, high aspect ratio, and mechanical flexibility. Raman spectroscopy has thus become an effective method for studying the mechanical and failure behavior of SWCNTs. Therefore, when SWCNTs are combined with silicon-based active materials in electrodes, they can theoretically serve as a sensitive mechanical probe to monitor local strain caused by volume changes in the electrode material and reflect the contact state between them. Based on this, the present invention provides a method for detecting the electrical contact state and changes in expansion stress during electrode charging and discharging, the specific implementation of which is as follows:

[0029] Figure 1 A flowchart of the detection method for electrical contact state and expansion stress changes during electrode charging and discharging provided in an embodiment of the present invention is shown, as follows: Figure 1 As shown, the detection method includes the following steps:

[0030] S1. A network of single-walled carbon nanotubes is formed by self-assembly of single-walled carbon nanotubes relying on van der Waals forces.

[0031] S2. The electrode material, the mesh single-walled carbon nanotube structure and the current collector are rolled together to prepare the electrode, and then assembled in the in-situ cell to form an in-situ half cell.

[0032] S3. Connect the in-situ half-cell to the electrochemical workstation to perform in-situ charge-discharge tests and in-situ Raman tests to obtain the Raman spectrum of the single-walled carbon nanotubes.

[0033] S4. Calculate the stress generated by the single-walled carbon nanotube based on the shift of the G peak in the Raman spectrum, and deduce the electrical contact state and expansion stress changes during the charging and discharging process of the electrode based on the stress changes.

[0034] In practical implementation, the method for detecting changes in electrical contact state and expansion stress during electrode charging and discharging provided by this invention uses single-walled carbon nanotubes (SUVs) as sensitive mechanical probes to form an in-situ half-cell in contact with the electrode material. Due to strong van der Waals interactions, the SUVs and electrode material initially have good interfacial contact. In-situ Raman testing is performed during the charging and discharging process of the in-situ half-cell. When the electrical contact between the SUV and the electrode material is good, the volume expansion of the electrode material imparts a certain stress to the carbon nanotube; when the electrical contact is poor, the stress will not change significantly. Since the Raman signal is highly sensitive to changes in the stress of the SUV, the shift of the G peak in the Raman spectrum can accurately assess the changes in electrical contact state and stress caused by the expansion of the electrode material during the charging and discharging process. The detection method is simple and practical.

[0035] In some embodiments, the electrode material includes silicon-based active materials or silicon-carbon active materials, specifically silicon suboxide@carbon or silicon@carbon.

[0036] In some implementations, single-walled carbon nanotubes, due to their excellent conductivity, high aspect ratio and mechanical flexibility, can self-assemble under van der Waals forces to form a network of single-walled carbon nanotube structures with a thickness of 3-10000 nm and a sheet resistance of 10-50 Ω.

[0037] In some embodiments, the in-situ charge-discharge process includes a discharge process and a charging process;

[0038] The discharge process includes: the in-situ half-cell discharging from 1.5V to 0.01V;

[0039] The charging process includes charging the in-situ half-cell from 0.01V to 1.5V.

[0040] In some implementations, the in-situ Raman spectrometer emits a Raman laser with a wavelength of 532 nm, which is used to irradiate the single-arm carbon nanotube in contact with the electrode material. During the charging and discharging process, a Raman spectrum is collected at regular voltage intervals. The voltage intervals can be 0.1V-0.5V, such as 0.1V, 0.2V, 0.3V, 0.4V, or 0.5V.

[0041] In some implementations, the G peak shift of the acquired Raman spectrum is calculated as ΔG, based on every 8 wavenumbers (cm²). -1 For a 1% strain in carbon nanotubes, the Young's modulus is approximately 1.1 TPa. Therefore, the derivation formula for the stress (tensile stress) generated by single-walled carbon nanotubes can be expressed as follows:

[0042] F = -ΔG / 8 * 1.1 = -1.375 * ΔG (unit: TPa)

[0043] To enable those skilled in the art to better understand this application, the following embodiments will be used to describe in detail the method for detecting changes in electrical contact state and expansion stress during electrode charging and discharging.

[0044] Example 1

[0045] At room temperature, single-walled carbon nanotubes are self-assembled into a conductive network (network single-walled carbon nanotube structure) by van der Waals forces.

[0046] A half-cell was assembled in an in-situ cell using silicon-based material SiOx@C as the electrode active material, a network of single-walled carbon nanotubes as the stress indicator, and a graphite current collector.

[0047] The Raman laser was set to 532 nm and then applied to a single-walled carbon nanotube in contact with SiOx@C.

[0048] Start the charge-discharge test (discharge from 1.5V to 0.01V, then charge back to 1.5V), and collect one Raman spectrum every 0.3V interval;

[0049] After a certain number of cycles, stop the charge-discharge test and turn off the Raman laser;

[0050] Analyzing the G peak shift in the acquired Raman spectrum, the force on the carbon nanotubes can be expressed by the following formula:

[0051] F = -ΔG / 8 * 1.1 = -1.375 * ΔG (unit: TPa)

[0052] Tables 1 and 2 show the G-peak shift and corresponding force conditions during the charging and discharging process, respectively.

[0053] Table 1. G-peak shift and carbon nanotube stress during in-situ battery discharge process.

[0054]

[0055]

[0056] Table 2. G-peak shift and carbon nanotube stress during in-situ battery charging process.

[0057] 0.01V 0.3V 0.6V 0.9V 1.2V 1.5V <![CDATA[G peak position (cm 1 )]]> 1577.5 1577.7 1577.5 1577.7 1577.8 1577.5 <![CDATA[Offset (cm -1 )]]> -0.37 -0.12 -0.32 -0.16 0 -0.34 Force (MPa) 555 180 480 240 0 510

[0058] The present invention provides a detailed description of a method for detecting changes in electrical contact state and expansion stress during electrode charging and discharging. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for detecting changes in electrical contact state and expansion stress during electrode charging and discharging, characterized in that, The detection method includes the following steps: S1. A network structure of single-walled carbon nanotubes with conductive network function is formed by self-assembly of single-walled carbon nanotubes by van der Waals forces. S2. The electrode material, the mesh single-walled carbon nanotube structure and the current collector are rolled together to prepare the electrode, and then assembled in the in-situ cell to form an in-situ half cell. S3. Connect the in-situ half-cell to the electrochemical workstation to perform in-situ charge-discharge tests and in-situ Raman tests to obtain the Raman spectrum of the single-walled carbon nanotubes. S4. Calculate the stress generated by the single-walled carbon nanotube based on the shift of the G peak in the Raman spectrum, and deduce the electrical contact state and expansion stress changes during the charging and discharging process of the electrode based on the stress changes. The derivation formula for the stress generated by the network single-walled carbon nanotube structure is as follows: F=(1.1TPa) (-ΔG / 8 1%)=-0.001375 ΔG(TPa); Where ΔG represents the G peak offset.

2. The detection method according to claim 1, characterized in that, The electrode material includes silicon-based active materials or silicon-carbon active materials.

3. The detection method according to claim 1, characterized in that, The thickness of the network of single-walled carbon nanotube structures is 3-10000 nm.

4. The detection method according to claim 1, characterized in that, The sheet resistance of the reticulated single-walled carbon nanotube structure is 10-50Ω.

5. The detection method according to claim 1, characterized in that, In the in-situ Raman test, the Raman laser emitted by the Raman spectrometer has a wavelength of 532 nm.

6. The detection method according to claim 1, characterized in that, The in-situ charge-discharge process includes a discharge process and a charging process; The discharge process includes: the in-situ half-cell discharging from 1.5V to 0.01V; The charging process includes charging the in-situ half-cell from 0.01V to 1.5V.

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