Method for detecting silicon distribution uniformity in silicon-containing negative pole piece

Abstract

The invention discloses a method for detecting silicon distribution uniformity in a silicon-containing negative pole piece, and belongs to the technical field of lithium ion batteries. The detection method provided by the invention comprises the following steps: reacting a silicon-containing negative pole piece with an oxidizing gas, then carrying out a coupling reaction on the reacted silicon-containing negative pole piece and an amino-containing silane coupling agent in an aqueous solution, washing, putting into a rhodamine B aqueous solution, reacting, and washing to obtain a treated wet silicon-containing negative pole piece; and selecting a plurality of detection points on the treated wet silicon-containing negative pole piece for fluorescence intensity detection, and judging the silicon distribution uniformity in the silicon-containing negative pole piece according to the fluorescence intensity difference of different detection points. The method adopted by the invention is low in cost, does not need to adopt a complex and expensive scanning electron microscope or energy disperse spectroscopy, can measure a plurality of positions of the silicon-containing negative pole piece, can macroscopically judge the silicon distribution uniformity, and is beneficial to screening of the silicon-containing negative pole piece with relatively high coating quality.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode sheet. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Silicon anode materials have a theoretical capacity of 4200 mAh / g, far exceeding the theoretical capacity of graphite-based anode materials (372 mAh / g). Consequently, these materials have attracted widespread attention. However, during the charge-discharge process, silicon anode materials undergo dramatic volume changes due to the repeated insertion and extraction of lithium ions, with a theoretical volume expansion rate as high as 300-320%. This volume expansion effect is further amplified by the inherent brittleness of the material and imperfections in the electrode fabrication process. In particular, during the coating process, uneven distribution of silicon particles can lead to localized stress concentrations, causing distortion and deformation of the electrode sheet due to the uneven expansion. This can lead to risks such as electrochemical performance degradation, thermal runaway, and short circuits. Therefore, monitoring the silicon distribution in silicon-containing anode plates is crucial. By monitoring the silicon distribution and determining appropriate coating parameters, the safety and service life of silicon-containing anode plates can be enhanced. However, currently, no suitable method exists to qualitatively characterize the uniformity of silicon distribution in silicon-containing anode plates.

[0004] Since the silicon-containing negative electrode is black, the only relatively expensive means of detecting silicon content currently available are electron microscopy and energy spectrum. Moreover, the above detection methods can only detect the silicon content in a small area and cannot determine the content distribution of the entire silicon-containing negative electrode. Therefore, there is an urgent need to provide a low-cost detection method that can comprehensively reflect the uniformity of silicon distribution. Summary of the Invention

[0005] In view of this, the present invention provides a method for detecting the uniformity of silicon distribution in silicon-containing negative electrode sheets. The detection method provided by the present invention can detect the overall silicon distribution of silicon-containing negative electrode sheets. At the same time, the detection cost is low and there is no need to use expensive equipment such as scanning electron microscopes.

[0006] The present invention provides a method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode plate, comprising the following steps: reacting the silicon-containing negative electrode plate with an oxidizing gas, then coupling the reacted silicon-containing negative electrode plate with an amino-containing silane coupling agent in an aqueous solution, washing the plate and reacting the plate in a rhodamine B aqueous solution, and washing the plate to obtain a treated wet silicon-containing negative electrode plate; Several detection points are selected on the treated wet silicon-containing negative electrode sheet to perform fluorescence intensity detection, and the uniformity of silicon distribution in the silicon-containing negative electrode sheet is judged based on the difference in fluorescence intensity at different detection points.

[0007] Preferably, the oxidizing gas is selected from one or more of oxygen, air, water vapor, fluorine gas, chlorine gas, iodine vapor and nitrogen trifluoride.

[0008] Preferably, the temperature for reacting the silicon-containing negative electrode plate with the oxidizing gas is 80-200° C., and the time is 0.1-2 h.

[0009] Preferably, the amino-containing silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropylmethyldimethoxysilane, anilinemethyltriethoxysilane, methyltris(cyclohexylamino)silane or trimethyl[3-(triethoxysilyl)propyl]ammonium chloride.

[0010] Preferably, the coupling reaction time is 0.5-3 h, the coupling reaction temperature is 80-100° C.; and the concentration of the amino-containing silane coupling agent in the aqueous solution is 0.05-10 mol / L.

[0011] Preferably, the concentration of the Rhodamine B aqueous solution is 0.02-50 mol / L.

[0012] Preferably, the reaction temperature of the reaction in the rhodamine B aqueous solution is 10-40° C., the reaction time is 0.5-3 h; the reaction catalyst is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, and the concentration of the reaction catalyst is 0.5-2 mol / L.

[0013] Preferably, in the step of reacting in a Rhodamine B aqueous solution after washing and the step of obtaining a treated wet silicon-containing negative electrode sheet after washing, the solvent used for washing is one or more of toluene, methanol, ethanol, hexane or water.

[0014] Preferably, the fluorescence intensity is detected using a fluorescence microscope, and the excitation wavelength of the fluorescence intensity detection is 530-550 nm.

[0015] Preferably, in the detection method, the content of silicon-based material in the active material of the silicon-containing negative electrode plate is S wt%, the concentration of the silane coupling agent is C mol / L, and the concentration of the rhodamine B aqueous solution is D mol / L, wherein the relationship between S, C and D satisfies the following formula: 0.2≤S / C+S / D≤5600, 0.07≤S*C+S*D≤1600; the value range of S is 1~80, the value range of C is 0.05~10, and the value range of D is 0.02~50.

[0016] Compared with the prior art, the present invention has achieved the following beneficial effects: The present invention introduces hydroxyl groups on the surface of the silicon-containing negative electrode piece by reacting the silicon-containing negative electrode piece with an oxidizing gas, and then couples the hydroxyl groups with the amino-containing silane coupling agent through a covalent bond; the amino groups on the silane coupling agent are coupled with rhodamine B through a condensation reaction, and the uniformity of silicon distribution is indirectly judged by fluorescence intensity detection; the method adopted by the present invention is low-cost, does not require the use of complex and expensive scanning electron microscopes or energy spectrometers, and can measure multiple positions of the silicon-containing negative electrode piece, can judge the uniformity of silicon distribution on a macro scale, is conducive to screening silicon-containing negative electrode pieces with higher coating quality, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute undue limitations thereon. It is obvious that one of ordinary skill in the art could derive other drawings based on these drawings without inventive effort.

[0018] Figure 1 1 is a schematic diagram of the detection process of Example 1 of the present invention; Figure 2 1. It is a diagram showing the positions of nine detection points on the surface of the silicon-containing negative electrode sheet after treatment in Examples 1 to 8 of the present invention and Comparative Examples 1 to 3; Figure 3 Graphs of fluorescence intensity at nine detection points on the surface of the silicon-containing negative electrode sheet after treatment in Examples 1 to 8 of the present invention and Comparative Examples 1 to 3; Figure 4 This is a macroscopic picture of the lithium-ion battery assembled with the silicon-containing negative electrode sheet of Comparative Example 3 of the present invention after the first charge and discharge. DETAILED DESCRIPTION

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0020] In the actual preparation process of silicon-containing negative electrode sheets, the uniformity of silicon distribution is affected by parameters such as silicon content, pulping and coating process. If the silicon distribution is uneven and the silicon content in different parts of the sheet varies greatly, the sheet will expand and twist during the subsequent operation of the lithium-ion battery, thereby causing risks such as electrochemical performance degradation, thermal runaway, and short circuit. Therefore, it is very necessary to monitor the uniformity of silicon distribution in silicon-containing negative electrode sheets. However, there is currently no low-cost and high-feasibility solution. In view of this, the present invention provides a method for detecting the uniformity of silicon distribution in silicon-containing negative electrode sheets, comprising the following steps: reacting the silicon-containing negative electrode plate with an oxidizing gas, then coupling the reacted silicon-containing negative electrode plate with an amino-containing silane coupling agent in an aqueous solution, washing the plate and reacting the plate in a rhodamine B aqueous solution, and washing the plate to obtain a treated wet silicon-containing negative electrode plate; Several detection points are selected on the treated wet silicon-containing negative electrode sheet to perform fluorescence intensity detection, and the uniformity of silicon distribution in the silicon-containing negative electrode sheet is judged based on the difference in fluorescence intensity at different detection points.

[0021] In the above technical solution of the present invention, the silicon-containing negative electrode plate first reacts with the oxidizing gas to form a stable silicon oxide on the surface of the plate, which is conducive to the coupling reaction with the amino-containing silane coupling agent through the Si-O-Si bond. Through the modification of the amino-containing silane coupling agent, the surface of the plate is provided with amino groups, which then undergo a condensation reaction with the carboxyl group of Rhodamine B to form a connection. Rhodamine B can emit fluorescence under the irradiation of laser, and the fluorescence intensity is detected at multiple detection points. The degree of difference in the fluorescence intensity of each detection point can indirectly reflect the uniformity of silicon distribution in the silicon-containing negative electrode plate; when the silicon content is high, the fluorescence intensity of the detection point is strong; when the silicon content is low, the fluorescence intensity of the detection point is weak. By detecting the uniformity of silicon distribution, it can play a certain guiding role in the preparation process of the silicon-containing negative electrode plate, which is conducive to improving the safety of the plate and extending the service life of the plate.

[0022] The present invention does not impose any particular restrictions on the preparation method of the silicon-containing negative electrode sheet, and preferably adopts a pulping method for preparation. The detection method of the present invention can, to a certain extent, evaluate the silicon distribution of the electrode sheets obtained by different preparation processes.

[0023] In the present invention, the oxidizing gas is selected from one or more of oxygen, air, water vapor, fluorine, chlorine, iodine vapor, and nitrogen trifluoride. In one or more embodiments of the present invention, the oxidizing gas is oxygen. The oxidizing gas reacts with the silicon-containing negative electrode plate, resulting in the formation of hydroxyl groups (isolated hydroxyl groups, double hydroxyl groups, or hydrogen-bonded hydroxyl groups, etc.) on the surface of the plate, which then form Si-O-Si covalent bonds with the silane coupling agent.

[0024] In the present invention, the temperature for reacting the silicon-containing negative electrode plate with the oxidizing gas is 80-200°C for 0.1-2 hours. A suitable reaction temperature can promote the reaction between the silicon-containing negative electrode plate and the oxidizing gas. Excessively high reaction temperatures or prolonged reaction times can damage the plate structure, rendering the detection method ineffective.

[0025] In the present invention, the amino-containing silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropylmethyldimethoxysilane, anilinemethyltriethoxysilane, methyltris(cyclohexylamino)silane, or trimethyl[3-(triethoxysilyl)propyl]ammonium chloride. In one or more embodiments of the present invention, the amino-containing silane coupling agent is γ-aminopropyltriethoxysilane, i.e., KH-550.

[0026] In the present invention, the coupling reaction time is 0.5~3h, and the coupling reaction temperature is 80~100℃; the concentration of the amino-containing silane coupling agent in the aqueous solution is 0.05~10 mol / L, more preferably 0.5~5 mol / L. The specific concentration can be determined according to the silicon content in the silicon-containing negative electrode plate to ensure that the silane coupling agent reacts completely with the silicon oxygen group on the plate, thereby ensuring the accuracy of the detection.

[0027] In the present invention, the concentration of the rhodamine B aqueous solution is 0.02 to 50 mol / L, more preferably 0.1 to 20 mol / L. The concentration of rhodamine B affects the amount of rhodamine B grafted onto the electrode surface; the more rhodamine B grafted, the higher the fluorescence intensity. Those skilled in the art can determine the appropriate amount of rhodamine B to add based on specific experimental needs.

[0028] In the present invention, the reaction in the rhodamine B aqueous solution is carried out at a temperature of 10 to 40°C, preferably at room temperature, for a reaction time of 0.5 to 3 hours. The reaction catalyst is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, and the concentration of the reaction catalyst is 0.5 to 2 mol / L. The appropriate temperature and time ensure that the rhodamine B reacts completely with the amino group, thereby ensuring the accuracy of the test results.

[0029] In the present invention, in the steps of reacting in a rhodamine B aqueous solution after washing and obtaining a treated wet silicon-containing negative electrode sheet after washing, the solvent used for washing is one or more of toluene, methanol, ethanol, hexane, or water. Unreacted monomers are removed by washing to avoid adverse effects on the detection process.

[0030] In the present invention, the fluorescence intensity is measured using a fluorescence microscope with an excitation wavelength of 530-550 nm. The present invention does not impose any particular restrictions on the type of fluorescence microscope. Rhodamine B emits light at 570-590 nm under the aforementioned excitation wavelength. The uniformity of silicon distribution is determined by measuring the fluorescence intensity at this emission wavelength.

[0031] The present invention can also place the fluorescence intensities measured at multiple detection points in the same coordinate system, with the detection point number as the horizontal axis and the fluorescence intensity as the vertical axis. The fluorescence intensity values of each detection point are connected, and the silicon distribution uniformity is judged based on the fluctuation. The greater the fluctuation, the worse the silicon distribution uniformity, and the smaller the fluctuation, the better the silicon distribution uniformity. The silicon distribution uniformity can also be further and more intuitively determined using a three-dimensional coordinate system, and the present invention does not impose any special limitations on this.

[0032] The present invention summarizes an empirical formula through a large number of experiments. In the detection method, the content of the silicon-based material in the active material of the silicon-containing negative electrode plate is S wt%, the concentration of the silane coupling agent is C mol / L, and the concentration of the rhodamine B aqueous solution is D mol / L. The relationship between S, C and D satisfies the following formula: 0.2≤S / C+S / D≤5600, 0.07≤S*C+S*D≤1600; the value range of S is 1~80, more preferably 5~60; the value range of C is 0.05~10, more preferably 0.5~5; the value range of D is 0.02~50, more preferably 0.1~20.

[0033] The technical solution of the present invention is further described below with reference to specific examples. The present invention has no particular limitation on the sources of the reagents used in the following examples, and commercially available products known to those skilled in the art can be used.

[0034] Example 1 This embodiment provides a method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode. The detection process diagram is shown in FIG. Figure 1 In this embodiment, the mass of silicon carbon is 30 wt % of the total mass of the active material.

[0035] (1) Preparation of silicon-containing negative electrode sheets: Artificial graphite (first active material), silicon carbon (second active material), conductive carbon (SP-Li), carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber latex, and polyacrylic acid were mixed in a mass ratio of 13.37:5.73:0.2:0.02:0.08:0.10:0.5 to form a mixture. NMP was then added in a high-speed blender at a mass ratio of 0.35:1 to the mixture at 30 rpm and 4000 rpm, and stirred for 60 minutes. Deionized water was then added at a mass ratio of 5.35:1 to the mixture, and stirred for 80 minutes to form a slurry with a solids content of 40 wt%.

[0036] The slurry was applied to one side of a 6 μm thick copper foil using a transfer coater at a coating speed ratio of 1.1 and dried to maintain a coating weight per unit area of 78.12 g / m 2 Then, the same process is used to coat and dry the other side of the copper foil to obtain a semi-finished silicon-containing negative electrode. 3 Roll pressing is performed to obtain a rolled silicon-containing negative electrode sheet.

[0037] (2) Detection of silicon distribution uniformity: The silicon-containing negative electrode prepared in step (1) was placed in a tube furnace, set at 100°C, and oxygen was introduced for 30 minutes. Dry argon gas was then introduced to remove moisture. The electrode was cooled and then taken out. It was immersed in a reaction vessel containing a 1 mol / L γ-aminopropyltriethoxysilane aqueous solution and reacted at 95°C for 1 hour to form a certain number of amino groups (-NH2) on the surface of the silicon oxide. After treatment, it was rinsed with anhydrous ethanol solution.

[0038] The silicon-containing negative electrode sheet with amino groups was placed in a 0.5 mol / L Rhodamine B aqueous solution, and a catalyst 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide 1 mol / L was added to react at 25°C for 0.5 h, and then rinsed with an anhydrous ethanol solution to obtain a treated wet silicon-containing negative electrode sheet.

[0039] After the treatment in this embodiment, 9 detection points are set on the surface of the wet silicon-containing negative electrode plate, such as Figure 2 The cells were then placed in a fluorescence microscope and the fluorescence intensity was recorded at an excitation wavelength of 540 nm and an emission wavelength of 580 nm.

[0040] Example 2 This embodiment provides a method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode. In this embodiment, the mass of silicon carbon is 30 wt% of the total mass of the active material.

[0041] (1) Preparation of silicon-containing negative electrode sheets: Artificial graphite (first active material), silicon carbon (second active material), conductive carbon (SP-Li), carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber latex, and polyacrylic acid were mixed in a mass ratio of 13.37:5.73:0.2:0.02:0.08:0.10:0.5 to form a mixture. NMP was then added in a high-speed blender at a mass ratio of 0.35:1 to the mixture at 30 rpm and 4000 rpm, and stirred for 60 minutes. Deionized water was then added at a mass ratio of 5.35:1 to the mixture, and stirred for 80 minutes to form a slurry with a solids content of 40 wt%.

[0042] The slurry was applied to one side of a 6 μm thick copper foil using a transfer coater at a coating speed ratio of 1.1 and dried to maintain a coating weight per unit area of 78.12 g / m 2 Then, the same process is used to coat and dry the other side of the copper foil to obtain a semi-finished silicon-containing negative electrode. 3 Roll pressing is performed to obtain a rolled silicon-containing negative electrode sheet.

[0043] (2) Detection of silicon distribution uniformity: The silicon-containing negative electrode prepared in step (1) was placed in a tube furnace, set at 100°C, and oxygen was introduced for 1 hour. Dry argon was then introduced to remove moisture. The electrode was cooled and then taken out. It was immersed in a reaction vessel containing a 1 mol / L γ-aminopropyltriethoxysilane aqueous solution and reacted at 95°C for 1 hour to form a certain number of amino groups (-NH2) on the surface of the silicon oxide. After treatment, it was rinsed with anhydrous ethanol solution.

[0044] The silicon-containing negative electrode sheet with amino groups was placed in a 0.5 mol / L Rhodamine B aqueous solution, and a catalyst 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide 1 mol / L was added to react at 25°C for 0.5 h, and then rinsed with an anhydrous ethanol solution to obtain a treated wet silicon-containing negative electrode sheet.

[0045] After the treatment in this embodiment, 9 detection points are set on the surface of the wet silicon-containing negative electrode plate, such as Figure 2 The cells were then placed in a fluorescence microscope and the fluorescence intensity was recorded at an excitation wavelength of 540 nm and an emission wavelength of 580 nm.

[0046] Example 3 This embodiment provides a method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode. In this embodiment, the mass of silicon carbon is 30 wt% of the total mass of the active material.

[0047] (1) Preparation of silicon-containing negative electrode sheets: Artificial graphite (first active material), silicon carbon (second active material), conductive carbon (SP-Li), carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber latex, and polyacrylic acid were mixed in a mass ratio of 13.37:5.73:0.2:0.02:0.08:0.10:0.5 to form a mixture. NMP was then added in a high-speed blender at a mass ratio of 0.35:1 to the mixture at 30 rpm and 4000 rpm, and stirred for 60 minutes. Deionized water was then added at a mass ratio of 5.35:1 to the mixture, and stirred for 80 minutes to form a slurry with a solids content of 40 wt%.

[0048] The slurry was applied to one side of a 6 μm thick copper foil using a transfer coater at a coating speed ratio of 1.1 and dried to maintain a coating weight per unit area of 78.12 g / m 2 Then, the same process is used to coat and dry the other side of the copper foil to obtain a semi-finished silicon-containing negative electrode. 3 Roll pressing is performed to obtain a rolled silicon-containing negative electrode sheet.

[0049] (2) Detection of silicon distribution uniformity: The silicon-containing negative electrode prepared in step (1) was placed in a tube furnace, set at 100°C, and oxygen was introduced for 2 hours. Dry argon gas was then introduced to remove moisture. The electrode was cooled and then taken out. It was immersed in a reaction vessel containing a 1 mol / L γ-aminopropyltriethoxysilane aqueous solution and reacted at 95°C for 1 hour to form a certain number of amino groups (-NH2) on the surface of the silicon oxide. After treatment, it was rinsed with anhydrous ethanol solution.

[0050] The silicon-containing negative electrode sheet with amino groups was placed in a 0.5 mol / L Rhodamine B aqueous solution, and a catalyst 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide 1 mol / L was added to react at 25°C for 0.5 h, and then rinsed with an anhydrous ethanol solution to obtain a treated wet silicon-containing negative electrode sheet.

[0051] After the treatment in this embodiment, 9 detection points are set on the surface of the wet silicon-containing negative electrode plate, such as Figure 2 The cells were then placed in a fluorescence microscope and the fluorescence intensity was recorded at an excitation wavelength of 540 nm and an emission wavelength of 580 nm.

[0052] Example 4 This embodiment provides a method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode. In this embodiment, the mass of silicon carbon is 30 wt% of the total mass of the active material.

[0053] (1) Preparation of silicon-containing negative electrode sheets: Artificial graphite (first active material), silicon carbon (second active material), conductive carbon (SP-Li), carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber latex, and polyacrylic acid were mixed in a mass ratio of 13.37:5.73:0.2:0.02:0.08:0.10:0.5 to form a mixture. NMP was then added in a high-speed blender at a mass ratio of 0.35:1 to the mixture at 30 rpm and 4000 rpm, and stirred for 60 minutes. Deionized water was then added at a mass ratio of 5.35:1 to the mixture, and stirred for 80 minutes to form a slurry with a solids content of 40 wt%.

[0054] The slurry was applied to one side of a 6 μm thick copper foil using a transfer coater at a coating speed ratio of 1.1 and dried to maintain a coating weight per unit area of 78.12 g / m 2 Then, the same process is used to coat and dry the other side of the copper foil to obtain a semi-finished silicon-containing negative electrode. 3 Roll pressing is performed to obtain a rolled silicon-containing negative electrode sheet.

[0055] (2) Detection of silicon distribution uniformity: The silicon-containing negative electrode prepared in step (1) was placed in a tube furnace, set at 200°C, and oxygen was introduced. The reaction was continued for 30 minutes. Dry argon gas was then introduced to remove moisture. The electrode was cooled and then taken out. It was immersed in a reaction vessel containing a 1 mol / L γ-aminopropyltriethoxysilane aqueous solution and reacted at 95°C for 1 hour to form a certain number of amino groups (-NH2) on the surface of the silicon oxide. After treatment, it was rinsed with anhydrous ethanol solution.

[0056] The silicon-containing negative electrode sheet with amino groups was placed in a 0.5 mol / L Rhodamine B aqueous solution, and a catalyst 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide 1 mol / L was added to react at 25°C for 0.5 h, and then rinsed with an anhydrous ethanol solution to obtain a treated wet silicon-containing negative electrode sheet.

[0057] After the treatment in this embodiment, 9 detection points are set on the surface of the wet silicon-containing negative electrode plate, such as Figure 2 The cells were then placed in a fluorescence microscope and the fluorescence intensity was recorded at an excitation wavelength of 540 nm and an emission wavelength of 580 nm.

[0058] Example 5 This embodiment provides a method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode. In this embodiment, the mass of silicon carbon is 5 wt% of the total mass of the active material.

[0059] (1) Preparation of silicon-containing negative electrode sheets: Artificial graphite (first active material), silicon carbon (second active material), conductive carbon (SP-Li), carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber latex, and polyacrylic acid were mixed in a mass ratio of 18.15:0.955:0.2:0.02:0.08:0.10:0.5 to form a mixture. NMP was then added in a high-speed blender at a mass ratio of 0.35:1 to the mixture and stirred for 60 minutes. Deionized water was then added at a mass ratio of 5.35:1 to the mixture and stirred for 80 minutes to form a slurry with a solids content of 40wt%.

[0060] The slurry was applied to one side of a 6 μm thick copper foil using a transfer coater at a coating speed ratio of 1.1 and dried to maintain a coating weight per unit area of 78.12 g / m 2 Then, the same process is used to coat and dry the other side of the copper foil to obtain a semi-finished silicon-containing negative electrode. 3 Roll pressing is performed to obtain a rolled silicon-containing negative electrode sheet.

[0061] (2) Detection of silicon distribution uniformity: The silicon-containing negative electrode prepared in step (1) was placed in a tube furnace, set at 100°C, and oxygen was introduced for 30 minutes. Dry argon gas was then introduced to remove moisture. The electrode was cooled and then taken out. It was immersed in a reaction vessel containing a 1 mol / L γ-aminopropyltriethoxysilane aqueous solution and reacted at 95°C for 1 hour to form a certain number of amino groups (-NH2) on the surface of the silicon oxide. After treatment, it was rinsed with anhydrous ethanol solution.

[0062] The silicon-containing negative electrode sheet with amino groups was placed in a 0.5 mol / L Rhodamine B aqueous solution, and a catalyst 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide 1 mol / L was added to react at 25°C for 0.5 h, and then rinsed with an anhydrous ethanol solution to obtain a treated wet silicon-containing negative electrode sheet.

[0063] After the treatment in this embodiment, 9 detection points are set on the surface of the wet silicon-containing negative electrode plate, such as Figure 2 The cells were then placed in a fluorescence microscope and the fluorescence intensity was recorded at an excitation wavelength of 540 nm and an emission wavelength of 580 nm.

[0064] Example 6 This embodiment provides a method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode. In this embodiment, the mass of silicon carbon is 50 wt% of the total mass of the active material.

[0065] (1) Preparation of silicon-containing negative electrode sheets: Artificial graphite (first active material), silicon carbon (second active material), conductive carbon (SP-Li), carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber latex, and polyacrylic acid were mixed in a mass ratio of 9.55:9.55:0.2:0.02:0.08:0.10:0.5 to form a mixture. NMP was then added in a high-speed blender at a mass ratio of 0.35:1 to the mixture and stirred for 60 minutes. Deionized water was then added at a mass ratio of 5.35:1 to the mixture and stirred for 80 minutes to form a slurry with a solids content of 40wt%.

[0066] The slurry was applied to one side of a 6 μm thick copper foil using a transfer coater at a coating speed ratio of 1.1 and dried to maintain a coating weight per unit area of 78.12 g / m 2 Then, the same process is used to coat and dry the other side of the copper foil to obtain a semi-finished silicon-containing negative electrode. 3 Roll pressing is performed to obtain a rolled silicon-containing negative electrode sheet.

[0067] (2) Detection of silicon distribution uniformity: The silicon-containing negative electrode prepared in step (1) was placed in a tube furnace, set at 100°C, and oxygen was introduced for 30 minutes. Dry argon gas was then introduced to remove moisture. The electrode was cooled and then taken out. It was immersed in a reaction vessel containing a 1 mol / L γ-aminopropyltriethoxysilane aqueous solution and reacted at 95°C for 1 hour to form a certain number of amino groups (-NH2) on the surface of the silicon oxide. After treatment, it was rinsed with anhydrous ethanol solution.

[0068] The silicon-containing negative electrode sheet with amino groups was placed in a 0.5 mol / L Rhodamine B aqueous solution, and a catalyst 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide 1 mol / L was added to react at 25°C for 0.5 h, and then rinsed with an anhydrous ethanol solution to obtain a treated wet silicon-containing negative electrode sheet.

[0069] After the treatment in this embodiment, 9 detection points are set on the surface of the wet silicon-containing negative electrode plate, such as Figure 2 The cells were then placed in a fluorescence microscope and the fluorescence intensity was recorded at an excitation wavelength of 540 nm and an emission wavelength of 580 nm.

[0070] Example 7 This embodiment provides a method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode. In this embodiment, the mass of silicon carbon is 30 wt% of the total mass of the active material.

[0071] (1) Preparation of silicon-containing negative electrode sheets: Artificial graphite (first active material), silicon carbon (second active material), conductive carbon (SP-Li), carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber latex, and polyacrylic acid were mixed in a mass ratio of 13.37:5.73:0.2:0.02:0.08:0.10:0.5 to form a mixture. NMP was then added in a high-speed blender at a mass ratio of 0.35:1 to the mixture at 30 rpm and 4000 rpm, and stirred for 60 minutes. Deionized water was then added at a mass ratio of 5.35:1 to the mixture, and stirred for 80 minutes to form a slurry with a solids content of 40 wt%.

[0072] The slurry was applied to one side of a 6 μm thick copper foil using a transfer coater at a coating speed ratio of 1.1 and dried to maintain a coating weight per unit area of 78.12 g / m 2 Then, the same process is used to coat and dry the other side of the copper foil to obtain a semi-finished silicon-containing negative electrode. 3 Roll pressing is performed to obtain a rolled silicon-containing negative electrode sheet.

[0073] (2) Detection of silicon distribution uniformity: The silicon-containing negative electrode prepared in step (1) was placed in a tube furnace, set at 100°C, and oxygen was introduced for 30 minutes. Dry gas was then introduced to remove moisture. After cooling, the electrode was taken out and immersed in a reaction vessel containing a 2 mol / L γ-aminopropyltriethoxysilane aqueous solution. The reaction was carried out at 95°C for 1 hour to form a certain number of amino groups (-NH2) on the surface of the silicon oxide. After treatment, it was rinsed with anhydrous ethanol solution.

[0074] The silicon-containing negative electrode sheet with amino groups was placed in a 0.5 mol / L Rhodamine B aqueous solution, and a catalyst 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide 1 mol / L was added to react at 25°C for 0.5 h, and then rinsed with an anhydrous ethanol solution to obtain a treated wet silicon-containing negative electrode sheet.

[0075] After the treatment in this embodiment, 9 detection points are set on the surface of the wet silicon-containing negative electrode plate, such as Figure 2 The cells were then placed in a fluorescence microscope and the fluorescence intensity was recorded at an excitation wavelength of 540 nm and an emission wavelength of 580 nm.

[0076] Example 8 This embodiment provides a method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode. In this embodiment, the mass of silicon carbon is 30 wt% of the total mass of the active material.

[0077] (1) Preparation of silicon-containing negative electrode sheets: Artificial graphite (first active material), silicon carbon (second active material), conductive carbon (SP-Li), carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber latex, and polyacrylic acid were mixed in a mass ratio of 13.37:5.73:0.2:0.02:0.08:0.10:0.5 to form a mixture. NMP was then added in a high-speed blender at a mass ratio of 0.35:1 to the mixture at 30 rpm and 4000 rpm, and stirred for 60 minutes. Deionized water was then added at a mass ratio of 5.35:1 to the mixture, and stirred for 80 minutes to form a slurry with a solids content of 40 wt%.

[0078] The slurry was applied to one side of a 6 μm thick copper foil using a transfer coater at a coating speed ratio of 1.1 and dried to maintain a coating weight per unit area of 78.12 g / m 2 Then, the same process is used to coat and dry the other side of the copper foil to obtain a semi-finished silicon-containing negative electrode. 3 Roll pressing is performed to obtain a rolled silicon-containing negative electrode sheet.

[0079] (2) Detection of silicon distribution uniformity: The silicon-containing negative electrode prepared in step (1) was placed in a tube furnace, set at 100°C, and oxygen was introduced for 30 minutes. Dry argon gas was then introduced to remove moisture. The electrode was cooled and then taken out. It was immersed in a reaction vessel containing a 1 mol / L γ-aminopropyltriethoxysilane aqueous solution and reacted at 95°C for 1 hour to form a certain number of amino groups (-NH2) on the surface of the silicon oxide. After treatment, it was rinsed with anhydrous ethanol solution.

[0080] The silicon-containing negative electrode sheet with amino groups was placed in a 5 mol / L Rhodamine B aqueous solution, and a catalyst 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide 1 mol / L was added to react at 25°C for 0.5h, and then rinsed with an anhydrous ethanol solution to obtain a treated wet silicon-containing negative electrode sheet.

[0081] After the treatment in this embodiment, 9 detection points are set on the surface of the wet silicon-containing negative electrode plate, such as Figure 2 The cells were then placed in a fluorescence microscope and the fluorescence intensity was recorded at an excitation wavelength of 540 nm and an emission wavelength of 580 nm.

[0082] Comparative Example 1 The difference between this comparative example and Example 1 is that in step (2) of this comparative example, oxygen is introduced and the reaction is continued for 4 hours.

[0083] Comparative Example 2 The difference between this comparative example and Example 1 is that in step (2) of this comparative example, the temperature is set to 300° C., oxygen is introduced, and the reaction is continued for 30 minutes.

[0084] Comparative Example 3 The difference between this comparative example and Example 1 is that the preparation method of the silicon-containing negative electrode plate is different. The preparation method of the silicon-containing negative electrode plate in this comparative example is as follows: Artificial graphite (first active material), silicon carbon (second active material), conductive carbon (SP-Li), carbon nanotubes, sodium carboxymethyl cellulose, styrene-butadiene rubber latex, and polyacrylic acid were mixed in a mass ratio of 13.37:5.73:0.2:0.02:0.08:0.10:0.5 to form a mixture. NMP was then added in a high-speed blender at a mass ratio of 0.35:1 to the mixture and stirred for 30 minutes. Deionized water was then added at a mass ratio of 5.35:1 to the mixture and stirred for 40 minutes to form a slurry with a solids content of 40wt%.

[0085] The above slurry was coated on one side of a 6 micron thick copper foil using a transfer coater at a coating speed ratio of 1.1 and dried to maintain a coating weight per unit area of 78.12 g / m 2 Then, the same process is used to coat and dry the other side of the copper foil to obtain a semi-finished silicon-containing negative electrode. 3 Roll pressing is performed to obtain a rolled silicon-containing negative electrode sheet.

[0086] Test example 1. Fluorescence intensity detection: Table 1 summarizes the technical solutions and experimental results of Examples 1 to 8 and Comparative Examples 1 to 3.

[0087] Table 1 Technical solutions and experimental results of Examples 1 to 8 and Comparative Examples 1 to 3

[0088] Note: In Table 1, the silicon-carbon content in the active material of the silicon-containing negative electrode is S, the concentration of the silane coupling agent is C mol / L, and the concentration of the rhodamine B aqueous solution is D mol / L. Formula 1 is S / C + S / D, and Formula 2 is S*C + S*D. In the experimental results, "OK" indicates that the experimental effect was demonstrated, and "NG" indicates that the experimental effect was not demonstrated.

[0089] Nine detection points were set on the surface of the silicon-containing negative electrode sheet after treatment in Examples 1 to 8 and Comparative Examples 1 to 3, such as Figure 2As shown, it was then placed in a fluorescence microscope, and under an excitation wavelength of 540 nm, the fluorescence intensity at an emission wavelength of 580 nm was recorded, as shown in Table 2, and a curve was drawn, as shown in Figure 3 shown.

[0090] Table 2 Fluorescence intensity at each detection point of the silicon-containing negative electrode sheets after treatment in Examples 1 to 8 and Comparative Examples 1 to 3

[0091] Comparing the effects of 0.5h, 1h, 2h, and 4h reaction times in Examples 1-3 and Comparative Example 1 under the same conditions of γ-aminopropyltriethoxysilane solution, rhodamine B solution, and silicon content, it was found that Example 3 ≈ Example 2 > Example 1 > Comparative Example 4 (electrode structure failure). This is because the longer the reaction time, the more silicon oxide produced by the reaction, until the surface layer is completely formed and the optimal effect is achieved. Because the electrode contains graphite, it will continue to react with the reaction gas to generate carbon oxide gas molecules. Continued reaction will destroy the electrode structure. Compared with Comparative Example 2, the fluorescence intensity of Example 4 is slightly greater than that of Example 2, and the electrode of Comparative Example 2 fails and cannot be measured. This is because under high temperature conditions, the temperature promotes the reaction of silicon oxide, thereby generating more silicon oxide, and excessively high temperature will destroy the electrode structure in the sample, affecting the experimental results. Comparing Examples 2, 5, and 6, Example 2 exhibited superior uniformity to Example 6, with Example 5 exhibiting the best uniformity. This is due to the increased silicon content, which, to a certain extent, increased the unevenness of silicon distribution. Furthermore, the fluorescence intensities of the three samples ranked in the order of Example 6 > Example 2 > Example 5, which corresponds to the trend of silicon content. Compared with Example 7, Example 2 exhibited a higher fluorescence intensity due to the increased γ-aminopropyltriethoxysilane content, which allowed for a more complete reaction with the silicon oxide. This resulted in a higher content of modified silicon oxide, allowing for more covalent bonding with the fluorescent dye Rhodamine B. Compared with Example 2, Example 8 exhibited a higher fluorescence intensity due to the increased content of the fluorescent dye Rhodamine B. This resulted in more covalent bonding between the carboxylic acid groups (-COOH) of Rhodamine B and the amino groups (-NH2) on the surface of the modified silicon oxide, resulting in a greater amount of Rhodamine B adsorbed and retained on the surface. Compared with Example 1, Comparative Example 3 exhibited greater fluctuations in fluorescence intensity across the nine measurement points, indicating poorer silicon distribution uniformity. This was due to the shortened stirring time, which resulted in uneven dispersion of the silicon-based material.

[0092] 2. Battery distortion The silicon-containing negative electrode obtained by the preparation method of Comparative Example 3 is assembled into a lithium-ion battery and charged and discharged. The macroscopic picture of the battery after the first charge and discharge is as follows: Figure 3 As shown, it can be seen that the pole piece of comparative example 3 is twisted, indicating that uneven silicon distribution can cause the pole piece to be twisted.

[0093] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for detecting the uniformity of silicon distribution in a silicon-containing negative electrode sheet, characterized in that: The steps include: reacting the silicon-containing negative electrode plate with an oxidizing gas, then coupling the reacted silicon-containing negative electrode plate with an amino-containing silane coupling agent in an aqueous solution, washing the plate and reacting the plate in a rhodamine B aqueous solution, and washing the plate to obtain a treated wet silicon-containing negative electrode plate; Several detection points are selected on the treated wet silicon-containing negative electrode sheet to perform fluorescence intensity detection, and the uniformity of silicon distribution in the silicon-containing negative electrode sheet is judged based on the difference in fluorescence intensity at different detection points.

2. The detection method according to claim 1, wherein The oxidizing gas is selected from one or more of oxygen, air, water vapor, fluorine gas, chlorine gas, iodine vapor and nitrogen trifluoride.

3. The detection method according to claim 1, wherein The temperature for reacting the silicon-containing negative electrode plate with the oxidizing gas is 80-200° C., and the time is 0.1-2 hours.

4. The detection method according to claim 1, wherein The amino-containing silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropylmethyldimethoxysilane, anilinemethyltriethoxysilane, methyltris(cyclohexylamino)silane or trimethyl[3-(triethoxysilyl)propyl]ammonium chloride.

5. The detection method according to claim 1, wherein The coupling reaction time is 0.5-3 hours, the coupling reaction temperature is 80-100° C.; the concentration of the amino-containing silane coupling agent in the aqueous solution is 0.05-10 mol / L.

6. The detection method according to claim 1, wherein The concentration of the Rhodamine B aqueous solution is 0.02-50 mol / L.

7. The detection method according to claim 1, wherein The reaction temperature of the reaction in the Rhodamine B aqueous solution is 10-40° C., and the reaction time is 0.5-3 h.

8. The detection method according to claim 1, wherein In the step of reacting in a Rhodamine B aqueous solution after washing and the step of obtaining a treated wet silicon-containing negative electrode sheet after washing, the solvent used for washing is one or more of toluene, methanol, ethanol, hexane or water.

9. The detection method according to claim 1, wherein The fluorescence intensity was detected using a fluorescence microscope, and the excitation wavelength of the fluorescence intensity was 530-550 nm.

10. The detection method according to claim 1, wherein In the detection method, the content of silicon-based material in the active material of the silicon-containing negative electrode plate is S wt%, the concentration of the silane coupling agent is C mol / L, and the concentration of the rhodamine B aqueous solution is D mol / L, wherein the relationship between S, C and D satisfies the following formula: 0.2≤S / C+S / D≤5600, 0.07≤S*C+S*D≤1600; the value range of S is 1~80, the value range of C is 0.05~10, and the value range of D is 0.02~50.

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