Method for detecting fiber foreign matter content in negative electrode active material of secondary battery

Abstract

The invention provides a method for detecting the content of fiber foreign matters in a negative electrode active material of a secondary battery, the negative electrode active material is graphite, and the method comprises the following steps: (S1) providing a flotation solution; (S2) graphite containing fiber foreign matters is dispersed in the flotation liquid to form dispersion liquid, the graphite is moved out after the graphite is settled, so that the graphite and supernatant liquid are separated, and then the supernatant liquid is filtered through a filter membrane; (S3) after filtering is completed, shooting the filter membrane through an optical microscope to obtain an image; and (S4) the image obtained in the step (S3) is processed through an image processing device, the image processing device comprises an input module, a judgment module, a data analysis module and an output module, and the image processing device recognizes the fiber foreign matter through an image recognition algorithm.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a method for detecting the content of fibrous foreign matter in negative electrode active materials of secondary batteries. Background Art

[0002] In the production of secondary batteries, graphite is used in large quantities as a negative electrode active material. During the production and transportation of graphite raw materials, natural fibers such as cotton and linen from packaging or artificial fibers are often mixed in. These fibers can damage the performance of electrochemical devices during the production of electrochemical devices. For example, the graphite coating layer containing fiber foreign matter can have pits and pitting after battery cycling, resulting in a loss of battery capacity.

[0003] Currently, technicians mainly use screening methods to detect and separate fibrous foreign matter in graphite raw materials. However, due to the large mesh size (usually 50 μm), fibrous foreign matter can easily pass through the mesh holes, making it difficult to obtain accurate detection results through screening methods.

[0004] Therefore, there is a need in the art for a method that can accurately detect the content of fiber foreign matter in negative electrode active materials of secondary batteries, especially in graphite. Summary of the invention

[0005] In order to solve the above problems, the purpose of the present application is to provide a method for detecting the content of fibrous foreign matter in the negative electrode active material of a secondary battery, wherein the negative electrode active material is graphite, and the method comprises the following steps: (S1) providing a flotation liquid; (S2) dispersing graphite containing fibrous foreign matter in the flotation liquid to form a dispersion, removing the graphite after the graphite settles to separate the graphite and the upper liquid, and then filtering the upper liquid through a filter membrane; (S3) photographing the filter membrane through an optical microscope after the filtration is completed to obtain an image; (S4) processing the image obtained in step (S3) through an image processing device, wherein the image processing device comprises an input module, a judgment module, a data analysis module and an output module, and wherein the image processing device identifies the fibrous foreign matter through an image recognition algorithm.

[0006] The method of the present application can quantitatively detect fiber foreign matter in graphite, and can accurately count the number and size distribution of fiber foreign matter. More advantageously, compared with the screening method limited by the mesh aperture, the method of the present application can detect fiber foreign matter with a size less than 50 μm. Thus, the content of fiber foreign matter in the graphite raw material can be controlled by the method of the present application, so that when these graphite raw materials are used to prepare the negative electrode sheet of the electrochemical device, the appearance of the electrode sheet, the stability of the battery quality, the cycle performance and safety performance of the battery can be improved.

[0007] In addition, the method of the present application does not require long-term visual observation of the screen or filter membrane under an optical microscope to determine whether there are fibrous foreign matter therein, thereby eliminating the subjective errors of human judgment and counting.

[0008] According to one embodiment of the method of the present application, in the step (S2), separation of graphite and upper layer liquid is performed in a flotation device, and the flotation device has an upper port and a lower port in the vertical direction, wherein the dispersion is transferred to the flotation device through the upper port, and after the graphite is settled, the settled graphite is first discharged from the flotation device through the lower port, and then the upper layer liquid is discharged through the lower port.

[0009] According to one embodiment of the method of the present application, in step (S2), the separation of graphite and fibrous foreign matter is accelerated by placing a flotation device on the drum machine.

[0010] According to one embodiment of the method of the present application, the flotation liquid is selected such that the fibrous foreign matter is present in the upper layer liquid in step (S2).

[0011] According to one embodiment of the method of the present application, the flotation liquid includes water, ethanol, NaCl and a surfactant, wherein the volume ratio of water to ethanol is 1:1 to 1:3.

[0012] According to one embodiment of the method of the present application, the concentration of NaCl is 2 mol / L to 4 mol / L, preferably 2.5 mol / L to 3.5 mol / L.

[0013] According to one embodiment of the method of the present application, the surfactant includes at least one of sodium dodecylbenzene sulfonate, stearic acid, sorbitan fatty acid, and polysorbate, and the concentration of the surfactant is 2 g / L to 4 g / L, preferably 2.5 g / L to 3.5 g / L.

[0014] According to one embodiment of the method of the present application, the filter membrane is a PTEF woven filter membrane to eliminate the interference of the filter membrane's own material on the detection of fiber foreign matter. Preferably, the filter membrane is a PTEF woven filter membrane with a thickness of 15 μm.

[0015] According to one embodiment of the method of the present application, the optical microscope uses coaxial light and / or annular light as a light source, thereby obtaining an image that is more conducive to the image recognition device to recognize fiber foreign matter.

[0016] According to one embodiment of the method of the present application, the judgment module identifies the suspicious area through a target detection algorithm, and judges whether there is fibrous foreign matter in the suspicious area through a neural network classifier.

[0017] According to one embodiment of the method of the present application, the judgment module can distinguish between fiber foreign matter, bubbles, the texture of the filter membrane, and dust introduced during the detection process. Therefore, the method of the present application can avoid the influence of interference factors such as bubbles and the texture of the filter membrane on the detection results.

[0018] According to one embodiment of the method of the present application, the analysis module obtains the contour of the fiber foreign matter through an edge detection algorithm, and calculates the size, quantity and distribution of the fiber foreign matter.

[0019] According to one embodiment of the method of the present application, the length of the fiber foreign matter is more than 5 microns. According to one embodiment of the method of the present application, the method of the present application can detect fiber foreign matter with a length ranging from 5 microns to 50 microns, for example, fiber foreign matter with a length of 5 microns, 10 microns, 15 microns, 20 microns, 25 microns, 30 microns, 35 microns, 40 microns, 45 microns, 50 microns or any range thereof, because the inventors of the present application have found that even if the length of the fiber foreign matter in the graphite is less than 50 microns, when the graphite is used as the negative electrode of the electrochemical device, such fiber length can still have a negative impact on the cycle performance of the electrochemical device.

[0020] According to one embodiment of the method of the present application, the fiber foreign matter includes fiber foreign matter having a length ranging from 5 microns to 50 microns.

[0021] According to one embodiment of the method of the present application, the fiber foreign matter is transparent. In contrast to naked eye observation, the transparent fiber foreign matter can still be identified by the image processing device, thereby avoiding the transparent fiber foreign matter from being missed.

[0022] According to one embodiment of the method of the present application, the output module can output the number and size distribution of fiber foreign matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to make the above-mentioned purposes, features and advantages of the present application easier to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to fully understand the present application, but the present application can also be implemented in other ways different from those described herein, so the present application is not limited to the specific embodiments disclosed below.

[0025] Figure 1 A flotation device according to the present application is schematically shown,

[0026] Figure 2 The detection results of Example 1 are schematically shown;

[0027] Figure 3The detection results of Example 2 are schematically shown. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described in conjunction with the embodiments below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. The relevant embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application. Based on the technical scheme provided by the present application and the embodiments given, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application.

[0029] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0030] In the description herein, unless otherwise specified, “above” and “below” include the number.

[0031] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0032] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0033] In the context of the present application, "fibrous foreign matter" refers to fibrous foreign matter, and "fibers" and "fibrous foreign matter" are not composed of graphite and do not contain graphite.

[0034] It will be appreciated that, unless otherwise stated, features of any specific embodiment discussed herein may be combined with one or more features of any one or more embodiments otherwise discussed or considered herein.

[0035] In the context of this application, an "electrochemical device" comprises a negative electrode, a positive electrode, an electrolyte and a separator.

[0036] In some embodiments, the electrochemical device of the present application includes, but is not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors.

[0037] In some embodiments, the electrochemical device is a sodium ion battery.

[0038] In some embodiments, the electrochemical device is a lithium secondary battery.

[0039] In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0040] Figure 1 The preferred implementation device of the flotation device according to the present application is shown, and the flotation device has an upper port 1 and a lower port 2, wherein the upper port 1 can be equipped with a threaded cover to seal the flotation device to prevent leakage of graphite and mixing of external impurities during operation, and the lower port can be equipped with a valve so that the graphite can leave the flotation device through the lower port after settling in the flotation liquid. The main part of the flotation device is preferably an elongated cylindrical shape, which is conducive to the sedimentation of graphite under the action of gravity and improves the separation effect of graphite and fiber foreign matter. The lower port 2 is preferably a funnel shape with a circular arc transition to reduce the adhesion of graphite and fiber foreign matter to the bottom of the device.

[0041] Example 1

[0042] Method for detecting fiber foreign matter content in graphite by following the steps below:

[0043] (i) adding 350.64 g of NaCl solid and 6 g of dodecylbenzene sulfonic acid to 1000 ml of water, transferring the solution to a 2 L volumetric flask and adding water to make the volume 2 L; mixing 2 L of the aqueous solution of NaCl and sodium dodecylbenzene sulfonate with 1 L of anhydrous ethanol solution to obtain a flotation solution for separating fiber foreign matter from graphite;

[0044] (ii) Add 100g of GSN-17 artificial graphite produced by Shenzhen Bettery Company into 500ml of flotation liquid and transfer the flotation liquid to the flotation device through the upper port of the flotation device with the help of a glass rod. Place the flotation device on a roller machine and roll it for 2 hours to accelerate the separation of graphite and fiber. The speed of the roller machine is set to 30 rpm. Then, use an appropriate amount of flotation liquid to flush the graphite on the inner wall of the flotation device. Cover the bottle cap and let it stand for 12 hours, then open the valve at the lower port of the flotation device. After the graphite leaves the flotation device from the lower port, collect the upper liquid flowing out from the lower port; filter the upper liquid through a suction filtration device, using a sand core funnel covered with a 15-micron polytetrafluoroethylene filter membrane, and place the filter membrane in an oven at 60°C to dry for 6 hours;

[0045] (iii) placing the dried filter membrane under the lens of an optical microscope, adjusting the appropriate magnification and focal length, and then photographing the filter membrane to obtain an image;

[0046] (iv) The obtained image is processed by an image processing device, and the processing result is shown in Figure 2 middle.

[0047] Example 2

[0048] Method for detecting fiber foreign matter content in graphite by following the steps below:

[0049] (i) adding 350.64 g of NaCl solid and 6 g of dodecylbenzene sulfonic acid to 1000 ml of water, transferring the solution to a 2 L volumetric flask and adding water to make the volume 2 L; mixing 2 L of the aqueous solution of NaCl and sodium dodecylbenzene sulfonate with 1 L of anhydrous ethanol solution to obtain a flotation solution for separating fiber foreign matter from graphite;

[0050] (ii) Add a total of 100 PET fibers with a length of less than 100 μm to 100 g of GSN-17 artificial graphite produced by Shenzhen Beite Company, add the artificial graphite mixed with fiber foreign matter into 500 ml of flotation liquid and transfer the flotation liquid to the flotation device through the upper port of the flotation device with the help of a glass rod. Place the flotation device on a drum machine and roll it for 2 hours to accelerate the separation of graphite and fiber. The drum machine speed is set to 30 rpm. Then use an appropriate amount of flotation liquid to flush the graphite on the inner wall of the flotation device. Cover the bottle cap and let it stand for 12 hours, then open the valve at the lower port of the flotation device. After the graphite leaves the flotation device from the lower port, collect the upper liquid flowing out from the lower port; filter the upper liquid through a suction filtration device, using a sand core funnel covered with a 15-micron polytetrafluoroethylene filter membrane, and place the filter membrane in an oven at 60°C to dry for 6 hours;

[0051] (iii) placing the dried filter membrane under the lens of an optical microscope, adjusting the appropriate magnification and focal length, and then photographing the filter membrane to obtain an image;

[0052] (iv) The obtained image is processed by an image processing device, and the processing result is shown in Figure 3 middle.

[0053] It should be understood by those skilled in the art that the modules of the present application described above can be implemented by a general-purpose computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, optionally, they can be implemented by a program code executable by a computer device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present application is not limited to any specific combination of hardware and software.

[0054] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims, and these modifications and changes also fall within the scope of protection of the present application.

Claims

1. A method for detecting the content of fiber foreign matter in the negative electrode active material of a secondary battery, wherein the negative electrode active material is graphite, characterized in that: The method comprises the following steps: (S1) providing a flotation liquid; (S2) dispersing graphite containing fibrous foreign matter in the flotation liquid to form a dispersion, removing the graphite after the graphite settles to separate the graphite and an upper liquid, and then filtering the upper liquid through a filter membrane; (S3) photographing the filter membrane through an optical microscope after the filtration is completed to obtain an image; (S4) Processing the image obtained in step (S3) by an image processing device, wherein the image processing device includes an input module, a judgment module, a data analysis module and an output module, and the image processing device identifies the fiber foreign matter by an image recognition algorithm.

2. The method according to claim 1, characterized in that In the step (S2), the graphite and the upper layer of liquid are separated in a flotation device, and the flotation device has an upper port and a lower port in the vertical direction, wherein the dispersion is transferred to the flotation device through the upper port, and after the graphite is settled, the settled graphite is first discharged from the flotation device through the lower port, and then the upper layer of liquid is discharged through the lower port.

3. The method according to claim 1, characterized in that The flotation liquid is selected such that the fibrous foreign matter is present in the supernatant liquid in step (S2).

4. The method according to claim 1, characterized in that The flotation liquid comprises water, ethanol, NaCl and a surfactant, wherein the volume ratio of water to ethanol is 1:1 to 1:3, and / or the concentration of NaCl is 2 mol / L to 4 mol / L; The surfactant includes at least one of sodium dodecylbenzene sulfonate, stearic acid, sorbitan fatty acid, and polysorbate, and the concentration of the surfactant is 2 g / L to 4 g / L.

5. The method according to claim 1, characterized in that The filter membrane is a PTEF woven filter membrane, and / or the optical microscope uses at least one of coaxial light and annular light as a light source.

6. The method according to claim 1, characterized in that The judgment module identifies the suspicious area through a target detection algorithm, and judges whether there is fiber foreign matter in the suspicious area through a neural network classifier.

7. The method according to claim 1, characterized in that The judgment module can distinguish between fiber foreign matter, bubbles, the texture of the filter membrane and dust introduced during the detection process.

8. The method according to claim 1, characterized in that The analysis module obtains the contour of the fiber foreign matter through an edge detection algorithm and calculates the size, quantity and distribution of the fiber foreign matter.

9. The method according to claim 1, characterized in that: The length of the fiber foreign matter is greater than 5 micrometers, and / or the fiber foreign matter is transparent.

10. The method according to claim 1, characterized in that The output module can output the number and size distribution of fiber foreign matter.

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