Method for detecting fiber foreign matters in artificial graphite negative electrode material

Abstract

The invention discloses a method for detecting fiber foreign matters in an artificial graphite negative electrode material. The method comprises the following steps: 1, dispersing the artificial graphite negative electrode material by using a dispersing agent to form a first mixed solution; step 2, filtering the first mixed solution by using a first filter screen, so that large-size fiber foreign matters are intercepted on the first filter screen; 3, repeatedly washing the first filter screen to enable part of residual graphite to pass through the first filter screen along with the washing liquid; 4, the first filter screen is repeatedly washed, filter residues are washed away, and liquid and the filter residues obtained after washing are collected; 5, dispersing filter residues in the flushed liquid to form second mixed liquid; step 6, filtering the second mixed solution by using a second filter screen, so that large-size fiber foreign matters are intercepted on the second filter screen; 7, repeatedly washing the second filter screen to enable part of residual graphite to pass through the second filter screen along with the washing liquid; and 8, detecting and counting fiber foreign matters on the second filter screen. The method is beneficial to accurate evaluation of the fiber foreign matters in the artificial graphite negative electrode material.

Description

Technical Field

[0001] The present application relates to the technical field of battery negative electrode material detection, and in particular to a method for detecting fiber foreign matter in artificial graphite negative electrode materials. Background Art

[0002] There are three main effects of fibrous foreign matter on graphite negative electrode materials: excessive number or large length will penetrate the battery separator, causing internal short circuit of the battery and causing serious safety hazards; fibrous foreign matter in the negative electrode material may interfere with the infiltration of the electrolyte and hinder the transfer of ions, thereby affecting the battery's charge and discharge capabilities and rate performance; excessive number of foreign matter or large size will occupy a certain battery volume, increase the internal pressure of the battery, cause battery expansion and abnormality, and affect the battery life.

[0003] The evaluation of fibrous foreign matter in artificial graphite negative electrode materials usually involves dissolving graphite with a dispersant and filtering it with a 250-mesh stainless steel filter. After the filter is dried, it is observed under a high-power microscope, and the introduction of fibrous foreign matter and its cleanliness level are evaluated by manually counting the number and length. However, after filtration according to the existing method, there is a lot of graphite on the surface of the filter, and the cleanliness level is completely insufficient, making it difficult to accurately evaluate the fibrous foreign matter in artificial graphite negative electrode materials. Moreover, the existing method is to manually observe each part of the filter under a high-power microscope, mark the length of the foreign matter and count the number. Visual observation is prone to large errors and consumes a lot of human resources. The statistical results are highly subjective, making it difficult to guarantee the accuracy of the results, and also restricting the detection efficiency. Summary of the invention

[0004] The purpose of this application is to provide a method for detecting fiber foreign matter in artificial graphite negative electrode materials, which can solve at least one technical problem existing in the above-mentioned background technology.

[0005] To achieve the above-mentioned purpose, the present application provides a method for detecting fiber foreign matter in an artificial graphite negative electrode material, comprising:

[0006] Step 1: using a dispersant to disperse the artificial graphite negative electrode material to form a first mixed solution;

[0007] Step 2: filtering the first mixed liquid by using a first filter screen, so that large-sized fiber foreign matter in the first mixed liquid is trapped on the first filter screen;

[0008] Step 3, repeatedly flushing the first filter screen, so that part of the residual graphite on the first filter screen passes through the first filter screen along with the flushing liquid;

[0009] Step 4, repeatedly flushing the first filter screen to flush away the filter residue on the first filter screen and collecting the flushed liquid and the filter residue flushed therein;

[0010] Step 5, dispersing the filter residue in the rinsed liquid to form a second mixed liquid;

[0011] Step 6, filtering the second mixed liquid with a second filter screen, so that large-sized fiber foreign matter in the second mixed liquid is trapped on the second filter screen;

[0012] Step 7, repeatedly washing the second filter screen, so that part of the residual graphite on the second filter screen passes through the second filter screen along with the washing liquid;

[0013] Step eight, detecting and counting fiber foreign matter on the second filter screen.

[0014] Optionally, the dispersant is a non-ionic surfactant.

[0015] Optionally, the nonionic surfactant is an aqueous solution of alkylphenol polyoxyethylene ether.

[0016] Optionally, the method includes at least one of the following features (1) and (2):

[0017] (1) The content of alkylphenol polyoxyethylene ether in the alkylphenol polyoxyethylene ether aqueous solution is 0.1% to 1%.

[0018] (2) The alkylphenol polyoxyethylene ether aqueous solution is at least one of polyethylene glycol octyl phenyl ether, polyethylene glycol heptyl phenyl ether, polyethylene glycol nonyl phenyl ether and polyethylene glycol decyl phenyl ether.

[0019] Optionally, the method includes at least one of the following features ① to ⑦:

[0020] ①The first filter is a nylon filter;

[0021] ②The first filter screen has a mesh size of 250 to 325;

[0022] ③The second filter is a nylon filter;

[0023] ④The second filter screen has a mesh size of 250 to 325;

[0024] ⑤ In step 2, placing the first filter screen in a first filtration device to filter the first mixed liquid;

[0025] ⑥ In step 6, placing the second filter screen in a second filtration device to filter the second mixed liquid;

[0026] ⑦ In step 4, the first filter screen is repeatedly rinsed with ethanol.

[0027] Optionally, step three includes the following steps:

[0028] Repeatedly flushing the first filter screen with a nonionic surfactant;

[0029] Repeatedly rinse the first filter screen with anhydrous ethanol;

[0030] and / or

[0031] Step seven includes the following steps:

[0032] Repeatedly flushing the second filter screen with a nonionic surfactant;

[0033] Repeatedly rinse the second filter screen with anhydrous ethanol;

[0034] Optionally, the nonionic surfactant is an aqueous solution of alkylphenol polyoxyethylene ether.

[0035] Optionally, in step 2, placing the first filter screen in a first filtration device to filter the first mixed liquid;

[0036] Step three also includes: repeatedly rinsing the first suction filtration bottle of the first suction filtration device so that the residue on the first suction filtration bottle falls onto the first filter screen for filtration;

[0037] and / or

[0038] In step six, placing the second filter screen in a second filtration device to filter the second mixed liquid;

[0039] Step seven also includes: repeatedly rinsing the second suction filtration bottle of the second suction filtration device so that the residue on the second suction filtration bottle falls onto the second filter screen for filtration.

[0040] Optionally, step eight includes:

[0041] Using a cleanliness analyzer to obtain an image of the second filter;

[0042] The fiber foreign matter is identified from the image of the second filter screen and the number of the fiber foreign matter is counted.

[0043] Optionally, the method further comprises:

[0044] Detecting and counting fiber foreign matter on the first filter screen;

[0045] The total amount of fibrous foreign matter in the artificial graphite negative electrode material is obtained by adding the amount of fibrous foreign matter on the first filter screen and the amount of fibrous foreign matter on the second filter screen.

[0046] In the embodiment of the present application, the artificial graphite negative electrode material is first dispersed and filtered to separate the large-sized fibrous foreign matter therein on the first filter screen, and then the first filter screen is repeatedly rinsed so that some of the residual graphite on the first filter screen passes through the first filter screen with the rinsing liquid, and then the filter residue on the first filter screen is rinsed off and the rinsed liquid and the filter residue washed therein are collected, and then the filter residue in the rinsed liquid is dispersed and filtered to separate the large-sized fibrous foreign matter therein on the second filter screen, and then the second filter screen is repeatedly rinsed so that some of the residual graphite on the second filter screen passes through the second filter screen with the rinsing liquid, and then the evaluation of the fibrous foreign matter in the artificial graphite negative electrode material can be achieved based on the detection and statistics of the fibrous foreign matter on the second filter screen. In the embodiment of the present application, the filter residue on the first filter screen is flushed away, the flushed liquid and the filter residue flushed therein are collected, and the filter residue is dispersed and filtered again, and the residual graphite on the second filter screen is repeatedly flushed away, and the stubborn graphite that is difficult to filter will be stuck on the first filter screen when the filter residue on the first filter screen is flushed away and will not be brought into the secondary dispersion and subsequent operations, so that only a very small amount of graphite will exist on the second filter screen, with a higher cleanliness, which is conducive to the accurate evaluation of fibrous foreign matter in artificial graphite negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a surface comparison chart of stainless steel filter and PET material filter.

[0048] Figure 2 This is a comparison chart of the effects of the first filter and the second filter.

[0049] Figure 3 It is a schematic diagram of grayscale processing performed by the software.

[0050] Figure 4 It is a comparison chart of the test results of using 5% dilute ethanol solution as a dispersant and 0.5% polyethylene glycol octylphenyl ether aqueous solution as a dispersant. DETAILED DESCRIPTION

[0051] In order to explain the technical content and structural features of the present application in detail, further description is given below in combination with the implementation methods and the accompanying drawings.

[0052] The present application embodiment discloses a method for detecting fiber foreign matter in an artificial graphite negative electrode material, comprising:

[0053] Step 1: using a dispersant to disperse the artificial graphite negative electrode material to form a first mixed solution.

[0054] Dispersants can be conventional alcohol compound solutions (such as ethanol solutions), inorganic dispersant bases (such as metal phosphates), cationic wetting dispersants (such as alkyl trimethyl ammonium salts), and anionic surfactants (such as sulfonates), etc. Among them, ethanol solution is a more commonly used and effective dispersant, but ethanol solution is expensive, which is not conducive to controlling the detection cost.

[0055] Therefore, the embodiment of the present application proposes to use a non-ionic surfactant as a dispersant to disperse the artificial graphite negative electrode material, replacing the commonly used ethanol solution, etc., so as to reduce the detection cost.

[0056] During the preparation process of artificial graphite, the crystal surface structure is rough and porous. These micropores and cracks make it difficult for water molecules to form a continuous wetting layer on the graphite surface, causing its particles to aggregate in water, which is not conducive to testing. Since graphite is prepared by heat treatment of carbon materials such as asphalt, petroleum coke, and coal coke, alkyl and aromatic groups are pyrolyzed to form lipophilic carbon-hydrogen bonds and carbon-carbon bonds. Nonionic surfactants have hydrophilic groups and hydrophobic groups and have the ability to disperse graphite. The hydrophilic groups interact with water molecules, and the hydrophobic groups interact with the oil molecules on the particle surface. This characteristic enables nonionic surfactants to establish an interface between the liquid phase and the particle surface to form a colloidal dispersion system. The nonionic surfactant molecules aggregate into a micellar structure in the liquid phase. The hydrophilic head group of the micelle interacts with the water molecules outward, and the hydrophobic tail group interacts with the oil molecules on the particle surface inward. Due to the role of nonionic surfactant molecules in micelles, the deposition of solid particles is reduced and the dispersion effect is significant. The micellar structure after the nonionic surfactant is dispersed can effectively prevent the aggregation and precipitation between particles and maintain the stability of the dispersion system. The hydrophobic tail groups of micelles shield the interaction forces between particles, making them difficult to aggregate. In addition, the hydrophilic head groups form strong interactions between water and micelles with water molecules, which also contributes to the stability of the dispersed system.

[0057] Specifically, the nonionic surfactant can be an alkylphenol polyoxyethylene ether aqueous solution. The alkylphenol polyoxyethylene ether aqueous solution is mainly obtained by the addition reaction of alkylphenol and ethylene oxide. Polyethylene glycol obtained by the addition of ethylene oxide to water is a commonly used polyol, which can play a role in thickening, wetting and dispersing in the preparation of polyether surfactants. Alkylphenol is an aromatic compound with good permeability and dispersibility. Alkylphenol polyoxyethylene ether is composed of these two components, combining their advantages and having good surface active properties. Its HLB value (hydrophilic-lipophilic balance value) is about 15, and it can form an oil / water emulsion, which can significantly reduce the interfacial tension between graphite particles and water and has a strong hydration effect.

[0058] In order to illustrate the effect of using alkylphenol polyoxyethylene ether aqueous solution as a dispersant to disperse artificial graphite negative electrode materials in the embodiment of the present application, a common graphite material was dispersed with a variety of different types of dispersants and then the particle size test comparison was shown in the following table:

[0059]

[0060] In the above test, the alkylphenol polyoxyethylene ether aqueous solution adopts 1% polyethylene glycol monooctylphenyl ether aqueous solution, metal phosphates adopt 20% sodium hexametaphosphate aqueous solution, alkyl trimethyl ammonium salt type adopts dodecyl trimethyl ammonium chloride, and sulfonate adopts alkyl sodium sulfonate. After multiple tests based on each type of dispersant, the D50 mean value of graphite particles is respectively 14.6, 14.6, 14.9, 14.8, 14.7, and the RSD (relative standard deviation) value of graphite particles is respectively 0.35%, 0.52%, 0.37%, 0.43%, 1.03%. This shows that, on the D50 mean value in the test results, the alkylphenol polyoxyethylene ether has the result that is basically consistent with the ethanol solution, and on the RSD value in the test results, the alkylphenol polyoxyethylene ether has a good test result equally. Therefore, the alkylphenol polyoxyethylene ether aqueous solution can be used as the replacement of the common dispersant ethanol solution, and then the detection cost can be significantly reduced.

[0061] Specifically, the content of alkylphenol polyoxyethylene ether in the alkylphenol polyoxyethylene ether aqueous solution is 0.1% to 1%.

[0062] Specifically, the alkylphenol polyoxyethylene ether aqueous solution is at least one of polyethylene glycol octylphenyl ether, polyethylene glycol heptylphenyl ether, polyethylene glycol nonylphenyl ether and polyethylene glycol decylphenyl ether.

[0063] Specifically, the mass ratio of the artificial graphite negative electrode material to the dispersant is 1:1-5.

[0064] Specifically, the dispersant and the artificial graphite negative electrode material are mixed and stirred for 3 to 10 minutes.

[0065] Exemplarily, artificial graphite negative electrode material and alkylphenol polyoxyethylene ether aqueous solution are weighed in a certain proportion and added into a clean 5L beaker A, and stirred with a clean glass rod for 3-10 minutes to fully disperse.

[0066] Step 2: Filter the first mixed liquid using a first filter screen, so that large-sized fiber foreign matter in the first mixed liquid is retained on the first filter screen.

[0067] After the artificial graphite negative electrode material is fully dispersed with a dispersant to form a first mixed liquid, the first mixed liquid can be filtered using a first filter screen. The purpose is to allow the graphite particles in the first mixed liquid to pass through the first filter screen with the filtrate, and to retain large-sized fibrous foreign matter on the first filter screen to facilitate subsequent detection of large-sized fibrous foreign matter.

[0068] It needs to be explained that the "large-sized fibrous foreign matter" in the embodiments of the present application can be defined as needed. When the length of the fibrous foreign matter is small, the effect on the electrochemical properties of the artificial graphite negative electrode material is not obvious. The fibrous foreign matter exceeding a certain length will have a significant effect on the electrochemical properties of the artificial graphite negative electrode material. Therefore, at least these fibrous foreign matter exceeding a certain length need to be detected, and they can be defined as large-sized fibrous foreign matter. Of course, they can also be defined based on other factors. When filtering with a filter, it is necessary to ensure that large-sized fibrous foreign matter will not pass through the filter under normal circumstances, but will be retained on the filter. At the same time, without considering special circumstances, when simply considering the size of the graphite particles, it is required that most or all of the graphite particles can pass through the filter with the filtrate.

[0069] Specifically, the first filter is a nylon filter, specifically a PET (polyethylene terephthalate) material filter. The PET material has good mechanical properties, the impact strength is 3 to 5 times that of ordinary materials, and the folding resistance is good; it is resistant to oil, fat, dilute acid, dilute alkali, and most solvents; it has excellent high and low temperature resistance; low gas and water vapor permeability; high transparency, easy to observe, good gloss; non-toxic, odorless, good hygiene and safety; long-fiber polyester fibers are interlaced and evenly distributed; good wear resistance, and can withstand pulse backwashing of gas and water flow. Figure 1 The surface comparison of PET material filter and traditional stainless steel filter is given. Stainless steel filter will have obvious reflection phenomenon, and the cleanliness analyzer cannot accurately identify the fiber foreign matter in it, while PET material filter basically has no reflection phenomenon, which will not affect the recognition of the cleanliness analyzer.

[0070] Specifically, the first filter screen has a mesh size of 250 to 325. The mesh size of the first filter screen is 250-325 because the fiber type introduced in the manufacturing process of artificial graphite is basically fixed. Secondly, too small a size will trap more graphite particles, resulting in a large grayscale of the filter screen that cannot be identified by the instrument. In addition, too small a size of fiber foreign matter has no obvious effect on the electrochemical properties of the material; while too large a size will filter out the fiber foreign matter that needs to be detected.

[0071] Specifically, the first filter screen is placed in the first suction filtration device to filter the first mixed liquid. But the invention is not limited thereto.

[0072] Step three, repeatedly flushing the first filter screen, so that part of the residual graphite on the first filter screen passes through the first filter screen along with the flushing liquid.

[0073] Step three is equivalent to the continuation of the filtering operation. Since there will be residual graphite and the like on the first filter screen after filtering in step two, in order to allow as much graphite and the like that can pass through the first filter screen as possible to pass through the first filter screen, the first filter screen needs to be repeatedly rinsed, so that the filter residue on the first filter screen can contain less graphite and the like, thereby reducing interference with the detection of fiber foreign matter. In order to ensure the flushing effect and allow as much graphite and the like that can pass through the first filter screen as possible to pass through the first filter screen, the filtrate can be rinsed until it is clear and transparent, so that only the fiber foreign matter that needs to be detected and some graphite and the like that are really difficult to filter out are left on the first filter screen as much as possible, such as due to being stuck, forming lumps, or a very small number of graphite particles having large particle sizes.

[0074] Repeatedly flushing the first filter screen in step 3 may include the following flushing steps:

[0075] (1) Repeatedly use a non-ionic surfactant to rinse the first filter. Since non-ionic surfactants are cheaper than ethanol, using non-ionic surfactants to fully rinse the first filter helps reduce costs. In order to ensure the rinsing effect, the filtrate can be rinsed until it becomes clear and transparent.

[0076] Specifically, the non-ionic surfactant is an alkylphenol polyoxyethylene ether aqueous solution. Further, the content of the alkylphenol polyoxyethylene ether in the alkylphenol polyoxyethylene ether aqueous solution is 0.1% to 1%.

[0077] (2) Repeatedly rinse the first filter screen with anhydrous ethanol. Since bubbles will be generated after the first filter screen is fully rinsed with some non-ionic surfactants, the first filter screen is repeatedly rinsed with anhydrous ethanol after rinsing to remove bubbles. To ensure the rinsing effect, it can be rinsed more than 5 times until the filtrate is clear and transparent. Since the non-ionic surfactant has been used for sufficient rinsing, the use of anhydrous ethanol to rinse the first filter screen is mainly to remove bubbles. Therefore, compared with rinsing with ethanol solution, the use of ethanol can be greatly reduced, which is conducive to cost control.

[0078] When the first filter screen is placed in the first filtration device to filter the first mixed liquid, in order to avoid residual fiber foreign matter on the first filtration bottle on the first filtration device, when repeatedly flushing the first filter screen in step three, the first filtration bottle can also be repeatedly flushed to make the residue on the first filtration bottle fall onto the first filter screen for filtration. After the first filtration bottle and the first filter screen are fully flushed, the large-sized fiber foreign matter that may exist in these residues and the large-sized fiber foreign matter originally on the first filter screen will remain on the first filter screen, and a considerable portion of other residues and residual graphite originally on the first filter screen will pass through the first filter screen with the filtrate under flushing, leaving the fiber foreign matter that needs to be detected and some graphite that is difficult to filter out on the first filter screen.

[0079] Step 4: repeatedly rinse the first filter screen to rinse off the filter residue on the first filter screen and collect the rinsed liquid and the filter residue washed off therein.

[0080] The purpose of repeatedly flushing the first filter screen in step 4 is different from the purpose of repeatedly flushing the first filter screen in step 3. In step 3, the residual graphite and the like that did not pass through the first filter screen with the filtrate during the filtration in step 2 can pass through the first filter screen as much as possible under flushing, while the purpose of step 4 is to flush away the fiber foreign matter on the first filter screen. In addition to the fiber foreign matter, the flushed filter residue also includes some graphite residues that still exist on the first filter screen. Of course, after repeated flushing in step 4, there will still be a small amount of stubborn filter residue stuck on the first filter screen. In this way, when the collected filter residue is subjected to secondary dispersion, filtration and other operations, these very stubborn filter residues such as graphite will not be brought in, which makes it easier to obtain a cleaner second filter screen later. Of course, it is not ruled out that a very small number of fiber foreign matter is not flushed away.

[0081] In order to completely collect the rinsed liquid and the washed-off filter residue, the first filter screen after step 3 can be transferred to a clean beaker or other container for rinsing. Specifically, the edge of the first filter screen can be clamped with tweezers for transfer. During the rinsing process, the first filter screen can be held for easy rinsing. By rinsing in a beaker or other container, the rinsed liquid and filter residue can be directly retained in the beaker or container, so that they can be directly dispersed in the beaker or container to prevent the loss of filter residue.

[0082] Specifically, in step 4, the first filter screen is repeatedly rinsed with anhydrous ethanol to rinse off part of the filter residue on the first filter screen.

[0083] Step 5: Disperse the filter residue in the rinsed liquid to form a second mixed liquid.

[0084] After the rinsing in step 4 is completed, a dispersant can be directly added to the beaker or container where the rinsed liquid and the filter residue are located to fully disperse the graphite in the filter residue. Of course, it is not ruled out that the rinsed liquid in step 4 can be directly used for dispersion without adding a dispersant.

[0085] The dispersant may be the same as that in step 1, or a different dispersant may be used. Specifically, a cheap nonionic surfactant may be used, such as a 0.1% to 1% aqueous solution of alkylphenol polyoxyethylene ether.

[0086] In order to achieve rapid and sufficient dispersion, a clean glass rod can be used to stir for 3 to 10 minutes.

[0087] Step six, filtering the second mixed liquid with a second filter screen, so that the large-sized fiber foreign matter in the second mixed liquid is retained on the second filter screen.

[0088] The purpose of this step is to allow part of the graphite particles in the second mixed liquid to pass through the second filter screen along with the filtrate, so that only a small amount of graphite and the like remains on the second filter screen except for large-sized fiber foreign matter.

[0089] Specifically, the second filter is a nylon filter, specifically a PET material filter.

[0090] Specifically, the second filter screen has a mesh size of 250 to 325.

[0091] Specifically, the second filter screen is placed in the second suction filtration device to filter the second mixed liquid. However, it is not limited thereto. In addition, it is not excluded that the second suction filtration device and the first suction filtration device are the same suction filtration device.

[0092] Step seven, repeatedly flushing the second filter screen, so that the residual graphite particles on the second filter screen pass through the second filter screen along with the flushing liquid.

[0093] In order to allow as much interference as possible, such as graphite, to pass through the second filter, the second filter needs to be rinsed repeatedly so that the filter residue on the second filter can contain even less graphite, etc., thereby reducing interference with fiber foreign matter detection.

[0094] After the first dispersion, filtration and flushing, the filter residue on the first filter contains only a small amount of graphite and other interfering substances. After the step of flushing away the filter residue on the first filter, most of the graphite and the like that are difficult to filter and flush away are stuck on the first filter and will not be brought into the secondary dispersion, filtration and flushing operations. In other words, during the secondary dispersion, interfering substances such as graphite are relatively few, and there are very few graphites and the like that are difficult to filter. In this way, when filtering and flushing operations are performed after the secondary dispersion, most of the graphite in the second mixed liquid can pass through the second filter. In this way, in addition to the fiber foreign matter that needs to be detected, only a few interfering substances such as graphite are left on the second filter. The whole filter is very clean, which makes it easy to accurately identify and count the fiber foreign matter on the second filter.

[0095] In step 7, the second filter screen can be repeatedly rinsed in the same manner as in step 3, for example, the second filter screen can be repeatedly rinsed with a non-ionic surfactant and then with anhydrous ethanol. Of course, it can also be a different manner from step 3, for example, since the second filter screen has much less graphite than the first filter screen after filtration, it can be directly rinsed repeatedly with anhydrous ethanol.

[0096] When flushing the second filter, in order to ensure the flushing effect, it can be flushed until the filtrate is clear and transparent.

[0097] When the second filter screen is placed in the second filtration device to filter the second mixed liquid, in order to avoid residual fiber foreign matter on the second filtration bottle on the second filtration device, when repeatedly flushing the second filter screen in step seven, the second filtration bottle can also be repeatedly flushed to make the residue on the second filtration bottle fall onto the second filter screen for filtration. After the second filtration bottle and the second filter screen are fully flushed, the large-sized fiber foreign matter that may exist in these residues and the large-sized fiber foreign matter originally existing on the second filter screen will remain on the first filter screen, and a considerable portion of other residues and residual graphite originally on the second filter screen will pass through the second filter screen with the filtrate under flushing, leaving the fiber foreign matter that needs to be detected and some graphite that is difficult to filter out on the second filter screen.

[0098] Step eight, detecting and counting the fiber foreign matter on the second filter.

[0099] After the processing in step four, the first filter screen either no longer contains any fibrous foreign matter or contains only a very small amount of fibrous foreign matter. Therefore, the fibrous foreign matter in the artificial graphite negative electrode material can be evaluated simply by detecting and counting the fibrous foreign matter on the second filter screen.

[0100] In the embodiment of the present application, the filter residue on the first filter screen is flushed away, the flushed liquid and the filter residue flushed therein are collected, and the filter residue is dispersed and filtered again, and the residual graphite on the second filter screen is repeatedly flushed away, and the stubborn graphite that is difficult to filter will be stuck on the first filter screen when the filter residue on the first filter screen is flushed away and will not be brought into the secondary dispersion and subsequent operations, so that only a very small amount of graphite will exist on the second filter screen, with a higher cleanliness, which is conducive to the accurate evaluation of fibrous foreign matter in artificial graphite negative electrode materials.

[0101] In order to better detect and count the fiber foreign matter on the second filter screen, the second filter screen can be fully dried before the fiber foreign matter identification and counting operation is performed. Specifically, the second filter screen can be placed in a culture dish and transferred to detect the fiber foreign matter after the ethanol is completely volatilized.

[0102] Specifically, after drying, the second filter screen can be transferred to a quartz fixture for detection.

[0103] Specifically, the detection and counting of fiber foreign matter on the second filter screen can be performed in the following manner:

[0104] obtaining an image of the second filter using a cleanliness analyzer;

[0105] Fiber foreign matter is identified from the image of the second filter and the number of the fiber foreign matter is counted.

[0106] Since the second filter is already very clean except for the fiber foreign matter, after using the cleanliness analyzer to obtain the image of the second filter, it is easy to detect and count the fiber foreign matter therein, which can obtain more accurate results and help improve the efficiency of detection and statistics. Figure 2 A comparison chart of the effects of the second filter and the first filter is shown, and it can be seen that the second filter is already very clean.

[0107] In addition, by performing inspection after image acquisition, the length of the fiber foreign matter can be accurately obtained and the morphological characteristics of the fiber foreign matter can be efficiently analyzed.

[0108] Since the existing solution is to use a stainless steel filter for filtering and observe the stainless steel filter using a high-power microscope, but due to the reflection problem of the stainless steel filter, it is difficult to accurately identify the location of the fiber foreign matter using a cleanliness analyzer, so in the embodiment of the present application, the second filter uses a nylon filter.

[0109] Specifically, when using the cleanliness analyzer for scanning, its optical magnification can be set to 0.7-5 times, and the adjustment threshold can be set to 98-130.

[0110] In order to verify the relationship between the cleanliness of the filter and the recognition rate of the cleanliness analyzer for identifying fiber foreign matter, the inventor conducted multiple tests as shown in the following table. In each test, the high-definition image of the filter surface was processed into a grayscale image using Photoshop (such as Figure 3 As shown). Each pixel with an RGB value greater than 128 (maximum 255) is a contaminated (not cleaned) part, defined as gray; a pixel with an RGB value less than 128 is defined as white.

[0111]

[0112] The test results show that the higher the cleanliness of the filter (the lower the proportion of gray), the higher the recognition rate of the cleanliness analyzer. In this application, after the second filtration and flushing, the cleanliness of the second filter is already very high, so when the cleanliness analyzer is used for testing, very accurate test results can be obtained. Compared with testing after one filtration and flushing, the recognition rate of fiber foreign matter can be increased from 30%-40% to more than 95%.

[0113] In addition, an example of a statistical table of test results output by a cleanliness analyzer is given below.

[0114] Category Name Classification range (um) Actual quantity A 5≤x＜15 0 B 15≤x＜25 0 C 25≤x＜50 1 D 50≤x＜100 15 E 100≤x＜150 5 F 150≤x＜200 4 G 200≤x＜400 3 H 400≤x＜600 0 I 600≤x＜1000 0 J 1000≤x＜1500 0 K 1500≤x＜2000 0 L 2000≤x＜3000 0 M 3000≤x 0

[0115] Of course, in order to more accurately evaluate the fiber foreign matter, the first filter screen after step 4 may also be tested for fiber foreign matter. Afterwards, the number of fiber foreign matter on the first filter screen and the number of fiber foreign matter on the second filter screen may be added together to obtain the total number of fiber foreign matter in the artificial graphite negative electrode material.

[0116] In order to better detect and count the fiber foreign matter on the first filter screen, the first filter screen can be fully dried before the fiber foreign matter identification and counting operation is performed. Specifically, after drying, the first filter screen can be transferred to a quartz fixture for detection.

[0117] Similarly, the fiber foreign matter on the first filter screen can also be detected based on the cleanliness analyzer. The specific detection method can refer to the method of detecting fiber foreign matter on the second filter screen using the cleanliness analyzer, which will not be repeated here.

[0118] In order to better illustrate the purpose, technical solution and beneficial effects of this application, this application will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of this application and should not be used as a limitation of this application.

[0119] Example 1

[0120] Step 1: first weigh artificial graphite negative electrode material and 0.5% polyethylene glycol octylphenyl ether aqueous solution in a certain ratio (1:2) and add them into a clean 5L beaker A, and stir with a clean glass rod for 5 minutes to fully disperse them to form a first mixed solution.

[0121] Step 2: Place all the first mixed liquid in a first filtration device and filter it using a first filter screen made of 250 mesh new nylon material, so that large-sized fiber foreign matter in the first mixed liquid is retained on the first filter screen.

[0122] Step 3: repeatedly rinse the first filter screen with 0.5% polyethylene glycol octylphenyl ether aqueous solution until the filtrate is clear and transparent, and then repeatedly rinse the first suction bottle and the first filter screen of the first suction filtration device with anhydrous ethanol for more than 5 times until the filtrate is clear and transparent.

[0123] Step 4: Carefully transfer the first filter screen to a clean beaker B, hold its edge with tweezers, and then use an anhydrous ethanol washing bottle to repeatedly rinse the filter residue on the first filter screen for more than 5 times, so that the washed-off filter residue and filtrate are retained in beaker B.

[0124] Step 5: Stir and disperse the filtrate and filter residue obtained in step 4 with a 0.5% polyethylene glycol octylphenyl ether aqueous solution to form a second mixed solution.

[0125] Step 6: Place a second filter screen made of 250 mesh nylon material on a second filtration device to filter the second mixed liquid, so that large-sized fiber foreign matter in the second mixed liquid is trapped on the second filter screen;

[0126] Step seven, repeatedly rinse the second filter screen with 0.5% polyethylene glycol octylphenyl ether aqueous solution until the filtrate is clear and transparent, and then repeatedly rinse the second suction bottle and the second filter screen of the second suction filtration device with anhydrous ethanol for more than 5 times until the filtrate is clear and transparent.

[0127] Step 8: After drying, carefully transfer the second filter to a quartz fixture and use a cleanliness analyzer to scan and test. The parameters are set as follows: optical magnification 2.5 times, adjustment threshold 125. The test result is 45, that is, the number of fiber foreign matter on the second filter is 45.

[0128] In addition, after step 4 is completed, the first filter is dried and carefully transferred to a quartz fixture, and scanned and tested using a cleanliness analyzer. The parameters are set as follows: optical magnification 2.5 times, adjustment threshold 125. The test result is 3, that is, the number of fiber foreign matter on the first filter is 3.

[0129] The total number of fibrous foreign matter obtained by adding the number of fibrous foreign matter on the first filter screen and the number of fibrous foreign matter on the second filter screen is 48.

[0130] Example 2

[0131] Step 1: weigh the same artificial graphite negative electrode material and 5% dilute ethanol solution in a certain ratio (1:2) and add them into a clean 5L beaker A, and stir with a clean glass rod for 5 minutes to fully disperse them to form a first mixed solution.

[0132] Step 2: Place all the first mixed liquid in a first filtration device and filter it using a first filter screen made of 250 mesh new nylon material, so that large-sized fiber foreign matter in the first mixed liquid is retained on the first filter screen.

[0133] Step 3: repeatedly rinse the first filter screen with 5% dilute ethanol solution until the filtrate is clear and transparent, and then repeatedly rinse the first suction bottle and the first filter screen of the first suction filtration device with anhydrous ethanol for more than 5 times until the filtrate is clear and transparent.

[0134] Step 4: Carefully transfer the first filter screen to a clean beaker B, hold its edge with tweezers, and then use an anhydrous ethanol washing bottle to repeatedly rinse the filter residue on the first filter screen for more than 5 times, so that the washed-off filter residue and filtrate are retained in beaker B.

[0135] Step 5: Stir and disperse the filtrate and filter residue obtained in step 4 with a 5% dilute ethanol solution to form a second mixed solution.

[0136] Step six, placing a second filter screen made of 250 mesh new nylon material on a second filtration device to filter the second mixed liquid, so that large-sized fiber foreign matter in the second mixed liquid is retained on the second filter screen.

[0137] Step seven, repeatedly rinse the second filter screen with 5% dilute ethanol solution until the filtrate is clear and transparent, and then repeatedly rinse the second suction bottle and the second filter screen of the second suction filtration device with anhydrous ethanol for more than 5 times until the filtrate is clear and transparent.

[0138] Step 8: After drying, carefully transfer the second filter to a quartz fixture and use a cleanliness analyzer to scan and test. The parameters are set as follows: optical magnification 2.5 times, adjustment threshold 125. The test result is 45, that is, the number of fiber foreign matter on the second filter is 48.

[0139] In addition, after step 4 is completed, the first filter is dried and carefully transferred to a quartz fixture, and scanned and tested using a cleanliness analyzer. The parameters are set as follows: optical magnification 2.5 times, adjustment threshold 125. The test result is 1, that is, the number of fiber foreign matter on the first filter is 1.

[0140] The total number of fibrous foreign matter obtained by adding the number of fibrous foreign matter on the first filter screen and the number of fibrous foreign matter on the second filter screen is 49.

[0141] It can be seen from Examples 1 and 2 that the test results obtained by using a 0.5% polyethylene glycol octylphenyl ether aqueous solution as a non-ionic surfactant as a dispersant and a flushing liquid are similar to those obtained by using a dilute ethanol solution as a dispersant and a flushing liquid. Therefore, a non-ionic surfactant can be used to replace a more expensive dilute ethanol solution, which is beneficial to reducing the detection cost.

[0142] In addition, in order to illustrate the effect of non-ionic surfactant as a dispersant, the inventors tested the particle size of the same graphite after dispersing it with 5% dilute ethanol solution as a dispersant and 0.5% polyethylene glycol octylphenyl ether aqueous solution as a dispersant. The test results are compared in the following figure: Figure 4 (the horizontal axis is particle size, the vertical axis is volume density) is shown by Figure 4 It can be seen that the test result curves of the two methods basically overlap, indicating that their dispersion effects are basically the same and they can be replaced.

[0143] In order to illustrate the technical effect of the detection method of the present application, a comparative example is provided below:

[0144] Step 1: Weigh the same artificial graphite negative electrode material and 5% dilute ethanol solution in a certain ratio (2:3) and add them into a clean 5L beaker A. Stir with a clean glass rod for 5 minutes to fully disperse them to form a mixed solution.

[0145] Step 2: Place all the mixed liquid in a filtration device and filter it using a 250-mesh stainless steel filter screen. Large-sized fiber foreign matter in the mixed liquid must be retained on the filter screen.

[0146] Step 3: Rinse the filter repeatedly with 5% dilute ethanol solution until the filtrate is clear and transparent.

[0147] Step 4: After the filter is dry, carefully transfer it to a high-power microscope for observation. Focus by adjusting the magnification of the microscope, carefully observe the fiber foreign matter on the filter, and record the number.

[0148] The detection result of step four is 31, that is, the number of fiber foreign matter on the filter is 31.

[0149] In order to verify the test results of Example 1, Example 2 and the comparative example, the filter screen in each example was reviewed for data using a scanning electron microscope. The results showed that there were a large number of omissions in the test results of the comparative example, and the test results of Example 1 and Example 2 were consistent with the test results of the scanning electron microscope, thereby verifying that the detection method of the present application can greatly reduce the number of missed detections of fiber foreign matter.

[0150] It can be seen from the above-mentioned Example 1, Example 2 and the comparative example that the detection method of the present application can more accurately detect fiber foreign matter in the artificial graphite negative electrode material, greatly reducing the number of missed detections of fiber foreign matter. Moreover, compared with the manual detection in the comparative example, Example 1 and Example 2 significantly reduce the detection time.

[0151] The above disclosure is only the preferred embodiment of the present application, which certainly cannot be used to limit the scope of rights of the present application. Therefore, equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A method for detecting fiber foreign matter in artificial graphite negative electrode materials, characterized in that: include: Step 1, using a dispersant to disperse the artificial graphite negative electrode material to form a first mixed solution; Step 2: filtering the first mixed liquid by using a first filter screen, so that large-sized fiber foreign matter in the first mixed liquid is trapped on the first filter screen; Step 3, repeatedly flushing the first filter screen, so that part of the residual graphite on the first filter screen passes through the first filter screen along with the flushing liquid; Step 4, repeatedly flushing the first filter screen to flush away the filter residue on the first filter screen and collecting the flushed liquid and the filter residue flushed therein; Step 5, dispersing the filter residue in the rinsed liquid to form a second mixed liquid; Step 6, filtering the second mixed liquid with a second filter screen, so that large-sized fiber foreign matter in the second mixed liquid is trapped on the second filter screen; Step 7, repeatedly washing the second filter screen, so that part of the residual graphite on the second filter screen passes through the second filter screen along with the washing liquid; Step eight, detecting and counting fiber foreign matter on the second filter screen.

2. The method for detecting fiber foreign matter in artificial graphite negative electrode material according to claim 1, characterized in that: The dispersant is a nonionic surfactant.

3. The method for detecting fiber foreign matter in artificial graphite negative electrode material according to claim 2, characterized in that: The nonionic surfactant is an aqueous solution of alkylphenol polyoxyethylene ether.

4. The method for detecting fiber foreign matter in artificial graphite negative electrode material according to claim 3, characterized in that: The invention comprises at least one of the following features (1) and (2): (1) The content of alkylphenol polyoxyethylene ether in the alkylphenol polyoxyethylene ether aqueous solution is 0.1% to 1%. (2) The alkylphenol polyoxyethylene ether aqueous solution is at least one of polyethylene glycol octyl phenyl ether, polyethylene glycol heptyl phenyl ether, polyethylene glycol nonyl phenyl ether and polyethylene glycol decyl phenyl ether.

5. The method for detecting fiber foreign matter in artificial graphite negative electrode material according to claim 1, characterized in that: Includes at least one of the following features ① to ⑦: ①The first filter is a nylon filter; ②The first filter screen has a mesh size of 250 to 325; ③The second filter is a nylon filter; ④The second filter screen has a mesh size of 250 to 325; ⑤ In step 2, placing the first filter screen in a first filtration device to filter the first mixed liquid; ⑥ In step 6, placing the second filter screen in a second filtration device to filter the second mixed liquid; ⑦ In step 4, the first filter screen is repeatedly rinsed with anhydrous ethanol.

6. The method for detecting fiber foreign matter in artificial graphite negative electrode material according to claim 1, characterized in that: Step three includes the following steps: Repeatedly flushing the first filter screen with a nonionic surfactant; Repeatedly rinse the first filter screen with anhydrous ethanol; and / or Step seven includes the following steps: Repeatedly flushing the second filter screen with a nonionic surfactant; The second filter was rinsed repeatedly with anhydrous ethanol.

7. The method for detecting fiber foreign matter in artificial graphite negative electrode material according to claim 6, characterized in that: The nonionic surfactant is an aqueous solution of alkylphenol polyoxyethylene ether.

8. The method for detecting fiber foreign matter in artificial graphite negative electrode material according to claim 1, characterized in that: In step 2, placing the first filter screen in a first filtration device to filter the first mixed liquid; Step three also includes: repeatedly rinsing the first suction filtration bottle of the first suction filtration device so that the residue on the first suction filtration bottle falls onto the first filter screen for filtration; and / or In step six, placing the second filter screen in a second filtration device to filter the second mixed liquid; Step seven also includes: repeatedly rinsing the second suction filtration bottle of the second suction filtration device so that the residue on the second suction filtration bottle falls onto the second filter screen for filtration.

9. The method for detecting fiber foreign matter in artificial graphite negative electrode material according to claim 1, characterized in that: Step eight includes: Using a cleanliness analyzer to obtain an image of the second filter; The fiber foreign matter is identified from the image of the second filter screen and the number of the fiber foreign matter is counted.

10. The method for detecting fiber foreign matter in artificial graphite negative electrode material according to claim 1, characterized in that: Also includes: Detecting and counting fiber foreign matter on the first filter screen; The total amount of fibrous foreign matter in the artificial graphite negative electrode material is obtained by adding the amount of fibrous foreign matter on the first filter screen and the amount of fibrous foreign matter on the second filter screen.

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