CN113376063A - Detection method of magnetic foreign matter - Google Patents
Detection method of magnetic foreign matter Download PDFInfo
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- CN113376063A CN113376063A CN202110563422.XA CN202110563422A CN113376063A CN 113376063 A CN113376063 A CN 113376063A CN 202110563422 A CN202110563422 A CN 202110563422A CN 113376063 A CN113376063 A CN 113376063A
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
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Abstract
The invention discloses a detection method of magnetic foreign matters, which adopts two treatment modes to adsorb the magnetic foreign matters, wherein the first magnetic suction piece is used for adsorbing the liquid to be treated under the state of dynamic stirring for the first time, the liquid to be treated is treated under the second static state, dilute acid is used for further eliminating an oxide layer on the surface of an adsorbate during the treatment process, the second magnetic suction piece is more easily used for adsorbing the magnetic foreign matters after surface treatment, and the magnetic foreign matters in the liquid to be treated can be completely adsorbed after multiple operations. The improvement of the slurry performance has important significance in ensuring the quality of the coating.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a method for detecting magnetic foreign matters in lithium ion battery coating diaphragm slurry.
Background
With the development of battery research and development technology, the diaphragm is lighter, thinner and more functional, for example, the functional coating diaphragm has heat resistance, infiltration improvement, heat sensitivity and adhesion, and is more and more widely applied. The application of the coating diaphragm requires that the slurry mixing and coating process of the coating slurry is coated on a base film in a single-sided or double-sided coating mode, inorganic or organic fillers with different hardness and various types of assistants are mostly adopted for the coating, and a sanding or high-speed dispersion slurry mixing process is used, wherein metal impurities can be carried in the slurry raw materials and the slurry mixing process, and if the metal foreign matters enter a battery through the coating diaphragm, a reduction reaction can be generated in the battery to form metal dendrites, so that the electrical property and the safety performance of the battery are greatly influenced.
In addition, through experimental verification and analysis, the content of the metal foreign matters in the battery influences the relevant performance of the battery, and the size and quantity range of the metal foreign matters have certain correlation with the performance of the battery. Therefore, the detection of metal impurities in the raw materials and the slurry in the production process is of great importance to the final battery performance.
At present, the conventional method for detecting the content of the metal foreign matters in the slurry is to use an element analysis method for testing, the reproducibility of the test result of the element analysis method is low, and the relevance between the test result and the practical application requirement of the battery cell is not obvious. The thickness of the common diaphragm coating is less than or equal to 4 microns and is smaller and smaller, metal foreign matters with different sizes can directly influence the process short-circuit rate and the self-discharge performance of the battery cell, and the influence degree on the safety performance of the battery cell is higher. At present, the magnetic foreign matters are extracted mainly by extracting the magnetic foreign matters in the liquid to be tested under the dynamic state, hydrochloric acid is added to stir again to form the filter membrane to be tested, the processing step introduces operations such as stirring again, the foreign matters quantity is possibly influenced, the test precision of the foreign matters quantity is high, small differences possibly cause large deviation to the test result, and accurate and effective test cannot be realized.
Disclosure of Invention
In view of the above, the present invention needs to provide a detection method capable of accurately extracting magnetic foreign matters, which is simple in operation and reliable in detection result, and can accurately and quickly detect the size and the number of the magnetic foreign matters in each process of the lithium ion battery coating diaphragm slurry mixing process, so that the detection method has important significance for optimally designing the slurry mixing process, monitoring the content state of the magnetic foreign matters in the slurry mixing process, and improving the performance of the slurry to ensure the quality of the coating.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a method for detecting magnetic foreign matters, which comprises the following steps:
s1, obtaining samples to be tested, wherein the samples to be tested are respectively raw materials used in lithium ion battery diaphragm coating slurry and slurry mixed in each feeding process;
s2, preparing the samples to be detected into dispersion liquid respectively, stirring the dispersion liquid, and performing adsorption treatment in the dispersion liquid by using a first magnetic suction piece with a coating layer sleeved on the surface;
s3, processing the adsorbate on the surface of the coating into adsorption liquid, moving a second magnetic suction piece outside the adsorption liquid container to extract magnetic foreign matters until the adsorption liquid is clarified, maintaining the suction force of the second magnetic suction piece, and pouring out the clarified liquid, wherein the step is repeated at least twice;
s4, removing the second magnetic attraction piece, pouring dilute acid with the concentration of 1-2mol/L into the container for extracting the magnetic foreign matters, dispersing, moving the second magnetic attraction piece outside the container again for adsorption treatment until the liquid in the container is clarified, pouring out the dilute acid, and repeating the steps at least twice;
s5, adding a solvent into the container to obtain a treatment solution, carrying out suction filtration on the treatment solution to obtain magnetic foreign matters, and testing the size and the number of the magnetic foreign matters.
Further, in step S1, the raw material includes at least one of ceramic powder, polyvinylidene fluoride hexafluoropropylene powder or emulsion, deionized water, binder, and surfactant.
Further, in step S2, the material of the coating layer is one of polyvinyl chloride and polyethylene terephthalate.
Further, the first magnetic part is a magnetic rod, the magnetic force of the magnetic rod is more than or equal to 10000 Gauss, the stirring speed of the dispersion liquid is 600-800r/min, and the adsorption treatment time is 30-60 min.
Further, in step S3, the specific steps of treating the adsorbate on the surface of the coating layer into an adsorption solution are as follows: and washing the coating layer by using deionized water to obtain the adsorption solution.
Further, in step S3, the second magnetic attraction member is a magnetic block, the magnetic force of the magnetic block is greater than or equal to 10000 gauss, the magnetic block is disposed at the bottom of the container and is tightly attached to the outer side of the container, the magnetic block moves along the bottom of the container in a circling manner, and the circling frequency is greater than or equal to 10 times.
Further, in step S4, the diluted acid is selected from diluted hydrochloric acid, diluted sulfuric acid or diluted nitric acid.
Further, the usage amount of the dilute acid is 15-20mL, the dispersion time is 3-4min, and the movement of the second magnetic attraction piece is the same as the step S3.
Further, in step S5, the solvent is selected from deionized water or an alcohol solvent.
Further, in step S5, the suction filtration is performed using a microfiltration membrane, the microfiltration membrane is selected from one of a mixed cellulose membrane, a polyethersulfone membrane and a nylon membrane, and the pore diameter is 0.1 to 5 μm.
Compared with the prior art, the detection method has the following beneficial effects:
the detection method is simple to operate, completely adsorbs magnetic foreign matters, has reliable detection results, can accurately and quickly test the size and the quantity of the metal magnetic foreign matters in each procedure of the lithium ion battery coating diaphragm slurry mixing process, and has important significance for quickly optimally designing the slurry mixing process, monitoring and knowing the content state of the magnetic foreign matters in the slurry mixing process and improving the performance of the slurry to ensure the quality of the coating.
Drawings
FIG. 1 is a flow chart of a method for detecting magnetic foreign objects according to a preferred embodiment of the present invention;
FIG. 2 is a diagram illustrating the operation of step S2 according to a preferred embodiment of the present invention;
FIG. 3 is a schematic view illustrating the operation of the second magnetic element 5 in steps S3 and S4 according to a preferred embodiment of the present invention.
In the figure: 1-stirring part, 2-first magnetic attraction piece, 3-magnetic block, 4-container and 5-second magnetic attraction piece.
Detailed Description
In order that the invention may be more fully understood, reference will now be made to the specific embodiments illustrated. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
The present invention provides a method for detecting a magnetic foreign object, as shown in fig. 1, comprising the steps of:
s1, obtaining samples to be tested, wherein the samples to be tested are respectively raw materials used in lithium ion battery diaphragm coating slurry and slurry mixed in each feeding process;
s2, respectively preparing the samples to be detected into dispersion liquid, stirring the dispersion liquid, and simultaneously carrying out adsorption treatment in the dispersion liquid by using a first magnetic suction piece with a coating layer sleeved on the surface, wherein the configuration of the dispersion liquid is not particularly limited, and a conventional mode in the field can be adopted, such as deionized water or an alcohol solvent is used as a solvent, and preferably, the deionized water is adopted for dispersion;
s3, processing the adsorbate on the surface of the coating into adsorption liquid, moving a second magnetic suction piece outside the adsorption liquid container to extract magnetic foreign matters until the adsorption liquid is clarified, maintaining the suction force of the second magnetic suction piece, and pouring out the clarified liquid, wherein the step is repeated at least twice, preferably 5-6 times;
s4, removing the second magnetic attraction piece, pouring 1-2mol/L diluted acid into the container for extracting the magnetic foreign matters, dispersing, moving the second magnetic attraction piece outside the container again for adsorption treatment until the liquid in the container is clarified, pouring out the diluted acid, and repeating the step at least twice, preferably 5-6 times;
s5, adding a solvent into the container to obtain a treatment solution, carrying out suction filtration on the treatment solution to obtain magnetic foreign matters, and testing the size and the number of the magnetic foreign matters.
The invention relates to a detection method of a magnetic substance, which comprises the steps of carrying out adsorption treatment on magnetic foreign matters by using a magnetic rod static adsorption mode in a stirring dynamic process, carrying out adsorption treatment by using a first magnetic piece under the state of dynamically stirring liquid to be treated for the first time, but adsorbing partial magnetic foreign matters in the dynamic treatment process, so that the liquid to be treated is treated under a second static state, an oxide layer on the surface of the adsorbent is further eliminated by using dilute acid in the treatment process, the magnetic foreign matters after surface treatment are more easily adsorbed by using a second magnetic piece, and the magnetic foreign matters in the liquid to be treated can be completely adsorbed after multiple operations, so that the test result is more accurate. Fig. 2 shows a device diagram for implementing the detection method of the present invention, as shown in fig. 2, after a sample to be detected is made into a dispersion liquid, the dispersion liquid is contained in a container 4, the dispersion liquid is stirred by a stirring part 1, meanwhile, a first magnetic attraction member 2 with a coating layer sleeved on the surface is fixed in the dispersion liquid, the fixing mode of the first magnetic attraction member 2 is not particularly limited, and the first magnetic attraction member 2 is mainly placed in the dispersion liquid to realize the adsorption of magnetic foreign matters, in the embodiment shown in fig. 2, a magnetic block 3 is arranged on the outer wall of the container 4, and the first magnetic attraction member 2 is fixed by utilizing the adsorption force between the magnetic block 3 and the first magnetic attraction member 2. Further, fig. 3 shows an operation schematic diagram of the second magnetic attraction member 5 according to some embodiments of the present invention, the second magnetic attraction member 5 is tightly attached to the outer wall of the container 4, the second magnetic attraction member 5 is moved to attract the magnetic foreign object in the container 4, the magnetic foreign object may be on the side wall of the container 4 or on the bottom of the container 4, and the second magnetic attraction member 5 shown in fig. 3 attracts on the bottom, so that the effect is better.
Further, the detection method of the present invention is mainly used for detecting raw materials used in lithium ion battery separator coating slurry and slurry obtained after slurry mixing in each feeding process, and includes raw materials and an intermediate production process, wherein in step S1, the raw materials include at least one of ceramic powder, polyvinylidene fluoride hexafluoropropylene powder or emulsion, deionized water, binder, and surfactant, it is understood that the above raw materials are only examples, and the raw materials involved in the separator coating slurry can be detected by the detection method of the present invention.
Further, in the present invention, a coating layer is sleeved on the surface of the first magnetic element, so as to collect the magnetic foreign matters adsorbed by the first magnetic element and avoid directly placing the first magnetic element in the dispersion liquid to introduce new impurities, preferably, in step S2, the coating layer is made of one of polyvinyl chloride and polyethylene terephthalate, such as a heat shrink tube, and the specific shape of the coating layer can be adjusted according to the shape of the first magnetic element, without specific limitation.
Further, in some specific embodiments of the present invention, the first magnetic attraction member is a magnetic rod, and the magnetic force of the magnetic rod is greater than or equal to 10000 gauss; the mass ratio of the powder sample to the deionized water in the dispersion liquid is 1: 5-1: for example, if the raw material is a solution, it may be diluted to an appropriate ratio, and if the raw material is a powder, deionized water is added to prepare a dispersion. Further, the stirring rate of the dispersion is not particularly limited, and can be adjusted as required, but is not suitable to be too fast or too slow, preferably, the stirring rate is 600-800r/min, the adsorption treatment time can be appropriately prolonged or shortened according to the specific adsorption condition, and is not particularly limited, and in some specific embodiments of the invention, the adsorption time is 30-60 min.
Further, in step S3, the specific steps of treating the adsorbate on the surface of the coating layer into an adsorption solution are as follows: and washing the coating layer by using deionized water to obtain the adsorption liquid, specifically, taking out the first magnetic part, and repeatedly washing the coating layer by using deionized water for 10-15 times.
Further, in step S3, the second magnetic attraction member is a magnetic block, the magnetic force of the magnetic block is greater than or equal to 10000 gauss, the magnetic block is tightly attached to the outside of the container to attract magnetic foreign matters in the container, preferably, the magnetic block is arranged at the bottom of the container and tightly attached to the outside of the container, so that the attraction efficiency and the attraction effect are improved under the dual actions of the magnetic block and gravity, the magnetic block moves along the bottom of the container in a circling manner, the circling frequency is greater than or equal to 10 times, the attraction is ensured to be more sufficient, and the test accuracy can be improved.
Further, in step S4, the magnetic foreign matter is acid-washed with dilute acid, which can quickly remove the surface layer of metal oxide in the adsorbate, so that the surface gloss of the adsorbate is more obvious, and the adsorbate after treatment can be detected more easily and accurately. The type of the dilute acid is not particularly limited, and may be selected from dilute hydrochloric acid, dilute sulfuric acid, or dilute nitric acid. In addition, the amount of the diluted acid used is not particularly limited, and it is preferable that the magnetic foreign material is dispersed in the diluted acid, and in some embodiments of the present invention, the amount of the diluted acid is 15 to 20mL, the dispersion time is adjusted as needed, preferably 3 to 4min, and the second magnetic member moves in the same manner as in step S3.
Further, in step S5, the solvent is selected from deionized water or an alcohol solvent, preferably deionized water.
Further, in step S5, the suction filtration is performed using a microfiltration membrane, the microfiltration membrane is selected from one of a mixed cellulose membrane, a polyethersulfone membrane and a nylon membrane, and the pore diameter is 0.1 to 5 μm.
The technical solution of the present invention will be more clearly described below with reference to specific examples.
Example 1
The ceramic slurry mixing process of 100kg for the ceramic diaphragm coating in the embodiment specifically comprises the following steps: the adding mass ratio of effective components of alumina ceramic powder, deionized water, adhesive acrylates and surfactant polyether modified organic silicon in the ceramic slurry with the solid content of 36% is 30: 64: 5.9: 0.1, firstly mixing the alumina ceramic powder, the surfactant and the deionized water according to the mass ratio, dispersing at a high speed, wherein the dispersion power is 2000W, the dispersion temperature is 25 ℃, the dispersion time is 1h to obtain a dispersion liquid 1, obtaining a dispersion liquid 2 through 5 permanent magnet demagnetizers with the magnetic force of 1 ten thousand gauss, adding the binder into the dispersion liquid according to the adding proportion, dispersing at a low speed, wherein the dispersion power is 400W, the dispersion temperature is 25 ℃, the dispersion time is 1.5h to obtain a dispersion liquid 3, and passing the slurry through a 300-mesh screen and 5 permanent magnet demagnetizers with the magnetic force of 1 ten thousand gauss to obtain a ceramic slurry 4.
The method for detecting the magnetic foreign matters in the slurry of the aluminum oxide ceramic diaphragm ceramic coating of the lithium ion battery comprises the following steps:
s1, wherein the ceramic slurry comprises raw materials of alumina, deionized water, a binder with a solid content of 50% and a surfactant with a solid content of 100%, and samples to be tested are respectively 1kg of alumina ceramic powder (A), 1kg of deionized water (B), 2kg of binder (C), 1kg of surfactant (D), 3.32kg of dispersion liquid 1(E), 3.32kg of dispersion liquid 2(F), 2.78kg of dispersion liquid 3(G) and 2.78kg of ceramic slurry 4 (H).
S2, processing the samples to be tested in the step S1 into dispersion liquid respectively and then placing the dispersion liquid in a plastic cup, specifically, mixing alumina ceramic powder (A) with 5000mL of deionized water (metal foreign matters are adsorbed and processed for 5 times by a magnetic bar so as to reduce the influence of external introduction of magnetic foreign matters), directly taking other samples to be tested as the dispersion liquid, placing the dispersion liquid obtained by the samples to be tested below an electric stirrer, enabling a stirring paddle (which is cleaned for 5 times) to be perpendicular to the center of the plastic cup (the paddle is 2-4 cm away from the bottom of the beaker), starting the electric stirrer, and stirring for 15min to mix uniformly; putting a magnetic rod with the magnetic force of 1 kilo gauss into a polyvinyl chloride heat-shrinkable tube (cleaned for 5 times), placing the magnetic rod in a beaker, placing a magnetic block on the outer side of the beaker corresponding to the magnetic rod for fixing, starting an electric stirrer, stirring at the dispersion rate of 800r/min for 60min, and carrying out adsorption treatment.
S3, taking out the magnetic rod sleeved with the heat-shrinkable tube, placing the magnetic rod in a 500mL clean plastic beaker, drawing the magnetic rod out of the heat-shrinkable tube, washing the surface of the heat-shrinkable tube for 10-15 times up and down by deionized water (the metal foreign matter is adsorbed by the magnetic rod for 5 times), placing a magnetic block with the magnetic force of 1 ten thousand gauss outside the beaker and tightly attaching the magnetic block to the bottom of the beaker, slowly adsorbing the magnetic block for 10 circles along the bottom of the beaker, pressing the magnetic block to pour the water in the beaker, slowly adding the water, and repeating the operation for 5-6 times until the liquid is clear.
S4, pouring 20mL of dilute acid into the beaker for extracting the magnetic substances, sealing the cup mouth with a preservative film, ultrasonically dispersing for 3-4min, adding 50mL of deionized water into the beaker (the metal foreign matters are adsorbed and treated by a magnetic rod for 5 times), slowly adsorbing the deionized water at the bottom of the outer side of the beaker for 10 circles by a magnetic 1 ten thousand gauss magnet again, pouring out the solution in the beaker, repeating the operation for 5-6 times, and adding 20mL of deionized water to obtain the final treatment liquid.
S5, clamping the mixed cellulose microporous filter membrane with the aperture of 0.1-5 μm by using a ceramic forceps, placing the mixed cellulose microporous filter membrane on a sand core funnel for suction filtration, opening a circulating water type multipurpose vacuum pump, completely suction-filtering the dispersion liquid, and testing the cleanliness of the collected filter membrane sample by using a cleanliness tester.
Comparative example 1
In the comparative example, 100kg of ceramic slurry for coating the ceramic diaphragm was used (same as example 1).
The method for detecting the magnetic foreign matters in the slurry of the aluminum oxide ceramic diaphragm ceramic coating of the lithium ion battery in the comparative example comprises the following steps:
s1, wherein the ceramic slurry comprises raw materials of alumina, deionized water, a binder with a solid content of 50% and a surfactant with a solid content of 100%, and samples to be tested are respectively 1kg of alumina ceramic powder (A), 1kg of deionized water (B), 2kg of binder (C), 1kg of surfactant (D), 3.32kg of dispersion liquid 1(E), 3.32kg of dispersion liquid 2(F), 2.78kg of dispersion liquid 3(G) and 2.78kg of ceramic slurry 4 (H).
S2, respectively processing the samples to be tested in the step S1 into dispersion liquid, and then placing the dispersion liquid in a plastic cup, specifically, mixing the alumina ceramic powder (A) with 5000mL of deionized water (metal foreign matters are adsorbed and processed for 5 times by a magnetic bar), directly taking other samples to be tested as the dispersion liquid, placing the dispersion liquid obtained by the samples to be tested below an electric stirrer, enabling a stirring paddle (which is cleaned for 5 times) to be vertical to the center of the plastic cup (the leaf spread is 2-4 cm away from the bottom of the beaker), starting the electric stirrer, and stirring for 15min to mix uniformly; putting a magnetic rod with the magnetic force of 1 kilo gauss into a polyvinyl chloride heat-shrinkable tube (cleaned for 5 times), placing the magnetic rod in a beaker, placing a magnetic block on the outer side of the beaker corresponding to the magnetic rod for fixing, starting an electric stirrer, stirring at the dispersion rate of 800r/min for 60min, and carrying out adsorption treatment.
S3, taking out the magnetic rod sleeved with the heat-shrinkable tube, placing the magnetic rod in a 500mL clean plastic beaker, drawing the magnetic rod out of the heat-shrinkable tube, and washing the surface of the heat-shrinkable tube for 10-15 times up and down by deionized water (the metal foreign bodies are adsorbed and treated by the magnetic rod for 5 times) to obtain adsorption treatment liquid.
S4, pouring 20mL of dilute acid into the beaker of the adsorption treatment solution for extracting the magnetic substances, sealing the cup mouth with a preservative film, ultrasonically dispersing for 3-4min, and adding 20mL of deionized water to obtain the final treatment solution.
S5, clamping the mixed cellulose microporous filter membrane with the aperture of 0.1-5 μm by using a ceramic forceps, placing the mixed cellulose microporous filter membrane on a sand core funnel for suction filtration, opening a circulating water type multipurpose vacuum pump, completely suction-filtering the dispersion liquid, and testing the cleanliness of the collected filter membrane sample by using a cleanliness tester.
Example 2
The 100kg slurry mixing process of the aqueous adhesive slurry for gluing the diaphragm coating in the embodiment is as follows: the glue slurry with the solid content of 20% comprises active ingredients of polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) powder, deionized water, adhesive acrylates and surfactant acrylic epoxy resin, wherein the addition mass ratio of the active ingredients is 13: 80: 6.9: 0.1, mixing PVDF-HFP powder, a surfactant and deionized water according to a ratio, dispersing at a high speed with a dispersion power of 1600W and a dispersion temperature of 28 ℃ to obtain a dispersion liquid 1, adding a binder into the dispersion liquid according to an addition ratio, dispersing at a low speed with a dispersion power of 500W and a dispersion temperature of 25 ℃ for 2h to obtain a dispersion liquid 2, and passing the slurry through a 200-mesh screen and 5 permanent magnet demagnetizers with a magnetic force of 1 ten thousand gauss to obtain a ceramic slurry 3.
The method for detecting the magnetic foreign matters in the aqueous adhesive slurry for the gluing of the diaphragm coating in the embodiment comprises the following steps:
s1, wherein the raw materials in the gluing slurry comprise PVDF-HFP, deionized water, a binder with a solid content of 50% and a surfactant with a solid content of 100%, and samples of a sample to be tested are 1kg of PVDF-HFP powder (A), 1kg of deionized water (B), 2kg of the binder (C), 1kg of the surfactant (D), 3.32kg of dispersion liquid 1(E), 7.6kg of dispersion liquid 2(F) and 5kg of ceramic slurry 3 (G).
S2, processing the samples to be tested in the step S1 into dispersion liquid respectively and then placing the dispersion liquid in a plastic cup, specifically, mixing PVDF-HFP powder with 5000mL of deionized water, directly taking other samples to be tested as the dispersion liquid, placing the plastic cup containing the samples below an electric stirrer, enabling a stirring paddle (which is cleaned for 5 times) to be perpendicular to the center of the beaker (the distance between the leaf span and the bottom of the beaker is 2 cm-4 cm), starting the electric stirrer, stirring for 15min, uniformly mixing, and closing the electric stirrer; placing a magnetic rod with magnetic force of 1 ten thousand gauss into a polyvinyl chloride heat-shrinkable tube (cleaned 5 times), operating with the device in FIG. 2, dispersing at a rate of 600r/min, stirring for 30min, and closing the electric stirrer after the stirring is finished.
S3, taking out the magnetic rod sleeved with the heat-shrinkable tube, placing the magnetic rod in a 500mL clean plastic beaker, drawing the magnetic rod out of the heat-shrinkable tube, washing the surface of the heat-shrinkable tube up and down for 10-15 times by using deionized water (the metal foreign matter is adsorbed and treated by the magnetic rod for 5 times), placing a magnetic block with the magnetic force of 1 ten thousand gauss outside the beaker and tightly attaching the magnetic block to the bottom of the beaker, slowly adsorbing the magnetic block for 10 circles along the bottom of the beaker as shown in the figure 3, then pressing the magnetic block to pour the water in the beaker, slowly adding the water, and repeating the operation for 5-6 times until the liquid is clear.
S4, pouring 20mL of dilute acid into the beaker for extracting the magnetic substances, sealing the cup mouth with a preservative film, ultrasonically dispersing for 3-4min, adding 50mL of deionized water into the beaker (the metal foreign matters are adsorbed and treated by a magnetic rod for 5 times), slowly adsorbing the deionized water at the bottom of the outer side of the beaker for 10 circles by a magnetic 1 ten thousand gauss magnet as shown in the figure 3, pouring out the solution in the beaker, repeating the operation for 5-6 times, and adding 20mL of deionized water to obtain the final treatment liquid.
S5, clamping the mixed cellulose microporous filter membrane with the aperture of 0.1-5 μm by using a ceramic forceps, placing the mixed cellulose microporous filter membrane on a sand core funnel for suction filtration, opening a circulating water type multipurpose vacuum pump, completely suction-filtering the dispersion liquid, and testing the cleanliness of the collected filter membrane sample by using a cleanliness tester.
Comparative example 2
In this example, 100kg of aqueous adhesive slurry was used for coating the separator (same as example 2).
The method for detecting the magnetic foreign matters in the aqueous adhesive slurry for the gluing of the diaphragm coating in the embodiment comprises the following steps:
s1, wherein the raw materials in the gluing slurry comprise PVDF-HFP, deionized water, a binder with a solid content of 50% and a surfactant with a solid content of 100%, and samples of a sample to be tested are 1kg of PVDF-HFP powder (A), 1kg of deionized water (B), 2kg of the binder (C), 1kg of the surfactant (D), 3.32kg of dispersion liquid 1(E), 7.6kg of dispersion liquid 2(F) and 5kg of ceramic slurry 3 (G).
S2, processing the samples to be tested in the step S1 into dispersion liquid respectively and then placing the dispersion liquid in a plastic cup, specifically, mixing PVDF-HFP powder with 5000mL of deionized water, directly taking other samples to be tested as the dispersion liquid, placing the plastic cup containing the samples below an electric stirrer, enabling a stirring paddle (which is cleaned for 5 times) to be perpendicular to the center of the beaker (the distance between the leaf span and the bottom of the beaker is 2 cm-4 cm), starting the electric stirrer, stirring for 15min, uniformly mixing, and closing the electric stirrer; placing a magnetic rod with magnetic force of 1 ten thousand gauss into a polyvinyl chloride heat-shrinkable tube (cleaned 5 times), operating with the device in FIG. 2, dispersing at a rate of 600r/min, stirring for 30min, and closing the electric stirrer after the stirring is finished.
S3, taking out the magnetic rod sleeved with the heat-shrinkable tube, placing the magnetic rod in a 500mL clean plastic beaker, drawing the magnetic rod out of the heat-shrinkable tube, and washing the surface of the heat-shrinkable tube for 10-15 times by deionized water (the metal foreign matter is adsorbed and treated by the magnetic rod for 5 times) to obtain the adsorption treatment solution.
S4, pouring 20mL of dilute acid into the beaker for extracting the magnetic substances, sealing the cup mouth with a preservative film, ultrasonically dispersing for 3-4min, and adding 20mL of deionized water to obtain the final treatment liquid.
S5, clamping the mixed cellulose microporous filter membrane with the aperture of 0.1-5 μm by using a ceramic forceps, placing the mixed cellulose microporous filter membrane on a sand core funnel for suction filtration, opening a circulating water type multipurpose vacuum pump, completely suction-filtering the dispersion liquid, and testing the cleanliness of the collected filter membrane sample by using a cleanliness tester.
The results of the cleanliness tester on the tests in examples 1-1 and comparative examples 1-2 are shown in table 1:
table 1 test results of the amount and size of magnetic foreign matters in examples and comparative examples 1 to 2
As can be seen from the test results in table 1, in example 1, the four raw materials a to D contain magnetic particles of different sizes and numbers, and the content of magnetic foreign matters in the dispersion liquid 2 after high-speed dispersion in the slurry mixing process is significantly greater than that in the dispersion liquid 1, which indicates that the permanent magnet demagnetizer provided in the high-speed dispersion process has a demagnetizing effect, and the binder material is added to the dispersion liquid 3 obtained after low-speed dispersion, so that the content of magnetic foreign matters in the dispersion liquid is increased, and the total number of magnetic particles in the ceramic slurry 4 obtained after permanent magnet demagnetizer is less than 20. Comparative example 1 does not adopt secondary treatment operation of magnetic block adsorption, only one-time magnetic bar adsorption is used for reducing adsorption and extraction of magnetic foreign particles in liquid to be tested in a dynamic state, the number of the magnetic foreign particles tested in the A-H sample and the overall reduction trend in example 1 are reduced, and the total number of test results shows that the foreign particle adsorption treatment can better realize complete adsorption treatment on the sample to be tested, and the test results are more accurate, more real and more effective.
In example 2, the four raw materials a to D also contained magnetic particles of different sizes and numbers, the number of magnetic foreign particles in the dispersion obtained by high-speed dispersion and low-speed dispersion was not very different, and the number of magnetic foreign particles in the slurry treated by the final permanent magnet demagnetizer was < 10. Compared with the prior art, the method has the advantages that the secondary treatment operation of magnetic block adsorption is not adopted in the comparative example 2, the adsorption and extraction of the magnetic foreign particles in the liquid to be tested under the dynamic condition are reduced by only using the magnetic rod for adsorption once, the number of the magnetic foreign particles with the particle size of less than 50 mu m tested in the sample is less than that of the test result in the comparative example, and the foreign particle adsorption treatment can better realize the complete adsorption treatment on the sample to be tested, so that the test result is more accurate, more real and more effective.
The above test results show that the slurry mixing scheme and the demagnetization design in examples 1 and 2 can remove magnetic metal foreign matters in the slurry, and the implementation shows that the detection method can be used for detecting the magnetic foreign matters in the raw materials and the intermediate slurry mixing process, so that the slurry mixing scheme and the demagnetization design are improved according to the detection results, and the performance of the lithium ion battery is improved. The detection method has the advantages of strong applicability, simple operation of the test treatment method and reliable detection result, can accurately and quickly test the size and the quantity of the metal magnetic foreign matters in each procedure of the lithium ion battery coating diaphragm slurry mixing process, can quickly optimize and design the slurry mixing process, monitors and knows the content state of the magnetic foreign matters in the slurry mixing process, and improves the performance of the slurry to ensure the quality of the coating. And as can be seen from the comparison results of the example 1 and the comparative example 1, and the comparison results of the example 2 and the comparative example 2, the detection accuracy of the state of the magnetic foreign matter can be obviously improved by adopting the testing method disclosed by the invention, so that the slurry performance is improved, and the quality of the coating is ensured.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A method for detecting a magnetic foreign object, comprising the steps of:
s1, obtaining samples to be tested, wherein the samples to be tested are respectively raw materials used in lithium ion battery diaphragm coating slurry and slurry mixed in each feeding process;
s2, preparing the samples to be detected into dispersion liquid respectively, stirring the dispersion liquid, and performing adsorption treatment in the dispersion liquid by using a first magnetic suction piece with a coating layer sleeved on the surface;
s3, processing the adsorbate on the surface of the coating into adsorption liquid, moving a second magnetic suction piece outside the adsorption liquid container to extract magnetic foreign matters until the adsorption liquid is clarified, maintaining the suction force of the second magnetic suction piece, and pouring out the clarified liquid, wherein the step is repeated at least twice;
s4, removing the second magnetic attraction piece, pouring dilute acid with the concentration of 1-2mol/L into the container for extracting the magnetic foreign matters, dispersing, moving the second magnetic attraction piece outside the container again for adsorption treatment until the liquid in the container is clarified, pouring out the dilute acid, and repeating the steps at least twice;
s5, adding a solvent into the container to obtain a treatment solution, carrying out suction filtration on the treatment solution to obtain magnetic foreign matters, and testing the size and the number of the magnetic foreign matters.
2. The detection method according to claim 1, wherein in step S1, the raw material includes at least one of ceramic powder, polyvinylidene fluoride hexafluoropropylene powder or emulsion, deionized water, binder, and surfactant.
3. The detecting method according to claim 1, wherein in step S2, the material of the coating layer is one of polyvinyl chloride and polyethylene terephthalate.
4. The detecting method according to claim 1, wherein the first magnetic member is a magnetic rod, the magnetic force of the magnetic rod is greater than or equal to 10000 Gauss, the stirring rate of the dispersion liquid is 600-800r/min, and the adsorption treatment time is 30-60 min.
5. The detection method according to claim 1, wherein the step of treating the adsorbate on the surface of the coating layer into an adsorption solution in step S3 comprises the specific steps of: and washing the coating layer by using deionized water to obtain the adsorption solution.
6. The detecting method according to claim 1, wherein in step S3, the second magnetic member is a magnetic block, the magnetic force of the magnetic block is greater than or equal to 10000 gauss, the magnetic block is disposed at the bottom of the container and closely attached to the outer side of the container, and the magnetic block moves along the bottom of the container in a circling manner, and the circling frequency is greater than or equal to 10 times.
7. The detection method according to claim 1, wherein in step S4, the dilute acid is selected from dilute hydrochloric acid, dilute sulfuric acid, or dilute nitric acid.
8. The detecting method according to claim 1, wherein the diluted acid is used in an amount of 15-20mL, the dispersing time is 3-4min, and the second magnetic member moves as in step S3.
9. The detection method according to claim 1, wherein in step S5, the solvent is selected from deionized water or an alcohol solvent.
10. The detection method according to claim 1, wherein in step S5, the suction filtration is performed by using a microfiltration membrane, and the microfiltration membrane is selected from one of a mixed cellulose membrane, a polyethersulfone membrane and a nylon membrane, and has a pore size of 0.1-5 μm.
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