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CN-122016999-A - Lithium plasma magnetic foreign matter on-line monitoring method based on high-frequency resonance spectrum

CN122016999ACN 122016999 ACN122016999 ACN 122016999ACN-122016999-A

Abstract

The invention discloses a lithium plasma magnetic foreign matter on-line monitoring method based on high-frequency resonance spectrum, which belongs to the technical field of lithium ion battery slurry detection, and comprises the steps of firstly constructing a magnetic focusing resonance sensing area, applying broadband excitation, acquiring background impedance spectrum, monitoring and extracting multi-characteristic parameters in real time, measuring particle flow velocity, carrying out normalization processing on signal waveforms, realizing foreign matter identification through multi-characteristic fusion inversion, and optionally carrying out statistics and output. The invention adopts the magnetic focusing resonance structure to improve the signal-to-noise ratio, distinguishes interference through dual-feature collaborative analysis, eliminates the flow velocity influence by utilizing the layout of the dual sensing areas, realizes the full-flow, real-time, on-line and accurate monitoring of ferromagnetic foreign matters with the particle size of more than 25 mu m in lithium plasma, can be widely applied to the monitoring of metal pollutants of various fluids with high cleanliness requirements, and has important industrial application value.

Inventors

  • GU SHIRUI
  • LUO CHUNYAN
  • ZHAO XINGQIANG

Assignees

  • 南京信息工程大学

Dates

Publication Date
20260512
Application Date
20260414

Claims (10)

  1. 1. The lithium plasma magnetic foreign matter on-line monitoring method based on high-frequency resonance spectrum shooting is characterized by comprising the following steps: s1, constructing a magnetic focusing resonance sensing system, namely arranging at least two magnetic focusing resonance sensing units at preset positions of a lithium plasma conveying channel along the flow direction of the slurry, wherein each magnetic focusing resonance sensing unit restrains high-frequency electromagnetic field energy in a local space through a high-permeability magnetic core to form a sensing area with high energy density; s2, acquiring a background reference spectrogram, namely injecting a broadband high-frequency magnetic excitation signal into the magnetic focusing resonance sensing unit, and acquiring background impedance spectrum data when nonmagnetic foreign matters pass through, wherein the background impedance spectrum data comprises a resonance frequency reference value and a quality factor reference value; S3, acquiring and extracting features in real time, namely acquiring impedance spectrum change data of each magnetic focusing resonance sensing unit in real time when lithium plasma flows through the sensing area, and extracting two feature parameters of a resonance frequency offset and a quality factor change from the impedance spectrum change data, wherein the resonance frequency offset reflects magnetic permeability change in the sensing area, and the quality factor change reflects eddy current loss change in the sensing area; s4, utilizing the space layout of the multi-magnetic focusing resonance sensing units to obtain the time difference that the same magnetic foreign matter sequentially passes through different sensing units, calculating the instantaneous flow rate of the magnetic foreign matter by combining the fixed spacing between the sensing units, and then utilizing the instantaneous flow rate to normalize the resonance frequency offset signal to obtain normalized characteristic parameters related to the size of the magnetic foreign matter; S5, foreign matter identification and quantitative analysis, namely substituting the normalized characteristic parameters and the quality factor variation quantity into a preset inversion model, decoupling the equivalent size and the magnetic property of the foreign matters, and completing identification and quantification of the magnetic foreign matters.
  2. 2. The method for on-line monitoring of magnetic foreign matters of lithium plasma based on high-frequency resonance spectroscopy according to claim 1, wherein in the step S1, the high-permeability magnetic core of the magnetic focusing resonance sensing unit is selected from a C-type, E-type or ring-type manganese zinc ferrite magnetic core or an amorphous alloy magnetic core, a focusing air gap is formed at an opening of the high-permeability magnetic core, and the width of the focusing air gap is 0.5-5mm.
  3. 3. The method for on-line monitoring of magnetic foreign matters in lithium plasma based on high-frequency resonance spectroscopy according to claim 1, wherein in the step S1, the lithium plasma conveying channel is a bypass channel led out from a main conveying pipeline or an insulating pipe section embedded from the main conveying pipeline, and the insulating pipe section is made of polytetrafluoroethylene, high borosilicate glass or polydimethylsiloxane material and has insulating performance to avoid eddy current loss and non-ferromagnetic material to avoid interference to a magnetic field.
  4. 4. The method for on-line monitoring of lithium plasma magnetic foreign matters based on high-frequency resonance spectroscopy according to claim 1, wherein in the step S2, the frequency range of the broadband high-frequency excitation signal is 100kHz to 10MHz, the excitation signal is injected in a frequency sweep mode or a frequency division multiplexing mode, and the background impedance spectrum data is automatically updated when the system is started or according to a preset period so as to adapt to dynamic changes of the slurry formula, the temperature and the conductivity.
  5. 5. The method for on-line monitoring of magnetic foreign matters in lithium ion batteries based on high-frequency resonance spectroscopy according to claim 1, wherein in step S3, the resonance frequency offset is as follows And quality factor variation Calculated by the following formula: ; ; Wherein, the In order to monitor the obtained resonant frequency in real time, The resonance frequency reference value obtained in the step S2; In order to monitor the quality factor obtained in real time, The figure of merit is defined as the ratio of the resonant peak frequency to the half power bandwidth, or measured directly by an impedance analyzer.
  6. 6. The method for on-line monitoring of magnetic foreign matter in lithium plasma based on high-frequency resonance spectroscopy as set forth in claim 1, wherein step S4 comprises recording the corresponding resonance frequency shift amounts respectively when the same magnetic foreign matter sequentially passes through the upstream sensing region and the downstream sensing region of the magnetic focusing resonance sensing unit Pulse signal and calculating time difference between peak values of two pulse signals According to the fixed distance between the upstream sensing area and the downstream sensing area Sum and time difference Calculating the instantaneous flow velocity of magnetic foreign matter : 。
  7. 7. The method for on-line monitoring of magnetic foreign matters in lithium ion plasma based on high frequency resonance spectroscopy according to claim 1, wherein in step S4, the normalization process comprises And performing scaling operation on the resonant frequency offset pulse waveform, or correcting the frequency shift amplitude according to the flow velocity by a table look-up method to obtain the normalized frequency shift amplitude which is only related to the size of the magnetic foreign matter.
  8. 8. The method for on-line monitoring of magnetic foreign matters in lithium plasma based on high-frequency resonance spectroscopy according to claim 1, wherein in step S5, the inversion model is a classification regression model constructed based on a machine learning algorithm, training samples of the classification regression model comprise normalized characteristic parameters and quality factor variation characteristic pairs generated when magnetic foreign matters with different particle sizes and different materials pass through a sensing unit, and the materials comprise iron, nonferromagnetic metal particles and bubbles.
  9. 9. The method for on-line monitoring of magnetic foreign matters in lithium plasma based on high-frequency resonance spectroscopy according to claim 1, wherein in the step S5, the foreign matters are identified through collaborative analysis of normalized characteristic parameters and quality factor variation, wherein if the normalized characteristic parameters are larger than a first preset threshold value and the quality factor variation is smaller than a second preset threshold value, ferromagnetic metal particles are judged, if the normalized characteristic parameters are smaller than a third preset threshold value and the quality factor variation is larger than a fourth preset threshold value, non-magnetic conductive impurities or bubbles are judged, and if the normalized characteristic parameters are larger than the first preset threshold value and the quality factor variation is not significantly changed, special magnetic non-metal impurities are judged.
  10. 10. The method for on-line monitoring magnetic foreign matters in lithium ion battery based on high-frequency resonance spectrum as set forth in claim 1, further comprising the step of S6 of counting and outputting the result of foreign matter identification in accumulated unit time, counting the size distribution of the foreign matters and the total content of ferromagnetic foreign matters, and outputting the result, wherein the output content comprises a histogram of the size distribution of the foreign matters, the total content of ferromagnetic foreign matters in unit time, and an alarm signal triggered when the size of the foreign matters is detected to exceed a preset threshold value, wherein the preset threshold value is not less than 25 。

Description

Lithium plasma magnetic foreign matter on-line monitoring method based on high-frequency resonance spectrum Technical Field The invention belongs to the technical field of lithium ion battery slurry detection, and particularly relates to a high-frequency resonance spectrum-based lithium ion battery slurry magnetic foreign matter on-line monitoring method. Background The lithium ion battery is used as a core component for clean energy storage, and the safety of the lithium ion battery is important. The purity of the positive electrode slurry (such as ternary materials NCM, lithium iron phosphate LFP and the like) of the lithium battery directly determines the safety and electrochemical consistency of the battery. In the production processes of slurry preparation, transportation, coating and the like, micrometer-sized (especially more than 50 μm) ferromagnetic metal particles (such as iron, nickel, cobalt, alloys thereof and the like) are extremely easy to mix due to equipment wear, raw material impurity introduction or improper operation. Because of the extremely small inter-electrode spacing (typically on the order of microns) within the cell, such metal particles, if undetected and entering the finished cell, will puncture the separator or directly connect the positive and negative electrodes, causing serious internal short circuits, which may lead to catastrophic safety accidents such as thermal runaway, fire, explosion, etc. Currently, the lower limit of detection standard commonly implemented in industry is 100 μm, and the actual internal control requirements of manufacturers of mainstream batteries are already as fine as 25 μm, and synchronous monitoring of the size distribution and total content of particles is required to realize the overall process quality control. Currently, the detection of magnetic foreign matters in lithium battery slurry in industry mainly depends on off-line sampling detection methods, mainly comprising a strong magnetic adsorption method, a spectrum analysis method and the like, wherein the methods all need manual sampling and complex sample pretreatment processes, so that the detection efficiency is low, the real-time performance is poor, and the real-time monitoring and closed-loop control on the production process cannot be realized. Therefore, developing a technology for detecting magnetic foreign matters of lithium plasma, which can realize full-flow, real-time, online and continuous monitoring, becomes a difficult problem to be solved in industry. The lithium battery slurry is a high-viscosity and high-conductivity complex colloid system, contains conductive carbon black, a binder, an NMP solvent and other components, has high conductivity and complex dielectric characteristics, can generate huge background eddy current loss in a detection coil to form strong background noise, so that weak useful signals of target particles are submerged, the signal to noise ratio is rapidly reduced, the effective magnetic permeability change caused by the small ferromagnetic particles at the level of 25 mu m is extremely weak, the magnetic field of a conventional open magnetic circuit air coil structure diverges, the energy density is low, the change is difficult to effectively capture, the actual slurry always contains interferences such as bubbles, conductive carbon black agglomerates and the like, the interferences possibly generate signal characteristics similar to those of metal particles in the conventional inductance method detection, and serious false alarm is caused, the size inversion algorithm based on the signal amplitude is seriously distorted due to the change of the induction signal amplitude and waveform generated when the particles with the same size pass through a detection area in the pipeline in industrial production. Therefore, aiming at the special physical and chemical properties of high conductivity and high viscosity of lithium battery slurry, development of a brand new online monitoring method capable of effectively penetrating background noise, accurately capturing and quantitatively analyzing ferromagnetic metal particles with the particle diameter of more than 25 microns is needed, so as to solve the core technical problems of signal flooding, insufficient sensitivity, poor anti-interference capability, large flow velocity influence and the like in the prior art. Disclosure of Invention The invention aims to provide a lithium plasma magnetic foreign matter on-line monitoring method based on high-frequency resonance spectrum, which aims to solve the key technical problems that the existing off-line detection method cannot realize real-time on-line monitoring, and when the conventional fluid inductance detection method is applied to high-conductivity lithium battery slurry, signal flooding, insufficient sensitivity, incapability of effectively distinguishing interference such as bubbles, serious influence on quantitative accuracy due to flow velocity fluctuat