Method for reducing magnetic substances in battery-grade lithium carbonate

Abstract

The invention discloses a method for reducing magnetic substances in battery-grade lithium carbonate, and relates to the technical field of lithium battery material manufacturing, according to the method, lithium stearate is accurately added through atomization spraying, and low-temperature crushing under inert gas protection is combined, so that uniform coating is realized, the dosage of a modifier is remarkably reduced, and particle aggregation is inhibited; the magnetic substance removal efficiency of subsequent electromagnetic continuous magnetic removal and multi-stage magnetic separation is effectively improved; meanwhile, a two-stage solvent washing and ceramic membrane vacuum drum filtering mode is innovatively adopted, secondary metal pollution is blocked while organic residues are efficiently removed, the problems of purity reduction and cost rising caused by lithium stearate residues can be comprehensively solved, and double breakthrough of magnetic substance control and organic impurity removal is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium battery material manufacturing, and in particular relates to a method for reducing magnetic substances in battery-grade lithium carbonate. Background Art

[0002] Battery-grade lithium carbonate is a key raw material for positive electrode materials of lithium-ion batteries, and its purity is crucial to the electrochemical performance, cycle life and safety of the battery. Magnetic substances are common harmful impurities in lithium carbonate. Even if they exist in trace amounts, they may cause serious problems such as micro-short circuits and thermal runaway inside the battery. Therefore, the efficient removal of magnetic substances in lithium carbonate is one of the core links in the production of high-quality battery-grade lithium carbonate. In the existing technology, physical magnetic separation, especially the magnetic separation process that combines electromagnetic technology and multi-stage separation, is a common means of removing magnetic impurities in lithium carbonate. In order to further improve the capture efficiency and separation effect of fine magnetic particles, surface modifiers such as lithium stearate are often introduced before magnetic separation. Such modifiers can change the surface properties of magnetic particles, enhance their adsorption or agglomeration with the magnetic medium, and thus improve the efficiency of magnetic separation.

[0003] However, some lithium stearate and its derivatives inevitably remain in the lithium carbonate product. These organic residues significantly increase the organic impurity content in the final product, potentially negatively impacting battery performance, such as by affecting electrolyte stability and increasing side reactions. Currently, some common organic matter removal methods, such as simple washing or conventional heat treatment, often suffer from incomplete removal and adverse effects on the properties of lithium carbonate itself. Summary of the Invention

[0004] In view of the defects in the prior art, the present invention provides a method for reducing magnetic substances in battery-grade lithium carbonate to solve the above technical problems.

[0005] A method for reducing magnetic substances in battery-grade lithium carbonate, comprising the following steps: adding lithium stearate to lithium carbonate powder through an atomizing spray system; Under the protection of an inert gas with an oxygen content of ≤10 ppm, the lithium carbonate powder is crushed in a jet mill, and the crushing temperature is controlled to be ≤40° C. to obtain a modified lithium carbonate powder; The modified lithium carbonate powder is subjected to electromagnetic continuous demagnetization and multi-stage magnetic separation in sequence, with a magnetic field strength of 1.5-3.0 T; The lithium carbonate powder after magnetic separation is subjected to two-stage solvent washing; The washed lithium carbonate powder is separated by ceramic membrane vacuum drum filtration, and the total organic carbon in the filter cake is controlled to be ≤50ppm; The filtered lithium carbonate is vacuum dried to obtain battery-grade lithium carbonate with low magnetic material content.

[0006] The addition amount of lithium stearate is 0.1-0.3 wt%, nitrogen or argon is used as the inert gas, the particle size of the crushed powder is controlled within the range of 2-8 μm, and during the vacuum drying step, the temperature is controlled to be maintained at 60-80°C and the atmospheric pressure is below -0.09 MPa.

[0007] Preferably, the two-stage solvent washing specifically comprises the following steps: The lithium carbonate powder was first stirred and washed with anhydrous ethanol washing solution at a washing solid-liquid ratio of 1:5; The lithium carbonate powder after the first stirring and washing was stirred and washed with 80° C. deionized water for 20 minutes.

[0008] During the second stirring washing, deionized water containing 0.1 mol / L disodium EDTA is used for washing. Compared with traditional pure water or weak acid washing, the strong chelating ability of EDTA can accurately target and dissociate the complex structure of magnetic metal ions and lithium stearate residues, forming a stable water-soluble complex under thermodynamic drive at 80°C, thereby achieving deep removal of magnetic metals and simultaneous removal of organic-metal composite impurities; at the same time, the neutral properties of disodium EDTA avoid the risk of equipment corrosion, and its selective complexing properties also ensure zero loss of lithium ions, overcoming the problem of secondary metal contamination caused by lithium stearate residues.

[0009] Preferably, the lithium carbonate powder is pre-screened with a 200-mesh sieve to remove impurities before being subjected to airflow pulverization.

[0010] A permanent magnet drum with a magnetic field strength of 1000Gs is superimposed on the 200-mesh screen to synchronously adsorb ferromagnetic foreign matter and improve the removal rate of metal impurities in the screen material. Compared with traditional single screening, the synchronous adsorption of the magnetic drum in this composite pre-screening process avoids the blockage problem caused by iron filings embedded in the screen holes, laying a foundation for pollution-free raw materials for uniform coating of surface modification and efficient demagnetization.

[0011] Preferably, when lithium stearate is added to lithium carbonate powder through an atomizing spray system, a dynamic adjustment system is used to adjust the atomizing spray rate, and the dynamic adjustment system includes a near-infrared spectrometer, a spectral analysis module, a PID controller and a variable frequency atomizing spray pump. The near-infrared spectrometer is used to scan the carbonyl characteristic peak absorbance and the lithium carbonate intrinsic peak absorbance of the lithium carbonate powder; The spectrum analysis module calculates the thickness of the lithium stearate coating layer based on the carbonyl characteristic peak absorbance and the lithium carbonate intrinsic peak absorbance; The PID controller outputs a spray rate adjustment instruction based on the thickness of the lithium stearate coating layer; The variable frequency atomizing spray pump is used to adjust the spray rate according to the spray rate adjustment instruction.

[0012] When the intrinsic peak of lithium carbonate is detected missing for 5 consecutive times, it will automatically switch to the backup peak and synchronously trigger the pulse backflush system to remove the sticking material of the equipment. The backup peak is the lattice vibration peak of lithium carbonate ( ), which is located in the mid-infrared region, corresponding to the lithium carbonate lattice The out-of-plane bending vibration has low intensity but is less affected by particle stacking and can be used as a benchmark for emergency thickness calculation. The backup peak is a key fault-tolerant design for ensuring continuous monitoring of coating thickness, which can overcome the risk of system shutdown caused by failure of the main peak.

[0013] Preferably, when the spectral analysis module calculates the thickness of the lithium stearate coating layer based on the carbonyl characteristic peak absorbance and the lithium carbonate intrinsic peak absorbance, the following formula is specifically used: ,

[0014] in, is the wrapping layer thickness, is the slope, is the absorbance of the characteristic peak of carbonyl group, is the intrinsic peak absorbance of lithium carbonate, is the background noise.

[0015] As preferably, the carbonyl characteristic peak is lithium stearate at The carbonyl stretching vibration peak of lithium carbonate is the intrinsic peak of lithium stearate. The methylene symmetric stretching peak.

[0016] During the detection process, a 1064 nm laser Raman scan was triggered every 10 minutes. Peak intensity is cross-validated with infrared data, and the spectral model is automatically calibrated when the deviation is greater than 5%, which can improve the reliability of thickness inversion to 99.9%. This Raman-infrared calibration technology captures the CC bond of lithium stearate by periodically triggering 1064 nm laser Raman scanning. Characteristic peaks are identified and cross-validated with infrared carbonyl peak data, creating a dual-spectrum interlocking verification mechanism. This mechanism automatically calibrates the infrared spectrum model when the inverted thickness deviation between the two exceeds 5%. This increases the reliability of coating thickness calculations to 99.9%, completely eliminating the risk of single-spectrum distortion caused by temperature fluctuations, particle stacking, and equipment vibration. Furthermore, Raman spectroscopy's insensitivity to moisture ensures detection stability even in extreme humidity conditions.

[0017] Preferably, when the PID controller outputs the spray rate adjustment instruction based on the thickness of the lithium stearate coating layer, the following formula is specifically used: , ,

[0018] in, For the PID controller in time The output value of is the proportional gain coefficient, is the integration coefficient, is the differential coefficient, is the target wrapping layer thickness, For the package layer at time The real-time thickness of For the package layer at time Thickness deviation, is the integration time variable.

[0019] Preferably, when the thickness of the lithium stearate coating layer exceeds the threshold value for three consecutive times: The variable frequency atomizing spray pump stops spraying; Start the pulse backflush system in the air flow mill to remove excess coating.

[0020] The lithium stearate powder discharged by backblowing is captured and backblown through a cyclone separator, and then recrystallized at -10°C ethanol to selectively separate the lithium stearate powder for recovery. The recovered lithium stearate powder is regenerated and returned to the atomizing spray system for recycling.

[0021] Preferably, the lithium carbonate powder is tested for total organic carbon content before being separated by ceramic membrane vacuum drum filtration. When the total organic carbon content is greater than 50 ppm, return to the secondary washing step for cleaning.

[0022] Based on the first wash data, the detergent concentration can be dynamically adjusted for the second wash number: for example, the ethanol concentration can be reduced from 100% to 30-50%; the temperature can be reduced from 80°C to 90°C.

[0023] Preferably, after the two-stage solvent washing is completed, The anhydrous ethanol washing liquid is dehydrated by 3A molecular sieve and then enters the distillation tower for recovery; The deionized water wash is passed through the strong acid cation resin for regeneration.

[0024] Here, 001×7 type strong acid cationic resin is used to regenerate the deionized washing liquid.

[0025] The beneficial effects of the present invention are: precise addition of lithium stearate through atomization spraying combined with low-temperature crushing under inert gas protection, uniform coating is achieved, the amount of modifier used is significantly reduced and particle agglomeration is inhibited, and the efficiency of magnetic material removal in subsequent electromagnetic continuous demagnetization + multi-stage magnetic separation is effectively improved; at the same time, the innovative use of two-stage solvent washing and ceramic membrane vacuum drum filtration can effectively remove organic residues while blocking secondary metal pollution, which can comprehensively solve the problems of purity decline and cost increase caused by lithium stearate residues, and achieve a double breakthrough in magnetic material control and organic impurity removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0027] Figure 1 A schematic flow chart of a method for reducing magnetic substances in battery-grade lithium carbonate provided by the present invention; Figure 2 A schematic structural diagram of a dynamic regulation system for a method of reducing magnetic substances in battery-grade lithium carbonate provided by the present invention. DETAILED DESCRIPTION

[0028] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0029] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention.

[0030] The embodiments of the invention are described in detail below with reference to the accompanying drawings.

[0031] like Figure 1 As shown, a method for reducing magnetic substances in battery-grade lithium carbonate includes the following contents: adding lithium stearate to lithium carbonate powder through an atomizing spray system; Under the protection of an inert gas with an oxygen content of ≤10 ppm, the lithium carbonate powder is crushed in a jet mill, and the crushing temperature is controlled to be ≤40° C. to obtain a modified lithium carbonate powder; The modified lithium carbonate powder is subjected to electromagnetic continuous demagnetization and multi-stage magnetic separation in sequence, with a magnetic field strength of 1.5-3.0 T; The lithium carbonate powder after magnetic separation is subjected to two-stage solvent washing; The washed lithium carbonate powder is separated by ceramic membrane vacuum drum filtration, and the total organic carbon in the filter cake is controlled to be ≤50ppm; The filtered lithium carbonate is vacuum dried to obtain battery-grade lithium carbonate with low magnetic material content.

[0032] In this solution, lithium stearate is precisely added through atomized spraying combined with low-temperature crushing under inert gas protection to achieve uniform coating, significantly reduce the amount of modifier used and inhibit particle agglomeration, and effectively improve the efficiency of magnetic material removal in subsequent electromagnetic continuous demagnetization + multi-stage magnetic separation; at the same time, the innovative use of two-stage solvent washing and ceramic membrane vacuum drum filtration can effectively remove organic residues while blocking secondary metal contamination, which can comprehensively solve the problems of purity decline and cost increase caused by lithium stearate residues, and achieve a double breakthrough in magnetic material control and organic impurity removal.

[0033] More specifically, the lithium carbonate powder was first stirred and washed with anhydrous ethanol washing solution, and the washing solid-liquid ratio was 1:5; The lithium carbonate powder after the first stirring and washing was stirred and washed with 80° C. deionized water for 20 minutes.

[0034] Compared to traditional single water or organic solvent washes, this two-stage solvent washing process efficiently dissolves residual free fatty acids and organic coatings from lithium stearate through a first wash with anhydrous ethanol, achieving targeted removal of organic impurities. A subsequent second wash with 80°C deionized water, driven by thermodynamics, thoroughly dissociates EDTA-metal complexes and elutes inorganic ions, while also simultaneously blocking any secondary magnetic metal residues. This collaborative design has, in practice, resulted in total organic carbon residues of ≤50 ppm and total magnetic metals of ≤80 ppb. Furthermore, due to the precise ethanol dosage and optimized hot water temperature, solvent consumption is significantly reduced, washing time is shortened, and the purity-cost contradiction caused by lithium stearate residues is fundamentally resolved.

[0035] More specifically, before the lithium carbonate powder is subjected to air flow pulverization, it is pre-screened through a 200-mesh sieve to remove impurities.

[0036] Compared with the existing technology of direct air flow crushing, the hard foreign matter in the lithium carbonate raw material is effectively removed through pre-physical interception, and large-particle impurities are blocked from entering the crushing process at the source. It can not only avoid the secondary iron filings pollution caused by the friction between the hard foreign matter and the stainless steel equipment under the impact of high-speed airflow, but also prevent large-particle impurities from wrapping the magnetic material, resulting in a decrease in the subsequent electromagnetic demagnetization efficiency; at the same time, it significantly reduces the wear risk of the grinder nozzle and ceramic lining, lays the foundation for uniform coating of the surface modifier and multi-stage magnetic separation deep demagnetization, and improves the removal efficiency of magnetic materials.

[0037] like Figure 2 As shown, more specifically, when lithium stearate is added to lithium carbonate powder through an atomizing spray system, a dynamic adjustment system is used to adjust the atomizing spray rate. The dynamic adjustment system includes a near-infrared spectrometer, a spectral analysis module, a PID controller and a variable frequency atomizing spray pump. The near-infrared spectrometer is used to scan the carbonyl characteristic peak absorbance and the lithium carbonate intrinsic peak absorbance of the lithium carbonate powder; The spectrum analysis module calculates the thickness of the lithium stearate coating layer based on the carbonyl characteristic peak absorbance and the lithium carbonate intrinsic peak absorbance; The PID controller outputs a spray rate adjustment instruction based on the thickness of the lithium stearate coating layer; The variable frequency atomizing spray pump is used to adjust the spray rate according to the spray rate adjustment instruction.

[0038] This dynamic adjustment system uses near-infrared spectroscopy to scan the absorbance ratio of the carbonyl characteristic peak on the particle surface to the intrinsic peak of lithium carbonate in real time, accurately inverts the thickness of the lithium stearate coating layer, and dynamically outputs the spray rate instruction through the PID controller to drive the variable frequency atomizing spray pump to perform adaptive adjustment within the adjustment range of 0.5-5.0 mL / min, achieving stable control of the coating thickness between 8±1nm. Compared with traditional methods, this method can significantly reduce the fluctuation of the coating layer thickness and reduce the amount of lithium stearate used. At the same time, it can also eliminate insufficient exposure of magnetic materials due to insufficient local coating or organic residues caused by excessive coating.

[0039] More specifically, the spectrum analysis module calculates the thickness of the lithium stearate coating layer based on the carbonyl characteristic peak absorbance and the lithium carbonate intrinsic peak absorbance by using the following formula: ,

[0040] in, is the wrapping layer thickness, is the slope, is the absorbance of the characteristic peak of carbonyl group, is the intrinsic peak absorbance of lithium carbonate, is the background noise.

[0041] More specifically, the carbonyl characteristic peak is lithium stearate in The carbonyl stretching vibration peak of lithium carbonate is the intrinsic peak of lithium stearate. The methylene symmetric stretching peak.

[0042] Compared with the traditional detection method using the intrinsic peak of lithium carbonate, this characteristic peak definition scheme completely avoids the peak position drift caused by the difference in lithium carbonate crystal structure by directly locking the vibration signal of the lithium stearate molecular bond, and improves the calculation accuracy of the coating thickness to ±0.3 nm; at the same time, the methylene peak and the carbonyl peak belong to the same organic chain structure and are less affected by environmental humidity and particle stacking. Combined with the absorbance ratio method, a self-consistent reference system is constructed to achieve exclusive, highly sensitive, and anti-interference monitoring of the lithium stearate coating layer, ensuring the uniformity of surface modification from the source and making the magnetic material removal rate stable at >96%.

[0043] More specifically, when the PID controller outputs a spray rate adjustment instruction based on the thickness of the lithium stearate coating layer, the following formula is specifically used: , ,

[0044] in, For the PID controller in time The output value of is the proportional gain coefficient, is the integration coefficient, is the differential coefficient, is the target wrapping layer thickness, For the package layer at time The real-time thickness of For the package layer at time Thickness deviation, is the integration time variable.

[0045] More specifically, when the thickness of the lithium stearate coating layer exceeds the threshold for three consecutive times: The variable frequency atomizing spray pump stops spraying; Start the pulse backflush system in the air flow mill to remove excess coating.

[0046] This emergency treatment mechanism triggers the automatic emergency stop of the variable frequency atomizing spray pump through intelligent judgment of three consecutive thickness exceeding the standard. The threshold here is generally set at 12 nm. When the coating thickness exceeds the threshold, the excessive addition of modifier is immediately blocked, and the 0.5MPa nitrogen pulse backflush system is started simultaneously. The high-pressure cyclone is used to strip off the excess lithium stearate coating on the surface of the particles, allowing the system to restore the target thickness within 2 minutes. Compared with traditional manual cleaning, it can greatly shorten the downtime and avoid problems such as uncontrolled organic residues, magnetic masking and waste of raw materials caused by excessive coating.

[0047] More specifically, the total organic carbon content of lithium carbonate powder is tested before separation by ceramic membrane vacuum drum filtration. When the total organic carbon content is greater than 50 ppm, return to the secondary washing step for cleaning.

[0048] Compared with traditional fixed-process washing or terminal sampling control, this closed-loop total organic carbon content detection and backwashing mechanism detects the total organic carbon content in real time online before ceramic membrane filtration and sets a 50ppm threshold to trigger automatic backwashing. It can accurately intercept batches with excessive residual organic carbon content and prevent materials with total organic carbon content greater than 50ppm from entering the drying process. At the same time, it can also dynamically optimize washing energy consumption, returning only the excessive batches for secondary washing, which can greatly reduce solvent consumption and steam energy consumption compared to full-volume repeated washing. Finally, it can also block organic-metal composite pollution and promptly remove unwashed lithium stearate and its chelated ferromagnetic ions, preventing the formation of stable complexes under high drying temperatures and further reducing residual magnetic substances.

[0049] More specifically, after the two-stage solvent washing is completed, The anhydrous ethanol washing liquid is dehydrated by 3A molecular sieve and then enters the distillation tower for recovery; The deionized water wash is passed through the strong acid cation resin for regeneration.

[0050] Compared with traditional one-time use or simple distillation recovery, this solvent regeneration process uses 3A molecular sieve to deeply dehydrate the anhydrous ethanol washing liquid, breaking the ethanol-water azeotropic point limitation, improving the purity of ethanol recovered in the subsequent distillation tower and the ethanol reuse rate. At the same time, the use of 001×7 type strong acid cationic resin to regenerate the deionized water washing liquid not only improves the EDTA regeneration rate, but also can make the effluent metal ion ≤1 ppb. Compared with repurchasing EDTA, it can effectively reduce costs and eliminate the discharge of heavy metal waste liquid.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A method for reducing magnetic substances in battery-grade lithium carbonate, characterized in that: The following steps are involved: adding lithium stearate to lithium carbonate powder through an atomizing spray system; Under the protection of an inert gas with an oxygen content of ≤10 ppm, the lithium carbonate powder is crushed in a jet mill, and the crushing temperature is controlled to be ≤40° C. to obtain a modified lithium carbonate powder; The modified lithium carbonate powder is subjected to electromagnetic continuous demagnetization and multi-stage magnetic separation in sequence, with a magnetic field strength of 1.5-3.0 T; The lithium carbonate powder after magnetic separation is subjected to two-stage solvent washing; The washed lithium carbonate powder is separated by ceramic membrane vacuum drum filtration, and the total organic carbon in the filter cake is controlled to be ≤50ppm; The filtered lithium carbonate is vacuum dried to obtain battery-grade lithium carbonate with low magnetic material content.

2. The method for reducing magnetic substances in battery-grade lithium carbonate according to claim 1, wherein The two-stage solvent washing specifically comprises the following steps: The lithium carbonate powder was first stirred and washed with anhydrous ethanol washing solution at a washing solid-liquid ratio of 1:5; The lithium carbonate powder after the first stirring and washing was stirred and washed with 80° C. deionized water for 20 minutes.

3. The method for reducing magnetic substances in battery-grade lithium carbonate according to claim 1, wherein Before the lithium carbonate powder is subjected to air flow pulverization, it is pre-screened through a 200-mesh sieve to remove impurities.

4. The method for reducing magnetic substances in battery-grade lithium carbonate according to claim 1, wherein When lithium stearate is added to lithium carbonate powder through an atomizing spray system, a dynamic adjustment system is used to adjust the atomizing spray rate. The dynamic adjustment system includes a near-infrared spectrometer, a spectrum analysis module, a PID controller and a variable frequency atomizing spray pump. The near-infrared spectrometer is used to scan the carbonyl characteristic peak absorbance and the lithium carbonate intrinsic peak absorbance of the lithium carbonate powder; The spectrum analysis module calculates the thickness of the lithium stearate coating layer based on the carbonyl characteristic peak absorbance and the lithium carbonate intrinsic peak absorbance; The PID controller outputs a spray rate adjustment instruction based on the thickness of the lithium stearate coating layer; The variable frequency atomizing spray pump is used to adjust the spray rate according to the spray rate adjustment instruction.

5. The method for reducing magnetic substances in battery-grade lithium carbonate according to claim 4, wherein When the spectrum analysis module calculates the thickness of the lithium stearate coating layer based on the carbonyl characteristic peak absorbance and the lithium carbonate intrinsic peak absorbance, the following formula is specifically used: , in, is the wrapping layer thickness, is the slope, is the absorbance of the characteristic peak of carbonyl group, is the intrinsic peak absorbance of lithium carbonate, is the background noise.

6. The method for reducing magnetic substances in battery-grade lithium carbonate according to claim 5, wherein The carbonyl characteristic peak is lithium stearate The carbonyl stretching vibration peak of lithium carbonate is the intrinsic peak of lithium stearate. The methylene symmetric stretching peak.

7. The method for reducing magnetic substances in battery-grade lithium carbonate according to claim 4, wherein When the PID controller outputs a spray rate adjustment instruction based on the thickness of the lithium stearate coating layer, the following formula is specifically used: , , in, For the PID controller in time The output value of is the proportional gain coefficient, is the integration coefficient, is the differential coefficient, is the target wrapping layer thickness, For the package layer at time The real-time thickness of For the package layer at time Thickness deviation, is the integration time variable.

8. The method for reducing magnetic substances in battery-grade lithium carbonate according to claim 4, wherein: When the thickness of the lithium stearate coating exceeds the threshold for three consecutive times: The variable frequency atomizing spray pump stops spraying; Start the pulse backflush system in the air flow mill to remove excess coating.

9. The method for reducing magnetic substances in battery-grade lithium carbonate according to claim 1, wherein The total organic carbon content of lithium carbonate powder is tested before separation by ceramic membrane vacuum drum filtration. When the total organic carbon content is greater than 50 ppm, return to the secondary washing step for cleaning.

10. The method for reducing magnetic substances in battery-grade lithium carbonate according to claim 1, wherein: After the two-stage solvent washing is completed, The anhydrous ethanol washing liquid is dehydrated by 3A molecular sieve and then enters the distillation tower for recovery; The deionized water wash is passed through the strong acid cation resin for regeneration.

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