Method for reducing magnetic substances in battery-grade lithium carbonate

Abstract

The application discloses a method for reducing magnetic substances in battery-grade lithium carbonate, and relates to the technical field of lithium battery material manufacturing. The method realizes uniform coating by means of precise addition of lithium stearate through atomization spraying and low-temperature crushing under the protection of inert gas, significantly reduces the amount of modifier, inhibits particle agglomeration, effectively improves the magnetic substance removal efficiency of subsequent electromagnetic continuous demagnetization and multi-stage magnetic separation, and simultaneously innovatively adopts a two-stage solvent washing and ceramic membrane vacuum drum filtering mode to efficiently remove organic residues and block secondary metal pollution, so that the problems of purity reduction and cost increase caused by lithium stearate residue can be comprehensively solved, and a dual breakthrough of magnetic substance control and organic impurity removal is realized.

Description

TECHNICAL FIELD

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

[0002] Battery-grade lithium carbonate is a key raw material for the positive electrode material of a lithium ion battery, and the purity of the battery-grade lithium carbonate is crucial to the electrochemical performance, cycle life and safety of the battery. Magnetic substances are common harmful impurities in lithium carbonate, and even trace amounts of the magnetic substances can cause serious problems such as internal micro-short circuit and thermal runaway of the battery. Therefore, efficient removal of the magnetic substances in the lithium carbonate is one of the core links in the production of high-quality battery-grade lithium carbonate. In the prior art, a physical magnetic separation method, in particular a magnetic separation process combined with electromagnetic technology and multi-stage separation, is a common means for removing the magnetic impurities in the lithium carbonate. In order to further improve the trapping efficiency and separation effect of the fine magnetic particles, a lithium stearate or the like surface modifier is often introduced before the magnetic separation. The surface modifier can change the surface properties of the magnetic particles and enhance the adsorption or agglomeration of the magnetic particles with the magnetic medium, thereby improving the magnetic separation efficiency.

[0003] However, the lithium stearate and its derivatives are inevitably partially left in the lithium carbonate product. These organic residues can significantly increase the content of organic impurities in the final product, and have a potential negative impact on the battery performance, such as affecting the stability of the electrolyte and increasing the side reactions of the battery. SUMMARY

[0004] In view of the defects in the prior art, the application 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 contents:

[0006] Lithium stearate is added to lithium carbonate powder through an atomizing spraying system;

[0007] The lithium carbonate powder is crushed in an airflow crusher under the protection of an inert gas with an oxygen content of ≤10 ppm, and the crushing temperature is controlled to be ≤40℃, to obtain modified lithium carbonate powder;

[0008] The modified lithium carbonate powder is sequentially subjected to electromagnetic continuous demagnetization and multi-stage magnetic separation, and the magnetic field strength is 1.5-3.0 T;

[0009] The lithium carbonate powder after the magnetic separation is subjected to two-stage solvent washing;

[0010] The washed lithium carbonate powder is separated by ceramic membrane vacuum drum filtration, and the total organic carbon of the filter cake is controlled to be less than or equal to 50 ppm;

[0011] The filtered lithium carbonate is vacuum dried to obtain battery-grade lithium carbonate with low magnetic material content.

[0012] The lithium stearate is added in an amount of 0.1-0.3 wt%, the inert gas is nitrogen or argon, the particle size of the crushed powder is controlled in the range of 2-8 μm, and in the step of vacuum drying, the temperature is controlled to be kept at 60-80°C, and the atmospheric pressure is controlled to be below -0.09 MPa.

[0013] As preferred, the two-stage solvent washing specifically comprises the following steps:

[0014] The lithium carbonate powder is washed with anhydrous ethanol washing liquid for the first time, and the solid-liquid ratio of washing is 1:5;

[0015] The lithium carbonate powder after the first stirring washing is stirred and washed with 80°C deionized water washing liquid for 20 minutes.

[0016] In the second stirring washing, the deionized water washing liquid containing 0.1 mol / L EDTA disodium is used for washing. Compared with traditional pure water or weak acid washing, the strong chelating ability of EDTA can accurately target the complex structure of magnetic metal ions and lithium stearate residues, form stable water-soluble complexes under the driving of 80°C thermodynamics, realize the synchronous removal of magnetic metal deep removal and organic-metal complex impurities, and at the same time, the neutral property of EDTA disodium avoids the risk of equipment corrosion, and the selective complexing property also ensures zero loss of lithium ions, overcoming the problem of secondary metal pollution caused by lithium stearate residues.

[0017] As preferred, before airflow crushing of the lithium carbonate powder, the impurities are pre-screened through a 200-mesh screen.

[0018] In the permanent magnetic roller with a 200-mesh screen and a magnetic field strength of 1000Gs, the ferromagnetic impurities are simultaneously adsorbed, and the metal impurity removal rate of the oversize material is improved. Compared with the traditional single screening, the simultaneous adsorption of the magnetic roller avoids the problem of blockage caused by the embedding of iron chips in the screen holes, and lays a foundation for pollution-free raw materials for uniform coating and efficient demagnetization of surface modification.

[0019] As preferred, when the lithium stearate is added to the lithium carbonate powder through the atomizing spraying system, the atomizing spraying rate is adjusted by a dynamic adjustment system, the dynamic adjustment system comprises a near-infrared spectrometer, a spectrum analysis module, a PID controller and a variable frequency atomizing spraying pump,

[0020] The near-infrared spectrometer is used to scan the carbonyl characteristic peak absorbance and lithium carbonate intrinsic peak absorbance of the lithium carbonate powder.

[0021] The spectral analysis module calculates the thickness of the lithium stearate coating based on the absorbance of the carbonyl characteristic peak and the intrinsic peak absorbance of lithium carbonate.

[0022] The PID controller outputs spray rate adjustment commands based on the thickness of the lithium stearate coating.

[0023] The variable frequency atomizing spray pump is used to adjust the spray rate according to the spray rate adjustment command.

[0024] When the intrinsic peak of lithium carbonate is detected as missing five times consecutively, the system automatically switches to the backup peak and simultaneously triggers the pulse backflushing system to remove material adhering to the equipment. The backup peak is the lattice vibration peak of lithium carbonate. This peak is located in the mid-infrared region, corresponding to the lithium carbonate lattice. Although the out-of-plane bending vibration has a low intensity, it is less affected by particle stacking and can be used as an emergency thickness calculation benchmark. The backup peak is a key fault-tolerant design to ensure continuous monitoring of the coating thickness and can overcome the risk of system shutdown caused by the failure of the main peak.

[0025] Preferably, when the spectral analysis module calculates the coating thickness of lithium stearate based on the absorbance of the carbonyl characteristic peak and the intrinsic peak absorbance of lithium carbonate, it specifically uses the following formula: ,

[0026] in, The thickness of the coating layer, The slope The absorbance is the characteristic peak of the carbonyl group. The absorbance is the intrinsic peak of lithium carbonate. This is the background noise.

[0027] Preferably, the carbonyl characteristic peak is that of lithium stearate. The carbonyl stretching vibration peak, the intrinsic peak of lithium carbonate is that of lithium stearate. The methylene symmetric stretching peak.

[0028] During the detection process, a 1064 nm laser Raman scan is triggered every 10 minutes. Cross-validation with peak intensity and infrared data, and automatic calibration of the spectral model when the deviation is >5%, can improve the reliability of thickness inversion to 99.9%. This Raman-infrared coupled calibration technique captures the C-bonds of lithium stearate by periodically triggering 1064 nm laser Raman scanning. The characteristic peaks are cross-verified with the infrared carbonyl peak data to form a dual-spectrum interlocking verification mechanism, that is, when the thickness deviation of the two is greater than 5%, the infrared spectrum model is automatically calibrated. The reliability of the coating thickness calculation can be improved to 99.9%, and the single-spectrum distortion risk caused by temperature fluctuations, particle stacking, and equipment vibration can be completely solved; at the same time, the Raman spectrum is not sensitive to moisture, which can ensure the detection stability under extreme humidity.

[0029] As preferred, when the PID controller outputs the spray rate adjustment instruction based on the lithium stearate coating thickness, the following formula is specifically used: , ,

[0030] Wherein, is the output value of the PID controller at time , is the proportional gain coefficient, is the integral coefficient, is the differential coefficient, is the target coating thickness, is the real-time thickness of the coating at time , is the thickness deviation of the coating at time , is the integral time variable.

[0031] As preferred, when the coating thickness of lithium stearate is detected to exceed the threshold value for three consecutive times:

[0032] The frequency conversion atomization spray pump stops spraying;

[0033] The pulse backflushing system in the airflow pulverizer is started to remove excess coating.

[0034] The lithium stearate powder discharged by backflushing is captured by a cyclone separator, and then low-temperature recrystallization is performed at -10℃ ethanol to selectively separate and recover the lithium stearate powder. The recovered lithium stearate powder is regenerated and returned to the atomization spray system for recycling.

[0035] As preferred, the total organic carbon content of the lithium carbonate powder is detected before the ceramic membrane vacuum drum filtration separation,

[0036] When the total organic carbon content is greater than 50ppm, return to the secondary washing step for cleaning.

[0037] Based on the first washing data, the detergent concentration can be dynamically adjusted for the number of secondary washing times: such as reducing the ethanol concentration from 100% to 30-50%; reducing the temperature from 80℃ to 90℃.

[0038] As preferred, after the two-stage solvent washing is completed,

[0039] The anhydrous ethanol washing liquid is dehydrated by 3A molecular sieve and then enters the rectifying column for recovery;

[0040] The deionized water washing liquid is regenerated by strong acid cation resin.

[0041] Here, the 001x7 type strong acid cation resin is used to regenerate the deionized washing liquid.

[0042] The beneficial effects of the present application are: through precise addition of lithium stearate by atomization spraying combined with low-temperature crushing under the protection of inert gas, uniform coating is realized, the amount of modifier is significantly reduced, and particle agglomeration is inhibited, the efficiency of removing magnetic substances by subsequent electromagnetic continuous demagnetization + multi-stage magnetic separation is effectively improved; at the same time, the two-stage solvent washing and ceramic membrane vacuum drum filtration method is innovatively used, which can effectively remove organic residues while blocking secondary metal pollution, and can comprehensively solve the problems of purity reduction and cost increase caused by lithium stearate residue, and realize the dual breakthrough of magnetic substance control and organic impurity removal. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0044] Figure 1 A flowchart of a method for reducing magnetic substances in battery-grade lithium carbonate provided by the present application;

[0045] Figure 2 A structure diagram of a dynamic adjustment system of a method for reducing magnetic substances in battery-grade lithium carbonate provided by the present application. DETAILED DESCRIPTION

[0046] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0047] The following disclosure provides many different embodiments or examples for implementing different aspects of the present application. For simplicity of the disclosure, the following description often refers to specific examples of components and arrangements of components. One skilled in the art will appreciate that there are many ways to implement the same function or achieve the same results.

[0048] Embodiments of the application will be described in detail below with reference to the drawings.

[0049] As Figure 1 shown in the figure, a method for reducing magnetic substances in battery-grade lithium carbonate includes the following contents:

[0050] Lithium stearate is added to lithium carbonate powder through an atomizing spray system;

[0051] The lithium carbonate powder is crushed in a jet mill under the protection of an inert gas with an oxygen content ≤10 ppm, and the crushing temperature is controlled to be ≤40°C, to obtain modified lithium carbonate powder;

[0052] The modified lithium carbonate powder is sequentially subjected to electromagnetic continuous demagnetization and multi-stage magnetic separation, and the magnetic field strength is 1.5-3.0 T;

[0053] The lithium carbonate powder after magnetic separation is subjected to two-stage solvent washing;

[0054] The washed lithium carbonate powder is subjected to ceramic membrane vacuum drum filtration separation, and the total organic carbon of the filter cake is controlled to be ≤50 ppm;

[0055] The filtered lithium carbonate is vacuum dried to obtain battery-grade lithium carbonate with low magnetic substance content.

[0056] In this scheme, by precisely adding lithium stearate through an atomizing spray system and combining low-temperature crushing under the protection of an inert gas, uniform coating is achieved, the amount of modifier is significantly reduced, particle agglomeration is inhibited, and the efficiency of removing magnetic substances in subsequent electromagnetic continuous demagnetization + multi-stage magnetic separation is effectively improved. At the same time, the two-stage solvent washing and ceramic membrane vacuum drum filtration method is innovatively adopted, which can effectively remove organic residues while blocking secondary metal pollution, and can comprehensively solve the problems of purity reduction and cost increase caused by lithium stearate residue, and realize the dual breakthrough of magnetic substance control and organic impurity removal.

[0057] More specifically, the lithium carbonate powder is first stirred and washed with anhydrous ethanol washing liquid, and the solid-liquid ratio is 1:5;

[0058] The lithium carbonate powder after the first stirring and washing is stirred and washed with 80°C deionized water washing liquid for 20 min.

[0059] Compared with the traditional single water washing or organic solvent washing, the two-stage solvent washing process can efficiently dissolve the free fatty acid and organic coating layer of lithium stearate residue by the first water-free ethanol washing, so as to realize the targeted removal of organic impurities; then the second washing with 80 DEG C deionized water can completely dissociate the EDTA-metal complex and elute inorganic ions under the driving of thermodynamics, and can also block the secondary residue of magnetic metal. The above-mentioned synergistic design is detected in practice, and the total organic carbon residue is less than or equal to 50 ppm, and the total amount of magnetic metal is less than or equal to 80 ppb. Due to the precise amount of ethanol and the optimized hot water temperature, compared with the traditional process, the solvent consumption is greatly reduced, and the washing time is shortened, so as to solve the contradiction between purity and cost caused by lithium stearate residue from the root.

[0060] More specifically, the lithium carbonate powder is pre-screened by a 200-mesh screen before airflow crushing.

[0061] Compared with the prior art of directly airflow crushing, the hard foreign matter in the lithium carbonate raw material is effectively removed by the pre-positioned physical interception, which blocks the large particle impurities from entering the crushing link from the source, not only can avoid the secondary iron contamination caused by the friction between the hard foreign matter and the stainless steel equipment under the impact of high-speed airflow, but also can prevent the large particle impurities from wrapping the magnetic material, which leads to the decrease of the efficiency of the subsequent electromagnetic demagnetization; at the same time, it can significantly reduce the wear risk of the nozzle and ceramic lining of the crusher, lay a foundation for uniform coating of the surface modifier and deep magnetic separation of multi-stage magnetic separation, and improve the removal efficiency of magnetic material.

[0062] As shown in Figure 2 More specifically, when the lithium stearate is added to the lithium carbonate powder through the atomizing spraying system, the atomizing spraying rate is adjusted by a dynamic adjustment system, the dynamic adjustment system comprises a near-infrared spectrometer, a spectrum analysis module, a PID controller and a variable frequency atomizing spraying pump,

[0063] The near-infrared spectrometer is used to scan the carbonyl characteristic peak absorbance and lithium carbonate intrinsic peak absorbance of the lithium carbonate powder;

[0064] The spectrum analysis module calculates the coating thickness of lithium stearate based on the carbonyl characteristic peak absorbance and lithium carbonate intrinsic peak absorbance;

[0065] The PID controller outputs a spraying rate adjustment instruction based on the coating thickness of lithium stearate;

[0066] The variable frequency atomizing spraying pump is used to adjust the spraying rate according to the spraying rate adjustment instruction.

[0067] This dynamic adjustment system accurately inverts the thickness of the lithium stearate coating by scanning the absorbance ratio of the carbonyl characteristic peak to the intrinsic peak of lithium carbonate on the particle surface in real time using near-infrared spectroscopy. The system then dynamically outputs spray rate commands via a PID controller to drive a variable frequency atomizing spray pump for adaptive adjustment within a range of 0.5–5.0 mL / min, achieving stable control of the coating thickness between 8±1 nm. Compared with traditional methods, this method can significantly reduce coating thickness fluctuations and reduce the amount of lithium stearate used. It can also prevent insufficient exposure of magnetic materials due to localized insufficient coating or organic residues caused by excessive coating.

[0068] More specifically, when the spectral analysis module calculates the coating thickness of lithium stearate based on the absorbance of the carbonyl characteristic peak and the intrinsic peak absorbance of lithium carbonate, it uses the following formula: ,

[0069] in, The thickness of the coating layer, The slope The absorbance is the characteristic peak of the carbonyl group. The absorbance is the intrinsic peak of lithium carbonate. This is the background noise.

[0070] More specifically, the carbonyl characteristic peak is found in lithium stearate. The carbonyl stretching vibration peak, the intrinsic peak of lithium carbonate is that of lithium stearate. The methylene symmetric stretching peak.

[0071] Compared to traditional detection methods that use the intrinsic peak of lithium carbonate, this characteristic peak definition scheme directly locks the molecular bond vibration signal of lithium stearate, completely avoiding peak position drift caused by differences in the lithium carbonate crystal structure, and improving the accuracy of coating thickness calculation 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 to construct a self-consistent reference system, it realizes the specialization, high sensitivity 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 consistently >96%.

[0072] More specifically, when the PID controller outputs the spray rate adjustment command based on the thickness of the lithium stearate coating, it uses the following formula: , ,

[0073] in, For PID controller in time The output value, This is the proportional gain coefficient. The integral coefficient is... These are the differential coefficients. For the target coating thickness, the real-time thickness of the coating layer over time, the thickness deviation of the coating layer over time, is the integral time variable.

[0074] More specifically, when the coating layer thickness of lithium stearate is detected to exceed the threshold value for three consecutive times:

[0075] the variable frequency atomizing spray pump stops spraying;

[0076] the pulse back blowing system in the airflow pulverizer is started to remove excess coating layer.

[0077] The emergency treatment mechanism triggers the automatic emergency stop of the variable frequency atomizing spray pump through the intelligent judgment of three consecutive thickness overruns, and the threshold value is generally set to 12 nm. When the coating layer thickness exceeds the threshold value, the addition of the modifier is immediately blocked, and a 0.5 MPa nitrogen pulse back blowing system is started at the same time. The high-pressure cyclone is used to strip the excess lithium stearate coating layer on the surface of the particles, so that the system can recover to the target thickness within 2 minutes. Compared with traditional manual cleaning, the downtime can be greatly shortened, and problems such as out-of-control organic residue, magnetic material masking, and raw material waste caused by excessive coating thickness can be avoided.

[0078] More specifically, the total organic carbon content of the lithium carbonate powder is detected before ceramic membrane vacuum drum filtration separation,

[0079] when the total organic carbon content is > 50 ppm, return to the secondary washing step for cleaning.

[0080] Compared with traditional fixed process washing or terminal sampling control, the closed-loop total organic carbon content detection and backwashing mechanism can accurately intercept batches with excessive residual by detecting the total organic carbon content online before ceramic membrane filtration and setting a 50 ppm threshold to trigger automatic backwashing, avoid materials with total organic carbon content > 50 ppm entering the drying link, dynamically optimize washing energy consumption, and only make batches with excessive residual return to secondary washing. Compared with full-volume repeated washing, solvent consumption and steam energy consumption can be greatly reduced. Finally, it can also block organic-metal composite pollution, and timely remove uncleaned lithium stearate and its chelated ferromagnetic ions, which can prevent the formation of stable complexes at high temperatures during drying and further reduce the residual of magnetic materials.

[0081] More specifically, after the two-stage solvent washing is completed,

[0082] The anhydrous ethanol washing solution is dehydrated by 3A molecular sieves and then enters the rectifying column for recovery;

[0083] The deionized water washing solution is regenerated by strong acid cation resin.

[0084] ​​Compared with the traditional one-time use or simple distillation recovery, the solvent regeneration process breaks the ethanol-water azeotropic point limit by deep dehydration of the anhydrous ethanol washing liquid with 3A molecular sieve, improves the ethanol purity and ethanol reuse rate of the subsequent rectifying column recovery, at the same time, the 001x7 type strong acid cation resin is used to regenerate the deionized water washing liquid, which can improve the regeneration rate of EDTA, and also can make the metal ion in the effluent ≤1 ppb, compared with the re-purchase of EDTA, it can effectively reduce the cost, and eliminate the heavy metal waste liquid discharge.

[0085] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application.

Claims

1. A method of reducing magnetic substances in battery-grade lithium carbonate, characterized by, The method comprises the following steps: adding lithium stearate into lithium carbonate powder through an atomizing spraying system; pulverizing the lithium carbonate powder in an inert gas protection with oxygen content ≤10 ppm in an airflow pulverizer, and controlling the pulverizing temperature ≤40 ℃ to obtain modified lithium carbonate powder; sequentially performing electromagnetic continuous demagnetization and multi-stage magnetic separation on the modified lithium carbonate powder, and the magnetic field strength is 1.5-3.0 T; performing two-stage solvent washing on the lithium carbonate powder after the magnetic separation; performing ceramic membrane vacuum drum filtration separation on the washed lithium carbonate powder, and controlling the total organic carbon content of the filter cake ≤50 ppm; performing vacuum drying on the filtered lithium carbonate to obtain battery-grade lithium carbonate with low magnetic material content.

2. The method of reducing magnetic materials in battery-grade lithium carbonate according to claim 1, characterized by, The two-stage solvent washing specifically comprises the following steps: performing first stirring washing on the lithium carbonate powder with anhydrous ethanol washing liquid, and the solid-liquid ratio is 1:5; performing stirring washing on the lithium carbonate powder after the first stirring washing with 80 ℃ deionized water washing liquid for 20 min.

3. The method of reducing magnetic materials in battery-grade lithium carbonate according to claim 1, wherein, Before the airflow pulverization of the lithium carbonate powder, impurities are removed through a 200-mesh screen.

4. The method of reducing magnetic materials in battery-grade lithium carbonate according to claim 1, wherein When the lithium stearate is added into the lithium carbonate powder through the atomizing spraying system, a dynamic adjustment system is used to adjust the atomizing spraying rate, the dynamic adjustment system comprises a near-infrared spectrometer, a spectrum analysis module, a PID controller and a variable-frequency atomizing spraying 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 is used to calculate the coating thickness of the lithium stearate based on the carbonyl characteristic peak absorbance and the lithium carbonate intrinsic peak absorbance; the PID controller is used to output spraying rate adjustment instructions based on the coating thickness of the lithium stearate; the variable-frequency atomizing spraying pump is used to adjust the spraying rate according to the spraying rate adjustment instructions.

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

6. The method of reducing magnetic materials in battery-grade lithium carbonate according to claim 5, wherein, The carbonyl feature is the lithium stearate peak at 1710 cm"1 and the lithium carbonate intrinsic peak is the methylene symmetric stretch of lithium stearate at 720 cm"1 .

7. The method of reducing magnetic materials in battery-grade lithium carbonate according to claim 4, wherein 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: , , wherein, is the output value of the PID controller at time , is the proportional gain coefficient, is the integral coefficient, is the derivative coefficient, is the target cladding thickness, is the real-time thickness of the cladding at time , is the thickness deviation of the cladding at time , is the integral time variable.

8. The method of reducing magnetic materials in battery-grade lithium carbonate according to claim 4, wherein When the coating thickness of the lithium stearate is detected to exceed a threshold value for three times in succession: the variable-frequency atomizing spraying pump stops spraying; a pulse back-blowing system in the airflow pulverizer is started to remove the excess coating.

9. The method of reducing magnetic materials in battery-grade lithium carbonate according to claim 1, wherein, Before the ceramic membrane vacuum drum filtration separation of the lithium carbonate powder, total organic carbon content detection is performed, when the total organic carbon content is >50 ppm, the second washing step is returned to perform cleaning.

10. The method of reducing magnetic materials 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 through 3A molecular sieves and then enters a rectifying column for recovery; the deionized water washing liquid is regenerated through a strong-acid cation resin.

Images