Mirror polishing process of lithium battery pole piece roller

Abstract

The present application relates to a kind of mirror polishing process of lithium battery pole piece roll, it includes: step 1: cleaning removes the oxide and oil dirt on the surface of roll;Step 2: magnetic field assisted electrolytic polishing, electrolyte contains 18-22% phosphoric acid, 9-11% acetic acid, 9-11% cerium nitrate, the balance is ethylene glycol;Step 3: laser micro-melt shaping is carried out to the surface of roll using laser system;Step 4: using the composite polishing slurry of 5-50nm nanodiamond 3-6%, CeO2 Abrasive 1-2%, Fe3O4@SiO2 Core-shell particles 1-2%, pH 7.2-7.8 phosphate is polished pad polished;Step 5: after polishing, cleaning and surface passivation treatment are carried out.The mirror polishing process of lithium battery pole piece roll of the present application adopts twice polishing and once laser micro-melt shaping and cleaning and passivation etc.post-processing, laser micro-melt shaping is between twice polishing, can fill the pit and hollow generated by first polishing, further reduce the Ra of roll surface, and make the hardness of roll surface be recovered and promoted.

Description

Technical Field

[0001] This invention relates to the field of rolling mill technology, and more specifically to a mirror polishing process for lithium battery electrode rolling mill rolls. Background Technology

[0002] Lithium-ion battery electrode rolls are equipment components used in the lithium-ion battery production process to compact the positive and negative electrode sheets. During lithium-ion battery manufacturing, a slurry composed of active materials, conductive agents, and binders is coated onto a current collector (such as copper or aluminum foil) to form electrode sheets. These electrode sheets then need to be compacted by rollers to improve their density and stability, thereby improving battery performance. The main functions of the rollers include: ① Enhancing the adhesion strength between the active material and the current collector, preventing the active material from peeling off during electrolyte immersion or battery use. ② Reducing the porosity between the active material, conductive agent, and binder within the electrode sheet, reducing battery resistance and improving battery performance. ③ Increasing the battery's energy density, as the compacted electrode sheet has a smaller volume, allowing more active material to be packed into the same volume. ④ Controlling the thickness and flatness of the electrode sheets, ensuring battery consistency and safety.

[0003] The common diameter range of lithium battery electrode rolls is approximately [missing information]. In some high-end applications, the roll diameter can reach... In summary, the length of the rolls determines the width of the electrode sheets that can be processed. With the development of battery manufacturing technology, roll lengths are gradually increasing to improve production efficiency. Currently, the common roll length range is approximately 500-700 mm, but rolls exceeding 1 meter are also used in special applications.

[0004] Generally, to ensure electrode surface quality and avoid electrode damage or quality problems caused by rough roll surfaces, the roll surface needs to have a high degree of smoothness. For lithium battery electrode rolls, the requirement for mirror polishing is high, sometimes requiring Ra 0.01μm or even lower. In addition, the roll surface also needs to have a certain degree of wear resistance to ensure stability and consistency during long-term operation. Commonly used materials are high-strength, wear-resistant materials with excellent mechanical properties, such as alloy steel (9Cr2MoV), cemented carbide (such as tungsten-cobalt alloy WC-10Co or titanium-nickel-molybdenum alloy TiC-NiMo), etc. Furthermore, some high-performance rolls may use ceramic materials (however, the brittleness of ceramic materials may limit their use in some applications). To improve the surface properties of the rolls, special coating techniques are sometimes applied to the base material (such as steel), such as chromium plating and nitride coatings. These coatings can significantly improve the roll's wear resistance, corrosion resistance, and surface finish. Therefore, it is evident that the surface hardness of lithium battery electrode rolls is relatively high, making polishing them quite challenging. Furthermore, to ensure the rolls' performance, the polishing process should minimize damage to the roll surface hardness. Traditional mechanical polishing easily produces microscopic scratches (Ra>0.05μm), affecting the uniformity of the electrode coating, while electrolytic polishing tends to passivate the roll surface, reducing its adhesion to the electrode surface during subsequent electrode rolling. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a mirror polishing process for lithium battery electrode rolls. After polishing alloy steel (such as 9Cr2MoV) or cemented carbide (such as WC-Co) rolls by this process, the surface Ra can reach 0.004-0.005μm, and the roll hardness retention rate before and after polishing is ≥98% or even slightly increased (5-8%). At the same time, the process has the advantages of high efficiency and short polishing time per roll.

[0007] (II) Technical Solution

[0008] In a first aspect, the present invention provides a mirror polishing process for lithium battery electrode rolls, which includes the following steps:

[0009] Step 1: Clean and remove oxides and oil stains from the surface of the rolls;

[0010] Step 2: Magnetic field-assisted electropolishing

[0011] The electrolyte is prepared by adding 18-22% phosphoric acid, 9-11% acetic acid, 9-11% cerium nitrate, and the balance being ethylene glycol. During polishing, the electrolyte temperature is 25±1℃, and the current density is 12-16 A / dm³. 2, the pulse frequency is 500Hz-1kHz, the orthogonal magnetic field intensity is 0.3-0.5T, and the polishing time is 1-1.5h;

[0012] Step 3: Performing laser micro-melting reshaping on the roll surface treated in Step 2 by using a laser system;

[0013] Step 4: Nano-diamond fluid polishing

[0014] Preparing a composite polishing slurry dispersed in a phosphate buffer solution with a pH of 7.2-7.8, which contains 3-6% of 5-50nm nano-diamond, 1-2% of CeO2 abrasive, and 1-2% of Fe3O4@SiO2 core-shell particles; the Fe3O4@SiO2 core-shell particles and CeO2 abrasive preferably have a particle size of 50-200nm;

[0015] The linear velocity of the polishing platform is 1-1.5m / s, the contact pressure is 0.01-0.1MPa, and the polishing treatment is carried out for 20-40min;

[0016] Step 5: After polishing, cleaning and surface passivation treatment are carried out. Finally, the method further includes performing polishing quality inspection on the roll surface, and the polishing is qualified when the surface roughness Ra is ≤0.005μm.

[0017] According to a preferred embodiment of the present invention, in Step 1, the roll is an alloy steel or cemented carbide roll, the alloy steel is preferably 9Cr2MoV, and the initial Ra of the 9Cr2MoV roll is 0.20-0.35μm (typically 0.25μm); the cemented carbide is preferably tungsten-cobalt alloy WC-Co, and the initial Ra of the tungsten-cobalt alloy roll is 0.25-0.40μm (typically 0.30μm).

[0018] According to a preferred embodiment of the present invention, in Step 1, the method for cleaning and removing oxides and oil stains on the roll surface is: using 40kHz ultrasound combined with Ar plasma cleaning to completely remove surface oxides and oil stains; at the same time, the plasma-activated surface can also improve the wettability of the subsequent polishing liquid, reduce the contact angle of the polishing liquid, and provide favorable basic conditions for subsequent polishing.

[0019] According to a preferred embodiment of the present invention, in Step 2, the composition of the electrolyte is: 60% ethylene glycol, 20% phosphoric acid, 10% acetic acid and 10% cerium nitrate.

[0020] According to a preferred embodiment of the present invention, the specific operation method of Step 2 is:

[0021] (1) Using the roll as the anode and a stainless steel or graphite plate as the cathode, installing them in an electrolytic cell filled with the electrolyte; keeping the distance between the two electrodes at 1-5cm, starting the cooling circulation system, and keeping the temperature of the electrolyte constant at 25±1°C;

[0022] (2) Turn on the orthogonal alternating magnetic field with a magnetic field strength of 0.3-0.5T and a magnetic field direction perpendicular to the current direction to enhance fluid disturbance and material removal uniformity; set the current density to 12-16A / dm. 2 Pulse frequency 500Hz-1kHz;

[0023] Preferably, the current density is set to 15 A / dm. 2 The pulse frequency is 1kHz, and the orthogonal magnetic field strength is 0.5T;

[0024] (3) Turn on the power to start the electrolysis process, and control the duration to 1-1.5 hours; turn off the power and magnetic field system, remove the workpiece, and rinse it with plenty of deionized water to remove residual electrolyte. After the polishing treatment in step 2, the Ra of the roll surface decreases from the initial value to Ra = 0.03 μm.

[0025] According to a preferred embodiment of the present invention, in step 3, the laser micro-melting shaping is performed by scanning with a fiber laser in a Gaussian-flat-top composite spot mode. The scanning is performed under a protective atmosphere, which is a He + 5% H2 mixture to prevent surface oxidation.

[0026] Preferably, the fiber laser wavelength is 532nm or 1064nm, the power is 500W, the spot diameter is 50μm, and the scanning speed is 100-500mm / s, preferably 200-300mm / s. After step 3, the Ra of the roll surface decreases from 0.03μm to 0.008μm, and the surface hardness of the roll is restored and improved.

[0027] According to a preferred embodiment of the present invention, in step 4, the method for preparing the composite polishing slurry is as follows:

[0028] (1) Prepare the raw materials according to the following formula: 3-6% nanodiamond with a particle size of 5-50nm, 1-2% CeO2 abrasive, 1-2% Fe3O4@SiO2 core-shell particles, and PBS buffer with pH 7.2-7.8;

[0029] (2) First, add nanodiamonds and CeO2 to a small amount of deionized water and use an ultrasonic oscillator to disperse them ultrasonically to prevent agglomeration;

[0030] (3) Add to the pre-prepared phosphate buffer, add Fe3O4@SiO2 core-shell particles, and sonicate again for 10-15 min to ensure homogeneous suspension; stir continuously with a stirrer to keep the slurry uniform.

[0031] According to a preferred embodiment of the present invention, in step 4, the polishing process is as follows:

[0032] (1) The polishing platform is an adjustable speed rotary disk or a linear motion platform. The roller is placed in the polishing fixture and fixed. A soft porous material is used as the polishing pad. The cleaned polishing pad is installed on the polishing platform to ensure that it is flat and wrinkle-free.

[0033] (2) Adjust the contact pressure to 0.01-0.1MPa and install an electromagnetic field device below the polishing head (use the response magnetic field of Fe3O4@SiO2 core-shell particles to achieve dynamic distribution control);

[0034] (3) Start the polishing platform and set the linear velocity to 1-1.5 m / s; start the liquid supply system to continuously supply the composite polishing slurry and uniformly coat it onto the surface of the polishing pad; polish under the set contact pressure for 20-40 minutes; simultaneously, optionally apply an alternating magnetic field to dynamically distribute the Fe3O4@SiO2 core-shell particles, improving polishing uniformity. The parameters of this alternating magnetic field are: 10-100 Hz, 5-20 mT, perpendicular to the polishing surface or parallel to the polishing motion direction, which can effectively drive the Fe3O4@SiO2 particles and other abrasives to move without causing excessive aggregation.

[0035] (4) After polishing is completed, stop the polishing platform and liquid supply system and remove the workpiece.

[0036] Preferably, the polishing platform has a linear speed of 1.2 m / s, a contact pressure of 0.05 MPa, and a polishing treatment time of 30 min. Applying an alternating magnetic field is optional, not mandatory.

[0037] According to a preferred embodiment of the present invention, in step 5, the cleaning is a multi-stage ultrasonic-cyclone cleaning: (1) First-stage cleaning: ultrasonic cleaning is performed first using deionized water containing 0.1% nonionic surfactant, preferably at 40 kHz for 10 min; (2) Second-stage cleaning: residual organic matter is removed under supercritical carbon dioxide; (3) Third-stage cleaning: cleaning is performed using a gas-liquid two-phase nozzle. Nanodiamonds and CeO2 in the pre-processing stage are easily embedded in surface micropores and can easily contaminate the electrode sheets. Therefore, thorough cleaning is necessary to improve the quality of the battery electrode sheets.

[0038] According to a preferred embodiment of the present invention, in step 5, due to the series of polishing processes in the preceding steps, the highly active polished surface exposed to air will oxidize rapidly, which affects the consistency of the rolled electrode sheets. Therefore, surface passivation treatment is required. Surface passivation treatment can be performed using low-temperature plasma nitriding passivation (300°C, N2 / H2 = 4:1, 2h; suitable for alloy steel rolls) or atomic layer deposition passivation (e.g., 100nm Al2O3 coating, 150°C; suitable for cemented carbide rolls).

[0039] Herein, when a 9Cr2MoV alloy steel roll is passivated at 300°C under N2 / H2=4:1 for 2h, nitrides (such as ε-Fe 2～3 N) will be formed on the roll surface, and the hardness of the roll surface at this time will be increased by more than 10% compared with that before passivation;

[0040] Herein, after a 100nm Al2O3 coating is deposited on the tungsten-cobalt alloy roll by using the atomic layer deposition technology, the corrosion resistance of the roll can be greatly improved and the service life can be prolonged.

[0041] According to a preferred embodiment of the present invention, in step 5, the polishing quality inspection includes Ra inspection, for example, measurement is performed using a surface profiler, and Ra ≤ 0.005μm is judged as qualified. In addition, XPS can also be used to detect the amount of residual heteroatoms on the roll surface to avoid excessively high impurity content. It is also possible to perform an electrode sheet fabrication performance test on the polished roll, for example, using CM811 positive electrode slurry for trial rolling, and judging the roll as qualified if the detected thickness fluctuation of the electrode sheet is within ±1μm.

[0042] (III) Beneficial Effects

[0043] The mirror polishing process for lithium battery electrode sheet rolls of the present invention includes two polishing steps, one laser micro-melting reshaping step, and post-treatments such as cleaning and passivation. The laser micro-melting reshaping is interposed between the two polishing steps, which can fill the pits generated by the first polishing, further reduce the Ra of the roll surface, restore and improve the hardness of the roll surface, and ensure the application performance of the roll. Experiments show that for alloy steel or hard alloy rolls, the laser micro-melting reshaping can increase the surface hardness of the alloy steel roll by about 8-10% compared with that after the first polishing.

[0044] Herein, the first polishing adopts magnetic field-assisted electrolytic polishing. Through the design of the electrolyte formula, cerium salt is added. Cerium ions have a certain corrosion inhibition effect, can form a protective film (oxide or hydroxide film), inhibit the preferential corrosion of the grain boundary region, make the inside of the grain easier to dissolve, and keep the grain boundary relatively stable, thereby helping to reduce the Ra value of the roll (grain boundaries are usually the weaker and more susceptible to corrosion parts in the material. If the grain boundaries are corroded without control, the grain boundaries will be dented, the surface will not be smooth, and the Ra value will increase). In addition, inhibiting grain boundary corrosion means that the grains themselves are dissolved more uniformly, which can improve the compactness of the surface layer of the roll, and the roll exhibits higher hardness.

[0045] In the process of laser micro-melting reshaping, a Gaussian-flat-top composite spot mode is used for laser scanning, which helps to avoid microcracks in the heat-affected zone.

[0046] The second polishing process employs nanodiamond fluid polishing, which uses a magnetorheological carrier (Fe3O4@SiO2 core-shell particles) to achieve dynamic distribution control of the abrasive. This effectively drives the movement of Fe3O4@SiO2 particles and diamond and cerium oxide abrasives without causing excessive aggregation, thus improving polishing uniformity and the consistency of the roll surface.

[0047] After polishing, thorough cleaning and passivation are carried out. Cleaning removes residual organic matter and abrasives from the roll surface to improve the quality of the battery electrode. Passivation stabilizes the micro-morphology of the roll surface and improves the surface hardness or corrosion resistance, all of which help ensure the rolling quality of the battery electrode. Detailed Implementation

[0048] To better explain and facilitate understanding of this invention, specific embodiments are described in detail below. The percentages below refer to mass percentages. The Fe3O4@SiO2 particles used in this invention can be purchased from the market (e.g., Xi'an Qiyue Biotechnology Co., Ltd.), and can be spherical or other customized shapes, with a purity of over 95%, suitable for scientific research and industrial applications; alternatively, they can be synthesized in-house, with Fe3O4@SiO2 particles and CeO2 particle sizes of 50-200 nm meeting the requirements.

[0049] Example 1

[0050] This embodiment provides a mirror polishing process for lithium battery electrode rolls, the steps of which are as follows:

[0051] (1) Cleaning removes oxides and oil stains from the surface of the rolls.

[0052] Prepare an ultrasonic cleaning tank suitable for the roll size, and clean it for 10 minutes at 40 kHz using deionized water containing 0.1% nonionic surfactant. Next, place the ultrasonically cleaned roll in a vacuum chamber, introduce an appropriate amount of argon gas into the chamber, and use a radio frequency power supply to excite the Ar gas to form plasma, treating it at 500W for 10 minutes. At this point, the roll material is 9Cr2MoV alloy steel, with a diameter of 600 mm, a length of 500 mm, and a surface Ra = 0.25 μm.

[0053] (2) Magnetic field-assisted electropolishing

[0054] An electrolyte solution with the composition of 60% ethylene glycol + 20% phosphoric acid + 10% acetic acid + 10% cerium nitrate was prepared. A roller was used as the anode, and a graphite plate as the cathode, installed in an electrolytic cell containing the electrolyte solution, with a 2cm gap between the electrodes. The cooling circulation system was activated to maintain a constant electrolyte temperature of 25±1℃. An orthogonal alternating magnetic field with a strength of 0.5T was applied, perpendicular to the current direction. The current density was set to 15A / dm³. 2With a pulse frequency of 1kHz, turn on the power to start electrolytic polishing, process for 1.5 hours, then turn off the power and magnetic field system, remove the workpiece, rinse with plenty of deionized water, dehydrate and dry with ethanol, and measure the surface profile of the roller Ra = 0.03μm.

[0055] (3) Laser micro-melting shaping of roll surface using laser system

[0056] The roll was placed in a cavity filled with a protective atmosphere of He + 5% H2. A fiber laser with a wavelength of 1064nm was used to scan the roll in a Gaussian-flat-top composite spot mode. The scanning power was 500W, the spot diameter was 50μm, and the scanning speed was 200mm / s. After one scan, the surface profiler measured the roll Ra to be 0.008μm.

[0057] (4) Nanodiamond fluid polishing

[0058] A composite polishing slurry containing 5% 5-50 nm nanodiamonds, 1.5% CeO2 abrasive, and 1.5% Fe3O4@SiO2 core-shell particles was prepared using a phosphate buffer solution at pH 7.5. In the preparation process, the nanodiamonds and CeO2 were first added to a small amount of deionized water and ultrasonically dispersed using an ultrasonic oscillator. This dispersion was then added to the pre-prepared phosphate buffer solution, followed by the addition of the Fe3O4@SiO2 core-shell particles. The mixture was then ultrasonically treated again for 10 minutes to ensure homogeneous suspension.

[0059] The roller is fixed in the polishing fixture. The cleaned soft porous material polishing pad is installed on the adjustable-speed rotary polishing platform, and the contact pressure is adjusted to 0.05 MPa. An electromagnetic field device is installed below the polishing head. The linear speed of the polishing platform is set to 1.2 m / s. The polishing platform and liquid supply system are started, and the liquid supply system continuously supplies composite polishing slurry and evenly coats it onto the surface of the polishing pad. An alternating magnetic field is applied using the electromagnetic field device, with magnetic field parameters of 50 Hz, 15 mT, and the magnetic field direction parallel to the rotation direction of the polishing platform. Polishing is performed for 30 minutes, then the polishing platform and liquid supply system are stopped, and the workpiece is removed.

[0060] (5) Thorough cleaning, passivation and testing

[0061] Multi-stage ultrasonic-cyclone cleaning: First, ultrasonic cleaning is performed using deionized water containing 0.1% nonionic surfactant, preferably at 40KHz for 10 minutes; then, residual organic matter is removed under supercritical carbon dioxide; finally, cleaning is performed using a gas-liquid two-phase nozzle.

[0062] Surface passivation: Low-temperature plasma nitriding was performed for 2 hours at 300℃ in an atmosphere with N2 / H2 = 4:1. The presence of nitrides on the roll surface was detected by AES.

[0063] Polishing inspection: The Ra of the roll and the specular reflectivity (wavelength 550nm) were measured using a surface profilometer.

[0064] In this embodiment, the single-roller polishing process takes 2 hours, and the total process time is approximately 5 hours.

[0065] Example 2

[0066] The main difference between this embodiment and Embodiment 1 is the composition of the electrolyte in step (2): In this embodiment, the electrolyte composition is 58% ethylene glycol + 22% phosphoric acid + 9% acetic acid + 11% cerium nitrate. Other steps and conditions are the same as in Embodiment 1.

[0067] Example 3

[0068] The main difference between this embodiment and Embodiment 1 is the laser wavelength used in step (3). In this embodiment, the laser wavelength is 532nm and the scanning speed is 300mm / s. Other steps and conditions are the same as in Embodiment 1.

[0069] Example 4

[0070] The main difference between this embodiment and Example 1 is the composition of the composite polishing slurry in step (4): the composite polishing slurry containing 4% 5-50nm nanodiamonds, 2% CeO2 abrasive, and 2% Fe3O4@SiO2 core-shell particles is prepared using a phosphate buffer solution with a pH of 7.6. Other steps and conditions are the same as in Example 1.

[0071] Example 5

[0072] This embodiment provides a mirror polishing process for lithium battery electrode rolls, the steps of which are as follows:

[0073] (1) Cleaning removes oxides and oil stains from the surface of the rolls.

[0074] The rolls processed in this embodiment have the following specifications: diameter 500 mm, length 500 mm. The roll material is a tungsten-cobalt alloy WC-10%Co, with a surface Ra = 0.30 μm. The cleaning method is described in Example 1.

[0075] (2) Magnetic field-assisted electropolishing

[0076] An electrolyte solution with the composition of 60% ethylene glycol + 20% phosphoric acid + 10% acetic acid + 10% cerium nitrate was prepared. A rolling mill was used as the anode, and a graphite plate as the cathode, installed in an electrolytic cell containing the electrolyte solution, with a 3cm distance between the electrodes. The cooling circulation system was activated to maintain a constant electrolyte temperature of 25±1℃. An orthogonal alternating magnetic field with a strength of 0.4T was applied, perpendicular to the current direction. The current density was set to 16A / dm³. 2With a pulse frequency of 1kHz, turn on the power to start electrolytic polishing, process for 1.5 hours, then turn off the power and magnetic field system, remove the workpiece, rinse with plenty of deionized water, dehydrate and dry with ethanol, and measure the surface profile of the roll Ra ≤ 0.03μm.

[0077] (3) Laser micro-melting shaping of roll surface using laser system

[0078] The roll was placed in a cavity filled with a protective atmosphere of He + 5% H2. A fiber laser with a wavelength of 1064nm was used to scan the roll in a Gaussian-flat-top composite spot mode. The scanning power was 500W, the spot diameter was 50μm, and the scanning speed was 260mm / s. After one round of scanning, the surface profiler measured the roll's Ra to be ≤0.008μm.

[0079] (4) Nanodiamond fluid polishing

[0080] A composite polishing slurry containing 4% 5-50nm nanodiamonds, 2% CeO2 abrasives, and 2% Fe3O4@SiO2 core-shell particles was prepared using a phosphate buffer solution at pH 7.6.

[0081] The rollers and polishing pads were fixed according to the method in Example 1, and the contact pressure was adjusted to 0.05 MPa. The polishing platform linear speed was set to 1.5 m / s, and the polishing platform and liquid supply system were started. An alternating magnetic field was applied using an electromagnetic field device with magnetic field parameters of 100 Hz, 12 mT, and the magnetic field direction parallel to the rotation direction of the polishing platform. Polishing was performed for 40 minutes, then the polishing platform and liquid supply system were stopped, and the workpiece was removed.

[0082] (5) Thorough cleaning, passivation and testing

[0083] Multi-stage ultrasonic-cyclone cleaning was performed as described in Example 1.

[0084] Surface passivation: A 100nm Al2O3 coating is deposited using atomic layer deposition technology.

[0085] Polishing inspection: The Ra of the roll and the specular reflectivity (wavelength 550nm) were measured using a surface profilometer.

[0086] In this embodiment, the single-roller polishing process takes 2 hours, and the total process time is less than 4 hours.

[0087] Example 6

[0088] The main difference between this embodiment and Example 5 is the composition of the electrolyte in step (2): In this embodiment, the electrolyte composition is 61% ethylene glycol + 20% phosphoric acid + 10% acetic acid + 9% cerium nitrate. Other steps and conditions are the same as in Example 5.

[0089] Example 7

[0090] The main difference between this embodiment and Example 5 is the composition of the composite polishing slurry in step (4): the composite polishing slurry containing 6% 5-50nm nanodiamonds, 1% CeO2 abrasive, and 1.5% Fe3O4@SiO2 core-shell particles is prepared using a phosphate buffer solution with a pH of 7.6. Other steps and conditions are the same as in Example 5.

[0091] Comparative Example 1

[0092] The main difference between this comparative example and Example 1 is that this example does not include the laser micro-melting shaping in step (3).

[0093] Comparative Example 2

[0094] The main difference between this comparative example and Example 1 is that the electrolyte in step (2) of this example does not contain cerium nitrate.

[0095] Comparative Example 3

[0096] This comparative example is based on Example 1, but does not include the surface passivation treatment in step (5).

[0097] The following product parameters were measured on the roll surfaces of the above embodiments and comparative examples after polishing, including profilometry, specular reflection, and surface hardness retention rate (the ratio of roll surface hardness before and after the process):

[0098] Example 1 0.005μm ≥94％ 97％ Example 2 0.004μm ≥95％ 98％ Example 3 0.004μm ≥95％ 98％ Example 4 0.005μm ≥95％ 97％ Example 5 0.004μm ≥92％ 98％ Example 6 0.005μm ≥92％ 96％ Example 7 0.005μm ≥91％ 97％ Comparative Example 1 0.01μm ≥88％ 91％ Comparative Example 2 0.008μm ≥90％ 92％ Comparative Example 3 0.008μm ≥91％ 88％

[0099] If the initial product of the roll before polishing is a qualified product, the lithium battery electrode roll treated according to the polishing process of this invention is tested with CM811 positive electrode slurry. The thickness fluctuation of the electrode is detected to be within ±1μm, indicating that the polishing process of the roll has made its surface achieve high precision and consistency.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions, or combinations of technical features in the above embodiments that do not conflict with each other, can be made in accordance with the manner described in the embodiments. These modifications, substitutions or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A mirror polishing process for lithium battery electrode rolls, characterized in that, Including the following steps: Step 1: Clean and remove oxides and oil stains from the surface of the rolls; Step 2: Magnetic field-assisted electropolishing Prepare an electrolyte solution containing 18-22% phosphoric acid, 9-11% acetic acid, 9-11% cerium nitrate, and the balance being ethylene glycol. During polishing, the electrolyte temperature is 25±1℃, the current density is 12-16A / dm², the pulse frequency is 500Hz-1kHz, the orthogonal magnetic field strength is 0.3-0.5T, and the polishing time is 1-1.5h. Step 3: Laser micro-melting shaping is performed on the roll surface treated in Step 2 using a laser system. Laser micro-melting shaping is performed by scanning with a fiber laser in a Gaussian-flat-top composite spot mode under a protective atmosphere composed of He + 5% H2 mixture. The fiber laser wavelength is 532nm or 1064nm, the power is 500W, the spot diameter is 50μm, and the scanning speed is 100-500 mm / s. Step 4: Nanodiamond fluid polishing A composite polishing slurry containing 3-6% 5-50nm nanodiamond, 1-2% CeO2 abrasive, and 1-2% Fe3O4@SiO2 core-shell particles dispersed in a phosphate buffer solution with pH 7.2-7.8 was prepared. The linear speed of the polishing platform is 1-1.5 m / s, the contact pressure is 0.01-0.1 MPa, and the polishing process takes 20-40 minutes. Step 5: After polishing, cleaning and surface passivation are performed; the surface passivation is performed by low-temperature plasma nitriding passivation or atomic layer deposition passivation.

2. The mirror polishing process according to claim 1, characterized in that, In step 1, the roll is an alloy steel or cemented carbide roll. The alloy steel is 9Cr2MoV, and the cemented carbide is a tungsten-cobalt alloy WC-Co.

3. The mirror polishing process according to claim 1, characterized in that, In step 1, the method for cleaning and removing oxides and oil stains from the surface of the rolls is: using 40kHz ultrasound combined with Ar plasma cleaning.

4. The mirror polishing process according to claim 1, characterized in that, In step 2, the electrolyte consists of 60% ethylene glycol, 20% phosphoric acid, 10% acetic acid, and 10% cerium nitrate.

5. The mirror polishing process according to claim 1 or 4, characterized in that, The specific operation method for step 2 is as follows: (1) The rolling mill roll is used as the anode and the stainless steel or graphite plate is used as the cathode. The rolling mill roll is installed in the electrolytic cell and the electrolyte is filled in the electrolytic cell. The two electrodes are kept 1-5 cm apart. The cooling circulation system is started to keep the electrolyte temperature constant at 25±1℃. (2) Turn on the orthogonal alternating magnetic field with a magnetic field strength of 0.3-0.5T and the magnetic field direction is perpendicular to the current direction to enhance fluid disturbance and material removal uniformity; Set the current density to 12-16 A / dm² and the pulse frequency to 500 Hz-1 kHz. (3) Turn on the power and start the electrolysis process. The duration is controlled at 1-1.5 hours. Turn off the power and magnetic field system, take out the workpiece, rinse with a lot of deionized water to remove the residual electrolyte.

6. The mirror polishing process according to claim 1, characterized in that, In step 4, the preparation method of the composite polishing slurry is as follows: (1) Prepare the raw materials according to the following formula: 3-6% nanodiamond with a particle size of 5-50nm, 1-2% CeO2 abrasive, 1-2% Fe3O4@SiO2 core-shell particles, and PBS buffer with pH 7.2-7.8; (2) First, add nanodiamonds and CeO2 to a small amount of deionized water and use an ultrasonic oscillator to disperse them ultrasonically to prevent agglomeration; (3) Add to the pre-prepared phosphate buffer, then add Fe3O4@SiO2 core-shell particles, and sonicate again for 10-15 minutes to ensure homogeneous suspension; the stirrer continues to stir to keep the slurry uniform.

7. The mirror polishing process according to claim 6, characterized in that, In step 4, the polishing process is as follows: (1) The polishing platform is an adjustable speed rotary disk or a linear motion platform. The roller is placed in the polishing fixture and fixed. A soft porous material is used as the polishing pad. The cleaned polishing pad is installed on the polishing platform to ensure that it is flat and wrinkle-free. (2) Adjust the contact pressure to 0.01-0.1MPa and install an electromagnetic field device below the polishing head; (3) Start the polishing platform and set the linear speed to 1-1.5 m / s; Start the liquid supply system to continuously supply composite polishing slurry and evenly coat it onto the surface of the polishing pad. Polishing is carried out under the set contact pressure for 20-40 minutes. At the same time, an alternating magnetic field can be optionally applied to cause the Fe3O4@SiO2 core-shell particles to be dynamically distributed. (4) After polishing is completed, stop the polishing platform and liquid supply system and remove the workpiece.

8. The mirror polishing process according to claim 1, characterized in that, In step 5, the cleaning is a multi-stage ultrasonic-cyclone cleaning: first, ultrasonic cleaning is performed using deionized water containing 0.1% nonionic surfactant, then residual organic matter is removed under supercritical carbon dioxide, and finally, cleaning is performed using a gas-liquid two-phase nozzle.