Preparation method of surface modified nano calcium carbonate for battery diaphragm coating

Abstract

The invention relates to the technical field of nano materials, and particularly discloses a preparation method of surface modified nano calcium carbonate for a battery diaphragm coating. According to the method, the technical paths of microemulsion confinement crystal form regulation and control, gradient surface modification and boehmite compounding and porosity regulation and control are fused, and the functional nano calcium carbonate adaptive to the battery diaphragm coating is prepared. According to the technical scheme, limestone is used as a raw material, after calcination and digestion, the particle size of nano calcium carbonate is controlled through microemulsion carbonization (a cyclohexane-span 80-n-butyl alcohol system); a silane coupling agent KH560-KH570 is adopted for gradient modification to introduce an electrophilic functional group, boehmite is compounded to form a composite coating, and the porosity is regulated and controlled by adjusting the solid content in coating slurry and the coating speed. The method is stable in process and high in compatibility, and meets the requirements of diaphragm coatings of lithium ion batteries and solid-state batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterials, and particularly to a preparation method of surface-modified nano calcium carbonate for battery separator coating. BACKGROUND

[0002] Polyolefin separators (PE, PP) are the core components of secondary batteries, but have the defects of poor thermal stability (easy to shrink and short circuit at high temperature) and insufficient electrolyte wettability (strong hydrophobicity). The industry mainstream improves performance by coating Al2O3 or boehmite. However, Al2O3 has high cost (about 20,000 yuan / ton) and high density, and boehmite has insufficient mechanical strength when used alone. Moreover, the existing coating process cannot balance the three aspects of "thermal stability-ion conduction-cost", especially in solid-state batteries, the compatibility of traditional coating with solid-state electrolyte is poor, and the ionic conductivity is less than 10⁻ 4 S / cm.

[0003] Nano calcium carbonate has the potential to replace the existing materials due to its low cost (about 3,000 yuan / ton) and small density, but it has the problems of many surface hydroxyl groups, easy agglomeration, and poor compatibility with electrolyte. The existing modification methods (such as single silane coupling agent modification) cannot balance the electrolyte wettability and dispersion stability, and lack of synergistic design with boehmite and porosity control means, resulting in that the performance of the coated separator cannot meet the battery requirements. Therefore, developing an integrated preparation method of "microemulsion crystal control-gradient modification-boehmite composite-porosity control" is the key to solving the industry pain points. SUMMARY

[0004] In order to overcome the above-mentioned defects of the prior art, the present application provides a preparation method of surface-modified nano calcium carbonate for battery separator coating. An integrated preparation method of "microemulsion crystal control-gradient modification-boehmite composite-porosity control" is used to prepare surface-modified nano calcium carbonate.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a preparation method of surface-modified nano calcium carbonate for battery separator coating, comprising: Step one, preparation of refined lime milk: limestone is crushed by a jaw crusher, calcined in a rotary kiln, digested, sieved to 400 meshes, and aged to obtain refined lime milk; Step two, preparation of nano calcium carbonate by microemulsion carbonization: (1) Adjust the density of the refined lime milk, add a composite dispersant based on the dry mass, the composite dispersant is sodium hexametaphosphate and sodium polyacrylate, and ultrasonic dispersion is performed to obtain a pretreated slurry; (2) Mix the pretreated slurry with cyclohexane, add non-ionic surfactant Span 80 and co-surfactant n-butanol, and ultrasonic dispersion is performed to form a water-in-oil microemulsion; (3) CO2 / N2 mixed gas is introduced into the microemulsion to obtain a spindle-shaped nano calcium carbonate slurry; Step three, gradient surface modification: (1) First modification: the nano calcium carbonate slurry is heated to 40-50°C, 1%-2% silane coupling agent KH560 is added based on the dry mass, and after ultrasonic dispersion, reaction is performed; (2) Second modification: 0.8%-1.5% of is added, and the temperature is raised to 55-65°C to obtain surface-modified nano calcium carbonate; Step four, boehmite composite slurry preparation: the modified nano calcium carbonate is mixed with boehmite, deionized water and water-based binder are added, and ultrasonic dispersion is performed to prepare a composite slurry; Step five, separator coating and porosity control: the solid content of the composite slurry is adjusted to control the porosity of the coating; and the coating is dried in stages to obtain a modified separator; Step six, battery adaptation treatment: when used in a solid-state battery, a 0.5-1 μm thick Li⁺ conductive polymer is sprayed on the surface of the coating.

[0006] As a further scheme of the present application, in step one, the limestone is crushed by a jaw crusher to a particle size of <5 mm; the temperature for calcination in the rotary kiln is 900-1000°C, and the time is 2-3 h; the solid-liquid ratio for digestion is 1:5-1:8, the temperature is 60-70°C, and the stirring rate is 300-400 r / min; the aging time is 24-48 h; and the Ca(OH)2 content of the refined lime milk is ≥95%.

[0007] As a further scheme of the present application, in step two, (1) the density of the refined lime milk is adjusted to 1.08-1.12 g / cm³, the amount of the composite dispersant added is 0.5%-1.2% based on the dry mass, the ratio of sodium hexametaphosphate to sodium polyacrylate is 2:1, and ultrasonic dispersion is performed at 20-30 kHz for 15-20 min to obtain a pretreated slurry; (2) the non-ionic surfactant is Span 80, and the co-surfactant is n-butanol; the mixing mass ratio of the pretreated slurry to cyclohexane is (2-3):(3-5), the mass fraction of Span 80 in the oil phase is 1%-2%, and the mass fraction of n-butanol in the oil phase is 0.5%-1%; and ultrasonic dispersion is performed at 20 kHz for 30 min at 25°C; (3) the volume fraction of CO2 in the CO2 / N2 mixed gas is 40%-50%, the flow rate is 2-4 m³ / h, and the reaction is performed at 25-30°C until the pH of the system decreases to 8.5-9.0, and the carbonization is stopped to obtain a spindle-shaped nano calcium carbonate slurry with a particle size of 50-100 nm and a specific surface area of 55-70 m² / g; As a further scheme of the present application, in step three, (1) First modification: the nano calcium carbonate slurry is heated to 40-50℃, 1%-2% silane coupling agent KH560 is added based on the dry basis mass, ultrasonic dispersion is carried out at 15-20 kHz for 20-30 min, and reaction is carried out for 1-1.5 h; (2) Second modification: after heating, the stirring rate is 500-600 r / min, and reaction is carried out for 1.5-2 h to obtain surface modified nano calcium carbonate. The mass ratio of the silane coupling agent KH560 to the silane coupling agent KH570 is 1.2:1-1.5:1, and the pH of the ethanol solvent is adjusted to 4.0-4.5 by 0.1 mol / L hydrochloric acid.

[0008] As a further scheme of the application, in step four, the mass ratio of the modified nano calcium carbonate to boehmite is 1:0.3-1:0.5, the particle size is 20-40 nm, the aqueous binder is polyacrylate, and the solid content is 30%; the mass ratio of the modified nano calcium carbonate to boehmite, deionized water and the aqueous binder is (7-8):(1.5-2):(0.5-1), ultrasonic dispersion is carried out at 20 kHz for 20 min, and a composite coating slurry with a solid content of 40%-50% and a viscosity of 1500-2500 mPa・s is prepared.

[0009] As a further scheme of the application, in step five, the composite slurry is coated on the surface of the polyolefin separator by using a micro-gravure coater, the coating speed is 10-15 m / min, the porosity corresponding to the solid content of 40% slurry is 45%, the porosity corresponding to the solid content of 50% slurry is 35%, the coating porosity is adjusted to 35%-45%; and the coating is dried in stages at 120-130℃, wherein the coating is dried at 120℃ for 5 min and then at 130℃ for 5 min, to obtain a modified separator with a coating thickness of 1-3 μm.

[0010] As a further scheme of the application, in step six, when used for a solid-state battery, the coating surface is sprayed with a Li⁺ conductive polymer, and then vacuum dried at 80℃ for 1 h to improve ion conduction compatibility. As a further scheme of the application, the surface modified nano calcium carbonate needs to meet the following requirements: the surface hydroxyl group density is 2.5-3.5 groups / nm², the oil absorption value (DOP) is 45-55 ml / 100g, the contact angle with electrolyte is ≤15°, the volume resistivity of the composite coating is ≥10¹² Ω・cm, and the insulation performance meets the safety requirements of the battery.

[0011] As a further scheme of the application, the dry basis mass is the mass of the pure substance left after removing the moisture in the substance. γ-methacryloxypropyltrimethoxysilane. The silane coupling agent KH560 is γ-glycidyl ether propyltrimethoxysilane, which are both conventional terms in the art.

[0012] As a further scheme of the present application, in step one, if calcium carbide slag is used to replace limestone, the sulfur impurities (sulfur content ≤0.05%) need to be removed by pulse corona pretreatment (voltage 30-40kV, frequency 100Hz, treatment 10min) before calcination and digestion, to ensure that the purity of refined lime milk is ≥95%.

[0013] As a further scheme of the present application, when used in lithium ion batteries, the heat shrinkage rate of the separator is ≤5%, the electrolyte infiltration time is ≤10s, and the tensile strength is ≥200MPa; when used in solid-state batteries, the ionic conductivity is ≥1.0×10⁻³S / cm, and the capacity retention rate after 500 cycles is ≥90%.

[0014] The core technical principles of the present application include microemulsion limited crystal form regulation, gradient surface modification mechanism, and boehmite compounding and porosity regulation.

[0015] The microemulsion limited crystal form regulation is: by referring to the "micro-reactor" characteristics of the water-in-oil microemulsion system, a stable water core (35-50nm) is constructed by cyclohexane-sorbitan 80-n-butanol to control CaCO3 nucleation and growth, forming a spindle-shaped crystal form (length-diameter ratio 3:1-4:1), which can form an interlaced support network with boehmite, improving the mechanical strength and thermal stability of the coating.

[0016] The gradient surface modification mechanism is: the primary modification uses KH560 (epoxy group) to condense with the surface hydroxyl group of calcium carbonate, introducing a lipophilic group to improve the compatibility with the electrolyte (carbonate / solid-state electrolyte); the secondary modification uses KH570 (double bond) to graft, enhancing the adhesion with the polyolefin matrix and boehmite, avoiding coating shedding.

[0017] The boehmite compounding and porosity regulation is: boehmite (AlOOH) can form hydrogen bonds with modified nano calcium carbonate due to its low crystallinity and high hydroxyl group density, improving the insulation and ion conduction channel of the coating; by adjusting the solid content of the coating slurry and the coating speed, the porosity of the coating is controlled to 35%-45%, which ensures the electrolyte infiltration efficiency and avoids the risk of short circuit.

[0018] As a further scheme of the present application, in step one, the limestone is pretreated, and the lime milk is prepared after crushing and digestion. The pretreatment step aims to calcine the limestone, and then perform digestion to prepare the lime milk. In step two, the microemulsion is taken to prepare the nano calcium carbonate by carbonization, and the lime milk is taken to generate the pre-prepared emulsion after dispersant treatment, and then the CO2 / N2 mixed gas is introduced for carbonization. In step three, the nano calcium carbonate slurry is taken for gradient surface modification. In this step, the temperature is first increased, and then the silane coupling agent is added for reaction, and then the temperature is increased again, and another coupling agent is added for grafting double bond, and then the dispersion, pressure filtration, drying and crushing treatment are performed to obtain the powder, so as to improve the affinity to the electrolyte and the adhesion. In step four, the nano calcium carbonate powder is taken for boehmite modification to prepare the composite coating slurry. The boehmite is first pretreated to improve the compatibility, and then the two are mixed, deionized water and binder are added for dispersion, and the slurry is prepared, which provides stable raw materials for subsequent membrane coating, and guarantees the coating performance. In step five, the composite slurry is taken for membrane coating and performance optimization. The micro-gravure coater is used to coat the slurry on the surface of the PE membrane, and the segmented temperature control drying is performed to avoid carbonization of the binder, and then the uniformity and adhesion of the coating are detected after winding, so as to guarantee the thermal stability and electrolyte wettability of the membrane. In step six, the nano calcium carbonate, the modified membrane and the assembled battery are taken for product performance detection. The key performances of the three are detected respectively, the adaptability of the nano calcium carbonate, the comprehensive performance of the membrane and the use effect of the battery are verified, and the safety and cycle requirements of the battery are ensured.

[0019] As a further scheme of the present application, the present application aims at the industry pain points of poor thermal stability (150℃x1h thermal shrinkage rate>15%) of the traditional polyolefin membrane, insufficient electrolyte wettability (contact angle>60°) and high cost of the Al2O3 coating, and innovatively combines the technical path of "microemulsion limited crystal type regulation-gradient surface modification-boehmite compounding and porosity regulation", to prepare the functional nano calcium carbonate suitable for the battery membrane coating. The limestone is taken as the raw material, and after calcination and digestion, the nano calcium carbonate with a particle size of 50-100nm and a specific surface area of 55-70m² / g is prepared by microemulsion carbonization (cyclohexane-sorbitan 80-n-butanol system); the silane coupling agent KH560-KH570 is used for gradient modification to introduce the electrophilic functional groups, the boehmite (AlOOH) is compounded to form the composite coating, and the porosity (35%-45%) is regulated by adjusting the solid content of the coating slurry and the coating speed. The composite coating is coated on the surface of the polyolefin membrane (thickness 1-3um), the thermal shrinkage rate of the membrane is ≤5%, the electrolyte contact angle is ≤30°, the tensile strength is improved by more than 25%, and the composite coating can replace 30%-50% of the Al2O3 coating, and the cost is reduced by 40%; when applied to the solid-state battery, the ionic conductivity is improved to 1.2x10⁻³S / cm, and the capacity retention rate is ≥90% after 500 cycles. The method has stable process and strong compatibility, and meets the needs of the lithium ion battery and the solid-state battery membrane coating.

[0020] The technical effects of the present application are: (1) Performance synergy: The composite coating realizes "thermal shrinkage rate ≤ 5% + contact angle ≤ 30% + tensile strength increased by 25%", far exceeding traditional Al2O3 coating; (2) Cost advantage: Replacing 30%-50% Al2O3, coating cost reduced by 40%, and raw materials are easy to obtain; (3) Scene adaptation: Through conductive polymer spraying, it can adapt to solid-state batteries, and the ionic conductivity is increased to the order of 10⁻³ S / cm; (4) Process stability: The whole process can be continuously produced, the composite slurry is not layered after standing for 24 h, and the batch-to-batch deviation is ≤ 5%. DETAILED DESCRIPTION

[0021] The technical solutions in the present application will be described below. Obviously, the described technical solutions are only a part of the present application, not the whole. Based on the content of the present application, all other technical solutions obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. Example 1

[0022] A preparation method of surface modified nano calcium carbonate for battery separator coating, comprising the following steps: Step one, 500 kg of limestone is crushed to a particle size of <5 mm by a jaw crusher, sent to a rotary kiln, calcined at 950℃ for 2.5h to generate CaO (purity ≥ 92%); after calcination, CaO is added to 65℃ deionized water at a solid-liquid ratio of 1:6, stirred in a planetary stirring digestion tank at 350r / min for 1h to complete the digestion reaction; the digestion liquid is filtered through a 400 mesh nylon screen to remove unreacted impurities, and aged for 36h to obtain refined lime milk with Ca(OH)2 content of 96.2% and density of 1.05g / cm³.

[0023] Step two, add 0.8% composite dispersant (sodium hexametaphosphate: sodium polyacrylate = 2:1, based on the dry basis mass of lime milk) to the refined lime milk, ultrasonic dispersion for 18min at 25kHz, adjust the density to 1.10g / cm³, and obtain the pretreated slurry; add the pretreated slurry and cyclohexane to the microemulsion reaction kettle at a mass ratio of 2:3.5, add 1.5% Span 80 and 0.8% n-butanol based on the mass of the oil phase, ultrasonic dispersion for 30min at 25℃ and 20kHz, and form water core diameter of 40nm water-in-oil (W / O) type microemulsion; pass CO2 / N2 mixed gas (CO2 volume fraction 45%, flow rate 3m³ / h) from the bottom of the reaction kettle, react at 28℃, and monitor the pH in real time with an online pH meter. When the pH of the system decreases to 8.8, stop carbonization to obtain a spindle-shaped nano calcium carbonate slurry (laser particle size instrument detects particle size of 75nm, BET specific surface area of 62m² / g).

[0024] Step three, the nano calcium carbonate slurry is heated to 45℃, 1.5% silane coupling agent KH560 (12% ethanol solution, 0.1 mol / L hydrochloric acid to adjust pH 4.2) is added based on the mass of dry basis, ultrasonic dispersion is carried out at 20 kHz for 25 min, constant temperature reaction is carried out for 1.2 h, the silanol generated by hydrolysis of KH560 is condensed with the surface hydroxyl of calcium carbonate; 1.0% KH570 (10% ethanol solution) is added to the system, heated to 60℃, stirring rate 550 r / min, reaction 1.8 h, through infrared spectrum (FTIR) detection, double bond characteristic peak appears at 1630 cm⁻¹, double bond grafting rate is 82%; 0.4% polyvinylpyrrolidone (PVP~K30) is added, ultrasonic dispersion is carried out at 20 kHz for 15 min, plate and frame filter pressing (pressure 0.7 MPa) is used for dehydration to 18% water content, 85℃ vacuum drying is carried out for 3 h, airflow crushing (classification accuracy ±5 nm) is carried out, and the surface modified nano calcium carbonate powder is obtained.

[0025] Step four, the boehmite is pretreated by 1% silane coupling agent KH550 (60℃ reaction for 2 h), so that the compatibility with the modified nano calcium carbonate is improved; the modified nano calcium carbonate and the pretreated boehmite are mixed according to the mass ratio of 7.5:2.5, deionized water (18 parts) and polyacrylate binder (7 parts) are added, ultrasonic dispersion is carried out at 20 kHz for 20 min, and the composite coating slurry with a solid content of 45% and a viscosity of 2000 mPa・s is prepared (the stratification rate is ≤2% after standing for 24 h).

[0026] Step five, the composite slurry is coated on the surface of the PE separator by using a micro-gravure coater, the coating speed is controlled to be 12 m / min, and the wet coating thickness is 3 μm; after coating, the separator is sent into a drying tunnel, and segmented temperature control (120℃ for 5 min→130℃ for 5 min) is used to avoid carbonization of the binder, finally the dry coating thickness is 2 μm, and the porosity is 40%; after drying, the separator is wound by a winding machine, and the coating uniformity (deviation ≤0.2 μm) and the adhesion (42 N / m) are detected.

[0027] Step six, according to the requirements of GB / T19590~2023 standard, the properties of nano calcium carbonate are detected, the surface hydroxyl density is 3.0 / nm², the oil absorption value (DOP) is 50 ml / 100 g, and the contact angle with electrolyte is 12°; the performance of the modified separator is that the thermal shrinkage rate is 4.2% at 150℃×1h, the electrolyte immersion time is 8 s, the tensile strength is 215 MPa, and the air permeability is 120 s / 100 mL; the battery performance is that the 18650 lithium ion battery (positive electrode LiNi1 / 3Co1 / 3Mn1 / 3O2, negative electrode graphite) is assembled by using the modified separator, the capacity retention rate is 91.5% after 500 times of 0.5C charge-discharge cycle, and the 1C rate discharge capacity reaches 95% of the rated capacity. Example 2

[0028] In the present embodiment, the surface-modified nano calcium carbonate is used for adapting solid-state batteries, for adapting PP separators of solid-state batteries. A method for preparing a surface-modified nano calcium carbonate for a battery separator coating comprises the following steps: Step one, take 500 kg of limestone and crush it to a particle size of <5 mm with a jaw crusher, then send it to a rotary kiln and calcine it at 980°C for 2.8 h to produce CaO (purity ≥93%); after calcination, add deionized water to the CaO at a solid-liquid ratio of 1:7, stir it in a planetary stirring digestion tank at 380 r / min for 1.2 h to complete the digestion reaction; filter the digestion liquid through a 400-mesh nylon screen to remove unreacted impurities, and let it stand for 40 h to obtain refined lime milk with a Ca(OH)2 content of 96.5% and a density of 1.07 g / cm³.

[0029] Step two, add 1.0% of a composite dispersant (sodium hexametaphosphate: sodium polyacrylate = 2:1, based on the dry mass of the lime milk) to the refined lime milk, and ultrasonically disperse it for 20 min at 28 kHz to adjust the density to 1.11 g / cm³ to obtain a pretreated slurry; add the pretreated slurry and cyclohexane to a microemulsion reaction kettle at a mass ratio of 2:4, add 1.8% of Span 80 and 1.0% of n-butanol based on the mass of the oil phase, and ultrasonically disperse it for 35 min at 20 kHz at 25°C to form a water-in-oil (W / O) type microemulsion with a water core diameter of 45 nm; introduce a CO2 / N2 mixed gas (CO2 volume fraction 48%, flow rate 3.5 m³ / h) into the bottom of the reaction kettle, and react at 29°C while monitoring the real-time pH with an online pH meter; stop the carbonization when the pH of the system drops to 8.6 to obtain a spherical-like nano calcium carbonate slurry (laser particle size analyzer detection particle size 80 nm, BET specific surface area 58 m² / g).

[0030] Step three, heat the nano calcium carbonate slurry to 48°C, add 1.8% of silane coupling agent KH560 (14% ethanol solution, 0.1 mol / L hydrochloric acid to adjust pH to 4.3) based on the dry mass, ultrasonically disperse for 30 min at 20 kHz, and react at constant temperature for 1.4 h to generate silanol from the hydrolysis of KH560, which condenses with the surface hydroxyl groups of calcium carbonate; add 1.2% of KH570 (11% ethanol solution) to the system, heat to 62°C, stir at a speed of 580 r / min, and react for 1.9 h; through infrared spectroscopy (FTIR) detection, a double bond characteristic peak appears at 1630 cm⁻¹, and the double bond grafting rate is 83%; add 0.5% of polyvinylpyrrolidone (PVP-K30), ultrasonically disperse for 18 min at 20 kHz, and dehydrate to a water content of 17% by plate and frame filter pressing (pressure 0.75 MPa); vacuum dry at 88°C for 3.5 h, and airflow crush (classification accuracy ±5 nm) to obtain surface-modified nano calcium carbonate powder.

[0031] Step four, the boehmite is pretreated with 1.5% silane coupling agent KH550 (62℃ for 2.2h) to improve the compatibility with modified nano calcium carbonate; the modified nano calcium carbonate and the pretreated boehmite are mixed at a mass ratio of 7:3, deionized water (20 parts) and polyacrylate binder (8 parts) are added, and the composite coating slurry with a solid content of 48% and a viscosity of 2300mPa・s is prepared by ultrasonic dispersion at 20kHz for 25min (the stratification rate is ≤1.8% after standing for 24h).

[0032] Step five, the composite slurry is coated on the surface of the PP separator by using a micro-gravure coater, the coating speed is controlled at 14m / min, and the wet coating thickness is 3.5μm; after coating, the separator is sent into a drying tunnel, and the temperature is controlled in stages (120℃×6min→130℃×6min) to avoid carbonization of the binder; the final dry coating thickness is 2.5μm, and the porosity is 38%; after drying, a 0.8μm thick PEO-LiTFSI conductive polymer is sprayed on the surface of the coating, and vacuum drying is carried out at 80℃ for 1h; after winding by a winding machine, the coating uniformity (deviation ≤0.18μm) and adhesion (45N / m) are detected.

[0033] Step six, according to the requirements of GB / T19590-2023 standard, the properties of nano calcium carbonate are detected: surface hydroxyl density 3.2 / nm², oil absorption value (DOP) 52ml / 100g, contact angle with electrolyte 11°; the performance of the modified separator: thermal shrinkage rate 4.5% at 150℃×1h, electrolyte immersion time 9s, tensile strength 220MPa, air permeability 125s / 100mL, and ion conductivity 1.2×10⁻³S / cm; battery performance: the modified separator is assembled into a solid-state lithium ion battery (positive electrode LiFePO4, negative electrode Li metal), and the capacity retention rate is 90.2% after 500 cycles of 0.5C charge and discharge, and the 1C rate discharge capacity reaches 94% of the rated capacity. Example 3

[0034] In this embodiment, calcium carbide slag is used to replace limestone, which is beneficial to the resource utilization of solid waste. A method for preparing surface modified nano calcium carbonate for battery separator coating, comprising the following steps: Step one, 500 kg carbide slag (Ca(OH)2content 88%, sulfur content 0.8%) was crushed to particle size <5 mm by a jaw crusher, and then sent to a pulse corona reactor (electrode spacing 8 cm, voltage 35 kV, frequency 100 Hz) with 15 L / min nitrogen gas protection for 10 min, and the sulfur content was reduced to 0.04%. The pretreated carbide slag was sent to a rotary kiln, calcined at 950 ℃ for 2.5 h to generate CaO (purity ≥92%). The CaO was added into deionized water at 65 ℃ with a solid-liquid ratio of 1:7, and stirred in a planetary stirring digestion tank at 350 r / min for 1.2 h to complete the digestion reaction. The digestion liquid was filtered through a 400 mesh nylon screen, and aged for 48 h to obtain refined milk of lime with Ca(OH)2content 95.5% and density 1.06 g / cm³.

[0035] Step two, 0.9% of a composite dispersant (sodium hexametaphosphate: sodium polyacrylate = 2:1, based on the dry mass of the lime milk) was added to the refined lime milk, and ultrasonic dispersion was performed at 25 kHz for 19 min to adjust the density to 1.10 g / cm³ to obtain a pretreated slurry. The pretreated slurry and cyclohexane were added to a microemulsion reaction kettle at a mass ratio of 2:3.5, and 1.6% of Span 80 and 0.9% of n-butanol were added based on the mass of the oil phase. Ultrasonic dispersion was performed at 20 kHz for 32 min at 25 ℃ to form a water-in-oil (W / O) type microemulsion with a water core diameter of 42 nm. CO2 / N2 mixed gas (CO2volume fraction 46%, flow rate 3.2 m³ / h) was introduced from the bottom of the reaction kettle, and the reaction was carried out at 28 ℃. The online pH meter was used for real-time monitoring, and the carbonation was stopped when the pH of the system dropped to 8.7 to obtain a spindle-shaped nano calcium carbonate slurry (laser particle size analyzer detected particle size 78 nm, BET specific surface area 59 m² / g).

[0036] Step three, the nano calcium carbonate slurry was heated to 45 ℃, and 1.6% of silane coupling agent KH560 (13% ethanol solution, 0.1 mol / L hydrochloric acid was used to adjust the pH to 4.2) was added based on the dry mass. Ultrasonic dispersion was performed at 20 kHz for 27 min, and the hydrolysis of KH560 generated silanol which condensed with the surface hydroxyl groups of calcium carbonate. 1.1% of KH570 (10% ethanol solution) was added to the system, heated to 60 ℃, and stirred at a speed of 560 r / min for 1.8 h. Through infrared spectroscopy (FTIR) detection, a double bond characteristic peak appeared at 1630 cm⁻¹, and the double bond grafting rate was 81%. 0.45% of polyvinylpyrrolidone (PVP-K30) was added, ultrasonic dispersion was performed at 20 kHz for 16 min, and plate and frame pressure filtration (pressure 0.7 MPa) was used to dewater to a moisture content of 18%. Vacuum drying was performed at 85 ℃ for 3.2 h, and airflow crushing (classification accuracy ±5 nm) was performed to obtain surface-modified nano calcium carbonate powder.

[0037] Step four, the boehmite was pretreated with 1.2% silane coupling agent KH550 (60℃ for 2h) to improve the compatibility with modified nano calcium carbonate; the modified nano calcium carbonate and the pretreated boehmite were mixed at a mass ratio of 7.2:2.8, deionized water (19 parts) and polyacrylate binder (7.5 parts) were added, and the composite coating slurry with a solid content of 46% and a viscosity of 2100 mPa・s was prepared by ultrasonic dispersion at 20 kHz for 22 min (the stratification rate was ≤2% after standing for 24 h).

[0038] Step five, the composite slurry was coated on the surface of the PE separator by using a micro-gravure coater, the coating speed was controlled at 13 m / min, and the wet coating thickness was 3.2 μm; after coating, the separator was sent into a drying tunnel, and the temperature was controlled in stages (120℃ for 5 min→130℃ for 5 min) to avoid carbonization of the binder; the final dry coating thickness was 2.1 μm, and the porosity was 39%; after drying, the separator was wound by a winding machine, and the coating uniformity (deviation ≤0.2 μm) and adhesion (43 N / m) were detected.

[0039] Step six, according to the requirements of GB / T19590~2023 standard, the properties of nano calcium carbonate were detected: the surface hydroxyl density was 2.9 / nm², the oil absorption value (DOP) was 51 ml / 100g, and the contact angle with electrolyte was 13°; the performance of the modified separator: the thermal shrinkage rate at 150℃ for 1h was 4.5%, the electrolyte immersion time was 9s, the tensile strength was 210 MPa, and the air permeability was 122 s / 100mL; the battery performance: the modified separator was assembled into a 18650 lithium ion battery (positive electrode LiNi1 / 3Co1 / 3Mn1 / 3O2, negative electrode graphite), and the capacity retention rate was 90.8% after 500 cycles of 0.5C charge and discharge, and the 1C rate discharge capacity reached 93% of the rated capacity. Example 4

[0040] In this embodiment, the microemulsion formula was optimized by adjusting the ratio of Span 80 and n-butanol. A method for preparing surface modified nano calcium carbonate for battery separator coating, comprising the following steps: Step one, same as example 1, refined lime milk with Ca(OH)2 content of 96.2% and density of 1.05 g / cm³ was obtained.

[0041] Step two, add 0.8% of the composite dispersant (sodium hexametaphosphate: sodium polyacrylate = 2:1, based on the dry mass of lime milk) into the refined lime milk, and disperse for 18 min under 25 kHz ultrasonic. Adjust the density to 1.10 g / cm³ to obtain the pretreated slurry. Add the pretreated slurry and cyclohexane into the microemulsion reactor in a mass ratio of 2:3.5. Add 2.0% of Span 80 and 1.0% of n-butanol (Span 80:n-butanol = 2:1) based on the mass of the oil phase. Disperse for 30 min under 20 kHz ultrasonic at 25°C to form a water-in-oil (W / O) microemulsion with a water core diameter of 38 nm. Pass CO2 / N2 mixed gas (CO2 volume fraction 45%, flow rate 3 m³ / h) into the bottom of the reactor. React at 28°C. Monitor the pH in real time with an online pH meter. Stop carbonization when the pH of the system drops to 8.8 to obtain a spindle-shaped nano calcium carbonate slurry (laser particle size analyzer detection particle size 72 nm, BET specific surface area 63 m² / g).

[0042] Step three, same as Example 1, to obtain the surface-modified nano calcium carbonate powder (double bond grafting rate 83%).

[0043] Step four, same as Example 1, to prepare a composite coating slurry with a solid content of 45% and a viscosity of 1950 mPa・s (layering rate ≤1.5% after standing for 24 h).

[0044] Step five, same as Example 1, the final coating dry thickness is 2 μm, the porosity is 40%, the coating uniformity (deviation ≤0.15 μm) and adhesion (44 N / m) are detected.

[0045] Step six, according to the requirements of GB / T19590-2023 standard, the properties of nano calcium carbonate are detected: surface hydroxyl density 3.1 / nm², oil absorption value (DOP) 49 ml / 100 g, contact angle with electrolyte 11°; modified separator performance: thermal shrinkage rate 4.0% at 150°C×1h, electrolyte immersion time 7 s, tensile strength 218 MPa, air permeability 118 s / 100 mL; battery performance: assemble 18650 lithium ion battery with the modified separator, capacity retention rate 92.0% after 500 cycles of 0.5C charge and discharge, and the 1C rate discharge capacity reaches 96% of the rated capacity. Example 5

[0046] In this example, the boehmite addition amount is adjusted for optimization (i.e., the mass ratio of modified nano calcium carbonate to boehmite is 1:0.5). A surface-modified nano calcium carbonate preparation method for a battery separator coating, comprising the following steps: Step one, same as Example 1, to obtain refined lime milk with a Ca(OH)2 content of 96.2% and a density of 1.05 g / cm³.

[0047] Step two, same as example 1, to obtain a spindle-shaped nano calcium carbonate slurry (particle size 75 nm, specific surface area 62 m² / g).

[0048] Step three, same as example 1, to obtain a surface-modified nano calcium carbonate powder.

[0049] Step four, boehmite is pretreated with 1% silane coupling agent KH550 (60°C for 2h); the modified nano calcium carbonate is mixed with the pretreated boehmite at a mass ratio of 1:0.5, deionized water (18 parts) and polyacrylate binder (9 parts) are added, and ultrasonic dispersion is performed at 20 kHz for 20 min to prepare a composite coating slurry with a solid content of 47% and a viscosity of 2200 mPa・s (static stratification rate ≤1.9% after 24h).

[0050] Step five, the composite slurry is coated on the surface of the PE separator by using a micro-gravure coater, the coating speed is controlled at 12 m / min, and the wet coating thickness is 3 μm; after coating, the separator is sent into a drying tunnel, and the temperature is controlled in stages (120°C for 5 min→130°C for 5 min), and the final dry coating thickness is 2 μm and the porosity is 37%; after drying, the separator is wound by a winding machine, and the coating uniformity (deviation ≤0.19 μm) and adhesion (46 N / m) are detected.

[0051] Step six, according to the requirements of GB / T19590-2023 standard, the properties of nano calcium carbonate are detected: surface hydroxyl density 3.0 / nm², oil absorption value (DOP) 50 ml / 100g, contact angle with electrolyte 12°; the performance of the modified separator: heat shrinkage rate 3.8% at 150°C for 1h, electrolyte immersion time 8s, tensile strength 225 MPa, air permeability 121 s / 100mL; battery performance: the modified separator is assembled into a 18650 lithium ion battery, the capacity retention rate is 91.8% after 500 cycles of 0.5C charge and discharge, and the 1C rate discharge capacity reaches 95% of the rated capacity. Example 6

[0052] In this example, the porosity is controlled by solid content (solid content 50%, coating speed 15 m / min). A method for preparing surface-modified nano calcium carbonate for battery separator coating, comprising the following steps: Step one, same as example 1, to obtain refined milk of lime with Ca(OH)2content 96.2% and density 1.05 g / cm³.

[0053] Step two, same as example 1, to obtain a spindle-shaped nano calcium carbonate slurry (particle size 75 nm, specific surface area 62 m² / g).

[0054] Step three, same as example 1, to obtain a surface-modified nano calcium carbonate powder.

[0055] Step four, adjust the solid content to 50% to prepare a composite coating slurry with a viscosity of 2500 mPa-s (static 24 h stratification rate ≤2%) as in Example 1.

[0056] Step five, use a micro-gravure coater to coat the composite slurry on the surface of the PE separator, control the coating speed at 15 m / min, and the wet coating thickness at 3 μm; after coating, the separator is sent into a drying tunnel, and a segmented temperature control is used (120°C for 5 min→130°C for 5 min), and the final dry coating thickness is 2 μm, and the porosity is 35%; after drying, the separator is wound by a winding machine, and the coating uniformity (deviation ≤0.2 μm), adhesion (43 N / m) are detected.

[0057] Step six, according to the requirements of GB / T19590-2023 standard, the properties of nano calcium carbonate are detected: surface hydroxyl density 3.0 / nm², oil absorption value (DOP) 50 ml / 100 g, contact angle with electrolyte 12°; modified separator performance: heat shrinkage rate 4.1% at 150°C for 1 h, electrolyte immersion time 10 s, tensile strength 216 MPa, air permeability 130 s / 100 mL; battery performance: assemble 18650 lithium ion batteries with the modified separator, 0.5C charge-discharge cycle 500 times, capacity retention rate 91.2%, 1C rate discharge capacity reaches 94% of the rated capacity. Example 7

[0058] In this example, a low-temperature adapted modified nano calcium carbonate is prepared by adjusting the temperature (adapted to -20°C low-temperature environment). A method for preparing a surface modified nano calcium carbonate for a battery separator coating, comprising the following steps: Step one, take 500 kg of limestone, crush it to a particle size of <5 mm by a jaw crusher, and send it into a rotary kiln, calcine it at 950°C for 2.5 h to generate CaO (purity ≥92%); after calcination, add deionized water to the CaO at a solid-liquid ratio of 1:6, stir it in a planetary stirring digestion tank at 350 r / min for 1 h to complete the digestion reaction; filter the digestion liquid through a 400 mesh nylon screen, and let it stand for 36 h to obtain refined lime milk with a Ca(OH)2 content of 96.2% and a density of 1.05 g / cm³.

[0059] Step two, 0.8% of the composite dispersant (sodium hexametaphosphate: sodium polyacrylate = 2:1, based on the dry mass of lime milk) was added to the refined lime milk, and ultrasonic dispersion was carried out at 25 kHz for 18 min. The density was adjusted to 1.10 g / cm³ to obtain a pretreated slurry. The pretreated slurry and cyclohexane were added to a microemulsion reactor in a mass ratio of 2:3.5. 1.5% of Span 80 and 0.8% of n-butanol were added to the oil phase. Ultrasonic dispersion was carried out at 25°C and 20 kHz for 30 min to form a water-in-oil (W / O) microemulsion with a water core diameter of 40 nm. CO2 / N2 mixed gas (CO2 volume fraction 45%, flow rate 3 m³ / h) was introduced from the bottom of the reactor. The reaction (low-temperature carbonization) was carried out at 25°C. The online pH meter was used for real-time monitoring. When the pH of the system dropped to 8.8, the carbonization was stopped. Spindle-shaped nano calcium carbonate slurry was obtained (laser particle size analyzer detected particle size 70 nm, BET specific surface area 65 m² / g).

[0060] Step three, the nano calcium carbonate slurry was heated to 45°C. 1.5% of silane coupling agent KH560 (12% ethanol solution, 0.1 mol / L hydrochloric acid was used to adjust the pH to 4.2) was added based on the dry mass. Ultrasonic dispersion was carried out at 20 kHz for 25 min. The constant temperature reaction was carried out for 1.2 h. 1.0% of KH570 (10% ethanol solution) + 0.3% of low-temperature compatibilizer (polyethylene glycol 400) was added to the system. The temperature was raised to 60°C. The stirring speed was 550 r / min. The reaction was carried out for 1.8 h. Through infrared spectroscopy (FTIR) detection, a double bond characteristic peak appeared at 1630 cm⁻¹. The double bond grafting rate was 82%. 0.4% of polyvinylpyrrolidone (PVP-K30) was added. Ultrasonic dispersion was carried out at 20 kHz for 15 min. Plate and frame pressure filtration (pressure 0.7 MPa) was used for dehydration to a water content of 18%. Vacuum drying was carried out at 85°C for 3 h. Airflow crushing (classification accuracy ± 5 nm) was used to obtain surface-modified nano calcium carbonate powder.

[0061] Step four, boehmite was pretreated with 1% silane coupling agent KH550 (60°C reaction for 2 h). The modified nano calcium carbonate and the pretreated boehmite were mixed in a mass ratio of 7.5:2.5. Deionized water (18 parts), polyacrylate binder (7 parts) + 0.2% low-temperature plasticizer (dibutyl phthalate) were added. Ultrasonic dispersion was carried out at 20 kHz for 20 min. A composite coating slurry with a solid content of 45% and a viscosity of 2000 mPa・s was prepared (the stratification rate was ≤2% after standing for 24 h).

[0062] Step five, the composite slurry was coated on the surface of the PE separator using a micro-gravure coater. The coating speed was controlled at 12 m / min. The wet coating thickness was 3 μm. After coating, the separator was sent into a drying tunnel. The temperature was controlled in stages (120°C for 5 min→130°C for 5 min). The final coating dry thickness was 2 μm. The porosity was 40%. After drying, the separator was wound by a winding machine. The coating uniformity (deviation ≤0.2 μm) and adhesion (42 N / m) were detected.

[0063] Step six, according to GB / T19590-2023 standard, the performance of nano calcium carbonate is detected: surface hydroxyl density 3.0 / nm2, oil absorption value (DOP) 50ml / 100g, contact angle with electrolyte 12°; the performance of modified separator is: heat shrinkage rate 4.2% at 150℃x1h, electrolyte immersion time 12s at-20℃, tensile strength 215MPa, air permeability 120s / 100mL; the performance of battery is: the modified separator is assembled into 18650 lithium ion battery, capacity retention rate 85% after 0.2C charge-discharge cycle 200 times at-20℃, capacity retention rate 91.5% after 0.5C charge-discharge cycle 500 times. Example 8

[0064] In this embodiment, the performance of the products prepared in examples 1-7 is compared and analyzed. The performance of the surface modified nano calcium carbonate and modified separator and battery prepared in examples 1-7 is uniformly detected, and the results are shown in the following table:

[0065] The particle size of the nano calcium carbonate prepared in examples 1-7 is concentrated in 70-80nm, and the specific surface area is 58-65m2 / g, which meets the requirements of the battery separator coating on the dispersibility and specific surface area of nano particles, proving that the process of the application can still stably control the core performance of nano calcium carbonate under different parameter adjustments.

[0066] Example 5 is optimized by adjusting the amount of boehmite (i.e. adjusting the mass ratio of modified nano calcium carbonate and boehmite 1:0.5), and the modified separator (heat shrinkage rate at 150℃) is the lowest (3.8%), because the boehmite and nano calcium carbonate form a more dense interlaced support network; the modified separators (heat shrinkage rate at 150℃) of examples 1, 2 and 7 are all ≤4.5%, which meets the high temperature safety requirement of battery (≤5%).

[0067] The modified separators (electrolyte contact angle) in all examples are all ≤13°, proving that the gradient surface modification effectively improves the electrolyte affinity, among which the contact angle of examples 2 and 4 is as low as 11° due to the optimization of the coupling agent ratio, and the immersion efficiency is optimal.

[0068] Tensile strength: example 5 is the highest (225MPa), because more boehmite enhances the mechanical properties of the coating; examples 1-7 are all ≥210MPa, which is 2%-10% higher than the traditional Al2O3 coating (205MPa).

[0069] Battery performance comparison: Example 4 (microemulsion formulation optimization) has the highest cycle retention rate (92.0%), due to the improved microemulsion stability reducing particle agglomeration and optimal coating uniformity; Example 7 still maintains 85% cycle retention rate for 200 cycles at -20℃ low temperature, proving that the addition of low-temperature compatibility agent and plasticizer effectively improves low-temperature adaptability; all examples have a 500-cycle retention rate of ≥90.2%, far exceeding traditional coating batteries (about 85%).

[0070] The present application can flexibly adjust process parameters according to different application scenarios (conventional / solid / low temperature / high mechanical strength) through the technical path of "microemulsion limited crystal form regulation-gradient surface modification-boehmite composite and porosity regulation", and the prepared surface modified nano calcium carbonate and composite coating separator performs excellently in thermal stability (thermal shrinkage rate ≤4.5%), electrol yte affinity (contact angle ≤13°), mechanical strength (tensile strength ≥210MPa) and battery cycle performance (500-cycle retention rate ≥90.2%). Among them, microemulsion formulation optimization (Example 4) and high proportion of boehmite addition (Example 5) perform outstandingly in cycle stability and mechanical strength, respectively, providing a low-cost solution for battery separator coating in multiple scenarios, and having significant industrial application potential.

[0071] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0072] Finally: the above is only a specific embodiment of the present application and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a surface-modified nano-sized calcium carbonate for a battery separator coating, characterized by, Comprise: Step one, the preparation of refined milk of lime: the limestone is crushed by jaw crusher, calcined by rotary kiln, digested, sieved to 400 mesh, and aged to obtain the refined milk of lime; Step two, the preparation of nano calcium carbonate by microemulsion carbonization: (1) Adjust the density of the refined milk of lime, add composite dispersant based on the dry mass, the composite dispersant is sodium hexametaphosphate and sodium polyacrylate, and ultrasonic dispersion is performed to obtain a pretreated slurry; (2) The pretreated slurry is mixed with cyclohexane, non-ionic surfactant and co-surfactant are added, ultrasonic dispersion is performed to form a water-in-oil microemulsion; (3) CO2 / N2 mixed gas is introduced into the microemulsion to obtain a spindle-shaped nano calcium carbonate slurry; Step three, gradient surface modification: (1) First modification: the nano calcium carbonate slurry is heated to 40-50℃, 1%-2% silane coupling agent KH560 is added based on the dry mass, and ultrasonic dispersion is performed before reaction; (2) Secondary modification: add 0.8%~1.5% , to 55~65℃, to obtain surface modified nano calcium carbonate; Step four, preparation of boehmite composite slurry: the modified nano calcium carbonate is mixed with boehmite, deionized water and water-based binder are added, and ultrasonic dispersion is performed to prepare a composite slurry; Step five, coating of the separator and porosity control: the solid content of the composite slurry is adjusted to control the porosity of the coating; the modified separator is obtained by section drying; Step six, battery adaptation treatment: when used in solid-state batteries, a 0.5-1 μm thick Li⁺ conductive polymer is sprayed on the surface of the coating.

2. The method for preparing surface-modified nano-sized calcium carbonate for coating of battery separators according to claim 1, characterized in that, In step one, the particle size of the limestone crushed by jaw crusher is less than 5 mm; the temperature of the rotary kiln calcination is 900-1000℃, and the time is 2-3 h; the solid-liquid ratio of the digestion is 1:5-1:8, the temperature is 60-70℃, and the stirring rate is 300-400 r / min; the aging time is 24-48 h; the Ca(OH)2 content of the refined milk of lime is ≥95%.

3. The method for preparing surface-modified nano-sized calcium carbonate for coating of battery separators according to claim 1, characterized in that, In step two, (1) the density of the refined milk of lime is adjusted to 1.08-1.12 g / cm³, the amount of composite dispersant added is 0.5%-1.2% based on the dry mass, the ratio of sodium hexametaphosphate to sodium polyacrylate is 2:1, and ultrasonic dispersion is performed at 20-30 kHz for 15-20 min to obtain a pretreated slurry; (2) The non-ionic surfactant is Span 80, and the co-surfactant is n-butanol; the mixing mass ratio of the pretreated slurry to cyclohexane is (2-3):(3-5), the mass fraction of Span 80 in the oil phase is 1%-2%, and the mass fraction of n-butanol in the oil phase is 0.5%-1%; ultrasonic dispersion is performed at 20 kHz for 30 min at 25℃; (3) The volume fraction of CO2 in the CO2 / N2 mixed gas is 40%-50%, the flow rate is 2-4 m³ / h, the reaction is carried out at 25-30℃ until the pH of the system decreases to 8.5-9.0, and the carbonization is stopped to obtain a spindle-shaped nano calcium carbonate slurry with a particle size of 50-100 nm and a specific surface area of 55-70 m² / g.

4. The method for preparing surface-modified nano-sized calcium carbonate for coating of battery separators according to claim 1, characterized in that, In step three, (1) First modification: the nano calcium carbonate slurry is heated to 40-50℃, 1%-2% silane coupling agent KH560 is added based on the dry mass, and ultrasonic dispersion is performed at 15-20 kHz for 20-30 min, and the reaction is carried out for 1-1.5 h. (2) Secondary modification: after heating, the stirring rate is 500-600 r / min, and the reaction is carried out for 1.5-2 h to obtain the surface-modified nano calcium carbonate; The mass ratio of silane coupling agent KH560 to silane coupling agent KH570 is 1.2:1-1.5:1, and the pH of the ethanol solvent is adjusted to 4.0-4.5 by 0.1 mol / L hydrochloric acid.

5. The method for preparing surface-modified nano-sized calcium carbonate for coating of battery separators according to claim 1, characterized in that, In step four, the mass ratio of modified nano calcium carbonate to boehmite is 1:0.3-1:0.5, the particle size is 20-40 nm, the water-based binder is polyacrylate, and the solid content is 30%; the mass ratio of modified nano calcium carbonate, boehmite, and deionized water, and water-based binder is (7-8):(1.5-2):(0.5-1), and the composite coating slurry with a solid content of 40%-50% and a viscosity of 1500-2500 mPa・s is prepared by ultrasonic dispersion at 20 kHz for 20 min.

6. The method for preparing surface-modified nano-sized calcium carbonate for coating of battery separators according to claim 1, characterized in that, In step five, the composite slurry is coated on the surface of the polyolefin separator by using a micro-gravure coater, the coating speed is 10-15 m / min, the porosity corresponding to the solid content of 40% slurry is 45%, the porosity corresponding to the solid content of 50% slurry is 35%, and the coating porosity is controlled to be 35%-45%; the coating is dried in stages at 120-130℃, wherein the coating is dried at 120℃ for 5 min and then at 130℃ for 5 min, to obtain a modified separator with a coating thickness of 1-3 μm.

7. The method for preparing surface-modified nano-sized calcium carbonate for coating of battery separators according to claim 1, characterized in that, In step six, when used in a solid-state battery, the coating surface is sprayed with a Li⁺ conductive polymer, and then vacuum dried at 80℃ for 1 h.

8. The method for preparing surface-modified nano-sized calcium carbonate for coating of battery separators according to claim 1, characterized in that, The surface-modified nano calcium carbonate needs to meet the following requirements: surface hydroxyl density of 2.5-3.5 / nm², oil absorption value (DOP) of 45-55 ml / 100g, contact angle with electrolyte ≤15°; volume resistivity of the composite coating ≥10¹² Ω・cm, and insulation performance meets the safety requirements of the battery.

9. The method for preparing surface-modified nano-calcium carbonate for battery separator coating according to claim 1, characterized in that, In step one, if calcium slag is used to replace limestone, the sulfur impurities (sulfur content ≤0.05%) need to be removed by pulse corona pretreatment (voltage 30-40 kV, frequency 100 Hz, treatment time 10 min) before calcination and digestion to ensure that the purity of refined lime milk is ≥95%.

10. The method of claim 1, wherein the surface-modified nano-sized calcium carbonate for a battery separator coating layer is characterized by, The modified separator prepared is used in a lithium ion battery, and has a heat shrinkage rate ≤5%, an electrolyte immersion time ≤10 s, and a tensile strength ≥200 MPa; when applied to a solid-state battery, the ionic conductivity is ≥1.0×10⁻³ S / cm, and the capacity retention rate of the battery after 500 cycles is ≥90%.

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