Nanoparticle, high-heat-resistance lithium battery diaphragm, preparation method and lithium battery

Abstract

The invention belongs to the technical field of lithium battery materials, and particularly relates to a nanoparticle, a high-heat-resistance lithium battery diaphragm, a preparation method and a lithium battery, the nanoparticle is of a core-shell structure and comprises a core material and a shell material, the core material is scandium-doped zirconium oxide, and the shell material is AlN; the base membrane, namely the polybenzothiazole-polyquinoxaline cross-linked copolymer, provides ultrahigh heat resistance, the nanoparticles are of an Sc-ZrO2-coated AlN core-shell structure, 'insulation-heat conduction-corrosion resistance 'synergy is achieved, and the nanofiber structure guarantees high porosity and electrolyte wettability.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery material technology, specifically relating to a nanoparticle, a high heat-resistant lithium battery separator, a preparation method, and a lithium battery. Background Technology

[0002] The separator in a lithium-ion battery is a crucial component. It serves two purposes: firstly, it isolates the positive and negative electrodes to prevent internal short circuits; secondly, it allows lithium ions to pass through, ensuring normal electrochemical reactions. Therefore, the separator needs sufficient heat resistance and strength to guarantee battery safety, and it also requires a uniform pore structure to ensure stable charging and discharging.

[0003] Currently, lithium-ion battery separators mainly use polyolefin materials such as polyethylene (PE) and polypropylene (PP), which have good pore structure and mechanical strength. However, they will experience thermal shrinkage at high temperatures, leading to short circuits and thermal runaway in the battery. To address the problem of high-temperature shrinkage of separators, existing methods mainly improve the heat resistance of the separator by coating the surface with high-heat-resistant materials, such as ceramic coating or high-heat-resistant polymer coating. However, polyolefin separators themselves have poor heat resistance, which can only reduce the degree of thermal shrinkage and cannot fundamentally solve the problem. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide nanoparticles, a high heat-resistant lithium battery separator, a preparation method and a lithium battery, which can effectively improve heat resistance and electrochemical performance.

[0005] This invention provides a nanoparticle with a core-shell structure, comprising a core material and an outer shell material. The core material is scandium-doped zirconium oxide, and the outer shell material is AlN.

[0006] Preferably, the nanoparticles are further modified with a silane coupling agent.

[0007] This invention provides a method for preparing nanoparticles, comprising the following steps: Zirconium oxychloride, scandium chloride, and a solvent (preferably water) are mixed, and the pH is controlled to 9-11 (preferably 9-10). The reaction is carried out (preferably at a temperature of 80-90℃, and the holding time is 2-3 hours). The mixture is then separated to obtain scandium-doped zirconium oxide. The scandium-doped zirconium oxide, aluminum trichloride, and urea are mixed (preferably with anhydrous ethanol as the solvent), reacted (preferably at 120-140℃ for 4-6 hours), separated, washed, dried, and calcined (preferably at 600-700℃ for 2-3 hours) to obtain nanoparticles. The preferred mass ratio of aluminum trichloride to scandium-doped zirconium oxide is 0.8-1.2:1, and the preferred molar ratio of urea to aluminum trichloride is 3:1.

[0008] Preferably, the nanoparticles are dispersed in anhydrous ethanol and mixed with a silane coupling agent (such as KH-550, which is 3-5% of the mass of the nanoparticles), reacted (preferably at a temperature of 70-80°C for 3-4 hours), separated, washed, and dried to obtain the modified nanoparticles.

[0009] In the scandium-doped zirconium oxide, the scandium doping amount is 2-5% of the zirconium oxide mass, and the core-shell mass ratio is 1:(0.8-1.2), preferably 1:1.

[0010] This invention provides a high heat-resistant lithium battery separator, comprising a base membrane, wherein the base membrane comprises a nanofiber membrane and nanoparticles added to the nanofiber membrane, wherein the nanofiber membrane is a cross-linked copolymer of polybenzoxide and polyquinoxaline, and the polybenzoxide is polybenzothiazole, polybenzobisoxazole or polybenzoxazine.

[0011] Preferably, the weight of the nanoparticles is 1.5-3.5% of the weight of the nanofiber membrane.

[0012] Preferably, a positive polarity coating and a negative polarity coating are respectively provided on both sides of the base film; The positive polarity coating contains holmium manganese titanium oxide (Ho(Mn,Ti)O). 3+ δ) nanoparticles or cerium-doped tantalum oxide (Ta2O5:Ce) nanoparticles (Ce doping amount is 1-3% of Ta2O5 mass), coating thickness is 1-3μm, and nanoparticle size is 30-80nm; The negative polarity coating contains molybdenum sulfide-graphene quantum dot composite (MoS2-GQDs) nanoparticles or phosphorus-doped gallium nitride (GaN:P) nanoparticles (P doping amount is 0.5-2% of GaN mass), the coating thickness is 1-3 μm, and the nanoparticle size is 20-60 nm.

[0013] Preferably, the positive polar coating contains holmium manganese titanium oxide nanoparticles; preferably, the Mn / Ti molar ratio is (0.3-0.6):1, and the oxygen defect content δ=0.1-0.3.

[0014] The negative polar coating contains molybdenum sulfide-graphene quantum dot composite nanoparticles; preferably, the mass ratio of MoS2 to graphene quantum dots is (8-12):1, and the particle size of the graphene quantum dots is 2-5 nm.

[0015] The positive polarity coating and the negative polarity coating form a built-in electric field. The nanofibers of the base film have a diameter of 50-200 nm, and the total thickness of the diaphragm is 5-100 μm.

[0016] The high heat-resistant lithium battery separator has a 5% thermal weight loss temperature ≥480℃, a tensile strength ≥40MPa, a heat shrinkage rate ≤0.4% at 180℃, and a heat shrinkage rate ≤1.0% at 200℃.

[0017] This invention provides a method for preparing the high heat-resistant lithium battery separator, comprising the following steps: Polybenzo[a] derivative monomers, polyquinoxaline monomers, crosslinking arm monomers, and solvents are mixed and reacted under the action of a catalyst (at a temperature of 130-150℃, a Yamamoto-type polycondensation reaction occurs) to obtain a prepolymer (number-average molecular weight Mn of 25-35 kDa, molecular weight distribution...). (The solubility is 1.8-2.1, and the solubility in strongly polar aprotic solvents such as NMP, DMAc, or DMSO is not less than 12 wt%, and it is a carboxylic acid-terminated copolymer). The prepolymer is subjected to acyl chloride (reaction with thionyl chloride), and then reacted with 2-azidoethanol to obtain a copolymer (with azide groups as side chains, soluble in solvents). The copolymer and nanoparticles are then mixed (using a DMAc / CHCl3 mixed solvent, with a volume ratio of DMAc to CHCl3 of 6-7:3-4) to obtain a spinning solution (the copolymer has a mass fraction of 8-12 wt%, and the nanoparticles have a mass fraction of 1.5-3.5 wt%). The spinning solution is then spun (electrospinning parameters are: needle size 22-25 G, flow rate 0.6-1.0 mL / h, voltage 16-20 kV, receiving distance 12-18 cm, ambient humidity controlled below 30%, and the receiver is a roller with a rotation speed of 200-400 rpm). The solution is then cured (preferably under a pressure of 0.1-0.3 MPa, with a programmed temperature increase at a rate of 1-3 °C / min, first holding at 90-110 °C for 1-3 h to remove the solvent, then holding at 140-160 °C for 1-3 h for pre-crosslinking, and finally holding at 190-210 °C for 3-5 h to complete deep crosslinking) to obtain a base film. The spinning solution also contains lithium chloride (the mass fraction of lithium chloride in the spinning solution is 0.5-1.5 wt%). The cross-linked structure of the base film is formed by the thermal decomposition of the side chain azide groups at 150-250℃ to generate nitrogen bene radicals, which then insert into CH bonds or couple with each other.

[0018] Preferably, the polybenzo derivative monomer is a polybenzothiazole monomer, a polybenzobisoxazole monomer, or a polybenzoxazine monomer; the polyquinoxaline monomer is 5,8-dibromo-2,3-bis(4-carboxyphenyl)quinoxaline; the crosslinking arm monomer is 1,4-bis(azidomethyl)benzene (molar fraction of 5-15% of the total monomer molars); the solvent is a strongly polar aprotic solvent (preferably NMP, DMAC, DMF, or DMSO); and the catalyst is bis(1,5-cyclooctadiene)nickel (Ni(COD)2) and 2,2'-bipyridine.

[0019] Preferably, a positive polarity coating slurry and a negative polarity coating slurry are coated on both sides of the base film, and then dried to obtain a high heat-resistant lithium battery separator; when the positive polarity coating slurry is coated first, it is dried at 80-100℃ for 1-1.5h, and then the negative polarity coating slurry is coated and dried at 80-160℃ for 1-1.5h, and then vacuum dried at 120-150℃ for 2-3h to obtain a high heat-resistant lithium battery separator.

[0020] The positive polarity coating slurry contains holmium manganese titanium oxide nanoparticles, N-methylpyrrolidone, and a binder (preferably polyvinylidene fluoride, with a mass of 5-8% of the nanoparticle mass), ultrasonically dispersed (300-500W, time 30-40min), and has a solid content of 10-15%. The negative polar coating contains molybdenum sulfide-graphene quantum dot composite nanoparticles, N-methylpyrrolidone, and a binder (preferably polyvinylidene fluoride, at 5-8% of the nanoparticle mass), ultrasonically dispersed (300-500W, 30-40 min), with a solid content of 10-15%.

[0021] Preferably, the preparation method of the holmium manganese titanium oxide nanoparticles is as follows: holmium nitrate, manganese nitrate, citric acid or glycine, and tetrabutyl titanate are mixed (using water or water with added ethylene glycol as solvent), reacted (at 80°C) to obtain a sol; then dried (at 120°C), heated (ignited at 350°C) to obtain a precursor powder; the precursor powder is calcined (calcined in air at 650-750°C) and reduced (heated to 450°C in an Ar atmosphere containing 5% H2, and held for 1 hour) to obtain primary particles; the primary particles are ball-milled (at 400 rpm for 2 hours) and dried (spray dried) to obtain holmium manganese titanium oxide nanoparticles (particle size 30-50 nm). The molar ratio of holmium nitrate, manganese nitrate, and tetrabutyl titanate is determined according to Ho∶Mn∶Ti = 1∶(1-x)∶x (x≈0.1-0.3). The ratio of the molar number of citric acid or glycine to the total molar number of metal ions is 1.2-1.5∶1.

[0022] The preparation method of the molybdenum sulfide-graphene quantum dot composite nanoparticles is as follows: sodium molybdate, cysteine, graphene quantum dots (particle size 3-4 nm), and water are mixed, and the pH value is controlled at 8-10 (preferably controlled by ammonia water, pH preferably 8.3-8.7). The mixture is heated (heated to 200℃ at 3℃ / min and held for 18-24 h, stirred during heating to prevent sedimentation), centrifuged (cooled before centrifugation, 8000 rpm for 10 min), separated (filtered through a 0.22 µm hydrophilic PTFE membrane), dialyzed (using a 1000 Da dialysis bag, circulating deionized water for 6 h to remove salt), and dried (freeze-dried) to obtain molybdenum sulfide-graphene quantum dot composite nanoparticles (particle size 30-50 nm).

[0023] The molar ratio of S source (i.e., cysteine) to Mo source (sodium molybdate) is 2.8-3.2:1. The mass ratio of MoS2 to GQDs is 10:1.

[0024] This invention provides a lithium battery, including the aforementioned high heat-resistant lithium battery separator. In the high heat-resistant lithium battery separator, the positive polarity coating is located near the positive electrode side, and the negative polarity coating is located near the negative electrode side.

[0025] The lithium battery also includes a positive electrode, a negative electrode, and an electrolyte; the high heat-resistant lithium battery separator has a positive electrode side coating facing the positive electrode and a negative electrode side coating facing the negative electrode, and is completely immersed in the electrolyte; the positive electrode active material is a ternary material, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, or lithium cobalt oxide, the negative electrode active material is a silicon-carbon composite material, artificial graphite, natural graphite, or lithium titanate, and the electrolyte is 1 mol / L LiPF6 / ethylene carbonate-methyl ethyl carbonate-fluoroethylene carbonate (4:5:1).

[0026] The beneficial effects of this invention are that the base film of this invention, namely polybenzothiazole-polyquinoxaline crosslinked copolymer, provides ultra-high heat resistance, the nanoparticles are Sc-ZrO2@AlN core-shell structure, realizing "insulation-thermal conduction-corrosion resistance" synergy, and the nanofiber structure ensures high porosity and electrolyte wettability.

[0027] The positive polar nanoparticles (Ho(Mn,Ti)O3+δ or Ta2O5:Ce) on the positive electrode side and the negative polar nanoparticles (MoS2-GQDs or GaN:P) on the negative electrode side form a potential difference, constructing a built-in electric field to guide lithium ions from the negative electrode to the positive electrode in a directional manner, reducing concentration polarization and improving ion transport efficiency by more than 20%.

[0028] The separator of this invention exhibits excellent thermal stability. The main material of the separator possesses extremely high thermal stability (decomposition temperature > 480℃). After nanofiberization and heat setting treatment, the separator maintains structural integrity even at temperatures above 300℃, without melting, shrinkage, or breakage (thermal shrinkage rate < 1% at 200℃). This characteristic fundamentally solves the safety hazard of traditional polyolefin separators (temperature resistance < 180℃) causing short circuits between the positive and negative electrodes due to melting during battery thermal runaway, significantly improving the high-temperature safety of lithium batteries.

[0029] This invention has good electrochemical compatibility. The polybenzothiazole-polyquinoxaline cross-linked copolymer material has excellent chemical stability and does not react with electrolytes (such as carbonates). The separator has good wettability to the electrolyte, which can ensure the battery cycle performance.

[0030] The separator of this invention has high strength, which meets the assembly requirements. Its mechanical strength of not less than 40MPa ensures safety and meets the battery assembly requirements. Detailed Implementation

[0031] Example 1 A method for preparing a base film includes the following steps: 1) Preparation of modified Sc-ZrO2@AlN core-shell nanosheets 1.1 Preparation of Sc-ZrO2 nanonuclei Weigh 5.0 g of analytical grade zirconium oxychloride (ZrOCl2). . 8H2O) and 0.3g analytical grade scandium chloride (ScCl3) . Add 6H2O) to 100mL of deionized water and stir magnetically until completely dissolved to obtain a mixed solution; adjust the pH of the mixed solution to 9.5 with 25% ammonia water, transfer to a three-necked flask, and keep it in an oil bath at 85℃ for 2.5h with continuous stirring (300r / min); after the reaction is completed, cool to room temperature, centrifuge (8000r / min, 10min), collect the precipitate, wash it 3 times with deionized water (50mL each time), and dry it under vacuum at 60℃ for 12h to obtain Sc-ZrO2 nanonuclei.

[0032] 1.2 Preparation of Sc-ZrO2@AlN core-shell nanosheets Weigh 2.0 g of the above Sc-ZrO2 nanonuclei, add 80 mL of anhydrous ethanol, and ultrasonically disperse for 30 min (300 W) to obtain a nanonuclei dispersion; add 2.0 g of analytical grade aluminum trichloride (AlCl3) to the dispersion. .6H2O (aluminum source and nanonucleus mass ratio of 1:1) and 1.5g analytical grade urea were stirred until completely dissolved, then transferred to a 100mL high-pressure reactor and reacted under sealed conditions at 130℃ and 0.4MPa for 5h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged (8000r / min, 10min), the precipitate was collected, washed twice with anhydrous ethanol (50mL each time), and dried under vacuum at 60℃ for 12h. The dried solid was placed in a tube furnace and heated to 650℃ at a rate of 5℃ / min in air atmosphere, calcined for 2.5h, and then naturally cooled to room temperature to obtain Sc-ZrO2@AlN core-shell nanosheets.

[0033] 1.3 Preparation of modified Sc-ZrO2@AlN core-shell nanosheets Weigh 1.0 g of the above Sc-ZrO2@AlN core-shell nanosheets, add 50 mL of anhydrous ethanol, and ultrasonically disperse for 20 min (300 W) to obtain a core-shell nanosheet dispersion. Add 0.04 g of silane coupling agent KH-550 (4% of the mass of Sc-ZrO2@AlN core-shell nanosheets) to the dispersion, and react with magnetic stirring (250 r / min) in an oil bath at 75 °C for 3.5 h. After the reaction is completed, centrifuge (8000 r / min, 10 min), collect the solid, wash twice with anhydrous ethanol (30 mL each time), and vacuum dry at 60 °C for 10 h to obtain modified Sc-ZrO2@AlN core-shell nanosheets.

[0034] 2) Preparation of soluble prepolymers: In an argon-filled glove box, 2,2′-bis(5-bromobenzothiazol-6-carboxylic acid)hexanediol (A1, 4.5 mmol), 5,8-dibromo-2,3-bis(4-carboxyphenyl)quinoxaline (B1, 4.5 mmol), 1,4-bis(azidomethyl)benzene (C1, 1.0 mmol), bis(1,5-cyclooctadiene)nickel (Ni(COD)2, 10.5 mmol) and 2,2′-bipyridine (10.5 mmol) were dissolved in 30 mL of anhydrous NMP to obtain a mixture.

[0035] The mixture was stirred at 140°C for 24 hours. After the reaction was complete, the mixture was poured into ice-cold methanol to precipitate, filtered, washed successively with dilute hydrochloric acid and methanol, and dried under vacuum to obtain a carboxylic acid-terminated prepolymer (Mn≈ 30 kDa). ≈1.9).

[0036] The prepolymer was dissolved in excess thionyl chloride and refluxed for 3 hours. After removing excess SOCl2 by evaporation, the acyl-chlorinated polymer was obtained. This polymer was dissolved in THF and slowly added dropwise at 0°C to an excess THF solution of 2-azidoethanol and pyridine, and reacted at room temperature for 12 hours. After precipitation, washing, and drying, the target copolymer PBZT-co-PPQ-N3 with side-chain azidation was obtained, exhibiting a solubility ≥12 wt% in DMAc (N,N-dimethylacetamide).

[0037] 3) Electrospinning: The target copolymer PBZT-co-PPQ-N3 was dissolved at a concentration of 10 wt% in a mixed solvent of DMAc / CHCl3 (volume ratio 7:3), and 1 wt% LiCl and 2 wt% of the modified Sc-ZrO2@AlN core-shell nanosheets from step 1) were added. The mixture was then magnetically stirred for 24 hours to form a uniform spinning solution.

[0038] Electrospinning was performed in an environment with a temperature of 25℃ and a humidity of 30%, using a 25 G stainless steel needle, a flow rate of 0.8 mL / h, a voltage of 18 kV, a receiving distance of 15 cm, and a roller receiver rotation speed of 300 rpm, to obtain a white non-woven nanofiber membrane. The membrane thickness was approximately 10 μm, and the average fiber diameter was approximately 180 nm.

[0039] 4) Cross-linking and curing: The nanofiber membrane obtained in step 3) is sandwiched between two polytetrafluoroethylene (PTFE) membranes and placed in a vacuum hot press, where a pressure of 0.2 MPa is applied.

[0040] The temperature was programmed under a nitrogen atmosphere as follows: the temperature was increased from room temperature to 100°C at a rate of 2°C / min and held for 2 hours; then increased to 150°C and held for 2 hours; and finally increased to 200°C and held for 4 hours.

[0041] After natural cooling, the cross-linked membrane was subjected to Soxhlet extraction in DMAc and THF (tetrahydrofuran) for 6 hours each to obtain the base membrane.

[0042] Example 2 A method for preparing a high heat-resistant lithium battery separator includes the following steps: 1) Preparation of positive polar nanoparticles 1.1 Weighing and mixing of raw materials Weigh the following raw materials according to the molar ratio Ho∶Mn∶Ti=1∶0.8∶0.2 (i.e., x=0.2): Holmium nitrate hexahydrate (Ho(NO3)3) . 6H2O, purity ≥99.9%: 5.10g (0.01mol); Manganese nitrate tetrahydrate (Mn(NO3)2) . 4H₂O, purity ≥ 99%): 2.01 g (0.008 mol); Tetrabutyl titanate (C 16 H 36 O4Ti, purity ≥98%): 0.68g (0.002mol); Complexing agent (citric acid, C6H8O7) . H2O, purity ≥99.5%: 5.00g (0.026mol, molar ratio of H2O to total metal ions is 1.3:1, total amount of metal ions = 0.01 + 0.008 + 0.002 = 0.02mol).

[0043] 1.2 Sol Preparation The Ho(NO3)3 weighed in step 1.1 . 6H2O, Mn(NO3)2 . 4H2O and citric acid were added sequentially to 50 mL of deionized water and magnetically stirred (300 r / min) until completely dissolved. Then, tetrabutyl titanate was slowly added dropwise, along with 5 mL of ethylene glycol (to adjust viscosity), and stirring was continued for 10 min. The mixture was then transferred to an 80 °C oil bath and stirred at a constant temperature for 2 h to form a uniform and transparent sol.

[0044] 1.3 Preparation of dry gel The sol was transferred to a vacuum drying oven, and the temperature was set to 120℃ and the vacuum degree to -0.09MPa. After drying for 6 hours, a loose dry gel block was obtained.

[0045] 1.4 Preparation of precursor powder After the dry gel block is broken up, it is transferred to a corundum crucible and placed in a muffle furnace. The temperature is directly raised to 350℃ (heating rate 10℃ / min) and held for 30 min. The dry gel self-propagates and ignites at this temperature, generating a fluffy black precursor powder.

[0046] 1.5 Calcination and Annealing The precursor powder was spread evenly in a corundum boat and placed in an air-atmosphere tube furnace. The temperature was increased to 700°C at a rate of 5°C / min and held for 3 hours (to remove residual organic matter and oxidize and solidify). After naturally cooling to room temperature, it was transferred to a quartz tube reactor, and a 5% H2 / Ar mixed gas (flow rate 50 mL / min) was introduced. The temperature was increased to 450°C at a rate of 3°C / min and held for 1 hour (reduction treatment). The mixture was then cooled to room temperature in the furnace to obtain primary particles.

[0047] 1.6 Ball milling and spray drying Primary particles were mixed with anhydrous ethanol at a mass ratio of 1:3 and added to an agate ball mill jar (ball-to-particle ratio 10:1). The mixture was then ball-milled in a planetary ball mill at 400 rpm for 2 hours to obtain a slurry with a solid content of 30%. The slurry was then fed into a spray dryer (inlet temperature 180℃, outlet temperature 80℃, atomization pressure 0.3MPa). After drying, the product was collected to obtain 30–50 nm near-spherical positive polar nanoparticles.

[0048] 2) Preparation of negative polar nanoparticles 2.1 Preparation of precursor solution Weigh the following raw materials: Sodium molybdate dihydrate (Na2MoO4) . 2H₂O (analytical grade, purity ≥99%): 2.42 g (0.01 mol, providing Mo element); L-cysteine ​​(C3H7NO2S, purity ≥99%): 3.33g (0.03mol, providing sulfur, S / Mo molar ratio = 3.0:1). Graphene quantum dots (GQDs, particle size 3–4 nm, laboratory-made, carbon content ≥95%): 0.30 g (MoS2 to GQDs mass ratio = 10:1, theoretically generated MoS2 mass is about 3.0 g). Add the above raw materials sequentially to 100 mL of deionized water and stir magnetically (250 r / min) for 30 min until completely dissolved to obtain a mixed solution; adjust the pH of the mixed solution dropwise to 8.5 with 25% ammonia water (using a pH meter for real-time monitoring, closed-loop control of fluctuation range ≤ ±0.1), and continue stirring for 10 min to obtain the precursor solution.

[0049] 2.2 Hydrothermal Reaction The precursor solution was transferred to a 150 mL polytetrafluoroethylene-lined high-pressure reactor (the solution volume occupied 70% of the lining volume), sealed, and placed in a homogeneous reactor. The heating program was set: the temperature was increased from room temperature to 200℃ at a rate of 3℃ / min, and the temperature was maintained for 20 h after reaching the target temperature. During the reaction, the magnetically coupled stirring was turned on (30 rpm) to prevent GQDs from settling.

[0050] 2.3 Product purification Cooling: After the reaction is complete, turn off the reactor heating and allow it to cool naturally to 35℃ (≤40℃); Centrifugation: Transfer the reaction solution to a centrifuge tube and centrifuge at 8000 rpm for 10 min in a high-speed centrifuge. Discard the large unreacted precipitate at the bottom and retain the supernatant. Filtration: The supernatant was vacuum filtered through a 0.22μm hydrophilic polytetrafluoroethylene (PTFE) membrane to remove micron-sized impurities, and the filtrate was collected; Dialysis: Transfer the filtrate to a dialysis bag with a molecular weight cutoff of 1000 Da, place it in deionized water (5 L), turn on the magnetic stirrer to circulate the deionized water, and dialyze for 6 hours (replace the deionized water every 2 hours) to remove residual salts. Freeze-drying: The dialyzed solution was transferred to a freeze-drying bottle and placed in a freeze dryer (temperature -50℃, vacuum degree 10Pa) for 24 hours to obtain a black fluffy powder, which is a negative polar nanoparticle with a particle size of 30-50nm.

[0051] 3) Positive electrode side slurry: Take 10g of positive polar nanoparticles (Ho(Mn,Ti)O3+δ nanoparticles, Mn / Ti=4:1, δ=0.2, particle size 50-70nm), add 85g of N-methylpyrrolidone, add 0.6g of polyvinylidene fluoride, and ultrasonically disperse at 500W for 35min to obtain a slurry with a solid content of 10%.

[0052] 4) Negative electrode side slurry: Take 10g of negative polar nanoparticles (MoS2-GQDs, MoS2:GQDs=10:1, GQDs particle size 3-4nm, negative polar nanoparticle particle size 30-50nm), add 85g of N-methylpyrrolidone, add 0.6g of polyvinylidene fluoride, and ultrasonically disperse at 500W for 35min to obtain a slurry with a solid content of 10%.

[0053] 5) Composite molding: The positive electrode slurry (wet film thickness 3μm, dry film thickness 2μm) was coated on the base film of Example 1 using a microgravure method and dried at 90℃ for 1.2h; the base film was flipped over and the negative electrode slurry (wet film thickness 3μm, dry film thickness 2μm) was coated and dried at 90℃ for 1.2h; vacuum dried at 130℃ for 2.5h to obtain a separator with a total thickness of 13μm, namely a high heat-resistant lithium battery separator.

[0054] Example 3 Compared with Example 2, Example 3 differs in that step 5) is as follows: A positive electrode slurry (wet film thickness 6 μm, dried thickness 4 μm) is coated onto the base film of Example 1 using a microgravure method, dried at 90°C for 1.2 h, and then vacuum dried at 130°C for 2.5 h to obtain a separator with a total thickness of 13 μm, i.e., a high heat-resistant lithium battery separator. Everything else is the same as in Example 2.

[0055] Example 4 Compared with Example 2, Example 4 differs in that step 5) involves: applying a negative electrode slurry (wet film thickness 6 μm, dried thickness 4 μm) to the base film of Example 1 using a microgravure method, drying at 90°C for 1.2 h, and then vacuum drying at 130°C for 2.5 h to obtain a separator with a total thickness of 13 μm, i.e., a high heat-resistant lithium battery separator. Everything else is the same as in Example 2.

[0056] Example 5 Compared with Example 2, Example 5 differs in that step 5) is as follows: A positive electrode slurry (wet film thickness 3 μm, dried thickness 2 μm) is coated onto the base film of Example 1 using a microgravure method, and dried at 90°C for 1.2 h; the base film is then flipped over, and a positive electrode slurry (wet film thickness 3 μm, dried thickness 2 μm) is coated again, dried at 90°C for 1.2 h; and then vacuum dried at 130°C for 2.5 h to obtain a separator with a total thickness of 13 μm, i.e., a high heat-resistant lithium battery separator. Everything else is the same as in Example 2.

[0057] Example 6 Compared with Example 2, Example 6 differs in the following ways: Step 3) is replaced with a common Al2O3 ceramic coating material; Step 4) is replaced with a common Al2O3 ceramic coating material. Everything else is the same as Example 2.

[0058] Example 7 Compared with Example 2, Example 7 differs in that: step 3) is replaced with lithium titanate; and step 4) is replaced with silicon dioxide. Everything else is the same as in Example 2.

[0059] Example 8 Compared with Example 1, Example 8 differs in that: in step 3) electrospinning, the Sc-ZrO2@AlN core-shell nanosheets are replaced with Al2O3 ceramic. Everything else is the same as in Example 1, and a base film is prepared.

[0060] A high heat-resistant lithium battery separator was prepared using the base film described in Example 2.

[0061] Comparative Example 1 Commercially available 9μm pure PE diaphragm.

[0062] Comparative Example 2 Commercially available lithium battery separator consisting of 2μm Al2O3 ceramic + 9μm PE membrane + 2μm Al2O3 ceramic.

[0063] The separators prepared in the examples and comparative examples were assembled into lithium batteries. The performance of the separators and assembled lithium batteries in the examples and comparative examples was tested, and the results are shown in Table 1 below.

[0064] Table 1. Performance of the separators and assemblies used in the examples and comparative examples of lithium batteries.

[0065] As can be seen from the comparison of Example 1 and Comparative Examples 1-2, compared with conventional PE separators and ceramic-coated PE separators, lithium battery separators with polybenzothiazole-polyquinoxaline crosslinked copolymer nanofibers with added Sc-ZrO2@AlN core-shell nanosheets have excellent heat resistance and good electrochemical performance.

[0066] As can be seen from the comparison between Examples 1 and 8, compared with the addition of conventional ceramics, Sc-ZrO2@AlN nanosheets can enhance the strength of nanofiber membranes, improve thermal shrinkage, enhance thermal conductivity, and improve battery electrical performance.

[0067] As can be seen from the comparison between Example 1 and Example 2, adding a built-in electric field coating can significantly improve the diaphragm's cycle performance, rate performance, and low-temperature performance.

[0068] As can be seen from the comparison of Examples 2-5, a simple positive or negative polarity coating has little impact on the electrical performance of the battery cell, and a synergistic effect is required.

[0069] As can be seen from the comparison of Examples 2 and 6-7, the conventional coating (lithium titanate / silicon dioxide) that may have a built-in electric field effect is not as effective as the Ho(Mn,Ti)O3+δ / MoS2-GQDs synergistic coating, and the coating (Al2O3) that does not have a built-in electric field function has little impact on the battery cell's electrical performance.

[0070] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0071] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A nanoparticle, characterized in that, The nanoparticles have a core-shell structure, comprising a core material and an outer shell material. The core material is scandium-doped zirconium oxide, and the outer shell material is AlN.

2. The nanoparticles as described in claim 1, characterized in that, The nanoparticles are also modified with a silane coupling agent.

3. The method for preparing nanoparticles as described in claim 1, characterized in that, Includes the following steps: Zirconium oxychloride, scandium chloride, and solvent were mixed, and the pH was controlled to 9-11. The mixture was reacted and separated to obtain scandium-doped zirconium oxide. The scandium-doped zirconium oxide, aluminum trichloride, and urea were mixed, reacted, separated, washed, dried, and calcined to obtain nanoparticles.

4. The preparation method according to claim 3, characterized in that, The nanoparticles were dispersed in anhydrous ethanol, mixed with a silane coupling agent, reacted, separated, washed, and dried to obtain the modified nanoparticles.

5. A high heat-resistant lithium battery separator, characterized in that, The membrane includes a base membrane comprising a nanofiber membrane and nanoparticles as described in claim 1 or 2 added to the nanofiber membrane, wherein the nanofiber membrane is a cross-linked copolymer of a polybenzoxanthin derivative and a polyquinoxaline derivative, and the polybenzoxanthin derivative is a polybenzothiazole, a polybenzobisoxazole, or a polybenzoxazine.

6. The high heat-resistant lithium battery separator as described in claim 5, characterized in that, The weight of the nanoparticles is 1.5-3.5% of the weight of the nanofiber membrane.

7. The high heat-resistant lithium battery separator as described in claim 5, characterized in that, The base film has a positive polarity coating and a negative polarity coating on its two sides, respectively. The positive polar coating contains holmium manganese titanium oxide nanoparticles or cerium-doped tantalum oxide nanoparticles. The negative polarity coating contains molybdenum sulfide-graphene quantum dot composite nanoparticles or phosphorus-doped gallium nitride nanoparticles.

8. The high heat-resistant lithium battery separator as described in claim 7, characterized in that, The positive polar coating contains holmium manganese titanium oxide nanoparticles; the negative polar coating contains molybdenum sulfide-graphene quantum dot composite nanoparticles.

9. A method for preparing a high heat-resistant lithium battery separator as described in claim 5 or 6, characterized in that, Includes the following steps, Polybenzo[a] derivative monomer, polyquinoxaline monomer, crosslinking arm monomer, and solvent are mixed and reacted in the presence of a catalyst to obtain a prepolymer. The prepolymer is subjected to acyl chlorination and then reacted with 2-azidoethanol to obtain a copolymer; The copolymer and nanoparticles are then mixed to obtain a spinning solution, which is then spun and cured to obtain a base film.

10. The preparation method according to claim 9, characterized in that, The polybenzo[a] derivative monomer is a polybenzothiazole monomer, a polybenzobisoxazole monomer, or a polybenzoxazine monomer; the polyquinoxaline monomer is 5,8-dibromo-2,3-bis(4-carboxyphenyl)quinoxaline; the crosslinking arm monomer is 1,4-bis(azidomethyl)benzene; the solvent is a strongly polar aprotic solvent; and the catalyst is bis(1,5-cyclooctadiene)nickel and 2,2'-bipyridine.

11. The preparation method according to claim 9, characterized in that, The base film is coated with a positive polarity coating slurry and a negative polarity coating slurry on both sides, and then dried to obtain a high heat-resistant lithium battery separator. The positive polarity coating slurry contains holmium manganese titanium oxide nanoparticles, N-methylpyrrolidone, and a binder; The negative polarity coating contains molybdenum sulfide-graphene quantum dot composite nanoparticles, N-methylpyrrolidone, and a binder.

12. The preparation method according to claim 11, characterized in that, The method for preparing the holmium manganese titanium oxide nanoparticles is as follows: holmium nitrate, manganese nitrate, citric acid or glycine, and tetrabutyl titanate are mixed and reacted to obtain a sol; then dried and heated to obtain a precursor powder; the precursor powder is calcined and reduced to obtain primary particles; the primary particles are ball-milled and dried to obtain holmium manganese titanium oxide nanoparticles. The preparation method of the molybdenum sulfide-graphene quantum dot composite nanoparticles is as follows: sodium molybdate, cysteine, graphene quantum dots and water are mixed, the pH value is controlled at 8-10, heated, centrifuged, separated, dialyzed and dried to obtain molybdenum sulfide-graphene quantum dot composite nanoparticles.

13. A lithium battery, characterized in that, Including the high heat-resistant lithium battery separator as described in any one of claims 5-8.

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