CN115966775B - Rechargeable lithium battery with ultralow self-discharge rate and preparation method thereof - Google Patents
Rechargeable lithium battery with ultralow self-discharge rate and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a rechargeable lithium battery with ultralow self-discharge rate and a preparation method thereof, wherein the rechargeable lithium battery comprises the following components: the positive electrode shell, the negative electrode shell, the gasket, the elastic sheet, the ceramic coating diaphragm, the positive electrode material, the negative electrode material and the electrolyte; the positive electrode material is formed by compounding niobium chloride and titanium dioxide at high temperature. Compared with the prior art, the rechargeable lithium battery prepared by the invention can reduce self-discharge in long-term storage and improve the safety performance and the cycle stability of the battery.
Description
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a rechargeable lithium battery with ultralow self-discharge rate and a preparation method thereof.
Background
The rechargeable lithium battery is placed for a period of time in a specified environment and is in a thermodynamic unstable state, and is continuously converted to an equilibrium state, so that a part of electric quantity is lost, and in the long-term charge and discharge process, irreversible damage is easy to occur to the battery, so that the capacity of the battery is reduced, and therefore, the development of a rechargeable lithium battery with lower self-discharge performance and cycle stability is very important through the development of a diaphragm and an electrode.
Chinese patent CN209329064U discloses a rechargeable lithium battery that self-discharge rate performance is good, including the lithium battery shell, the inside of lithium battery shell is fixed to be equipped with positive plate and negative plate, be provided with first barrier film between positive plate and the negative plate, the upper end of positive plate and negative plate is fixed respectively to be equipped with anodal utmost point ear and negative pole utmost point ear, anodal utmost point ear and negative pole utmost point ear's upper end is fixed respectively to be equipped with anodal post and negative pole post, the top of anodal post and negative pole post all runs through the top of lithium battery shell and upwards extend, the top inner wall of lithium battery shell is fixed to be equipped with the second barrier film, the second barrier film still with the lateral wall fixed connection of lithium battery shell, the downside and the upside fixed connection of first barrier film of second barrier film, the outside joint of lithium battery shell has the U-shaped cooling plate. The utility model can reduce the self-discharge rate of the lithium battery, and simultaneously the lithium battery can effectively dissipate heat during charging. However, the rechargeable lithium battery prepared by the patent has the defects of low cycle performance and poor self-discharge performance.
Disclosure of Invention
In view of the defects of low cycle performance and high self-discharge rate of the rechargeable lithium battery in the prior art, the technical problem to be solved by the utility model is to provide the rechargeable lithium battery with low self-discharge rate and high cycle performance and the ultra-low self-discharge rate and the preparation method thereof.
In order to achieve the above object, the present invention adopts the following technical scheme:
an ultra-low self-discharge rate rechargeable lithium battery comprises the following components: positive electrode shell, negative electrode shell, gasket, shell fragment, ceramic coating diaphragm, positive electrode material, negative electrode material, electrolyte.
The positive electrode shell comprises an aluminum layer material component and a copper layer material component, wherein the copper layer material component is arranged above the aluminum layer material component, the total thickness of the positive electrode shell cover is 0.1-0.25 mm, and the thickness of the aluminum layer material component accounts for 1/3-2/3 of the total thickness.
The negative electrode shell comprises a nickel layer material component and an aluminum layer material component, wherein the nickel layer material component is arranged above the aluminum layer material component, the total thickness of the negative electrode shell is 0.1-0.25 mm, and the thickness of the aluminum layer material component accounts for 1/3-2/3 of the total thickness.
The negative electrode material is graphite.
The preparation method of the rechargeable lithium battery comprises the following steps:
assembling in a glove box filled with high-purity argon, placing an anode shell on an insulating table, then dripping 1-3 mL of electrolyte, then placing an anode material, placing a ceramic coating diaphragm, then placing graphite as a cathode material, installing a gasket, then installing an elastic sheet, and finally installing a cathode shell to obtain a button cell; placing the button cell on a manual button electric sealing machine, locking a switch of the sealing machine, shaking the handle up and down for multiple times, wherein the pressure is 0.5-0.9 Mpa, taking out the assembled button cell after the assembly is completed, and placing for 10-20 h to obtain the rechargeable lithium cell.
The preparation method of the positive electrode material comprises the following steps of:
adding 2-6 parts of niobium chloride into 30-50 parts of absolute ethyl alcohol, stirring for 10-20 min at the stirring speed of 1000-1500 rpm, adding 5-15 parts of water into the solution, then adding 2-6 parts of titanium dioxide, stirring for 0.5-2 h at the stirring speed of 500-1000 rpm, conveying the solution into a Teflon autoclave, heating for 10-20 h at the temperature of 150-200 ℃, washing with water for 2-3 times, drying for 0.5-2 h at the temperature of 50-70 ℃ in a vacuum oven, and treating for 0.5-2 h at the temperature of 400-800 ℃ in air to obtain the anode material.
The ceramic coating diaphragm comprises ceramic coating slurry and a substrate diaphragm, wherein the ceramic coating slurry comprises: 15 to 25 weight percent of alumina, 30 to 40 weight percent of water, 38 to 48 weight percent of modified slurry, 0.5 to 2 weight percent of binder, 0.1 to 1 weight percent of additive and 0.05 to 0.3 weight percent of auxiliary agent.
Preferably, the ceramic coating diaphragm comprises a ceramic coating slurry and a substrate diaphragm, wherein the ceramic coating slurry comprises: 20wt% alumina, 35 wt% water, 43.4wt% modified slurry, 1wt% binder, 0.5wt% additive and 0.1wt% adjuvant.
Preferably, the alumina is nano alumina powder.
Preferably, the binder is at least one of polyvinyl acetate, styrene-acrylic latex, styrene-butadiene latex and polyvinylpyrrolidone.
Preferably, the additive is at least one of perfluoroalkyl ethoxy methyl ether, polyoxyethylene alkylamide, fatty alcohol polyoxyethylene ether, sodium butylnaphthalene sulfonate, sodium isethionate and sodium dodecyl sulfonate.
Preferably, the auxiliary agent is sodium carboxymethyl cellulose.
Preferably, the substrate membrane is one of a polypropylene microporous membrane, a polyethylene microporous membrane, a polypropylene microporous membrane, a polyester microporous membrane and a polyimide microporous membrane; the thickness of the microporous membrane is 10-30 mu m.
The preparation method of the ceramic coated diaphragm comprises the following steps:
step 1, weighing the raw materials according to the weight percentage, adding the modified slurry into water, stirring for 5-20 min at the stirring speed of 200-500 rpm, adding aluminum oxide, stirring for 10-30 min at the stirring speed of 100-500 rpm, then adding an auxiliary agent, dispersing by double-planetary stirring and a sand mill for 20-50 min, adding a binder, stirring for 20-40 min at the stirring speed of 300-800 rpm, adding an additive, stirring for 10-30 min at the stirring speed of 300-800 rpm, and obtaining the ceramic coating slurry;
And 2, coating the ceramic coating slurry prepared in the step 1 on the surfaces of the two sides of the substrate diaphragm, wherein the coating speed is 20-60 m/min, the thickness of the coating is 3-6 mu m, and drying the ceramic coating slurry at 40-80 ℃ for 10-20 min to obtain the ceramic coating diaphragm.
Preferably, the coating mode is one of screen printing coating, gravure coating, knife coating, spray coating or anilox roll coating.
Preferably, the ceramic coating has a thickness of 1.0 to 6.0 μm.
The preparation method of the modified slurry comprises the following steps of:
s1, adding 10-30 parts of polyoxyethylene cetyl ether into 120-180 parts of cyclohexane, heating to 40-60 ℃, stirring to fully mix the solutions, maintaining the temperature, then adding 1-5 parts of methacryloxypropyl trimethoxysilane, stirring for 0.5-2 h at a stirring speed of 100-300 rpm, and cooling to room temperature to form a microemulsion system; adding 20-30 parts of 25-28 wt% ammonia water solution into the microemulsion system, stirring for 0.3-0.8 h, wherein the stirring speed is 100-500 rpm, adding 10-30 parts of tetraethyl orthosilicate, reacting for 1-3 h, adding 120-180 parts of isopropanol, performing ultrasonic treatment for 3-10 min, performing ultrasonic frequency of 20-30 kHz, ultrasonic power of 200-400W, centrifuging for 5-15 min at 5000-8000 rpm, taking precipitate, washing for 1-3 times by using isopropanol, and drying for 10-30 h at 80-120 ℃ to obtain a dried product;
S2, adding 3-10 parts of the dried product prepared in the step S1 into 200-400 parts of toluene, stirring, adding 0.02-0.2 part of an initiator and 10-20 parts of 4-dimethylaminopyridine to obtain a mixture, vacuumizing the mixture for 10-40 min each time, heating to 60-80 ℃ and stirring for 10-30 h, cooling with ice water to stop the reaction, centrifuging at 5000-8000 rpm for 5-20 min, washing the precipitate with toluene for 1-3 times, and drying at 80-120 ℃ for 10-30 h to obtain modified particles;
s3, adding 5-10 parts of modified particles and 1-5 parts of polyvinylidene fluoride into 40-60 parts of N, N-dimethylformamide, carrying out ultrasonic treatment for 5-15 min, wherein the ultrasonic frequency is 20-35 kHz, the ultrasonic power is 200-300W, adding 1-3 parts of modified biomass and 0.1-0.8 part of functional agent, and stirring and mixing for 5-20 h at a speed of 200-500 rpm to obtain modified slurry.
Preferably, the initiator is azobisisobutyronitrile.
The preparation method of the functional agent comprises the following steps of: mixing 5-10 parts of zinc oxide powder and 10-20 parts of boric acid powder, grinding for 1h, then placing into a quartz crucible, heating in a muffle furnace at 800-1000 ℃ for 1-3 h, and obtaining the functional agent at a heating rate of 3-5 ℃/min.
The preparation method of the modified biomass comprises the following steps of:
z1, grinding 80-120 parts of rice hulls, sieving with a 50-200 mesh sieve, immersing in 400-600 parts of 5-15wt% ammonium chloride aqueous solution for 5-15 h, drying at 60-90 ℃ for 5-20 h, adding the dried sample into a tubular furnace, heating for 20-40 min at 200-300 ℃ under air atmosphere, switching to nitrogen environment, continuously heating to 500-700 ℃ for 0.5-2 h, and heating at a heating rate of 3-6 ℃/min to obtain carbide;
z2, heating and refluxing 40-60 parts of the carbide prepared in the step Z1 in 200-400 parts of 2-6wt% sodium hydroxide aqueous solution for 1-3 h at the reflux temperature of 60-80 ℃, and then drying at 80-120 ℃ for 5-20 h to obtain a reflux; heating the reflux material for 0.5-2 h at 700-800 ℃ in a tube furnace under nitrogen atmosphere, washing the obtained sample to be neutral by water, and drying for 5-20 h at 80-120 ℃ to obtain a pretreated material;
z3, grinding 20-40 parts of the pretreated substance prepared in the step Z2 with 3-8 parts of asphalt powder for 0.5-2 hours, adding the mixture into 800-1200 parts of absolute ethyl alcohol, stirring for 0.5-2 hours, wherein the stirring speed is 100-300 rpm, drying for 10-30 hours at 60-90 ℃, heating the dried sample to 80-120 ℃, the heating rate is 0.5-2 ℃/min, and maintaining the mixture for 0.5-2 hours in a nitrogen atmosphere, then heating to 700-900 ℃, the heating rate is 2-4 ℃/min, and maintaining the mixture for 0.5-2 hours to obtain the modified biomass.
The ceramic coated diaphragm prepared by the invention can be applied to lithium ion batteries.
The invention adopts the modified slurry to mix with water, and prepares ceramic coating slurry by adding nano alumina powder, sodium carboxymethyl cellulose, polyvinyl acetate and perfluoroalkyl ethoxymethyl ether and stirring and mixing, and coats the ceramic coating slurry on a polypropylene microporous membrane to prepare the ceramic coating membrane; the modified slurry is prepared by adding polyoxyethylene cetyl ether into cyclohexane, adding methacryloxypropyl trimethoxy silane to form a microemulsion system, adding ammonia water solution and tetraethyl orthosilicate to dry to prepare a dry product, adding 4-dimethylaminopyridine into the dry product to react under the action of an initiator to obtain modified particles, reacting the modified particles with polyvinylidene fluoride in N, N-dimethylformamide, and further mixing the modified particles with modified biomass and a functional agent; wherein the modified biomass is obtained by carbonizing rice hulls, treating the carbonized biomass with sodium hydroxide aqueous solution and compositing the carbonized biomass with asphalt powder; the functional agent is obtained by grinding and calcining zinc oxide powder and boric acid powder.
In general, battery self-discharge is attributed to the following two aspects: first, the faraday process near the interface of the electrode and the electrolyte; another is an internal short circuit that may occur when assembling and manufacturing the capacitor. The former is mainly derived from the surface oxygen-containing functional groups of the electrode material, if not considered. The modified biomass is distributed with pores with different sizes, and the surface of the modified biomass is changed from hydrophilic to hydrophobic. Asphalt powder becomes an oil phase with fluidity at high temperature, and asphalt carbon can slowly permeate into and spread to the pores and the surface of the pretreated material along with the increase of carbonization temperature. The obtained modified biomass has higher specific surface area, can provide more active sites for electrolyte ions, and is favorable for forming higher capacitance. The conductivity of the pretreated substance after the modification of the asphalt powder screw site is improved, which is possibly related to the soft carbon characteristic of asphalt, and the asphalt is rich in polycyclic aromatic hydrocarbon and easy to graphitize. Through asphalt chemical modification, a certain oxygen consumption reaction can occur in the heating carbonization process to obtain modified biomass with low oxygen content, and oxygen-containing groups (such as-COOH, C=O and-OH) on the surface of the modified biomass are removed, so that the oxygen-containing functional groups can prevent ions from being transported to pores to a certain extent, and the modified biomass can be stored for a long time and has lower self-discharge. And the pore structure of the modified biomass after asphalt modification is regulated and optimized, charge redistribution can be inhibited to a certain extent, and the increase of C-O groups is beneficial to the interfacial stability of the modified biomass. The modified particles and polyvinylidene fluoride react in N, N-dimethylformamide, modified biomass and a functional agent are added and mixed to obtain modified slurry, and the prepared ceramic coated diaphragm can improve energy storage efficiency and reduce self-discharge. As the methacryloxypropyl trimethoxysilane is added with ammonia water solution and tetraethyl orthosilicate to be dried to prepare a dried product, double bond polymerization is carried out between the methacryloxypropyl trimethoxysilane and 4-dimethylaminopyridine, modified particles are generated by reaction between the methacryloxypropyl trimethoxysilane and the 4-dimethylaminopyridine, and silicon and zinc boron are distributed on the ceramic coating in a large quantity by adding a functional agent into the modified particles, so that the ceramic coating diaphragm can be helped to maintain the shape of the ceramic coating diaphragm at a higher temperature. Meanwhile, the heat resistance of the ceramic coating diaphragm is improved, and the high-temperature shrinkage rate is reduced. The possible reasons are that the silicon, zinc, boron-containing compounds are released from the ceramic coating slurry during heating, which can maintain their state at higher temperatures and significantly improve the thermal stability. The technology maintains the characteristics of ceramics, and introduces compounds such as silicon, zinc boron and the like, thereby improving the thermal stability of the ceramic coated diaphragm. The addition of the modified biomass imparts lower self-discharge properties for long-term storage. Therefore, the battery assembled by the ceramic coated separator has excellent safety performance and good electrochemical performance, little loss of irreversible capacity and excellent self-discharge performance.
The invention combines niobium chloride and titanium dioxide at high temperature to form the positive electrode material with conjugated structure, and the positive electrode material with conjugated structure is more stable than the traditional nickel cobalt lithium manganate in terms of self-discharge and cycle performance. Although titanium dioxide has high stability, pure titanium dioxide cannot be used directly for energy storage. Titanium dioxide can be embedded with lithium ions in electrolyte to provide stable charge and discharge effects, and the titanium dioxide and niobium chloride have good miscibility, and the uniformly mixed titanium dioxide and the positive electrode material prepared from the niobium chloride have synergistic effect, and have good self-discharge resistance and cycle stability.
Compared with the prior art, the invention has the beneficial effects that: 1) The modified slurry is mixed with water, nano alumina powder, sodium carboxymethyl cellulose, polyvinyl acetate and perfluoroalkyl ethoxymethyl ether are added and stirred to prepare ceramic coating slurry, the ceramic coating slurry is coated on a polypropylene microporous membrane, and the ceramic coating membrane is prepared, so that the high-temperature shrinkage rate is low; when the battery is used in a battery, the self-discharge of long-term storage can be reduced, and the safety performance and the electrochemical performance of the battery are improved; 2) The niobium chloride and the titanium dioxide are compounded at high temperature to form the positive electrode material with conjugated configuration, and the positive electrode material has better self-discharge resistance and cycle stability.
Detailed Description
The technical scheme of the present invention will be described in detail by means of specific examples, which should be explicitly set forth for illustration, but should not be construed as limiting the scope of the present invention.
The parameters of some of the raw materials in the examples and comparative examples of the present invention are as follows:
nano alumina powder, particle size: 3+ -1 nm; polypropylene microporous membrane, model number of new material limited, shanghai Mingli: PPDG, thickness: 30 μm, pore size: 0.05 μm; polyoxyethylene cetyl ether, jiangsu province sea Ann petrochemical plant, product number: polyoxyethylene ether (Brij 52), CAS:9004-95-9; methacryloxypropyl trimethoxysilane, model: KH-570; grinding rice husk into powder, and sieving with 30 mesh sieve; asphalt powder, density: 1.15g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Polyvinyl acetate, shandong Guangshen electronic technology Co., ltdCargo number: GS458962, density: 1.023g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Polyvinylidene fluoride, dongguan city good flourishing plastic raw materials limited company, product number: JS283; zinc oxide powder, particle size: 50nm; boric acid powder, particle size: 200 meshes; gasket, dongguan city wetting electronic materials limited company, material: PP, model YR-320; shrapnel, dongguan city, the electronic limited company of the counter-metal, the material: beryllium copper number: f-04, electrolyte, model LB-315, produced by national Tay Hua Rong chemical New material Co., ltd.
Example 1
A ceramic coated diaphragm is prepared by the following steps:
step 1, adding 43.4g of modified slurry into 35g of water, stirring for 10min at a stirring speed of 400rpm, adding 20g of nano alumina powder, stirring for 20min at a stirring speed of 300rpm, then adding 0.1g of sodium carboxymethyl cellulose, dispersing by double-planetary stirring and a sand mill for 30min, adding 1g of polyvinyl acetate, stirring for 30min at a stirring speed of 500rpm, adding 0.5g of perfluoroalkyl ethoxy methyl ether, stirring for 20min at a stirring speed of 500rpm, and obtaining ceramic coating slurry;
and 2, coating the ceramic coating slurry prepared in the step 1 on the surfaces of the two sides of the polypropylene microporous membrane in a screen printing coating mode, wherein the coating speed is 40m/min, the thickness of the coating is 5 mu m, and drying at 60 ℃ for 15min to obtain the ceramic coating membrane.
The preparation method of the modified slurry comprises the following steps:
s1, adding 20g of polyoxyethylene cetyl ether into 150g of cyclohexane, heating to 50 ℃, stirring to fully mix the solution, maintaining the temperature, then adding 3g of methacryloxypropyl trimethoxysilane, continuously stirring for 1h at a stirring speed of 200rpm, and cooling to room temperature to form a microemulsion system; dropwise adding 24g of 25wt% ammonia water solution into the microemulsion system, stirring for 0.5h at the stirring speed of 300rpm, adding 20g of tetraethyl orthosilicate, reacting for 2h, adding 150g of isopropanol, performing ultrasonic treatment for 5min, performing ultrasonic frequency of 25kHz and ultrasonic power of 300W, centrifuging for 10min at 6000rpm, collecting precipitate, washing for 2 times by using isopropanol, and drying at 100 ℃ for 24h to obtain a dried product;
S2, adding 5g of the dried product prepared in the step S1 into 300g of toluene, stirring, then adding 0.1g of azodiisobutyronitrile and 15g of 4-dimethylaminopyridine to obtain a mixture, vacuumizing the mixture for 30min each time, heating to 70 ℃ and stirring for 24h, cooling with ice water to stop the reaction, centrifuging at 6000rpm for 10min, washing the precipitate with toluene for 2 times, and drying at 100 ℃ for 24h to obtain modified particles;
s3, adding 7g of the modified particles prepared in the step S2 and 3g of polyvinylidene fluoride into 50g of N, N-dimethylformamide, carrying out ultrasonic treatment for 10min at an ultrasonic frequency of 30kHz and an ultrasonic power of 250W, adding 2g of modified biomass and 0.4g of functional agent, and stirring and mixing at a speed of 400rpm for 10h to obtain modified slurry.
The preparation method of the functional agent comprises the following steps: 7g of zinc oxide powder and 14g of boric acid powder are mixed and ground for 1h, then the mixture is put into a quartz crucible, and heated in a muffle furnace (air atmosphere) at 900 ℃ for 2h, wherein the heating speed is 5 ℃/min, and the functional agent is obtained.
The preparation method of the modified biomass comprises the following steps:
z1, crushing 100g of rice hulls, sieving with a 100-mesh sieve, immersing in 500g of 10wt% ammonium chloride aqueous solution for 10h, drying at 80 ℃ for 12h, heating the dried sample in a tubular furnace at 250 ℃ for 30min in an air atmosphere, switching to a nitrogen environment, continuously heating to 600 ℃ for 1h at a heating rate of 5 ℃/min, and obtaining a carbide;
Z2, heating and refluxing 50g of the carbide prepared in the step Z1 in 300g of 5wt% sodium hydroxide aqueous solution for 2h at a reflux temperature of 70 ℃, and then drying at 100 ℃ for 12h to obtain a reflux; heating the reflux material for 1h at 750 ℃ in a tube furnace under nitrogen atmosphere, washing the obtained sample to be neutral, and drying the sample for 12h at 100 ℃ to obtain a pretreated material;
z3, grinding 30g of the pretreated substance prepared in the step Z2 with 6g of asphalt powder for 1h, adding into 1kg of absolute ethyl alcohol, stirring for 1h, drying at the stirring speed of 200rpm and 80 ℃ for 24h, heating the dried sample to 100 ℃, keeping the heating speed of 1 ℃/min in a nitrogen atmosphere for 1h, then heating to 800 ℃, keeping the heating speed of 3 ℃/min for 1h, and obtaining the modified biomass.
Example 2
The preparation of the ceramic coated separator was essentially the same as in example 1, the only difference being that: the preparation methods of the modified slurry are different.
The preparation method of the modified slurry comprises the following steps: 3g of polyvinylidene fluoride is added into 50g of N, N-dimethylformamide, ultrasonic treatment is carried out for 10min, ultrasonic frequency is 30kHz, ultrasonic power is 250W, 2g of modified biomass and 0.4g of functional agent are added, and stirring and mixing are carried out for 10h at a speed of 400rpm, thus obtaining modified slurry.
The preparation method of the modified biomass is the same as in example 1.
The preparation method of the functional agent is the same as that of the example 1.
Example 3
The preparation of the ceramic coated separator was essentially the same as in example 1, the only difference being that: the preparation methods of the modified slurry are different.
The preparation method of the modified slurry comprises the following steps:
s1, adding 20g of polyoxyethylene cetyl ether into 150g of cyclohexane, heating to 50 ℃, stirring to fully mix the solution, maintaining the temperature, then adding 3g of methacryloxypropyl trimethoxysilane, continuously stirring for 1h at a stirring speed of 200rpm, and cooling to room temperature to form a microemulsion system; dropwise adding 24g of 25wt% ammonia water solution into the microemulsion system, stirring for 0.5h at the stirring speed of 300rpm, adding 20g of tetraethyl orthosilicate, reacting for 2h, adding 150g of isopropanol, performing ultrasonic treatment for 5min, performing ultrasonic frequency of 25kHz and ultrasonic power of 300W, centrifuging for 10min at 6000rpm, collecting precipitate, washing for 2 times by using isopropanol, and drying at 100 ℃ for 24h to obtain a dried product;
s2, adding 5g of the dried product prepared in the step S1 into 300g of toluene, stirring, then adding 0.1g of azodiisobutyronitrile and 15g of 4-dimethylaminopyridine to obtain a mixture, vacuumizing the mixture for 30min each time, heating to 70 ℃ and stirring for 24h, cooling with ice water to stop the reaction, centrifuging at 6000rpm for 10min, washing the precipitate with toluene for 2 times, and drying at 100 ℃ for 24h to obtain modified particles;
S3, adding 7g of the modified particles prepared in the step S2 and 3g of polyvinylidene fluoride into 50g of N, N-dimethylformamide, carrying out ultrasonic treatment for 10min, wherein the ultrasonic frequency is 30kHz, the ultrasonic power is 250W, adding 0.4g of functional agent, and stirring and mixing at the speed of 400rpm for 10h to obtain modified slurry.
The preparation method of the functional agent is the same as that of the example 1.
Example 4
The preparation of the ceramic coated separator was essentially the same as in example 1, the only difference being that: the preparation methods of the modified slurry are different.
The preparation method of the modified slurry comprises the following steps:
s1, adding 20g of polyoxyethylene cetyl ether into 150g of cyclohexane, heating to 50 ℃, stirring to fully mix the solution, maintaining the temperature, then adding 3g of methacryloxypropyl trimethoxysilane, stirring for 1h at a stirring speed of 200rpm, and cooling to room temperature to form a microemulsion system; dropwise adding 24g of 25wt% ammonia water solution into the microemulsion system, stirring for 0.5h at the stirring speed of 300rpm, adding 20g of tetraethyl orthosilicate, reacting for 2h, adding 150g of isopropanol, performing ultrasonic treatment for 5min, performing ultrasonic frequency of 25kHz and ultrasonic power of 300W, putting into 6000rpm for centrifugation for 10min, collecting precipitate, washing for 2 times by using isopropanol, and drying at 100 ℃ for 24h to obtain a dried product;
S2, adding 5g of the dried product prepared in the step S1 into 300g of toluene, stirring, then adding 0.1g of azodiisobutyronitrile and 15g of 4-dimethylaminopyridine to obtain a mixture, vacuumizing the mixture for 30min each time, heating to 70 ℃ and stirring for 24h, cooling with ice water to stop the reaction, centrifuging at 6000rpm for 10min, washing the precipitate with toluene for 2 times, and drying at 100 ℃ for 24h to obtain modified particles;
s3, adding 7g of the modified particles prepared in the step S2 and 3g of polyvinylidene fluoride into 50g of N, N-dimethylformamide, carrying out ultrasonic treatment for 10min, wherein the ultrasonic frequency is 30kHz, the ultrasonic power is 250W, adding 2g of modified biomass, and stirring and mixing at a speed of 400rpm for 10h to obtain modified slurry.
The preparation method of the modified biomass is the same as in example 1.
Comparative example 1
The preparation of the ceramic coated separator was essentially the same as in example 1, the only difference being that: in the preparation method of the ceramic coated diaphragm, the modified slurry is replaced by slurry.
The preparation method of the slurry comprises the following steps: 3g of polyvinylidene fluoride was added to 50g of N, N-dimethylformamide, and the mixture was subjected to ultrasonic treatment for 10 minutes at an ultrasonic frequency of 30kHz and an ultrasonic power of 250W to obtain a slurry.
Comparative example 2
The preparation of the ceramic coated separator was essentially the same as in example 1, the only difference being that: the preparation method of the ceramic coated diaphragm is free from adding modified slurry.
Comparative example 3
The preparation method of the rechargeable lithium battery comprises the following steps:
assembling in a glove box filled with high-purity argon, wherein the model of the assembled button cell is CR-2025, placing a positive electrode shell on an insulating table, then dripping 2mL of electrolyte, then placing a positive electrode material, placing a ceramic coating diaphragm prepared in example 1, then placing graphite as a negative electrode material, installing a gasket, then installing an elastic sheet, and finally installing a negative electrode shell to obtain the button cell; placing the button cell on a manual button cell sealing machine, locking a switch of the sealing machine, shaking the handle up and down for multiple times, wherein the pressure is 0.8Mpa, taking out the assembled button cell after the assembly is completed, and placing for 12 hours to obtain the rechargeable lithium cell.
The positive electrode shell is composed of an aluminum layer material component and a copper layer material component, the copper layer material component is arranged above the aluminum layer material component, the total thickness of the positive electrode shell cover after compounding is 0.18mm, and the thickness of the aluminum layer material component is 2/5 of the total thickness.
The negative electrode shell comprises a nickel layer material component and an aluminum layer material component, wherein the nickel layer material component is arranged above the aluminum material component, the total thickness of the negative electrode shell after being compounded is 0.18mm, and the thickness of the aluminum layer material component accounts for 2/5 of the total thickness.
The preparation method of the positive electrode material comprises the following steps:
adding 4g of niobium chloride into 40g of absolute ethyl alcohol, stirring for 15min by using a magnetic stirrer at the stirring speed of 1200rpm, adding 10g of water into the solution, then adding 4g of titanium dioxide, stirring for 1h by using the magnetic stirrer at the stirring speed of 800rpm, conveying the solution into a Teflon autoclave, heating for 12h at 180 ℃, washing for 3 times by using water, drying for 1h at 60 ℃ in a vacuum oven, and treating for 1h at 600 ℃ in air to obtain the anode material.
Test example 1
Thermal shrinkage test
The ceramic coated diaphragms prepared in examples and comparative examples were cut into 17mm sized wafer samples, the samples were clamped with two glass plates, placed in an oven, warmed to 200 ℃ and held for 30min. The rate of thermal shrinkage of the separator is expressed as the rate of change of the diameter of the separator. The calculation formula is as follows:
heat shrinkage% = (R Front part -R Rear part (S) )/R Front part ×100％
R Front part Is the diameter before temperature rise; r is R Rear part (S) The diameter is the diameter after heating for 30 min;
each example and comparative example was tested three times and the test results are shown in table 1.
Table 1: results of Heat shrinkage test
| Scheme for the production of a semiconductor device | Heat shrinkage/% |
| Example 1 | 11.6 |
| Example 2 | 15.4 |
| Example 3 | 16.2 |
| Example 4 | 17.6 |
| Comparative example 1 | 24.9 |
| Comparative example 2 | 26.8 |
Test example 2
Self discharge performance
The ceramic coated diaphragm prepared by the invention is assembled into a button cell by matching with conventional materials, the model of the assembled button cell is CR-2025, and the assembled button cell is assembled in a glove box filled with high-purity argon. Wherein, nickel cobalt lithium manganate is the positive pole, graphite is the negative pole, and the equipment steps are: placing the anode shell on an insulating table, dripping 2mL of electrolyte, placing a pole piece, placing the ceramic coating diaphragm prepared by the method, graphite, a gasket, an elastic sheet and a cathode shell; the assembled button cell is lightly arranged on a manual button sealing machine in a glove box, a switch of the sealing machine is locked, and the handle is rocked up and down for a plurality of times, and the pressure is about 0.8 Mpa. After the assembly is completed, the assembled button cell is taken out and placed for 12 hours, after electrolyte fully infiltrates the ceramic coating diaphragm and the pole piece, the relevant electrical performance test of the cell is carried out, and the cell prepared in comparative example 3 is also tested by adopting the same method.
The battery charging process is as follows: the current is 60mAh/g, the time is 7.5h, the junction beam is charged and kept stand for 10 minutes, and the discharge is started after the electrode potential of the battery is stabilized. The discharge current and the charge current are the same, the discharge cutoff potential is-0.6 v, and when the discharge capacity of the battery electrode reaches the maximum value, the battery electrode is considered to reach the fully activated state, and the discharge capacity at that time is taken as the maximum discharge capacity of the battery.
After the battery electrode is circularly activated, charging for 7.5 hours at a current density of 60mAh/g, standing for 1 year at normal temperature, discharging to a voltage of-0.6 v at a current density of 60mAh/g after standing, and representing the self-discharge performance of the electrode by using a charge retention rate. The calculation formula is as follows:
charge retention = C 0 /C 1 ×100％
C 0 The discharge capacity of the battery after one year; c (C) 1 The last discharge capacity before the storage;
each example and comparative example was tested three times and the test results are shown in table 2.
Table 2: self-discharge performance test results
| Scheme for the production of a semiconductor device | Charge retention (%) |
| Example 1 | 97.8 |
| Example 2 | 93.6 |
| Example 3 | 92.4 |
| Example 4 | 92.0 |
| Example 5 | 84.3 |
| Comparative example 1 | 75.2 |
| Comparative example 2 | 74.8 |
| Comparative example 3 | 97.5 |
From the test results in tables 1 and 2, it can be seen that the heat shrinkage rate was the lowest in example 1 and the self-discharge performance was the best. The possible reason is that the ceramic coating slurry is prepared by mixing modified slurry with water, adding nano alumina powder, sodium carboxymethyl cellulose, polyvinyl acetate and perfluoroalkyl ethoxymethyl ether, stirring and mixing, and coating on a polypropylene microporous membrane to prepare the ceramic coating membrane; the modified slurry is prepared by adding polyoxyethylene cetyl ether into cyclohexane, adding methacryloxypropyl trimethoxy silane to form a microemulsion system, adding ammonia water solution and tetraethyl orthosilicate to dry to prepare a dry product, adding 4-dimethylaminopyridine into the dry product to react under the action of an initiator to obtain modified particles, reacting the modified particles with polyvinylidene fluoride in N, N-dimethylformamide, and further mixing the modified particles with modified biomass and a functional agent; wherein the modified biomass is obtained by carbonizing rice hulls, treating the carbonized biomass with sodium hydroxide aqueous solution and compositing the carbonized biomass with asphalt powder; the functional agent is obtained by grinding and calcining zinc oxide powder and boric acid powder.
In general, battery self-discharge is attributed to the following two aspects: first, the faraday process near the interface of the electrode and the electrolyte; another is an internal short circuit that may occur when assembling and manufacturing the capacitor. The former is mainly derived from the surface oxygen-containing functional groups of the electrode material, if not considered. The modified biomass is distributed with pores with different sizes, and the surface of the modified biomass is changed from hydrophilic to hydrophobic. Asphalt powder becomes an oil phase with fluidity at high temperature, and asphalt carbon can slowly permeate into and spread to the pores and the surface of the pretreated material along with the increase of carbonization temperature. The obtained modified biomass has higher specific surface area, can provide more active sites for electrolyte ions, and is favorable for forming higher capacitance. The conductivity of the pretreated substance after the modification of the asphalt powder screw site is improved, which is possibly related to the soft carbon characteristic of asphalt, and the asphalt is rich in polycyclic aromatic hydrocarbon and easy to graphitize. Through asphalt chemical modification, a certain oxygen consumption reaction can occur in the heating carbonization process to obtain modified biomass with low oxygen content, and oxygen-containing groups (such as-COOH, C=O and-OH) on the surface of the modified biomass are removed, so that the oxygen-containing functional groups can prevent ions from being transported to pores to a certain extent, and the modified biomass can be stored for a long time and has lower self-discharge. And the pore structure of the modified biomass after asphalt modification is regulated and optimized, charge redistribution can be inhibited to a certain extent, and the increase of C-O groups is beneficial to the interfacial stability of the modified biomass. The modified particles and polyvinylidene fluoride react in N, N-dimethylformamide, modified biomass and a functional agent are added and mixed to obtain modified slurry, and the prepared ceramic coated diaphragm can improve energy storage efficiency and reduce self-discharge. As the methacryloxypropyl trimethoxysilane is added with ammonia water solution and tetraethyl orthosilicate to be dried to prepare a dried product, double bond polymerization is carried out between the methacryloxypropyl trimethoxysilane and 4-dimethylaminopyridine, modified particles are generated by reaction between the methacryloxypropyl trimethoxysilane and the 4-dimethylaminopyridine, and silicon and zinc boron are distributed on the ceramic coating in a large quantity by adding a functional agent into the modified particles, so that the ceramic coating diaphragm can be helped to maintain the shape of the ceramic coating diaphragm at a higher temperature. Meanwhile, the heat resistance of the ceramic coating diaphragm is improved, and the high-temperature shrinkage rate is reduced. The possible reasons are that the silicon, zinc, boron-containing compounds are released from the ceramic coating slurry during heating, which can maintain their state at higher temperatures and significantly improve the thermal stability. The technology maintains the characteristics of ceramics, and introduces compounds such as silicon, zinc boron and the like, thereby improving the thermal stability of the ceramic coated diaphragm. The addition of the modified biomass imparts lower self-discharge properties for long-term storage. Therefore, the battery assembled by the ceramic coated separator has excellent safety performance and good electrochemical performance, little loss of irreversible capacity and excellent self-discharge performance.
Test example 3
Cycle performance test
The battery prepared in test example 2 and comparative example 3 of example 1 were charged to 4.2V at constant current and constant voltage of 0.5C, cut-off current was 0.05C, and then discharged to 3.0V at constant current of 0.5C at 25C, and after 500 cycles of charge/discharge, the 500 th cycle capacity retention rate was calculated. The test results are shown in Table 3.
Table 3: charge and discharge test results
| Scheme for the production of a semiconductor device | 25 ℃, 500 cycle capacity retention (%) |
| Example 1 | 92.1 |
| Comparative example 3 | 94.7 |
As can be seen from the test data in tables 2 and 3, the battery prepared in comparative example 3 has better self-discharge resistance and charge-discharge cycle performance, probably because the invention combines niobium chloride and titanium dioxide at high temperature to form a cathode material with a conjugated structure, and the cathode material with a conjugated structure is more stable than the conventional nickel cobalt lithium manganate in terms of self-discharge and cycle performance. Although titanium dioxide has high stability, pure titanium dioxide cannot be used directly for energy storage. Titanium dioxide can be embedded with lithium ions in electrolyte to provide stable charge and discharge effects, and the titanium dioxide and niobium chloride have good miscibility, and the uniformly mixed titanium dioxide and the positive electrode material prepared from the niobium chloride have synergistic effect, so that the lithium ion battery has good self-discharge resistance and cycle stability.
Claims (8)
1. An ultra-low self-discharge rate rechargeable lithium battery is characterized by comprising the following components: the positive electrode shell, the negative electrode shell, the gasket, the elastic sheet, the ceramic coating diaphragm, the positive electrode material, the negative electrode material and the electrolyte;
the positive electrode shell comprises an aluminum layer material component and a copper layer material component, the copper layer material component is arranged above the aluminum layer material component, the total thickness of the positive electrode shell cover is 0.1 mm-0.25 mm, and the thickness of the aluminum layer material component accounts for 1/3-2/3 of the total thickness;
the negative electrode shell comprises a nickel layer material component and an aluminum layer material component, wherein the nickel layer material component is arranged above the aluminum material component, the total thickness of the negative electrode shell is 0.1 mm-0.25 mm, and the thickness of the aluminum layer material component accounts for 1/3-2/3 of the total thickness;
the negative electrode material is graphite;
the preparation method of the positive electrode material comprises the following steps of: adding 2-6 parts of niobium chloride into 30-50 parts of absolute ethyl alcohol, stirring for 10-20 min at the stirring speed of 1000-1500 rpm, adding 5-15 parts of water into the solution, then adding 2-6 parts of titanium dioxide, stirring for 0.5-2 h at the stirring speed of 500-1000 rpm, conveying the solution into a Teflon autoclave, heating for 10-20 h at 150-200 ℃, washing for 2-3 times by adopting water, drying for 0.5-2 h at 50-70 ℃ in a vacuum oven, and treating for 0.5-2 h at 400-800 ℃ in air to obtain a positive electrode material;
The ceramic coating diaphragm is made by coating the surface of a substrate diaphragm with a ceramic coating slurry, wherein the ceramic coating slurry comprises: 15-25wt% of aluminum oxide, 30-40% of water, 38-48wt% of modified slurry, 0.5-2wt% of binder, 0.1-1wt% of additive and 0.05-0.3wt% of auxiliary agent;
the alumina is nano alumina powder;
the preparation method of the ceramic coated diaphragm comprises the following steps:
step 1, weighing the raw materials according to the weight percentage, adding the modified slurry into water, stirring for 5-20 min at the stirring speed of 200-500 rpm, adding aluminum oxide, stirring for 10-30 min at the stirring speed of 100-500 rpm, then adding an auxiliary agent, dispersing by double-planetary stirring and a sand mill for 20-50 min, adding a binder, stirring for 20-40 min at the stirring speed of 300-800 rpm, adding an additive, stirring for 10-30 min at the stirring speed of 300-800 rpm, and obtaining the ceramic coating slurry;
step 2, coating the ceramic coating slurry prepared in the step 1 on the surfaces of the two sides of the substrate diaphragm, wherein the coating speed is 20-60 m/min, the thickness of the coating is 3-6 mu m, and drying the coating at 40-80 ℃ for 10-20 min to obtain the ceramic coating diaphragm;
the coating mode is one of screen printing coating, gravure coating, knife coating, spray coating or anilox roller coating; the thickness of the ceramic coating is 1.0-6.0 mu m;
The preparation method of the modified slurry comprises the following steps of:
s1, adding 10-30 parts of polyoxyethylene cetyl ether into 120-180 parts of cyclohexane, heating to 40-60 ℃, stirring to fully mix the solutions, maintaining the temperature, then adding 1-5 parts of methacryloxypropyl trimethoxysilane, stirring for 0.5-2 hours at a stirring speed of 100-300 rpm, and cooling to room temperature to form a microemulsion system; adding 20-30 parts of 25-28wt% ammonia water solution into the microemulsion system, stirring for 0.3-0.8 h, wherein the stirring speed is 100-500 rpm, adding 10-30 parts of tetraethyl orthosilicate, reacting for 1-3 h, adding 120-180 parts of isopropanol, performing ultrasonic treatment for 3-10 min, performing ultrasonic frequency of 20-30 kHz and ultrasonic power of 200-400W, centrifuging for 5-15 min at 5000-800 rpm, washing the precipitate with isopropanol for 1-3 times, and drying at 80-120 ℃ for 10-30 h to obtain a dried product;
s2, adding 3-10 parts of the dried product prepared in the step S1 into 200-400 parts of toluene, stirring, adding 0.02-0.2 part of an initiator and 10-20 parts of 4-dimethylaminopyridine to obtain a mixture, vacuumizing the mixture for 10-40 min each time, heating to 60-80 ℃ and stirring for 10-30 h, cooling with ice water to stop the reaction, centrifuging at 5000-8000 rpm for 5-20 min, washing the precipitate with toluene for 1-3 times, and drying at 80-120 ℃ for 10-30 h to obtain modified particles;
S3, adding 5-10 parts of modified particles and 1-5 parts of polyvinylidene fluoride into 40-60 parts of N, N-dimethylformamide, carrying out ultrasonic treatment for 5-15 min, wherein the ultrasonic frequency is 20-35 kHz, the ultrasonic power is 200-300W, adding 1-3 parts of modified biomass and 0.1-0.8 part of functional agent, and stirring and mixing at the speed of 200-500 rpm for 5-20 h to obtain modified slurry;
the preparation method of the modified biomass comprises the following steps of:
z1, grinding 80-120 parts of rice hulls, sieving with a 50-200 mesh sieve, immersing in 400-600 parts of 5-15 wt% ammonium chloride aqueous solution for 5-15 h, drying at 60-90 ℃ for 5-20 h, adding the dried sample into a tube furnace, heating for 20-40 min at 200-300 ℃ under air atmosphere, switching to a nitrogen environment, continuously heating to 500-700 ℃ for 0.5-2 h, and heating at a heating rate of 3-6 ℃/min to obtain carbide;
z2, heating and refluxing 40-60 parts of the carbide prepared in the step Z1 in 200-400 parts of 2-6wt% sodium hydroxide aqueous solution for 1-3 hours at a reflux temperature of 60-80 ℃, and then drying at 80-120 ℃ for 5-20 hours to obtain a reflux; heating the reflux material for 0.5-2 hours at 700-800 ℃ in a tube furnace under nitrogen atmosphere, washing the obtained sample to be neutral by water, and drying for 5-20 hours at 80-120 ℃ to obtain a pretreated material;
and Z3, grinding 20-40 parts of the pretreated substance prepared in the step Z2 with 3-8 parts of asphalt powder for 0.5-2 hours, adding the mixture into 800-1200 parts of absolute ethyl alcohol, stirring for 0.5-2 hours, wherein the stirring speed is 100-300 rpm, drying for 10-30 hours at 60-90 ℃, heating the dried sample to 80-120 ℃, heating at a heating rate of 0.5-2 ℃/min, maintaining for 0.5-2 hours in a nitrogen atmosphere, and then heating to 700-900 ℃, wherein the heating rate is 2-4 ℃/min, and maintaining for 0.5-2 hours to obtain the modified biomass.
2. A method of preparing the ultra-low self-discharge rate rechargeable lithium battery of claim 1, comprising the steps of: assembling in a glove box filled with high-purity argon, placing an anode shell on an insulating table, then dripping 1-3 mL of electrolyte, then placing an anode material, placing a ceramic coating diaphragm, then placing graphite as a cathode material, installing a gasket, then installing an elastic sheet, and finally installing a cathode shell to obtain a button cell; and placing the button cell on a manual button electric sealing machine, locking a switch of the sealing machine, shaking the handle up and down for multiple times, wherein the pressure is 0.5-0.9 mpa, and taking out the assembled button cell after the assembly is completed, and placing for 10-20 hours to obtain the rechargeable lithium cell.
3. The method of claim 2, wherein the ceramic coated membrane is formed by coating a ceramic coating slurry on a surface of the substrate membrane, the ceramic coating slurry comprising: 15-25wt% of aluminum oxide, 30-40% of water, 38-48wt% of modified slurry, 0.5-2wt% of binder, 0.1-1wt% of additive and 0.05-0.3wt% of auxiliary agent;
the alumina is nano alumina powder;
the preparation method of the modified slurry comprises the following steps of:
s1, adding 10-30 parts of polyoxyethylene cetyl ether into 120-180 parts of cyclohexane, heating to 40-60 ℃, stirring to fully mix the solutions, maintaining the temperature, then adding 1-5 parts of methacryloxypropyl trimethoxysilane, stirring for 0.5-2 hours at a stirring speed of 100-300 rpm, and cooling to room temperature to form a microemulsion system; adding 20-30 parts of 25-28wt% ammonia water solution into the microemulsion system, stirring for 0.3-0.8 h, wherein the stirring speed is 100-500 rpm, adding 10-30 parts of tetraethyl orthosilicate, reacting for 1-3 h, adding 120-180 parts of isopropanol, performing ultrasonic treatment for 3-10 min, performing ultrasonic frequency of 20-30 kHz and ultrasonic power of 200-400W, centrifuging for 5-15 min at 5000-800 rpm, washing the precipitate with isopropanol for 1-3 times, and drying at 80-120 ℃ for 10-30 h to obtain a dried product;
S2, adding 3-10 parts of the dried product prepared in the step S1 into 200-400 parts of toluene, stirring, adding 0.02-0.2 part of an initiator and 10-20 parts of 4-dimethylaminopyridine to obtain a mixture, vacuumizing the mixture for 10-40 min each time, heating to 60-80 ℃ and stirring for 10-30 h, cooling with ice water to stop the reaction, centrifuging at 5000-8000 rpm for 5-20 min, washing the precipitate with toluene for 1-3 times, and drying at 80-120 ℃ for 10-30 h to obtain modified particles;
s3, adding 5-10 parts of modified particles and 1-5 parts of polyvinylidene fluoride into 40-60 parts of N, N-dimethylformamide, carrying out ultrasonic treatment for 5-15 min, wherein the ultrasonic frequency is 20-35 kHz, the ultrasonic power is 200-300W, adding 1-3 parts of modified biomass and 0.1-0.8 part of functional agent, and stirring and mixing at the speed of 200-500 rpm for 5-20 h to obtain modified slurry;
the preparation method of the modified biomass comprises the following steps of:
z1, grinding 80-120 parts of rice hulls, sieving with a 50-200 mesh sieve, immersing in 400-600 parts of 5-15 wt% ammonium chloride aqueous solution for 5-15 h, drying at 60-90 ℃ for 5-20 h, adding the dried sample into a tube furnace, heating for 20-40 min at 200-300 ℃ under air atmosphere, switching to a nitrogen environment, continuously heating to 500-700 ℃ for 0.5-2 h, and heating at a heating rate of 3-6 ℃/min to obtain carbide;
Z2, heating and refluxing 40-60 parts of the carbide prepared in the step Z1 in 200-400 parts of 2-6wt% sodium hydroxide aqueous solution for 1-3 hours at a reflux temperature of 60-80 ℃, and then drying at 80-120 ℃ for 5-20 hours to obtain a reflux; heating the reflux material for 0.5-2 hours at 700-800 ℃ in a tube furnace under nitrogen atmosphere, washing the obtained sample to be neutral by water, and drying for 5-20 hours at 80-120 ℃ to obtain a pretreated material;
and Z3, grinding 20-40 parts of the pretreated substance prepared in the step Z2 with 3-8 parts of asphalt powder for 0.5-2 hours, adding the mixture into 800-1200 parts of absolute ethyl alcohol, stirring for 0.5-2 hours, wherein the stirring speed is 100-300 rpm, drying for 10-30 hours at 60-90 ℃, heating the dried sample to 80-120 ℃, heating at a heating rate of 0.5-2 ℃/min, maintaining for 0.5-2 hours in a nitrogen atmosphere, and then heating to 700-900 ℃, wherein the heating rate is 2-4 ℃/min, and maintaining for 0.5-2 hours to obtain the modified biomass.
4. A method according to claim 3, wherein the method of preparing the ceramic coated separator comprises the steps of:
step 1, weighing the raw materials according to the weight percentage, adding the modified slurry into water, stirring for 5-20 min at the stirring speed of 200-500 rpm, adding aluminum oxide, stirring for 10-30 min at the stirring speed of 100-500 rpm, then adding an auxiliary agent, dispersing by double-planetary stirring and a sand mill for 20-50 min, adding a binder, stirring for 20-40 min at the stirring speed of 300-800 rpm, adding an additive, stirring for 10-30 min at the stirring speed of 300-800 rpm, and obtaining the ceramic coating slurry;
Step 2, coating the ceramic coating slurry prepared in the step 1 on the surfaces of the two sides of the substrate diaphragm, wherein the coating speed is 20-60 m/min, the thickness of the coating is 3-6 mu m, and drying the coating at 40-80 ℃ for 10-20 min to obtain the ceramic coating diaphragm;
the coating mode is one of screen printing coating, gravure coating, knife coating, spray coating or anilox roller coating; the thickness of the ceramic coating is 1.0-6.0 mu m.
5. The method of claim 3 or 4, wherein the binder is at least one of polyvinyl acetate, styrene-acrylic latex, styrene-butadiene latex, or polyvinylpyrrolidone.
6. The method of claim 3 or 4, wherein the additive is at least one of perfluoroalkyl ethoxy methyl ether, polyoxyethylene alkyl amide, fatty alcohol polyoxyethylene ether, sodium butylnaphthalene sulfonate, sodium isethionate, sodium dodecyl sulfonate; the auxiliary agent is sodium carboxymethyl cellulose.
7. The method of claim 3 or 4, wherein the substrate membrane is one of a polypropylene microporous membrane, a polyethylene microporous membrane, a polypropylene microporous membrane, a polyester microporous membrane, a polyimide microporous membrane; the thickness of the microporous membrane is 10-30 mu m.
8. A method according to claim 3, wherein the functional agent is prepared by the following method in parts by weight: mixing 5-10 parts of zinc oxide powder and 10-20 parts of boric acid powder, grinding for 1h, then placing into a quartz crucible, heating in a muffle furnace at 800-1000 ℃ for 1-3 h, and obtaining the functional agent at a heating rate of 3-5 ℃/min.
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