CN112216928A - Modified composite heat-resistant lithium ion battery diaphragm and preparation method thereof - Google Patents
Modified composite heat-resistant lithium ion battery diaphragm and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the field of high polymer materials, and discloses a preparation method of a modified composite heat-resistant lithium ion battery diaphragm, which comprises the following steps: A. modifying aramid fibers; B. modification of inorganic nano materials; C. mixing the modified aramid fiber slurry and the modified inorganic nano slurry with a solvent according to a ratio to prepare organic-inorganic mixed modified slurry; D. and coating the organic-inorganic mixed modified slurry on a base film, and performing moisture solidification, washing, solvent removal and drying to obtain the modified composite heat-resistant lithium ion battery diaphragm. The invention solves the problems of insufficient heat resistance, high moisture, large static electricity and the like of the existing aramid fiber coating diaphragm.
Description
Technical Field
The invention relates to the field of high polymer materials, in particular to a modified composite heat-resistant lithium ion battery diaphragm and a preparation method thereof.
Background
Aramid fiber is used as a novel special polymer material, and the aramid fiber varieties which are commercially produced at present mainly comprise meta-aramid (PMIA, aramid 1313), para-aramid (PPTA, aramid 1414) and copolymerization modified aramid. The molecular structure of the meta-aramid is shown in figure 1-a, and amido bonds are connected to the No. 1 and No. 3 positions of two benzene rings. The meta-aramid fiber has excellent heat resistance, flame resistance, insulativity and textile processability, and is mainly used for fire prevention, electrical insulation, individual protection and high-temperature filtration, dust removal and flue gas treatment in chemical production. The poly-copolymerized aramid fiber also has excellent heat resistance, dimensional stability, aging resistance, radiation resistance, electrical insulation and mechanical properties, and is mainly used for coating rubber products, wires and cables. The molecular structure of the para-aramid is shown in figure 1-b, and amido bonds are connected to the No. 1 and No. 4 positions of two benzene rings. The para-aramid material has high strength and high modulus, and is mainly applied to the fields of advanced composite materials, protective materials, industrial fabrics, building structure reinforcing materials, friction materials, sealing materials and the like.
With the rise of the domestic and foreign diaphragm coating industries, many researches on domestic aramid fiber coating are focused in recent years, the aspects of physical and chemical modification of aramid fiber are focused, unmodified or modified meta-aramid fiber can be directly applied to diaphragm coating, and the fiber is filled in the coating as a filler, so that the heat resistance of the diaphragm is favorably improved; because meta-aramid is easily dissolved in a polar organic solvent, meta-aramid can be dissolved in the polar organic solvent and then prepared into slurry by adding an inorganic filler and coated on a diaphragm to prepare a meta-aramid coating diaphragm, but aramid coating diaphragms prepared by two schemes have some defects: the meta-aramid fiber is directly applied to the coating, and has a series of problems of poor dispersion, agglomeration, uneven coating thickness, unstable heat resistance and the like; the prepared slurry after the meta-aramid fiber is dissolved is coated on the diaphragm, the lyophilic capability of the coating is poor, the porosity is low, the uniformity is general, the problems of insufficient heat resistance, high moisture and large static electricity exist, and the prepared coating diaphragm can not completely embody the advantages of the aramid fiber coating diaphragm when applied to a battery. Therefore, the aramid fiber coating diaphragm prepared by the two schemes is not satisfactory.
The para-aramid has high structural symmetry, higher regularity, higher product orientation degree and crystallinity and better heat resistance. The problem of insufficient heat resistance can be obviously improved by adopting the para-aramid fiber, but if the para-aramid fiber is directly applied to the diaphragm, the problem of consistency with the meta-aramid fiber also exists; and because the para-aramid can only be dissolved in concentrated sulfuric acid and is not dissolved in any other organic solvent, the para-aramid can not be prepared into a solution and can not be coated and applied to the diaphragm in the form of slurry.
In addition, inorganic nano materials used in the traditional process are not generally modified, and the problems of poor powder dispersion, agglomeration and sedimentation and uneven coating exist in practical application, so that the uniformity and the appearance quality of a coating are seriously influenced.
CN 201510453815.X replaces inorganic particle pore-forming agent by adding hydrophilic emulsifier, so that coating uniformity and pore-forming uniformity are improved, interface hydrophilicity between aramid fiber slurry and water is improved, and coagulation bath time required after coating can be reduced; in the preparation method, the emulsifier cannot be uniformly distributed, so that the lyophilic property of the coating surface layer is poor, the emulsifier is easy to separate from the coating layer, and the electrochemical performance in actual use is not high.
CN 201610847515.4 design and prepared two-sided coated lithium battery diaphragm, one side is aramid fiber coating, and the opposite side is inorganic particle coating, has aramid fiber and inorganic coating's advantage concurrently, but need carry out the coating of two aspect respectively in actual production, and the coating mode is complicated, and the coating separates scheduling problem easily to appear, though can solve these problems, whole coating process is difficult to stable production.
CN 201711023392.3 is through the mode that uses graphite alkene-aramid fiber mixed coating, including the base film, graphite alkene-aramid fiber composite coating, through setting up graphite alkene/aramid fiber composite coating, coating thick liquid aramid fiber, solvent, cosolvent, binder, pore-forming agent and graphite alkene and make, this invention has combined the graphite alkene system of hot door, but the graphite system adhesion that uses is very little in the actual industrialization, easy emergence is peeled off, if use the binder too much will take place the phenomenon of stifled hole, unsuitable with actual industrial application.
CN 201711025311.3 is through using microwave radiation heating two-sided coated meta-aramid to coat wet film, and microwave heating method and plasma method all belong to high energy modification field, cause destruction to surface layer structure very easily, although can produce the specific surface area who increases the aramid fiber surface, can not follow the problem that changes lyophilic performance from fundamental, are not suitable for industrial production.
Therefore, the following problems generally exist in the conventional process:
1. the added emulsifier cannot be uniformly distributed, so that the hydrophilicity of the coating surface is poor, the emulsifier is easy to separate from the coating, and the electrochemical performance in actual use is not high;
2. multiple coating, multilayer structure, complex process, difficult solution of the interface cohesiveness and film-forming hole blocking problem among different coatings, difficult guarantee of product quality;
3. the added graphite material has small adhesive force and is easy to peel off, and if the adhesive is used too much, the phenomenon of hole blocking can occur, so that the graphite material is not suitable for practical industrial application;
4. both the microwave heating method and the plasma method belong to the field of high-energy modification, damage to a surface layer structure is easily caused, the specific surface area of the aramid fiber surface is increased, but the lyophilic performance cannot be fundamentally changed, and the method is not suitable for industrial production.
Disclosure of Invention
The invention aims to solve the problems of insufficient heat resistance, high moisture, large static electricity and the like of the conventional aramid fiber coating diaphragm. Most of the existing modified meta-aramid fiber technologies stay in theoretical and laboratory stages at present, the quality and cost control requirements of large-scale industrialization cannot be met, and the consistency of products cannot be guaranteed.
In order to solve the technical problems, the invention adopts the following technical scheme:
a preparation method of a modified composite heat-resistant lithium ion battery diaphragm comprises the following steps:
A. modification of aramid fiber: selecting meta-aramid, adding a sodium hydroxide solution at first for chemical modification, then adding terephthalic acid, adjusting the pH to be weakly acidic, finally adding a p-phenylenediamine solution at a low temperature environment for chemical copolymerization modification, and adjusting the pH to be neutral by using the sodium hydroxide solution after the chemical copolymerization modification is completed to obtain modified aramid slurry;
B. modification of inorganic nano materials: adopting a coupling agent to perform chemical reaction with hydroxyl on the surface of the inorganic nano-particle to obtain modified inorganic nano-slurry;
C. mixing the modified aramid fiber slurry and the modified inorganic nano slurry with a solvent according to a ratio to prepare organic-inorganic mixed modified slurry;
D. and coating the organic-inorganic mixed modified slurry on a base film, and performing moisture solidification, washing, solvent removal and drying to obtain the modified composite heat-resistant lithium ion battery diaphragm.
The common para-aramid or meta-aramid has respective advantages, but the disadvantages of the common para-aramid or meta-aramid cannot be fully exerted, so that the existing material needs to be searched or modified, and the new material has the heat resistance of the para-aramid and the solubility of the meta-aramid at the same time, is easy to coat on a diaphragm in a slurry form, and is convenient for industrialization.
The invention is switched in from a modification method to prepare controllable modified slurry, and designs a ceramic supporting layer and a lyophilic aramid fiber surface layer to synergistically enhance the electrochemical performance and the mechanical performance of the diaphragm. Based on the respective advantages and disadvantages of para-aramid and meta-aramid, the invention designs the structure modification of the para-aramid based on meta-aramid resin, thereby endowing the copolymerization modified aramid with excellent heat resistance and good dissolution processing performance, and further providing the copolymerization modified aramid coated lithium ion battery diaphragm which can be continuously produced.
Firstly, carrying out chemical modification on meta-aramid fiber by using sodium hydroxide, opening a part of high molecular chain segment, then neutralizing by using terephthalic acid to remove excessive alkali, adjusting the solution to be weakly acidic, adding a solution containing p-phenylenediamine at a low temperature for carrying out chemical copolymerization modification, and adding the solution while rapidly stirring until the reaction is finished. Under the alkaline condition, terephthalic acid preferentially reacts with sodium hydroxide inorganic strong base to be consumed, p-phenylenediamine is added till the weak acid environment, the activity of the terephthalic acid can be ensured, and the terephthalic acid reacts with the p-phenylenediamine to generate a three-dimensional structure at a high molecular chain segment where the meta-aramid fiber is opened. The reaction has violent heat release and needs to be carried out in a low-temperature environment, otherwise, the solution is easy to lose heat, implosion occurs, byproducts are generated, and the like. And after the reaction is finished, adjusting the pH value to be neutral by using the sodium hydroxide solution, thereby preparing the meta-aramid copolymerized modified resin solution. Before modification, the meta-aramid fiber is in a straight-chain structure and has obvious orientation regularity, so that the bonding force between long-chain molecules is weak, and the heat resistance is poor. The modified chain structure is rich, a criss-cross multilayer network structure is presented, the bonding force among molecular chains is improved, the heat resistance of the meta-aramid material is further improved, the meta-aramid copolymerized modified resin has a three-dimensional structure and has excellent lyophilic and liquid retention performances, the porosity of a formed film is high, the uniformity is good, the pore structure is four-way and eight-way, more lithium ion channels can be provided, the improvement of the internal resistance and the rate capability of a battery is facilitated, the improvement of the battery application performance of the modified aramid coating composite diaphragm is facilitated, and the safety performance of the battery is improved.
The invention adopts the chemical reaction of the coupling agent and the hydroxyl on the surface of the inorganic particle, and the surface of the inorganic particle is keyed in the hydrophobic organic group after modification, so that the surface property is changed, the surface energy is reduced, the compatibility and the dispersibility of the inorganic particle in an organic system are enhanced, the interface bonding between the nano powder and the modified aramid fiber is improved, and the product uniformity is improved. The hydrophobic organic group mainly comprises unsaturated double bond functional groups, and can perform chemical crosslinking reaction with the modified meta-aramid surface, so that the interface compatibility and the bonding force of the resin and the inorganic filler are further improved, and the cohesive force of the coating and the overall heat resistance of the coating diaphragm are improved.
Preferably, the specific operation of step a is as follows: selecting meta-aramid fiber, firstly adding the sodium hydroxide solution at the temperature of 30-100 ℃ for treatment for 10-120 min, wherein the mass concentration of the sodium hydroxide solution is 0.1-10%, the using amount of the sodium hydroxide solution is 0.01-1% of the mass percentage of the meta-aramid fiber, then adding powdery terephthalic acid, adjusting the pH to 4.0-5.0, finally cooling to 0-5 ℃, adding the p-phenylenediamine solution with the concentration of 1-20%, rapidly stirring while adding until no new yellow precipitate is generated, and adjusting the pH to 6.0-7.0 by using the sodium hydroxide solution after the completion; the mass ratio of the meta-aramid to the terephthalic acid to the p-phenylenediamine is 10-30: 1.6-2.0: 1.
During the process, the pH value of the solution is monitored by a pH meter. The pH value of the weak acid environment adjusted by terephthalic acid is 4.0-5.0, and the preferable pH value is 4.2-4.8. The final neutralization with sodium hydroxide solution is aimed at removing excess terephthalic acid, but the sodium hydroxide is not preferably in excess.
Preferably, in the step B, the mass ratio of the inorganic nanoparticles to the meta-aramid is 1-10: 1; the inorganic nano particles are spherical or quasi-spherical, have the particle size of 0.05-2.0 microns and comprise one or more of bauxite, boehmite, magnesium hydroxide, alumina, silica, zirconia, magnesia, glass powder and silicate; the coupling agent is KH-570, and the concentration is 0.5 wt% -3 wt%.
Preferably, in the step C, the concentration of the modified aramid slurry is 1-15%, and the amount of the modified aramid slurry is 1-10 wt% of the weight of the solvent; the concentration of the modified inorganic nano slurry is 10-50%, and the dosage is 1 wt% -20 wt% of the weight of the solvent.
The dosage of the modified aramid fiber slurry is 1 wt% -10 wt% of the weight of the solvent, and the dosage of the modified inorganic nano slurry is 1 wt% -20 wt% of the weight of the solvent. If the dosage of the aramid fiber slurry is too high, the high-temperature thermal shrinkage rate of the coating diaphragm is increased and the dimensional stability is reduced due to excessive aramid fiber resin, and meanwhile, the air permeability value of the coating diaphragm is increased and the porosity is reduced; if the dosage of the aramid fiber slurry is too low, the adhesive force of the coating is insufficient if the dosage of the aramid fiber slurry is too small, the powder falling problem exists, the film breaking temperature can also be reduced, and the heat resistance is insufficient. If the use amount of the modified inorganic nano slurry is too high, the proportion of the inorganic nano particles is too high, the powder falling problem exists, the coating is brittle at high temperature, and the heat resistance is reduced; if the dosage of the inorganic nano slurry is too low, the proportion of the inorganic nano particles is too low, the number of the inorganic nano particles used as skeleton nodes is reduced, the high-temperature heat shrinkage rate of the coating diaphragm is increased, the heat-resistant support is insufficient, the safety performance is reduced, and the optimization is not preferable.
Preferably, the solvent includes, but is not limited to, one or more of N, N-dimethylacetamide, N-dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, ethanol, isopropanol, dimethyl carbonate, pyridine, deionized water.
The organic solvent is used as the main component, the modified aramid fiber slurry has better compatibility, and a small amount of deionized water can be used for adjustment.
Preferably, the organic-inorganic mixed modified slurry also comprises a film-forming assistant and an antistatic agent; the antistatic agent is a nonionic polymer material.
The antistatic agent is made of a non-ionic polymer material, and the material is stable in performance, good in heat resistance, free of migration effect and lasting in effect. The antistatic agent of high molecular material contains polar chain segment, and can be easily combined with water in air by means of hydrogen bond to form conductive channel, and the antistatic agent can be distributed in the coating layer in the form of fine layer or rib to form conductive network structure, and can be used as channel for leaking static charge. The lithium ion battery base film is generally a high-molecular polyethylene or polypropylene diaphragm which is a nonpolar high polymer and has good insulation property. The meta-aramid copolymer modified resin and the inorganic nano material are prepared into organic-inorganic mixed slurry and coated on one side or two sides of a base film, so that the prepared composite diaphragm usually has very large static electricity which is easy to adsorb dust and impurities,the quality of the product is influenced; meanwhile, a diaphragm with large static electricity is easy to deviate when a battery is wound, so that poor winding is caused, the yield of the battery is low, and the like. Therefore, there is an urgent need to eliminate the static electricity generated from the membrane and the coating from the source. The invention introduces macromolecule antistatic agent, the material contains hydrophilic group and oleophylic group, the polar chain segment is easy to combine with water in the air through hydrogen bond and form conductive channel, the antistatic agent can present fine layered or rib distribution in the coating, the static in the coating diaphragm can be transferred to the surface of the coating through resin to form conductive network structure, thus solving the static problem fundamentally. Meanwhile, the macromolecular antistatic agent has good solubility in a polar solvent and good affinity with the meta-aramid copolymerized modified resin, and can form a homogeneous solution with a film-forming assistant, the meta-aramid copolymerized modified resin and the solvent, so that the uniformity of the coating is ensured. Adding high molecular antistatic agent, preferably containing-OH and-OCH2CH3、-CONH2、-SO3H、-COOH、-N(CH3)2And (3) functional group-like high molecular materials.
Preferably, the film forming aid includes, but is not limited to, one or more of ethylene glycol, glycerol, polyethylene glycol, ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether; the amount of the film-forming assistant is 0.5-5 wt% of the solvent.
The meta-aramid copolymer modified resin has high polarity and is easy to dissolve in a polar solvent, so that slurry which can be coated is prepared, but because the meta-aramid copolymer modified resin contains a large amount of benzene rings which are hard monomers, the film forming uniformity of the resin is easy to be poor, and improvement is needed. The film forming auxiliary agent has the characteristics of high boiling point, excellent environmental protection performance, good miscibility, low volatility and the like, has good affinity with the meta-aramid copolymerized modified resin, can improve the plastic fluidity and elastic deformation of a high molecular chain segment, enables the high molecular chain segment to be fully stretched and uniformly distributed, and enables the resin to be uniform and consistent during film forming. Meanwhile, the film-forming assistant has good solvent compatibility, and can be added according to the formula in proportion, and the film-forming assistant, the meta-aramid copolymerized modified resin and the solvent form a homogeneous solution. The solution is coated on one side or two sides of a diaphragm substrate, then moisture is solidified and washed, a film forming auxiliary agent can be washed out, and nano holes are left, so that the porous and high-porosity structure of the coating is facilitated, the battery application performance of the modified aramid coating composite diaphragm is improved, for example, the battery multiplying power and the cycle life can be obviously improved.
Preferably, the antistatic agent includes, but is not limited to, one or more of polyoxyethylene castor oil, polyoxyethylene laurate, polyoxyethylene, polyether amide imide; the dosage of the antistatic agent is 0.3-3 wt% of the weight of the solvent.
Preferably, in the step D, the organic-inorganic hybrid modified slurry is coated on one side or both sides of the base film; the coating comprises one of dip coating, roll coating or extrusion coating; the base film comprises one of a PE-based lithium ion battery diaphragm or a PP-based lithium ion battery diaphragm, the thickness of the base film is 5-16 mu m, and the porosity of the base film is 35-50%.
The lithium ion battery base film is generally produced by a wet process and mainly comprises a PE base and a PP base. Other suitable lithium ion battery-based membranes can also be coated using the slurry of the present invention.
A modified composite heat-resistant lithium ion battery diaphragm prepared by the preparation method of the modified composite heat-resistant lithium ion battery diaphragm.
Compared with the prior art, the implementation of the invention has the following beneficial effects:
1. the invention carries out chemical modification on aramid fiber resin which is a core material for forming the coating. Before modification, the meta-aramid fiber is in a straight-chain structure and has obvious orientation regularity, so that the bonding force between long-chain molecules is weak, and the heat resistance is poor. The modified chain structure is rich, a criss-cross multilayer network structure is presented, the bonding force among molecular chains is improved, the heat resistance of the meta-aramid resin is improved, the meta-aramid copolymerized modified resin has a three-dimensional structure, excellent lyophilic and liquid retention performances are realized, the porosity of a formed film is high, the uniformity is good, the pore structure is four-way and eight-way, more lithium ion channels can be provided, and the improvement of the internal resistance of a battery and the improvement of the rate capability are facilitated. The inorganic nano ceramic particles are chemically modified, so that the interface compatibility and the chemical binding force of the aramid resin (organic) -inorganic nano ceramic particles are improved, the integral component distribution uniformity and the integral cohesion of the coating are improved, the integral heat resistance of the modified meta-aramid coated diaphragm is obviously improved, and the safety application performance of the battery is improved.
2. According to the invention, by adding the film forming auxiliary agent, the molding fluidity and elastic deformation of the high molecular chain segment can be improved, so that the high molecular chain segment is fully stretched and uniformly distributed, and thus the resin becomes more uniform and consistent during film forming. Meanwhile, the film-forming assistant can be washed out in the process flow, and nano holes are left, so that the porosity and high-porosity structure of the coating are facilitated, and the battery application performance (the multiplying power and the cycle life are improved) of the modified aramid coating composite diaphragm is improved.
3. The invention creatively adds the high molecular antistatic agent, and solves the problem that the organic composite diaphragm in the industry usually has very large static electricity; static electricity easily adsorbs dust and impurities, and the quality of products is influenced; meanwhile, the separator with large static electricity is easy to deviate when the battery is wound, so that poor winding is caused, the yield of the battery is low, and the like. The solution of the static problem is beneficial to improving the quality and the yield of products and reducing the manufacturing cost of the coating diaphragm and the battery core.
4. The invention designs a multilayer coated lithium battery composite diaphragm, selects a proper slurry preparation route and a proper formula by comparing the effect of modification, avoids the hidden danger of reaction with electrolyte in use caused by using a series of additives, can reduce the air permeability of a base membrane to a smaller extent, has good lyophilic rate after modification, has the effects of three-dimensional support and porosity of a nano ceramic material with good crystal form, and has excellent electrochemical performance due to the construction of a three-dimensional net-shaped structure by the composite coating; the composite coating has puncture resistance and high temperature resistance, and the battery assembly test proves that the ionic conductivity of lithium ions is also improved by the composite diaphragm.
5. The invention provides a heat-resistant modified aramid composite lithium ion battery diaphragm and a preparation method thereof, the process technology is controllable, continuous production can be realized, and the prepared aramid coated lithium ion battery diaphragm has the characteristics of strong coating cohesiveness, good pore-forming uniformity, reliable modification method, simple coating mode and convenience for large-scale continuous production.
Drawings
FIG. 1 is a schematic structural diagram of different aramids, wherein a is m-aramid and b is p-aramid;
FIG. 2 is an electron microscope image of the three-dimensional structure of the heat-resistant modified aramid fiber of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings.
Example 1
A preparation method of a modified composite heat-resistant lithium ion battery diaphragm comprises the following steps:
A. modification of aramid fiber: selecting meta-aramid fiber, wherein the structure is shown in figure 1a, adding a sodium hydroxide solution with the mass concentration of 4.5% at 60 ℃ for treatment for 60min, carrying out chemical modification, locally hydrolyzing the meta-aramid fiber, opening part of a high molecular chain segment, then adding terephthalic acid to remove excessive alkali, sampling, monitoring the pH value of the solution through a pH meter, adjusting the pH to be 4.5 in a weak acid environment, finally cooling to 3 ℃, adding a p-phenylenediamine solution, rapidly stirring while adding, carrying out chemical copolymerization modification, and after the completion, adjusting the pH to be 7.0 by using the sodium hydroxide solution to obtain modified aramid fiber slurry, wherein the structure is shown in figure 2.
B. Modification of inorganic nano materials: selecting spherical silicon oxide, adopting a coupling agent KH-570 to perform chemical reaction with hydroxyl on the surface of the nano silicon oxide, and keying hydrophobic organic groups on the surface to obtain the modified inorganic nano slurry.
C. Mixing the following components in proportion, and calculating the proportion of the components to the solvent: 5 wt% of modified aramid fiber slurry, 10 wt% of modified inorganic nano slurry, 3 wt% of film-forming additive and 1.5 wt% of antistatic agent. The solvent is ethanol and DMAc1:1, the film-forming aid is glycerol, and the antistatic agent is polyoxyethylene laurate.
D. And coating the organic-inorganic mixed modified slurry on the two sides of the base film by dip coating. The base film is a PE-based lithium ion battery diaphragm with a thickness of 12 μm and a porosity of 49%. And then carrying out moisture solidification, washing, solvent removal and drying to obtain the modified composite heat-resistant lithium ion battery diaphragm with the total thickness of the double-sided coating of 4 mu.
Example 2
A preparation method of a modified composite heat-resistant lithium ion battery diaphragm comprises the following steps:
A. modification of aramid fiber: selecting meta-aramid, wherein the structure is shown in fig. 1a, adding a sodium hydroxide solution with the mass concentration of 0.1% at 30 ℃ for treatment for 120min, performing chemical modification to partially hydrolyze the meta-aramid, opening part of a high molecular chain segment, adding terephthalic acid to remove excessive alkali, sampling, monitoring the pH value of the solution through a pH meter, adjusting the pH to be 4.2 in a weak acid environment, cooling to 5 ℃, adding a p-phenylenediamine solution, rapidly stirring while adding, performing chemical copolymerization modification, and adjusting the pH to be 6.8 by using the sodium hydroxide solution after the completion to obtain modified aramid pulp, wherein the structure is shown in fig. 2.
B. Modification of inorganic nano materials: selecting spherical bauxite, adopting a coupling agent KH-570 to perform chemical reaction with hydroxyl on the surface of the nano bauxite, and keying hydrophobic organic groups on the surface of the nano bauxite to obtain the modified inorganic nano slurry.
C. Mixing the following components in proportion, and calculating the proportion of the components to the solvent: 1 wt% of modified aramid fiber slurry, 20 wt% of modified inorganic nano slurry, 0.5 wt% of film-forming additive and 3 wt% of antistatic agent. The solvent is N, N-dimethylacetamide, the film forming assistant is a mixture of ethylene glycol and ethylene glycol butyl ether in a ratio of 1:1, and the antistatic agent is polyoxyethylene castor oil.
D. And coating the organic-inorganic mixed modified slurry on one side of the base film by adopting a roller coating method. The basement membrane is a dry PP-based lithium ion battery diaphragm with the thickness of 14 mu m and the porosity of 42 percent. And then carrying out moisture solidification, washing, solvent removal and drying to obtain the modified composite heat-resistant lithium ion battery diaphragm with the thickness of 4 mu at the single-side coating.
Example 3
A preparation method of a modified composite heat-resistant lithium ion battery diaphragm comprises the following steps:
A. modification of aramid fiber: selecting meta-aramid, wherein the structure is shown in fig. 1a, adding a sodium hydroxide solution with the mass concentration of 10% at 100 ℃ for treatment for 10min, performing chemical modification to partially hydrolyze the meta-aramid, opening part of a high molecular chain segment, adding terephthalic acid to remove excessive alkali, sampling, monitoring the pH value of the solution by a pH meter, adjusting the pH value to be 4.8 in a weak acid environment, cooling to 0 ℃, adding a p-phenylenediamine solution, rapidly stirring while adding, performing chemical copolymerization modification, and adjusting the pH value to be 6.0 by using the sodium hydroxide solution after the completion to obtain modified aramid pulp, wherein the structure is shown in fig. 2.
B. Modification of inorganic nano materials: selecting spherical glass powder, adopting a coupling agent KH-570 to perform chemical reaction with hydroxyl on the surface of the nano glass powder, and keying hydrophobic organic groups on the surface to obtain the modified inorganic nano slurry.
C. Mixing the following components in proportion, and calculating the proportion of the components to the solvent: 10 wt% of modified aramid fiber slurry, 1 wt% of modified inorganic nano slurry, 5 wt% of film-forming additive and 0.3 wt% of antistatic agent, and preparing into organic-inorganic mixed modified slurry. The solvent is selected from N-methyl pyrrolidone to be mixed with deionized water in a ratio of 10:1, the film-forming additive is selected from polyethylene glycol, and the antistatic agent is selected from polyoxyethylene to be mixed with polyether amide imide in a ratio of 1: 1.
D. And (3) coating the organic-inorganic mixed modified slurry on the two sides of the base film by extrusion coating. The basement membrane is a dry PP-based lithium ion battery diaphragm with the thickness of 16 mu m and the porosity of 35 percent. And then carrying out moisture solidification, washing, solvent removal and drying to obtain the modified composite heat-resistant lithium ion battery diaphragm with the total thickness of the double-sided coating of 4 mu.
Comparative example 1
A. Mixing the following components in proportion, and calculating the proportion of the components to the solvent: 5 wt% of meta-aramid, 10 wt% of nano silicon oxide, 3 wt% of film-forming assistant and 1.5 wt% of antistatic agent, and preparing into organic-inorganic mixed slurry. The solvent is ethanol and DMAc1:1, the film-forming aid is glycerol, and the antistatic agent is polyoxyethylene laurate.
B. And dip-coating the organic-inorganic mixed slurry on the two sides of the base film. The base film is a PE-based lithium ion battery diaphragm with a thickness of 12 μm and a porosity of 40%. And then the composite heat-resistant lithium ion battery diaphragm with the total thickness of the double-sided coating of 4 mu is obtained through moisture solidification, washing, solvent removal and drying.
Comparative example 2
A. Modification of inorganic nano materials: selecting spherical silicon oxide, adopting a coupling agent KH-570 to perform chemical reaction with hydroxyl on the surface of the nano silicon oxide, and keying hydrophobic organic groups on the surface to obtain the modified inorganic nano slurry.
B. Mixing the following components in proportion, and calculating the proportion of the components to the solvent: 5 wt% of meta-aramid, 10 wt% of modified inorganic nano slurry, 3 wt% of film-forming assistant and 1.5 wt% of antistatic agent, and preparing into organic-inorganic mixed slurry. The solvent is ethanol and DMAc1:1, the film-forming aid is glycerol, and the antistatic agent is polyoxyethylene laurate.
C. And dip-coating the organic-inorganic mixed slurry on the two sides of the base film. The base film is a PE-based lithium ion battery diaphragm with a thickness of 12 μm and a porosity of 41%. And then the composite heat-resistant lithium ion battery diaphragm with the total thickness of the double-sided coating of 4 mu is obtained through moisture solidification, washing, solvent removal and drying.
Comparative example 3
A preparation method of a modified composite heat-resistant lithium ion battery diaphragm comprises the following steps:
A. modification of aramid fiber: selecting meta-aramid, wherein the structure is shown in fig. 1a, adding a sodium hydroxide solution with the mass concentration of 4.5% at 60 ℃ for treatment for 60min, carrying out chemical modification, locally hydrolyzing the meta-aramid, opening part of a high-molecular chain segment, adding terephthalic acid to remove excessive alkali, sampling, monitoring the pH value of the solution through a pH meter, adjusting the pH value to be 5.0 in a weak acid environment, cooling to 3 ℃, adding a p-phenylenediamine solution, rapidly stirring while adding, carrying out chemical copolymerization modification, and adjusting the pH value to be 7.0 by using the sodium hydroxide solution after the completion to obtain modified aramid slurry.
B. Mixing the following components in proportion, and calculating the proportion of the components to the solvent: 5 wt% of modified aramid fiber slurry, 10 wt% of nano silicon oxide, 3 wt% of film-forming additive and 1.5 wt% of antistatic agent, and preparing into organic-inorganic mixed slurry. The solvent is ethanol and DMAc1:1, the film-forming aid is glycerol, and the antistatic agent is polyoxyethylene laurate.
D. And dip-coating the organic-inorganic mixed slurry on the two sides of the base film. The base film is a PE-based lithium ion battery diaphragm with a thickness of 12 μm and a porosity of 44%. And then the composite heat-resistant lithium ion battery diaphragm with the total thickness of the double-sided coating of 4 mu is obtained through moisture solidification, washing, solvent removal and drying.
Comparative example 4
A preparation method of a modified composite heat-resistant lithium ion battery diaphragm comprises the following steps:
A. modification of aramid fiber: selecting meta-aramid, wherein the structure is shown in fig. 1a, adding a sodium hydroxide solution with the mass concentration of 4.5% at 60 ℃ for treatment for 60min, carrying out chemical modification, locally hydrolyzing the meta-aramid, opening part of a high-molecular chain segment, adding terephthalic acid to remove excessive alkali, sampling, monitoring the pH value of the solution through a pH meter, adjusting the pH value to be 5.0 in a weak acid environment, cooling to 3 ℃, adding a p-phenylenediamine solution, rapidly stirring while adding, carrying out chemical copolymerization modification, and adjusting the pH value to be 7.0 by using the sodium hydroxide solution after the completion to obtain modified aramid slurry.
B. Modification of inorganic nano materials: selecting spherical silicon oxide, adopting a coupling agent KH-570 to perform chemical reaction with hydroxyl on the surface of the nano silicon oxide, and keying hydrophobic organic groups on the surface to obtain the modified inorganic nano slurry.
C. Mixing the following components in proportion, and calculating the proportion of the components to the solvent: 5 wt% of modified aramid fiber slurry, 10 wt% of modified inorganic nano slurry and 1.5 wt% of antistatic agent, and preparing into organic-inorganic mixed modified slurry. The solvent is ethanol and DMAc1:1, and the antistatic agent is polyoxyethylene laurate.
D. And coating the organic-inorganic mixed modified slurry on the two sides of the base film by dip coating. The base film is a PE-based lithium ion battery diaphragm with a thickness of 12 μm and a porosity of 39%. And then carrying out moisture solidification, washing, solvent removal and drying to obtain the modified composite heat-resistant lithium ion battery diaphragm with the total thickness of the double-sided coating of 4 mu.
Comparative example 5
A preparation method of a modified composite heat-resistant lithium ion battery diaphragm comprises the following steps:
A. modification of aramid fiber: selecting meta-aramid, wherein the structure is shown in fig. 1a, adding a sodium hydroxide solution with the mass concentration of 4.5% at 60 ℃ for treatment for 60min, carrying out chemical modification, locally hydrolyzing the meta-aramid, opening part of a high-molecular chain segment, adding terephthalic acid to remove excessive alkali, sampling, monitoring the pH value of the solution through a pH meter, adjusting the pH value to be 5.0 in a weak acid environment, cooling to 3 ℃, adding a p-phenylenediamine solution, rapidly stirring while adding, carrying out chemical copolymerization modification, and adjusting the pH value to be 7.0 by using the sodium hydroxide solution after the completion to obtain modified aramid slurry.
B. Modification of inorganic nano materials: selecting spherical silicon oxide, adopting a coupling agent KH-570 to perform chemical reaction with hydroxyl on the surface of the nano silicon oxide, and keying hydrophobic organic groups on the surface to obtain the modified inorganic nano slurry.
C. Mixing the following components in proportion, and calculating the proportion of the components to the solvent: 5 wt% of modified aramid fiber slurry, 10 wt% of modified inorganic nano slurry and 3 wt% of film-forming assistant, and preparing into organic-inorganic mixed modified slurry. The solvent is ethanol and DMAc1:1, the film-forming aid is glycerol, and the antistatic agent is polyoxyethylene laurate.
D. And coating the organic-inorganic mixed modified slurry on the two sides of the base film by dip coating. The base film is a PE-based lithium ion battery diaphragm with a thickness of 12 μm and a porosity of 47%. And then the modified composite heat-resistant lithium ion battery diaphragm with the total thickness of the double-sided coating of 4 mu is obtained through moisture solidification, washing, solvent removal and drying
Effect example 1
The lithium ion battery separators prepared in examples 1 to 3 and comparative examples 1 to 3 were sampled into square sample blocks each having an area of 15cm × 15cm, and performance tests were performed. Wherein the air permeability test temperature is 25 ℃, the test airflow flow rate is 100cc/s, the pressure is 1.5Kpa, and the air permeability deviation is obtained by analyzing a test group (test points are more than 10) of data; the porosity is calculated by the gram weight and the area of the coating; and the thermal shrinkage and the film breaking temperature are tested by adjusting the oven to the specified temperature, simultaneously baking all the samples for 1.0 hour, and simultaneously taking out the samples for testing. The moisture content is the result of a test carried out with a Karl Fischer moisture meter, Vanton, Switzerland. Static magnitude the coated film surface was tested directly using a multimeter.
The results are as follows:
as can be seen from the data in the table, the air permeability values and the deviation fluctuation and the moisture values of the air permeability values of the diaphragms of the examples 1 to 3 are smaller than those of the diaphragms of the comparative examples 1 to 3, which shows that the diaphragms of the examples 1 to 3 are porous, have higher porosity, good pore-forming uniformity and reduced hydrophilic groups; the membrane rupture temperature and the thermal shrinkage rate of 150 ℃/1 hour of the membranes in the embodiments 1-3 are superior to those in the comparative examples 1-3, and further show that the modified slurry has good heat resistance and stability when being coated on the membranes, the modified inorganic nanoparticles play a role in three-dimensional support and form a network porous structure with the modified aramid fibers, and the composite membrane has the advantages of high membrane rupture temperature, low high-temperature thermal shrinkage rate, good air permeability and good heat resistance.
As can be seen from the comparison of the data of the example and the comparative example 5, the air permeability value and the air permeability deviation of the diaphragm of the example are smaller than those of the comparative example 4, the liquid absorption rate is high, and the difference of the other properties is not large, which indicates that the film-forming aid is beneficial to the porosification of the coating and plays a role of a pore-forming agent. As can be seen from comparison of the data of the examples with the data of comparative example 5, the electrostatic voltage of the examples was smaller than that of comparative example 5, indicating that the antistatic agent can effectively reduce the electrostatic voltage of the separator. The modified composite heat-resistant diaphragm prepared by coating the modified slurry has the advantages of low moisture content, low static electricity and high liquid absorption rate.
Effect example 2
The lithium ion battery diaphragms prepared in the embodiments 1 to 3 and the comparative examples 1 to 3 are prepared into lithium ion batteries by the same prior art under the same conditions, and performance tests are carried out, wherein the results are as follows:
according to the table data, the lithium ion battery prepared by applying the lithium ion battery diaphragm disclosed by the invention has the advantages that the internal resistance is smaller, the capacity retention rate is obviously improved, the capacity retention rate is still over 90% after the test of 1C cycle for 500 weeks, and the service life of the lithium ion battery is effectively prolonged.
The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the scope of the present invention, therefore, the present invention is not limited by the appended claims.
Claims (10)
1. A preparation method of a modified composite heat-resistant lithium ion battery diaphragm is characterized by comprising the following steps:
A. modification of aramid fiber: selecting meta-aramid, adding a sodium hydroxide solution at first for chemical modification, then adding terephthalic acid, adjusting the pH to be weakly acidic, finally adding a p-phenylenediamine solution at a low temperature environment for chemical copolymerization modification, and adjusting the pH to be neutral by using the sodium hydroxide solution after the chemical copolymerization modification is completed to obtain modified aramid slurry;
B. modification of inorganic nano materials: adopting a coupling agent to perform chemical reaction with hydroxyl on the surface of the inorganic nano-particle to obtain modified inorganic nano-slurry;
C. mixing the modified aramid fiber slurry and the modified inorganic nano slurry with a solvent according to a ratio to prepare organic-inorganic mixed modified slurry;
D. and coating the organic-inorganic mixed modified slurry on a base film, and performing moisture solidification, washing, solvent removal and drying to obtain the modified composite heat-resistant lithium ion battery diaphragm.
2. The preparation method of the modified composite heat-resistant lithium ion battery separator according to claim 1, wherein the specific operation of the step A is as follows: selecting meta-aramid fiber, firstly adding the sodium hydroxide solution at the temperature of 30-100 ℃ for treatment for 10-120 min, wherein the mass concentration of the sodium hydroxide solution is 0.1-10%, the using amount of the sodium hydroxide solution is 0.01-1% of the mass percentage of the meta-aramid fiber, then adding powdery terephthalic acid, adjusting the pH to 4.0-5.0, finally cooling to 0-5 ℃, adding the p-phenylenediamine solution with the concentration of 1-20%, rapidly stirring while adding until no new yellow precipitate is generated, and adjusting the pH to 6.0-7.0 by using the sodium hydroxide solution after the completion; the mass ratio of the meta-aramid to the terephthalic acid to the p-phenylenediamine is 10-30: 1.6-2.0: 1.
3. The preparation method of the modified composite heat-resistant lithium ion battery separator according to claim 1, wherein in the step B, the mass ratio of the inorganic nanoparticles to the meta-aramid fiber is 1-10: 1; the inorganic nano particles are spherical or quasi-spherical, have the particle size of 0.05-2.0 mu m and comprise one or more of bauxite, boehmite, magnesium hydroxide, alumina, silicon oxide, zirconia, magnesium oxide, glass powder and silicate; the coupling agent is KH-570, and the concentration is 0.5 wt% -3 wt%.
4. The preparation method of the modified composite heat-resistant lithium ion battery separator according to claim 1, wherein in the step C, the concentration of the modified aramid slurry is 1-15% and the amount of the modified aramid slurry is 1-10 wt% of the weight of the solvent; the concentration of the modified inorganic nano slurry is 10-50%, and the dosage is 1 wt% -20 wt% of the weight of the solvent.
5. The method for preparing the modified composite heat-resistant lithium ion battery separator according to claim 4, wherein the solvent comprises one or more of N, N-dimethylacetamide, N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, ethanol, isopropanol, dimethyl carbonate, pyridine and deionized water.
6. The preparation method of the modified composite heat-resistant lithium ion battery separator according to claim 1, wherein the organic-inorganic mixed modified slurry further comprises a film-forming assistant and an antistatic agent; the antistatic agent is a nonionic polymer material.
7. The modified composite heat-resistant lithium ion battery separator and the preparation method thereof according to claim 6, wherein the film forming auxiliary agent comprises one or more of ethylene glycol, glycerol, polyethylene glycol, ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, dipropylene glycol monomethyl ether and dipropylene glycol monopropyl ether; the amount of the film-forming assistant is 0.5-5 wt% of the solvent.
8. The modified composite heat-resistant lithium ion battery separator and the preparation method thereof according to claim 6, wherein the antistatic agent comprises one or more of polyoxyethylene castor oil, polyoxyethylene laurate, polyoxyethylene and polyether amide imide; the dosage of the antistatic agent is 0.3-3 wt% of the weight of the solvent.
9. The preparation method of the modified composite heat-resistant lithium ion battery separator according to claim 1, wherein in the step D, the organic-inorganic mixed modified slurry is coated on one side or both sides of the base film; the coating comprises one of dip coating, roll coating or extrusion coating; the base film comprises one of a PE-based lithium ion battery diaphragm or a PP-based lithium ion battery diaphragm, the thickness of the base film is 5-16 mu m, and the porosity of the base film is 35-50%.
10. The modified composite heat-resistant lithium ion battery separator prepared by the preparation method of the modified composite heat-resistant lithium ion battery separator according to any one of claims 1 to 9.
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