CN114079124B - Organic-inorganic composite lithium ion battery diaphragm and preparation method thereof - Google Patents
Organic-inorganic composite lithium ion battery diaphragm and preparation method thereof Download PDFInfo
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Abstract
The invention discloses an organic-inorganic composite lithium ion battery diaphragm and a preparation method thereof. The organic-inorganic composite lithium ion battery diaphragm comprises polymer master batches P (VdF-HFP) which are uniformly compounded in a nano-scale manner and inorganic lithium ion conductor ceramic particles, wherein the inorganic lithium ion conductor ceramic particles are Li 3 PO 4 、LiZr 2 (PO 4 ) 3 、Li 7 La 3 Zr 2 O 12 、LiBPO 4 、Li 4 SiO 3 、Li 1+x Ti 2‑x Al x (PO 4 ) 3 （0≤x≤0.5）、Li 7 P 2 S 8 I、Li 10 GeP 2 S 12 One or more of the above; the mass ratio of the polymer master batch P (VdF-HFP) to the inorganic lithium ion conductor ceramic particles is 50:1~5:1.
Description
Technical Field
The invention relates to an organic-inorganic composite lithium ion battery diaphragm and a preparation method thereof, in particular to a lithium ion battery composite diaphragm uniformly compounded by poly (vinylidene fluoride-co-hexafluoropropylene) and novel inorganic lithium ion conductor ceramic in a nanoscale and a preparation method thereof.
Background
The diaphragm is a layer of thin film material clamped between the anode and the cathode of the lithium ion battery and plays roles in isolating electrons, preventing short circuit and conducting ions. The performance of the separator itself greatly affects the service behavior of the battery: firstly, the diaphragm itself must have certain rigidity and good toughness to withstand the mechanical impact in the battery forming process and the penetration of lithium dendrites that may occur in the service of the battery; secondly, the diaphragm needs to have better heat resistance, the contraction of the diaphragm is avoided when the temperature is too high,causing the contact of the positive electrode and the negative electrode of the battery to be short-circuited; thirdly, the diaphragm has good conductivity to lithium ions so as to reduce the internal resistance of the battery and improve the open-circuit voltage and the multiplying power performance of the battery; finally, the separator itself should be a layer of inert material that does not chemically or electrochemically react to affect the chemical environment inside the cell. With decades of development, most lithium ion battery manufacturers have chosen porous Polyethylene (PE), porous Polypropylene (PP) separators. The polyolefin diaphragm has the advantages of mature manufacturing process, low price, ideal porosity and mechanical strength, obvious short plates and poor heat resistance of polyolefin. PE will shrink sharply at 150 ℃ and PP at 170 ℃, which causes the contact short circuit of the positive and negative electrodes of the battery. In order to improve the heat resistance of polyolefin separators, manufacturers often coat the surface of polyolefin separators with a ceramic coating having a thickness of 1 to 3 μm, such as AL 2 O 3 AlOOH, etc., to make an organic-inorganic composite separator. Practice shows that the additional ceramic coating can greatly improve the heat resistance of the polyolefin diaphragm, but the defect is very obvious, and the additional coating can often improve the polarization internal resistance of the diaphragm. The reason for this is that although ceramic particles have a good affinity for the electrolyte and the ion conductivity of the separator as a whole is increased, the thickness of the separator is increased and its internal resistance is actually a net increase. Therefore, how to balance the thermal stability and ionic conductance of the separator is a central problem in the research of the separator.
As already mentioned above, organic-inorganic composite membranes coated with ceramic coatings can improve the thermal stability of purely organic membranes, but have a negative effect on the membrane resistance, the underlying reason being that the organic bulk of the membrane is still not "intimate" with the inorganic part, and the ceramic component remains as an additional coating. If the ceramic coating can be immersed into the separator, the win-win effect of high thermal stability and high ionic conductivity can be expected. Simply embedding small-particle ceramic inside the separator cell by dip coating is often difficult to do, because it blocks the separator cell, which increases the curvature of the lithium ion transmission path and increases the internal resistance of the separator. Therefore, the ideal state of recombination of the organic matrix with the inorganic portion should be uniform dispersion in the nanometer scale. To do this, organic and inorganic substances having relatively good affinity must be carefully selected.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a lithium ion battery composite diaphragm formed by uniformly compounding poly (vinylidene fluoride-co-hexafluoropropylene) (hereinafter referred to as P (VdF-HFP)) and novel inorganic lithium ion conductor ceramic in a nano scale and a preparation method thereof. The novel diaphragm has the advantages of ultrahigh thermal stability, low swelling effect, high lithium ion conductivity and the like, can be produced in a roll-to-roll mode continuously, and can be effectively applied to the existing lithium ion battery systems, including buttons, soft packages, columns and the like.
In a first aspect, the invention provides an organic-inorganic composite lithium ion battery separator, which comprises nano-scale uniformly-compounded polymer master batch P (VdF-HFP) and inorganic lithium ion conductor ceramic particles, wherein the inorganic lithium ion conductor ceramic particles are Li 3 PO 4 、LiZr 2 (PO 4 ) 3 、Li 7 La 3 Zr 2 O 12 、LiBPO 4 、Li 4 SiO 3 、Li 1+x Ti 2-x Al x (PO 4 ) 3 (0≤x≤0.5)、 Li 7 P 2 S 8 I、Li 10 GeP 2 S 12 One or more of them.
Wherein the mass ratio of the polymer master batch P (VdF-HFP) to the inorganic lithium ion conductor ceramic particles is 50:1 to 5:1.
Preferably, the inorganic lithium ion conductor ceramic particles are inorganic lithium ion conductor ceramic particles modified by surface modification of organic amine, and the organic amine is one or more of ethylenediamine, triethylamine, diethanolamine and triethanolamine.
Preferably, to prevent the thermal shrinkage failure of the separator, the glass transition temperature of the P (VdF-HFP) polymer should be higher than the typical limit temperature (130 ℃) of the lithium ion battery. Based on the above, the number average molecular weight of the polymer master batch P (VdF-HFP) is 8 x 10 4 ～2×10 5 Preferably 1X 10 5 ～1.5×10 5 。
Preferably, the particle diameter D50 of the inorganic lithium ion conductor ceramic particles is 1 to 100nm, preferably 3 to 15nm.
Preferably, the width of the separator is 6-200 cm, the thickness is 9-45 μm, and the porosity is 30-55%.
In a second aspect, the invention also provides a preparation method of the organic-inorganic composite lithium ion battery separator, which comprises the following steps:
(1) Adding the polymer master batch P (VdF-HFP) into a solvent, heating, refluxing and stirring until the polymer master batch is completely dissolved to obtain a solution A;
(2) Dispersing inorganic lithium ion conductor ceramic particles in dispersion liquid to obtain liquid B;
(3) Mixing the solution A and the solution B, and adding a pore-forming agent to obtain a membrane casting solution;
(4) Forming a film from the casting solution to prepare a wet film, and immersing the wet film in the coagulating liquid to complete phase conversion to form a solid film;
(5) And washing, drying and separating the solid membrane to obtain the organic-inorganic composite lithium ion battery diaphragm.
Preferably, in the step (1), the solvent is one or a mixture of acetone, N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, triethylamine, toluene, dichloromethane and chloroform; the mass ratio of the polymer master batch P (VdF-HFP) to the solvent is 1.
Preferably, in the step (2), the dispersion liquid is one or a mixture of more of acetone, N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, triethylamine, toluene, dichloromethane, chloroform and ethanol; the solid content of the inorganic lithium ion conductor ceramic particles in the dispersion liquid is 1 to 20%, preferably 5 to 15%.
Preferably, in the step (3), the pore-forming agent is one or more of methanol, ethanol, isopropanol, ethylene glycol, polyethylene glycol 200 and polyethylene glycol 400; the pore-forming agent accounts for 4-40% of the mass of the casting solution, and preferably 10-20%.
Preferably, the coagulating liquid is one or more of deionized water, methanol, ethanol, n-propanol and n-butanol; the temperature of the condensation liquid is 25-80 ℃, and preferably 35-60 ℃; preferably, the phase inversion time is from 0.5 to 20s, preferably from 3 to 10s.
Drawings
FIG. 1 is a simplified schematic process flow diagram of the preparation of novel organic-inorganic composite lithium ion battery separators in examples 1-3;
fig. 2 shows a comparison of battery rate performance of the novel organic-inorganic composite lithium ion battery separator prepared in example 2 with a commercial separator assembly;
fig. 3 shows a comparison of the cycle performance of the novel organic-inorganic composite lithium ion battery separator prepared in example 2 with a commercial separator assembled battery;
fig. 4 shows the cross-sectional SEM morphology of the novel organic-inorganic composite lithium ion battery separator prepared in example 2;
fig. 5 shows TEM morphology of inorganic lithium ion conductor ceramic particles modified by organic amine surface modification in an embodiment of the present invention.
Detailed Description
The present invention is further illustrated by the following examples, which are to be understood as merely illustrative of, and not restrictive on, the present invention.
The novel organic-inorganic composite lithium ion battery separator and the preparation method thereof according to the present invention are shown below with reference to fig. 1.
First, dope solution a was prepared. Adding high-molecular master batch P (VdF-HFP) (also called polyvinylidene fluoride-hexafluoroethylene copolymer) into a solvent, and stirring for a period of time under the condition of reflux heating until the high molecules are completely dissolved to prepare casting solution A.
The polymer mother particles P (VdF-HFP) preferably have a number average molecular weight (Mn) of 8X 10 4 ～2×10 5 More preferably 1X 10, to the polymer of (4) 5 ～1.5×10 5 The high molecular polymer of (2). The solvent includes but is not limited to one or a mixture of more of acetone, N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, triethylamine, toluene, dichloromethane and chloroform. Preferably acetone, N-methylpyrroleOne or more of alkanone, N-dimethylformamide and chloroform. In some embodiments, the mass ratio of the polymer master batch to the solvent can be controlled to be 1.
In the heating reflux process, the heating temperature and time are preferably that the polymer master batch is completely dissolved in the solvent. The reflux heating temperature may be 30 to 80 deg.C, more preferably 40 to 60 deg.C. The reflux heating time may be 4 to 12 hours, more preferably 5 to 10 hours.
Then, casting solution B was prepared. Dispersing inorganic lithium ion conductor ceramic particles in the dispersion liquid to prepare casting solution liquid B.
The inorganic lithium ion conductor ceramic particles can be inorganic lithium ion conductor ceramic particles modified by organic amine surface modification, such as Li modified by organic amine surface modification 3 PO 4 、LiZr 2 (PO 4 ) 3 、Li 7 La 3 Zr 2 O 12 、LiBPO 4 、Li 4 SiO 3 、 Li 1+x Ti 2-x Al x (PO 4 ) 3 、Li 7 P 2 S 8 I、Li 10 GeP 2 S 12 One or more of them. Wherein x is more than or equal to 0 and less than or equal to 0.5. According to the invention, organic amine is used as an end-capping reagent, so that the growth process of the inorganic lithium ion conductor ceramic particles can be terminated at a liquid-phase nucleation stage, and the inorganic lithium ion conductor ceramic particles with extremely small particle size and extremely high dispersity are obtained. Meanwhile, due to the hydrogen bond action between the amine group in the organic amine molecule and the F-containing group in the P (VdF-HFP) macromolecule, the inorganic lithium ion conductor ceramic particles can be uniformly dispersed in the macromolecule in a nanoscale range, and the crystallinity of the macromolecule in the liquid-solid phase transition process is reduced, so that the lithium ion conductivity is greatly improved.
Such organic amines include, but are not limited to, ethylene diamine, triethylamine, diethanolamine, triethanolamine, and the like. In some embodiments, li modified by organic amine surface modification is preferred 3 PO 4 、LiZr 2 (PO 4 ) 3 、Li 7 La 3 Zr 2 O 12 、Li 1+x Ti 2-x Al x (PO 4 ) 3 One or more of them. The particle size D50 of the inorganic lithium ion conductor ceramic particles is 1-100 nm, preferably 3-15 nm.
The inorganic lithium ion conductor ceramic particles modified by organic amine surface modification can be prepared by adopting a solution coprecipitation method. And (4) preparing the solution A. The metal precursor is added into a certain amount of solvent successively according to a certain proportion and dosage. The metal precursor must include a lithium salt, including but not limited to lithium chloride and/or lithium acetate. The metal precursor may also include compounds soluble in the selected solvent that contain other higher valent elements. For example, the compound containing other high valence state elements includes but is not limited to one or more of zirconium oxychloride hydrate, titanium tetrachloride, tetrabutyl titanate, aluminum trichloride and tetrabutyl silicate. The solvent is a polar solvent with low dielectric constant, preferably one or a mixture of methanol, ethanol and N, N-dimethylformamide. The concentration of metal ions is 5-50 mmol.L -1 Preferably 30 to 40 mmol.L -1 . The proportion of metal ions (e.g. of lithium and other higher valency elements) is the same as in the corresponding crystalline compound. Dispersion can be carried out by ultrasonic agitation to give a clear and transparent solution. And (4) preparing a solution B. Adding polyoxometalates and micromolecular organic amine into a certain amount of solvent according to a certain proportion, and stirring and mixing. The polyoxoacids include, but are not limited to, carbonic acid, sulfuric acid, phosphoric acid, and the like. Phosphoric acid with the mass fraction of 80-90% is preferred. The molar ratio of the polyoxometalates to the metallic lithium ions may be 3 to 8, preferably 3 to 4. The micromolecule organic amine is a volatile amine substance. Preferably, the small molecular organic amine is one or more of ethylenediamine, triethylamine, diethanolamine and triethanolamine. The mol ratio of the small molecular organic amine to the metal ions is 5 to 30, preferably 10 to 20. The solvent used in the preparation of solution B may be the same as the solvent used in the preparation of solution A. The volume of the solvent used in the preparation process of the solution B can be 1/4-1/2 of that used in the preparation of the solution A. The reaction solutions were mixed. Adding the solution B into the solution A, and keeping stirring at a certain temperature until the two solutions A, B are completely and uniformly mixed and stirred for reaction. The adding mode can be one-time adding or slow dripping. Reaction temperatureIs 20 to 60 ℃, preferably 25 to 40 ℃. The stirring speed can be 100-300 r/min, and the stirring time can be 10-60 min, preferably 30-40 min. The reaction solution was separated, and the gel was collected and the solvent was recovered. For example, the reaction solution is separated and concentrated by an appropriate means to form a gel, and the remaining solvent is recovered. It is understood that a gel structure may also be obtained by leaving the reaction solution at room temperature for a certain period of time. The gel structure can be obtained more quickly and conveniently in a separation mode in practical experiments. The separation method includes but is not limited to one or more of centrifugation, suction filtration and salting out. Preferably, the centrifugation speed is 8000 to 12000r/min. The gel structure is essentially particulate inorganic nanoclusters. The inorganic nanoclusters have an anisotropic structure, and are terminated with electronegative groups containing oxygen atoms. The nature of the inorganic nanoclusters is nanoparticles with anisotropy. Therefore, the gel structure is also called as inorganic lithium ion conductor ceramic particles modified by organic amine surface modification. In order to ensure that the small-molecular organic amine plays the function of the end-capping reagent in the reaction system of the invention, the small-molecular organic amine needs to meet the following requirements: 1. is volatile under the drying condition; 2. capable of forming stable hydrogen bonds with the oxygen atoms at the end of the nanoclusters.
In the process of preparing the casting solution B, the dispersion liquid can be one or a mixture of more of acetone, N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, triethylamine, toluene, dichloromethane, chloroform and ethanol. Preferably one or more of acetone, N-methyl pyrrolidone, N-dimethylformamide and chloroform.
The dispersion method of the inorganic lithium ion conductor ceramic particles can be one or more of stirring, ultrasonic and planetary ball milling. In some embodiments, the inorganic lithium ion conductor ceramic particles have a solid content in the dispersion of 1% to 20%, preferably 5% to 15%. The inorganic lithium ion conductive ceramic particles should be kept free from coagulation for 2 to 15 days, preferably 10 to 15 days, in the dispersion liquid.
Then, the dope solution a and the dope solution B were mixed. Wherein the adding sequence of the casting solution A and the casting solution B is not limited. For example, dope solution B is slowly added to dope solution a in portions with constant stirring. Meanwhile, adding a certain amount of pore-forming agent into the mixed casting solution A and casting solution B, and then keeping stirring until the two solutions A, B are completely and uniformly mixed to obtain the casting solution.
The pore-forming agent can be one or more of methanol, ethanol, isopropanol, ethylene glycol, polyethylene glycol 200, and polyethylene glycol 400. In some embodiments, the pore-forming agent comprises 4 to 40%, preferably 10 to 20%, by mass of the casting solution. In addition, the mass ratio of the casting solution A to the casting solution B is 10. The stirring time may be 4 to 24 hours, preferably 8 to 16 hours.
Subsequently, the casting solution is formed into a film to form a wet film. The casting solution can be pulled on the base band by a casting mode Cheng Shimo, and the wet film thickness is determined by the distance between a casting cutter head and a copper roller. The base tape used for casting can be a tape made of polyethylene terephthalate. The casting tape speed can be 100-700 mm/min, preferably 150-300 mm/min. The distance from the casting head to the copper roll may be 100 to 500. Mu.m, preferably 100 to 300. Mu.m.
And then, immersing the wet film into a condensation pool filled with a condensation liquid, and finishing the phase conversion process under the condition of certain temperature and time. The coagulating liquid includes, but is not limited to, one or more of deionized water, methanol, ethanol, n-propanol and n-butanol, preferably one or more of deionized water, ethanol and n-butanol. The temperature of the coagulation liquid is controlled between 25 and 80 ℃, preferably between 35 and 60 ℃. The phase inversion time may be from 0.5 to 20s, preferably from 3 to 10s. After the phase inversion process was completed, a solid film was obtained.
And finally, washing, drying, separating and rolling. For example, the solid film after phase conversion is immersed in a washing tank containing a washing liquid to wash the residual organic solvent on the film, and then the film is sent to a high-temperature air blowing device to bake out the residual liquid component. And finally, separating and rolling the finished film and the base band.
The washing solution includes, but is not limited to, one or a mixture of deionized water, ethanol and acetone. The washing time may be 0.5 to 3min, preferably 1 to 1.5min. The high temperature blast temperature may be 60 to 150 deg.C, preferably 80 to 120 deg.C. The time for subjecting the solid film to high temperature blasting may be 1 to 10min, preferably 2 to 5min.
The organic-inorganic composite lithium ion battery diaphragm obtained by the preparation method realizes the uniform composition of high polymer P (VdF-HFP) and novel inorganic lithium ion conductor ceramic in a nano scale. In addition, the diaphragm prepared by a Phase inversion method has the color from off-white to milky white, the width of the diaphragm is 6-200 cm, the thickness of the diaphragm is 9-45 mu m, the porosity of the diaphragm is 30-55%, and the diaphragm can be produced in a continuous roll-to-roll mode. Preferably, the novel organic-inorganic composite lithium ion battery separator has the width of 6-100 cm, the thickness of 12-25 μm and the porosity of 40-50%.
Compared with a sequential film forming method, the method has the following outstanding beneficial effects that P (VdF-HFP) and inorganic lithium ion conductor ceramic particles modified by organic amine are selected to prepare mixed slurry, and then one-step film forming is carried out: firstly, the hydrogen bond interaction between the amido in the organic amine molecule and the F-containing group in the P (VdF-HFP) macromolecule enables the inorganic lithium ion conductor ceramic particles to achieve uniform dispersion in the nanometer scale range in the macromolecule, and simultaneously reduces the crystallinity of the macromolecule in the liquid-solid phase transition process, so that the lithium ion conductivity is greatly improved; secondly, the inorganic lithium ion conductor ceramic particles uniformly dispersed in the polymer matrix can effectively reduce the swelling effect of pure polymers in the lithium ion battery electrolyte, and meanwhile, the fracture elongation of the polymer diaphragm is greatly improved.
The technical solution of the present invention is illustrated by specific examples below. It is to be understood that one or more method steps mentioned in the present invention do not exclude the presence of other method steps before or after the combination step or that other method steps may be inserted between the explicitly mentioned steps; it should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Moreover, unless otherwise indicated, the numbering of the various method steps is merely a convenient tool for identifying the various method steps, and is not intended to limit the order in which the method steps are arranged or the scope of the invention in which the invention may be practiced, nor does it limit the relative adaptations or modifications of those steps to the scope of the invention without materially changing the technical details.
It is to be understood that the process equipment or devices not specifically mentioned in the following examples are conventional in the art.
Organic amine surface modification modified LiZr used in each example 2 (PO 4 ) 3 The preparation process comprises the following steps: 0.21g LiCl and 3.2g ZrClO were added 2 ·8H 2 And adding O into 100mL of ethanol, and stirring by ultrasonic to obtain clear and transparent solution A. 1.9mL of phosphoric acid and 8mL of triethylamine were added to 40mL of ethanol, and the mixture was stirred and mixed to obtain solution B. And pouring the liquid B into the liquid A, and keeping stirring at room temperature for 1h to obtain a milky white suspension. Pouring the milky white suspension into a centrifuge tube, centrifuging for 5min at 8000r/min, recovering the residual solvent, and centrifuging the translucent gel at the bottom of the centrifuge tube to obtain the organic amine surface modification modified LiZr 2 (PO 4 ) 3 。
Example 1
The preparation process of the organic-inorganic composite lithium ion battery diaphragm comprises the following steps:
and preparing casting solution A. 10g of polymer master batch P (VdF-HFP) (Mn = 1X 10) 5 ) Adding 80g of N, N-dimethylacetamide, and stirring for 6 hours under the condition of reflux heating at 60 ℃ until the macromolecules are completely dissolved to obtain the casting solution A.
And preparing casting solution B. 3g of LiZr modified by organic amine surface modification 2 (PO 4 ) 3 Ultrasonically dispersing in 17g of ethanol to prepare casting solution B.
And mixing the casting solution A and the casting solution B. And slowly adding the casting solution B into the casting solution A in 5 batches, and continuously stirring. 15g of ethylene glycol were simultaneously added dropwise. And after the membrane casting solution is mixed, keeping stirring for 10 hours until the two liquids A, B are completely and uniformly mixed to form the membrane casting solution.
And (5) film forming by the casting solution. And (3) pulling the casting solution on a base band by a casting mode Cheng Shimo, wherein the distance between a casting cutter head and a copper roller is 100 mu m. The wet film was immersed in a coagulation bath containing deionized water and held at 40 ℃ for 5 seconds to complete the phase inversion process.
Washing, drying, separating and rolling. Immersing the solid film after phase conversion into deionized water: acetone: ethanol =1 (mass ratio). And finally, separating and rolling the finished film and the base band.
Example 2
Example 2 is essentially the same as example 1, except that: the casting head was spaced 300 μm from the copper roll.
As can be seen from the SEM topography of FIG. 4, the LiZr modified by organic amine surface modification 2 (PO 4 ) 3 Tightly bonded to the porous base membrane. As can be seen from fig. 5, the hundred nanometer scale particles in fig. 4 are actually secondary particles formed of smaller sized particles.
Example 3
Example 3 is essentially the same as example 1, except that: the casting head was spaced 500 μm from the copper roll.
Table 1 comparison of performance of novel organic-inorganic composite lithium ion battery separators in examples 1 to 3 with commercial PE separators
The multiplying power performance and the cycle performance of the battery are both completed by a Xinwei CT-4000T testing system. Combining examples 1-3, the battery devices of examples 1-3 had increased rate performance and cycle performance compared to commercial PE separators, as shown in fig. 2 and 3.
Example 4
Example 4 is essentially the same as example 1, except that:
and mixing the casting solution. And slowly adding the casting solution B into the casting solution A in 5 batches, and continuously stirring. 5g of ethylene glycol were simultaneously added dropwise. And after the membrane casting solution is mixed, keeping stirring for 10 hours until the two liquids A, B are completely and uniformly mixed.
And (4) film forming. And (3) pulling the casting solution on a base band by a casting mode Cheng Shimo, wherein the distance between a casting cutter head and a copper roller is 300 mu m.
Example 5
Example 5 is essentially the same as example 1, except that:
and preparing casting solution B. 3g of organic amine surface modified LiZr 2 (PO 4 ) 3 Ultrasonically dispersing in 20g of ethanol to obtain casting solution B.
And (5) mixing the casting solution. And slowly adding the casting solution B into the casting solution A in 5 batches, and continuously stirring. 20g of ethylene glycol were simultaneously added dropwise. And after the membrane casting solution is mixed, keeping stirring for 10 hours until the two liquids A, B are completely and uniformly mixed.
And (4) film forming. And (3) pulling the casting solution on a base band by a casting mode Cheng Shimo, wherein the distance between a casting cutter head and a copper roller is 300 mu m.
Table 2 lists the porosity contrast ratio of the novel organic-inorganic composite lithium ion battery separators in example 2, example 4 and example 5 in table 1.
Table 2 porosity of the novel organic-inorganic composite lithium ion battery separator in example 2, example 4 and example 5.
| Example 2 | Example 4 | Example 5 | |
| Porosity (%) | 45 | 32 | 52 |
Comparative example 1
The preparation process of the lithium ion battery diaphragm comprises the following steps:
and preparing a casting film liquid. 10g of polymer master batch P (VdF-HFP) (Mn = 1X 10) 5 ) Adding 80g of N, N-dimethylacetamide, and stirring for 6 hours under the condition of reflux heating at 60 ℃ until the macromolecules are completely dissolved to obtain the membrane casting solution.
And (5) film forming by the casting solution. And (3) pulling the casting solution on a base band by a casting mode Cheng Shimo, wherein the distance between a casting cutter head and a copper roller is 500 mu m. The wet film was immersed in a coagulation bath containing deionized water and held at 40 ℃ for 5 seconds to complete the phase inversion process.
Washing, drying, separating and rolling. Immersing the solid film after phase conversion into deionized water: acetone: ethanol =1 (mass ratio) in a washing tank, washing for 1min, washing residual organic solvent on the film, immediately sending the film into a high-temperature air blowing device, wherein the air blowing temperature is 80 ℃ and the time is 4min, and baking out residual liquid components. And finally, separating and rolling the finished film and the base band.
Elongation at break of the diaphragm was performed by an Instron-5566 Universal Material testing machine. Table 3 shows the tensile elongation at break of example 3 and comparative example 1.
Table 3 tensile elongation at break comparison of separators in example 3 and comparative example 1
| Example 3 | Comparative example 1 | |
| Elongation at Break (%) | 140 | 95 |
As can be seen from the comparison of the elongation at break data in table 3, the inorganic lithium ion conductor ceramic particles can greatly enhance the elongation at break in tension of the separator, which is probably because the modified amine groups on the surface of the inorganic particles interact with the hydrogen bonds between the F-containing groups in the P (VdF-HFP) polymer, and the introduction of the inorganic substance reduces the crystallinity of the polymer, so that the mechanical properties of the separator are improved.
Example 6
The preparation process of the membrane casting solution comprises the following steps:
and preparing casting solution A. 10g of polymer master batch P (VdF-HFP) (Mn = 1X 10) 5 ) Adding 80g of N, N-dimethylacetamide, stirring for 6h under the condition of reflux heating at 60 ℃ until the macromolecule is completely dissolved,and obtaining casting solution A.
And preparing casting solution B. 3g of LiZr which is not modified by organic amine surface modification 2 (PO 4 ) 3 (D50 =150 nm) was ultrasonically dispersed in 17g of ethanol to prepare casting solution B.
And mixing the casting solution A and the casting solution B. And slowly adding the casting solution B into the casting solution A in 5 batches, and continuously stirring. Simultaneously, 15g of ethylene glycol was added dropwise. And after the membrane casting solution is mixed, keeping stirring for 10 hours until the two solutions A, B are completely and uniformly mixed to form the membrane casting solution.
The casting solution was allowed to stand for 2d, and the dispersibility was observed.
Table 4 shows the dispersibility of the casting solutions of examples 1 and 6 after standing for 2 d.
TABLE 4 comparison of the dispersibility of the casting solutions of example 1 and example 6 after standing for 2d
| Example 1 | Example 6 | |
| Phenomenon(s) | Uniformly dispersed without sedimentation | The inorganic component completely settles and the liquid separates into layers |
As can be seen from table 4, the inorganic particles not modified with the organic amine have poor dispersibility in the casting solution, resulting in failure of the film-forming process. In addition, compared with the diaphragm of inorganic lithium ion problem ceramic which is not modified by the organic amine surface, the diaphragm of inorganic lithium ion conductor ceramic particles modified by the organic amine surface breaks up the order of the polymer in the liquid-solid phase transition process due to the hydrogen bond action between the amine group on the surface of the inorganic lithium ion conductor ceramic particles and the F-containing group in the P (VdF-HFP) polymer, reduces the crystallinity of the polymer, greatly improves the porosity and the elongation at break of the polymer diaphragm, and greatly improves the lithium ion conductivity.
Claims (16)
1. The organic-inorganic composite lithium ion battery diaphragm is characterized by comprising polymer master batches P (VdF-HFP) which are uniformly compounded in a nanometer scale and granular inorganic nanoclusters;
the preparation method of the granular inorganic nanocluster comprises the following steps: 0.21g LiCl and 3.2g ZrClO were added 2 ·8H 2 Adding O into 100mL ethanol, and performing ultrasonic stirring to obtain clear and transparent solution A; adding 1.9mL phosphoric acid and 8mL triethylamine into 40mL ethanol, and stirring and mixing to obtain solution B; pouring the solution B into the solution A, and stirring the solution A at room temperature for 1h to obtain milky white suspension; pouring the milky white suspension into a centrifuge tube, centrifuging for 5min at 8000r/min, and recovering the residual solvent to obtain semitransparent gel at the bottom of the centrifuge tube, namely the granular inorganic nanoclusters;
the mass ratio of the polymer master batch P (VdF-HFP) to the granular inorganic nanoclusters is 50:1~5:1.
2. the separator according to claim 1, wherein the number average molecular weight of the polymer mother particle P (VdF-HFP) is 8 x 10 4 ~2×10 5 。
3. The separator according to claim 2, wherein the number average molecular weight of the polymer masterbatch particles P (VdF-HFP) is 1 x 10 5 ~1.5×10 5 。
4. The separator according to claim 1, wherein the particle diameter D50 of the particulate inorganic nanoclusters is 1 to 100 nm.
5. The separator according to claim 4, wherein the particle diameter D50 of the particulate inorganic nanoclusters is 3 to 15nm.
6. The membrane according to claim 1, wherein the membrane has a width of 6 to 200cm, a thickness of 9 to 45 μm, and a porosity of 30 to 55%.
7. A preparation method of an organic-inorganic composite lithium ion battery separator, which is characterized in that the organic-inorganic composite lithium ion battery separator is the organic-inorganic composite lithium ion battery separator according to any one of claims 1 to 6, and the preparation method comprises the following steps:
(1) Adding the polymer master batch P (VdF-HFP) into a solvent, heating, refluxing and stirring until the polymer master batch is completely dissolved to obtain a solution A;
(2) Dispersing the granular inorganic nanoclusters in the dispersion liquid to obtain a liquid B;
(3) Mixing the solution A and the solution B, and adding a pore-forming agent to obtain a membrane casting solution;
(4) Forming a film from the casting solution to prepare a wet film, and immersing the wet film in the coagulating liquid to complete phase conversion to form a solid film;
(5) And washing, drying and separating the solid membrane to obtain the organic-inorganic composite lithium ion battery diaphragm.
8. The preparation method according to claim 7, wherein in the step (1), the solvent is one or a mixture of acetone, N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, triethylamine, toluene, dichloromethane and chloroform; the mass ratio of the polymer master batch P (VdF-HFP) to the solvent is 1 to 20 to 1.
9. The preparation method according to claim 8, wherein the mass ratio of the polymer masterbatch P (VdF-HFP) to the solvent is 1 to 10 to 1.
10. The preparation method according to claim 7, wherein in the step (2), the dispersion is one or a mixture of acetone, N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, triethylamine, toluene, dichloromethane, chloroform and ethanol; the solid content of the granular inorganic nanoclusters in the dispersion liquid is 1-20%.
11. The method according to claim 10, wherein the solid content of the particulate inorganic nanoclusters in the dispersion is 5 to 15%.
12. The preparation method according to claim 7, wherein in the step (3), the pore-forming agent is one or more of methanol, ethanol, isopropanol, ethylene glycol, polyethylene glycol 200 and polyethylene glycol 400; the pore-forming agent accounts for 4-40% of the mass of the casting solution.
13. The preparation method according to claim 12, characterized in that the pore-forming agent accounts for 10-20% of the mass of the casting solution.
14. The preparation method according to any one of claims 7 to 13, wherein in the step (4), the condensed liquid is one or more of deionized water, methanol, ethanol, n-propanol and n-butanol; the temperature of the condensation liquid is 25 to 80 ℃.
15. The preparation method according to claim 14, wherein the temperature of the condensate is 35 to 60 ℃; the phase transition time is 0.5 to 20 s.
16. The method of claim 15, wherein the phase inversion time is 3 to 10 seconds.
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