CN116014358A - Composite diaphragm for inhibiting lithium dendrite and preparation method and application thereof - Google Patents
Composite diaphragm for inhibiting lithium dendrite and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the technical field of batteries, in particular to a composite diaphragm for inhibiting lithium dendrites, and a preparation method and application thereof. The composite membrane for inhibiting lithium dendrite comprises a base membrane and a composite coating layer arranged on at least one side surface of the base membrane; the composite coating comprises a crosslinked structure coating formed by modified fluoride and an adhesive; the modified fluoride comprises fluoride and a modifier coated on at least part of the surface of the fluoride, wherein the modifier comprises polydopamine. The diaphragm provided by the invention has excellent wettability and thermal stability, can regulate lithium ion transmission when being applied to a lithium metal battery, generates a stable SEI layer in situ, promotes uniform deposition of lithium ions, thereby inhibiting growth of lithium dendrites and improving cycle stability of the lithium metal battery.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to a composite diaphragm for inhibiting lithium dendrites, and a preparation method and application thereof.
Background
In various chemical power systems, the lithium ion battery has the advantages of environmental friendliness, high specific energy, long cycle life, rapid charge and discharge, no memory effect and the like, and is widely applied to the fields of electric automobiles, portable electronic products, aerospace and the like. However, due to limitations of electrode materials, process conditions and the like, the development of energy density of the traditional lithium ion battery using the graphite-based anode tends to be limited, and the increasing requirements of high-energy applications such as electric power energy storage, electric automobiles and the like cannot be met.
Lithium metal anodes are considered to be ideal cathodes for the development of next-generation high-energy secondary batteries, due to their ultra-high theoretical specific capacity and low redox potential. However, the high reactivity of lithium metal and serious lithium dendrite problems, and the large volume change during charge and discharge severely restrict the development thereof. First, lithium dendrites formed by non-uniform deposition on the surface of lithium metal may puncture the separator, resulting in internal short circuits and safety hazards. Second, highly reactive metallic lithium spontaneously reacts with the electrolyte to form an unstable solid electrolyte layer (SEI). However, the fragile SEI cannot adapt to the huge volume change of the lithium anode, cracks or breaks occur, so that fresh lithium is exposed in the electrolyte and reacts with the electrolyte, thereby causing growth of lithium dendrite, reconstruction of SEI and consumption of electrolyte, and greatly reducing the cycle life and coulombic efficiency of the lithium metal battery.
At present, the method for improving the problem of the lithium metal battery mainly adopts strategies such as optimizing electrolyte, protecting a negative electrode and designing a current collector structure, constructing an artificial solid electrolyte layer, modifying a diaphragm and the like. The optimized electrolyte typically employs a solid electrolyte, a gel electrolyte, an electrolyte additive, or the like, however its low ionic conductivity limits its application. By designing the three-dimensional current collector structure, the specific surface area of the electrode can be increased, the local current density is reduced, the uniform deposition of lithium is induced, and uneven surface of the electrode can lead to uneven distribution of lithium ions. The construction of the artificial protection layer and the artificial solid electrolyte layer on the negative electrode has positive effects on the aspect of inhibiting lithium dendrites, but the stability exertion is influenced by the larger surface resistance and the lower mechanical strength. In addition, the above strategies often need to be performed in harsh environments, which is detrimental to large-scale production.
In view of this, the present invention has been made.
Disclosure of Invention
An object of the present invention is to provide a composite separator for inhibiting lithium dendrites, so as to solve the above technical problems.
The invention also aims to provide a preparation method of the composite membrane for inhibiting lithium dendrites, which is simple and easy to implement.
Another object of the present invention is to provide a lithium metal battery, including the composite separator for inhibiting lithium dendrite, which can inhibit growth of lithium dendrite and improve cycle stability of the lithium metal battery.
In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:
the composite membrane for inhibiting lithium dendrite comprises a base membrane and a composite coating layer arranged on at least one side surface of the base membrane; the composite coating comprises a crosslinked structure coating formed by modified fluoride and an adhesive; the modified fluoride comprises fluoride and a modifier coated on at least part of the surface of the fluoride, wherein the modifier comprises polydopamine.
In one embodiment, the fluoride comprises at least one of magnesium fluoride, aluminum fluoride, copper fluoride, iron fluoride, cobalt fluoride, silver fluoride, vanadium fluoride, nickel fluoride, manganese fluoride, gallium fluoride, titanium fluoride, scandium fluoride, chromium fluoride, calcium fluoride, strontium fluoride, iridium fluoride, zirconium fluoride, niobium fluoride, molybdenum fluoride, cadmium fluoride, indium fluoride, palladium fluoride, rhodium fluoride, ruthenium fluoride, technetium fluoride, barium fluoride, radium fluoride, tungsten fluoride, osmium fluoride, and rhenium fluoride;
in one embodiment, the modified fluoride has a D50 particle size of 0.1 to 5 μm.
In one embodiment, the modifier is at least one of a phenolic resin and a urea-formaldehyde resin.
In one embodiment, the mass ratio of the modified fluoride to the adhesive in the composite coating is (2-50): (2-15).
In one embodiment, the composite coating has a thickness of 0.01 to 10 μm.
In one embodiment, the base film has a thickness of 3 to 20 μm.
In one embodiment, the base film comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyimide, aramid, polyetheretherketone, polyethylene terephthalate, cellulose, and polyurethane.
In one embodiment, the adhesive includes at least one of polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene-acrylic latex, polyacrylonitrile, polyethyl acrylate, polyvinyl acetate, polyacrylate, and polyurethane.
The preparation method of the composite diaphragm for inhibiting lithium dendrites comprises the following steps:
(a) Grinding the modifier solution, fluoride and the mixture, collecting the solid, washing and drying to obtain modified fluoride; the modifier solution comprises a mixed solution of dopamine, an alcohol solvent and a Tris buffer solution;
(b) Mixing the modified fluoride obtained in the step (a) with an adhesive and water to obtain a coating liquid; and coating the coating liquid on at least one side surface of the base film, and then drying.
In one embodiment, the concentration of dopamine in the modifier solution is 1% to 15%.
In one embodiment, the volume ratio of the alcoholic solvent to the Tris buffer is (0.1-3): 1, a step of; the pH of the Tris buffer is 7-10.
In one embodiment, the modifier solution is obtained by mixing dopamine, an alcoholic solvent and a Tris buffer for 10-15 hours.
In one embodiment, the milling comprises ball milling and/or sanding.
In one embodiment, the grinding medium used for grinding is zirconium beads, and the mass ratio of the zirconium beads to the fluoride and modifier solution is (50-130): 5-10): 1-5.
In one embodiment, the rotational speed of the grinding is greater than or equal to 10rpm.
In one embodiment, the milling is for a period of time ranging from 1 to 28 hours.
In one embodiment, the mass content of the modified fluoride in the coating liquid is 2-50%, and the mass content of the adhesive is 2-15%.
In one embodiment, the coating liquid further comprises an auxiliary agent, wherein the mass content of the auxiliary agent is 0.001% -2%;
in one embodiment, the adjuvant includes at least one of fluoroalkyl ethoxy alcohol ether, polyoxyethylene alkyl amide, fatty alcohol polyoxyethylene ether, sodium Ding Bennai sulfonate, sodium isethionate, and sodium dodecylbenzene sulfonate.
In one embodiment, the coating comprises at least one of micro gravure coating, extrusion coating, wire bar coating, dip coating, and spray coating;
in one embodiment, the temperature of the drying process is 40 to 90 ℃.
A lithium metal battery comprising the composite separator for inhibiting lithium dendrite.
Compared with the prior art, the invention has the beneficial effects that:
(1) The composite diaphragm contains a large amount of polar groups, has excellent electrolyte wettability and ion conductivity, can enable ion transmission to be more uniform, and reduces generation of lithium dendrites; the composite diaphragm has excellent mechanical strength and heat resistance, and the inorganic fluoride and the polydopamine have good high temperature resistance, so that the heat resistance of the diaphragm at high temperature can be improved, the polydopamine can be crosslinked with the polar adhesive to form a three-dimensional structure, the puncture resistance of the composite diaphragm can be improved, the modified coating and the matrix can be firmly fixed, the cohesiveness between the coating and the matrix is improved, and the influence of the falling of the coating on the battery performance is prevented.
(2) The preparation method of the composite diaphragm is simple, low in cost and easy to industrialize.
(3) When the composite diaphragm is applied to a lithium metal battery, the fluoride coating can spontaneously react in situ to generate an artificial SEI layer rich in LiF when contacting with metal lithium, and the artificial SEI layer is covered on the surface of a lithium metal anode, so that direct contact between a lithium metal negative electrode and electrolyte is prevented, and less side reaction occurs. LiF has wide bandgap insulation, high chemical stability, and low lithium ion diffusion barrier, which can prevent electrons from tunneling through the SEI layer and promote uniform deposition of lithium ions. Meanwhile, the metal atomic layer generated by the reaction of the fluoride and the lithium has excellent lithium affinity, so that lithium nucleation at a hot spot on the surface of blank lithium in the early lithium deposition process can be avoided. Therefore, the safety and long-term cycle performance of the lithium metal battery can be improved when the lithium metal battery is applied to the lithium metal battery.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
In one aspect, the invention relates to a composite separator for inhibiting lithium dendrites, comprising a base film and a composite coating layer arranged on at least one side surface of the base film; the composite coating comprises a crosslinked structure coating formed by modified fluoride and an adhesive; the modified fluoride comprises fluoride and a modifier coated on at least part of the surface of the fluoride, wherein the modifier comprises polydopamine.
The composite diaphragm provided by the invention contains a large number of polar groups, has excellent electrolyte wettability and ion conductivity, can make ion transmission more uniform, and reduces the generation of lithium dendrites. The composite diaphragm has excellent mechanical strength and heat resistance. The inorganic fluoride and the polydopamine have good high temperature resistance, the heat resistance of the diaphragm at high temperature can be improved, the polydopamine can be crosslinked with the polar adhesive to form a three-dimensional structure, the puncture resistance of the composite diaphragm can be improved, the modified coating and the matrix can be firmly fixed, the adhesiveness between the coating and the matrix is improved, and the influence of the falling of the coating on the battery performance is prevented.
When the composite diaphragm is applied to a lithium metal battery, lithium ion transmission can be regulated, a stable SEI layer is generated in situ, uniform deposition of lithium ions is promoted, growth of lithium dendrites is inhibited, and cycle stability of the lithium metal battery is improved.
In one embodiment, the coating ratio of the polydopamine on the fluoride surface is 10% to 100%, for example 30%, 40%, 50%, 60%, 70%, 80%, 100%, etc.
In one embodiment, the fluoride comprises at least one of magnesium fluoride, aluminum fluoride, copper fluoride, iron fluoride, cobalt fluoride, silver fluoride, vanadium fluoride, nickel fluoride, manganese fluoride, gallium fluoride, titanium fluoride, scandium fluoride, chromium fluoride, calcium fluoride, strontium fluoride, iridium fluoride, zirconium fluoride, niobium fluoride, molybdenum fluoride, cadmium fluoride, indium fluoride, palladium fluoride, rhodium fluoride, ruthenium fluoride, technetium fluoride, barium fluoride, radium fluoride, tungsten fluoride, osmium fluoride, and rhenium fluoride. In one embodiment, the fluoride comprises at least two of the above fluorides, each having a mass ratio of 1:1.
In one embodiment, the D50 particle size of the modified fluoride is 0.1 to 5 μm, for example 0.1 μm, 0.2 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.
In one embodiment, the modifier is at least one of a phenolic resin and a urea-formaldehyde resin.
In one embodiment, the mass ratio of the modified fluoride to the adhesive in the composite coating is (2-50): (2-15).
In one embodiment, the composite coating has a thickness of 0.01 to 10 μm, for example 0.01 μm, 1 μm, 2 μm, 3 μm, 5 μm, 8 μm or 10 μm, etc.
In one embodiment, the base film has a thickness of 3 to 20 μm, for example, 3 μm, 5 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc.
In one embodiment, the base film comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyimide, aramid, polyetheretherketone, polyethylene terephthalate, cellulose, and polyurethane. The base film may be any one of the above base films, or a composite base film of at least two of the above base films.
In one embodiment, the adhesive includes at least one of polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene-acrylic latex, polyacrylonitrile, polyethyl acrylate, polyvinyl acetate, polyacrylate, and polyurethane. The adhesive of the present invention may be any one of the above adhesives, or may be a combination of a plurality of kinds, for example, a mixture of polyvinyl alcohol and styrene-butadiene rubber, a mixture of styrene-acrylic latex, polyacrylonitrile and ethyl polyacrylate, or the like.
According to another aspect of the invention, the invention also relates to a preparation method of the composite membrane for inhibiting lithium dendrites, which comprises the following steps:
(a) Grinding the modifier solution, fluoride and the mixture, collecting the solid, washing and drying to obtain modified fluoride; the modifier solution comprises a mixed solution of dopamine, an alcohol solvent and a Tris buffer solution;
(b) Mixing the modified fluoride obtained in the step (a) with an adhesive and water to obtain a coating liquid; and coating the coating liquid on at least one side surface of the base film, and then drying.
The method is simple and easy to implement, and the dopamine can undergo self-oxidation-reduction reaction under the slightly alkaline condition to generate polydopamine, and the polydopamine is coated on the surface of the fluoride to strengthen the polarity, so as to obtain the modified fluoride; mixing the modified fluoride with an adhesive and water, coating the surface of a base film, and drying to obtain a three-dimensional crosslinked structure coating; the composite membrane has excellent wettability and thermal stability.
In one embodiment, the concentration of dopamine in the modifier solution is 1% to 15%. For example, 1%, 2%, 3%, 5%, 6%, 7%, 8%, 10%, 12%, 15%, etc.
In one embodiment, the volume ratio of the alcoholic solvent to the Tris buffer is (0.1-3): 1, e.g., 0.1:1, 0.5:1, 0.8:1, 1:1, 2:1, 3:1, etc. The pH of the Tris buffer is 7 to 10, for example 7.5, 8, 9, 10, etc.
In one embodiment, the modifier solution is obtained by mixing dopamine, an alcoholic solvent and Tris buffer for 10-15 hours, such as 12 hours, 14 hours, etc.
In one embodiment, the milling comprises ball milling and/or sanding. Grinding by a grinder, wherein the grinder is a ball mill or a sand mill.
In one embodiment, the grinding medium used for grinding is zirconium beads, and the mass ratio of the zirconium beads to the fluoride and modifier solution is (50-130): (5-10): (1-5). Such as 50:5:1, 60:7:2, 100:8:3, 130:10:5, etc. The zirconium beads, fluoride and modifier solution adopt proper mass ratio, so that the fluoride is more favorable for grinding to the required granularity and shape, and a polydopamine coating layer is formed on the surface of the fluoride.
In one embodiment, the rotational speed of the grinding is greater than or equal to 10rpm, such as 10 to 600rpm, for example 50rpm, 100rpm, 120rpm, 150rpm, 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, etc. In one embodiment, the milling is for a period of time ranging from 1 to 28 hours, such as 2 hours, 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, and the like. The invention can further prepare the modified fluoride with proper size by adopting proper grinding rotation speed and grinding time, and simultaneously ensures the coating effect of the polydopamine.
In one embodiment, the mass content of the modified fluoride in the coating liquid is 2% to 50%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc.
In one embodiment, the mass content of the adhesive is 2% -15%, such as 2%, 5%, 8%, 10%, 12%, 15%, etc.
In one embodiment, the coating liquid further includes an auxiliary agent, and the mass content of the auxiliary agent is 0.001% -2%, for example, 0.01%, 0.05%, 0.08%, 1%, 1.2%, 1.5%, 1.8%, 2.0%, etc.
In one embodiment, the auxiliary comprises at least one of fluoroalkyl ethoxy alcohol ether, polyoxyethylene alkyl amide, fatty alcohol polyoxyethylene ether, ding Bennai sodium sulfonate, sodium isethionate, and sodium dodecylbenzene sulfonate. By adding the auxiliary agent, the uniform dispersion of the mixed system is facilitated.
In one embodiment, the solid is collected for washing and drying, specifically comprising: repeatedly cleaning with deionized water, and vacuum drying.
In one embodiment, the coating means comprises at least one of micro gravure coating, extrusion coating, wire bar coating, dip coating, and spray coating.
In one embodiment, the temperature of the drying process is 40 to 90 ℃, e.g., 50 ℃, 55 ℃,60 ℃, 65 ℃, 70 ℃, 75 ℃, or the like.
According to another aspect, the present invention also relates to a lithium metal battery comprising the composite separator for suppressing lithium dendrites.
When the composite diaphragm is applied to a lithium metal battery, the fluoride coating can spontaneously react in situ to generate an artificial SEI layer rich in LiF when contacting with lithium metal, and the artificial SEI layer is covered on the surface of a lithium metal anode, so that direct contact between a lithium metal negative electrode and electrolyte is prevented, and less side reaction occurs. LiF has wide bandgap insulation, high chemical stability, and low lithium ion diffusion barrier, which can prevent electrons from tunneling through the SEI layer and promote uniform deposition of lithium ions. Meanwhile, the metal atomic layer generated by the reaction of the fluoride and the lithium has excellent lithium affinity, so that lithium nucleation at a hot spot on the surface of blank lithium in the early lithium deposition process can be avoided. Therefore, the safety and long-term cycle performance of the lithium metal battery can be improved when the lithium metal battery is applied to the lithium metal battery.
The following is a further explanation in connection with specific examples, comparative examples.
Example 1
The preparation method of the composite diaphragm comprises the following steps:
(1) Preparing a modifier solution: ethanol and Tris buffer solution are mixed according to the volume ratio of 1:1 to obtain a mixed solvent, and dopamine is added and stirred for 12 hours to prepare a dopamine solution with the concentration of 8%;
(2) Preparation of modified fluoride: adding zirconium beads, dopamine solution and aluminum fluoride into a ball milling tank in a mass ratio of 120:5:1 for ball milling, wherein the ball milling speed is 500rpm, and the ball milling time is 10 hours; then the ball-milled material is washed by deionized water, and is put into a vacuum oven for drying at 70 ℃ for 6 hours, so that polydopamine coated modified aluminum fluoride is obtained, and the size D50 of the modified aluminum fluoride is 800nm measured by a particle sizer;
(3) Preparing a composite diaphragm: mechanically stirring and mixing modified aluminum fluoride and deionized water to prepare a suspension with the concentration of 40%, then adding adhesive sodium carboxymethyl cellulose and polyethyl acrylate (the mass ratio of the two is 1:1), and preparing auxiliary agent polyoxyethylene alkylamide and water into a 30% coating solution by using a high-speed dispersing agent or a stirrer; based on the total mass of sodium carboxymethyl cellulose, polyacrylic acid adhesive and auxiliary agent, the mass content of modified aluminum fluoride is 94%, the mass content of the adhesive is 5.5%, and the mass content of the auxiliary agent is 0.5%; the thickness of the composite coating before and after modification was measured by using a bar coated on one side of a 9 μm polyethylene-based film, dried at 60℃and measured by using a micrometer to obtain a modified coating thickness of 3. Mu.m.
Example 2
The preparation method of the composite membrane is the same as in example 1 except that the ball milling time is 24 hours.
Example 3
The preparation method of the composite membrane is the same as in example 1 except that the ball milling time is 2 h.
Example 4
The preparation method of the composite separator was the same as in example 1 except that aluminum fluoride was replaced with magnesium fluoride.
Example 5
The preparation method of the composite diaphragm comprises the following steps:
(1) Preparing a modifier solution: ethanol and Tris buffer solution are mixed according to the volume ratio of 1:1 to obtain a mixed solvent, and dopamine is added and stirred for 12 hours to prepare a dopamine solution with the concentration of 1%;
(2) Preparation of modified fluoride: adding zirconium beads, dopamine solution and aluminum fluoride into a ball milling tank in a mass ratio of 50:5:1 for ball milling, wherein the ball milling speed is 100rpm, and the ball milling time is 20 hours; then the ball-milled material is washed by deionized water, and is put into a vacuum oven for drying at 70 ℃ for 6 hours, so that polydopamine coated modified aluminum fluoride is obtained, and the size D50 of the modified aluminum fluoride is 300nm measured by a particle sizer;
(3) Preparing a composite diaphragm: mechanically stirring and mixing modified aluminum fluoride and deionized water to prepare a suspension with the concentration of 40%, then adding adhesive polybutylmethacrylate and styrene-acrylic latex (the mass ratio of the two is 1:1), and preparing auxiliary Ding Bennai sulfonic acid and water into a 30% coating solution by using a high-speed dispersing agent or a stirrer; based on the total mass of sodium carboxymethyl cellulose, polyacrylic acid adhesive and auxiliary agent, the mass content of modified aluminum fluoride is 80%, the mass content of the adhesive is 19.5%, and the mass content of the auxiliary agent is 0.5%; the thickness of the composite coating before and after modification was measured by using a bar coated on one side of a 9 μm polyethylene-based film, dried at 90℃and measured by using a micrometer to obtain a modified coating thickness of 3. Mu.m.
Example 6
The preparation method of the composite diaphragm comprises the following steps:
(1) Preparing a modifier solution: ethanol and Tris buffer solution are mixed according to the volume ratio of 1:1 to obtain a mixed solvent, and dopamine is added and stirred for 12 hours to prepare a dopamine solution with the concentration of 15%;
(2) Preparation of modified fluoride: then adding zirconium beads, dopamine solution and aluminum fluoride into a ball milling tank for ball milling in a mass ratio of 130:5:1, wherein the ball milling speed is 600rpm, and the ball milling time is 5 hours; then the ball-milled material is washed by deionized water, and is put into a vacuum oven for drying at 70 ℃ for 6 hours, so that polydopamine coated modified aluminum fluoride is obtained, and the size D50 of the modified aluminum fluoride is 480nm measured by a particle sizer;
(3) Preparing a composite diaphragm: mechanically stirring and mixing modified aluminum fluoride and deionized water to prepare a suspension with the concentration of 40%, then adding adhesive polyvinyl acetate, auxiliary agent fluoroalkyl ethoxy alcohol ether and water, and preparing a 30% coating solution by using a high-speed dispersing agent or a stirrer; the mass content of the modified aluminum fluoride is 85%, the mass content of the adhesive is 14.5%, and the mass content of the auxiliary agent is 0.5% based on the total mass of sodium carboxymethyl cellulose, the polyacrylic acid adhesive and the auxiliary agent; the modified coating thickness was 3 μm by coating a wire bar on one side of a 9 μm polyethylene-based film, drying at 40℃and measuring the thickness of the composite coating before and after modification using a micrometer.
Comparative example 1
Preparation of unmodified aluminum fluoride coating diaphragm: the conditions were the same as in example 1 except that the modification was not performed with the modifier solution.
Comparative example 2
A 9 μm polyethylene separator.
Experimental example
1. Diaphragm performance test
1. Testing coating thickness
The test is carried out by using a micrometer, a ten-thousandth ruler or a thickness gauge, and the test method refers to GB/T36363-20186.4.1.
Heat shrinkage performance at 2.150 ℃/1h
The separator was cut into square strips of 100mmX100mm, placed in an oven at 150 ℃ for baking for 1 hour, taken out to measure the length in the Transverse Direction (TD) and the length in the Machine Direction (MD), and the change rate of the length in each direction was calculated.
3. Peel strength of
A 3M adhesive tape is stuck on a steel plate, a diaphragm sample (the length is 200mm, the width is 25 mm) is cut, the coating surface is stuck on the 3M adhesive tape, the diaphragm is pre-stripped and then is held on a tensile machine for testing, the test speed is 150mm/min, and the width of the 3M adhesive tape is 20mm; peel strength = peel force/20 mm.
4. Needling strength
The test was performed at 100mm/min using a needle machine with a 1mm round-head needle.
The test results are shown in Table 1.
TABLE 1 results of diaphragm Performance test
2. Battery assembly and performance testing
And (3) battery assembly: the composite diaphragm prepared in the embodiment and the diaphragms of comparative examples 1-2 are respectively assembled together with a positive plate, electrolyte and a lithium plate to form a lithium metal battery, and the lithium metal battery is subjected to battery performance test after standing for 10 hours; wherein the electrolyte is 1M LiPF 6 The solvent is a mixed solvent of DEC and EC in a volume ratio of 1:1; the positive plate is prepared by taking NCM811 as an active substance, super P as a conductive additive and PVDF as a binder in a mass ratio of 8:1:1; the negative electrode sheet is a lithium sheet.
Performance test of the battery: the test temperature was 25℃and the test voltage interval was 2.8-4.2V, and the test performance was 500 cycles under 1C conditions, and the results are shown in Table 2.
Table 2 battery performance
As can be seen from tables 1 and 2, compared with comparative example 2, the composite separator prepared in each example has better electrolyte wettability, needling strength, temperature resistance and good adhesion between the substrate and the coating, and the assembled lithium metal battery has higher specific discharge capacity and cycle stability.
The specific discharge capacity and the capacity retention ratio after cycling in example 2 and example 3 were both reduced as compared with example 1. Example 2 is that a thinner modified coating layer can result in a lower strength of the in-situ generated SEI, which is detrimental to the improvement of cycle performance; example 3 is that the thicker modified coating layer can affect the energy density of the battery, increase the internal resistance of the battery and affect the capacity exertion.
Compared with comparative example 1, the composite membrane of example 1 has more excellent performance and cycle performance, which means that the modified modifier further improves the wettability, puncture resistance and heat resistance of the membrane, and can adjust lithium ion transmission and reduce the generation of lithium dendrite.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (10)
1. The composite diaphragm for inhibiting lithium dendrite is characterized by comprising a base film and a composite coating layer arranged on at least one side surface of the base film; the composite coating comprises a crosslinked structure coating formed by modified fluoride and an adhesive; the modified fluoride comprises fluoride and a modifier coated on at least part of the surface of the fluoride, wherein the modifier comprises polydopamine.
2. The lithium dendrite suppressing composite separator of claim 1 comprising at least one of the following features (1) to (3):
(1) The fluoride includes at least one of magnesium fluoride, aluminum fluoride, copper fluoride, iron fluoride, cobalt fluoride, silver fluoride, vanadium fluoride, nickel fluoride, manganese fluoride, gallium fluoride, titanium fluoride, scandium fluoride, chromium fluoride, calcium fluoride, strontium fluoride, iridium fluoride, zirconium fluoride, niobium fluoride, molybdenum fluoride, cadmium fluoride, indium fluoride, palladium fluoride, rhodium fluoride, ruthenium fluoride, technetium fluoride, barium fluoride, radium fluoride, tungsten fluoride, osmium fluoride, and rhenium fluoride;
(2) The D50 particle size of the modified fluoride is 0.1-5 mu m;
(3) The modifier is at least one of phenolic resin and urea resin.
3. The lithium dendrite suppressing composite separator of claim 1 comprising at least one of the following features (1) to (2):
(1) In the composite coating, the mass ratio of the modified fluoride to the adhesive is (2-50): (2-15);
(2) The thickness of the composite coating is 0.01-10 mu m.
4. The lithium dendrite suppressing composite separator of claim 1 comprising at least one of the following features (1) to (2):
(1) The thickness of the base film is 3-20 mu m;
(2) The base film comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyimide, aramid, polyether ether ketone, polyethylene terephthalate, cellulose and polyurethane.
5. The lithium dendrite suppressing composite separator of claim 1, wherein the adhesive comprises at least one of polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene-acrylic latex, polyacrylonitrile, polyethyl acrylate, polyvinyl acetate, polyacrylate, and polyurethane.
6. The method for producing a lithium dendrite suppressing composite separator according to any one of claims 1 to 5, comprising the steps of:
(a) Grinding the modifier solution, fluoride and the mixture, collecting the solid, washing and drying to obtain modified fluoride; the modifier solution comprises a mixed solution of dopamine, an alcohol solvent and a Tris buffer solution;
(b) Mixing the modified fluoride obtained in the step (a) with an adhesive and water to obtain a coating liquid; and coating the coating liquid on at least one side surface of the base film, and then drying.
7. The method of producing a lithium dendrite suppressing composite separator according to claim 6, characterized by comprising at least one of the following features (1) to (3):
(1) In the modifier solution, the concentration of dopamine is 1% -15%;
(2) The volume ratio of the alcohol solvent to the Tris buffer is (0.1-3): 1, a step of; the pH value of the Tris buffer solution is 7-10;
(3) The modifier solution is obtained by mixing dopamine, an alcohol solvent and a Tris buffer solution for 10-15 hours.
8. The method of producing a lithium dendrite suppressing composite separator according to claim 6, characterized by comprising at least one of the following features (1) to (4):
(1) The grinding includes ball milling and/or sand milling;
(2) The grinding medium adopted by the grinding is zirconium beads, and the mass ratio of the zirconium beads to the fluoride to the modifier solution is (50-130): 5-10): 1-5;
(3) The rotational speed of the grinding is greater than or equal to 10rpm;
(4) The grinding time is 1-28 h.
9. The method of producing a lithium dendrite suppressing composite separator according to claim 6, characterized by comprising at least one of the following features (1) to (5):
(1) In the coating liquid, the mass content of the modified fluoride is 2-50%, and the mass content of the adhesive is 2-15%;
(2) The coating liquid also comprises an auxiliary agent, wherein the mass content of the auxiliary agent is 0.001% -2%;
(3) The auxiliary agent comprises at least one of fluoroalkyl ethoxy alcohol ether, polyoxyethylene alkylamide, fatty alcohol polyoxyethylene ether, ding Bennai sodium sulfonate, sodium isethionate and sodium dodecyl benzene sulfonate;
(4) The coating comprises at least one of micro gravure coating, extrusion coating, wire bar coating, dip coating and spray coating;
(5) The temperature of the drying treatment is 40-90 ℃.
10. A lithium metal battery comprising the composite separator for suppressing lithium dendrites according to any one of claims 1 to 5.
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