CN108630867B - Diaphragm, preparation method thereof and lithium ion battery - Google Patents
Diaphragm, preparation method thereof and lithium ion battery Download PDFInfo
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- CN108630867B CN108630867B CN201810410204.0A CN201810410204A CN108630867B CN 108630867 B CN108630867 B CN 108630867B CN 201810410204 A CN201810410204 A CN 201810410204A CN 108630867 B CN108630867 B CN 108630867B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2220/00—Batteries for particular applications
- H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Materials Engineering (AREA)
- Cell Separators (AREA)
Abstract
The invention discloses a diaphragm, a preparation method thereof and a lithium ion battery, and belongs to the technical field of lithium batteries. The separator of the present invention comprises: the base film is non-woven fabric; and the conducting layer is attached to the base film. The preparation method of the diaphragm comprises the following steps: a conductive layer preparation step: forming a conductive layer on the surface of the non-woven fabric base film by adopting an in-situ polymerization method; preparing a closed pore layer: and coating the closed pore layer slurry on the conductive layer, and drying to obtain the diaphragm. The lithium ion battery of the present invention includes the separator of the present invention. After the diaphragm is used for the lithium ion battery, the energy density of the battery can be improved, and the thermal stability and the high temperature resistance are good.
Description
Technical Field
The invention belongs to the technical field of lithium batteries, and relates to a diaphragm, a preparation method of the diaphragm, and a lithium ion battery containing the diaphragm.
Background
Long-term development planning in the automobile industry provides that the energy density of a single battery in 2020 is 300wh/kg, and at present, LiFePO4The energy density of the monomer reaches 150-. With the continuous improvement of energy density, people question the safety performance of power batteries. Energy density and safety performance are two major bottlenecks affecting the rapid development of power batteries at the present stage.
Generally, the energy density of a single battery is mainly improved by depending on positive and negative electrode materials, and the function of a diaphragm of another key component of the lithium ion battery is often ignored. The separator plays a crucial role in battery internal resistance, capacity, cycle life, energy density and safety performance. However, increasing the cell energy density by reducing the separator thickness is extremely limited, while increasing the risk of separator puncture. At present, the lithium ion battery diaphragm mainly comprises a polyolefin diaphragm and a non-woven fabric diaphragm, wherein the polyolefin diaphragm is mainly made of polypropylene and polyethylene, and has low melting point, poor thermal stability and poor safety performance; the non-woven fabric diaphragm is made of polyethylene glycol terephthalate, cellulose, polyimide, aramid fiber and the like, has the characteristics of high melting point, good thermal stability and high temperature resistance, does not have the characteristic of high-temperature closed pores, is poor in safety performance, and cannot meet the requirement of improving the energy density of the lithium ion battery
Therefore, it is highly desirable to provide a separator having good thermal stability and high temperature resistance and capable of improving the energy density of a lithium ion battery, and/or a separator having high-temperature closed-cell characteristics and high safety performance.
Disclosure of Invention
Technical problem to be solved
In order to overcome the drawbacks of the prior art, it is an object of the present invention to provide a separator. The diaphragm has good thermal stability and high temperature resistance, and can improve the energy density of the lithium ion battery.
The second purpose of the invention is to provide a preparation method of the diaphragm, the diaphragm prepared by the preparation method can improve the energy density of the lithium ion battery, and has good thermal stability, high temperature resistance, high-temperature closed pore characteristic and high safety performance.
The invention also aims to provide a lithium ion battery comprising the diaphragm or the lithium ion battery comprising the diaphragm prepared by the preparation method.
(II) technical scheme
In order to achieve the purpose, the invention adopts the main technical scheme that:
the present invention provides a separator, comprising:
the base film is non-woven fabric;
a conductive layer attached to the base film.
According to the present invention, the conductive layer includes at least one of polyaniline, polypyrrole, and polythiophene; and/or the thickness of the conducting layer is 1-40 nm.
According to the invention, the membrane further comprises a closed pore layer, wherein the closed pore layer is applied to the conductive layer.
According to the invention, the closed-orifice layer comprises: polyethylene particles, inorganic ceramic particles, and a binder, wherein,
the mass ratio of the polyethylene particles to the inorganic ceramic particles is 1: 1-3;
the binder accounts for 5-30% of the total mass of the polyethylene particles and the inorganic ceramic particles.
According to the invention, the thickness of the closed pore layer is 1-5 μm; and/or
The particle size of the polyethylene particles is 50 nm-1 mu m; and/or
The inorganic ceramic particles are aluminum oxide and/or silicon oxide; and/or
The particle size of the inorganic ceramic particles is 50 nm-1 mu m.
According to the invention, the non-woven fabric is aramid and/or polyimide; and/or
The thickness of the non-woven fabric is 10-15 mu m; and/or
The porosity of the non-woven fabric is 40-70%; and/or
The aperture of the non-woven fabric is 40-100 nm.
The invention provides a preparation method of the diaphragm, which comprises the following steps:
a conductive layer preparation step: forming a conductive layer on the surface of the non-woven fabric base film by adopting an in-situ polymerization method;
preparing a closed pore layer: and coating the closed pore layer slurry on the conductive layer, and drying to obtain the diaphragm.
According to the present invention, in the conductive layer preparing step, the non-woven fabric base film is soaked in a solution containing a reactive monomer, an oxidant and a protonic acid, and the reactive monomer is polymerized in situ on the surface of the non-woven fabric base film to form the conductive layer.
According to the present invention, the closed-pore layer slurry comprises polyethylene particles, inorganic ceramic particles, a binder and a solvent; wherein the content of the first and second substances,
the mass ratio of the polyethylene particles to the inorganic ceramic particles is 1: 1-3;
the binder accounts for 5-30% of the total mass of the polyethylene particles and the inorganic ceramic particles;
the solvent accounts for 40-80% of the total mass of the polyethylene particles, the inorganic ceramic particles and the binder.
The invention also provides a lithium ion battery, which comprises a positive electrode, a negative electrode, electrolyte and a diaphragm, wherein the diaphragm is any one of the diaphragms; or
The diaphragm is obtained by the preparation method.
(III) advantageous effects
Compared with the prior art, the invention has the following advantages:
1. the diaphragm comprising the base film and the conducting layer can improve the energy density of the single battery, has good thermal stability, is heated for 2 hours at 200 ℃, has the thermal shrinkage rate of less than 1 percent, has good high temperature resistance, and does not break when heated for 1 hour at 400 ℃.
2. The diaphragm comprising the closed-pore layer has the closed-pore characteristic, and the diaphragm is closed at the temperature of 130-200 ℃.
3. The diaphragm battery comprising the base film, the conducting layer and the closed pore layer has good rate capability, good safety performance and high needle punching test passing rate.
3. The diaphragm prepared by the preparation method can improve the energy density of the lithium ion battery, has good thermal stability, high temperature resistance and high-temperature closed pore characteristic, and has high safety performance.
Detailed Description
For a better understanding of the present invention, reference will now be made in detail to the present invention by way of specific embodiments thereof.
This embodiment provides a preferred separator including a base film and a conductive layer attached to the base film, and a closed pore layer coated on the conductive layer.
The conductive layer of the embodiment has a conductive characteristic, and can improve the energy density of the single battery. The closed pore layer has the characteristic of high-temperature closed pores, and the diaphragm is closed at the temperature of 130-200 ℃. Through the arrangement of the conducting layer and the closed pore layer, the battery adopting the diaphragm disclosed by the invention has the advantages of good rate capability, good safety performance and high needle punching test passing rate.
Specifically, in the present embodiment, aramid and/or polyimide is preferable as the base film material. Aramid fiber is a novel high-tech polymer material, has excellent flame retardance and heat resistance, cannot be melted at high temperature, and can be used as a base material of a base film. Polyimide is one of organic high molecular materials with the best comprehensive performance, resists high temperature of more than 400 ℃, and can be used as a base material of a basement membrane. Therefore, the diaphragm prepared by adopting the base film material has good thermal stability, the thermal shrinkage rate is less than 1% when the diaphragm is heated for 2 hours at 200 ℃, and the diaphragm has high temperature resistance and does not break when heated for 1 hour at 400 ℃.
In the present embodiment, the thickness of the base film is limited to a range of 10 to 15 μm, and for example, the thickness of the base film may be any one of 10 μm, 12 μm, 14 μm, and 15 μm. The surface of the base film is provided with a uniform nanoscale pore structure with the pore diameter of 40-100 nm, the porosity of the base film is guaranteed to be 40-70%, for example, the porosity of the base film can be maintained at any value of 45%, 55%, 65% and 70%, and the conductive polymer material can be adsorbed in the nanopores on the surface of the base film uniformly, so that the lithium ion battery has good conductivity.
Furthermore, the base film is preferably made by adopting a tape casting thermal induced phase separation method, the made base film has a pore structure which is uniformly distributed and has a moderate size, and the conductive high polymer material of the conductive layer can be uniformly adsorbed on the base film and is not easy to block pores.
In this embodiment mode, the conductive polymer material of the conductive layer is preferably at least one selected from polyaniline, polypyrrole, and polythiophene. Polyaniline can be conductive after being doped with protonic acid. The polyaniline of the embodiment is synthesized by an in-situ chemical oxidation polymerization method, and at room temperature and a low temperature as much as possible, the polyaniline and the oxidant are respectively prepared into solutions by taking an acid solution as a solvent, and then the solutions are mixed and stirred to react for a certain time, so that the polyaniline can be obtained.
The polypyrrole is a heterocyclic conjugated conductive polymer, and the polypyrrole of the embodiment takes pyrrole as a monomer, selects ferric trichloride, ammonium persulfate and the like as oxidants, and is subjected to chemical oxidative polymerization to prepare a conductive thin film coating with high conductivity and good thermal stability.
The polythiophene has very good environmental stability, very high conductivity and luminescent property due to the structure similar to an aromatic ring, has extremely small size, can be regulated and controlled from insulation to close to metal, and can endow the material with the characteristics of electricity, optics, mechanics and the like after being processed. The polythiophene with high conductivity is synthesized by adopting a chemical oxidation polymerization method, taking thiophene as a monomer, selecting ferric trichloride, aluminum trichloride and the like as oxidants and selecting trichloromethane as a solvent.
Of course, the conductive polymer material of the conductive layer of the present embodiment is not limited to the above, and an organic conductive polymer such as polyacetylene may be selected.
In the present embodiment, the closed-cell layer includes polyethylene particles, inorganic ceramic particles, and a binder, and the thickness of the closed-cell layer is 1 to 5 μm, for example, the thickness of the closed-cell layer may be any one of 1 μm, 2.5 μm, 3.8 μm, 4.3 μm, and 5 μm. Wherein, the polyethylene particles are heated and melted at high temperature (above 120 ℃), so that the diaphragm can realize closed pores. The polyethylene of the present embodiment is preferably linear low density polyethylene (density of 0.918 to 0.935g/cm), and the polyethylene particles have a particle diameter of 50nm to 1 μm. The inorganic ceramic particles are generally in a sheet shape or a granular shape, and have the characteristic of enhancing the structural strength of the base film, the inorganic ceramic particles of the embodiment are preferably low-cost aluminum oxide and/or silicon oxide, and the particle size of the inorganic ceramic particles is 50nm to 1 μm. The binder can bind the polyethylene particles and the inorganic ceramic particles together, and polyvinylidene fluoride is preferable as the binder of the present embodiment. The solvent is preferably N-methylpyrrolidone and/or N, N-dimethylformamide.
Meanwhile, the embodiment provides a preparation method of the diaphragm, which comprises the following steps:
(1) and forming a conductive layer on the surface of the non-woven fabric base film by adopting an in-situ polymerization method.
Specifically, the step (1) comprises the following substeps:
placing the non-woven fabric base film in an acid solution containing a reaction monomer, and soaking for 0.5-2 hours to enable the non-woven fabric base film to fully adsorb the reaction monomer; then adding an oxidant and protonic acid, controlling the pH value of the solution to be 1-4, uniformly stirring, and reacting at the temperature of 0-25 ℃ for 1-3 hours to enable a reaction monomer to generate an in-situ polymerization reaction on the surface of the non-woven fabric base film; and after the reaction is finished, cleaning the non-woven fabric base film for several times by using an acid solution and deionized water in sequence, drying for 2-5 hours at the temperature of 80-120 ℃, and forming a conductive layer on the surface of the non-woven fabric base film.
In the step (1), the reactive monomer is selected from one or a combination of at least two of aniline, pyrrole and thiophene, and the concentration of the reactive monomer is 0.05-0.2 mol/L, for example, the concentration of the reactive monomer can be any one of 0.05mol/L, 0.1mol/L, 0.15mol/L, 0.18mol/L and 0.2 mol/L. The oxidizing agent is capable of oxidatively polymerizing the reactive monomer to the polymer, and the oxidizing agent of the present embodiment is preferably (NH)4)2S2O4And/or FeCl3·6H2And O, wherein the molar concentration ratio of the oxidant to the reaction monomer is 1: 1-2, and preferably, the molar concentration ratio of the oxidant to the reaction monomer is 1:1.4 or 1: 1.7.
The protonic acid is doped to make the polymer conductive, and the protonic acid of the present embodiment is preferably one of hydrochloric acid, acetic acid and p-toluenesulfonic acid, and the concentration of the protonic acid is 0.1 to 0.5 mol/L. The conductive polymer formed on the surface of the non-woven fabric base film is formed into a conductive layer, the thickness of the conductive layer is 1-40 nm, and for example, the thickness of the conductive layer can be any value of 5nm, 15nm, 30nm, 34nm and 40 nm.
In example 1, the nonwoven fabric-based film is finally washed with an acidic solution in order to wash away unreacted reactive monomers and/or non-adsorbed conductive polymers; and then deionized water is adopted for washing, so that redundant washing acid solution is washed away until the mixed solution is neutral.
(2) And coating the closed pore layer slurry on the conductive layer, and drying to obtain the diaphragm.
The step (2) comprises the following substeps:
and sequentially adding a solvent, a binder, inorganic ceramic particles and polyethylene particles, mixing and uniformly stirring, coating on the surface of the conductive layer of the conductive base film layer to form a closed hole layer, and rolling and drying to obtain the diaphragm.
Wherein the mass ratio of the polyethylene particles to the inorganic ceramic particles is 1: 1-3, and preferably, the mass ratio of the polyethylene particles to the inorganic ceramic particles is 1:1.5 or 1:2 or 1:2.5 or 1: 3; the percentage of the binder in the total mass of the polyethylene particles and the inorganic ceramic particles is 5-30%, preferably, the percentage of the binder in the total mass of the polyethylene particles and the inorganic ceramic particles is any one of 10%, 20% and 26%; the percentage of the solvent in the total mass of the polyethylene particles, the inorganic ceramic particles and the binder is 40-80%, and preferably, the percentage of the solvent in the total mass of the polyethylene particles, the inorganic ceramic particles and the binder is any one of 50%, 58%, 65% and 70%.
The diaphragm prepared by the preparation method can improve the energy density of the lithium ion battery, and has good thermal stability, high temperature resistance, high-temperature closed hole characteristic and high safety performance.
In addition, the embodiment also provides a lithium ion battery, which comprises a positive electrode, a negative electrode, an electrolyte and the diaphragm.
The anode, the cathode, the diaphragm and the electrolyte are all arranged in an outer packaging shell, and the outer packaging shell can be a conventional lithium ion battery outer packaging shell in the field, and is generally an aluminum shell, a plastic shell or an aluminum plastic film. The anode material can be selected from ternary materials conventionally used in the field, and the cathode material can be selected from graphite or silicon carbon conventionally used in the field. The separator is laminated in a manner conventional in the art, typically a zigzag lamination or a wound lamination wherein a conductive base film layer is adjacent to the positive electrode. The electrolyte can be selected from electrolyte conventionally used in the field, and is generally selected from organic solvent and lithium hexafluorophosphate, and is filled in the gaps among the positive electrode, the negative electrode and the separator.
See in particular the examples below:
example 1
Example 1 proposes a method for preparing a separator, comprising the steps of:
(1) a conductive layer preparation step: forming a conductive layer on the surface of the non-woven fabric base film by adopting an in-situ polymerization method;
soaking polyimide base membrane with thickness of 12 μm, porosity of 60% and pore diameter of 60nm in 0.15mol/L aniline hydrochloric acid solution for 1h to allow the base membrane to sufficiently adsorb aniline monomer, and adding 0.15mol/L (NH)4)2S2O4Controlling the pH value of the solution and 0.3mol/L hydrochloric acid solution to be 2, uniformly stirring, and reacting at the temperature of 10 ℃ for 2 hours to enable aniline monomer to generate in-situ polymerization reaction on the surface of the base film. And after the reaction is finished, cleaning the conductive base film for 5 times by using hydrochloric acid and deionized water in sequence, and drying at 80 ℃ for 5 hours to form a conductive layer with the thickness of 20nm on the surface of the base film.
(2) Preparing a closed pore layer: coating the closed pore layer slurry on the conductive layer, and drying to obtain the diaphragm
Sequentially adding N-methyl pyrrolidone, polyvinylidene fluoride, aluminum oxide particles with the particle size of 0.5 mu m and low-density polyethylene particles with the particle size of 0.4 mu m, mixing and stirring uniformly, then coating on the conductive layer to form a closed pore layer with the thickness of 3 mu m, rolling and drying at 80 ℃ to obtain the diaphragm.
Wherein the N-methyl pyrrolidone accounts for 70% of the total mass of the low-density polyethylene particles, the aluminum oxide particles and the polyvinylidene fluoride, the polyvinylidene fluoride accounts for 20% of the total mass of the low-density polyethylene particles and the aluminum oxide particles, and the mass ratio of the aluminum oxide particles to the low-density polyethylene particles is 2: 1.
Embodiment 1 also provides a lithium ion battery containing the above diaphragm, which includes an aluminum-plastic film outer packaging shell, and a positive plate, a negative plate, a diaphragm and electrolyte arranged in the aluminum-plastic film outer packaging shell. The anode material is a ternary material, the cathode material is graphite which is conventionally used in the field, and the electrolyte is selected from an organic solvent and lithium hexafluorophosphate. The diaphragm is laminated according to the Z shape, the conductive base film layer of the diaphragm is close to the anode, and the electrolyte is filled in the gaps among the anode plate, the cathode plate and the diaphragm.
Example 2
Embodiment 2 proposes a method for preparing a separator, comprising the steps of:
(1) a conductive layer preparation step: forming a conductive layer on the surface of the non-woven fabric base film by adopting an in-situ polymerization method;
soaking aramid fiber basal membrane with thickness of 10 μm, porosity of 40% and aperture of 100nm in 0.2mol/L pyrrole hydrochloric acid solution for 2h to allow the basal membrane to fully adsorb pyrrole monomer, and adding 0.1mol/L FeCl3·6H2And (3) controlling the pH value of the solution to be 1, uniformly stirring the solution and the hydrochloric acid solution with the concentration of 0.5mol/L, and reacting at the temperature of 0 ℃ for 0.5h to enable the pyrrole monomer to generate in-situ polymerization reaction on the surface of the base film. After the reaction is finished, the conductive base film is sequentially washed for 5 times by hydrochloric acid and deionized water, and dried for 5 hours at 80 ℃, and a conductive layer with the thickness of 40nm is formed on the surface of the base film.
(2) Preparing a closed pore layer: coating the closed pore layer slurry on the conductive layer, and drying to obtain the diaphragm;
sequentially adding N-methyl pyrrolidone, polyvinylidene fluoride, aluminum oxide particles with the particle size of 50nm and low-density polyethylene particles with the particle size of 1 mu m, mixing and uniformly stirring, then coating on the conductive layer to form a closed hole layer with the thickness of 5 mu m, rolling and drying at 80 ℃ to obtain the diaphragm.
Wherein the N-methyl pyrrolidone accounts for 40% of the total mass of the low-density polyethylene particles, the aluminum oxide particles and the polyvinylidene fluoride, the polyvinylidene fluoride accounts for 5% of the total mass of the low-density polyethylene particles and the aluminum oxide particles, and the mass ratio of the aluminum oxide particles to the low-density polyethylene particles is 3: 1.
Embodiment 2 also provides a lithium ion battery containing the above diaphragm, which includes an aluminum case, and a positive plate, a negative plate, a diaphragm and an electrolyte disposed in the aluminum case. The anode material is a ternary material, the cathode material is silicon carbon which is conventionally used in the field, and the electrolyte is selected from an organic solvent and lithium hexafluorophosphate. The diaphragm is laminated according to the winding, the conductive layer of the diaphragm is close to the anode, and the electrolyte is filled in the gaps among the anode plate, the cathode plate and the diaphragm.
Example 3
Embodiment 3 proposes a method for preparing a separator, comprising the steps of:
(1) a conductive layer preparation step: forming a conductive layer on the surface of the non-woven fabric base film by adopting an in-situ polymerization method;
soaking polyimide base membrane with thickness of 15 μm, porosity of 70% and pore diameter of 40nm in 0.05mol/L thiophene hydrochloric acid solution for 0.5h to allow the base membrane to sufficiently adsorb thiophene monomer, and adding 0.05mol/L (NH)4)2S2O4Controlling the pH value of the solution and 0.1mol/L hydrochloric acid solution to be 4, uniformly stirring, and reacting at the temperature of 25 ℃ for 3 hours to enable thiophene monomers to generate in-situ polymerization reaction on the surface of the basement membrane. And after the reaction is finished, cleaning the conductive base film for 5 times by using hydrochloric acid and deionized water in sequence, and drying at 80 ℃ for 5 hours to form a conductive layer with the thickness of 1nm on the surface of the base film.
(2) Preparing a closed pore layer: coating the closed pore layer slurry on the conductive layer, and drying to obtain the diaphragm;
sequentially adding N-methyl pyrrolidone, polyvinylidene fluoride, aluminum oxide particles with the particle size of 1 mu m and low-density polyethylene particles with the particle size of 50nm, mixing and uniformly stirring, then coating on the conductive layer to form a closed hole layer with the thickness of 1 mu m, rolling and drying at 80 ℃ to obtain the diaphragm.
Wherein the N-methyl pyrrolidone accounts for 80 percent of the total mass of the low-density polyethylene particles, the aluminum oxide particles and the polyvinylidene fluoride, the polyvinylidene fluoride accounts for 30 percent of the total mass of the low-density polyethylene particles and the aluminum oxide particles, and the mass ratio of the aluminum oxide particles to the low-density polyethylene particles is 1:1.
Embodiment 3 also provides a lithium ion battery containing the diaphragm, which includes a plastic shell, and a positive plate, a negative plate, a diaphragm and electrolyte arranged in the plastic shell. The anode material is a ternary material, the cathode material is silicon carbon which is conventionally used in the field, and the electrolyte is selected from an organic solvent and lithium hexafluorophosphate. The diaphragm is laminated according to the Z shape, the conductive base film layer of the diaphragm is close to the anode, and the electrolyte is filled in the gaps among the anode plate, the cathode plate and the diaphragm.
Comparative example 1
Comparative example 1 proposes a conventional polyethylene composite separator including a polyethylene layer as a base film and an alumina particle layer, specifically, the alumina particles are mixed with an adhesive and then bonded with the polyethylene layer to produce the polyethylene composite separator. Wherein the thickness of the polyethylene layer is 12 μm, the porosity is 60%, and the pore diameter is 45 nm; the thickness of the alumina particle layer was 3 μm.
Comparative example 1 also proposes a lithium ion battery comprising the above polyethylene composite separator, which was prepared under substantially the same conditions as those of the lithium ion battery of example 1, except that: the separator used in comparative example 1 is different from that used in example 1, that is, the base film material used in comparative example 1 is different from that used in example 1: the base film adopted in comparative example 1 is a polyethylene base film, and the base film adopted in example 1 is a polyimide non-woven fabric base film; meanwhile, comparative example 1 did not have the conductive layer and closed pore layer described in example 1.
Comparative example 2
Comparative example 2 proposes a cellulose composite separator comprising the steps of:
(1) a conductive layer preparation step: forming a conductive layer on the surface of a cellulose-based film by in-situ polymerization
Adding pyrrole hydrochloric acid solution with concentration of 0.15mol/L into well dispersed cellulose water solution, stirring for 1h, and then adding (NH) with concentration of 0.15mol/L4)2S2O4Controlling the pH value of the solution and 0.3mol/L hydrochloric acid solution to be 2, uniformly stirring, reacting at the temperature of 10 ℃ for 2h, and polymerizing pyrrole monomers on the surface of cellulose to form a conductive layer with the thickness of 15 nm. After the reaction is finished, the conductive cellulose aqueous solution is washed for 5 times by hydrochloric acid and deionized water in sequence for standby.
(2) The preparation method of the cellulose composite diaphragm comprises the following steps:
and (2) vacuumizing the cellulose aqueous solution dispersed in the step (1) on a nylon membrane to form a cellulose layer with the thickness of 5 microns, adding the dispersed conductive cellulose aqueous solution, and continuously performing vacuum filtration to form a cellulose composite membrane with the thickness of 15 microns.
Comparative example 2 also proposes a lithium ion battery comprising the above cellulose composite separator, which was prepared under substantially the same conditions as those of the lithium ion battery of example 1, except that: the separator used in comparative example 2 is different from that used in example 1, that is, the base film material used in comparative example 2 is different from that used in example 1: the base film adopted in comparative example 2 is a cellulose non-woven fabric base film, and the base film adopted in example 1 is a polyimide non-woven fabric base film; meanwhile, comparative example 2 did not have the closed cell layer described in example 1.
Example 1 compares the performance effects of comparative example 1 and comparative example 2, respectively
The separator of example 1 and comparative example 1 and the lithium ion battery comprising the same were tested and compared for various properties, which were measured using conventional test methods well known to those skilled in the art, and the test results are shown in table 1.
Table 1 test results of various properties of the separators of example 1 and comparative example 1 and the lithium ion batteries including the same
The separators of example 1 and comparative example 2 and the lithium ion batteries including the same were tested and compared in terms of various properties, and the test results are shown in table 2.
Table 2 test results of various properties of the separators of example 1 and comparative example 2 and the lithium ion batteries including the same
As can be seen from tables 1 and 2, the following conclusions can be drawn:
(1) the diaphragm prepared in example 1 can be kept intact at 400 ℃, while the diaphragms prepared in comparative examples 1 and 2 can be subjected to melt degradation or degradation and breakage at 400 ℃, because the base diaphragm membrane material prepared in example 1 is selected from polyimide which can resist high temperature of more than 400 ℃, and the base diaphragm membrane materials prepared in comparative examples 1 and 2 are respectively prepared from polyethylene and cellulose which cannot resist high temperature of more than 400 ℃, so that the diaphragm prepared in example 1 has good high temperature resistance and can not be broken when heated at 400 ℃ for 1 h.
(2) The separator prepared in comparative example 1 was heated at 200 c for 2 hours, and a melt-curling phenomenon occurred. The separator prepared in example 1 was heated at 200 ℃ for 2 hours, and the longitudinal thermal shrinkage (0.35%) and the transverse thermal shrinkage (0.15%) were respectively lower than those of comparative example 2 (1.75%) and transverse thermal shrinkage (1.33%), and the longitudinal thermal shrinkage and the transverse thermal shrinkage of example 1 were both less than 1%, because the base membrane material of the separator prepared in example 1 was selected from polyimide having good thermal stability, while the base membrane materials of the separators prepared in comparative examples 1 and 2 were respectively selected from polyethylene and cellulose having poor thermal stability, as a result, it can be shown that the thermal stability of the separator of example 1 was good, and the thermal shrinkage was less than 1% when the separator was heated at 200 ℃ for 2 hours.
(3) Example 1 the cell capacity (2.41@1C/Ah) and energy density (170Wh/kg) of the cell prepared using the polyimide separator were substantially the same as those of the cell prepared using the cellulose composite separator of comparative example 2 (2.34@1C/Ah) and energy density (165Wh/kg), and the cell capacity and energy density were higher than those of the cell prepared using the polyethylene separator of comparative example 1 (2.17@1C/Ah) and energy density (153Wh/kg), which may be attributed to the polyethylene separator of comparative example 1 having no conductive layer, while the separators of comparative example 2 and example 1 both have conductive layers of the same composition, thus demonstrating that the conductive layers have the property of improving the cell capacity and energy density of the cell.
(4) The membrane of example 1 was closed-cell at 130 c, whereas the membranes of comparative examples 1 and 2 could not achieve closed-cell at 130 c, because neither of the membranes of comparative examples 1 and 2 had a closed-cell layer, so it can be shown that the membrane containing a closed-cell layer had high-temperature closed-cell characteristics.
(5) The battery prepared by the polyimide diaphragm in the embodiment 1 is discharged at the 2C rate and the 1C rate respectively, the rate retention rate (98.9%) of the battery is higher than the rate retention rate (84.6%) of the battery prepared by the cellulose diaphragm in the comparative example 2, probably because the battery diaphragm in the embodiment 1 simultaneously has a conductive layer and a closed pore layer which are interacted with each other, the rate performance of the battery can be improved;
(6) the battery prepared by using the polyimide separator in example 1 passed the needle punching test without causing fire or explosion, and the battery temperature was only increased by 27.8 ℃, while the battery prepared by using the polyethylene separator in comparative example 1 passed the needle punching test without causing fire or explosion, but the battery temperature was increased by 90.5 ℃, and the battery prepared by using the cellulose separator in comparative example 2 passed the needle punching test without causing fire or explosion, but the battery temperature was increased by 76.1 ℃, which is probably because the battery separator in example 1 has both the conductive layer and the closed pore layer, which interact with each other, improving the safety performance, and increasing the needle punching test throughput.
(7) The longitudinal tensile strength (51.40MPa) and the transverse tensile strength (31.31MPa) of the membrane prepared in the example 1 are respectively higher than those (26.55MPa) and the transverse tensile strength (12.69MPa) of the membrane prepared in the comparative example 2, which is probably caused by the fact that the base membrane material of the membrane prepared in the example 1 is selected from polyimide which the tensile strength is higher than that of cellulose.
It should be understood that the above description of specific embodiments of the present invention is only for the purpose of illustrating the technical lines and features of the present invention, and is intended to enable those skilled in the art to understand the contents of the present invention and to implement the present invention, but the present invention is not limited to the above specific embodiments. It is intended that all such changes and modifications as fall within the scope of the appended claims be embraced therein.
Claims (8)
1. A separator, characterized by: the diaphragm is composed of a base film, a conductive layer and a closed-cell layer; wherein the content of the first and second substances,
the base film is non-woven fabric;
the conductive layer is attached to the base film; the thickness of the conducting layer is 1-40 nm;
the closed pore layer is coated on the conductive layer; the thickness of the closed pore layer is 1-5 μm;
the base film is made of polyimide, the thickness of the base film is 10-15 mu m, the surface of the base film is provided with a uniform nano-scale pore structure with the pore diameter of 40-100 nm, the porosity of the base film is 40-70%, and the base film is prepared by adopting a curtain coating thermal induced phase separation method;
the closed-pore layer includes: polyethylene particles, inorganic ceramic particles and a binder; the polyethylene particles are linear low-density polyethylene, and the density of the polyethylene is 0.918-0.935 g/cm3。
2. A diaphragm according to claim 1, wherein:
the conductive layer includes at least one of polyaniline, polypyrrole, and polythiophene.
3. A diaphragm according to claim 1, wherein: the mass ratio of the polyethylene particles to the inorganic ceramic particles is 1: 1-3; the binder accounts for 5-30% of the total mass of the polyethylene particles and the inorganic ceramic particles.
4. A diaphragm according to claim 3, wherein:
the particle size of the polyethylene particles is 50 nm-1 mu m; and/or
The inorganic ceramic particles are aluminum oxide and/or silicon oxide; and/or
The particle size of the inorganic ceramic particles is 50 nm-1 mu m.
5. A method for preparing a separator, comprising: the method comprises the following steps:
a conductive layer preparation step: forming a conductive layer on the surface of the non-woven fabric base film by adopting an in-situ polymerization method;
preparing a closed pore layer: coating the closed pore layer slurry on the conductive layer, and drying to obtain the diaphragm;
the base film is made of aramid fiber and/or polyimide, is 10-15 mu m thick, has a uniform nano-scale pore structure with the pore diameter of 40-100 nm on the surface, has the porosity of 40-70%, and is prepared by adopting a tape casting thermal induced phase separation method;
the closed-pore layer includes: polyethylene particles, inorganic ceramic particles and binder, and a method for producing the sameThe polyethylene particles are linear low-density polyethylene, and the density of the polyethylene is 0.918-0.935 g/cm3。
6. The method according to claim 5, wherein in the conductive layer preparing step, the non-woven fabric base film is soaked in a solution containing a reactive monomer, an oxidizing agent and a protonic acid, and the reactive monomer is polymerized in situ on the surface of the non-woven fabric base film to form the conductive layer.
7. The method of claim 5, wherein: the closed-cell layer slurry comprises polyethylene particles, inorganic ceramic particles, a binder and a solvent; wherein the content of the first and second substances,
the mass ratio of the polyethylene particles to the inorganic ceramic particles is 1: 1-3;
the binder accounts for 5-30% of the total mass of the polyethylene particles and the inorganic ceramic particles;
the solvent accounts for 40-80% of the total mass of the polyethylene particles, the inorganic ceramic particles and the binder.
8. A lithium ion battery comprises a positive electrode, a negative electrode, electrolyte and a diaphragm, and is characterized in that: the membrane is according to any one of claims 1 to 4; or
The separator is obtained by the preparation method according to any one of claims 5 to 7.
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| CN109686908A (en) * | 2018-11-16 | 2019-04-26 | 华为技术有限公司 | Battery isolation film, battery core, lithium ion battery and preparation method |
| CN110048062B (en) * | 2019-03-25 | 2022-04-15 | 惠州锂威电子科技有限公司 | Overcharge-preventing battery diaphragm and lithium ion battery using same |
| CN113451702A (en) * | 2020-12-02 | 2021-09-28 | 华东理工大学 | Modified lithium battery diaphragm and preparation method thereof |
| CN113690547A (en) * | 2021-08-03 | 2021-11-23 | 惠州锂威新能源科技有限公司 | Safety diaphragm, preparation method and lithium ion battery |
| CN113690548A (en) * | 2021-08-03 | 2021-11-23 | 惠州锂威新能源科技有限公司 | Safety diaphragm, preparation method thereof and lithium ion battery |
| CN114335905A (en) * | 2021-12-30 | 2022-04-12 | 横店集团东磁股份有限公司 | Lithium ion battery cell and preparation method thereof |
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| CN115241606A (en) * | 2022-06-30 | 2022-10-25 | 合肥国轩高科动力能源有限公司 | Aramid resin-based composite coating lithium battery diaphragm and preparation method thereof |
| CN115275523A (en) * | 2022-07-01 | 2022-11-01 | 张健明 | Diaphragm for polyvinyl lithium battery and preparation method thereof |
| CN115911753B (en) * | 2022-10-11 | 2024-04-26 | 天津工业大学 | Preparation method of composite lithium-sulfur battery diaphragm material with polyphenylene sulfide as substrate |
| CN115602997A (en) * | 2022-10-13 | 2023-01-13 | 河北工业大学（Cn） | Co 3 O 4 -PVA-PPy-PP diaphragm, preparation method and application thereof, and lithium-sulfur battery containing diaphragm |
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| CN103199209B (en) * | 2013-04-01 | 2015-09-02 | 中国海诚工程科技股份有限公司 | There is lithium ion battery nonwoven fabrics ceramic diaphragm and the technique of excellent closed pore performance |
| CN104103791A (en) * | 2013-04-08 | 2014-10-15 | 中国科学院金属研究所 | Composite diaphragm for battery and preparation method thereof |
| CN105140447A (en) * | 2015-07-23 | 2015-12-09 | 中国科学院上海硅酸盐研究所 | Functional composite membrane for lithium-sulfur battery and preparation method of functional composite membrane |
| CN105820372B (en) * | 2016-03-30 | 2019-04-09 | 青岛大学 | A kind of conduction aeroge and preparation method thereof |
| CN107230764B (en) * | 2017-07-19 | 2020-05-05 | 宁波柔创纳米科技有限公司 | Preparation method of lithium-sulfur battery diaphragm, lithium-sulfur battery diaphragm and lithium-sulfur battery |
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