CN113178561A - Negative electrode material modified by reactive two-dimensional molecular brush SEI film, and preparation method and application thereof - Google Patents
Negative electrode material modified by reactive two-dimensional molecular brush SEI film, and preparation method and application thereof Download PDFInfo
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- H01M4/00—Electrodes
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/381—Alkaline or alkaline earth metals elements
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
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- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H01M4/00—Electrodes
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
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Abstract
The invention discloses a negative electrode material modified by a reactive two-dimensional molecular brush SEI film, and a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) grafting functional polymer salt on the surface of graphene oxide through free radical polymerization to obtain a two-dimensional molecular brush with a side chain of the functional polymer salt; (2) through ion exchange, a two-dimensional molecular brush with a side chain containing metal ion macromolecular salt is obtained; (3) filtering the synthesized two-dimensional molecular brush on a porous membrane to obtain a two-dimensional molecular brush membrane; (4) and transferring the two-dimensional molecular brush film to the surface of the lithium metal sheet by a film transfer technology to construct the negative electrode material modified by the artificial SEI film of the two-dimensional molecular brush. The cathode material has excellent mechanical property, can effectively reduce interface impedance, and can induce lithium ions to be uniformly deposited on the surface of a lithium metal cathode, so that the assembled lithium ion battery has excellent electrochemical property.
Description
Technical Field
The invention relates to the field of artificial solid electrolyte interface membrane materials for lithium secondary batteries, in particular to an artificial solid electrolyte interface membrane based on a reactive two-dimensional molecular brush, a preparation method thereof and a lithium ion battery applying the artificial solid electrolyte interface membrane.
Background
In order to meet the requirements of advanced equipment such as electric automobiles, portable electronic equipment, aerospace planes and the like on energy storage devices, the development of high-performance energy storage devices has become a research hotspot. Among various energy storage devices, lithium ion batteries are receiving attention due to their advantages of high voltage, high energy density, no memory effect, etc.; as one of the most mature energy storage devices with the highest market share in the current technology, lithium ion batteries are widely used in many fields. However, the theoretical specific capacity of the negative graphite material in the lithium ion battery is lower and is only 372mAh g-1It is difficult to meet the demand for high energy density secondary batteries for the rapid development of new energy technologies.
The lithium metal negative electrode has the advantages of high specific capacity, low oxidation-reduction potential, low density and the like, and is expected to become a negative electrode material of next-generation high-performance energy storage systems such as lithium-sulfur batteries and lithium air batteries. However, the growth of lithium metal uncontrollable dendrites and their high reactivity consume large amounts of active lithium, resulting in irreversible capacity fading of the battery system; on the other hand, further growth of lithium dendrites can pierce the separator, resulting in internal short circuits of the battery, causing combustion and even explosion of the battery, and causing serious safety problems. Therefore, the application of lithium metal in next generation energy storage systems is greatly limited.
In recent years, many strategies for inhibiting the growth of lithium dendrites in lithium metal batteries have been reported. For example, a three-dimensional lithium-carrying skeleton is designed, a novel separator is constructed, or the separator is modified, and a solid electrolyte is used instead of a liquid electrolyte.
It is well known that SEI films play a very critical role in the stabilization of lithium metal anodes. Therefore, there are research reports that various additives are added to optimize electrolyte components to generate a uniform and stable SEI film on the surface of lithium metal in situ, thereby effectively limiting the growth of lithium dendrites and prolonging the battery life. However, such in situ-generated protective films are typically mechanically weak and not sufficiently resistant to stress tearing due to lithium dendrite growth; in addition, the additives are continuously consumed during the cycling of the battery, and thus long cycle stability of the battery cannot be guaranteed.
A strategy of using an artificial SEI film has been proposed to prevent lithium metal from contacting the electrolyte, thereby inhibiting the reaction of lithium metal with the electrolyte, and at the same time, to inhibit the growth of lithium dendrites by its high mechanical strength. However, the artificial SEI films reported so far, including organic artificial SEI films (such as polyvinylidene fluoride, plasticine, polyurea, etc.), inorganic artificial SEI films (such as alumina, functionalized graphene, molybdenum disulfide, etc.), or organic-inorganic hybrid artificial SEI films (cuprous nitride-styrene butadiene rubber, polyvinylidene fluoride-hexafluoropropylene-zirconium dioxide, etc.), cannot realize the cycle of large current density (usually, the cycle of large current density cannot be realized) because the polarization voltage of the battery is increased due to the inability to realize the rapid transmission in the lithium ion SEI film<2mAcm-2). In addition, these artificial SEI films lack the general lack of lithium-philic sites, and thus cannot induce uniform dispersion and nucleation of lithium ions on the electrode surface, and thus cannot ensure long-term cycling stability of the lithium metal negative electrode.
Disclosure of Invention
The artificial SEI film has high-efficiency lithium ion transmission channels, abundant lithium-philic and lithium nucleation sites and excellent mechanical strength, and the lithium ion battery assembled by the lithium metal sheets protected by the reactive two-dimensional molecular brush artificial SEI film has excellent electrochemical performance.
In order to achieve the above purpose, the present application provides the following technical solutions:
a preparation method of a reactive two-dimensional molecular brush artificial SEI film modified negative electrode material comprises the following steps:
(1) grafting functional polymer salt on the surface of graphene oxide through free radical polymerization to obtain a two-dimensional molecular brush with a side chain of the functional polymer salt;
(2) through ion exchange, a two-dimensional molecular brush with a side chain containing metal ion macromolecular salt is obtained;
(3) filtering the synthesized two-dimensional molecular brush on a porous membrane to obtain a two-dimensional molecular brush membrane;
(4) and transferring the two-dimensional molecular brush film to the surface of the lithium metal sheet by a film transfer technology to construct the negative electrode material modified by the artificial SEI film of the two-dimensional molecular brush.
Preferably, the method comprises the following steps:
(1) mixing and stirring a monomer, an initiator and the graphene oxide aqueous dispersion uniformly, introducing inert gas to remove oxygen, sealing, and reacting for 6-48 hours at the temperature of 65-85 ℃; centrifuging after the reaction is finished, and washing with water to obtain a two-dimensional molecular brush with a side chain being functional polymer salt;
(2) dispersing the two-dimensional molecular brush prepared in the step (1) in an acid solution again, stirring, centrifuging, acid washing, centrifuging, and washing with deionized water to be neutral; then, dispersing the product after acid washing in a metal salt water solution, carrying out light-shielding stirring reaction, centrifuging, and washing with deionized water to obtain a two-dimensional molecular brush with a side chain containing metal ion macromolecular salt;
(3) re-dispersing the two-dimensional molecular brush with the side chain containing the metal ion macromolecular salt, which is prepared in the step (2), in deionized water to prepare a two-dimensional molecular brush water dispersion solution, re-dispersing the water dispersion solution in an ethanol/water mixed solvent, and performing suction filtration on a porous membrane to obtain a two-dimensional molecular brush membrane;
(4) and (3) dropwise adding dioxane on the surface of the lithium metal sheet, covering the two-dimensional molecular brush film prepared in the step (3) on the surface of the lithium metal sheet (the two-dimensional molecular brush film layer is in contact with the lithium metal sheet), applying pressure, and transferring the two-dimensional molecular brush film to the surface of the lithium metal sheet to construct the two-dimensional molecular brush artificial SEI film.
Preferably, the monomer in the step (1) is one or more of p-styrene sulfonate, (4-styrene sulfonyl) (trifluoromethane sulfonyl) imide salt and 4-styrene sulfonyl (benzene sulfonyl) imide salt; the initiator is one or more of potassium persulfate, sodium persulfate and ammonium persulfate.
Preferably, the acid in the step (2) is one or more of nitric acid, hydroiodic acid, hydrobromic acid, hydrochloric acid, sulfuric acid and acetic acid; the metal salt is one or more of silver nitrate, zinc acetate, stannous chloride, lithium nitrate, lithium acetate, lithium chloride and lithium hydroxide.
Preferably, the porous film in step (3) is a porous polyethylene film or a porous polypropylene film.
Preferably, the molar ratio of the monomer to the initiator in the step (1) is 200-2000: 1; the mass ratio of the monomer to GO is 10-100: 1; the concentration of the graphene oxide aqueous dispersion is 0.2-2 mg/mL-1。
Preferably, the concentration of the acid solution in the step (2) is 1-10 wt%; the concentration of the metal salt solution is 0.2-2 mol.L-1The mass-to-volume ratio of the acid-washed product to the aqueous metal salt solution is 0.2 to 2 g.L-1。
Preferably, the concentration of the aqueous dispersion of the two-dimensional molecular brush in the step (3) is 1 mg/mL-1(ii) a The volume ratio of ethanol to water in the ethanol/water mixed solvent is 1: 1.
The application of the reactive two-dimensional molecular brush artificial SEI film in a lithium metal ion battery.
The invention provides a lithium ion battery which comprises a positive electrode and a lithium metal negative electrode plate modified by a reactive artificial SEI film, and is prepared by assembling.
The principle of the invention is as follows: firstly, functional polymer salt is grafted on the surface of Graphene Oxide (GO) through free radical polymerization to obtain a two-dimensional molecular brush with a side chain of the functional polymer salt. Then, a series of two-dimensional molecular brushes with side chains containing various metal ion macromolecular salts and a molecular framework of GO are obtained by an ion exchange technology. And then, the synthesized two-dimensional molecular brush is subjected to suction filtration on a commercial porous membrane through a simple green suction filtration technology, and then the two-dimensional molecular brush membrane is transferred to the surface of a lithium metal sheet through a membrane transfer technology, so that the artificial SEI membrane of the two-dimensional molecular brush is constructed.
Compared with the prior art, the invention has the following beneficial effects:
(1) because lithium metal has the lowest chemical potential, the molecular brush side chain macromolecular salt can generate a displacement reaction with the lithium metal to generate macromolecular lithium salt and metal nano-particles; the metal nano particles can be used as nucleation sites for lithium ion deposition, so that lithium ions are induced to be uniformly nucleated and deposited, and the stability of the lithium metal negative electrode is obviously improved.
(2) The lithium salt of macromolecule produced by the replacement reaction can be used as the lithium single ion conductor, thus effectively improving the transmission efficiency of lithium ion in SEI film and reducing the interface impedance; and the electrostatic interaction between the polymer and the lithium ions can induce the lithium ion flow to be uniformly dispersed on the molecular level of the surface of the electrode, so that the deposition morphology of the lithium is improved.
(3) The molecular skeleton of the two-dimensional molecular brush is high-modulus graphene oxide, so that the mechanical strength of the SEI film can be effectively improved, and the artificial SEI film can sufficiently resist stress tearing caused by volume change of a lithium metal negative electrode.
(4) The two-dimensional molecular brush has excellent film forming property, and the two-dimensional molecular brush obtained by the vacuum filtration technology is uniform and compact, so that direct contact between electrolyte and lithium metal can be effectively prevented, and side reaction between the electrolyte and the lithium metal can be inhibited, thereby further improving the stability of the lithium metal cathode.
Lithium metal negative electrode protected by artificial SEI film based on four-point two-dimensional molecular brush at high current density (5 mAhcm)-2) The ultra-high cycling stability (over 1000h) is still demonstrated.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.
Fig. 1 is an infrared spectrum (fig. 1a), an X-ray photoelectron spectrum (fig. 1b) and a scanning electron micrograph (fig. 1c) of an intermediate product i provided in example 1 of the present invention.
Fig. 2 is an X-ray photoelectron spectrum (fig. 2a) and a scanning electron micrograph (fig. 2b) of an intermediate product two provided in example 1 of the present invention.
Fig. 3 is a digital photograph (fig. 3a), a scanning electron microscope (fig. 3b) and an atomic force microscope (fig. 3c) of intermediate product three provided in example 1 of the present invention.
Fig. 4 is a digital photograph (fig. 4a) and a scanning electron microscope (sem) photograph (4b) of the lithium metal sheet modified by the reactive two-dimensional brush artificial SEI film provided in example 1 of the present invention.
Fig. 5 is an Ag element fine X-ray photoelectron spectrum (fig. 5a), a selected area electron diffraction pattern (5b), and a high-resolution transmission electron micrograph (fig. 5c) of the lithium metal sheet modified by the reactive two-dimensional brush artificial SEI film provided in example 1 of the present invention.
Fig. 6 is a time-voltage curve of a CR2032 coin cell provided in example 1 of the invention.
FIG. 7 shows that the CR2032 coin cell provided by embodiment 1 of the invention is at 1mAcm-2-1mAhcm-2Scanning electron micrographs of the lithium metal sheets after 10 cycles of cycling under the conditions.
FIG. 8 shows that the CR2032 coin cell provided by embodiment 2 of the invention has a density of 1mAcm-2-1mAhcm-2Scanning electron micrographs of the lithium metal sheets after 10 cycles of cycling under the conditions.
FIG. 9 shows a CR2032 coin cell of embodiment 3 of the invention at 1mAcm-2-1mAhcm-2Scanning electron micrographs of the lithium metal sheets after 10 cycles of cycling under the conditions.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention and the accompanying drawings.
It is understood that the step of infrared spectrogram testing comprises: the intermediate product one was mixed with potassium bromide in a ratio of about 1: mixing at a mass ratio of 50, grinding uniformly, and tabletting. Next, the infrared spectrum of the sample from the infrared spectrometer was Fourier transformed using TENSOR27 from Bruker.
It is understood that the steps of the sem test include: fixing the product sample on a sample table by using conductive adhesive, and placing the sample table in a vacuum drying oven for drying treatment for 12 h. After the metal spraying treatment, the structural morphology of the sample is observed by an S-4800 cold field emission scanning electron microscope produced by Hitachi high and new technology under the voltage of 10 kV.
It is understood that the atomic force microscopy test includes the steps of: and transferring the two-dimensional molecular brush film on the third intermediate product onto a glass sheet, and then placing the sample in a vacuum drying oven for drying treatment for 12 h. Next, the thickness of the two-dimensional brush film was measured by means of a Dimension Fastscan probe microscope manufactured by Bruker.
The invention is further illustrated by the following examples.
Example 1
A preparation method of a reactive two-dimensional molecular brush artificial SEI film modified negative electrode material comprises the following steps:
step (1): 2.291g (10mmol) of sodium p-styrenesulfonate (SSNa) and 0.0135g (0.05mmol) of potassium persulfate were added to a 50mL eggplant-shaped bottle, and then 50mL of GO aqueous dispersion (1 mgmL in concentration)-1) Adding into a eggplant-shaped bottle, introducing nitrogen for 30min, reacting for 12h at 65 ℃, and stopping reaction. After the reaction is finished, performing centrifugal separation, and centrifugally washing for 3 times by using deionized water to obtain an intermediate product I (GO-g-PSSNa);
step (2): dispersing the GO-g-PSSNa prepared in the step (1) in a nitric acid aqueous solution (30mL of water +3mL of 65% nitric acid), stirring for 10min, centrifuging, and repeatedly performing acid washing-stirring-centrifuging operations for 3 times to remove Na+And then centrifugally washing the product to be neutral by using deionized water to obtain GO-g-PSSH. Next, GO-g-PSSH was dispersed in 30mL of silver nitrate aqueous solution (concentration 0.2mol L)-1) After stirring for 12h in a shading mode, centrifugally washing for 5 times by using deionized water to obtain an intermediate product II (GO-g-PSSAg);
and (3): re-dispersing the GO-g-PSSAg prepared in the step (2) in deionized water (the concentration is 1 mgmL)-1) Further dispersing 1mLGO-g-PSSAg aqueous dispersion in a mixed solvent of 25mL ethanol and 25mL deionized water, taking a Celgard2500 porous polypropylene diaphragm as a filter membrane, and carrying out suction filtration on the GO-g-PSSAg to obtain an intermediate product III (GO-g-PSSAg @ PP);
and (4): dropwise adding a small amount of dioxane on the surface of a lithium metal sheet, covering the GO-g-PSSAg @ PP film on the surface of the lithium metal sheet (one side of the GO-g-PSSAg film layer is in contact with the lithium metal sheet), applying a certain pressure by using an oil press, and spontaneously transferring the GO-g-PSSAg film layer to the surface of the lithium metal sheet from a PP diaphragm, thereby constructing the GO-g-PSSAg two-dimensional molecular brush lithium metal sheet (GO-g-PSSAg @ Li) protected by an artificial SEI film.
The GO-g-PSSAg @ Li is applied to a lithium ion battery, in the lithium ion battery, the GO-g-PSSAg @ Li is used as a working electrode, an unmodified lithium metal sheet is used as a counter electrode, a lithium ion symmetrical battery is assembled in a glove box in an argon atmosphere, and the content of water and oxygen in the glove box needs to be kept lower than 0.1 ppm. The assembled button cell is CR2032, the diaphragm is Celgard2325, the electrolyte used is prepared by dissolving lithium bistrifluoromethanesulfonimide in a mixed solvent consisting of 1, 3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1 and adding 1% of LiNO3The prepared electrolyte dosage is 30 mu L.
The lithium ion symmetric battery is subjected to constant-current charge and discharge performance test on a LAND battery test system (provided by Wuhan blue-electron Co., Ltd.), and the charge and discharge current density is 1 or 5mAcm-2The charge and discharge capacity is 1mAhcm-2。
To further illustrate the effect of the GO-g-PSSAg artificial SEI film prepared in example 1, the following characterization was performed.
FIG. 1 shows an infrared spectrum, an X-ray photoelectron spectrum and a scanning electron micrograph of the first intermediate product obtained in example 1. As can be seen from fig. 1, PSSNa has been successfully grafted onto GO and maintains a good two-dimensional sheet morphology after PSSNa macromolecules are grafted.
FIG. 2 shows an X-ray photoelectron spectrum and a scanning electron micrograph of a second intermediate obtained in example 1. As can be seen from FIG. 2, the ion exchange technique was successfully performed, and the intermediate product II obtained after ion exchange still maintains good two-dimensional sheet morphology.
Fig. 3 is a digital photograph, a scanning electron microscope photograph, and an atomic force microscope photograph of intermediate product three provided in example 1 of the present invention. As can be seen from FIG. 3, the intermediate product II covers the surface of the porous polypropylene membrane to form a uniform and dense two-dimensional molecular brush membrane layer, and the thickness of the membrane layer is only 84 nm.
Fig. 4 is a digital photograph (4a) and a scanning electron micrograph (4b) of the GO-g-PSSAg two-dimensional molecular brush artificial SEI film prepared in example 1. As can be seen from fig. 4, the two-dimensional molecular brush artificial SEI film on the surface of the lithium metal sheet is uniform and dense.
Fig. 5 shows fine X-ray photoelectron spectrum (fig. 5a), selective electron diffraction pattern (fig. 5b) and high-resolution transmission electron micrograph (fig. 5c) of Ag element of the lithium metal sheet modified with the reactive two-dimensional brush artificial SEI film according to example 1. FIG. 5 demonstrates Ag in GO-g-PSSAg films+Is reduced into Ag simple substance.
Fig. 6 shows the cycling performance of the assembled CR2032 coin cell of example 1. Compared to lithium metal sheets without protective film (pristine Li) and lithium metal sheets with GO protective film (GO @ Li), symmetric batteries assembled with the GO-g-PSSAg @ Li exhibited superior cycling stability.
FIG. 7 shows the assembled CR2032 coin cell of example 1 at 1mA cm-2-1mAh cm-2Scanning electron micrographs of the lithium metal sheets after 10 cycles of cycling under the conditions. As can be seen from FIG. 7, the GO-g-PSSAg @ Li surface still keeps a flat and compact morphology after cycling, and no lithium dendrite is observed, so that the protection effect of the GO-g-PSSAg artificial SEI on the lithium metal negative electrode is further confirmed.
Example 2
A preparation method of a reactive two-dimensional molecular brush artificial SEI film modified negative electrode material comprises the following steps:
step (1): 2.291g (10mmol) of sodium p-styrenesulfonate (SSNa) and 0.0135g (0.05mmol) of potassium persulfate were added to a 50mL eggplant-shaped bottle, and then 50mL of GO aqueous dispersion (1 mgmL in concentration)-1) Adding into a eggplant-shaped bottle, introducing nitrogen for 30min, reacting for 12h at 65 ℃, and stopping reaction. After the reaction is finished, performing centrifugal separation, and centrifugally washing for 3 times by using deionized water to obtain an intermediate product I (GO-g-PSSNa);
step (2): dispersing the GO-g-PSSNa prepared in the step (1) in aqueous nitric acid (30mL of water +3mL of 65% nitrate)Acid), stirring for 10min, centrifuging, repeating acid washing-stirring-centrifuging operation for 3 times to remove Na+And then centrifugally washing the product to be neutral by using deionized water to obtain GO-g-PSSH. Next, GO-g-PSSH was dispersed in 30mL of an aqueous lithium acetate solution (2.0 mol L concentration)-1) After stirring for 12h in a shading mode, centrifugally washing for 5 times by using deionized water to obtain an intermediate product II (GO-g-PSSLi);
and (3): re-dispersing the GO-g-PSSLi prepared in the step (2) in deionized water (the concentration is 1 mgmL)-1) Further dispersing 1mLGO-g-PSSLi aqueous dispersion in a mixed solvent of 25mL ethanol and 25mL deionized water, taking a Celgard2500 porous polypropylene diaphragm as a filter membrane, and carrying out suction filtration on GO-g-PSSLi on the diaphragm to obtain an intermediate product III (GO-g-PSSLi @ PP);
and (4): dropwise adding a small amount of dioxane on the surface of a lithium metal sheet, covering the GO-g-PSSLi @ PP film on the surface of the lithium metal sheet (one side of the GO-g-PSSLi film layer is in contact with the lithium metal sheet), applying a certain pressure by using an oil press, and spontaneously transferring the GO-g-PSSLi film layer from a PP diaphragm to the surface of the lithium metal sheet to construct the GO-g-PSSLi two-dimensional molecular brush lithium metal sheet (GO-g-PSSLi @ Li) protected by the artificial SEI film.
The GO-g-PSSLi @ Li is applied to a lithium ion battery, wherein the GO-g-PSSLi @ Li is used as a working electrode, an unmodified lithium metal sheet is used as a counter electrode, a lithium ion symmetrical battery is assembled in a glove box in an argon atmosphere, and the content of water and oxygen in the glove box needs to be kept lower than 0.1 ppm. The assembled button cell is CR2032, the diaphragm is Celgard2325, the electrolyte used is prepared by dissolving lithium bistrifluoromethanesulfonimide in a mixed solvent consisting of 1, 3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1 and adding 1% of LiNO3The prepared electrolyte dosage is 30 mu L.
The lithium ion symmetric battery is subjected to constant-current charge and discharge performance test on a LAND battery test system (provided by Wuhan blue-electron Co., Ltd.), and the charge and discharge current density is 1mAcm-2The charge and discharge capacity is 1mAhcm-2。
To further illustrate the effect of the GO-g-PSSLi artificial SEI film prepared in example 2, the following characterization was performed.
FIG. 8 shows the assembled CR2032 coin cell of example 2 at 1mA cm-2-1mAh cm-2Scanning electron micrographs of the lithium metal sheets after 10 cycles of cycling under the conditions. As can be seen from FIG. 8, the GO-g-PSSLi @ Li surface still keeps a flat and compact morphology after cycling, and no lithium dendrite is observed, so that the protection effect of the GO-g-PSSLi artificial SEI on the lithium metal negative electrode is further verified.
Example 3
A preparation method of a reactive two-dimensional molecular brush artificial SEI film modified negative electrode material comprises the following steps:
step (1): 2.291g (10mmol) of sodium p-styrenesulfonate (SSNa) and 0.0135g (0.05mmol) of potassium persulfate were added to a 50mL eggplant-shaped bottle, and then 50mL of GO aqueous dispersion (1 mgmL in concentration)-1) Adding into a eggplant-shaped bottle, introducing nitrogen for 30min, reacting for 12h at 65 ℃, and stopping reaction. After the reaction is finished, performing centrifugal separation, and centrifugally washing for 3 times by using deionized water to obtain an intermediate product I (GO-g-PSSNa);
step (2): dispersing the GO-g-PSSNa prepared in the step (1) in a nitric acid aqueous solution (30mL of water +3mL of 65% nitric acid), stirring for 10min, centrifuging, and repeatedly performing acid washing-stirring-centrifuging operations for 3 times to remove Na+And then centrifugally washing the product to be neutral by using deionized water to obtain GO-g-PSSH. Next, GO-g-PSSH was dispersed in 30mL of an aqueous zinc acetate solution (concentration 2.0mol L)-1) After stirring for 12h in a shading mode, centrifugally washing the mixture for 5 times by using deionized water to obtain an intermediate product II (GO-g-PSSZn);
and (3): re-dispersing the GO-g-PSSZn prepared in the step (2) in deionized water (the concentration is 1 mgmL)-1) Further dispersing 1mLGO-g-PSSZn aqueous dispersion in a mixed solvent of 25mL ethanol and 25mL deionized water, taking a Celgard2500 porous polypropylene diaphragm as a filter membrane, and carrying out suction filtration on GO-g-PSSZn on the diaphragm to obtain an intermediate product III (GO-g-PSSZn @ PP);
and (4): dropwise adding a small amount of dioxane on the surface of a lithium metal sheet, covering the GO-g-PSSZn @ PP film on the surface of the lithium metal sheet (one side of the GO-g-PSSZn film layer is in contact with the lithium metal sheet), applying a certain pressure by using an oil press, and spontaneously transferring the GO-g-PSSZn film layer to the surface of the lithium metal sheet from a PP diaphragm to construct the GO-g-PSSZn two-dimensional molecular brush lithium metal sheet (GO-g-PSSZn @ Li) protected by an artificial SEI film.
The GO-g-PSSZn @ Li is applied to a lithium ion battery, in the lithium ion battery, the GO-g-PSSZn @ Li is used as a working electrode, an unmodified lithium metal sheet is used as a counter electrode, a lithium ion symmetrical battery is assembled in a glove box in an argon atmosphere, and the content of water and oxygen in the glove box needs to be kept lower than 0.1 ppm. The assembled button cell is CR2032, the diaphragm is Celgard2325, the electrolyte used is prepared by dissolving lithium bistrifluoromethanesulfonimide in a mixed solvent consisting of 1, 3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1 and adding 1% of LiNO3The prepared electrolyte dosage is 30 mu L.
The lithium ion symmetric battery is subjected to constant-current charge and discharge performance test on a LAND battery test system (provided by Wuhan blue-electron Co., Ltd.), and the charge and discharge current density is 1mAcm-2The charge and discharge capacity is 1mAhcm-2。
To further illustrate the effect of the GO-g-PSSZn artificial SEI film prepared in example 3, the following characterization was performed.
FIG. 9 shows the assembled CR2032 coin cell of this example 3 at 1mA cm-2-1mAh cm-2Scanning electron micrographs of the lithium metal sheets after 10 cycles of cycling under the conditions. As can be seen from FIG. 9, the surface of GO-g-PSSZn @ Li still keeps a flat and compact morphology after cycling, and no lithium dendrite is observed, so that the protection effect of the artificial SEI of GO-g-PSSZn on the lithium metal negative electrode is further verified.
Claims (10)
1. A preparation method of a reactive two-dimensional molecular brush SEI film modified negative electrode material is characterized by comprising the following steps:
(1) grafting functional polymer salt on the surface of graphene oxide through free radical polymerization to obtain a two-dimensional molecular brush with a side chain of the functional polymer salt;
(2) through ion exchange, a two-dimensional molecular brush with a side chain containing metal ion macromolecular salt is obtained;
(3) filtering the synthesized two-dimensional molecular brush on a porous membrane to obtain a two-dimensional molecular brush membrane;
(4) and transferring the two-dimensional molecular brush film to the surface of the lithium metal sheet by a film transfer technology to construct the negative electrode material modified by the two-dimensional molecular brush SEI film.
2. The method of claim 1, comprising the steps of:
(1) mixing and stirring a monomer, an initiator and the graphene oxide aqueous dispersion uniformly, introducing inert gas to remove oxygen, sealing, and reacting for 6-48 hours at the temperature of 65-85 ℃; centrifuging after the reaction is finished, and washing with water to obtain a two-dimensional molecular brush with a side chain being functional polymer salt;
(2) dispersing the two-dimensional molecular brush prepared in the step (1) in an acid solution again, stirring, centrifuging, acid washing, centrifuging, and washing with deionized water to be neutral; then, dispersing the product after acid washing in a metal salt water solution, carrying out light-shielding stirring reaction, centrifuging, and washing with deionized water to obtain a two-dimensional molecular brush with a side chain containing metal ion macromolecular salt;
(3) re-dispersing the two-dimensional molecular brush with the side chain containing the metal ion macromolecular salt, which is prepared in the step (2), in deionized water to prepare a two-dimensional molecular brush water dispersion solution, re-dispersing the water dispersion solution in an ethanol/water mixed solvent, and performing suction filtration on a porous membrane to obtain a two-dimensional molecular brush membrane;
(4) and (3) dropwise adding dioxane on the surface of the lithium metal sheet, covering the two-dimensional molecular brush film prepared in the step (3) on the surface of the lithium metal sheet (the two-dimensional molecular brush film layer is in contact with the lithium metal sheet), applying pressure, and transferring the two-dimensional molecular brush film to the surface of the lithium metal sheet to construct the two-dimensional molecular brush artificial SEI film.
3. The preparation method according to claim 2, wherein the monomer in step (1) is one or more of p-styrenesulfonate, (4-styrenesulfonyl) (trifluoromethanesulfonyl) imide salt, and 4-styrenesulfonyl (phenylsulfonyl) imide salt; the initiator is one or more of potassium persulfate, sodium persulfate and ammonium persulfate.
4. The preparation method according to claim 3, wherein the acid in step (2) is one or more of nitric acid, hydroiodic acid, hydrobromic acid, hydrochloric acid, sulfuric acid and acetic acid; the metal salt is one or more of silver nitrate, zinc acetate, stannous chloride, lithium nitrate, lithium acetate, lithium chloride and lithium hydroxide.
5. The production method according to claim 4, wherein the porous film in the step (3) is a porous polyethylene film or a porous polypropylene film.
6. The production method according to any one of claims 2 to 5,
the molar ratio of the monomer to the initiator in the step (1) is 200-2000: 1; the mass ratio of the monomer to GO is 10-100: 1; the concentration of the graphene oxide aqueous dispersion is 0.2-2 mg/mL-1；
The concentration of the acid solution in the step (2) is 1-10 wt%; the concentration of the metal salt solution is 0.2-2 mol.L-1The mass-to-volume ratio of the acid-washed product to the aqueous metal salt solution is 0.2 to 2 g.L-1。
7. The method according to claim 6, wherein the concentration of the aqueous dispersion of the two-dimensional molecular brush in the step (3) is 1 mg-mL-1(ii) a The volume ratio of ethanol to water in the ethanol/water mixed solvent is 1: 1.
8. The negative electrode material modified by the SEI film of the reactive two-dimensional molecular brush prepared by the method of any one of claims 1 to 7.
9. The use of the reactive two-dimensional molecular brush SEI film modified negative electrode material of claim 8 in a lithium metal ion battery.
10. A lithium ion battery, comprising a positive electrode and the negative electrode material modified by the SEI film of claim 9.
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