Multifunctional two-dimensional hybrid polymer artificial SEI (solid electrolyte interface) membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium battery negative electrode interface modification, and discloses a multifunctional two-dimensional hybrid polymer artificial SEI membrane and a preparation method and application thereof. Comprising a compound as shown in a formula I, a polymer brush is grafted on the surface of brominated graphene oxide through atom transfer radical polymerization (ATRP), monomers of the polymer brush are carboxyl-containing monomers and fluorine-containing monomers, and the artificial SEI membrane is constructed through spin coating and membrane forming. The multifunctional artificial SEI film provided by the invention has the structural and functional characteristics of two-dimensional graphene oxide and in-situ reaction type macromolecules, the mechanical property of the film can be remarkably improved by an accumulated two-dimensional skeleton, the Young modulus can reach 3.7 GPa, the growth of lithium dendrites is inhibited, and the performance of the film is improved. Functional groups (carboxyl and fluoro) in the hybrid polymer brush and lithium metal are subjected to in-situ chemical reaction, so that the electrode interface stability and the lithium deposition uniformity are improved, and the hybrid polymer brush has wide application prospects in the field of lithium batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery negative electrode interface modification, and particularly relates to a multifunctional two-dimensional hybrid polymer artificial SEI film and a preparation method and application thereof. BACKGROUND

[0002] Lithium metal anode is considered as the core material of the next generation of high energy density batteries due to its ultra-high theoretical specific capacity (3860 mAh g -1 ) and the lowest electrochemical potential (-3.04 V vs. SHE). However, the practical application of lithium metal anode still faces many challenges. Since lithium metal is extremely reactive, it will spontaneously react with solvent molecules in the liquid electrolyte system, consuming active lithium and electrolyte, and finally producing a solid electrolyte interface (SEI) layer on the surface of lithium metal, which is mainly composed of inorganic and organic by-products. Unfortunately, the unstable original SEI layer leads to uneven lithium nucleation and plating (uncontrollable dendritic lithium growth), and exacerbates the consumption of lithium metal and organic electrolyte during charging and discharging, thereby causing serious safety problems, low coulombic efficiency and rapid capacity decay during cycling.

[0003] At present, various functional materials, including inorganic materials (such as Li3PO4, LiF, Li3N and TiO2, etc.) and organic polymers (such as poly (vinylidene carbonate-acrylonitrile copolymer) (P(VC-co-AN), poly (dimethylsiloxane) (PDMS), polymethyl methacrylate (PMMA), polyurea and perfluoropolyether (PFPE), etc.), have been developed as artificial SEI protective layers to improve the stability of lithium metal anode interface. Inorganic SEI layer usually allows fast shuttling of lithium ions, has low energy barrier, and resists lithium dendrite penetration, but due to its fragility and weak interface contact, inorganic artificial SEI film is easy to break during cycling and can cause lithium dendrite growth along the grain boundary, thereby causing short circuit risk. Polymer SEI layer has excellent flexibility and provides excellent electrode interface, while organic polymer-based artificial SEI film usually has low mechanical modulus and low ionic conductivity, and is difficult to inhibit dendrite growth during long-term cycling, such as a class of all-organic artificial SEI film (xPCMS-g-PEGMA / LN) prepared by Wu et al., which has a low mechanical modulus (1.01 GPa) and ionic transference number (0.63) (Nature Nanotechnology, 2022, 17, 613-621).

[0004] Therefore, developing a new artificial SEI film with high mechanical modulus, high ionic transference efficiency and high current density resistance is the key to breaking through the technical bottleneck of lithium metal negative electrode. SUMMARY

[0005] In view of the defects and shortcomings in the prior art, a primary object of the present application is to provide a multifunctional two-dimensional hybrid polymer artificial SEI film, which fundamentally solves the technical bottleneck of high interface impedance and poor cycle stability, and has a breakthrough significance for improving the rate performance and safety of high-energy-density lithium batteries.

[0006] A further object of the present application is to provide a preparation method of the multifunctional two-dimensional hybrid polymer artificial SEI film, which designs a composite SEI film with self-adaptive repair characteristics by constructing a new hybrid interface structure based on a two-dimensional graphene oxide skeleton and using a functional molecule brush in-situ reaction concept. A functional group is in-situ chemically reacted with lithium metal through an atomic transfer radical polymerization (ATRP) technology for grafting a fluorine / carboxyl bicomponent copolymer brush (P(TFEA-co-MA)) on the surface of brominated graphene oxide and a spin coating film forming process. The graphene oxide skeleton not only forms a dense mechanical barrier layer, but also optimizes the lithium ion transmission path in the nanochannel of the stacked structure; at the same time, a lithium fluoride-lithium carboxylate gradient interface in-situ generated in the molecular brush guides uniform deposition of lithium ions, thereby simultaneously realizing dendrite inhibition and interface stabilization.

[0007] A further object of the present application is to provide an application of the multifunctional two-dimensional hybrid polymer artificial SEI film.

[0008] The object of the present application is achieved by the following technical solutions.

[0009] A multifunctional two-dimensional hybrid polymer artificial SEI film, comprising a compound shown in formula I, denoted as GO-g-P(TFEA-co-MA):

[0010]

[0011] wherein R2= m in R2 is 800-1000, and n is 500-600.

[0012] Preferably, the molecular weight of the grafted side chain high polymer in the compound is 145000-178000, and more preferably, the side chain high polymer is P(TFEA-co-MA), wherein TFEA is 2,2,2-trifluoroethyl acrylate, and MA is methyl acrylate.

[0013] Preferably, the thickness of the multifunctional two-dimensional hybrid polymer artificial SEI film is 450±100 nm, the Young's modulus is 2-4 GPa, and the ion migration number is 0.6-0.82.

[0014] A preparation method of a multifunctional two-dimensional hybrid polymer artificial SEI film, wherein the multifunctional two-dimensional hybrid polymer artificial SEI film is obtained by grafting polymer brushes on the surface of brominated graphene oxide through an atom transfer radical polymerization reaction, and then being formed into a film through spin coating.

[0015] The monomers of the polymer brushes are carboxyl-containing monomers and fluorine-containing monomers.

[0016] Preferably, the method comprises the following specific steps:

[0017] (1) Preparation of brominated graphene oxide: graphene oxide and triethylamine are dispersed in a solvent, ultrasonic treatment is performed, a bromination reagent is added, stirring is performed, and then reaction is performed, after the reaction is completed, centrifugation, washing and drying are performed, and brominated graphene oxide is obtained;

[0018] (2) ATRP reaction: the brominated graphene oxide is dispersed in a solvent, monomers, a ligand, a catalyst and a reducing agent are added, and ATRP reaction is performed in an inert atmosphere, after the reaction is completed, washing and drying are performed, and a two-dimensional hybrid polymer GO-g-P(TFEA-co-MA) is obtained;

[0019] (3) Film formation through spin coating: the GO-g-P(TFEA-co-MA) is dispersed in dimethyl sulfoxide to form a solution A, pure dimethyl sulfoxide is spin coated first, then the solution A is spin coated, and after heat treatment, a multifunctional two-dimensional hybrid polymer artificial SEI film is obtained.

[0020] Preferably, the molar ratio of the carboxyl-containing monomers to the fluorine-containing monomers in the monomers in step (2) is 2-6:1;

[0021] The carboxyl-containing monomers are at least one selected from the group consisting of acrylic acid, methacrylic acid, tert-butyl acrylate, tert-butyl methacrylate and maleic acid;

[0022] The fluorine-containing monomers are at least one selected from the group consisting of 2,2,2-trifluoroethyl acrylate, hexafluoroisopropyl methacrylate and trifluoroethyl methacrylate.

[0023] Preferably, the ligand in step (2) is at least one selected from the group consisting of pentamethyldiethylenetriamine, bipyridine and tris(2-dimethylaminoethyl)amine;

[0024] The catalyst is cuprous bromide, cupric chloride or ferrous chloride; and the reducing agent is ascorbic acid.

[0025] Preferably, the mass ratio of the total mass of the monomers to the mass of the brominated graphene oxide in step (2) is 14-28:1;

[0026] The mass ratio of the monomers to the catalyst in step (2) is 40-100:1;

[0027] The temperature of the ATRP reaction in step (2) is 60±5℃, and the reaction time is 24±6h.

[0028] Preferably, the reaction time in step (1) is 24±6h.

[0029] The mass-volume ratio g / mL / mL of the graphene oxide, triethylamine and brominating agent is 1:10-30:6-18.

[0030] The lateral size of the graphene oxide is 1-5μm, and the thickness is about 0.2-2nm.

[0031] The brominating agent is 2-bromoisobutyryl bromide.

[0032] The washing is 3-5 times of washing with DMF, ethanol and water in sequence.

[0033] Preferably, the ultrasonic in step (1) is ice bath ultrasonic.

[0034] Preferably, the concentration of solution A in step (3) is 0.01-0.03g / mL; and the volume ratio of pure dimethyl sulfoxide to solution A is 1:1-3.

[0035] The heat treatment temperature is 80-120℃, and the treatment time is 10-50min.

[0036] Preferably, the heat treatment is completed in an argon glove box (O2<0.5ppm, H2O<0.1ppm).

[0037] Preferably, the spin coating speed is 2000±1000rpm, and the spin coating time is 60±30s.

[0038] The above multifunctional two-dimensional hybrid polymer artificial SEI film is applied in the field of lithium batteries.

[0039] Preferably, the negative electrode, the positive electrode and the electrolyte are assembled into a symmetric lithium metal battery or a lithium iron phosphate (LFP) full battery, and the negative electrode is a coated lithium negative electrode (GO-g-P(TFEA-co-MA)@Li).

[0040] Preferably, the electrolyte comprises:

[0041] Symmetric lithium metal battery: 1M LiTFSI in DOL / DME (1:1v / v) containing 2wt% LiNO3, DOL / DME is 1,3-dioxolane / ethylene glycol dimethyl ether;

[0042] Lithium iron phosphate (LFP) full battery: 1M LiPF6 in EC / DEC (1:1v / v), EC / DEC is ethylene carbonate / diethyl carbonate.

[0043] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0044] (1) By precise grafting strategy, functional polymer brushes are constructed on the surface of graphene oxide, and the dense stacking of two-dimensional skeleton forms a high-strength barrier structure, which significantly improves the interface mechanical strength and effectively inhibits the penetration of lithium dendrites; at the same time, the ordered microchannels between the polymer brushes provide a fast path for lithium ion transmission, greatly improving the ion migration efficiency and reducing the deposition energy barrier.

[0045] (2) The active groups (carboxyl and fluorine groups) in the functional molecular brush react with lithium metal in situ to form a composite interface layer with gradient characteristics. The lithium fluoride component guides the uniform nucleation of lithium ions, and the lithium carboxylate component forms a flexible buffer network, both of which cooperatively realize the dynamic self-adaptation of the interface, ensuring the structural integrity of the electrode in the long cycle process.

[0046] (3) The graphene oxide matrix endows the interface film with excellent thermal stability and chemical inertness, and its unique layered stacking structure effectively alleviates the volume strain in the lithium deposition / peeling process; the covalently bonded molecular brush avoids the interface delamination risk of traditional composite materials, so that the artificial SEI film maintains long-term functional stability under severe electrochemical conditions, significantly prolonging the cycle life of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 Synthetic scheme of GO-g-P(TFEA-co-MA) artificial SEI film;

[0048] Figure 2 Infrared spectrum of GO-g-P(TFEA-co-MA);

[0049] Figure 3 SEM images of the cross-section (a) and surface (b) of GO-g-P(TFEA-co-MA) artificial SEI film;

[0050] Figure 4 AFM image of the Young's modulus of GO-g-P(TFEA-co-MA);

[0051] Figure 5 Potentiostatic polarization curve of the symmetric lithium battery based on GO-g-P(TFEA-co-MA) artificial SEI film (built-in graph: impedance graph before and after polarization);

[0052] Figure 6 Lithium deposition / peeling voltage-time curve of the symmetric lithium battery based on bare Li and GO-g-P(TFEA-co-MA)@Li electrode;

[0053] Figure 7Cycling performance of lithium iron phosphate full battery based on bare Li and GO-g-P(TFEA-co-MA)@Li electrodes at 2C condition.

[0054] Figure 8 Cycling performance of lithium iron phosphate full battery based on GO-g-PTFEA@Li and GO-g-PMA@Li electrodes at 2C condition. DETAILED DESCRIPTION

[0055] The application will be further described in detail below with specific examples, but the embodiments of the application are not limited thereto. For the process parameters not specifically mentioned, the conventional techniques can be referred to.

[0056] Graphene oxide nanoplatelets: lateral size of 1-5 μm, thickness of about 1.2 nm.

[0057] Electrolyte: LiPF6 is dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), wherein the volume ratio of EC and DEC is 1:1, and the concentration of LiPF6 in the electrolyte is 1M.

[0058] Example 1

[0059] This example provides a preparation of a two-dimensional hybrid polymer artificial SEI film and its application in lithium metal batteries, comprising the following steps:

[0060] (1) 100 mg of graphene oxide (rGO) and 2 mL of triethylamine were dispersed in 100 mL of anhydrous DMF, and ultrasonicated for 30 min in an ice bath. Then, 1.2 mL of 2-bromoisobutyryl bromide was added dropwise, and stirred at 0℃ for 2 h, and then reacted at room temperature for 24 h. Centrifugation was performed at 2000 r / min, and then sequentially washed with DMF, ethanol and deionized water for three times, and then freeze-dried to obtain GO-Br;

[0061] (2) 50 mg of GO-Br obtained in step (1) was dispersed in 50 mL of anhydrous DMF, and then 0.05 g of pentamethyl diethylene triamine, 1 g (11.6 mmol) of methacrylic acid (MA) and 0.4 g (2.6 mmol) of 2,2,2-trifluoroethyl acrylate (TFEA) were added. After degassing for three times, 0.03 g of cuprous bromide and 0.02 g of ascorbic acid were added, and then reacted at 60℃ under argon protection for 24 h. Filtration was performed through a 0.22 μm filter membrane, and then sequentially washed with DMF, methanol and deionized water until the filtrate was colorless, and then freeze-dried to obtain GO-g-P(TFEA-co-MA);

[0062] (3) 20 mg GO-g-P(TFEA-co-MA) was dispersed in 2 mL anhydrous dimethyl sulfoxide to form a solution (0.01 g / mL), 100 μL of the solvent was added dropwise to the surface of lithium foil, and spin-coated at 2000 rpm for 30 s; 100 μL of the solution was spin-coated for 60 s, and the electrode was treated on a hot stage at 100°C for 30 min to obtain a GO-g-P(TFEA-co-MA)@Li electrode, and the electrode was covered with a GO-g-P(TFEA-co-MA) film, i.e., a two-dimensional hybrid polymer artificial SEI film. Testing showed that the thickness of the GO-g-P(TFEA-co-MA) film was 0.45 μm, the Young's modulus was 3.7 GPa, the ion transference number was 0.79, and the maximum current could reach 10 mA cm -2 ;

[0063] (4) The film-covered lithium electrode, Celgard 2400 separator, 40 μL electrolyte (1 M LiPF6, EC / DEC, 1:1 v / v), and lithium iron phosphate positive electrode were assembled into a CR2032 button cell in an argon glove box, and a pressure of 0.8 MPa was applied for 3 h.

[0064] Example 2

[0065] The present embodiment provides a preparation of a two-dimensional hybrid polymer artificial SEI film and its application in a lithium metal battery, comprising the following steps:

[0066] (1) 100 mg of graphene oxide (rGO) and 2 mL of triethylamine were dispersed in 100 mL of anhydrous DMF, and ultrasonic treatment was performed for 30 min in an ice bath. Then, 1.2 mL of 2-bromoisobutyryl bromide was added dropwise, and stirring was performed at 0°C for 2 h, followed by room temperature reaction for 24 h. Centrifugation was performed at 2000 r / min, and the obtained product was washed with DMF, ethanol, and deionized water in sequence for three times, and then freeze-dried to obtain GO-Br.

[0067] (2) 50 mg of GO-Br obtained in step (1) was dispersed in 50 mL of anhydrous DMF, and 0.05 g of pentamethyldiethylenetriamine, 1 g of methacrylic acid (MA), and 0.4 g of 2,2,2-trifluoroethyl acrylate (TFEA) were added. After degassing for three times, 0.03 g of cuprous bromide and 0.02 g of ascorbic acid were added, and reaction was performed at 60°C under argon protection for 48 h. Filtration was performed through a 0.22 μm filter membrane, and the obtained product was washed with DMF, methanol, and deionized water in sequence until the filtrate was colorless, and then freeze-dried to obtain GO-g-P(TFEA-co-MA).

[0068] (3) 20 mg GO-g-P(TFEA-co-MA) was dispersed in 2 mL anhydrous dimethyl sulfoxide to form a solution, 100 μL of the solvent was added dropwise to the surface of lithium foil, and spin-coated at 2000 rpm for 30 s; 100 μL of the solution was spin-coated for 60 s, and the electrode was treated on a hot stage at 100°C for 30 min to obtain a GO-g-P(TFEA-co-MA)@Li electrode, and the electrode was covered with a GO-g-P(TFEA-co-MA) film, i.e., a two-dimensional hybrid polymer artificial SEI film, wherein the thickness of the GO-g-P(TFEA-co-MA) film was 0.45 μm;

[0069] (4) The film-coated lithium electrode, Celgard 2400 separator, 40 μL of electrolyte (1M LiPF6, EC / DEC, 1:1 v / v), and lithium iron phosphate positive electrode were assembled into a CR2032 button cell in an argon glove box, and a pressure of 0.8 MPa was applied for 3 h.

[0070] Example 3

[0071] The present embodiment provides a preparation of a two-dimensional hybrid polymer artificial SEI film and its application in a lithium metal battery, comprising the following steps:

[0072] (1) 100 mg of graphene oxide (rGO) and 2 mL of triethylamine were dispersed in 100 mL of anhydrous DMF, and ultrasonicated in an ice bath for 30 min. 1.2 mL of 2-bromoisobutyryl bromide was added, and stirred at 0°C for 2 h, and then reacted at room temperature for 24 h. Centrifugation was performed at 2000 r / min, and the product was washed with DMF, ethanol, and deionized water in sequence for three times, and then freeze-dried to obtain GO-Br;

[0073] (2) 50 mg of GO-Br obtained in step (1) was dispersed in 50 mL of anhydrous DMF, and 0.05 g of pentamethyldiethylenetriamine, 1 g of methacrylic acid (MA), and 0.4 g of 2,2,2-trifluoroethyl acrylate (TFEA) were added. After degassing three times, 0.03 g of cuprous bromide and 0.02 g of ascorbic acid were added, and the reaction was carried out at 60°C under argon protection for 24 h. Filtration was performed through a 0.22 μm filter membrane, and the filtrate was washed with DMF, methanol, and deionized water in sequence until the filtrate was colorless, and then freeze-dried to obtain GO-g-P(TFEA-co-MA);

[0074] (3) 20 mg GO-g-P(TFEA-co-MA) was dispersed in 2 mL anhydrous dimethyl sulfoxide to form a solution, 100 μL of the solvent was added dropwise to the surface of lithium foil, and spin-coated at 2000 rpm for 30 s; 120 μL of the solution was spin-coated for 60 s, and the electrode was treated on a hot stage at 100°C for 30 min to obtain a GO-g-P(TFEA-co-MA)@Li electrode, and the electrode was covered with a GO-g-P(TFEA-co-MA) film, i.e., a two-dimensional hybrid polymer artificial SEI film, wherein the thickness of the GO-g-P(TFEA-co-MA) film was 0.48 μm;

[0075] (4) The film-coated lithium electrode, Celgard 2400 separator, 40 μL of electrolyte (1M LiPF6, EC / DEC, 1:1 v / v), and lithium iron phosphate positive electrode were assembled into a CR2032 button cell in an argon glove box, and a pressure of 0.8 MPa was applied for 3 h.

[0076] Example 4

[0077] The present embodiment provides a preparation of a two-dimensional hybrid polymer artificial SEI film and its application in a lithium metal battery, comprising the following steps:

[0078] (1) 100 mg of graphene oxide (rGO) and 2 mL of triethylamine were dispersed in 100 mL of anhydrous DMF, and ultrasonicated in an ice bath for 30 min. 1.2 mL of 2-bromoisobutyryl bromide was added, and stirred at 0°C for 2 h, and then reacted at room temperature for 24 h. Centrifugation was performed at 2000 r / min, and the product was washed with DMF, ethanol, and deionized water in sequence for three times, and then freeze-dried to obtain GO-Br;

[0079] (2) 50 mg of GO-Br obtained in step (1) was dispersed in 50 mL of anhydrous DMF, and 0.05 g of pentamethyldiethylenetriamine, 1 g of methacrylic acid (MA), and 0.4 g of 2,2,2-trifluoroethyl acrylate (TFEA) were added. After degassing three times, 0.03 g of cuprous bromide and 0.02 g of ascorbic acid were added, and the reaction was carried out at 60°C under argon protection for 24 h. Filtration was performed through a 0.22 μm filter membrane, and the filtrate was washed with DMF, methanol, and deionized water in sequence until the filtrate was colorless, and then freeze-dried to obtain GO-g-P(TFEA-co-MA);

[0080] (3) 20 mg GO-g-P(TFEA-co-MA) was dispersed in 2 mL anhydrous dimethyl sulfoxide to form a solution, 100 μL of the solvent was added dropwise to the surface of lithium foil, and spin-coated at 2000 rpm for 30 s; 150 μL of the solution was spin-coated for 60 s, and the electrode was treated on a hot stage at 100°C for 30 min to obtain a GO-g-P(TFEA-co-MA)@Li electrode, and the electrode was covered with a GO-g-P(TFEA-co-MA) film, i.e., a two-dimensional hybrid polymer artificial SEI film, wherein the thickness of the GO-g-P(TFEA-co-MA) film was 0.53 μm;

[0081] (4) The film-coated lithium electrode, Celgard 2400 separator, 40 μL of electrolyte (1M LiPF6, EC / DEC, 1:1 v / v), and lithium iron phosphate positive electrode were assembled into a CR2032 button cell in an argon glove box, and a pressure of 0.8 MPa was applied for 3 h.

[0082] Example 5

[0083] Different from Example 1, the fluorine-containing monomer in step (2) can be selected from hexafluoroisopropyl methacrylate, trifluoroethyl methacrylate, or 2,2,3,3,3-pentafluoropropyl acrylate.

[0084] Example 6

[0085] The carboxyl monomer in step (2) can be selected from acrylic acid, tert-butyl acrylate, or tert-butyl methacrylate.

[0086] Test Example

[0087] (1) Infrared characterization

[0088] The GO-g-P(TFEA-co-MA) of Example 1 was characterized by infrared spectroscopy, and the results are shown in FIG. 1. Figure 2 Compared with GO, the GO-g-P(TFEA-co-MA) spectrum appeared new characteristic peaks at 1145.8 cm -1 , 1706.5 cm -1 , and 1450.7 cm -1 , which were attributed to the vibrations of -CF3, C=O, and CH3 groups, respectively, indicating that we successfully synthesized the GO-g-P(TFEA-co-MA) hybrid molecular brush.

[0089] (2) SEM characterization

[0090] Figure 3The SEM images of the cross-section (a) and surface (b) of the two-dimensional hybrid polymer artificial SEI film of Example 1 show that the artificial SEI film prepared in the application has a thickness of about 450 nm, and the thickness is uniform, which is beneficial to the rapid transmission of ions. As shown in the figure (b), the artificial SEI film prepared in the application has a smooth surface without pores, which is beneficial to prevent the consumption of electrolyte and side reactions in the cycle process, and improve the cycle stability.

[0091] (3) Young's modulus

[0092] Young's modulus determination method: the Young's modulus test was performed using a scanning probe microscope (SPM), and the probe type was RTESPA, and the test mode was PeakForce QNM (Quantitative Nanomechanical Mapping) mode.

[0093] Figure 4 The AFM image of the Young's modulus of the two-dimensional hybrid polymer artificial SEI film of Example 1 shows that the Young's modulus is as high as 3.7 GPa, which can effectively inhibit the growth of lithium dendrites.

[0094] (4) Lithium ion transference number

[0095] Ion transference number determination method: experimental device and test steps: the artificial SEI film of Example 1 was clamped between two lithium sheets, and a lithium / lithium symmetric battery was assembled, and the structure was Li|artificial SEI film|Li (two lithium sheets were symmetrically pressed to avoid poor interface contact). The electrolyte used 1M lithium hexafluorophosphate (LiPF6) dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio = 1:1): constant voltage polarization and EIS test were performed using CHI660E electrochemical workstation, and the polarization voltage was 10mV,

[0096] Constant voltage polarization: the voltage was applied to make Li + Oriented migration, record the initial polarization current I0and the steady-state current I S .

[0097] EIS test: obtain the resistance R0and R S .

[0098] Data processing: the lithium ion transference number of the electrolyte was calculated by formula (1)

[0099]

[0100] Where, ΔV is the polarization voltage, I0is the initial polarization current, I S is the steady-state current after polarization, R0and R S are the resistances before and after polarization, respectively.

[0101] Figure 5 The lithium ion transference number is calculated to be 0.79 based on the above data, and the high ion transference number can reduce the concentration polarization of the battery, homogenize the lithium ion flow, and inhibit the growth of lithium dendrites.

[0102] (5) Cycle performance test

[0103] Lithium symmetric battery test: Two pieces of GO-g-P(TFEA-co-MA)@Li electrodes and Celgard 2400 separator, 40 μL electrolyte (1M LiTFSI, dimethyl ether (DME) / 2,6-dioxolane (DOL) 1:1 v / v), lithium iron phosphate positive electrode were assembled into CR2032 button cells in an argon glove box; using a new battery test system, constant current charge-discharge test was carried out at 10 mA cm -2 The constant current charge-discharge test was carried out at a current density of 10 mA cm and a surface capacity of 10 mAh, and the change curve of voltage with time was recorded, and the test temperature was 30.℃

[0104] Figure 6 The lithium deposition stripping voltage-time curve of the symmetric lithium battery based on bare Li and GO-g-P(TFEA-co-MA)@Li electrode. The results show that the GO-g-P(TFEA-co-MA)@Li electrode has no obvious voltage fluctuation after 1000h of cycle, showing good stability, while the bare lithium electrode starts to fluctuate after only 300h of cycle, indicating that the lithium deposition is uneven and lithium dendrites appear.

[0105] Figure 7 The cycle performance of lithium iron phosphate full battery based on bare Li and GO-g-P(TFEA-co-MA)@Li electrode at 2C is shown in the figure. The full battery results show that the GO-g-P(TFEA-co-MA)@Li electrode can be stably cycled at a large current of 2C for 260 cycles, showing excellent practical performance; as a sharp contrast, the bare lithium electrode only cycles for 60 cycles, and the discharge specific capacity starts to rapidly decay, and after 100 cycles, the capacity retention rate is only 14%.

[0106] Comparative Example 1

[0107] Unlike specific embodiment 1, only monomer MA (1.4 g) is added in step (2) to obtain GO-g-PMA hybrid molecular brush, and GO-g-PMA@Li electrode is obtained by using the same spin coating method, and the capacity retention rate is only 73% after 190 cycles of assembling button cells, see Figure 8 .

[0108] Comparative Example 2

[0109] Different from the specific embodiment 1, only monomer TFEA (1.4 g) was added in step (2) to obtain GO-g-PTFEA hybrid molecular brush, and the GO-g-PTFEA@Li electrode was obtained by using the same spin coating method, and the assembled button cell had a capacity retention of only 71% after 190 cycles, see Figure 8 .

[0110] The above embodiments are preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are all included in the protection scope of the present application.

Claims

1. A multifunctional two-dimensional hybrid polymer artificial SEI membrane, characterized in that: Including the compound shown in formula I, recorded as GO-gP (TFEA-co-MA): in In R2, m=800-1000, n=500-600.

2. The multifunctional two-dimensional hybrid polymer artificial SEI membrane according to claim 1, characterized in that: The multifunctional two-dimensional hybrid polymer artificial SEI film has a thickness of 450±100 nm, a Young's modulus of 2 to 4 GPa, and an ion migration number of 0.6 to 0.

82.

3. A method for preparing the multifunctional two-dimensional hybrid polymer artificial SEI membrane according to claim 1, characterized in that: The multifunctional two-dimensional hybrid polymer artificial SEI film is obtained by grafting a polymer brush on the surface of brominated graphene oxide through atom transfer radical polymerization, and then spin coating to form a film; The monomers of the polymer brush are carboxyl-containing monomers and fluorine-containing monomers.

4. The method for preparing a multifunctional two-dimensional hybrid polymer artificial SEI membrane according to claim 3, characterized in that: The specific steps include: (1) Preparation of brominated graphene oxide: Graphene oxide and triethylamine are dispersed in a solvent, ultrasonicated, a bromination reagent is added and stirred to react, and after the reaction is completed, centrifuged, washed and dried to obtain brominated graphene oxide; (2) ATRP reaction: Brominated graphene oxide is dispersed in a solvent, and monomers, ligands, catalysts, and reducing agents are added. ATRP reaction is carried out under an inert atmosphere. After the reaction is completed, the two-dimensional hybrid polymer GO-gP (TFEA-co-MA) is obtained after washing and drying. (3) Spin coating: GO-gP (TFEA-co-MA) was dispersed in dimethyl sulfoxide to prepare solution A. Pure dimethyl sulfoxide was first spin-coated, and then solution A was spin-coated. After heat treatment, a multifunctional two-dimensional hybrid polymer artificial SEI film was obtained.

5. The method for preparing a multifunctional two-dimensional hybrid polymer artificial SEI membrane according to claim 4, characterized in that: The molar ratio of the carboxyl-containing monomer to the fluorine-containing monomer in the monomer of step (2) is 2 to 6:1; The carboxyl group-containing monomer is selected from at least one of acrylic acid, methacrylic acid, tert-butyl acrylate, tert-butyl methacrylate or maleic acid; The fluorine-containing monomer is selected from at least one of 2,2,2-trifluoroethyl acrylate, hexafluoroisopropyl methacrylate, and trifluoroethyl methacrylate.

6. The method for preparing the multifunctional two-dimensional hybrid polymer artificial SEI membrane according to 4, characterized in that: The ligand in step (2) is selected from at least one of pentamethyldiethylenetriamine, bipyridine or tris(2-dimethylaminoethyl)amine; The catalyst is cuprous bromide, cupric chloride or ferrous chloride; the reducing agent is ascorbic acid.

7. The method for preparing a multifunctional two-dimensional hybrid polymer artificial SEI membrane according to 4, characterized in that: The mass ratio of the total mass of the monomers in step (2) to the brominated graphene oxide is 14 to 28:1; The mass ratio of the monomer to the catalyst in step (2) is 40 to 100:1; The temperature of the ATRP reaction in step (2) is 60±5° C., and the reaction time is 24±6 h.

8. The method for preparing a multifunctional two-dimensional hybrid polymer artificial SEI membrane according to 4, characterized in that: The reaction time of step (1) is 24±6h; The mass volume ratio of the graphene oxide, triethylamine and brominating agent is 1:10-30:6-18 in g / mL / mL; The brominating agent is 2-bromoisobutyryl bromide; The washing step comprises sequentially washing with DMF, ethanol and water for 3 to 5 times.

9. The method for preparing a multifunctional two-dimensional hybrid polymer artificial SEI membrane according to 4, characterized in that: The concentration of the solution A in step (3) is 0.01 to 0.03 g / mL; the volume ratio of the pure dimethyl sulfoxide to the solution A is 1:1 to 3; The heat treatment temperature is 80-120° C., and the treatment time is 10-50 minutes.

10. Application of the multifunctional two-dimensional hybrid polymer artificial SEI membrane according to claim 1 or 2 in the field of lithium batteries.

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