A method for fabricating nafion-li or nafion membranes in a two-dimensional array of capillaries and its use in batteries

Abstract

The application discloses a method for preparing Nafion-Li or Nafion membrane by array capillary and application thereof in batteries. The research result shows that the array capillary can precisely control the transfer of polymer solution to form a uniform ultrathin liquid film, and on this basis, the dynamic viscosity of the liquid film can be well controlled to inhibit the Marangoni flow and capillary flow caused by liquid evaporation, thereby forming a uniform and ultrathin Nafion-Li or Nafion membrane. The method solves the problem that the prior art cannot prepare an ultrathin and uniform ion-selective membrane. The Nafion-Li or Nafion membrane prepared according to the strategy exhibits high ion selectivity and lithium ion transmission flux in lithium batteries, effectively inhibits the shuttle effect of polysulfides, and improves the coulombic efficiency and energy efficiency of the batteries.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of preparation of polymer ion-selective membranes, and particularly relates to a method for preparing Nafion-Li or Nafion membranes by two-dimensional array capillary and application thereof in batteries. BACKGROUND

[0002] Ion-selective transport polymer thin films play an extremely important role in seawater desalination, element extraction and electrochemical energy conversion devices, such as fuel cell proton exchange membranes and ion exchange membranes of flow batteries. Ion-selective transport membranes can achieve high selectivity of specific ions while inhibiting the shuttling of other molecules or ions (such as inhibiting the shuttling of redox molecules in flow batteries), thereby achieving efficient separation and extraction of specific ions. On the basis of obtaining high ion-selective transport of polymer membranes, how to achieve high flux ion transport of thin films is the key to realizing the process of efficient ion separation and extraction. Although different kinds of ion transport materials, such as perfluorosulfonic acid resin (Nafion), polystyrene sulfonic acid (PSS), polybenzimidazole (PBI), polydiallyldimethylammonium chloride (PDDA), are developed to improve the ion transport selectivity and flux of thin films. However, the high molecular thin films prepared by the existing preparation technology have high and uneven thickness, which limits the high selectivity and high flux of polymer membranes, and becomes the core challenge of their wide application.

[0003] At present, ion-selective polymer membranes are mainly prepared by simple solution processing methods, such as spray coating, blade coating and spin coating. Among them, the solution film is coated on the substrate, and then the solvent is evaporated to obtain the ion-selective polymer membrane. In fact, these ion-selective thin films prepared by these solution processing techniques do not simultaneously achieve high energy efficiency and high coulomb efficiency of the device due to low ion flux caused by thick film or low selectivity caused by the existence of pore defects. The main reason is that the existing technology cannot form a uniform liquid film or cannot control the uniform precipitation of polymer molecules, resulting in thick and uneven thin films.

[0004] To solve the above problems, the application provides a method for preparing a Nafion-Li film with ultra-thin and uniform characteristics by using a two-dimensional array capillary. The thin and uniform solution film is obtained by stable solution transfer through a one-dimensional liquid bridge formed by the two-dimensional array capillary. On the basis of the thin and uniform solution film, the dynamic viscosity of the liquid film is controlled by changing the concentration of Nafion-Li and the solution evaporation temperature to inhibit the Marangoni flow and capillary flow caused by solution evaporation, thereby avoiding polymer molecular diffusion and finally forming a uniform and ultra-thin Nafion-Li film. The Nafion-Li film prepared according to this strategy exhibits a high lithium ion transmission flux in the lithium ion transmission test, which is 160 times that of a traditional commercial Nafion-117 film. It is worth noting that the application uses a lithium-sulfur battery as a display, and the Nafion-Li film prepared exhibits a high lithium ion transmission flux and high ion selectivity in the lithium-sulfur battery, which can effectively inhibit the polysulfide shuttle effect and improve the cycle stability of the battery while maintaining high energy efficiency of the battery. SUMMARY

[0005] To solve the problems of the prior art, the purpose of the application is to provide a method for preparing a Nafion-Li or Nafion film by using a two-dimensional array capillary and the application of the film in a battery.

[0006] Based on the above purpose, the application adopts the following technical solutions:

[0007] A method for preparing a Nafion-Li or Nafion film by using a two-dimensional array capillary, the process is as follows:

[0008] (1) A plurality of capillaries are closely arranged to obtain a two-dimensional array capillary;

[0009] (2) The two-dimensional array capillary is fixed on a multi-axis moving platform;

[0010] (3) The two-dimensional array capillary is immersed in a Nafion-Li solution or a Nafion solution to obtain a two-dimensional array capillary containing a Nafion-Li or Nafion solution; the concentration of the Nafion-Li solution or the Nafion solution is 20-100 mg / mL;

[0011] (4) The substrate is heated and kept at a temperature of 30-90°C, and the two-dimensional array capillary containing the Nafion-Li or Nafion solution is controlled to contact the substrate by the moving platform to form a one-dimensional liquid bridge; the array capillary is moved directionally to form a uniform solution film; after the solvent in the solution film is volatilized, a Nafion-Li or Nafion film is obtained;

[0012] (5) Repeat steps (3) and (4) to obtain Nafion-Li or Nafion films with different numbers of layers.

[0013] Further, in step (1), the capillary is a glass capillary with a diameter of 100-3000 μm; in step (4), the substrate is glass, a glass fiber porous membrane, or a polymer porous membrane. Preferably, the substrate is a glass substrate or a PP membrane.

[0014] Furthermore, the moving speed of the two-dimensional array capillary is 0.1~50 mm / s; in step (5), the number of layers of Nafion-Li or Nafion film is 1~100 layers.

[0015] The preparation process of the above Nafion-Li solution is as follows:

[0016] (1) Add Nafion powder to a mixed solvent of water and ethanol in a volume ratio of 1:1 and stir at room temperature to obtain a Nafion solution;

[0017] (2) Add 0.5~2 mol / mL lithium hydroxide aqueous solution to the Nafion solution in step (1) and adjust the pH to 7 to obtain Nafion-Li solution;

[0018] (3) Centrifuge the Nafion-Li solution from step (2) to obtain the supernatant of Nafion-Li;

[0019] (4) Dry the Nafion-Li supernatant solution from step (3) to obtain a Nafion-Li sample. Weigh the Nafion-Li sample and dissolve it in ethanol to obtain a Nafion-Li solution. Preferably, the drying is carried out at 70~90℃.

[0020] Preferably, the assembled battery separator is a Nafion-Li film prepared on a PP film using arrayed capillaries (substrate temperature 30°C, arrayed capillary movement speed 1 mm / s). The Nafion-Li films have 1 layer (abbreviated as N-Li-1), 2 layers (abbreviated as N-Li-2), 3 layers (abbreviated as N-Li-3), and lithium-ionized commercial Nafion-117 film (abbreviated as N-Li-117).

[0021] The preparation process of the electrolyte is as follows: lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2) is dissolved in a mixed solvent of DOL (1,3-dioxolane) and DME (ethylene glycol dimethyl ether) in a volume ratio of 1:1, and the concentration of lithium salt (LiN(CF3SO2)2) in the solvent is 1 M; LiN(CF3SO2)2 and lithium nitrate (LiNO3) are dissolved in a mixed solvent of DOL (1,3-dioxolane) and DME (ethylene glycol dimethyl ether) in a volume ratio of 1:1, the concentration of LiN(CF3SO2)2 in the solvent is 1 M, and the concentration of lithium salt LiNO3 is 0.4 M.

[0022] A stainless steel symmetric cell is assembled using the Nafion-Li film prepared above, stainless steel gaskets are selected as the positive and negative electrodes of the cell, different layer numbers of Nafion-Li films and commercial Nafion-117 films that are lithiumated are selected as the cell separators, and after adding the electrolyte, the electrolyte is assembled and packaged to obtain the lithium-sulfur battery.

[0023] A lithium-sulfur battery is assembled using the Nafion-Li film prepared above, lithium is selected as the negative electrode, and the positive electrode is an aluminum foil coated with carbon material, binder, and active material or a self-supporting positive electrode mixed with carbon material, binder, and active material, different layer numbers of Nafion-Li films prepared on a PP film using an array of capillaries and commercial Nafion-117 films that are lithiumated are selected as the cell separators, and after adding 45-60 µL of electrolyte, the electrolyte is assembled and packaged to obtain the lithium-sulfur battery.

[0024] The above substrate can be a commonly used conductive substrate in the battery field, such as an aluminum foil, and the electrode area is a commonly used electrode area, such as an area of 1.13 cm 2 . The active material sulfur is loaded on the substrate, and the carbon material has various options such as porous carbon, conductive carbon black, carbon nanotubes, carbon fibers, ketchen carbon black, and graphene. Taking conductive carbon black as an example, the preparation process of the sulfur-containing positive electrode is as follows: the active material sulfur and porous carbon are mixed in a mass ratio of 7:3, and then heated at 155 ℃ for 12 hours in a sealed argon atmosphere to obtain sulfur-carbon material; the sulfur-carbon material, conductive carbon black, and binder are uniformly mixed in N-methyl-2-pyrrolidone in a mass ratio of 8:1:1, and then coated on an aluminum foil and dried at 80 ℃ for 8 hours to obtain the sulfur-containing positive electrode, and the loading amount of the active material sulfur on the electrode is 1.5-4 mg cm -2 .

[0025] The above substrate can be a commonly used conductive substrate in the battery field, such as a self-supporting positive electrode, and the electrode area is 0.985 cm 2The active material of the positive electrode material loaded on the substrate is sulfur, and the carbon material has multiple options such as porous carbon, conductive carbon black, carbon nanotubes, carbon fibers, ketchen carbon black and graphene. Taking conductive carbon black and carbon fibers as examples, the preparation process of the sulfur-containing positive electrode is as follows: the active material sulfur is mixed with porous carbon at a mass ratio of 7:3, and then kept at 155 DEG C for 12 hours under a sealed argon atmosphere to obtain a sulfur-carbon material; the sulfur-carbon material, conductive carbon, carbon fiber and binder are uniformly mixed in N-methyl-2-pyrrolidone at a mass ratio of 8:0.9:0.1:1, and then poured into a silica gel mold for vacuum drying to obtain a self-supporting positive electrode. The loading amount of the active material sulfur on the electrode is 10-12 mg cm -2 .

[0026] The stainless steel symmetric battery and the lithium-sulfur battery with the Nafion-Li film obtained by the above method are prepared.

[0027] Array capillary is used to prepare Nafion-Li films with different layers (N-Li-1, N-Li-2, N-Li-3) and commercial Nafion-117 films (N-Li-117) after being lithiated in lithium metal batteries. When the number of layers of the Nafion-Li film is reduced, the transmission path of lithium ions in the thin film is shortened, and the lithium ion transmission flux of the Nafion-Li film is significantly improved. The high lithium ion transmission flux improves the active material conversion speed of the lithium-sulfur battery and improves the energy efficiency of the battery. At the same time, in the cycle process, the sulfonate negative ions in the Nafion-Li film can effectively repel the polysulfide intermediate product of the lithium-sulfur battery in the charging and discharging process to avoid the loss of the active material and the corrosion of the lithium sheet.

[0028] The array capillary is used to prepare the ultra-thin and uniform Nafion-Li film, and the influence of the dynamic viscosity of the solution on the uniformity of the film is studied. In the preparation process, the two-dimensional array capillary can stably and controllably realize the transfer of the Nafion-Li solution to form a uniform and ultra-thin solution film. On this basis, the dynamic viscosity of the solution can be controlled by changing the concentration of the Nafion-Li and the evaporation temperature to effectively suppress the Marangoni flow and capillary flow of the solution in the evaporation process, avoid the movement of the polymer molecules, and make the polymer molecules uniformly precipitate to realize the preparation of the ultra-thin and uniform Nafion-Li film. The Nafion-Li film with the characteristics of uniformity and ultra-thin has high lithium ion transmission flux and high lithium ion selectivity. In the application in the lithium-sulfur battery, the ultra-thin and uniform Nafion-Li film has high lithium ion flux, which can effectively improve the energy efficiency of the battery, and has high lithium ion selectivity, which can effectively inhibit the shuttle of the redox active material polysulfide and improve the cycle stability of the battery.

[0029] The application designs a kind of based on two-dimensional array capillary de-stabilization transfer polymer solution to form thin and uniform liquid film, simultaneously benefit from controllable solution dynamic viscosity preparation ultra-thin uniform Nafion-Li film, realizes the high selectivity and high flux transmission of ion selective membrane, breaks the balance of selectivity and permeability, solves the problem that existing solution technology cannot prepare ultra-thin uniform ion selective membrane.The research results show that the uniform ultra-thin Nafion-Li film (N-Li-1, the thickness is about 200 nm) can reduce the lithium ion transmission distance and improve the lithium ion transmission flux of the film to 4.9×10 -4 ; compared with commercial Nafion-117 film (N-Li-117, the thickness is 183 μm), it is improved by two orders of magnitude.The reduction of thickness does not reduce the high lithium ion selectivity of Nafion-Li film.The lithium-sulfur battery assembled with it, under the condition of current density of 0.1 C, the first circle coulombic efficiency is improved from 25.1% to 99.8%, and the capacity is improved from 1179.3 mAh g −1 to 1360.6 mAh g −1 . Under the condition of current density of 0.5 C, the average capacity attenuation rate of each cycle is reduced from 0.47% to 0.25% after 200 cycles, and the average coulombic efficiency reaches 99%.Therefore, the preparation of large-size ultra-thin uniform Nafion-Li film can be realized by changing the number of capillaries in array capillary. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a schematic diagram of the preparation process of several different solution methods; (a) the process of preparing polymer by spraying; (b) the process of preparing polymer by doctor blading; (c) the process of preparing polymer by spin coating; (d) the process of preparing polymer by array capillary;

[0031] Figure 2 is an optical photograph of the solution transfer process by doctor blading; (a) the formation of solution film on the substrate during the doctor blading process; (b) the change of the morphology of liquid bridge during the transfer from left to right by doctor blading;

[0032] Figure 3 (a) the process of preparing polymer by array capillary; (b) the optical photograph of array capillary containing Nafion-Li solution; (c) the optical photograph of array capillary containing Nafion-Li solution forming liquid bridge on the substrate; (d, e) the optical photograph of the process of forming liquid film by array capillary; (f) the formation of solution film on the substrate during the solution transfer process by array capillary; (g) the change of the morphology of liquid bridge during the transfer from left to right by array capillary;

[0033] Figure 4Middle: optical photographs of array capillaries with different widths (a-c) are (a) 2 cm, (b) 4 cm, (c) 6 cm, respectively; d-f are optical photographs of solution films prepared by array capillaries with different areas (d) 2*10 cm 2 , (e) 4*10 cm 2 , (f) 6*10 cm 2 ;

[0034] Figure 5 Viscosity of Nafion-Li solution with different concentrations;

[0035] Figure 6 Influence of concentration parameter on Nafion-Li film thickness: a-d are SEM photographs of Nafion-Li film thickness, prepared at 30 ℃ and with a moving speed of 1 mm / s, and with concentrations of (a) 20 mg / mL, 6 layers, (b) 30 mg / mL, 5 layers, (c) 40 mg / mL, 4 layers, (d) 50 mg / mL, 3 layers;

[0036] (e) Schematic diagram of Nafion-Li film formation prepared by array capillaries under different Nafion-Li concentrations (at high polymer concentration, the dynamic solution viscosity can rapidly increase to the limit threshold of polymer diffusion, thus generating a uniform and thin polymer film);

[0037] Figure 7 SEM photographs of Nafion-Li film prepared at 30 ℃ and with a moving speed of 1 mm / s under different concentrations (a) 20 mg / mL, 6 layers, (b) 30 mg / mL, 5 layers, (c) 40 mg / mL, 4 layers, (d) 50 mg / mL, 3 layers;

[0038] Figure 8 Solution film evaporation process of different Nafion-Li concentrations (a) 20 mg / mL, (b) 30 mg / mL, (c) 40 mg / mL, (d) 50 mg / mL;

[0039] Figure 9Effect of temperature parameter on Nafion-Li membrane thickness. a-d SEM images of Nafion-Li membrane thickness, prepared with Nafion-Li concentration of 20 mg / mL, moving speed of 1 mm / s, and layer number of 6, at different temperatures of (a) 40 ℃, (b) 50 ℃, (c) 60 ℃, (d) 70 ℃, (e) schematic diagram of Nafion-Li membrane formation by array capillary at different temperatures (at high temperature, the dynamic solution viscosity can rapidly increase to the limiting threshold of polymer diffusion, so that a uniform and thin polymer membrane is generated);

[0040] Figure 10 SEM images of Nafion-Li membrane at different positions prepared by array capillary at different temperatures with Nafion-Li concentration of 20 mg / mL, moving speed of 1 mm / s, and layer number of 6, (a) 40 ℃, (b) 50 ℃, (c) 60 ℃, (d) 70 ℃.

[0041] Figure 11 Effect of speed parameter on Nafion-Li membrane thickness. a-d SEM images of Nafion-Li membrane thickness, prepared with Nafion-Li concentration of 50 mg / mL, layer number of 3, and different moving speeds of (a) 3 mm / s, (b) 5 mm / s, (c) 7 mm / s, (d) 10 mm / s, (e) schematic diagram of Nafion-Li membrane formation by array capillary at different moving speeds (at low speed, the solution film formed is thinner, and the dynamic solution viscosity can rapidly increase to the limiting threshold of polymer diffusion, so that a uniform and thin polymer membrane is generated);

[0042] Figure 12 SEM images of Nafion-Li membrane at different positions prepared by array capillary at different moving speeds with Nafion-Li concentration of 50 mg / mL, layer number of 3, and temperature of 30 ℃, (a) 3 mm / s, (b) 5 mm / s, (c) 7 mm / s, (d) 10 mm / s;

[0043] Figure 13 Characterization of Nafion-Li membranes prepared by different methods. a-c, optical images of Nafion-Li membranes prepared by different methods (a) array capillary, (b) doctor blade, (c) spin coating; d-f, thickness of Nafion-Li membranes at different positions prepared by different methods (d) array capillary, (e) doctor blade, (f) spin coating; g-i, AFM images of Nafion-Li membranes prepared by different methods (g) array capillary, (h) doctor blade, (i) spin coating;

[0044] Figure 14 SEM images of Nafion-Li films with different thicknesses at different positions, prepared at 30 °C with Nafion-Li concentration of 50 mg / mL, 3 layers of array, and a capillary speed of 1 mm / s;

[0045] Figure 15 SEM images of Nafion-Li films with different thicknesses at different positions, prepared at 30 °C with Nafion-Li concentration of 50 mg / mL, 1 layer of blade coating, and a speed of 1 mm / s;

[0046] Figure 16 SEM images of Nafion-Li films with different thicknesses at different positions, prepared at 30 °C with Nafion-Li concentration of 50 mg / mL, 1 layer of spin coating, and a speed of 2000 rpm;

[0047] Figure 17 Middle: (a) SEM image of the surface of the PP film; (b) SEM image of the surface of the N-Li-1 film on the PP film;

[0048] Figure 18 SEM images of the thickness of the Nafion-Li film on the PP film: (a) N-Li-1; (b) N-Li-2;

[0049] Figure 19 Effect of Nafion-Li film thickness on lithium ion transport and lithium-sulfur battery reaction kinetics: (a) lithium ion transport rate of Nafion-Li films with different thicknesses at 25 °C; (b) lithium ion transport rate of Nafion-Li films with different thicknesses at different temperatures; (c) impedance spectra of lithium-sulfur batteries of Nafion-Li films with different thicknesses; (d) changes in bulk impedance and interfacial impedance of lithium-sulfur batteries of Nafion-Li films with different thicknesses; (e) cyclic voltammetry of lithium-sulfur batteries of Nafion-Li films with different thicknesses at a scan rate of 0.05 mv; (f) potential and lithium ion diffusion coefficient at the cyclic voltammetry P A1 point of Nafion-Li films with different thicknesses; (g-h) Tafel slope of lithium-sulfur batteries of Nafion-Li films with different thicknesses (cyclic voltammetry P A1 point and P C1); (i) Charge-discharge curves of lithium-sulfur batteries with N-Li-1 membrane at different current densities; (j) Charge-discharge curves of lithium-sulfur batteries with N-Li-117 membrane at different current densities; (k) Polarization voltage (600 mAh / g) of lithium-sulfur batteries with different thickness of Nafion-Li membrane at different current densities (600 mAh / g); (l) Discharge capacity of lithium-sulfur batteries with different thickness of Nafion-Li membrane at different current densities;

[0050] Figure 20 Summary: (a) Potentials at the P B1 Summary: (a) Potentials at the P C1 Summary: (a) Potentials at the P

[0051] Figure 21 Summary: (a) Charge-discharge curves of lithium-sulfur batteries with N-Li-2 membrane at different current densities; (b) Charge-discharge curves of lithium-sulfur batteries with N-Li-3 membrane at different current densities;

[0052] Figure 22 Summary: (a) Li2S8 permeability experiment of PP membrane; (b) Li2S8 permeability experiment of N-Li-1 membrane; (c) Charge-discharge curves of lithium-sulfur batteries with N-Li-1 membrane and PP membrane at current density of 0.1 C; (d) Cycle performance of lithium-sulfur batteries with N-Li-1 membrane and PP membrane at 0.5 C without LiNO3 as additive; (e) Cycle performance of lithium-sulfur batteries with N-Li-1 membrane and PP membrane at sulfur loading of 10.6 mg / cm 2 current density of 0.1 C and with LiNO3 as additive; f-i SEM images of lithium ribbons of lithium-sulfur batteries with N-Li-1 membrane and PP membrane after 100 cycles, (f, g) Lithium ribbons of lithium-sulfur batteries with PP membrane after 100 cycles, (h, i) Lithium ribbons of lithium-sulfur batteries with N-Li-1 membrane after 100 cycles; (j) XPS S 2p spectra of lithium ribbons of lithium-sulfur batteries with N-Li-1 membrane and PP membrane after 10 cycles at current density of 0.5 C;

[0053] Figure 23 Summary: (a) Optical images of lithium ribbons of lithium-sulfur batteries with PP membrane after 100 cycles; (b) Optical images of lithium ribbons of lithium-sulfur batteries with N-Li-1 membrane after 100 cycles;

[0054] Figure 24 Elemental content table of XPS S 2p of lithium ribbons of lithium-sulfur batteries with N-Li-1 membrane and PP membrane after 10 cycles at current density of 0.5 C. Detailed Implementation

[0055] To make the technical objectives, technical solutions, and superior effects of the present invention clearer, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0056] Material sources: Perfluorosulfonic acid resin powder (Nafion-H), ethanol (CH3CH2OH), and lithium hydroxide (LiOH) were purchased directly from Maclean's. The commercial Nafion-117 membrane was purchased from DuPont. Polyvinylidene fluoride (PVDF), N-methyl-2-pyrrolidone (NMP), sulfur powder (S8), and lithium sulfide (Li2S) were purchased from Aladdin. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), DOL (1,3-dioxocyclopentane), and DME (ethylene glycol dimethyl ether) were purchased from Suzhou Duoduo Chemical Co., Ltd., China. The polypropylene membrane (PP membrane) was a battery-grade separator, model Celgard 2400.

[0057] The argon gas used in the experiment was 99.99% pure. All materials used for battery assembly were stored in a glove box filled with argon gas.

[0058] Example 1:

[0059] The preparation process of Nafion-Li solution is as follows:

[0060] S1. Add Nafion powder to a mixed solvent of water and ethanol in a volume ratio of 1:1, and stir at room temperature to obtain a Nafion solution.

[0061] S2. Add 1 mL of lithium hydroxide aqueous solution to the Nafion solution in step S1, and adjust the pH until it is 7 to obtain Nafion-Li solution;

[0062] S3. The Nafion-Li solution from step S2 is purified by centrifugation (10000 rpm / s) for 15 minutes to obtain the supernatant of Nafion-Li.

[0063] S4. The Nafion-Li supernatant solution from step S3 was dried under vacuum at 80°C for 24 hours to obtain Nafion-Li samples. Different masses of Nafion-Li samples were weighed and dissolved in ethanol to obtain Nafion-Li solutions with concentrations of 20 mg / mL, 30 mg / mL, 40 mg / mL, and 50 mg / mL. The viscosities of the Nafion-Li solutions at each concentration were tested, and the results are detailed below. Figure 5 ,Depend on Figure 5 It can be seen that the higher the concentration of Nafion-Li solution, the higher its viscosity.

[0064] The process of array capillary preparation of Nafion-Li film is shown in Figure 3 , and the specific process is as follows:

[0065] (1) A certain number of glass capillaries are closely arranged to obtain a two-dimensional array capillary, as shown in Figure 3 (a) and Figure 4 ;

[0066] (2) The two-dimensional array capillary is fixed on a programmable multi-axis moving platform, which is used to control the preparation process;

[0067] (3) The two-dimensional array capillary is immersed in a Nafion-Li solution with different concentrations to obtain a two-dimensional array capillary containing Nafion-Li solution, as shown in Figure 3 (b).

[0068] (4) With glass as the substrate, the substrate is heated (at 30℃, 40℃, 50℃, 60℃ and 70℃, respectively), and the substrate temperature is maintained at 30℃, 40℃, 50℃, 60℃ and 70℃, and the two-dimensional array capillary containing Nafion-Li solution is controlled to contact the glass substrate by the moving platform to form a one-dimensional liquid bridge, as shown in Figure 3 (c). After setting different temperature and speed parameters (the moving speed of the array capillary is 1 mm / s, 3 mm / s, 5 mm / s, 7 mm / s and 10 mm / s, respectively), the array capillary is moved directionally to form a uniform solution film, as shown in Figure 3 (d-f); and the Nafion-Li film is obtained after the solvent in the liquid film is volatilized.

[0069] (5) Steps (3) and (4) are repeated to obtain Nafion-Li films with different layers (one layer of Nafion-Li film is formed by the two-dimensional array capillary containing Nafion-Li solution contacting the glass substrate once).

[0070] As shown in Figure 3 (c), when the array capillary containing Nafion-Li solution contacts the substrate, the solution inside the capillary flows out to form a liquid bridge under the action of the substrate. Figure 3 (f) is the process of solution transfer by the array capillary. Since the liquid inside the capillary spontaneously supplies to the substrate to maintain the stability of the array capillary liquid bridge, the polymer solution can form a continuous and uniform liquid film under the action of the array capillary. From Figure 3 (g), it can be seen that the contact angle between the liquid bridge and the substrate and the appearance of the liquid bridge do not change. Figure 3 (f) and Figure 3 (g) prove that the array capillary can stably transfer the polymer solution to form a uniform liquid film.

[0071] As shown inFigure 4 It can be seen that solution films of different widths can be obtained by controlling the width of the array capillary.

[0072] Five points (labeled P1, P2, P3, P4, P5) within a 2 cm range were selected from the above-prepared Nafion-Li thin film to observe its thickness uniformity under a scanning electron microscope.

[0073] Figure 6 As shown in Figure 6(ac), at lower Nafion-Li concentrations of 20–40 mg / mL, the film thickness exhibits non-uniformity. However, at higher Nafion-Li concentrations of 50 mg / mL (d), a uniform film thickness is observed. These results indicate that at high polymer concentrations, the dynamic solution viscosity can rapidly increase to the polymer diffusion limitation threshold, thereby generating a uniform and thin polymer film. Figure 6 As shown in (e).

[0074] Figure 7 These are SEM images of Nafion-Li films with different numbers of layers prepared at different concentrations at a temperature of 30 ℃ and an array capillary transfer speed of 1 mm / s. Figure 7 The results from ac show that at lower Nafion-Li concentrations of 20–40 mg / mL, the film thickness exhibits non-uniformity at different locations, while... Figure 7 At a relatively high Nafion-Li concentration of 50 mg / mL, a uniform film thickness was observed. This indicates that at high polymer concentrations, the dynamic solution viscosity can rapidly increase to the polymer diffusion limitation threshold, resulting in a uniform and thin polymer film.

[0075] Figure 8 The evaporation process of the solution film at different Nafion-Li concentrations is shown in the figure. It can be seen that the liquid film tends to evaporate unevenly at lower Nafion-Li concentrations of 20-40 mg / mL, while it tends to evaporate evenly at higher Nafion-Li concentrations of 50 mg / mL.

[0076] Figure 9 The effect of temperature parameters on the thickness of Nafion-Li films. Figure 9 In Figure 9(ac), the film thickness exhibits non-uniformity at temperatures ranging from 40 to 60 °C. However, in Figure 9(d), a uniform film thickness is observed at 70 °C. These results indicate that at high temperatures, rapid evaporation of the solution can quickly increase the dynamic solution viscosity to the limiting threshold for polymer diffusion, thereby generating a uniform and thin polymer film, such as... Figure 9 As shown in (e).

[0077] Figure 10 SEM images of the thickness of Nafion-Li films at different locations prepared at different temperatures for Nafion-Li concentration of 20 mg / mL, array capillary moving speed of 1 mm / s, and 6 layers (a) 40 ℃, (b) 50 ℃, (c) 60 ℃, (d) 70 ℃. From Figure 10 It can be seen from a-c that the thickness of the film at different locations presents non-uniformity at lower temperatures of 40-60 ℃, while Figure 10 In d, it can be observed that the thickness of the film at different locations presents consistent uniformity at higher temperature of 70 ℃. The results show that at high temperature, the dynamic solution viscosity can rapidly increase to the limiting threshold of polymer diffusion, so that a uniform and thin polymer film is formed.

[0078] Figure 11 Effect of speed parameter on the thickness of Nafion-Li films. SEM images of the thickness of Nafion-Li films at different locations prepared at different speeds of array capillary (a-d) the film thickness presents non-uniformity at speeds of 3-10 mm / s. The above results show that when a thinner solution film is formed at low speed, the dynamic solution viscosity can rapidly increase to the limiting threshold of polymer diffusion, so that a uniform and thin polymer film is formed (e).

[0079] Figure 12 SEM images of the thickness of Nafion-Li films at different locations prepared at different speeds of array capillary for temperature of 30 ℃, Nafion-Li concentration of 50 mg / mL, and 3 layers (a) 3 mm / s, (b) 5 mm / s, (c) 7 mm / s, (d) 10 mm / s. From Figure 12 It can be seen from a-c that the thickness of the film at different locations presents non-uniformity at higher moving speeds of 3-10 mm / s, while Figure 12 In d, it can be observed that the thickness of the film at different locations presents consistent uniformity at lower speed of 1 mm / s. The results show that when a thinner solution film is formed at low speed, the dynamic solution viscosity can rapidly increase to the limiting threshold of polymer diffusion, so that a uniform and thin polymer film is formed.

[0080] According to the above experimental results, when the speed of array capillary is 1 mm / s and the concentration of Nafion-Li is 50 mg / mL, a uniform Nafion-Li film can be obtained under the simple condition of heating at 30 ℃ (see Figure 6 d and 7d).

[0081] The above results prove that the two-dimensional array capillary can stably and controllably realize the transfer of Nafion-Li solution and then form a uniform and ultra-thin solution film. On this basis, by changing the concentration of Nafion-Li and the evaporation temperature, the solution dynamic viscosity can be controlled to effectively inhibit the Marangoni flow and capillary flow of the solution in the solution evaporation process, avoid the movement of polymer molecules, and realize the preparation of an ultra-thin and uniform Nafion-Li film.

[0082] Example 2:

[0083] The process of preparing a Nafion-Li film by an array capillary is as follows:

[0084] (1) A certain number of glass capillaries are closely arranged to obtain a two-dimensional array capillary.

[0085] (2) The two-dimensional array capillary is fixed on a programmable multi-axis moving platform, which is used to control the preparation process.

[0086] (3) The two-dimensional array capillary containing Nafion-Li solution is obtained by immersing the two-dimensional array capillary in a Nafion-Li solution with a concentration of 50 mg / mL.

[0087] (4) The two-dimensional array capillary containing Nafion-Li solution is controlled to contact the glass substrate by the moving platform to form a one-dimensional liquid bridge. The temperature is 30°C, the moving speed is 1 mm / s, the array capillary is moved directionally, and a uniform solution film is formed. After the solvent in the liquid film evaporates, a Nafion-Li film is obtained.

[0088] (5) Steps (3) and (4) are repeated to obtain Nafion films with different layers.

[0089] The process of preparing a Nafion-Li film by a scraping method is as follows:

[0090] (1) A glass plate is fixed as a scraping head on a programmable multi-axis moving platform, which is used to control the preparation process.

[0091] (2) A Nafion-Li solution with a concentration of 50 mg / mL is added dropwise to the glass substrate.

[0092] (3) The glass scraping head is controlled to contact the Nafion-Li solution on the glass substrate by the moving platform to form a one-dimensional liquid bridge. Under the conditions of a temperature of 30°C and a speed of 1 mm / s, the glass plate scraping head is moved directionally to form a solution film; after the solvent in the solution film evaporates, a Nafion-Li film is obtained.

[0093] The process of preparing a Nafion-Li film by a spin coating method is as follows:

[0094] The glass substrate was placed on the spin coater, and the Nafion-Li solution with a concentration of 50 mg / mL was dropped onto the substrate glass substrate. The spin coating was set at a temperature of 30°C and a rotation speed of 2000 rpm for 15 s, and the Nafion-Li film was obtained after the solvent was volatilized.

[0095] Figure 1 (a) is the process of preparing a polymer by a spraying method, wherein Figure 1 (a) is known, the low-viscosity polymer solution is transferred to the substrate in the form of microdroplets, and a uniform film cannot be formed due to uncontrollable solution transfer and uneven evaporation of the droplets. Figure 1 (b) is the process of preparing a polymer by a doctor blade method, wherein Figure 1 (b) is known, the polymer solution forms a continuous liquid film under the action of the doctor blade, and a uniform film cannot be formed due to the decrease in the gravity of the solution caused by the consumption of the solution under the doctor blade, which cannot maintain the stability of the liquid bridge, regardless of whether the solution is uniformly evaporated. Figure 1 (c) is the process of preparing a polymer by a spin coating method, wherein Figure 1 (c) is known, the polymer solution cannot be uniformly evaporated at different positions in the liquid film due to different centrifugal forces at different positions (from the inside to the outside) in the spin coating method, and the polymer molecules quickly move (from the inside to the outside), which causes the uniformity of the polymer film to decrease and a uniform film cannot be formed. Figure 1 (d) is the process of preparing a polymer by an array capillary method, wherein Figure 1 (d) is known, the polymer solution can form a continuous and uniform liquid film under the action of the array capillary due to the spontaneous supply of the liquid in the capillary to the substrate to maintain the stability of the liquid bridge of the array capillary.

[0096] Figure 2 is an optical photograph of the solution transfer process by the doctor blade method, from Figure 2 (a) in the middle, it can be observed that in the process of preparing a polymer by the doctor blade method, the polymer solution cannot form a continuous and uniform liquid film under the action of the doctor blade, and the liquid film gradually thins due to the decrease in the gravity of the solution caused by the consumption of the solution under the doctor blade. Figure 2 (b) in the middle, it can be seen that the contact angle between the liquid bridge and the substrate changes from small to large, and the appearance of the liquid bridge changes.

[0097] The single-layer Nafion-Li films prepared by different methods were observed under an optical microscope, as shown in Figure 13 (a-c), from the figures, it can be observed that the Nafion-Li film prepared by the array capillary method has a smooth and uniform surface, while the Nafion-Li films prepared by the doctor blade method and the spin coating method have a significantly uneven appearance.

[0098] The Nafion-Li film prepared above was selected 5 points (marked as P1, P2, P3, P4, P5) in the range of 2 cm along the liquid transfer direction to observe the thickness uniformity under the scanning electron microscope.

[0099] Figure 13 (d) and Figure 14 The thickness of the Nafion-Li film prepared by the array capillary method is uniform at different positions along the solution transfer method. The thickness of the Nafion-Li film prepared by the blade coating method varies from thick to thin at different positions along the solution transfer method Figure 13 (e) and Figure 15 This is mainly due to the blade coating method, in which the polymer solution forms a continuous liquid film under the action of the scraper. As the solution is consumed, the gravity of the solution under the scraper decreases, and therefore a uniform liquid film cannot be formed. See Figure 1 (b) and Figure 2 The thickness of the Nafion-Li film prepared by the spin coating method varies from thin to thick at different positions along the solution transfer method Figure 13 (f) and Figure 16 Due to the different centrifugal forces at different positions (from inside to outside) in the spin coating method, the solution at different positions in the liquid film cannot evaporate uniformly, and the polymer molecules will quickly move (from inside to outside), causing the uniformity of the polymer film to decrease. See Figure 1 (c).

[0100] The single-layer Nafion-Li films prepared by different methods were observed under an atomic force microscope.

[0101] Figure 13 (g) The Nafion-Li film prepared by the array capillary method has the smallest roughness of 0.47 nm, Figure 13 (h) The roughness of the Nafion-Li film prepared by the blade coating method is 0.60 nm. Figure 13 (i) The roughness of the Nafion-Li film prepared by the spin coating method is 0.56 nm.

[0102] Example 3:

[0103] Assembly of stainless steel symmetrical batteries of Nafion-Li films:

[0104] The process of preparing Nafion-Li films on pp films by array capillary is as follows:

[0105] (1) A certain number of glass capillaries are arranged closely to obtain a two-dimensional array of capillaries.

[0106] (2) The two-dimensional array of capillaries is fixed on a programmable multi-axis moving platform, which is used to control the preparation process.

[0107] (3) The two-dimensional array of capillaries is immersed in a Nafion-Li solution with a concentration of 50 mg / mL to obtain a two-dimensional array of capillaries containing a Nafion-Li solution.

[0108] (4) The two-dimensional array of capillaries containing a Nafion-Li solution is moved to contact the PP membrane substrate to form a one-dimensional liquid bridge. The temperature is 30°C, the moving speed is 1 mm / s, the array of capillaries is moved in a direction, and a uniform solution film is formed. After the solvent in the liquid film is volatilized, a Nafion-Li film is obtained.

[0109] (5) Steps (3) and (4) are repeated to obtain Nafion films with different numbers of layers (one layer is denoted as N-Li-1, two layers are denoted as N-Li-2, and three layers are denoted as N-Li-3).

[0110] The preparation process of the electrolyte is as follows: lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2) is dissolved in a mixed solvent of DOL (1,3-dioxolane) and DME (ethylene glycol dimethyl ether) in a volume ratio of 1:1, and the concentration of lithium salt in the solvent is 1 M.

[0111] Battery assembly: stainless steel gaskets are selected as the positive and negative electrodes of the battery, different numbers of Nafion-Li films and commercial Nafion-117 films are used as the battery separators, and 30 microliters of electrolyte is added to assemble and package the battery.

[0112] The above stainless steel symmetric battery is subjected to impedance testing on an electrochemical workstation.

[0113] Figure 17 and Figure 18 The morphology and thickness of the Nafion-Li film prepared by the array of capillaries on the porous PP membrane are shown, and it can be seen that the Nafion-Li film uniformly covers the surface of the porous PP membrane without defects, and the single-layer Nafion-Li film has an ultra-thin thickness of about 200 nm. In Figure 19 (a) shows the lithium ion transmission rate of different thicknesses of the separator at room temperature 25°C. Here, the N-Li-1 film, the N-Li-2 film, and the N-Li-3 film prepared by the array of capillaries have lithium ion transmission rates of 4.9×10 -4 S cm -1 , 2.2×10 -4 S cm -1 , 1.7×10 -4 S cm -1 , respectively, indicating that the reduction of the film thickness can improve the lithium ion transmission rate. In sharp contrast, the lithium ion transmission rate of the commercial Nafion-117 film is only 3.1×10 -6S cm -1 The N-Li-1 membrane has a lithium ion transference number of 0. 48, which is two orders of magnitude lower than that of the Nafion membrane (160 times lower). Figure 19 (b) shows the lithium ion transference rate of different thickness of the membrane at different temperatures. It can be seen that the N-Li-1 membrane has the highest lithium ion transference rate at different temperatures. The above results demonstrate that the array capillary prepared ultra-thin and uniform Nafion-Li membrane can greatly improve the transport flux of the membrane, which is crucial for realizing high energy efficiency of the device.

[0114] Example 4:

[0115] Assembly of lithium-sulfur battery using Nafion-Li membrane:

[0116] The process of array capillary preparation of Nafion-Li membrane on pp membrane is as follows:

[0117] (1) A certain number of glass capillaries are closely arranged to obtain a two-dimensional array of capillaries.

[0118] (2) The two-dimensional array of capillaries is fixed on a programmable multi-axis moving platform, which is used to control the preparation process.

[0119] (3) The two-dimensional array of capillaries is immersed in a Nafion-Li solution with a concentration of 50 mg / mL to obtain a two-dimensional array of capillaries containing Nafion-Li solution.

[0120] (4) The two-dimensional array of capillaries containing Nafion-Li solution is controlled by the moving platform to contact the pp membrane substrate to form a one-dimensional liquid bridge. The temperature is 30 ℃, the moving speed is 1 mm / s, and the array capillary is moved directionally to form a uniform solution film. After the solvent in the liquid film is volatilized, a Nafion-Li membrane is obtained.

[0121] (5) Repeat steps (3) and (4) to obtain Nafion membranes with different layers.

[0122] The preparation process of the electrolyte is as follows: lithium bis (trifluoromethyl sulfonyl) imide (LiN(CF3SO2)2) is dissolved in a mixed solvent of DOL (1, 3-dioxolane) and DME (ethylene glycol dimethyl ether) with a volume ratio of 1:1, and the concentration of lithium salt in the solvent is 1 M;

[0123] Battery assembly: Selecting lithium as the negative electrode, the positive electrode is coated with carbon material, binder, active material aluminum foil, coated with carbon material, binder, active material aluminum foil preparation process as follows: sulfur and carbon mixed in the mass ratio of 7:3, under argon atmosphere 155 ℃ for 12 hours to get sulfur carbon material; sulfur carbon material, conductive carbon black, binder were uniformly mixed in N-methyl-2-pyrrolidone according to the mass ratio of 8:1:1, then coated on the aluminum foil, dried, the loading of sulfur on the electrode was 1.5 mg cm -2 .

[0124] Selecting array capillary to prepare different layers of Nafion-Li membrane on PP membrane and commercial Nafion-117 membrane and PP membrane as battery separator, after adding 45 μL electrolyte, the battery was assembled and packaged.

[0125] The lithium-sulfur battery of the above-prepared different layers of Nafion-Li membrane and commercial Nafion-117 membrane was tested by impedance test and cyclic voltammetry test and rate test in an electrochemical workstation.

[0126] Figure 19 (c-d) shows the impedance of lithium-sulfur batteries of different layers of Nafion-Li membrane and commercial Nafion-117 membrane, from which it can be seen that the single-layer N-Li-1 membrane prepared by array capillary has the smallest interfacial charge transfer impedance and bulk impedance, and the interfacial charge transfer impedance and bulk impedance gradually increase with the increase of the number of membrane layers. The above results show that the single-layer N-Li-1 membrane prepared by array capillary can effectively reduce the lithium ion transmission impedance inside the battery. Figure 19 (e-h) and Figure 20 show the reaction kinetics of lithium-sulfur batteries of different layers of Nafion-Li membrane and commercial Nafion-117 membrane. From Figure 19 (e) the cyclic voltammetry of the battery can obviously see that the single-layer N-Li-1 membrane prepared by array capillary has higher reduction potential and lower oxidation potential, and has the highest redox peak current, while the reduction potential of the battery gradually decreases, the oxidation potential gradually increases, and the redox peak current also gradually decreases with the increase of the number of membrane layers. The redox peaks of the battery in the cyclic voltammetry are marked as P A1 , P B1 and P C1 , respectively. The potential size and lithium ion diffusion coefficient of lithium-sulfur batteries of different layers of Nafion-Li membrane and commercial Nafion-117 membrane at P A1 , P B1 and P C1 , respectively, are shown in Figure 19 (f) and Figure 20 . Figure 19(g) The Tafel slopes of lithium-sulfur batteries S8→ Li2S with different layer numbers of Nafion-Li membranes and lithiated commercial Nafion-117 membrane are 28.0, 45.8, 47.9, 97.6 mV dec n , -1 , Figure 19 (h) The Tafel slopes of lithium-sulfur batteries Li2S→ Li2S with different layer numbers of Nafion-Li membranes and lithiated commercial Nafion-117 membrane are 84.4, 90.9, 94.5, 143.3 mV dec n -1 . The Tafel slopes indicate that the reaction kinetics of lithium-sulfur batteries can be effectively improved with the decrease of the thickness of Nafion-Li membranes, which is consistent with the results of cyclic voltammetry tests. Figure 19 (i-l) and Figure 21 show the charge-discharge curves and the trends of polarization voltage and discharge capacity of lithium-sulfur batteries with different layer numbers of Nafion-Li membranes and lithiated commercial Nafion-117 membrane. Figure 19 (i-j) and Figure 21 The charge-discharge curves of lithium-sulfur batteries with different layer numbers of Nafion-Li membranes and lithiated commercial Nafion-117 membrane can be seen that the lithium-sulfur battery with single layer N-Li-1 membrane prepared by array capillary has the best rate performance, and the rate performance of the battery gradually decreases with the increase of the layer number of Nafion-Li membrane, it is worth noting that the polarization voltage of the lithium-sulfur battery with lithiated commercial Nafion-117 membrane (N-Li-117) is too large at a current density of 0.5 C, and the battery cannot operate normally. Figure 19 (k-l) are the trends of polarization voltage and discharge capacity of lithium-sulfur batteries with different layer numbers of Nafion-Li membranes and lithiated commercial Nafion-117 membrane, respectively, here it can be seen that the lithium-sulfur battery with single layer N-Li-1 membrane prepared by array capillary has the smallest polarization voltage and the highest discharge capacity at different current densities, while the polarization voltage of the lithium-sulfur battery gradually increases and the discharge capacity gradually decreases with the increase of the layer number of Nafion-117 membrane.

[0127] Example 5:

[0128] Assembly of lithium-sulfur batteries with Nafion-Li membranes:

[0129] The process of preparing Nafion-Li membranes on pp membranes by array capillary is as follows:

[0130] (1) A certain number of glass capillaries are closely arranged to obtain a two-dimensional array of capillaries.

[0131] ​(2) Fix the two-dimensional array of capillaries on a programmable multi-axis motion platform, which is used to control the preparation process.

[0132] (3) Dip the two-dimensional array of capillaries into a Nafion-Li solution with a concentration of 50 mg / mL to obtain a two-dimensional array of capillaries containing Nafion-Li solution.

[0133] (4) Control the two-dimensional array of capillaries containing Nafion-Li solution to contact the pp film substrate by moving the platform to form a one-dimensional liquid bridge. The temperature is 30 °C, the moving speed is 1 mm / s, and the array of capillaries is moved directionally to form a uniform solution film. After the solvent in the liquid film evaporates, a Nafion-Li film is obtained.

[0134] (5) Repeat steps (3) and (4) to obtain a single-layer Nafion film.

[0135] The preparation process of the electrolyte is as follows: dissolve lithium salt bis(trifluoromethylsulfonyl) imide lithium (LiN(CF3SO2)2) in a mixed solvent of DOL (1,3-dioxolane) and DME (ethylene glycol dimethyl ether) with a volume ratio of 1:1, and the concentration of lithium salt in the solvent is 1 M; dissolve lithium salt LiN(CF3SO2)2 and lithium nitrate (LiNO3) in a mixed solvent of DOL (1,3-dioxolane) and DME (ethylene glycol dimethyl ether) with a volume ratio of 1:1, and the concentration of lithium salt LiN(CF3SO2)2 in the solvent is 1 M, and the concentration of lithium salt LiNO3 is 0.4 M [only used for experiments on high-load lithium-sulfur batteries (load ~ 10.6 mg cm -2 Battery Figure 22 e, i.e., except Figure 22 (e) In addition to using an electrolyte containing lithium salt LiN(CF3SO2)2 with a concentration of 1 M in the solvent and lithium salt LiNO3 with a concentration of 0.4 M, other experiments use an electrolyte containing lithium salt LiN(CF3SO2)2 with a concentration of 1 M in the solvent.

[0136] Battery assembly: lithium is selected as the negative electrode, the positive electrode is an aluminum foil coated with carbon material, binder, and active material, a single-layer Nafion-Li film prepared by array capillaries on a PP film and a conventional PP film are selected as the battery separator, and after 45 µL of electrolyte is added, the battery is assembled and packaged to obtain the final product.

[0137] Battery assembly: lithium is selected as the negative electrode, and the positive electrode is an aluminum foil coated with carbon material, binder, and active material or a self-supporting positive electrode. The preparation process of the aluminum foil positive electrode coated with carbon material, binder, and active material is as follows: sulfur and carbon are mixed in a mass ratio of 7:3, and sulfur-carbon material is obtained by keeping at 155°C for 12 hours under an argon atmosphere; the sulfur-carbon material, conductive carbon black, and binder are uniformly mixed in N-methyl-2-pyrrolidone in a mass ratio of 8:1:1, and then coated on an aluminum foil and dried, so that the loading of sulfur on the electrode is 1.5 mg cm -2 The preparation process of the self-supporting positive electrode is as follows: sulfur and carbon are mixed in a mass ratio of 7:3, and sulfur-carbon material is obtained by keeping at 150-160°C for 10-15 hours under an argon atmosphere; the sulfur-carbon material, conductive carbon, carbon fiber, and binder are uniformly mixed in N-methyl-2-pyrrolidone in a mass ratio of 8:0.9:0.1:1, and then cast in a silica gel mold and dried, so that the self-supporting positive electrode is obtained, and the loading of sulfur on the electrode is about 10-12 mg cm -2 The battery of the high-loading lithium-sulfur battery (loading ~ 10.6 mg cm -2 Figure 22 e).

[0138] The lithium-sulfur battery of the Nafion-Li film prepared above and the conventional pp film is subjected to charge-discharge test and cycle performance test.

[0139] Figure 22 (a-b) First, the permeability experiment of the Nafion-Li film and the pp film to the redox active material Li2S8 is demonstrated, and the permeation of Li2S8 can be observed after 6 hours in the permeability experiment of the pp film to the redox active material Li2S8, and the single-layer N-Li-1 film prepared by the capillary tube still does not have the permeation of Li2S8 after 240 hours, indicating that the single-layer N-Li-1 film prepared by the capillary tube has high ion selectivity.

[0140] Figure 22 (c) The charge-discharge curve of the lithium-sulfur battery of the single-layer N-Li-1 film prepared by the capillary tube and the conventional pp film at 0.1 C is demonstrated, and the lithium-sulfur battery of the conventional pp film has the "shuttle effect" of the redox active material Li2S n , resulting in serious overcharge, and the coulombic efficiency is only 25.1%. The lithium-sulfur battery of the N-Li-1 film does not have the "shuttle effect" of Li2S n , and the coulombic efficiency is as high as 99.8%. Figure 22 ​(d) In 200 cycles of 0.5 C, the Li-S battery with N-Li-1 membrane exhibited higher capacity retention rate with an average capacity fade rate of 0.25% per cycle, compared to the Li-S battery with conventional pp membrane with an average capacity fade rate of 0.47% per cycle. The average coulombic efficiency was 99%. Figure 22 (e) The cycling performance of high loading Li-S battery at 0.1 C current density (loading ~ 10.6 mg cm -2 ), where the Li-S battery with conventional pp membrane could only cycle for 25 cycles, after which the capacity decayed rapidly, while the Li-S battery with N-Li-1 membrane could stably cycle for 120 cycles with an average capacity fade rate of 0.12% per cycle and a capacity retention rate of 86.6%. Figure 22 (f-g) The SEM images of lithium sheet of Li-S battery with conventional pp membrane cycled at 0.5 C for 100 cycles, where severe corrosion of the lithium sheet surface with rough surface and a byproduct thickness of 114 pm could be observed, see Figure 23 (a). In contrast, the lithium sheet surface of Li-S battery with N-Li-1 membrane cycled at 0.5 C for 100 cycles was much smoother with no severe side reactions and a byproduct thickness of only 49 pm Figure 22 (h-i), see Figure 23 (b). Figure 22 (j) The XPS spectra of lithium sheet of Li-S battery with N-Li-1 membrane and conventional pp membrane cycled at 0.5 C for 10 cycles, where the lithium sheet surface of Li-S battery with conventional pp membrane had a strong polysulfide peak signal, while the lithium sheet surface of Li-S battery with N-Li-1 membrane had a very weak polysulfide peak signal, see Figure 24 .

Claims

1. Use of a Nafion-Li membrane as a battery separator in a lithium-sulfur battery, characterized in that, Lithium sheet is selected as the negative electrode, the positive electrode is the aluminum foil coated with carbon material, binder and active material or the self-supporting positive electrode mixed with carbon material, binder and active material, Nafion-Li film is used as the battery separator, the electrolyte is added dropwise, and then the battery is assembled and packaged. The Nafion-Li film is obtained by the following process: (1) A plurality of capillaries are closely arranged to obtain a two-dimensional array of capillaries; the capillaries are glass capillaries with a diameter of 100-3000 μm; (2) The two-dimensional array of capillaries is fixed on a multi-axis moving platform; (3) The two-dimensional array of capillaries is immersed in a Nafion-Li solution to obtain a two-dimensional array of capillaries containing Nafion-Li solution; the Nafion-Li solution is prepared by the following process: a Nafion-Li sample is weighed and dissolved in ethanol to obtain a 50 mg / mL Nafion-Li solution; (4) The substrate is heated and kept at a temperature of 30℃, and the two-dimensional array of capillaries containing Nafion-Li solution is controlled to contact the substrate by the moving platform to form a one-dimensional liquid bridge; The array of capillaries is moved directionally to form a uniform solution film; the solvent in the solution film is volatilized to obtain a Nafion-Li film; the substrate is a glass fiber porous membrane or a polymer porous membrane; the moving speed of the two-dimensional array of capillaries is 1 mm / s; and the number of layers of the Nafion-Li film is 1 layer.

2. Use according to claim 1, characterized in that, The positive electrode is prepared by the following process: The preparation process of the aluminum foil coated with carbon material, binder and active material is as follows: sulfur and carbon are mixed in a mass ratio of 7:3, and kept at 150-160°C for 10-15 hours under argon atmosphere to obtain sulfur-carbon material; the sulfur-carbon material, conductive carbon black and binder are uniformly mixed in N-methyl-2-pyrrolidone in a mass ratio of 8:1:1, and then coated on an aluminum foil and dried, thereby obtaining the product, and the loading amount of sulfur on the electrode is 1.5-4 mg cm -2 ; The preparation process of the self-supporting positive electrode is as follows: sulfur and carbon are mixed according to a mass ratio of 7:3, and a sulfur-carbon material is obtained by keeping at 150-160°C for 10-15 hours under an argon atmosphere; the sulfur-carbon material, conductive carbon, black carbon fiber and binder are uniformly mixed in N-methyl-2-pyrrolidone according to a mass ratio of 8:0.9:0.1:1, and then poured into a silica gel mold for drying, to obtain the self-supporting positive electrode, and the loading amount of sulfur on the electrode is 10-12 mg cm -2 .

3. Use according to claim 1, characterized in that, The electrolyte is prepared by the following process: lithium bis(trifluoromethylsulfonyl)imide is dissolved in a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether at a volume ratio of 1:1, and the concentration of lithium bis(trifluoromethylsulfonyl)imide in the solvent is 1 M; or lithium bis(trifluoromethylsulfonyl)imide and lithium nitrate are dissolved in a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether at a volume ratio of 1:1, and the concentration of lithium bis(trifluoromethylsulfonyl)imide in the solvent is 1 M, and the concentration of lithium nitrate in the solvent is 0.4 M.

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