Modified diaphragm, preparation method thereof and negative-electrode-free sodium metal battery

Abstract

The invention relates to the technical field of battery materials, and discloses a modified diaphragm, a preparation method thereof and a negative-electrode-free sodium metal battery. The modified diaphragm comprises a base membrane and a first functional layer arranged on one side of the base membrane; the first functional layer comprises an isotropic elastic matrix and inorganic nanoparticles distributed in the elastic matrix, and the mass ratio of the inorganic nanoparticles to the elastic matrix is (150-200): (100-125). The modified diaphragm can uniformly buffer the huge expansive force of the non-cathode sodium battery, so that the permeation of sodium metal into pores of the diaphragm is inhibited, and the occurrence of short circuit of the battery is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a modified separator, a preparation method thereof and a negative electrode-free sodium metal battery. BACKGROUND

[0002] The negative electrode-free sodium ion battery is a representative of the next generation of high-energy density energy storage devices. However, there are still many problems in its actual use, which limit its application, for example: During the charging process, the deposition of sodium metal on the negative electrode current collector will produce a huge volume expansion, which will generate a great mechanical pressure on the internal components of the battery, especially the separator, leading to the penetration of sodium metal into the separator, resulting in short circuit of the battery; During the first charging process of the negative electrode-free sodium ion battery, sodium ions of the positive electrode will be deposited on the negative electrode current collector to form a sodium metal negative electrode, and an SEI film will be formed at the interface. This process will irreversibly consume a large amount of sodium ions, resulting in a decrease in the initial coulombic efficiency of the battery and a decrease in the actual available capacity.

[0003] In view of this, the present application is proposed. SUMMARY

[0004] The purpose of the present application is to provide a modified separator, a preparation method thereof and a negative electrode-free sodium metal battery, aiming to improve at least one problem mentioned in the background art.

[0005] The present application is implemented as follows: In a first aspect, the present application provides a modified separator, comprising a base film and a first functional layer arranged on one side of the base film, respectively. The first functional layer comprises an isotropic elastic matrix and inorganic nanoparticles distributed in the elastic matrix, and the mass ratio of the inorganic nanoparticles to the elastic matrix is 150-200:100-125.

[0006] In an optional embodiment, the material of the elastic matrix is selected from at least one of polyurethane, hydrogenated nitrile rubber and polyacrylate; And / or, the inorganic nanoparticles are selected from alpha phase aluminum oxide, fumed silica and zirconium oxide nanopowder; Optionally, the particle size of the inorganic nanoparticles is 50-500 nm; Optionally, the thickness of the base film is 18-20 μm; Optionally, the thickness of the first functional layer is 2-8 μm.

[0007] In an optional embodiment, a second functional layer is arranged on the other side of the base film, and the second functional layer comprises an adhesive matrix and a sodium supplementing agent distributed in the adhesive matrix, and the ratio of the sodium supplementing agent to the adhesive is 10-15:4-8. Optionally, the material of the adhesive matrix is selected from at least one of polyacrylic acid, styrene butadiene rubber, and polyvinyl alcohol; Optionally, the sodium supplement is selected from at least one of sodium oxalate, sodium acetate, sodium citrate, NaCl, NaClO4, and NaTFSI.

[0008] In an optional embodiment, the second functional layer further comprises a conductive agent distributed in the adhesive matrix, and the ratio of the adhesive to the conductive agent is 4-8:1-3. Optionally, the conductive agent is selected from at least one of Ketjen black, graphene, Super P, and CNTs. Optionally, the thickness of the second functional layer is 12-20 μm.

[0009] In an optional embodiment, the base film is a polyolefin film. Optionally, the polyolefin film is a polyethylene film or a polypropylene film.

[0010] In a second aspect, the present application provides a method for preparing a modified separator, comprising: Coating the first slurry on one side of the base film, and forming the first functional layer after the first slurry is dried and solidified.

[0011] In an optional embodiment, the method further comprises performing corona treatment on the surface of the base film before coating the slurry.

[0012] In an optional embodiment, the method for preparing the first slurry comprises, by weight fraction: Stirring and mixing 400-500 parts of deionized water and 1-3 parts of a thickening agent (CMC) to obtain a first glue solution; Adding 2-6 parts of a wetting agent and an emulsion containing 100-125 parts of an elastic polymer to the first glue solution, and stirring and mixing to obtain a polymer slurry; Adding 150-200 parts of inorganic nanoparticles to the polymer slurry, stirring and mixing, and then defoaming to obtain the first slurry; Optionally, the thickening agent is selected from at least one of carboxymethyl cellulose, polyvinyl alcohol, and polyethylene oxide. Optionally, the wetting agent is selected from at least one of sodium dodecyl sulfate, octylphenol polyoxyethylene ether, and sodium dodecyl sulfonate. Optionally, the emulsion containing 100-125 parts of an elastic polymer has a solid content of 35-45%. Optionally, the emulsion is a polyurethane emulsion, a hydrogenated styrene butadiene rubber emulsion, or a polyacrylate emulsion.

[0013] In an optional embodiment, a second slurry is further coated on the other side of the base film, and a second functional layer is formed after the second slurry is dried and cured; the second functional layer comprises an adhesive matrix and a sodium supplement distributed in the adhesive matrix, and the ratio of the sodium supplement to the adhesive is 10-15:4-8; Optionally, the sodium supplement is selected from at least one of sodium oxalate, sodium acetate, sodium citrate, NaCl, NaClO4 and NaTFSI; Optionally, the second functional layer further comprises a conductive agent distributed in the adhesive matrix, and the ratio of the adhesive to the conductive agent is 1-3:1; Optionally, the conductive agent is selected from at least one of Ketjen black, graphene, Super P and CNTs; Optionally, the thickness of the second functional layer is 12-20 μm; The preparation method of the second slurry comprises the following steps, by weight fraction: 4-8 parts of the adhesive is dispersed in 60-80 parts of the solvent to obtain a second glue solution by mixing and stirring uniformly; 1-3 parts of the conductive agent and 10-15 parts of the sodium supplement are added to the second glue solution to obtain the second slurry after mixing uniformly; Optionally, the solvent is selected from at least one of N-methyl pyrrolidone, N-ethyl-2-pyrrolidone and dimethyl sulfoxide.

[0014] In a third aspect, the application provides a negative electrode-free sodium metal battery comprising the modified separator according to any one of the preceding embodiments or prepared by the preparation method according to any one of the preceding embodiments, and the first functional layer of the modified separator faces the negative electrode current collector.

[0015] The application has the following beneficial effects: The modified separator provided by the application has the first functional layer facing the negative electrode current collector when assembled, and the isotropic elastic matrix can "neutralize" the anisotropy of the base film, so that the modified separator can uniformly buffer the huge expansion force of the negative electrode-free sodium battery, inhibit the penetration of sodium metal into the pores of the separator, and avoid the occurrence of battery short circuit; and due to the poor electrical conductivity and mechanical strength of the elastic matrix, the addition of an appropriate amount of inorganic nanoparticles in the first functional layer can improve the ion conductivity and mechanical strength of the layer. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0017] Figure 1 A structure diagram of a negative electrode-free sodium metal battery is provided. DETAILED DESCRIPTION

[0018] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. If specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by manufacturers are adopted. If manufacturers of reagents or instruments are not specified, all are conventional products that can be purchased in the market.

[0019] The features and performances of the present application will be further described in detail below in combination with embodiments.

[0020] The modified separator provided by the embodiments of the present application comprises a base film and a first functional layer arranged on one side of the base film. The first functional layer comprises an isotropic elastic matrix and inorganic nanoparticles distributed in the elastic matrix, and the mass ratio of the inorganic nanoparticles to the elastic matrix is 150-200:100-125.

[0021] The modified separator provided by the present application is assembled with the first functional layer arranged towards the negative electrode current collector. The isotropic elastic matrix can "neutralize" the anisotropy of the base film, so that the modified separator can uniformly buffer the huge expansion force of the negative electrode-free sodium battery, inhibit the penetration of sodium metal into the pores of the separator, and avoid the occurrence of battery short circuit. Since the electrical conductivity and mechanical strength of the elastic matrix are poor, the addition of an appropriate amount of inorganic nanoparticles in the first functional layer can improve the ion conductivity and mechanical strength of the layer.

[0022] It should be noted that the ratio of the inorganic nanoparticles to the elastic matrix in the first functional layer needs to be within the above range. If the inorganic nanoparticles are added too much, the rigidity will be too strong, and if they are added too little, the ion conductivity will be insufficient.

[0023] Optionally, the base film is a polyolefin film, such as a polyethylene film or a polypropylene film.

[0024] Optionally, the thickness of the base film is 18-20 μm (for example, 18 μm, 19 μm or 20 μm).

[0025] Optionally, the thickness of the first functional layer is 2-8 μm (for example, 2 μm, 4 μm, 6 μm or 8 μm). The thickness of the first functional layer within this range can better maintain the isotropic elasticity, relieve the huge expansion of the battery, and not affect the cycle performance of the battery.

[0026] Optionally, the material of the elastic matrix is selected from at least one of polyurethane, hydrogenated nitrile rubber and polyacrylate. These materials have the characteristics of isotropy, can well "neutralize" the anisotropy of the base film, and exhibit good effects of buffering the huge expansion force of the negative electrode-free sodium battery.

[0027] Optionally, the inorganic nanoparticles are selected from at least one of alpha phase aluminum oxide (α-Al2O3), fumed silica, and zirconium oxide nanopowder. These inorganic nanoparticles can better improve the electrical conductivity and mechanical strength of the first functional layer.

[0028] Optionally, the inorganic nanoparticles have a particle size of 50-500 nm (e.g., 50 nm, 100 nm, 200 nm, 300 nm, or 500 nm).

[0029] Optionally, the other side of the base film is provided with a second functional layer, and the second functional layer comprises an adhesive matrix and a sodium supplementing agent distributed in the adhesive matrix, and the ratio of the sodium supplementing agent to the adhesive is 10-15:4-8 (e.g., 10:4, 10:6, 10:8, 12:4, 12:6, 12:8, 15:4, 15:6, or 15:8).

[0030] The second functional layer adds the sodium supplementing agent, which releases sodium ions through a controllable reaction after activation of the battery, effectively compensates for the sodium ions consumed during formation of the sodium metal anode and the SEI film, reduces the loss of irreversible capacity, and improves the initial efficiency of the battery.

[0031] Optionally, the thickness of the second functional layer is 12-20 μm (e.g., 12 μm, 15 μm, 18 μm, or 20 μm). The thickness of the second functional layer in this range can effectively compensate for the loss of the first-week irreversible capacity and improve the initial efficiency.

[0032] Optionally, the material of the adhesive matrix is selected from at least one of polyacrylic acid (PAA), styrene butadiene rubber (SBR), and polyvinyl alcohol (PVA).

[0033] Optionally, the sodium supplementing agent is selected from at least one of sodium oxalate, sodium acetate, sodium citrate, NaCl, NaClO4, and NaTFSI.

[0034] Optionally, the second functional layer further comprises a conductive agent distributed in the adhesive matrix, and the ratio of the adhesive to the conductive agent is 4-8:1-3 (e.g., 4:1, 4:2, 4:3, 6:1, 6:2, 6:3, 8:1, 8:2, or 8:3). The addition of the conductive agent can improve the electrical conductivity of the second functional layer.

[0035] Optionally, the conductive agent is selected from at least one of Ketjen black, graphene, Super P, and CNTs.

[0036] The preparation method of the modified separator provided by the embodiment of the present application comprises: The first slurry is coated on one side of the base film, and after the first slurry is dried and solidified, the first functional layer is formed.

[0037] Specifically, the preparation method comprises: S1, base film treatment The base film (commercial polyolefin film, such as polyethylene, polypropylene, etc.) is cut into the required size, and then the surface thereof is treated by a corona machine to improve the surface energy and the adhesion to the coating.

[0038] S2, providing a first slurry The preparation method of the first slurry is as follows in terms of weight fraction: (1) 400-500 parts (e.g. 400 parts, 450 parts or 500 parts) of deionized water and 1-3 parts (e.g. 1 part, 2 parts or 3 parts) of a thickening agent are stirred and mixed uniformly to obtain a first glue solution.

[0039] Optionally, the thickening agent is at least one selected from carboxymethyl cellulose (CMC), polyvinyl alcohol and polyethylene oxide. The thickening agent, as a component of the first slurry, can increase the viscosity of the first slurry, thereby improving the ionic conductivity.

[0040] Optionally, the uniform stirring manner is stirring at a rate of 750-850 rpm (e.g. 750 rpm, 800 rpm or 850 rpm) for 1.5-2.5 h (1.5 h, 2 h or 2.5 h).

[0041] (2) 2-6 parts (e.g. 2 parts, 4 parts or 6 parts) of a wetting agent and an emulsion containing 100-125 parts (e.g. 100 parts, 105 parts, 110 parts, 115 parts or 125 parts) of an elastic polymer are added to the first glue solution, and stirred and mixed uniformly to obtain a polymer slurry.

[0042] Optionally, the wetting agent is at least one selected from sodium dodecyl sulfate, octylphenol polyoxyethylene ether and sodium dodecyl sulfonate. The addition of the wetting agent can improve the wettability of the slurry, so that the slurry is easily and more uniformly spread on the surface of the base film.

[0043] Optionally, the solid content (mass percentage content of the elastic polymer) of the emulsion is 35-45% (e.g. 35%, 40% or 45%).

[0044] Optionally, the emulsion is a polyurethane emulsion, a hydrogenated butadiene-styrene rubber emulsion or a polyacrylate emulsion.

[0045] Optionally, the uniform mixing manner is to continue stirring at the stirring rate of the previous step for 25-35 min (e.g. 25 min, 30 min or 35 min).

[0046] (3) 150-200 parts (e.g. 150 parts, 180 parts or 200 parts) of inorganic nanoparticles are added to the polymer slurry, and stirred and mixed uniformly, and then defoaming treatment is performed to obtain the first slurry.

[0047] Optionally, the solid content of the first slurry is 20-30% (e.g. 20%, 25% or 30%).

[0048] Optionally, the inorganic nanoparticles are added to the polymer slurry gradually and slowly so as to be mixed well and prevent the nanoparticles from agglomerating.

[0049] Optionally, after the inorganic nanoparticles are added, the stirring speed is increased to 1400-1600 rpm (e.g. 1400 rpm, 1500 rpm or 1600 rpm) and the stirring is continued for 3-6 h (e.g. 3 h, 4 h, 5 h or 6 h) to ensure that the inorganic nanoparticles are mixed well with the polymer slurry.

[0050] Optionally, the defoaming treatment is carried out at a stirring speed of 1900-2100 rpm (e.g. 1900 rpm, 2000 rpm or 2100 rpm) for 12-17 min (e.g. 12 min, 15 min or 17 min).

[0051] S3, Preparation of the second slurry The preparation method of the second slurry is as follows in terms of weight fractions: (1) 4-8 parts (e.g. 4 parts, 6 parts or 8 parts) of the binder are dispersed in 60-80 parts (e.g. 60 parts, 70 parts or 80 parts) of the solvent, and the mixture is stirred uniformly to obtain a second glue solution.

[0052] Optionally, the solvent is at least one selected from N-methyl pyrrolidone, N-ethyl-2-pyrrolidone and dimethyl sulfoxide.

[0053] Optionally, the uniform stirring is carried out at a speed of 450-550 rpm (e.g. 450 rpm, 500 rpm or 550 rpm) for 1.5-2.5 h (e.g. 1.5 h, 2 h or 2.5 h).

[0054] (2) 1-3 parts (e.g. 1 part, 2 parts or 3 parts) of the conductive agent and 10-15 parts (e.g. 10 parts, 13 parts or 15 parts) of the sodium supplement are added to the second glue solution, and the mixture is stirred uniformly to obtain the second slurry.

[0055] Optionally, the conductive agent and the sodium supplement are added to the second glue solution at a stirring speed of 250-350 rpm (e.g. 250 rpm, 300 rpm or 350 rpm), and then the stirring speed is increased to 900-1100 rpm (e.g. 900 rpm, 1000 rpm or 1100 rpm) and the stirring is continued for 5-7 h (e.g. 5 h, 6 h or 7 h) to obtain the second slurry.

[0056] S4, Coating and drying The first slurry is coated on one side of the base film by gravure roll under normal environment, and after drying and curing, the first functional layer is formed. In this step, the drying temperature is preferably 60-100°C (for example, 60°C, 80°C or 100°C).

[0057] The above semi-finished product is transferred to a dew point room, and the second slurry is coated on the other side of the base film by another gravure roll, and after low-temperature drying and removal of the solvent, the second functional layer is formed, and finally the finished modified separator is obtained. In this step, the drying temperature is preferably 50-60°C (for example, 50°C, 55°C or 60°C).

[0058] As shown in Figure 1 The negative electrode-free sodium metal battery provided by the embodiment of the present application comprises the modified separator provided by the embodiment of the present application, the first functional layer of the modified separator is arranged towards the negative electrode current collector, and the second functional layer is arranged towards the positive electrode.

[0059] Example 1 A commercial polyethylene film with a thickness of 20 μm is cut, and then subjected to corona treatment.

[0060] According to weight parts, 500 parts of deionized water and 3 parts of thickening agent (CMC) are added to a blender, and stirred at a speed of 800 rpm for 2 h to make it fully dissolved to form a transparent first glue solution; While stirring, 6 parts of wetting agent (sodium dodecyl sulfate) and an emulsion containing 125 parts of elastic polymer (WPUA-40 (Wanate), polyurethane, solid content 40%) are slowly added in sequence, and stirred for 30 min to make them fully mixed; 200 parts of inorganic nanoparticles (α-Al2O3) are slowly added, and then the stirring speed of the blender is increased to 1500 rpm, and maintained for 4 h; Finally, the first slurry is obtained by defoaming stirring at a speed of 2000 rpm for 15 min.

[0061] According to weight parts, 4 parts of adhesive (PAA) are dispersed in 60 parts of solvent (NMP) at a speed of 500 rpm for 2 h to obtain a uniform and stable glue solution; Under a stirring speed of 300 rpm, 1 part of conductive agent (CNT) and 10 parts of sodium supplementing agent (NaCl) are added in sequence, and then the stirring speed is increased to 1000 rpm, and maintained for 6 h.

[0062] The first slurry is coated on one side of the base film by gravure roll under normal environment, and after drying and curing, the first functional layer is formed. In this step, the drying temperature is preferably 60-100°C (for example, 60°C, 80°C or 100°C).

[0063] The above semi-finished product is transferred to a dew point room, the second slurry is coated on the other side of the base film by another gravure roll, and after the solvent is removed by low-temperature drying at 60°C, the second functional layer is formed, and finally a finished modified separator is obtained, the thickness of the first functional layer is 5 μm, and the thickness of the second functional layer is 15 μm.

[0064] Example 2 A commercial polyethylene film with a thickness of 18 is cut, and then subjected to a corona treatment.

[0065] 400 parts of deionized water and 1 part of thickening agent (CMC) are added to a blender, stirred at a speed of 800 rpm for 2 h, and fully dissolved to form a transparent first glue solution; While stirring, 2 parts of wetting agent (octylphenol polyoxyethylene ether) and an emulsion containing 100 parts of elastic polymer (Zetpol series, hydrogenated nitrile rubber, solid content 40%) are slowly added in sequence, and stirred for 30 min to fully mix; 150 parts of inorganic nanoparticles (silicon dioxide) are slowly added, and then the stirring speed of the blender is increased to 1500 rpm and maintained for 4 h; Finally, defoaming stirring is carried out at a speed of 2000 rpm for 15 min to obtain the first slurry.

[0066] 8 parts of adhesive (SBR) are dispersed in 80 parts of solvent (NMP) at a speed of 500 rpm for 2 h to obtain a uniform and stable glue solution; 3 parts of conductive agent (graphene) and 15 parts of sodium supplementing agent (sodium oxalate) are added in sequence at a stirring speed of 300 rpm, and then the stirring speed is increased to 1000 rpm for 6 h.

[0067] The first slurry is coated on one side of the base film by a gravure roll under normal environment, and after drying and curing by a program of 60°C / 2 min+80°C / 5 min+100°C / 3 min, the first functional layer is formed.

[0068] The above semi-finished product is transferred to a dew point room, the second slurry is coated on the other side of the base film by another gravure roll, and after the solvent is removed by low-temperature drying at 60°C, the second functional layer is formed, and finally a finished modified separator is obtained, the thickness of the first functional layer is 5 μm, and the thickness of the second functional layer is 15 μm.

[0069] Example 3 A commercial polyethylene film with a thickness of 19 is cut, and then subjected to a corona treatment.

[0070] Add 450 parts of deionized water and 2 parts of thickening agent (CMC) into a stirrer, stir at a speed of 800 rpm for 2 h to make it fully dissolved and form a transparent first glue liquid; Keep stirring, slowly add 4 parts of wetting agent (sodium dodecyl sulfonate) and emulsion containing 110 parts of elastic polymer (Wallpol 40-700, polyacrylate, solid content 40%) in turn, and stir for 30 min to make it fully mixed; Slowly continue to add 170 parts of inorganic nanoparticles (zirconium oxide), then increase the stirring speed of the stirrer to 1500 rpm and keep for 4 h; Finally, defoaming stirring at a speed of 2000 rpm for 15 min to obtain a first slurry.

[0071] Disperse 6 parts of adhesive (PVA) in 70 parts of solvent (NMP) by weight, stir at a speed of 500 rpm for 2 h to obtain a uniform and stable glue liquid; Add 2 parts of conductive agent (Super P) and 12 parts of sodium supplement agent (sodium citrate) in turn at a stirring speed of 300 rpm, then increase the stirring speed to 1000 rpm and keep for 6 h.

[0072] Coat the first slurry on one side of the base film by gravure roll under normal environment, and form a first functional layer after drying and curing through the program of 60℃ / 2 min+80℃ / 5 min+100℃ / 3 min.

[0073] Transfer the above semi-finished product to a dew point room, coat the second slurry on the other side of the base film by another gravure roll, and form a second functional layer after removing the solvent by low-temperature drying at 60℃, finally obtain a finished modified separator, the thickness of the first functional layer is 2 μm, and the thickness of the second functional layer is 12 μm.

[0074] Example 4 This example is basically the same as Example 1, the difference is only that no conductive agent is added in the second slurry.

[0075] Example 5 This comparative example is basically the same as Example 1, the difference is only that the base film with a thickness of 35 μm is selected, no second functional layer is arranged on the surface of the base film, and the total thickness of the separator prepared is the same as that of Example 1.

[0076] Comparative Example 1 This comparative example is basically the same as Example 2, the difference is only that no inorganic nanoparticles are added.

[0077] Comparative Example 2 This comparative example is basically the same as Example 1, the difference is only that the amount of inorganic nanoparticles added is 250 parts.

[0078] Comparative Example 3 This comparative example is basically the same as Example 1, except that the base film is selected to have a thickness of 23 μm, and the base film surface is not provided with the first functional layer, and a separator having the same total thickness as that of Example 1 is prepared.

[0079] Comparative Example 4 This comparative example provides a separator having the same base film material as in Example 1, and having the same thickness as the modified separator prepared in Example 1.

[0080] Experimental Example The separators provided in each of the examples and comparative examples are assembled into a negative electrode-free sodium metal battery, and the separators having the first functional layer and / or the second functional layer are arranged with the first functional layer facing the negative electrode and the second functional layer facing the positive electrode.

[0081] The negative electrode current collector of the negative electrode-free sodium metal battery is a carbon-coated aluminum foil; The positive electrode active layer is: 95.1:2.0:2.4:0.5 of sodium iron pyrophosphate, PVDF, conductive carbon black, and dispersant; The electrolyte is: 1M NaPF6, solvent diethylene glycol dimethyl ether.

[0082] The first coulombic efficiency and cycle performance of the negative electrode-free sodium metal battery prepared in each of the examples and comparative examples are tested, and the specific test methods are as follows: Battery first coulombic efficiency test: after the assembled battery is left for 10h, it is charged to 3.5V at 0.2C constant current and constant voltage, and then left for 0.5h, and then discharged to 2.0V at 0.5C constant current, and the ratio of the battery discharge capacity to the charge capacity is calculated as CE; Cycle life test: after the assembled battery is left for 10h, it is charged to 3.5V at 0.5C constant current and constant voltage at room temperature 25℃, left for 0.5h, and then discharged to 2.0V at 1C constant current, and the capacity retention rate is recorded after 100 cycles; Volume change test: after the battery is left for 10h at room temperature 25℃ after formation and capacity measurement, the initial volume of the battery is measured by the drainage method, denoted as V1; then it is placed in a 45℃ high-temperature room, stored for 7D, taken out, and cooled to room temperature 25℃, then the volume after storage is measured by the drainage method, denoted as V2, and the volume change rate of 45℃ high-temperature storage for 7D is ΔV=(V2-V1) / V1*100%.

[0083] Table 1 Performance statistics of the batteries prepared in each of the examples and comparative examples

[0084] As can be seen from Table 1, the modified separators prepared by various embodiments of the present application have better electrochemical performance when assembled into batteries compared to Comparative Example 4.

[0085] Comparing Example 4 with Example 1, the performance of Example 4 is slightly worse, indicating that adding a conductive agent to the second functional layer can improve the utilization rate of the sodium source; Comparing Example 5 with Example 1, the performance of Example 1 is significantly better, indicating that setting the second functional layer can improve the initial efficiency of the battery and the capacity of the battery; Comparing Comparative Example 1 with Example 2, the performance of Comparative Example 1 is significantly worse, indicating that if the first functional layer does not add inorganic nanoparticles, the mechanical strength of the separator will be insufficient, leading to the destruction of the structure, thereby causing the capacity retention rate to deteriorate and the volume change rate to be higher; Comparing Comparative Example 2 with Example 1, the performance of Comparative Example 2 is significantly worse, indicating that if too many inorganic nanoparticles are added to the second functional layer, the coating will be too brittle, thereby causing it to crack easily during the cycling process and the performance to be worse; Comparing Comparative Example 3 with Example 1, the performance of Comparative Example 3 is significantly worse, indicating that if the first functional layer is not set, the separator cannot withstand the expansion stress of the battery.

[0086] In summary, the modified separator provided by the present application has the following characteristics: The isotropic elastic matrix on the negative electrode side can "neutralize" the anisotropy of the base film, so that the overall composite separator can uniformly buffer the huge expansion force of the sodium metal battery, inhibit the penetration of sodium metal into the pores of the separator, and avoid the occurrence of battery short circuit; The second functional layer on the positive electrode side adds a sodium supplement agent, which releases sodium ions through a controllable reaction after the battery is activated, effectively compensating for the sodium ions consumed during the formation of the sodium metal negative electrode and the SEI film, reducing the loss of irreversible capacity, and improving the initial efficiency of the battery; The cooperation of the first functional layer and the second functional layer solves the two core problems of "mechanical stress management" and "sodium source compensation" of the sodium metal battery, so that the modified separator applied to the battery can ultimately improve the coulomb efficiency, cycle life and safety of the sodium metal battery.

[0087] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A modified separator, characterized by, The base film and the first functional layer disposed on one side of the base film respectively; The first functional layer comprises an isotropic elastic matrix and inorganic nanoparticles distributed in the elastic matrix, and the mass ratio of the inorganic nanoparticles to the elastic matrix is 150-200:100-125.

2. The modified separator according to claim 1, wherein The material of the elastic matrix is selected from at least one of polyurethane, hydrogenated nitrile rubber and polyacrylate; And / or, the inorganic nanoparticles are selected from alpha phase aluminum oxide, fumed silica and zirconium oxide nanopowder; Optionally, the particle size of the inorganic nanoparticles is 50-500 nm; Optionally, the thickness of the base film is 18-20 μm; Optionally, the thickness of the first functional layer is 2-8 μm.

3. The modified separator of claim 1, wherein The other side of the base film is provided with a second functional layer, and the second functional layer comprises an adhesive matrix and a sodium supplementing agent distributed in the adhesive matrix, and the ratio of the sodium supplementing agent to the adhesive is 10-15:4-8; Optionally, the material of the adhesive matrix is selected from at least one of polyacrylic acid, styrene butadiene rubber and polyvinyl alcohol; Optionally, the sodium supplementing agent is selected from at least one of sodium oxalate, sodium acetate, sodium citrate, NaCl, NaClO4 and NaTFSI.

4. The modified separator of claim 3, wherein The second functional layer further comprises a conductive agent distributed in the adhesive matrix, and the ratio of the adhesive to the conductive agent is 4-8:1-3; Optionally, the conductive agent is selected from at least one of ketjen black, graphene, Super P and CNTs; Optionally, the thickness of the second functional layer is 12-20 μm.

5. The modified separator of claim 1, wherein The base film is a polyolefin film; Optionally, the polyolefin film is a polyethylene film or a polypropylene film.

6. The method of producing a modified separator according to any one of claims 1 to 3, wherein It comprises: A first slurry is coated on one side of the base film, and the first functional layer is formed after the first slurry is dried and cured.

7. The preparation method according to claim 6, characterized in that, The base film is also subjected to corona treatment before the slurry is coated on the surface of the base film.

8. The preparation method according to claim 6, characterized in that, The preparation method of the first slurry comprises, by weight fraction: 400-500 parts of deionized water and 1-3 parts of thickening agent (CMC) are stirred and mixed uniformly to obtain a first glue solution; 2-6 parts of wetting agent and an emulsion containing 100-125 parts of elastic polymer are added to the first glue solution, and the mixture is stirred and mixed uniformly to obtain a polymer slurry; 150-200 parts of inorganic nanoparticles are added to the polymer slurry, and the mixture is stirred and mixed uniformly, and then defoaming treatment is performed to obtain the first slurry; Optionally, the thickening agent is selected from at least one of carboxymethyl cellulose, polyvinyl alcohol and polyethylene oxide; Optionally, the wetting agent is selected from at least one of sodium dodecyl sulfate, octylphenol polyoxyethylene ether and sodium dodecyl sulfonate; Optionally, the solid content of the emulsion containing 100-125 parts of elastic polymer is 35-45%; Optionally, the emulsion is a polyurethane emulsion, a hydrogenated butadiene-styrene rubber emulsion or a polyacrylate emulsion.

9. The preparation method according to claim 6, characterized in that, It further comprises coating a second slurry on the other side of the base film, and a second functional layer is formed after the second slurry is dried and cured; the second functional layer comprises an adhesive matrix and a sodium supplementing agent distributed in the adhesive matrix, and the ratio of the sodium supplementing agent to the adhesive is 10-15:4-8; Optionally, the sodium supplement is at least one selected from sodium oxalate, sodium acetate, sodium citrate, NaCl, NaClO4 and NaTFSI; Optionally, the second functional layer further comprises an electrically conductive agent distributed in the adhesive matrix, and the ratio of the adhesive to the electrically conductive agent is 1-3:1; Optionally, the electrically conductive agent is at least one selected from Ketjen black, graphene, Super P and CNTs; Optionally, the thickness of the second functional layer is 12-20 μm; The preparation method of the second slurry comprises, by weight fraction: 4-8 parts of an adhesive is dispersed in 60-80 parts of a solvent to obtain a second glue solution by uniform mixing and stirring; 1-3 parts of an electrically conductive agent and 10-15 parts of a sodium supplement are added to the second glue solution to obtain the second slurry after uniform mixing; Optionally, the solvent is at least one selected from N-methyl pyrrolidone, N-ethyl-2-pyrrolidone and dimethyl sulfoxide.

10. A sodium metal battery without a negative electrode, characterized by The modified separator as claimed in any one of claims 1-5 or prepared by the preparation method as claimed in any one of claims 6-9, wherein the first functional layer of the modified separator is arranged towards the negative electrode current collector.

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