Sodium-supplementing diaphragm, preparation method and application thereof, and sodium ion battery

Abstract

The invention provides a sodium-supplementing diaphragm, a preparation method and application thereof and a sodium-ion battery, and belongs to the technical field of sodium-ion batteries. According to the invention, the base film layer is used as the basis of the sodium-supplementing diaphragm, and the protective layer is arranged to maintain the stability and insulativity of the sodium-supplementing diaphragm, so that the puncture effect of burrs and compounds generated in the battery cell manufacturing process and the charging and discharging process on the diaphragm is reduced, and the risk of positive and negative electrode contact short circuit is reduced; sodium ions are dissociated through the sodium supplementing layer, sodium loss of the battery in the using process is made up, and then the first coulombic efficiency, the charge-discharge capacity and the energy density of the sodium ion battery are effectively improved; through mutual cooperation of the oxygen absorption layer and the sodium supplementing layer, by-product gas and solid of the sodium supplementing layer are adsorbed, side reaction products generated by electrolyte are adsorbed, decomposition of an SEI film is prevented, gas production is reduced, and the cycle performance and safety performance of the battery are further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a sodium supplementing diaphragm, a preparation method and application thereof, and a sodium ion battery. Background Art

[0002] Similar to lithium-ion batteries, the electrode materials in sodium-ion batteries also suffer from Na + The main reasons for irreversible capacity loss in sodium-ion batteries are as follows: (1) The electrolyte decomposes to form the SEI film (the electrolyte of sodium-ion batteries is prone to irreversible decomposition reactions at low potentials to form the SEI film). The SEI film is constantly decomposed and reconstructed during the electrochemical cycle, resulting in a decrease in the active Na + Further consumption; (2) defective structures capture Na + ; The negative electrode material has a variety of structural defects and sodium-philic functional groups, which capture Na + It cannot be deintercalated normally, resulting in Na + (3) Na caused by side reactions + Loss: For example, the presence of coordinated water in positive electrode materials such as Prussian blue can easily cause electrolyte side reactions at high potentials, resulting in Na + Consumption. Sodium-ion batteries can improve and maintain their cycle life by adding sodium supplements.

[0003] The existing sodium supplementation technologies mainly include the sodium metal pre-sodium method, adding sodium supplement agents to the positive electrode sheet, and sodium supplementation through a diaphragm. The sodium metal pre-sodium method requires the use of sodium metal. Sodium metal has high reactivity and is prone to spontaneous combustion when in contact with water. Therefore, a strict water-free and oxygen-free environment is required for use, and safety cannot be guaranteed. The addition of a sodium supplement agent to the positive electrode sheet is to add the sodium supplement agent to the positive electrode slurry, and then coat it on the current collector to make a positive electrode sheet; diaphragm sodium supplementation is to coat the sodium supplement agent and the conductive agent on the surface of the diaphragm; both methods achieve sodium supplementation by generating sodium ions after the sodium supplement agent reacts. However, a certain amount of gas and residual solids will be produced after the sodium supplement agent reacts. These by-products will remain in the battery and even pass through the diaphragm to react with the negative electrode, resulting in the decomposition of the SEI film, battery bulging and battery inflation, thereby affecting the battery's cycle life and safety performance. Summary of the invention

[0004] The object of the present invention is to provide a sodium-supplementing diaphragm, a preparation method and application thereof, and a sodium-ion battery. The sodium-supplementing diaphragm provided by the present invention can avoid byproduct gas and solid residue caused by sodium supplementation, thereby improving the cycle life and safety performance of the battery.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: The present invention provides a sodium-supplementing diaphragm, comprising a base film layer, a protective layer, a sodium-supplementing layer and an oxygen-absorbing layer, wherein the sodium-supplementing layer and the oxygen-absorbing layer are arranged adjacent to each other; the protective layer comprises an inorganic filler and a binder; and the oxygen-absorbing layer comprises an oxygen absorber, a binder, a dispersant and a conductive agent.

[0006] Preferably, the oxygen absorber includes one or more of butylated hydroxytoluene, 2,2,6,6-tetramethylpiperidinoxide, dithioaminomethane, methyl cinnamate, UV-531, UV-538, UV-0, UV-9, UV-P, UV-234, UV-326, UVP-327 and UVP-328.

[0007] Preferably, the inorganic filler includes one or more of alumina, zirconia, boehmite, magnesium hydroxide, barium sulfate, silicon oxide, aluminum nitride, magnesium oxide and titanium dioxide.

[0008] Preferably, the base film layer is made of polypropylene or polyethylene, and the thickness of the base film layer is 6 μm to 9 μm.

[0009] Preferably, the thickness of the protective layer, the sodium supplement layer and the oxygen absorption layer are independently 0.5 μm to 4 μm.

[0010] Preferably, the sodium supplement layer comprises a sodium supplement agent, a binder, a dispersant and a conductive agent.

[0011] Preferably, the mass ratio of the sodium supplement in the sodium supplement layer to the oxygen absorber in the oxygen absorption layer is 1:(0.2~1).

[0012] The present invention also provides a method for preparing the sodium-supplementing diaphragm described in the above technical solution, comprising: coating a protective layer slurry, a sodium-supplementing layer slurry and an oxygen-absorbing layer slurry on the surface of the base film, drying each layer of slurry after coating, and then coating the next layer of slurry to obtain a sodium-supplementing diaphragm.

[0013] The present invention also provides applications of the sodium supplementing diaphragm described in the above technical solution, and the applications include applications in sodium ion energy storage materials.

[0014] The present invention also provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a sodium-supplementing diaphragm arranged between the positive electrode sheet and the negative electrode sheet; the sodium-supplementing diaphragm is the sodium-supplementing diaphragm described in the above technical solution; the sodium-supplementing layer of the sodium-supplementing diaphragm is arranged opposite to the positive electrode sheet.

[0015] The present invention provides a sodium-supplementing diaphragm, comprising a base film layer, a protective layer, a sodium-supplementing layer and an oxygen-absorbing layer, wherein the sodium-supplementing layer and the oxygen-absorbing layer are arranged adjacent to each other; the protective layer comprises an inorganic filler and a binder; and the oxygen-absorbing layer comprises an oxygen absorber, a binder, a dispersant and a conductive agent. The present invention uses a base film layer as the basis of a sodium-supplementing diaphragm, and maintains the stability and insulation of the sodium-supplementing diaphragm by setting a protective layer, reduces the puncture effect of burrs and compounds generated in the battery cell manufacturing process and the charging and discharging process on the diaphragm, and reduces the risk of short circuit between the positive and negative electrodes. The protective layer can also reduce the contact area between the sodium compounds in the electrolyte and the base film layer, and reduce the risk of the base film layer being blocked by decomposition products and active substances of the electrolyte; sodium ions are dissociated through the sodium-supplementing layer to compensate for the sodium loss of the battery during use, thereby effectively improving the first coulomb efficiency, charging and discharging capacity and energy density of the sodium ion battery; the oxygen absorption layer cooperates with the sodium-supplementing layer to adsorb by-product gas and solid residues of the sodium-supplementing layer, and at the same time adsorbs side reaction products generated by the electrolyte, thereby preventing the decomposition of the SEI film, reducing gas production, and further improving the cycle performance and safety performance of the battery. The results of the examples show that when the sodium-supplementing diaphragm provided by the present invention is used in sodium-ion batteries, the first coulombic efficiency is 87.23%~92.58%, the capacity retention rate after 500 cycles at 0.5C is 97.26%~99.34%, and the gas production after 15 days of full-charge storage is 0.31mL / Ah~0.46mL / Ah. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the structure of the sodium supplementing membrane prepared in Example 1 of the present invention, wherein 101 is a base membrane layer, 102 is a protective layer, 103 is a sodium supplementing layer, and 104 is an oxygen absorption layer; Figure 2 This is a schematic diagram of the structure of the sodium supplement membrane prepared in Example 6 of the present invention; Figure 3 This is a schematic diagram of the structure of the sodium-supplementing diaphragm prepared in Example 7 of the present invention. DETAILED DESCRIPTION

[0017] All raw materials of the present invention have no particular limitation on their sources and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0018] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses high-purity raw materials or raw materials with a purity commonly used in the field of sodium ion batteries.

[0019] The present invention provides a sodium-supplementing diaphragm, comprising a base film layer, a protective layer, a sodium-supplementing layer and an oxygen-absorbing layer, wherein the sodium-supplementing layer and the oxygen-absorbing layer are arranged adjacent to each other; the protective layer comprises an inorganic filler and a binder; and the oxygen-absorbing layer comprises an oxygen absorber, a binder, a dispersant and a conductive agent.

[0020] The sodium supplementing diaphragm provided by the invention comprises a basement membrane layer.

[0021] In the present invention, the material of the base film layer is preferably polypropylene or polyethylene; the thickness of the base film layer is preferably 6μm~9μm, more preferably 7μm~8μm. As the basis of the sodium supplementation diaphragm, the base film layer plays the role of isolating the positive and negative electrodes and preventing short circuits. The diaphragm is also the transmission channel of ions in the electrolyte; using the above materials and thickness is conducive to further improving the isolation effect and ion transmission of the diaphragm.

[0022] The sodium supplementing diaphragm provided by the present invention also includes a protective layer.

[0023] In the present invention, the protective layer includes an inorganic filler and a binder; the inorganic filler preferably includes one or more of aluminum oxide, zirconium oxide, boehmite, magnesium hydroxide, barium sulfate, silicon oxide, aluminum nitride, magnesium oxide and titanium dioxide. The use of the above inorganic fillers is conducive to further improving the protective effect of the base film layer.

[0024] The present invention has no special requirements on the type of the binder, and any binder commonly used in the art can be used. In the embodiment of the present invention, PVDF binder is used.

[0025] As an embodiment of the present invention, the mass ratio of the inorganic filler to the binder may be (1-3):(3-6), or 1:(3-6).

[0026] In the present invention, the thickness of the protective layer is preferably 0.5 μm to 4 μm, more preferably 1 μm to 3 μm. As an embodiment of the present invention, the thickness of the protective layer can be 0.5 μm, 0.8 μm, 1.2 μm, 1.8 μm, 2.4 μm, 2.8 μm, 3.3 μm or 3.6 μm. The thickness of the protective layer within the above range is conducive to further improving the protective effect of the base film layer.

[0027] The sodium supplementing membrane provided by the present invention also includes a sodium supplementing layer.

[0028] In the present invention, the sodium supplement layer preferably includes a sodium supplement agent, a binder, a dispersant and a conductive agent.

[0029] In the present invention, the sodium supplement preferably includes Na2O, Na2O2, NaO2, Na2CO3 or Na2C2O4, more preferably Na2O2. The use of the above sodium supplement is conducive to further improving the sodium supplement effect.

[0030] In the present invention, the conductive agent preferably includes one or more of conductive carbon black, acetylene black, SuperP, carbon nanotubes and graphene conductive agents. The use of the above conductive agents is beneficial to improving the sodium supplementation effect of the sodium supplementation layer.

[0031] In the present invention, the binder preferably includes one or more of polyvinylidene fluoride, vinylidene fluoride-hexachloropropylene polymer, styrene-butadiene rubber, polypropylene, sodium carboxymethyl cellulose, polyacrylic acid and polymethyl methacrylate. The use of the above binder is conducive to further improving the sodium supplementation effect.

[0032] The present invention has no particular limitation on the specific type of the dispersant, and any dispersant commonly used in the art can be used. In the embodiment of the present invention, a PVP dispersant is used.

[0033] In the present invention, the mass ratio of the sodium supplementing agent, the binder, the dispersant and the conductive agent in the sodium supplementing layer is preferably (60-80): (5-10): (2-8): (1-5), and more preferably (65-75): (6-9): (3-7): (2-4). In an embodiment of the present invention, the mass ratio of the sodium supplementing agent, the binder, the dispersant and the conductive agent is 70:6:3:1. The mass ratio of each raw material within the above range is conducive to further improving the sodium supplementing effect.

[0034] In the present invention, the thickness of the sodium supplement layer is preferably 0.5 μm to 4 μm, more preferably 1 μm to 3 μm. As an embodiment of the present invention, the thickness of the sodium supplement layer can be 0.5 μm, 0.8 μm, 1.2 μm, 1.8 μm, 2.4 μm, 2.8 μm, 3.3 μm or 3.6 μm. The thickness of the sodium supplement layer within the above range is conducive to further improving the sodium supplement effect.

[0035] The sodium supplementing membrane provided by the present invention further comprises an oxygen absorbing layer arranged adjacent to the sodium supplementing layer.

[0036] In the present invention, the oxygen absorbing layer includes an oxygen absorber, a binder, a dispersant and a conductive agent.

[0037] In the present invention, the oxygen absorber preferably includes one or more of butylated hydroxytoluene, 2,2,6,6-tetramethylpiperidinoxide, dithioaminomethane, methyl cinnamate, UV-531, UV-538, UV-0, UV-9, UV-P, UV-234, UV-326, UVP-327 and UVP-328. The use of the above oxygen absorber is beneficial to further improve the safety and stability of the battery.

[0038] The binder, dispersant and conductive agent in the oxygen absorbing layer of the present invention are the same as the raw materials used in the sodium supplementing layer, and will not be described in detail here.

[0039] In the present invention, the mass ratio of the oxygen absorber, the binder, the dispersant and the conductive agent in the oxygen absorbing layer is preferably (50-70): (2-10): (1-5): (1-5), and more preferably (55-65): (3-9): (2-4): (2-4). In an embodiment of the present invention, the mass ratio of the oxygen absorber, the binder, the dispersant and the conductive agent is 65:5:3:2. The mass ratio of each raw material within the above range is conducive to further improving the safety and stability of the battery.

[0040] In the present invention, the thickness of the oxygen absorbing layer is preferably 0.5 μm to 4 μm, more preferably 1 μm to 3 μm. As an embodiment of the present invention, the thickness of the oxygen absorbing layer may be 0.5 μm, 0.8 μm, 1.2 μm, 1.8 μm, 2.4 μm, 2.8 μm, 3.3 μm or 3.6 μm. The thickness of the oxygen absorbing layer within the above range is conducive to further improving the safety and stability of the battery.

[0041] In the present invention, the mass ratio of the sodium supplement in the sodium supplement layer to the oxygen absorber in the oxygen absorption layer is preferably 1:(0.2-1), more preferably 1:(0.4-0.8); as an embodiment of the present invention, the mass ratio of the sodium supplement in the sodium supplement layer to the oxygen absorber in the oxygen absorption layer can be 1:0.25, 1:0.35, 1:0.45, 1:0.55, 1:0.65, 1:0.75, 1:0.85 or 1:0.95. The mass ratio of the sodium supplement to the oxygen absorber is within the above range, which is conducive to further improving the coulombic efficiency and capacity retention rate of the battery.

[0042] In the present invention, the sodium supplement layer and the oxygen absorption layer are arranged adjacent to each other. The present invention arranges the sodium supplement layer and the oxygen absorption layer adjacent to each other, so that the gas and solid by-products of the sodium supplement layer can be absorbed in time to avoid damage to the battery, thereby improving the safety and stability of the battery.

[0043] As an embodiment of the present invention, the protective layer can be arranged on the surface of the base film layer, or it can be not adjacent to the base film layer and be arranged on the surface of the sodium supplement layer or the oxygen absorption layer; the protective layer and the sodium supplement layer / oxygen absorption layer can be arranged on both sides of the base film layer, or they can be arranged on the same side of the base film layer; in an embodiment of the present invention, the sodium supplement membrane is a base film layer, a protective layer, a sodium supplement layer and an oxygen absorption layer arranged in sequence, or a base film layer, a protective layer, an oxygen absorption layer and a sodium supplement layer arranged in sequence, or a base film layer, a sodium supplement layer, an oxygen absorption layer and a protective layer arranged in sequence, or a base film layer, a sodium supplement layer, an oxygen absorption layer and a protective layer arranged in sequence.

[0044] The present invention uses a base film layer as the basis of a sodium-supplementing diaphragm, and maintains the stability and insulation of the sodium-supplementing diaphragm by setting a protective layer, reduces the puncture effect of burrs and compounds generated during the manufacturing process of the battery cell and the charging and discharging process on the diaphragm, and reduces the risk of short circuit between the positive and negative electrodes; dissociates sodium ions through the sodium-supplementing layer to compensate for the sodium loss of the battery during use, thereby effectively improving the initial coulomb efficiency, charging and discharging capacity and energy density of the sodium ion battery; and cooperates with the oxygen absorption layer to adsorb by-product gases and solids of the sodium-supplementing layer, and at the same time adsorbs side reaction products generated by the electrolyte, thereby preventing the decomposition of the SEI film, reducing gas production, and further improving the cycle performance and safety performance of the battery.

[0045] The present invention also provides a method for preparing the sodium-supplementing diaphragm described in the above technical solution, comprising: coating a protective layer slurry, a sodium-supplementing layer slurry and an oxygen-absorbing layer slurry on the surface of the base film, drying each layer of slurry after coating, and then coating the next layer of slurry to obtain a sodium-supplementing diaphragm.

[0046] The present invention has no particular limitation on the source of the base film, and the base film can be prepared in a manner well known to those skilled in the art or a commercially available product. In an embodiment of the present invention, the base film is a commercially available PP porous base film.

[0047] The present invention has no particular limitation on the preparation method of the protective layer slurry, the sodium supplement layer slurry and the oxygen absorption layer slurry, and the conventional preparation method in the art can be used. As an embodiment of the present invention, the raw materials of each component of the protective layer can be mixed with a solvent to obtain a protective layer slurry, the solvent is preferably NMP, and the amount of the solvent is preferably 25wt%~40wt% of the protective layer slurry; the raw materials of each component of the sodium supplement layer are mixed with a solvent to obtain a sodium supplement layer slurry, the solvent is preferably one or more of N-methylpyrrolidone, ethylene carbonate, dimethyl carbonate, fluoro-n-hexane, fluorocyclohexane, fluoroethylene carbonate and propylene carbonate, and the amount of the solvent is preferably 10wt%~25wt% of the sodium supplement layer slurry; the raw materials of each component of the oxygen absorption layer are mixed with a solvent to obtain an oxygen absorption layer slurry, the solvent is preferably NMP, and the amount of the solvent is preferably 15wt%~50wt% of the oxygen absorption layer slurry. The above solvent can disperse the raw materials well, which is easy to remove, and the pores formed after removal are beneficial to the permeability of the sodium supplement diaphragm.

[0048] The present invention does not particularly limit the specific method of the coating, and the coating method well known to those skilled in the art can be used to coat layer by layer in the order of the layer structure of the sodium supplementing diaphragm. As one embodiment of the present invention, the coating method can be gravure coating, roller coating or extrusion coating. In another embodiment of the present invention, gravure coating is used, and the coating parameters are: speed ratio 80%~150%, preferably 120%~130%; main machine speed 2m / min~6m / min; wrap angle size 5°~15°; scraper pressure 2kg~5kg.

[0049] The present invention has no particular limitation on the drying parameters, and the drying parameters known in the art can be used. As an embodiment of the present invention, the drying temperature can be 60°C to 100°C, or 70°C to 90°C; the drying time can be 2h to 5h, or 3h to 4h.

[0050] The present invention also provides application of the sodium supplementing diaphragm described in the above technical solution.

[0051] In the present invention, the application includes application in sodium ion energy storage materials. The present invention has no particular limitation on the application of the sodium supplementing membrane, and conventional application methods in the art can be used.

[0052] The present invention also provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a sodium-supplementing diaphragm arranged between the positive electrode sheet and the negative electrode sheet; the sodium-supplementing diaphragm is the sodium-supplementing diaphragm described in the above technical solution; the sodium-supplementing layer of the sodium-supplementing diaphragm is arranged opposite to the positive electrode sheet.

[0053] The present invention has no particular limitation on the raw materials and assembly methods of the sodium ion battery, and conventional raw materials and assembly methods in the art may be used.

[0054] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Example 1 like Figure 1 As shown, the sodium-supplementing membrane in this embodiment is composed of a base membrane layer 101 and a protective layer 102, a sodium-supplementing layer 103, and an oxygen absorption layer 104 which are sequentially arranged on the surface of the base membrane layer 101.

[0056] The preparation method of the sodium supplementation diaphragm is: (1) Preparation and coating of protective layer slurry The binder (PVDF), Al2O3 and solvent (NMP) were mixed in a mass ratio of 15:50:35 and mixed evenly to obtain a protective layer slurry; the protective layer slurry was coated on the surface of a PP porous base film (Xingyuan Material Technology Co., Ltd., model: SCXC-SH312W13, thickness 6μm) by a gravure coating process, and the coating parameters of the gravure coating were: speed ratio of 120%; main machine speed of 5m / min; wrap angle of 10°; scraper pressure of 3kg; dried at 90°C for 3h to form a protective layer with a thickness of 1μm on the surface of the base film.

[0057] (2) Preparation and coating of sodium supplementation layer slurry Na2O2, solvent (NMP), binder (PVDF), dispersant (PVP) and conductive carbon black are prepared in a mass ratio of 70:20:6:3:1. After preliminary mixing, the solvent (NMP) is added to adjust the viscosity to obtain a sodium-replenishing layer slurry with a solid content of 68%. The sodium-replenishing layer slurry is coated on the surface of the protective layer by a gravure coating process. The coating parameters of the gravure coating are: speed ratio of 120%; main machine speed of 5m / min; wrap angle of 15°; scraper pressure of 3kg; dried at 90°C for 3h to form a sodium-replenishing layer with a thickness of 1.5μm on the surface of the protective layer.

[0058] (3) Preparation and coating of oxygen absorption layer slurry The oxygen absorber (BHT), solvent (NMP), binder (PVDF), dispersant (PVP) and conductive carbon black are prepared in a mass ratio of 65:25:5:3:2, and mixed evenly to obtain an oxygen absorption layer slurry; the oxygen absorption layer slurry is coated on the surface of the sodium supplement layer by a gravure coating process, and the coating parameters of the gravure coating are: speed ratio is 120%; main machine speed is 5m / min; wrap angle size is 10°; scraper pressure is 3kg; dry at 90°C for 3h, and form an oxygen absorption layer with a thickness of 1μm on the surface of the sodium supplement layer. Among them, the mass ratio of the sodium supplement agent to the oxygen absorber is 1:0.6.

[0059] Example 2 A sodium supplementing membrane has the same structure and preparation method as Example 1, except that the mass ratio of the sodium supplementing agent to the oxygen absorber is 1:0.2.

[0060] Example 3 A sodium supplementing membrane has the same structure and preparation method as Example 1, except that the mass ratio of the sodium supplementing agent to the oxygen absorber is 1:0.4.

[0061] Example 4 A sodium supplementing membrane has the same structure and preparation method as Example 1, except that the mass ratio of the sodium supplementing agent to the oxygen absorber is 1:0.8.

[0062] Example 5 A sodium supplementing membrane has the same structure and preparation method as Example 1, except that the mass ratio of the sodium supplementing agent to the oxygen absorber is 1:1.

[0063] Example 6 like Figure 2 As shown, the sodium-supplementing membrane in this embodiment is composed of a base film layer 101 and an oxygen absorption layer 104 , a sodium-supplementing layer 103 , and a protective layer 102 which are sequentially arranged on the surface of the base film layer 101 .

[0064] The preparation method of the sodium supplementation diaphragm is: (1) Preparation and coating of oxygen absorption layer slurry An oxygen absorber (BHT), a solvent (NMP), a binder (PVDF), a dispersant (PVP) and conductive carbon black are prepared in a mass ratio of 65:25:5:3:2, and mixed evenly to obtain an oxygen absorption layer slurry; the oxygen absorption layer slurry is coated on the surface of a PP porous base film (same as in Example 1) by a gravure coating process, and the coating parameters of the gravure coating are: a speed ratio of 120%; a main machine speed of 5 m / min; a wrap angle of 10°; a scraper pressure of 3 kg; and drying at 90° C. for 3 hours to form an oxygen absorption layer with a thickness of 1 μm on the surface of the base film.

[0065] (2) Preparation and coating of sodium supplementation layer slurry Na2O2, solvent (NMP), binder (PVDF), dispersant (PVP) and conductive carbon black were prepared in a mass ratio of 70:20:6:3:1, and after preliminary mixing, solvent (NMP) was further added to adjust the viscosity to obtain a sodium supplement layer slurry with a solid content of 68%; the sodium supplement layer slurry was coated on the surface of the oxygen absorption layer by gravure coating process, and the coating parameters of gravure coating were: speed ratio of 120%; main machine speed of 5m / min; wrap angle of 15°; scraper pressure of 3kg; dried at 90℃ for 3h, and a sodium supplement layer with a thickness of 1.5μm was formed on the surface of the oxygen absorption layer. Among them, the mass ratio of sodium supplement agent to oxygen absorber was 1:0.6.

[0066] (3) Preparation and coating of protective layer slurry The binder (PVDF), Al2O3 and solvent (NMP) are mixed in a mass ratio of 15:50:35 and uniformly mixed to obtain a protective layer slurry; the protective layer slurry is coated on the surface of the sodium supplement layer by a gravure coating process, and the coating parameters of the gravure coating are: speed ratio of 120%; main machine speed of 5m / min; wrap angle of 10°; scraper pressure of 3kg; dried at 90°C for 3h to form a protective layer with a thickness of 1μm on the surface of the sodium supplement layer.

[0067] Example 7 like Figure 3As shown, the sodium-supplementing membrane in this embodiment is composed of a base membrane layer 101 and a protective layer 102 , an oxygen absorbing layer 104 , and a sodium-supplementing layer 102 which are sequentially arranged on the surface of the base membrane layer 101 .

[0068] The preparation method of the sodium supplementation diaphragm is: (1) Preparation and coating of protective layer slurry The binder (PVDF), Al2O3 and solvent (NMP) are mixed in a mass ratio of 15:50:35 and uniformly mixed to obtain a protective layer slurry; the protective layer slurry is coated on the surface of the PP porous base film (same as in Example 1) by a gravure coating process, and the coating parameters of the gravure coating are: speed ratio of 120%; main machine speed of 5m / min; wrap angle of 10°; scraper pressure of 3kg; dried at 90°C for 3h to form a protective layer with a thickness of 1μm on the surface of the base film.

[0069] (2) Preparation and coating of oxygen absorption layer slurry Oxygen absorber (BHT), solvent (NMP), binder (PVDF), dispersant (PVP) and conductive carbon black are prepared in a mass ratio of 65:25:5:3:2 and mixed evenly to obtain oxygen absorption layer slurry; the oxygen absorption layer slurry is coated on the surface of the protective layer by gravure coating process, and the coating parameters of the gravure coating are: speed ratio of 120%; main machine speed of 5m / min; wrap angle of 10°; scraper pressure of 3kg; dried at 90°C for 3h to form an oxygen absorption layer with a thickness of 1μm on the surface of the protective layer.

[0070] (3) Preparation and coating of sodium supplementation layer slurry Na2O2, solvent (NMP), binder (PVDF), dispersant (PVP) and conductive carbon black were prepared in a mass ratio of 70:20:6:3:1, and after preliminary mixing, solvent (NMP) was further added to adjust the viscosity to obtain a sodium supplement layer slurry with a solid content of 68%; the sodium supplement layer slurry was coated on the surface of the oxygen absorption layer by gravure coating process, and the coating parameters of gravure coating were: speed ratio of 120%; main machine speed of 5m / min; wrap angle of 15°; scraper pressure of 3kg; dried at 90℃ for 3h, and a sodium supplement layer with a thickness of 1.5μm was formed on the surface of the oxygen absorption layer. Among them, the mass ratio of sodium supplement agent to oxygen absorber was 1:0.6.

[0071] Example 8 A sodium supplementing diaphragm, the structure and preparation method of which are the same as those of Example 1, except that the thickness of the protective layer is 0.5 μm.

[0072] Example 9 A sodium supplementing diaphragm, the structure and preparation method of which are the same as those of Example 1, except that the thickness of the protective layer is 1.5 μm.

[0073] Example 10 A sodium supplementing diaphragm, the structure and preparation method of which are the same as those of Example 1, except that the thickness of the protective layer is 2 μm.

[0074] Embodiment 11 A sodium supplementing membrane, the structure and preparation method of which are the same as those of Example 1, except that the thickness of the protective layer is 4 μm.

[0075] Example 12 A sodium-supplementing membrane has the same structure and preparation method as that of Example 1, except that the thickness of the sodium-supplementing layer is 0.5 μm.

[0076] Embodiment 13 A sodium-supplementing membrane, the structure and preparation method of which are the same as those of Example 1, except that the thickness of the sodium-supplementing layer is 1 μm.

[0077] Embodiment 14 A sodium-supplementing membrane, the structure and preparation method of which are the same as those of Example 1, except that the thickness of the sodium-supplementing layer is 2 μm.

[0078] Embodiment 15 A sodium-supplementing membrane has the same structure and preparation method as that of Example 1, except that the thickness of the sodium-supplementing layer is 4 μm.

[0079] Example 16 A sodium supplementing membrane, the structure and preparation method of which are the same as those of Example 1, except that the thickness of the oxygen absorbing layer is 0.5 μm.

[0080] Embodiment 17 A sodium supplementing membrane, the structure and preparation method of which are the same as those of Example 1, except that the thickness of the oxygen absorbing layer is 1.5 μm.

[0081] Embodiment 18 A sodium supplementing membrane, the structure and preparation method of which are the same as those of Example 1, except that the thickness of the oxygen absorbing layer is 2 μm.

[0082] Embodiment 19 A sodium supplementing membrane has the same structure and preparation method as Example 1, except that the thickness of the oxygen absorbing layer is 4 μm.

[0083] Comparative Example 1 A sodium supplementing diaphragm consists of a base membrane layer and a protective layer arranged on the surface of the base membrane layer.

[0084] The preparation method of the sodium supplementation diaphragm is: The binder (PVDF), Al2O3 and solvent (NMP) were mixed in a mass ratio of 15:50:35 to obtain a protective layer slurry. The protective layer slurry was coated on the surface of the PP porous base film (same as in Example 1) by a gravure coating process (same as in Example 1), and a protective layer with a thickness of 1 μm was formed on the surface of the base film after drying.

[0085] Comparative Example 2 A sodium supplementing diaphragm consists of a base membrane layer, a protective layer and a sodium supplementing layer which are sequentially arranged on the surface of the base membrane layer.

[0086] The preparation method of the sodium supplementation diaphragm is: (1) Preparation and coating of protective layer slurry The binder (PVDF), Al2O3 and solvent (NMP) were mixed in a mass ratio of 15:50:35 to obtain a protective layer slurry. The protective layer slurry was coated on the surface of the PP porous base film (same as in Example 1) by a gravure coating process (same as in Example 1), and a protective layer with a thickness of 1 μm was formed on the surface of the base film after drying.

[0087] (2) Preparation and coating of sodium supplementation layer slurry Na2O2, solvent (NMP), binder (PVDF), dispersant (PVP) and conductive carbon black are prepared in a mass ratio of 70:20:6:3:1, and mixed evenly to obtain a sodium-replenishing layer slurry; the sodium-replenishing layer slurry is coated on the surface of the protective layer by a gravure coating process (same as in Example 1), and a sodium-replenishing layer with a thickness of 1.5 μm is formed on the surface of the protective layer after drying.

[0088] Comparative Example 3 A sodium supplementing diaphragm consists of a base film layer, a protective layer and an oxygen absorbing layer arranged on the surface of the base film layer.

[0089] The preparation method of the sodium supplementation diaphragm is: (1) Preparation and coating of protective layer slurry The binder (PVDF), Al2O3 and solvent (NMP) were mixed in a mass ratio of 15:50:35 to obtain a protective layer slurry. The protective layer slurry was coated on the surface of the PP porous base film (same as in Example 1) by a gravure coating process (same as in Example 1), and a protective layer with a thickness of 1 μm was formed on the surface of the base film after drying.

[0090] (2) Preparation and coating of oxygen absorption layer slurry An oxygen absorber (BHT), a solvent (NMP), a binder (PVDF), a dispersant (PVP) and conductive carbon black were prepared in a mass ratio of 65:25:5:3:2 and mixed evenly to obtain an oxygen absorption layer slurry; the slurry was coated on the surface of the protective layer by a gravure coating process (same as in Example 1) to form an oxygen absorption layer with a thickness of 1 μm on the surface of the protective layer.

[0091] Test Case The sodium supplementing diaphragm in the above embodiment and comparative example is assembled into a sodium ion battery with a positive electrode sheet, a negative electrode sheet, and an electrolyte, and the specific steps are as follows: (1) Preparation of negative electrode sheet: hard carbon, conductive carbon black, SBR, and CMC were mixed with deionized water in a mass ratio of 94:3:1:2 and stirred for 4 hours to obtain a negative electrode slurry with a solid content of 45%, a pH of 8.5, a fineness of 20 μm, and a viscosity of 4097 MPa·S. The slurry was coated on aluminum foil and dried at 90° C., then coated on aluminum foil and dried, rolled, and cut to make negative electrode sheets. (2) Preparation of positive electrode sheet: composite sodium iron phosphate (NFPP), solvent (NMP), binder (PVDF), dispersant (PVP) and conductive carbon black were mixed in a mass ratio of 65:25:3:2:5 and homogenized for 5 hours to obtain a positive electrode slurry with a solid content of 67%, a fineness of 36 μm and a viscosity of 7240 MPa·S. The slurry was coated on aluminum foil and dried at 90°C for 3 hours. The positive electrode sheet was then produced by coating, drying, rolling and slitting on the aluminum foil. (3) Preparation of electrolyte: Sodium hexafluorophosphate, ethyl cellulose (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 94:2:2:2 to obtain an electrolyte; (4) Battery assembly and activation: The positive electrode sheet, negative electrode sheet and sodium-supplementing separator are wound into a battery cell, wherein the sodium-supplementing separator is located between adjacent positive electrode sheets and negative electrode sheets; wherein the side of the sodium-supplementing separator with the sodium-supplementing layer is opposite to the positive electrode sheet, the wound core is placed in a metal shell and then injected with electrolyte, and a sodium-ion battery is manufactured after standing, forming and dividing the capacity.

[0092] First coulombic efficiency test At 25±2°C, three cells were taken from each embodiment and comparative example for testing. The battery was first allowed to stand for 40 min, then charged to 4.0 V at a constant current of 0.5 C, allowed to stand for 20 min, and then charged to 0.05 C at a constant voltage, allowed to stand for 30 min to obtain the charging capacity C0 of the battery; the charged battery was allowed to stand for 30 min, and then discharged to 2.0 V at a constant current of 0.5 C to obtain the first discharge capacity C1; the average value of the first coulomb efficiency of the three cells was calculated by the formula: C1 / C0, and the results are shown in Table 1.

[0093] Capacity retention test At 25±2°C, 3 cells were taken from each embodiment and comparative example for capacity test. The battery was first allowed to stand for 40 min, then charged to 4.0 V at 0.5 C constant current and constant voltage, allowed to stand for 20 min, and then charged to 0.05 C at constant voltage; after standing for 30 min, the battery was discharged to 2.0 V at 0.5 C constant current. The above process was continued, and the average value of the capacity retention rate of each group of batteries after 500 cycles was recorded. The results are shown in Table 1.

[0094] High temperature storage gas production test Under normal temperature of 25±2℃, 3 cells were taken from each embodiment and comparative example for testing. The battery was first left to stand for 40 minutes, then charged to 4.0V at 0.5C constant current and constant voltage, left to stand for 20 minutes, then charged to 0.05C at constant voltage, and left to stand for 30 minutes. The battery was then stored at 60℃ for 15 days, and the volume change of the cell before and after high temperature storage was tested in silicone oil using the Archimedes principle. The average gas production of each group of batteries was recorded, and the results are shown in Table 1.

[0095] Table 1 Performance test table of batteries prepared using the sodium supplement membranes of the embodiments and comparative examples

[0096] By analyzing the experimental results of Examples 1 to 5 in Table 1, it can be seen that when the ratio of the sodium supplement to the oxygen absorber is in the range of 1: (0.2 to 1), the first coulombic efficiency of the battery and the capacity retention rate after 500 cycles are effectively improved, avoiding the situation where the oxygen absorber is too little and cannot completely absorb the by-products in the battery or the oxygen absorber is too much, resulting in a decrease in the energy density of the battery.

[0097] The results in Table 1 show that the first coulombic efficiency and the capacity retention rate after 500 cycles of Examples 1 to 5 are effectively improved, which is due to the addition of the sodium supplement to make up for the SEI film formation and electrolyte side reactions during the formation process. + consumption, further improving the capacity and energy density of the battery; at the same time, the oxygen absorber can absorb the by-products produced by the electrolyte, preventing the decomposition of the SEI film and the battery bulging and gassing during the charge and discharge process, further improving the battery's cycle performance and safety performance.

[0098] Compared with Comparative Example 1, Comparative Example 2 adds a sodium supplement layer. It can be seen from Table 1 that after adding the sodium supplement layer, the first coulomb efficiency of the battery and the capacity retention rate of 500 cycles are increased, which shows that the sodium supplement can effectively make up for the Na in the battery. + loss.

[0099] Compared with Comparative Example 1, Comparative Example 3 adds an oxygen absorption layer. As can be seen from Table 1, Comparative Example 3 produces less gas than Comparative Example 1 during long-term high-temperature storage, which indicates that the oxygen absorption layer can effectively absorb the active oxygen, free radicals and by-products released by the battery, reduce the gas production of the battery, and avoid battery bulging and inflation.

[0100] Examples 8 to 11 are sodium-supplemented diaphragms with protective layers of different thicknesses. As can be seen from Table 1, the thickness of the protective layer is in the range of 0.5 μm to 4 μm, which can effectively protect the diaphragm, improve the cycle performance and first efficiency of the battery, and avoid the protective layer being too thin and having limited protective effect or the protective layer being too thick and affecting the energy density of the battery.

[0101] Examples 12 to 15 are sodium-supplementing membranes with sodium-supplementing layers of different thicknesses. As can be seen from Table 1, the thickness of the sodium-supplementing layer is in the range of 0.5 μm to 4 μm. + It can fully compensate for the Na + Loss, improve the cycle performance and initial efficiency of the battery, and avoid sodium precipitation and more by-products caused by the sodium replenishment layer being too thin, insufficient or too thick.

[0102] Examples 16 to 19 are sodium-supplemented diaphragms with oxygen absorption layers of different thicknesses. As can be seen from Table 1, when the thickness of the oxygen absorption layer is in the range of 0.5 μm to 4 μm, the active oxygen and free radicals generated by the sodium supplement are fully absorbed, which improves the cycle performance and first efficiency of the battery, and avoids the oxygen absorption layer being too thin to fully absorb or too thick to reduce the energy density of the battery.

[0103] The relative positions of the protective layer, the sodium supplement layer, and the oxygen absorption layer in Examples 6 and 7 are changed, but the sodium supplement layer and the oxygen absorption layer are always adjacent to each other. It can be seen from Table 1 that the sodium ion batteries prepared by the sodium supplement diaphragms provided in Examples 1, 6, and 7 can improve the cycle performance of the battery and effectively reduce the gas production of the battery.

[0104] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A sodium supplementing membrane, characterized in that: It comprises a base film layer, a protective layer, a sodium supplement layer and an oxygen absorption layer, wherein the sodium supplement layer and the oxygen absorption layer are arranged adjacent to each other; the protective layer comprises an inorganic filler and a binder; and the oxygen absorption layer comprises an oxygen absorber, a binder, a dispersant and a conductive agent.

2. The sodium supplement membrane according to claim 1, characterized in that: The oxygen absorber includes one or more of butylated hydroxytoluene, 2,2,6,6-tetramethylpiperidinoxide, dithioaminomethane, methyl cinnamate, UV-531, UV-538, UV-0, UV-9, UV-P, UV-234, UV-326, UVP-327 and UVP-328.

3. The sodium supplement membrane according to claim 1, characterized in that: The inorganic filler includes one or more of alumina, zirconia, boehmite, magnesium hydroxide, barium sulfate, silicon oxide, aluminum nitride, magnesium oxide and titanium dioxide.

4. The sodium supplement membrane according to claim 1, characterized in that: The base film layer is made of polypropylene or polyethylene, and the thickness of the base film layer is 6 μm to 9 μm.

5. The sodium supplement membrane according to claim 1, characterized in that: The thickness of the protective layer, the sodium supplement layer and the oxygen absorption layer are independently 0.5 μm to 4 μm.

6. The sodium supplement membrane according to claim 1, characterized in that: The sodium supplement layer comprises a sodium supplement agent, a binder, a dispersant and a conductive agent.

7. The sodium supplement membrane according to claim 6, characterized in that: The mass ratio of the sodium supplement in the sodium supplement layer to the oxygen absorber in the oxygen absorption layer is 1:(0.2-1).

8. The method for preparing the sodium supplementing diaphragm according to any one of claims 1 to 7, characterized in that: include: A protective layer slurry, a sodium supplementing layer slurry and an oxygen absorbing layer slurry are coated on the surface of the base film. After each layer of slurry is coated, it is dried and then coated with the next layer of slurry to obtain a sodium supplementing diaphragm.

9. Use of the sodium supplementing membrane according to any one of claims 1 to 7 or the sodium supplementing membrane prepared by the preparation method according to claim 8, characterized in that: The applications include applications in sodium ion energy storage materials.

10. A sodium ion battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a sodium-supplementing diaphragm arranged between the positive electrode sheet and the negative electrode sheet; the sodium-supplementing diaphragm is the sodium-supplementing diaphragm according to any one of claims 1 to 7 or the sodium-supplementing diaphragm prepared by the preparation method according to claim 8; the sodium-supplementing layer of the sodium-supplementing diaphragm is arranged opposite to the positive electrode sheet.

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