Sodium-supplementing diaphragm as well as preparation method and application thereof

Abstract

The invention relates to a sodium supplementing diaphragm which comprises a first conducting layer, a diaphragm layer and a second conducting layer, the first conducting layer is arranged on one side, facing a positive electrode, of the diaphragm layer, the second conducting layer is arranged on one side, facing a negative electrode, of the diaphragm layer, and the first conducting layer is made of aluminum oxide; the second conductive layer is arranged to be boehmite. According to the technical scheme, the conductivity of the battery is remarkably improved based on the ceramic layer with the conductive effect. In particular, the ceramic layer provided with boehmite and alumina achieves maintenance of thermal stability, exhaust control of dynamic gases, and impact of membrane ion transport based on the following aspects.

Description

Technical Field

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

[0002] Sodium-ion batteries, with their safety, significant cost advantages (sodium resources are 440 times more abundant than lithium), and excellent low-temperature performance (capacity retention >88% at -20°C), have become a highly competitive new electrochemical energy storage system in areas such as energy storage systems and low-speed electric vehicles. In their "rocking chair" operating mechanism, the reversible migration of sodium ions between the positive and negative electrodes is the core of energy storage. However, during the initial charge cycle, approximately 15-30% of the sodium ions are irreversibly consumed by the formation of the negative electrode SEI film, resulting in significant capacity decay. This drawback severely limits their energy density and commercialization.

[0003] The constraints of the membrane system on the sodium replenishment process have not been fully understood: the pore size distribution of commercial polyolefin membranes (PP / PE) is highly discrete (0.1~1μm), which cannot effectively block the penetration of nano-scale sodium dendrites, and easily induces micro-short circuits during the pre-sodiumization process, resulting in a reduced utilization rate of the sodium replenisher (failure of electron / ion selective separation); the surface of traditional membranes lacks functional groups (such as sulfonic acid groups and quaternary ammonium groups), resulting in the sodium ion migration number being far lower than the anion mobility, thereby inducing concentration polarization and reducing the pre-sodiumization efficiency by 20%~40% (imbalance in interfacial ion transport kinetics); the lateral shrinkage rate of PE membrane exceeds 10% at 120°C, and the pore structure is prone to closure under high current density (>1 C) conditions during the sodium replenishment process, resulting in uneven local sodium deposition.

[0004] Prior art optimizations for sodium-ion batteries include the use of sodium supplements on diaphragms or electrodes. Chinese Patent Publication No. CN118073777A discloses a sodium-supplemented diaphragm comprising a diaphragm substrate, a sodium-supplemented coating, and an adhesive layer. The sodium-supplemented coating is coated on at least one surface of the diaphragm substrate, and the adhesive layer is coated on the sodium-supplemented coating. The sodium-supplemented coating comprises a sodium-supplemented additive, a first conductive agent, a first dispersant, and a first binder. The adhesive layer comprises a second binder, a second conductive agent, and a second dispersant. Chinese Patent Publication No. CN117936788A discloses a method for preparing a sodium-supplemented slurry, comprising mixing a sodium-supplemented additive, a dispersant, a conductive agent, and a solvent to obtain a first slurry; sand-milling the first slurry to a particle size of 100-500 nm to obtain a second slurry; and dispersing the second slurry to obtain a sodium-supplemented slurry.

[0005] Although the above-mentioned sodium supplement agents directly or indirectly increase the efficiency of the battery by improving ion circulation, the sodium supplement layer / sodium supplement slurry involved in the above-mentioned comparative documents, whether set on the electrode or the diaphragm, does not optimize the ion conductivity of the diaphragm, resulting in a decrease in the ion migration rate; at the same time, the electrolyte used does not form a synergistic solvation structure with the Na⁺ released by the sodium supplement agent, and cannot achieve an efficient sodium supplement effect.

[0006] For example, the sodium supplement disclosed in the Chinese patent publication number CN118073777A may be embedded in the pores of the positive electrode when the sand is ground too finely (100-500nm), thereby hindering the diffusion path of Na⁺ to the diaphragm and causing local concentration polarization.

[0007] In addition, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the inventor studied a large number of documents and patents when making the present invention, but due to space limitations, not all details and contents are listed in detail. However, this does not mean that the present invention does not have the characteristics of these prior arts. On the contrary, the present invention already has all the characteristics of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0008] Based on the above technical problems, one of the objectives of the present invention is to provide a sodium-supplementing diaphragm and its preparation method and application to overcome the shortcomings of the prior art.

[0009] To achieve the above object, the present invention adopts the following technical solutions: A sodium-supplementing diaphragm comprises a diaphragm layer and ceramic layers disposed on both sides of the diaphragm layer. The ceramic layers include a first conductive layer disposed on the side of the diaphragm layer facing the positive electrode and a second conductive layer disposed on the side of the diaphragm layer facing the negative electrode. The first conductive layer is aluminum oxide, and the second conductive layer is boehmite. The first and second conductive layers are used to isolate electronic current and enhance ionic current.

[0010] According to a preferred embodiment, the diaphragm layer is selected from one or more of PP film, PE film, PET film, and glass fiber film.

[0011] According to a preferred embodiment, the thickness of the first conductive layer is 1-5 μm. Preferably, the thickness of the first conductive layer is 2-4 μm. Preferably, the thickness of the first conductive layer is 3 μm.

[0012] According to a preferred embodiment, the thickness of the second conductive layer is 0.5-3 μm. Preferably, the thickness of the second conductive layer is 1-2 μm. Preferably, the thickness of the second conductive layer is 1.5 μm.

[0013] According to a preferred embodiment, the boehmite is γ-AlOOH.

[0014] Another object of the present invention is to provide a sodium ion battery using the sodium-supplementing membrane.

[0015] According to a preferred embodiment, the electrolyte of the sodium ion battery comprises ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate, and NaPF6. Preferably, the electrolyte comprises a solvent, an additive, and a sodium salt, wherein the solvent comprises propylene carbonate at a mass fraction of 70% and ethylene carbonate at a mass fraction of 30%, the additive comprises fluoroethylene carbonate at a mass fraction of 12% calculated based on the total mass of the solvent, and the sodium salt comprises NaPF6 at a molar concentration of 1 M in the electrolyte.

[0016] One of the objects of the present invention is to provide a method for preparing a sodium supplementation membrane, which comprises the following steps: (1) preparing a first conductive layer slurry containing β-alumina, applying it to the side of the separator layer facing the positive electrode, and drying it; (2) Prepare a second conductive layer slurry containing boehmite, apply it to the side of the separator layer facing the negative electrode, and dry it.

[0017] According to a preferred embodiment, the preparation method further comprises the following steps: A sodium supplement layer prepared for releasing sodium ions is coated on the surface of the first conductive layer.

[0018] According to a preferred embodiment, the sodium-replenishing layer comprises 90% sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinyl pyrrolidone by weight. For example, 100 g of the sodium-replenishing layer contains 90 g sodium squarate, 4 g conductive carbon black, 4 g polyvinylidene fluoride, and 2 g polyvinyl pyrrolidone.

[0019] The technical solution of the present invention significantly improves the ion conductivity of the battery by utilizing a conductive ceramic layer. Specifically, the sodium-supplemented membrane, which is provided with boehmite and alumina, maintains thermal stability, controls the discharge of dynamic gases, and influences ion transport through the membrane.

[0020] The ceramic layer can not only improve the mechanical strength and liquid retention capacity of the diaphragm, but also effectively prevent the growth of sodium dendrites from piercing the diaphragm during the circulation process after the decomposition of the sodium replenishment layer, thereby improving battery safety.

[0021] The ceramic layer effectively improves battery safety. The alumina and boehmite in the ceramic layer act as a refractory insulation layer, slowing heat transfer to the electrodes. This thermal conductivity and heat transfer effect of the ceramic layer reduces the thermal shrinkage of the separator, thus avoiding the risk of uneven sodium ion distribution and reduced conductivity.

[0022] The boehmite in the ceramic layer has significantly higher ionic conductivity than traditional ceramic materials, reducing the migration resistance of lithium and sodium ions at the separator-electrode interface. Furthermore, the uniform pore structure of β-alumina and its high wettability with the electrolyte work synergistically to improve electrolyte penetration and reduce interfacial polarization.

[0023] In addition, the technical solution of the present invention is further optimized in conjunction with the ceramic layer based on the transmission efficiency of various ions and electrons in the electrolyte. The electrolyte solvent composition includes a solvent, an additive, and a sodium salt, wherein the solvent includes propylene carbonate (PC) with a mass fraction of 70% and ethylene carbonate (EC) with a mass fraction of 30%, the additive includes fluoroethylene carbonate (FEC) with a mass fraction of 12% calculated based on the total mass of the solvent as the denominator, and the sodium salt includes NaPF6 with a molar concentration of 1 M in the electrolyte. Fluoroethylene carbonate can stabilize the SEI film structure on the negative electrode side, regulate the solvation behavior and deposition process of sodium ions, and can be combined with the boehmite layer facing the negative electrode side to further promote the uniform deposition of sodium ions and reduce the occurrence of sodium precipitation in the battery.

[0024] In the present invention, the alumina material used for diaphragm modification can efficiently adsorb electrolyte, which is beneficial to increasing the battery cycle life. When it is applied to the modification of the positive electrode side diaphragm, the overall liquid retention of the battery can be significantly improved; boehmite has the characteristic of high ion mobility, which helps the rapid migration and uniform deposition of sodium ions. When it is applied to the modification of the negative electrode side diaphragm, it can effectively alleviate the sodium precipitation phenomenon of the negative electrode; in addition, combined with the fluoroethylene carbonate contained in the electrolyte provided by the present invention, it can promote the rapid migration of sodium ions while stabilizing the negative electrode SEI interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a design diagram of the diaphragm structure involved in the present invention.

[0026] Reference numerals 100: diaphragm layer; 200: ceramic layer; 210: first conductive layer; 220: second conductive layer; 300: sodium supplement layer. DETAILED DESCRIPTION

[0027] In the description of the present invention, terms are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly indicate the number of technical features indicated. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0028] The diaphragm layer in the following embodiments is configured as a base film composed of a PE film.

[0029] Example 1 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0030] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1 As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0031] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 3 μm. The sodium-filling layer 300 is composed of 90% by mass sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinylpyrrolidone, with a thickness of 2 μm. The second conductive layer 210 is composed of 92% by mass boehmite, 5% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 1.5 μm.

[0032] Example 2 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0033] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1 As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0034] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 3 μm. The sodium-replenishing layer 300 is composed of 90% by mass sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinylpyrrolidone, with a thickness of 3 μm. The second conductive layer 220 is composed of 92% by mass boehmite, 5% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 1.5 μm.

[0035] Example 3 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0036] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1 As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0037] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 3 μm. The sodium-replenishing layer 300 is composed of 90% by mass sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinylpyrrolidone, with a thickness of 1 μm. The second conductive layer 220 is composed of 92% by mass boehmite, 5% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 1.5 μm.

[0038] Example 4 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0039] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1 As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0040] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 3 μm. The sodium-replenishing layer 300 is composed of 95% by mass sodium squarate, 1.5% by mass conductive carbon black, 1.5% by mass polyvinylidene fluoride, and 2% by mass polyvinylpyrrolidone, with a thickness of 2 μm. The second conductive layer 220 is composed of 92% by mass boehmite, 5% by mass polyvinylidene fluoride, and 3% by mass polyvinylpyrrolidone, with a thickness of 1.5 μm.

[0041] Example 5 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0042] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1 As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0043] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 3 μm. The sodium-replenishing layer 300 is composed of 85% by mass sodium squarate, 6.5% by mass conductive carbon black, 6.5% by mass polyvinylidene fluoride, and 2% by mass polyvinylpyrrolidone, with a thickness of 2 μm. The second conductive layer 220 is composed of 92% by mass boehmite, 5% by mass polyvinylidene fluoride, and 3% by mass polyvinylpyrrolidone, with a thickness of 1.5 μm.

[0044] Example 6 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0045] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1 As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0046] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 2 μm. The sodium-filling layer 300 is composed of 90% by mass sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinylpyrrolidone, with a thickness of 2 μm. The second conductive layer 220 is composed of 92% by mass boehmite, 5% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 1.5 μm.

[0047] Example 7 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0048] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1 As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0049] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 4 μm. The sodium-replenishing layer 300 is composed of 90% by mass sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinylpyrrolidone, with a thickness of 2 μm. The second conductive layer 220 is composed of 92% by mass boehmite, 5% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 1.5 μm.

[0050] Example 8 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0051] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1 As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0052] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 3 μm. The sodium-replenishing layer 300 is composed of 90% by mass sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinylpyrrolidone, with a thickness of 2 μm. The second conductive layer 220 is composed of 92% by mass boehmite, 5% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 1 μm.

[0053] Example 9 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0054] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1 As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0055] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinyl pyrrolidone, with a thickness of 3 μm. The sodium-replenishing layer 300 is composed of 90% by mass sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinyl pyrrolidone, with a thickness of 2 μm. The second conductive layer 220 is composed of 92% by mass boehmite, 5% polyvinylidene fluoride, and 3% polyvinyl pyrrolidone, with a thickness of 2 μm.

[0056] Example 10 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0057] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0058] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 3 μm. The sodium-filling layer 300 is composed of 90% by mass sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinylpyrrolidone, with a thickness of 2 μm. The second conductive layer 220 is composed of 95% by mass boehmite, 3% polyvinylidene fluoride, and 2% polyvinylpyrrolidone, with a thickness of 1.5 μm.

[0059] Example 11 This embodiment provides a method for preparing a sodium-supplementing membrane. The method for preparing a sodium-supplementing membrane comprises the following steps: The sodium-supplementing diaphragm includes a diaphragm layer 100 , a ceramic layer 200 , and a sodium-supplementing layer 300 .

[0060] The ceramic layer 200 includes a first conductive layer 210 and a second conductive layer 220. The sodium supplementing membrane of the present invention is sequentially arranged as a sodium supplementing layer 300, a first conductive layer 210, a membrane layer 100 and a second conductive layer 220 (eg Figure 1 As shown in FIG. 1 ). The separator layer 100 is provided with the first conductive layer 210 on one side facing the positive electrode of the battery. The separator layer 100 is provided with the second conductive layer 220 on the other side facing the negative electrode of the battery.

[0061] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The first conductive layer 210 is composed of 90% by mass (mass fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, with a thickness of 3 μm. The sodium-filling layer 300 is composed of 90% by mass sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinylpyrrolidone, with a thickness of 2 μm. The second conductive layer 220 is composed of 89% by mass boehmite, 6% polyvinylidene fluoride, and 5% polyvinylpyrrolidone, with a thickness of 1.5 μm.

[0062] Example 12 The diaphragm used in this embodiment is the diaphragm layer 100 , that is, the diaphragm is not coated with the ceramic layer 200 and the sodium supplement layer 300 .

[0063] Example 13 The diaphragm used in this embodiment is a diaphragm coated only with the ceramic layer 200 , that is, a diaphragm not coated with the sodium supplement layer 300 .

[0064] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The ceramic layer 200 includes a first conductive layer 210 disposed on the side of the separator layer 100 facing the positive electrode. This first conductive layer 210 is composed of 90% by mass (weight fraction) β-alumina, 7% polyvinylidene fluoride, and 3% polyvinylpyrrolidone, and has a thickness of 3 μm.

[0065] Example 14 The diaphragm used in this embodiment is a diaphragm coated only with the sodium supplement layer 300 , that is, a diaphragm not coated with the ceramic layer 200 .

[0066] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The sodium supplement layer 300 is composed of 90% sodium squarate, 4% conductive carbon black, 4% polyvinylidene fluoride, and 2% polyvinyl pyrrolidone by mass percentage (mass fraction), and has a thickness of 2 μm.

[0067] Example 15 The diaphragm used in this embodiment is a diaphragm coated only with the ceramic layer 200 , that is, a diaphragm not coated with the sodium supplement layer 300 .

[0068] The separator layer 100 is a PE film with a thickness of 9 μm and a porosity of 42%. The ceramic layer 200 includes a second conductive layer 220. This second conductive layer 220 is disposed on the side of the separator layer 100 facing the negative electrode. This second conductive layer 220 is composed of 92% boehmite, 5% polyvinylidene fluoride, and 3% polyvinylpyrrolidone by mass percentage (mass fraction), and has a thickness of 1.5 μm.

[0069] The sodium-supplementing diaphragm obtained in the above embodiment is laminated with the positive electrode sheet and the negative electrode sheet to produce a sodium battery cell, which is then assembled into an aluminum shell and then baked, injected with liquid, formed, and divided into different volumes to produce a sodium ion battery.

[0070] The positive electrode sheet preparation method includes: S1: composite sodium iron phosphate: conductive carbon black: polyvinylidene fluoride = 94:3:3 (mass ratio), composite sodium iron phosphate, conductive carbon black and polyvinylidene fluoride are mixed in this ratio; S2: Add 0.2% of the total mass of the positive electrode dry material to oxalic acid and 2% of the total mass of the positive electrode dry material to N-methylpyrrolidone, and add the mixture in step S1 and mix evenly to obtain a positive electrode slurry; S3: After coating, rolling, slitting and die-cutting, the positive electrode sheet is obtained.

[0071] The negative electrode sheet preparation method includes: Hard carbon: conductive carbon black: sodium carboxymethyl cellulose: styrene-butadiene rubber = 95:2:1.5:1.5 (mass ratio) was dispersed in deionized water to prepare the negative electrode slurry. The subsequent preparation steps were the same as the preparation method of the positive electrode sheet.

[0072] The electrolyte is configured as: A mixture of 70% by mass of propylene carbonate and 30% by mass of ethylene carbonate; Taking the total mass of the above mixture as the denominator, add 12% by mass of fluoroethylene carbonate; Add NaPF6 sodium salt to adjust the concentration to 1 M.

[0073] For example: to prepare the electrolyte, first weigh 700 g of propylene carbonate and 300 g of ethylene carbonate and mix them; then add 120 g of fluoroethylene carbonate and mix evenly; finally, add 150 g of NaPF6 sodium salt.

[0074] Electrical Performance Test: At 25°C, the battery cells were first formed. Constant-current charging was performed in two steps at 0.2 C and 0.33 C. The resulting capacity was the initial charge capacity. Discharging was then performed at varying capacity to obtain the initial discharge capacity. Initial Coulombic Efficiency = Initial Discharge Capacity / Initial Charge Capacity. After capacity separation, charge and discharge tests were performed at 0.5 C on a charge and discharge tester. For cyclic disassembly, the battery was subjected to the first complete charge and discharge cycle after capacity separation, followed by 50 cycles of charge and discharge testing.

[0075] Table 1 Sodium ion battery performance data

[0076] According to the results shown in Table 1, Example 1 exhibits relatively high performance indicators, with an initial coulombic efficiency of 88.4% and a capacity retention rate of 98.6% after 500 cycles at a 0.5 C rate.

[0077] The first coulombic efficiency of Example 2 is slightly higher than that of Example 1, reaching 89.7%, while the capacity retention rate under the same conditions is 97.5%.

[0078] The first coulombic efficiency of Example 3 is 86.3%, and the capacity retention rate after 500 cycles at 0.5 C is 98.0%.

[0079] Example 4 has an initial coulombic efficiency of 88.7% and a capacity retention rate of 98.4% after 500 cycles at 0.5 C.

[0080] Example 5 showed an initial coulombic efficiency of 87.8% and a capacity retention rate of 98.3% after 500 cycles at 0.5 C.

[0081] In Example 6, the initial coulombic efficiency is 88.6%, and the capacity retention rate after 500 cycles at 0.5 C is 96.9%.

[0082] The first coulombic efficiency of Example 7 is 88.7%, and its capacity retention rate after 500 cycles at 0.5 C is 97.2%.

[0083] Example 8 is lower in both indicators, with an initial coulombic efficiency of 87.6% and a capacity retention rate of 97.9% after 500 cycles at 0.5 C.

[0084] The first coulombic efficiency of Example 9 is 89.1%, and the capacity retention rate after 500 cycles at 0.5 C is 97.4%.

[0085] In Example 10, the initial coulombic efficiency is 84.3%, and the capacity retention rate after 500 cycles at 0.5 C is 91.8%.

[0086] The first coulombic efficiency of Example 11 is 84.5%, and its capacity retention rate after 500 cycles at 0.5 C is 93.4%.

[0087] The first coulombic efficiency of Example 12 is 88.3%, and the capacity retention rate after 500 cycles at 0.5 C is 92.2%.

[0088] The first coulombic efficiency of Example 13 is 84.7%, and its capacity retention rate after 500 cycles at 0.5 C is 92.9%.

[0089] The first coulombic efficiency of the battery under different conditions ranged from 84.3% to 89.7%, while the capacity retention rate after 500 cycles at 0.5 C varied from 91.8% to 98.6%.

[0090] According to the data in Table 1, it can be seen that the technical solution involved in the present invention can significantly improve the ion conductivity of sodium ion batteries, thereby improving the performance of sodium ion batteries (first coulombic efficiency and 0.5 C cycle 500 cycle capacity retention rate).

[0091] Examples 1-9 all employed a sodium-supplemented separator. Compared to Examples 10, 12, and 13, which were not coated with the sodium-supplemented layer 300, Examples 1-9 demonstrated significant improvements in the initial coulombic efficiency, demonstrating that the added sodium-supplemented compound successfully compensated for the sodium ion loss in the battery. While the addition of a single sodium-supplemented layer 300 effectively improved the initial efficiency of the battery compared to Example 13, its cycling performance was poor due to the insufficient liquid retention of the separator coated solely with the sodium-supplemented layer 300. Furthermore, due to the lack of a ceramic coating, residual conductive agent and binder from the sodium-supplemented layer 300 posed a potential threat to battery safety.

[0092] Based on Examples 1-9, it can be seen that, under the same formulation conditions, the thickness of the sodium-replenishing layer 300 has a direct impact on the sodium-replenishing effect: the thicker the sodium-replenishing layer 300, the better the sodium-replenishing effect. However, increasing the thickness of the sodium-replenishing layer 300 can shorten the cycle life. This is because the thicker sodium-replenishing layer 300 increases the interfacial impedance during the charge-discharge process, hindering ion migration and thus affecting the cycling performance. Conversely, while a thinner sodium-replenishing layer 300 helps extend the cycle life, its sodium-replenishing effect is reduced. This result demonstrates the need to precisely control the thickness of the sodium-replenishing layer 300 to achieve an optimal balance.

[0093] Comparing Examples 1, 4, and 5, the results show that the change in the sodium supplementing agent content has no significant effect on the sodium supplementing effect. Considering that the conductivity of sodium squarate itself is not high, reducing the amount of conductive agent may affect its decomposition effect; and a lower sodium supplementing compound content cannot achieve the ideal sodium supplementing effect.

[0094] Comparisons of Examples 1, 6, 7, 8, and 9 show that different ceramic layer 200 thicknesses have varying degrees of impact on the sodium replenishment and cycle performance of the sodium replenishment separator. When the ceramic layer 200 is thin, the sodium replenishment effect is good, but the cycle performance is poor. As the thickness of the ceramic layer 200 increases, the cycle performance improves, while the sodium replenishment effect decreases. When the second conductive layer 220 in the ceramic layer 200 is thin, the sodium replenishment effect decreases, while the cycle performance improves. However, when the second conductive layer 220 in the ceramic layer 200 is thicker, the sodium replenishment effect increases, but the cycle performance decreases. This is because β-alumina has excellent liquid absorption capacity and can effectively extend the cycle life of the battery. However, when the β-alumina (first conductive layer 210) coating thickness is too high, the ion migration path increases, resulting in increased interfacial impedance and reducing the practical application effect of the sodium replenisher. While boehmite's high ion transport properties allow for rapid sodium ion transfer to the negative electrode, a thicker coating thickness can also limit its practical application to some extent. When the ceramic layer 200 is coated too thickly, the overall energy density of the battery will be affected.

[0095] It should be noted that the above-described specific embodiments are illustrative only. Those skilled in the art may devise various solutions based on the disclosure of the present invention, and such solutions fall within the scope of the present invention and are intended to be protected by the present invention. Those skilled in the art should understand that the present description and its accompanying drawings are intended to be illustrative only and are not intended to limit the scope of the claims. The scope of protection of the present invention is defined by the claims and their equivalents.

Claims

1. A sodium supplementing membrane, characterized in that: The invention comprises a diaphragm layer (100) and ceramic layers (200) distributed on both sides of the diaphragm layer (100), wherein the ceramic layer (200) comprises a first conductive layer (210) arranged on the side of the diaphragm layer (100) facing the positive electrode and a second conductive layer (220) arranged on the side of the diaphragm layer (100) facing the negative electrode, wherein: The first conductive layer (210) is configured as aluminum oxide; The second conductive layer (220) is configured as boehmite.

2. The sodium supplement membrane according to claim 1, characterized in that The diaphragm layer (100) is selected from one or more of PP film, PE film, PET film, and glass fiber film.

3. The sodium supplement membrane according to claim 1 or 2, characterized in that The thickness of the first conductive layer (210) is 1-5 μm.

4. The sodium supplementing membrane according to any one of claims 1 to 3, characterized in that The thickness of the second conductive layer (220) is 0.5-3 μm.

5. The sodium supplement membrane according to any one of claims 1 to 4, characterized in that: The boehmite is γ-AlOOH.

6. A sodium ion battery using the sodium-supplementing diaphragm according to any one of claims 1 to 5.

7. The sodium ion battery according to claim 6, characterized in that The electrolyte of the sodium ion battery comprises propylene carbonate, ethylene carbonate, fluoroethylene carbonate and NaPF6.

8. A method for preparing a sodium supplementing diaphragm, characterized in that: The preparation method comprises the following steps: (1) preparing a first conductive layer (210) slurry containing β-alumina, applying the slurry to the side of the separator layer (100) facing the positive electrode, and drying the slurry; (2) preparing a second conductive layer (220) slurry containing boehmite, applying it to the side of the separator layer (100) facing the negative electrode, and drying it.

9. The preparation method according to claim 8, characterized in that The preparation method further comprises the following steps: A sodium supplement layer (300) configured to release sodium ions is coated on the surface of the first conductive layer (210).

10. The preparation method according to claim 9, characterized in that The sodium supplement layer (300) is composed of 90% by mass of sodium squarate, 4% by mass of conductive carbon black, 4% by mass of polyvinylidene fluoride, and 2% by mass of polyvinyl pyrrolidone.

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