Sodium supplementing diaphragm and preparation method thereof, sodium ion battery and power utilization device

Abstract

The invention discloses a sodium supplementing diaphragm and a preparation method thereof, a sodium ion battery and a power utilization device, the sodium supplementing diaphragm comprises a main body material and a sodium supplementing agent, the main body material comprises at least one of cellulose and derivatives thereof, and cellulose nanofibers and derivatives thereof; the surface of the main body material is coated with the sodium supplementing agent; and the sodium supplementing diaphragm is of a single-layer structure. The sodium-supplementing diaphragm provided by the invention can effectively improve the cycle performance of the sodium-ion battery while realizing a sodium-supplementing effect.

Description

Technical Field

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

[0002] Sodium-ion batteries have become a hot topic in the current research field of new secondary batteries because they have similar chemical properties to lithium-ion batteries and have advantages such as abundant resources and low price. Existing sodium-ion batteries have a large irreversible capacity loss in the first cycle. When hard carbon is used as the negative electrode material, the formation of the negative electrode SEI film consumes the active sodium from the positive electrode, resulting in a very obvious irreversible capacity loss, which significantly reduces the capacity and energy density of the battery in practical applications. In order to improve the battery capacity and cycle stability, the demand for sodium supplementation is proposed. The main sodium supplementation methods reported so far are: (1) electrochemical pre-sodium method; (2) direct pre-sodium method; (3) sodium-rich compounds; (4) adding sodium supplements to the positive electrode; (5) sodium supplementation membranes. However, the electrochemical pre-sodium method, direct pre-sodium method, sodium-rich compounds and adding sodium supplements to the positive electrode have problems such as low safety, complex operation, special selectivity and damage to the positive electrode structure, making them difficult to apply on a large scale. Therefore, sodium supplementation membranes are a more ideal method. Currently, sodium-supplementing separators are typically prepared by coating the positive electrode sodium-supplementing material onto the surface of a polymer separator such as polypropylene (PP) or polyethylene (PE). However, during use, the sodium-supplementing agent decomposes and produces gas, which adversely affects the contact between the separator and the electrode, leading to a decrease in battery cycle performance. Summary of the Invention

[0003] The present invention aims to solve, at least to some extent, one of the technical problems in the related art. To this end, one object of the present invention is to provide a novel sodium-supplementing diaphragm that can effectively improve the cycle performance of sodium-ion batteries while achieving a sodium-supplementing effect.

[0004] Specifically, the first aspect of the present invention provides a sodium-supplementing membrane, comprising a main material and a sodium-supplementing agent, wherein the main material comprises at least one of cellulose and its derivatives, cellulose nanofibers and their derivatives; the sodium-supplementing agent is coated on the surface of the main material; and the sodium-supplementing membrane is a single-layer structure.

[0005] The sodium-supplementing diaphragm of the present invention is different from the traditional sodium-supplementing diaphragm. The traditional sodium-supplementing diaphragm is usually a double-layer or three-layer structure, that is, the positive electrode sodium-supplementing material is coated on the surface of a polymer diaphragm such as PP or PE. The sodium-supplementing diaphragm of the present invention is a single-layer structure, and the sodium-supplementing agent is coated on the surface of the main material. For example, when the main material is cellulose nanofiber, the sodium-supplementing agent is coated on the surface of the linear cellulose nanofiber, rather than coated on the surface of the diaphragm formed by cellulose nanofiber. The main structure of the sodium-supplementing diaphragm of the present invention is composed of main materials such as cellulose nanofibers interwoven together, so that it can play the role of isolating the positive and negative electrodes; at the same time, the sodium-supplementing agent is coated on the surface of the main material, and as the sodium-supplementing agent decomposes, Na + Compensate for the sodium loss caused by the formation of the negative electrode SEI film, and at the same time the three-dimensional structure of the diaphragm becomes loose, which improves the liquid absorption rate and wettability of the diaphragm and provides abundant ion transmission channels, thereby improving the battery's cycle performance, energy density and rate performance.

[0006] According to some specific embodiments of the present invention, based on the total weight of the sodium-supplementing membrane, the mass proportion of the sodium-supplementing agent is 5 wt% to 20 wt%, preferably 10 wt% to 18 wt%.

[0007] According to some specific embodiments of the present invention, based on the total weight of the sodium-supplementing diaphragm, the mass proportion of the main material is 80 wt% to 95 wt%, preferably 82 wt% to 90 wt%.

[0008] According to some specific embodiments of the present invention, the sodium supplement agent is coated on the surface of the main material to form a sodium supplement layer, and the thickness of the sodium supplement layer is 50nm to 500nm, preferably 100nm to 200nm.

[0009] According to some specific embodiments of the present invention, the thickness of the sodium-supplementing membrane is 4 μm to 40 μm, preferably 10 μm to 35 μm.

[0010] According to some specific embodiments of the present invention, the sodium supplement comprises Na x C y O z , x≥1, y≥0, z≥0; optionally, Na x C y O z Including one or more of Na2CO3, Na2C2O4, Na2C4O4.

[0011] According to some specific embodiments of the present invention, the sodium-supplementing membrane is formed by interweaving the main material.

[0012] The second aspect of the present invention provides a method for preparing the sodium supplementation diaphragm according to the first aspect of the present invention, comprising the following steps:

[0013] Mixing the main material, the sodium supplement and the solvent to obtain a mixed slurry;

[0014] The mixed slurry is dried to obtain the sodium-supplementing diaphragm.

[0015] The sodium-supplementing diaphragm of the present invention has simple preparation process, low cost, good reproducibility and is suitable for large-scale industrial promotion.

[0016] According to some embodiments of the present invention, the mixing includes ultrasonic mixing; the drying temperature is 70°C-100°C; the solvent includes any one of water and a mixture of water and an organic solvent; the organic solvent includes one or more of ethanol, methanol, isopropanol, and acetone.

[0017] A third aspect of the present invention provides a sodium ion battery, comprising the sodium-supplementing diaphragm of the first aspect of the present invention or the sodium-supplementing diaphragm obtained by the method of the second aspect of the present invention.

[0018] Since the sodium-supplementing diaphragm of the first aspect of the present invention is adopted, the sodium-ion battery of the present invention has all the advantages of the sodium-supplementing diaphragm, which will not be described in detail here.

[0019] A fourth aspect of the present invention provides an electrical device comprising the sodium ion battery of the third aspect of the present invention.

[0020] Since the sodium-supplementing diaphragm of the first aspect of the present invention is adopted, the electrical device of the present invention has all the advantages of the sodium-supplementing diaphragm, which will not be described in detail here.

[0021] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The structural schematic diagram of the sodium-supplementing membrane of the present invention is given, a: sodium-supplementing membrane, b: structural schematic diagram of a fiber wrapped with a sodium-supplementing agent in the sodium-supplementing membrane, c: cross-sectional schematic diagram of the fiber wrapped with a sodium-supplementing agent. DETAILED DESCRIPTION

[0023] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0024] In the description of the present invention, unless otherwise specified, "plurality" means two or more. "Multiple" means two or more. As used herein, the terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in the present invention but do not exclude other aspects.

[0025] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0026] Sodium-ion batteries have become a hot topic in the current research field of new secondary batteries because they have similar chemical properties to lithium-ion batteries and have advantages such as abundant resources and low price. Existing sodium-ion batteries have a large irreversible capacity loss in the first cycle. When hard carbon is used as the negative electrode material, the formation of the negative electrode SEI film consumes the active sodium from the positive electrode, resulting in a very obvious irreversible capacity loss, which significantly reduces the capacity and energy density of the battery in practical applications. In order to improve the battery capacity and cycle stability, the demand for sodium supplementation is proposed. The main sodium supplementation methods reported so far are: (1) electrochemical pre-sodium method; (2) direct pre-sodium method; (3) sodium-rich compounds; (4) adding sodium supplements to the positive electrode; (5) sodium supplementation membranes. However, the electrochemical pre-sodium method, direct pre-sodium method, sodium-rich compounds and adding sodium supplements to the positive electrode have problems such as low safety, complex operation, special selectivity and damage to the positive electrode structure, making them difficult to apply on a large scale. Therefore, sodium supplementation membranes are a more ideal method. Currently, sodium-supplementing separators are typically prepared by coating the positive electrode sodium-supplementing material onto the surface of a polymer separator such as polypropylene (PP) or polyethylene (PE). However, during use, the sodium-supplementing agent decomposes and produces gas, which adversely affects the contact between the separator and the electrode, leading to a decrease in battery cycle performance.

[0027] In order to solve the above problems, the present invention proposes a new type of sodium-supplementing membrane, which is different from the traditional sodium-supplementing membrane. The traditional sodium-supplementing membrane is usually a double-layer or three-layer structure, that is, the positive electrode sodium-supplementing material is coated on the surface of a polymer membrane such as PP or PE. The sodium-supplementing membrane of the present invention is a single-layer structure, and the sodium-supplementing agent is coated on the surface of the main material. For example, when the main material is cellulose nanofiber, the sodium-supplementing agent is coated on the surface of the linear cellulose nanofiber, rather than coated on the surface of the membrane formed by cellulose nanofiber. The main structure of the sodium-supplementing membrane of the present invention is composed of main materials such as cellulose nanofibers interwoven together, so that it can play the role of isolating the positive and negative electrodes; at the same time, the sodium-supplementing agent is coated on the surface of the main material, and as the sodium-supplementing agent decomposes, Na + Compensate for the sodium loss caused by the formation of the negative electrode SEI film, and at the same time the three-dimensional structure of the diaphragm becomes loose, improving the liquid absorption rate and wettability of the diaphragm and providing rich ion transmission channels, thereby improving the battery's cycle performance, energy density and rate performance.

[0028] Specifically, the first aspect of the present invention provides a sodium-supplementing membrane, comprising a main material and a sodium-supplementing agent, wherein the main material comprises at least one of cellulose and its derivatives, cellulose nanofibers and their derivatives; the sodium-supplementing agent is coated on the surface of the main material; and the sodium-supplementing membrane is a single-layer structure.

[0029] The sodium-supplementing diaphragm of the present invention is interwoven with a main material. The main material of the present invention is linear or filamentous, and these linear or filamentous main materials are interwoven with each other to form a three-dimensional network structure. The sodium-supplementing agent is coated on the surface of the linear or filamentous main material, rather than being coated on the surfaces on both sides of the three-dimensional network structure. Therefore, the sodium-supplementing diaphragm of the present invention is a single-layer structure, rather than a double-layer or multi-layer structure formed by stacking a sodium-supplementing layer and a three-dimensional network structure layer. The sodium-supplementing diaphragm of the present invention solves the problems in the prior art of damage to the positive electrode layer after the sodium-supplementing agent is added to the positive electrode and decomposes, poor contact between the diaphragm and the electrode piece after the sodium-supplementing agent is coated on the surface of the diaphragm and decomposes, and difficulty in scrapping petrochemical diaphragms (PP or PE) and glass fiber diaphragms. In addition, the preparation method of the sodium-supplementing diaphragm of the present invention is simple and efficient, does not introduce invalid components such as adhesives into the battery, and can further improve the liquid absorption rate of the diaphragm, providing new ideas for the subsequent industrialization of sodium-supplementing agents and biomass diaphragms.

[0030] In some embodiments, the main material includes at least one of cellulose nanofibers (CNF) and its derivatives. Cellulose nanofibers are a cellulose material with a nanometer-scale diameter. The cellulose molecules can be connected to each other by strong hydrogen bonds. Therefore, the three-dimensional network structure formed by the cellulose nanofibers has high strength and elasticity, which is beneficial to improving the mechanical properties of the diaphragm. The present invention does not particularly limit the types of CNF derivatives, and commonly used CNF derivatives can be used in the present invention. For example, CNF derivatives include one or more of carboxymethyl cellulose nanofibers, hydroxyalkyl cellulose nanofibers, cellulose nanofiber acetate, cellulose nanofiber fatty acid esters, sulfonated cellulose nanofibers, carboxylated cellulose nanofibers, and aldehyde-modified cellulose nanofibers.

[0031] In some embodiments, based on the total weight of the sodium-supplementing diaphragm, the mass proportion of the sodium-supplementing agent may be 5wt% to 20wt%, preferably 10wt% to 18wt%. The important role of the sodium-supplementing diaphragm of the present invention is to supplement sodium for sodium-ion batteries to make up for the sodium loss caused by the formation of SEI on the surface of the negative electrode. The amount of sodium-supplementing agent affects the sodium-supplementing effect. Too little sodium-supplementing agent will result in poor sodium-supplementing effect. Too much sodium-supplementing agent will affect the interweaving of the main material and may cause a short circuit between the positive and negative electrodes. The mass proportion of the sodium-supplementing agent is beneficial to the battery performance within the scope of the present invention. In addition, since the sodium-supplementing agent is coated on the surface of the main material, as the sodium-supplementing agent decomposes, the three-dimensional structure of the diaphragm will become loose, and the degree of looseness can be controlled by the content of the sodium-supplementing agent.

[0032] In some specific embodiments, the mass percentage of the sodium supplement may be 5 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt% or 20 wt%.

[0033] In some embodiments, the mass proportion of the host material, based on the total weight of the sodium-supplementing separator, can be 80 wt% to 95 wt%, preferably 82 wt% to 90 wt%. The primary function of the sodium-supplementing separator of the present invention is to isolate the positive and negative electrodes to prevent short circuits. If the content of the host material is too low, effective isolation of the positive and negative electrodes cannot be ensured. If the content is too high, the sodium-supplementing effect and subsequent pore size distribution will be affected. The mass proportion of the host material within the range of the present invention is beneficial to battery performance.

[0034] In some specific embodiments, the weight percentage of the main material may be 80wt%, 81wt%, 83wt%, 85wt%, 87wt%, 89wt%, 91wt%, 93wt% or 95wt%.

[0035] In the present invention, the sodium supplement agent is coated on the surface of the main material to form a sodium supplement layer. In some embodiments, the thickness of the sodium supplement layer may be 50nm to 500nm, preferably 100nm to 200nm. The thickness of the sodium supplement layer is related to the amount of the sodium supplement agent. When the amount of the sodium supplement agent is too little, the sodium supplement layer is too thin and the sodium supplement effect is not good. When the amount of the sodium supplement agent is too much, the sodium supplement layer is too thick, the interweaving and bonding of the main material is blocked, and a short circuit between the positive and negative electrodes may occur. The thickness of the sodium supplement layer is beneficial to the battery performance within the scope of the present invention.

[0036] In some embodiments, the thickness of the sodium-replenishing layer can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm.

[0037] In some embodiments, the thickness of the sodium-supplementing membrane can be 4 μm to 40 μm, preferably 10 μm to 35 μm. Optimizing the thickness of the sodium-supplementing membrane is beneficial to improving ion transfer efficiency, reducing internal resistance, and improving battery safety and cycle life.

[0038] In some specific embodiments, the sodium-supplementing membrane may have a thickness of 4 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, or 40 μm.

[0039] In some embodiments, the sodium supplement comprises Na x C y O z , x≥1, y≥0, z≥0; optionally, Na x C y O z The sodium supplement comprises one or more of Na2CO3, Na2C2O4 and Na2C4O4, thereby achieving a better sodium supplementation effect.

[0040] The second aspect of the present invention provides a method for preparing the sodium supplementation diaphragm according to the first aspect of the present invention, comprising the following steps:

[0041] Mixing the main material, the sodium supplement and the solvent to obtain a mixed slurry;

[0042] The mixed slurry is dried to obtain the sodium-supplementing diaphragm.

[0043] The sodium-supplementing diaphragm of the present invention has simple preparation process, low cost, good reproducibility and is suitable for large-scale industrial promotion.

[0044] In some embodiments, the mixing includes ultrasonic mixing, which can evenly disperse the host material in the solvent, thereby facilitating the formation of a homogeneous separator and improving the safety of the battery.

[0045] In some embodiments, the drying temperature may be 70°C-100°C, for example 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C.

[0046] In some embodiments, the solvent includes any one of water and a mixture of water and an organic solvent. The organic solvent includes one or more of ethanol, methanol, isopropanol, and acetone.

[0047] In some embodiments, mixing the host material, the sodium supplement, and the solvent comprises: dissolving the sodium supplement in a first solvent to obtain a sodium supplement solution; dispersing the host material in a second solvent to obtain a dispersed slurry; and adding the dispersed slurry to the sodium supplement solution to obtain a mixed slurry. The first solvent may be water, and the second solvent may include one or more of water, ethanol, methanol, isopropanol, and acetone. The first and second solvents may be the same or different, but the first solvent includes water.

[0048] A third aspect of the present invention provides a sodium ion battery, comprising the sodium-supplementing diaphragm of the first aspect of the present invention or the sodium-supplementing diaphragm obtained by the method of the second aspect of the present invention.

[0049] Since the sodium-supplementing diaphragm of the first aspect of the present invention is adopted, the sodium-ion battery of the present invention has all the advantages of the sodium-supplementing diaphragm, which will not be described in detail here.

[0050] The sodium ion battery includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive electrode active material. The positive electrode active material may include one or more of a layered oxide, a Prussian blue compound, and a polyanion compound. The surface density of the positive electrode sheet may be 110 g / m 2 ~130g / m 2 , for example 110g / m 2 , 115g / m 2 , 120g / m 2 , 125g / m 2 or 130g / m 2 The negative electrode plate includes a negative electrode active material. The negative electrode active material may include hard carbon.

[0051] A fourth aspect of the present invention provides an electrical device comprising the sodium ion battery of the third aspect of the present invention.

[0052] Since the sodium-supplementing diaphragm of the first aspect of the present invention is adopted, the electrical device of the present invention has all the advantages of the sodium-supplementing diaphragm, which will not be described in detail here.

[0053] Below, the scheme of the present invention will be explained in conjunction with embodiment.It will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.In the embodiment, if specific technology or conditions are not indicated, the technology or conditions described in the literature in this area or the product instructions are used.The reagents or instruments used are not indicated by the manufacturer, and are all conventional products that can be obtained by commercial purchase.

[0054] Example 1

[0055] (1) Na2C2O4 is used as the sodium supplement agent, and its mass fraction is 5wt% based on the total weight of the sodium supplement membrane. CNF is selected as the main material of the membrane, and its mass fraction is 95wt% based on the total weight of the sodium supplement membrane. After dissolving Na2C2O4 in water, a slurry of well-dispersed CNF in water is immediately added. After ultrasonic treatment for 1 hour, the obtained slurry is immediately placed in a watch glass and vacuum-dried at a temperature of 80°C to finally obtain a sodium supplement membrane with a thickness of 20μm. By measuring the thickness of the sodium supplement layer in the cross-sectional SEM image of the sodium supplement membrane, it can be found that the thickness of the Na2C2O4 coating layer is about 50nm. The structural schematic diagram of the sodium supplement membrane is shown in the figure. Figure 1 As shown in (a), Figure 1 (b) shows the schematic diagram of the structure of a fiber wrapped with sodium supplement in the sodium supplement membrane. Figure 1 (c) shows a schematic cross-sectional view of the fiber coated with the sodium supplement.

[0056] (2) The polyanion composite sodium iron phosphate material NFPP, PVDF and carbon black were mixed in a ratio of 8:1:1, added to the solvent NMP to prepare a slurry, and finally coated on the surface of aluminum foil and vacuum dried at a temperature of 80°C to finally obtain the NFPP positive electrode.

[0057] (3) Hard carbon, sodium carboxymethyl cellulose (CMC) and carbon black were mixed in a ratio of 4:0.08:0.12, added to solvent water for slurry preparation, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to finally obtain a hard carbon negative electrode.

[0058] (4) The sodium-supplemented separator, NFPP cathode, and hard carbon anode prepared in the above steps were assembled and then injected with electrolyte to obtain a finished button cell. The electrolyte solvent was a 1:1 volume ratio ethylene carbonate-propylene carbonate (EC-PC) mixture, and the solute was 1 mol / L sodium hexafluorophosphate.

[0059] Example 2

[0060] (1) Na2C2O4 was used as the sodium supplement agent, with a mass fraction of 10 wt% based on the total weight of the sodium supplement membrane. CNF was selected as the main material of the membrane, with a mass fraction of 90 wt% based on the total weight of the sodium supplement membrane. After dissolving Na2C2O4 in water, a slurry of well-dispersed CNF in water was added. After ultrasonic treatment for 1 hour, the resulting slurry was immediately placed in a watch glass and vacuum-dried at 80°C to obtain a sodium supplement membrane with a thickness of 20 μm. The thickness of the sodium supplement layer in the cross-sectional SEM image of the sodium supplement membrane was measured, and it was found that the thickness of the Na2C2O4 coating layer was about 100 nm.

[0061] (2) NFPP, PVDF, and carbon black were mixed in a ratio of 8:1:1, added to the solvent NMP to prepare a slurry, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to finally obtain the NFPP positive electrode.

[0062] (3) Hard carbon, CMC, and carbon black were mixed in a ratio of 4:0.08:0.12, added to solvent water for slurry preparation, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to obtain a hard carbon negative electrode.

[0063] (4) The sodium-supplemented separator, NFPP cathode, and hard carbon anode prepared in the above steps were assembled and then injected with electrolyte to obtain a finished button cell. The electrolyte solvent was a 1:1 volume ratio ethylene carbonate-propylene carbonate (EC-PC) mixture, and the solute was 1 mol / L sodium hexafluorophosphate.

[0064] Example 3

[0065] (1) Na2C2O4 was used as the sodium supplement agent, with a mass fraction of 18 wt% based on the total weight of the sodium supplement membrane. CNF was selected as the main material of the membrane, with a mass fraction of 82 wt% based on the total weight of the sodium supplement membrane. After dissolving Na2C2O4 in water, a slurry of well-dispersed CNF in water was added. After ultrasonic treatment for 1 hour, the resulting slurry was immediately placed in a watch glass and vacuum-dried at 80°C to obtain a sodium supplement membrane with a thickness of 20 μm. The thickness of the sodium supplement layer in the cross-sectional SEM image of the sodium supplement membrane was measured, and it was found that the thickness of the Na2C2O4 coating layer was about 200 nm.

[0066] (2) NFPP, PVDF, and carbon black were mixed in a ratio of 8:1:1, added to the solvent NMP to prepare a slurry, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to finally obtain the NFPP positive electrode.

[0067] (3) Hard carbon, CMC, and carbon black were mixed in a ratio of 4:0.08:0.12, added to solvent water for slurry preparation, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to obtain a hard carbon negative electrode.

[0068] (4) The sodium-supplemented separator, NFPP cathode, and hard carbon anode prepared in the above steps were assembled and then injected with electrolyte to obtain a finished button cell. The electrolyte solvent was a 1:1 volume ratio ethylene carbonate-propylene carbonate (EC-PC) mixture, and the solute was 1 mol / L sodium hexafluorophosphate.

[0069] Example 4

[0070] (1) Na2C4O4 was used as the sodium supplement agent, with a mass fraction of 18 wt% based on the total weight of the sodium supplement membrane. CNF was selected as the main material of the membrane, with a mass fraction of 82 wt% based on the total weight of the sodium supplement membrane. After dissolving Na2C4O4 in water, a slurry of well-dispersed CNF in water was added. After ultrasonic treatment for 1 hour, the resulting slurry was immediately placed in a watch glass and vacuum-dried at 80°C to obtain a sodium supplement membrane with a thickness of 20 μm. The thickness of the sodium supplement layer in the cross-sectional SEM image of the sodium supplement membrane was measured, and it was found that the thickness of the Na2C4O4 coating layer was about 200 nm.

[0071] (2) NFPP, PVDF, and carbon black were mixed in a ratio of 8:1:1, added to the solvent NMP to prepare a slurry, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to finally obtain the NFPP positive electrode.

[0072] (3) Hard carbon, CMC, and carbon black were mixed in a ratio of 4:0.08:0.12, added to solvent water for slurry preparation, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to obtain a hard carbon negative electrode.

[0073] (4) The sodium-supplemented separator, NFPP cathode, and hard carbon anode prepared in the above steps were assembled and then injected with electrolyte to obtain a finished button cell. The electrolyte solvent was a 1:1 volume ratio ethylene carbonate-propylene carbonate (EC-PC) mixture, and the solute was 1 mol / L sodium hexafluorophosphate.

[0074] Example 5

[0075] (1) Na2C2O4 was used as the sodium supplement agent, with a mass fraction of 20 wt% based on the total weight of the sodium supplement membrane. CNF was selected as the main material of the membrane, with a mass fraction of 80 wt% based on the total weight of the sodium supplement membrane. After dissolving Na2C2O4 in water, a slurry of well-dispersed CNF in water was added. After ultrasonic treatment for 1 hour, the resulting slurry was immediately placed in a watch glass and vacuum-dried at 80°C to obtain a sodium supplement membrane with a thickness of 20 μm. The thickness of the sodium supplement layer in the cross-sectional SEM image of the sodium supplement membrane was measured, and it was found that the thickness of the Na2C2O4 coating layer was about 50 nm.

[0076] (2) NFPP, PVDF, and carbon black were mixed in a ratio of 8:1:1, added to the solvent NMP to prepare a slurry, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to finally obtain the NFPP positive electrode.

[0077] (3) Hard carbon, CMC, and carbon black were mixed in a ratio of 4:0.08:0.12, added to solvent water for slurry preparation, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to obtain a hard carbon negative electrode.

[0078] (4) The sodium-supplemented separator, NFPP cathode, and hard carbon anode prepared in the above steps were assembled and then injected with electrolyte to obtain a finished button cell. The electrolyte solvent was a 1:1 volume ratio ethylene carbonate-propylene carbonate (EC-PC) mixture, and the solute was 1 mol / L sodium hexafluorophosphate.

[0079] Example 6

[0080] (1) Na2C2O4 was used as the sodium supplement agent, with a mass fraction of 30 wt% based on the total weight of the sodium supplement membrane. CNF was selected as the main material of the membrane, with a mass fraction of 70 wt% based on the total weight of the sodium supplement membrane. After dissolving Na2C2O4 in water, a slurry of well-dispersed CNF in water was added. After ultrasonic treatment for 1 hour, the resulting slurry was immediately placed in a watch glass and vacuum-dried at 80°C to obtain a sodium supplement membrane with a thickness of 20 μm. The thickness of the sodium supplement layer in the cross-sectional SEM image of the sodium supplement membrane was measured, and it was found that the thickness of the Na2C2O4 coating layer was about 500 nm.

[0081] (2) NFPP, polyvinylidene fluoride (PVDF) and carbon black were mixed in a ratio of 8:1:1, added to the solvent N-methylpyrrolidone (NMP) to prepare a slurry, and finally coated on the surface of aluminum foil and vacuum dried at a temperature of 80°C to finally obtain the NFPP positive electrode.

[0082] (3) Hard carbon, CMC, and carbon black were mixed in a ratio of 4:0.08:0.12, added to solvent water for slurry preparation, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to obtain a hard carbon negative electrode.

[0083] (4) The sodium-supplemented separator, NFPP cathode, and hard carbon anode prepared in the above steps were assembled and then injected with electrolyte to obtain a finished button cell. The electrolyte solvent was a 1:1 volume ratio ethylene carbonate-propylene carbonate (EC-PC) mixture, and the solute was 1 mol / L sodium hexafluorophosphate.

[0084] Example 7

[0085] (1) Na2C2O4 was used as the sodium supplement agent, with a mass fraction of 3 wt% based on the total weight of the sodium supplement membrane. CNF was selected as the main material of the membrane, with a mass fraction of 97 wt% based on the total weight of the sodium supplement membrane. After dissolving Na2C2O4 in water, a slurry of well-dispersed CNF in water was added. After ultrasonic treatment for 1 hour, the resulting slurry was immediately placed in a watch glass and vacuum-dried at 80°C to obtain a sodium supplement membrane with a thickness of 20 μm. By measuring the thickness of the sodium supplement layer in the cross-sectional SEM image of the sodium supplement membrane, it was found that the thickness of the Na2C2O4 coating layer was about 50 nm.

[0086] (2) NFPP, PVDF, and carbon black were mixed in a ratio of 8:1:1, added to the solvent NMP to prepare a slurry, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to finally obtain the NFPP positive electrode.

[0087] (3) Hard carbon, CMC, and carbon black were mixed in a ratio of 4:0.08:0.12, added to solvent water for slurry preparation, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to obtain a hard carbon negative electrode.

[0088] (4) The sodium-supplemented separator, NFPP cathode, and hard carbon anode prepared in the above steps were assembled and then injected with electrolyte to obtain a finished button cell. The electrolyte solvent was a 1:1 volume ratio ethylene carbonate-propylene carbonate (EC-PC) mixture, and the solute was 1 mol / L sodium hexafluorophosphate.

[0089] Comparative Example 1

[0090] (1) CNF was selected as the membrane material. CNF was dispersed in water and ultrasonically treated for 1 h. The resulting slurry was immediately placed in a watch glass and vacuum-dried at 80°C to obtain a sodium-supplementing membrane with a thickness of 20 μm.

[0091] (2) NFPP, PVDF, and carbon black were mixed in a ratio of 8:1:1, added to the solvent NMP to prepare a slurry, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to finally obtain the NFPP positive electrode.

[0092] (3) Hard carbon, CMC, and carbon black were mixed in a ratio of 4:0.08:0.12, added to solvent water for slurry preparation, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to obtain a hard carbon negative electrode.

[0093] (4) The sodium-supplemented separator, NFPP cathode, and hard carbon anode prepared in the above steps were assembled and then injected with electrolyte to obtain a finished button cell. The electrolyte solvent was a 1:1 volume ratio ethylene carbonate-propylene carbonate (EC-PC) mixture, and the solute was 1 mol / L sodium hexafluorophosphate.

[0094] Comparative Example 2

[0095] (1) NFPP, PVDF, and carbon black were mixed in a ratio of 8:1:1, added to the solvent NMP to prepare a slurry, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to obtain the NFPP positive electrode.

[0096] (2) Hard carbon, CMC, and carbon black were mixed in a ratio of 4:0.08:0.12, added to solvent water for slurry preparation, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to obtain a hard carbon negative electrode.

[0097] (3) The NFPP cathode, hard carbon anode, and 20 μm thick polyethylene separator prepared in the above steps were directly assembled and then injected with electrolyte to obtain a finished button cell. The electrolyte solvent was a 1:1 volume ratio ethylene carbonate-propylene carbonate (EC-PC) mixture, and the solute was 1 mol / L sodium hexafluorophosphate.

[0098] Comparative Example 3

[0099] (1) Na2C2O4 and polyvinylidene fluoride (PVDF) were added to NMP solution in a ratio of 9:1 and mixed. After mixing evenly, they were coated on the surface of polyethylene membrane. The mass fraction of sodium supplement agent was 5% and the mass fraction of polyethylene was 95%. Finally, a sodium supplement membrane with a thickness of 20 μm was obtained, and the thickness of the sodium supplement coating was 1 μm.

[0100] (2) NFPP, polyvinylidene fluoride (PVDF) and carbon black were mixed in a ratio of 8:1:1, added to the solvent N-methylpyrrolidone (NMP) to prepare a slurry, and finally coated on the surface of aluminum foil and vacuum dried at a temperature of 80°C to finally obtain the NFPP positive electrode.

[0101] (3) Hard carbon, CMC, and carbon black were mixed in a ratio of 4:0.08:0.12, added to solvent water for slurry preparation, and finally coated on the surface of aluminum foil and vacuum dried at 80°C to obtain a hard carbon negative electrode.

[0102] (4) The sodium-supplemented separator, NFPP cathode, and hard carbon anode prepared in the above steps were assembled and then injected with electrolyte to obtain a finished button cell. The electrolyte solvent was a 1:1 volume ratio ethylene carbonate-propylene carbonate (EC-PC) mixture, and the solute was 1 mol / L sodium hexafluorophosphate.

[0103] Test Method

[0104] 1. Sodium supplement layer thickness test

[0105] The cross-sectional images of the sodium-supplementing membranes prepared in the above examples and comparative examples were taken using a SEM electron microscope, and then the thickness of the sodium-supplementing agent coated on the CNF was measured.

[0106] 2. Diaphragm liquid absorption rate test

[0107] Liquid absorption was tested with reference to QB / T2303.11-2008 "Paper for Battery Use - Part 11: Determination of Liquid Absorption." The results are shown in Table 1.

[0108] 3. Battery decomposition performance test

[0109] The charge-discharge specific capacity test used in this experiment was performed on a charge-discharge tester. The battery was set to the charging state (de-sodiumizing the working electrode) with a charge current density of 0.1C. Charging was stopped at a cutoff voltage of 4.5V, and the initial charge specific capacity was calculated. The discharge current density was 0.1C, and discharge was terminated at a cutoff voltage of 2.0V. The initial discharge specific capacity was then calculated.

[0110] First charge specific capacity (mAh / g) = first charge capacity / mass of positive electrode active material

[0111] First discharge specific capacity (mAh / g) = first discharge capacity / mass of positive electrode active material

[0112] The results are shown in Table 1.

[0113] Table 1

[0114]

[0115] The test results show that the batteries of Examples 1-7 have significantly improved sodium replenishment effects compared to the batteries of Comparative Examples 1-3. The sodium replenishment separator of the present invention can meet the basic function of isolating the positive and negative electrodes and has better actual effects than polyolefin separators, while also having a significant sodium replenishment effect.

[0116] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0117] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A sodium supplement membrane, characterized in that: The invention comprises a main material and a sodium supplement, wherein the main material comprises at least one of cellulose and its derivatives, cellulose nanofibers and their derivatives; the sodium supplement is coated on the surface of the main material; and the sodium supplement membrane is a single-layer structure.

2. The sodium supplement membrane according to claim 1, characterized in that Based on the total weight of the sodium-supplementing membrane, the mass proportion of the sodium-supplementing agent is 5 wt% to 20 wt%, preferably 10 wt% to 18 wt%.

3. The sodium supplement membrane according to claim 1, characterized in that Based on the total weight of the sodium-supplementing diaphragm, the mass proportion of the main material is 80wt% to 95wt%, preferably 82wt% to 90wt%.

4. The sodium supplement membrane according to claim 1, characterized in that The sodium supplement agent is coated on the surface of the main material to form a sodium supplement layer. The thickness of the sodium supplement layer is 50nm to 500nm, preferably 100nm to 200nm.

5. The sodium supplement membrane according to claim 1, characterized in that The thickness of the sodium supplementing membrane is 4 μm to 40 μm, preferably 10 μm to 35 μm.

6. The sodium supplement membrane according to claim 1, characterized in that The sodium supplement includes Na x C y O z , x≥1, y≥0, z≥0; optionally, Na x C y O z Including one or more of Na2CO3, Na2C2O4, Na2C4O4.

7. The sodium supplement membrane according to claim 1, characterized in that The sodium supplement diaphragm is formed by interweaving the main body material.

8. A method for preparing the sodium supplementation membrane according to any one of claims 1 to 7, characterized in that: The following steps are involved: Mixing the main material, the sodium supplement and the solvent to obtain a mixed slurry; The mixed slurry is dried to obtain the sodium-supplementing diaphragm.

9. The method according to claim 8, characterized in that The mixing includes ultrasonic mixing; The drying temperature is 70℃-100℃; The solvent includes any one of water and a mixture of water and an organic solvent; the organic solvent includes one or more of ethanol, methanol, isopropanol and acetone.

10. A sodium ion battery, characterized in that: The invention comprises the sodium-supplementing diaphragm according to any one of claims 1 to 7 or the sodium-supplementing diaphragm obtained by the method according to claim 8 or 9.

11. An electrical device, characterized in that: Including the sodium ion battery according to claim 10.

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