Sodium supplementing agent, sodium ion battery positive electrode diaphragm and sodium ion battery

Abstract

The invention discloses a sodium supplementing agent, a sodium ion battery positive electrode diaphragm and a sodium ion battery, and provides application of alpha-keto acid sodium salt as the sodium supplementing agent, the alpha-keto acid sodium salt as the sodium supplementing agent is applied to the sodium ion battery, and the sodium supplementing agent comprises the alpha-keto acid sodium salt, a conductive auxiliary agent and a solvent, the alpha-keto acid sodium salt is a salt compound formed by alpha-keto acid and sodium ions, the number of main carbon chain atoms of the alpha-keto acid sodium salt is smaller than or equal to 5, the content of the alpha-keto acid sodium salt is larger than 0, the content of the conductive additive is larger than or equal to 0, and the content of the solvent is larger than or equal to 0. The sodium supplementing agent has the advantages that the specific capacity is high, the cost is low, the decomposition voltage is low, the decomposition byproduct is mainly gas, sodium can be stably supplemented, and the application requirement of the sodium ion battery is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and particularly relates to a sodium supplement agent, a positive electrode film of a sodium ion battery, and a sodium ion battery. Background Art

[0002] A sodium ion battery is a secondary battery that realizes charge and discharge based on the migration of sodium ions between the positive and negative electrodes, and its working principle is similar to that of a lithium ion battery. During the charge and discharge process of a sodium ion battery, due to the formation of the negative electrode SEI, the existence of material surface defects, and the occurrence of side reactions, active sodium will be consumed, which directly affects the energy density and cycle performance of the sodium ion battery.

[0003] Sodium supplement technology (pre-sodiation) can solve the problem of active sodium consumption. At present, the positive electrode sodium supplement process in sodium supplement technology has attracted much attention due to its advantages such as simple operation, direct adaptation to existing processes, and no residual pollution. The positive electrode sodium supplement process refers to adding a sodium supplement agent to the positive electrode material, and during the charging process, the sodium supplement agent will oxidize and decompose to release active sodium ions to achieve sodium supplementation.

[0004] For the positive electrode sodium supplement process, the selection of the sodium supplement agent is a key link. Currently, it is generally considered that the selection of the sodium supplement agent needs to follow four principles: (1) having a suitable decomposition potential and de-sodiation within the battery working window; (2) having a high sodium supplement capacity to reduce the negative impact of exogenous inactive substances on the energy density of the positive electrode material; (3) the sodium supplement agent itself and the oxidation product have stable properties and do not affect the battery performance; (4) adapting to the existing process and being able to be well compatible with common electrolyte, binder, solvent and other components. Currently applicable positive electrode sodium supplement agents can meet the above (2)-(4) principles, but there are few compounds that meet principle (1). For example, the decomposition voltages of common existing sodium supplement agents such as sodium oxalate, sodium formate, and sodium acetate are generally higher than 4.2V (vs Na+ / Na), which does not match the working window of sodium ion batteries and is difficult to apply. Currently, the only publicly reported organic sodium supplement agents with a decomposition voltage lower than 4.0V are sodium squarate, N-methyliminodiacetic acid disodium salt, sodium hydroxybenzoate, and sodium aminobenzoate. Among them, the first two sodium supplement agents have high costs, and the latter two sodium supplement agents have specific capacity and product residues and cannot meet the application requirements of sodium ion batteries.

[0005] Currently, the research direction for sodium supplement agents is mainly to reduce the decomposition voltage. A large amount of scientific research work is dedicated to developing catalysts to reduce the decomposition voltage of common sodium supplement agents, but it is inevitable to introduce other side reactions. Therefore, it is very necessary to develop a new type of sodium supplement agent with a low decomposition voltage. Summary of the Invention

[0006] To solve the above technical problems, the object of the present invention is to provide a sodium supplement agent, a positive electrode diaphragm for a sodium-ion battery, and a sodium-ion battery. The sodium supplement agent of the present invention has the advantages of high specific capacity, low cost, low decomposition voltage, and mainly gaseous decomposition by-products, can stably supplement sodium, and meet the application requirements of sodium-ion batteries.

[0007] To achieve the above object of the invention, the technical solutions adopted by the present invention are as follows:

[0008] In the first aspect of the present invention, the present invention proposes the application of α-ketosodium salt as a sodium supplement agent, and the α-ketosodium salt is applied as a sodium supplement agent to a sodium-ion battery.

[0009] In the second aspect of the present invention, the present invention proposes a sodium supplement agent, which includes α-ketosodium salt, a conductive additive, and a solvent. Among them, the α-ketosodium salt is a salt compound formed by an α-keto acid with a main carbon chain atom number ≤ 5 and sodium ions. The content of the α-ketosodium salt > 0, the content of the conductive additive ≥ 0, and the content of the solvent ≥ 0.

[0010] Preferably, the α-ketosodium salt includes one or more of sodium pyruvate, sodium α-ketoglutarate, sodium α-ketoisovalerate, and sodium α-ketobutyrate. More preferably, the α-ketosodium salt includes sodium pyruvate.

[0011] Preferably, the conductive additive includes conductive carbon;

[0012] The conductive carbon includes one or more of carbon black, Ketjen black, carbon nanotubes, activated carbon, and graphene.

[0013] Preferably, the mass ratio of the α-ketosodium salt to the conductive additive ≥ 4;

[0014] More preferably, the mass ratio of the α-ketosodium salt to the conductive additive is 4 - 99;

[0015] More preferably, the mass ratio of the α-ketosodium salt to the conductive additive is 9 - 19.

[0016] Preferably, when the content of the conductive additive > 0 and the content of the solvent is 0, the sodium supplement agent includes the α-ketosodium salt and the conductive additive, and the α-ketosodium salt and the conductive additive form a composite material. The preparation method is as follows:

[0017] Add the conductive additive to an aqueous solution of a dispersant, then add the α-ketosodium salt, and after uniform dispersion, obtain a mixed solution. After drying the mixed solution, a composite material containing the α-ketosodium salt is prepared, where the dispersant is a surfactant.

[0018] Preferably, when the content of the conductive additive > 0 and the content of the solvent > 0, the sodium supplement agent includes the α-ketosodium salt, the conductive additive, and the solvent. The α-ketosodium salt and the conductive additive form a composite material and exist in the solvent. The preparation method is as follows:

[0019] Add a conductive additive to a solvent containing a dispersant, and then add a sodium α-ketone salt. A sodium supplement agent slurry is obtained through grinding treatment or ultrasonic fragmentation and dispersion treatment.

[0020] Preferably, when the content of the conductive additive is 0 and the content of the solvent > 0, the sodium supplement agent includes a sodium α-ketone salt and a solvent, and the sodium supplement agent is in a solution state or a slurry state;

[0021] When the content of the conductive additive is 0 and the content of the solvent is 0, the sodium supplement agent includes a sodium α-ketone salt.

[0022] In the third aspect of the present invention, the present invention provides a positive electrode membrane sheet for a sodium-ion battery, which includes a sodium supplement agent, and further includes a positive electrode material, a binder, and a conductive agent. The sodium supplement agent, the positive electrode material, the binder, and the conductive agent are uniformly dispersed in a solvent of the positive electrode slurry of the battery to form a positive electrode slurry. The positive electrode slurry is coated on a current collector to form a positive electrode membrane sheet, wherein, based on the mass of the positive electrode membrane sheet, the mass percentage of the sodium supplement agent ≤ 10%, and more preferably, based on the mass of the positive electrode membrane sheet, the mass percentage of the sodium supplement agent ≤ 5%.

[0023] In the fourth aspect of the present invention, the present invention provides a sodium-ion battery, which includes a positive electrode membrane sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the positive electrode membrane sheet is the positive electrode membrane sheet added with the above-mentioned sodium supplement agent.

[0024] Beneficial effects:

[0025] The present invention uses a sodium α-ketone salt as a sodium supplement agent, and its addition amount is small. Taking sodium pyruvate as an example, the decomposition voltage of sodium pyruvate is closer to the working voltage of a sodium-ion battery compared with existing sodium supplement agents, and it is easier to decompose at the working voltage to release active sodium ions. Moreover, the main by-product of the decomposition of the sodium α-ketone salt is carbon dioxide, and the carbon dioxide gas escapes from the positive electrode material system during the battery formation process, which does not affect the battery performance, can stably supplement sodium, and meets the application requirements of sodium-ion batteries. Description of the drawings

[0026] Figure 1 Shown is the XRD pattern of the sodium supplement agent prepared in Example 1 of the sodium supplement agent;

[0027] Figure 2 Shown is the relationship diagram between voltage and specific capacity of Example 1 of the sodium supplement agent;

[0028] Figure 3 Shown is the relationship diagram between voltage and specific capacity of Example 2 of the sodium supplement agent;

[0029] Figure 4 Shown is the relationship diagram between voltage and specific capacity of Example 3 of the sodium supplement agent;

[0030] Figure 5The figure shows the relationship between voltage and specific capacity of Example 4 of the sodium supplement agent;

[0031] Figure 6 The figure shows the charge-discharge test data graph of Example 1 of the battery application;

[0032] Figure 7 The figure shows the charge-discharge test data graph of Example 2 of the battery application;

[0033] Figure 8 The figure shows the charge-discharge test data graph of Comparative Example 1 of the battery application. Detailed implementation manners

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation manners of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings, and other implementation manners can be obtained.

[0035] The present invention proposes the application of α-ketone sodium salt as a sodium supplement agent. The α-ketone sodium salt is applied to a sodium ion battery as a sodium supplement agent. The α-ketone sodium salt of the present invention refers to a salt compound formed by α-keto acid (α-keto acid is an organic acid in which the α-position carbon atom in the carboxylic acid is replaced by a ketone group) and sodium ions, and its chemical general formula can be expressed as R-CO-COONa (R is an organic group). The present invention innovatively uses α-ketone sodium salt in the sodium supplement agent by utilizing the characteristics of high sodium capacity of α-ketone sodium salt and mainly gaseous electrolysis by-products.

[0036] To ensure the specific capacity of the sodium supplement agent and reduce the production amount of by-products, the α-ketone sodium salt of the present invention is preferably an α-ketone sodium salt with the number of main chain carbon atoms ≤ 5, such as sodium pyruvate (i.e., sodium pyruvate), sodium α-ketoglutarate (i.e., disodium α-ketoglutarate), sodium α-ketoisovalerate, sodium α-ketobutyrate, and so on. When the α-ketone sodium salt with the number of main chain carbon atoms ≤ 5 is electrolyzed, in addition to active sodium ions, mainly gases are produced and separated from the positive electrode material system during the battery formation process. More preferably, the α-ketone sodium salt of the present invention includes sodium pyruvate. Taking sodium pyruvate as an example, the theoretical specific capacity of sodium pyruvate is 243 mAh / g, and it has excellent sodium supplement effect with less addition amount. The decomposition voltage of sodium pyruvate is close to 3.8 V. Compared with the existing sodium supplement agents, sodium pyruvate is closer to the working voltage of the sodium ion battery, that is, sodium pyruvate is more likely to decompose and release active sodium ions at the working voltage. Moreover, the main by-product of the decomposition of sodium pyruvate is carbon dioxide, and the content of the remaining by-products is small and stable. The carbon dioxide gas separates from the positive electrode material system during the battery formation and does not affect the battery performance. The present invention uses the α-ketone sodium salt with the number of main chain carbon atoms ≤ 5 as the sodium supplement agent, which can meet the four principles of the sodium supplement agent.

[0037] In the present invention, the sodium supplement agent specifically includes α-ketone sodium salt, a conductive aid, and a solvent. Among them, the content of α-ketone sodium salt > 0, the content of the conductive aid ≥ 0, and the solvent ≥ 0. Both the conductive aid and the solvent remain stable during the sodium supplementation process, without decomposition and without reacting with other components of the positive electrode of the sodium-ion battery.

[0038] Based on the contents of the conductive aid and the solvent, the sodium supplement agent specifically includes four cases.

[0039] (Ⅰ) When the contents of both the conductive aid and the solvent are 0, the sodium supplement agent is α-ketone sodium salt. It is easy to understand that α-ketone sodium salt is the component in the sodium supplement agent that plays the role of sodium supplementation. When the sodium supplement agent contains only α-ketone sodium salt, the sodium supplement agent can also play a role in sodium supplementation. Adding α-ketone sodium salt directly to the positive electrode of the sodium-ion battery releases active sodium ions during formation, achieving sodium supplementation.

[0040] (Ⅱ) When the content of the conductive aid > 0 and the content of the solvent is 0, the sodium supplement agent includes α-ketone sodium salt and a conductive aid, and α-ketone sodium salt and the conductive aid form a composite material. The sodium supplementation effect of the sodium supplement agent is related to its decomposition degree. The more thoroughly α-ketone sodium salt decomposes, the better the sodium supplementation effect. For example, when α-ketone sodium salt is sodium pyruvate, sodium pyruvate and the conductive aid form a composite material.

[0041] In the present invention, the conductive aid is a conductive material with stable chemical properties, which can be a single substance, a compound, or a mixture. Preferably, the conductive aid includes conductive carbon, and it can also be other materials that can conduct electricity. When α-ketone sodium salt combines with the conductive aid, when the particle size of the conductive aid is small, with α-ketone sodium salt as the core, the conductive aid forms a shell; when the particle size of the conductive aid is large, with the conductive aid as the core, α-ketone sodium salt adheres to the surface of the conductive aid.

[0042] Taking the conductive aid as conductive carbon as an example, existing carbon single substances that can play a conductive role are all applicable to the present invention, such as one or more of carbon black, Ketjen black, carbon nanotubes, activated carbon, and graphene. Based on the sodium supplement agent being added to the positive electrode for use, the type of conductive carbon is preferably the same as the type of conductive agent of the sodium-ion positive electrode material.

[0043] The preparation method of the composite material containing α-ketone sodium salt is: adding the conductive aid to an aqueous solution of a dispersant, the concentration of the dispersant can be 0.2 - 2%, which is not specifically limited in the present invention, and then adding α-ketone sodium salt. After uniform dispersion, a mixed solution is obtained, and the mixed solution is dried to obtain the composite material containing α-ketone sodium salt.

[0044] The dispersant is a conventional existing surfactant, such as polyvinylpyrrolidone.

[0045] (Ⅲ) When the content of the conductive additive is 0 and the content of the solvent > 0, the sodium supplement agent contains α-ketone sodium salt and the solvent. The function of the solvent is to make the sodium supplement agent in a solution or slurry state.

[0046] Adding the sodium supplement agent to the positive electrode of the battery is actually that the sodium supplement agent is uniformly mixed with the positive electrode material, binder, and conductive agent in the solvent of the positive electrode slurry of the battery to form a slurry. Therefore, when the sodium supplement agent formed by mixing α-ketone sodium salt and the solvent is added and used, the amount of the solvent of the positive electrode slurry of the battery can be reduced, and even the use of the solvent of the positive electrode slurry of the battery can be omitted. It is easy to understand that the solvent of the sodium supplement agent is the same as the solvent of the positive electrode slurry of the battery. The commonly used solvent for the positive electrode slurry of the battery is N-methylpyrrolidone. Preferably, the solvent of the sodium supplement agent is N-methylpyrrolidone.

[0047] It is easy to understand that when the α-ketone sodium salt is soluble in the solvent, the α-ketone sodium salt and the solvent form a sodium supplement agent solution, and when the α-ketone sodium salt is insoluble in the solvent, the α-ketone sodium salt and the solvent form a sodium supplement agent slurry.

[0048] (Ⅳ) When the contents of both the conductive additive and the solvent are > 0, the sodium supplement agent contains α-ketone sodium, conductive additive, and solvent. Similar to the composite material in case (Ⅱ), the α-ketone sodium salt and the conductive additive form a composite material and exist in the solvent. The preparation method is: adding the conductive additive into the solvent containing a dispersant, and then adding the α-ketone sodium salt, and obtaining the sodium supplement agent slurry through grinding treatment or ultrasonic fragmentation and dispersion treatment.

[0049] In (Ⅰ), (Ⅱ), (Ⅲ), and (Ⅳ), the component with sodium supplement effect in the sodium supplement agent is the α-ketone sodium salt. The sodium supplement agents in (Ⅰ) and (Ⅱ) are in powder state, the sodium supplement agent in (Ⅲ) is in solution or slurry state, and the sodium supplement agent in (Ⅳ) is in slurry state.

[0050] Since the conductive additive in the sodium supplement agent has no sodium supplement effect, the higher the content of the conductive additive in the sodium supplement agent per unit mass, the worse its sodium supplement effect. Preferably, in the sodium supplement agent, the mass ratio of the α-ketone sodium salt to the conductive additive ≥ 4. It is easy to understand that when the mass of the α-ketone sodium salt far exceeds the mass of the conductive additive, it is similar to the case of pure α-ketone sodium salt. The amount of the conductive additive cannot be too much, otherwise the sodium capacity of the sodium supplement agent will decrease significantly, affecting the sodium supplement effect.

[0051] Further, in the positive electrode of a sodium-ion battery, in addition to the sodium supplement agent and the positive electrode material, it also contains a conductive agent (such as carbon black) and a binder. When the conductive auxiliary agent in the sodium supplement agent is conductive carbon and the content of the conductive auxiliary agent > 0, the application method of the sodium supplement agent varies according to the content of the conductive carbon. When the content of conductive carbon in the composite material is relatively high, the conductive carbon in the sodium supplement agent can be regarded as part or all of the conductive agent in the positive electrode in addition to improving the decomposition efficiency of sodium α-ketocarboxylate. When the content of conductive carbon in the composite material is relatively low, the conductive carbon in the sodium supplement agent is not regarded as the conductive agent of the positive electrode material, but only as an auxiliary agent to improve the decomposition efficiency of sodium α-ketocarboxylate.

[0052] Preferably, the mass ratio of sodium α-ketocarboxylate to the conductive auxiliary agent is 4 to 99, and more preferably, the mass ratio of sodium α-ketocarboxylate to the conductive auxiliary agent is 9 to 19.

[0053] Based on the above sodium supplement agent, the present invention also provides a positive electrode film for a sodium-ion battery, which includes the sodium supplement agent, and also includes a positive electrode material, a binder, and a conductive agent. The sodium supplement agent, the positive electrode material, the binder, and the conductive agent are uniformly dispersed in the solvent of the positive electrode slurry of the battery to form a positive electrode slurry, and the positive electrode slurry is coated on the current collector to form a positive electrode film.

[0054] Compared with the positive electrode material, the density of the sodium supplement agent of the present invention is relatively small. The addition of a large amount of sodium supplement agent affects the compaction density of the positive electrode film, and further affects the energy density of the battery. Therefore, the addition amount of the sodium supplement agent should not be too much. Based on the mass of the positive electrode film, the mass percentage of the sodium supplement agent ≤ 10%, and preferably, the mass percentage of the sodium supplement agent ≤ 5%.

[0055] The positive electrode material includes any one or more of sodium composite phosphate, sodium vanadium phosphate, layered oxide, Prussian white, and sodium iron sulfate. The layered oxide includes one or more of Na 0.44 MnO2, Na 2 / 3 Fe 1 / 2 Mn 1 / 2 O2, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0056] Based on the above positive electrode film for a sodium-ion battery, the present invention also provides a sodium-ion battery, which includes the above positive electrode film, and also includes a negative electrode sheet, an electrolyte, and a separator. The positive electrode film, the negative electrode sheet, the electrolyte, and the separator constitute a sodium-ion battery.

[0057] The technical solution of the present invention will be described in detail below with specific examples.

[0058] Sodium supplement agent Example 1

[0059] The sodium supplement in this example is a composite material of sodium pyruvate and carbon black, and the mass ratio of sodium pyruvate to carbon black is 9 (i.e., the mass ratio of sodium pyruvate to carbon black = 9:1).

[0060] Prepare an aqueous solution of non-ionic surfactant polyvinylpyrrolidone at 0.5 g / L, add carbon black with a mass concentration of 5 g / L, disperse the carbon black solution using grinding and ultrasonic equipment, add sodium pyruvate to dissolve, continuously ultrasonic the mixture, spray dry, collect the powder product to obtain a composite material of carbon composite sodium pyruvate. The XRD data of the composite material is as Figure 1 shown, and the specific capacity of the composite material is as Figure 2 shown.

[0061] Among them, the test method for the specific capacity of the composite material: Prepare the positive electrode film: Disperse the composite material, conductive carbon black, and polyvinylidene fluoride binder in N-methylpyrrolidone in a ratio of 50%:30%:20%, stir to obtain a uniform slurry, and then coat it on the positive electrode current collector aluminum foil. After drying, obtain the positive electrode film for sodium supplementation. Assemble the button battery: Assemble the button battery with metallic sodium (negative electrode), separator, and the composite material film. The button battery model used is CR2032, and the electrolyte is a mixed electrolyte of ethylene carbonate, propylene carbonate, and ethyl methyl carbonate containing 1 mol / L sodium perchlorate. Among them, the mass ratio of ethylene carbonate, propylene carbonate, and ethyl methyl carbonate is 47.5:47.5:5.

[0062] Sodium supplement Example 2

[0063] The sodium supplement in this example is a composite material of sodium pyruvate and carbon black, and the mass ratio of sodium pyruvate to carbon black is 49 (i.e., the mass ratio of sodium pyruvate to carbon black = 49:1).

[0064] Prepare an aqueous solution of non-ionic surfactant polyvinylpyrrolidone at 0.5 g / L, add carbon black with a mass concentration of 10 g / L, disperse the carbon black solution using grinding and ultrasonic equipment, add sodium pyruvate to dissolve, continuously ultrasonic the mixture, spray dry, collect the powder product to obtain a composite material of carbon composite sodium pyruvate. The test method for the specific capacity of the composite material is the same as that in Sodium supplement Example 1, and the specific capacity of the composite material is as Figure 3 shown.

[0065] Sodium supplement Example 3

[0066] The sodium supplement in this example is pure sodium pyruvate. The test method for the specific capacity of pure sodium pyruvate is the same as that in Sodium supplement Example 1, and the specific capacity of pure sodium pyruvate is as Figure 4 shown.

[0067] Sodium supplement Example 4

[0068] The sodium supplement in this embodiment is a slurry formed by mixing sodium pyruvate, carbon black and a solvent, and the mass ratio of sodium pyruvate to carbon black is 5 (i.e., the mass ratio of sodium pyruvate to carbon black = 5:1).

[0069] Prepare 1L of 1.5g / L nonionic surfactant polyvinyl pyrrolidone solution in N-methyl pyrrolidone, add 30g of carbon black and 150g of sodium pyruvate, and use a nano grinder or ultrasonic equipment to crush and disperse to obtain a composite slurry of carbon composite sodium pyruvate. The test method of the composite slurry specific capacity is the same as that of the sodium supplement example 1. The specific capacity of the composite slurry is as follows: Figure 5 shown.

[0070] according to Figure 2-5 It can be seen that Figure 2 When the carbon content is 10%, the decomposition voltage of sodium pyruvate is about 3.8V. When the carbon content is reduced to 2%, Figure 3 , the decomposition voltage of sodium pyruvate increases to 3.9V. When there is no carbon compound at all, the decomposition voltage of sodium pyruvate is also low, such as Figure 4 Compared to Example 1 (10% carbon content), the slope of the sodium pyruvate decomposition curve decreases. Both the increased decomposition voltage and the decreased slope indicate deteriorated decomposition kinetics. Adding an appropriate amount of conductive material facilitates the decomposition of sodium pyruvate. These data demonstrate that an appropriate amount of conductive additive can improve the kinetics of the sodium supplement. Reducing the particle size of the material can also improve the kinetics of the sodium supplement.

[0071] Sodium Supplement Example 4 The particle size of the sodium pyruvate composite material in the slurry prepared by grinding sodium pyruvate with a nano-grinder is about 0.5 μm, which is smaller than the particle size of the sodium supplement in Examples 1-3. Figure 5 As shown, the electrode sheet made of pyruvic acid nanoparticles has improved kinetics and the decomposition voltage is lower than 3.8V.

[0072] Battery Application Example 1

[0073] S1. Preparation of a sodium supplement: Prepare a 0.5 g / L aqueous solution of a nonionic surfactant polyvinyl pyrrolidone, add carbon black with a mass concentration of 5 g / L, use grinding and ultrasonic equipment to disperse the carbon black solution, add sodium pyruvate to dissolve, wherein the mass ratio of sodium pyruvate to carbon black is 9 (i.e., the mass ratio of sodium pyruvate to carbon black = 9:1), continuously ultrasonicate the dispersion, spray dry, and collect the powder product to obtain a composite material of carbon and sodium pyruvate.

[0074] S2. Preparation of positive electrode membrane: Disperse composite sodium iron phosphate, sodium supplement (carbon composite sodium pyruvate), conductive carbon black, and polyvinylidene fluoride binder in nitrogen methyl pyrrolidone in a ratio of 87.5%:4.5%:4%:4%, and obtain a uniform slurry by stirring. Then, apply the slurry on the positive electrode current collector aluminum foil and dry it to obtain a sodium supplemented positive electrode membrane.

[0075] S3. Assemble the button battery: Assemble the button battery with metallic sodium (negative electrode), separator and positive electrode diaphragm. The button battery model used is CR2032, and the electrolyte is a mixed electrolyte of ethylene carbonate, propylene carbonate and ethyl methyl carbonate containing 1 mol / L sodium perchlorate. Among them, the mass ratio of ethylene carbonate, propylene carbonate and ethyl methyl carbonate is 47.5:47.5:5.

[0076] Battery Application Example 2

[0077] Compared with Battery Application Example 1, the difference in this example is that: in step S2, the mass ratio of sodium composite phosphate, sodium supplement agent (carbon composite sodium pyruvate), conductive carbon black and polyvinylidene fluoride binder is 80%:10%:5%:5%.

[0078] Battery Application Comparative Example 1

[0079] Compared with Battery Application Example 1, the difference in this comparative example is that the sodium supplement agent is not added.

[0080] Battery Application Comparative Example 2

[0081] Compared with Battery Application Example 1, the difference in this comparative example is that: in step S2, the mass fraction of the sodium supplement agent is 15%, that is, the mass ratio of sodium composite phosphate, sodium supplement agent, conductive carbon black and polyvinylidene fluoride binder is 75%:15%:5%:5%. The sodium supplement agent does not provide reversible capacity, and if the addition amount of the sodium supplement agent is too much, the risk of reducing the battery energy density increases.

[0082] Battery Application Comparative Example 3

[0083] Compared with Battery Application Example 1, the difference in this comparative example is that: in step S1, the mass ratio of sodium pyruvate to carbon black is 2 (i.e., the mass ratio of sodium pyruvate to carbon black = 2:1). The sodium supplement agent material is composed of carbon black and sodium pyruvate, and sodium comes from sodium pyruvate. If the carbon content is too high, the sodium content in the sodium supplement agent decreases, and the specific capacity of the corresponding sodium supplement agent decreases. When the content of sodium pyruvate is only 2 / 3, the specific capacity of the sodium supplement agent decreases to 162 mAh / g. If the specific capacity is too low, it has no practical application value.

[0084] Test the charge and discharge data of the button batteries prepared in Battery Application Examples 1-2 and Battery Application Comparative Example 1. The test method is as follows:

[0085] (1) Let the battery stand at room temperature for 10 h;

[0086] (2) Charge at a constant current of 0.1C to 4.0V / 4.2V, and charge at a constant voltage of 4.0V / 4.2V to 0.05C (Cycle1 charging);

[0087] (3) Let it stand for 10 min;

[0088] (4) Discharge at a constant current of 0.1C to 2.0V (Cycle 1 discharge);

[0089] (5) Let it stand for 10 min.

[0090] The charge and discharge data of Battery Application Example 1 are as Figure 6 shown, the charge and discharge data of Battery Application Example 2 are as Figure 7 shown, and the charge and discharge data of Battery Application Comparative Example 1 are as Figure 8 shown.

[0091] Comparison Figure 6-8 It can be seen that, compared with Battery Application Comparative Example 1 without adding sodium supplement agent, the positive electrode charge specific capacity with 5% or 10% sodium supplement agent added has been significantly improved, indicating that the sodium supplement agent exerts its sodium supplement effect within the charging voltage range of 4.0V.

[0092] The above has elaborated in detail on the embodiments provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the core idea of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. Use of sodium α-ketone salt as a sodium supplement, characterized in that, Sodium α-ketone salt is applied as a sodium supplement in sodium-ion batteries.

2. A sodium supplement, characterized in that, It includes sodium α-ketone salt, a conductive additive, and a solvent. Among them, the sodium α-ketone salt is a salt compound formed by an α-keto acid with a main carbon chain atom number ≤ 5 and sodium ions. The content of the sodium α-ketone salt > 0, the content of the conductive additive ≥ 0, and the content of the solvent ≥ 0.

3. The sodium supplement according to claim 1, wherein The sodium α-ketone salt includes one or more of sodium pyruvate, sodium α-ketoglutarate, sodium α-ketoisovalerate, and sodium α-ketobutyrate; Preferably, the sodium α-ketone salt includes sodium pyruvate.

4. The sodium supplement according to claim 1, characterized in that, The conductive additive includes conductive carbon; The conductive carbon includes one or more of carbon black, Ketjen black, carbon nanotubes, activated carbon, and graphene.

5. The sodium supplement according to claim 1, characterized in that, The mass ratio of the sodium α-ketone salt to the conductive additive ≥ 4; Preferably, the mass ratio of the sodium α-ketone salt to the conductive additive is 4 - 99; More preferably, the mass ratio of the sodium α-ketone salt to the conductive additive is 9 - 19.

6. The sodium supplement according to any one of claims 2-5, characterized in that, When the content of the conductive additive > 0 and the content of the solvent is 0, the sodium supplement includes the sodium α-ketone salt and the conductive additive, and the sodium α-ketone salt and the conductive additive form a composite material. The preparation method is as follows: Add the conductive additive to an aqueous dispersant solution, then add the sodium α-ketone salt, and after uniform dispersion, obtain a mixed solution. Dry the mixed solution to obtain a composite material containing the sodium α-ketone salt, where the dispersant is a surfactant.

7. The sodium supplement according to any one of claims 2-5, characterized in that, When the content of the conductive additive > 0 and the content of the solvent > 0, the sodium supplement includes the sodium α-ketone salt, the conductive additive, and the solvent. The sodium α-ketone salt and the conductive additive form a composite material and exist in the solvent. The preparation method is as follows: Add the conductive additive to a solvent containing a dispersant, then add the sodium α-ketone salt, and obtain a sodium supplement slurry through grinding treatment or ultrasonic fragmentation dispersion treatment.

8. The sodium supplement according to any one of claims 2-5, characterized in that, When the content of the conductive additive is 0 and the content of the solvent > 0, the sodium supplement includes the sodium α-ketone salt and the solvent, and the sodium supplement is in a solution state or a slurry state; When the content of the conductive additive is 0 and the content of the solvent is 0, the sodium supplement includes the sodium α-ketone salt.

9. A positive electrode membrane sheet for a sodium-ion battery, characterized in that, It includes the sodium supplement as described in any one of claims 1 - 8, and also includes a positive electrode material, a binder, and a conductive agent. The sodium supplement, the positive electrode material, the binder, and the conductive agent are uniformly dispersed in the solvent of the battery positive electrode slurry to form a positive electrode slurry. Coating the positive electrode slurry on a current collector forms a positive electrode film. Among them, based on the mass of the positive electrode film, the mass percentage of the sodium supplement ≤ 10%; Preferably, based on the mass of the positive electrode film, the mass percentage of the sodium supplement ≤ 5%.

10. A sodium-ion battery, characterized in that, It includes a positive electrode film, a negative electrode sheet, an electrolyte, and a separator. Among them, the positive electrode film is a positive electrode film added with the sodium supplement as described in any one of claims 2 - 8.

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