Sodium ion battery positive electrode sodium supplementing additive, preparation method and application thereof

Abstract

This invention belongs to the field of sodium-ion battery material preparation technology, specifically relating to sodium-ion battery cathode sodium supplementation additives, their preparation methods, and applications. The sodium-ion battery cathode sodium supplementation additive of this invention uses sodium ferrocyanide as the main component, and has a specific surface area greater than 1000 m². 2 The first conductive carbon (g) is impregnated and adsorbed, and then ball-milled and mixed with a second conductive carbon with better conductivity to obtain a sodium-ion battery cathode additive. When the cathode of the battery uses the sodium-ion battery additive of this invention, the dissolved metal ions M react with sodium ferrocyanide Na4[Fe(CN)6] adhering to the cathode material to form Prussian blue Na2M[Fe(CN)6] small crystals, which can continuously exert sodium storage performance for a period of time, delaying the capacity and lifespan decay of the battery; and Na is released during the formation of small crystals Na2M[Fe(CN)6]. + It plays a role in continuously replenishing sodium during the use of sodium-ion batteries, further delaying capacity decay.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery material preparation technology, specifically relating to sodium-ion battery cathode sodium supplementation additives, their preparation methods, and applications. Background Technology

[0002] Sodium-ion batteries are strong contenders for next-generation energy storage batteries due to their wide availability, low cost, safety, and long cycle life. Prussian blue compounds (PBAs) are currently attracting attention as cathode materials for sodium-ion batteries, possessing a unique three-dimensional open framework and large-pore structure that can provide two Na+ atoms. + Fast transmission channel with high theoretical specific capacity (170mAh g) -1 PBAs exhibit rapid ion kinetics. However, they are generally prepared via solution precipitation, a process that forms Fe(CN)6 in their structure. 4- Vacancies and abundant water of crystallization hinder Na + The embedding of PBAs in the lattice limits their sodium storage capacity. More importantly, the water of crystallization in PBAs gradually dissolves during the battery reaction, causing more structural defects, leading to the dissolution of transition metals, and further release of water of crystallization into the electrolyte. This triggers HF corrosion of the aluminum current collector and positive electrode active material, resulting in rapid battery performance degradation, side reactions, and gas expansion.

[0003] Meanwhile, during the first charge and discharge cycle of a sodium-ion battery, the formation of the SEI film consumes sodium ions, leading to irreversible sodium ion loss and resulting in Initial Capacity Loss (ICL). ICL has a significant impact on battery performance indicators such as energy density. Currently, the main methods for sodium replenishment include sodium powder spraying, organic sodium solution spraying, and positive electrode additives. Among these, positive electrode additives are a promising technology, but commonly used positive electrode additives such as Na3P are toxic, and Na2CO3 releases oxygen, affecting battery performance.

[0004] Given that Prussian blue-based sodium-ion batteries suffer from performance degradation due to structural defects and water of crystallization, and require sodium replenishment, there is an urgent need to develop a sodium-ion battery cathode additive and a sodium-ion battery. Summary of the Invention

[0005] The purpose of this invention is to provide a sodium-ion battery cathode additive, its preparation method, and its application, in order to solve the aforementioned problems.

[0006] According to a first aspect of the present invention, a sodium-ion battery positive electrode sodium supplement additive is provided, which is prepared from sodium ferrocyanide, a conductive agent, and deionized water. The atomic molar ratio of Na to Fe in the obtained positive electrode sodium supplement additive is controlled at 3.5-4.0:1. The conductive agent includes a first conductive carbon and a second conductive carbon, wherein the first conductive carbon has a specific surface area greater than 1000 m². 2 / g, the second conductive carbon is at least one of carbon black, acetylene black, conductive graphite, carbon nanotubes, and graphene.

[0007] The raw materials used, by mass fraction, are: 15-32 parts sodium ferrocyanide, 0.8-1.0 parts first conductive carbon, 0.1-0.2 parts second conductive carbon, and 50 parts deionized water.

[0008] This invention uses sodium ferrocyanide as the main component of the positive electrode sodium supplementation additive. Sodium ferrocyanide is insoluble in organic solvents and will not cause adverse effects such as local collapse of the positive electrode layer and poor contact caused by the large-scale dissolution of other soluble sodium supplementation additives.

[0009] Furthermore, sodium ferrocyanide (Na4[Fe(CN)6]) can undergo self-decomposition in the presence of acid, generating ferrous ions that react with undecomposed sodium ferrocyanide to produce Prussian blue material. Therefore, this invention selects sodium ferrocyanide as the main component of the positive electrode additive, which can eliminate HF corrosion that may occur in the electrolyte due to various reasons and extend the battery cycle life.

[0010] During the initial charging process, the sodium ferrocyanide (Na4[Fe(CN)6]) additive is partially oxidized to sodium ferrocyanide (Na3[Fe(CN)6]), and the oxidized Na... + This helps to replenish the Na+ caused by the film formation at the electrode / electrolyte interface during the first pass. + Losses can improve the efficiency of the first round of Coulombs to some extent.

[0011] Sodium ferrocyanide and substances with a specific surface area greater than 1000 m² 2 The first conductive carbon (at a concentration of 1 g) is impregnated and adsorbed, then ball-milled and mixed with a second conductive carbon (which has better conductivity). The sodium ferrocyanide is tightly bonded to the conductive carbon, which helps maintain the conductive network of the Na2M[Fe(CN)6] small crystals after the metal ions are anchored, thus continuously exerting its sodium storage capacity. The first conductive carbon can be Ketjen Black, which has a large specific surface area (approximately 1000-1600 m²). 2 / g), can adsorb sodium ferrocyanide, and can be compounded with a second conductive carbon (such as acetylene black) to form a positive electrode sodium replenishing agent.

[0012] Prussian blue materials fail during charge-discharge cycles due to structural instability, continuously leaching metal ions and ultimately causing structural collapse and rapid capacity decay. When the cathode additive of this invention is used, the leached metal ions M react with sodium ferrocyanide Na4[Fe(CN)6] adhering to the cathode material to form small Prussian blue Na2M[Fe(CN)6] crystals, which can continuously maintain sodium storage performance for a period of time, delaying battery capacity and lifespan decay; and Na is released during the formation of the small Na2M[Fe(CN)6] crystals. + It plays a role in continuously replenishing sodium during the use of sodium-ion batteries, further delaying capacity decay.

[0013] According to a second aspect of the present invention, a method for preparing a sodium-ion battery cathode additive is provided, comprising the following steps:

[0014] S1. Dissolve sodium ferrocyanide in deionized water to prepare a sodium ferrocyanide solution;

[0015] S2. Add the first conductive carbon to the sodium ferrocyanide solution prepared in S1, stir, filter, and then vacuum dry at below 100°C.

[0016] S3. After drying S2, transfer the product to a ball mill jar, add a second conductive carbon to the ball mill jar, add grinding balls for dry mixing and ball milling, and dry to obtain the positive electrode sodium supplement additive.

[0017] In some embodiments, the preparation method of the sodium-ion battery cathode additive includes the following steps:

[0018] S1. Dissolve sodium ferrocyanide in deionized water to prepare a 1-2 mol / L sodium ferrocyanide solution;

[0019] S2. Take 50 mL of the sodium ferrocyanide solution prepared in S1 and place it in a beaker. Add 0.8-1.0 g of the first conductive carbon, stir for 1-2 h, filter, and then vacuum dry at below 100℃.

[0020] S3. After drying S2, transfer the product to a ball mill jar, add 0.1-0.2g of second conductive carbon to the ball mill jar, add grinding balls and dry mix and ball mill for 20-30 minutes, then vacuum dry at below 100℃ to obtain the positive electrode sodium supplement additive.

[0021] Therefore, a lower temperature is used for vacuum drying to prevent Na4[Fe(CN)6] from being oxidized and desodiumed. Specifically, sodium ferrocyanide has an atomic ratio of Na:Fe of 4. During its dissolution in aqueous solution, carbon adsorption drying, and ball milling, some oxidation is unavoidable, leading to desodium removal. This invention employs low-temperature vacuum drying and other measures to minimize oxidation, ensuring that the Na:Fe atomic ratio can reach 3.5 or higher.

[0022] According to a third aspect of the present invention, the application of the above-described positive electrode sodium supplementation additive in the preparation of sodium-ion batteries is provided.

[0023] According to a fourth aspect of the present invention, a sodium-ion battery positive electrode sheet containing the above-mentioned positive electrode sodium supplementation additive is provided. The sodium-ion battery positive electrode sheet includes a current collector aluminum foil and a positive electrode layer. The positive electrode layer includes a positive electrode active material, a binder, a conductive agent, and the above-mentioned positive electrode sodium supplementation additive. The various materials can be proportioned according to existing ratios or according to specific ratios.

[0024] In some embodiments, the proportions of raw materials in the positive electrode layer are as follows, by weight: 75-80 parts of positive electrode active material, 5-10 parts of binder, 5-10 parts of conductive agent; and 1-5 wt% of positive electrode sodium supplementation additive.

[0025] In some embodiments, the positive electrode active material is a Prussian blue-based positive electrode material, including Prussian blue, Prussian white, multi-element or high-entropy Prussian blue materials; the conductive agent includes at least one of conductive carbon black, conductive graphite, SP (Super P), carbon nanotubes and graphene; the binder includes at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETEF) and fluorinated ethylene propylene copolymer (FEP).

[0026] In some embodiments, the positive electrode sheet can be prepared by: thoroughly stirring the positive electrode active material, binder, conductive agent and positive electrode sodium supplementation additive in a solvent to form a uniformly dispersed slurry; coating the obtained slurry onto a current collector aluminum foil and drying it to obtain the positive electrode sheet; wherein the solvent used includes N-methylpyrrolidone.

[0027] According to a fifth aspect of the present invention, a sodium-ion battery is provided, comprising a positive electrode sheet containing the above-mentioned positive electrode sodium supplementation additive, a hard carbon negative electrode, a separator, and an electrolyte. Attached Figure Description

[0028] Figure 1 Cycle life graphs (100mA / g) for different battery groups. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments. Unless otherwise specified, all raw materials are commercially available.

[0030] Example 1

[0031] The preparation method of sodium-ion battery cathode additive includes the following steps:

[0032] Take 50 mL of 1 mol / L sodium ferrocyanide solution and place it in a beaker. Add 1.0 g of Ketjen black, stir for 2 h, and then filter and dry. Transfer the dried filter to a ball mill jar, add 0.2 g of acetylene black to the ball mill jar, add grinding balls and dry mix and ball mill for 4 h. After drying at 100 °C, obtain sodium supplementation additive for sodium-ion battery positive electrode.

[0033] The sodium-ion battery positive electrode sheet was prepared by the above-mentioned sodium-ion battery positive electrode additive using the following method:

[0034] The positive electrode material is prepared by mixing 80 parts of iron-based Prussian blue, 10 parts of PVDF binder, and 5 parts of conductive carbon black. The amount of positive electrode sodium supplement is 5 wt% of the amount of positive electrode active material. The mixture is stirred thoroughly in the solvent N-methylpyrrolidone to form a uniformly dispersed slurry. The obtained slurry is coated onto an aluminum foil current collector and dried to obtain a positive electrode sheet.

[0035] Sodium-ion batteries can be prepared by assembling the above-mentioned positive electrode, hard carbon negative electrode, separator and electrolyte into a 2Ah sodium-ion battery according to existing processes.

[0036] Comparative Example 1

[0037] Compared to Example 1, the positive electrode prepared in Comparative Example 1 does not contain the sodium-supplementing additive of Example 1. The sodium-ion battery positive electrode of Comparative Example 1 was prepared by the following method:

[0038] The positive electrode material is prepared by mixing 80 parts of iron-based Prussian blue cathode material, 10 parts of PVDF binder, and 10 parts of conductive carbon black in N-methylpyrrolidone to form a uniformly dispersed slurry. The slurry is then coated onto an aluminum foil current collector and dried to obtain the positive electrode sheet.

[0039] The above-mentioned positive electrode, hard carbon negative electrode, separator and electrolyte are assembled into a 2Ah sodium-ion battery according to the existing process.

[0040] The performance of the batteries prepared in Example 1 and Comparative Example 1 was tested, and the results are shown in Table 1 and... Figure 1 As shown, the sodium-ion battery prepared using the technique of Example 1 has an initial coulombic efficiency of 86.75%, and retains 86% of its capacity after 1000 cycles at a current density of 100 mA / g. In contrast, the sodium-ion battery in Comparative Example 1 has an initial coulombic efficiency of 82.47%, and retains 73.9% of its capacity after 500 cycles at a current density of 100 mA / g.

[0041] The above battery performance comparison shows that the sodium-ion cathode sodium supplement additive of the present invention can appropriately improve the first-cycle coulombic efficiency and significantly improve the battery cycle performance when used in batteries.

[0042] Table 1. First-cycle discharge capacity and coulombic efficiency of batteries in different groups

[0043] Group First-cycle discharge capacity First lap Coulomb efficiency Example 1 126.13mAh / g 86.75％ Comparative Example 1 120.62mAh / g 82.47％

[0044] In other embodiments, the amount of raw materials used to prepare the sodium-ion battery cathode additive can be changed within the scope of this invention. For example, based on Example 1, the amount of sodium ferrocyanide solution can be changed to 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L, 1.7 mol / L, 1.8 mol / L, or 2 mol / L. Ketjen black can also be 0.8 g, 0.85 g, 0.9 g, or 0.95 g, etc., and acetylene black can also be 0.1 g, 0.12 g, 0.13 g, 0.15 g, 0.16 g, 0.18 g, or 0.19 g, etc.

[0045] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A sodium-ion battery positive electrode sodium replenishment additive, characterized in that, It is prepared from sodium ferrocyanide, a conductive agent, and deionized water by the following method: S1. Dissolve sodium ferrocyanide in deionized water to prepare a sodium ferrocyanide solution; S2. Add the first conductive carbon to the sodium ferrocyanide solution prepared in S1, stir, filter and dry. S3. After drying S2, transfer the product to a ball mill jar, add a second conductive carbon to the ball mill jar, add grinding balls to dry mix and ball mill, and dry to obtain the positive electrode sodium supplementation additive. The atomic molar ratio of Na:Fe in the obtained positive electrode sodium supplement additive is controlled at 3.5-4.0:1; the conductive agent includes a first conductive carbon and a second conductive carbon, wherein the first conductive carbon has a specific surface area greater than 1000 m². 2 / g, the second conductive carbon is at least one of carbon black, acetylene black, conductive graphite, carbon nanotubes, and graphene.

2. The sodium-ion battery positive electrode sodium supplementation additive according to claim 1, characterized in that, By mass fraction, sodium ferrocyanide 15-32 parts, first conductive carbon 0.8-1.0 parts, second conductive carbon 0.1-0.2 parts, and deionized water 50 parts.

3. The method for preparing the sodium-ion battery positive electrode sodium supplementation additive according to claim 1 or 2, characterized in that, Includes the following steps: S1. Dissolve sodium ferrocyanide in deionized water to prepare a sodium ferrocyanide solution; S2. Add the first conductive carbon to the sodium ferrocyanide solution prepared in S1, stir, filter and dry. S3. After drying S2, transfer the product to a ball mill jar, add a second conductive carbon to the ball mill jar, add grinding balls for dry mixing and ball milling, and dry to obtain the positive electrode sodium supplement additive.

4. The method for preparing the sodium-ion battery positive electrode sodium supplementation additive according to claim 3, characterized in that, Includes the following steps: S1. Dissolve sodium ferrocyanide in deionized water to prepare a 1-2 mol / L sodium ferrocyanide solution; S2. Take 50 mL of the sodium ferrocyanide solution prepared in S1 and place it in a beaker. Add 0.8-1.0 g of the first conductive carbon, stir for 1-2 h, filter, and then vacuum dry at below 100℃. S3. After drying S2, transfer the product to a ball mill jar, add 0.1-0.2g of second conductive carbon to the ball mill jar, add grinding balls and dry mix and ball mill for 3-5 hours, then vacuum dry at below 100℃ to obtain the positive electrode sodium supplement additive.

5. The application of the sodium-ion battery positive electrode sodium supplementation additive as described in claim 1 or 2 in the preparation of sodium-ion batteries.

6. A sodium-ion battery positive electrode, characterized in that, It includes a current collector aluminum foil and a positive electrode layer, wherein the positive electrode layer is prepared from a positive electrode active material, a binder, a conductive agent, and a sodium-supplementing additive for sodium-ion batteries as described in claim 1 or 2.

7. The sodium-ion battery positive electrode sheet according to claim 6, characterized in that, The proportions of the raw materials in the positive electrode layer are as follows, by mass: 75-80 parts of positive electrode active material, 5-10 parts of binder, and 5-10 parts of conductive agent; the amount of sodium-ion battery positive electrode sodium supplementation additive is 1-5 wt% of the amount of positive electrode active material.

8. The sodium-ion battery positive electrode sheet according to claim 6 or 7, characterized in that, The positive electrode active material is a Prussian blue-based positive electrode material; the conductive agent includes at least one of conductive carbon black, conductive graphite, SP, carbon nanotubes, and graphene; the binder includes at least one of PTFE, PVDF, ETEF, and FEP.

9. The method for preparing the sodium-ion battery positive electrode sheet according to any one of claims 6-8, characterized in that, The process includes the following steps: mixing the positive electrode active material, binder, conductive agent, and sodium-ion battery positive electrode sodium supplementation additive as described in claim 1 or 2 in a solvent to form a uniformly dispersed slurry; coating the obtained slurry onto a current collector aluminum foil and drying it to obtain a positive electrode sheet.

10. A sodium-ion battery, characterized in that, It is assembled from the sodium-ion battery positive electrode, hard carbon negative electrode, separator and electrolyte as described in any one of claims 6-8.

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