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

Abstract

The invention belongs to the technical field of sodium-ion battery material preparation, and particularly relates to a sodium-ion battery positive electrode sodium supplementing additive and a preparation method and application thereof. According to the sodium ion battery positive electrode sodium supplement additive, sodium ferrocyanide is used as a main component of the sodium ion battery positive electrode sodium supplement additive, and the sodium ferrocyanide and the first conductive carbon with the specific surface area larger than 1000 m < 2 > / g are subjected to infiltration adsorption and ball-milling mixing with the second conductive carbon with better conductivity, so that the sodium ion battery positive electrode sodium supplement additive is obtained. When a battery positive electrode adopts the positive electrode sodium supplementing additive disclosed by the invention, dissolved metal ions M react with sodium ferrocyanide Na4 [Fe (CN) 6] adhered to the periphery of a positive electrode material to generate Prussian blue Na2M [Fe (CN) 6] small crystals, so that the sodium storage performance can be continuously exerted within a period of time, and the capacity and service life attenuation of the battery can be delayed; na < + > is released in the generation process of the small crystal Na2M [Fe (CN) 6], so that the effect of continuously supplementing sodium in the use process of the sodium-ion battery is achieved, and the capacity fading is further delayed.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion battery material preparation, and specifically relates to a sodium ion battery positive electrode sodium supplement additive and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries have become a strong competitor for the next generation of energy storage batteries due to their wide availability, low cost, safety and long cycle life. Prussian blue compounds (PBAs) are currently attracting much attention as positive electrode materials for sodium-ion batteries. They have a unique three-dimensional open framework and large pore structure, which can provide two Na + Fast transmission channel, with high theoretical specific capacity (170mAh g -1 ) and fast ion kinetics. However, PBAs are generally prepared by solution precipitation, which forms Fe(CN)6 4- Vacancy defects and a large amount of crystal water hinder the Na + Embedded in the PBAs lattice, limiting its sodium storage capacity. More importantly, the crystal water in the PBAs will gradually dissolve during the battery reaction, causing more structural defects, leading to the dissolution of transition metals, and further release of crystal water into the electrolyte, triggering the generation of HF to corrode the aluminum current collector and the positive electrode active material, leading to rapid battery performance decay, side reactions, flatulence and other problems.

[0003] At the same time, the formation of SEI film consumes sodium ions when the negative electrode material of the sodium ion battery is charged and discharged for the first time, which will cause irreversible loss of sodium ions and thus produce the problem of initial capacity loss (ICL). ICL has a great impact on performance indicators such as the energy density of the battery. At present, the main methods of sodium supplementation mainly include spraying sodium powder, spraying organic sodium solution, and positive electrode additive sodium supplementation. Among them, the positive electrode additive sodium supplementation method is a more promising sodium supplementation technology, but commonly used positive electrode additives such as Na3P are toxic, and Na2CO3 will release oxygen and affect battery performance.

[0004] In view of the fact that Prussian blue-based sodium ion batteries suffer from battery performance degradation and the need for sodium supplementation due to structural defects and crystal water, it is urgent to develop a sodium ion battery positive electrode sodium supplement additive and a sodium ion battery. Summary of the invention

[0005] The object of the present invention is to provide a sodium ion battery positive electrode sodium supplement additive and a preparation method and application thereof to solve the above-mentioned 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, wherein 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 comprises a first conductive carbon and a second conductive carbon, wherein the specific surface area of ​​the first conductive carbon is greater than 1000m 2 / g, and the second conductive carbon is at least one of carbon black, acetylene black, conductive graphite, carbon nanotubes, and graphene.

[0007] The raw materials used are calculated by weight as follows: 15-32 parts of sodium ferrocyanide, 0.8-1.0 parts of the first conductive carbon, 0.1-0.2 parts of the second conductive carbon, and 50 parts of deionized water.

[0008] The present invention adopts sodium ferrocyanide as the main component of the positive electrode sodium supplement 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 supplement additives.

[0009] Moreover, sodium ferrocyanide (Na4[Fe(CN)6]) can self-decompose in the presence of acid and generate ferrous ions that react with undecomposed sodium ferrocyanide to generate Prussian blue material. Therefore, the present invention selects sodium ferrocyanide as the main component of the positive electrode additive, which can eliminate HF corrosion that may be generated in the electrolyte due to various reasons and prolong the battery cycle life.

[0010] During the first charge, the sodium ferrocyanide (Na4[Fe(CN)6]) additive will be partially oxidized to sodium ferrocyanide (Na3[Fe(CN)6]). + It plays a role in replenishing the Na2+ caused by the first-cycle electrode / electrolyte interface film formation. + loss, the first-cycle Coulomb efficiency can be improved to a certain extent.

[0011] Sodium ferrocyanide with a specific surface area greater than 1000m 2 / g of the first conductive carbon is soaked and adsorbed, and then mixed with the second conductive carbon with better conductivity by ball milling. Sodium ferrocyanide is closely linked to the conductive carbon, which helps to maintain the conductive network of small Na2M[Fe(CN)6] crystals after anchoring the dissolved metal ions, and continuously exert its sodium storage capacity. Among them, the first conductive carbon can be selected from Ketjen black with a larger specific surface area (its specific surface area is about 1000-1600m 2 / g), can adsorb sodium ferrocyanide, and be compounded with the second conductive carbon (such as acetylene black) to form a positive electrode sodium supplement.

[0012] During the charge and discharge cycle, Prussian blue materials will fail due to structural instability, continuous dissolution of metal ions, and eventually structural collapse and rapid capacity decay. When the positive electrode additive of the present invention is used, the dissolved metal ions M react with sodium ferrocyanide Na4[Fe(CN)6] adhered to the positive electrode 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 life decay of the battery; and during the formation of small crystals Na2M[Fe(CN)6], Na is released. + , which plays the role of continuously replenishing sodium during the use of sodium-ion batteries, further delaying capacity decay.

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

[0014] S1, dissolving sodium ferrocyanide in deionized water to prepare a sodium ferrocyanide solution;

[0015] S2, adding the first conductive carbon to the sodium ferrocyanide solution prepared in S1, stirring, filtering, and then vacuum drying below 100° C.;

[0016] S3, transferring the dried product of S2 to a ball mill, adding a second conductive carbon to the ball mill, adding grinding balls for dry mixing and ball milling, and drying to obtain a positive electrode sodium supplement additive.

[0017] In some embodiments, a method for preparing a sodium ion battery positive electrode sodium supplement additive comprises 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 dry in vacuum at below 100°C;

[0020] S3. The dried product of S2 is transferred to a ball mill, and then 0.1-0.2 g of the second conductive carbon is added to the ball mill, and grinding balls are added to dry mix and ball mill for 20-30 minutes. After vacuum drying below 100° C., a positive electrode sodium supplement additive is obtained.

[0021] Therefore, vacuum drying is performed at a relatively low temperature to prevent Na4[Fe(CN)6] from being oxidized and de-sodiumized. Specifically, the atomic ratio of Na:Fe in sodium ferrocyanide is 4, and it is inevitable to produce a certain amount of oxidation during dissolution in aqueous solution, carbon adsorption drying, and ball milling, and oxidation leads to de-Na. The present invention adopts measures such as low-temperature vacuum drying to avoid oxidation as much as possible, and the atomic ratio of Na:Fe is ensured to be above 3.5.

[0022] According to a third aspect of the present invention, there is provided a use of the above-mentioned positive electrode sodium supplement additive in the preparation of a sodium ion battery.

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

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

[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 the following method: the positive electrode active material, the binder, the conductive agent and the positive electrode sodium supplement additive are fully stirred in a solvent to form a uniformly dispersed slurry, the obtained slurry is coated on a current collector aluminum foil and dried 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 supplement additive, a hard carbon negative electrode, a separator and an electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure shows the cycle life of batteries of different groups (100mA / g). DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with specific embodiments. Unless otherwise specified, the following raw materials are commercially available.

[0030] Example 1

[0031] A method for preparing a sodium ion battery positive electrode sodium supplement additive comprises 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 hours and filter and dry; transfer the dried filtrate to a ball mill, add 0.2 g of acetylene black to the ball mill, add grinding balls and dry mix for 4 hours, and dry at 100°C to obtain a sodium ion battery positive electrode sodium supplement additive.

[0033] The sodium ion battery positive electrode sodium supplement additive is used to prepare a sodium ion battery positive electrode sheet by the following method:

[0034] The amount of iron-based Prussian blue positive electrode material is 80 parts, the amount of PVDF adhesive is 10 parts, and the amount of conductive agent carbon black is 5 parts; the amount of positive electrode sodium supplement additive is 5wt% of the positive electrode active material. The slurry is fully stirred in solvent N-methylpyrrolidone to prepare a uniformly dispersed slurry, and the obtained slurry is coated on an aluminum foil current collector and dried to obtain a positive electrode sheet.

[0035] The sodium ion battery is prepared by the following method: the above-mentioned positive electrode sheet, hard carbon negative electrode, separator and electrolyte are assembled into a 2Ah sodium ion battery according to the existing process.

[0036] Comparative Example 1

[0037] Compared with Example 1, the positive electrode sheet prepared in Comparative Example 1 does not contain the positive electrode sodium supplement additive in Example 1. The positive electrode sheet of the sodium ion battery in Comparative Example 1 is prepared as follows:

[0038] The amount of iron-based Prussian blue positive electrode material is 80 parts, the amount of PVDF adhesive is 10 parts, and the amount of conductive agent carbon black is 10 parts; they are fully stirred in N-methylpyrrolidone to prepare a uniformly dispersed slurry, and the obtained slurry is coated on an aluminum foil current collector and dried to obtain a positive electrode sheet.

[0039] The positive electrode sheet, 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. The results are shown in Table 1 and Figure 1 As shown, the sodium ion battery prepared by the technology of Example 1 has a first cycle coulombic efficiency of 86.75%, and its capacity retention rate is 86% after 1000 cycles at a current density of 100 mA / g. The sodium ion battery in Comparative Example 1 has a first cycle coulombic efficiency of 82.47%, and its capacity retention rate is 73.9% after 500 cycles at a current density of 100 mA / g.

[0041] The above battery performance comparison shows that the sodium ion positive electrode sodium supplement additive of the present invention can be used in the battery to appropriately improve the first cycle coulomb efficiency and greatly improve the battery cycle performance.

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

[0043] Group First cycle discharge capacity First-cycle 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 positive electrode sodium supplement additive can be changed within the scope of the present invention. For example, based on Example 1, the amount of sodium ferrocyanide solution is 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 taken as 0.8 g, 0.85 g, 0.9 g or 0.95 g, etc., and acetylene black can also be taken as 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 are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A sodium-supplementing additive for a positive electrode of a sodium-ion battery, characterized in that: The conductive agent is prepared from sodium ferrocyanide, conductive carbon and deionized water, wherein 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 comprises a first conductive carbon and a second conductive carbon, wherein the specific surface area of ​​the first conductive carbon is greater than 1000m 2 / g, and 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 supplement additive according to claim 1, characterized in that: By mass, the sodium ferrocyanide is 15-32 parts, the first conductive carbon is 0.8-1.0 parts, the second conductive carbon is 0.1-0.2 parts, and the deionized water is 50 parts.

3. The method for preparing the sodium-supplementing additive for the positive electrode of a sodium ion battery according to claim 1 or 2, characterized in that: The steps include: S1, dissolving sodium ferrocyanide in deionized water to prepare a sodium ferrocyanide solution; S2, adding the first conductive carbon to the sodium ferrocyanide solution prepared in S1, stirring, filtering and drying; S3, the dried product of S2 is transferred to a ball mill, and then a second conductive carbon is added to the ball mill, and grinding balls are added for dry mixing and ball milling, and the positive electrode sodium supplement additive is obtained after drying.

4. The method for preparing the sodium-supplementing additive for the positive electrode of a sodium ion battery according to claim 3, characterized in that: The steps include: 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 dry in vacuum at below 100°C; S3. Transfer the dried product of S2 to a ball mill, add 0.1-0.2 g of the second conductive carbon to the ball mill, add grinding balls and dry-mix for 3-5 hours, and vacuum dry below 100° C. to obtain the positive electrode sodium supplement additive.

5. Use of the sodium ion battery positive electrode sodium supplement additive according to claim 1 or 2 in the preparation of sodium ion batteries.

6. A sodium ion battery positive electrode sheet, characterized in that: The invention comprises 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 the positive electrode sodium supplement additive for a sodium ion battery according to claim 1 or 2.

7. The sodium ion battery positive electrode sheet according to claim 6, characterized in that: In terms of mass fractions, the proportion of raw materials in the positive electrode layer is as follows: the amount of positive electrode active material is 75-80 parts, the amount of adhesive is 5-10 parts, and the amount of conductive agent is 5-10 parts; the amount of the sodium ion battery positive electrode sodium supplement additive is 1-5wt% 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 positive electrode material; the conductive agent includes at least one of conductive carbon black, conductive graphite, SP, carbon nanotubes and graphene; and the binder includes at least one of PTFE, PVDF, ETEF and FEP.

9. The method for preparing a positive electrode sheet for a sodium ion battery according to any one of claims 6 to 8, characterized in that: The method comprises the following steps: stirring a positive electrode active material, a binder, a conductive agent and the positive electrode sodium supplement additive for a sodium ion battery according to claim 1 or 2 in a solvent to prepare a uniformly dispersed slurry, coating the obtained slurry on a current collector aluminum foil and drying it to obtain a positive electrode sheet.

10. A sodium ion battery, characterized in that The sodium ion battery is assembled from the positive electrode sheet, hard carbon negative electrode, separator and electrolyte according to any one of claims 6 to 8.

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