A sodium ferric sulfate composite material, a preparation method and application thereof

Abstract

The embodiment of the present application discloses a kind of sodium ferrosulfate composite material and its preparation method and application.The preparation method of sodium ferrosulfate composite material of the present application includes the following steps: sodium source, iron source, sulfur source and antioxidant are mixed with sodium ferrosulfate preparation raw materials and eutectic solvent to obtain mixture material I, heating reaction is carried out, to obtain the mixture material II containing sodium ferrosulfate, then mixed with the preparation raw materials of Prussian blue compound, reaction is carried out, to obtain the sodium ferrosulfate composite material of the present application.The preparation method of the present application can make the uniform composite between sodium ferrosulfate and Prussian blue-like two materials, and make full use of high capacity and rate performance of Prussian blue-like material to effectively improve the sodium storage performance of sodium ferrosulfate.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a sodium ferric sulfate composite material, its preparation method, and its application. Background Technology

[0002] Sodium and lithium both belong to Group 1 elements and have similar physicochemical properties. Sodium is abundant (2.75% of the Earth's crust) and evenly distributed, making sodium-ion batteries a focal point of competition in new energy technologies worldwide. The development of cathode materials in sodium-ion batteries has been relatively slow, accounting for over 30% of the total battery cost. Currently, cathode materials for sodium-ion batteries mainly include layered oxides and polyanionic compounds. Among them, polyanionic compounds have attracted widespread attention due to their high operating voltage and good cycle stability. Sodium iron sulfate, as a typical representative of polyanionic compound cathode materials, also has the advantage of low raw material (sodium salt, iron salt, etc.) costs. However, the large number of inactive polyanionic groups in this type of material leads to a relatively low theoretical specific capacity, which to some extent affects the application prospects of sodium iron sulfate materials in batteries. Summary of the Invention

[0003] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a method for preparing sodium ferric sulfate composite material, which adopts a two-step liquid-phase method based on a eutectic solvent to improve the sodium storage performance of sodium ferric sulfate by combining a Prussian blue-like material with high capacity and high rate capability.

[0004] This invention also proposes a sodium ferric sulfate composite material.

[0005] The present invention also proposes a positive electrode material.

[0006] The present invention also proposes a positive electrode.

[0007] The present invention also proposes a secondary battery.

[0008] In a first aspect, the present invention provides a method for preparing a sodium ferric sulfate composite material, comprising the following steps: mixing sodium ferric sulfate preparation raw materials containing sodium source, iron source, sulfur source and antioxidant with a eutectic solvent to obtain mixture I, reacting by heating to obtain mixture II containing sodium ferric sulfate, and then mixing with a Prussian blue-like compound preparation raw material and reacting to obtain the sodium ferric sulfate composite material.

[0009] The method for preparing the sodium ferric sulfate composite material according to embodiments of the present invention has at least the following beneficial effects:

[0010] The method for preparing sodium ferric sulfate composite material provided by this invention includes configuring a eutectic solvent system; fully dissolving sodium, iron, sulfur, and antioxidant raw materials for preparing sodium ferric sulfate in the eutectic solvent, and carrying out a liquid-phase reaction at a certain temperature to obtain sodium ferric sulfate; then adding raw materials for preparing Prussian blue-like compounds (such as transition metal salts and sodium ferrocyanide) to react, thereby obtaining a composite material of sodium ferric sulfate and Prussian blue-like compounds. This method mixes sodium ferric sulfate with the raw materials for preparing Prussian blue-like compounds, resulting in a more uniform composite between the two materials. Furthermore, the Prussian blue-like cathode material, due to its high specific capacity and unique three-dimensional open-framework structure, facilitates rapid and reversible insertion / extraction of sodium ions, thus fully utilizing the high capacity and rate performance of the Prussian blue-like material to effectively improve the sodium storage performance of sodium ferric sulfate.

[0011] In related technologies, simple Prussian blue-like materials are typically synthesized using a simple aqueous solution precipitation method, resulting in materials with a high content of water of crystallization. If sodium ferric sulfate is simply mixed with the Prussian blue-like material prepared in an aqueous solution, the sodium ferric sulfate is easily degraded due to the water of crystallization in the Prussian blue-like material. This invention employs a two-step liquid-phase method based on a eutectic solvent to prepare the composite material, avoiding the problem of sodium ferric sulfate deterioration caused by the high water of crystallization content in the Prussian blue-like material prepared in an aqueous solution system. This method effectively combines the raw materials for Prussian blue-like material preparation with sodium ferric sulfate, resulting in a composite material formed from sodium ferric sulfate and Prussian blue-like material. This allows for the comprehensive utilization of the advantages of both, yielding a composite cathode material with high specific capacity, rate performance, and cycle stability. The sodium ferric sulfate composite material in this invention exhibits good uniformity, and when used as a cathode material in sodium-ion batteries, it contributes to the high specific capacity, rate performance, and cycle stability of the sodium-ion battery.

[0012] In some embodiments of the present invention, in the preparation method, the mixture II is cooled and then mixed with the raw materials for preparing the Prussian blue-like compound, and reacted to obtain the sodium ferric sulfate composite material. In the present invention, the raw materials containing sodium, iron, sulfur, and antioxidants are mixed with a eutectic solvent, heated, and then cooled before being mixed with the raw materials for preparing the Prussian blue-like compound to continue the reaction, thereby obtaining the sodium ferric sulfate composite material.

[0013] In this invention, a two-step liquid-phase method is used to prepare a composite cathode material of sodium ferric sulfate and Prussian blue-like material in a eutectic solvent system. The liquid-phase method allows for a thorough and uniform composite between the two materials, thereby enabling the use of the high-capacity and high-rate performance of the Prussian blue-like material to enhance the sodium storage performance of sodium ferric sulfate.

[0014] In some embodiments of the present invention, the temperature after cooling in the cooling step is 20-80°C.

[0015] In some embodiments of the present invention, after the mixed material II is cooled, the reaction time after mixing with the raw materials for preparing the Prussian blue-like compound is 2 to 40 h.

[0016] In some embodiments of the present invention, the heating temperature in the heating reaction step is 80 to 300 °C.

[0017] In some embodiments of the present invention, the heating time in the heating reaction step is 2 to 40 h.

[0018] In some embodiments of the present invention, the Prussian blue-like compound includes: Na x M y Fe(CN)6, where M is a transition metal element, 0 < x < 2; 0 < y < 1. Optionally, the M is selected from at least one of Fe, Co, Ni, Mn, Cu, and Zn.

[0019] In some embodiments of the present invention, the raw materials for preparing the Prussian blue-like compound include a transition metal salt and sodium ferrocyanide.

[0020] In some embodiments of the present invention, the transition metal salt includes at least one of nickel chloride, nickel nitrate, nickel sulfate, zinc chloride, zinc nitrate, zinc sulfate, zinc acetate, ferrous chloride, ferrous nitrate, ferrous sulfate, iron acetate, cobalt chloride, cobalt nitrate, cobalt sulfate, manganese chloride, manganese nitrate, manganese sulfate, manganese acetate, copper chloride, copper nitrate, copper sulfate, and their hydrates. That is, the transition metal salt includes at least one of nickel chloride, nickel nitrate, nickel sulfate, zinc chloride, zinc nitrate, zinc sulfate, zinc acetate, ferrous chloride, ferrous nitrate, ferrous sulfate, iron acetate, cobalt chloride, cobalt nitrate, cobalt sulfate, manganese chloride, manganese nitrate, manganese sulfate, manganese acetate, copper chloride, copper nitrate, copper sulfate, nickel chloride hydrate, nickel nitrate hydrate, nickel sulfate hydrate, zinc chloride hydrate, zinc nitrate hydrate, zinc sulfate hydrate, zinc acetate hydrate, ferrous chloride hydrate, ferrous nitrate hydrate, ferrous sulfate hydrate, iron acetate hydrate, cobalt chloride hydrate, cobalt nitrate hydrate, cobalt sulfate hydrate, manganese chloride hydrate, manganese nitrate hydrate, manganese sulfate hydrate, manganese acetate hydrate, copper chloride hydrate, copper nitrate hydrate, and copper sulfate hydrate.

[0021] In some embodiments of the present invention, the molar ratio of the transition metal salt to sodium ferrocyanide is 1:(0.4 - 1.6), and can be optionally 1:(1 - 1.2).

[0022] In some embodiments of the present invention, the deep eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor.

[0023] In some embodiments of the present invention, the hydrogen bond acceptor includes at least one of choline chloride, choline bromide, tetramethylammonium chloride, tetraethylammonium chloride, triethylmethylammonium chloride, tetrapropylammonium chloride, tetrabutylammonium chloride, benzyltrimethylammonium chloride, tetrapropylammonium bromide, tetrabutylammonium bromide, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, tetrabutylphosphine bromide, methyltriphenylphosphine bromide, betaine, or L-carnitine. Optionally, the hydrogen bond donor is choline chloride.

[0024] In some embodiments of the present invention, the hydrogen bond donor includes at least one selected from ethylene glycol, propylene glycol, butanediol, glycerol, sorbitol, xylitol, phenol, hydroquinone, resorcinol, 2-cresol, urea, thiourea, methylurea, 1,1-dimethylurea, 1,3-dimethylurea, succinic acid, ethanolamine, acetamide, benzamide, imidazole, or indole. Optionally, the hydrogen bond donor is ethylene glycol.

[0025] In some embodiments of the present invention, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:(0.5-5), such as 1:(1-5), specifically 1:2.

[0026] In some embodiments of the present invention, the sodium source includes at least one of sodium salt or sodium salt hydrate.

[0027] In some embodiments of the present invention, the sodium salt includes at least one selected from sodium sulfate, sodium bisulfate, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium oxalate, sodium acetate, or sodium citrate. That is, the sodium source includes at least one selected from sodium sulfate, sodium bisulfate, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium citrate, sodium sulfate hydrate, sodium bisulfate hydrate, sodium carbonate hydrate, sodium bicarbonate hydrate, sodium nitrate hydrate, sodium oxalate hydrate, sodium acetate hydrate, and sodium citrate hydrate. Optionally, the sodium source is sodium sulfate or sodium sulfate hydrate.

[0028] In some embodiments of the present invention, the iron source includes at least one of iron salts or hydrates of iron salts.

[0029] In some embodiments of the present invention, the iron salt includes at least one of ferrous sulfate, ferrous ammonium sulfate, ferrous nitrate, ferrous chloride, ferrous bromide, ferric sulfate, ferric ammonium sulfate, ferric nitrate, ferric chloride, or ferric ammonium citrate. That is, the iron source includes at least one of ferrous sulfate, ferrous ammonium sulfate, ferrous nitrate, ferrous chloride, ferrous bromide, ferric sulfate, ferric ammonium sulfate, ferric nitrate, ferric chloride, ferric ammonium citrate, hydrated ferrous sulfate, hydrated ferrous ammonium sulfate, hydrated ferrous nitrate, hydrated ferrous chloride, hydrated ferrous bromide, hydrated ferric sulfate, hydrated ferric ammonium sulfate, hydrated ferric nitrate, hydrated ferric chloride, or hydrated ferric ammonium citrate. Optionally, the iron source is ferrous sulfate or hydrated ferrous sulfate.

[0030] In some embodiments of the present invention, the sulfur source includes at least one of sulfate or sulfate hydrate.

[0031] In some embodiments of the present invention, the sulfate includes at least one of sodium sulfate, sodium bisulfate, ammonium bisulfate, ammonium sulfate, ferric sulfate, ferrous sulfate, ferrous ammonium sulfate, or ferric ammonium sulfate. That is, the sulfur source includes at least one of sodium sulfate, sodium bisulfate, ammonium bisulfate, ammonium sulfate, ferric sulfate, ferrous sulfate, ferrous ammonium sulfate, ferric ammonium sulfate, hydrated sodium sulfate, hydrated sodium bisulfate, hydrated ammonium bisulfate, hydrated ammonium sulfate, hydrated ferric sulfate, hydrated ferrous ammonium sulfate, or hydrated ferric ammonium sulfate.

[0032] In some embodiments of the present invention, at least one of the iron source or sodium source serves as the sulfur source. Specifically, sodium sulfate can serve as both a sodium source and a sulfur source, and ferrous sulfate can serve as both an iron source and a sulfur source.

[0033] In some embodiments of the present invention, the antioxidant includes at least one selected from ascorbic acid, D-isoascorbic acid, citric acid, oxalic acid, sodium sulfite, or propyl gallate. Optionally, the antioxidant is ascorbic acid.

[0034] In some embodiments of the present invention, the preparation method includes the following steps:

[0035] S1, take hydrogen bond acceptor and hydrogen bond donor, stir at 60-100℃ to form a transparent liquid, and obtain a eutectic solvent;

[0036] S2, mix sodium source, sulfur source, iron source, antioxidant and eutectic solvent to obtain mixture I, heat to 80-300℃ and react for 2-40h to obtain mixture II containing sodium ferric sulfate;

[0037] S3. After the mixture II has cooled down, add the transition metal salt and sodium ferrocyanide, react for 2-40 hours, and then separate to obtain the sodium ferric sulfate composite material.

[0038] In some embodiments of the present invention, the reaction temperature in step S2 is 100–240°C.

[0039] In some embodiments of the present invention, the reaction time in step S2 is 4 to 24 hours.

[0040] In some embodiments of the present invention, the temperature after cooling in step S3 is 20-80°C, such as 20-50°C.

[0041] In some embodiments of the present invention, the reaction time in step S3 is 4 to 24 hours.

[0042] In some embodiments of the present invention, the molar ratio of the transition metal salt to sodium ions in the sodium source is (0.02-2):1, or optionally (0.1-0.5):1.

[0043] In some embodiments of the present invention, in step S3, the separated solid is washed and dried to obtain the sodium ferric sulfate composite material. In some embodiments of the present invention, the washing agent used includes, but is not limited to, ethanol. The number of washing cycles is not limited; it may be one or multiple washing cycles. In some embodiments of the present invention, the drying temperature is 60–150°C, and the drying time is 12–24 hours.

[0044] The mixture I of the present invention contains sodium ions, iron ions, sulfate ions and an antioxidant. In some embodiments of the present invention, the molar ratio of sodium, iron, sulfur and antioxidant in the mixture I is 1:(0.2-2.5):(0.8-3.0):(0.002-2.0), or optionally 1:(0.5-1.5):(1.0-2.0):(0.005-1.0).

[0045] In some embodiments of the present invention, the concentration of sodium source in the mixture I is 0.05 to 4.0 mol / L, such as 0.5 mol / L.

[0046] Through the above embodiments, eutectic solvents are a special type of liquid composed of hydrogen bond donors and acceptors in a certain stoichiometric ratio, combined through strong hydrogen bonds, weak electrostatics, and van der Waals forces. They possess advantages such as easy synthesis, low cost, environmental friendliness, low volatility, strong solubility, and biodegradability, making them a new generation of green solvents applicable to the field of nanomaterial preparation. The preparation method of the sodium ferric sulfate composite material in this invention involves first dissolving sodium, iron, sulfur salts, and antioxidants in a eutectic solvent system to prepare sodium ferric sulfate. Then, transition metal salts and sodium ferrocyanide are added to this solution, and the reaction continues to synthesize the sodium ferric sulfate composite cathode material. The liquid-phase method based on the eutectic solvent system allows for the uniform composite of sodium ferric sulfate and Prussian blue-like materials, thereby fully utilizing the high capacity and rate performance of the Prussian blue-like material to effectively improve the sodium storage performance of sodium ferric sulfate.

[0047] In a second aspect, this invention provides a sodium ferric sulfate composite material, prepared using the aforementioned method for preparing sodium ferric sulfate composite materials. The sodium ferric sulfate composite material of this invention exhibits good uniformity, and when used as a cathode material in sodium-ion batteries, it contributes to the high specific capacity, rate performance, and cycle stability of the sodium-ion battery.

[0048] In some embodiments of the present invention, the particle size of the sodium ferric sulfate composite material is 0.2 to 20 μm, and may be 1 to 10 μm.

[0049] In a third aspect, the present invention provides a positive electrode material comprising the above-mentioned sodium ferric sulfate composite material.

[0050] In a fourth aspect, the present invention provides a positive electrode comprising the above-described positive electrode material or the above-described sodium ferric sulfate composite material.

[0051] In some embodiments of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer.

[0052] In some embodiments of the present invention, the positive electrode active material layer comprises the sodium ferric sulfate composite material.

[0053] In some embodiments of the present invention, the positive electrode current collector includes, but is not limited to, one or more of aluminum, iron, tin, zinc, nickel, titanium, manganese, and carbon. Optionally, the positive electrode current collector is selected from at least one of aluminum foil, carbon-coated aluminum foil, iron foil, tin foil, zinc foil, nickel foil, titanium foil, and manganese foil. For example, the positive electrode current collector may be carbon-coated aluminum foil.

[0054] In a fifth aspect, the present invention provides a secondary battery comprising the above-described positive electrode or the above-described positive electrode material or the above-described sodium iron sulfate composite material.

[0055] In some embodiments of the present invention, the secondary material includes sodium-ion batteries.

[0056] In some embodiments of the present invention, the secondary material further includes a negative electrode, an electrolyte, and a separator.

[0057] In some embodiments of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer.

[0058] In some embodiments of the present invention, the negative electrode current collector includes, but is not limited to, one or more of aluminum, copper, titanium, carbon, and nickel. Optionally, the negative electrode current collector comprises a metal foil, such as one or more of aluminum foil, copper foil, titanium foil, stainless steel, or nickel foil. For example, the negative electrode current collector may be aluminum foil.

[0059] In some embodiments of the present invention, the negative electrode active material layer comprises a negative electrode active material.

[0060] In some embodiments of the present invention, the negative electrode active material includes, but is not limited to, one or more of conversion and alloying materials, organic materials, and carbon-based materials. For example, the negative electrode active material may be hard carbon.

[0061] In some embodiments of the present invention, the electrolyte includes an electrolyte and an electrolyte solvent.

[0062] In some embodiments of the present invention, the electrolyte comprises a sodium salt electrolyte. Optionally, the electrolyte is selected from one or more of the following: sodium trifluoromethanesulfonate (NaCF3SO3), sodium bis(trifluoromethanesulfonyl)imide [NaN(CF3SO2)2] and its derivatives, sodium perfluoroalkyl phosphate [NaPF3(C2F5)3], sodium tetrafluorooxalate phosphate [NaPF4(C2O4)], sodium bis(oxalate borate) [NaB(C2O4)2], sodium tri(catechol) phosphate (NTBP), sodium sulfonated polysulfonamide, sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluoroarsenate (NaAsF6), sodium nitrate (NaNO3), sodium carbonate (NaCO3), and sodium chloride (NaCl).

[0063] In some embodiments of the present invention, the concentration of the electrolyte in the electrolyte solution is 0.05 to 20 mol / L, such as 0.1 to 10 mol / L, and even more preferably 1 mol / L.

[0064] In some embodiments of the present invention, the electrolyte solvent includes, but is not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl formate (MF), methyl acetate (MA), N,N-dimethylacetamide (DMA), fluoroethylene carbonate (FEC), methyl propionate (MP), ethyl propionate (EP), ethyl acetate (EA), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF), 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane (4MeDOL), dimethoxymethane (DMM), 1,2-dimethoxypropane (DMP), triethylene glycol dimethyl ether (TEGDME), dimethyl sulfone (MSM), diethylene glycol dimethyl ether (DME), vinyl sulfite (ES), propylene sulfite (PS), dimethyl sulfite (DMS), and diethyl sulfite. (DES), crown ether (12-crown-4), 1-ethyl-3-methylimidazolium-hexafluorophosphate, 1-ethyl-3-methylimidazolium-tetrafluoroborate, 1-ethyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide, 1-propyl-3-methylimidazolium-hexafluorophosphate, 1-propyl-3-methylimidazolium-tetrafluoroborate, 1-propyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide, 1-butyl-1-methylimidazolium-hexafluorophosphate, 1-butyl-1-methylimidazolium-tetrafluorophosphate The electrolyte is composed of one or more organic solvents such as esters, sulfones, ethers, nitriles, or ionic liquids, including borates, 1-butyl-1-methylimidazolium-bis(trifluoromethanesulfonyl)imide salt, N-butyl-N-methylpyrrolidine-bis(trifluoromethanesulfonyl)imide salt, 1-butyl-1-methylpyrrolidine-bis(trifluoromethanesulfonyl)imide salt, N-methyl-N-propylpyrrolidine-bis(trifluoromethanesulfonyl)imide salt, N-methyl,propylpiperidine-bis(trifluoromethanesulfonyl)imide salt, and N-methyl,butylpiperidine-bis(trifluoromethanesulfonyl)imide salt. Optionally, the electrolyte solvent includes propylene carbonate and fluoroethylene carbonate. Further optionally, the volume ratio of propylene carbonate to fluoroethylene carbonate is 95:5.

[0065] In some embodiments of the present invention, the separator includes, but is not limited to, one or more of insulating porous polymer films or inorganic porous films. Optionally, the separator may be one or more of porous polypropylene films, porous polyethylene films, porous composite polymer films, glass fiber paper, and porous ceramic separators. Specifically, the separator may be glass fiber paper.

[0066] In a sixth aspect, the present invention provides a method for preparing a secondary battery, comprising the following steps: taking a negative electrode, an electrolyte, a separator, and a positive electrode, assembling them, and obtaining the secondary battery.

[0067] In some embodiments of the present invention, the preparation method includes the following steps: taking a negative electrode, an electrolyte, a separator, a positive electrode, and a casing, and assembling them to obtain the secondary battery. Optionally, the casing can be used for battery encapsulation.

[0068] In some embodiments of the present invention, the preparation method further includes a step of preparing a positive electrode, specifically comprising: taking a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder, adding a solvent to mix them to obtain a positive electrode slurry, coating it onto the surface of a positive electrode current collector, drying it, and forming a positive electrode active material layer on the surface of the positive electrode current collector to obtain the positive electrode. Optionally, the positive electrode current collector needs to be cleaned before coating with the positive electrode slurry.

[0069] In some embodiments of the present invention, the preparation method further includes a step of preparing a negative electrode, specifically comprising: taking a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, adding a solvent to mix them to obtain a negative electrode slurry, coating it onto the surface of a negative electrode current collector, drying it, and forming a negative electrode active material layer on the surface of the negative electrode current collector to obtain the negative electrode. Optionally, the negative electrode current collector needs to be cleaned before coating with the negative electrode slurry.

[0070] In some embodiments of the present invention, the preparation method further includes preparing an electrolyte, specifically including: mixing an electrolyte and an electrolyte solvent to obtain the electrolyte. Attached Figure Description

[0071] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0072] Figure 1 Photographs of the eutectic solvent used in Example 1 of this invention;

[0073] Figure 2 The image shows the XRD pattern of the sodium ferric sulfate composite material prepared in Example 1 of this invention.

[0074] Figure 3 This is a SEM image of the sodium ferric sulfate composite material prepared in Example 1 of the present invention. Detailed Implementation

[0075] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0076] Unless otherwise specified, the experimental methods described in the following examples are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used are all commercially available from the conventional market unless otherwise specified.

[0077] Example 1

[0078] This embodiment discloses a sodium ferric sulfate composite material. Choline chloride is used as the hydrogen bond acceptor, ethylene glycol as the hydrogen bond donor, sodium sulfate (Na₂SO₄) as both sodium and sulfate salts, ferrous sulfate heptahydrate (FeSO₄·7H₂O) as both iron and sulfate salts, ascorbic acid as the antioxidant, and manganese nitrate tetrahydrate (Mn(NO₃)₂·4H₂O) as the transition metal salt to prepare the sodium ferric sulfate composite material. Specifically, the preparation process of the sodium ferric sulfate composite material includes the following steps:

[0079] (I) Weigh 2.5 mol of choline chloride and 5 mol of ethylene glycol, stir at 80°C to form a homogeneous, transparent liquid, then cool to room temperature to obtain a eutectic solvent (e.g. Figure 1 (As shown).

[0080] (II) Add 0.05 mol Na2SO4, 0.1 mol FeSO4·7H2O and 0.001 mol ascorbic acid to 100 mL of the eutectic solvent in step (I), stir thoroughly to dissolve and form a mixed solution, and heat to 120 °C for 6 h.

[0081] (III) After cooling to room temperature, add 0.02 mol Mn(NO3)2·4H2O, stir to dissolve, then add 0.02 mol sodium ferrocyanide, continue stirring at room temperature for 12 h, filter, wash the solid filter residue with ethanol several times, and dry in an 80℃ forced-air drying oven for 12 h to obtain sodium ferric sulfate composite material. Figure 2 and Figure 3 (XRD and SEM images of the sodium ferric sulfate composite material prepared in this embodiment are shown respectively).

[0082] This embodiment also discloses a positive electrode material, including the sodium ferric sulfate composite material of this embodiment.

[0083] This embodiment also discloses a battery positive electrode, including the sodium iron sulfate composite material of this embodiment.

[0084] Examples 2-5

[0085] Examples 2-5 disclose a series of sodium ferric sulfate composite materials, which differ from Example 1 in that the molar ratio of choline chloride to ethylene glycol in the eutectic solvent is different, while the other experimental parameters and procedures are the same as in Example 1. The molar ratio of choline chloride to ethylene glycol in the eutectic solvent in Examples 2-5 is detailed in Table 1 below.

[0086] Examples 2 to 5 also disclose a series of battery positive electrodes, which differ from Example 1 only in that the battery positive electrodes of Examples 2 to 5 respectively include the sodium iron sulfate composite material prepared in Examples 2 to 5.

[0087] Examples 6-25

[0088] Examples 6-25 disclose a series of sodium ferric sulfate composite materials, which differ from Example 1 in that the hydrogen bond donors in the eutectic solvent are different, while the other experimental parameters and procedures are the same as in Example 1. The hydrogen bond donors in Examples 6-25 are detailed in Table 2 below.

[0089] Examples 6 to 25 also disclose a series of battery positive electrodes, which differ from Example 1 only in that the battery positive electrodes of Examples 6 to 25 respectively include the sodium iron sulfate composite material prepared in Examples 6 to 25.

[0090] Examples 26-27

[0091] Examples 26 and 27 disclose a series of sodium ferric sulfate composite materials, which differ from Example 1 in that the volume of the eutectic solvent used in step (II) is different, while the other experimental parameters and steps are the same as in Example 1.

[0092] The volumes of the eutectic solvents in Examples 26 and 27 are detailed in Table 3 below.

[0093] Examples 26-27 also disclose a series of battery positive electrodes, which differ from Example 1 only in that the battery positive electrodes of Examples 26-27 respectively correspond to the sodium iron sulfate composite material prepared in Examples 26-27.

[0094] Examples 28-32

[0095] Examples 28-32 disclose a series of sodium ferric sulfate composite materials, which differ from Example 1 in that the heat treatment reaction temperature in step (II) is different, while the other experimental parameters and steps are the same as in Example 1. The heat treatment reaction temperatures in Examples 28-32 are detailed in Table 4 below.

[0096] Examples 28 to 32 also disclose a series of battery positive electrodes, which differ from Example 1 only in that the battery positive electrodes of Examples 28 to 32 respectively include the sodium iron sulfate composite material prepared in Examples 28 to 32.

[0097] Examples 33-45

[0098] Examples 33-45 disclose a series of sodium ferric sulfate composite materials, which differ from Example 1 in that the sodium salt and / or iron salt and / or sulfate used in step (II) are different, while the remaining experimental parameters and steps are the same as in Example 1. Information on the sodium salt, iron salt, and sulfate used in Examples 33-45 is detailed in Table 5 below.

[0099] Examples 33 to 45 also disclose a series of battery positive electrodes, which differ from Example 1 only in that the battery positive electrodes of Examples 33 to 45 respectively include the sodium iron sulfate composite material prepared in Examples 33 to 45.

[0100] Examples 46-50

[0101] Examples 46-50 disclose a series of sodium ferric sulfate composite materials, which differ from Example 1 in that the type of antioxidant used in step (II) is different, while the remaining experimental parameters and steps are the same as in Example 1. The types of antioxidants used in Examples 46-50 are detailed in Table 6 below.

[0102] Examples 46-50 also disclose a series of battery positive electrodes, which differ from Example 1 only in that the battery positive electrodes of Examples 46-50 respectively include the sodium iron sulfate composite material prepared in Examples 46-50.

[0103] Examples 51-70

[0104] Examples 51-70 disclose a series of sodium ferric sulfate composite materials, which differ from Example 1 in that the type of transition metal salt used in step (III) is different, while the remaining experimental parameters and steps are the same as in Example 1. The antioxidants used in Examples 51-70 are detailed in Table 7 below.

[0105] Examples 51 to 70 also disclose a series of battery positive electrodes, which differ from Example 1 only in that the battery positive electrodes of Examples 51 to 70 respectively include the sodium iron sulfate composite material prepared in Examples 51 to 70.

[0106] Examples 71-140

[0107] Examples 71-140 also disclose a series of sodium-ion half-cells, the preparation process of which specifically includes:

[0108] Positive electrode: The sodium iron sulfate composite material prepared in Examples 1 to 70 is mixed with carbon black and polyvinylidene fluoride (mass ratio 7:2:1), and N-methylpyrrolidone is added to form the positive electrode active material of the half cell in Examples 71 to 140. The positive electrode current collector is coated with carbon aluminum foil (16 μm thick) and cleaned. Then, the positive electrode active material is uniformly coated on the surface of the positive electrode current collector (coating thickness 200 μm). After the positive electrode active material layer is completely dry, it is cut to obtain the battery positive electrode of the required size.

[0109] Counter electrode: Sodium metal sheet (thickness 400-500 μm);

[0110] Electrolyte: 1 mol / L NaClO4 / PC-FEC (95:5, v / v);

[0111] Assembly (assembling a half-cell according to the sodium-ion battery assembly method) includes: assembling the positive electrode and the counter electrode, and injecting electrolyte to obtain a half-cell. The half-cells obtained in Examples 71 to 140 are numbered B1 to B70 respectively.

[0112] Examples 141-210

[0113] Examples 141-210 also disclose a series of sodium-ion full batteries, the preparation process of which specifically includes:

[0114] Positive electrode: The sodium iron sulfate composite material prepared in Examples 1-70 is mixed with carbon black and polyvinylidene fluoride (mass ratio 7:2:1), and N-methylpyrrolidone is added to form the positive electrode active material of the full cell in Examples 141-210. The positive electrode current collector is coated with carbon aluminum foil (16 μm thick) and cleaned. Then, the positive electrode active material is uniformly coated on the surface of the positive electrode current collector (coating thickness 200 μm). After the positive electrode active material layer is completely dry, it is cut to obtain the battery positive electrode of the required size.

[0115] The electrolyte was 1 mol / L NaClO4 / PC-FEC (95:5, v / v);

[0116] The diaphragm is made of fiberglass paper (0.47mm thick); cut the diaphragm to the required size and clean it thoroughly;

[0117] The negative electrode is prepared by mixing hard carbon, conductive carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. Then, N-methylpyrrolidone (NMP) solvent is added and stirred thoroughly to obtain a slurry. The slurry is then uniformly coated on the surface of aluminum foil (16 μm thick) (coating thickness 300 μm). After that, it is placed in a vacuum oven for drying at 80℃ for 48 hours.

[0118] Assembly includes assembling the battery using the negative electrode, electrolyte, separator, and positive electrode to obtain a sodium-ion full cell. The sodium-ion full cells obtained in Examples 141 to 210 are numbered C1 to C70 respectively.

[0119] Comparative Example 1

[0120] This comparative example discloses a sodium ferric sulfate cathode material prepared based on the eutectic solvent method, the specific preparation process of which includes:

[0121] Weigh 2.5 mol of choline chloride and 5 mol of ethylene glycol, stir at 80 °C to form a homogeneous, transparent liquid, and then cool to room temperature to obtain a eutectic solvent. Add 0.05 mol of Na₂SO₄, 0.1 mol of FeSO₄·7H₂O, and 0.001 mol of ascorbic acid to 100 mL of the eutectic solvent, stir thoroughly to dissolve and form a mixed solution, and heat to 120 °C for 6 h. Wash the solid filter residue several times with ethanol and dry in an 80 °C forced-air drying oven for 12 h to obtain sodium ferric sulfate cathode material.

[0122] This comparative example also discloses a sodium-ion half-cell, which differs from Examples 71-140 only in that the sodium iron sulfate cathode material of this comparative example is used instead of the sodium iron sulfate composite material prepared in Examples 1-70. The resulting half-cell is D1.

[0123] This comparative example also discloses a sodium-ion full cell, which differs from Examples 141-210 only in that the sodium iron sulfate cathode material of this comparative example is used instead of the sodium iron sulfate composite material prepared in Examples 1-70. The resulting full cell is E1.

[0124] Comparative Example 2

[0125] This comparative example discloses a sodium ferric sulfate cathode material prepared based on a mixed compound. The preparation process specifically includes: weighing 0.05 mol Na₂SO₄, 0.1 mol FeSO₄·7H₂O, and 0.001 mol ascorbic acid, ball milling for 8 h, vacuum drying, and calcining at 350℃ for 24 h in an argon atmosphere to obtain sodium ferric sulfate material. Simultaneously, weighing 0.02 mol Mn(NO₃)₂·4H₂O, dissolving it in 100 mL of water, adding 0.02 mol sodium ferrocyanide, continuing stirring at room temperature for 12 h, filtering, washing the solid filter residue multiple times with ethanol, and drying in an 80℃ forced-air drying oven for 12 h to obtain a Prussian blue-like material. Finally, grinding and mixing the obtained sodium ferric sulfate and the Prussian blue-like material yields the final product.

[0126] This comparative example also discloses a sodium-ion half-cell, which differs from Examples 71-140 only in that the sodium iron sulfate cathode material of this comparative example is used instead of the sodium iron sulfate composite material prepared in Examples 1-70. The resulting half-cell is D2.

[0127] This comparative example also discloses a sodium-ion full cell, which differs from Examples 141-210 only in that the sodium iron sulfate cathode material of this comparative example is used instead of the sodium iron sulfate composite material prepared in Examples 1-70. The resulting full cell is E2.

[0128] Test case

[0129] This experimental example tested the performance of half-cells and full-cells in each embodiment and comparative example, specifically including:

[0130] 1. Performance tests were conducted on the sodium-ion half-cells of Examples 71-140 and Comparative Examples 1-2, including: specific capacity (mAh / g) at 200 mA / g and 500 mA / g, and capacity retention after 500 cycles at 500 mA / g. It was found that the specific capacity at 200 mA / g was 96-127 mAh / g, the specific capacity at 500 mA / g was 90-122 mAh / g, and the capacity retention after 500 cycles at 500 mA / g was 80.3-92%. The sodium iron sulfate composite material prepared in this invention exhibits excellent capacity, rate performance, and cycle stability in sodium-ion half-cells.

[0131] The specific test results are as follows:

[0132] Table 1

[0133]

[0134] Table 2

[0135]

[0136]

[0137] Table 3

[0138]

[0139] Table 4

[0140]

[0141] Table 5

[0142]

[0143]

[0144]

[0145] Table 6

[0146]

[0147]

[0148] Table 7

[0149]

[0150]

[0151] 2. Performance tests were conducted on the sodium-ion full batteries of Examples 141-210 and Comparative Examples 1-2, including: specific capacity (mAh / g) at 200 mA / g and 500 mA / g, and capacity retention after 300 cycles at 500 mA / g. It was found that the specific capacity at 200 mA / g was 92-121 mAh / g, the specific capacity at 500 mA / g was 84-116 mAh / g, and the capacity retention after 300 cycles at 500 mA / g was 81.5-92.5%. The sodium iron sulfate composite material prepared in this invention exhibits excellent capacity, rate performance, and cycle stability in sodium-ion full batteries.

[0152] The specific test results are as follows:

[0153] Table 8

[0154]

[0155] Table 9

[0156]

[0157]

[0158] Table 10

[0159]

[0160] Table 11

[0161]

[0162] Table 12

[0163]

[0164]

[0165]

[0166] Table 13

[0167]

[0168]

[0169] Table 14

[0170]

[0171]

[0172] This invention prepares a composite material containing sodium ferric sulfate and Prussian blue-like material using a two-step liquid-phase method in a eutectic solvent system. This method can achieve uniform compounding between sodium ferric sulfate and Prussian blue-like material, while avoiding the problem of sodium ferric sulfate being easily degraded by simply mixing with Prussian blue-like material prepared by conventional aqueous solution system (which has a high water content of crystallization). This fully utilizes the high capacity and rate performance of the Prussian blue-like material to effectively improve the sodium storage performance of sodium ferric sulfate.

[0173] Unless otherwise specified, the term "about" in this invention actually means that the allowable error is within ±2%, for example, about 100 is actually 100 ± 2% × 100. The terms "room temperature" and "room temperature" in this invention, unless otherwise specified, are approximately 20 to 30°C. The phrase "between..." in this invention includes the number itself; for example, "between 2 and 3" includes the endpoints 2 and 3.

[0174] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for preparing a sodium ferric sulfate composite material, characterized in that, The process includes the following steps: mixing sodium ferric sulfate preparation raw materials containing sodium source, iron source, sulfur source and antioxidant with a eutectic solvent to obtain mixture I, heating and reacting to obtain mixture II containing sodium ferric sulfate, cooling to 20~80℃, and then mixing with the preparation raw materials of Prussian blue-like compound and reacting to obtain the sodium ferric sulfate composite material. The raw materials for preparing the Prussian blue-like compound include transition metal salts and sodium ferrocyanide; the transition metal salts include at least one of manganese chloride, manganese nitrate, manganese sulfate, manganese acetate, and their hydrates.

2. The method for preparing the sodium ferric sulfate composite material according to claim 1, characterized in that, After the mixture II is cooled, the reaction time after mixing with the raw materials for preparing the Prussian blue-like compound is 2 to 40 hours.

3. The method for preparing the sodium ferric sulfate composite material according to claim 1, characterized in that, The heating temperature in the heating reaction step is 80~300℃; or / and, the heating time in the heating reaction step is 2~40h; or / and, in the mixture I, the molar ratio of sodium, iron, sulfur to antioxidant is 1:(0.2~2.5):(0.8~3.0):(0.002~2.0); or / and, in the mixture I, the concentration of sodium source is 0.05~4.0mol / L.

4. The method for preparing the sodium ferric sulfate composite material according to claim 1, characterized in that, The preparation method includes the following steps: S1, take hydrogen bond acceptor and hydrogen bond donor, stir at 60~100℃ to form a transparent liquid, and obtain a eutectic solvent; S2, mix sodium source, sulfur source, iron source, antioxidant and eutectic solvent to obtain mixture I, heat to 80~300℃ and react for 2~40h to obtain mixture II containing sodium ferric sulfate; S3. After the mixture II has cooled down, add the transition metal salt and sodium ferrocyanide, react for 2-40 hours, separate, and obtain the sodium ferric sulfate composite material.

5. The method for preparing the sodium ferric sulfate composite material according to claim 1, characterized in that, The molar ratio of the transition metal salt to sodium ferrocyanide is 1:(0.4~1.6); and / or, the molar ratio of the transition metal salt to sodium ions in the sodium source is (0.02~2):

1.

6. The method for preparing the sodium ferric sulfate composite material according to claim 1, characterized in that, The eutectic solvent includes hydrogen bond acceptors and hydrogen bond donors.

7. The method for preparing the sodium ferric sulfate composite material according to claim 6, characterized in that, The hydrogen bond acceptor includes at least one of choline chloride, choline bromide, tetramethylammonium chloride, tetraethylammonium chloride, triethylmethylammonium chloride, tetrapropylammonium chloride, tetrabutylammonium chloride, benzyltrimethylammonium chloride, tetrapropylammonium bromide, tetrabutylammonium bromide, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, tetrabutylphosphine bromide, methyltriphenylphosphine bromide, betaine, or L-carnitine.

8. The method for preparing the sodium ferric sulfate composite material according to claim 6, characterized in that, The hydrogen bond donor includes at least one of ethylene glycol, propylene glycol, butanediol, glycerol, sorbitol, xylitol, phenol, hydroquinone, resorcinol, 2-cresol, urea, thiourea, methylurea, 1,1-dimethylurea, 1,3-dimethylurea, succinic acid, ethanolamine, acetamide, benzamide, imidazole, or indole.

9. The method for preparing the sodium ferric sulfate composite material according to claim 6, characterized in that, The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:(0.5~5).

10. The method for preparing the sodium ferric sulfate composite material according to claim 1, characterized in that, The sodium source includes at least one of sodium salt or sodium salt hydrate; and / or the iron source includes at least one of iron salt or iron salt hydrate; and / or the sulfur source includes at least one of sulfate or sulfate hydrate; and / or the antioxidant includes at least one of ascorbic acid, D-isoascorbic acid, citric acid, oxalic acid, sodium sulfite, or propyl gallate.

11. The method for preparing the sodium ferric sulfate composite material according to claim 10, characterized in that, The sodium salt includes at least one of sodium sulfate, sodium bisulfate, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium oxalate, sodium acetate, or sodium citrate; and / or the iron salt includes at least one of ferrous sulfate, ferrous ammonium sulfate, ferrous nitrate, ferrous chloride, ferrous bromide, ferric sulfate, ferric ammonium sulfate, ferric nitrate, ferric chloride, or ferric ammonium citrate; and / or the sulfate includes at least one of sodium sulfate, sodium bisulfate, ammonium bisulfate, ammonium sulfate, ferric sulfate, ferrous ammonium sulfate, or ferric ammonium sulfate.

12. A sodium ferric sulfate composite material, characterized in that, It was prepared by the method for preparing sodium ferric sulfate composite material according to any one of claims 1 to 11.

13. A positive electrode material, characterized in that, The composite material containing sodium ferric sulfate prepared by the preparation method according to any one of claims 1 to 11 or the composite material containing sodium ferric sulfate according to claim 12.

14. A positive electrode, characterized in that, The composite material containing sodium ferric sulfate prepared by the preparation method according to any one of claims 1 to 11, or the composite material containing sodium ferric sulfate according to claim 12, or the cathode material according to claim 13.

15. A secondary battery, characterized in that, The invention includes the sodium ferric sulfate composite material prepared by the preparation method according to any one of claims 1 to 11, the sodium ferric sulfate composite material according to claim 12, the positive electrode material according to claim 13, or the positive electrode according to claim 14.

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