Comprehensive preparation method of sodium ion battery positive electrode material

Abstract

The invention provides a comprehensive preparation method of a sodium ion battery positive electrode material, which comprises the following steps: adjusting the pH value of an iron-phosphorus-sodium-sulfur mixed solution of which the pH value is less than or equal to 2.8 to 2.8-4.5 to obtain a solid-liquid mixture consisting of FexHyOz (POa) b.mH2O precursor precipitate and a sodium sulfate mother solution; and carrying out solid-liquid separation on the solid-liquid mixture to obtain a FexHyOz (POa) b.mH2O precursor precipitate for preparing ferric sodium pyrophosphate and a sodium sulfate mother solution for preparing sodium ferric sulfate. According to the comprehensive preparation method provided by the invention, all-component conversion of four elements of Fe, P, Na and S can be realized, ferric pyrophosphate and sodium ferric sulfate can be prepared from an iron-phosphorus-sodium-sulfur mixed solution at the same time, and the preparation cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of sodium battery technology, and relates to a cathode material, and more particularly to a comprehensive preparation method for a sodium-ion battery cathode material. Background Technology

[0002] Sodium-ion batteries are considered a potential alternative to lithium-ion batteries due to their abundant resources and low cost. Among cathode materials, sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7, NFPP) and sodium iron sulfate (Na2Fe(SO4)2, NFS) have become current research hotspots due to their high operating voltage and good cycle stability.

[0003] Conventional methods for preparing NFPP use FeSO4, Fe2O3, FeC2O4, or ferric phosphate as the iron source, mixed with phosphorus sources such as NaH2PO4 and (NH4)2HPO4 via solid-phase ball milling, followed by calcination at 600℃–700℃ in an inert atmosphere. However, this method requires the additional introduction of expensive sodium sources such as sodium dihydrogen phosphate and disodium hydrogen phosphate. Furthermore, when using FeSO4 as the iron source, sulfur is not fully utilized, resulting in high production costs. Traditional methods for NFS use FeSO4·7H2O and Na2SO4 as raw materials, synthesized through a solid-phase composite high-temperature calcination reaction. However, this requires high-purity anhydrous sodium sulfate, which needs to be prepared separately, leading to high energy consumption. Existing NFPP preparation technologies also fail to, and do not require, the simultaneous conversion of sulfate ions in FeSO4 into cathode material components. When using ferric phosphate as the iron-phosphorus source, a large amount of alkaline solution is needed to adjust the pH during the precipitation method for preparing the ferric phosphate precursor. The byproducts of sulfur and sodium are wasteful, and the treatment of the sodium sulfate wastewater also adds to the cost.

[0004] In summary, existing technologies cannot achieve the co-production of NFPP and NFS in the same system, and also suffer from problems such as sulfur waste, lengthy process chains, and high pollution risks. Therefore, there is a need to provide a comprehensive preparation method for sodium-ion battery cathode materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a comprehensive preparation method for sodium-ion battery cathode materials. The comprehensive preparation method provided by the present invention can achieve the full component conversion of four elements: Fe, P, Na, and S. It can also simultaneously prepare sodium iron pyrophosphate and sodium iron sulfate from a mixture of iron, phosphorus, sodium, and sulfur, thereby reducing preparation costs.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a comprehensive preparation method for a sodium-ion battery cathode material, the comprehensive preparation method comprising the following steps:

[0008] Adjust the pH of the iron-phosphorus-sodium-sulfur mixed solution (pH ≤ 2.8) to 2.8–4.5 to obtain Fe. x H y O z (PO a ) b A solid-liquid mixture consisting of the mH2O precursor precipitate and the sodium sulfate mother liquor;

[0009] The solid-liquid mixture was subjected to solid-liquid separation to obtain Fe. x H y O z (PO a ) b ·mH2O precursor precipitate and sodium sulfate mother liquor;

[0010] The Fe x H y O z (PO a ) b The mH2O precursor precipitate is used to prepare sodium iron pyrophosphate; the sodium sulfate mother liquor is used to prepare sodium iron sulfate.

[0011] Existing technologies for preparing NFPP or NFS can only utilize iron from the iron source, and sulfate ions are often discharged as Na2SO4 waste liquid. The process chain is lengthy and energy-intensive. In the NFPP preparation process, a precursor needs to be prepared first, and then mixed with sodium and phosphorus sources for calcination. In the NFS preparation process, Na2SO4 needs to be prepared first, and then mixed with FeSO4 and carbon sources for calcination. The NFPP and NFS preparation processes are independent, and it is impossible to achieve simultaneous production of both products in a single feed, which increases the cost when scaling up.

[0012] Therefore, existing technologies suffer from three major contradictions: the inability to resolve sulfur waste, the lengthy process chain, and the inefficiency of step-by-step processes. These contradictions result in high production costs for sodium-ion battery cathode materials, hindering the industrialization process.

[0013] The preparation method provided by this invention adjusts the pH value of the iron-phosphorus-sodium-sulfur mixed solution to 2.8-4.5 (for example, it can be 2.8, 3, 3.5, 4 or 4.5, etc.). Within this pH range, the composite precipitation of iron and phosphate is the main reaction, which can completely precipitate phosphate. If the pH value is higher than 4.5, there will be a reaction of iron phosphate to iron hydroxide, which will inevitably increase the phosphorus content in the liquid of the solid-liquid mixture, which is not conducive to the subsequent preparation of sodium ferric sulfate from sodium sulfate mother liquor.

[0014] This invention, after obtaining a solid-liquid mixture, can obtain Fe for the preparation of sodium ferric pyrophosphate through solid-liquid separation. x H y O z (PO a )b The method provides a precursor of mH2O and a mother liquor of sodium sulfate for preparing sodium ferric sulfate. In other words, the comprehensive preparation method provided by this invention can simultaneously produce Fe through a single feeding of an iron-phosphorus-sodium-sulfur mixed solution. x H y O z (PO a ) b The preparation of mH2O precursor and sodium sulfate mother liquor achieves zero-waste, low-cost, and integrated production, solving the technical problems of sulfur waste, high pollution, and long process chain in existing technologies.

[0015] In some embodiments, the iron-phosphorus-sodium-sulfur mixture is obtained by mixing a first iron source, a first phosphorus source, and an alkaline sodium salt.

[0016] The pH value of the iron-phosphorus-sodium-sulfur mixture is <2.8, which is achieved by controlling the amount of alkaline sodium salt added.

[0017] In some embodiments, the iron-phosphorus molar ratio in the iron-phosphorus-sodium-sulfur mixture is 1:0.5 to 1:1, for example, it can be 1:0.5, 1:0.6, 1:0.8, 1:0.9 or 1:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] The compounds used in this invention may contain water of crystallization, as long as they meet the process requirements of this invention.

[0019] In some embodiments, the first iron source comprises ferric sulfate and / or ferrous sulfate.

[0020] In some embodiments, the first phosphorus source includes any one or a combination of at least two of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, pyrophosphate, sodium pyrophosphate, or sodium pyrophosphate acid salts. Typical but non-limiting combinations include combinations of phosphoric acid and sodium phosphate, combinations of sodium dihydrogen phosphate and sodium phosphate, combinations of pyrophosphate and sodium pyrophosphate, combinations of sodium phosphate and sodium pyrophosphate, or combinations of phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, pyrophosphate, sodium pyrophosphate, and sodium pyrophosphate acid salts.

[0021] In some embodiments, the alkaline sodium salt includes any one or a combination of at least two of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, or sodium peroxide. Typical but non-limiting combinations include combinations of sodium carbonate and sodium bicarbonate, sodium hydroxide and sodium oxide, sodium bicarbonate and sodium peroxide, or combinations of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, and sodium peroxide.

[0022] In some embodiments, when the iron in the iron-phosphorus-sodium-sulfur mixture is ferrous iron, an oxidant is used to oxidize the ferrous iron to ferric iron before adjusting the pH value to 2.8-4.5.

[0023] Similarly, if the iron in the iron-phosphorus-sodium-sulfur mixture is ferric iron, then no oxidant needs to be added.

[0024] This invention adds the oxidant before adjusting the pH value to 2.8–4.5, which is beneficial for oxidizing ferrous iron to ferric iron after the oxidant is added. Within a pH range of ≤2.8, the reaction rate between the oxidant and ferrous iron is fast, the oxidation efficiency is high, and there is less precipitation reaction, which is conducive to the contact between the oxidant and ferrous iron and also helps to improve the oxidation efficiency.

[0025] In some embodiments, the oxidant includes any one or a combination of at least two of hydrogen peroxide, sodium peroxide, sodium persulfate, sodium percarbonate, oxygen, ozone, or air. Typical but non-limiting combinations include combinations of hydrogen peroxide and sodium peroxide, combinations of sodium persulfate and sodium percarbonate, combinations of oxygen, ozone, and air, or combinations of hydrogen peroxide, sodium peroxide, sodium persulfate, sodium percarbonate, oxygen, ozone, and air.

[0026] Under conditions of pH ≤ 2.8, considering the disproportionation reaction of the oxidant itself, the oxidant needs to be in excess, but excessive excess will lead to waste of raw materials. In some embodiments, the molar ratio of the divalent iron to the oxidant is 0.2:1 to 0.5:1, for example, it can be 0.2:1, 0.3:1, 0.4:1 or 0.5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] In some embodiments, an alkaline sodium salt is used to adjust the pH to 2.8–4.5, wherein the alkaline sodium salt includes any one or a combination of at least two of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, or sodium peroxide. Typical but non-limiting combinations include combinations of sodium carbonate and sodium bicarbonate, combinations of sodium hydroxide and sodium oxide, combinations of sodium bicarbonate and sodium peroxide, or combinations of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, and sodium peroxide.

[0028] In some embodiments, the solid-liquid separation method includes any one or a combination of at least two of centrifugation, pressure filtration, or vacuum filtration. Typical but non-limiting combinations include a combination of centrifugation and pressure filtration, a combination of centrifugation and vacuum filtration, a combination of pressure filtration and vacuum filtration, or a combination of centrifugation, pressure filtration, and vacuum filtration.

[0029] In some embodiments, the Fe x H y O z (PO a ) b The ·mH2O precursor precipitate used to prepare sodium iron pyrophosphate includes: drying Fe x H y Oz (PO a ) b The precipitate of the mH2O precursor yielded Fe. x H y O z (PO a ) b ·mH2O precursor; the Fe x H y O z (PO a ) b The mH2O precursor is mixed with a second phosphorus source, a sodium source, and a first carbon source, granulated, and then calcined in a protective atmosphere to obtain the sodium iron pyrophosphate.

[0030] In some embodiments, the drying method includes any one or a combination of at least two of vacuum drying, freeze drying, forced air drying, spray drying, flash drying, or natural evaporation. Typical but non-limiting combinations include a combination of vacuum drying and freeze drying, a combination of forced air drying and spray drying, a combination of flash drying and natural evaporation, or a combination of vacuum drying, freeze drying, forced air drying, spray drying, flash drying, and natural evaporation.

[0031] In some embodiments, Fe is mixed x H y O z (PO a ) b The methods for processing the mH2O precursor with the second phosphorus source, the first sodium source, and the first carbon source include ball milling and / or sand milling.

[0032] In some embodiments, the granulation method includes spray drying and / or ball milling.

[0033] In some embodiments, the protective atmosphere uses gases including nitrogen and / or argon.

[0034] In some embodiments, the second phosphorus source includes any one or a combination of at least two of sodium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, triammonium phosphate, pyrophosphate, sodium pyrophosphate, or sodium dihydrogen pyrophosphate. Typical but non-limiting combinations include combinations of sodium dihydrogen phosphate and sodium phosphate, combinations of sodium monohydrogen phosphate and phosphoric acid, combinations of ammonium dihydrogen phosphate and triammonium phosphate, combinations of pyrophosphate, sodium pyrophosphate, and sodium dihydrogen pyrophosphate, or combinations of sodium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, triammonium phosphate, pyrophosphate, sodium pyrophosphate, and sodium dihydrogen pyrophosphate.

[0035] In some embodiments, the first sodium source includes any one or a combination of at least two of sodium dihydrogen phosphate, sodium phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium sulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, or sodium dihydrogen pyrophosphate. Typical but non-limiting combinations include combinations of sodium dihydrogen phosphate and sodium phosphate, combinations of sodium carbonate and sodium nitrate, combinations of sodium oxalate and sodium acetate, combinations of sodium sulfate and sodium hydroxide, combinations of sodium formate, sodium citrate, sodium pyrophosphate, and sodium dihydrogen pyrophosphate, or combinations of sodium dihydrogen phosphate, sodium phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium sulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, and sodium dihydrogen pyrophosphate.

[0036] In some embodiments, the first carbon source includes any one or a combination of at least two of oxalic acid, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, starch, sucrose, or glucose. Typical but non-limiting combinations include combinations of oxalic acid and ascorbic acid, combinations of formaldehyde and acetaldehyde, combinations of n-butyraldehyde and lactic acid, combinations of citric acid and malic acid, combinations of oxalic acid, adipic acid, and starch, combinations of starch, sucrose, and glucose, or combinations of oxalic acid, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, starch, sucrose, and glucose.

[0037] In some embodiments, the sodium sulfate mother liquor is used to prepare sodium ferric sulfate by: obtaining a sodium sulfate solution or sodium sulfate crystals from the sodium sulfate mother liquor; then mixing it with a second iron source, a second sodium source, and a second carbon source, granulating it, and calcining it in a protective atmosphere to obtain the sodium ferric sulfate.

[0038] In some embodiments, the method for obtaining sodium sulfate crystals from sodium sulfate mother liquor includes any one or a combination of at least two of the following: vacuum drying, freeze drying, forced air drying, spray drying, flash drying, vacuum drying, natural evaporation, or recrystallization. Typical but non-limiting combinations include a combination of vacuum drying and freeze drying, a combination of forced air drying and spray drying, a combination of flash drying and vacuum drying, a combination of natural evaporation and recrystallization, a combination of vacuum drying, freeze drying, and forced air drying, or a combination of vacuum drying, freeze drying, forced air drying, spray drying, flash drying, vacuum drying, natural evaporation, and recrystallization.

[0039] In some embodiments, the second iron source includes any one or a combination of at least two of iron, ferrous oxide, iron oxide, magnetite, ferric hydroxide, or iron hydroxide. Typical but non-limiting combinations include combinations of iron and ferrous oxide, combinations of iron oxide and magnetite, combinations of ferric hydroxide and iron hydroxide, combinations of ferrous oxide, iron oxide, and magnetite, or combinations of iron, ferrous oxide, iron oxide, magnetite, ferric hydroxide, and iron hydroxide.

[0040] In some embodiments, the second sodium source includes any one or a combination of at least two of sodium dihydrogen phosphate, sodium phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium sulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, or sodium dihydrogen pyrophosphate. Typical but non-limiting combinations include combinations of sodium dihydrogen phosphate and sodium phosphate, combinations of sodium carbonate and sodium nitrate, combinations of sodium oxalate and sodium acetate, combinations of sodium sulfate and sodium hydroxide, combinations of sodium formate, sodium citrate, sodium pyrophosphate, and sodium dihydrogen pyrophosphate, or combinations of sodium dihydrogen phosphate, sodium phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium sulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, and sodium dihydrogen pyrophosphate.

[0041] In some embodiments, the second carbon source includes any one or a combination of at least two of oxalic acid, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, starch, sucrose, or glucose. Typical but non-limiting combinations include combinations of oxalic acid and ascorbic acid, combinations of formaldehyde and acetaldehyde, combinations of n-butyraldehyde and lactic acid, combinations of citric acid and malic acid, combinations of oxalic acid, adipic acid, and starch, combinations of starch, sucrose, and glucose, or combinations of oxalic acid, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, starch, sucrose, and glucose.

[0042] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The comprehensive preparation method provided by the present invention realizes the "zero waste" four-element closed loop, and the conversion and utilization rate of the four elements Fe, P, Na and S can reach 100%. Moreover, the pH value of the iron-phosphorus-sodium-sulfur mixture is adjusted to 2.8 to 4.5. Within this pH range, the composite precipitation of iron and phosphate is the main reaction, which can completely precipitate phosphate.

[0045] (2) The comprehensive preparation method provided by the present invention can simultaneously produce Fe through a single feeding of an iron-phosphorus-sodium-sulfur mixed solution. x H y O z (PO a ) b The preparation of mH2O precursor and sodium sulfate mother liquor achieves zero-waste, low-cost, and integrated production, solving the technical problems of sulfur waste, high pollution, and long process chain in existing technologies.

[0046] (3) The comprehensive preparation method provided by the present invention can be used for mixing, granulation and calcination equipment when producing sodium iron pyrophosphate and sodium iron sulfate, saving equipment investment; moreover, the calcination temperature of NFPP is higher than that of NFS, and the tail heat in the calcination process of NFPP can be fully used for the calcination of NFS, which greatly saves energy consumption. Attached Figure Description

[0047] Figure 1 A process flow diagram of the comprehensive preparation method provided by the present invention. Detailed Implementation

[0048] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0049] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for specific parameters, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this invention, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0050] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0051] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0052] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0053] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0054] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0055] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0056] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0057] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0058] In this invention, "room temperature" generally refers to 4℃ to 35℃, and may refer to 20℃ ± 5℃. In some embodiments of this invention, room temperature refers to 20℃ to 30℃.

[0059] Example 1

[0060] This invention provides a comprehensive preparation method for a sodium-ion battery cathode material, comprising the following steps:

[0061] S1. Mix 151.908g of ferrous sulfate and 115.294g of 85wt% phosphoric acid, add 1L of deionized water, and adjust the pH to 1.8 with sodium hydroxide to obtain a mixed solution of iron, phosphorus, sodium and sulfur (iron-phosphorus molar ratio of 1:1).

[0062] S2. Add 227g of a 30wt% hydrogen peroxide aqueous solution to the iron-phosphorus-sodium-sulfur mixture at a molar ratio of iron to oxidant of 0.5:1. Then add sodium hydroxide to adjust the pH to 3, yielding a milky white suspension. The main components of this milky white suspension are sodium sulfate and Fe. x H y O z (PO a ) b·mH2O precursor precipitation;

[0063] S3, a milky white suspension was separated into solid and liquid components to obtain Fe. x H y O z (PO a ) b ·mH2O precursor precipitate and sodium sulfate mother liquor;

[0064] S4, Fe x H y O z (PO a ) b The ·mH2O precursor precipitate was vacuum dried to obtain Fe. x H y O z (PO a ) b ·mH2O precursor; Fe x H y O z (PO a ) b The mH2O precursor was ball-milled with sodium dihydrogen phosphate, sodium carbonate, and citric acid in a solid phase, and then calcined at 550℃ for 10h under a nitrogen atmosphere at a heating rate of 2℃ / min to obtain sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7).

[0065] Sodium sulfate mother liquor was directly mixed with iron oxide and sucrose by sand milling (sodium sulfate was added as needed), spray dried, and then calcined at 480°C for 8 hours under a nitrogen atmosphere at a heating rate of 2°C / min to obtain sodium ferric sulfate.

[0066] Example 2

[0067] This invention provides a comprehensive preparation method for a sodium-ion battery cathode material, comprising the following steps:

[0068] S1. Mix 151.908g of ferrous sulfate and 115.294g of 85wt% phosphoric acid, add 1L of deionized water, and adjust the pH to 1.8 with sodium hydroxide to obtain a mixed solution of iron, phosphorus, sodium and sulfur (iron-phosphorus molar ratio of 1:1).

[0069] S2. Add 227g of a 30wt% hydrogen peroxide aqueous solution to the iron-phosphorus-sodium-sulfur mixture at a molar ratio of iron to oxidant of 0.5:1. Then add sodium hydroxide to adjust the pH to 3, yielding a milky white suspension. The main components of this milky white suspension are sodium sulfate and Fe. x H y O z (PO a ) b·mH2O precursor precipitation;

[0070] S3, a milky white suspension was separated into solid and liquid components to obtain Fe. x H y O z (PO a ) b ·mH2O precursor precipitate and sodium sulfate mother liquor;

[0071] S4, Fe x H y O z (PO a ) b The ·mH2O precursor precipitate was vacuum dried to obtain Fe. x H y O z (PO a ) b ·mH2O precursor; Fe x H y O z (PO a ) b The mH2O precursor was ball-milled with sodium dihydrogen phosphate, sodium carbonate, and citric acid in a solid phase, and then calcined at 580℃ for 8 hours in a nitrogen atmosphere at a heating rate of 2℃ / min to obtain sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7).

[0072] Sodium sulfate mother liquor was directly mixed with ferric hydroxide and citric acid by sand milling (sodium sulfate was added as needed), spray dried, and then calcined at 500°C for 6 hours under a nitrogen atmosphere at a heating rate of 2°C / min to obtain sodium ferric sulfate.

[0073] Example 3

[0074] This invention provides a comprehensive preparation method for a sodium-ion battery cathode material, comprising the following steps:

[0075] S1. Mix 278g of ferrous sulfate heptahydrate and 119.959g of sodium dihydrogen phosphate, add 1L of deionized water, and adjust the pH to 2.8 with sodium hydroxide to obtain a mixed solution of iron, phosphorus, sodium and sulfur (iron-phosphorus molar ratio of 1:1).

[0076] S2. Add a 30wt% hydrogen peroxide aqueous solution to the iron-phosphorus-sodium-sulfur mixture at a molar ratio of iron to oxidant of 0.5:1, then add sodium carbonate to adjust the pH to 4, yielding a milky white suspension. The main components of this milky white suspension are sodium sulfate and Fe. x H y O z (PO a ) b·mH2O precursor precipitation;

[0077] S3, a milky white suspension was separated into solid and liquid components to obtain Fe. x H y O z (PO a ) b ·mH2O precursor precipitate and sodium sulfate mother liquor;

[0078] S4, Fe x H y O z (PO a ) b The ·mH2O precursor precipitate was vacuum dried to obtain Fe. x H y O z (PO a ) b ·mH2O precursor; Fe x H y O z (PO a ) b The mH2O precursor was subjected to liquid-phase sand milling with sodium phosphate, sodium carbonate and glucose, and then calcined at 580℃ for 8h under nitrogen atmosphere at a heating rate of 3℃ / min to obtain sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7).

[0079] Sodium sulfate mother liquor was directly mixed with ferric hydroxide and citric acid by sand milling (sodium sulfate was added as needed), spray dried, and then calcined at 480°C for 8 hours under a nitrogen atmosphere at a heating rate of 3°C / min to obtain sodium ferric sulfate.

[0080] Example 4

[0081] This invention provides a comprehensive preparation method for a sodium-ion battery cathode material, comprising the following steps:

[0082] S1. Mix 200g of ferric sulfate and 115.294g of 85wt% phosphoric acid, add 1L of deionized water, and adjust the pH to 2.8 with sodium hydroxide to obtain a mixed solution of iron, phosphorus, sodium and sulfur (iron-phosphorus molar ratio of 1:1).

[0083] Sodium hydroxide was added to a mixture of S2, iron, phosphorus, sodium, and sulfur to adjust the pH to 3.5, resulting in a milky white suspension. The main components of this milky white suspension were sodium sulfate and Fe. x H y O z (PO a ) b ·mH2O precursor precipitation;

[0084] S3, a milky white suspension was separated into solid and liquid components to obtain Fe. x H y O z (PO a ) b ·mH2O precursor precipitate and sodium sulfate mother liquor;

[0085] S4, Fe x H y O z (PO a ) b The ·mH2O precursor precipitate was vacuum dried to obtain Fe. x H y O z (PO a ) b ·mH2O precursor; Fe x H y O z (PO a ) b The mH2O precursor was ball-milled with sodium dihydrogen phosphate, sodium carbonate, and citric acid in a solid phase, and then calcined at 580℃ for 8 hours in a nitrogen atmosphere at a heating rate of 2℃ / min to obtain sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7).

[0086] Sodium sulfate mother liquor was directly mixed with iron and sucrose by sand milling (sodium sulfate was added as needed), spray dried, and then calcined at 490°C for 7 hours under a nitrogen atmosphere at a heating rate of 3°C / min to obtain sodium ferric sulfate.

[0087] Example 5

[0088] This invention provides a comprehensive preparation method for a sodium-ion battery cathode material, comprising the following steps:

[0089] S1. Mix 151.908g of ferrous sulfate, 86.4705g of 85wt% phosphoric acid, and 33.24g of sodium pyrophosphate. Add 1L of deionized water and adjust the pH to 1.8 using sodium hydroxide to obtain a mixed solution of iron, phosphorus, sodium, and sulfur (iron-phosphorus molar ratio of 1:1).

[0090] S2. Add 227g of a 30wt% hydrogen peroxide aqueous solution to the iron-phosphorus-sodium-sulfur mixture, then add sodium hydroxide to adjust the pH to 3, resulting in a milky white suspension. The main components of this milky white suspension are sodium sulfate and Fe. x H y O z (PO a ) b ·mH2O precursor precipitation;

[0091] S3, a milky white suspension was separated into solid and liquid components to obtain Fe. x H y O z (PO a ) b ·mH2O precursor precipitate and sodium sulfate mother liquor;

[0092] S4, Fe x H y O z (PO a ) b The ·mH2O precursor precipitate was vacuum dried to obtain Fe. x H y O z (PO a ) b ·mH2O precursor; Fe x H y O z (PO a ) b The mH2O precursor was ball-milled with sodium dihydrogen phosphate, sodium carbonate, and citric acid in a solid phase, and then calcined at 530℃ for 12 h in a nitrogen atmosphere at a heating rate of 2℃ / min to obtain sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7).

[0093] Sodium sulfate mother liquor was directly mixed with iron oxide and sucrose by sand milling (sodium sulfate was added as needed), spray dried, and then calcined at 450°C for 8 hours under a nitrogen atmosphere at a heating rate of 3°C / min to obtain sodium ferric sulfate.

[0094] Comparative Example 1

[0095] This invention provides a comprehensive preparation method for a sodium-ion battery cathode material, comprising the following steps:

[0096] S1. Mix 151.908g of ferrous sulfate and 115.294g of 85wt% phosphoric acid, add 1L of deionized water, and adjust the pH to 1.8 with sodium hydroxide to obtain a mixed solution of iron, phosphorus, sodium and sulfur (iron-phosphorus molar ratio of 1:1).

[0097] S2. Add 227g of a 30wt% hydrogen peroxide aqueous solution to the iron-phosphorus-sodium-sulfur mixed solution according to a molar ratio of iron to oxidant of 0.5:1. Then add sodium hydroxide to adjust the pH to 5, obtaining a light yellow suspension. The main components of this light yellow suspension are sodium sulfate and Fe. x H y O z (PO a ) b ·mH2O precursor precipitate and sodium phosphate.

[0098] The presence of sodium phosphate salts affects the subsequent processing of sodium sulfate mother liquor, making it impossible to simultaneously prepare sodium ferric pyrophosphate and sodium ferric sulfate.

[0099] Performance Characterization

[0100] Electrochemical performance tests were conducted on the sodium ferric pyrophosphate and sodium ferric sulfate obtained in the above examples. The charge / discharge conditions for sodium ferric pyrophosphate were: initial activation at a current of 0.2C within a voltage range of 2V to 4V; the charge / discharge conditions for sodium ferric sulfate were: initial activation at a current of 0.2C within a voltage range of 2V to 4.5V; where 1C is defined as 100mA / g. The electrochemical test results for sodium ferric pyrophosphate are shown in Table 1, and the electrochemical test results for sodium ferric sulfate are shown in Table 2.

[0101] Table 1

[0102]

[0103] Table 2

[0104]

[0105]

[0106] As can be seen from Examples 1 and 2, the comprehensive preparation method provided by the present invention can simultaneously produce Fe through a single feeding of an iron-phosphorus-sodium-sulfur mixed solution. x H y O z (PO a ) b The precursor mH2O and sodium sulfate mother liquor were used simultaneously to synthesize sodium iron pyrophosphate and sodium iron sulfate, respectively. The synthesized cathode materials exhibited excellent electrochemical performance. The four elements of phosphorus, sodium, sulfur and iron in the iron-phosphorus-sodium-sulfur mixed solution were 100% utilized. In the preparation of the two precursors and two cathode materials, there was no waste of the four elements, which greatly reduced the production cost.

[0107] As can be seen from Examples 2, 3, 4 and Comparative Example 1, the pH value during the oxidation reaction affects the color of the suspension. This is because when the pH value of the solution is high, some ferric phosphate will be converted into ferric hydroxide precipitate, resulting in the incomplete precipitation of phosphorus element. This leads to low purity of sodium sulfate mother liquor, which cannot be directly used for the synthesis of sodium ferric sulfate. Therefore, the pH must be strictly controlled during the synthesis process.

[0108] As can be seen from Example 4, when ferric sulfate is used as the source of ferric sulfate, there is no need to introduce an oxidant.

[0109] The product prepared in Comparative Example 1 had a pH value of 5 in step S2, which was not adjusted to the pH range (2.8-4.5) of the present invention. As a result, the liquid phase of the solid-liquid mixture contained residual phosphorus. Using this mother liquor as a raw material for sodium ferric sulfate would lead to phosphorus doping and would also prevent the full utilization of phosphorus, resulting in waste of raw materials. Therefore, the conditions for integrated preparation of sodium ferric pyrophosphate and sodium ferric sulfate were not met.

[0110] In summary, the comprehensive preparation method provided by this invention achieves a "zero-waste" four-element closed-loop process, with a 100% conversion and utilization rate of all four elements (Fe, P, Na, and S). Furthermore, by adjusting the pH of the iron-phosphorus-sodium-sulfur mixed solution to 2.8–4.5, within this pH range, the composite precipitation of iron and phosphate is the dominant reaction, ensuring complete precipitation of phosphate. The comprehensive preparation method provided by this invention can simultaneously produce Fe through a single feeding of the iron-phosphorus-sodium-sulfur mixed solution. x H y O z (PO a ) b The preparation of mH2O precursor and sodium sulfate mother liquor achieves zero-waste, low-cost, and integrated production, solving the technical problems of sulfur waste, high pollution, and long process chains in existing technologies. The comprehensive preparation method provided by this invention allows for the use of interchangeable equipment for mixing, granulation, and calcination when producing sodium ferric pyrophosphate and sodium ferric sulfate, saving on equipment investment. Moreover, the calcination temperature of NFPP is higher than that of NFS, and the tail heat in the NFPP calcination process can be fully utilized for the calcination of NFS, greatly saving energy consumption.

[0111] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A comprehensive preparation method for a sodium-ion battery cathode material, characterized in that, The comprehensive preparation method includes the following steps: Adjust the pH of the iron-phosphorus-sodium-sulfur mixed solution (pH ≤ 2.8) to 2.8–4.5 to obtain Fe. x H y O z (PO a ) b A solid-liquid mixture consisting of the mH2O precursor precipitate and the sodium sulfate mother liquor; The solid-liquid mixture was subjected to solid-liquid separation to obtain Fe. x H y O z (PO a ) b ·mH2O precursor precipitate and sodium sulfate mother liquor; The Fe x H y O z (PO a ) b The mH2O precursor precipitate is used to prepare sodium iron pyrophosphate; the sodium sulfate mother liquor is used to prepare sodium iron sulfate.

2. The comprehensive preparation method according to claim 1, characterized in that, The iron-phosphorus-sodium-sulfur mixture is obtained by mixing a first iron source, a first phosphorus source, and an alkaline sodium salt. And / or, the iron-phosphorus molar ratio in the iron-phosphorus-sodium-sulfur mixture is 1:0.5 to 1:

1.

3. The comprehensive preparation method according to claim 2, characterized in that, The first iron source includes ferric sulfate and / or ferrous sulfate; And / or, the first phosphorus source includes any one or a combination of at least two of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, pyrophosphate, sodium pyrophosphate, or sodium pyrophosphate acid salts; And / or, the alkaline sodium salt includes any one or a combination of at least two of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, or sodium peroxide.

4. The comprehensive preparation method according to claim 1, characterized in that, When the iron in the iron-phosphorus-sodium-sulfur mixture is ferrous iron, before adjusting the pH value to 2.8-4.5, an oxidant is used to oxidize the ferrous iron to ferric iron. And / or, the oxidant includes any one or a combination of at least two of hydrogen peroxide, sodium peroxide, sodium persulfate, sodium percarbonate, oxygen, ozone, or air; And / or, the molar ratio of the divalent iron to the oxidant is 0.2:1 to 0.5:

1.

5. The comprehensive preparation method according to claim 1, characterized in that, The pH value is adjusted to 2.8–4.5 using an alkaline sodium salt, wherein the alkaline sodium salt includes any one or a combination of at least two of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, or sodium peroxide.

6. The comprehensive preparation method according to claim 1, characterized in that, The solid-liquid separation method includes any one or a combination of at least two of centrifugation, pressure filtration, or vacuum filtration.

7. The comprehensive preparation method according to claim 1, characterized in that, The Fe x H y O z (PO a ) b The ·mH2O precursor precipitate used to prepare sodium iron pyrophosphate includes: drying Fe x H y O z (PO a ) b The precipitate of the mH2O precursor yielded Fe. x H y O z (PO a ) b ·mH2O precursor; the Fe x H y O z (PO a ) b The mH2O precursor is mixed with a second phosphorus source, a first sodium source, and a first carbon source, granulated, and then calcined in a protective atmosphere to obtain the sodium iron pyrophosphate.

8. The comprehensive preparation method according to claim 7, characterized in that, The drying method includes any one or a combination of at least two of the following: vacuum drying, freeze drying, forced air drying, spray drying, flash drying, or natural evaporation; And / or, the second phosphorus source includes any one or a combination of at least two of sodium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, triammonium phosphate, pyrophosphate, sodium pyrophosphate, or sodium dihydrogen pyrophosphate. And / or, the first sodium source includes any one or a combination of at least two of sodium dihydrogen phosphate, sodium phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium sulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, or sodium dihydrogen pyrophosphate. And / or, the first carbon source includes any one or a combination of at least two of oxalic acid, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, starch, sucrose, or glucose.

9. The comprehensive preparation method according to claim 1, characterized in that, The sodium sulfate mother liquor is used to prepare sodium ferric sulfate by: obtaining a sodium sulfate solution or sodium sulfate crystals from the sodium sulfate mother liquor; then mixing it with a second iron source, a second sodium source, and a second carbon source, granulating it, and calcining it in a protective atmosphere to obtain the sodium ferric sulfate.

10. The comprehensive preparation method according to claim 9, characterized in that, The second iron source includes any one or a combination of at least two of the following: iron, ferrous oxide, ferric oxide, iron(II) oxide, ferric hydroxide, or ferric hydroxide. And / or, the second sodium source includes any one or a combination of at least two of sodium dihydrogen phosphate, sodium phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium sulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, or sodium dihydrogen pyrophosphate; And / or, the second carbon source includes any one or a combination of at least two of oxalic acid, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, starch, sucrose, or glucose.

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