A modified sodium-ion cathode material, cathode slurry, preparation method thereof, and secondary battery

Abstract

This invention relates to a modified sodium-ion cathode material, a cathode slurry, a method for preparing the same, and a secondary battery. The modified sodium-ion cathode material comprises a sodium-ion cathode material core and a hydrogen-absorbing coating layer covering the outer surface of the core. The hydrogen-absorbing coating layer is made of a hydrogen-absorbing material, which includes any one or a combination of at least two of imidazole compounds, nitrogen-containing heterocyclic compounds, sulfonic acid polymers, sulfonated polyaryl ethers, or amine compounds. This invention forms a hydrogen-absorbing coating layer on the surface of the sodium-ion cathode material using a hydrogen-absorbing material. This coating layer effectively blocks direct contact between the cathode active material and water and / or hydrogen ions, thereby significantly improving the storage stability and coating performance of the aqueous cathode slurry. The provided cathode sheet exhibits excellent cycle stability and rate performance in secondary batteries while reducing manufacturing costs.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a modified sodium-ion cathode material, cathode slurry, preparation method thereof, and secondary battery. Background Technology

[0002] Since their commercial application in 1991, lithium-ion batteries have achieved tremendous success in consumer electronics and other fields thanks to their excellent electrochemical performance. However, the finite nature and uneven geographical distribution of lithium resources have prompted researchers to actively explore new sustainable energy storage systems. Sodium, belonging to the same group as lithium and possessing similar physicochemical properties, is abundant in the Earth's crust and offers significant cost advantages; therefore, sodium-ion batteries are considered an important complement to lithium-ion battery systems. In recent years, with the increasing demand for energy storage, the application prospects of sodium-ion batteries in large-scale energy storage have received increasing attention.

[0003] However, sodium-ion battery cathode materials face a key challenge: their poor stability in air, especially susceptible to moisture. When the material comes into contact with humid air, active sodium ions in the crystal lattice continuously dissolve, causing structural distortion and rapid capacity decay. Even more seriously, hydrogen ions in water can pass through the Na+ ions... + / H + The exchange process enters the material's crystal lattice, occupies sodium ion sites, thereby destroying the material's electrochemical activity and causing the positive electrode function to fail.

[0004] To mitigate the air sensitivity issue of cathode materials, two main slurry preparation processes are currently employed: oil-based and water-based slurry preparation. Oil-based processes typically use polyvinylidene fluoride (PVDF) as a binder and N-methylpyrrolidone (NMP) as a solvent. This system is not only costly, but the solvent also poses certain toxicity and environmental risks.

[0005] In contrast, aqueous processes, using water as a medium, offer advantages such as low cost, environmental friendliness, and process simplicity, effectively compensating for the shortcomings of oil-based processes. However, research shows that while aqueous processes avoid organic solvents, they fail to prevent hydrogen ions from migrating into the material during pulping, and Na+... + / H + The exchange problem still exists, which directly affects the long-cycle performance of sodium-ion batteries.

[0006] Therefore, developing novel sodium-ion battery cathode materials and corresponding processes suitable for aqueous homogenization systems is crucial to effectively suppress sodium ion content while leveraging the economic and environmental advantages of aqueous routes. + / H + Improving the stability of material structures through exchange has become a key issue that urgently needs to be addressed to promote the large-scale application of sodium-ion batteries. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a modified sodium-ion cathode material, cathode slurry, preparation method thereof, and secondary battery. The modified sodium-ion cathode material of the present invention consists of a sodium-ion cathode material core and a coating layer formed by depositing hydrogen-absorbing material on its surface. It can effectively block direct contact between water and / or hydrogen ions and the material, significantly improving the structural stability of the sodium-ion cathode material during preparation and service, thereby enabling the prepared secondary battery to have excellent cycle life.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a modified sodium ion cathode material, the modified sodium ion cathode material comprising a sodium ion cathode material core and a hydrogen-absorbing coating layer covering the outer surface of the core;

[0010] The hydrogen-absorbing coating layer is made of a hydrogen-absorbing material.

[0011] The hydrogen-absorbing material includes any one or a combination of at least two of the following: imidazole compounds, nitrogen-containing heterocyclic compounds, sulfonic acid polymers, sulfonated polyarylethers, or amine compounds.

[0012] This invention employs a hydrogen-absorbing material to form a coating layer on the surface of a sodium-ion cathode material. This coating layer can effectively block direct contact between the cathode active material and water and / or hydrogen ions, thereby significantly improving the storage stability and coating processing performance of the aqueous cathode slurry.

[0013] Compared to other coating materials in the prior art, the hydrogen-absorbing molecules selected in this invention have the function of adsorbing hydrogen elements, thereby inhibiting the penetration of hydrogen elements into the sodium ion cathode material. While commonly used coating materials in the prior art can only prevent water molecules from entering, they cannot prevent hydrogen ions. The hydrogen-absorbing material coated in this invention not only blocks water molecules from directly entering but also blocks the entry of hydrogen ions, thus more thoroughly and comprehensively inhibiting the penetration of sodium ions into the cathode material. + / H + The exchange process improved the structural stability of the material.

[0014] This invention does not impose any special restrictions on the type of sodium ion cathode material, including but not limited to any one or at least a combination of two of layered oxides, Prussian blue-based materials, or polyanionic materials.

[0015] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0016] In some embodiments, the imidazole compound includes any one or a combination of at least two of 2-methylimidazolium, benzimidazole, aminoimidazolium, carboxyl-containing imidazolium, or polybenzimidazole, preferably carboxyl-containing imidazolium. The anion head group can stably anchor hydrogen-absorbing molecules to the core surface of the sodium-ion cathode material to form a coating layer. The imidazole group has the function of adsorbing hydrogen elements, thereby inhibiting hydrogen elements from entering the cathode material through the coating layer, ultimately achieving a significant improvement in the electrochemical performance of the battery.

[0017] In some embodiments, the nitrogen-containing heterocyclic compound includes any one or a combination of at least two of pyridine, histidine, triazole, pyrimidine, or purine. Typical but non-limiting combinations include combinations of pyridine and histidine, combinations of triazole and pyrimidine, combinations of pyrimidine and purine, and combinations of pyridine, histidine, and triazole.

[0018] In some embodiments, the sulfonic acid polymer includes a perfluorosulfonic acid membrane.

[0019] In some embodiments, the sulfonated polyarylene ethers include any one or a combination of at least two of sulfonated polyether ether ketone, sulfonated polyarylene ether sulfone, or sulfonated polybenzimidazole. Typical but non-limiting combinations include combinations of sulfonated polyether ether ketone and sulfonated polyarylene ether sulfone, combinations of sulfonated polyarylene ether sulfone and sulfonated polybenzimidazole, combinations of sulfonated polyether ether ketone and sulfonated polybenzimidazole, and combinations of sulfonated polyether ether ketone, sulfonated polyarylene ether sulfone, and sulfonated polybenzimidazole.

[0020] In some embodiments, the amine compounds include aliphatic amines and / or aromatic amines.

[0021] In some embodiments, the average thickness of the hydrogen-absorbing coating is 2nm-12nm, for example, it can be 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm or 12nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] In this invention, the average thickness of the hydrogen absorption coating layer is further controlled to be 2nm-12nm. The thickness of the hydrogen absorption coating layer has a significant impact on its performance. On the one hand, if the thickness is less than 2nm, its ability to block hydrogen permeation will be significantly weakened, making it difficult to maintain the structural stability of the material. On the other hand, if the thickness exceeds 12nm, it will severely restrict sodium ion conduction, thereby damaging the electrochemical performance of the battery.

[0023] In a second aspect, the present invention provides a method for preparing the modified sodium-ion cathode material as described in the first aspect, the method comprising the following steps:

[0024] The modified sodium ion cathode material is obtained by preparing a hydrogen-absorbing coating layer on the surface of the sodium ion cathode material using a liquid-phase method and / or a gas-phase method.

[0025] This invention employs molecular self-assembly technology to construct an ultrathin, uniform, and dense hydrogen-absorbing molecular coating layer on the surface of a cathode material. This hydrogen-absorbing coating layer can effectively maintain the material's good dispersibility while ensuring its stability in aqueous slurries.

[0026] In some embodiments, the liquid-phase preparation step includes: mixing sodium ion cathode material, hydrogen-absorbing material and solvent, and reacting to obtain the modified sodium ion cathode material.

[0027] In some embodiments, the mass ratio of the sodium ion cathode material to the hydrogen absorption material is 1:(0.05-1), for example, it can be 1:0.05, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 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.

[0028] This invention further controls the mass ratio of sodium-ion cathode material to hydrogen-absorbing material to be 1:(0.05-1). The mass ratio of sodium-ion cathode material to hydrogen-absorbing material directly determines the proportion of active material, thus affecting its electrochemical performance. If the mass ratio of sodium-ion cathode material to hydrogen-absorbing material is too large, it will lead to low density, uneven distribution, and insufficient thickness of the hydrogen-absorbing coating layer, thereby limiting the improvement of the overall electrochemical performance of the battery. If the mass ratio of sodium-ion cathode material to hydrogen-absorbing material is too small, the insufficient proportion of active material will restrict the overall performance of the battery.

[0029] In some embodiments, the solvent includes any one or a combination of at least two of tetrahydrofuran, ethanol, or propanol. Typical but non-limiting combinations include a combination of tetrahydrofuran and ethanol, a combination of ethanol and propanol, a combination of tetrahydrofuran and propanol, or a combination of tetrahydrofuran, ethanol, and propanol.

[0030] In some embodiments, the reaction temperature is 60°C-80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0031] In some embodiments, the reaction time is 5h-10h, for example, it can be 5h, 6h, 7h, 8h, 9h or 10h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] In some embodiments, the reaction is followed by solid-liquid separation, washing, and drying before obtaining the modified sodium-ion cathode material.

[0033] In some embodiments, the gas-phase preparation step includes:

[0034] The hydrogen-absorbing material is heated to volatilize, resulting in a hydrogen-absorbing gas. This gas is then deposited on the surface of the sodium ion cathode material to obtain the modified sodium ion cathode material.

[0035] In some embodiments, the heating temperature is 100℃-160℃, for example, it can be 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃ or 160℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0036] In some embodiments, the heating time is 4h-8h, for example, it can be 4h, 5h, 6h, 7h or 8h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0038] The hydrogen-absorbing material is dissolved in a water-soluble solvent, and sodium ion cathode material is added and stirred to obtain the modified sodium ion cathode material.

[0039] Alternatively, the hydrogen-absorbing material is heated and volatilized at a temperature of 100℃-160℃ to form a gas. After cooling, the gas is deposited on the surface of the sodium ion cathode material to form a hydrogen-absorbing coating layer. The deposition process is repeated 2-4 times to obtain the modified sodium ion cathode material.

[0040] Thirdly, the present invention provides a positive electrode slurry comprising the modified sodium ion positive electrode material as described in the first aspect.

[0041] Fourthly, the present invention provides a method for preparing the positive electrode slurry as described in the third aspect, the method comprising the following steps:

[0042] The conductive agent, binder, water, and the modified sodium ion cathode material described in the first aspect are mixed and stirred to obtain the cathode slurry;

[0043] This invention employs an aqueous slurry mixing process that significantly reduces the manufacturing cost of sodium-ion batteries while exhibiting excellent and stable comprehensive physical, chemical, and electrochemical properties. Furthermore, the aqueous slurry preparation process effectively improves the safety and operability of the electrode preparation process, reduces organic solvent emissions, and offers greater environmental benefits. It is also suitable for large-scale continuous production and has promising prospects for industrialization.

[0044] The present invention does not specifically limit the type of conductive agent, which may be selected from any one or at least two combinations of acetylene black, graphene, carbon fiber, fullerene, carbon nanotube, conductive graphite or SuperP. Typical but non-limiting combinations include the combination of acetylene black and graphene, the combination of carbon fiber, fullerene and carbon nanotube, the combination of conductive graphite and SuperP, the combination of graphene and carbon fiber, the combination of acetylene black and carbon nanotube, and the combination of acetylene black, graphene and SuperP.

[0045] This invention uses a water-soluble binder, which is a stable suspension system formed by a polymer or resin in an aqueous phase. The type of water-soluble binder is not specifically limited, and includes, but is not limited to, any one or at least two combinations of polyacrylic acid, sodium polymethacrylate, sodium alginate, sodium carboxymethyl cellulose, xanthan gum, starch, guar gum, and gelatin. Typical but non-limiting combinations include combinations of polyacrylic acid and sodium polymethacrylate, combinations of sodium alginate and sodium carboxymethyl cellulose, combinations of xanthan gum, starch, and guar gum, combinations of starch, guar gum, and gelatin, combinations of polyacrylic acid and sodium alginate, and combinations of xanthan gum, guar gum, and gelatin.

[0046] Fifthly, the present invention provides a positive electrode sheet, which is prepared using the positive electrode slurry described in the third aspect.

[0047] The positive electrode provided by this invention can reduce the interfacial impedance of sodium-ion batteries, improve the initial coulombic efficiency, and exhibit excellent cycle stability.

[0048] In a sixth aspect, the present invention provides a secondary battery, the secondary battery comprising the positive electrode sheet described in the fifth aspect.

[0049] The secondary battery provided by this invention exhibits excellent performance in terms of cycle stability and rate capability. Its performance indicators have reached the level of oil-based homogenization process and are significantly superior to existing technologies.

[0050] 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.

[0051] Compared with the prior art, the present invention has at least the following beneficial effects:

[0052] (1) The present invention uses hydrogen-absorbing material to form a coating layer on the surface of sodium ion cathode material. This coating layer can effectively block the direct contact between the cathode active material and water and / or hydrogen ions, thereby significantly improving the storage stability and coating processing performance of the aqueous cathode slurry.

[0053] (2) The present invention employs molecular self-assembly technology to construct an ultrathin, uniform and dense molecular coating layer on the surface of the cathode material. This coating layer can effectively maintain the good dispersibility of the material while ensuring its stable existence in aqueous slurry.

[0054] (3) The aqueous slurry mixing process of this invention significantly reduces the manufacturing cost of sodium-ion batteries, while possessing excellent and stable physical, chemical and electrochemical comprehensive properties. At the same time, the aqueous slurry mixing process can effectively improve the safety and operability of the electrode preparation process, reduce organic solvent emissions, have higher environmental benefits, and is suitable for large-scale continuous production, with good industrialization prospects.

[0055] (4) The positive electrode sheet provided by the present invention can reduce the interfacial impedance of sodium-ion batteries, improve the initial coulombic efficiency, and exhibit excellent cycle stability. The secondary battery provided by the present invention exhibits excellent performance in terms of cycle stability and rate performance, and its performance indicators have reached the level of oil-based homogenization process and are significantly better than the prior art. Attached Figure Description

[0056] Figure 1 This is a TEM image of the modified sodium-ion cathode material obtained in Example 1 of this invention;

[0057] Figure 2 This is a TEM mapping image of the modified sodium ion cathode material obtained in Example 1 of this invention;

[0058] Figure 3 This is a linear scan of the modified sodium-ion cathode material obtained in Example 1 of the present invention;

[0059] Figure 4 This is a long-cycle diagram of the sodium-ion battery obtained by Application Example 1, Comparative Application Example 1, Comparative Application Example 2 and Comparative Application Example 3 of the present invention. Detailed Implementation

[0060] 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.

[0061] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0062] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The 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" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0063] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. 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 locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0064] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0065] Unless otherwise specified, all reagents and consumables used in the following examples and comparative examples were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used were conventional methods and techniques in the art.

[0066] Example 1

[0067] This embodiment provides a modified sodium ion cathode material, which includes a sodium ion cathode material core and a hydrogen-absorbing coating layer with an average thickness of 3 nm covering the outer surface of the core; the hydrogen-absorbing coating layer is made of 2-methylimidazole.

[0068] The method for preparing the modified sodium-ion cathode material provided in this embodiment includes the following steps:

[0069] The hydrogen-absorbing material 2-methylimidazole was dissolved in tetrahydrofuran solvent and stirred until completely dissolved. Then, the sodium ion cathode material core NaNi was added. 0.33 Fe 0.33 Mn 0.33 O2 (commercially available), with sodium ion cathode material core NaNi 0.33 Fe 0.33 Mn 0.33 The mass ratio of O2 to 2-methylimidazole is 1:0.15. The reaction is carried out in a water bath at 70℃ for 6 hours, so that the hydrogen-absorbing material is deposited on the surface of the sodium ion positive electrode material core to form a hydrogen-absorbing coating layer.

[0070] After the reaction was completed and cooled to room temperature, the mixture was filtered, and the resulting solid was washed three times with tetrahydrofuran and dried to obtain the modified sodium ion cathode material.

[0071] SEM images of the prepared modified sodium ion cathode material are shown below. Figure 1 As shown, from Figure 1 As can be seen, a uniform hydrogen-absorbing coating layer was successfully deposited on the surface of the sodium ion cathode material core through self-assembly technology.

[0072] The TEM mapping image of the obtained modified sodium ion cathode material is shown below. Figure 2 As shown, from Figure 2 As can be seen, silicon and nitrogen elements on the surface of sodium ion cathode material exhibit obvious aggregation, thus confirming the existence of hydrogen absorption coating layer.

[0073] Example 2

[0074] This embodiment provides a modified sodium-ion cathode material, which includes a sodium-ion cathode material core and a hydrogen-absorbing coating layer with an average thickness of 5 nm covering the outer surface of the core; the hydrogen-absorbing coating layer is made of aminoimidazole.

[0075] The method for preparing the modified sodium-ion cathode material provided in this embodiment includes the following steps:

[0076] The hydrogen-absorbing material, aminoimidazole, was dissolved in tetrahydrofuran solvent and stirred until completely dissolved. Then, sodium iron Prussian white (Na2Fe2(CN)6) (commercially available) was added to the sodium ion cathode material core, with a mass ratio of Na2Fe2(CN)6 to aminoimidazole of 1:0.4. The reaction was carried out in a 70°C water bath for 8 hours, allowing the hydrogen-absorbing material to deposit on the surface of the sodium ion cathode material core, forming a hydrogen-absorbing coating layer.

[0077] After the reaction was completed and cooled to room temperature, the mixture was filtered, and the resulting solid was washed three times with tetrahydrofuran and dried to obtain the modified sodium ion cathode material.

[0078] Example 3

[0079] This embodiment provides a modified sodium ion cathode material, which includes a sodium ion cathode material core and a hydrogen-absorbing coating layer with an average thickness of 4 nm covering the outer surface of the core; the hydrogen-absorbing coating layer is made of sulfonated polybenzimidazole.

[0080] The method for preparing the modified sodium-ion cathode material provided in this embodiment includes the following steps:

[0081] Sulfonated polybenzimidazole was placed in a petri dish, and sodium vanadium phosphate cathode material NaVPO4 (commercially available) was suspended in the container above it. The mixture was heated at 120°C for 6 hours to allow the sulfonated polybenzimidazole to volatilize. After cooling, a hydrogen-absorbing coating layer was spontaneously deposited on the surface of the cathode material. The mass ratio of the sodium ion cathode material core NaVPO4 to sulfonated polybenzimidazole was 1:0.3.

[0082] After cooling to room temperature, the powder in the system is stirred, and the above process is repeated for a total of 4 cycles to obtain the modified sodium ion cathode material.

[0083] Example 4

[0084] This embodiment provides a modified sodium ion cathode material. The only difference from Embodiment 1 is that, in preparing this modified sodium ion cathode material, the hydrogen-absorbing molecule is replaced with 1-ethylimidazolium dihydrogen phosphate, while the other steps remain unchanged.

[0085] Example 5

[0086] This embodiment provides a modified sodium ion cathode material. The only difference from Embodiment 1 is that, in preparing this modified sodium ion cathode material, the hydrogen-absorbing molecule is replaced with 4-pyridine phosphoric acid, while the other steps remain unchanged.

[0087] Example 6

[0088] This embodiment provides a modified sodium-ion cathode material. The only difference from Example 3 is that, when preparing this modified sodium-ion cathode material, the mass ratio of the sodium-ion cathode material core NaVPO4 and sulfonated polybenzimidazole is changed to 1:0.6, while the other steps remain unchanged.

[0089] Example 7

[0090] This embodiment provides a modified sodium ion cathode material. The only difference from Embodiment 1 is that the mass ratio of sodium ion cathode material to hydrogen absorption material is changed to 1:1 when preparing the modified sodium ion cathode material, while the other steps remain unchanged.

[0091] Example 8

[0092] This embodiment provides a modified sodium ion cathode material. The only difference from Embodiment 1 is that the mass ratio of sodium ion cathode material to hydrogen absorption material is changed to 1:0.01 when preparing the modified sodium ion cathode material, while the other steps remain unchanged.

[0093] Example 9

[0094] This embodiment provides a modified sodium-ion cathode material. The only difference from Embodiment 1 is that the mass ratio of sodium-ion cathode material to hydrogen-absorbing material is changed to 1:1.5 when preparing the modified sodium-ion cathode material, while the other steps remain unchanged.

[0095] Comparative Example 1

[0096] This comparative example provides a sodium ion cathode material, which differs from Example 1 only in that hydrogen-absorbing material is not added in step (1) when preparing the sodium ion cathode material.

[0097] Comparative Example 2

[0098] This comparative example provides a sodium ion cathode material, which differs from Example 1 only in that, in the preparation of this sodium ion cathode material, the hydrogen-absorbing material in step (1) is replaced with an equal amount of hydrophobic alkyl molecules pentafluorophenyltriethoxysilane.

[0099] Application Example 1

[0100] This application example provides a positive electrode slurry, the preparation method of which includes the following steps:

[0101] Carbon nanotubes (conductive agent), sodium carboxymethyl cellulose (binder), and the modified sodium ion cathode material obtained in Example 1 were added to water at a mass ratio of 1:1:8, mixed, and stirred for 12 hours to obtain the cathode slurry.

[0102] Application Example 2

[0103] This application example provides a positive electrode slurry, the preparation method of which includes the following steps:

[0104] Acetylene black (conductive agent), sodium alginate (binder), and the modified sodium ion cathode material obtained in Example 2 were added to water at a mass ratio of 1:1:8, mixed, and stirred for 12 hours to obtain the cathode slurry.

[0105] Application Examples 3-9

[0106] Application Examples 3-9 each provide a positive electrode slurry. The only difference from Application Example 1 is that, when preparing the positive electrode slurry, the modified sodium ion positive electrode material obtained in Example 1 is replaced with the modified sodium ion positive electrode material prepared in Examples 3-9, while the other preparation methods remain unchanged.

[0107] Comparative Application Example 1 - Comparative Application Example 2

[0108] Comparative Application Examples 1-2 each provide a positive electrode slurry. The only difference from Application Example 1 is that, when preparing the positive electrode slurry, the modified sodium ion positive electrode material obtained in Example 1 is replaced with the sodium ion positive electrode material prepared in Comparative Examples 1-2.

[0109] Comparative Application Example 3

[0110] This comparative example provides a positive electrode slurry, which differs from Comparative Application Example 1 only in that it does not use a hydrogen-absorbing material and replaces the solvent water with an equal amount of N-methylpyrrolidone, while the rest of the preparation method remains unchanged.

[0111] test:

[0112] Preparation of the positive electrode sheet: The positive electrode slurries prepared in Application Examples 1-9 and Comparative Application Examples 1-3 were coated onto aluminum foil and dried at 100°C under vacuum for 6 hours. Subsequently, the electrode sheet was rolled using a roller press at a pressure of 10 MPa to reduce its thickness from 60 μm to 30 μm. The compacted density of the electrode sheet after rolling was 3.0 g·cm³. -3 Finally, the rolled electrode sheet is punched into a round sheet with a diameter of 12mm to obtain the positive electrode sheet.

[0113] Preparation of secondary batteries: A CR2032 type button secondary battery was assembled in an argon atmosphere glove box using a 16 mm diameter sodium metal sheet as the negative electrode, a glass fiber membrane (GradeGF / A) as the separator, and NaClO4 (PC=100Vol%, 3%FEC) as the electrolyte.

[0114] Test Method: The coin cells were subjected to constant current charge-discharge tests using a Xinwei electrochemical workstation at a constant temperature of 26℃. The test voltage range was 2.0V-4.0V. Pre-cycle activation was performed for 3 cycles at a current density of 0.1C, followed by long-cycle performance testing at a current density of 1C. The test results are shown in Table 1 below.

[0115] The linear scan graph of the sodium-ion battery obtained from Example 1 is shown below. Figure 3 As shown, from Figure 3 As can be seen, signal peaks of silicon and nitrogen elements appear in the edge region of the sodium ion cathode material, indicating that a hydrogen absorption coating layer has been successfully constructed on the surface of the cathode material.

[0116] The long-cycle diagram of the sodium-ion battery obtained from Example 1 is shown below. Figure 4 As shown, from Figure 4 As can be seen, the hydrogen-absorbing coating effectively inhibits the penetration of hydrogen into the cathode material, thereby improving the structural stability of the material and ultimately significantly enhancing the cycle performance of the battery.

[0117] Table 1

[0118]

[0119] The test results show that:

[0120] (1) As can be seen from Application Examples 1-7, the present invention uses a hydrogen-absorbing material to form a coating layer on the surface of the sodium-ion cathode material. This coating layer can effectively block the direct contact between the cathode active material and water and / or hydrogen ions, thereby significantly improving the storage stability and coating processing performance of the aqueous cathode slurry. The provided cathode sheet and secondary battery exhibit excellent performance in terms of cycle stability and rate performance, and their performance indicators have reached the level of oil-based homogenization process and are significantly superior to the prior art. At the same time, the aqueous slurry preparation process can effectively reduce the production cost of sodium-ion batteries, improve the safety and operability of the electrode preparation process, reduce organic solvent emissions, have higher environmental benefits, and are suitable for large-scale continuous production, with good industrialization prospects.

[0121] (2) By comparing Application Example 1 with Application Examples 8-9, it can be seen that the present invention further controls the mass ratio of sodium ion cathode material to hydrogen absorption material to be 1:(0.05-1). The mass ratio of sodium ion cathode material to hydrogen absorption material directly determines the proportion of active material, thereby affecting its electrochemical performance. If the mass ratio of sodium ion cathode material to hydrogen absorption material is too large, it will lead to low density, uneven distribution and insufficient thickness of hydrogen absorption coating layer, thereby limiting the improvement of the overall electrochemical performance of battery. If the mass ratio of sodium ion cathode material to hydrogen absorption material is too small, the overall performance of battery will be restricted due to insufficient proportion of active material.

[0122] (3) As can be seen from Application Example 1 and Comparative Application Example 1, the present invention forms a coating layer on the surface of the sodium ion cathode material by using a hydrogen-absorbing material. This coating layer can effectively block the direct contact between the cathode active material and water and / or hydrogen ions, thereby significantly improving the storage stability and coating processing performance of the aqueous cathode slurry. If the hydrogen-absorbing coating layer is not applied, it is impossible to inhibit the penetration of water and / or hydrogen ions into the sodium ion cathode material, which leads to battery capacity loss and rapid failure.

[0123] (4) As can be seen from Application Example 1 and Comparative Application Example 2, the hydrogen-absorbing material selected in this invention has the advantage of adsorbing hydrogen elements and thus inhibiting hydrogen elements from penetrating into the cathode material. However, when other commonly used coating materials in the prior art are used for coating, they cannot achieve the technical effect of inhibiting hydrogen elements from penetrating into the cathode material.

[0124] (5) As can be seen from Application Example 1 and Comparative Application Example 3, the performance of sodium-ion batteries obtained by homogenizing the modified sodium-ion cathode material prepared by this invention using aqueous slurry and oil-based slurry is not significantly different, or even better. This process uses water as a solvent, which has the advantages of being non-toxic, harmless, and low-cost, and eliminates the high energy consumption of organic solvent recovery and distillation, thereby significantly reducing environmental impact and production costs. In summary, this invention achieves a unity of battery performance, economic benefits, and environmental protection characteristics, demonstrating broad industrialization prospects.

[0125] In summary, this invention utilizes a hydrogen-absorbing material to form a coating layer on the surface of the sodium-ion cathode material. This coating layer effectively blocks direct contact between the cathode active material and water and / or hydrogen ions, thereby significantly improving the storage stability and coating performance of the aqueous cathode slurry. The provided cathode sheet and secondary battery exhibit excellent cycle stability and rate performance, with performance indicators reaching the level of oil-based homogenization processes and significantly outperforming existing technologies. Simultaneously, the aqueous slurry preparation process effectively reduces the production cost of sodium-ion batteries, improves the safety and operability of the electrode preparation process, reduces organic solvent emissions, and possesses greater environmental benefits. Furthermore, it is suitable for large-scale continuous production and has promising industrialization prospects.

[0126] 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 modified sodium-ion cathode material, characterized in that, The modified sodium ion cathode material includes a sodium ion cathode material core and a hydrogen-absorbing coating layer covering the outer surface of the core; The hydrogen-absorbing coating layer is made of a hydrogen-absorbing material; The hydrogen-absorbing material includes any one or a combination of at least two of the following: imidazole compounds, nitrogen-containing heterocyclic compounds, sulfonic acid polymers, sulfonated polyarylethers, or amine compounds.

2. The modified sodium-ion cathode material according to claim 1, characterized in that, The imidazole compounds include any one or a combination of at least two of 2-methylimidazolium, benzimidazole, aminoimidazolium, carboxyl-containing imidazolium, or polybenzimidazole; And / or, the nitrogen-containing heterocyclic compound includes any one or a combination of at least two of pyridine, histidine, triazole, pyrimidine or purine; And / or, the sulfonic acid polymer includes a perfluorosulfonic acid membrane; And / or, the sulfonated polyarylene ethers include any one or a combination of at least two of sulfonated polyether ether ketone, sulfonated polyarylene ether sulfone, or sulfonated polybenzimidazole; And / or, the amine compounds include aliphatic amines and / or aromatic amines; And / or, the average thickness of the hydrogen-absorbing coating is 2nm-12nm.

3. A method for preparing the modified sodium-ion cathode material as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: The modified sodium ion cathode material is obtained by preparing a hydrogen-absorbing coating layer on the surface of the sodium ion cathode material using a liquid-phase method and / or a gas-phase method.

4. The preparation method according to claim 3, characterized in that, The preparation steps of the liquid phase method include: The modified sodium ion cathode material is obtained by mixing sodium ion cathode material, hydrogen absorption material and solvent and reacting them.

5. The preparation method according to claim 4, characterized in that, The mass ratio of the sodium ion cathode material to the hydrogen absorption material is 1:(0.05-1); And / or, the solvent includes any one or a combination of at least two of tetrahydrofuran, ethanol or propanol; And / or, the temperature of the reaction is 60°C-80°C; And / or, the reaction time is 5h-10h; And / or, after the reaction and before obtaining the modified sodium ion cathode material, solid-liquid separation, washing, and drying are also performed.

6. The preparation method according to claim 3, characterized in that, The preparation steps of the gas-phase method include: The hydrogen-absorbing material is heated to volatilize, resulting in a hydrogen-absorbing gas. This gas is then deposited on the surface of the sodium ion cathode material to obtain the modified sodium ion cathode material.

7. A positive electrode slurry, characterized in that, The positive electrode slurry includes the modified sodium ion positive electrode material as described in claim 1 or 2.

8. A method for preparing the positive electrode slurry as described in claim 7, characterized in that, The preparation method includes the following steps: The conductive agent, binder, water, and the modified sodium ion cathode material according to claim 1 or 2 are mixed and stirred to obtain the cathode slurry; The adhesive is a water-based adhesive.

9. A positive electrode sheet, characterized in that, The positive electrode sheet is prepared using the positive electrode slurry described in claim 7.

10. A secondary battery, characterized in that, The secondary battery includes the positive electrode sheet as described in claim 9.

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