Sulfate polyanionic material, positive electrode sheet, battery, battery pack, electric device

Abstract

The application provides a sulfate polyanion material, a positive electrode sheet, a battery, a battery pack and an electric device. The sulfate polyanion material comprises sulfate polyanion nanosheets, and can improve the discharge performance and rate performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to sulfate polyanionic materials, positive electrode sheets, batteries, battery packs, and electrical equipment. Background Technology

[0002] Sodium-ion batteries have shown great promise in recent years in energy storage systems, low-speed electric vehicles, and power tools due to their abundant resources, low cost, and high safety. As the core component of sodium-ion batteries, the performance of the cathode material directly determines the battery's energy density, cycle life, rate performance, and low-temperature adaptability. Sulfate polyanionic materials are considered highly promising cathode materials due to their high theoretical capacity, low raw material cost, and environmental friendliness. However, existing sulfate polyanionic materials generally suffer from poor conductivity, low sodium-ion diffusion rate, and poor structural stability, affecting the discharge performance and rate performance of sodium-ion batteries. Summary of the Invention

[0003] This application provides a sulfate polyanionic material and its preparation method, a positive electrode sheet, a battery, a battery pack, and an electrical device, which can improve the conductivity, ion transport efficiency, and structural stability of the positive electrode material, and enhance the discharge performance and rate performance of the battery.

[0004] One aspect of the present invention provides a sulfate polyanionic material comprising sulfate polyanionic nanosheets.

[0005] The sulfate polyanionic material provided in this application has an ultrathin nanosheet structure, which increases the specific surface area of ​​the sodium-ion battery cathode material and provides more active sites for the adsorption and desorption of sodium ions. This structural design effectively reduces ion transport resistance and improves the diffusion rate of sodium ions, thereby enhancing the charge and discharge performance of the battery.

[0006] In a second aspect, this application provides a method for preparing the above-mentioned sulfate polyanionic material, comprising the following steps: drying a mixture including an iron source, a sodium source, a sulfur source and a viscosity reducer to obtain a precursor; and annealing the precursor to obtain the sulfate polyanionic material.

[0007] The preparation method provided in this application incorporates a viscosity reducer during the synthesis process. The viscosity reducer works synergistically through multiple mechanisms during spray drying to prevent particle agglomeration and maintain the sheet-like structure: its core function is to reduce solution viscosity, improve fluidity and atomization effect, generate fine and uniform droplets and accelerate evaporation, thereby reducing particle contact and aggregation; at the same time, it forms a protective layer through surface adsorption, inhibiting agglomeration through steric hindrance and electrostatic repulsion, and can also regulate the hydrophobicity or hydrophilicity of the particle surface to reduce adhesion; in addition, it can accelerate particle dehydration and solidification, avoiding sticky adhesion and internal stress accumulation in the semi-dry state, ultimately ensuring the stability of the material structure and performance.

[0008] In another aspect, the present invention provides a positive electrode comprising the above-described sulfate polyanionic material or a sulfate polyanionic material prepared according to the above-described method for preparing sulfate polyanionic materials. The positive electrode provided in this application has high capacity and good stability.

[0009] In another aspect, the present invention provides a battery comprising the aforementioned positive electrode. The battery provided in this application has high energy density and good cycle performance.

[0010] In another aspect, the present invention provides a battery pack comprising at least two interconnected batteries as described above. The battery pack provided in this application has high energy density and good cycle performance.

[0011] In another aspect, the present invention provides an electrical device including the aforementioned battery or battery pack. The electrical device provided in this application exhibits excellent electrochemical performance. Attached Figure Description

[0012] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0013] Figure 1 The X-ray diffraction (XRD) patterns are of the sulfate polyanionic materials of Examples 3, 9, 10 and Comparative Example 1 of this application.

[0014] Figure 2 This is a scanning electron microscope (SEM) image of the sulfate polyanionic material in Example 3 of this application.

[0015] Figure 3 This is a scanning electron microscope (SEM) image of the sulfate polyanionic material in Example 3 of this application.

[0016] Figure 4 This is a scanning electron microscope (SEM) image of the sulfate polyanionic material in Comparative Example 1 of this application.

[0017] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0018] To enable those skilled in the art to better understand the solutions of this invention, the following provides a more detailed description of this application. The specific embodiments listed below are merely descriptions of the principles and features of this invention; the examples are only for explaining the invention and are not intended to limit its scope. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0019] In the field of new energy storage and power batteries, sodium-ion batteries have become an important alternative to lithium-ion batteries due to their abundant resources and low cost. However, the performance of cathode materials directly determines their energy density, rate performance, and cycle life, making it one of the core bottlenecks for industrialization. Polyanionic cathode materials have become a research focus due to their stable crystal structure and high operating voltage. However, existing products generally suffer from poor electronic conductivity and high sodium-ion transport resistance, resulting in poor rate performance, weak low-temperature discharge capability, and easy structural degradation and limited lifespan during cycling.

[0020] Traditional sulfate polyanionic materials are mostly dense, blocky, or large-sized granular structures. On the one hand, these structures have limited specific surface area, resulting in a small number of active sites for sodium ion adsorption and desorption, which directly increases ion transport resistance. This not only reduces the battery's charge and discharge efficiency and high-rate performance, but also further slows down the ion diffusion rate at low temperatures, leading to a significant decrease in the battery's low-temperature discharge capability. On the other hand, the dense structure lacks volume buffer space. During battery charge and discharge cycles, repeated insertion and extraction of sodium ions can cause periodic expansion and contraction of the material's lattice. The resulting internal stress can easily lead to particle cracking and pulverization, which not only disrupts the continuity of the electrode conductive network and reduces conductivity, but also significantly shortens the battery's cycle life. In addition, the small contact area between the blocky or coarse particle surface and the electrolyte results in insufficient electrolyte wetting, further hindering ion transport on the material's surface and inside, forming an "ion transport bottleneck" that restricts the full realization of the electrochemical performance of sulfate polyanionic materials.

[0021] In view of this, embodiments of the present invention provide a sulfate polyanionic material comprising sulfate polyanionic nanosheets.

[0022] The sulfate polyanionic material provided in this application has at least a nanosheet structure. This nanosheet structure, through its optimized microstructure, helps alleviate the performance limitations of traditional bulk / coarse-grained structures: its ultrathin two-dimensional morphology significantly increases the specific surface area, providing more active sites for sodium ion adsorption and desorption, which to some extent helps improve battery charge / discharge capacity and reaction kinetic efficiency; the nanoscale thickness can significantly shorten the diffusion path of sodium ions within the material, reducing ion transport resistance and positively impacting high-rate performance and low-temperature discharge capability; simultaneously, the flexibility of the sheets and the natural gaps between them can buffer some of the volumetric stress caused by sodium ion insertion / extraction, alleviating material cracking and pulverization problems; and the loose porous structure formed by stacked nanosheets can optimize electrolyte wetting, increase the interfacial contact area between the material and the electrolyte, and to some extent reduce interfacial transport resistance, thereby supporting the improvement of the overall electrochemical performance of the battery.

[0023] In one embodiment, the thickness of the sulfate polyanionic nanosheets is 20 nm to 160 nm. This thickness range facilitates the formation of sufficient specific surface area for the nanosheets, providing more active sites for sodium ion adsorption and desorption, and also helps to shorten the ion diffusion path and reduce transport resistance. It also reduces the problems of insufficient mechanical strength and easy agglomeration and breakage caused by excessive thickness; furthermore, it alleviates the problems of weakened ultrathin nanosheet characteristics and impaired ion diffusion and electrolyte wetting caused by excessive thickness. Simultaneously, it is compatible with electrode coating and assembly processes, helping to maintain the uniformity of the electrode structure. Optionally, the thickness of the sulfate polyanionic material can be 20 nm, 40 nm, 60 nm, 100 nm, 140 nm, 160 nm, or any value between any two of the above.

[0024] In this application, the thickness of the sulfate polyanionic material can be measured using conventional methods, such as TEM (transmission electron microscopy) and cross-sectional analysis.

[0025] In one embodiment, the molecular formula of the sulfate polyanionic material is Na. 2+2x Fe 2-2x (SO4)3, 0≤x<1. Adjusting the ratio of sodium and iron by regulating the value of x helps optimize the material's crystal structure and defect state, facilitating the insertion and desorption of sodium ions and improving the material's structural stability and electrochemical reactivity to some extent. In one specific embodiment, the molecular formula of the sulfate polyanionic material is Na... 2.5 Fe 1.75 (SO4)3.

[0026] In one embodiment, the sulfate polyanionic material further includes a conductive carbon material, with at least a portion of the conductive carbon material distributed within the sulfate polyanionic material. The presence of at least a portion of the conductive carbon material within the sulfate polyanionic material forms a continuous conductive network within the material itself, effectively addressing the problem of insufficient conductivity inherent in the material, thus contributing to improved electron transport efficiency and allowing the material's capacity to be fully utilized.

[0027] In one embodiment, the specific surface area of ​​the sulfate polyanionic material is 5-12 m². 2 / g. This specific surface area range ensures that the material has a suitable reaction contact area, providing sufficient active sites for sodium ion adsorption and desorption, thus helping to improve the kinetic efficiency of the electrochemical reaction; it also avoids the problems of loose material structure and insufficient mechanical strength caused by excessively large specific surface area, and prevents the situation of insufficient active sites and blocked ion transport caused by excessively small specific surface area. Optionally, the specific surface area of ​​the sulfate polyanionic material can be 5 m² / g, 7 m² / g, 9 m² / g, 12 m² / g, or any value between any two of the above.

[0028] In this application, the specific surface area can be measured by conventional methods, such as by using a BST-BET400 instrument.

[0029] In one embodiment, the particle size D50 of the sulfate polyanion material is 5 μm-10 μm. This particle size range ensures that the material has a suitable reaction surface area, which is beneficial for the adsorption, desorption, and transport of sodium ions. It also avoids the problems of excessively small particle size leading to agglomeration and poor dispersibility, while preventing excessively large particle size from causing prolonged ion diffusion paths and affecting the sufficiency of the reaction. Optionally, the particle size D50 of the sulfate polyanion material can be 5 μm, 7 μm, 9 μm, 10 μm, or any value between any two of the above.

[0030] In this application, particle size D50 refers to the median value of the particle size volume distribution, which can be measured by conventional methods, such as by a laser particle size analyzer.

[0031] In one embodiment, such materials typically possess good conductivity, which helps to construct a continuous conductive network in sulfate polyanionic materials, improves their intrinsic conductivity deficiency, enhances electron transport efficiency, and facilitates fuller utilization of capacity.

[0032] In one embodiment, the mass ratio of conductive carbon material to sulfate polyanionic material is 1%-8%. This range ensures that an appropriate amount of conductive carbon material participates in the construction of the conductive network, which helps improve the conductivity of the host material and enhance electron transport efficiency; it also reduces the possibility of the conductive carbon material crowding out space and affecting the structure and electrochemical performance of the host material if the ratio is too high; and it avoids the problem of discontinuous conductive network and obstructed electron transport caused by the ratio being too low. Optionally, the mass ratio can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any value between any two of the above. It is understood that, in the calculation, the mass of sulfate polyanionic material includes the mass of conductive carbon material.

[0033] In this application, the mass of the conductive carbon material can be measured by conventional methods, such as by a carbon-sulfur analyzer.

[0034] In one embodiment, the sulfate polyanionic material further includes anionic doping and / or cationic doping. Typically, sulfate polyanionic materials are prone to absorbing water and forming a hydrated phase, which affects their performance. By introducing anions and cations with lower hydration energies under acidic conditions to replace ions with high hydration energies (such as some sulfate ions) in the material, the tendency for the material to absorb water can be reduced, effectively improving its stability in air and reducing the impact of hydration on its performance during storage.

[0035] In one embodiment, the cation includes Al 3+ Mg 2+ Ti 4+ Cu 2+ Mn 2+ At least one of them.

[0036] The present invention also provides a method for preparing the above-mentioned sulfate polyanionic material, comprising the following steps:

[0037] The mixture containing an iron source, a sodium source, a sulfur source, and a viscosity reducer is dried to obtain a precursor.

[0038] Annealing the precursor yields sulfate polyanionic materials.

[0039] In the above preparation process, iron, sodium, and sulfur sources are used as raw materials for synthesizing sulfate polyanionic materials. After drying the mixture, a sheet-like precursor containing iron, sodium, and sulfur elements is formed. During the annealing process, the internal moisture of the material is evaporated, forming a sulfate polyanionic material with a nanosheet structure. This nanosheet structure allows the sulfate polyanionic material to be more uniformly distributed in the electrode, and the nanosheet morphology allows for more effective contact with the electrolyte, thereby effectively improving the cycle rate performance of the material.

[0040] In this application, the viscosity reducer lowers the viscosity of high-solids slurry, improves fluidity, and helps generate fine, uniform droplets. It accelerates water evaporation, shortens drying time to reduce particle contact and aggregation, and simultaneously regulates solution surface tension to promote droplet spreading, which helps maintain the sheet-like structure and prevents the formation of spherical particles. Its amphiphilic properties can form a protective layer through surface adsorption, and counteract van der Waals forces through mechanisms such as steric hindrance, electrostatic repulsion (giving particles the same charge), and reduced surface tension, reducing droplet collisions and particle contact, and inhibiting agglomeration from the source. It can also modify the particle surface through chemical adsorption or physical coating to form a hydrophobic protective layer to reduce adhesion or retain hydrophilic groups to maintain surface wettability, both of which reduce agglomeration caused by electrostatic forces and van der Waals forces. In addition, it can accelerate water evaporation to promote rapid particle solidification, reduce the sticky residue and adhesion in the semi-dry state, and promote uniform droplet atomization to avoid the accumulation of internal stress in particles caused by the lag in the migration of water inside large droplets, further helping to maintain the target sheet-like structure.

[0041] In one embodiment, the sodium source includes at least one selected from sodium sulfate, sodium carbonate, sodium hydroxide, sodium chloride, sodium nitrate, and sodium sulfite. This selection provides stable sodium for material synthesis, adapting to different process and cost requirements.

[0042] In one embodiment, the iron source includes at least one selected from ferrous sulfate, ferrous chloride, ferrous oxide, and ferrous ammonium sulfate. This selection provides highly reactive iron elements for material synthesis and is compatible with different reaction systems.

[0043] In one embodiment, the sodium-iron molar ratio is set between 1.1 and 1.5. The design of a relative excess of sodium reduces impurities and ensures the integrity of the material's crystal structure.

[0044] In one embodiment, the sodium source is added first, followed by the iron source, during the stirring and dissolution process. This method avoids the dissolution and agglomeration of sodium source, ensuring a precise sodium-iron ratio and reducing the impact on the electrochemical performance of the material.

[0045] In one embodiment, the mixture includes water. Water, as a solvent, can dissolve raw materials such as sodium and iron sources, promoting uniform dispersion of the components and providing a basis for the uniformity of subsequent reactions; at the same time, it is widely available and low in cost, making it suitable for large-scale preparation needs.

[0046] In one embodiment, the mixture further includes a conductive carbon material, which includes at least one of carbon nanotubes, carbon black, acetylene black, Ketjen black, and graphene. This type of material is uniformly dispersed during the mixing stage, interspersed within the material to construct a continuous conductive network, thus optimizing the ion transport path.

[0047] In a preferred embodiment, the amount of conductive carbon material added accounts for 1%-5% of the total mass. Adding conductive carbon material within this range can promote the formation of a continuous conductive network, effectively improving the conductivity of the material, while avoiding excessive addition that could encroach on the space of the main material and affect structural stability and capacity. Optionally, the amount of conductive carbon material added can be 1%, 2%, 3%, 4%, 5%, or any value between any two of the above values.

[0048] In one embodiment, the mixture further includes an antioxidant, which includes at least one selected from ascorbic acid, vitamin C, glutathione, sodium citrate, sodium sulfite, and ferrous gluconate. The addition of the antioxidant ensures that ferrous iron is not oxidized upon contact with air throughout the material preparation process, thus maintaining stable performance.

[0049] In one embodiment, the amount of antioxidant added is 1%-2% of the total mass of the finished material. This proportion can effectively inhibit the oxidation reaction of the material during the preparation process, protecting the structural integrity and performance stability of the material. Optionally, the amount of antioxidant added can be 1%, 1.2%, 1.5%, 1.8%, 2%, or any value between any two of the above.

[0050] In one embodiment, the mixture further includes a dopant, which includes at least one selected from disodium hydrogen phosphate, sodium carbonate, sodium chloride, sodium bromide, sodium hypochlorite, magnesium carbonate, magnesium sulfate, aluminum sulfate, titanium sulfate, and copper sulfate. Anionic dopant can introduce anions with lower hydration energies under acidic conditions, replacing the high hydration energies of sulfate ions in the material, reducing the material's water absorption tendency, thereby effectively improving its air stability. Cationic dopant can optimize the structural stability and electrochemical performance of sodium ferric sulfate-based materials.

[0051] In one embodiment, the amount of dopant added accounts for 1%-3% of the total mass of the finished material. This ratio can ensure effective improvement of the material's air stability while avoiding excessive doping that could damage the main structure. Optionally, the amount of dopant added can be 1%, 2%, 3%, or any value between any two of the above.

[0052] In one embodiment, the mixture further includes an aqueous dispersant for CNTs (carbon nanotubes), comprising at least one of carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), sodium dodecyl sulfate (SDS), and polyacrylic acid (PAA). Such dispersants promote uniform dispersion of the components, inhibit CNT particle agglomeration, and enhance the structural stability of the material.

[0053] In a preferred embodiment, the amount of dispersant added is 0.1%-3% of the total mass. This ratio ensures good dispersion, inhibits particle agglomeration, and avoids excessive addition that could affect the intrinsic properties of the material. Optionally, the amount of dispersant added can be 0.1%, 1%, 2%, 3%, or any value between any two of the above.

[0054] In one embodiment, the viscosity reducer includes at least one of sodium dodecylbenzenesulfonate, fatty alcohol polyoxyethylene ether, polymaleic anhydride, xanthan gum, and sodium tripolyphosphate. Such viscosity reducers can effectively reduce the viscosity of the mixture, improve its flowability, promote uniform dispersion of the components, and inhibit particle agglomeration.

[0055] In one embodiment, the viscosity reducer is added at a rate of 0.1%-2% of the total mass of the finished material. This ratio can effectively reduce the viscosity of the mixture and improve its fluidity, while avoiding excessive addition that could adversely affect the intrinsic properties of the material. Optionally, the amount of viscosity reducer added can be 0.1%, 0.5%, 1%, 1.5%, 2%, or any value between any two of the above, to suit different raw material systems and viscosity control requirements.

[0056] In some embodiments, the drying process may include: spray drying the mixture to obtain a precursor; preferably, the mixture is fed into a spray dryer for spray drying, wherein the inlet temperature of the spray dryer is 160℃-260℃, for example, a range of 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃ or any two thereof; the feed rate of the mixture is 5mm / s-15mm / s, for example, a range of 8mm / s, 9mm / s, 10mm / s, 11mm / s, 12mm / s, 13mm / s, 14mm / s or any two thereof; and the rotational speed of the spray dryer is 200 rpm / min-600 rpm / min, for example, 200 rpm / min, 210 rpm / min, 220 rpm / min, 250 rpm / min, 300 rpm / min, 400 rpm / min, 500 rpm / min, 600 rpm / min. The range of rpm / min or any two thereof; the outlet temperature of the spray dryer is 95℃-115℃, for example, it can be a range of 95℃, 100℃, 105℃, 110℃, 115℃ or any two thereof.

[0057] In the spray drying process, the morphology and particle size distribution of the precursor can be controlled by adjusting parameters such as the inlet temperature of the spray dryer and the feed rate of the mixture, thereby affecting the morphology and electrochemical properties of the material. Specifically, a higher inlet temperature and a slower feed rate are more conducive to the formation of nanosheet structures in the precursor.

[0058] In this application, a conventional spray dryer can be used to spray dry the mixture, such as the Buqi spray dryer (S390-S395).

[0059] In some embodiments, annealing can be performed under a protective atmosphere, which is more conducive to avoiding the oxidation of ferrous iron, thereby improving the material preparation efficiency and enhancing the material performance.

[0060] Specifically, the protective atmosphere may include an inert gas atmosphere, such as at least one of nitrogen, helium, neon, and argon atmospheres.

[0061] In some embodiments, the annealing temperature can be between 300°C and 450°C, for example, a range of 300°C, 350°C, 400°C, 450°C, or any combination thereof. An annealing temperature not lower than 300°C is more conducive to the uniform dispersion of the material, thereby improving the electronic conductivity of the material and enhancing the rate performance of the battery; an annealing temperature not exceeding 450°C is more conducive to avoiding the decomposition of the material and the generation of byproducts, thereby improving the electrochemical performance of the material.

[0062] In some embodiments, the annealing time can be 4h-24h, for example, a range of 4h, 8h, 12h, 16h, 18h, 20h, 24h or any two of these.

[0063] In some embodiments, the precursor is calcined and then annealed. The calcination temperature can be 180℃-220℃, for example, a range of 180℃, 190℃, 200℃, 210℃, 220℃ or any two of these. The calcination time can be 3h-5h, for example, a range of 3h, 3.5h, 4h, 4.5h, 5h or any two of these.

[0064] After calcining the precursor, annealing it not only facilitates the evaporation of internal moisture and the formation of nanosheet structures, but also improves the purity of the material and reduces the impact of impurities on the electrochemical performance of the cathode material. At the same time, during the calcination process, the Na, Fe, and S elements in the precursor will further diffuse and mix, making the components more uniform at the microscopic scale, which is more conducive to forming materials with stable structure and consistent performance, thereby improving the electrochemical performance of the battery.

[0065] In some specific embodiments, the precursor can be laid flat in a crucible for calcination. It should be noted that the thickness of the precursor layer in the crucible generally does not exceed 10 cm. This is because if the precursor layer is too thick, it is not conducive to the uniform mixing of Na and Fe in the precursor. Therefore, by setting an appropriate thickness of the precursor layer in the crucible, it is more beneficial to the uniform formation of the sulfate polyanionic material, thereby improving the electrochemical performance and stability of the battery.

[0066] In some specific embodiments, sodium sulfate is used as the sodium source, ferrous sulfate as the iron source, and the sodium-iron molar ratio can be selected as 2.5:1.75. The conductive agent can be small-diameter carbon nanotubes, the dispersant can be PVP, and the addition amount can be 1%. The antioxidant for ferrous iron can be sodium citrate, and the addition amount can be 2.5%. Magnesium ion doping can be used for cation doping, and phosphate ion doping is preferred for anion doping, both of which can be added at 2%. The viscosity reducer can be dodecylbenzenesulfonic acid, and the addition amount can be 1%. The solution solid content can be 45%, and the final sample is Na. 2.5 Fe 1.75 (SO4)3.

[0067] This application also provides a positive electrode sheet, comprising the above-described sulfate polyanionic material or a sulfate polyanionic material prepared according to the above-described method for preparing sulfate polyanionic materials. This positive electrode sheet has advantages corresponding to the above-described sulfate polyanionic materials, which will not be elaborated further.

[0068] Specifically, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side of the surface of the positive current collector. The positive active layer includes the aforementioned sulfate polyanionic material, which serves as the positive active material of the positive electrode sheet.

[0069] In one specific embodiment, the positive electrode active layer comprises, by weight percentage, 70-99 wt% of positive electrode material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder; further, the positive electrode active layer comprises 80-98 wt% of positive electrode material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0070] The positive electrode current collector material may include at least one of aluminum foil and nickel foil; the conductive agent may be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; the binder may be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0071] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional coating method. For example, the positive electrode material of the present invention and the raw materials such as conductive agent and binder used to form the positive electrode active layer can be dispersed in N-methylpyrrolidone (NMP) solvent, and thoroughly stirred and mixed to form a uniform positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and cutting, the positive electrode sheet is obtained.

[0072] The present invention also provides a battery comprising the above-described positive electrode. This battery has advantages corresponding to the above-described positive electrode, which will not be elaborated further.

[0073] It is conceivable that the battery provided by the present invention, in addition to the aforementioned positive electrode, also includes a negative electrode, an electrolyte, and a separator.

[0074] Specifically, a battery may include a cell and a casing for encapsulating the cell. The cell includes a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. Electrolyte is injected into the casing to wet the cell.

[0075] This invention does not strictly limit the negative electrode active material in the negative electrode sheet. It can be a negative electrode active material commonly used in batteries, such as at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrode), and tin-based negative electrode materials (mainly including tin and tin alloy).

[0076] This invention does not strictly limit the choice of electrolyte. Conventional electrolytes in the art can be used, such as non-aqueous electrolytes. The electrolyte includes an organic solvent and an electrolyte salt. The organic solvent may include one or more solvents commonly used in current battery electrolytes. The electrolyte salt may include lithium salts, specifically lithium salts commonly used in current lithium-ion electrolytes. For example, the solvent may include one or more of ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc. The lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0077] This invention does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0078] The battery of the present invention can be manufactured according to conventional methods in the art. For example, when manufacturing the battery, the positive electrode sheet, separator and negative electrode sheet are wound or stacked to obtain a bare cell, and the bare cell is packaged into a pre-stamped shell (such as an aluminum-plastic film bag). After the packaged battery precursor is dried at 85°C, the electrolyte is injected into the dried battery precursor. After the process of resting, formation and secondary sealing, the battery manufacturing is completed.

[0079] The present invention also provides a battery pack comprising at least two interconnected batteries as described above, which has advantages corresponding to the batteries described above, and will not be described in detail hereafter.

[0080] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0081] The present invention also provides an electrical device, including the battery or battery pack described above, which has advantages corresponding to the battery or battery pack described above, and will not be described in detail here.

[0082] The electrical equipment used in the embodiments of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations on this.

[0083] The present invention will be further described below through specific embodiments. In the following embodiments and comparative examples, unless otherwise specified, the separator used is a Celgard 2400 polypropylene porous membrane, the negative electrode is a 15mm diameter sodium sheet from Krohde Chemical Co., Ltd., the conductive agent is TC-35 from Greenpowder Technology Co., Ltd., and the binders PVDF, NMP, carbon-coated aluminum foil, and propylene carbonate solution were all purchased from Krohde Chemical Co., Ltd. The ferrous sulfate and sodium sulfate used were industrial grade purchased from McLean Chemical Company.

[0084] Example 1:

[0085] 0.56 mol of anhydrous sodium sulfate and 0.78 mol of ferrous sulfate heptahydrate were dissolved in 600 g of pure water. Then, 0.01 mol of sodium citrate and 2% magnesium carbonate were added to the above solution, and the mixture was stirred for 30 min to obtain solution A. Next, carbon nanotubes (CNTs) at a mass fraction of 5% (the total mass of iron, sodium, sulfur, and dopants) were dispersed in 100 mL of deionized water. Then, 2% disodium hydrogen phosphate and 0.1% dodecylbenzenesulfonic acid (a viscosity reducer) were added, and the mixture was ultrasonically dispersed at 100 Hz for 30 min to form CNT pre-dispersion B. Solution B was then added to solution A, and the mixture was ultrasonically dispersed for 30 min to obtain spray-dried solution C. Solution C was continuously stirred at 200 rpm / min and spray-dried under the following conditions: inlet temperature 220℃, spray atomization pressure 0.2 MPa, feed rate 11 mm / s, and outlet temperature 105℃ to obtain precursor powder for sodium ferrous sulfate cathode material. Approximately 20 g of the precursor powder was then spread evenly in an alumina crucible and subjected to a two-step calcination process in a tube furnace (first stage: initial temperature 30℃, heating rate 5℃ / min to 200℃, holding for 4 h; second stage: heating rate 3℃ / min to 450℃, annealing for 8 h) to obtain the sulfate polyanionic material, specifically Na... 2.5 Fe 1.75 (SO4)3.

[0086] Battery preparation: The prepared sulfate polyanionic material was used as the positive electrode material for sodium-ion batteries, acetylene black as the conductive agent, polyvinylidene fluoride (PVDF) as the binder, and N-methylpyrrolidone (NMP) as the dispersant. The materials were mixed evenly in a mass ratio of positive electrode material:acetylene black:PVDF:NMP = 95:3:2:50 and coated on carbon-coated aluminum foil. The mixture was then vacuum dried in a 120℃ oven for 24 hours, and then pressed and rolled to form a positive electrode sheet with a compaction density of 2.08 g / cc. A 1 mol / L NaClO4 PC (propylene carbonate) solution was used as the electrolyte. Sodium sheets with a diameter of 15 mm from KELOD were purchased directly as negative electrodes. A Celgard 2400 polypropylene porous membrane was used as the separator to assemble a 2023 type button battery.

[0087] Example 2:

[0088] Compared to Example 1, the difference lies in the amount of dodecylbenzenesulfonic acid, the viscosity reducer, being added, which is changed to 0.5%. All other conditions are the same as in Example 1.

[0089] Example 3:

[0090] Compared to Example 1, the difference lies in the amount of dodecylbenzenesulfonic acid, the viscosity reducer, being added at 1%. All other conditions are the same as in Example 1.

[0091] Example 4:

[0092] Compared to Example 1, the difference lies in the amount of dodecylbenzenesulfonic acid, the viscosity reducer, being added, which is changed to 1.5%. All other conditions are the same as in Example 1.

[0093] Example 5:

[0094] Compared to Example 1, the difference lies in the amount of dodecylbenzenesulfonic acid, the viscosity reducer, being added at 2%. All other conditions are the same as in Example 1.

[0095] Example 6:

[0096] The amount of carbon nanotubes added in Example 3 was changed to 1%. All other conditions were the same as in Example 3.

[0097] Example 7

[0098] The amount of carbon nanotubes added in Example 3 was changed to 3%. All other conditions were the same as in Example 3.

[0099] Example 8:

[0100] The amount of carbon nanotubes added in Example 3 was changed to 7%.

[0101] The remaining conditions are the same as in Example 3.

[0102] Example 9:

[0103] The addition of carbon nanotubes was removed from the formulation of Example 3, while the other conditions remained the same as in Example 3.

[0104] Example 10:

[0105] Remove Mg from the formula in Example 3 2+ and PO4 3- Doping (i.e., removing the addition of magnesium carbonate and disodium hydrogen phosphate).

[0106] The remaining conditions are the same as in Example 3.

[0107] Comparative Example 1:

[0108] The water-soluble additive, dodecylbenzenesulfonic acid viscosity reducer, was removed from the formulation of Example 3.

[0109] The remaining conditions are the same as in Example 3.

[0110] In addition, the sulfate polyanionic materials in the examples and comparative examples were subjected to the following physical property tests, and the test results are shown in Table 1 and Table 2.

[0111] (1) Particle size test: 0.1 g of sulfate polyanionic material was dissolved in 20 mL of anhydrous ethanol and ultrasonically treated for 20 min to disperse it evenly. Then, the particle size was measured by a Malvern laser particle size analyzer and recorded as D. 50 D 100 .

[0112] (2) Specific surface area test: Take 0.5g of sulfate polyanionic material, crush it, and then use BST-BET400 instrument to test the specific surface area of ​​the cathode material.

[0113] (3) Nanosheet thickness test: The thickness was measured using a Zeiss Gemini SEM 300 scanning electron microscope.

[0114] (4) XRD test: The sulfate polyanionic material was tested by XRD using a BruKer D8 instrument from Bruker GmbH, Germany, and the XRD pattern was obtained.

[0115] (5) Test of conductive carbon material content: The content was determined using a DEK HCS-140 enhanced infrared carbon-sulfur analyzer.

[0116] In addition, the following performance tests were performed on the batteries in the embodiments and comparative examples, and the test results are shown in Table 2.

[0117] (6) Charge and discharge test

[0118] The charging test was conducted on the Xinwei BTS-51 battery test cabinet. Within the charge / discharge cutoff voltage range of 2.0V-4.0V, the discharge specific capacity and discharge efficiency of the sulfate polyanionic material were tested at a charge / discharge rate of 0.1C (discharge efficiency = first-cycle discharge capacity / first-cycle charging capacity).

[0119] (7) Ratio performance test

[0120] The battery was installed in the Xinwei BTS-51 battery test cabinet. At 25℃, the discharge cutoff voltage was within the range of 2.0V-4.0V. The discharge efficiency (discharge capacity at 30C rate / charging capacity at 0.1C rate) was tested under 30C conditions.

[0121] Table 1

[0122] Viscosity reducer addition amount (%) Conductive carbon content (%) <![CDATA[BET(m 2 / g)]]> Thickness (nm) D50 (μm) D100 (μm) Example 1 0.1 5.003 7.8 81.62 9.95 26.1 Example 2 0.5 5.011 9.3 60.01 8.35 25.2 Example 3 1 5 12 42.77 5.1 23.47 Example 4 1.5 5.006 8.8 137.6 7.01 24.8 Example 5 2 5.002 5.2 153.4 8.46 25 Example 6 1 1.01 10.8 20.62 5.49 30.2 Example 7 1 3.016 11.6 70.22 6.02 31.1 Example 8 1 7.019 12 92.9 5.9 28.8 Example 9 1 0 11.3 160 5.02 23.9 Example 10 1 4.99 11.7 149.2 5.5 25 Comparative Example 1 0 5.02 1.2 spherical structure 3.2 12

[0123] Table 2

[0124] Discharge specific capacity (mAh / g) Discharge efficiency (%) 30C discharge rate (%) Example 1 83.96 94.58 87.18 Example 2 86.58 96.58 88.6 Example 3 90.2 98.01 91.7 Example 4 84.19 97.58 86.5 Example 5 85.84 97.28 84.5 Example 6 76.3 89.66 79.96 Example 7 79.29 92.1 82.55 Example 8 90 98 91 Example 9 63.04 88.24 73.2 Example 10 72.6 85.02 77.22 Comparative Example 1 34.9 77.32 66.6

[0125] The test results for specific surface area and particle size are shown in Table 1. As can be seen from the examples, with the increase of viscosity reducer content, the specific surface area of ​​the material shows a trend of increasing and then decreasing, accompanied by a decrease in particle size followed by an increase. This is because when the initial addition amount is low, the dispersing effect is dominant, which can deagglomerate and stabilize the dispersion. When the addition amount reaches its peak, the optimal dispersion state is achieved, resulting in the spray-dried material having the largest specific surface area. When the addition amount is further increased, the supersaturation adsorption of the viscosity reducer will have the opposite effect, thus reducing the specific surface area of ​​the material again.

[0126] XRD test results are as follows Figure 1 As shown, the phases of the prepared examples and comparative materials are all similar to Na. 2.5 Fe 1.75 The standard card (PDF#97-025-2379) for (SO4)3 is completely identical, which indicates that the present invention has successfully prepared a pure-phase sodium ferrous sulfate cathode material, and the presence of viscosity reducers and antioxidants does not affect the generation of the pure-phase sodium ferrous sulfate.

[0127] SEM test results are as follows: Figure 2-4 As shown, the cathode material prepared in Example 1 has a distinct ultrathin sheet-like structure. Figure 2 As shown in the figure, this unique structure can significantly increase the specific surface area of ​​the cathode material in sodium batteries, providing more active sites for the adsorption and desorption of sodium ions, and making it easier to be completely wetted by the electrolyte, thus effectively improving the electrochemical performance of the battery. Compared with Comparative Column 1 ( Figure 4 From a morphological comparison perspective, the slurry that is spray-dried directly without adding viscosity reducers has a conventional spherical shape after drying and does not have any performance advantages.

[0128] Analysis of Tables 1 and 2 shows that adding a viscosity reducer during the preparation of sulfate polyanionic materials can promote the formation of nanosheet structures and improve the discharge and rate performance of the battery. Furthermore, composite materials with conductive carbon materials or doping with anions / cations in the sulfate polyanionic materials can further improve the discharge and rate performance of the battery.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sulfate polyanionic material, characterized in that, The sulfate polyanionic material comprises sulfate polyanionic nanosheets.

2. The sulfate polyanionic material according to claim 1, characterized in that, The thickness of the sulfate polyanionic nanosheets is 20 nm-160 nm; And / or, the molecular formula of the sulfate polyanionic material is Na. 2+2x Fe 2-2x (SO4)3, 0 ≤ x < 1.

3. The sulfate polyanionic material according to claim 1 or 2, characterized in that, The sulfate polyanionic material further includes conductive carbon material, at least a portion of which is distributed within the sulfate polyanionic material.

4. The sulfate polyanionic material according to any one of claims 1-3, characterized in that, The specific surface area of ​​the sulfate polyanionic material is 5-12 m². 2 / g; And / or, the particle size D50 of the sulfate polyanionic material is 5μm-10μm.

5. The sulfate polyanionic material according to any one of claims 1-4, characterized in that, The conductive carbon material includes at least one of carbon nanotubes, carbon black, acetylene black, Ketjen black, and graphene. And / or, the mass ratio of the conductive carbon material to the sulfate polyanionic material is 1%-8%.

6. The sulfate polyanionic material according to any one of claims 1-5, characterized in that, The sulfate polyanionic material further includes anionic doping and / or cationic doping; The anions include HF⁻, HPO₄²⁻, CO₃²⁻, Cl⁻, Br⁻, ClO⁻, and PO₄²⁻. 3- middle At least one of; and / or, The cations include Al 3+ Mg 2+ Ti 4+ Cu 2+ Mn 2+ At least one of them.

7. A method for preparing the sulfate polyanionic material according to any one of claims 1-6, characterized in that, Includes the following steps: The mixture containing an iron source, a sodium source, a sulfur source, and a viscosity reducer is dried to obtain a precursor. The precursor is annealed to obtain the sulfate polyanionic material.

8. The method for preparing sulfate polyanionic materials according to claim 7, characterized in that, The mixture includes water; And / or, the mixture further includes a conductive carbon material, the conductive carbon material including at least one of carbon nanotubes, carbon black, acetylene black, Ketjen black, and graphene; And / or, the mixture further includes an antioxidant, which includes at least one of ascorbic acid, vitamin C, glutathione, sodium citrate, sodium sulfite and ferrous gluconate; And / or, the mixture further includes a dispersant, the dispersant comprising at least one of carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, sodium dodecyl sulfate, and polyacrylic acid; And / or, the mixture further includes a dopant, the dopant being at least one of disodium hydrogen phosphate, sodium carbonate, sodium chloride, sodium bromide, sodium hypochlorite, magnesium carbonate, magnesium sulfate, aluminum sulfate, titanium sulfate, and copper sulfate; And / or, the viscosity reducer includes at least one of sodium dodecylbenzenesulfonate, fatty alcohol polyoxyethylene ether, polymaleic anhydride, xanthan gum, and sodium tripolyphosphate.

9. The method for preparing sulfate polyanionic materials according to claim 7 or 8, characterized in that, The drying process includes: spray drying the mixture to obtain the precursor.

10. The method for preparing the sulfate polyanionic material according to any one of claims 7-9, characterized in that, The annealing process is performed under a protective atmosphere; And / or, the annealing treatment is performed at a temperature of 300℃-450℃ for a time of 4h-24h.

11. A positive electrode plate, characterized in that, This includes the sulfate polyanionic material according to any one of claims 1-6 or the sulfate polyanionic material prepared according to the preparation method according to any one of claims 7-10.

12. A battery, characterized in that, Includes the positive electrode sheet as described in claim 11.

13. A battery pack, characterized in that, It includes at least two interconnected batteries as described in claim 12.

14. An electrical appliance, characterized in that, Includes the battery of claim 12 or the battery pack of claim 13.

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