Composite sodium electric layered oxide positive electrode material and preparation method and use thereof

Abstract

The application relates to a composite sodium battery layered oxide positive electrode material and a preparation method and application thereof. The composite sodium battery layered oxide positive electrode material comprises a sodium battery layered oxide material core and a MXene coating layer coated on the surface of the sodium battery layered oxide material core; the sodium battery layered oxide material core is doped with fluorine ions and chlorine ions, and the raw material of the chlorine ions is a eutectic salt containing chlorine ions. The positive electrode material provided by the application can simultaneously improve the structural stability of the near-surface region of the material and the ion transmission rate of the bulk phase deep layer through the internal fluorine ion doping, the special raw material chlorine ion doping and the coating of the MXene material, can construct an efficient ion transmission path to improve the ion migration efficiency, can effectively inhibit the interface side reaction between the electrode and the electrolyte, and can improve the performance of a sodium battery.

Description

A composite sodium-ion layered oxide cathode material, its preparation method and applications Technical Field

[0001] This invention belongs to the technical field of sodium electrochemical devices, and relates to a composite sodium electrochemical layered oxide cathode material, its preparation method, and its applications. Background Technology

[0002] With the rapid development of the large-scale energy storage and low-speed electric vehicle markets, sodium-ion batteries (sodium battery system), which are abundant in resources and inexpensive, are considered an important supplement and alternative to lithium-ion batteries. Among the various cathode materials for sodium battery systems, layered transition metal oxides have become one of the most promising technical routes due to their high theoretical capacity and mature synthesis process.

[0003] However, for sodium-based transition oxides, the core positive electrode active material in sodium-ion batteries, the electrochemical performance hinges on the uniformity and long-term stability of their crystal structure. During the electrochemical reaction of sodium ion insertion / extraction, the Na+ ions deep within the material structure... + It is difficult to effectively extract ions because the deeper structure of the material is denser, and the ion diffusion path is narrower. + The diffusion barrier is significantly higher than that of Na near the surface of the material. + The diffusion barrier results in poor rate performance of the material, limiting the application scenarios of layered oxide materials. Furthermore, during sodium ion insertion / extraction, the layered structure is prone to the O3→P3→O3′ phase transition, leading to abrupt changes in cell parameters and accumulation of lattice stress, causing microcracks and particle breakage, such as in Ni. 3+ Octahedral distortion (Jan Taylor effect) and transition metal layer slippage disrupt sodium ion transport channels. On the other hand, the periodic expansion and contraction of interlayer spacing in the near-surface region of the material during cycling accelerates structural fatigue, leading to a decline in cycle performance. Simultaneously, interfacial side reactions easily occur between the material surface and the electrolyte, generating a thick and electrochemically unstable interfacial impedance film (CEI), which significantly increases the interfacial charge transfer impedance. Byproducts accumulate at the interface, further hindering sodium ion diffusion, ultimately leading to a decrease in battery rate performance.

[0004] Therefore, how to effectively improve the structural stability of the near-surface region of the material and the deep ion transport rate in the bulk phase, and improve the structural stability while avoiding interfacial side reactions, is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a composite sodium-ion battery layered oxide cathode material, its preparation method, and its applications. The cathode material provided by this invention, through the synergistic doping of internal fluorine ions and chloride ions from a special raw material, combined with the coating of MXene material, can simultaneously improve the structural stability of the near-surface region and the deep ion transport rate in the bulk phase. This not only constructs an efficient ion transport pathway to enhance ion migration efficiency but also effectively suppresses interfacial side reactions between the electrode and the electrolyte, thereby improving the performance of sodium-ion batteries.

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

[0007] In a first aspect, the present invention provides a composite sodium-electric layered oxide cathode material, the composite sodium-electric layered oxide cathode material comprising a sodium-electric layered oxide material core and an MXene coating layer covering the surface of the sodium-electric layered oxide material core;

[0008] The core of the sodium-electric layered oxide material is doped with fluoride ions and chloride ions, and the raw material for the chloride ions is a chloride-containing eutectic salt.

[0009] Preferably, the general chemical formula of the sodium-electric layered oxide material is Na. u+v Ni 1-m-n Fe m Mn n M z O α F β Cl γ Wherein, 0.9≤u+v≤1.05, 0≤m<1, 0≤n<1, 1-mn>0, 0≤v≤0.1, 0≤z≤0.2, 0.02≤β≤0.04, 0.02≤γ≤0.04, 3.9≤2α+β+γ≤5, where v is the sodium ion content in the chloride-containing eutectic salt, and M is the dopant ion. Preferably, the interlayer spacing of the sodium-electric layered oxide material is 5.35Å~5.37Å.

[0010] Preferably, the MXene material in the MXene coating layer includes TiCNT. x Base material.

[0011] Preferably, the TiCNT x The base material also includes doping elements, including Ca and / or Zn.

[0012] Preferably, the doping elements include Ca and Zn.

[0013] Preferably, undoped TiCNTs are used. x The mass of the base material is 100%, and the doping mass of the Ca element is 2% to 10%.

[0014] Preferably, undoped TiCNTs are used. x The mass of the base material is 100%, and the doping mass of the Zn element is 2% to 10%.

[0015] In a second aspect, the present invention provides a method for preparing the composite sodium-ion layered oxide cathode material as described in the first aspect, the method comprising the following steps:

[0016] (1) Mix sodium-ion cathode precursor material, basic sodium source, chloride-containing eutectic salt and fluorine source, and perform first calcination to obtain sodium-ion layered oxide material core;

[0017] (2) The sodium-electric layered oxide material core and MXene material are mixed and coated, and then a second calcination is performed to obtain the composite sodium-electric layered oxide cathode material.

[0018] Preferably, the sodium-ion cathode precursor material in step (1) includes a hydroxide-based sodium-ion cathode precursor material.

[0019] Preferably, the chloride-containing eutectic salt in step (1) includes any one or a combination of at least two of the following: NaCl-KCl eutectic salt, NaCl-CaCl2 eutectic salt, NaCl-ZnCl2 eutectic salt, NaCl-Na2CO3 eutectic salt, MgCl2-KCl eutectic salt, or NaCl-AlCl3 eutectic salt.

[0020] Preferably, the fluorine source includes fluorides.

[0021] Preferably, the raw materials mixed in step (1) further include a dopant containing element M.

[0022] Preferably, in step (1), the first calcination is carried out in an oxygen-containing atmosphere, the heating rate of the first calcination in step (1) is 2℃ / min~6℃ / min, the holding temperature after the first calcination is 850℃~1100℃, and the holding time after the first calcination is 10h~20h.

[0023] Preferably, in step (2), the mass of the added MXene material is 0.2% to 10% of the mass of the sodium-electric layered oxide material core.

[0024] Preferably, in step (2), the second calcination is carried out under a protective atmosphere, the holding temperature after the second calcination is raised in step (2) is 550℃~900℃, and the holding time after the second calcination is raised in step (2) is 5h~12h.

[0025] Preferably, in step (2), after the second calcination treatment, a cooling treatment is performed, and the cooling rate of the cooling treatment is 1℃ / min to 6℃ / min.

[0026] Thirdly, the present invention also provides a sodium electrochemical device, the sodium electrochemical device comprising the composite sodium electrochemical layered oxide cathode material as described in the first aspect or the composite sodium electrochemical layered oxide cathode material prepared by the preparation method described in the second aspect.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The cathode material of the present invention uses fluoride and chloride ions to dope sodium-electric layered oxide materials, and uses a chloride-containing eutectic salt as a raw material. On the one hand, dual-ion doping can achieve partial substitution of O. Based on the electronegativity rule (F>O), the substitution of F improves the structural stability of the near-surface region of the material, avoiding the periodic expansion and contraction during cycling that accelerates the structural fatigue of the material and leads to interlayer slippage of the transition metal. On the other hand, using a chloride-containing eutectic salt can broaden the diffusion path of the deep bulk structure of the sodium-electric layered oxide material during the preparation process. Chloride ions can penetrate into the deep structure of the material, and based on the electronegativity rule (O>Cl), The partial substitution of chloride ions weakens the bond energy of the Na-O bond, which helps to increase the interlayer spacing of sodium ions, reduce the diffusion barrier of sodium ions, and improve the diffusion rate of sodium ions in the deep layers of the particles. Furthermore, the MXene coating layer on the core surface works synergistically. MXene material has ultra-high conductivity, which reduces ion migration impedance and simultaneously constructs an efficient ion transport pathway to improve ion migration efficiency. The surface coating also avoids direct contact between the bulk phase and the electrolyte and can effectively suppress interfacial side reactions between the electrode and the electrolyte. Through the synergistic effect of specific doping and coating methods, this invention improves the cycling performance and rate performance of sodium-ion layered oxide materials.

[0029] (2) The preparation method provided by this invention involves the co-reaction of a basic sodium source, a chloride-containing eutectic salt, a fluorine source, and a sodium-ion cathode precursor material. While forming a layered oxide material with sodium, it also achieves bulk doping of chloride and fluorine ions, improving the structural stability of the near-surface region of the bulk phase. The chloride-containing eutectic salt effectively reduces the melting temperature of the system, thereby widening the reaction temperature window between the sodium source and the precursor, providing favorable thermodynamic conditions for the full reaction, and lowering the reaction temperature. The eutectic salt, as a co-solvent, can regulate the crystal growth process, promote the orientation growth of active crystal faces, and improve the Na+ structure. + The transport dynamics characteristics enhance the rate performance of the material, and also enable the transport of chloride ions (Cl) to be carried. -It penetrates deep into the particles, broadening the ion diffusion path in the deep particles; based on the core, it works in conjunction with the coating of MXene material with excellent surface conductivity to construct a multidimensional ion transport channel, simultaneously improving the ion migration rate and surface structure stability, and finally preparing a sodium-ion cathode material with high cycle stability and high rate performance. Attached Figure Description

[0030] Figure 1 is a SEM image of the composite sodium electrochemical layered oxide cathode material in Example 1.

[0031] Figure 2 shows the rate performance of the sodium-ion battery provided in Example 1.

[0032] Figure 3 shows the cycle performance of the sodium-ion battery provided in Example 1. Detailed Implementation

[0033] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0034] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0035] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0037] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0038] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0039] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0040] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0041] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0042] In this invention, "optional" means that something is optional, that is, it refers to either "with" or "without". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0043] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0044] In one embodiment, the present invention provides a composite sodium-electric layered oxide cathode material, the composite sodium-electric layered oxide cathode material comprising a sodium-electric layered oxide material core and an MXene coating layer covering the surface of the sodium-electric layered oxide material core;

[0045] The core of the sodium-electric layered oxide material is doped with fluoride ions and chloride ions, and the raw material for the chloride ions is a chloride-containing eutectic salt.

[0046] It should be noted that the chloride-containing eutectic salt mentioned in this invention refers to a specific mixture composed of two or more salts, having a eutectic point, and at least one salt having a chloride ion as its anion, and having a relatively low melting point; the MXene material refers to a class of two-dimensional transition metal carbides, nitrides, or carbonitrides, whose surface contains hydroxyl groups or terminal oxygen functional groups and has metallic conductivity.

[0047] The cathode material of this invention employs fluoride and chloride ions for doping of sodium-ion-based layered oxide materials, while using a chloride-containing eutectic salt as a raw material. On one hand, dual-ion doping allows for partial substitution of oxygen (O). Based on the electronegativity rule (F>O), the substitution of F improves the structural stability of the near-surface region of the material, preventing the accelerated structural fatigue caused by periodic expansion and contraction during cycling, which could lead to interlayer slippage of the transition metal. On the other hand, using a chloride-containing eutectic salt during preparation broadens the diffusion path of the deep bulk structure of the sodium-ion-based layered oxide material. Chloride ions can penetrate deep into the material's structure, and based on the electronegativity rule (O>Cl),... The partial substitution of chloride ions weakens the bond energy of the Na-O bond, which helps to increase the interlayer spacing of sodium ions, reduce the diffusion barrier of sodium ions, and improve the diffusion rate of sodium ions in the deep layers of the particles. Furthermore, the MXene coating layer on the core surface works synergistically. MXene material has ultra-high conductivity, which reduces ion migration impedance and simultaneously constructs an efficient ion transport pathway to improve ion migration efficiency. The surface coating also avoids direct contact between the bulk phase and the electrolyte and can effectively suppress interfacial side reactions between the electrode and the electrolyte. Through the synergistic effect of specific doping and coating methods, this invention improves the cycling performance and rate performance of sodium-ion layered oxide materials.

[0048] In some embodiments, the general chemical formula of the sodium-electric layered oxide material is Na. u+v Ni 1-m-n Fe m Mn n M z O α F β Cl γ Wherein, 0.9≤u+v≤1.05, 0≤m<1, 0≤n<1, 1-mn>0, 0≤v≤0.1, 0≤z≤0.2, 0.02≤β≤0.04, 0.02≤γ≤0.04, 3.9≤2α+β+γ≤5, where v is the sodium ion content in the chloride-containing eutectic salt, and M is the dopant ion.

[0049] For example, the Na u+v Ni 1-m-n Fe m Mn n M z O α F β Cl γIn this equation, u+v can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, or 1.05, etc.; m can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, etc.; and n can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, or 0. 6, 0.7, 0.8, or 0.9, etc.; v can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1, etc.; z can be 0, 0.05, 0.08, 0.1, 0.13, 0.15, 0.18, or 0.2, etc.; β can be 0.02, 0.03, or 0.04, etc.; γ can be 0.02, 0.03, or 0.04, etc.

[0050] It is understood that when the chloride-containing eutectic salt in this invention includes sodium chloride, it can also be used as a sodium source in the sodium sintering process of the cathode material.

[0051] In the sodium-electric layered oxide material core provided by this invention, by regulating Na u+v Ni 1-m-n Fe m Mn n M z O α F β Cl γ The stoichiometric ratios of the various elements further increase the material's configurational entropy, reduce its Gibbs free energy, and force the system towards thermodynamic steady state, thus decreasing the material's phase separation tendency. The M-doped ions include, but are not limited to, Li. + K + Ca 2+ 、Sr 2+ Zn 2+ Cu 2+ Mg 2+ Al 3+ Y 3+ Zr 4+ Ti 4+ or Sn 4+ One or more of them.

[0052] In some embodiments, the interlayer spacing of the sodium-electric layered oxide material is 5.35 Å to 5.37 Å, for example 5.35 Å, 5.36 Å or 5.37 Å.

[0053] The sodium-ion layered oxide material of the present invention has a relatively larger interlayer spacing under the action of chloride-containing eutectic salt raw material. Chloride ions can penetrate into the deep layers of the particles, increasing the diffusion rate of sodium ions in deeper positions of the material and improving the rate performance of the material.

[0054] In some embodiments, the MXene material in the MXene coating layer includes TiCNT. x Base material.

[0055] In some embodiments, the TiCNT x The base material also includes doping elements, including Ca and / or Zn.

[0056] In the embodiments of the present invention, TiCNT is selected. x The base material, MXene, exhibits extremely high conductivity due to the presence of surface functional groups (such as -O or -OH), which further reduces the ion migration impedance of the cathode material. Furthermore, doping with Ca and / or Zn facilitates rapid diffusion of sodium ions and the formation of TiCNTs. x The stability of the base material is enhanced.

[0057] In some embodiments, the doping elements include Ca and Zn.

[0058] In some implementations, undoped TiCNTs are used. x The mass of the base material is 100%, and the doping mass of the Ca element is 2% to 10%, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0059] In some implementations, undoped TiCNTs are used. x The mass of the base material is 100%, and the doping mass of the Zn element is 2% to 10%, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0060] This invention in TiCNT x The base material is doped with both Ca and Zn elements simultaneously, and the two elements work synergistically to achieve TiCNTs. x The expansion of the channels in the base material significantly improves the ion transport kinetics; while Zn doping can fill the Ti vacancy defect sites, reduce the surface dangling bond density, and construct an oxygen diffusion barrier, thus enhancing the performance of TiCNTs. x The base material exhibits enhanced stability; the combined effect of the two elements results in improved TiCNT modification. xWhen the base material is coated with a core, on the one hand, defect passivation is used to suppress side reactions at the electrode / electrolyte interface, thereby better enhancing the surface stability of the material; on the other hand, the Na layer structure is optimized. + Diffusion kinetics can be used to further improve the overall performance of sodium batteries.

[0061] Furthermore, the present invention modulates the Ca element in the TiCNT x The doping mass of the base material is 2%~10%, and the Zn element in the TiCNT is... x The doping mass in the base material is 2%~10%; this is more favorable for TiCNTs. x Improvements in the stability of the base material and ion transport dynamics.

[0062] It is understood that the present invention does not limit the source of MXene materials. Those skilled in the art can purchase them according to actual needs, or prepare them themselves using conventional preparation methods. The present invention applies to any preparation process that can be reasonably known by those skilled in the art without departing from the overall inventive concept of the present invention.

[0063] Example, but not limitation, of the present invention provides a Ca and Zn co-doped TiCNT x A method for preparing MXene material based on a base material, the method comprising:

[0064] According to the target doping amount, Ti powder, Al powder, graphite powder, TiN powder and doping sources calcium and zinc are ball-milled and mixed in stoichiometric ratio. Under the protection of argon atmosphere, high-temperature solid-state sintering is carried out to form a (Zn, Ca) co-doped Ti3AlCN solid solution (MAX phase). The obtained Ti3AlCN solid solution is immersed in etching solution and continuously stirred to achieve interlayer stripping. After centrifugation and washing to remove residual etchant, the target MXene material is obtained by freeze drying.

[0065] Optionally, the calcium source includes, but is not limited to, at least one of calcium fluoride, calcium oxide, or calcium carbonate, and the zinc source includes, but is not limited to, at least one of zinc fluoride, zinc oxide, or zinc powder.

[0066] Optionally, the atmosphere for the high-temperature solid-state sintering includes a protective atmosphere, such as nitrogen, argon, or helium.

[0067] Optionally, the heating rate of the high-temperature solid-state sintering is 3℃ / min to 10℃ / min, for example, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min; the holding temperature after the high-temperature solid-state sintering is 1400℃ to 1600℃, for example, 1400℃, 1450℃, 1500℃, 1550℃, or 1600℃; and the holding time after the high-temperature solid-state sintering is 2h to 4h, for example, 2h, 3h, or 4h.

[0068] Optionally, the etching solution includes an acid solution containing fluoride salts, which may be selected from hydrofluoric acid (HF) solution, wherein the mass concentration of the HF solution is 10wt% to 30wt%, for example, 10wt%, 15wt%, 20wt%, 25wt% or 30wt%.

[0069] Optionally, the stirring temperature is 20℃~40℃, such as 20℃, 25℃, 30℃, 35℃ or 40℃; the stirring time can be 12h~48h, such as 12h, 15h, 18h, 20h, 24h, 25h, 27h, 30h, 33h, 35h, 36h, 38h, 40h, 42h, 45h or 48h.

[0070] In one embodiment, a second aspect of the present invention provides a method for preparing a composite sodium-ion layered oxide cathode material as described in the first aspect, the method comprising the following steps:

[0071] (1) Mix sodium-ion cathode precursor material, basic sodium source, chloride-containing eutectic salt and fluorine source, and perform first calcination to obtain sodium-ion layered oxide material core;

[0072] (2) The sodium-electric layered oxide material core and MXene material are mixed and coated, and then a second calcination is performed to obtain the composite sodium-electric layered oxide cathode material.

[0073] The preparation method provided by this invention involves the co-reaction of a basic sodium source, a chloride-containing eutectic salt, a fluorine source, and a sodium-ion cathode precursor material. While forming a layered oxide material with sodium, it also achieves bulk doping of chloride and fluorine ions, improving the structural stability of the near-surface region of the bulk phase. The chloride-containing eutectic salt effectively lowers the melting temperature of the system, thereby widening the reaction temperature window between the sodium source and the precursor, providing favorable thermodynamic conditions for the full reaction and reducing the reaction temperature. The eutectic salt, acting as a co-solvent, can regulate the crystal growth process, promote the orientation growth of active crystal faces, and improve the Na+ structure. + The transport dynamics characteristics enhance the rate performance of the material, and also enable the transport of chloride ions (Cl) to be carried. -It penetrates deep into the particles, broadening the ion diffusion path in the deep particles; based on the core, it works in conjunction with the coating of MXene material with excellent surface conductivity to construct a multidimensional ion transport channel, simultaneously improving the ion migration rate and surface structure stability, and finally preparing a sodium-ion cathode material with high cycle stability and high rate performance.

[0074] More specifically, in this invention, the near-surface region of the sodium-electric layered oxide material core refers to a position 1 μm to 4 μm away from the particle surface, while the deep layer of the particle refers to a position 4 μm to 8 μm deep from the particle surface.

[0075] In some embodiments, the sodium-ion cathode precursor material in step (1) includes a hydroxide-based sodium-ion cathode precursor material.

[0076] It is understood that the sodium-ion cathode precursor material in this invention can be a nickel-based sodium-ion cathode precursor material, and its general chemical formula can be Ni. 1-m-n Fe m Mn n (OH)₂, 0≤m<1, 0≤n<1, 1-mn>0, further preferably 0.2≤m≤0.4, 0.2≤n≤0.4, corresponding to Na u+v Ni 1-m-n Fe m Mn n M z O α F β Cl γ The stoichiometric ratio of m and n is further preferred to be 0.2≤m≤0.4 and 0.2≤n≤0.4.

[0077] At this time, m can be 0.2, 0.23, 0.25, 0.28, 0.3, 0.33, 0.35, 0.38 or 0.4, etc., and n can be 0.2, 0.23, 0.25, 0.28, 0.3, 0.33, 0.35, 0.38 or 0.4, etc.

[0078] In some embodiments, the chloride-containing eutectic salt in step (1) includes any one or a combination of at least two of the following: NaCl-KCl eutectic salt, NaCl-CaCl2 eutectic salt, NaCl-ZnCl2 eutectic salt, NaCl-Na2CO3 eutectic salt, MgCl2-KCl eutectic salt, or NaCl-AlCl3 eutectic salt; preferably, the chloride-containing eutectic salt in step (1) includes at least NaCl.

[0079] In the embodiments of the present invention, the chloride-containing eutectic salt in step (1) contains both sodium ions and chloride ions. In particular, when it contains NaCl, it can be used as a raw material for chloride ions and simultaneously as a supplementary sodium source. Working together with the basic sodium source, it can simultaneously ensure the cycling stability and rate performance of the material. If only the chloride-containing eutectic salt is used as the sodium source in the system, it will lead to excessive growth of the active crystal face of the material and excessive increase in specific surface area to a certain extent, which will aggravate the side reaction with the electrolyte and deteriorate the long-term cycling stability of the material. Conversely, if only the basic sodium source is used, due to the dense structure formed deep in the particles, the Na⁺ diffusion barrier is high, which will significantly restrict the rate performance of the material. When the present invention uses a small proportion of eutectic salt and basic sodium source to compound, the Cl carried by the eutectic salt - It can penetrate deep into the particles and effectively reduce sodium. + A diffusion barrier is used to improve rate performance without adversely affecting the cycling stability of the material.

[0080] In some embodiments, the fluorine source includes a fluoride, specifically sodium fluoride.

[0081] In some embodiments, the raw materials mixed in step (1) also include a dopant containing element M.

[0082] During the preparation process, the present invention can simultaneously perform conventional doping of element M, further improving the performance of the cathode material according to requirements; the dopant containing element M can be selected from carbonates, oxides or hydroxides, etc.

[0083] In some embodiments, the first calcination in step (1) is carried out in an oxygen-containing atmosphere.

[0084] In some embodiments, the heating rate of the first calcination in step (1) is 2℃ / min to 6℃ / min, for example 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or 6℃ / min.

[0085] In some embodiments, the holding temperature after the first calcination heating in step (1) is 850℃~1100℃, such as 850℃, 900℃, 950℃, 1000℃, 1050℃ or 1100℃.

[0086] In some implementations, the holding time after the first calcination heating in step (1) is 10h~20h, for example 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h or 20h.

[0087] In some embodiments, in step (2), the mass of the added MXene material is 0.2% to 10% of the mass of the sodium-electric layered oxide material core, for example, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0088] In an embodiment of the present invention, by adjusting the added mass of the MXene material to 0.2% to 10% of the mass of the sodium-electric layered oxide material core, it is more beneficial to improve the conductivity of the material, reduce the ion migration impedance, and thus improve the rate performance of the material.

[0089] In some embodiments, step (2) the second calcination is carried out under a protective atmosphere, which includes a nitrogen atmosphere or an inert gas atmosphere, and the inert gas includes, but is not limited to, argon and / or helium.

[0090] In some embodiments, the holding temperature after the second calcination heating in step (2) is 550℃~900℃, for example 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃ or 900℃.

[0091] In some embodiments, the holding time after the second calcination heating in step (2) is 5h~12h, for example 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h.

[0092] In some embodiments, after the second calcination treatment in step (2), a cooling treatment is performed, and the cooling rate of the cooling treatment is 1℃ / min to 6℃ / min, for example, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or 6℃ / min.

[0093] After the second calcination, the present invention employs a regular cooling process to prevent cracks in the particles and improve particle stability.

[0094] It should also be noted that the basic sodium source in this invention is the sodium source commonly used in the preparation of sodium in non-eutectic salt systems, including but not limited to sodium carbonate, sodium bicarbonate, etc., and does not contain sodium chloride. In addition, the amount of the corresponding basic sodium source is adaptively adjusted according to the type of chloride ion raw material and fluorine source to ensure that the sodium content of the entire system meets the requirement that the molar ratio of sodium to the total metal in the precursor material is (0.9~1.05):1, for example, 0.95:1, 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1 or 1.05:1, etc.

[0095] In one embodiment, the third aspect of the present invention also provides a sodium electrochemical device, the sodium electrochemical device comprising a composite sodium electrochemical layered oxide cathode material as described in the first aspect or a composite sodium electrochemical layered oxide cathode material prepared by the preparation method described in the second aspect.

[0096] The sodium electrochemical device in this invention can be selected from sodium-ion batteries, including sodium-ion secondary batteries or sodium-ion primary batteries, etc. Those skilled in the art can make adaptive selections and adjustments according to actual needs.

[0097] In sodium-ion batteries, the composite sodium-ion layered oxide cathode material provided by this invention is used as a cathode active material in the cathode sheet. It can be used alone or mixed with other types of sodium-ion cathode materials. Those skilled in the art can make adaptive selections and adjustments according to actual needs. Apart from the composite sodium-ion layered oxide cathode material provided by this invention, other substances and structures in the sodium-ion battery are not limited by this invention and are all conventional technical solutions. Under the premise of not violating the overall technical concept of this invention, any solution that can be reasonably obtained by those skilled in the art is applicable to this invention.

[0098] 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.

[0099] Example 1

[0100] This embodiment provides a composite sodium-electric layered oxide cathode material, which includes a sodium-electric layered oxide material core and an MXene coating layer covering the surface of the sodium-electric layered oxide material core;

[0101] The chemical formula of the sodium-electric layered oxide material core is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3Sr 0.05 Ti 0.05 O 2.12 F 0.03 Cl 0.03 The raw material for the chloride ions is a NaCl-Na2CO3 eutectic salt;

[0102] The MXene material in the MXene coating layer is Ca and Zn co-doped TiCNT. x The base material, and the Ca doping quality is the same as that of undoped TiCNT. x The mass of the base material is 5%, and the doping mass of Zn is the same as that of undoped TiCNT. x 5% of the mass of the base material.

[0103] The preparation method of the composite sodium-ion layered oxide cathode material includes:

[0104] (1) According to NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.12 F 0.03 Cl 0.03 Weigh the nickel-iron-manganese hydroxide precursor Ni according to the stoichiometric ratio. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, sodium carbonate (basic sodium source), NaCl-Na2CO3 eutectic salt, sodium fluoride, strontium carbonate dopant, and titanium oxide dopant were stirred at 300 r / min for 15 min to obtain a homogeneous material. The homogeneous material was heated to 900℃ at a heating rate of 3℃ / min and held for 16 h in an oxygen atmosphere (first calcination) at a furnace pressure of -5 Pa. After pulverizing and sieving, a calcined material, namely the core of sodium-electric layered oxide material, was obtained.

[0105] (2) The sintered material described in the previous step is combined with Ca and Zn co-doped TiCNT. x The MXene material of the base material is mixed, and the mass of the added MXene material is 5% of the mass of the sodium-electric layered oxide material core. Then, it is calcined for 8 hours at 850°C in a nitrogen atmosphere with a furnace pressure of +2Pa. Finally, it is cooled to room temperature at a rate of 3°C / min and then sieved to obtain the composite sodium-electric layered oxide cathode material.

[0106] Figure 1 shows a SEM image of the composite sodium-ion layered oxide cathode material in Example 1. As can be seen from Figure 1, the diameter of the particles, i.e., the median particle size D, is... v The particles are around 15μm in size, with no obvious adhesion or agglomeration between them, and good dispersibility; and there are no visible cracks or broken marks on the particle surface.

[0107] Example 2

[0108] This embodiment provides a composite sodium-electric layered oxide cathode material, which includes a sodium-electric layered oxide material core and an MXene coating layer covering the surface of the sodium-electric layered oxide material core;

[0109] The chemical formula of the sodium-electric layered oxide material core is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3Sr 0.05 Ti 0.05 O2.12 F 0.03 Cl 0.03 The raw material for the chloride ions is a NaCl-Na2CO3 eutectic salt;

[0110] The MXene material in the MXene coating layer is Ca and Zn co-doped TiCNT. x The base material, and the Ca doping quality is the same as that of undoped TiCNT. x The base material mass is 2%, and the Zn doping mass is the same as that of undoped TiCNT. x 2% of the mass of the base material.

[0111] The preparation method of the composite sodium-ion layered oxide cathode material includes:

[0112] (1) According to NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.12 F 0.03 Cl 0.03 Weigh the nickel-iron-manganese hydroxide precursor Ni according to the stoichiometric ratio. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, sodium carbonate (basic sodium source), eutectic salt NaCl-Na2CO3, sodium fluoride, strontium carbonate dopant, and titanium oxide dopant were stirred at 500 r / min for 10 min to obtain a homogeneous material. The homogeneous material was then heated to 1100℃ at a heating rate of 5℃ / min and held for 10 h (first calcination) under an oxygen atmosphere and a furnace pressure of -25 Pa. After pulverization and sieving, a calcined material was obtained, namely the core of a sodium-electric layered oxide material. The particle diameter (median particle size D) v 50) Around 16μm;

[0113] (2) The sintered material described in the previous step is combined with Ca and Zn co-doped TiCNT. x The MXene material of the base material is mixed, and the mass of the added MXene material is 10% of the mass of the sodium-electric layered oxide material core. Then, it is calcined for 12 hours at 550°C in a nitrogen atmosphere with a furnace pressure of +5Pa. Finally, it is cooled to room temperature at a rate of 1°C / min and then sieved to obtain the composite sodium-electric layered oxide cathode material.

[0114] Example 3

[0115] This embodiment provides a composite sodium-electric layered oxide cathode material, which includes a sodium-electric layered oxide material core and an MXene coating layer covering the surface of the sodium-electric layered oxide material core;

[0116] The chemical formula of the sodium-electric layered oxide material core is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3Sr 0.05 Ti 0.05 O 2.12 F 0.03 Cl 0.03 The raw material for the chloride ions is a NaCl-Na2CO3 eutectic salt;

[0117] The MXene material in the MXene coating layer is Ca and Zn co-doped TiCNT. x The base material, and the Ca doping quality is the same as that of undoped TiCNT. x The base material accounts for 10% of the mass, and the Zn doping mass is the same as that of undoped TiCNT. x 10% of the mass of the base material.

[0118] The preparation method of the composite sodium-ion layered oxide cathode material includes:

[0119] (1) According to NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.12 F 0.03 Cl 0.03 Weigh the nickel-iron-manganese hydroxide precursor Ni according to the stoichiometric ratio. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, sodium carbonate (basic sodium source), eutectic salt NaCl-Na2CO3, sodium fluoride, strontium carbonate dopant, and titanium oxide dopant were stirred at 300 r / min for 15 min to obtain a homogeneous material. The homogeneous material was then heated to 850℃ at a heating rate of 2℃ / min and held for 20 h (first calcination) under an oxygen atmosphere and a furnace pressure of -5 Pa. After pulverization and sieving, a calcined material was obtained, namely the core of a sodium-electric layered oxide material. The particle diameter (median particle size D) v 50) Around 14μm;

[0120] (2) The sintered material described in the previous step is combined with Ca and Zn co-doped TiCNT. x The MXene material of the base material is mixed, and the mass of the added MXene material is 0.2% of the mass of the sodium-electric layered oxide material core. Then, it is calcined for 5 hours at 900°C in an argon atmosphere with a furnace pressure of +2Pa. Finally, it is cooled to room temperature at a rate of 6°C / min and then sieved to obtain the composite sodium-electric layered oxide cathode material.

[0121] Example 4

[0122] The difference between this embodiment and Embodiment 1 is that the chemical formula of the sodium-electric layered oxide material core in this embodiment is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 K 0.015 Sr 0.18 Al 0.005 O 2.165 F 0.03 Cl 0.03 The raw material for the chloride ions is a NaCl-KCl eutectic salt.

[0123] In step (1) of the preparation method, based on the adjusted NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 K 0.015 Sr 0.18 Al 0.005 O 2.165 F 0.03 Cl 0.03 The raw materials are weighed according to the stoichiometric ratio.

[0124] All other conditions remain the same as in Example 1.

[0125] Example 5

[0126] The difference between this embodiment and Embodiment 1 is that the chemical formula of the sodium-electric layered oxide material core in this embodiment is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 Zn 0.01 O 1.98 F 0.03 Cl 0.03 The raw material for the chloride ions is NaCl-ZnCl2 eutectic salt.

[0127] In step (1) of the preparation method, based on the adjusted NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Zn 0.01 O 1.98 F 0.03 Cl 0.03 The raw materials are weighed according to the stoichiometric ratio.

[0128] All other conditions remain the same as in Example 1.

[0129] Example 6

[0130] The difference between this embodiment and Embodiment 1 is that the chemical formula of the sodium-electric layered oxide material core in this embodiment is NaNi. 1 / 3Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.13 F 0.02 Cl 0.02 .

[0131] In step (1) of the preparation method, based on the adjusted NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.13 F 0.02 Cl 0.02 The raw materials are weighed according to the stoichiometric ratio.

[0132] All other conditions remain the same as in Example 1.

[0133] Example 7

[0134] The difference between this embodiment and Embodiment 1 is that the chemical formula of the sodium-electric layered oxide material core in this embodiment is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.11 F 0.04 Cl 0.04 .

[0135] In step (1) of the preparation method, based on the adjusted NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.11 F 0.04 Cl 0.04 The raw materials are weighed according to the stoichiometric ratio.

[0136] All other conditions remain the same as in Example 1.

[0137] Example 8

[0138] The difference between this embodiment and Embodiment 1 is that the chemical formula of the sodium-electric layered oxide material core in this embodiment is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.085 F 0.03 Cl 0.1 .

[0139] In step (1) of the preparation method, based on the adjusted NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.085 F 0.03 Cl 0.1 The raw materials are weighed according to the stoichiometric ratio.

[0140] All other conditions remain the same as in Example 1.

[0141] Example 9

[0142] The difference between this embodiment and Embodiment 1 is that the chemical formula of the sodium-electric layered oxide material core in this embodiment is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.085 F 0.1 Cl 0.03 .

[0143] In step (1) of the preparation method, based on the adjusted NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Sr 0.05 Ti 0.05 O 2.085 F 0.1 Cl 0.03 The raw materials are weighed according to the stoichiometric ratio.

[0144] All other conditions remain the same as in Example 1.

[0145] Example 10

[0146] The difference between this embodiment and Embodiment 1 is that the eutectic salt in this embodiment is MgCl2-KCl eutectic salt.

[0147] All other conditions remain the same as in Example 1.

[0148] Example 11

[0149] The difference between this embodiment and Embodiment 1 is that the MXene material in this embodiment is undoped TiCNT. x Base material.

[0150] All other conditions remain the same as in Example 1.

[0151] Example 12

[0152] The difference between this embodiment and Embodiment 1 is that in this embodiment, the MXene material is TiCNT doped only with Ca. x Base material.

[0153] All other conditions remain the same as in Example 1.

[0154] Example 13

[0155] The difference between this embodiment and Embodiment 1 is that in this embodiment, the MXene material is TiCNT doped only with Zn. x Base material.

[0156] All other conditions remain the same as in Example 1.

[0157] Example 14

[0158] The difference between this embodiment and Embodiment 1 is that in this embodiment, the MXene material is TiCNT co-doped with Ca and Zr elements. x Base material.

[0159] All other conditions remain the same as in Example 1.

[0160] Example 15

[0161] The difference between this embodiment and Embodiment 1 is that in this embodiment, the mass of MXene material added is 15% of the mass of the sodium-electric layered oxide material core.

[0162] All other conditions remain the same as in Example 1.

[0163] Comparative Example 1

[0164] The difference between this comparative example and Example 1 is that the composite sodium-ion layered oxide cathode material in this comparative example is not doped with fluoride ions or chloride ions, nor is it coated with MXene material.

[0165] In the preparation method, no eutectic salt and sodium fluoride are added in step (1), and the preparation process in step (2) is not carried out.

[0166] All other conditions remain the same as in Example 1.

[0167] Comparative Example 2

[0168] The difference between this comparative example and Example 1 is that the composite sodium-ion layered oxide cathode material in this comparative example is not doped with fluoride ions and chloride ions.

[0169] In the preparation method, no eutectic salt and sodium fluoride are added in step (1).

[0170] All other conditions remain the same as in Example 1.

[0171] Comparative Example 3

[0172] The difference between this comparative example and Example 1 is that the composite sodium-ion layered oxide cathode material in this comparative example is not coated with MXene material.

[0173] In the preparation method, step (2) is not performed.

[0174] All other conditions remain the same as in Example 1.

[0175] Comparative Example 4

[0176] The difference between this comparative example and Example 1 is that the raw material for chloride ions in this comparative example is pure NaCl material, i.e., non-eutectic salt material.

[0177] All other conditions remain the same as in Example 1.

[0178] The interlayer spacing of the composite sodium-ion layered oxide cathode materials provided in Examples 1-15 and Comparative Examples 1-4 was calculated. The calculation conditions were as follows: XRD tests were performed on the materials, and the interlayer spacing was calculated using the Bragg equation 2dsinθ=nλ after the test, where: d: interlayer spacing; θ: diffraction angle; λ: wavelength of X-rays; n: diffraction order, usually taken as 1. The calculation results are shown in Table 1.

[0179] Table 1

[0180]

[0181] Battery fabrication and performance testing

[0182] Battery manufacturing

[0183] The composite sodium-ion layered oxide positive electrode materials provided in the examples and comparative examples were mixed uniformly with conductive agent acetylene black and binder polyvinylidene fluoride at a mass ratio of 8:1:1 to form an electrode sheet with a diameter of 14 mm, which was then dried in a vacuum at 100°C for 12 hours. This electrode sheet was transferred to a glove box as the positive electrode, with a metallic sodium sheet as the negative electrode and glass fiber as the separator. The electrolyte was a 1 mol / L NaPF6 solution, wherein the solvent was a mixture of EC:DMC = 1:1 vol% and 5% FEC (vol%). The positive electrode, negative electrode, separator, and electrolyte were assembled into a 2032 coin cell.

[0184] Performance testing

[0185] The batteries prepared in the examples and comparative examples were subjected to performance testing on the Blue Electric System under the following conditions:

[0186] (a) Cyclic performance: Charge and discharge tests were conducted at room temperature of 25°C, voltage range of 2V to 4V, and 1C rate to obtain the initial specific capacity and capacity retention rate after 100 cycles.

[0187] (b) Rate performance: At room temperature of 25°C, the battery was tested at a voltage range of 2V to 4V. The battery was charged and discharged at 0.1C, 0.5C, 1C, 2C, 3C and 4C in sequence, and then the battery was tested again at a rate of 0.1C to obtain the capacity retention rate of 4C / 0.1C.

[0188] Figure 2 shows the rate performance of the sodium-ion battery provided in Example 1. As the discharge rate gradually increases from 0.1C to 4C, the rate retention of the material shows a continuous but gradual decrease. At the high current density of 4C, it still retains more than 92% of its capacity, reflecting that the material has excellent high rate tolerance.

[0189] Figure 3 shows the cycle performance of the sodium-ion battery provided in Example 1. During 50 1C charge-discharge cycles, the capacity retention of the material remained above 99.8% throughout, with no significant decay trend, demonstrating extremely excellent cycle stability and indicating minimal structural damage during charge and discharge.

[0190] As can be seen from Figures 2 and 3, the gradual capacity loss at high rates and the near-zero decay under long cycles work synergistically, indicating that the material has both efficient ion transport capabilities and extremely strong structural stability, making it an excellent candidate among sodium-ion cathode materials that combines dynamic and energy storage characteristics.

[0191] The test results are shown in Table 2.

[0192] Table 2

[0193]

[0194] From Table 1 and Table 2, we can obtain:

[0195] The cathode material provided by this invention, through the synergistic doping of internal fluorine ions and chloride ions from special raw materials with the coating of MXene material, and the preparation using a chloride-containing eutectic salt as the chloride ion raw material, can simultaneously improve the structural stability of the near-surface region of the material and the deep ion transport rate in the bulk phase. It can not only construct an efficient ion transport pathway to improve ion migration efficiency, but also effectively suppress the interfacial side reactions between the electrode and the electrolyte, thereby improving the performance of sodium-ion batteries.

[0196] Data analysis of Examples 1, 4, and 5 shows that the composite sodium-ion layered oxide cathode material of the present invention is suitable for various types of chloride-containing eutectic salts and can be doped with different elements M. All of these combinations can broaden the ion diffusion path deep within the particles of the layered oxide material, significantly improving the rate performance of the battery.

[0197] Data analysis of Examples 1, 6, 7, 8, and 9 shows that the present invention regulates Na u+v Ni 1-m-n Fe m Mn n M z O α F β Cl γ The stoichiometric ratio of fluoride ions and chloride ions in the preparation process simultaneously affects the selection of the amount of fluoride source and chloride ion source used. The preferred ratios are 0.02≤β≤0.04 and / or 0.02≤γ≤0.04, which better improves the structural stability of the material in the near-surface region (1~4μm) and the ion transport rate in the deep bulk phase (4~8μm).

[0198] Data analysis of Examples 1 and 10 shows that when the chloride-containing eutectic salt contains NaCl, it can synergistically work with the basic sodium source to achieve partial substitution of O by Cl⁻ particles through deep penetration, resulting in deep penetration of Cl⁻ particles. - Doping broadens the sodium ion transport path.

[0199] Data analysis of Examples 1, 11, 12, 13, and 14 shows that in the MXene material of the present invention, TiCNT... x Co-doping the base material with Ca and Zn further enhances the synergistic effect of the two, which is more conducive to improving the surface stability and ion transport dynamics of the material.

[0200] Data analysis of Examples 1 and 15 shows that, in the coating process of step (2) of the present invention, the addition of MXene material must be controlled within a suitable range of 0.2% to 10% in order to further improve the ion transport rate.

[0201] Data analysis of Examples 1, 1, 2, 3 and 4 shows that, in this invention, the doping of fluoride and chloride ions, the selection of MXene materials and chloride-containing eutectic salts must be coordinated and multiple conditions must work together to truly solve the problems of high ion diffusion barriers in deep particles, easy interlayer slippage in the near-surface region during long-term cycling, and side reactions between the material surface and the electrolyte.

[0202] 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 composite sodium-ion layered oxide cathode material, characterized in that, The composite sodium-electric layered oxide cathode material includes a sodium-electric layered oxide material core and an MXene coating layer covering the surface of the sodium-electric layered oxide material core; the sodium-electric layered oxide material core is doped with fluoride ions and chloride ions, and the raw material for the chloride ions is a chloride-containing eutectic salt.

2. The composite sodium-ion layered oxide cathode material according to claim 1, characterized in that, The general chemical formula of the sodium-electric layered oxide material is Na. u+v Ni 1-m-n Fe m Mn n M z O α F β Cl γ Wherein, 0.9≤u+v≤1.05, 0≤m<1, 0≤n<1, 1-mn>0, 0≤v≤0.1, 0≤z≤0.2, 0.02≤β≤0.04, 0.02≤γ≤0.04, 3.9≤2α+β+γ≤5, where v is the sodium ion content in the chloride-containing eutectic salt, and M is the dopant ion; and / or, the interlayer spacing of the sodium-electric layered oxide material is 5.35Å~5.37Å.

3. The composite sodium-ion layered oxide cathode material according to claim 1 or 2, characterized in that, The MXene material in the MXene coating layer includes TiCNT. x Base material.

4. The composite sodium-ion layered oxide cathode material according to claim 3, characterized in that, The TiCNT x The base material also includes doping elements, including Ca and / or Zn.

5. The composite sodium-ion layered oxide cathode material according to claim 4, characterized in that, The doping elements include Ca and Zn; and / or, with undoped TiCNTs x The doping mass of the Ca element is 2% to 10% based on 100% of the base material; and / or, using undoped TiCNTs. x The mass of the base material is 100%, and the doping mass of the Zn element is 2% to 10%.

6. A method for preparing a composite sodium-ion layered oxide cathode material as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) mixing sodium-ion cathode precursor material, basic sodium source, chloride-containing eutectic salt and fluorine source, and performing a first calcination to obtain sodium-ion layered oxide material core; (2) mixing and coating sodium-ion layered oxide material core and MXene material, and then performing a second calcination to obtain the composite sodium-ion layered oxide cathode material.

7. The preparation method according to claim 6, characterized in that, The sodium-ion cathode precursor material in step (1) includes a hydroxide-based sodium-ion cathode precursor material; and / or, the chloride-containing eutectic salt in step (1) includes any one or a combination of at least two of the following: NaCl-KCl eutectic salt, NaCl-CaCl2 eutectic salt, NaCl-ZnCl2 eutectic salt, NaCl-Na2CO3 eutectic salt, MgCl2-KCl eutectic salt, or NaCl-AlCl3 eutectic salt; and / or, the fluorine source includes fluorides; and / or, the mixed raw materials in step (1) also include a dopant containing element M; and / or, the first calcination in step (1) is carried out in an oxygen-containing atmosphere, the heating rate of the first calcination in step (1) is 2℃ / min~6℃ / min, the holding temperature after the first calcination in step (1) is 850℃~1100℃, and the holding time after the first calcination in step (1) is 10h~20h.

8. The preparation method according to claim 6 or 7, characterized in that, In step (2), the mass of the added MXene material is 0.2% to 10% of the mass of the sodium-electric layered oxide material core; and / or, in step (2), the second calcination is carried out under a protective atmosphere, the holding temperature after the second calcination in step (2) is 550℃ to 900℃, and the holding time after the second calcination in step (2) is 5h to 12h.

9. The preparation method according to claim 6, characterized in that, In step (2), after the second calcination treatment, a cooling treatment is performed, and the cooling rate of the cooling treatment is 1℃ / min to 6℃ / min.

10. A sodium electrochemical device, characterized in that, The sodium electrochemical device includes the composite sodium electrochemical layered oxide cathode material as described in any one of claims 1-5 or the composite sodium electrochemical layered oxide cathode material prepared by the preparation method described in any one of claims 6-9.

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