Fusion coated high-entropy layered oxide sodium battery positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium ion batteries, and discloses a fusion coated high-entropy layered oxide sodium battery positive electrode material and a preparation method and application thereof. The preparation method comprises the following steps: (1) blending a sodium source, a nickel source, a chromium source, a vanadium source, a molybdenum source, a titanium source and a cerium source, ball-milling, tabletting and calcining to obtain a basic layered oxide Na [Ni0. 3Cr0. 15VxCe0. 1Ti0. 1Mo0. 05] O2, 0.18 < = x < = 0.22; and (2) crushing and sieving the basic layered oxide, carrying out ball-milling mixing on the basic layered oxide and nano ZrO2 powder, and calcining again to obtain the fused coated high-entropy layered oxide sodium battery positive electrode material. According to the preparation method of the high-entropy and fusion coating combined material, the capacity exertion of the material can be effectively improved, meanwhile, the discharge capacity and voltage attenuation caused by structure degeneration in the circulation process of the material are inhibited, and the stability is improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and particularly relates to a method for preparing a high-entropy layered oxide. Background Technology

[0002] Sodium-ion batteries, as a promising new energy storage technology, have received widespread attention from the industry in recent years. Their core advantage lies in the extremely high abundance of sodium resources in the Earth's crust, hundreds of times that of lithium resources, and their widespread distribution, making their raw material cost far lower than that of lithium-ion batteries. This provides a more economical solution for large-scale energy storage and electric vehicles. Among the many cathode materials for sodium-ion batteries, layered transition metal oxides have become a research focus due to their clear two-dimensional sodium-ion diffusion channels, high theoretical specific capacity, and suitable operating voltage. These materials typically provide reversible capacities of 140-160 mAh / g and exhibit excellent rate performance. However, a long-standing technical bottleneck is that during repeated charge-discharge cycles, the extraction and insertion of sodium ions in layered oxides triggers drastic changes in the crystal structure and irreversible phase transitions (such as the P2-O2 phase transition), leading to material structure collapse and rapid capacity decay, severely limiting their cycle life in practical applications.

[0003] To address the aforementioned structural stability issues, the design concept of high-entropy materials has been introduced into the development of layered oxide cathode materials. High-entropy oxides (HEOs) are single-phase solid solutions formed by five or more elements occupying the same lattice positions in near-equimolar or non-equimolar ratios. Their unique high-entropy effect can effectively stabilize the crystal structure, suppress phase separation, and regulate the electrochemical performance of the material through the "cocktail effect" of multiple elements. For example, publication number CN114927681A relates to a P2-type pentagonal high-entropy sodium layered cathode material, its preparation method, and its application. This cathode material is a pentagonal metal oxide containing Mn, Ni, Cu, Mg, and Ti, with the specific chemical formula Na. a [Mn 0.67 Ni x Cu y Mg z Ti d O2. This material shows a certain improvement in discharge capacity and cycle stability compared to ordinary layered cathode materials, but its surface still has a fragile layered lattice structure. During long cycles, irreversible phase transitions involving lattice rearrangement can still occur in side reactions involving the electrolyte, resulting in reversible capacity loss and decreased kinetic performance. For example, publication number CN116425212A relates to a high-entropy doped layered oxide and its preparation method, cathode material, and sodium-ion battery. The chemical formula of this high-entropy doped layered oxide can be represented as Na. x A y Mz O2, where A is selected from at least two elements from nickel, manganese, and iron, and M is selected from five or more metal dopants from the third to fifth periods, with each dopant element having a low content (≤0.05%), forming a stable lattice structure through high-entropy doping. Because the element combination in the material prepared by this patent has low reversible capacity for sodium, the overall structural entropy improvement compared to the original nickel-manganese-iron-based material is very limited. Furthermore, the surface of this material still has an exposed layered structure and some residual sodium compounds, resulting in poor high-rate cycling performance.

[0004] While multi-element high-entropy design can enhance the bulk structural stability of layered oxide cathode materials to some extent, the types and contents of elements in the material still need careful design to increase the number of active sodium ions and improve reversible capacity. Furthermore, the interface problem between the material surface and the electrolyte is also significant. During high-rate, long-cycle operation, the exposed electrode material surface is prone to violent side reactions with the electrolyte, forming an unstable cathode solid electrolyte interphase (CEI) film, which is then susceptible to erosion by trace amounts of moisture or acidic substances in the electrolyte. These interfacial side reactions not only consume active sodium ions but also lead to surface structure damage and increased interfacial impedance, ultimately causing continuous capacity decay. This indicates that bulk modification alone cannot completely solve the material failure problem. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a fused-coated high-entropy layered oxide sodium cathode material, its preparation method, and its applications. The preparation process of this material is simple and inexpensive, and the prepared material exhibits good air stability, thermal stability, reversible capacity, and cycle performance.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A method for preparing a fused-coated high-entropy layered oxide sodium cathode material includes the following steps: (1) Sodium source, nickel source, chromium source, vanadium source, molybdenum source, titanium source and cerium source are weighed and mixed in a certain proportion, and ball-milled into powder; then the powder is pressed into tablets and calcined to obtain basic layered oxide (Na[Ni 0.3 Cr 0.15 V x Ce 0.1 Ti 0.1 Mo 0.05 O2 (0.18≤x≤0.22).

[0007] (2) The basic layered oxide obtained in step (1) is crushed and sieved, and then mixed with nano ZrO2 powder by ball milling to obtain a mixture; wherein the molar ratio of zirconium in nano ZrO2 powder to vanadium in vanadium source is (0.36-0.67):1.

[0008] (3) The mixture obtained in step (2) is calcined again to obtain a fused coated high-entropy layered oxide sodium cathode material.

[0009] Furthermore, in step (1) above, the sodium source is Na2CO3, the nickel source is NiO, the chromium source is Cr2O3, the vanadium source is V2O3, the molybdenum source is Mo2O3, the titanium source is TiO2, and the cerium source is CeO2.

[0010] In step (1) above, the pressure of the tablet is 8-12 MPa, the tablet is round, the size is 10-30 mm, and the thickness is 2-6 mm. Calcination treatment refers to heating to 850-1000℃ at a heating rate of 3-10℃ / min and holding at a constant temperature for 8-15 h.

[0011] In step (2) above, the sieve density is 200-400 mesh; the particle size of the nano ZrO2 powder is 20-50 nm.

[0012] The ball milling time in steps (1) and (2) above is 4-8 h.

[0013] The conditions for the second calcination in step (3) above are: heating to 950-1050℃ at a heating rate of 3-10℃ / min and holding at that temperature for 6-10 h.

[0014] Furthermore, the sintering atmosphere for the calcination treatment in step (1) and the recalcination in step (3) is air or oxygen.

[0015] A fusion-coated high-entropy layered oxide sodium cathode material was prepared using the above-described preparation method.

[0016] Among the elements introduced above, Ni and V can stably realize Ni 2+ / Ni 3+ / Ni 4+ V 3+ / V 4+ / V 5+ In two-electron redox reactions, each Ni atom can contribute more than one electron for charge compensation, thus improving the material's reversible capacity; the related redox couple of Cr... 3+ / Cr 4+ or Cr 4+ / Cr 6+It possesses a very high redox potential, typically >4.0 V vs. Na⁺ / Na, which can effectively improve the working potential of the material; Mo's high-valence cation Mo 6+ It possesses high electronegativity and an empty 4d orbital, enabling it to form strong hybridization with the O 2p orbital, thereby triggering the formation of the oxygen anion (O 2- Ti participates in redox reactions, providing additional over-theoretical capacity; for Ti, it usually exists in the +4 form in these oxides, and its bond energy for forming covalent bonds with O is very high, and Ti... 4+ Without the JT distortion effect, it can dilute the distortion center of the material and use its own regular octahedral structure as a "template" to reduce the overall degree of lattice distortion, thereby enhancing the mechanical strength of the entire metal layer lattice and improving the structural stability of the material under high-pressure cycling; Ce relies on Ce 3+ / Ce 4+ Variable valence states actively participate in and regulate redox processes, and Ce 4+ Zr has a relatively large ionic radius, and when doped into materials, it can act as an effective "pillar," widening the gap between sodium layers or transition metal layers and improving rate performance. The covalent bond energy between Zr and O is extremely high, serving as a robust pillar and enhancing the stability of the transition metal layer. Zr oxide itself is difficult to react with H2O and CO2 in the air; its introduction reduces the material's environmental sensitivity. Simultaneously, its chemical inertness can inhibit interfacial side reactions involving the electrolyte, improving the material's cycle life. In sodium-ion layered oxide cathodes containing V, intelligent management of the Zr's form is achieved by precisely controlling the amount of Zr introduced and its inverse relationship with V. The V content determines the amount of Zr available. 4+ The number of doped lattice sites and the amount of doped material compete for dopant. The key importance of controlling this ratio lies in its ability to synergistically optimize the material's intrinsic and extrinsic stability. When a small amount of Zr... 4+ Successfully doped bulk phases, with their strong Zr-O bonds acting like "rivets," reinforce the crystal lattice and suppress phase transitions; while undoped Zr automatically forms a ZrO2 protective layer on the surface, isolating it from electrolyte corrosion. This "combination of internal and external" mechanism, achieved through proportional control, simultaneously enhances the structural robustness and interfacial stability of the material without sacrificing excessive capacity, thus yielding an electrode material with optimal overall performance.

[0017] The above-mentioned fusion-coated high-entropy layered oxide sodium cathode material is used in sodium-ion batteries.

[0018] The beneficial effects of this invention are: (1) In this invention, multiple metal cations (Ni, Cr, V, Mo, Ti, Ce, Zr) are dissolved in a transition metal layer, and their relative contents are controlled according to their respective characteristics, while increasing the configuration entropy (ΔS) of the system. configThe configurational entropy of the fused-coated high-entropy layered oxide sodium cathode material prepared in Example 1 is 1.808 R. Besides the unique properties of each element, the high-entropy effect induced by the combined participation of multiple elements can also suppress multiphase separation and the formation of impurity phases (such as spinel phase, rock salt phase, etc.), promoting the formation of a single, uniform layered solid solution structure. This thermodynamic "entropy-driven" stability is the fundamental guarantee for the material to maintain structural integrity during harsh electrochemical cycles. Furthermore, the chemical environment around each cation in the high-entropy lattice is extremely different, making the migration of cations (especially transition metal ions) within the lattice very difficult, i.e., the "sluggish diffusion effect." During electrochemical cycling, this effect can effectively suppress the dissolution and migration of transition metal ions, reducing their deposition on the negative electrode, thereby mitigating damage to the CEI film and loss of active material, and extending the battery's cycle life.

[0019] (2) In the second sintering process of this invention, some Zr in the highly active nano ZrO2 powder will be thermally diffused and fused into the main oxide lattice, becoming one of the many metal elements that increase the material's configuration entropy, strengthening the lattice Me-O bonds (Zr-O bond energy is higher), and inhibiting surface lattice reconstruction and oxygen precipitation; another part will undergo an in-situ solid-state reaction with the harmful residual sodium on the material surface (e.g., Na2CO3+2ZrO2→Na2Zr2O5+2CO2↑). This type of reaction not only removes surface impurities, but also generates a dense, uniform, and conductive Na layer in situ on the particle surface. + Furthermore, the sodium zirconium oxide coating exhibits chemical stability. This coating inhibits the oxidative decomposition of the electrolyte, the dissolution of transition metal ions, and the structural degradation of the material caused by H2O / CO2 corrosion in the air, significantly improving the material's air stability and electrochemical cycling stability.

[0020] (3) The present invention fundamentally enhances the intrinsic structural stability of the material through high entropy design, while the unique two-step sintering fusion coating method constructs a functional artificial CEI protective layer with ion conductivity on the material surface. The two complement each other and jointly solve the key technical bottlenecks of traditional layered oxides such as rapid capacity decay, voltage drop and sensitivity to air / moisture during cycling. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The images show SEM images of the layered oxide materials prepared in Example 1 and Comparative Examples 1-3.

[0023] Figure 2 The images show the XRD patterns of the layered oxide materials prepared in Example 1 and Comparative Example 1.

[0024] Figure 3 The CV lines are the multi-turn spectral lines of the layered oxide material prepared in Example 1 at a scan rate of 0.1 mv / s. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1 The preparation method of the fused-coated high-entropy layered oxide sodium cathode material in this embodiment includes the following steps: (1) Mix Na2CO3, NiO, Cr2O3, V2O3, Mo2O3, TiO2, and CeO2 according to Na[Ni 0.3 Cr 0.15 V 0.2 Ce 0.1 Ti 0.1 Mo 0.05 The molar ratio of the corresponding metal elements in the O2 structural formula was mixed, and the mixture was ball-milled for 6 h; then the ball-milled powder was pressed into discs with a diameter of 20 mm and a thickness of 3 mm at 10 MPa; the resulting compressed sample was heated to 950 °C at 5 °C / min in an oxygen atmosphere and held at that temperature for 15 h.

[0027] (2) The sintered material in step (1) is sieved using a 300-mesh sieve. The sieved material and ZrO2 powder with a particle size of 20 nm are mixed by ball milling for 4 h to obtain a mixture. The molar ratio of the amount of ZrO2 added to the amount of V2O3 added in step (1) is 1:1.

[0028] (3) The mixture obtained in step (2) is heated to 1000℃ in air at 5℃ / min and kept at the temperature for 6 h to obtain a fused coated high-entropy layered oxide sodium cathode material.

[0029] Example 2 The preparation method of the fused-coated high-entropy layered oxide sodium cathode material in this embodiment includes the following steps: (1) Mix Na2CO3, NiO, Cr2O3, V2O3, Mo2O3, TiO2, and CeO2 according to Na[Ni 0.3 Cr 0.15 V 0.22 Ce 0.1 Ti 0.1 Mo 0.05 The molar ratio of the corresponding metal elements in the O2 structural formula was mixed, and the mixture was ball-milled for 4 h; then the ball-milled powder was pressed into discs with a diameter of 10 mm and a thickness of 2 mm at 8 MPa; the resulting pressed sample was heated to 1000℃ at 3℃ / min in an oxygen atmosphere and held at that temperature for 8 h.

[0030] (2) The sintered material in step (1) is sieved using a 200-mesh sieve. The sieved material and ZrO2 powder with a particle size of 20 nm are mixed by ball milling for 4 h to obtain a mixture. The molar ratio of the amount of ZrO2 added to the amount of V2O3 added in step (1) is 0.727:1.

[0031] (3) The mixture obtained in step (2) is heated to 1000℃ in air at 3℃ / min and kept at the temperature for 6 h to obtain a fused coated high-entropy layered oxide sodium cathode material.

[0032] Example 3 The preparation method of the fused-coated high-entropy layered oxide sodium cathode material in this embodiment includes the following steps: (1) Mix Na2CO3, NiO, Cr2O3, V2O3, Mo2O3, TiO2, and CeO2 according to Na[Ni 0.3 Cr 0.15 V 0.18 Ce 0.1 Ti 0.1 Mo 0.05 The molar ratio of the corresponding metal elements in the O2 structural formula was mixed, and the mixture was ball-milled for 4 h; then the ball-milled powder was pressed into discs with a diameter of 30 mm and a thickness of 6 mm at 12 MPa; the resulting compressed sample was heated to 850 °C at 8 °C / min in an oxygen atmosphere and held at that temperature for 15 h.

[0033] (2) The sintered material in step (1) is sieved using a 400-mesh sieve. The sieved material and ZrO2 powder with a particle size of 50 nm are mixed by ball milling for 6 h to obtain a mixture. The molar ratio of the amount of ZrO2 added to the amount of V2O3 added in step (1) is 1.333:1.

[0034] (3) The mixture obtained in step (2) is heated to 1050℃ in air at 8℃ / min and kept at the temperature for 6 h to obtain a fused coated high-entropy layered oxide sodium cathode material.

[0035] Example 4 The preparation method of the fused-coated high-entropy layered oxide sodium cathode material in this embodiment includes the following steps: (1) Mix Na2CO3, NiO, Cr2O3, V2O3, Mo2O3, TiO2, and CeO2 according to Na[Ni 0.3 Cr 0.15 V 0.21 Ce 0.1 Ti 0.1 Mo 0.05 The molar ratio of the corresponding metal elements in the O2 structural formula was mixed, and the mixture was ball-milled for 4 h; then the ball-milled powder was pressed into discs with a diameter of 20 mm and a thickness of 6 mm at 12 MPa; the resulting compressed sample was heated to 950 °C at 5 °C / min in an oxygen atmosphere and held at that temperature for 10 h.

[0036] (2) The sintered material in step (1) is sieved using a 300-mesh sieve. The sieved material and ZrO2 powder with a particle size of 40 nm are mixed by ball milling for 6 h to obtain a mixture. The molar ratio of the amount of ZrO2 added to the amount of V2O3 added in step (1) is 0.857:1.

[0037] (3) The mixture obtained in step (2) is heated to 950°C at 5°C / min in an air atmosphere and kept at a constant temperature for 10 h to obtain a fused coated high-entropy layered oxide sodium cathode material.

[0038] Example 5 The preparation method of the fused-coated high-entropy layered oxide sodium cathode material in this embodiment includes the following steps: (1) Mix Na2CO3, NiO, Cr2O3, V2O3, Mo2O3, TiO2, and CeO2 according to Na[Ni 0.3 Cr 0.15 V 0.19 Ce 0.1 Ti 0.1 Mo 0.05 The molar ratio of the corresponding metal elements in the O2 structural formula was mixed, and the mixture was ball-milled for 4 h; then the ball-milled powder was pressed into discs with a diameter of 40 mm and a thickness of 4 mm at 10 MPa; the resulting compressed sample was heated to 950 °C at 5 °C / min in an oxygen atmosphere and held at that temperature for 10 h.

[0039] (2) The sintered material in step (1) is sieved using a 300-mesh sieve. The sieved material and ZrO2 powder with a particle size of 20 nm are mixed by ball milling for 6 h to obtain a mixture. The molar ratio of the amount of ZrO2 added to the amount of V2O3 added in step (1) is 1.158:1.

[0040] (3) The mixture obtained in step (2) is heated to 1000℃ in air at 5℃ / min and kept at a constant temperature for 10h to obtain a fused coated high-entropy layered oxide sodium cathode material.

[0041] Comparative Example 1 This comparative example shows a fusion-coated high-entropy layered oxide sodium cathode material (Na[Ni)). 0.3 Cr 0.15 V 0.2 Ce 0.1 Ti 0.1 Mo 0.05 Zr 0.1 The preparation method of O2 is as follows: (1) Mix Na2CO3, NiO, Cr2O3, V2O3, Mo2O3, TiO2, CeO2 and ZrO2 according to Na[Ni 0.3 Cr 0.15 V 0.2 Ce 0.1 Ti 0.1 Mo 0.05 Zr 0.1 The molar ratio of the corresponding metal elements in the O2 structural formula was mixed, and the mixture was ball-milled for 6 hours. Then, the ball-milled powder was pressed into discs with a diameter of 20 mm and a thickness of 3 mm at 10 MPa. The resulting compressed sample was heated to 950 °C at 5 °C / min in an oxygen atmosphere and held at that temperature for 15 hours.

[0042] (2) The material obtained in step (1) is heated to 1000℃ in air at a rate of 5℃ / min and held at that temperature for 6 h to obtain a fused coated high-entropy layered oxide sodium cathode material, namely Na[Ni 0.3 Cr 0.15 V 0.2 Ce 0.1 Ti 0.1 Mo 0.05 Zr 0.1 O2.

[0043] Comparative Example 2 The preparation method of the fusion-coated high-entropy layered oxide sodium cathode material in this comparative example includes the following steps: (1) Mix Na2CO3, NiO, Cr2O3, V2O3, Mo2O3, TiO2, and CeO2 according to Na[Ni0.3 Cr 0.15 V 0.25 Ce 0.1 Ti 0.1 Mo 0.05 The molar ratio of the corresponding metal elements in the O2 structural formula was mixed, and the mixture was ball-milled for 6 h; then the ball-milled powder was pressed into discs with a diameter of 20 mm and a thickness of 3 mm at 10 MPa; the resulting compressed sample was heated to 950 °C at 5 °C / min in an oxygen atmosphere and held at that temperature for 15 h.

[0044] (2) The sintered material in step (1) is sieved using a 300-mesh sieve. The sieved material and ZrO2 powder with a particle size of 20 nm are mixed by ball milling for 4 h to obtain a mixture. The molar ratio of the amount of ZrO2 added to the amount of V2O3 added in (1) is 0.4:1.

[0045] (3) The mixture obtained in step (2) is heated to 1000℃ in air at 5℃ / min and kept at the temperature for 6 h to obtain a fused coated high-entropy layered oxide sodium cathode material.

[0046] Comparative Example 3 The preparation method of the fusion-coated high-entropy layered oxide sodium cathode material in this comparative example includes the following steps: (1) Mix Na2CO3, NiO, Cr2O3, V2O3, Mo2O3, TiO2, and CeO2 according to Na[Ni 0.3 Cr 0.15 V 0.15 Ce 0.1 Ti 0.1 Mo 0.05 The molar ratio of the corresponding metal elements in the O2 structural formula was mixed, and the mixture was ball-milled for 6 h; then the ball-milled powder was pressed into discs with a diameter of 20 mm and a thickness of 3 mm at 10 MPa; the resulting compressed sample was heated to 950 °C at 5 °C / min in an oxygen atmosphere and held at that temperature for 15 h.

[0047] (2) The sintered material in step (1) is sieved using a 300-mesh sieve. The sieved material and ZrO2 powder with a particle size of 20 nm are mixed by ball milling for 4 h to obtain a mixture. The molar ratio of the amount of ZrO2 added to the amount of V2O3 added in step (1) is 2:1.

[0048] (3) The mixture obtained in step (2) is heated to 1000℃ in air at 5℃ / min and kept at the temperature for 6 h to obtain a fused coated high-entropy layered oxide sodium cathode material.

[0049] Figure 1As shown, in Examples 1 and Comparative Examples 1 and 2, Zr element is enriched on the surface to form sodium zirconium oxide. This oxide can form a uniform coating layer on the surface of the single crystal material, suppressing surface and interface side reactions and improving the electrochemical performance of the material. The particle size of this high-entropy material is about 2-3 μm, and its surface has a dense coating material. Adjusting the amount of Zr involved in the material shows that the surface coating morphology of different materials is very different. In Comparative Example 1, the sodium zirconium oxide on the surface of the material has less segregation and does not form a dense coating layer. In Example 1, the material forms a thinner and denser coating layer. In Comparative Example 3, the coating layer of the material further thickens and agglomerates on the material surface. In the XRD spectrum ( Figure 2 As can be seen in Example 1, the 003 / 104 peak intensity ratio of the material in Comparative Example 1 is larger than that of the material in Comparative Example 1, proving that the control of the content of Zr inside and outside the material makes the layered structure formed by this coated high-entropy oxide better.

[0050] Comparative Example 4 The preparation method of the fusion-coated high-entropy layered oxide sodium cathode material in this comparative example includes the following steps: (1) Mix Na2CO3, NiO, Cr2O3, V2O3, Mo2O3, TiO2, and CeO2 according to Na[Ni 0.3 Cr 0.15 V 0.2 Ce 0.1 Ti 0.1 Mo 0.05 The molar ratio of the corresponding metal elements in the O2 structural formula was mixed, and the mixture was ball-milled for 6 h; then the ball-milled powder was pressed into discs with a diameter of 20 mm and a thickness of 3 mm at 10 MPa; the resulting compressed sample was heated to 950 °C at 5 °C / min in an oxygen atmosphere and held at that temperature for 15 h.

[0051] (2) The sintered material in step (1) is sieved using a 300-mesh sieve. The sieved material and Al2O3 powder with a particle size of 20 nm are mixed by ball milling for 4 h to obtain a mixture. The molar ratio of the amount of Al2O3 added to the amount of V2O3 added in step (1) is 0.5:1.

[0052] (3) The mixture obtained in step (2) is heated to 1000℃ in air at 5℃ / min and kept at the temperature for 6 h to obtain a fused coated high-entropy layered oxide sodium cathode material.

[0053] The total elemental content and surface elemental content of the materials prepared by Example 1 and Comparative Examples 1-4 were tested, and the specific results are shown in Table 1.

[0054] Table 1. Overall elemental content (ICP) and surface elemental content (EDS mapping) of the samples As shown in Table 1, the overall content of each element in the examples and comparative examples is similar to the stoichiometric ratio of the prepared materials. Elemental surface content detection shows that Zr is enriched on the material surface, and its surface content exhibits a non-linear increase with the linear increase of the total content. In Comparative Example 2 and Example 1, the total Zr content of the materials is 4.6 at% and 9.7 at%, respectively, while the Zr surface content is 9.8 at% and 25.3 at%, respectively. The total Zr content increases by 5 at%, while the surface content increases by 15.5%. Furthermore, in Comparative Example 3, the total Zr content of the material also increases by approximately 5 at%, while the Zr surface content increases to 57.9 at%, an increase of 32.6 at%. Combined with... Figure 1 SEM comparative analysis showed that when the Zr content was low, most of it fused into the material bulk to participate in the formation of a high-entropy layered structure. However, as the content increased, it formed a coating layer on the surface, with the coating layer formed in Example 1 exhibiting the best uniformity. Furthermore, in Comparative Example 1, the material using a single sintering method did not form a Zr-enriched coating layer on the surface; therefore, the surface content of each element was relatively close to the total content. In Comparative Example 4, the introduced element was replaced with Al in the secondary sintering process; when Al coordinates with O... 3+ The ionic radius (0.053 nm) is smaller than that of Zr. 4+ With an ionic radius of 0.072 nm, it can more easily replace transition metal ions in the crystal lattice to form a stable solid solution, a process that is energy-efficient. Therefore, this element does not tend to accumulate on the surface; although the total content is 10.1 at%, similar to the Zr content in Example 1, the surface content is only 14.6 at%, far lower than the Zr surface content in Example 1.

[0055] Application examples The cathode materials prepared in Examples 1-5 and Comparative Examples 1-4 were respectively applied in sodium-ion batteries. The preparation method of the sodium-ion batteries is as follows: (1) Preparation of positive electrode sheet: The full-concentration gradient layered oxide material, binder PVDF and conductive agent SP obtained above are weighed at a mass ratio of 8:1:1, dissolved in NMP, and stirred to prepare a slurry of a certain viscosity. The slurry is coated on the current collector copper foil, dried at 100℃, rolled, and cut to obtain the positive electrode sheet with an areal density of about 4 mg.

[0056] (2) Dissolve NaClO4 (1 mol / L) in a mixed solvent with an EC:PC mass ratio of 1:1, and then add 5% FEC by total volume mass as an additive.

[0057] (3) Assemble the positive and negative electrode sheets, sodium metal sheet and glass fiber membrane obtained in step 1 and add 100 uL of the above electrolyte. After sealing and standing for 10 h, a sodium ion button half cell is obtained.

[0058] The prepared batteries were subjected to reversible capacity, rate capability, and cycle performance tests. The charge / discharge voltage atmosphere was set to 2.0-4.2 V. The batteries were first formed at a current of 0.1 C. The electrochemical test results are as follows: Figure 3 As shown in Table 2, the multi-cycle slow-scan CV test spectrum also shows that the peak position difference of the material in Example 1 is small, proving that a relatively stable CEI (Chemical Equivalent Injection) is rapidly formed on its surface. Figure 3 ).

[0059] Table 2 Performance test results of sodium-ion coin cells assembled in the Examples and Comparative Examples As shown in Table 2, the material in Example 1 exhibits a reversible capacity of 182.2 mAh / g in the first cycle within a voltage range of 2.0-4.2 V, while the capacity of Comparative Example 1 is slightly lower at 177.3 mAh / g. The two materials demonstrate similar capacity performance, with the difference attributed to the more complete layered structure of the former, consistent with the XRD pattern analysis results mentioned earlier. In the 1 C-300 cycle long-term cycling test, Example 1 achieved a capacity retention of 93.5%, while Comparative Example 1 only retained 65.2%. This is because the material in Example 1 forms a sodium zirconium oxide coating layer, which effectively mitigates side reactions involving the electrolyte at the interface and suppresses irreversible phase transitions on the material surface, thus better preserving the number of active sodium ions and improving cycle life. The initial discharge capacity fractions of Comparative Examples 2 (insufficient coating) and 3 (excessive coating) were 181.8 and 162.7 mAh / g, respectively, with reversible capacity retention rates of 76.3% and 82.5% during cycling. The coating layer, lacking uniform surface coverage, had limited inhibitory effect on the irreversible phase transition of the material surface, while excessive surface coating significantly reduced the reversible capacity. Therefore, controlling the amount of sodium zirconium oxide surface coating is crucial for achieving long cycle life with high capacity. In Comparative Example 4, the introduction of Al during secondary sintering failed to form a well-enriched elemental surface layer. Furthermore, Al's strong inertness allowed the active Na... + Due to the reduced quantity, the initial discharge capacity and cycle retention of this modified material are only 166.8 mAh / g and 71.5%, respectively.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a fusion-coated high-entropy layered-oxide sodium battery cathode material, characterized in that, The steps are as follows: (1) blending a sodium source, a nickel source, a chromium source, a vanadium source, a molybdenum source, a titanium source and a cerium source, and ball-milling into a powder; then, after tabletting and calcination treatment, obtaining a basic layered oxide Na[Ni 0.3 Cr 0.15 V x Ce 0.1 Ti 0.1 Mo 0.05 ]O2, wherein 0.18≤x≤0.22; (2) The base-layered oxide obtained in step (1) is crushed and sieved, and then mixed with nano-ZrO2 powder by ball milling to obtain a mixture; wherein the molar ratio of zirconium element in the nano-ZrO2 powder to vanadium element in the vanadium source is (0.36-0.67):1; (3) The mixture obtained in step (2) is calcined again to obtain a fusion-coated high-entropy layered oxide sodium battery positive electrode material.

2. The method for preparing the fused-coated high-entropy layered oxide sodium cathode material according to claim 1, characterized in that, In step (1), the sodium source is Na2CO3, the nickel source is NiO, the chromium source is Cr2O3, the vanadium source is V2O3, the molybdenum source is Mo2O3, the titanium source is TiO2, and the cerium source is CeO2.

3. The method for preparing the fused-coated high-entropy layered oxide sodium cathode material according to claim 2, characterized in that, In step (1), the pressure for tabletting is 8-12 MPa, the tabletting is circular, the size is 10-30 mm, and the thickness is 2-6 mm.

4. The method for preparing the fused-coated high-entropy layered oxide sodium cathode material according to claim 3, characterized in that, In step (1), the calcination treatment refers to heating at a heating rate of 3-10℃ / min to 850-1000℃ and maintaining the temperature for 8-15 h.

5. The method for preparing the fused-coated high-entropy layered oxide sodium cathode material according to claim 4, characterized in that, In step (2), the screen density for sieving is 200-400 mesh; the particle size of the nano-ZrO2 powder is 20-50 nm.

6. The method for preparing the fused-coated high-entropy layered oxide sodium cathode material according to claim 5, characterized in that, In steps (1) and (2), the ball milling time is 4-8 h.

7. The method for preparing the fused-coated high-entropy layered oxide sodium cathode material according to claim 6, characterized in that, In step (3), the conditions for the second calcination are as follows: heating at a heating rate of 3-10℃ / min to 950-1050℃ and maintaining the temperature for 6-10 h.

8. The method for preparing the fused-coated high-entropy layered oxide sodium cathode material according to claim 7, characterized in that, The sintering atmosphere for the calcination treatment in step (1) and the second calcination in step (3) is air or oxygen.

9. A fusion-coated high-entropy layered oxide sodium battery positive electrode material prepared by the preparation method of any one of claims 1-8.

10. The use of the fusion-coated high-entropy layered oxide sodium battery positive electrode material of claim 9 in a sodium-ion battery.

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