Layered oxide material, method for producing the same, positive electrode material, positive electrode sheet, sodium-ion battery

Abstract

The application provides a layered oxide material and a preparation method, a positive electrode material, a positive electrode sheet and a sodium ion battery thereof. The layered oxide material is an O3-type layered metal oxide; the surface of the O3-type layered metal oxide is enriched with Ti elements, and the molar content of the Ti elements in the surface layer region is higher than that in the internal region; the chemical general formula of the layered oxide material is Na x (Ni a Mn b Fe c ) 1‑y‑z‑ d Zn y Cu z Ti d O 2+δ , wherein 0.8<=x<=1, 0.1<=a<=0.4, 0.2<=b<=0.45, 0.2<=c<=0.45, 0.02<=y<=0.1, 0.01<=z<=0.06, 0.001<=d<=0.04, a+b+c=1, and -0.08<=delta<=0.02. The layered oxide material can balance high energy density, long cycle life and low cost.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a layered oxide material and its preparation method, a cathode material, a cathode sheet, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries are considered an ideal technology for next-generation large-scale energy storage systems and some power battery applications due to the abundance of sodium resources, low cost, and high safety. They are particularly suitable for scenarios such as grid peak shaving and frequency regulation, renewable energy grid integration, and low- and medium-speed electric vehicles. However, existing sodium-ion battery cathode materials, especially O3-type layered oxides, still face a series of problems in practical applications.

[0003] First, cost and resource dependence are prominent issues. Currently, mainstream O3-type layered oxide cathodes generally use a high nickel content (Ni element mass content > 0.3%), which can provide a high initial capacity, but the price of nickel resources is expensive and fluctuates frequently, which seriously affects the stability of material costs and the economics of large-scale promotion.

[0004] Secondly, energy density is limited. Due to Na... + Due to its large radius (1.02Å), O3-type layered oxides suffer from severe kinetic lag and irreversible structural evolution during charge and discharge, resulting in insufficient capacity output. The actual reversible capacity is often less than 130mAh / g, which is insufficient to meet the needs of high-energy-density energy storage systems.

[0005] Third, there are issues with cycle stability and structural degradation. During charge and discharge, O3-type layered oxides are prone to multi-stage phase transitions, accompanied by lattice slip, volumetric stress accumulation, and microcrack formation. These structural evolutions lead to gradual instability of the material structure and rapid capacity decay, severely restricting the application of long-life energy storage and power batteries.

[0006] Finally, poor air stability is also a major obstacle to industrialization. O3-type layered oxides often retain alkaline byproducts (Na2CO3, NaOH) on their surfaces, making them prone to hygroscopic deliquescence in air. This leads to powder agglomeration and surface structure damage, significantly increasing the difficulty of electrode processing, transportation, and storage, as well as raising manufacturing and maintenance costs. This problem is particularly prominent in energy storage stations in humid or coastal environments, necessitating the development of materials with high air stability to simplify electrode fabrication processes and improve product consistency.

[0007] In summary, O3-type layered oxide cathode materials currently face multiple challenges, including high cost, insufficient capacity, cycle degradation, and air sensitivity, making it difficult to simultaneously meet the comprehensive requirements of high energy density, long cycle life, low cost, and process stability. This has become a core bottleneck restricting the large-scale market application of sodium-ion batteries. Summary of the Invention

[0008] The main objective of this invention is to provide a layered oxide material and its preparation method, a cathode material, a cathode sheet, and a sodium-ion battery, so as to solve the problem that the existing O3-type layered oxide cathode material cannot simultaneously meet the requirements of high energy density, long cycle life, and low cost.

[0009] To achieve the above objectives, according to one aspect of the present invention, a layered oxide material is provided, which is an O3-type layered metal oxide. The O3-type layered metal oxide comprises an inner region and a surface region from the inside out. The surface region is a region ≤500 nm from the outer surface of the O3-type layered metal oxide. The surface of the O3-type layered metal oxide is enriched with Ti element, which is doped into the lattice of the surface region of the O3-type layered metal oxide in the form of a solid solution. The molar content of Ti element in the surface region is higher than that in the inner region. The general chemical formula of the layered oxide material is Na. x (Ni a Mn b Fe c ) 1-y-z-d Zn y Cu z Ti d O 2+δ Wherein, 0.8≤x≤1, 0.1≤a≤0.4, 0.2≤b≤0.45, 0.2≤c≤0.45, 0.02≤y≤0.1, 0.01≤z≤0.06, 0.001≤d≤0.04, a+b+c=1, -0.08≤δ≤0.02; the layered oxide material satisfies the following parameter conditions: the layered oxide material is acid-etched with an acid solution with a molar concentration of 0.5~1.5mol / L for 30~60s, and the filtrate obtained after filtration is denoted as solution A; the solution obtained after completely dissolving the same mass of layered oxide material in the acid solution is denoted as solution B; the ratio of the molar amount of Ti element in solution A to the total molar amount of all metal elements in solution A is defined as C(Ti). A The ratio of the molar amount of Ti in solution B to the total molar amount of all metal elements in solution B is C(Ti). B The surface enrichment of layered oxide materials is R(Ti) = C(Ti). A / C(Ti) B Surface enrichment R(Ti)≥1.5.

[0010] Furthermore, 0.9≤x≤1, 0.2≤a≤0.3, 0.3≤b≤0.4, 0.3≤c≤0.4, 0.02≤y≤0.05, 0.02≤z≤0.05, and 0.002≤d≤0.02.

[0011] Furthermore, x: (a+b+c)×(1-yzd):(y+z+d) is (0.9~1):(0.9~0.95):(0.05~0.1); and / or, a:b:c is (2~3):(3~4):(3~4); and / or, y:z is (0.3~5):1.

[0012] Furthermore, the acid solution is selected from any one or more of hydrochloric acid, sulfuric acid, and nitric acid; and / or, the O3-type layered metal oxide is a spherical secondary particle formed by the stacking of primary particles; the D of the secondary particles 50 The particle size is 3~15μm.

[0013] According to another aspect of the present invention, a method for preparing the above-mentioned layered oxide material is provided, the method comprising: step S1, taking Ni... a Mn b Fe c (OH)2, sodium source and doped metal source raw materials are mixed and then subjected to a first mixing, calcination and cooling to obtain an O3-type layered oxide matrix; in step S2, the raw materials including the O3-type layered oxide matrix and titanium source are subjected to a second mixing and heat treatment to obtain a layered oxide material; wherein, the doped metal source includes zinc source and copper source; based on the Na element in the sodium source, and Ni a Mn b Fe c The total amount of Ni, Mn, and Fe elements in (OH)₂, calculated based on the total metal elements in the metal doping source, includes sodium source, Ni a Mn b Fe c The molar ratio of (OH)2 to the metal dopant source is 0.8~1:0.9~0.95:0.03~0.1; where a, b and c are each independently equivalent to a, b and c above; the mass ratio of titanium source to O3-type layered oxide matrix is ​​0.1~1.5:100; the heat treatment temperature is 750~850℃ and the heat treatment time is 10~60min.

[0014] Further, in step S2 above, the titanium source is nano-TiO2, and the D50 particle size of nano-TiO2 is 20~200nm; and / or, the rotation speed of the second mixing is 300~800rpm, and the second mixing time is 10~60min; and / or, the heat treatment atmosphere is air.

[0015] Further, in step S1 above, the sodium source is sodium carbonate and / or sodium bicarbonate; the zinc source is selected from any one or more of zinc acetate, zinc oxide, and zinc hydroxide; the copper source is selected from any one or more of copper acetate, copper oxide, and copper hydroxide; and / or, the calcination temperature is 800~1000℃, the calcination heating rate is 1~10℃ / min, and the calcination holding time is 4~16h; and / or, the cooling rate is 1~5℃ / min.

[0016] According to another aspect of the present invention, a positive electrode material is provided, which is the layered oxide material described above or prepared by the preparation method described above.

[0017] According to another aspect of the present invention, a positive electrode sheet is provided, comprising a current collector and a positive electrode active layer sequentially stacked along the thickness direction, the positive electrode active layer comprising a positive electrode material, which is the aforementioned positive electrode material.

[0018] According to another aspect of the present invention, a sodium-ion battery is provided, comprising a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0019] Applying the technical solution of this invention, compared to physically coating the outer surface of O3-type layered metal oxides with TiO2, the outer surface of the layered oxide material of this application is enriched with Ti elements to form a Ti-containing layer, and the TiO2 crystal phase is not doped independently. On the one hand, since the Ti elements enter the crystal lattice to form a solid solution, the physical phase interface between the physical coating layer and the matrix material can be eliminated, thereby significantly reducing the interface impedance and avoiding the problem of coating layer peeling off due to volume expansion or contraction mismatch during long cycling, thus greatly improving the interface structure stability and cycle life of the layered oxide material. On the other hand, compared with the insulating TiO2 coating layer, the Ti elements in the crystal lattice can form continuous Na + The transmission channel will not obstruct Na + The insertion and extraction of Ti elements ensures the excellent rate performance of the layered oxide material. Furthermore, this application did not employ high-entropy Ti doping (i.e., Ti was not uniformly doped throughout the entire particle) because Ti… 4+Ti is an electrochemically inert element and does not contribute to capacity. However, excessive doping of Ti in the bulk phase can occupy sites of active metals (Ni / Mn / Fe), leading to a decrease in the overall specific capacity of the layered oxide material. Therefore, this application employs a "surface enrichment" strategy, distributing a high concentration of Ti only in the surface region in contact with the electrolyte. This utilizes the strong Ti-O bonds to stabilize the surface lattice oxygen, suppressing lattice collapse under high desodiumization conditions and its side reactions with the electrolyte. Simultaneously, a high content of active elements is retained in the core region of the layered oxide material particles, maximizing the material's specific capacity while significantly improving its surface stability and high-voltage cycling performance. This application can characterize the Ti surface enrichment content using low-cost methods such as acid etching and ICP. Preferably, controlling R(Ti) within the aforementioned range allows for quantification of the degree of surface structure modification. When R(Ti)≥1.5, it indicates that Ti element effectively establishes a high-concentration protective barrier in the particle surface region. This titanium-rich surface layer can effectively resist the erosion of water molecules and carbon dioxide in the air, prevent the formation of residual alkali, and thus significantly improve the air storage stability of the layered oxide material. At the same time, the gradient distribution structure within this range can alleviate the stress mismatch between the surface and the interior during charging and discharging, thereby inhibiting the generation of microcracks and further extending the cycle life of the battery. The layered oxide material of this application achieves multiple modification effects through multi-element synergistic doping: on the one hand, Zn element enters the transition metal layer as a pillar ion. Utilizing its stable chemical properties, it can not only reduce surface reactivity and block the erosion of the crystal lattice by water and carbon dioxide in the air, thereby improving the air stability of the layered oxide material, but also enhance the lattice rigidity and significantly inhibit the erosion of the crystal lattice by Na during charging and discharging. + Interlayer slip and volume expansion caused by insertion / extraction. Cu doping can improve the high voltage stability of layered oxide materials, and by stabilizing the lattice oxygen in the high desodium state, it is beneficial to Na… + Reversible insertion / extraction in the high-voltage range improves the battery's cycle performance in that range. Secondly, the larger ionic radius of Zn... 2+ (0.74Å) and Cu 2+ (0.72Å) Ni substitution 2+ (0.69Å) can effectively increase the O-Na-O interlayer spacing and reduce Na + The diffusion barrier is thus effectively enhanced for Na. + The diffusion coefficient is improved, thereby enhancing the rate performance of the layered oxide material. Furthermore, this application optimizes the phase transition path through multi-element synergistic modification, promoting the formation of a stable OP2 symbiotic phase during charge-discharge processes. This OP2 phase has an alternating structure of octahedral (O) and triangular prism (P) layers, acting as a "structural buffer" to block the continuous lattice expansion of the P3 phase. The P-type layers effectively alleviate the Na+ diffusion problem. +Migration-induced interlaminar stress, the O-type layer can ensure Na + Storage sites. This mechanism can significantly reduce lattice distortion under high voltage (such as suppressing malignant c-axis expansion), thereby greatly improving the long-cycle stability of layered oxide materials. Simultaneously, multi-element synergistic doping ensures that Fe and Ni elements, as redox centers, synergistically participate in charge compensation, enabling the layered oxide material to reversibly provide high electrochemical capacity. The Ni content in this application is within the aforementioned range, which reduces cost. In summary, the layered oxide material of this application can balance high energy density, long cycle life, and low cost, thus making it better suited for sodium-ion batteries. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0021] Figure 1 The images show a comparison of scanning electron microscope (SEM) images of the layered oxide materials in Example 1 and the comparative example of this application in their freshly prepared state and after being left in air for 14 days.

[0022] Figure 2 The X-ray diffraction (XRD) patterns of the layered oxide materials in Example 1 and Comparative Example 1 of this application are shown in comparison, one in a freshly prepared state and the other after being left in air for 14 days.

[0023] Figure 3 A comparison graph of the first charge-discharge curves of Embodiment 1 and Comparative Example 1 of this application at a 0.1C rate is shown;

[0024] Figure 4 The diagram shows a comparison of the discharge specific capacity of Embodiment 1 and Comparative Example 1 at different rates from 0.1C to 10C.

[0025] Figure 5 The diagram shows a comparison of the capacity retention rates of Embodiment 1 and Comparative Example 1 after 100 charge-discharge cycles at 1C. Detailed Implementation

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] As analyzed in the background section of this application, the existing technology has the problem that O3-type layered oxide cathode materials cannot simultaneously meet the requirements of high energy density, long cycle life and low cost. In order to solve the above problems, this application provides a layered oxide material and its preparation method, cathode material, cathode sheet and sodium-ion battery.

[0028] In a typical embodiment of this application, a layered oxide material is provided. This layered oxide material is an O3-type layered metal oxide, which comprises an inner region and a surface region from the inside out. The surface region is a region ≤500 nm from the outer surface of the O3-type layered metal oxide. The surface of the O3-type layered metal oxide is enriched with Ti element, which is doped into the lattice of the surface region of the O3-type layered metal oxide in the form of a solid solution. The molar content of Ti element in the surface region is higher than that in the inner region. The general chemical formula of the layered oxide material is Na. x (Ni a Mn b Fe c ) 1-y-z-d Zn y Cu z Ti d O 2+δ Wherein, 0.8≤x≤1, 0.1≤a≤0.4, 0.2≤b≤0.45, 0.2≤c≤0.45, 0.02≤y≤0.1, 0.01≤z≤0.06, 0.001≤d≤0.04, a+b+c=1, -0.08≤δ≤0.02; the layered oxide material satisfies the following parameter conditions: the layered oxide material is acid-etched with an acid solution with a molar concentration of 0.5~1.5mol / L for 30~60s, and the filtrate obtained after filtration is denoted as solution A; the solution obtained after completely dissolving the same mass of layered oxide material in the acid solution is denoted as solution B; the ratio of the molar amount of Ti element in solution A to the total molar amount of all metal elements in solution A is defined as C(Ti). A The ratio of the molar amount of Ti in solution B to the total molar amount of all metal elements in solution B is C(Ti). B The surface enrichment of layered oxide materials is R(Ti) = C(Ti). A / C(Ti) B Surface enrichment R(Ti)≥1.5.

[0029] Compared to physically coating TiO2 metal oxides on the outer surface of O3-type layered metal oxides, the layered oxide material of this application enriches Ti elements on its outer surface to form a Ti-containing layer, and the TiO2 crystal phase is not doped independently. On the one hand, since Ti elements enter the crystal lattice to form a solid solution, the physical phase interface between the physical coating layer and the matrix material can be eliminated, thereby significantly reducing the interfacial impedance and avoiding the problem of coating layer peeling off due to volume expansion or contraction mismatch during long cycling, thus greatly improving the interfacial structure stability and cycle life of the layered oxide material. On the other hand, compared to the insulating TiO2 coating layer, the Ti elements in the crystal lattice can form continuous Na + The transmission channel will not obstruct Na + The insertion and extraction of Ti elements ensures the excellent rate performance of the layered oxide material. Furthermore, this application did not employ high-entropy Ti doping (i.e., Ti was not uniformly doped throughout the entire particle) because Ti… 4+ Ti is an electrochemically inert element and does not contribute to capacity. However, excessive doping of Ti in the bulk phase can occupy sites of active metals (Ni / Mn / Fe), leading to a decrease in the overall specific capacity of the layered oxide material. Therefore, this application employs a "surface enrichment" strategy, distributing a high concentration of Ti only in the surface region in contact with the electrolyte. This utilizes the strong Ti-O bonds to stabilize the surface lattice oxygen, suppressing lattice collapse under high desodiumization conditions and its side reactions with the electrolyte. Simultaneously, a high content of active elements is retained in the core region of the layered oxide material particles, maximizing the material's specific capacity while significantly improving its surface stability and high-voltage cycling performance. This application can characterize the Ti surface enrichment content using low-cost methods such as acid etching and ICP. Preferably, controlling R(Ti) within the aforementioned range allows for quantification of the degree of surface structure modification. When R(Ti)≥1.5, it indicates that Ti element effectively establishes a high-concentration protective barrier in the particle surface region. This titanium-rich surface layer can effectively resist the erosion of water molecules and carbon dioxide in the air, prevent the formation of residual alkali, and thus significantly improve the air storage stability of the layered oxide material. At the same time, the gradient distribution structure within this range can alleviate the stress mismatch between the surface and the interior during charging and discharging, thereby inhibiting the generation of microcracks and further extending the cycle life of the battery. The layered oxide material of this application achieves multiple modification effects through multi-element synergistic doping: on the one hand, Zn element enters the transition metal layer as a pillar ion. Utilizing its stable chemical properties, it can not only reduce surface reactivity and block the erosion of the crystal lattice by water and carbon dioxide in the air, thereby improving the air stability of the layered oxide material, but also enhance the lattice rigidity and significantly inhibit the erosion of the crystal lattice by Na during charging and discharging. +Interlayer slip and volume expansion caused by insertion / extraction. Cu doping can improve the high voltage stability of layered oxide materials, and by stabilizing the lattice oxygen in the high desodium state, it is beneficial to Na… + Reversible insertion / extraction in the high-voltage range improves the battery's cycle performance in that range. Secondly, the larger ionic radius of Zn... 2+ (0.74Å) and Cu 2+ (0.72Å) Ni substitution 2+ (0.69Å) can effectively increase the O-Na-O interlayer spacing and reduce Na + The diffusion barrier is thus effectively enhanced for Na. + The diffusion coefficient is improved, thereby enhancing the rate performance of the layered oxide material. Furthermore, this application optimizes the phase transition path through multi-element synergistic modification, promoting the formation of a stable OP2 symbiotic phase during charge-discharge processes. This OP2 phase has an alternating structure of octahedral (O) and triangular prism (P) layers, acting as a "structural buffer" to block the continuous lattice expansion of the P3 phase. The P-type layers effectively alleviate the Na+ diffusion problem. + Migration-induced interlaminar stress, the O-type layer can ensure Na + Storage sites. This mechanism can significantly reduce lattice distortion under high voltage (such as suppressing malignant c-axis expansion), thereby greatly improving the long-cycle stability of layered oxide materials. Simultaneously, multi-element synergistic doping ensures that Fe and Ni elements, as redox centers, synergistically participate in charge compensation, enabling the layered oxide material to reversibly provide high electrochemical capacity. The Ni content in this application is within the aforementioned range, which reduces cost. In summary, the layered oxide material of this application can balance high energy density, long cycle life, and low cost, thus making it better suited for sodium-ion batteries.

[0030] The preferred surface enrichment R(Ti) is 1.5~3.4.

[0031] To further improve the energy density, cycle life, and reduce the cost of layered oxide materials, in one embodiment of this application, 0.9≤x≤1, 0.2≤a≤0.3, 0.3≤b≤0.4, 0.3≤c≤0.4, 0.02≤y≤0.05, 0.02≤z≤0.05, and 0.002≤d≤0.02.

[0032] In one embodiment of this application, x: (a+b+c)×(1-yzd):(y+z+d) is (0.9~1):(0.9~0.95):(0.05~0.1); and / or, a:b:c is (2~3):(3~4):(3~4); and / or, y:z is (0.3~5):1.

[0033] Preferred control of x: (a+b+c)×(1-yzd):(d+y+z) within the above range helps to introduce appropriate amounts of inactive and stabilizing elements to strengthen the crystal framework while ensuring sufficient sodium ion reserves and high redox center density in the layered oxide material, thereby balancing specific capacity and structural stability. Specifically, a sufficient x value (0.9~1) facilitates the formation of pure-phase O3 structures and the formation of abundant Na+. + The concentration of (a+b+c) at 0.9~0.95 helps to provide a high content of Ni / Fe active sites, thus establishing the basis for the high specific capacity of the material; while the concentration of (y+z+d) at 0.05~0.1 is the "threshold" for the formation of multi-element synergistic effect, which helps to alleviate the significant decrease in specific capacity caused by excessive doping, and also helps to provide enough heteroatoms to pin the lattice plane and induce the formation of beneficial OP2 buffer phase.

[0034] Controlling the ratio of a:b:c within the aforementioned range helps enhance the synergistic effect of Ni, Mn, and Fe elements, thereby further stabilizing the redox active centers of Fe and Ni while constructing a high-mechanical-strength Mn-O framework to support the layered structure. Specifically, this ratio helps to stabilize the inert Mn... 4+ This effectively separates active Ni and Fe ions, suppressing the migration of Fe ions to the sodium layer and the irreversible phase transition of Ni ions under high voltage. Simultaneously, this ratio helps reduce dependence on expensive Ni sources while maintaining high energy density, thus lowering raw material costs while preserving the material's specific capacity and cycle stability. Controlling the y:z ratio within the aforementioned range helps enhance the synergistic effect of Zn and Cu elements, balancing lattice rigidity and reaction kinetics. Specifically, inactive Zn preferentially and significantly weakens the tendency for interlayer slip; while appropriate Cu doping, utilizing its high electronegativity and excellent electronic conductivity, not only helps improve the rate performance and average operating voltage of layered oxide materials but also enhances the surface resistance to water molecule erosion. The synergistic effect of these two elements at this ratio helps to better suppress the harmful transformation from the O3 phase to the P3 phase and broadens the stable operating voltage window of the material.

[0035] In one embodiment of this application, the acid solution is selected from any one or more of hydrochloric acid, sulfuric acid, and nitric acid; the layered oxide material is a spherical secondary particle formed by stacking primary particles; the D of the secondary particles... 50 The particle size is 3~15μm.

[0036] Selecting acid solutions within the aforementioned range helps improve the efficiency of element extraction from the surface of layered oxides and the accuracy of detection data, thereby achieving precise quantification of "Ti element surface enrichment". The principle is that hydrochloric acid, sulfuric acid, and nitric acid are all strong inorganic acids, and their corresponding transition metal salts (such as chlorides, sulfates, and nitrates) have extremely high solubility in aqueous solutions. Compared to weak or organic acids, these strong acids can rapidly and completely destroy and dissolve the outermost crystal structure of the particles within a very short time (30-60 seconds), quantitatively and without residue transferring the Ti element and matrix metal ions dissolved in the surface crystal lattice into solution A. This reduces the possibility of incomplete dissolution due to insufficient acidity or the formation of metal precipitates due to improper anion selection, thereby eliminating background interference and data deviation in ICP spectroscopy, and ultimately improving the accuracy and reliability of R(Ti) ratio calculation.

[0037] Secondary particles are formed by the aggregation of primary particles and exhibit a regular spherical shape. It is preferable to control the particle size of secondary particles within the above-mentioned range. Such a micron-sized spherical structure not only helps to increase the compaction density of layered oxide materials, thereby increasing the energy density of the battery, but also has better wettability in the electrolyte, which helps to increase the contact area between the cathode material and the electrolyte, further improving its electrochemical performance and cycle stability.

[0038] In another typical embodiment of this application, a method for preparing the above-mentioned layered oxide material is provided, the method comprising: step S1, taking Ni... a Mn b Fe c (OH)2, sodium source, and doped metal source are mixed and then subjected to a first mixing, calcination, and cooling to obtain an O3-type layered oxide matrix; in step S2, the raw materials including the O3-type layered oxide and titanium source are subjected to a second mixing and heat treatment to obtain a layered oxide material; wherein, the doped metal source includes a zinc source and a copper source; based on the Na element in the sodium source, and Ni a Mn b Fe c The total amount of Ni, Mn, and Fe elements in (OH)₂, calculated based on the total metal elements in the metal doping source, includes sodium source, Ni a Mn b Fe c The molar ratio of (OH)2 to the metal dopant source is 0.8~1:0.9~0.95:0.03~0.1; where a, b and c are each independently equivalent to a, b and c above; the mass ratio of titanium source to O3-type layered oxide matrix is ​​0.1~1.5:100; the heat treatment temperature is 750~850℃ and the heat treatment time is 10~60min.

[0039] The layered oxide material prepared by the above method in this application can balance high energy density, long cycle life, and low cost, thus making it better suited for use in sodium-ion batteries. Specifically, in step S1, Ni... a Mn b Fe c (OH)₂, a sodium source, and a doped metal source, when mixed and calcined, can form a stable O₃-type layered metal oxide. Preferably, controlling the types of metal elements in the doped metal source within the aforementioned range helps to improve both the structural stability and kinetic properties of the layered oxide material, making Na… + Rapid transport in structurally stable layered oxide materials improves the rate performance and cycle life of batteries. Preferred control of the sodium source and Ni... a Mn b Fe c When the molar ratio of (OH)₂ to the metal dopant source is within the above range, it is possible to control the final formation of a co-doped O₃-type layered metal oxide, allowing for more Na₂O to be produced. + Rapid transport between layered oxide materials and the electrolyte optimizes the reversible specific capacity, rate performance, and cycle performance of the battery. In step S2, the O3-type layered oxide is mixed with a titanium source in a second process, allowing the titanium source to be fully and uniformly distributed on the outer surface of the O3-type layered oxide. Subsequently, a Ti surface enrichment is formed through heat treatment, allowing Ti elements to be doped into the lattice of the surface region of the O3-type layered metal oxide in the form of a solid solution. That is, a Ti-containing layer is formed on the outer surface of the O3-type layered oxide, thereby using thermal driving force to promote the in-situ diffusion of Ti elements into the surface lattice sites of the O3-type layered oxide, constructing a stable "solid solution" surface structure. This structure can eliminate the physical phase interface between the exogenous component and the matrix. Compared with simple physical mixing or coating, it can significantly enhance the bonding force between the modified layer and the matrix, preventing surface peeling caused by volume expansion during long-term cycling. At the same time, the Ti entering the lattice 4+The strong Ti-O bonds formed effectively stabilize the surface oxygen framework, suppressing oxygen release and electrolyte decomposition under high sodium desorption conditions. Precisely controlling the temperature and time of the heat treatment within the aforementioned range allows for precise control of the radial diffusion depth of Ti elements, achieving "shallow doping" rather than "uniform bulk doping." Specifically, this particular sub-low temperature short-time treatment process (750~850℃, 10~60min) is based on the solid-phase diffusion kinetics of Ti ions in layered oxides: on the one hand, this heat treatment condition provides sufficient activation energy, enabling the Ti source to break the energy barrier and enter the surface lattice to form a solid solution, thus avoiding Ti from merely physically adhering to the surface as a high-resistivity TiO2 phase due to excessively low temperatures; on the other hand, this condition effectively limits the deep diffusion of Ti ions into the core region of the particles. Unlike conventional "high-entropy doping" processes (which typically require high-temperature, long-time sintering to achieve uniform element distribution in the bulk), the preparation method of this application prevents electrochemically inert Ti elements from occupying active Ni / Fe sites within the particles, thereby avoiding a decrease in the overall specific capacity of the material due to bulk doping. By controlling the mass ratio of titanium source to O3-type layered oxide matrix within the aforementioned range, the integrity of the surface modification layer can be maintained while further reducing the negative impact on the electrochemical activity of the layered oxide material. This allows the layered oxide material to better balance high surface stability and high specific capacity. Furthermore, the preparation method of this application exhibits good production stability, and the prepared layered oxide material demonstrates high quality stability. In summary, the preparation method of this application combines precursor co-precipitation with dry mechanical fusion-thermal driven diffusion technology. The process flow is controllable, requiring no complex liquid-phase coating equipment and eliminating the need for expensive organic solvents. By precisely controlling the heat treatment temperature (750~850℃) and time, the R(Ti) value can be stably controlled, resulting in high product consistency and facilitating large-scale industrial production.

[0040] In addition, to compensate for the loss of Na due to volatilization at high temperatures, the molar amount of sodium source can be in excess by 3-5%.

[0041] In one embodiment of this application, in step S2 above, the titanium source is nano-TiO2, and the D50 particle size of the nano-TiO2 is 20~200nm; and / or, the rotation speed of the second mixing is 300~800rpm, and the second mixing time is 10~60min; and / or, the heat treatment atmosphere is air.

[0042] Preferably controlling the type of titanium source and the D50 particle size of nano-TiO2 within the aforementioned range helps the titanium source to be fully and uniformly distributed on the outer surface of the O3-type layered oxide matrix, thereby facilitating subsequent Ti surface enrichment and shallow doping. The second mixing method is preferably dry mechanical fusion, carried out in a mechanical fusion device. Preferably controlling the rotation speed and time of the second mixing within the aforementioned range helps to prevent significant particle fragmentation, thus maintaining the integrity of the secondary particle morphology.

[0043] The preferred heat treatment conditions within the above range facilitate the construction of a Ti-enriched gradient solid solution protective layer (R(Ti)≥1.5) on the surface of O3-type layered oxide particles. This dense surface structure helps to isolate the active lattice from the erosion of water molecules (H2O) and carbon dioxide (CO2) in the air, thereby further inhibiting H2O corrosion. + / Na + Exchange reaction and the formation of surface residual alkali (sodium carbonate / sodium hydroxide).

[0044] In one embodiment of this application, in step S1 above, the sodium source is sodium carbonate and / or sodium bicarbonate; the zinc source is selected from any one or more of zinc acetate, zinc oxide, and zinc hydroxide; the copper source is selected from any one or more of copper acetate, copper oxide, and copper hydroxide; and / or, the calcination temperature is 800~1000℃, the calcination heating rate is 1~10℃ / min, and the calcination holding time is 4~16h; and / or, the cooling rate is 1~5℃ / min.

[0045] Preferably using sodium, zinc, and copper sources within the aforementioned ranges helps in forming O3-type layered metal oxides with stable crystal structures. Controlling the calcination temperature and holding time within the aforementioned ranges helps improve the crystal structure stability and purity of the O3-type layered metal oxides. Controlling the heating rate during calcination within the aforementioned range helps improve the thermal uniformity of the material's internal structure, thereby further enhancing the crystal structure stability of the O3-type layered metal oxides. The preferred calcination atmosphere is air. Cooling to room temperature (20~30°C) is preferred.

[0046] In another typical embodiment of this application, a positive electrode material is provided, which is the above-described layered oxide material or prepared by the above-described preparation method.

[0047] The cathode material of this application has high energy density, long cycle life and low cost, and can be better applied to sodium-ion batteries.

[0048] In another typical embodiment of this application, a positive electrode sheet is provided, including a current collector and a positive electrode active layer stacked sequentially along the thickness direction. The positive electrode active layer includes a positive electrode material, which is the positive electrode material described above.

[0049] Because the above-mentioned positive electrode contains the layered oxide material of this application, the positive electrode has high rate performance and cycle stability.

[0050] In another typical embodiment of this application, a sodium-ion battery is provided, including a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0051] The layered oxide material of this application has a low cost and high specific capacity and air stability. Sodium-ion batteries including the above-mentioned positive electrode have high reversible specific capacity, rate performance and cycle stability.

[0052] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0053] Example 1

[0054] Sodium carbonate was used as the sodium source, Ni 0.25 Mn 0.375 Fe 0.375 The ingredients are prepared using (OH)2 as a precursor, zinc oxide as a zinc source, and copper oxide as a copper source, with the molar ratio of sodium source, precursor, zinc source, and copper source being 0.9:0.9:0.075:0.015, based on the total amount of Na in the sodium source, Ni, Mn, and Fe in the precursor, Zn in the zinc source, and Cu in the copper source.

[0055] The raw materials were first mixed in a high-speed mixer until homogeneous, then placed in a muffle furnace for calcination in air atmosphere. The temperature was increased to 900℃ at a heating rate of 5℃ / min and calcined at this temperature for 10 hours. After calcination, the mixture was cooled to room temperature (25℃) at a cooling rate of 5℃ / min, crushed, and sieved to obtain the chemical formula Na. 0.9 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 O 1.95 O3-type layered metal oxide matrix.

[0056] Nano-TiO2 and O3-type layered oxide matrix with a D50 particle size of 100 nm were mixed a second time at a mass ratio of 0.73:100. The second mixing process was carried out by dry mechanical fusion at 500 rpm for 30 min in a mechanical fusion device. Subsequently, it was heat-treated at 800℃ in air for 30 min to obtain a layered oxide material with the chemical formula Na. 0.9 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 Ti 0.01 O 1.97The layered oxide material consists of an internal region and a surface region from the inside out. The surface region is the area ≤500nm from the outer surface of the O3-type layered metal oxide. The surface of the O3-type layered metal oxide is enriched with Ti element. The Ti element is doped into the lattice of the surface region of the O3-type layered metal oxide in the form of a solid solution, and the molar content of Ti element in the surface region is higher than that in the internal region.

[0057] Example 2

[0058] The difference from Example 1 is that, based on the total amount of Na in the sodium source, Ni, Mn, and Fe in the precursor, Zn in the zinc source, and Cu in the copper source, the molar ratio of the sodium source, precursor, zinc source, and copper source is 0.8:0.9:0.075:0.015, the mixture is prepared to obtain the chemical formula Na. 0.8 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 O 1.9 The O3-type layered metal oxide matrix; the mass ratio of nano-TiO2 and O3-type layered oxide matrix is ​​0.73:100, and the chemical formula of the resulting layered oxide material is Na. 0.8 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 Ti 0.01 O 1.92 .

[0059] Example 3

[0060] The difference from Example 1 is that, based on the total amount of Na in the sodium source, Ni, Mn, and Fe in the precursor, Zn in the zinc source, and Cu in the copper source, the molar ratio of the sodium source, precursor, zinc source, and copper source is 1:0.9:0.075:0.015, resulting in the chemical formula NaNi. 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 The O3-type layered metal oxide matrix of O2; the mass ratio of nano-TiO2 to O3-type layered oxide matrix is ​​0.73:100, and the chemical formula of the resulting layered oxide material is NaNi. 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 Ti 0.01 O2.02 .

[0061] Example 4

[0062] The difference from Example 1 is that, based on the total amount of Na in the sodium source, Ni, Mn, and Fe in the precursor, Zn in the zinc source, and Cu in the copper source, the molar ratio of sodium source, precursor, zinc source, and copper source is 0.9:0.942:0.02:0.02, the mixture is prepared to obtain a product with the chemical formula Na. 0.9 Ni 0.236 Mn 0.353 Fe 0.353 Zn 0.02 Cu 0.02 O 1.97 The O3-type layered metal oxide matrix; the mass ratio of nano-TiO2 and O3-type layered oxide matrix is ​​0.73:100, and the chemical formula of the resulting layered oxide material is Na. 0.9 Ni 0.236 Mn 0.353 Fe 0.353 Zn 0.02 Cu 0.02 Ti 0.01 O 1.99 .

[0063] Example 5

[0064] The difference from Example 1 is that Ni is used. 0.2 Mn 0.4 Fe 0.4 Using (OH)₂ as a precursor, the mixture was prepared according to the following formula: based on the total amount of Na in the sodium source, Ni, Mn, and Fe in the precursor, Zn in the zinc source, and Cu in the copper source. The molar ratio of sodium source, precursor, zinc source, and copper source was 0.9:0.9:0.075:0.015. This yielded a product with the chemical formula Na. 0.9 Ni 0.18 Mn 0.36 Fe 0.36 Zn 0.075 Cu 0.015 O 1.98 The O3-type layered metal oxide matrix, with a mass ratio of nano-TiO2 to O3-type layered oxide matrix of 0.73:100, yields a layered oxide material with the chemical formula Na. 0.9 Ni 0.18 Mn 0.36 Fe 0.36 Zn 0.075 Cu 0.015 Ti 0.01 O2.

[0065] Example 6

[0066] The difference from Example 1 is that, based on the total amount of Na in the sodium source, Ni, Mn, and Fe in the precursor, Zn in the zinc source, and Cu in the copper source, the molar ratio of the sodium source, precursor, zinc source, and copper source is 0.9:0.9:0.08:0.01, resulting in a product with the chemical formula Na. 0.9 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.08 Cu 0.01 O 1.95 The O3-type layered metal oxide matrix; the mass ratio of nano-TiO2 and O3-type layered oxide matrix is ​​0.73:100, and the chemical formula of the resulting layered oxide material is Na. 0.9 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.08 Cu 0.01 Ti 0.01 O 1.97 .

[0067] Example 7

[0068] The difference from Example 1 is that TiO2 with a D50 particle size of 20 nm was used to finally obtain a layered oxide material.

[0069] Example 8

[0070] The difference from Example 1 is that the mass ratio of nano-TiO2 (D50 particle size of 100 nm) to O3-type layered oxide matrix is ​​0.15:100, and the chemical formula of the resulting layered oxide material is Na. 0.9 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 Ti 0.002 O 1.95 .

[0071] Example 9

[0072] The difference from Example 1 is that nano-TiO2 with a D50 particle size of 400 nm was used, and the mass ratio of nano-TiO2 to O3-type layered oxide matrix was 1.5:100. The chemical formula of the resulting layered oxide material is Na. 0.9 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 Ti 0.02 O 1.99 .

[0073] Example 10

[0074] The difference from Example 1 is that the heat treatment temperature after mechanically fusing TiO2 is 850°C and the heat treatment time is 10 min, and the final product is a layered oxide material.

[0075] Example 11

[0076] The difference from Example 1 is that the heat treatment temperature after mechanically fusing TiO2 is 750°C and the heat treatment time is 60 min, finally obtaining a layered oxide material.

[0077] Comparative Example 1

[0078] The difference from Example 1 is that, based on the elemental Na in the sodium source, the Ni... 0.25 Mn 0.375 Fe 0.375 The total amount of Ni, Mn, and Fe elements in (OH)2, and the sodium source sodium carbonate and Ni 0.25 Mn 0.375 Fe 0.375 The molar ratio of (OH)₂ is 0.9:1, ultimately yielding the chemical formula Na. 0.9 Ni 0.25 Mn 0.375 Fe 0.375 A layered oxide material with O2 and no Ti-rich layer.

[0079] Comparative Example 2

[0080] The difference from Example 1 is that the layered oxide material is an O3-type layered metal oxide matrix Na. 0.9 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 O 1.95 Furthermore, there is no Ti-rich layer.

[0081] Comparative Example 3

[0082] The difference from Example 1 is that the ingredients are prepared according to the following proportions: Na in the sodium source, Ni, Mn and Fe in the precursor, Zn in the zinc source, Cu in the copper source, and Ti in the titanium source, with a molar ratio of 0.9:0.9:0.075:0.015:0.01.

[0083] The raw materials were first mixed in a high-speed mixer. After uniform mixing, the mixture was placed in a muffle furnace and calcined in air atmosphere. The temperature was increased to 900℃ at a heating rate of 5℃ / min and calcined at this temperature for 10 hours. After calcination, the mixture was cooled to room temperature (25℃) at a cooling rate of 5℃ / min, crushed, and sieved to obtain a layered oxide material with the chemical formula Na. 0.9 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 Ti 0.010 O 1.97 .

[0084] Comparative Example 4

[0085] The difference from Example 1 is that the heat treatment temperature after mechanically fusing TiO2 is 450°C, the heat treatment time is 2 hours, and the chemical formula of the resulting layered oxide material is Na. 0.9 Ni 0.225 Mn 0.3375 Fe 0.3375 Zn 0.075 Cu 0.015 Ti 0.010 O 1.97 The outer surface of the layered oxide material is coated with a TiO2 layer.

[0086] Test method:

[0087] Solution A is the mixture obtained by etching the layered oxide material with a 0.8 mol / L hydrochloric acid solution for 40 s. The filtrate obtained after filtration is also denoted as solution A. Solution B is the solution obtained by completely dissolving an equal mass of the layered oxide material in hydrochloric acid solution. The ratio of the molar amount of Ti in solution A to the total molar amount of all metal elements in solution A is defined as C(Ti). A The ratio of the molar amount of Ti in solution B to the total molar amount of all metal elements in solution B is C(Ti). B Surface enrichment R(Ti) = C(Ti) A / C(Ti) B The test results are shown in Table 1.

[0088] Battery preparation: The above-mentioned layered oxide materials, conductive agents (carbon black Super P and Ketjen black KB), and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 96:2.5:1.5. An appropriate amount of solvent N-methylpyrrolidone was added, and the mixture was stirred at 2000 rpm for 5 minutes in a high-speed mixer-degassing machine. This process was repeated twice to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated onto carbon-containing aluminum foil. The slurry was heated from room temperature (25℃) to 110℃, and after drying and rolling to obtain a dried electrode, it was punched into circular positive electrode sheets with a diameter of 13 mm and placed in a vacuum drying oven at 120℃ for 8 hours. After complete drying, the sheets were transferred to an argon-filled glove box for later use (water content <0.01 ppm, oxygen content <0.01 ppm). A 15.6 mm diameter sodium sheet was used as the negative electrode of the battery, glass fiber (manufacturer: Whatman) was used as the separator, 1.0 mol / L electrolyte salt NaClO4 was dissolved in propylene carbonate solvent, and 2% fluoroethylene carbonate FEC was added as the electrolyte. The button cell was assembled in an anhydrous and oxygen-free vacuum glove box.

[0089] The button cells were tested within a voltage range of 2~4.1V for their initial discharge specific capacity at 0.1C, initial discharge specific capacity at 10C, and capacity retention after 100 cycles at 1C. The results are shown in Table 2.

[0090] Coin cells prepared by placing layered oxide materials in air at 25°C and 40% humidity for 14 days were tested for their first discharge specific capacity at 0.1C under 2~4.1V conditions. The capacity ratio after 14 days of storage was calculated as: first discharge specific capacity at 0.1C after 14 days of storage / first discharge specific capacity at 0.1C before storage. The first discharge specific capacity at 0.1C before storage is the data in column 1 of Table 2. The results are shown in Table 3.

[0091] Table 1

[0092]

[0093] Table 2

[0094]

[0095] Table 3

[0096]

[0097] As can be seen from the data in Table 1, the R(Ti) values ​​of the embodiments of this application all fall within the range of 1.6 to 3.4, and all meet the requirement of R(Ti) ≥ 1.5, proving that this application has successfully constructed a "Ti element enrichment" structure on the surface of O3 type layered oxide particles through the above heat treatment process.

[0098] As can be seen from the data in Table 2, the layered oxide material prepared in Example 1 of this application exhibits the best comprehensive electrochemical performance, with a first discharge specific capacity of 151.09 mAh / g at 0.1C, a discharge specific capacity of 95.01 mAh / g at a high rate of 10C, and a capacity retention rate of 85.20% after 100 cycles at 1C.

[0099] Compared with Comparative Example 1 (without high-entropy element doping and without Ti-rich layer): Example 1 shows significant improvements in capacity, rate capability and cycling performance. In particular, at a high rate of 10C, the capacity increased from 64.32 mAh / g in Comparative Example 1 to 95.01 mAh / g, demonstrating that the strategy of multi-element synergistic doping and surface enrichment significantly reduces impedance and improves structural stability.

[0100] Compared with Comparative Example 2 (doped with only high-entropy elements, without a Ti-rich layer): Although Comparative Example 2 introduced Zn and Cu doping, and its performance was improved compared with Comparative Example 1, its cycle retention rate (80.97%) was still lower than that of Example 1 (83.99%), indicating that the enrichment of Ti elements on the surface can further suppress side reactions and enhance interface stability.

[0101] Compared to Comparative Example 3 (high entropy doping of all elements): Although Comparative Example 3 has acceptable cycle stability (82.65%), its 0.1C specific capacity (146.55 mAh / g) is significantly lower than that of Example 1. This demonstrates that if a large amount of Ti element enters the bulk lattice and occupies active sites, it will lead to a decrease in specific capacity; while the "surface enrichment" strategy of this application (Example 1) successfully balances high capacity and high stability.

[0102] Compared to Comparative Example 4 (physical coating): the 10C rate performance (75.88 mAh / g) and cycling performance (74.31%) of Comparative Example 4 were significantly inferior to those of Example 1. This indicates that a simple physical coating layer increases interfacial ion transport impedance and is prone to peeling off due to volume effects during cycling; while the Ti solid solution structure formed in Example 1 eliminates the physical interface, thereby ensuring Na + A fast transmission channel.

[0103] As can be seen from the data in Table 3, Example 1 of this application can still retain 97.7% of its capacity after being left in the air for 14 days, demonstrating excellent air stability.

[0104] Compared to Comparative Example 1 (unmodified): Comparative Example 1 retained only 63.2% of its capacity after 14 days of rest, indicating that the unmodified O3 phase material is extremely sensitive to air and readily undergoes H2O reaction. + / Na + It deteriorates through exchange or reaction with CO2; while Example 1, through the protection of the surface titanium-rich solid solution, can effectively isolate water and oxygen erosion.

[0105] Compared to Comparative Example 2 (without Ti layer) and Comparative Example 3 (Ti bulk doping): Comparative Examples 2 and 3 retained 89.8% and 90.7% of their capacity, respectively, after 14 days of rest. Although Zn / Cu / Ti doping exhibited better electrochemical performance, its air stability remained poor. This directly demonstrates that Ti enrichment on the surface is a key factor in improving air stability, and the enriched structure with R(Ti) ≥ 1.5 constructed a dense protective barrier.

[0106] in, Figure 1 These are scanning electron microscope (SEM) comparison images of the layered oxide materials in Example 1 and Comparative Example 1 in their freshly prepared state and after being left in air for 14 days. (a) is the SEM image of the fresh sample from Example 1, (b) is the SEM image of the sample from Example 1 after being left in air for 14 days, (c) is the SEM image of the fresh sample from Comparative Example 1, and (d) is the SEM image of the sample from Comparative Example 1 after being left in air for 14 days. Figure 1 It can be seen that, in its fresh state, Example 1 ( Figure 1 a) and Comparative Example 1 ( Figure 1 c) The layered oxide materials all exhibit a morphology of near-spherical secondary particles formed by the close packing of primary particles, with a relatively smooth surface and clear outlines of the primary particles. However, after 14 days of exposure to air, the surface morphology of both changed drastically: Comparative Example 1 ( Figure 1 The surface of d) underwent severe corrosion and deterioration, with the primary particle surface becoming rough and blurred, and some fine particulate matter adhering to the surface. This is because the unmodified O3 phase material reacted violently with water molecules and carbon dioxide in the air, generating residual alkali byproducts such as sodium carbonate and sodium hydroxide, which covered the surface of the active material. In contrast, Example 1 ( Figure 1 b) The surface still maintains a smooth and clear morphology, the boundaries of the primary particles are clearly visible, and no obvious traces of corrosion or deposits are observed. Its morphology is similar to that of a fresh state. Figure 1 a) Highly consistent.

[0107] This demonstrates that by using multi-element doping and constructing a Ti-rich solid solution protective layer on the particle surface, this application can effectively isolate the layered oxide material from direct contact with water and oxygen in the air, thereby significantly suppressing surface side reactions and the generation of residual alkali, thus enabling the layered oxide material to have excellent air storage stability.

[0108] Figure 2These are comparison images of the X-ray diffraction (XRD) patterns of the layered oxide materials in Example 1 and Comparative Example 1 in their freshly prepared state and after being left in air for 14 days. (a) is the XRD pattern of the fresh sample in Example 1, (b) is the XRD pattern of the sample in Example 1 after being left in air for 14 days, (c) is the XRD pattern of the fresh sample in Comparative Example 1, and (d) is the XRD pattern of the sample in Comparative Example 1 after being left in air for 14 days. Figure 2 It can be seen that, in their fresh state (a and c), both Example 1 and Comparative Example 1 exhibit typical O3 phase layered oxide diffraction patterns with sharp characteristic peaks and flat baselines, indicating that both have good crystallinity. After exposure to air (b and d), Comparative Example 1 ( Figure 2 The diffraction peak intensity of Example d) shows a significant decrease, and some weak impurity peaks appear, while the main peak position may shift. This indicates that water molecules intruding into the crystal lattice triggers proton / sodium ion exchange, leading to the collapse of the layered structure or a transformation to a hydrated phase, thus destroying the crystal structure. Example 1 (…) Figure 2 b) diffraction pattern and fresh state ( Figure 2 a) The peaks are almost completely overlapping, the characteristic peaks are still sharp, and no impurity peaks appear, indicating that its O3-type layered crystal structure remains intact after long-term exposure to air.

[0109] This demonstrates that the Ti element enriched on the surface in Example 1 not only protects the particle surface, but also stabilizes the surface lattice through solid solution strengthening, thereby effectively blocking the diffusion path of water molecules into the interior of the lattice, preventing the bulk phase transformation caused by water absorption, and fundamentally ensuring the structural stability of the layered oxide material.

[0110] Figure 3 This is a comparison chart of the first charge-discharge curves of Example 1 and Comparative Example 1 at a 0.1C rate. Figure 3 It can be seen that both Example 1 and Comparative Example 1 exhibit the typical charge-discharge voltage curve characteristics of O3-type layered oxides. However, the discharge specific capacity of Example 1 is significantly higher than that of Comparative Example 1, and the degree of polarization is relatively smaller, indicating that the modified material has higher utilization of active sodium ions and better electrochemical reaction reversibility.

[0111] Figure 4 This is a comparison graph of the discharge specific capacity of Example 1 and Comparative Example 1 at different rates from 0.1C to 10C. Figure 4 As can be seen, the capacity difference between Example 1 and Comparative Example 1 gradually widens with the gradual increase of the charge / discharge rate. Especially under high rate conditions of 5C and 10C, the capacity of Comparative Example 1 decreases sharply, while Example 1 still maintains an extremely high discharge specific capacity (95.01 mAh / g at 10C). This indicates that Example 1 can maintain excellent structural stability and rapid ion transport capability even at high current densities.

[0112] Figure 5 This is a comparison chart of the capacity retention rates of Example 1 and Comparative Example 1 after 100 charge-discharge cycles at a 1C rate. Figure 5 As can be seen, during long-term cycling, Example 1 consistently maintains a higher discharge specific capacity than Comparative Example 1, and its capacity decay curve is smoother. After 100 cycles, the capacity retention rate of Example 1 is significantly better than that of Comparative Example 1, demonstrating excellent cycling stability.

[0113] therefore, Figures 3 to 5 The data collectively demonstrate that this application achieves significant results through a synergistic modification strategy of Zn / Cu bulk doping and surface Ti enrichment: First, the introduction of Zn / Cu increases the interlayer spacing and significantly reduces Na... + The diffusion energy barrier is high, thus endowing the material with excellent rate performance. Figure 4 Secondly, the surface-enriched Ti solid solution layer can effectively suppress electrolyte interfacial side reactions and prevent lattice collapse during long-term cycling, thereby significantly improving cycle life. Figure 5 Finally, the stable crystal structure ensures more active Na. + It can participate in reversible insertion and extraction, thereby achieving a higher specific capacity ( Figure 3 ).

[0114] In summary, this application has the following advantages:

[0115] 1) Significantly improves the air storage stability and processing performance of layered oxide materials:

[0116] This application utilizes the above heat treatment process to construct a Ti-enriched gradient solid solution protective layer (R(Ti)≥1.5) on the surface of O3-type layered oxide particles. This dense surface structure effectively isolates the active lattice from the erosion of water molecules and carbon dioxide in the air, thereby significantly inhibiting H2O corrosion. + / Na + The exchange reaction and the formation of residual alkali (sodium carbonate / sodium hydroxide) on the surface. The above experiments show that the layered oxide material of the embodiments of this application retains its crystal structure intact after being left in air for 14 days, and the capacity retention rate can even reach more than 97%, which can solve the problems of traditional O3 type cathode materials being prone to water absorption and deterioration, and slurry gelation.

[0117] 2) Balancing high specific capacity with excellent interface stability:

[0118] This application employs a "shallow doping" strategy, utilizing thermal driving forces to induce Ti elements to form a solid solution only in the surface region, thus restricting their diffusion into the particle core. This structural design, on the one hand, uses the strong Ti-O bonds on the surface to stabilize the oxygen framework, suppressing surface lattice collapse and electrolyte side reactions under high desodium states; on the other hand, it prevents electrochemically inert Ti elements from occupying the active sites (Ni / Fe) inside the particles. Compared to bulk homogeneous doping, the layered oxide material of this application significantly improves cycle stability while maximizing the retention of its high reversible specific capacity.

[0119] 3) It achieves excellent rate capability and good dynamic characteristics:

[0120] This application significantly optimizes the transport kinetics of sodium ions by combining multi-element synergistic doping of Zn and Cu with Ti surface modification. Firstly, the introduction of large-radius ions such as Zn and Cu effectively expands the transport range of Na+. + The diffusion channels (interlayer spacing) lower the migration barrier; secondly, unlike conventional TiO2 physical coating, the "solid solution" structure formed in this application eliminates the physical phase interface between the coating layer and the substrate, which can significantly reduce the interfacial impedance. The above data show that the layered oxide material of this application can still exhibit extremely high discharge specific capacity at a high rate of 10C, far superior to the comparative material with physical coating.

[0121] 4) Significantly extends battery cycle life:

[0122] This application utilizes Zn as a "lattice rivet" to enhance the rigidity of the layered structure, and Cu to stabilize the redox centers under high voltage. Combined with the protective effect of the Ti solid solution on the surface, a dual protection mechanism of "internal stable framework and external corrosion protection" is formed. This synergistic effect can effectively suppress harmful irreversible phase transitions (such as the slippage of P3 to O3 phase) and the generation of microcracks during charge and discharge, resulting in a high capacity retention rate of the layered oxide material after 100 cycles at 1C, which is significantly better than materials modified by a single method.

[0123] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0124] Compared to physically coating TiO2 metal oxides on the outer surface of O3-type layered metal oxides, the layered oxide material of this application enriches Ti elements on its outer surface to form a Ti-containing layer, and the TiO2 crystal phase is not doped independently. On the one hand, since Ti elements enter the crystal lattice to form a solid solution, the physical phase interface between the physical coating layer and the matrix material can be eliminated, thereby significantly reducing the interfacial impedance and avoiding the problem of coating layer peeling off due to volume expansion or contraction mismatch during long cycling, thus greatly improving the interfacial structure stability and cycle life of the layered oxide material. On the other hand, compared to the insulating TiO2 coating layer, the Ti elements in the crystal lattice can form continuous Na + The transmission channel will not obstruct Na + The insertion and extraction of Ti elements ensures the excellent rate performance of the layered oxide material. Furthermore, this application did not employ high-entropy Ti doping (i.e., Ti was not uniformly doped throughout the entire particle) because Ti… 4+ Ti is an electrochemically inert element and does not contribute to capacity. However, excessive doping of Ti in the bulk phase can occupy sites of active metals (Ni / Mn / Fe), leading to a decrease in the overall specific capacity of the layered oxide material. Therefore, this application employs a "surface enrichment" strategy, distributing a high concentration of Ti only in the surface region in contact with the electrolyte. This utilizes the strong Ti-O bonds to stabilize the surface lattice oxygen, suppressing lattice collapse under high desodiumization conditions and its side reactions with the electrolyte. Simultaneously, a high content of active elements is retained in the core region of the layered oxide material particles, maximizing the material's specific capacity while significantly improving its surface stability and high-voltage cycling performance. This application can characterize the Ti surface enrichment content using low-cost methods such as acid etching and ICP. Preferably, controlling R(Ti) within the aforementioned range allows for quantification of the degree of surface structure modification. When R(Ti)≥1.5, it indicates that Ti element effectively establishes a high-concentration protective barrier in the particle surface region. This titanium-rich surface layer can effectively resist the erosion of water molecules and carbon dioxide in the air, prevent the formation of residual alkali, and thus significantly improve the air storage stability of the layered oxide material. At the same time, the gradient distribution structure within this range can alleviate the stress mismatch between the surface and the interior during charging and discharging, thereby inhibiting the generation of microcracks and further extending the cycle life of the battery. The layered oxide material of this application achieves multiple modification effects through multi-element synergistic doping: on the one hand, Zn element enters the transition metal layer as a pillar ion. Utilizing its stable chemical properties, it can not only reduce surface reactivity and block the erosion of the crystal lattice by water and carbon dioxide in the air, thereby improving the air stability of the layered oxide material, but also enhance the lattice rigidity and significantly inhibit the erosion of the crystal lattice by Na during charging and discharging. +Interlayer slip and volume expansion caused by insertion / extraction. Cu doping can improve the high voltage stability of layered oxide materials, and by stabilizing the lattice oxygen in the high desodium state, it is beneficial to Na… + Reversible insertion / extraction in the high-voltage range improves the battery's cycle performance in that range. Secondly, the larger ionic radius of Zn... 2+ (0.74Å) and Cu 2+ (0.72Å) Ni substitution 2+ (0.69Å) can effectively increase the O-Na-O interlayer spacing and reduce Na + The diffusion barrier is thus effectively enhanced for Na. + The diffusion coefficient is improved, thereby enhancing the rate performance of the layered oxide material. Furthermore, this application optimizes the phase transition path through multi-element synergistic modification, promoting the formation of a stable OP2 symbiotic phase during charge-discharge processes. This OP2 phase has an alternating structure of octahedral (O) and triangular prism (P) layers, acting as a "structural buffer" to block the continuous lattice expansion of the P3 phase. The P-type layers effectively alleviate the Na+ diffusion problem. + Migration-induced interlaminar stress, the O-type layer can ensure Na + Storage sites. This mechanism can significantly reduce lattice distortion under high voltage (such as suppressing malignant c-axis expansion), thereby greatly improving the long-cycle stability of layered oxide materials. Simultaneously, multi-element synergistic doping ensures that Fe and Ni elements, as redox centers, synergistically participate in charge compensation, enabling the layered oxide material to reversibly provide high electrochemical capacity. The Ni content in this application is within the aforementioned range, which reduces cost. In summary, the layered oxide material of this application can balance high energy density, long cycle life, and low cost, thus making it better suited for sodium-ion batteries.

[0125] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A layered oxide material, characterized in that, The layered oxide material is an O3-type layered metal oxide, which comprises an inner region and a surface region from the inside out. The surface region is defined as the area ≤500 nm from the outer surface of the O3-type layered metal oxide. The surface of the O3-type layered metal oxide is enriched with Ti, which is doped into the crystal lattice of the surface region in the form of a solid solution. The molar content of Ti in the surface region is higher than that in the inner region. The general chemical formula of the layered oxide material is Na. x (Ni a Mn b Fe c ) 1-y-z-d Zn y Cu z Ti d O 2+δ Where, 0.8≤x≤1, 0.1≤a≤0.4, 0.2≤b≤0.45, 0.2≤c≤0.45, 0.02≤y≤0.1, 0.01≤z≤0.06, 0.001≤d≤0.04, a+b+c=1, -0.08≤δ≤0.02; The layered oxide material satisfies the following parameters: The layered oxide material is etched with an acid solution of 0.5~1.5 mol / L for 30~60 s, and the resulting filtrate is denoted as solution A; the solution obtained by completely dissolving an equal mass of the layered oxide material in the acid solution is denoted as solution B; the ratio of the molar amount of Ti in solution A to the total molar amount of all metal elements in solution A is defined as C(Ti). A The ratio of the molar amount of Ti in solution B to the total molar amount of all metal elements in solution B is C(Ti). B The surface enrichment of the layered oxide material is R(Ti) = C(Ti). A / C(Ti) B The surface enrichment R(Ti) ≥ 1.5; The preparation method of the layered oxide material includes: heat-treating a raw material comprising an O3-type layered oxide matrix and a titanium source; the heat treatment temperature is 750~850℃, and the heat treatment time is 10~60min.

2. The layered oxide material according to claim 1, characterized in that, 0.9≤x≤1, 0.2≤a≤0.3, 0.3≤b≤0.4, 0.3≤c≤0.4, 0.02≤y≤0.05, 0.02≤z≤0.05, 0.002≤d≤0.

02.

3. The layered oxide material according to claim 1, characterized in that, x: (a+b+c)×(1-yzd):(y+z+d) is (0.9~1):(0.9~0.95):(0.05~0.1); and / or, a:b:c is (2~3):(3~4):(3~4); and / or, y:z is (0.3~5):

1.

4. The layered oxide material according to claim 1, characterized in that, The acid solution is selected from any one or more of hydrochloric acid, sulfuric acid, and nitric acid; And / or, the O3-type layered metal oxide is a spherical secondary particle formed by the stacking of primary particles; the D of the secondary particles 50 The particle size is 3~15μm.

5. A method for preparing the layered oxide material according to any one of claims 1 to 4, characterized in that, The preparation method includes: Step S1 will include Ni a Mn b Fe c (OH)2, sodium source and doped metal source raw materials are mixed and then subjected to first mixing, calcination and cooling in sequence to obtain O3 type layered oxide matrix; Step S2 involves sequentially mixing and heat-treating the raw materials, including the O3-type layered oxide matrix and the titanium source, to obtain the layered oxide material. The doped metal source includes a zinc source and a copper source; Based on the Na element in the sodium source, and based on the Ni element... a Mn b Fe c The total amount of Ni, Mn, and Fe elements in (OH)₂, calculated based on the total metal elements in the doped metal source, includes the sodium source and the Ni... a Mn b Fe c The molar ratio of (OH)2 to the doped metal source is 0.8~1:0.9~0.95:0.03~0.1; wherein, the definitions of a, b and c are each independently equivalent to a, b and c in any one of claims 1 to 4; The mass ratio of the titanium source to the O3-type layered oxide matrix is ​​0.1~1.5:100; The heat treatment temperature is 750~850℃, and the heat treatment time is 10~60min.

6. The preparation method according to claim 5, characterized in that, In step S2, the titanium source is nano-TiO2 with a D50 particle size of 20-200 nm; and / or, the second mixing speed is 300-800 rpm and the second mixing time is 10-60 min; and / or, the heat treatment atmosphere is air.

7. The preparation method according to claim 5, characterized in that, In step S1, the sodium source is sodium carbonate and / or sodium bicarbonate; the zinc source is selected from any one or more of zinc acetate, zinc oxide, and zinc hydroxide; and the copper source is selected from any one or more of copper acetate, copper oxide, and copper hydroxide. And / or, the calcination temperature is 800~1000℃, the heating rate of the calcination is 1~10℃ / min, and the holding time of the calcination is 4~16h; And / or, the cooling rate is 1~5℃ / min.

8. A positive electrode material, characterized in that, The cathode material is a layered oxide material as described in any one of claims 1 to 4 or is prepared by the preparation method described in any one of claims 5 to 7.

9. A positive electrode sheet, comprising a current collector and a positive electrode active layer sequentially stacked along the thickness direction, wherein the positive electrode active layer comprises a positive electrode material, characterized in that, The cathode material is the cathode material as described in claim 8.

10. A sodium-ion battery, comprising a positive electrode, an electrolyte, and a negative electrode, characterized in that, The positive electrode is the positive electrode as described in claim 9.

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