Sodium-ion battery positive electrode material, preparation method and application thereof

Abstract

This invention relates to the field of sodium battery materials technology, and discloses sodium-ion battery cathode materials, their preparation methods, and applications. The disclosed sodium-ion battery cathode material comprises a host material and a composite surface layer coated on the host material and chemically bonded to it; the interface between the host material and the composite surface layer is located at 80-90% of the particle size; the host material is an O3 phase layered oxide or sodium iron pyrophosphate; the composite surface layer comprises an aluminum-rich phase in a continuous film-like structure, and multiple nanopillar-shaped NASICON solid solutions embedded within the continuous film layer; the concentrations of aluminum and titanium elements in the sodium-ion battery cathode material particles gradually increase from the inside to the outside, with a stepwise jump in concentration at the composite surface layer. The cathode material provided by this invention exhibits excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of sodium battery materials technology, and more specifically, to sodium-ion battery cathode materials, their preparation methods, and applications. Background Technology

[0002] Sodium-ion batteries, due to their abundant sodium resources, low cost, and high safety, have broad application prospects in large-scale energy storage and low-speed electric vehicles. The cathode material is a key component determining the energy density, cycle life, and rate performance of sodium-ion batteries. Currently, layered oxides and polyanionic compounds are the most studied. However, both types of materials face challenges in practical applications: layered oxides are prone to irreversible phase transitions and lattice oxygen release during charge and discharge, leading to structural degradation and capacity decay; polyanionic materials are limited by low intrinsic electronic conductivity and severe interfacial side reactions. To address these issues, researchers have explored modification strategies such as elemental doping and surface coating.

[0003] In the prior art, Liyang Zhongke Haina Company disclosed a gradient-doped layered oxide material (CN118841535 A), which improves the rate performance and stability of the material to some extent by introducing elements such as Ca and Sr into the material for gradient doping and coating the surface with elements such as Ti, Zr, and Al. However, in this scheme, the doping elements and the coating layer are relatively independent in function. Doping aims at bulk stability, while coating aims at interface protection. The synergistic effect between the two is limited, and the coating layer is mostly physically bonded to the substrate, making it easy to peel off during long-term cycling. Zhao Jinbao et al. (CN 117855421 A) disclosed a cathode material with Mn and X elements (X is at least one of Cu, Co, and Ti) enriched on the surface. The enrichment of inert elements on the surface improves the interface stability, but the surface enrichment layer has a single function and fails to optimize the interface ion transport dynamics at the same time.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a sodium-ion battery cathode material, its preparation method, and its application, aiming to improve at least one of the problems mentioned in the background art.

[0006] This invention is implemented as follows: In a first aspect, embodiments of the present invention provide a sodium-ion battery cathode material, the particles of which include a main material and a composite surface layer that is coated on the outside of the main material and chemically bonded to the main material. The interface between the main material and the composite surface layer is located at 80-90% of the particle size. The main material is O3 phase layered oxide or sodium iron pyrophosphate; The composite surface layer comprises an aluminum-rich phase in the form of a continuous film, and multiple NASICON solid solutions in the form of nanopillars embedded in the continuous film layer; The expression for NASICON solid solution is Na 1+x Ti 2-y Al y (PO4)3, where 0.1≤x≤0.5, 0.05≤y≤0.2, and the aluminum-rich phase is one or more of NaAlO2 and Al2O3; In sodium-ion battery cathode materials, the concentrations of aluminum and titanium gradually increase from the inside out, and the concentrations increase in a stepwise manner at the composite surface layer.

[0007] In an optional embodiment, the chemical formula for the O3 phase layered oxide is Na. b Ni c Fe d Mn e O2, where 0.8≤b≤1.2, 0.1≤c≤0.6, 0.1≤d≤0.5, 0.1≤e≤0.5, and c+d+e=1; the chemical formula of sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7.

[0008] In an optional embodiment, the concentration distribution of Al element in the particles of the sodium-ion battery cathode material satisfies the following: the concentration in the core region from the center of the particle to 5%–10% of the particle size is ≤0.05 at%; the concentration in the core region to 30–50% of the particle size is 0.5–1.0 at%; the concentration in the particle from 30–50% of the particle size to 80–90% of the particle size is 1.0–2.0 at%; and the concentration in the particle from 80–90% of the particle size to the outermost surface is 3.0–6.0 at%. The concentration distribution of Ti element in the particles of the sodium-ion battery cathode material satisfies the following: the concentration in the core region from the center of the particle to 5%–10% of the particle size is ≤0.02 at; the concentration in the core region to 30–50% of the particle size is 0.2–0.8 at; the concentration in the particle from 30–50% of the particle size to 80–90% of the particle size is 0.8–1.5 at; and the concentration in the particle from 80–90% of the particle size to the outermost surface is 1.5–5.0 at.

[0009] In an optional embodiment, the particle size of a single particle of the sodium-ion battery cathode material is 2–20 μm; The average thickness of the continuous film-like aluminum-rich phase is 1–3 nm.

[0010] In an optional embodiment, the D50 of the sodium-ion battery cathode material is 5–20 μm, and the specific surface area is 0.2–1.5 m². 2 / g.

[0011] In an optional embodiment, the host material is connected to the composite surface layer via Al-OM bonds and Ti-OP bonds, wherein M refers to at least one of Ni, Fe, and Mn.

[0012] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned sodium-ion battery cathode material, comprising: Raw materials provided: metal salt solution, precipitant, complexing agent, high-concentration doping solution, pH buffer, and sodium source; the metal salt solution includes a base metal salt solution and a doped metal salt solution, wherein the base metal salt solution contains metal elements for forming the host material, and the doped metal salt contains aluminum and titanium; the high-concentration doping solution contains aluminum and titanium, and the molar concentration of the metal elements therein is 5 to 20 times that of the metal elements in the doped metal salt solution; Preliminary precipitation stage: The basic metal salt solution, the precipitant and the complexing agent are injected into the reactor in parallel flow, and the pH is controlled at 10~11 and the temperature at 40~70℃, while stirring the reaction. Doping and precipitation stage: By monitoring particle size changes, when the particles grow to 10-30% of the target particle size, the injection rate of the doped metal salt solution into the reactor is increased while the injection rate of the base metal salt solution is simultaneously decreased, so that the total injection rate of the metal salt solution into the reactor remains constant. The injection rate of the doped metal salt increases exponentially, and the injection rate of the doped metal salt solution satisfies the exponential growth relationship: R t =R0 e kt The growth coefficient k ranges from 0.01 to 0.05 min. - ¹, R t Rt represents the injection rate at time t, and R0 represents the initial injection rate into the reactor. During the injection of the doped metal salt, the pH inside the reactor is controlled to decrease to 9.5. Surface precipitation stage: When the particles are monitored to have grown to 80-90% of the target particle size, the metal salt solution is switched to the high-concentration doping solution and the pH buffer is injected. The pH is controlled at 8.0-9.0 during the precipitation process. Extraction stage: After the particles in the reactor grow to the target particle size, the mixture in the reactor is subjected to solid-liquid separation, and the obtained solid is purified to obtain the precursor; Sintering: The precursor is mixed with a sodium source and sintered in an oxygen atmosphere.

[0013] In an optional embodiment, the base metal salt solution is a solution containing a source M, wherein the source M is selected from at least one of nickel sulfate, nickel nitrate, ferric sulfate, ferric nitrate, manganese sulfate, and manganese nitrate. Optionally, the molar concentration of element M in the basic metal salt solution is 0.5–2.0 mol / L; Optionally, the injection rate of the metal salt solution is 0.3–1.2 L / h; Optionally, the doped metal salt solution is a metal salt solution containing an aluminum source and a titanium source; optionally, the aluminum source is selected from at least one of aluminum sulfate, aluminum nitrate and aluminum acetate; optionally, the titanium source is selected from at least one of titanium oxysulfate, tetrabutyl titanate and titanium dioxide. Optionally, the molar concentration of aluminum in the doped metal salt solution is 0.1–0.5 mol / L, and the molar concentration of titanium is 0.1–0.5 mol / L. Optionally, the precipitant is selected from at least one of sodium hydroxide, sodium carbonate, and ammonia water; optionally, the concentration of the precipitant is 2-5 mol / L. Optionally, the complexing agent is selected from at least one of citric acid and ethylenediaminetetraacetic acid; optionally, the concentration of the complexing agent is 0.1–0.5 mol / L; optionally, the volume flow ratio of the complexing agent to the metal salt solution is 1:2–5. Optionally, the pH buffer is selected from at least one of ammonium acetate and sodium bicarbonate; optionally, the concentration of the pH buffer is 0.5–2.0 mol / L; optionally, the injection rate of the pH buffer is 0.1–0.5 L / h. Optionally, the sodium source is selected from at least one of sodium carbonate, sodium hydroxide, and sodium oxalate.

[0014] In optional embodiments, the sintering method specifically includes: Pre-firing stage: 500-600℃, hold for 2-4 hours, oxygen partial pressure is 10. -3 ~10 -2 atm; Mid-burning stage: 750–800℃, hold for 4–6 hours, oxygen partial pressure is 10. -2 ~10 -1 atm; Final firing stage: 880–920℃, held for 6–10 hours, oxygen partial pressure 10. -4 ~10 -3 atm; After sintering, it is cooled in the furnace.

[0015] Thirdly, the embodiments of the present invention provide the application of the above-mentioned sodium-ion battery cathode material or the sodium-ion battery cathode material prepared by the above-mentioned preparation method in sodium-ion batteries.

[0016] The present invention has the following beneficial effects: The sodium-ion battery cathode material provided in this invention features a progressively increasing distribution of doped titanium and aluminum from the inside out within the particles, with a stepwise increase in size at the surface, forming a compositional abrupt change interface. This provides a structural basis for dynamic functional conversion during charge and discharge. The aluminum-rich surface phase provides a continuous and dense chemical barrier, inhibiting electrolyte erosion and transition metal dissolution. NASICON nanopillars provide three-dimensional fast ion transport channels, accelerating sodium ion transport at the interface. The mechanical interlocking effect between the nanopillars and the base film further enhances the interfacial bonding force, preventing the composite surface layer from peeling off. During the initial charging phase and deep charging, the solid solution and nanopillars at the surface layer can also achieve functional conversion. The host material and the composite surface layer are connected by chemical bonds, resulting in a much stronger interfacial bonding than physical coating, significantly reduced interfacial impedance, and significantly improved cycle stability and rate performance. Therefore, the sodium-ion battery cathode material provided in this invention exhibits excellent electrochemical performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a partial SEM image of the positive electrode sheet made from the sodium ion positive electrode material prepared in Example 1. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0021] The present invention provides a sodium-ion battery cathode material, the particles of which include a host material and a composite surface layer that is coated on the host material and chemically bonded to the host material; The interface between the main material and the composite surface layer is located at 80-90% of the particle size. The main material is O3 phase layered oxide or sodium iron pyrophosphate; The composite surface layer comprises an aluminum-rich phase in the form of a continuous film, and multiple NASICON solid solutions in the form of nanopillars embedded in the continuous film layer; The expression for NASICON solid solution is Na1+x Ti 2-y Al y (PO4)3, where 0.1≤x≤0.5, 0.05≤y≤0.2, and the aluminum-rich phase is one or more of NaAlO2 and Al2O3; In sodium-ion battery cathode materials, the concentrations of aluminum and titanium gradually increase from the inside out, and the concentrations increase in a stepwise manner at the composite surface layer.

[0022] The sodium-ion battery cathode material provided in this invention has the following characteristics: The distribution pattern of dopant elements (aluminum and titanium) in the main material, with their concentration gradually increasing from the inside to the outside, can effectively alleviate the lattice mismatch stress caused by sodium ion insertion / extraction in the bulk phase. When reaching the composite surface layer, the aluminum and titanium increase in a stepwise manner, which can form a compositional abrupt interface. This interface induces the formation of a special transition phase structure (i.e., the special structure of the composite surface layer), which enhances the interfacial bonding strength and provides a structural basis for dynamic functional conversion during the charging and discharging process. The unique structure of the composite surface (including continuous film layers and nanopillar structures embedded in the continuous film layers) forms a three-dimensional interpenetrating network on the particle surface. The aluminum-rich phase provides a continuous and dense chemical barrier to inhibit electrolyte erosion and transition metal dissolution, while the NASICON nanopillars provide three-dimensional fast ion transport channels to accelerate sodium ion transport at the interface. The mechanical interlocking effect between the nanopillars and the base film further enhances the interfacial bonding force and prevents the composite surface from peeling off. Based on Na + Due to the difference in diffusion rates between the Al phase and the Ti-based NASICON phase, during the initial charging stage, the Ti-based NASICON phase dominates the interface Na. + During transmission, the Al phase primarily serves a protective function; during deep charging, the surface Na... + As the concentration decreases, some Al 3+ A small amount of reversible migration occurs, temporarily participating in framework stabilization or local charge compensation. During discharge, Na... + Embedded back, Al 3+ By restoring the material to its original position, this functional conversion enables the material to maintain optimal interfacial properties under different SOC states. The main material and the composite surface are connected by chemical bonds, and the interfacial bonding strength is much higher than that of physical coating. The interfacial impedance is significantly reduced, and the cycle stability and rate performance are significantly improved.

[0023] Optionally, the chemical formula for the O3 phase layered oxide is Na. b Ni c Fe d Mn eO2, where 0.8≤b≤1.2, 0.1≤c≤0.6, 0.1≤d≤0.5, 0.1≤e≤0.5, and c+d+e=1; the chemical formula of sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7.

[0024] Optionally, the concentration distribution of Al in the particles of the sodium-ion battery cathode material satisfies: The concentration in the core region (5%–10% of particle size) is ≤0.05 at%; the concentration in the core region (30–50% of particle size) is 0.5–1.0 at%; the concentration in the region (30–50% of particle size) is 1.0–2.0 at%; and the concentration in the region (80–90% of particle size) is 3.0–6.0 at% to the outermost surface. The concentration distribution of Ti element in the particles of the sodium-ion battery cathode material satisfies the following: the concentration in the core region from the center of the particle to 5%–10% of the particle size is ≤0.02 at; the concentration in the core region to 30–50% of the particle size is 0.2–0.8 at; the concentration in the particle from 30–50% of the particle size to 80–90% of the particle size is 0.8–1.5 at; and the concentration in the particle from 80–90% of the particle size to the outermost surface is 1.5–5.0 at.

[0025] When the distribution of aluminum and titanium elements meets the above requirements, the electrochemical performance of the material is better.

[0026] Optionally, to achieve better structural compactness and ion transport efficiency in the cathode material, the particle size of a single particle in the sodium-ion battery cathode material is 2–20 μm; the average thickness of the continuous film-like aluminum-rich phase is 1–3 nm.

[0027] Furthermore, the D50 of the sodium-ion battery cathode material is 5–20 μm, and the specific surface area is 0.2–1.5 m². 2 / g. When the cathode material meets this parameter, it possesses both excellent processing and coating performance and electrolyte wettability, as well as high solid density and rapid sodium ion insertion / extraction kinetics.

[0028] Optionally, the host material and the composite surface layer are connected by Al-OM bonds and Ti-OP bonds, where M refers to at least one of Ni, Fe and Mn.

[0029] The method for preparing sodium-ion battery cathode material provided in this invention includes: S1. Provide raw materials: Metal salt solutions, precipitants, complexing agents, highly concentrated doped solutions, pH buffers, and sodium sources.

[0030] Metal salt solutions include basic metal salt solutions and doped metal salt solutions; The base metal salt solution contains a metal element (M element, i.e., at least one of Ni, Fe, and Mn) for forming the host material. The base metal salt solution is a solution containing an M source, optionally selected from at least one of nickel sulfate, nickel nitrate, ferric sulfate, ferric nitrate, manganese sulfate, and manganese nitrate; optionally, the molar concentration of the M element in the base metal salt solution is 0.5–2.0 mol / L.

[0031] The doped metal salt solution is a metal salt solution containing an aluminum source and a titanium source; optionally, the aluminum source is selected from at least one of aluminum sulfate, aluminum nitrate and aluminum acetate; optionally, the titanium source is selected from at least one of titanium oxysulfate, tetrabutyl titanate and titanium dioxide; optionally, the molar concentration of aluminum in the doped metal salt solution is 0.1 to 0.5 mol / L (e.g., 0.1 mol / L, 0.3 mol / L or 0.5 mol / L), and the molar concentration of titanium is 0.1 to 0.5 mol / L (e.g., 0.1 mol / L, 0.3 mol / L or 0.5 mol / L).

[0032] The highly concentrated doped solution contains aluminum and titanium, with a molar concentration of the metal elements 5 to 20 times (e.g., 5, 10, 15, or 20 times) that of the metal elements in the doped metal salt solution. Optionally, the molar concentration of aluminum is 0.5 to 2.5 mol / L (e.g., 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L), and the molar concentration of titanium is 0.5 to 2.5 mol / L (e.g., 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L). Optionally, the specific types of aluminum and titanium sources are the same as those in the doped metal salt solution.

[0033] Optionally, the precipitant is selected from at least one of sodium hydroxide, sodium carbonate, and ammonia water. Optionally, the concentration of the precipitant is 2.0 to 5.0 mol / L (e.g., 2 mol / L, 3 mol / L, 4 mol / L, or 5 mol / L).

[0034] Optionally, the complexing agent is selected from at least one of citric acid and ethylenediaminetetraacetic acid. Optionally, the concentration of the complexing agent is 0.1 to 0.5 mol / L (e.g., 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L).

[0035] Optionally, the pH buffer is selected from at least one of ammonium acetate and sodium bicarbonate; optionally, the concentration of the pH buffer is 0.5 to 2.0 mol / L (e.g., 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L).

[0036] Optionally, the sodium source is selected from at least one of sodium carbonate, sodium hydroxide, and sodium oxalate.

[0037] S2, Preliminary sedimentation stage: The basic metal salt solution, precipitant, and complexing agent are injected into the reactor in a parallel flow, and the pH is controlled at 10-11 and the temperature at 40-70℃ (e.g., 40℃, 50℃, 60℃, or 70℃), while stirring the reaction.

[0038] Optionally, the injection rate of the base metal salt solution in this step is 0.3 to 1.2 L / h (e.g., 0.3 L / h, 0.5 L / h, 0.8 L / h, 1 L / h or 1.2 L / h), which is the injection rate of the metal salt solution (including the base metal salt solution and the doped metal salt solution).

[0039] Optionally, the injection rate of the precipitant can be dynamically adjusted according to the required pH value.

[0040] Optionally, the volumetric flow rate ratio of the complexing agent to the metal salt solution is 1:2 to 5 (e.g., 1:2, 1:3, 1:4 or 1:5).

[0041] S3, Doping and Precipitation Stage: By monitoring changes in particle size, when the particles grow to 10–30% (e.g., 10%, 20%, or 30%) of the target particle size based on the core, the injection of doped metal salt solution into the reactor is increased while the injection rate of the base metal salt solution is simultaneously reduced, so that the total rate of metal salt solution injected into the reactor remains constant (i.e., 0.3–1.2 L / h). The injection rate of doped metal salt increases exponentially. During the injection of doped metal salt, the pH in the reactor is controlled to decrease to 9.5.

[0042] Optionally, to improve the performance of the resulting cathode material, the injection rate of the doped metal salt solution follows an exponential growth relationship: R t =R0 e kt The growth coefficient k ranges from 0.01 to 0.05 min. - ¹(e.g., 0.01 min) - ¹、0.03 min - ¹ or 0.05 min - ¹), R t R0 is the injection rate at time t, and R0 is the initial injection rate into the reactor, which is 0.5 ~ 1.5 mL / min (e.g., 0.5 mL / min, 1 mL / min or 1.5 mL / min).

[0043] In this step, the volumetric flow rate ratio of the complexing agent to the metal salt solution remains constant at 1:2~5.

[0044] S3, Surface sedimentation stage: When the particles are monitored to have grown to 80-90% (e.g., 80%, 85% or 90%) of the target particle size, the metal salt solution is switched to a highly concentrated doped solution and a pH buffer is injected. The pH is controlled at 8.0-9.0 during the precipitation process.

[0045] Optionally, to ensure that the composite surface of the obtained cathode material is continuous, dense, and free of pores and defects, thereby improving the electrochemical performance of the cathode material, the pH buffer injection rate is 0.1 to 0.5 L / h (e.g., 0.1 L / h, 0.3 L / h, or 0.5 L / h).

[0046] S4. Extraction Stage: Once the particles in the reactor have grown to the target particle size, the mixture in the reactor is subjected to solid-liquid separation, and the resulting solid is purified to obtain the precursor.

[0047] Optionally, the purification method includes solid-liquid separation (filtration), washing the obtained solid with deionized water, and then drying to obtain the precursor.

[0048] S5, Sintering: The precursor was mixed with a sodium source and sintered in an oxygen-rich atmosphere.

[0049] Optionally, the oxygen-containing atmosphere is a mixture of an inert gas and oxygen. The inert gas is nitrogen or a group 0 element gas.

[0050] Specifically, sintering methods include: Pre-firing stage: 500–600℃ (e.g., 500℃, 550℃, or 600℃), hold for 2–4 hours (e.g., 2 hours, 3 hours, or 4 hours), oxygen partial pressure is 10. - ³~10 - ² atm (e.g., 10) -3 atm, 5× -3 atm or 10 - ² atm). During this stage, the precursor dehydrates, inhibiting the premature Al / Ti reaction.

[0051] Mid-burning stage: 750–800℃ (e.g., 750℃, 780℃, or 800℃), hold for 4–6 hours (e.g., 4 hours, 5 hours, or 6 hours), oxygen partial pressure is 10. - ²~10 - ¹atm (e.g., 10) -2 atm, 5× -2 atm or 10 -1 (atm). During this stage, Al preferentially reacts to form an aluminum-rich phase precursor.

[0052] Final firing stage: 880–920℃ (e.g., 880℃, 900℃, or 920℃), held for 6–10 h (e.g., 6h, 8h, or 10h), with an oxygen partial pressure of 10. -4 ~10 - ³atm (e.g., 10) -4 atm, 5× -4 atm or 10 -3 (atm). During this stage, Ti reacts with Na, P, and O elements in the matrix to form NASICON solid solution, while simultaneously promoting the formation of chemical bonds between Al / Ti and the matrix.

[0053] After sintering, the furnace is cooled at a rate of 1 to 5 °C / min (e.g., 1 °C / min, 3 °C / min or 5 °C / min).

[0054] Since the particle size is monitored during the preparation process by taking samples and measuring the D50 of the particles, the target particle size mentioned throughout the preparation process refers to the D50 of the particles.

[0055] Through three-stage atmosphere sintering, a triple chemical bond between the functional layer and the matrix was achieved: Al-OM bonds (M=Ni / Fe / Mn) connect the aluminum-rich phase and the layered oxide matrix; Ti-OP bonds connect the NASICON phase and the polyanionic matrix; and Al-O-Ti bonds formed at the interface between the host material and the composite surface layer further strengthen the bonding within the functional layer. This in-situ self-generated chemical bond results in a much stronger interfacial bonding than physical coating, a significant reduction in interfacial impedance, and a significant improvement in cycle stability and rate performance.

[0056] This invention provides the application of the above-mentioned sodium-ion battery cathode material in sodium-ion batteries. Its application in sodium-ion batteries imparts good electrochemical performance to the batteries.

[0057] Example 1 This embodiment provides a sodium-ion battery cathode material and its preparation method.

[0058] (1) The preparation method is as follows: S1. Provide raw materials: The raw materials include metal salt solution, precipitant, complexing agent, high-concentration doping solution, pH buffer, and sodium source.

[0059] Metal salt solutions include basic metal salt solutions and doped metal salt solutions; The basic metal salt solution is a solution obtained by dissolving nickel sulfate, ferric sulfate, and manganese sulfate in deionized water. The molar concentration of Ni, Fe, and Mn elements in the basic metal salt solution is 1.0 mol / L.

[0060] The doped metal salt solution is a solution obtained by dissolving aluminum sulfate and titanium oxysulfate in deionized water, wherein the molar concentration of aluminum is 0.2 mol / L and the molar concentration of titanium is 0.2 mol / L.

[0061] The high-concentration doping solution is a solution obtained by dissolving aluminum sulfate and titanium oxysulfate in deionized water; wherein the molar concentration of aluminum is 1.0 mol / L and the molar concentration of titanium is 1.0 mol / L.

[0062] The precipitant was a 4.0 mol / L aqueous solution of sodium hydroxide.

[0063] The complexing agent is an aqueous solution of citric acid with a concentration of 0.3 mol / L.

[0064] The pH buffer is an aqueous solution of ammonium acetate with a concentration of 1.0 mol / L.

[0065] The sodium source is sodium carbonate.

[0066] S2, Core Development Stage: The basic metal salt solution, precipitant, and complexing agent are injected into the reactor in a parallel flow, and the pH is controlled at 10-11 and the temperature at 55°C, while stirring the reaction.

[0067] In this step, the injection rate of the base metal salt solution is 0.6 L / h. The injection rate of the precipitant is dynamically adjusted according to the required pH value. The volumetric flow ratio of the complexing agent to the metal salt solution is 1:3.

[0068] S3, Doping and Precipitation Stage: By monitoring the particle size change, when the particles grow to 30% of the target particle size based on the core, the injection of doped metal salt solution into the reactor is increased while the injection rate of the base metal salt solution is reduced simultaneously, so that the total rate of metal salt solution injected into the reactor remains constant (i.e. 0.6 L / h). The injection rate of doped metal salt increases exponentially. During the injection of doped metal salt, the pH in the reactor is controlled to decrease to 9.5.

[0069] The injection rate of the doped metal salt solution follows an exponential growth relationship: R t =R0 e kt The growth coefficient k is 0.02min. - ¹, R0 is 1 mL / min.

[0070] In this step, the volumetric flow ratio of the complexing agent to the metal salt solution remains constant at 1:3.

[0071] S4, Surface sedimentation stage: When the particles are monitored to have grown to 85% of the target particle size, the metal salt solution is switched to a highly concentrated doped solution and a pH buffer is injected. The pH is controlled at 8.0~9.0 during the precipitation process.

[0072] The pH buffer was injected at a rate of 0.2 L / h.

[0073] S5. Extraction Stage: Once the particles in the reactor have grown to the target particle size, the mixture in the reactor is subjected to solid-liquid separation, and the resulting solid is purified to obtain the precursor.

[0074] Optionally, the purification method includes solid-liquid separation (filtration), washing the obtained solid with deionized water, and then drying to obtain the precursor.

[0075] S6, Sintering: Pre-firing stage: 550℃, held for 3 hours, in a mixed atmosphere of oxygen and argon, with an oxygen partial pressure of 10. -2 atm; Mid-burning stage: 780℃, held for 5 hours, in a mixed atmosphere of oxygen and argon, with an oxygen partial pressure of 10. -1 atm; Final combustion stage: 900℃, held for 8 hours, in a mixed atmosphere of oxygen and argon, with an oxygen partial pressure of 10. -3 atm; After sintering, the furnace is cooled at a rate of approximately 3°C / min.

[0076] (2) The prepared sodium-ion battery cathode material has the following characteristics: The main material of the particles is an O3 phase layered oxide, with the chemical formula Na1Ni. 0.4 Fe 0.3 Mn 0.3 O2, the aluminum-rich phase is a mixture of NaAlO2 and Al2O3, the chemical formula of the NASICON solid solution is Na 1.3 Ti 1.9 Al 0.1 (PO4)3.

[0077] Note: The chemical composition of each part of the particle was tested using X-ray photoelectron spectroscopy (XPS) combined with transmission electron microscopy (TEM-EDS).

[0078] The average thickness of the continuous layered NASICON solid solution ranges from 1 to 3 nm. Here, average thickness refers to the average thickness of the continuous layer within a single particle, and the average thickness range refers to the average thickness of all particles in the prepared sodium-ion battery cathode material falling within this range. The cathode material particle size distribution ranges from 2 to 20 μm; D50 is 13 μm, and specific surface area is 0.9 m². 2 / g.

[0079] Note: The physical characteristics of each part of the particle were tested using scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

[0080] The concentration distribution of Al in the particles satisfies the following: the concentration in the core region from the center of the particle to 5% of the particle size is ≤0.05 at%; the concentration from 5% to 40% of the particle size increases from the inside to the outside within the range of 0.5 to 1.0 at%; the concentration from 40% to 85% of the particle size increases from the inside to the outside within the range of 1.0 to 2.0 at%; and the concentration from 85% of the particle size to the outermost surface increases from the inside to the outside within the range of 3.0 to 6.0 at%. The concentration distribution of Ti in the particles satisfies the following: the concentration in the core region from the center of the particle to 5% of the particle size is ≤0.02 at%; the concentration from 5% of the particle size to 40% of the particle size increases from the inside to the outside in the range of 0.2 to 0.8 at%; the concentration from 40% of the particle size to 85% of the particle size increases from the inside to the outside in the range of 0.8 to 1.5 at%; and the concentration from 85% of the particle size to the outermost surface increases from the inside to the outside in the range of 1.5 to 5.0 at%.

[0081] Note: The concentration distribution of Al and Ti elements in the particles was determined by transmission electron microscopy energy-dispersive X-ray spectroscopy mapping (TEM-EDS mapping).

[0082] The positive electrode material prepared in Example 1, after being fabricated into a positive electrode sheet, has a local SEM image of its positive electrode active coating as shown in Figure 1. Figure 1 As shown.

[0083] Example 2 This embodiment provides a sodium-ion battery cathode material and its preparation method.

[0084] (1) The preparation method is as follows: S1. Provide raw materials: The raw materials include metal salt solution, precipitant, complexing agent, high-concentration doping solution, pH buffer, and sodium source.

[0085] Metal salt solutions include basic metal salt solutions and doped metal salt solutions; The basic metal salt solution is a solution obtained by dissolving nickel nitrate, ferric nitrate, and manganese nitrate in deionized water. The total molar concentration of Ni, Fe, and Mn in the basic metal salt solution is 0.8 mol / L.

[0086] The doped metal salt solution is a solution obtained by dissolving aluminum nitrate and tetrabutyl titanate in deionized water, wherein the molar concentration of aluminum is 0.1 mol / L and the molar concentration of titanium is 0.1 mol / L.

[0087] The high-concentration doped solution is a solution obtained by dissolving aluminum nitrate and tetrabutyl titanate in deionized water; wherein the molar concentration of aluminum is 0.8 mol / L and the molar concentration of titanium is 0.8 mol / L.

[0088] The precipitant was a 5.0 mol / L aqueous solution of sodium carbonate.

[0089] The complexing agent is an aqueous solution of ethylenediaminetetraacetic acid with a concentration of 0.2 mol / L.

[0090] The pH buffer is a 1.5 mol / L sodium bicarbonate aqueous solution.

[0091] The sodium source is sodium hydroxide.

[0092] S2, Core Development Stage: The basic metal salt solution, precipitant, and complexing agent were injected into the reactor in a parallel flow, and the pH was controlled at 10-11 and the temperature at 40°C. The reaction was stirred.

[0093] In this step, the injection rate of the base metal salt solution is 0.5 L / h. The injection rate of the precipitant is dynamically adjusted according to the required pH value. The volumetric flow ratio of the complexing agent to the metal salt solution is 1:4.

[0094] S3, Doping and Precipitation Stage: By monitoring the particle size change, when the particles grow to 30% of the target particle size based on the core, the injection of doped metal salt solution into the reactor is increased while the injection rate of the base metal salt solution is reduced simultaneously, so that the total rate of metal salt solution injected into the reactor remains constant (i.e., 0.5 L / h). The injection rate of doped metal salt increases exponentially. During the injection of doped metal salt, the pH in the reactor is controlled to decrease to 9.5.

[0095] The injection rate of the doped metal salt solution follows an exponential growth relationship: R t =R0 e kt The growth coefficient k is 0.01min. - ¹, R0 is 0.5 mL / min.

[0096] In this step, the volumetric flow ratio of the complexing agent to the metal salt solution remains constant at 1:4.

[0097] S4, Surface sedimentation stage: When the particles are monitored to have grown to 80% of the target particle size, the metal salt solution is switched to a high-concentration doping solution and a pH buffer is injected. The pH is controlled at 8.0~9.0 during the precipitation process.

[0098] The pH buffer was injected at a rate of 0.3 L / h.

[0099] S5. Extraction Stage: Once the particles in the reactor have grown to the target particle size, the mixture in the reactor is subjected to solid-liquid separation, and the resulting solid is purified to obtain the precursor.

[0100] Optionally, the purification method includes solid-liquid separation (filtration), washing the obtained solid with deionized water, and then drying to obtain the precursor.

[0101] S6, Sintering: Pre-firing stage: 500℃, held for 4 hours, in a mixed atmosphere of oxygen and argon, with an oxygen partial pressure of 10. -2 atm; Mid-burning stage: 750℃, held for 6 hours, in a mixed atmosphere of oxygen and argon, with an oxygen partial pressure of 10. -1 atm; Final combustion stage: 920℃, held for 6 hours, in a mixed atmosphere of oxygen and argon, with an oxygen partial pressure of 10. -3 atm; After sintering, the furnace is cooled at a rate of approximately 3°C / min.

[0102] (2) The prepared sodium-ion battery cathode material has the following characteristics: The main material of the particles is a layered oxide of the O3 phase, with the chemical formula Na. 0.8 Ni 0.1 Fe 0.5 Mn 0.4 O2, the aluminum-rich phase is a mixture of NaAlO2 and Al2O3, the chemical formula of the NASICON solid solution is Na 1.1 Ti 1.95 Al 0.01 (PO4)3.

[0103] The average thickness of the continuous, layered NASICON solid solution ranges from 1 to 3 nm. The particle size distribution of the cathode material ranges from 2 to 20 μm; the D50 is 20 μm, and the specific surface area is 0.2 m². 2 / g.

[0104] The concentration distribution of Al in the particles satisfies the following: the concentration in the core region from the center of the particle to 5% of the particle size is ≤0.05 at%; the concentration from 5% to 30% of the particle size increases from the inside to the outside within the range of 0.5 to 1.0 at%; the concentration from 30% to 80% of the particle size increases from the inside to the outside within the range of 1.0 to 2.0 at%; and the concentration from 80% of the particle size to the outermost surface increases from the inside to the outside within the range of 3.0 to 6.0 at%. The concentration distribution of Ti element in the particles satisfies the following: the concentration in the core region from the center of the particle to 5% of the particle size is ≤0.02 at%; the concentration from 5% of the particle size to 30% of the particle size increases from the inside to the outside in the range of 0.2 to 0.8 at%; the concentration from 30% of the particle size to 80% of the particle size increases from the inside to the outside in the range of 0.8 to 1.5 at%; and the concentration from 80% of the particle size to the outermost surface increases from the inside to the outside in the range of 1.5 to 5.0 at%.

[0105] Example 3 This embodiment provides a sodium-ion battery cathode material and its preparation method.

[0106] (1) The preparation method is as follows: S1. Provide raw materials: The raw materials include metal salt solution, precipitant, complexing agent, high-concentration doping solution, pH buffer, and sodium source.

[0107] Metal salt solutions include basic metal salt solutions and doped metal salt solutions; The basic metal salt solution is a solution obtained by dissolving nickel sulfate, ferric sulfate, and manganese sulfate in deionized water. The total molar concentration of Ni, Fe, and Mn in the basic metal salt solution is 1.5 mol / L.

[0108] The doped metal salt solution is a dispersion of aluminum acetate and titanium dioxide in deionized water, wherein the molar concentration of aluminum is 0.5 mol / L and the molar concentration of titanium is 0.5 mol / L.

[0109] The high-concentration doped solution is a dispersion of aluminum acetate and titanium dioxide in deionized water; wherein the molar concentration of aluminum is 2.5 mol / L and the molar concentration of titanium is 2.5 mol / L.

[0110] The precipitant was an aqueous ammonia solution with a concentration of 3.0 mol / L.

[0111] The complexing agent is an aqueous solution of ethylenediaminetetraacetic acid with a concentration of 0.5 mol / L.

[0112] The pH buffer is a 1.0 mol / L sodium bicarbonate aqueous solution.

[0113] The sodium source is sodium oxalate.

[0114] S2, Core Development Stage: The basic metal salt solution, precipitant, and complexing agent are injected into the reactor in a parallel flow, and the pH is controlled at 10-11 and the temperature at 70°C, while stirring the reaction.

[0115] In this step, the injection rate of the base metal salt solution is 1.0 L / h. The injection rate of the precipitant is dynamically adjusted according to the required pH value. The volumetric flow ratio of the complexing agent to the metal salt solution is 1:2.

[0116] S3, Doping and Precipitation Stage: By monitoring the particle size change, when the particles grow to 20% of the target particle size based on the core, the injection of doped metal salt solution into the reactor is increased while the injection rate of the base metal salt solution is reduced simultaneously, so that the total rate of metal salt solution injected into the reactor remains constant (i.e., 1.0 L / h). The injection rate of doped metal salt increases exponentially. During the injection of doped metal salt, the pH in the reactor is controlled to decrease to 9.5.

[0117] The injection rate of the doped metal salt solution follows an exponential growth relationship: R t =R0 e kt The growth coefficient k is 0.05min. - ¹, R0 is 1.5 mL / min.

[0118] In this step, the volumetric flow ratio of the complexing agent to the metal salt solution remains constant at 1:2.

[0119] S4, Surface sedimentation stage: When the particles are monitored to have grown to 90% of the target particle size, the metal salt solution is switched to a highly concentrated doped solution and a pH buffer is injected. The pH is controlled at 8.0~9.0 during the precipitation process.

[0120] The pH buffer was injected at a rate of 0.5 L / h.

[0121] S5. Extraction Stage: Once the particles in the reactor have grown to the target particle size, the mixture in the reactor is subjected to solid-liquid separation, and the resulting solid is purified to obtain the precursor.

[0122] Optionally, the purification method includes solid-liquid separation (filtration), washing the obtained solid with deionized water, and then drying to obtain the precursor.

[0123] S6, Sintering: Pre-firing stage: 600℃, held for 2 hours, in a mixed atmosphere of oxygen and argon, with an oxygen partial pressure of 10. -2 atm; Mid-burning stage: 800℃, held for 4 hours, in a mixed atmosphere of oxygen and argon, with an oxygen partial pressure of 10. -1 atm; Final combustion stage: 880℃, held for 10 hours, in a mixed atmosphere of oxygen and argon, with an oxygen partial pressure of 10. -3 atm; After sintering, the furnace is cooled at a rate of approximately 3°C / min.

[0124] (2) The prepared sodium-ion battery cathode material has the following characteristics: The main material of the particles is a layered oxide of the O3 phase, with the chemical formula Na. 1.2 Ni 0.6 Fe 0.1 Mn 0.3 O2, the aluminum-rich phase is a mixture of NaAlO2 and Al2O3, the chemical formula of the NASICON solid solution is Na 1.5 Ti 1.8 Al 0.2 (PO4)3.

[0125] The average thickness of the continuous, layered NASICON solid solution ranges from 1 to 3 nm. The particle size distribution of the cathode material ranges from 2 to 20 μm; the D50 is 5 μm, and the specific surface area is 1.5 m². 2 / g.

[0126] The concentration distribution of Al in the particles satisfies the following conditions: the concentration in the core region from the center of the particle to 10% of the particle size is ≤0.05 at%, the concentration from 10% to 50% of the particle size increases from the inside to the outside within the range of 0.5 to 1.0 at%, the concentration from 50% to 90% of the particle size increases from the inside to the outside within the range of 1.0 to 2.0 at%, and the concentration from 90% of the particle size to the outermost surface increases from the inside to the outside within the range of 3.0 to 6.0 at%. The concentration distribution of Ti element in the particles satisfies the following: the concentration in the core region from the center of the particle to 10% of the particle size is ≤0.02 at%; the concentration from 10% to 50% of the particle size increases from the inside to the outside within the range of 0.2 to 0.8 at%; the concentration from 50% to 90% of the particle size increases from the inside to the outside within the range of 0.8 to 1.5 at%; and the concentration from 90% of the particle size to the outermost surface increases from the inside to the outside within the range of 1.5 to 5.0 at%.

[0127] Example 4 This embodiment provides a sodium-ion battery cathode material and its preparation method.

[0128] (1) The preparation method is as follows: S1. Provide raw materials: The raw materials include metal salt solution, precipitant, complexing agent, high-concentration doping solution, pH buffer, and sodium source.

[0129] Metal salt solutions include basic metal salt solutions and doped metal salt solutions; The basic metal salt solution is a solution obtained by dissolving nickel sulfate, ferric sulfate, and manganese sulfate in deionized water. The total molar concentration of Ni, Fe, and Mn in the basic metal salt solution is 1.5 mol / L.

[0130] The doped metal salt solution is a dispersion of aluminum acetate and titanium dioxide in deionized water, wherein the molar concentration of aluminum is 0.5 mol / L and the molar concentration of titanium is 0.5 mol / L.

[0131] The high-concentration doped solution is a dispersion of aluminum acetate and titanium dioxide in deionized water; wherein the molar concentration of aluminum is 2.5 mol / L and the molar concentration of titanium is 2.5 mol / L.

[0132] The precipitant was an aqueous ammonia solution with a concentration of 3.0 mol / L.

[0133] The complexing agent is an aqueous solution of ethylenediaminetetraacetic acid at a concentration of 0.5 mol / L.

[0134] The pH buffer is a 1.0 mol / L sodium bicarbonate aqueous solution.

[0135] The sodium source is sodium oxalate.

[0136] S2, Core Development Stage: The basic metal salt solution, precipitant, and complexing agent are injected into the reactor in a parallel flow, and the pH is controlled at 10-11 and the temperature at 70°C, while stirring the reaction.

[0137] In this step, the injection rate of the base metal salt solution is 1.0 L / h. The injection rate of the precipitant is dynamically adjusted according to the required pH value. The volumetric flow ratio of the complexing agent to the metal salt solution is 1:2.

[0138] S3, Doping and Precipitation Stage: By monitoring the particle size change, when the particles grow to 30% of the target particle size based on the core, the injection of doped metal salt solution into the reactor is increased while the injection rate of the base metal salt solution is reduced simultaneously, so that the total rate of metal salt solution injected into the reactor remains constant (i.e., 1.0 L / h). The injection rate of doped metal salt increases exponentially. During the injection of doped metal salt, the pH in the reactor is controlled to decrease to 9.5.

[0139] The injection rate of the doped metal salt solution follows an exponential growth relationship: R t =R0 e kt The growth coefficient k is 0.05min. - ¹, R0 is 1.2 mL / min.

[0140] In this step, the volumetric flow ratio of the complexing agent to the metal salt solution remains constant at 1:2.

[0141] S4, Surface sedimentation stage: When the particles are monitored to have grown to 90% of the target particle size, the metal salt solution is switched to a highly concentrated doped solution and a pH buffer is injected. The pH is controlled at 8.0~9.0 during the precipitation process.

[0142] The pH buffer was injected at a rate of 0.5 L / h.

[0143] S5. Extraction Stage: Once the particles in the reactor have grown to the target particle size, the mixture in the reactor is subjected to solid-liquid separation, and the resulting solid is purified to obtain the precursor.

[0144] Optionally, the purification method includes solid-liquid separation (filtration), washing the obtained solid with deionized water, and then drying to obtain the precursor.

[0145] S6, Sintering: Pre-firing stage: 600℃, hold for 2 hours, oxygen partial pressure is 10. -2 atm; Mid-burning stage: 800℃, hold for 4 hours, oxygen partial pressure is 10. -1 atm; Final firing stage: 880℃, held for 10 hours, oxygen partial pressure 10. -3 atm; After sintering, the furnace is cooled at a rate of approximately 3°C / min.

[0146] (2) The prepared sodium-ion battery cathode material has the following characteristics: The main material of the particles is a layered oxide of the O3 phase, with the chemical formula Na. 1.2 Ni 0.3 Fe 0.2 Mn 0.5 O2, the aluminum-rich phase is a mixture of NaAlO2 and Al2O3, the chemical formula of the NASICON solid solution is Na 1.5 Ti 1.8 Al 0.2 (PO4)3.

[0147] The average thickness of the continuous film-like NASICON solid solution ranges from 1 to 3 nm. The particle size distribution of the cathode material ranges from 2 to 20 μm; the D50 is 8 μm, and the specific surface area is 1.2 m² / g.

[0148] The concentration distribution of Al in the particles satisfies the following conditions: the concentration in the core region from the center of the particle to 5% of the particle size is ≤0.05 at%; the concentration from the core to 50% of the particle size increases from the inside to the outside within the range of 0.5 to 1.0 at%; the concentration from 50% to 90% of the particle size increases from the inside to the outside within the range of 1.0 to 2.0 at%; and the concentration from 90% of the particle size to the outermost surface increases from the inside to the outside within the range of 3.0 to 6.0 at%. The concentration distribution of Ti element in the particles satisfies the following: the concentration at the particle core is ≤0.02 at%, the concentration from the particle core to 50% of the particle size increases from the inside to the outside in the range of 0.2 to 0.8 at%, the concentration from 50% of the particle size to 90% of the particle size increases from the inside to the outside in the range of 0.8 to 1.5 at%, and the concentration from 90% of the particle size to the outermost surface increases from the inside to the outside in the range of 1.5 to 5.0 at%.

[0149] Example 5 This embodiment provides a sodium-ion battery cathode material and its preparation method.

[0150] (1) The preparation method is as follows: S1. Provide raw materials: The raw materials include metal salt solution, precipitant, complexing agent, high-concentration doping solution, pH buffer, and sodium source.

[0151] Metal salt solutions include basic metal salt solutions and doped metal salt solutions; The basic metal salt solution is a solution obtained by dissolving ferrous sulfate and ammonium dihydrogen phosphate in deionized water, which satisfies the stoichiometric ratio of sodium iron pyrophosphate Na4Fe3(PO4)2P2O7 precursor, and the total molar concentration of metal cations is 1.2 mol / L.

[0152] The doped metal salt solution is a dispersion of aluminum acetate and titanium dioxide in deionized water, wherein the molar concentration of aluminum is 0.5 mol / L and the molar concentration of titanium is 0.5 mol / L.

[0153] The high-concentration doped solution is a dispersion of aluminum acetate and titanium dioxide in deionized water; wherein the molar concentration of aluminum is 2.5 mol / L and the molar concentration of titanium is 2.5 mol / L.

[0154] The precipitant was an aqueous ammonia solution with a concentration of 3.0 mol / L.

[0155] The complexing agent is an aqueous solution of ethylenediaminetetraacetic acid at a concentration of 0.5 mol / L.

[0156] The pH buffer is a 1.0 mol / L sodium bicarbonate aqueous solution.

[0157] The sodium source is sodium oxalate.

[0158] S2, Core Development Stage: The basic metal salt solution, precipitant, and complexing agent are injected into the reactor in a parallel flow, and the pH is controlled at 10-11 and the temperature at 70°C, while stirring the reaction.

[0159] In this step, the injection rate of the base metal salt solution is 1.0 L / h. The injection rate of the precipitant is dynamically adjusted according to the required pH value. The volumetric flow ratio of the complexing agent to the metal salt solution is 1:2.

[0160] S3, Doping and Precipitation Stage: By monitoring the particle size change, when the particles grow to 20% of the target particle size based on the core, the injection of doped metal salt solution into the reactor is increased while the injection rate of the base metal salt solution is reduced simultaneously, so that the total rate of metal salt solution injected into the reactor remains constant (i.e., 1.0 L / h). The injection rate of doped metal salt increases exponentially. During the injection of doped metal salt, the pH in the reactor is controlled to decrease to 9.5.

[0161] The injection rate of the doped metal salt solution follows an exponential growth relationship: R t =R0 e kt The growth coefficient k is 0.03min. - ¹, R0 is 0.8 mL / min.

[0162] In this step, the volumetric flow ratio of the complexing agent to the metal salt solution remains constant at 1:2.

[0163] S4, Surface sedimentation stage: When the particles are monitored to have grown to 90% of the target particle size, the metal salt solution is switched to a highly concentrated doped solution and a pH buffer is injected. The pH is controlled at 8.0~9.0 during the precipitation process.

[0164] The pH buffer was injected at a rate of 0.5 L / h.

[0165] S5. Extraction Stage: Once the particles in the reactor have grown to the target particle size, the mixture in the reactor is subjected to solid-liquid separation, and the resulting solid is purified to obtain the precursor.

[0166] Optionally, the purification method includes solid-liquid separation (filtration), washing the obtained solid with deionized water, and then drying to obtain the precursor.

[0167] S6, Sintering: Pre-firing stage: 600℃, hold for 2 hours, oxygen partial pressure is 10. -2 atm; Mid-burning stage: 800℃, hold for 4 hours, oxygen partial pressure is 10. -1 atm; Final firing stage: 880℃, held for 10 hours, oxygen partial pressure 10. -3 atm; After sintering, the furnace is cooled at a rate of approximately 3°C / min.

[0168] (2) The prepared sodium-ion battery cathode material has the following characteristics: The main material of the particles is sodium iron pyrophosphate, and the aluminum-rich phase is a mixture of NaAlO2 and Al2O3. The chemical formula of the NASICON solid solution is Na... 1.5 Ti 1.8 Al 0.2 (PO4)3.

[0169] The average thickness of the continuous film-like NASICON solid solution ranges from 1 to 3 nm. The particle size distribution of the cathode material ranges from 2 to 20 μm; the D50 is 10 μm, and the specific surface area is 1.0 m² / g.

[0170] The concentration distribution of Al in the particles satisfies the following conditions: the concentration in the core region from the center of the particle to 5% of the particle size is ≤0.05 at%; the concentration from 5% to 50% of the particle size increases from the inside to the outside within the range of 0.5 to 1.0 at%; the concentration from 50% to 90% of the particle size increases from the inside to the outside within the range of 1.0 to 2.0 at%; and the concentration from 90% of the particle size to the outermost surface increases from the inside to the outside within the range of 3.0 to 6.0 at%. The concentration distribution of Ti in the particles satisfies the following: the concentration in the core region from the center of the particle to 5% of the particle size is ≤0.02 at%; the concentration from 5% of the particle size to 50% of the particle size increases from the inside to the outside in the range of 0.2 to 0.8 at%; the concentration from 50% of the particle size to 90% of the particle size increases from the inside to the outside in the range of 0.8 to 1.5 at%; and the concentration from 90% of the particle size to the outermost surface increases from the inside to the outside in the range of 1.5 to 5.0 at%.

[0171] Example 6 This comparative example is basically the same as Example 1, except that the sintering is a single-stage sintering, which is held at 900°C for 16 hours.

[0172] Comparative Example 1 This comparative example is basically the same as Example 1, except that the surface precipitation stage is cancelled and the doping precipitation stage is maintained until the target particle size is achieved.

[0173] Comparative Example 2 This comparative example is basically the same as Example 1, except that during the doping precipitation stage, the injection rate of the doped metal salt remains unchanged at 0.54 L / h, and the base metal salt solution rate is 1 mL / min.

[0174] Comparative Example 3 This comparative example is basically the same as Example 1, except that in the undoped precipitation stage and the surface precipitation stage, the particles are precipitated to the target particle size according to the operation method of the core precipitation stage.

[0175] Comparative Example 4 This comparative example is basically the same as Example 1, except that: there is no aluminum element in the doped metal salt solution and no aluminum element in the high concentration doped element.

[0176] Comparative Example 5 This comparative example is basically the same as Example 1, except that: there is no titanium element in the doped metal salt solution and no titanium element in the high concentration doped element.

[0177] Experimental Example 1 The electrochemical performance of the cathode materials prepared in each embodiment and comparative example was tested, and the test results are recorded in Table 1.

[0178] The specific testing method is as follows: the positive electrode material, conductive agent (conductive carbon black), and binder (PVDF) are mixed in a mass ratio of 95:2.5:2.5 to form a slurry, which is then coated onto an aluminum foil current collector to form a coin cell sodium-ion battery. Using metallic sodium as the negative electrode, the initial coulombic efficiency, 3C rate performance, and capacity retention rate after 500 cycles are tested at a rate of 0.1C.

[0179] Table 1. Electrochemical performance of batteries prepared in each embodiment and comparative example.

[0180] As can be seen from the data in Table 1, the cathode materials prepared in each embodiment of the present invention have excellent electrochemical performance after being assembled into batteries, which is significantly better than conventional cathode materials (cathode materials prepared in Comparative Example 3). Comparing Example 6 with Example 1, the rate performance and long-cycle stability of Example 6 are significantly worse than those of Example 1, indicating that the cathode material prepared by three-stage sintering has significantly better performance than that prepared by one-stage sintering. Comparing Comparative Example 1 with Example 1, the interface stability and cycle life of Comparative Example 1 are significantly worse, indicating that if the surface precipitation stage is eliminated, it is impossible to form an aluminum-rich phase continuous film and an interpenetrating structure of NASICON nanopillars on the surface, thus making it impossible to obtain a cathode material with better electrochemical performance. Comparing Comparative Example 2 with Example 1, the rate performance of Comparative Example 2 is significantly worse. This indicates that if the doping metal salt solution is not injected in a gradually increasing manner during the doping precipitation stage, the concentration of aluminum and titanium elements in the obtained particles cannot be gradually increased from the inside to the outside. As a result, gradient ion transport and interface stress buffering cannot be achieved, and thus a cathode material with better electrochemical performance cannot be obtained. Comparing Comparative Example 3 with Example 1, the overall electrochemical performance of Comparative Example 3 is significantly worse, indicating that the cathode material with special element distribution and special surface provided by the present invention has significantly better electrochemical performance than the O3 phase layered oxide cathode material prepared by conventional methods. Comparing Comparative Examples 4 and 5 with Example 1, the cycling stability and rate performance of Comparative Examples 4 and 5 were significantly worse, indicating that doping with only aluminum or only titanium cannot significantly improve the electrochemical performance of the material.

[0181] In summary, the preparation method provided by this invention can produce the cathode material provided by this invention, with a distribution pattern combining increasing Al and Ti element concentrations with a step-like jump; and a three-dimensional interpenetrating network structure of NASICON solid solution and aluminum-rich phase is formed on the outermost layer of the particles; the three-dimensional interpenetrating network structure is chemically bonded to the matrix, and dynamic functional conversion is achieved during charging and discharging based on the difference in Al / Ti diffusion rates. The preparation method provided by this invention achieves a precise composite gradient distribution of Al / Ti and in-situ self-generation of the surface functional layer through co-precipitation combined with atmospheric sintering (preferably three-stage atmospheric sintering).

[0182] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 sodium-ion battery cathode material, characterized in that, Its particles include a main material and a composite surface layer that covers the main material and is chemically bonded to the main material; The interface between the main material and the composite surface layer is located at 80-90% of the particle size. The main material is O3 phase layered oxide or sodium iron pyrophosphate; The composite surface layer includes an aluminum-rich phase in the form of a continuous film, and a plurality of NASICON solid solutions in the form of nanopillars embedded in the continuous film layer; The expression for the NASICON solid solution is Na 1+x Ti 2-y Al y (PO4)3, wherein 0.1≤x≤0.5, 0.05≤y≤0.2, and the aluminum-rich phase is one or more of NaAlO2 and Al2O3; The concentrations of aluminum and titanium in the particles of the sodium-ion battery cathode material gradually increase from the inside to the outside, and the concentrations increase in a stepwise manner at the composite surface layer.

2. The sodium-ion battery cathode material according to claim 1, characterized in that, The chemical formula for the layered oxide of the O3 phase is Na. b Ni c Fe d Mn e O2, wherein 0.8≤b≤1.2, 0.1≤c≤0.6, 0.1≤d≤0.5, 0.1≤e≤0.5, and c+d+e=1; the chemical formula of the sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7.

3. The sodium-ion battery cathode material according to claim 1, characterized in that, The concentration distribution of Al in the particles of the sodium-ion battery cathode material satisfies the following: the concentration in the core region from the center of the particle to 5%–10% of the particle size is ≤0.05 at; the concentration in the core region to 30–50% of the particle size is 0.5–1.0 at; the concentration in the particle size range from 30–50% to 80–90% is 1.0–2.0 at; and the concentration in the particle size range from 80–90% to the outermost surface is 3.0–6.0 at%. The concentration distribution of Ti element in the particles of the sodium-ion battery cathode material satisfies the following: the concentration in the core region from the center of the particle to 5%–10% of the particle size is ≤0.02 at; the concentration in the core region to 30–50% of the particle size is 0.2–0.8 at; the concentration in the particle from 30–50% of the particle size to 80–90% of the particle size is 0.8–1.5 at; and the concentration in the particle from 80–90% of the particle size to the outermost surface is 1.5–5.0 at.

4. The sodium-ion battery cathode material according to claim 1, characterized in that, The particle size of the single particle of the sodium-ion battery cathode material is 2-20 μm; The average thickness of the continuous film-like aluminum-rich phase is 1–3 nm.

5. The sodium-ion battery cathode material according to claim 1, characterized in that, The D50 of sodium-ion battery cathode materials ranges from 5 to 20 μm, and the specific surface area ranges from 0.2 to 1.5 m². 2 / g.

6. The sodium-ion battery cathode material according to claim 1, characterized in that, The host material and the composite surface layer are connected by Al-OM bonds and Ti-OP bonds, wherein M refers to at least one of Ni, Fe and Mn.

7. The method for preparing the sodium-ion battery cathode material according to any one of claims 1 to 6, characterized in that, include: Raw materials provided: metal salt solution, precipitant, complexing agent, highly concentrated doping solution, pH buffer, and sodium source; The metal salt solution includes a base metal salt solution and a doped metal salt solution. The base metal salt solution contains metal elements for forming the host material, and the doped metal salt contains aluminum and titanium. The high-concentration doped solution contains aluminum and titanium, and the molar concentration of the metal elements is 5 to 20 times that of the metal elements in the doped metal salt solution. Preliminary precipitation stage: The basic metal salt solution, the precipitant and the complexing agent are injected into the reactor in parallel flow, and the pH is controlled at 10~11 and the temperature at 40~70℃, while stirring the reaction. Doping and precipitation stage: By monitoring particle size changes, when the particles grow to 10-30% of the target particle size, the injection rate of the doped metal salt solution into the reactor is increased while the injection rate of the base metal salt solution is simultaneously decreased, so that the total injection rate of the metal salt solution into the reactor remains constant. The injection rate of the doped metal salt increases exponentially, and the injection rate of the doped metal salt solution satisfies the exponential growth relationship: R t =R0 e kt The growth coefficient k ranges from 0.01 to 0.05 min. - ¹, R t Rt represents the injection rate at time t, and R0 represents the initial injection rate into the reactor. During the injection of the doped metal salt, the pH inside the reactor is controlled to decrease to 9.

5. Surface precipitation stage: When the particles are monitored to have grown to 80-90% of the target particle size, the metal salt solution is switched to the high-concentration doping solution and the pH buffer is injected. The pH is controlled at 8.0-9.0 during the precipitation process. Extraction stage: After the particles in the reactor grow to the target particle size, the mixture in the reactor is subjected to solid-liquid separation, and the obtained solid is purified to obtain the precursor; Sintering: The precursor is mixed with a sodium source and sintered in an oxygen atmosphere.

8. The preparation method according to claim 7, characterized in that, The basic metal salt solution is a solution containing source M, wherein source M is selected from at least one of nickel sulfate, nickel nitrate, ferric sulfate, ferric nitrate, manganese sulfate, and manganese nitrate; Optionally, the molar concentration of element M in the basic metal salt solution is 0.5–2.0 mol / L; Optionally, the injection rate of the metal salt solution is 0.3–1.2 L / h; Optionally, the doped metal salt solution is a metal salt solution containing an aluminum source and a titanium source; optionally, the aluminum source is selected from at least one of aluminum sulfate, aluminum nitrate and aluminum acetate; optionally, the titanium source is selected from at least one of titanium oxysulfate, tetrabutyl titanate and titanium dioxide. Optionally, the molar concentration of aluminum in the doped metal salt solution is 0.1–0.5 mol / L, and the molar concentration of titanium is 0.1–0.5 mol / L. Optionally, the precipitant is selected from at least one of sodium hydroxide, sodium carbonate, and ammonia water; optionally, the concentration of the precipitant is 2-5 mol / L. Optionally, the complexing agent is selected from at least one of citric acid and ethylenediaminetetraacetic acid; optionally, the concentration of the complexing agent is 0.1 to 0.5 mol / L; optionally, the volume flow ratio of the complexing agent to the metal salt solution is 1:2 to 5. Optionally, the pH buffer is selected from at least one of ammonium acetate and sodium bicarbonate; optionally, the concentration of the pH buffer is 0.5–2.0 mol / L; optionally, the injection rate of the pH buffer is 0.1–0.5 L / h. Optionally, the sodium source is selected from at least one of sodium carbonate, sodium hydroxide, and sodium oxalate.

9. The preparation method according to claim 7, characterized in that, Sintering methods specifically include: Pre-firing stage: 500-600℃, hold for 2-4 hours, oxygen partial pressure is 10. -3 ~10 -2 atm; Mid-burning stage: 750–800℃, hold for 4–6 hours, oxygen partial pressure is 10. -2 ~10 -1 atm; Final firing stage: 880–920℃, held for 6–10 hours, oxygen partial pressure 10. -4 ~10 -3 atm; After sintering, it is cooled in the furnace.

10. The application of the sodium-ion battery cathode material according to any one of claims 1 to 6 or the sodium-ion battery cathode material prepared by the preparation method according to any one of claims 7 to 9 in sodium-ion batteries.

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