High-nickel ternary modified layered oxide positive electrode material and preparation method and application thereof

Abstract

The invention discloses a high-nickel ternary modified layered oxide positive electrode material and a preparation method and application thereof, and relates to the technical field of sodium-ion battery positive electrode materials, the structural formula of the high-nickel ternary modified layered oxide positive electrode material is NaNixFeyMnzO2 (A), in the formula, x is greater than or equal to 0.6 and less than or equal to 0.9, y is greater than 0 and less than 0.4, x + y + z = 1, A is a doping element and is selected from one or more of Al, Zn, Mg, Zr and B, and z is greater than 0 and less than 1. The high-nickel ternary modified layered oxide positive electrode material with a stable layered structure and high ion mobility is prepared through a co-precipitation reaction-ion doping modification-gradient calcination synergistic process, is applied to the technical field of sodium ion batteries, and has better capacity and cycle performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion battery positive electrode materials, in particular to a high-nickel ternary modified layered oxide positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] As an important candidate technology for the next generation of energy storage systems, the research and development of sodium ion batteries is rooted in the dual demands of energy transformation and resource sustainability. With the lithium ion battery facing the bottlenecks of limited lithium resource reserves, uneven geographical distribution and cost fluctuations, sodium ion batteries have become a strategic research direction in the field of large-scale energy storage due to their high crust abundance (2.3%), low raw material cost and environmental friendliness. However, traditional sodium ion battery positive electrode materials (such as transition metal layered oxides and polyanion compounds) are difficult to meet the application requirements of high energy demand scenarios due to their low energy density (usually <200 Wh / kg) and slow diffusion dynamics caused by the large radius of sodium ions. Under this background, high-nickel ternary layered oxides (general formula Na x Ni y Fe z Mn 1-y-z O2, y>0.6) can significantly improve the specific capacity and working voltage of the material by introducing high-nickel content, and optimize the sodium ion deintercalation reversibility by using the multi-electron redox characteristics of nickel, thereby achieving a balance between energy density and cycle stability. The advantages of this system are: ① reducing cobalt dependence and mitigating strategic metal supply chain risks through high-nickel proportion and iron replacing cobalt; ② adapting to the low-cost characteristics of sodium ion batteries, balancing performance and economy; ③ strong crystal structure designability, which can alleviate the Jahn-Teller distortion and phase transition problems caused by high nickel through doping / coating modification.

[0003] However, the technical challenges cannot be ignored: the surface residual alkali (such as Na2CO3) of high-nickel materials easily triggers electrolyte side reactions, leading to increased interfacial impedance and capacity decay; repeated sodium ion deintercalation easily induces the transformation of layered structure to spinel or rock salt phase, reducing the cycle life; in addition, the high-temperature solid-phase synthesis process has strict requirements for precursor morphology control and element distribution uniformity, increasing the difficulty of large-scale preparation. SUMMARY

[0004] The first aspect of the application is to provide a high-nickel ternary modified layered oxide positive electrode material with better capacity and cycle performance.

[0005] The technical solutions adopted by the application are as follows: A high-nickel ternary modified layered oxide positive electrode material, which has a structural formula of: NaNi x Fe y Mn zO2(A), wherein: 0.6≤x≤0.9, 0

[0006] The second aspect of the present application is to provide a preparation method of high-nickel ternary modified layered oxide cathode material, comprising the following steps: (1) Preparation of precursor Preparation of reaction solution: dissolving soluble salts of nickel source, iron source and manganese source in deionized water according to preset stoichiometric ratio to form a metal salt solution; mixing sodium hydroxide solution and ammonia water in proportion to form a complexing agent solution; Co-precipitation reaction: pumping the metal salt solution and the complexing agent solution into the reaction kettle at a set flow rate for co-precipitation reaction, after the reaction is completed, aging treatment is carried out, then solid-liquid separation, washing and drying are carried out to obtain high-nickel layered oxide precursor particles; (2) Ion doping modification After the precursor particles obtained in step (1) are immersed in a modified ion solution and ion doping modification is carried out, solid-liquid separation, washing and drying are carried out to obtain a doped intermediate; (3) Gradient calcination Mixing the doped intermediate obtained in step (2) with a sodium source in a certain proportion, then placing it in a tube furnace for gradient calcination treatment under oxygen atmosphere to finally obtain a high-nickel ternary modified layered oxide cathode material.

[0007] Further provided is: In step (1), the soluble salts of nickel source, iron source and manganese source are selected from at least one of sulfate, nitrate or chloride, and the nickel source, iron source and manganese source are dissolved in deionized water according to the molar ratio of Ni:Fe:Mn=x:y:1-x-y, wherein: 0.6≤x≤0.9, 0

[0008] In step (1), the concentration of sodium hydroxide in the complexing agent solution is 2-6 mol / L, and the concentration of ammonia water is 0.1-2 mol / L.

[0009] In step (1), the co-precipitation reaction is carried out at 50-65℃ for 5-10 hours, and after the co-precipitation reaction is terminated, aging is carried out at 50-80℃ for 6-12 hours.

[0010] Preferably, in the co-precipitation reaction, the metal salt solution is continuously injected into the reaction kettle through a precision metering pump at a flow rate of 3-15 mL / min, while the complexing agent solution is added synchronously; nitrogen protective gas is introduced throughout to maintain an inert atmosphere, and the pH value of the reaction system is maintained between 10.5-12.0; In step (2), the modified ion solution: select one or more soluble salts containing but not limited to Al, Zn, Mg, Zr, B, dissolved in deionized water to configure 0.1-0.5 mol / L of doped ion solution.

[0011] In step (2), the ion doping modification is to mix the precursor particles with the modified ion solution at a solid-liquid ratio of 1:5-10 g / mL, and stir at a constant temperature of 30-60℃ for 4-12 hours, so that the doped ions fully penetrate into the crystal lattice gap of the precursor.

[0012] In step (3), the doped intermediate prepared in step (2) is mixed with a sodium source at a molar ratio of Na:doped ion=1-1.1:1 after ball milling.

[0013] In step (3), the gradient calcination process includes a precalcination stage and a high-temperature sintering, wherein: Pre-calcination stage: place the doped intermediate after mixing the sodium source in a tube furnace, and heat to 300-550℃ at a heating rate of 2-5℃ / min, and heat at a temperature of 300-550℃ for 1-8 hours under the condition of oxygen flow rate of 50-200 mL / min; High-temperature sintering: after pre-calcination, continue to heat at a rate of 3-8℃ / min to 700-880℃, and use two-stage temperature control, i.e., first heat at 750℃ for 4-6 hours, then heat to 850℃ for 8-12 hours, and the total sintering time is controlled to be 12-18 hours.

[0014] In step (3), after high-temperature sintering, slowly cool to 200℃ in the furnace, and then transfer to a vacuum drying box to quickly cool to room temperature, and grind the product to obtain a high-nickel ternary modified layered oxide positive electrode material.

[0015] The third aspect of the present application is to provide a use of the aforementioned high-nickel ternary modified layered oxide positive electrode material in the preparation of a sodium ion battery, which is specifically as follows: grinding the prepared high-nickel ternary modified layered oxide positive electrode material, then mixing with SP (conductive carbon black) and PVDF (polyvinylidene fluoride) at a mass ratio of 8:1:1, adding NMP (N-methyl pyrrolidone) to stir into a slurry, coating on an aluminum foil, and then drying, punching and pressing to prepare a sodium ion battery positive electrode material sheet, using metallic sodium as the negative electrode, glass fiber as the separator, and NaPF6 (sodium hexafluorophosphate), PC (propylene carbonate) and EMC (methyl ethyl carbonate) solution as the electrolyte, and assembling a CR2025 button cell in an argon-filled glove box.

[0016] The present application has the following advantages: (1) The application provides a preparation method of a high-nickel ternary modified layered oxide positive electrode material.

[0017] (2) The application realizes atomic-level uniform mixing of metal ions through pH regulation and ammonia complexation in a coprecipitation process.

[0018] (3) The application adopts a solution impregnation method for ion doping, effectively avoiding the problem of uneven doping in a traditional solid-phase method.

[0019] (4) The application innovatively designs a gradient calcination process, in which a precursor completes structure relaxation and oxygen vacancy regulation in a low-temperature section, and is subjected to two-section temperature control treatment in a high-temperature section, so as to realize densification and crystallization, thereby making the prepared positive electrode material have better capacity and cycle performance.

[0020] The application will be further described below in combination with the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 SEM image of the product prepared in Example 1.

[0022] Figure 2 SEM image of the product prepared in Example 2.

[0023] Figure 3 SEM image of the product prepared in Comparative Example 1.

[0024] Figure 4 SEM image of the product prepared in Comparative Example 2.

[0025] Figure 5 XRD spectrum of Examples 1 and 2 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0026] In order to make those skilled in the technical field better understand the technical solutions of the application, the preferred embodiments of the application are described below in combination with specific embodiments, but it should not be understood as a limitation to the patent. In the following examples, the test methods or test methods are conventional methods unless otherwise specified; the reagents and materials are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0027] In the following examples, "transition metal" refers to nickel Ni, iron Fe and manganese Mn, and the total amount of transition metal refers to the total number of moles of Ni, Fe and Mn.

[0028] Example 1

[0029] A preparation method of a high-nickel ternary modified layered oxide positive electrode material, comprising the following steps: Step 1: Preparation of precursor 1.1 Preparation of metal salt solution: Nickel sulfate hexahydrate (NiSO4·6H2O), ferrous sulfate heptahydrate (FeSO4·7H2O) and manganese sulfate monohydrate (MnSO4·H2O) are dissolved in deionized water in a molar ratio of 8:1:1 to prepare a metal salt solution of 1.0 mol / L in total metal ion concentration.

[0030] 1.2 Preparation of complexing agent solution: 95.98 grams of sodium hydroxide (NaOH) particles are weighed and dissolved in 1140 milliliters of deionized water to form a sodium hydroxide aqueous solution. Then, 47.5 milliliters of 20% ammonia water (NH3·H2O) are added to the solution and mixed thoroughly to obtain an alkaline complexing agent solution.

[0031] 1.3 Coprecipitation reaction: The metal salt solution and the complexing agent solution are added to the reactor at a flow rate of 5.6 mL / min using a precision metering pump, with the reaction temperature controlled at 50°C, the pH at 11.5±0.2, the stirring rate at 800 rpm, and the reaction time at 6 hours.

[0032] 1.4 Aging treatment: After the coprecipitation reaction is completed, the slurry is transferred to an aging tank and left to stand in a constant temperature environment at 50°C for 12 hours. Vacuum filtration equipment (vacuum degree -0.08 MPa) is used to achieve efficient solid-liquid separation, and the obtained spherical Ni 0.8 Fe 0.1 Mn 0.1 (OH)2 precursor particles are washed with deionized water for 3 times and then dried in a vacuum drying oven (vacuum degree -0.09 MPa) at 120°C for 12 hours.

[0033] Step 2: Ion doping modification 2.1 Preparation of modification solution: Al(NO3)3 is dissolved in deionized water to prepare a modification solution with an Al 3+ concentration of 0.1 mol / L.

[0034] 2.2 Solid-liquid doping treatment: The prepared precursor is added to the modification solution at a solid-liquid ratio of 1:10 (g / mL) and stirred at 60°C for 4 hours.

[0035] 2.3 Post-treatment: The vacuum filtration device (vacuum degree -0.08 MPa) is used to realize the efficient separation of solid and liquid, and the residual nitrate is removed by washing with anhydrous ethanol for 3 times (the solvent dosage is 3 times the mass of the solid phase each time). Then vacuum drying at 80°C for 12 hours to obtain Al 3+ Uniformly doped intermediate material.

[0036] Step 3: Gradient calcination 3.1 Mixing sodium source: The above prepared doped intermediate is mixed with NaOH particles according to the molar ratio of Na: transition metal = 1.05:1.

[0037] 3.2 Pre-burning stage: The above mixture is spread on an alumina crucible and placed in a programmed tube atmosphere furnace. The temperature is programmed to rise to 450°C at a rate of 3°C / min, 200 mL / min of high-purity oxygen (purity 99.99%) is introduced, and the temperature is kept for 4 hours to complete the removal of the surface hydroxyl group and the construction of the initial lattice oxygen structure of the precursor.

[0038] 3.3 High-temperature sintering: Continue to rise the temperature to 750°C at a rate of 5°C / min for primary crystallization (keep for 4 hours), and then control the temperature to rise to 850°C at a rate of 2°C / min for secondary lattice reorganization (keep for 10 hours). The total sintering time is 14 hours, and the oxygen flow is kept at 200 mL / min throughout the process to promote the ordered arrangement of cations.

[0039] 3.4 Cooling treatment: After sintering, the temperature is slowly cooled to 200°C at a rate of ≤5°C / min, and then transferred to a vacuum rapid cooling chamber (vacuum degree ≤1 Pa) to cool to room temperature. The sintered product is ground and sieved (400 mesh) to obtain the final product NaNi 0.8 Fe 0.1 Mn 0.1 O2(Al) positive electrode material.

[0040] Product confirmation: As Figure 1 shown, the SEM image of the NaNi 0.8 Fe 0.1 Mn 0.1 O2(Al) positive electrode material prepared in Example 1 shows significantly optimized micro-morphology characteristics, specifically: (1) Particle morphology and composition: The material is mainly composed of uniform spherical secondary particles, and the primary particles are rice-shaped. This morphology is beneficial to uniform coating and close packing during electrode preparation.

[0041] (2) Particle size distribution: The material particles have a narrow particle size distribution. The typical size range of the primary particles is about 1 micron; these primary particles are further assembled to form secondary particles, which have a typical size range of about 6-12 microns.

[0042] (3) Surface and structural features of the secondary particles: As shown clearly in FIG. 2, the surface of the secondary particles exhibits a highly compact state. Meanwhile, the grain boundaries between and within the particles are clearly visible, and the gaps are small. Figure 1

[0043] Example 2

[0044] Step 1: Preparation of the precursor 1.1 Preparation of the metal salt solution: Nickel sulfate hexahydrate (NiS04-6H20), ferrous sulfate heptahydrate (FeS04-7H20), and manganese sulfate monohydrate (MnS04-H20) were dissolved in deionized water at a molar ratio of 8:1:1 to prepare a metal salt solution 1L with a total metal ion concentration of 1.0 mol / L.

[0045] 1.2 Preparation of the precipitant solution: 95.98 grams of sodium hydroxide (NaOH) particles were weighed and dissolved in 1140 milliliters of deionized water to form a sodium hydroxide aqueous solution. Then, 47.5 milliliters of ammonia water (NH3-H20) with a mass concentration of 20% was added to the solution and mixed uniformly to prepare the alkaline complexing agent solution.

[0046] 1.3 Co-precipitation reaction: The salt solution and the precipitant solution were added to the reactor at a flow rate of 5.6 mL / min using a precision metering pump, and the reaction temperature was controlled at 50°C, the pH was controlled at 11.5±0.2, the stirring rate was 800 rpm, and the reaction time was 6 hours.

[0047] 1.4 Aging treatment: After the reaction was completed, the slurry was transferred to an aging tank and placed in a constant temperature environment at 50°C for 12 hours of aging. Vacuum filtration equipment (vacuum degree -0.08 MPa) was used to achieve efficient solid-liquid separation, and the particles were washed with deionized water three times. Then, the particles were dried in a vacuum drying oven (vacuum degree -0.09 MPa) at 120°C for 12 hours to obtain spherical Ni 0.8 Fe 0.1 Mn 0.1 (OH)2precursor.

[0048] Step 2: Ion doping modification 2.1 Preparation of the modification solution: ZnS04-7H20 was dissolved in deionized water to prepare a modification solution with a Zn 2+ ​0.1 mol / L.

[0049] 2.2 Solid-liquid doping treatment: The precursor prepared in the foregoing was added into the modified solution at a solid-liquid ratio of 1:10 (g / mL), and stirred at 60°C for 4 hours.

[0050] 2.3 Post-treatment: The solid-liquid efficient separation was realized by using a vacuum filtration device (vacuum degree -0.08 MPa), and the residual nitrate was removed by washing with anhydrous ethanol for 3 times (the solvent dosage was 3 times the mass of the solid each time). The Zn 2+ homogeneously doped intermediate material.

[0051] Step 3: Gradient calcination 3.1 Mixing of sodium source: The Zn-doped intermediate was mixed with NaOH particles at a molar ratio of Na: transition metal = 1.05:1.

[0052] 3.2 Pre-burning stage: The mixture was laid flat in an alumina crucible and placed in a programmed tube furnace. The temperature was programmed to rise to 450°C at a rate of 3°C / min, and 200 mL / min of high-purity oxygen (purity 99.99%) was introduced and kept for 4 hours to remove the surface hydroxyl groups and construct the initial lattice oxygen structure of the precursor.

[0053] 3.3 High-temperature sintering: The temperature was continued to rise to 750°C at a rate of 5°C / min for primary crystallization (keeping for 4 hours), and then the temperature was controlled to rise to 850°C at a rate of 2°C / min for secondary lattice reorganization (keeping for 10 hours). The total sintering time was 14 hours, and the oxygen flow was kept at 200 mL / min throughout the process to promote the ordered arrangement of cations.

[0054] 3.4 Cooling treatment: After sintering, the temperature was slowly cooled to 200°C at a natural cooling rate of ≤5°C / min, and then transferred to a vacuum rapid cooling chamber (vacuum degree ≤1 Pa) to cool to room temperature. The sintered product was ground and sieved (400 mesh) to obtain the final product NaNi 0.8 Fe 0.1 Mn 0.1 O2(Zn) cathode material.

[0055] Product confirmation: As Figure 2 shown, the SEM image of the NaNi 0.8 Fe 0.1 Mn 0.1 O2(Zn) cathode material prepared in Example 2, the material of Example 1 showed significantly optimized micro-morphology characteristics, specifically: Particle morphology and composition: The material is mainly composed of uniform spherical secondary particles, while the primary particles are rice-shaped. This morphology is conducive to uniform coating and close packing during electrode preparation.

[0056] Particle size distribution: The material particles have a narrow particle size distribution. The typical size of the primary particles is in the range of about 1-2 microns; these primary particles are further assembled to form secondary particles with a typical size in the range of about 5-10 microns.

[0057] Surface and structural features of secondary particles: As shown clearly in Figure 2 The surface of the secondary particles exhibits a highly dense state. At the same time, the grain boundaries between and within the particles are clearly visible, and the gaps are relatively small.

[0058] Comparative Example 1 This example mainly investigates the performance of the positive electrode material without ion doping modification.

[0059] Step 1: Preparation of precursor 1.1 Preparation of metal salt solution: Dissolve nickel sulfate hexahydrate (NiSO4·6H2O), ferrous sulfate heptahydrate (FeSO4·7H2O), and manganese sulfate monohydrate (MnSO4·H2O) in a molar ratio of 8:1:1 in deionized water to prepare a metal salt solution of 1.0 mol / L with a total metal ion concentration of 1L.

[0060] 1.2 Preparation of precipitant solution: Weigh 95.98 grams of sodium hydroxide (NaOH) particles and dissolve them in 1140 milliliters of deionized water to form a sodium hydroxide aqueous solution. Then, add 47.5 milliliters of 20% ammonia water (NH3·H2O) to the solution and mix well to obtain an alkaline complexing agent solution.

[0061] 1.3 Coprecipitation reaction: The salt solution and the precipitant solution are added to the reactor at a flow rate of 5.6 mL / min using a precision metering pump, with a reaction temperature of 50°C, pH=11.5±0.2, stirring speed of 800 rpm, and reaction time of 6 hours.

[0062] 1.4 Aging treatment: After the reaction is completed, the slurry is transferred to an aging tank and placed in a constant temperature environment at 50°C for 12 hours. High-efficiency solid-liquid separation is achieved using a vacuum filtration device (vacuum degree -0.08 MPa), with deionized water washing for 3 times, followed by drying in a vacuum drying oven (vacuum degree -0.09 MPa) at 120°C for 12 hours to obtain spherical Ni 0.8 Fe 0.1 Mn 0.1 (OH)2 precursor.

[0063] Step 2: Gradient calcination 2.1 Mixing sodium source: The precursor prepared in the preceding step was mixed with NaOH particles in a molar ratio of Na: transition metal = 1.05:1 by grinding.

[0064] 2.2 Pre-burning stage: The mixture was spread in an alumina crucible and placed in a programmable tube furnace. The temperature was programmed to increase to 450°C at a rate of 3°C / min, and 200 mL / min of high-purity oxygen (purity 99.99%) was introduced and maintained for 4 hours to remove the surface hydroxyl groups of the precursor and construct the initial lattice oxygen structure.

[0065] 2.3 High-temperature sintering: The temperature was continued to increase to 750°C at a rate of 5°C / min for primary crystallization (4 hours of holding), and then the temperature was controlled to increase to 850°C at a rate of 2°C / min for secondary lattice rearrangement (10 hours of holding). The total sintering time was 14 hours, and the oxygen flow was maintained at 200 mL / min throughout the process to promote the ordered arrangement of cations.

[0066] 2.4 Cooling treatment: After sintering, the temperature was slowly cooled to 200°C at a natural cooling rate of ≤5°C / min, and then transferred to a vacuum rapid cooling chamber (vacuum degree ≤1 Pa) to cool to room temperature. The sintered product was ground and sieved (400 mesh) to obtain the final product NaNi 0.8 Fe 0.1 Mn 0.1 O2 cathode material.

[0067] Product confirmation: As Figure 3 shown, the SEM image of the product NaNi 0.8 Fe 0.1 Mn 0.1 O2 cathode material prepared in Comparative Example 1, combined with Figure 3 shown: Particle morphology and composition: The material is mainly composed of uniformly stacked sheet-like particles, and no secondary spherical particles are formed.

[0068] Particle size distribution: The typical size of the particles ranges from about 1 micron to 4 microns.

[0069] Surface and structural features of secondary particles: As clearly shown in the accompanying Figure 3 clearly shown, the particle surface presents a state of dense packing. At the same time, the grain boundaries between and within the particles are clearly visible, and the gaps are large.

[0070] Comparative Example 2 This example mainly investigates the performance of the cathode material without gradient calcination.

[0071] Step 1: Preparation of precursor 1.1 Preparation of metal salt solution: Nickel sulfate hexahydrate (NiSO4·6H2O), ferrous sulfate heptahydrate (FeSO4·7H2O) and manganese sulfate monohydrate (MnSO4·H2O) were dissolved in deionized water in a molar ratio of 8:1:1 to prepare a metal salt solution with a total metal ion concentration of 1.0 mol / L.

[0072] 1.2 Preparation of complexing agent solution: 95.98 g of sodium hydroxide (NaOH) particles were weighed and dissolved in 1140 mL of deionized water to form a sodium hydroxide aqueous solution. Then, 47.5 mL of ammonia water (NH3·H2O) with a mass concentration of 20% was added to the solution and mixed thoroughly to obtain an alkaline complexing agent solution.

[0073] 1.3 Co-precipitation reaction: The metal salt solution and the complexing agent solution were added to the reactor at a flow rate of 5.6 mL / min using a precision metering pump, with a reaction temperature of 50°C, pH=11.5±0.2, stirring speed of 800 rpm, and reaction time of 6 hours.

[0074] 1.4 Aging treatment: After the co-precipitation reaction was completed, the slurry was transferred to an aging tank and placed in a constant temperature environment at 50°C for 12 hours of aging. Vacuum filtration equipment (vacuum degree -0.08 MPa) was used for efficient solid-liquid separation, and the obtained spherical Ni 0.8 Fe 0.1 Mn 0.1 (OH)2 precursor particles were washed with deionized water for 3 times, and then dried in a vacuum drying oven (vacuum degree -0.09 MPa) at 120°C for 12 hours.

[0075] Step 2: Ion doping modification 2.1 Preparation of modification solution: Al(NO3)3 was dissolved in deionized water to prepare a modification solution with an Al 3+ concentration of 0.1 mol / L.

[0076] 2.2 Solid-liquid doping treatment: The precursor powder was added to the modification solution at a solid-liquid ratio of 1:10 (g / mL) and stirred at 60°C for 4 hours.

[0077] 2.3 Post-treatment: Vacuum filtration equipment (vacuum degree -0.08 MPa) was used for efficient solid-liquid separation, and the obtained Al 3+ uniformly doped intermediate material was washed with anhydrous ethanol for 3 times (each time the solvent amount was 3 times the mass of the solid phase) to remove residual nitrate. Then, it was dried in a vacuum drying oven at 80°C for 12 hours.

[0078] Step 3: Calcination crystallization 3.1 Mixing sodium source: The above prepared Al-doped intermediate was mixed with NaOH particles at a molar ratio of Na: transition metal = 1.05:1.

[0079] 3.2 Pre-burning stage: The above mixture was spread in an alumina crucible and placed in a programmable tube atmosphere furnace. The temperature was programmed to rise to 450°C at a rate of 3°C / min, 200 mL / min of high-purity oxygen (purity 99.99%) was introduced and the temperature was maintained for 4 hours to complete the removal of the surface hydroxyl group of the precursor and the construction of the initial lattice oxygen structure.

[0080] 3.3 High-temperature sintering: The temperature was continued to rise to 850°C at a rate of 5°C / min for 14 hours of sintering time, and the oxygen flow was maintained at 200 mL / min throughout the process to promote the ordered arrangement of cations.

[0081] 3.4 Cooling treatment: After sintering, the temperature was slowly cooled to 200°C at a rate of ≤5°C / min, and then transferred to a vacuum rapid cooling chamber (vacuum degree ≤1 Pa) to cool to room temperature. The sintered product was ground and sieved (400 mesh) to obtain the final product NaNi 0.8 Fe 0.1 Mn 0.1 O2(Al) cathode material.

[0082] Product confirmation: As shown in Figure 4 , the SEM image of the NaNi 0.8 Fe 0.1 Mn 0.1 O2(Al) cathode material prepared in Comparative Example 2 showed significantly optimized micro-morphology characteristics, specifically: (1) Particle morphology and composition: The material is mainly composed of uniform spherical secondary particles, while the primary particles are in the form of granules.

[0083] (2) Particle size distribution: The material particles have a narrow particle size distribution. The typical size range of the primary particles is about 1 micron to 2 microns directly; these primary particles are further assembled to form secondary particles, and the typical size range is about 4 microns to 10 microns.

[0084] (3) Surface and structure characteristics of secondary particles: As Figure 4 clearly shown, the surface of the secondary particles shows a highly dense state. At the same time, the grain boundaries between and inside the particles are clearly visible, and the gap is large.

[0085] Product comparison: In combinationFigures 1-4 Comparing the SEM images of Examples 1-2 and Comparative Examples 1-2, in combination with the above analysis, it can be seen that: Figure 5 Comparing the XRD patterns of Examples 1, 2 and Comparative Examples 1, 2, it can be seen that: Basic structural features: The materials of Examples 1, 2 and Comparative Examples 1, 2 all show typical O3-type layered oxide crystal structure characteristics, and the diffraction patterns contain characteristic peak positions such as (003), (006), (101), (012), (104), etc.

[0086] Difference in diffraction peak quality: The diffraction peaks of Examples 1 and 2 show significantly better crystalline properties than Comparative Examples 1 and 2, which is embodied in: Peak sharpness and intensity: The diffraction peaks of Examples 1 and 2 are significantly higher in sharpness and stronger in intensity. In addition, the diffraction peak intensity of Comparative Example 2 is the weakest. This directly reflects that the materials prepared by the method of the embodiments of the present application have higher crystallinity and more perfect long-range order of crystal.

[0087] (006) / (012) peak intensity ratio: In the XRD patterns of Comparative Examples 1 and 2, the intensity ratio of the (006) diffraction peak to the (101) diffraction peak is less than 1. In contrast, the materials of Examples 1 and 2 of the present application exhibit the characteristic of an intensity ratio of the (006) diffraction peak to the (101) diffraction peak > 1. This clearly indicates that the materials of the embodiments of the present application have a highly ordered layered crystal structure.

[0088] (003) / (104) peak intensity ratio: Further observation found that the intensity ratio of the (003) diffraction peak to the (104) diffraction peak of Examples 1 and 2 materials is significantly higher than that of Comparative Examples 1 and 2. This ratio is a key indicator for evaluating the degree of cation mixing in O3-type layered oxides. A higher ratio strongly confirms that the materials successfully prepared by the method of the embodiments of the present application have a lower degree of cation mixing between the Na layer and the transition metal layer (TM layer).

[0089] Performance test: The positive electrode materials prepared in Examples 1-2 and Comparative Examples 1-2 above were applied to sodium ion batteries, respectively, and their performances were tested.

[0090] The test method is as follows: the positive electrode material powder is ground through a 200 mesh sieve, then is formulated with SP (conductive carbon black), PVDF (polyvinylidene fluoride) at a mass ratio of 8:1:1, NMP (N-methyl pyrrolidone) is added and stirred into a slurry, coated on an aluminum foil, dried, punched and pressed into a sodium ion battery positive electrode material sheet. With metal sodium as the negative electrode, glass fiber (brand Whatman GF / D) as the separator, and NaPF6 (sodium hexafluorophosphate) PC (propylene carbonate) / EMC (methyl ethyl carbonate) solution as the electrolyte, a CR2025 button cell is assembled in an argon-filled glove box, and charge-discharge test is carried out. Under the conditions of current density 100 mAh / g and voltage range 2.0-4.2 V, first cycle 2 times at 0.2C, then test the capacity and cycle performance at 1C, and the test results are shown in Table 1: Table 1

[0091] As shown in Table 1: the preparation method of the high-nickel ternary modified layered oxide positive electrode material of the application, the method is through the synergistic process of coprecipitation reaction-ion doping modification-gradient calcination, wherein: (1) through the accurate pH regulation and ammonia complexation in the coprecipitation process, the atomic level uniform mixing of metal ions is realized. (2) solution impregnation method is used for ion doping, which effectively avoids the problem of uneven doping in traditional solid phase method. (3) the gradient calcination process is innovatively designed, the precursor completes structure relaxation and oxygen vacancy regulation in the low temperature section, and densification crystallization is realized by two-stage temperature control treatment in the high temperature section. The high-nickel ternary modified layered oxide positive electrode material with stable layered structure and high ion migration rate is prepared by the application, which has better capacity and cycle performance compared with the existing undoped modification or non-gradient calcination process.

[0092] The above is only the preferred embodiment of the application, and it should be pointed out that the above preferred embodiment should not be regarded as a limitation of the application, and the protection scope of the application should be limited by the scope defined by the claims. For ordinary skilled persons in the art, several improvements and refinements can be made without departing from the spirit and scope of the application, and these improvements and refinements should also be regarded as the protection scope of the application.

Claims

1. A high-nickel ternary modified layered oxide cathode material, with the structural formula: NaNi x Fe y Mn z O2(A), where: 0.6≤x≤0.9, 0<y<0.4, x+y+z=1, and A is a doping element selected from one or more of Al, Zn, Mg, Zr, and B.

2. A method for preparing the high-nickel ternary modified layered oxide cathode material according to claim 1, characterized in that, Includes the following steps: (1) Preparation of precursor Preparation of reaction solution: Dissolve the soluble salts of nickel, iron and manganese sources in deionized water according to the preset stoichiometric ratio to form a metal salt solution; Sodium hydroxide solution and ammonia water are mixed in a certain proportion to form a complexing agent solution; Coprecipitation reaction: The metal salt solution and the complexing agent solution are simultaneously pumped into the reactor at a set flow rate to carry out the coprecipitation reaction. After the reaction is completed, the mixture is aged, and then subjected to solid-liquid separation, washing and drying to obtain high-nickel layered oxide precursor particles. (2) Ion doping modification The precursor particles obtained in step (1) are immersed in a modified ionic solution for ion doping modification. After solid-liquid separation, washing, and drying, a doped intermediate is obtained. (3) Gradient calcination The doped intermediate obtained in step (2) is mixed with a sodium source in a certain proportion and then placed in a tube furnace for gradient calcination under an oxygen atmosphere to obtain a high-nickel ternary modified layered oxide cathode material.

3. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 2, characterized in that, In step (1): the soluble salts of the nickel source, iron source and manganese source are selected from at least one of sulfate, nitrate or chloride, and the nickel source, iron source and manganese source are dissolved in deionized water in the molar ratio Ni:Fe:Mn=x:y:1-xy, where: 0.6≤x≤0.9, 0<y<0.

4.

4. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 2, characterized in that, In step (1): the concentration of sodium hydroxide in the complexing agent solution is 2-6 mol / L, and the concentration of ammonia is 0.1-2 mol / L.

5. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 2, characterized in that, In step (1): the coprecipitation reaction is carried out at 50-65℃ for 5-10 hours. After the coprecipitation reaction is terminated, it is kept at 50-80℃ for 6-12 hours.

6. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 2, characterized in that, In step (2): the modified ionic solution is prepared by dissolving one or more soluble salts, including but not limited to Al, Zn, Mg, Zr, and B, in deionized water to form a solution of 0.1-0.5 mol / L.

7. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 2, characterized in that, In step (2), the ion doping modification involves mixing the precursor particles with the modified ion solution at a solid-liquid ratio of 1:5-10 g / mL and stirring at a constant temperature of 30-60℃ for 4-12 hours.

8. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 2, characterized in that, In step (3), the doped intermediate is mixed with the sodium source at a molar ratio of Na:doped ion = 1 to 1.1:

1.

9. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 2, characterized in that, In step (3), the gradient calcination treatment includes a pre-calcination stage and a high-temperature sintering stage, wherein: Pre-calcination stage: The doped intermediate after mixing sodium source is placed in a tube atmosphere furnace and heated to 300-550℃ at a heating rate of 2-5℃ / min, and held at the temperature for 1-8 hours under the condition of oxygen flow rate of 50-200mL / min. High-temperature sintering stage: After pre-firing, continue to raise the temperature to 700-880℃ at a rate of 3-8℃ / min. Use a two-stage temperature control process, that is, first treat at 750℃ for 4-6 hours, and then raise to 850℃ for 8-12 hours. The total sintering time is controlled at 12-18 hours.

10. The application of the high-nickel ternary modified layered oxide cathode material of claim 1 in the preparation of sodium-ion batteries.

Images