A high-nickel ternary modified layered oxide positive electrode material and a preparation method and application thereof

Abstract

The application discloses a high-nickel ternary modified layered oxide positive electrode material and a preparation method and application thereof, relates to the technical field of sodium ion battery positive electrode materials, and has a structural formula: NaNi x Fe y Mn z O2(A), wherein 0.6<=x<=0.9, 0 The application discloses a high-nickel ternary modified layered oxide positive electrode material and a preparation method and application thereof, relates to the technical field of sodium ion battery positive electrode materials, and has a structural formula: NaNi x Fe y Mn z O2(A), wherein 0.6<=x<=0.9, 0 The application discloses a high-nickel ternary modified layered oxide positive electrode material and a preparation method and application thereof, relates to the technical field of sodium ion battery positive electrode materials, and has a structural formula: NaNi x Fe y Mn z O2(A), wherein 0.6<=x<=0.9, 0

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 bottleneck 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:

[0006] A high-nickel ternary modified layered oxide positive electrode material, which has the structural formula: NaNi x Fe y Mnz O2(A), wherein: 0.6≤x≤0.9, 0

[0007] 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:

[0008] (1) Preparation of precursor

[0009] Preparation of reaction solution: Dissolve soluble salts of nickel source, iron source and manganese source in deionized water according to the preset stoichiometric ratio to form a metal salt solution; mix sodium hydroxide solution and ammonia water in proportion to form a complexing agent solution;

[0010] Coprecipitation reaction: Pump the metal salt solution and the complexing agent solution into the reaction kettle at a set flow rate for coprecipitation reaction. After the reaction is completed, perform aging treatment, and then perform solid-liquid separation, washing and drying to obtain high-nickel layered oxide precursor particles;

[0011] (2) Ion doping modification

[0012] After the precursor particles obtained in step (1) are immersed in a modified ion solution and ion doping modification is performed, solid-liquid separation, washing and drying are performed to obtain a doped intermediate;

[0013] (3) Gradient calcination

[0014] Mix the doped intermediate obtained in step (2) with a sodium source in a certain proportion, and then place it in a tube furnace for gradient calcination treatment in an oxygen atmosphere to finally obtain a high-nickel ternary modified layered oxide cathode material.

[0015] Further provided is:

[0016] 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

[0017] 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.

[0018] In step (1), the coprecipitation reaction is performed at 50-65℃ for 5-10 hours. After the coprecipitation reaction is terminated, aging is performed at 50-80℃ for 6-12 hours.

[0019] Preferably, in the co-precipitation reaction, the metal salt solution is continuously injected into the reactor by a precision metering pump at a flow rate of 3-15 mL / min, while the complexing agent solution is added synchronously; nitrogen gas is passed through the whole process to maintain an inert atmosphere, and the pH value of the reaction system is maintained between 10.5-12.0;

[0020] In step (2), the modified ion solution: select one or more soluble salts containing but not limited to Al, Zn, Mg, Zr, B, dissolve in deionized water to prepare a doping ion solution of 0.1-0.5 mol / L.

[0021] 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 30-60°C for 4-12 hours to make the doping ions fully penetrate into the crystal lattice gap of the precursor.

[0022] In step (3), the doping intermediate prepared in step (2) is mixed with sodium source at a molar ratio of Na:doping ion=1-1.1:1 after ball milling.

[0023] In step (3), the gradient calcination process includes a precalcination stage and a high-temperature sintering stage, wherein:

[0024] Pre-calcination stage: place the mixed sodium source after doping intermediate in a tube furnace, and heat to 300-550°C at a heating rate of 2-5°C / min, and heat for 1-8 hours under the condition of oxygen flow rate of 50-200 mL / min;

[0025] High-temperature sintering: after pre-calcination, continue to heat at a rate of 3-8°C / min to 700-880°C, and use two-stage temperature control, i.e., first at 750°C for 4-6 hours, then at 850°C for 8-12 hours, and the total sintering time is controlled at 12-18 hours.

[0026] In step (3), after high-temperature sintering, slowly cool to 200°C 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.

[0027] The third aspect of the present application is to provide an application 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: the prepared high-nickel ternary modified layered oxide positive electrode material is ground and sieved, then is mixed with SP (conductive carbon black) and PVDF (polyvinylidene fluoride) at a mass ratio of 8:1:1, NMP (N-methyl pyrrolidone) is added and stirred to form a slurry, which is coated on an aluminum foil, dried, punched and pressed to form a sodium ion battery positive electrode material sheet, with metallic sodium as the negative electrode, glass fiber as the separator, NaPF6 (sodium hexafluorophosphate), PC (propylene carbonate) and EMC (ethyl methyl carbonate) solution as the electrolyte, and a CR2025 button cell is assembled in an argon-filled glove box.

[0028] The present application has the following beneficial effects:

[0029] (1) The present application provides a preparation method of a high-nickel ternary modified layered oxide positive electrode material, which prepares a high-nickel ternary modified layered oxide positive electrode material with stable layered structure and high ion migration rate through a synergistic process of co-precipitation reaction-ion doping modification-gradient calcination.

[0030] (2) The present application realizes atomic-level uniform mixing of metal ions through pH regulation and ammonia complexation during the co-precipitation process.

[0031] (3) The present application uses a solution impregnation method for ion doping, effectively avoiding the problem of uneven doping in traditional solid-phase methods.

[0032] (4) The present application innovatively designs a gradient calcination process, in which the precursor completes structure relaxation and oxygen vacancy regulation at a low temperature stage, and is treated by two-stage temperature control at a high temperature stage to realize densification and crystallization, so that the prepared positive electrode material has better capacity and cycle performance.

[0033] The present application will be further described below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 SEM image of the product prepared in Example 1.

[0035] Figure 2 SEM image of the product prepared in Example 2.

[0036] Figure 3 SEM image of the product prepared in Comparative Example 1.

[0037] Figure 4 SEM image of the product prepared in Comparative Example 2.

[0038] Figure 5 XRD pattern of Examples 1 and 2 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0039] In order to better understand the technical solutions of the present application by those skilled in the art, the preferred embodiments of the present application are described below in conjunction with specific examples, but it should not be understood as a limitation to the present patent. The test methods or test methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0040] 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 moles of Ni, Fe, and Mn.

[0041] Example 1

[0042] A preparation method of a high-nickel ternary modified layered oxide positive electrode material, comprising the following steps:

[0043] Step 1: Preparation of precursor

[0044] 1.1 Preparation of metal salt solution:

[0045] 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 total metal ion concentration, 1L.

[0046] 1.2 Preparation of complexing agent solution:

[0047] 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.

[0048] 1.3 Coprecipitation reaction:

[0049] The metal salt solution and the complexing agent solution are added to the reaction kettle 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 rate of 800 rpm, and reaction time of 6 hours.

[0050] 1.4 Aging treatment:

[0051] After the co-precipitation reaction is terminated, the slurry is transferred into 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 realize efficient solid-liquid separation, and deionized water is used for washing 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)2precursor particles.

[0052] Step 2: Ion doping modification

[0053] 2.1 Preparation of the modification solution:

[0054] Al(NO3)3is dissolved in deionized water to prepare the modification solution, and the Al 3+ concentration is 0.1 mol / L.

[0055] 2.2 Solid-liquid doping treatment:

[0056] The precursor prepared in the foregoing is added to the modification solution at a solid-liquid ratio of 1:10 (g / mL), and stirred at 60°C for 4 hours.

[0057] 2.3 Post-treatment:

[0058] Vacuum filtration equipment (vacuum degree -0.08 MPa) is used to realize efficient solid-liquid separation, and anhydrous ethanol is used for washing 3 times (each time the amount of solvent is 3 times the mass of the solid phase) to remove residual nitrate. Then, vacuum drying is performed at 80°C for 12 hours to obtain Al 3+ uniformly doped intermediate material.

[0059] Step 3: Gradient calcination

[0060] 3.1 Mixing of sodium source:

[0061] The doped intermediate prepared in the foregoing is mixed with NaOH particles at a molar ratio of Na: transition metal = 1.05:1.

[0062] 3.2 Pre-burning stage:

[0063] The above mixture is spread on an alumina crucible and placed in a programmed tube 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 maintained for 4 hours to remove the hydroxyl groups on the surface of the precursor and construct the initial lattice oxygen structure.

[0064] 3.3 High-temperature sintering:

[0065] Primary crystallization was carried out by increasing the temperature to 750℃ at a rate of 5℃ / min (holding for 4 hours), followed by secondary lattice restructuring by increasing the temperature to 850℃ at a rate of 2℃ / min (holding for 10 hours). The total sintering time was 14 hours, with an oxygen flow rate of 200 mL / min maintained throughout to promote the orderly arrangement of cations.

[0066] 3.4 Cooling treatment:

[0067] After sintering, the product 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 ≤1Pa) to cool to room temperature. The sintered product was then ground and sieved (400 mesh) to obtain the final product NaNi. 0.8 Fe 0.1 Mn 0.1 O2(Al) cathode material.

[0068] Product Confirmation:

[0069] like Figure 1 As shown, this is the NaNi prepared in Example 1. 0.8 Fe 0.1 Mn 0.1 SEM images of the O2(Al) cathode material. The material in Example 1 exhibits significantly optimized microstructure characteristics, specifically as follows:

[0070] (1) Particle morphology and composition: The material is mainly composed of uniform, spherical secondary particles, while the primary particles are rice-grain shaped. This morphological feature is beneficial for uniform coating and dense packing during the electrode preparation process.

[0071] (2) Particle size distribution: The material particles have a narrow particle size distribution. The typical size range of its primary particles is about 1 micrometer; these primary particles further assemble to form secondary particles, the typical size range of which is between about 6 micrometers and 12 micrometers.

[0072] (3) Surface and structural characteristics of secondary particles: such as Figure 1 As clearly shown, the surface of the secondary particles exhibits a highly dense state. Simultaneously, the grain boundaries between and within the particles are clearly visible, with very small gaps.

[0073] Example 2

[0074] Step 1: Precursor Preparation

[0075] 1.1 Preparation of metal salt solutions:

[0076] 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 1 L of metal salt solution with a total metal ion concentration of 1.0 mol / L.

[0077] 1.2 Preparation of the precipitant solution:

[0078] 95.98 g of NaOH particles were weighed and dissolved in 1140 mL of deionized water to form a NaOH aqueous solution. Then, 47.5 mL of 20% ammonia water (NH3·H2O) was added to the solution and mixed well to obtain a basic complexing agent solution.

[0079] 1.3 Co-precipitation reaction:

[0080] The salt solution and the precipitant solution were added into the reactor by a precision metering pump at a flow rate of 5.6 mL / min. The reaction temperature was controlled at 50°C, the pH was controlled at 11.5±0.2, the stirring speed was 800 rpm, and the reaction time was 6 hours.

[0081] 1.4 Aging treatment:

[0082] After the reaction was completed, the slurry was transferred to an aging tank and aged at 50°C for 12 hours. Vacuum filtration device (vacuum degree -0.08 MPa) was used to realize efficient solid-liquid separation, and deionized water was used for washing 3 times. Then, the sample was 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.

[0083] Step 2: Ion doping modification

[0084] 2.1 Preparation of the modification solution:

[0085] ZnSO4·7 H2O was dissolved in deionized water to prepare a modification solution, and the concentration of Zn 2+ was 0.1 mol / L.

[0086] 2.2 Solid-liquid doping treatment:

[0087] The precursor prepared in the foregoing was added into the modification solution at a solid-liquid ratio of 1:10 (g / mL), and stirred at 60°C for 4 hours.

[0088] 2.3 Post-treatment:

[0089] Vacuum filtration device (vacuum degree -0.08 MPa) was used to realize efficient solid-liquid separation, and anhydrous ethanol was used for washing 3 times (the amount of solvent was 3 times the mass of the solid phase each time) to remove residual nitrate. Vacuum drying at 80°C for 12 hours obtained Zn 2+ uniformly doped intermediate material.

[0090] Step 3: Gradient calcination

[0091] 3.1 Mixed sodium sources:

[0092] The Zn-doped intermediate and NaOH particles were ground and mixed evenly at a molar ratio of Na:transition metal = 1.05:1.

[0093] 3.2 Pre-firing stage:

[0094] The mixture was spread evenly in an alumina crucible and placed in a programmable tube furnace. The temperature was programmed to rise to 450°C at a rate of 3°C / min, and high-purity oxygen (99.99% purity) was introduced at a rate of 200 mL / min and held at that temperature for 4 hours to complete the removal of hydroxyl groups from the precursor surface and the construction of the initial lattice oxygen structure.

[0095] 3.3 High-temperature sintering:

[0096] Primary crystallization was carried out by increasing the temperature to 750℃ at a rate of 5℃ / min (holding for 4 hours), followed by secondary lattice restructuring by increasing the temperature to 850℃ at a rate of 2℃ / min (holding for 10 hours). The total sintering time was 14 hours, with an oxygen flow rate of 200 mL / min maintained throughout to promote the orderly arrangement of cations.

[0097] 3.4 Cooling treatment:

[0098] After sintering, the product 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 ≤1Pa) to cool to room temperature. The sintered product was then ground and sieved (400 mesh) to obtain the final product NaNi. 0.8 Fe 0.1 Mn 0.1 O2(Zn) cathode material.

[0099] Product Confirmation:

[0100] like Figure 2 As shown, this is the NaNi prepared in Example 2. 0.8 Fe 0.1 Mn 0.1 SEM images of the O2(Zn) cathode material. The material in Example 1 exhibits significantly optimized microstructure characteristics, specifically as follows:

[0101] Particle morphology and composition: The material is mainly composed of uniform, near-spherical secondary particles, while the primary particles are rice-grain shaped. This morphological characteristic is beneficial for uniform coating and dense packing during the electrode fabrication process.

[0102] Particle size distribution: The material particles have a narrow particle size distribution. The typical size range of its primary particles is between about 1 micrometer and 2 micrometers; these primary particles further assemble to form secondary particles, whose typical size range is between about 5 micrometers and 10 micrometers.

[0103] Surface and structural features of the secondary particles: As shown clearly, the surface of the secondary particles presents a highly dense state. Meanwhile, the grain boundaries between and inside the particles are clearly visible, and the gaps are relatively small. Figure 2 Surface and structural features of the secondary particles: As shown clearly, the surface of the secondary particles presents a highly dense state. Meanwhile, the grain boundaries between and inside the particles are clearly visible, and the gaps are relatively small.

[0104] Comparative Example 1

[0105] This example mainly investigates the performance of the positive electrode material without ion doping modification.

[0106] Step 1: Preparation of precursor

[0107] 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 deionized water at a molar ratio of 8:1:1 to prepare a metal salt solution of 1.0 mol / L in a total metal ion concentration.

[0108] 1.2 Preparation of precipitant solution:

[0109] 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.

[0110] 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 the reaction temperature controlled at 50°C, the pH at 11.5±0.2, the stirring speed at 800 rpm, and the reaction time at 6 hours.

[0111] 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. A vacuum filtration device (vacuum degree -0.08 MPa) is used for efficient solid-liquid separation, and the obtained Ni 0.8 Fe 0.1 Mn 0.1 (OH)2precursor is 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.

[0112] Step 2: Gradient calcination

[0113] 2.1 Mixing of sodium source: The precursor prepared in the foregoing step is mixed with NaOH particles at a molar ratio of Na: transition metal = 1.05:1.

[0114] 2.2 Pre-calcination stage: The mixture was spread evenly in an alumina crucible and placed in a programmable tube furnace. The temperature was programmed to rise to 450°C at a rate of 3°C / min, and high-purity oxygen (99.99% purity) was introduced at a rate of 200 mL / min and held at this temperature for 4 hours to complete the removal of hydroxyl groups from the precursor surface and the construction of the initial lattice oxygen structure.

[0115] 2.3 High-temperature sintering: Continue heating at 5℃ / min to 750℃ for primary crystallization (hold for 4 hours), then control the temperature increase at 2℃ / min to 850℃ for secondary lattice restructuring (hold for 10 hours). The total sintering time is 14 hours, with an oxygen flow rate of 200mL / min maintained throughout to promote the orderly arrangement of cations.

[0116] 2.4 Cooling Treatment: After sintering, the product was slowly cooled to 200℃ at a natural cooling rate of ≤5℃ / min, and then transferred to a vacuum rapid cooling chamber (vacuum degree ≤1Pa) 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.

[0117] Product Confirmation:

[0118] like Figure 3 As shown, this is the NaNi product prepared in Comparative Example 1. 0.8 Fe 0.1 Mn 0.1 SEM images of the O2 cathode material, combined with Figure 3 As shown:

[0119] Particle morphology and composition: The material is mainly composed of uniform, lamellar particles that are tightly packed together, and no spherical secondary particles are formed.

[0120] Particle size distribution: The typical particle size ranges from about 1 micrometer to 4 micrometers.

[0121] Secondary particle surface and structural characteristics: as shown in the attached figure. Figure 3 As clearly shown, the surface of the particles exhibits a densely packed state. Simultaneously, the grain boundaries between and within the particles are clearly visible, with relatively large gaps.

[0122] Comparative Example 2

[0123] This embodiment mainly examines the performance of cathode materials that have not undergone gradient calcination.

[0124] Step 1: Precursor Preparation

[0125] 1.1 Preparation of metal salt solutions:

[0126] 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.

[0127] 1.2 Preparation of complexing agent solution:

[0128] 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 20% ammonia water (NH3·H2O) was added to the solution and mixed thoroughly to obtain an alkaline complexing agent solution.

[0129] 1.3 Coprecipitation reaction:

[0130] 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.

[0131] 1.4 Aging treatment:

[0132] After the coprecipitation reaction was completed, the slurry was transferred to an aging tank and placed in a constant temperature environment at 50°C for 12 hours. Vacuum filtration equipment (vacuum degree -0.08 MPa) was used to achieve efficient solid-liquid separation, and the product was washed with deionized water three times. Then, the product was 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)2 precursor particles.

[0133] Step 2: Ion doping modification

[0134] 2.1 Preparation of modification solution:

[0135] Al(NO3)3 was dissolved in deionized water to prepare a modification solution with an Al 3+ concentration of 0.1 mol / L.

[0136] 2.2 Solid-liquid doping treatment:

[0137] 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.

[0138] 2.3 Post-treatment:

[0139] Vacuum filtration device (vacuum degree-0.08 MPa) was used to realize high-efficiency solid-liquid separation, and anhydrous ethanol was used to wash 3 times (the solvent dosage was 3 times the mass of the solid phase each time) to remove residual nitrate. Then vacuum drying at 80°C for 12 hours to obtain Al 3+ Homogeneously doped intermediate material.

[0140] Step 3: Calcination and crystallization

[0141] 3.1 Mixing sodium source:

[0142] The Al-doped intermediate prepared above was mixed with NaOH particles at a molar ratio of Na: transition metal = 1.05:1.

[0143] 3.2 Pre-burning stage:

[0144] The above mixture was spread on an alumina crucible and placed in a programmed 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 kept for 4 hours to complete the removal of the surface hydroxyl group and the construction of the initial lattice oxygen structure.

[0145] 3.3 High-temperature sintering:

[0146] The temperature was continued to rise to 850°C at a rate of 5°C / min for 14 hours, and the oxygen flow was kept at 200 mL / min throughout the process to promote the ordered arrangement of cations.

[0147] 3.4 Cooling treatment:

[0148] 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.

[0149] Product confirmation:

[0150] As shown in FIG. 1, 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: Figure 4 (1) Particle morphology and composition: The material was mainly composed of uniform spherical secondary particles, while the primary particles were in the form of particle blocks.

[0151]

[0152] ​(2) Particle size distribution: The material particles have a narrow particle size distribution. The typical size range of the primary particles is about 1-2 microns directly; these primary particles are further assembled to form secondary particles, which have a typical size range of about 4-10 microns.

[0153] (3) Surface and structural features of the secondary particles: As shown in Figure 4 clearly shown, the surface of the secondary particles presents a highly dense state. At the same time, the grain boundaries between and inside the particles are clearly visible, and the gap is large.

[0154] Product control:

[0155] In combination with the SEM images of Examples 1-2 and Comparative Examples 1-2 shown in Figures 1-4 , and in combination with the XRD patterns of Examples 1, 2 and Comparative Examples 1, 2 shown in Figure 5 , it can be seen that:

[0156] Basic structural features: The materials of Examples 1, 2 and Comparative Examples 1, 2 all show typical O3-type layered oxide crystal structure features, and the diffraction patterns contain characteristic peak positions, such as (003), (006), (101), (012), (104), etc.

[0157] 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:

[0158] Peak sharpness and intensity: The diffraction peaks of Examples 1 and 2 are significantly higher in sharpness, and the peak intensity is stronger. In addition, the diffraction peak intensity of Comparative Example 2 is the weakest. This directly reflects that the material prepared by the method of the embodiments of the present application has higher crystallinity and more perfect long-range order of the crystal.

[0159] (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 the intensity ratio of the (006) diffraction peak to the (101) diffraction peak > 1. This clearly indicates that the material of the embodiments of the present application has a highly ordered layered crystal structure.

[0160] (003) / (104) peak intensity ratio: Further observation found that the intensity ratio of the (003) diffraction peak to the (104) diffraction peak of the materials of Examples 1 and 2 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 material successfully prepared by the method of the embodiments of the present application has a lower degree of cation mixing between the Na layer and the transition metal layer (TM layer).

[0161] Performance test:

[0162] The positive electrode materials prepared in the above examples 1-2 and comparative examples 1-2 were applied to sodium ion batteries, respectively, and their performances were tested.

[0163] The test method was as follows: the positive electrode material powder was ground through a 200 mesh sieve, then was formulated with SP (conductive carbon black), PVDF (polyvinylidene fluoride) at a mass ratio of 8:1:1, NMP (N-methyl pyrrolidone) was added and stirred into a slurry, which was 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, CR2025 button cells were assembled in an argon-filled glove box, and charge-discharge tests were carried out. Under the conditions of current density 100 mAh / g and voltage range 2.0-4.2 V, the capacity and cycle performance were tested at 0.2 C for 2 cycles and then at 1 C, and the test results are shown in Table 1:

[0164] Table 1

[0165]

[0166] 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 precise pH control 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 stage, and densification crystallization is realized by two-stage temperature control in the high temperature stage. The high-nickel ternary modified layered oxide positive electrode material prepared by the application has stable layered structure and high ion migration rate, and has better capacity and cycle performance compared with the existing undoped modified or non-gradient calcination process.

[0167] The above is only a preferred embodiment of the application, and it should be noted 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 method for preparing a high-nickel ternary modified layered oxide cathode material, 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. In step (2): the modified ionic solution is prepared by dissolving one or more soluble salts of Al, Zn, Mg, Zr and B in deionized water to form a solution of 0.1-0.5 mol / L. (3) Gradient calcination The doped intermediate obtained in step (2) is mixed with sodium source in a certain proportion, and then placed in a tube furnace for gradient calcination under oxygen atmosphere to obtain high nickel ternary modified layered oxide cathode material. 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.

2. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 1, 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.

3. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 1, 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.

4. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 1, 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.

5. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 1, 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.

6. The method for preparing a high-nickel ternary modified layered oxide cathode material according to claim 1, 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.

7. The application of a high-nickel ternary modified layered oxide cathode material prepared by the method of claim 1 in the preparation of sodium-ion batteries.

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