A p2-type layered oxide positive electrode material with element non-uniform distribution, a sodium ion battery, and a preparation method and application thereof

Abstract

The application belongs to the technical field of sodium ion battery cathode materials, and relates to an element non-uniform distribution P2 type layered oxide cathode material, a sodium ion battery, and a preparation method and application. Metal salt solution and doped element salt solution are simultaneously introduced into a reaction kettle in a series connection mode, and react with a mixed alkali solution to obtain an element non-uniform distribution precursor. Then, the element non-uniform distribution precursor is mixed with a sodium source and sintered to obtain the P2 type layered oxide cathode material. The metal salt includes at least one of MnSO4, NiSO4, CuSO4, CoSO4 and FeSO4. The doped element salt solution includes at least one of MgSO4 solution, ZnSO4 solution and Al2(SO4)3 solution. The application realizes the non-uniform distribution of high surface concentration and low body concentration of the doped element through series connection feeding, significantly improves the cycle stability under the premise of reducing the initial capacity loss. The method is simple in process, strong in controllability, and easy to mass produce.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery cathode material technology, and relates to a P2-type layered oxide cathode material with non-uniform element distribution, a sodium-ion battery, its preparation method and application. Background Technology

[0002] Renewable energy sources such as wind and solar power are intermittent and fluctuating, requiring supporting energy storage facilities for peak shaving, valley filling, frequency regulation, and phase adjustment. Compared to pumped hydro storage, electrochemical energy storage offers advantages such as faster response times, shorter construction cycles, and higher energy density. In recent years, electrochemical energy storage capacity has gradually occupied half of the energy storage market. Among them, lithium-ion batteries account for as much as 96% of the electrochemical energy storage market. However, with the annual increase in installed capacity, resources related to lithium-ion batteries, such as lithium, cobalt, and nickel, are facing problems such as rising raw material prices and resource dependence on imports. Therefore, seeking a new energy storage battery system based on abundant elements and with independent control is imperative. Currently, large-scale energy storage batteries mainly include lithium-ion batteries, sodium-ion batteries, and flow batteries. Among them, sodium-ion batteries have advantages in cycle life, low-temperature performance, and safety, and their production lines are compatible with lithium-ion batteries, making them promising for large-scale energy storage.

[0003] Cathode materials are key components of sodium-ion batteries, determining their performance and cost. Currently, there are three main types of cathode materials: polyanionic compounds, Prussian blue analogs, and layered oxides. Among them, layered oxides have the advantages of high specific capacity and ease of preparation. Based on different lattice stacking methods, layered oxides are divided into P2-type and O3-type. Compared with the O3 phase, the P2 phase has a wider ion diffusion channel, which is conducive to sodium ion diffusion; the phase transition path is relatively simple, and the air stability is also better. Therefore, P2-type layered oxides are considered one of the most commercially promising cathode materials. However, these materials are prone to irreversible phase transitions and interfacial side reactions under deep desodiumization conditions, causing crack growth and loss of active elements, ultimately leading to capacity decay of layered oxide cathode materials, becoming a bottleneck restricting the cycle life of sodium-ion batteries.

[0004] Inactive element doping, such as Zn, Mg, Al, and Ti, is used to limit the number of sodium ions extracted from the sodium layer during charging. However, uniform doping simultaneously limits the extraction of sodium ions from both the bulk and surface phases of the cathode material, inevitably leading to a loss in specific capacity. Considering the interface and irreversible phase transition issues coupled to the cathode material surface, the degradation of surface morphology and structure is even more severe. Therefore, preparing cathode materials with the inactive element content gradually decreasing from the surface to the bulk phase can solve the capacity decay caused by phase transitions and interfacial side reactions in P2-type cathode materials while minimizing specific capacity loss.

[0005] However, existing gradient doping techniques (such as Chinese patent CN117878324A) are mostly based on O3-type layered structures, whose narrow ion diffusion channels limit the rapid migration of sodium ions. Furthermore, these methods often require complex multi-feed systems to achieve a gradient distribution of dopant elements, making process control difficult. More importantly, existing technologies primarily focus on constructing a single gradient of dopant elements, offering limited improvement to the overall structural stability of the material. Summary of the Invention

[0006] To address the aforementioned needs, this invention provides a P2-type layered oxide cathode material with non-uniform element distribution, a sodium-ion battery, and a preparation method and application. The method is simple and efficient, with controllable element distribution and morphology, and is easy to mass-produce. The prepared cathode material is applied in the field of sodium-ion batteries.

[0007] The objective of this invention is achieved through the following technical solution: The first aspect of this invention provides a method for preparing a P2-type layered oxide cathode material with non-uniform elemental distribution, comprising the following steps: (1) At the start of the reaction, deionized water is added to the reactor as the base liquid. The metal salt solution is introduced into the reactor through pump A, and the mixed alkaline solution is introduced into the reactor through pump C. The dopant element salt solution is pumped into the metal salt solution through pump B at a certain flow rate, so that the concentration of the dopant element in the metal salt solution gradually increases, and the concentration gradient distribution of the dopant element in the precursor is realized from the surface to the inside. That is, the metal salt solution and the dopant element salt solution are introduced into the reactor simultaneously in series. The reactor maintains the pH value required for the reaction by adjusting the flow rate of pump C in real time, and the mixture is stirred and mixed evenly to form a cathode material precursor with non-uniform element distribution. The metal salt includes at least one of MnSO4, NiSO4, CuSO4, CoSO4, and FeSO4, and the dopant element salt solution includes at least one of MgSO4 solution, ZnSO4 solution, and Al2(SO4)3 solution. (2) The elementally non-uniformly distributed cathode material precursor obtained in step (1) is mixed with sodium source, ground, sintered, and cooled to room temperature to obtain an elementally non-uniformly distributed P2 type layered oxide cathode material.

[0008] Preferably, the concentration of metal ions in the metal salt solution in step (1) is 1 M-3.5 M.

[0009] Preferably, the mixed alkaline solution is prepared by: preparing a Na2CO3 or NaOH solution of a certain concentration as a precipitant; preparing an ammonia solution of a certain concentration as a complexing agent; and mixing the precipitant and the complexing agent to obtain the mixed alkaline solution.

[0010] Preferably, the concentration of Na2CO3 in the mixed alkaline solution in step (1) is 1 M-3.5 M.

[0011] Preferably, the concentration of the doped element salt solution in step (1) is 0.2 M-4 M.

[0012] Preferably, the flow rate of pump A is 0.2-2 mL / min, the flow rate of pump B is set to 0.2-1 mL / min, the pH value is set to 7-9, and the stirring speed is 600-800 rpm.

[0013] Preferably, the sodium source and the cathode material precursor are mixed according to the molar ratio of Na to metal ions of 0.6-0.82:1, ground for 20-40 min, sintered at a temperature of 800-1000 ℃ for 15-20 h, all in an air atmosphere, with a heating rate of 5-15 ℃ / min.

[0014] Preferably, the sodium source is at least one of Na2CO3 and CH3COONa.

[0015] A second aspect of the present invention provides a P2-type layered oxide cathode material with non-uniform elemental distribution prepared by the above method.

[0016] A third aspect of the present invention provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is a P2-type layered oxide positive electrode material, and the negative electrode is a carbon material or a sodium sheet.

[0017] Preferably, the sodium salt in the electrolyte is sodium hexafluorophosphate or sodium perchlorate, and the solvent is at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

[0018] The fourth aspect of this invention provides the application of the above-mentioned non-uniformly distributed P2-type layered oxide cathode material in the preparation of sodium-ion batteries.

[0019] The advantages and beneficial effects of this invention are: (1) This invention prepares a layered oxide cathode material for P2 type sodium-ion batteries with non-uniform element distribution through a series feeding method combined with solid-state sintering. The series feeding method results in a non-uniform distribution of inactive dopant elements in the cathode material, with high concentrations on the surface and low concentrations in the bulk. This structure can solve the problem of specific capacity decay of the cathode material while minimizing capacity loss during electrochemical cycling. Non-uniform doping of Mg with Na 0.67 Mn 0.67 Ni 0.23 Mg 0.08 The O2 cathode material exhibits a first-cycle discharge specific capacity of 88 mAh·g at a 0.2 C rate. -1 After 300 weeks, the capacity retention rate was 83%.

[0020] (2) The process of the present invention is simple and controllable. It only requires pumping the dopant element solution into the main salt solution to achieve the concentration gradient. The equipment requirements are low and the operation is simple, which can realize large-scale preparation.

[0021] (3) The preparation method of the present invention controls the composition of the cathode material by controlling the concentration of various salts in the solution; and controls the phase structure of the material by controlling the ratio of sodium source to precursor during sintering, which has strong controllability. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope image of the carbonate precursor of the spherical cathode material with non-uniform elemental distribution obtained in Example 1.

[0023] Figure 2 This is a scanning electron microscope image of the P2-type layered oxide cathode material with non-uniform elemental distribution obtained in Example 1.

[0024] Figure 3 This is an elemental distribution diagram of the P2-type layered oxide cathode material with non-uniform elemental distribution obtained in Example 1.

[0025] Figure 4 The X-ray diffraction pattern of the P2-type layered oxide cathode material with non-uniform elemental distribution obtained in Example 1 is a refined pattern.

[0026] Figure 5 The X-ray diffraction pattern of the O3-type layered oxide cathode material with non-uniform elemental distribution obtained in Comparative Example 1 is a refined X-ray diffraction pattern.

[0027] Figure 6 This is a comparison of the cycle performance of the P2-type layered oxide cathode material with non-uniform element distribution obtained in Example 1, the undoped nickel-manganese-based cathode material with P2 phase obtained in Comparative Example 3, the O3-type layered oxide cathode material with non-uniform element distribution in Comparative Example 1, and the P2-type layered oxide cathode material with uniform element distribution prepared in Comparative Example 2. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. The following description is for illustrative purposes only and does not limit the scope of the invention.

[0029] Comparative Example 1 A method for preparing a layered oxide cathode material for sodium-ion batteries includes: (1) Prepare 1 L of a 2 M metal salt solution according to the ratio of MnSO4:NiSO4=67:33, and denote it as solution I; (2) Prepare 1 L of a mixed solution of 2 M Na2CO3 and 0.3 M NH4OH, and denote it as solution II; (3) Prepare 500 mL of MgSO4 solution with a concentration of 4 M as a source of non-uniform doping elements, and denote it as solution III; (4) At the start of the reaction, 500 mL of deionized water is added as the base liquid. Solution I in step (1) is connected to the reactor through pump A, solution II in step (2) is connected to the reactor through pump C, and solution III in step (3) is pumped into solution I through pump B at a flow rate of 0.4 mL / min, so that the concentration of doped elements in solution I gradually increases. Solution I and solution III are connected in series and introduced into the reactor together. The pH value of the reactor is set to 8.0, and the flow rates of pumps A and B are 0.8 mL / min. The automatic adjustment function of the reactor will maintain the pH value required for the reaction by adjusting the flow rate of pump C in real time. At the same time, the stirring paddle in the reactor is stirred at a speed of 700 rpm to ensure that the reaction solution is mixed evenly. After 24 hours of reaction, the precipitate is taken out and repeatedly filtered, washed and dried to obtain a spherical positive electrode material carbonate precursor with non-uniform element distribution. (5) The spherical positive electrode material carbonate precursor with non-uniform element distribution obtained in step (4) is mixed with CH3COONa at a molar ratio of Na:(Mn+Ni+Mg)=1.1:1 and ground for 30 minutes. The mixture is then transferred to a tube furnace and sintered at 900℃ for 15 hours in an oxygen atmosphere at a heating rate of 10℃ / min. After cooling to room temperature, the composition O3-Na is obtained. 0.67 Mn 0.67 Ni 0.23 Mg 0.08 The O3-type layered oxide cathode material, composed of O2, exhibits a gradual decrease in Mg content from the surface towards the center, while the contents of Mn and Ni gradually increase from the surface to a depth of 1 μm, before stabilizing. The refined X-ray diffraction pattern of the O3-type layered oxide cathode material is shown below. Figure 5 As shown, the diffraction peaks of the prepared material belong to the O3 phase, with no impurity peaks.

[0030] Comparative Example 2 A method for preparing a layered oxide cathode material for sodium-ion batteries includes: (1) Prepare 1 L of a mixed salt solution with a concentration of 2 M according to the ratio of MnSO4:NiSO4:MgSO4=67:23:10, and denote it as solution I; (2) Prepare 1 L of a mixed solution of 2 M Na2CO3 and 0.3 M NH4OH, and denote it as solution II; (3) At the start of the reaction, 500 mL of deionized water was added as the base liquid. Solution I in step (1) was connected to the reactor through pump A, and solution II in step (2) was connected to the reactor through pump C. The pH value of the reactor was set to 8.0, and the flow rates of pumps A and B were 0.8 mL / min. The automatic adjustment function of the reactor will maintain the pH value required for the reaction by adjusting the flow rate of pump C in real time. At the same time, the stirring paddle in the reactor was stirred at a speed of 700 rpm to ensure that the reaction solution was mixed evenly. After 24 hours of reaction, the precipitate was taken out and repeatedly filtered, washed and dried to obtain a spherical positive electrode material carbonate precursor with uniform element distribution. (4) The spherical positive electrode material carbonate precursor with uniform elemental distribution obtained in step (3) is mixed with CH3COONa at a molar ratio of Na:(Mn+Ni+Mg)=0.7:1 and ground for 30 minutes. The mixture is then transferred to a muffle furnace and sintered at 900℃ for 15 hours in air atmosphere at a heating rate of 10℃ / min. After cooling to room temperature, the P2-Na composition is obtained. 0.67 Mn 0.67 Ni 0.23 Mg 0.1 O2 is a layered oxide cathode material for sodium-ion batteries, in which the contents of Ni, Mn and Mg are uniformly distributed from the surface to the center.

[0031] Comparative Example 3 A method for preparing a layered oxide cathode material for sodium-ion batteries includes: (1) Prepare 1 L of a mixed salt solution with a concentration of 2 M according to the ratio of MnSO4:NiSO4=67:33, and denote it as solution I; (2) Prepare 1 L of a mixed solution of 2 M Na2CO3 and 0.3 M NH4OH, and denote it as solution II; (3) At the start of the reaction, 500 mL of deionized water was added as the base liquid. Solution I in step (1) was connected to the reactor through pump A, and solution II in step (2) was connected to the reactor through pump C. The pH value of the reactor was set to 8.0, and the flow rates of pumps A and B were 0.8 mL / min. The automatic adjustment function of the reactor will maintain the pH value required for the reaction by adjusting the flow rate of pump C in real time. At the same time, the stirring paddle in the reactor was stirred at a speed of 700 rpm to ensure that the reaction solution was mixed evenly. After 24 hours of reaction, the precipitate was taken out and repeatedly filtered, washed and dried to obtain a spherical positive electrode material carbonate precursor with uniform element distribution. (4) The spherical positive electrode material carbonate precursor with uniform elemental distribution obtained in step (3) is mixed with CH3COONa at a molar ratio of Na:(Mn+Ni)=0.7:1 and ground for 30 minutes. The mixture is then transferred to a muffle furnace and sintered at 900 °C for 15 hours in air atmosphere at a heating rate of 10 °C / min. After cooling to room temperature, the P2-Na composition is obtained. 0.67 Mn 0.67 Ni 0.33 O2 is a layered oxide cathode material for sodium-ion batteries, in which the contents of Ni and Mn are uniformly distributed from the surface to the center.

[0032] Example 1 A method for preparing a layered oxide cathode material for sodium-ion batteries includes: (1) Prepare 1 L of a 2 M metal salt solution according to the ratio of MnSO4:NiSO4=67:33, and denote it as solution I; (2) Prepare 1 L of a mixed alkaline solution of 2 M Na2CO3 and 0.3 M NH4OH as solution II; (3) Prepare 500 mL of MgSO4 solution with a concentration of 4 M as a salt solution for the doping element, providing the non-uniform doping element, denoted as solution III; (4) At the start of the reaction, 500 mL of deionized water was added as the base solution. Solution I from step (1) was connected to the reactor via pump A, and solution II from step (2) was connected to the reactor via pump C. Solution III from step (3) was pumped into solution I via pump B at a flow rate of 0.4 mL / min, so that the concentration of the doped elements in solution I gradually increased. That is, solution I and solution III were connected in series and introduced into the reactor together. The pH value of the reactor was set to 8.0, and the flow rates of pumps A and B were 0.8 mL / min. The automatic adjustment function of the reactor will maintain the pH value required for the reaction by adjusting the flow rate of pump C in real time. At the same time, the stirring paddle in the reactor will stir at a speed of 700 rpm to ensure that the reaction solution is mixed evenly. After 24 hours of reaction, the precipitate was taken out and repeatedly filtered, washed and dried to obtain a non-uniformly distributed positive electrode material carbonate precursor. Its scanning electron microscope image is as follows. Figure 1 As shown, the precursor particles are spherical particles with a diameter of about 10 μm.

[0033] (5) The spherical positive electrode material carbonate precursor with non-uniform element distribution obtained in step (4) is mixed with CH3COONa at a molar ratio of Na:(Mn+Ni+Mg)=0.7:1 and ground for 30 minutes. The mixture is then transferred to a muffle furnace and sintered at 900 °C for 15 hours in air atmosphere at a heating rate of 10 °C / min. After cooling to room temperature, the P2-Na composition is obtained. 0.67Mn 0.67 Ni 0.23 Mg 0.08 A P2-type layered oxide cathode material containing O2, in which the Mg content gradually decreases from the surface to the center, while the Mn and Ni content gradually increases from the surface to the center. Its scanning electron microscope image is shown below. Figure 2 As shown, the cathode material obtained by sintering is a spherical secondary particle with a diameter of about 10 μm. This secondary particle is formed by the accumulation of plate-shaped irregular primary particles.

[0034] The elemental distribution of the non-uniformly distributed P2-type layered oxide cathode material obtained in Example 1 is as follows: Figure 3 As shown, the refined X-ray diffraction pattern of the elementally non-uniformly distributed P2-type layered oxide cathode material obtained in Example 1 is as follows. Figure 4 As shown, the Mg content gradually decreases from the surface to the center of the sphere, while the Mn and Ni contents gradually increase from the surface to 1 μm from the surface, and then tend to stabilize.

[0035] Example 2 A method for preparing a layered oxide cathode material for sodium-ion batteries includes: (1) Prepare 1 L of a metal salt solution with a concentration of 2 M according to the ratio of MnSO4:CuSO4=9:1, and denote it as solution I; (2) Prepare 1 L of a mixed alkaline solution of 2 M Na2CO3 and 0.3 M NH4OH as solution II; (3) Prepare 500 mL of ZnSO4 solution with a concentration of 4 M as a salt solution for the doping element, providing the non-uniform doping element, denoted as solution III; (4) At the start of the reaction, 500 mL of deionized water was added as the base liquid. Solution I from step (1) was connected to the reactor through pump A, solution II from step (2) was connected to the reactor through pump C, and solution III from step (3) was pumped into solution I through pump B at a flow rate of 0.4 mL / min, so that the concentration of the doped elements in solution I gradually increased. Solution I and solution III were connected in series and then introduced into the reactor. The pH value of the reactor was set to 7.8, and the flow rates of pumps A and B were 0.8 mL / min. The automatic adjustment function of the reactor will maintain the pH value required for the reaction by adjusting the flow rate of pump C in real time. At the same time, the stirring paddle in the reactor was stirred at a speed of 700 rpm to ensure that the reaction solution was mixed evenly. After 24 hours of reaction, the precipitate was taken out and repeatedly filtered, washed and dried to obtain a spherical positive electrode material carbonate precursor with non-uniform element distribution. (5) The spherical positive electrode material carbonate precursor with non-uniform element distribution obtained in step (4) is mixed with CH3COONa at a molar ratio of Na:(Mn+Ni+Zn)=0.7:1 and ground for 30 minutes. The mixture is then transferred to a muffle furnace and sintered at 1000℃ in air for 16 hours at a heating rate of 10℃ / min. After cooling to room temperature, the P2-Na composition is obtained. 0.67 Mn 0.8 Cu 0.1 Zn 0.1 The P2-type layered oxide cathode material of O2 has a Zn content that gradually decreases from the surface to the center, while the Mn and Cu contents gradually increase from the surface to the center.

[0036] Example 3 A method for preparing a layered oxide cathode material for sodium-ion batteries includes: (1) Prepare 1 L of a 2 M metal salt solution according to the ratio of MnSO4:CoSO4=55:45, and denote it as solution I; (2) Prepare 1 L of a mixed alkaline solution of 2 M Na2CO3 and 0.5 M NH4OH as solution II; (3) Prepare 500 mL of Al2(SO4)3 solution with a concentration of 4 M as a salt solution for doping elements to provide non-uniform doping elements, denoted as solution III; (4) At the start of the reaction, 500 mL of deionized water was added as the base liquid. Solution I in step (1) was connected to the reactor through pump A, solution II in step (2) was connected to the reactor through pump C, and solution III in step (3) was pumped into solution I through pump B at a flow rate of 0.4 mL / min, so that the concentration of the doped elements in solution I gradually increased. Solution I and solution III were connected in series and then introduced into the reactor. The pH value of the reactor was set to 7.8, and the flow rates of pumps A and B were 0.8 mL / min. The automatic adjustment function of the reactor will maintain the pH value required for the reaction by adjusting the flow rate of pump C in real time. At the same time, the stirring paddle in the reactor was stirred at a speed of 800 rpm to ensure that the reaction solution was mixed evenly. After 24 hours of reaction, the precipitate was taken out and repeatedly filtered, washed and dried to obtain a spherical positive electrode material carbonate precursor with non-uniform element distribution. (5) The spherical positive electrode material carbonate precursor with non-uniform element distribution obtained in step (4) is mixed with CH3COONa at a molar ratio of Na:(Mn+Co+Al)=0.7:1 and ground for 30 minutes. The mixture is then transferred to a muffle furnace and sintered at 1000℃ in air for 16 hours at a heating rate of 10℃ / min. After cooling to room temperature, the P2-Na composition is obtained. 0.67 Mn 0.55 Co0.35 Al 0.1 The P2-type layered oxide cathode material of O2 has an Al content that gradually decreases from the surface to the center, while the Mn and Co contents gradually increase from the surface to the center.

[0037] Example 4 A method for preparing a layered oxide cathode material for sodium-ion batteries includes: (1) Prepare 1 L of a 2 M metal salt solution according to the ratio of MnSO4:NiSO4=67:33, and denote it as solution I; (2) Prepare 1 L of a mixed solution of 2 M NaOH and 0.3 M NH4OH as a mixed alkaline solution, denoted as solution II; (3) Prepare 500 mL of Al2(SO4)3 solution with a concentration of 2 M as a salt solution for the doping element, providing the non-uniform doping element, denoted as solution III; (4) At the start of the reaction, 500 mL of deionized water was added as the base liquid. Solution I from step (1) was connected to the reactor through pump A, solution II from step (2) was connected to the reactor through pump C, and solution III from step (3) was pumped into solution I through pump B at a flow rate of 0.4 mL / min, so that the concentration of the doped elements in solution I gradually increased. Solution I and solution III were connected in series and then introduced into the reactor. The pH value of the reactor was set to 9, and the flow rates of pumps A and B were set to 0.8 mL / min. The automatic adjustment function of the reactor will maintain the pH value required for the reaction by adjusting the flow rate of pump C in real time. At the same time, the stirring paddle in the reactor was stirred at a speed of 800 rpm to ensure that the reaction solution was mixed evenly. After 24 hours of reaction, the precipitate was taken out and repeatedly filtered, washed and dried to obtain a spherical positive electrode material carbonate precursor with non-uniform element distribution. (5) The spherical positive electrode material carbonate precursor with non-uniform element distribution obtained in step (4) is mixed with CH3COONa at a molar ratio of Na:(Mn+Ni+Al)=0.7:1 and ground for 30 minutes. The mixture is then transferred to a muffle furnace and sintered at 500℃ in air for 2 hours. Subsequently, the temperature is increased to 1000℃ and sintered for 18 hours at a heating rate of 10℃ / min. After cooling to room temperature, the P2-Na composition is obtained. 0.67 Mn 0.65 Nio 0.20 Al 0.05 The P2-type layered oxide cathode material of O2 has an Al content that gradually decreases from the surface to the center, while the Mn and Ni contents gradually increase from the surface to the center.

[0038] Example 5 In this embodiment, the P2-type layered oxide cathode materials with uneven and uniform Mg distribution prepared in Example 1 and Comparative Example 2, the undoped nickel-manganese-based cathode material of Comparative Example 3, and the O3-type layered oxide cathode material with uneven element distribution prepared in Comparative Example 1 were assembled into sodium-ion batteries according to the following method, and the battery performance was tested.

[0039] (1) Preparation of positive electrode material electrode sheet The cathode material, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed and ground in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) solvent was added and the mixture was dispersed evenly to obtain a mixed slurry of the cathode material. The mixed slurry was uniformly coated onto a current collector aluminum foil and dried in a vacuum drying oven at 110 °C for 12 hours. It was then cut into circular electrode sheets with a diameter of 10 mm using a cutting machine. Example 1 corresponds to a P2 phase nickel-manganese-based heterogeneously doped magnesium cathode, Comparative Example 2 corresponds to a P2 phase nickel-manganese-based uniformly doped magnesium cathode, and Comparative Example 1 corresponds to an O3 phase nickel-manganese-based heterogeneously doped magnesium cathode. Comparative Example 3 corresponds to a P2 phase undoped nickel-manganese-based cathode.

[0040] (2) Assembly of sodium-ion batteries Using the aforementioned circular electrode as the positive electrode, a sodium electrode as the negative electrode, and 1 M sodium hexafluorophosphate (NaPF6) + propylene carbonate (PC) + 2 wt% fluoroethylene carbonate (FEC) as the electrolyte, a button cell was assembled in an inert atmosphere glove box.

[0041] (3) Battery performance testing The batteries assembled using the above method were subjected to cycle performance testing in the Xinwei testing system at a test temperature of 25 ℃ and a voltage window of 2 V-4.2 V. Figure 6 As shown, the results indicate that the P2 phase nickel-manganese-based heterogeneously doped magnesium cathode provided in Example 1 has a first-cycle discharge specific capacity of 88 mAh·g at a rate of 0.2 C. -1 The first-cycle discharge specific capacity of the P2 phase nickel-manganese-based uniformly magnesium-doped cathode in Comparative Example 2 was 84 mAh·g. -1 The first-cycle discharge specific capacity of the O3-phase nickel-manganese-based heterogeneously doped magnesium cathode in Comparative Example 1 was 112 mAh·g. -1 Furthermore, compared to Comparative Example 3, the undoped P2 phase nickel-manganese based cathode (Na₂O₃) showed better performance. 0.67 Mn 0.67 Ni 0.33 O2) materials, the non-uniform doping of Mg elements in the cathode material significantly improves the cycle stability, with a capacity retention of 83% after 300 cycles.

[0042] Although the description of the invention has been quite detailed and particularly of several described embodiments, it is not intended to limit it to any of these details or embodiments or any particular embodiment, but should be considered as providing a broad possible interpretation of the claims by referring to the appended claims and taking into account the prior art, thereby effectively covering the intended scope of the invention. Furthermore, the invention has been described above with respect to embodiments foreseeable by the inventors in order to provide a useful description, and non-substantial modifications to the invention that have not yet been foreseen may still represent equivalent modifications.

Claims

1. A method for preparing a P2-type layered oxide cathode material with non-uniform elemental distribution, characterized in that, Includes the following steps: (1) At the start of the reaction, deionized water is added to the reactor as the base liquid. The metal salt solution is introduced into the reactor through pump A, and the mixed alkaline solution is introduced into the reactor through pump C. The dopant element salt solution is pumped into the metal salt solution through pump B at a certain flow rate, so that the concentration of the dopant element in the metal salt solution gradually increases, and the concentration gradient distribution of the dopant element in the precursor is realized from the surface to the inside. That is, the metal salt solution and the dopant element salt solution are introduced into the reactor simultaneously in series. The reactor maintains the pH value required for the reaction by adjusting the flow rate of pump C in real time, and the mixture is stirred and mixed evenly to form a cathode material precursor with non-uniform element distribution. The metal salt includes at least one of MnSO4, NiSO4, CuSO4, CoSO4, and FeSO4. The dopant element salt solution includes at least one of MgSO4 solution, ZnSO4 solution, and Al2(SO4)3 solution. (2) The elementally non-uniformly distributed cathode material precursor obtained in step (1) is mixed with sodium source, ground, sintered, and cooled to room temperature to obtain the elementally non-uniformly distributed P2 type layered oxide cathode material.

2. The preparation method according to claim 1, characterized in that, The concentration of metal ions in the metal salt solution is 1 M-3.5 M; the concentration of Na2CO3 in the mixed alkaline solution is 1 M-3.5 M; and the concentration of the doped element salt solution is 0.2-4 M.

3. The preparation method according to claim 1, characterized in that, In step (1), the flow rate of pump A is 0.2-2 mL / min, the flow rate of pump B is set to 0.2-1 mL / min, the pH value is set to 7-9, and the stirring speed is 600-800 rmp.

4. The preparation method according to claim 1, characterized in that, Sodium source and cathode material precursor are mixed according to a molar ratio of Na to metal ions of 0.6-0.82:

1.

5. The preparation method according to claim 1, characterized in that, The sodium source is at least one of Na2CO3 and CH3COONa.

6. The preparation method according to claim 1, characterized in that, The sintering temperature is 800-1000 ℃, the time is 15-20 h, and both are carried out in an air atmosphere with a heating rate of 5-15 ℃ / min.

7. A P2-type layered oxide cathode material with non-uniform elemental distribution prepared by the method according to any one of claims 1-6.

8. A sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The active material of the positive electrode is the P2-type layered oxide positive electrode material as described in claim 7.

9. The sodium-ion battery according to claim 8, characterized in that, The sodium salt in the electrolyte is sodium hexafluorophosphate or sodium perchlorate, and the solvent is at least one of propylene carbonate, ethylene carbonate, dimethyl carbonate, and diethyl carbonate.

10. The application of the P2-type layered oxide cathode material with non-uniform elemental distribution as described in claim 7 in the preparation of sodium-ion batteries.

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