P2-phase sodium ion positive electrode material with superlattice ordered structure and preparation method of P2-phase sodium ion positive electrode material

Abstract

The invention discloses a P2-phase sodium ion positive electrode material with a superlattice ordered structure and a preparation method of the P2-phase sodium ion positive electrode material. The chemical formula of the P2-phase sodium ion positive electrode material is Na < x > M < 1-a-b > A B O < 2 >, wherein M is a transition metal element Mn or / and Ni; a doping sites are transition metal vacancies, and / or doped metal elements Mg and / or doped metal elements Li; the doping site of B is doped with a transition metal element Fe or doped with a transition metal element Cu or doped with a transition metal element Zn; 0.8 < = x < = 0.9, 0.25 < = a, 0.04 < = b < = 0.09. According to the P2 type material with the superlattice ordered structure, the layered structure stability and the sodium ion transmission efficiency of the material can be remarkably improved, so that the problems of poor structure stability and low ion diffusion rate of a traditional sodium ion positive electrode material are effectively solved; the P2 type material with the superlattice ordered structure can be suitable for preparing a sodium ion battery system with high energy density.

Description

Technical Field

[0001] The present invention relates to a P2 phase sodium ion positive electrode material with a superlattice ordered structure, and also relates to a method for preparing the sodium ion positive electrode material. Background Art

[0002] Sodium-ion batteries are an emerging electrochemical energy storage device that has attracted widespread attention in recent years due to their abundant resource reserves and low cost. Compared with traditional lithium-ion batteries, sodium-ion batteries use sodium as the main ion carrier of the battery. Since the abundance of sodium in the earth's crust is much higher than that of lithium, sodium-ion batteries theoretically have lower material costs and higher economic efficiency. In addition, the electrochemical properties of sodium-ion batteries are similar to those of lithium-ion batteries, which gives them broad application prospects in energy storage technology. P2 phase layered oxide sodium-ion positive electrode materials have advantages such as simple synthesis process and good rate performance. However, due to the irreversible phase change during the charge and discharge process (especially at high voltage), it is easy to cause structural instability, which in turn leads to capacity decay and insufficient cycle stability. Therefore, the current P2 phase layered oxide sodium-ion positive electrode materials have problems such as limited sodium content, interlayer slip and phase change leading to capacity decay, and are not suitable for the preparation of high energy density sodium-ion battery systems. Summary of the Invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a P2 phase sodium ion positive electrode material with a superlattice ordered structure. The sodium ion positive electrode material has a superlattice ordered transition metal layer and a stable sodium ion transmission channel, thereby significantly improving the structural stability and cycle performance of the material when used as a sodium ion positive electrode material; another purpose of the present invention is to provide a method for preparing the above-mentioned sodium ion positive electrode material.

[0004] Technical solution: The P2 phase sodium ion positive electrode material with superlattice ordered structure of the present invention has the chemical formula: Na x M 1-a-b A a B b O2; wherein M is a transition metal element Mn or / and Ni; A doping site is to form a transition metal vacancy (TM V ), and / or is a doping metal element Mg and / or is a doping metal element Li; the B doping site is a doping transition metal element Fe or a doping transition metal element Cu or a doping transition metal element Zn; 0.8≤x≤0.9, 0.25≤a, 0.04≤b≤0.09.

[0005] The method for preparing the above-mentioned P2 phase sodium ion positive electrode material having a superlattice ordered structure comprises the following steps:

[0006] (1) adding sodium salt, a soluble salt of transition metal M, a soluble salt of the metal element corresponding to the A doping site, a soluble salt of the metal element corresponding to the B doping site, and citric acid to deionized water, stirring in a high-temperature water bath until a gel state is formed, and then drying to obtain a precursor;

[0007] (2) The precursor is ball-milled and then calcined in an air atmosphere to obtain a P2 phase sodium ion positive electrode material with a superlattice ordered structure.

[0008] Wherein, in step (1), the soluble salt is one of acetate, carbonate or nitrate.

[0009] In step (1), sodium salt, soluble salt of transition metal M, soluble salt of metal element corresponding to doping site A and soluble salt of metal element corresponding to doping site B are added in corresponding amounts according to the stoichiometric ratio of each metal element in the chemical formula.

[0010] Wherein, in step (1), the added molar amount of the citric acid is 1.5 to 2 times the total molar amount of the metal cations.

[0011] Wherein, in step (1), the reaction temperature is 60-80°C; the reaction speed is 800-1000 r / min; and the reaction time is 2-4 h.

[0012] Wherein, in step (1), the drying temperature is 80-120° C., and the drying time is 10-12 hours.

[0013] Wherein, in step (2), the ball-to-material ratio of ball milling beads to precursor is 5:1-1.5; the rotation speed of the ball mill is 300-350 r / min, and the ball milling time is 2-2.5 h.

[0014] In step (2), during the calcination process, heating is performed using a staged heat treatment method, specifically: in an air atmosphere, the temperature is first raised to 600-680°C, kept at this temperature for 2-4 hours, and then raised to 900-950°C at a heating rate of 3-5°C / min, and kept at this temperature for 16-20 hours. The synthesis of sodium ion layered oxide is a process of crystallization and growth. Providing a thermal insulation platform is to facilitate the consistency of the crystallization of the positive electrode material; adding such a thermal insulation platform will reduce the residual alkali of the material, which is beneficial to its electrical performance.

[0015] The present invention dopes metal elements (Mg, Li) at the transition metal element M (Mn, Ni) sites of the existing P2 phase sodium ion positive electrode material and simultaneously dopes transition metal elements (Fe or Cu or Zn) while forming transition metal vacancies, and controls the doping amount of the elements and the amount of transition metal vacancies formed, thereby being able to form a regular hexagonal "honeycomb" superlattice structure in which Mn and doping elements are alternating in an orderly manner on the transition metal layer. Doping element atoms replace manganese atoms to form periodically arranged structural units, and the repeatedly arranged structural units form the transition metal layer. This structural arrangement greatly improves the stability of the crystal structure and can significantly alleviate the problem of Mn being damaged. 3+ The crystal structure distortion and twisting caused by the Jahn-Teller effect, and the multiple phase transitions caused by it, are not only beneficial to improving the charge and discharge curve of the material, reducing its volume effect during the charge and discharge process, and improving the rate performance of the material, but also can alleviate the attenuation of the material's specific capacity during long cycles and extend the service life of the material.

[0016] On the one hand, the superlattice ordered structure can improve the migration path of sodium ions in the material, making the ions diffuse more smoothly within the crystal. It can also reduce obstacles and defects during sodium ion migration by optimizing the arrangement of sodium ions in the lattice, promoting faster ion insertion and extraction, which is crucial for improving the battery's rate performance. On the other hand, the superlattice ordered structure can also effectively improve the crystal structure stability of P2-type materials, thereby alleviating the structural expansion and contraction caused by the insertion or extraction of sodium ions, reducing the damage or instability of the crystal structure, effectively delaying the battery's capacity decline, and improving the cycle life.

[0017] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: the transition metal oxide layer of the P2-type material of the present invention has a superlattice ordered structure, and the P2-type material with a superlattice ordered structure can significantly improve the layered structure stability and sodium ion transmission efficiency of the material, thereby effectively solving the problems of poor structural stability and low ion diffusion rate in traditional sodium ion positive electrode materials; the P2-type material with a superlattice ordered structure of the present invention can be used to prepare a high-energy-density sodium-ion battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart for constructing a P2-type material with a superlattice ordered structure according to the present invention;

[0019] Figure 2 XRD patterns of the positive electrode materials in Comparative Example 1 and Examples 1 to 5;

[0020] Figure 3 This is a scanning electron microscope image of the positive electrode material in Example 4;

[0021] Figure 4 The transmission electron microscope image and selected area electron diffraction pattern of the positive electrode material in Example 4;

[0022] Figure 5 The charge and discharge curve of the sodium ion battery constructed with the positive electrode material of Comparative Example 1 at 0.1C and the comparison chart of 3 cycles;

[0023] Figure 6 The charge-discharge curve of the sodium-ion battery constructed with the positive electrode material of Example 1 at 0.1C and the comparison chart after 3 cycles;

[0024] Figure 7 The charge-discharge curve of the sodium ion battery constructed with the positive electrode material of Example 2 at 0.1C and the comparison chart after 3 cycles;

[0025] Figure 8 The charge-discharge curve of the sodium ion battery constructed with the positive electrode material of Example 3 at 0.1C and the comparison chart after 3 cycles;

[0026] Figure 9 The charge-discharge curve of the sodium ion battery constructed with the positive electrode material of Example 4 at 0.1C and the comparison chart after 3 cycles;

[0027] Figure 10 The charge-discharge curve of the sodium ion battery constructed with the positive electrode material of Example 5 at 0.1C and the comparison chart after 3 cycles;

[0028] Figure 11 0.1C charge and discharge curves of a sodium ion battery constructed with the positive electrode material of Example 4 at different voltages;

[0029] Figure 12 This is a graph showing the capacity retention of sodium ion batteries constructed with the positive electrode materials of Comparative Example 1 and Examples 1 to 5 after 150 cycles at 1C at a voltage of 2.0 to 4.3 V. DETAILED DESCRIPTION

[0030] Comparative Example 1

[0031] A P2 phase sodium ion cathode material Na 8 / 9 Ni 3 / 10 Mn 7 / 10 The preparation method of O2 comprises the following steps:

[0032] (1) According to the chemical formula Na 8 / 9 Ni 3 / 10 Mn 7 / 10The stoichiometric ratio of each metal element in O2 was calculated by weighing the acetate of each metal element, adding 0.0187mmol sodium acetate, 0.006mmol nickel acetate, 0.014mmol manganese acetate and 0.03mmol citric acid to 150mL deionized water, stirring at a stirring rate of 800r / min for 20 minutes, stirring in an 80℃ water bath for 4 hours after complete dissolution until the solution became sol-like, drying at 80℃ for 12 hours, grinding and collecting the sample for later use;

[0033] (2) The dried drugs were placed in an agate ball mill and rotated alternately forward and reverse at a speed of 300 r / min for 2 h to obtain a uniformly mixed powder precursor;

[0034] (3) The ball-milled sample was pressed into a sheet under a pressure of 20 MPa. In an air atmosphere, the room temperature was raised to 680 ° C. After the platform was kept warm for 2 hours, it was raised to 920 ° C and calcined for 16 hours at a heating rate of 3 ° C / min. After natural cooling, it was collected after passing through a 300 mesh sieve to obtain fine and uniform particles of P2 phase sodium ion positive electrode material Na 8 / 9 Ni 3 / 10 Mn 7 / 10 O2.

[0035] Example 1

[0036] The method for preparing a P2 phase sodium ion positive electrode material having a superlattice ordered structure of the present invention comprises the following steps:

[0037] (1) According to the chemical formula Na 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Ni 1 / 12 Mn 8 / 12 The stoichiometric ratio of each metal element in O2 was calculated by weighing the acetate of each metal element, adding 0.0187mmol sodium acetate, 0.0017mmol lithium acetate, 0.0017mmol magnesium acetate, 0.0017mmol nickel acetate, 0.013mmol manganese acetate and 0.03mmol citric acid to 150mL deionized water, stirring at a stirring rate of 800r / min for 20 minutes, stirring in an 80℃ water bath for 4 hours after complete dissolution until the solution becomes sol-like, drying at 80℃ for 12 hours, grinding and collecting the sample for later use;

[0038] (2) The dried drugs were placed in an agate ball mill and rotated alternately forward and reverse at a speed of 300 r / min for 2 h to obtain a uniformly mixed powder precursor;

[0039] (3) The ball-milled sample was pressed into a sheet under a pressure of 20 MPa. In an air atmosphere, the room temperature was raised to 680 ° C. After the platform was kept warm for 2 hours, it was raised to 920 ° C and calcined for 16 hours at a heating rate of 3 ° C / min. After natural cooling, it was collected after passing through a 300 mesh sieve to obtain fine and uniform particles of P2 phase sodium ion positive electrode material Na with a superlattice structure. 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Ni 1 / 12 Mn 8 / 12 O2; In the chemical formula, □ represents a transition metal vacancy (TM V ).

[0040] Example 2

[0041] The method for preparing a P2 phase sodium ion positive electrode material having a superlattice ordered structure of the present invention comprises the following steps:

[0042] (1) According to the chemical formula Na 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Cu 1 / 12 Mn 8 / 12 The stoichiometric ratio of each metal element in O2 was calculated by weighing the acetate of each metal element, adding 0.0187mmol sodium acetate, 0.0017mmol lithium acetate, 0.0017mmol magnesium acetate, 0.0017mmol copper acetate, 0.013mmol manganese acetate and 0.03mmol citric acid to 150mL deionized water, stirring at a stirring rate of 800r / min for 20 minutes, stirring in an 80℃ water bath for 4 hours after complete dissolution until the solution becomes sol-like, drying at 80℃ for 12 hours, grinding and collecting the sample for later use;

[0043] (2) The dried drugs were placed in an agate ball mill and rotated alternately forward and reverse at a speed of 300 r / min for 2 h to obtain a uniformly mixed powder precursor;

[0044] (3) The ball-milled sample was pressed into a sheet under a pressure of 20 MPa. In an air atmosphere, the room temperature was raised to 680 ° C. After the platform was kept warm for 2 hours, it was raised to 920 ° C and calcined for 16 hours at a heating rate of 3 ° C / min. After natural cooling, it was collected after passing through a 300 mesh sieve to obtain fine and uniform particles of P2 phase sodium ion positive electrode material Na with a superlattice structure. 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Cu 1 / 12 Mn 8 / 12O2; In the chemical formula, □ represents a transition metal vacancy (TM V ).

[0045] Example 3

[0046] The method for preparing a P2 phase sodium ion positive electrode material having a superlattice ordered structure of the present invention comprises the following steps:

[0047] (1) According to the chemical formula Na 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Fe 1 / 12 Mn 8 / 12 The stoichiometric ratio of each metal element in O2 was calculated by weighing the acetate of each metal element, adding 0.0187mmol sodium acetate, 0.0017mmol lithium acetate, 0.0017mmol magnesium acetate, 0.0017mmol iron acetate, 0.013mmol manganese acetate and 0.03mmol citric acid to 150mL deionized water, stirring at a stirring rate of 800r / min for 20 minutes, stirring in an 80℃ water bath for 4 hours after complete dissolution until the solution becomes sol-like, drying at 80℃ for 12 hours, grinding and collecting the sample for later use;

[0048] (2) The dried drugs were placed in an agate ball mill and rotated alternately forward and reverse at a speed of 300 r / min for 2 h to obtain a uniformly mixed powder precursor;

[0049] (3) The ball-milled sample was pressed into a sheet under a pressure of 20 MPa. In an air atmosphere, the room temperature was raised to 680 ° C. After the platform was kept warm for 2 hours, it was raised to 920 ° C and calcined for 16 hours at a heating rate of 3 ° C / min. After natural cooling, it was collected after passing through a 300 mesh sieve to obtain fine and uniform particles of P2 phase sodium ion positive electrode material Na with a superlattice structure. 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Fe 1 / 12 Mn 8 / 12 O2; In the chemical formula, □ represents a transition metal vacancy (TM V ).

[0050] Example 4

[0051] The method for preparing a P2 phase sodium ion positive electrode material having a superlattice ordered structure of the present invention comprises the following steps:

[0052] (1) According to the chemical formula Na 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Zn1 / 12 Mn 8 / 12 The stoichiometric ratio of each metal element in O2 was calculated by weighing the acetate of each metal element, adding 0.0187mmol sodium acetate, 0.0017mmol lithium acetate, 0.0017mmol magnesium acetate, 0.0017mmol zinc acetate, 0.013mmol manganese acetate and 0.03mmol citric acid to 150mL deionized water, stirring at a stirring rate of 800r / min for 20 minutes, stirring in an 80℃ water bath for 4 hours after complete dissolution until the solution becomes sol-like, drying at 80℃ for 12 hours, grinding and collecting the sample for later use;

[0053] (2) The dried drugs were placed in an agate ball mill and rotated alternately forward and reverse at a speed of 300 r / min for 2 h to obtain a uniformly mixed powder precursor;

[0054] (3) The ball-milled sample was pressed into a sheet under a pressure of 20 MPa. In an air atmosphere, the room temperature was raised to 680 ° C. After the platform was kept warm for 2 hours, it was raised to 920 ° C and calcined for 16 hours at a heating rate of 3 ° C / min. After natural cooling, it was collected after passing through a 300 mesh sieve to obtain fine and uniform particles of P2 phase sodium ion positive electrode material Na with a superlattice structure. 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Zn 1 / 12 Mn 8 / 12 O2; In the chemical formula, □ represents a transition metal vacancy (TM V ).

[0055] Example 5

[0056] The method for preparing a P2 phase sodium ion positive electrode material having a superlattice ordered structure of the present invention comprises the following steps:

[0057] (1) According to the chemical formula Na 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Ni 1 / 24 Zn 1 / 24 Mn 8 / 12The stoichiometric ratio of each metal element in O2 was calculated by weighing the acetate of each metal element, adding 0.0187mmol sodium acetate, 0.0017mmol lithium acetate, 0.0017mmol magnesium acetate, 0.00085mmol nickel acetate, 0.00085mmol zinc acetate, 0.013mmol manganese acetate and 0.03mmol citric acid to 150mL deionized water, stirring at a stirring rate of 800r / min for 20 minutes, stirring in an 80℃ water bath for 4 hours after complete dissolution until the solution becomes sol-like, drying at 80℃ for 12 hours, grinding and collecting the sample for later use;

[0058] (2) The dried drugs were placed in an agate ball mill and rotated alternately forward and reverse at a speed of 300 r / min for 2 h to obtain a uniformly mixed powder precursor;

[0059] (3) The ball-milled sample was pressed into a sheet under a pressure of 20 MPa. In an air atmosphere, the room temperature was raised to 680 ° C. After the platform was kept warm for 2 hours, it was raised to 920 ° C and calcined for 16 hours at a heating rate of 3 ° C / min. After natural cooling, it was collected after passing through a 300 mesh sieve to obtain fine and uniform particles of P2 phase sodium ion positive electrode material Na with a superlattice structure. 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Ni 1 / 24 Zn 1 / 24 Mn 8 / 12 O2; In the chemical formula, □ represents a transition metal vacancy (TM V ).

[0060] Example 6

[0061] The method for preparing a P2 phase sodium ion positive electrode material having a superlattice ordered structure of the present invention comprises the following steps:

[0062] (1) According to the chemical formula Na 8 / 9 Li 1 / 24 Mg 1 / 8 □ 1 / 12 Zn 1 / 12 Mn 8 / 12 The stoichiometric ratio of each metal element in O2 was calculated by weighing the acetate of each metal element, adding 0.0187mmol sodium acetate, 0.00085mmol lithium acetate, 0.00255mmol magnesium acetate, 0.0017mmol zinc acetate, 0.013mmol manganese acetate and 0.03mmol citric acid to 150mL deionized water, stirring at a stirring rate of 800r / min for 20 minutes, stirring in an 80℃ water bath for 4 hours after complete dissolution until the solution becomes sol-like, drying at 80℃ for 12 hours, grinding and collecting the sample for later use;

[0063] (2) The dried drugs were placed in an agate ball mill and rotated alternately forward and reverse at a speed of 300 r / min for 2 h to obtain a uniformly mixed powder precursor;

[0064] (3) The ball-milled sample was pressed into a sheet under a pressure of 20 MPa. In an air atmosphere, the room temperature was raised to 680 ° C. After the platform was kept warm for 2 hours, it was raised to 920 ° C and calcined for 16 hours at a heating rate of 3 ° C / min. After natural cooling, it was collected after passing through a 300 mesh sieve to obtain fine and uniform particles of P2 phase sodium ion positive electrode material Na with a superlattice structure. 8 / 9 Li 1 / 24 Mg 1 / 8 □ 1 / 12 Zn 1 / 12 Mn 8 / 12 O2; In the chemical formula, □ represents a transition metal vacancy (TM V ).

[0065] Example 7

[0066] The method for preparing a P2 phase sodium ion positive electrode material having a superlattice ordered structure of the present invention comprises the following steps:

[0067] (1) According to the chemical formula Na 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Zn 1 / 12 Mn 8 / 12 The stoichiometric ratio of each metal element in O2 was calculated by weighing the acetate of each metal element, adding 0.0187mmol sodium acetate, 0.0017mmol lithium acetate, 0.0017mmol magnesium acetate, 0.0017mmol zinc acetate, 0.013mmol manganese acetate and 0.03mmol citric acid to 150mL deionized water, stirring at a stirring rate of 800r / min for 20 minutes, stirring in an 80℃ water bath for 4 hours after complete dissolution until the solution becomes sol-like, drying at 80℃ for 12 hours, grinding and collecting the sample for later use;

[0068] (2) The dried drugs were placed in an agate ball mill and rotated alternately forward and reverse at a speed of 300 r / min for 2 h to obtain a uniformly mixed powder precursor;

[0069] (3) The ball-milled sample was pressed into a sheet under a pressure of 20 MPa, and calcined at room temperature to 920 °C for 16 h in an air atmosphere at a heating rate of 3 °C / min. After natural cooling, it was collected after being sieved through a 300-mesh sieve to obtain a P2 phase sodium ion positive electrode material Na with fine and uniform particles and a superlattice structure. 8 / 9 Li1 / 12 Mg 1 / 12 □ 1 / 12 Zn 1 / 12 Mn 8 / 12 O2; In the chemical formula, □ represents a transition metal vacancy (TM V ).

[0070] The P2 phase sodium ion cathode materials obtained in Comparative Example 1 and Examples 1 to 5 were characterized by X-ray diffractometer. Figure 2 .Depend on Figure 2 As can be seen, the X-ray diffraction peaks of the materials obtained in different examples correspond exactly to the standard card (PDF#054-0894) and are free of stray peaks, indicating the high crystallinity of the materials. Furthermore, a peak characteristic of a superlattice-ordered structure appears near 22°. The XRD patterns demonstrate that the present invention successfully prepared a P2-phase sodium-ion cathode material with a superlattice-ordered structure. Figure 3 、 4 is Na in Example 4 8 / 9 Li 1 / 12 Mg 1 / 12 □ 1 / 12 Zn 1 / 12 Mn 8 / 12 The scanning electron microscope image and transmission electron diffraction pattern of O2 show that the particles are single crystals and have good dispersion. The average particle size of the positive electrode material after sintering is 3 to 5 microns. The transmission electron diffraction pattern shows that it is a P2 phase crystal structure, which also shows that the present invention has successfully prepared a P2 phase sodium ion positive electrode material with a superlattice ordered structure.

[0071] Sodium ion batteries were prepared using the positive electrode materials obtained in Comparative Example 1 and Examples 1 to 5, respectively. The specific preparation methods are as follows:

[0072] The prepared cathode material powder was mixed with acetylene black and binder polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10, and then an appropriate amount of N-methylpyrrolidone (NMP) solution was added. The mixture was ground in a dry environment at room temperature to form a slurry. The slurry was then evenly coated on the current collector aluminum foil and dried under an infrared lamp before being cut into 8×8 mm squares. 2 The electrode was dried in a 120°C oven for 10 hours, compacted on a roller press, and cut into 14mm diameter pieces. The pieces were then transferred to a glove box for later use. A 2032 button cell was assembled in an argon-filled glove box using sodium metal as the negative electrode.

[0073] The assembled button cell was placed on the battery test system for constant current charge and discharge and long cycle tests. The current density was set according to different experimental designs, and the voltage window was 2 to 4.3 V. The test results are shown in the figure. Figures 5 to 12 .Depend on Figures 5-10 It can be seen that the sodium ion batteries made of the P2 phase positive electrode materials obtained in Comparative Example 1, Examples 1, 2, 3, 4, and 5 have discharge specific capacities of 142 mAh / g, 98.2 mAh / g, 102.7 mAh / g, 105.4 mAh / g, 147.1 mAh / g, and 130.2 mAh / g, respectively. Although the first-cycle discharge specific capacity of Comparative Example 1 is higher than that of Examples 1, 2, 3, and 5, it can be seen from the attenuation degree of the second and third cycles that the material is not stable in the 2-4.3 V discharge window. However, Examples 1, 2, 3, 4, and 5 have almost no attenuation (the charge and discharge curves have a high degree of overlap), indicating that the superlattice ordered structure P2 phase positive electrode material of the present invention has good structural stability in the 2-4.3 V discharge window.

[0074] Depend on Figure 11 It can be found that the Zn-doped P2 phase positive electrode material of Example 4 was subjected to charge and discharge tests under different voltage windows. In the 2-4.5V voltage window, the cycle performance remained stable in the first three cycles, and the first cycle discharge capacity reached 162.3mAh / g; further expanding the voltage window, it was found that in the 1.5-4.5V voltage window, the capacity was further increased to 189.8mAh / g, and no new phase change occurred, and the charge and discharge curves had a high degree of overlap. Figure 12 It can be found that the cycle performance of the samples of Examples 1 to 5 is significantly improved compared to that of Comparative Example 1. This shows that the superlattice ordered P2 phase material of the present invention can increase the operating voltage, and the ordered structure is very helpful in maintaining the structural stability of the material.

[0075] Comparison between Example 4 and Example 6 reveals that when the Li and Mg doping ratios are adjusted and their electrical performance is tested, the voltage window is 2-4.3V, and the discharge specific capacities are 147.1mAh / g and 136.8mAh / g, respectively, with a slight decrease in capacity and a significant decrease in cycling performance. After 150 cycles at 1C, the 1C capacity retention rate drops from 90% to 82%. Comparison between Example 4 and Example 7 reveals that when the 680°C 2h holding platform is removed and the battery performance is tested, the voltage window is 2-4.3V, and the discharge specific capacities are 147.1mAh / g and 140.2mAh / g, respectively, with a slight decrease in capacity and a significant decrease in cycling performance. After 150 cycles at 1C, the 1C capacity retention rate drops from 90% to 76%, indicating that the setting of the holding platform is beneficial to the electrical performance of the material. In contrast, in Example 4, the 1C capacity retention rate remains around 90% after 150 cycles at 1C.

Claims

1. A P2 phase sodium ion cathode material having a superlattice ordered structure, characterized in that: Its chemical formula is: Na x M 1-a-b A a B b O2; wherein, M is a transition metal element Mn and / or Ni; the A doping site is to form a transition metal vacancy, and / or is a doping metal element Mg and / or a doping metal element Li; the B doping site is a doping transition metal element Fe or a doping transition metal element Cu or a doping transition metal element Zn; 0.8≤x≤0.9, 0.25≤a, 0.04≤b≤0.

09.

2. The P2 phase sodium ion cathode material having a superlattice ordered structure according to claim 1, characterized in that: The A doping site corresponds to at least two situations of doping metal element Mg, doping metal element Li or forming transition metal vacancies, and the doping amounts of Mg and Li are consistent; or the doping amounts of Mg and Li are consistent with the stoichiometric ratio in the chemical formula for forming transition metal vacancies; the doping amount of the transition metal element corresponding to the B doping site is consistent with the doping amount of the metal element corresponding to the A doping site.

3. The method for preparing the P2 phase sodium ion positive electrode material having a superlattice ordered structure according to claim 1, characterized in that: The steps include: (1) adding sodium salt, a soluble salt of transition metal M, a soluble salt of the metal element corresponding to the A doping site, a soluble salt of the metal element corresponding to the B doping site, and citric acid to deionized water, stirring in a high-temperature water bath until a gel state is formed, and then drying to obtain a precursor; (2) The precursor is ball-milled and then calcined in an air atmosphere to obtain a P2 phase sodium ion positive electrode material with a superlattice ordered structure.

4. The preparation method according to claim 3, wherein: In step (1), the soluble salt is one of acetate, carbonate or nitrate.

5. The preparation method according to claim 3, wherein: In step (1), sodium salt, soluble salt of transition metal M, soluble salt of metal element corresponding to A doping site and soluble salt of metal element corresponding to B doping site are added in corresponding mass according to the stoichiometric ratio of each metal element in the chemical formula.

6. The preparation method according to claim 3, wherein: In step (1), the added molar amount of the citric acid is 1.5 to 2 times the total molar amount of the metal cations.

7. The preparation method according to claim 3, characterized in that: In step (1), the reaction temperature is 60-80° C.; the reaction speed is 800-1000 r / min; and the reaction time is 2-4 h.

8. The preparation method according to claim 3, wherein: In step (1), the drying temperature is 80-120° C., and the drying time is 10-12 hours.

9. The preparation method according to claim 3, wherein: In step (2), the ball-to-material ratio of ball milling beads to precursor is 5:1-1.5; the rotation speed of the ball mill is 300-350 r / min, and the ball milling time is 2-2.5 h.

10. The preparation method according to claim 3, characterized in that: In step (2), during the calcination process, heating is carried out by a staged heat treatment method, specifically: in an air atmosphere, the temperature is first raised to 600-680°C, kept warm for 2-4 hours, and then raised to 900-950°C, the heating rate is 3-5°C / min, and the holding time is 16-20 hours.

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