Ultrahigh-voltage O3-phase sodium-ion battery positive electrode material and preparation method thereof

Abstract

The invention discloses an ultrahigh-voltage O3-phase sodium-ion battery positive electrode material and a preparation method thereof, the chemical formula of the ultrahigh-voltage O3-phase sodium-ion battery positive electrode material is Na < 0.9 > Ni < 0.5-x > A < x > Mn < 0.5-y-z > B < y-z > O < 2 >, and x is greater than or equal to 0.1 and less than or equal to 0.3; 0.1 < = y + z < = 0.2, 0 < = z < = 0.1; the types of metal elements doped at the A doping site and the B doping site are different; -represents a transition metal vacancy. The O3-phase sodium-ion battery positive electrode material disclosed by the invention can keep good performance at 4.5 V, effectively solves the problems of unstable structure and poor rate capability of the existing sodium-ion battery positive electrode material at high voltage (4.5 V), reduces harmful stress caused by structural change in the charging and discharging process by inhibiting irreversible oxygen loss at high voltage, and improves the performance of the sodium-ion battery positive electrode material. The rate capability and the cycling stability of the material are greatly improved, so that the material can be suitable for preparing a sodium-ion battery system with high energy density.

Description

Technical Field

[0001] The present invention relates to an ultra-high voltage O3 phase sodium ion battery positive electrode material and also relates to a method for preparing the O3 phase sodium ion battery positive electrode material. Background Art

[0002] O3 phase sodium ion layered oxide (general formula NaTMO2, TM is transition metal) is considered to be one of the ideal cathode materials for sodium ion batteries due to its high theoretical capacity (about 200mAh / g) and structural advantages similar to lithium battery layered oxides. However, its traditional operating voltage window (2.0-4.0V vs. Na + / Na) limits the further improvement of its energy density. By increasing the charge cut-off voltage (such as to 4.2-4.5V), its theoretical potential can be fully released, which is one of the key paths to promote sodium ion batteries to high energy density and low cost energy storage technology. 1 / 3 Fe 1 / 3 Mn 1 / 3 For example, if the voltage is increased from 4.0V to 4.3V, the energy density can be increased by about 15%, directly pushing the energy density of a single cell to exceed 200Wh / kg (close to the level of lithium iron phosphate), meeting the high energy density requirements of electric vehicles and grid energy storage. In the high voltage range (>4.0V), oxygen anions (O 2- ) may participate in reversible redox reactions (such as O 2- →O n- , n<2), contributing additional capacity.

[0003] However, the O3 phase sodium ion layered oxides are + / Na) faces multiple problems in its application under high voltage, which seriously restricts its actual performance. The main problems under high voltage are as follows: 1. Structural instability: O3 phase materials are prone to irreversible phase transition (such as O3→P3 or O3→O1) under high sodium removal state, resulting in interlayer slip and lattice distortion, causing rapid capacity decay. 2. Intensified interface side reactions: Under high voltage, the oxidation and decomposition of the electrolyte intensifies, forming a thick and unstable cathode electrolyte interface (CEI), increasing the interface impedance and consuming active sodium. 3. Transition metal dissolution: TM ions (such as Mn 3+ Negative effects such as the Jahn-Teller effect and electrolyte corrosion at high voltages accelerate the dissolution and migration of transition metals, disrupting the material structure and triggering crosstalk. 4. Kinetic hysteresis: At high voltages, sodium vacancies become more ordered, hindering ion diffusion and increasing polarization, reducing rate performance. Summary of the Invention

[0004] Objective of the Invention: The objective of the present invention is to provide a cathode material for a super-high-voltage O3-phase sodium-ion battery, which can effectively solve the problems of unstable structure and poor rate performance of existing cathode materials for sodium-ion batteries at high voltages (4.5 V); another objective of the present invention is to provide a preparation method for the above-mentioned cathode material for a super-high-voltage O3-phase sodium-ion battery.

[0005] Technical Solution: The cathode material for a super-high-voltage O3-phase sodium-ion battery of the present invention has the chemical formula: where 0.1 ≤ x ≤ 0.3; 0.1 ≤ y + z ≤ 0.2, 0 ≤ z ≤ 0.1; the types of metal elements doped at the A doping site and the B doping site are different; represents a transition metal vacancy (TM V ).

[0006] Among them, the metal element doped at the A doping site is at least one of Li, Mg, or Co; the metal element doped at the B doping site is Ti.

[0007] Among them, when two or more metal elements are doped at the A doping site, the doping amount of each metal element relative to Ni is 10-20%.

[0008] The preparation method for the above-mentioned cathode material for a super-high-voltage O3-phase sodium-ion battery includes the following steps:

[0009] (1) According to the stoichiometric ratio, mix a sodium source, a nickel source, a manganese source, a soluble salt of the metal corresponding to the A doping site, an oxide of the metal corresponding to the B doping site, and citric acid in water, ultrasonically dissolve, and continuously stir at a high temperature until a wet gel is formed;

[0010] (2) Dry the wet gel to obtain a precursor; ball-mill the obtained precursor, and calcine it by a segmented heat treatment method to obtain a cathode material for a super-high-voltage O3-phase sodium-ion battery.

[0011] Among them, in step (1), the sodium source is sodium acetate or sodium carbonate; the nickel source is nickel acetate or nickel nitrate; the manganese source is manganese acetate or manganese carbonate; the soluble salt is one of acetate, carbonate, or nitrate.

[0012] Among them, in step (1), the added molar amount of citric acid is 1.5-2 times the total molar amount of metal cations.

[0013] Among them, in step (1), the stirring temperature is 80-90 °C; the stirring rate is 1000-2000 r / min; the reaction time is 4-6 h.

[0014] Among them, in step (2), the ball-to-material ratio in the ball milling process is 5:1 to 1.5; the rotation speed of the ball mill is 30 to 40 r / min, and the ball milling time is 2 to 4 h.

[0015] Among them, in step (2), it is calcined by a segmented heat treatment method, and the specific process is: first, it is heated from room temperature to 450 to 500 °C, then from 450 to 500 °C to 600 to 700 °C, held at 600 to 700 °C for 2 to 4 h, and finally from 600 to 700 °C to not less than 900 °C, and held at not less than 900 °C for 12 to 14 h.

[0016] The present invention modifies the O3-phase layered metal oxide Na 0.9 Ni 0.5 Mn 0.5 O2 by multi-element doping combined with transition metal vacancies. On the one hand, it can effectively inhibit the multiple harmful phase transitions of O3→OPn at high voltages, providing guarantee for capacity performance and cycling at 4.5 V ultra-high voltage; on the other hand, it can broaden the sodium ion transmission path, reduce the sodium ion transmission energy barrier, and is beneficial to the rate performance at high voltages; finally, multi-element doping and transition metal regulation can weaken the interlayer repulsive force of transition metals, further delaying the structural distortion, providing a mitigation effect for the irreversible oxygen excitation at ultra-high voltages, thereby effectively ensuring its structural stability at high voltages, and further improving its cycling stability performance.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: The O3-phase sodium ion battery cathode material of the present invention can maintain good performance at 4.5 V, effectively solving the problems of unstable structure and poor rate performance of the existing sodium ion battery cathode materials at high voltages (4.5 V). By inhibiting the irreversible oxygen loss at high voltages, reducing the harmful stress caused by the structural changes during charge and discharge, the rate performance and cycling stability of the material are greatly improved, so that it can be applied to the preparation of sodium ion battery systems with high energy density. Description of the Drawings

[0018] Figure 1 It is the XRD refined pattern of the phase of the cathode material in Example 4;

[0019] Figure 2 It is the crystal structure comparison diagram of the cathode materials of Comparative Example 1 (left) and Example 4 (right);

[0020] Figure 3 It is the scanning electron microscope image of the cathode material in Example 4;

[0021] Figure 4 It is the first charge-discharge curve diagram of the sodium ion batteries formed by the cathode materials of Comparative Example 1 and Example 1 at 0.1 C in the voltage range of 2.0 to 4.3 V;

[0022] Figure 5 The first charge-discharge curve diagram of the sodium-ion battery formed by the cathode materials of Comparative Example 1 and Example 2 at 0.1C in the voltage range of 2.0 - 4.3V;

[0023] Figure 6 The first charge-discharge curve diagram of the sodium-ion batteries formed by the cathode materials of Comparative Example 1 and Example 3 and Example 4 at 0.1C in the voltage range of 2.0 - 4.5V;

[0024] Figure 7 The first charge-discharge curve diagram of the sodium-ion batteries formed by the cathode materials of Comparative Example 1 and Example 5 at 0.1C in the voltage range of 2.0 - 4.5V;

[0025] Figure 8 The rate performance curve diagram of the sodium-ion batteries formed by the cathode materials of Comparative Example 1 and Example 3 and Example 4 in the voltage range of 2.0 - 4.5V;

[0026] Figure 9 The cycling curve diagram of the sodium-ion batteries formed by the cathode materials of Comparative Example 1 and Example 3 and Example 4 at 1C in the voltage range of 2.0 - 4.5V;

[0027] Figure 10 The cycling curve diagram of the sodium-ion batteries formed by the cathode materials of Comparative Example 1 and Example 3 and Example 4 at 3C in the voltage range of 2.0 - 4.5V. Detailed implementation manners

[0028] Comparative Example 1

[0029] A preparation method of an O3-phase sodium-ion battery cathode material Na 0.9 Ni 0.5 Mn 0.5 O2, comprising the following steps:

[0030] (1) Dissolve 0.0189 mmol of sodium acetate, 0.01 mmol of nickel acetate and 0.01 mmol of manganese acetate together in 50 mL of deionized water; dissolve 0.03 mmol of citric acid in 50 mL of deionized water, stir at a stirring rate of 800 r / min for 20 min. After the citric acid is completely dissolved, add the citric acid solution to the metal salt solution, continuously stir in a water bath at 80°C until the solution becomes a gel state, and then dry at 120°C for 12 h to obtain a precursor;

[0031] (2) Add the precursor to the ball milling beads, and keep the rotation speed constant on the ball mill to ball mill and crush it and mix it evenly; wherein, the ball-to-material ratio of the ball milling beads to the precursor is 5:1; the rotation speed of the ball mill is 30 r / min, and the ball milling time is 2 h;

[0032] (3) Place the ball-milled sample in an alumina crucible and perform solid-phase sintering in a muffle furnace. First, heat from room temperature to 500 °C at a heating rate of 3 °C / min, then heat from 500 °C to 680 °C at a heating rate of 1.5 °C / min, and hold for 2 h at the insulation platform of 680 °C; then heat from 680 °C to 900 °C at a heating rate of 1.5 °C / min and hold for 12 h at 900 °C for the reaction; after natural cooling, collect through a 300-mesh sieve to obtain the O3-phase sodium-ion cathode material Na 0.9 Ni 0.5 Mn 0.5 O2.

[0033] Example 1

[0034] The preparation method of the sodium-ion battery cathode material Na 0.9 Ni 0.4 Li 0.1 Mn 0.4 Ti 0.1 O2 of the present invention comprises the following steps:

[0035] (1) Add 0.0189 mmol of sodium acetate, 0.008 mmol of nickel acetate, 0.002 mmol of lithium acetate, 0.008 mmol of manganese acetate and 0.002 mmol of titanium dioxide into 50 mL of deionized water together; dissolve 0.03 mmol of citric acid in 50 mL of deionized water, stir at a stirring rate of 800 r / min for 20 min, and after the citric acid is completely dissolved, add the citric acid solution into the metal salt solution, continuously stir in a water bath at 80 °C until the solution becomes a gel state, and then dry at 120 °C for 12 h to obtain a precursor;

[0036] (2) Add the precursor into the ball-milling beads, and keep the rotation speed constant on the ball mill to ball-mill and crush it and mix it evenly; wherein, the ball-to-material ratio of the ball-milling beads to the precursor is 5:1; the rotation speed of the ball mill is 30 r / min and the ball-milling time is 2 h;

[0037] (3) Place the ball-milled sample in an alumina crucible and perform solid-phase sintering in a muffle furnace. First, heat from room temperature to 500 °C at a heating rate of 3 °C / min, then heat from 500 °C to 680 °C at a heating rate of 1.5 °C / min, and hold for 2 h at the insulation platform of 680 °C; then heat from 680 °C to 900 °C at a heating rate of 1.5 °C / min and hold for 12 h at 900 °C for the reaction; after natural cooling, collect through a 300-mesh sieve to obtain the O3-phase sodium-ion cathode material Na 0.9 [[ID=|33]]Ni 0.4 Li 0.1 Mn 0.4 Ti 0.1 O2.

[0038] Example 2

[0039] The preparation method of the positive electrode material Na 0.9 Ni 0.3 Li 0.1 Co 0.1 Mn 0.4 Ti 0.1 1O2 of the present invention includes the following steps:

[0040] (1) Add 0.0189 mmol of sodium acetate, 0.006 mmol of nickel acetate, 0.002 mmol of lithium acetate, 0.002 mmol of cobalt acetate, 0.008 mmol of manganese acetate and 0.002 mmol of titanium dioxide into 50 mL of deionized water together; dissolve 0.03 mmol of citric acid in 50 mL of deionized water, stir at a stirring rate of 800 r / min for 20 min. After the citric acid is completely dissolved, add the citric acid solution to the metal salt solution, continuously stir in a water bath at 80 °C until the solution becomes a gel state, and then dry at 120 °C for 12 h to obtain a precursor;

[0041] (2) Add the precursor into the ball milling beads, and keep the rotation speed constant on the ball mill to ball mill and crush it and mix it evenly; among them, the ball-to-material ratio of the ball milling beads to the precursor is 5:1; the rotation speed of the ball mill is 30 r / min, and the ball milling time is 2 h;

[0042] (3) Place the ball-milled sample in an alumina crucible and perform solid-phase sintering in a muffle furnace. First, heat from room temperature to 500 °C at a heating rate of 3 °C / min, then heat from 500 °C to 680 °C at a heating rate of 1.5 °C / min, and keep it at 680 °C on the heat preservation platform for 2 h; then heat from 680 °C to 900 °C at a heating rate of 1.5 °C / min, and keep it at 900 °C for a reaction of 12 h; after natural cooling, collect it through a 300-mesh sieve to obtain the O3-phase sodium-ion positive electrode material Na 0.9 Ni 0.3 Li 0.1 Co 0.1 Mn 0.4 Ti 0. 1O2.

[0043] Example 3

[0044] The preparation method of the positive electrode material Na 0.9 Ni 0.2 Li 0.1 Mg 0.1 Co 0.1 Mn 0.4 Ti 0.1 1O2 of the present invention includes the following steps:

[0045] (1) Add 0.0189 mmol of sodium acetate, 0.004 mmol of nickel acetate, 0.002 mmol of lithium acetate, 0.002 mmol of magnesium acetate, 0.002 mmol of cobalt acetate, 0.008 mmol of manganese acetate and 0.002 mmol of titanium dioxide into 50 mL of deionized water; dissolve 0.03 mmol of citric acid in 50 mL of deionized water, stir at a stirring rate of 800 r / min for 20 min. After the citric acid is completely dissolved, add the citric acid solution to the metal salt solution, continuously stir in a water bath at 80 °C until the solution becomes a gel state, and then dry at 120 °C for 12 h to obtain a precursor;

[0046] (2) Add the precursor into the ball milling beads, and keep the rotation speed constant on the ball mill to mill and crush it and mix it evenly; among them, the ball-to-material ratio of the ball milling beads to the precursor is 5:1; the rotation speed of the ball mill is 30 r / min, and the ball milling time is 2 h;

[0047] (3) Place the ball-milled sample in an alumina crucible and perform solid-phase sintering in a muffle furnace. First, heat from room temperature to 500 °C at a heating rate of 3 °C / min, then heat from 500 °C to 680 °C at a heating rate of 1.5 °C / min, and keep it at 680 °C on the heat preservation platform for 2 h; then heat from 680 °C to 900 °C at a heating rate of ½ °C / min, and keep it at 900 °C for 12 h for the heat preservation reaction; after natural cooling, collect it through a 300-mesh sieve to obtain the O3-phase sodium-ion cathode material Na 0.9 Ni 0.2 Li 0.1 Mg 0.1 Co 0.1 Mn 0. 4Ti 0.1 O2.

[0048] Example 4

[0049] The preparation method of the cathode material for sodium-ion batteries of the present invention includes the following steps:

[0050] (1) Add 0.0**189 mmol of sodium acetate, 0.004 mmol of nickel acetate, 0.002 mmol of lithium acetate, 0.002 mmol of magnesium acetate, 0.002 mmol of cobalt acetate, 0.007 mmol of manganese acetate and 0.002 mmol of titanium dioxide into 50 mL of deionized water; dissolve 0.03 mmol of citric acid in 50 mL of deionized water, stir at a stirring rate of 800 r / min for 20 min. After the citric acid is completely dissolved, add the citric acid solution to the metal salt solution, continuously stir in a water bath at 80 °C until the solution becomes a gel state, and then dry at 120 °C for 12 h to obtain a precursor;

[0051] It should be noted that there seems to be a small error in the original text where "½ °C / min" is written as "1.5 °C / min" in step (3) of the second part. I have translated it as per the original text. Also, the "0.0**189 mmol" in step (31) might be a typo in the original, but I've translated it as presented.(2) Add the precursor to the ball milling beads, and ball mill and crush it at a constant speed on a ball mill to achieve full and uniform mixing; among them, the ball-to-material ratio of the ball milling beads to the precursor is 5:1; the rotation speed of the ball mill is 30 r / min, and the ball milling time is 2 h;

[0052] (3) Place the ball-milled sample in an alumina crucible and perform solid-phase sintering in a muffle furnace. First, heat from room temperature to 500 °C at a heating rate of 3 °C / min, then heat from 500 °C to 680 °C at a heating rate of 1.5 °C / min, and hold for 2 h on the 680 °C holding platform; then heat from 680 °C to 900 °C at a heating rate of 1.5 °C / min, and hold for 12 h at 900 °C for the reaction; after natural cooling, collect through a 300-mesh sieve to obtain the O3-phase sodium-ion cathode material

[0053] Example 5

[0054] The preparation method of the cathode material for sodium-ion batteries of the present invention comprises the following steps:

[0055] (1) Add 0.0189 mmol of sodium acetate, 0.004 mmol of nickel acetate, 0.002 mmol of lithium acetate, 0.002 mmol of magnesium acetate, 0.002 mmol of cobalt acetate, 0.006 mmol of manganese acetate, and 0.002 mmol of titanium dioxide into 50 mL of deionized water; dissolve 0.03 mmol of citric acid in 50 mL of deionized water, stir at a stirring rate of 800 r / min for 20 min, and after the citric acid is completely dissolved, add the citric acid solution to the metal salt solution, continuously stir in a water bath at 80 °C until the solution becomes gel-like, and then dry at 120 °C for 12 h to obtain the precursor;

[0056] (2) Add the precursor to the ball milling beads, and ball mill and crush it at a constant speed on a ball mill to achieve full and uniform mixing; among them, the ball-to-material ratio of the ball milling beads to the precursor is 5:1; the rotation speed of the ball mill is 30 r / min, and the ball milling time is 2 h;

[0057] (3) Place the ball-milled sample in an alumina crucible and perform solid-phase sintering in a muffle furnace. First, heat from room temperature to 500 °C at a heating rate of 3 °C / min, then heat from 500 °C to 680 °C at a heating rate of 1.5 °C / min, and hold for 2 h on the 680 °C holding platform; then heat from 680 °C to 900 °C at a heating rate of 1.5 °C / min, and hold for 12 h at 900 °C for the reaction; after natural cooling, collect through a 300-mesh sieve to obtain the O3-phase sodium-ion cathode material

[0058] Example 6

[0059] Preparation method of cathode material for sodium-ion battery of the present invention comprises the following steps:

[0060] (1) Add 0.0189 mmol of sodium acetate, 0.005 mmol of nickel acetate, 0.001 mmol of lithium acetate, 0.002 mmol of magnesium acetate, 0.002 mmol of cobalt acetate, 0.007 mmol of manganese acetate and 0.002 mmol of titanium dioxide into 50 mL of deionized water together; dissolve 0.03 mmol of citric acid in 50 mL of deionized water, stir at a stirring rate of 800 r / min for 20 min. After the citric acid is completely dissolved, add the citric acid solution into the metal salt solution, continuously stir in a water bath at 80 °C until the solution becomes a gel state, and then dry at 120 °C for 12 h to obtain a precursor;

[0061] (2) Add the precursor into the ball milling beads, and keep the speed constant on the ball mill to mill and crush it and mix it evenly; wherein, the ball-to-material ratio of the ball milling beads to the precursor is 5:1; the rotation speed of the ball mill is 30 r / min, and the ball milling time is 2 h;

[0062] (3) Place the ball-milled sample in an alumina crucible, and perform solid-phase sintering in a muffle furnace. First, heat from room temperature to 500 °C at a heating rate of 3 °C / min, then heat from 500 °C to 680 °C at a heating rate of 1.5 °C / min, and keep it at 680 °C on the heat preservation platform for 2 h; then heat from 680 °C to 900 °C at a heating rate of 1.5 °C / min, and keep it at 900 °C for a reaction of 12 h; after natural cooling, collect it through a 300-mesh sieve to obtain an O3-phase sodium-ion cathode material

[0063] Example 7

[0064] Preparation method of cathode material for sodium-ion battery of the present invention comprises the following steps:

[0065] (1) Add 0.0189 mmol of sodium acetate, 0.004 mmol of nickel acetate, 0.002 mmol of lithium acetate, 0.002 mmol of magnesium acetate, 0.002 mmol of cobalt acetate, 0.007 mmol of manganese acetate and 0.002 mmol of titanium dioxide into 50 mL of deionized water together; dissolve 0.03 mmol of citric acid in 50 mL of deionized water, stir at a stirring rate of 800 r / min for 20 min. After the citric acid is completely dissolved, add the citric acid solution into the metal salt solution, continuously stir in a water bath at 80 °C until the solution becomes a gel state, and then dry at 120 °C for 12 h to obtain a precursor;

[0066] (2) Add the precursor into the ball milling beads, and ball mill and crush it at a constant speed on the ball mill to fully and evenly mix; wherein, the ball-to-material ratio of the ball milling beads to the precursor is 5:1; the rotation speed of the ball mill is 30 r / min, and the ball milling time is 2 h;

[0067] (3) Place the ball milled sample in an alumina crucible and perform solid-phase sintering in a muffle furnace. Heat from room temperature to 900 °C at a heating rate of 3 °C / min, hold for reaction for 12 h; after natural cooling, collect by passing through a 300-mesh sieve to obtain the O3-phase sodium ion cathode material.

[0068] Assemble and test the sodium ion cathode materials obtained in Examples 1-7 and Comparative Example 1 as follows: Dry the cathode material at 120 °C for 12 h, and then uniformly mix it with the conductive agent and binder for 4 h to obtain a slurry. The mass ratio of the conductive agent: binder: cathode material is 1:1:8. Uniformly coat the prepared slurry on the aluminum foil, then dry, press, and cut it into electrode sheets, and assemble it into a coin cell with a sodium sheet, a glass fiber separator, an electrolyte, etc. in a glove box under an inert atmosphere (such as argon). Perform capacity testing (2.0 - 4.3 V or 2.0 - 4.5 V, 0.1C / 0.1C) and cycle testing (2.0 - 4.5 V, 1C / 1C) on the assembled coin cells, and the obtained results are as Figures 4 to 10 shown.

[0069] Through Figure 1 and Figure 2 it can be known that for the XRD refinement test of the material in Example 4, its data graph shows a good O3-phase peak fitting and a pure phase structure. And by drawing the structure of the refined XRD data of the materials in Example 1 and Example 4, it can be seen that the sodium ion diffusion channel becomes wider after modification. Figure 3 Figure 17 is the scanning electron microscope image of the material in Example 4. Its particles are polygonal, and the particle size is between 4 - 6 μm, with good dispersion.

[0070] Through Figure 4 the charge-discharge curve, it can be known that for the material in Example 1, the multi-platform phase transformation is inhibited at a high voltage of 4.3 V, and the capacity is well exerted. The 0.1C discharge capacity is 149.7 mAh / g. Through Figure 5 the charge-discharge curve, it can be known that for the material in Example 2, the multi-platform phase transformation is inhibited at a high voltage of 4.3 V, and the capacity is well exerted. The 0.1C discharge capacity is 145.9 mAh / g. Through Figure 6 the charge-discharge curve, it can be known that for the material in Example 4, the multi-platform phase transformation is inhibited at a high voltage of 4.5 V, and the capacity is well exerted. Further perform 1C and 3C cycle performance tests (such as Figure 9 and Figure 10As shown, for 150 cycles at 1C, the capacity retention rate of the material in Example 4 is 77.6%, while that of the material in Comparative Example 1 is only 38.4%; for 350 cycles at 3C, the capacity retention rate of the material in Example 4 is 58.5%, while the capacity of the material in Comparative Example 1 has almost decayed completely.

[0071] From Figure 8 the rate performance curve, it can be seen that for the material in Example 4, at an ultra-high voltage of 4.5V, the rate performance is maintained well. After cycling at a rate of 0.1C, it drops from 178.3 mAh / g to 173.9 mAh / g, and there is still 79 mAh / g at a rate of 10C. For the material in Comparative Example 1, after cycling at a rate of 0.1C, it drops from 179.3 mAh / g to 118.8 mAh / g, and there is only 8 mAh / g at a rate of 10C. Therefore, the rate performance of the positive electrode material prepared by the present invention has been significantly improved. From Figure 7 the charge-discharge curve, it can be seen that for the material in Example 5, at a high voltage of 4.5V, the multi-platform phase change is suppressed, and the capacity is well exerted. The discharge capacity at 0.1C is 167.8 mAh / g.

[0072] By comparing Example 4 and Example 6, the doping ratio of Li and Ni was adjusted and its electrical properties were tested. The voltage window was 2 - 4.5V, and the discharge specific capacities were 178.3 mAh / g and 168.8 mAh / g respectively. The capacity decreased slightly, and the cycle performance showed a relatively obvious decline. After 150 cycles at 1C, the 1C capacity retention rate decreased from 77.6% to 68.2%. By comparing Example 4 and Example 7, the platform of holding at 680°C for 2h was cancelled and the performance of the battery was tested. The voltage window was 2 - 4.5V, and the discharge specific capacities were 178.3 mAh / g and 176.8 mAh / g respectively. The capacity decreased slightly, and the cycle performance showed a certain degree of decline. After 150 cycles at 1C, the 1C capacity retention rate decreased from 77.6% to 72.4%, indicating that the setting of the holding platform is beneficial to the exertion of the electrical properties of the material; while for Example 4, after 150 cycles at 1C, the 1C capacity retention rate remained at about 77.6%.

Claims

1. A cathode material for an ultra-high voltage O3-phase sodium-ion battery, characterized in that, Its chemical formula is: Na 0.9 Ni 0.5- x A x Mn 0.5-y-z B y □ z O2, where 0.1 ≤ x ≤ 0.3; 0.1 ≤ y + z ≤ 0.2, 0 ≤ z ≤ 0.1; the types of metal elements doped at the A doping site and the B doping site are different; □ represents a transition metal vacancy.

2. The cathode material for an ultra-high voltage O3-phase sodium ion battery according to claim 1, wherein: The metal element doped at the A doping site is at least one of Li, Mg, or Co; the metal element doped at the B doping site is Ti.

3. The cathode material for an ultra-high voltage O3-phase sodium-ion battery according to claim 2, wherein: When more than two metal elements are doped at the A doping site, the doping amount of each metal element relative to Ni is 10-20%.

4. The preparation method of the ultra-high voltage O3-phase sodium ion battery cathode material according to claim 1, characterized in that, It includes the following steps: (1) According to the stoichiometric ratio, mix the sodium source, nickel source, manganese source, soluble salt of the metal corresponding to the A doping site, oxide of the metal corresponding to the B doping site, and citric acid in water, ultrasonic dissolve and continuously stir at high temperature until a wet gel is formed; (2) Dry the wet gel to obtain a precursor; ball mill the obtained precursor and calcine it by a segmented heat treatment method to obtain a positive electrode material for an ultra-high voltage O3-phase sodium ion battery.

5. The preparation method according to claim 4, characterized in that: In step (1), the sodium source is sodium acetate or sodium carbonate; the nickel source is nickel acetate or nickel nitrate; the manganese source is manganese acetate or manganese carbonate; the soluble salt is one of acetate, carbonate, or nitrate.

6. The preparation method according to claim 4, characterized in that: In step (1), the molar amount of citric acid added is 1.5-2 times the total molar amount of metal cations.

7. The preparation method according to claim 4, characterized in that: In step (1), the stirring temperature is 80-90 °C; the stirring rate is 1000-2000 r / min; the reaction time is 4-6 h.

8. The preparation method according to claim 4, characterized in that: In step (2), the drying temperature is 100-120 °C and the drying time is 10-12 h.

9. The preparation method according to claim 4, characterized in that: In step (2), the ball-to-material ratio during the ball milling process is 5:1-1.5; the rotation speed of the ball mill is 30-40 r / min, and the ball milling time is 2-4 h.

10. The preparation method according to claim 4, characterized in that: In step (2), the calcination by the segmented heat treatment method is specifically as follows: first heat up from room temperature to 450-500 °C, then heat up from 450-500 °C to 600-700 °C, keep warm at 600-700 °C for 2-4 h, and finally heat up from 600-700 °C to not less than 900 °C and keep warm at not less than 900 °C for 12-14 h.

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