A sodium ion battery single crystal positive electrode active material and its preparation method and application

Abstract

The present invention belongs to the technical field of sodium ion batteries, and particularly relates to a Na x Ni a Fe b Mn c Cu d M 1‑a‑b‑c‑d O2 single crystal active material, 0.5

Description

Technical Field

[0001] The invention belongs to the field of sodium ion secondary batteries, and in particular relates to the technical field of positive electrode active materials for sodium ion batteries. Technical Background

[0002] Lithium-ion batteries are currently the most widely used batteries in commercial applications. However, with the increasing demand and the scarcity and uneven distribution of lithium resources, their production costs are also soaring year by year, so it is inevitable to seek new alternative energy storage devices. Sodium and lithium are in adjacent positions in the same main group in the periodic table and have similar physical and chemical properties. Compared with lithium, sodium reserves are abundant, widespread and cheap, making the use of sodium-ion batteries a possibility in the future.

[0003] In the research of sodium-ion batteries, the positive electrode is constrained by factors such as cycle life and capacity, and is a key research material for its development. At present, the positive electrode materials of sodium-ion batteries include oxides, polyanions, Prussian blue and organic materials. Among them, layered oxide positive electrode materials are most likely to follow the production process of lithium-ion batteries and achieve rapid commercialization due to their relatively high energy density, wide range of raw material selectivity, and multiple synthesis processes.

[0004] The crystal structure of layered oxide cathode materials consists of alternating alkali metal layers and transition metal layers. During the electrochemical cycle, the valence state of alkali metal elements changes due to the extraction / embedding of sodium ions, which causes some transition metal atoms to distort and slide toward the alkali metal layer, blocking the sodium ion transmission channel and causing the layered structure of the crystal to collapse. In addition, the repeated extraction / embedding of sodium ions and the accompanying changes in the valence state of transition metals will cause the unit cell parameters of the layered oxide crystal structure to expand and contract periodically. The huge stress changes caused by lattice strain will cause intercrystalline fragmentation of the material, aggravating the erosion of the layered oxide material by the electrolyte, and causing the electrochemical performance of the cathode material to decline rapidly. In addition, oxide cathode materials also have serious air stability problems, which makes the materials face great difficulties in application.

[0005] In order to solve the problem of structural collapse and poor air stability caused by transition metal migration in the electrochemical process, the main improvement methods are to introduce heteroatoms and construct interface protection layers, but both only alleviate the rate of material deterioration to a certain extent, and the introduction of inactive elements and interface protection layers will reduce the overall specific capacity of the material; in order to alleviate the material intercrystalline fragmentation and lattice cracks caused by huge stress under high voltage and the side reaction of electrolyte corrosion to the material, the current main improvement measure is to use single-particle positive electrode materials, but large-sized particles increase the ion migration path and reduce the rate performance. Therefore, how to design a high-performance sodium ion battery layered oxide positive electrode material that can alleviate lattice stress under high voltage and inhibit transition metal migration while taking into account excellent air stability requires further research. Summary of the invention

[0006] Aiming at the problems of unsatisfactory air stability and electrochemical performance of existing cathode materials for sodium-ion batteries, the first object of the present invention is to provide a Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 single-crystal active material, aiming to provide a new cathode active material with single particles, excellent air stability and electrochemical performance.

[0007] The second object of the present invention is to provide a preparation method of the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 single-crystal active material, aiming to solve the preparation problems such as hetero-phase formation and difficulty in inducing single-crystal formation in the preparation of the new material, and improve the performance of the prepared material.

[0008] The third object of the present invention is to provide the application of the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 single-crystal active material in the preparation of sodium-ion batteries.

[0009] The fourth object of the present invention is to provide a sodium-ion battery containing the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 single-crystal active material, its negative electrode and negative electrode material.

[0010] A Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 single-crystal active material, wherein 0.5 < x ≤ 1.1, 0 < a ≤ 0.8, 0 < b ≤ 0.8, 0 < c ≤ 0.8, 0 < d ≤ 0.5, and M is at least one of the elements B, Ti, Mg, Li, Al, Zn, Co, Nb, W, Mo, Zr.

[0011] The present invention provides a new Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The single crystal active material of the chemical formula has been found to have excellent mechanical properties, which is conducive to the formation of high-density electrode materials. Not only that, it is beneficial to alleviate lattice stress under high voltage and inhibit transition metal migration, reduce intercrystalline crushing and electrolyte side reactions in the cycle stage, and has excellent rate and energy density performance; not only that, it also has excellent air resistance stability and electrochemical stability under air storage.

[0012] The combination of the special chemical formula material and the single crystal structure of the new material described in the present invention is the key to synergistically giving the material excellent rate, air stability and electrochemical performance.

[0013] Preferably, x is 0.8 to 1.1, a is 0.1 to 0.8, b is 0.01 to 0.6, c is 0.01 to 0.7, and d is 0.01 to 0.6;

[0014] More preferably, x is 0.95 to 1.05, a is 0.2 to 0.8, b is 0.01 to 0.5, c is 0.05 to 0.6, and d is 0.01 to 0.5.

[0015] More preferably, x is 0.95 to 1.05, a is 0.3 to 0.8, b is 0.01 to 0.3, c is 0.1 to 0.5, and d is 0.01 to 0.2.

[0016] Preferably, the M comprises Mg; more preferably, the M further comprises at least one of zinc, Li and Ti. In the present invention, the preferred M can further improve the air resistance stability and cycle retention rate of the material under air.

[0017] The Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The crystal structure belongs to a layered structure in which sodium ion layers and transition metals exist alternately. According to the coordination environment of sodium and oxygen, their positions include triangular prism positions and octahedral positions.

[0018] Preferably, the Na x Ni a Fe b Mn c Cud M 1-a-b-c-d O 2 The D50 of the single crystalline active material is greater than or equal to 4 microns.

[0019] In the present invention, it is also attempted to provide the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The preparation method of single crystal active material, but in the early stage of technology development, there are often problems such as easy formation of preparation impurities, difficulty in forming single crystals, and unsatisfactory performance of the prepared material, especially the cycle stability under air. In view of the preparation difficulties of the new material described in the present invention, the inventors have conducted in-depth research and provide the following improvement scheme:

[0020] A kind of Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The method for preparing a single crystal active material comprises the steps of: performing a first stage roasting of a mixture comprising a Na source, a Ni source, a Fe source, a Mn source, a Cu source, an M source and a single crystal additive, and performing a second stage roasting after washing to obtain the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials;

[0021] The single crystal auxiliary agent is at least one of sodium borate, hydroxide, carbonate, organic acid salt, sulfate, nitrate and chloride;

[0022] The temperature of the first stage of calcination is 700-1200°C, and the temperature of the second stage of calcination is 500-900°C.

[0023] In view of the difficulties faced in the preparation of the new materials described in the present invention, the present invention innovatively further cooperates with single crystal additives and a two-stage roasting mechanism and temperature under the control of the raw material combination, so as to achieve synergy, effectively solve the problem of preparing impure phases, reduce the problem of crystal structure collapse, help induce single crystal formation, and facilitate obtaining high-purity single crystal new materials. Not only that, it also helps to significantly improve the electrochemical properties of the prepared materials, especially the rate, air resistance stability and capacity retention rate in air.

[0024] In the present invention, the combination of the chemical raw materials, the single crystal additive and the two-stage roasting process is the key to synergistically reducing the preparation of impurities, inducing single crystal formation, and improving the rate, energy stability, air resistance stability and cyclic stability under air storage of the prepared material.

[0025] Preferably, the Na source, Ni source, Fe source, Mn source, Cu source, and M source are at least one of the hydroxides, carbonates, bicarbonates, oxides, sulfates, nitrates, and organic acid salts of the respective metals. In the present invention, the organic acid salt is, for example, a C2-C6 1-3-membered carboxylate, and may further be an acetate.

[0026] Preferably, the Na source is at least one of sodium carbonate, sodium bicarbonate and sodium hydroxide.

[0027] More preferably, the Na source is sodium carbonate and sodium hydroxide. The present invention unexpectedly found that using sodium carbonate and sodium hydroxide as a composite Na source can unexpectedly further synergistically improve the pure phase, single crystal structure, air resistance stability and electrochemical performance of the prepared material.

[0028] In the present invention, among the raw materials, the Ni source, Fe source, Mn source, Cu source and M source are prepared according to the stoichiometric ratio, and the Na source can be greater than or equal to 0.5x, preferably 1 to 1.1x.

[0029] In the present invention, the raw materials are combined with the single crystal additive and the two-stage roasting process to synergistically improve the preparation of the new material impurities, induce single crystal formation, and improve the key to material performance.

[0030] Preferably, the single crystal auxiliary agent comprises one or more of sodium borate, sodium hydroxide, sodium carbonate, sodium acetate, sodium sulfate, sodium nitrate and sodium chloride;

[0031] Preferably, the single crystal auxiliary agent comprises two or more of sodium borate, sodium hydroxide and sodium chloride;

[0032] Further preferably, the single crystal additive comprises sodium borate, sodium hydroxide and sodium chloride;

[0033] More preferably, the single crystal additive is a mixture of sodium borate, sodium hydroxide and sodium chloride in a molar ratio of 0.1 to 0.5: 1 to 2: 1 to 2. The present invention also found that under the single crystal additive combination, a synergistic effect can be unexpectedly formed, which can further facilitate the pure phase of the new material and the induced formation of single crystals. Not only that, it can also synergistically improve the electrochemical properties of the material, especially its air resistance.

[0034] Preferably, in the mixture, the molar ratio of Na in the single crystal additive to the total molar ratio of (Ni-Fe-Mn-Cu-M) is 1 to 6:1; preferably 2 to 4:1.

[0035] Preferably, the mixed material is obtained by wet ball milling-drying method;

[0036] Preferably, the solvent for wet ball milling is one of water, ethanol and ether;

[0037] Preferably, the rotation speed of the wet ball mill is 80-800 r / min, and the ball milling time is 2-20 h.

[0038] Preferably, the first stage calcination and the second stage calcination are carried out in an oxygen-containing atmosphere; the oxygen-containing atmosphere is at least one of air, an oxygen-nitrogen mixed gas, and an oxygen-inert gas mixed gas;

[0039] Preferably, the heating rates of the first and second stage roasting are 0.5-5°C / min.

[0040] In the present invention, further joint control of the temperatures of the two-stage roasting is helpful for further coordination with other processes and for further improving the performance of the prepared material.

[0041] Preferably, the temperature of the first stage calcination is 900-1000°C;

[0042] Preferably, the first stage of roasting is 10-30 hours, preferably 15-20 hours;

[0043] Preferably, the first stage of roasting is followed by pre-cooling, washing and drying before the second stage of roasting; the cooling is, for example, furnace cooling, the washing is, for example, water washing, and the drying is normal pressure or negative pressure drying.

[0044] Preferably, the washing solvent is one or more of water and C1-C4 alcohol;

[0045] Preferably, the temperature of the second stage calcination is 500-750°C, more preferably 650-750°C;

[0046] Preferably, the second calcination time is 4 to 6 hours.

[0047] The preferred preparation process of the new material of the present invention includes:

[0048] 1) Adding sodium source, Ni source, Fe source, Mn source, Cu source, M source and single crystal additive into a ball mill, and adding dispersion medium at the same time, obtaining a uniform slurry of raw material mixture by wet ball milling, and then obtaining a precursor by ball-material separation and drying procedures;

[0049] 2) performing a first stage sintering of the precursor in an atmosphere of air or oxygen to obtain material A after sintering; adding material A to a cleaning solvent and washing it multiple times to remove the residual single crystal additive therein to obtain material B;

[0050] 3) Material B is sintered again in air or oxygen atmosphere for a second time to obtain Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal material.

[0051] The present invention also provides Na prepared by the preparation method x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The preparation method of the present invention can prepare a new material with completely new characteristics, and the new material has excellent rate, energy density, cycle stability and air resistance stability.

[0052] The present invention also provides the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The application of single crystal active materials is to use them as positive electrode active materials for the preparation of sodium ion batteries and their positive electrodes and positive electrode materials.

[0053] In the present invention, the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials are prepared to form the required sodium ion batteries and their components.

[0054] The present invention also provides a sodium ion battery positive electrode, comprising the Na x Ni a Fe b Mn c Cu d M 1-a-b-c- d O 2 Single crystal active material.

[0055] The positive electrode, in addition to comprising the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Except for the single crystal active material, other components and materials can be well known. For example, the positive electrode includes a current collector and a positive electrode material composited on its surface. The positive electrode material includes the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials;

[0056] Preferably, the positive electrode material further comprises a conductive agent and a binder;

[0057] Preferably, in the positive electrode material, the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The content of the single crystal active material is 70-90 wt / %; the content of the conductive agent is less than or equal to 10 wt / %; and the content of the binder is less than or equal to 10 wt / %.

[0058] The present invention also provides a sodium ion battery, comprising the novel Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active material for positive electrode.

[0059] The sodium ion battery of the present invention comprises the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Except for the single crystal active material, other components and structures may be known.

[0060] Beneficial Effects

[0061] 1. The present invention provides a new Na x Ni a Feb Mn c Cu d M 1-a-b-c-d O 2 The single crystal active material of the chemical formula has been found to have excellent mechanical properties, which is conducive to the formation of high-density electrode materials. Not only that, it is beneficial to alleviate lattice stress under high voltage and inhibit transition metal migration, reduce intercrystalline crushing and electrolyte side reactions in the cycle stage, and has excellent rate and energy density performance; not only that, it also has excellent air resistance stability and electrochemical stability under air storage.

[0062] 2. The present invention also provides the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The preparation method of single crystal active material, thanks to the combination of the combined raw materials, single crystal additives and two-stage roasting process, can solve the preparation problems faced by the preparation process of the new material, such as impurities and difficulty in forming single crystals, and can prepare new materials with high performance, especially high rate and air resistance stability.

[0063] On this basis, further coordination of sodium source, single crystal additive and two-stage calcination mechanism can further synergistically improve the various properties of the prepared materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a scanning electron microscope image of the single crystal sodium ion battery layered oxide positive electrode material in Example 1 of the present invention;

[0065] Figure 2 This is a scanning electron microscope image of the single crystal sodium ion battery layered oxide positive electrode material in Group A of Example 2 of the present invention;

[0066] Figure 3 This is a scanning electron microscope image of the single crystal sodium ion battery layered oxide positive electrode material in Group 3A of Example 3 of the present invention;

[0067] Figure 4 This is a charge and discharge curve diagram of the battery assembled with the layered oxide positive electrode material of the single crystal sodium ion battery in Group B of Example 3 of the present invention.

[0068] Figure 5 This is a scanning electron microscope image of the single crystal sodium ion battery layered oxide positive electrode material in Group A of Example 4 of the present invention;

[0069] Figure 6 This is a long cycle diagram of the single crystal sodium ion battery layered oxide positive electrode material in Group B of Example 5 of the present invention after assembling the battery. DETAILED DESCRIPTION

[0070] Example 1

[0071] (1) The raw materials used in this example are all analytically pure. Sodium carbonate (Na source), nickel oxide (Ni source), iron oxide (Fe source), manganese oxide (Mn source), cuprous oxide (Cu source), magnesium oxide (Mg source), and zinc oxide (Zn source) are mixed according to the molar ratio of Na, Ni, Fe, Mn, Cu, Mg, and Zn of 1:0.30:0.05:0.50:0.05:0.05:0.05 (a total of 500 g in this case), and then a single crystal additive (containing a molar ratio of 1:1:0 .2 of sodium chloride, sodium hydroxide, sodium borate), the molar ratio of Na as the single crystal additive to the total metal of the raw materials (calculated as the total molar amount of Ni, Fe, Mn, Cu, M (Mg-Zn in this case)) is 3:1 (the total amount in this case is 668g), and then 500mL of ethanol solution is added and stirred to form a paste slurry, which is then ball-milled for 8h at a speed of 400r / min. After ball-milling, it is baked at 80°C for 8h, and the ball mill beads are separated to obtain a precursor.

[0072] (2) The precursor was placed in an air atmosphere and heated to 900°C at a rate of 3°C / min (marked as T1 segment) and kept at this temperature for 20 hours, and then naturally cooled to room temperature in an air atmosphere to obtain material A.

[0073] (3) Grind material A into powder, wash with deionized water to remove residual single crystal additive, and dry the solid material after solid-liquid separation to obtain material B.

[0074] (4) Material B was placed in an air atmosphere and heated to 700°C at a rate of 5°C / min (marked as T2 segment) and kept at this temperature for 5 h, and then naturally cooled to room temperature in an air atmosphere to obtain NaNi 0.30 Fe 0.05 Mn 0.50 Cu 0.05 Mg 0.05 Zn 0.0 5 O 2 Single crystal layered oxide positive electrode material.

[0075] Example 2

[0076] Compared with Example 1, the only difference is that the type of Na source is changed, which are:

[0077] Group A: The Na source was sodium hydroxide, and other operations and parameters were the same as those in Example 1.

[0078] Group B: The Na source is a complex of sodium carbonate and sodium hydroxide in a molar ratio of 1:8, and other operations and parameters are the same as in Example 1.

[0079] Example 3

[0080] Compared with Example 1, the only difference is that the raw materials of step (1) are changed, which are: Group A: Compared with Example 1, the raw materials in step (1) are replaced by sodium carbonate (Na source), nickel oxide (Ni source), iron oxide (Fe source), manganese oxide (Mn source), cuprous oxide (Cu source), and titanium dioxide (Ti source) in a molar ratio of Na, Ni, Fe, Mn, Cu, and Ti of 1:0.30:0.05:0.50:0.05:0.10, and the other steps remain unchanged.

[0081] Group B: Compared with Example 1, the raw materials in step (1) are replaced by sodium carbonate (Na source), nickel oxide (Ni source), iron oxide (Fe source), manganese oxide (Mn source), cuprous oxide (Cu source), and aluminum oxide (aluminum source), and the molar ratio of Na, Ni, Fe, Mn, Cu, and Al elements is 1:0.30:0.30:0.30:0.05:0.05, and the other steps remain unchanged.

[0082] Group C: Compared with Example 1, the raw materials in step (1) are replaced by sodium carbonate (Na source), nickel oxide (Ni source), iron oxide (Fe source), manganese oxide (Mn source), cuprous oxide (Cu source), magnesium oxide (Mg source), and zinc oxide (Zn source), according to the molar ratio of Na, Ni, Fe, Mn, Cu, Mg, and Zn elements of 1:0.80:0.02:0.10:0.02:0.03:0.03, and the other steps remain unchanged.

[0083] Example 4

[0084] Compared with Example 1, the only difference is that the single crystal additives in step (1) are changed to:

[0085] Compared with Example 1, in Group A, the single crystal auxiliary agent in step (1) is replaced by sodium hydroxide alone, and the other steps remain unchanged.

[0086] Compared with Example 1, in Group B, the single crystal auxiliary agent in step (1) is replaced by sodium chloride and sodium hydroxide in a molar ratio of 1:1, and the other steps remain unchanged.

[0087] Compared with Example 1, in Group C, the single crystal auxiliary agent in step (1) is replaced by sodium chloride, sodium hydroxide and sodium borate in a molar ratio of 1:1:0.5, and the other steps remain unchanged.

[0088] Example 5

[0089] Compared with Example 1, the only difference is that the temperatures of T1 and T2 are changed to:

[0090] Compared with Example 1, in Group A, T1 in step (2) is replaced by 1000°C, T2 is replaced by 500°C, and the other steps remain unchanged.

[0091] Compared with Example 1, in Group B, T1 in step (2) is replaced by 1200°C, T2 is replaced by 900°C, and the other steps remain unchanged.

[0092] Compared with Example 1, in Group C, T1 in step (2) is replaced by 900°C; T2 is replaced by 600°C, and the other steps remain unchanged.

[0093] Comparative Example 1

[0094] Compared with Example 1, the only difference is that the Cu and M sources are missing. For example, the raw materials in step (1) are replaced by sodium carbonate (Na source), nickel oxide (Ni source), iron oxide (Fe source), and manganese oxide (Mn source), according to the molar ratio of Na, Ni, Fe, and Mn elements being 1:0.30:0.20:0.50, and the other steps remain unchanged.

[0095] Comparative Example 2

[0096] Compared with Example 1, the only difference is that the M source is missing. For example, the raw materials in step (1) are replaced by sodium carbonate (Na source), nickel oxide (Ni source), iron oxide (Fe source), manganese oxide (Mn source), and cuprous oxide (Cu source), and the molar ratio of Na, Ni, Fe, Mn, and Cu elements is 1:0.30:0.05:0.50:0.15, and the other steps remain unchanged.

[0097] Comparative Example 3

[0098] Compared with Example 1, the only difference is that V is used to replace the Mg and Zn. For example, the raw materials in step (1) are replaced by sodium carbonate (Na source), nickel oxide (Ni source), iron oxide (Fe source), manganese oxide (Mn source), cuprous oxide (Cu source), and vanadium pentoxide (V source), and the molar ratio of Na, Ni, Fe, Mn, Cu, and V elements is 1:0.30:0.05:0.5:0.05:0.10, and the other steps remain unchanged.

[0099] Comparative Example 4

[0100] Compared with Example 1, no single crystal additive is added in step (1), and the other steps remain unchanged.

[0101] Comparative Example 5

[0102] Compared with Example 1, the single crystal additive in step (1) is replaced by LiCl and LiNO in a ratio of 1:1. 3 The molar ratio of lithium content in the single crystal to the total transition metal content in the raw materials is 3:1, and the other steps remain unchanged.

[0103] Comparative Example 6

[0104] Compared with Example 1, T1 in step (2) is replaced by 650° C., and the other steps remain unchanged.

[0105] Comparative Example 7

[0106] Compared with Example 1, the material is obtained directly after the first stage sintering without performing the second stage sintering in step (4).

[0107] The main test steps are:

[0108] (1) The layered oxide positive electrode material obtained in the above examples and comparative examples was used as the positive electrode active material, the active material was mixed with conductive carbon (acetylene black) and binder (PVDF) in a mass ratio of 8:1:1, and an aluminum foil was used as a current collector to prepare a positive electrode, and glass fiber was used as a separator, a homemade metal sodium sheet was used as a negative electrode, and 1M NaClO 4 The PC solution was used as the electrolyte to prepare a 2032-type button battery.

[0109] (2) The assembled battery was placed at a constant temperature of 25°C for 10 h, and then subjected to an electrochemical test procedure of charging first and then discharging.

[0110] (3) The test voltage range is set to low voltage test (2.0-4.0V) and high voltage test (2.0-4.3V). The first three cycles are 0.05C activation steps, followed by 0.1C long cycle stability test. The number of long cycle cycles is set to 100, and the theoretical capacity is 170mAh / g.

[0111] The temperature of the storage process under air is room temperature, and the air humidity is 10-35RH%.

[0112] (4) The test results are shown in Table 1:

[0113] Table 1 Electrochemical test results

[0114]

[0115] In summary, the process of the present invention is used to obtain excellent electrochemical properties, especially excellent air-resistant electrochemical stability. In addition, by comparing Example 1 with Example 2, the combined sodium source used can obtain better electrochemical properties and air-resistant stability. By comparing Example 1 with Example 3, the use of Mg-Zn as the M source helps to further synergistically improve the electrochemical properties and air-resistant stability of the prepared material. Not only that, by comparing Example 1 with Example 4, it can be seen that the use of a single crystal auxiliary agent with a special composition can further synergistically improve the electrochemical properties and air-resistant stability of the product.

Claims

1. A Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials, It is characterized in that 0.5 < x ≤ 1.1, 0 < a ≤ 0.8, 0 < b ≤ 0.8, 0 < c ≤ 0.8, 0 < d ≤ 0.5, and M is at least one of the elements B, Ti, Mg, Li, Al, Zn, Co, Nb, W, Mo, and Zr; The Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The single crystal active material is prepared by the following steps: a mixture containing a Na source, a Ni source, a Fe source, a Mn source, a Cu source, an M source and a single crystal additive is subjected to a first stage of roasting, and then subjected to a second stage of roasting after washing to obtain the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials; The single crystal auxiliary agent is at least one of sodium borate, hydroxide, carbonate, organic acid salt, sulfate, nitrate and chloride; the organic acid salt is C 2 ~C 6 1-3 membered carboxylates; The temperature of the first-stage roasting is 700 - 1200 °C, and the temperature of the second-stage roasting is 500 - 900 °C.

2. Na as claimed in claim 1 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials, It is characterized in that x is 0.8 - 1.1, a is 0.1 - 0.8, b is 0.01 - 0.6, c is 0.01 - 0.7, and d is 0.01 - 0.

6.

3. Na as claimed in claim 1 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials, It is characterized in that x is 0.95 - 1.05, a is 0.2 - 0.8; b is 0.01 - 0.5; c is 0.05 - 0.6; d is 0.01 - 0.

5.

4. Na as claimed in claim 1 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials, It is characterized in that The described M contains Mg.

5. Na as claimed in claim 4 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials, It is characterized in that The described M further contains at least one of zinc, Li, and Ti.

6. Na as claimed in claim 1 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials, It is characterized in that The Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The single crystal active material is a single crystal material with a layered structure in which large-grained sodium ion layers and transition metal layers exist alternately in sequence; according to the coordination environment of sodium and oxygen, its position includes a triangular prism position and an octahedral position.

7. Na as claimed in claim 1 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials, It is characterized in that The Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The D50 of the single crystalline active material is greater than or equal to 4 microns.

8. A Na according to any one of claims 1 to 7 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The mixed material including Na source, Ni source, Fe source, Mn source, Cu source, M source and single crystal additive is subjected to a first stage of calcination, and then subjected to a second stage of calcination after washing to obtain the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active materials; The single-crystal promoter is at least one of sodium borate, hydroxide, carbonate, organic acid salt, sulfate, nitrate, and chloride; The temperature of the first-stage roasting is 700 - 1200 °C, and the temperature of the second-stage roasting is 500 - 900 °C.

9. Na as claimed in claim 8 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The described Na source, Ni source, Fe source, Mn source, Cu source, and M source are at least one of the hydroxides, carbonates, bicarbonates, oxides, sulfates, nitrates, and organic acid salts of their respective metals.

10. Na as claimed in claim 9 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The described Na source is at least one of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

11. Na as claimed in claim 10 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The described Na source is sodium carbonate and sodium hydroxide.

12. Na as claimed in claim 8 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The single-crystal promoter contains one or more of sodium borate, sodium hydroxide, sodium carbonate, sodium acetate, sodium sulfate, sodium nitrate, and sodium chloride.

13. Na as claimed in claim 12 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The single-crystal promoter contains two or more of sodium borate, sodium hydroxide, and sodium chloride.

14. Na as claimed in claim 13 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The single-crystal promoter contains sodium borate, sodium hydroxide, and sodium chloride.

15. Na as claimed in claim 14 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The single-crystal promoter is a mixture of sodium borate, sodium hydroxide, and sodium chloride with a molar ratio of 0.1 - 0.5:1 - 2:1 - 2.

16. The Na according to any one of claims 8 to 15 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that In the mixture, the molar ratio of the Na in the single-crystal promoter to the total molar amount of (Ni - Fe - Mn - Cu - M) is 1 - 6:

1.

17. The Na as claimed in claim 8 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material It is characterized in that The described mixture is obtained by the wet ball milling - drying method.

18. Na as claimed in claim 17 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The solvent for wet ball milling is one of water, ethanol, and ether.

19. Na as claimed in claim 17 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The rotation speed of wet ball milling is 80 - 800 r / min, and the ball milling time is 2 - 20 h.

20. Na as claimed in claim 8 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The first-stage roasting and the second-stage roasting are carried out in an oxygen-containing atmosphere; the described oxygen-containing atmosphere is at least one of air, oxygen - nitrogen mixture, and oxygen - inert gas mixture; The heating rate of the first-stage roasting and the second-stage roasting is 0.5 - 5 °C / min; The temperature of the first-stage roasting is 900 - 1000 °C; The time of the first-stage roasting is 10 - 30 h.

21. The Na as claimed in claim 8 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 A method for preparing a single crystal active material It is characterized in that The solvent for washing is one or more of water and C1 - C4 alcohols.

22. Na as claimed in claim 8 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Method for preparing single crystal active material, It is characterized in that The temperature of the second-stage roasting is 500~750 °C; The time of the second-stage roasting is 4~6 h.

23. A Na according to any one of claims 1 to 7 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active material or Na prepared by the preparation method according to any one of claims 8 to 22 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Application of single crystal active materials, It is characterized in that It is used as a positive electrode active material for preparing a sodium-ion battery, its positive electrode and positive electrode material.

24. A positive electrode of a sodium-ion battery It is characterized in that Containing the Na described in any one of claims 1 to 7 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active material or Na prepared by the preparation method according to any one of claims 8 to 22 x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active material.

25. The positive electrode of a sodium-ion battery according to claim 24 It is characterized in that It includes a current collector and a positive electrode material composited on its surface, wherein the positive electrode material includes the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 Single crystal active material.

26. The positive electrode of a sodium-ion battery according to claim 25 It is characterized in that In the positive electrode material described above, a conductive agent and a binder are further included; Among them, in the positive electrode material, the Na x Ni a Fe b Mn c Cu d M 1-a-b-c-d O 2 The content of the single crystal active material is 70-90wt / %; the content of the conductive agent is less than or equal to 10wt / %; and the content of the binder is less than or equal to 10wt / %.

27. A sodium-ion battery It is characterized in that It includes the positive electrode described in any one of claims 24~26.

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