Sodium ion battery positive electrode material and preparation method thereof

Abstract

The present invention discloses a sodium ion battery cathode material and a preparation method thereof. The chemical formula of the cathode material is Na i Ni x Mn y A z B (1‑x‑y‑z) O2, wherein 0.8<i≤1.0, 0<x≤0.60, 0<y≤0.50, 0<z≤0.2; A is at least one of Zr, V, Ti, Ru, Sn, Ir, Nb, Sb, Te or Bi; B is at least one of Mg, K or Ca. The preparation method comprises the following steps: (1) mixing NiO, MnO2, A oxide and sodium salt in water to form a mixed solution, and then sand-milling the mixed solution to obtain a slurry; (2) spray-drying the slurry to obtain a precursor powder; (3) sintering the precursor powder for the first time at a sintering temperature of 600-950°C, and then rapidly cooling to room temperature after sintering at a cooling rate of ≥20°C / min, and crushing the material to obtain a mixture A; (4) mixing the mixture A with B oxide or B hydroxide, sintering for the second time, crushing, and sieving to obtain a positive electrode material. The positive electrode material has the effects of stable high capacity and excellent cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery positive electrode materials, and in particular to a sodium ion battery positive electrode material and a preparation method thereof. Background Art

[0002] Energy or economic sustainability drives the increasing demand for clean fuels to replace traditional fossil fuels, such as the rapid development of lithium-ion batteries in electric vehicles and large-scale energy storage. However, the problem of insufficient lithium resources has seriously restricted the widespread application of lithium-ion batteries in large-scale energy storage. Since the development of low-cost, high-performance energy storage materials is crucial to the development of large-scale energy storage, sodium-ion batteries are considered to be a promising alternative for grid-scale storage applications because they have a similar "rocking chair" sodium storage mechanism to lithium-ion batteries and have the advantages of natural abundance and low cost of sodium resources. Among them, layered transition metal oxides have become an ideal cathode material due to their high specific capacity, pollution-free and simple synthesis. However, due to the Na + The radius is large, and Na + The intercalation and deintercalation of the layered materials will lead to complex phase transitions, especially the drastic phase transitions under high voltage and the 2- The redox reaction of anions causes significant expansion and contraction of the material's volume. The residual stress generated by repeated volume changes can lead to crack formation in the layered material. Furthermore, during the charge and discharge process, some elements undergo the Jahn-Teller effect, causing disproportionation reactions. This leads to the dissolution of transition metal elements into the electrolyte, exacerbating the structural failure of the layered material. This results in poor cycling stability for layered cathode materials, making them difficult to meet the requirements of commercial applications. Summary of the Invention

[0003] In view of the above problems, the object of the present invention is to provide a sodium ion battery positive electrode material and a preparation method thereof, wherein the sodium ion battery positive electrode material has stable high capacity and excellent cycle stability, is particularly suitable for high voltage, and can be used as a sodium ion battery positive electrode material in the field of large-scale energy storage.

[0004] In order to achieve the above object, the present invention provides a sodium ion battery positive electrode material, the chemical formula of the sodium ion battery positive electrode material is Na i Ni x Mn y A z B (1-x-y-z) O2, wherein 0.8<i≤1.0, 0<x≤0.60, 0<y≤0.50, 0<z≤0.2; A is at least one of Zr, V, Ti, Ru, Sn, Ir, Nb, Sb, Te or Bi; B is at least one of Mg, K or Ca.

[0005] In some embodiments, the positive electrode material of the sodium ion battery is a single crystal containing an O3 / P2 mixed phase. The positive electrode material of the sodium ion battery is a single crystal material, the single crystal structure is an O3 / P2 mixed phase, and a certain amount of electrochemically inert elements (Mg, K or Ca) are deposited and accumulated in part of the alkali metal layer or the O3 / P2 phase interface, which inhibits the volume expansion and contraction and dislocation expansion of the layered positive electrode material during charging and discharging, thereby achieving high capacity and long cycle performance.

[0006] In some embodiments, the chemical formula of the sodium ion battery positive electrode material is Na 0.95 Ni 0.4 Mn 0.4 A 0.15 B 0.05 O2, A is at least one of Zr, V, Ti, Ru, Sn, Ir, Nb, Sb, Te or Bi; B is at least one of Mg, K or Ca. For example, A is V and B is Mg, that is, the chemical formula of the positive electrode material of the sodium ion battery is Na 0.95 Ni 0.4 Mn 0.4 V 0.15 Mg 0.05 O2, but not limited to this.

[0007] In some embodiments, the mass fraction of the P2 phase in the material is 5-20%, such as 5-15%, 12-20%, 8-18%, etc. As an example, the mass fraction of the P2 phase in the material may be, but is not limited to, 5%, 8%, 11%, 14%, 17%, or 20%.

[0008] In some embodiments, the single crystal particle size Dv50 of the sodium ion battery positive electrode material is 3.0-6.0 μm, and the particle specific surface area is 0.2-0.8 m 2 / g, as an example, the Dv50 of the sodium ion battery positive electrode material may be but not limited to 3.0um, 4.0um, 5.0um, 6.0um; the particle specific surface area may be but not limited to 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g.

[0009] Accordingly, the present invention also provides a method for preparing a positive electrode material for a sodium ion battery, comprising the steps of:

[0010] (1) NiO, MnO2, A oxide and sodium salt are mixed in water at a certain molar ratio to form a mixed solution, and then the mixed solution is sand-milled to obtain a slurry;

[0011] (2) spray drying the slurry to obtain a precursor powder;

[0012] (3) sintering the precursor powder for the first time at a sintering temperature of 600-950°C. After sintering, the temperature is quickly cooled to room temperature at a cooling rate of ≥20°C / min. The material is then crushed to obtain a mixture A.

[0013] (4) Mixing the mixed material A with the oxide or hydroxide B, and then performing a second sintering, crushing, and sieving to obtain a positive electrode material for a sodium ion battery.

[0014] In some embodiments, in step (1), oxide A is at least one of ZrO2, V2O5, TiO2, RuO2, SnO2, Ir2O5, Nb2O5, Sb2O5, Bi2O5 and TeO3.

[0015] In some embodiments, in step (1), the sodium salt is at least one of NaOH, NaNO3, Na2CO3 or CH3COONa.

[0016] In some embodiments, in step (1), the molar ratio of sodium to metal element in the sodium salt is 0.85-1.05:1.

[0017] In some embodiments, the cooling rate is ≥30°C / min. For example, the cooling rate may be, but is not limited to, 30°C / min, 40°C / min, 50°C / min, 60°C / min, etc.

[0018] In some embodiments, in step (1), the particle size Dv50 of the slurry is 0.2-0.7 um. For example, the particle size Dv50 of the slurry may be, but is not limited to, 0.2 um, 0.3 um, 0.4 um, 0.5 um, 0.6 um, or 0.7 um.

[0019] In some embodiments, in step (2), the inlet air temperature of the spray drying spray is 220-280°C, and the exhaust air temperature of the spray is 80-100°C. For example, the inlet air temperature of the spray is 260°C, and the exhaust air temperature of the spray is 90°C, but not limited thereto.

[0020] In some embodiments, in step (3), the first sintering can be a single sintering or a staged sintering, preferably a staged sintering. Preferably, the first sintering process is as follows: introducing air, raising the temperature to 600-800°C at a heating rate of 2.5°C / min and holding the temperature for 3-10 hours, then raising the temperature to 800-950°C at a heating rate of 2.5°C / min and holding the temperature for 8-16 hours, and cooling to room temperature with air at a cooling rate of ≥20°C / min. It is worth noting that the cooling method is rapid cooling, which produces defects. When B oxide or B hydroxide is used for the second sintering, B oxide or B hydroxide is preferentially deposited at the defects, so that inert elements (Mg, K or Ca) are deposited in part of the alkali metal layer or the O3 / P2 phase interface, and more sodium is released under high voltage. The structural P2 or O3 phase change causes the crystal volume to change and form microcracks, so that the inert elements are deposited at the cracks to play a pinning role, thereby enhancing the structural strength, inhibiting the expansion of microcracks, and achieving stable high capacity and cycle stability.

[0021] In some embodiments, in step (3), the particle size Dv50 of the mixture A is 2.5-5.5 μm. For example, the particle size Dv50 of the mixture A may be, but is not limited to, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or 5.5 μm.

[0022] In some embodiments, the B oxide is at least one of MgO, CaO, and K2O.

[0023] In some embodiments, the B hydroxide is at least one of Mg(OH)2, Ca(OH)2, or KOH.

[0024] In some embodiments, in step (4), the second sintering process is as follows: introducing air, maintaining the temperature at 500-850°C for 5-10 hours, and naturally cooling to room temperature. Furthermore, the crushed product is sieved to obtain a sodium ion battery positive electrode material. For example, the crushed product is sieved through a 300-mesh sieve.

[0025] The beneficial effects of the present invention are as follows:

[0026] (1) The chemical formula of the sodium ion battery positive electrode material of the present invention is Na i Ni x Mn y A z B (1-x-y-z)O2, Ni in the internal element composition increases the capacity of the material, and Mn element reduces material cost and improves safety and stability. In particular, the high ionic potential of Mn and A element (Zr, V, Ti, Ru, Sn, Ir, Nb, Sb, Te or Bi) metal oxides induces P2 phase in high sodium O3 phase. Under high voltage, when the O3 / P2 phase releases more sodium, the phase transition between P2 and O3 phases is inhibited, making the O3 / P2 phase structure stable, maintaining the stability of the layered material structure, and giving it good cycle performance.

[0027] (2) The sodium ion battery positive electrode material of the present invention is rapidly cooled after the first sintering, so that the cooling rates of the surface and interior of the positive electrode material are different, thereby generating different shrinkage stresses in different parts of the positive electrode material and forming a large number of defects. Then, at high temperature, the inert element compound (B oxide or B hydroxide) with a smaller particle size gradually diffuses from the surface to the defect position along the lattice gap to form a deposition layer, which fills the defects of the layered positive electrode material, thereby forming an inert element deposition structure in part of the alkali metal layer or the O3 / P2 phase interface. Under high voltage, more sodium is released, and the structural P2 or O3 phase transition causes the crystal volume to change, forming microcracks. In this way, the inert element deposition at the crack plays a pinning role, enhances the structural strength, inhibits the expansion of microcracks, and achieves stable high capacity and long cycle performance.

[0028] (3) Some inert elements are doped in the alkali metal layer, which can play a supporting role and reduce the volume change of the material in the highly desodiumized state.

[0029] (4) The preparation method of the positive electrode material of the sodium ion battery has a simple process, low cost and can be industrially produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is an SEM image of the sodium ion battery positive electrode material prepared in Example 1 of the present invention.

[0031] Figure 2 This is the XRD test result diagram of the sodium ion battery positive electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0033] Example 1

[0034] The sodium ion battery positive electrode material of this embodiment has the chemical formula Na 0.95 Ni 0.4 Mn 0.4 V 0.15 Mg 0.05 O2, the morphology is single crystal, the crystal structure is O3 / P2 phase and Mg element deposition appears in some alkali metal layers or O3 / P2 phase interfaces. The mass fraction of P2 phase in the material is 10%, the single crystal particle size Dv50 is 4.5um, and the particle specific surface area is 0.35m 2 / g.

[0035] The method for preparing the positive electrode material for a sodium ion battery of this embodiment comprises the following steps:

[0036] (1) Using NiO, MnO2, V2O5 and Na2CO3 as raw materials, n Ni :n Mn :n V＝ 0.4:0.4:0.15, the molar ratio of sodium to metal is 0.95, the raw materials are mixed in water to form a mixture with a solid content of 30%, and then the mixture is added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.3 μm;

[0037] (2) spray drying the slurry at a spray inlet temperature of 260°C and a spray exhaust temperature of 90°C to obtain a spherical precursor powder;

[0038] (3) The precursor powder was sintered for the first time, and air was introduced. The temperature was raised to 800°C at a heating rate of 2.5°C / min and kept at this temperature for 6 h. The temperature was then raised to 900°C at a heating rate of 2.5°C / min and kept at this temperature for 12 h. The powder was cooled by air at a cooling rate of 50°C / min to obtain a black block material. The black block material was then subjected to rotary milling and mechanical milling in sequence to obtain a mixture A with a particle size Dv50 of 4.0 μm.

[0039] (4) Mixed material A and MgO were mixed and sintered for the second time. Air was introduced and the temperature was raised to 750°C at a heating rate of 2.5°C / min and kept at that temperature for 6 hours. The mixture was naturally cooled to room temperature and crushed by a roller mill. The mixture was sieved through a 300-mesh sieve to obtain a sodium ion battery positive electrode material with a particle size Dv50 of 4.5 μm.

[0040] Example 2

[0041] The sodium ion battery positive electrode material of this embodiment has the chemical formula Na 0.95 Ni 0.3 Mn 0.5 Ir 0.15 Mg 0.05O2, the morphology is single crystal, the crystal structure is O3 / P2 phase and Mg element deposition appears in some alkali metal layers or O3 / P2 phase interfaces. The mass fraction of P2 phase in the material is 13%, the single crystal particle size Dv50 is 4.3um, and the particle specific surface area is 0.37m 2 / g.

[0042] The method for preparing the positive electrode material for a sodium ion battery of this embodiment comprises the following steps:

[0043] (1) Using NiO, MnO2, Ir2O5 and Na2CO3 as raw materials, n Ni :n Mn :n Ir＝ 0.3:0.5:0.15, the molar ratio of sodium to metal is 0.95, the raw materials are mixed in water to form a mixture with a solid content of 30%, and then the mixture is added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.3 μm;

[0044] (2) spray drying the slurry at a spray inlet temperature of 260°C and a spray exhaust temperature of 90°C to obtain a spherical precursor powder;

[0045] (3) The precursor powder was sintered for the first time, and air was introduced. The temperature was raised to 800°C at a heating rate of 2.5°C / min and kept at this temperature for 6 h. The temperature was then raised to 900°C at a heating rate of 2.5°C / min and kept at this temperature for 12 h. The powder was cooled by air at a cooling rate of 50°C / min to obtain a black block material. The black block material was then subjected to rotary milling and mechanical milling in sequence to obtain a mixture A with a particle size Dv50 of 3.8 μm.

[0046] (4) Mixing the mixture A and MgO, the mixture was sintered for the second time, and air was introduced. The temperature was raised to 750°C at a heating rate of 2.5°C / min and kept at this temperature for 6 hours. The mixture was naturally cooled to room temperature, crushed by a roller mill, and passed through a 300-mesh sieve to obtain a sodium ion battery positive electrode material with a particle size Dv50 of 4.3 μm.

[0047] Example 3

[0048] The preparation method of the sodium ion battery positive electrode material in this embodiment is basically the same as that in Example 1, except that in step (3), the cooling rate in this embodiment is 30°C / min, while the cooling rate in Example 1 is 50°C / min. The rest is the same as that in Example 1 and is therefore not described again.

[0049] Example 4

[0050] The sodium ion battery positive electrode material of this embodiment has the chemical formula Na 0.95 Ni 0.4Mn 0.4 V 0.15 Mg 0.05 O2, the morphology is single crystal, the crystal structure is O3 / P2 phase and Mg element deposition appears in some alkali metal layers or O3 / P2 phase interfaces. The mass fraction of P2 phase in the material is 10%, the single crystal particle size Dv50 is 4.5um, and the particle specific surface area is 0.35m 2 / g.

[0051] The method for preparing the positive electrode material for a sodium ion battery of this embodiment comprises the following steps:

[0052] (1) Using NiO, MnO2, V2O5 and Na2CO3 as raw materials, n Ni :n Mn :n V＝ 0.4:0.4:0.15, the molar ratio of sodium to metal is 0.95, the raw materials are mixed in water to form a mixture with a solid content of 30%, and then the mixture is added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.3 μm;

[0053] (2) spray drying the slurry at a spray inlet temperature of 260°C and a spray exhaust temperature of 90°C to obtain a spherical precursor powder;

[0054] (3) The precursor powder was sintered for the first time, and air was introduced. The temperature was raised to 800°C at a heating rate of 2.5°C / min and kept at this temperature for 6 h. The temperature was then raised to 900°C at a heating rate of 2.5°C / min and kept at this temperature for 12 h. The powder was cooled by air at a cooling rate of 50°C / min to obtain a black block material. The black block material was then subjected to rotary milling and mechanical milling in sequence to obtain a mixture A with a particle size Dv50 of 4.0 μm.

[0055] (4) Mixed material A and MgOH were mixed and sintered for the second time. Air was introduced and the temperature was raised to 750°C at a heating rate of 2.5°C / min and kept at that temperature for 6 hours. The mixture was naturally cooled to room temperature and crushed by a roller mill. The mixture was sieved through a 300-mesh sieve to obtain a sodium ion battery positive electrode material with a particle size Dv50 of 4.5 μm.

[0056] Comparative Example 1

[0057] The sodium ion battery positive electrode material of this embodiment has the chemical formula Na 0.95 Ni 0.4 Mn 0.4 V 0.15 Mg 0.05O2, the morphology is single crystal, the crystal structure is O3 / P2 phase and Mg is doped in the alkali metal layer, the mass fraction of P2 phase in the material is 10%, the single crystal particle size Dv50 is 4.8um, and the particle specific surface area is 0.33m 2 / g.

[0058] The preparation method of the sodium ion battery positive electrode material in this comparative example is basically the same as that in Example 1, except that in step (3), the cooling method in this comparative example 1 is natural cooling with a cooling rate of 5°C / min, while in Example 1, air accelerated cooling is used with a cooling rate of 50°C / min. The rest is the same as in Example 1 and is therefore not further described.

[0059] Comparative Example 2

[0060] The sodium ion battery positive electrode material of this comparative example has the chemical formula Na 0.95 Ni 0.4 Mn 0.4 Cu 0.15 Mg 0.05 O2, the morphology is single crystal, the crystal structure is O3 phase and Mg element deposition appears in part of the alkali metal layer, the single crystal particle size Dv50 is 4.5um, and the particle specific surface area is 0.36m 2 / g.

[0061] The preparation method of the sodium ion battery positive electrode material of this comparative example comprises the following steps:

[0062] (1) Using NiO, MnO2, CuO and Na2CO3 as raw materials, n Ni :n Mn :n Cu＝ 0.4:0.4:0.15, the molar ratio of sodium to metal is 0.95, the raw materials are mixed in water to form a mixture with a solid content of 30%, and then the mixture is added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.3 μm;

[0063] (2) spray drying the slurry at a spray inlet temperature of 260°C and a spray exhaust temperature of 90°C to obtain a spherical precursor powder;

[0064] (3) The precursor powder was sintered for the first time, and air was introduced. The temperature was raised to 800°C at a heating rate of 2.5°C / min and kept at this temperature for 6 h. The temperature was then raised to 900°C at a heating rate of 2.5°C / min and kept at this temperature for 12 h. The powder was cooled by air at a cooling rate of 50°C / min to obtain a black block material. The black block material was then subjected to rotary milling and mechanical milling in sequence to obtain a mixture A with a particle size Dv50 of 4.0 μm.

[0065] (4) Mixed material A and MgO were mixed and sintered for the second time. Air was introduced and the temperature was raised to 750°C at a heating rate of 2.5°C / min and kept at that temperature for 6 hours. The mixture was naturally cooled to room temperature and crushed by a roller mill. The mixture was sieved through a 300-mesh sieve to obtain a sodium ion battery positive electrode material with a particle size Dv50 of 4.5 μm.

[0066] Comparative Example 3

[0067] The sodium ion battery positive electrode material of this comparative example has the chemical formula Na 0.95 Ni 0.4 Mn 0.4 V 0.15 Zn 0.05 O2, the morphology is single crystal, the crystal structure is O3 / P2 phase, the mass fraction of P2 phase in the material is 10%, the single crystal particle size Dv50 is 4.6um, and the particle specific surface area is 0.34m 2 / g.

[0068] The preparation method of the sodium ion battery positive electrode material of this comparative example comprises the following steps:

[0069] (1) Using NiO, MnO2, V2O5 and Na2CO3 as raw materials, n Ni :n Mn :n V＝ 0.4:0.4:0.15, the molar ratio of sodium to metal is 0.95, the raw materials are mixed in water to form a mixture with a solid content of 30%, and then the mixture is added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.3 μm;

[0070] (2) spray drying the slurry at a spray inlet temperature of 260°C and a spray exhaust temperature of 90°C to obtain a spherical precursor powder;

[0071] (3) The precursor powder was sintered for the first time, and air was introduced. The temperature was raised to 800°C at a heating rate of 2.5°C / min and kept at this temperature for 6 h. The temperature was then raised to 900°C at a heating rate of 2.5°C / min and kept at this temperature for 12 h. The powder was cooled by air at a cooling rate of 50°C / min to obtain a black block material. The black block material was then subjected to rotary milling and mechanical milling in sequence to obtain a mixture A with a particle size Dv50 of 4.0 μm.

[0072] (4) Mixed material A and ZnO were mixed and sintered for the second time. Air was introduced and the temperature was raised to 750°C at a heating rate of 2.5°C / min and kept at this temperature for 6 hours. The mixture was naturally cooled to room temperature and crushed by a roller mill. The mixture was sieved through a 300-mesh sieve to obtain a sodium ion battery positive electrode material with a particle size Dv50 of 4.6 μm.

[0073] Figure 1 The SEM image of the sodium ion battery cathode material prepared in Example 1 is shown. Figure 1 It can be seen that the morphology of the sodium ion battery positive electrode material is single crystal, the surface of the material is relatively smooth, and there is less fine powder.

[0074] Figure 2 The XRD pattern of the sodium ion battery cathode material prepared in Example 1 is shown. Figure 2 It can be seen that the XRD pattern shows that the peaks at 16.4° and 41.6° are the characteristic diffraction peaks (003) and (104) of the O3 phase, belonging to the trigonal crystal system with a space group of R-3m; the XRD pattern also shows that the peaks at 15.8° and 39.1° are the characteristic diffraction peaks (002) and (102) of the P2 phase, belonging to the hexagonal crystal system with a space group of P63 / mmc. Therefore, the XRD data show that the sodium ion battery positive electrode material is composed of two phases of O3 / P2.

[0075] The electrochemical performance of the sodium ion battery positive electrode materials of Examples 1 to 4 and Comparative Examples 1-3 was tested, and the results are shown in Table 1.

[0076] Electrochemical performance testing: The sodium-ion battery cathode material was used as the active material, mixed with the binder PVDF and the conductive agent (Super-P) in a mass ratio of 95:1.5:3.5, and an appropriate amount of N-vinyl pyrrolidone was added as a solvent to form a slurry. The slurry was coated on aluminum foil, vacuum dried, and roller-pressed to prepare the negative electrode sheet. Metallic lithium was used as the counter electrode, and the electrolyte was formed by mixing 1 mol / L LiPF6 and a three-component mixed solvent with EC:DMC:EMC = 1:1:1 (v / v). A polypropylene microporous membrane was used as the separator. The cells were assembled into CR2032 button cells in an inert gas glove box. The charge and discharge test of the button battery was carried out on the battery testing system of Wuhan Blue Electric Electronics Co., Ltd. At 25°C, it was charged at a constant current of 0.1C to 4.2V, then charged at a constant voltage to a cutoff current of 0.05C, and finally discharged at a constant current of 0.1C to 2.0V. The capacity was the first discharge specific capacity, and the ratio of the discharge capacity to the charge capacity was the first charge and discharge efficiency. After 100 cycles, the corresponding discharge specific capacity of the 100th cycle was obtained, and the charge and discharge efficiency of the 100th cycle was calculated.

[0077] Table 1 Test results

[0078]

[0079]

[0080] As shown in Table 1, the sodium ion battery cathode materials of Examples 1 to 4 have better initial discharge specific capacity and initial charge-discharge efficiency than those of Comparative Examples 1-3. This indicates that during the charge-discharge process, more sodium ions participate in the reaction and can be reintercalated, indicating that the side reactions are good and that the cathode materials have excellent kinetic properties. In particular, the 100th cycle discharge specific capacity and 100th cycle charge-discharge efficiency data indicate a high capacity retention rate, a stable high capacity, good cycle performance, and a stable structure during the cycle.

[0081] In Comparative Example 1, since the cooling rate is 5°C / min, rapid cooling cannot be achieved, and fewer defects are generated between the transition metal layers of the material or between the O3 / P2 phases, so that the inert metal ions cannot be deposited at the defects or can only be deposited in a small amount. As a result, the phase change of the material and the expansion of microcracks cannot be effectively suppressed, resulting in poor electrochemical performance of the material.

[0082] In Comparative Example 2, the oxide A is CuO. Since the valence of copper changes during the charge and discharge process, stress will be generated at the defects, resulting in poor structural stability of the material and poor electrochemical performance of the material.

[0083] In Comparative Example 3, B oxide uses ZnO, in which Zn ions can only enter the transition metal layer of the material, which improves the structural stability of the material, but cannot exist in the alkali metal layer, that is, there is no pillar. In this way, during the charging process, sodium ions are released, which easily leads to the collapse of the layered structure of the material, and the material structure cannot be stabilized well under high voltage.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a positive electrode material for a sodium ion battery, characterized in that: Including steps: (1) NiO, MnO2, A oxide and sodium salt are mixed in water at a certain molar ratio to form a mixed solution, and then the mixed solution is sand-milled to obtain a slurry; (2) spray drying the slurry to obtain a precursor powder; (3) The precursor powder is sintered for the first time at a sintering temperature of 600-950°C. After sintering, the temperature is quickly cooled to room temperature at a cooling rate of ≥20°C / min. The material is then crushed to obtain a mixture A. (4) Mixing the mixed material A with the oxide or hydroxide B, and then performing a second sintering, crushing, and screening to obtain a positive electrode material for a sodium ion battery; The chemical formula of the sodium ion battery positive electrode material is Na i Ni x Mn y A z B （1-x-y-z） O2, where 0.8<i≤1.0, 0<x≤0.60, 0<y≤0.50, 0<z≤0.2; A is at least one of Zr, V, Ti, Ru, Sn, Ir, Nb, Sb, Te or Bi; B is at least one of Mg, K or Ca; The sodium ion battery positive electrode material is a single crystal, contains an O3 / P2 mixed phase, and the B element is deposited at the interface of the O3 / P2 mixed phase.

2. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein The mass fraction of P2 phase in the material is 5-20%.

3. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein Oxide A is at least one of ZrO2, V2O5, TiO2, RuO2, SnO2, Ir2O5, Nb2O5, Sb2O5, Bi2O5 and TeO3.

4. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein In step (3), the particle size Dv50 of the mixture A is 2.5-5.5 μm.

5. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein: The sodium salt is at least one of NaNO3, Na2CO3 or CH3COONa.

6. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein: The B oxide is at least one of MgO, CaO, and K2O; the B hydroxide is at least one of Mg(OH)2, Ca(OH)2, or KOH.

7. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein: The first sintering process is as follows: introduce air, raise the temperature to 600-800°C at a heating rate of 2.5°C / min and keep it warm for 3-10 hours, then raise the temperature to 800-950°C at a heating rate of 2.5°C / min and keep it warm for 8-16 hours, and cool it to room temperature with air at a cooling rate of ≥20°C / min.

8. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein: In step (4), the second sintering process is as follows: introducing air, keeping the temperature at 500-850°C for 5-10 hours, and naturally cooling to room temperature.

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