Composite crystal domain sodium battery positive electrode material and preparation method, positive electrode sheet, battery and power device

Abstract

The present invention provides a composite crystal domain sodium-based cathode material and a preparation method thereof, a cathode electrode sheet, a battery and an electrical device. The composite crystal domain sodium-based cathode material has the general chemical formula of Na 1‑ a Ni b Fe c Mn d X x O2, 0<a≤0.25, b+c+d+x=1, X is a metal element with an average valence σ≤4; layered crystal domains A and B exist within the crystal structure; and the absolute value of microstress ε in the crystal structure is less than 10%. The composite crystal domain sodium cathode material provided by the present invention ensures that the material has a higher energy density by regulating the sodium content, material composition, valence, and X element doping, introduces other ions to provide charge compensation, and regulates the structure and coupling of crystal domains A and B. This reduces stress accumulation and lattice strain caused by uneven expansion in the material's bulk structure, increases the formation and migration barriers of oxygen vacancies in the structure, improves the stability of lattice oxygen in the material, and slows down voltage and capacity decay.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a composite crystal domain sodium battery positive electrode material and a preparation method thereof, a positive electrode sheet, a battery and an electrical device. Background Art

[0002] Sodium-ion batteries are considered to be another secondary battery technology suitable for large-scale commercial applications in addition to lithium-ion batteries due to their advantages in safety and cost. The layered oxide positive electrode materials in them have attracted much attention due to their high specific capacity, fast sodium ion diffusion kinetics, simple synthesis and low cost.

[0003] Currently, common sodium layered oxide cathode materials are usually of three types: O3 structure, P2 structure, and P / O mixed structure. Researchers have invested a lot of resources to achieve the reversible extraction / embedding of sodium ions in the interlayer structure. However, when Na + When the ions are deeply extracted, the transition metal ions with increased valence enhance the covalency of the transition metal-oxygen bond, making it easier for lattice oxygen to participate in the reaction to provide charge compensation. The lattice oxygen is oxidized and precipitated, resulting in a decrease in the van der Waals force between layers, the collapse of the spacing between alkali metal layers, a decrease in the number of sodium ions that can be intercalated and deintercalated, and a decrease in the reversible specific capacity. Moreover, the irreversible precipitation of lattice oxygen further aggravates the irreversible transformation of the structure, resulting in severe voltage decay, which is manifested as a loss of energy density during long cycles.

[0004] Therefore, it is urgent to start from the material structure design and improve the structural stability of the material in the deep desodium state at high potential by optimizing the material crystal structure, slow down the voltage decay, and improve the long-term energy cycle stability. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite crystal domain sodium battery positive electrode material and a preparation method, a positive electrode sheet, a battery and an electrical device to solve the problems existing in the background technology.

[0006] The technical solution of the present invention includes: a composite crystal domain sodium cathode material, wherein:

[0007] The chemical formula is Na 1-a Ni b Fe c Mn d X x O2, 0<a≤0.25, b+c+d+x=1, X is a metal element with an average valence σ≤4;

[0008] There are layered domains A and B in the crystal structure;

[0009] The absolute value of microstress in the crystal structure is ε<10%.

[0010] Furthermore, in an X-ray powder diffraction pattern measured using Cu-Kα rays, the composite crystal domain sodium cathode material has at least the following at 2θ of 15° to 18°:

[0011] Corresponding to the diffraction peak M of the (002) crystal plane in the crystal domain A, the diffraction angle of the diffraction peak M is θ M , half-peak width is β M ;

[0012] Corresponding to the diffraction peak N of the (003) crystal plane in the crystal domain B, the diffraction angle of the diffraction peak N is θ N , half-peak width is β N ;

[0013] Where: 2θ M <2θ N ,

[0014] Furthermore, X is one or more of Li, Mg, Al, Ca, Cu, Zn, Ti, Zr, Cr, Sr, Ba, Nb, Mo and W, and 0<x<0.15.

[0015] Furthermore, a≤db,

[0016] Furthermore, ordered Ni-O, Fe-O, and Mn-O octahedra exist in the crystal domain A and the crystal domain B, the Na-O in the crystal domain A is a triangular prism coordination structure, and the Na-O in the crystal domain B is an octahedral coordination structure.

[0017] The technical solution of the present invention also includes: a method for preparing the composite crystal domain sodium cathode material as described above, which comprises the steps of:

[0018] Mixing nickel source, iron source, manganese source, X source and type I sodium source to obtain a first sintering material;

[0019] sintering the first sintering material at a first temperature to obtain a first calcined product;

[0020] mixing the first calcined product and the type II sodium source to obtain a second sintered material;

[0021] sintering the second sintering material at a second temperature to obtain a second calcined product;

[0022] crushing and screening the second calcined product to obtain a composite crystal domain sodium cathode material;

[0023] Among them, the decomposition temperature or melting temperature of Class I sodium source is lower than that of Class II sodium source, the first temperature is lower than the second temperature, and the median particle size D50 of the composite crystal domain sodium cathode material is 2μm to 12μm.

[0024] Further, the Class I sodium source includes at least one of NaOH, CH3COONa and NaNO3;

[0025] In the first sintering material, the ratio of the molar amount of sodium element to the total molar amount of non-sodium metal elements is w1,0 <w1<0.5·(1-a);

[0026] Class II sodium sources include at least one of Na2CO3, NaHCO3 and Na2C2O4;

[0027] In the second sintered material, the ratio of the molar amount of sodium element in the type II sodium source to the total molar amount of non-sodium metal elements in the first calcined product is w2,1-a <w1+w2<1.05·(1-a);

[0028] The nickel source, iron source, manganese source and X source each include at least one of chloride, acetate, oxalate, carbonate, bicarbonate and nitrate containing the corresponding metal element;

[0029] The first temperature is 500° C., and the sintering is performed at the first temperature for 1 to 10 hours;

[0030] The second temperature is 850-1100° C., and the sintering is performed at the second temperature for 6-30 hours;

[0031] After sintering, the furnace is cooled. During the cooling process, the relative humidity of the environment is ≤30%;

[0032] During the process of crushing and screening the second calcined product, the relative humidity of the environment is ≤20%.

[0033] The technical solution of the present invention also includes: a positive electrode plate, wherein the positive electrode plate contains the composite crystal domain sodium positive electrode material as described above.

[0034] The technical solution of the present invention also includes: a battery, wherein the battery contains the positive electrode sheet as described above.

[0035] The technical solution of the present invention also includes: an electrical device, wherein the electrical device contains the battery as described above.

[0036] The present invention has the following beneficial effects: the composite crystal domain sodium cathode material provided by the present invention ensures that the material has a higher energy density by regulating the sodium content, material composition, valence state and X element doping, introduces other ions to provide charge compensation, and regulates the structure and coupling of crystal domain A and crystal domain B, thereby balancing the electrostatic attraction and repulsion between the sodium layer / transition metal layer; the method of step-by-step sodium supplementation and step-by-step calcination is adopted to achieve the uniform embedding of sodium in the interlayer structure, thereby inducing the differentiation of the material microstructure to form two different Na-O coordination structures and a material with an absolute microstress value of <10%. The low microstress feature of the composite crystal domain sodium cathode material reduces the stress accumulation and lattice strain caused by the uneven expansion in the bulk structure of the material, improves the interaction between oxygen ions and the transition metal layer, increases the formation and migration barrier of oxygen vacancies in the structure, and synergizes with the introduced charge compensation ions to improve the stability of the lattice oxygen in the material and slow down the voltage decay and capacity decay. Thus, the material provided by the present invention has a low microstress at high potential (4.2VvsNa / Na + ) exhibits stronger long-term cycle stability and specific capacity and voltage retention capabilities. In addition, the material process is simple and easy to scale up for industrial production, reducing product costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a SEM image of the composite crystal domain sodium cathode material prepared in Example 1 of the present invention;

[0038] Figure 2 This is the XRD diagram of the composite crystal domain sodium cathode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with the embodiments and accompanying drawings:

[0040] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments and comparative examples only and are not intended to limit the scope of protection of the present invention. It should be noted that the same organic structure may have multiple names; as long as the structure falls within the scope of this patent, all of them are protected by this patent.

[0041] Unless otherwise defined, the raw materials, reagents, etc. in the following examples can be purchased from the market or prepared according to reported methods.

[0042] In the first aspect of the present invention, a composite crystal domain sodium cathode material is proposed. By providing additional charge compensation ions and increasing the formation and migration barriers of oxygen vacancies, the structural stability of the material in the high potential deep desodium state is improved, the voltage decay is slowed down, and the energy long cycle stability is improved. According to the research on sodium cathode materials by the inventors of this technical solution, it is found that not only is the microstress state of the material crystal structure closely related to the oxygen vacancy concentration, but also the coupling effect of microstress and oxygen vacancies has an important influence on the formation energy and migration energy of oxygen vacancies. Reducing the microstress of the material crystal structure can increase the formation and migration barriers of oxygen vacancies in the structure and improve the stability of lattice oxygen; and the microstress of the material crystal structure is closely related to the coupling of crystal domains in the material. Therefore, the inventors of this technical solution adjust the microstress of the material by constructing a sodium cathode material with a composite crystal domain, adjusting the material composition, element valence, doping elements, synthesis formula, etc., and adjusting the state of each crystal domain.

[0043] Based on the above research and analysis, the inventors of this technical solution have determined through experiments and exploration that the chemical formula of the composite crystal domain sodium cathode material in this embodiment is Na 1-a Ni b Fe c Mn d X x O2, 0<a≤0.25, b+c+d+x=1, X is a metal element with an average valence state σ≤4; the crystal structure of the composite crystal domain sodium cathode material contains layered crystal domains A and B, and the coupling between crystal domains A and B changes the microstress of the material's crystal structure. According to the inventors of this technical solution, they found that when the absolute value ε of the microstress of the crystal structure is controlled within 10%, the oxygen vacancy concentration in the material can be effectively reduced, the interaction between oxygen ions and the transition metal layer can be improved, and the formation and migration barriers of oxygen vacancies in the structure can be increased, thereby improving the stability of lattice oxygen, suppressing voltage decay, and improving the energy retention rate during high cut-off voltage cycling.

[0044] In the above technical solution, the sodium content is controlled to ensure that the material has a higher energy density, and the structure of crystal domain A and crystal domain B is regulated, thereby regulating the microstress of the crystal structure. Charge compensation is provided by ions such as Ni, Fe, Mn, and X, thereby comprehensively improving the structural stability of the material in the high-potential deep desodium state, slowing down voltage decay, and improving the long-cycle energy stability.

[0045] In the composite crystal domain sodium cathode material that meets the above conditions, ordered Ni-O, Fe-O, and Mn-O octahedra exist in crystal domains A and B. The Na-O in crystal domain A has a triangular prism coordination structure, while the Na-O in crystal domain B has an octahedral coordination structure. The triangular prism coordination structure of Na-O in crystal domain A releases more sodium ions, ensuring that the composite crystal domain sodium cathode material has a higher specific capacity. The Na-O octahedral coordination structure with a larger sodium interlayer spacing in crystal domain B improves the diffusion rate of sodium ions between transition metal layers in the composite crystal domain sodium cathode material, reduces the migration barrier of sodium ions, and ensures that the material has high energy density and high charge-discharge efficiency. The ordered Ni-O, Fe-O, and Mn-O octahedra in crystal domains A and B provide a stable framework for the material structure, improving the structural stability of the material during charge-discharge cycles. By regulating the microstress state of the material's crystal structure, the structural stability of the material in the deep sodium-depleted state at high potential is improved.

[0046] In the inventor's further research, it was found that coupling of domains A and B with different Na-O coordination structures can reduce the microstress of the composite domain sodium cathode material and ensure that sodium ions have a complete and continuous deintercalation channel between the layers; and that in the composite domain sodium cathode material, the change in the material microstress caused by the coupling of domains A and B within the material is closely related to the half-peak width and diffraction angle of the characteristic peak in the powder X-ray diffraction pattern. The different Na-O coordination environments and distributions in domains A and B are manifested as different characteristic peaks in powder X-ray diffraction. In the X-ray powder diffraction pattern measured using Cu-Kα rays, the composite domain sodium cathode material has the following diffraction peak M corresponding to the (002) crystal plane in domain A in the range of 2θ=15°~18°, and the diffraction angle of diffraction peak M is θ M , half-peak width is β M , and the diffraction peak N corresponding to the (003) crystal plane in the crystal domain B, the diffraction angle of the diffraction peak N is θ N , half-peak width is β N , 2θ M <2θ N ; By optimizing the Williamson-Hall equation β hkl ·cosθ=kλ / D+4ε·sinθ,β hkl is the half-peak width of the (hkl) crystal plane in the XRD pattern, θ is the 1 / 2 diffraction angle, and ε is the lattice microstrain. The correlation formula between the absolute value of the microstress of the crystal structure of the composite crystal domain sodium cathode material and the characteristic peaks of the crystal domain A and the crystal domain B is obtained. Based on this correlation, the magnitude of microstress in the material's crystal structure can be intuitively judged. Combined with the formation of oxygen vacancies and migration barriers, it can be determined how to adjust the coupling state of crystal domain A and crystal domain B.

[0047] The states of the above-mentioned crystal domain A and crystal domain B are affected by various aspects such as material composition, valence states of each element, doping elements, and synthesis methods. According to the findings of the inventors in this technical solution during research: the contents of sodium and manganese elements in the material composition determine the number of deintercalatable sodium ions and the content of sodium ion vacancies in the material, and the content of sodium ion vacancies affects the spacings of the (003) crystal plane and the (002) crystal plane. When 0 < a ≤ 0.25, it can ensure that the material has a high specific capacity and a high diffusion rate of sodium ions between transition metal layers, reducing the migration barrier of sodium ions. When a ≤ d - b, by restricting the number of Na vacancies, on the one hand, it helps to lower the valence state of Ni ions and utilize Ni 2+ / 3+ / 4+ to provide more charge compensation, and on the other hand, it helps to increase the valence state of Mn ions, reduce the content of +3-valent manganese, and avoid Mn 3+ from causing lattice distortion and stress accumulation.

[0048] While doping metal elements into the sodium-ion battery cathode material has been partially proven to be helpful for improving structural stability, in the inventors' research, it was found that the electronic structure state of element X is quite different from that of Ni, Fe, and Mn. The introduction of such elements will activate the electrochemical activity of some oxygen ions. Especially when the average valence state σ of element X > 4, the element charge number and electron transfer ability increase. After bonding with oxygen, the electrochemical activity of oxygen ions is significantly improved, which easily induces the redox reaction of oxygen ions, resulting in the loss of voltage and energy density. Therefore, in order to further optimize the electrochemical performance of the composite crystal domain sodium-ion battery cathode material, the inventors of this technical solution conducted in-depth research and found that in the composite crystal domain sodium-ion battery cathode material that meets the above conditions, when the following conditions are met: X is one or more of Li, Mg, Al, Ca, Cu, Zn, Ti, Zr, Cr, Sr, Ba, Nb, Mo, and W, 0 < x < 0.15, and σ ≤ 4, it can ensure that Ni, Fe, and Mn, as the main stable electrochemical active elements, provide charge compensation and weaken the redox of oxygen anions.

[0049] In addition, starting from the mutual influence of each component, the inventors comprehensively considered the sodium content and sodium vacancies, the contents and valence states of non-sodium metal elements (Ni, Fe, Mn, X), etc., designed the composite crystal domain of the material, and determined another core technical parameter of this technical solution: The inventors discovered through a large number of experiments and explorations that when , accompanied by a relatively low number of sodium vacancies in the component and a relatively high content of manganese element compared to Ni, Fe, and X, it will further affect the valence state and distribution of Mn ions, bringing an adverse impact on the lattice distortion of the structure. When When the number of sodium vacancies in the components is relatively high and the manganese content is relatively low compared to Ni, Fe, and X, the former leads to an increase in the repulsion of the transition metal-oxygen layer, and the latter leads to a decrease in the structural stability of the material, making it difficult to achieve lower material microstress.

[0050] The inventors also found in their research that when the composite crystal domain sodium cathode material that meets the above conditions has a median particle size D50 of 2μm to 12μm, it helps to ensure the compaction density and electrochemical reaction activity of the material, avoiding the problem of too small particles leading to low compaction density or too large particles leading to difficulty in sodium ion deintercalation; its specific surface area is 0.1m 2 / g~1.5m 2 / g, it helps to ensure sufficient contact between the material and the electrolyte, thereby having better electrochemical reaction activity; when its water content is less than 500ppm, it helps to reduce the side reaction between trace water in the material and the electrolyte; when its residual sodium carbonate is less than 3.0wt.%, it helps to reduce the decomposition and gas production of sodium carbonate under high voltage, thereby improving the cycle performance of the battery.

[0051] The second aspect of the present invention provides a method for preparing the composite crystal domain sodium cathode material described in the first aspect. The preparation method provided in this embodiment comprises the following steps:

[0052] (1) mixing a nickel source, an iron source, a manganese source, an X source, and a Class I sodium source to obtain a first sintering material;

[0053] In this step, the Class I sodium source includes at least one of NaOH, CH3COONa and NaNO3, and the nickel source, iron source, manganese source and X source respectively include at least one of chloride, acetate, oxalate, carbonate, bicarbonate and nitrate containing the corresponding metal element; in the first sintered material, the ratio of the molar amount of the sodium element to the total molar amount of the non-sodium metal elements is w1.

[0054] (2) Sintering the first sintering material at a first temperature to obtain a first calcined product.

[0055] (3) mixing the first calcined product and the type II sodium source to obtain a second sintered material;

[0056] In this step, the Class II sodium source includes at least one of Na2CO3, NaHCO3 and Na2C2O4; in the second sintered material, the ratio of the molar amount of sodium element in the Class II sodium source to the total molar amount of non-sodium metal elements in the first calcined product is w2.

[0057] (4) Sintering the second sintering material at a second temperature to obtain a second calcined product.

[0058] (5) crushing and screening the second calcined product to obtain a composite crystal domain sodium cathode material with a median particle size D50 of 2 μm to 12 μm.

[0059] In contrast, type-I sodium source has a relatively low decomposition temperature or melting temperature. Therefore, the first temperature should be lower than the second temperature. Preferably, the first temperature is 500 °C, which can achieve the melting of the type-I sodium source. When 0 < w1 < 0.5·(1 - a), it can effectively promote the intercalation of sodium ions into the material matrix at low temperature, improve the uniformity of sodium ion distribution, and at the same time ensure that the material has low micro-stress. In the inventor's experimental exploration, it was found that when w1 > 0.5·(1 - a), the excessive type-I sodium source is likely to diffuse again during the secondary high-temperature calcination, causing segregation of the crystal domain in the material structure and increasing the micro-stress of the material.

[0060] Since the type-II sodium source has a relatively high decomposition temperature or melting temperature, it is preferably to set the second temperature to 850 - 1100 °C, so that the type-II sodium source is transformed into a molten state at high temperature, promoting the secondary intercalation of sodium ions into the material matrix, slowing down the non-uniformity of sodium ion diffusion and distribution, and reducing the structural micro-stress of the material.

[0061] Preferably, the sintering time at the first temperature is controlled within 1 - 10 h, and the sintering time at the second temperature is controlled within 6 - 30 h. After each sintering, it is cooled with the furnace. During the process of cooling with the furnace, the relative humidity of the environment ≤ 30%, which helps to reduce the water molecule intercalation reaction during the cooling process of the material, reduce the surface residual alkali and possible structural damage; during the process of crushing and sieving the second calcination product, the relative humidity of the environment ≤ 20%, which helps to reduce the moisture content and residual sodium carbonate content of the finished material.

[0062] In the third aspect of the present invention, a positive electrode sheet is proposed, which contains the composite crystal domain sodium-based positive electrode material described in the first aspect.

[0063] In the fourth aspect of the present invention, a battery is proposed, which contains the positive electrode sheet described in the third aspect.

[0064] In the fifth aspect of the present invention, an electrical device is proposed, which contains the battery described in the fourth aspect.

[0065] The present invention will be described in detail below through examples and comparative examples.

[0066] Example 1

[0067] (1) Mix the nickel source, iron source, manganese source, X source and type-I sodium source to obtain the first sintering material;

[0068] In this step, the Class I sodium source is NaOH, the nickel source is NiO, the iron source is Fe2O3, the manganese source is Mn2O3, and the X sources are ZnO, CuO, and Al2O3, which are taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Zn:Cu:Al=0.40:0.2225:0.2225:0.445:0.05:0.03:0.03, and are mixed evenly in a high-speed mixer after use.

[0069] (2) sintering the first sintering material at a first temperature of 500° C. for 5 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a first calcined product; the relative humidity of the environment during the cooling process is 20%.

[0070] (3) mixing the first calcined product and the type II sodium source to obtain a second sintered material;

[0071] In this step, the Class II sodium source is Na2CO3; it is taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Zn:Cu:Al=0.45:0.2225:0.2225:0.445:0.05:0.03:0.03, where Na refers to the sodium in the Class II sodium source, and after taking, it is mixed evenly by mechanical means.

[0072] (4) placing the second sintering material at a second temperature of 950° C. and sintering for 24 hours, and then cooling the material to below 100° C. in the furnace after sintering to obtain a second calcined product; the relative humidity of the environment during the cooling process is 20%.

[0073] (5) crushing and screening the second calcined product, wherein the relative humidity of the environment during the crushing and screening process is 5%, and the chemical formula is Na 0.85 Ni 0.2225 Fe 0.2225 Mn 0.445 Zn 0.05 Cu 0.03 Al 0.03 O2 composite crystal domain sodium battery positive electrode material.

[0074] Example 2

[0075] (1) mixing a nickel source, an iron source, a manganese source, an X source, and a Class I sodium source to obtain a first sintering material;

[0076] In this step, the Class I sodium source is NaNO3, the nickel source is NiO, the iron source is Fe2O3, the manganese source is Mn2O3, and the X sources are LiOH, CaO, and TiO2, which are taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Li:Ca:Ti=0.05:0.184:0.184:0.552:0.02:0.01:0.05, and then mixed evenly in a high-speed mixer.

[0077] (2) sintering the first sintering material at a first temperature of 500° C. for 3 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a first calcined product; the relative humidity of the environment during the cooling process is 20%.

[0078] (3) mixing the first calcined product and the type II sodium source to obtain a second sintered material;

[0079] In this step, the Class II sodium source is NaHCO3; it is taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Li:Ca:Ti=0.80:0.184:0.184:0.552:0.02:0.01:0.05, where Na refers to the sodium in the Class II sodium source, and after taking, it is mixed evenly by mechanical means.

[0080] (4) sintering the second sintering material at a second temperature of 1000° C. for 6 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a second calcined product; the relative humidity of the environment during the cooling process is 25%.

[0081] (5) crushing and screening the second calcined product, wherein the relative humidity of the environment during the crushing and screening process is 18%, and the chemical formula is Na 0.83 Ni 0.184 Fe 0.184 Mn 0.552 Li 0.02 Ca 0.01 Ti 0.05 O2 composite crystal domain sodium battery positive electrode material.

[0082] Example 3

[0083] (1) mixing a nickel source, an iron source, a manganese source, an X source, and a Class I sodium source to obtain a first sintering material;

[0084] In this step, the Class I sodium source is CH3COONa, the nickel source is Ni(OH)2, the iron source is FeCl3, the manganese source is MnCO3, and the X sources are TiO2, Cu(NO3)2, and ZrO2, which are taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Ti:Cu:Zr=0.35:0.276:0.184:0.46:0.02:0.05:0.01. After use, they are mixed evenly in a high-speed mixer.

[0085] (2) sintering the first sintering material at a first temperature of 500° C. for 3 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a first calcined product; the relative humidity of the environment during the cooling process is 20%.

[0086] (3) mixing the first calcined product and the type II sodium source to obtain a second sintered material;

[0087] In this step, the Class II sodium source is Na2C2O4; it is taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Ti:Cu:Zr=0.50:0.276:0.184:0.46:0.02:0.05:0.01, where Na refers to the sodium in the Class II sodium source, and after taking, it is mixed evenly by mechanical means.

[0088] (4) sintering the second sintering material at a second temperature of 1100° C. for 6 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a second calcined product; the relative humidity of the environment during the cooling process is 20%.

[0089] (5) crushing and screening the second calcined product, wherein the relative humidity of the environment during the crushing and screening process is 20%, and obtaining a product having the chemical formula Na 0.85 Ni 0.276 Fe 0.184 Mn 0.46 Ti 0.02 Cu 0.05 Zr 0.01 O2 composite crystal domain sodium battery positive electrode material.

[0090] Example 4

[0091] (1) mixing a nickel source, an iron source, a manganese source, an X source, and a Class I sodium source to obtain a first sintering material;

[0092] In this step, the type I sodium source is NaOH and NaNO3, the nickel source, iron source and manganese source are Ni 0.30 Fe 0.05 Mn 0.65 (OH)2, the X source is Mg(OH)2 and Cr2O3, which are taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Mg:Cr=0.40:0.267:0.0445:0.5785:0.1:0.01, and then mixed evenly in a high-speed mixer.

[0093] (2) sintering the first sintering material at a first temperature of 500° C. for 3 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a first calcined product; the relative humidity of the environment during the cooling process is 28%.

[0094] (3) mixing the first calcined product and the type II sodium source to obtain a second sintered material;

[0095] In this step, the Class II sodium source is NaHCO3; it is taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Mg:Cr=0.45:0.267:0.0445:0.5785:0.1:0.01, where Na refers to the sodium in the Class II sodium source, and after taking, it is mixed evenly by mechanical means.

[0096] (4) sintering the second sintering material at a second temperature of 900° C. for 30 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a second calcined product; the relative humidity of the environment during the cooling process is 28%.

[0097] (5) crushing and screening the second calcined product, wherein the relative humidity of the environment during the crushing and screening process is 20%, and obtaining a product having the chemical formula Na 0.84 Ni 0.267 Fe 0.0445 Mn 0.5785 Mg 0.1 Cr 0.01 O2 composite crystal domain sodium battery positive electrode material.

[0098] Example 5

[0099] (1) mixing a nickel source, an iron source, a manganese source, an X source, and a Class I sodium source to obtain a first sintering material;

[0100] In this step, the Class I sodium source is NaNO3, the nickel source is Ni(CH3COO)2, the iron source is Fe2(C2O4)3, the manganese source is MnCO3, and the X sources are Li2CO3 and WO3, which are taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Li:W=0.40:0.235:0.235:0.47:0.05:0.01, and then mixed evenly in a high-speed mixer.

[0101] (2) sintering the first sintering material at a first temperature of 500° C. for 3 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a first calcined product; the relative humidity of the environment during the cooling process is 30%.

[0102] (3) mixing the first calcined product and the type II sodium source to obtain a second sintered material;

[0103] In this step, the Class II sodium sources are NaHCO3 and Na2CO3; they are taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Li:W=0.50:0.235:0.235:0.47:0.05:0.01, where Na refers to the sodium in the Class II sodium source, and they are mixed uniformly by mechanical means after taking.

[0104] (4) sintering the second sintering material at a second temperature of 900° C. for 20 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a second calcined product; the relative humidity of the environment during the cooling process is 30%.

[0105] (5) crushing and screening the second calcined product, wherein the relative humidity of the environment during the crushing and screening process is 20%, and obtaining a product having the chemical formula Na 0.89 Ni 0.235 Fe 0.235 Mn0.47 Li 0.05 W 0.01 O2 composite crystal domain sodium battery positive electrode material.

[0106] Example 6

[0107] (1) mixing a nickel source, an iron source, a manganese source, an X source, and a Class I sodium source to obtain a first sintering material;

[0108] In this step, the type I sodium source is NaOH, the nickel source, iron source and manganese source are Ni 0.45 Fe 0.05 Mn 0.50 (OH)2, X sources are ZnO and SrCO3, which are taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Zn:Sr=0.30:0.414:0.046:0.46:0.04:0.04, and then mixed evenly in a high-speed mixer.

[0109] (2) sintering the first sintering material at a first temperature of 500° C. for 5 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a first calcined product; the relative humidity of the environment during the cooling process is 20%.

[0110] (3) mixing the first calcined product and the type II sodium source to obtain a second sintered material;

[0111] In this step, the Class II sodium source is Na2CO3; it is taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Zn:Sr=0.67:0.414:0.046:0.46:0.04:0.04, where Na refers to the sodium in the Class II sodium source, and after taking, it is mixed evenly by mechanical means.

[0112] (4) placing the second sintering material at a second temperature of 930° C. and sintering for 20 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a second calcined product; the relative humidity of the environment during the cooling process is 30%.

[0113] (5) crushing and screening the second calcined product, wherein the relative humidity of the environment during the crushing and screening process is 20%, and obtaining a product having the chemical formula Na 0.97 Ni 0.414 Fe 0.046 Mn 0.46 Zn 0.04 Sr 0.04 O2 composite crystal domain sodium battery positive electrode material.

[0114] Example 7

[0115] (1) mixing a nickel source, an iron source, a manganese source, an X source, and a Class I sodium source to obtain a first sintering material;

[0116] In this step, the Class I sodium source is NaOH, the nickel source is NiO, the iron source is Fe3O4, the manganese source is MnO2, and the X sources are CuO and Nb2O5, which are taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Zn:Sr=0.30:0.23625:0.23625:0.4725:0.05:0.005, and then mixed evenly in a high-speed mixer.

[0117] (2) sintering the first sintering material at a first temperature of 500° C. for 5 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a first calcined product; the relative humidity of the environment during the cooling process is 30%.

[0118] (3) mixing the first calcined product and the type II sodium source to obtain a second sintered material;

[0119] In this step, the Class II sodium source is NaHCO3; it is taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Zn:Sr=0.50:0.23625:0.23625:0.4725:0.05:0.005, where Na refers to the sodium in the Class II sodium source, and after taking, it is mixed evenly by mechanical means.

[0120] (4) placing the second sintering material at a second temperature of 960° C. and sintering for 20 hours, and then cooling the material to below 100° C. in the furnace after sintering to obtain a second calcined product; the relative humidity of the environment during the cooling process is 25%.

[0121] (5) crushing and screening the second calcined product, wherein the relative humidity of the environment during the crushing and screening process is 10%, and obtaining a product having the chemical formula Na 0.8 Ni 0.23625 Fe 0.23625 Mn 0.4725 Cu 0.05 Nb 0.005 O2 composite crystal domain sodium battery positive electrode material.

[0122] Example 8

[0123] (1) mixing a nickel source, an iron source, a manganese source, an X source, and a Class I sodium source to obtain a first sintering material;

[0124] In this step, the Class I sodium source is NaNO3, the nickel source is NiO, the iron source is Fe3O4, the manganese source is MnO2, and the X sources are BaCO3 and MoO3, which are taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Ba:Mo=0.30:0.22375:0.04475:0.6265:0.1:0.005, and are mixed evenly in a high-speed mixer after use.

[0125] (2) sintering the first sintering material at a first temperature of 500° C. for 5 hours, and cooling the material to below 100° C. in the furnace after sintering to obtain a first calcined product; the relative humidity of the environment during the cooling process is 20%.

[0126] (3) mixing the first calcined product and the type II sodium source to obtain a second sintered material;

[0127] In this step, the Class II sodium source is Na2C2O4; it is taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Ba:Mo=0.45:0.22375:0.04475:0.6265:0.1:0.005, where Na refers to the sodium in the Class II sodium source, and after taking, it is mixed evenly by mechanical means.

[0128] (4) placing the second sintering material at a second temperature of 850° C. and sintering for 20 hours, and then cooling the material to below 100° C. in the furnace after sintering to obtain a second calcined product; the relative humidity of the environment during the cooling process is 25%.

[0129] (5) crushing and screening the second calcined product, wherein the relative humidity of the environment during the crushing and screening process is 10%, and obtaining a product having the chemical formula Na 0.75 Ni 0.22375 Fe 0.04475 Mn 0.6265 Ba 0.1 Mo 0.005 O2 composite crystal domain sodium battery positive electrode material.

[0130] Comparative Example 1

[0131] The only difference compared with Example 1 is that in step (1) of Comparative Example 1: the X source is Nb2O5, and is taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Nb=0.40:0.2225:0.2225:0.445:0.11, and then mixed to obtain the first sintered material; in step (3), the X source is taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Nb=0.45:0.2225:0.2225:0.445:0.11, where Na refers to sodium of Class II sodium source, and then mixed to obtain the second sintered material.

[0132] The final chemical formula is Na 0.85 Ni 0.2225 Fe 0.2225 Mn 0.445 Nb 0.11 Sodium O2 cathode material.

[0133] Comparative Example 2

[0134] The only difference compared with Example 1 is that in step (1) of Comparative Example 2, no X source is added, and other raw materials are taken according to the following molar ratio of elements: Na:Ni:Fe:Mn=0.40:0.25:0.25:0.50, and then mixed to obtain the first sintered material; in step (3), the following molar ratio of elements are taken: Na:Ni:Fe:Mn=0.45:0.25:0.25:0.50, where Na refers to sodium of Class II sodium source, and then mixed to obtain the second sintered material.

[0135] The final chemical formula is Na 0.85 Ni 0.25 Fe 0.25 Mn 0.50 Sodium O2 cathode material.

[0136] Comparative Example 3

[0137] The only difference compared with Example 1 is that in step (1) of Comparative Example 3, the following elements are taken in a molar ratio: Na:Ni:Fe:Mn:Zn:Cu:Al=0.30:0.2225:0.2225:0.445:0.05:0.03:0.03, and then mixed to obtain the first sintering material.

[0138] The final chemical formula is Na 0.75 Ni 0.2225 Fe 0.2225 Mn 0.445 Zn 0.05 Cu 0.03 Al 0.03 Sodium O2 cathode material.

[0139] Comparative Example 4

[0140] The only difference compared with Example 1 is that in step (3) of Comparative Example 4, the following elements are taken in a molar ratio: Na:Ni:Fe:Mn:Zn:Cu:Al=0.55:0.2225:0.2225:0.445:0.05:0.03:0.03, where Na refers to sodium of Class II sodium source, which is taken and mixed to obtain the second sintering material.

[0141] The final chemical formula is Na 0.95 Ni 0.2225 Fe 0.2225 Mn 0.445 Zn 0.05 Cu 0.03 Al 0.03 Sodium O2 cathode material.

[0142] Comparative Example 5

[0143] The only difference compared with Example 1 is that in step (1) of Comparative Example 5, no Fe source is added, and other raw materials are taken according to the following molar ratio of elements: Na:Ni:Mn:Zn:Cu:Al=0.40:0.445:0.445:0.05:0.03:0.03, and then mixed to obtain the first sintered material; in step (3), the following molar ratio of elements are taken: Na:Ni:Mn:Zn:Cu:Al=0.60:0.445:0.445:0.05:0.03:0.03, where Na refers to sodium of Class II sodium source, and then mixed to obtain the second sintered material.

[0144] The final chemical formula is NaNi 0.445 Mn 0.445 Zn 0.05 Cu 0.03 Al 0.03 Sodium O2 cathode material.

[0145] Comparative Example 6

[0146] The only difference compared with Example 1 is that in step (1) of Comparative Example 6, other raw materials are not taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Zn:Cu:Al=0.40:0.2225:0.445:0.2225:0.05:0.03:0.03, and are mixed after taking to obtain the first sintering material; in step (3), the following molar ratio of elements are taken: Na:Ni:Fe:Mn:Zn:Cu:Al=0.45:0.2225:0.445:0.2225:0.05:0.03:0.03, wherein Na refers to sodium of Class II sodium source, and are taken and mixed to obtain the second sintering material.

[0147] The final chemical formula is Na 0.85 Ni 0.2225 Fe 0.445 Mn 0.2225 Zn 0.05 Cu 0.03 Al 0.03 Sodium O2 cathode material.

[0148] Comparative Example 7

[0149] The only difference compared with Example 1 is that in step (1) of Comparative Example 7, other raw materials are not taken according to the following molar ratio of elements: Na:Ni:Fe:Mn:Zn:Cu:Al=0.40:0.445:0.2225:0.2225:0.05:0.03:0.03, and are mixed after taking to obtain the first sintering material; in step (3), the following molar ratio of elements are taken: Na:Ni:Fe:Mn:Zn:Cu:Al=0.45:0.445:0.2225:0.2225:0.05:0.03:0.03, wherein Na refers to sodium of Class II sodium source, and are taken and mixed to obtain the second sintering material.

[0150] The final chemical formula is Na 0.85 Ni 0.2225 Fe 0.445 Mn 0.2225 Zn 0.05 Cu 0.03 Al 0.03 Sodium O2 cathode material.

[0151] Comparative Example 8

[0152] The only difference compared with Example 1 is that, in Comparative Example 8, the step-by-step mixing operation of Class I sodium source and Class II sodium source is cancelled, and instead: after all the raw materials are taken and mixed at one time according to the ratio in Example 1, the mixture is calcined at 500°C for 5h, then heated to 950°C and calcined for 24h, and then cooled to below 100°C during the furnace cooling process with an ambient relative humidity of 20% to obtain a calcined product.

[0153] The chemical formula of the calcined product is Na 0.85 Ni 0.2225 Fe 0.2225 Mn 0.445 Zn 0.05 Cu 0.03 Al 0.03 O2.

[0154] The present invention uses the following method to perform physical and chemical characterization tests on the composite crystal domain sodium cathode materials prepared in Examples 1-8 and the sodium cathode materials prepared in Comparative Examples 1-8 (hereinafter referred to as samples) and obtain corresponding test results.

[0155] (1) The morphology of the composite crystal domain sodium cathode material prepared in Example 1 was observed using a scanning electron microscope (SEM). Figure 1 As shown. Figure 1 It can be seen that the composite crystal domain sodium battery cathode material prepared in Example 1 is in the form of regular flaky single crystal particles with a particle size of about 3 μm to 5 μm.

[0156] (2) ICP test: The sample is dissolved in hydrochloric acid and prepared into a solution of a certain concentration. The content and chemical formula composition of the metal elements in the sample are tested by inductively coupled plasma atomic emission spectrometry. The calculation results are shown in Table 1.

[0157] (3) XPS testing: The elements on the cathode material surface were analyzed by measuring the value and change of the photoelectron kinetic energy / binding energy. Casa XPS software was used to fit the obtained data and analyze the chemical valence state of the material. The test and σ calculation results are shown in Table 1.

[0158] Table 1 ICP and XPS test results

[0159]

[0160] (4) XRD test: Cu-Kα target was used, emission wavelength λ = 0.154nm, scanning voltage was 40kV, current was 40mA, step scanning mode was used, scanning range was 10°~90°, and the absolute value of micro stress ε of the material was calculated using the test results. The results are shown in Table 2. Among them, the XRD spectrum of the composite crystal domain sodium cathode material prepared in Example 1 is shown in Table 2. Figure 2 As shown, it has excellent crystallinity, and there are two diffraction peaks in the range of 2θ = 15° to 18°. M and θ N They correspond to the (002) crystal plane of domain A and the (003) crystal plane of domain B, respectively.

[0161] Table 2 XRD test results and ε

[0162]

[0163]

[0164] (5) Test method for median particle size D50: The particle size distribution and median particle size D50 of the sample were tested using a Malvern laser particle size analyzer Mastersizer 3000. The results are shown in Table 3.

[0165] (6) Specific surface area test method: The specific surface area of the sample was tested using a dynamic method. The sample was placed in a U-shaped tube and a helium-nitrogen mixed gas with a volume ratio of 1:4 was introduced. After the mixed gas flowed through the sample, the adsorption amount of the sample was obtained based on the change in gas concentration before and after adsorption. The results are shown in Table 3.

[0166] (7) Moisture test method: Karl Fischer (coulometric method) is used for testing. The ambient dew point should not be lower than -18°C. The sample is weighed and placed in a sample bottle. The heating tank temperature of the Karl Fischer moisture analyzer is then set to 170°C and the carrier gas flow rate is 20 mL / min. After the test, the moisture content is read on the moisture analyzer. The results are shown in Table 3.

[0167] Table 3 Particle size, specific surface area and moisture test results

[0168]

[0169] (8) Electrochemical performance test

[0170] The specific preparation method of the sodium secondary battery and its positive electrode sheet is as follows: the sample is mixed with acetylene black, carbon nanotubes, and polyvinylidene fluoride in a mass ratio of 90:5:1:4, an appropriate amount of N-methylpyrrolidone is added as a dispersant, and the mixture is ground into a slurry; the slurry is then evenly coated on one side of an aluminum foil, vacuum-dried at 120°C for 10 hours, and the dried electrode sheet is rolled with a roller mill. The aluminum foil is cut with a slicer to form a circular electrode sheet with a diameter of 1.3 cm. The loading amount of the active material is controlled at 10 mg cm -2 The half-cell was assembled in an argon atmosphere glove box with a water partial pressure ≤ 0.1 ppm and an oxygen partial pressure ≤ 0.1 ppm. A CR2032 button cell was assembled using metallic sodium as the counter electrode and a 1M NaPF6 (EC / DEC, 1:1 volume ratio) solution as the electrolyte.

[0171] Sodium ion battery capacity and cycle test method: button cells were charged and discharged at room temperature using constant current charge and discharge mode. First, constant current charging was performed at a current density of 15 mA / g to 4.2 V (vs. Na / Na + ), and then discharged at a constant current density of 15 mA / g to 2.0 V (vs. Na / Na + ) to obtain the material's gram capacity and first coulombic efficiency. The cycle test was performed using a constant current charge-discharge mode at room temperature for 100 cycles, with a voltage range of 2.0V to 4.1V and a current density of 50mA·g -1 , record the discharge specific capacity (Cap1, Cap100) and discharge specific energy (En1, En100) of the 1st and 100th cycles, and the energy retention rate after 100 cycles is The voltage decays to The results are shown in Table 4.

[0172] Table 4 Electrochemical performance test results

[0173]

[0174]

[0175] As shown in Tables 1 to 4, when the X element in Comparative Example 1 is a high-valence (+5) Nb element and X is not added in Comparative Example 2, although the material has characteristic diffraction peaks M and N similar to the composite crystal domain structure, the microstress of the material is significantly increased, resulting in the deterioration of electrical properties. In Comparative Example 3, the sodium content is reduced, a>db, resulting in the disappearance of the composite crystal domain. In Comparative Example 4, The result is that the material does not have a composite crystal domain and the residual sodium carbonate content is high, thus not meeting the requirements. In Comparative Example 5, a=db, the material does not have a composite crystal domain and the residual sodium carbonate content is high, thus not meeting the requirements. In Comparative Examples 6 and 7, a>db and Although there are characteristic diffraction peaks M and N similar to the composite crystal domain structure, the material microstress and residual sodium carbonate content are significantly high, and the electrical properties are deteriorated. In Comparative Example 8, although the same raw materials and proportions as Example 1 are used, the gradient sodium supplementation process is not adopted. The obtained material has characteristic diffraction peaks M and N similar to the composite crystal domain structure. This is mainly due to the one-time addition of the mixed sodium source, but this is not conducive to the melting and diffusion of the sodium source in the two-step sintering process, resulting in poor sodium ion dispersion in the material, thereby causing high microstress and poor electrical properties.

[0176] As can be seen from Table 4, the first-cycle coulombic efficiency and energy retention rate after 100 cycles of the composite crystal domain sodium cathode materials prepared in Examples 1-8 are significantly higher than those of the comparative example, the voltage decay is significantly suppressed, and the materials have more excellent electrical properties.

[0177] The composite crystal domain sodium cathode material provided by the present invention ensures that the material has a higher energy density by regulating the sodium content, material composition, valence state and X element doping, introduces other ions to provide charge compensation, and regulates the structure and coupling of crystal domain A and crystal domain B, thereby balancing the electrostatic attraction and repulsion between the sodium layer / transition metal layer; the method of step-by-step sodium supplementation and step-by-step calcination is adopted to achieve the uniform embedding of sodium in the interlayer structure, thereby inducing the differentiation of the material microstructure to form two different Na-O coordination structures and a material with an absolute microstress value of <10%. The low microstress feature of the composite crystal domain sodium cathode material reduces the stress accumulation and lattice strain caused by the uneven expansion in the bulk structure of the material, improves the interaction between oxygen ions and the transition metal layer, increases the formation and migration barrier of oxygen vacancies in the structure, and synergizes with the introduced charge compensation ions to improve the stability of the lattice oxygen in the material and slow down the voltage decay and capacity decay. Thus, the material provided by the present invention has a low microstress at high potential (4.2Vvs.Na / Na + ) exhibits stronger long-term cycle stability and specific capacity and voltage retention capabilities. In addition, the material process is simple and easy to scale up for industrial production, reducing product costs.

[0178] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. Composite crystal domain sodium cathode material, characterized in that: The composite crystal domain sodium cathode material: The chemical formula is Na 1-a Ni b Fe c Mn d X x O2, 0<a≤0.25, b+c+d+x=1, X is a metal element with an average valence σ≤4; There are layered domains A and B in the crystal structure; The absolute value of microstress in the crystal structure ε<10%; In the X-ray powder diffraction pattern measured using Cu-Kα rays, the composite crystal domain sodium cathode material has at least the following at 2θ of 15° to 18°: Corresponding to the diffraction peak M of the (002) crystal plane in the crystal domain A, the diffraction angle of the diffraction peak M is θ M , half-peak width is β M ; Corresponding to the diffraction peak N of the (003) crystal plane in the crystal domain B, the diffraction angle of the diffraction peak N is θ N , half-peak width is β N ; Where: 2θ M <2θ N , ; The preparation method of the composite crystal domain sodium cathode material comprises the following steps: Mixing nickel source, iron source, manganese source, X source and type I sodium source to obtain a first sintering material; sintering the first sintering material at a first temperature to obtain a first calcined product; mixing the first calcined product and the type II sodium source to obtain a second sintered material; sintering the second sintering material at a second temperature to obtain a second calcined product; crushing and screening the second calcined product to obtain a composite crystal domain sodium cathode material; The decomposition temperature or melting temperature of the type I sodium source is lower than that of the type II sodium source, the first temperature is lower than the second temperature, and the median particle size D50 of the composite crystal domain sodium cathode material is 2 μm to 12 μm. The first temperature is 500°C, and the second temperature is 850-1100°C.

2. The composite crystal domain sodium cathode material according to claim 1, characterized in that X is one or more of Li, Mg, Al, Ca, Cu, Zn, Ti, Zr, Cr, Sr, Ba, Nb, Mo and W, and 0<x<0.

15.

3. The composite crystal domain sodium cathode material according to claim 2, characterized in that a≤d-b, 。 4. A method for preparing the composite crystal domain sodium cathode material according to any one of claims 1 to 3, characterized in that: Including steps: Mixing nickel source, iron source, manganese source, X source and type I sodium source to obtain a first sintering material; sintering the first sintering material at a first temperature to obtain a first calcined product; mixing the first calcined product and the type II sodium source to obtain a second sintered material; sintering the second sintering material at a second temperature to obtain a second calcined product; crushing and screening the second calcined product to obtain a composite crystal domain sodium cathode material; The decomposition temperature or melting temperature of the type I sodium source is lower than that of the type II sodium source, the first temperature is lower than the second temperature, and the median particle size D50 of the composite crystal domain sodium cathode material is 2 μm to 12 μm; The first temperature is 500°C, and the second temperature is 850-1100°C.

5. The method for preparing a composite crystal domain sodium cathode material according to claim 4, characterized in that: Class I sodium sources include at least one of NaOH, CH3COONa and NaNO3; In the first sintering material, the ratio of the molar amount of sodium element to the total molar amount of non-sodium metal elements is w1,0 <w1<0.5·(1-a); Class II sodium sources include at least one of Na2CO3, NaHCO3 and Na2C2O4; In the second sintered material, the ratio of the molar amount of sodium element in the type II sodium source to the total molar amount of non-sodium metal elements in the first calcined product is w2,1-a <w1+w2<1.05·(1-a); The nickel source, iron source, manganese source and X source each include at least one of chloride, acetate, oxalate, carbonate, bicarbonate and nitrate containing the corresponding metal element; The first sintering material is sintered at a first temperature for 1 to 10 hours; the second sintering material is sintered at a second temperature for 6 to 30 hours; After sintering, the furnace is cooled. The relative humidity during the cooling process is ≤30%; During the process of crushing and screening the second calcined product, the relative humidity of the environment is ≤20%.

6. A positive electrode plate, characterized in that: The positive electrode sheet contains the composite crystal domain sodium positive electrode material according to any one of claims 1 to 3.

7. A battery, characterized in that The battery contains the positive electrode sheet according to claim 6.

8. An electrical device, characterized in that: The electrical device contains the battery according to claim 7.

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