Sodium ion layered metal oxide material and preparation method therefor, positive electrode material, and sodium ion battery

Abstract

A sodium ion layered metal oxide material and a preparation method therefor, a positive electrode material, and a sodium ion battery, relating to the technical field of sodium ion batteries. The sodium ion layered metal oxide material has a chemical formula as shown in formula I: NaxNiaMnbTi(0.5-b)M(0.5-a)O(2-y)Fy, wherein 0.9≤x≤1.0, 0.3≤a<0.5, 0.3≤b≤0.4, 0.1≤1-a-b≤0.35, 0≤y<0.1, and M comprises at least one of Zn, Mg, Sn, Sb, Y and Cu. By doping the F element and the M element, the structural stability of the material is improved, the generation of an impurity phase can be reduced, and the M element in a finished product is more uniformly distributed, so that a positive electrode sheet and sodium ion battery containing the sodium ion layered metal oxide material have a high discharge specific capacity and good cycle performance.

Description

Sodium ion layered metal oxide material, preparation method thereof, positive electrode material and sodium ion battery Technical Field

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

[0002] The commercialization of electrochemical power sources, especially lithium-ion batteries (LIBs), has ushered in a new era of portable electronics and electric vehicles, greatly facilitating daily life. However, driven by concerns about lithium resource depletion and volatile prices for lithium, nickel, and cobalt raw materials, sodium-ion batteries (NIBs) have been intensively studied and have become a strong competitor in energy storage fields such as national grid and home energy storage. The cathode is an indispensable part of NIBs and directly determines all key performance of NIBs, such as cost, safety, energy density, power density, and cycle life. In addition, the ideal cathode material should be relatively environmentally friendly and easy to mass-produce, transport, and store.

[0003] Cost is the core factor driving the competition between sodium-ion batteries and lithium-ion batteries. Manganese has the advantages of being environmentally friendly, low in price, and high in annual output. x TMO2 (TMO2) contains numerous electrochemically redox-active elements, including Mn, Fe, Cu, Ni, Co, Cr, Ir, Ru, and O, allowing for flexible chemical composition design. Its high specific capacity and excellent safety make it a strong contender for commercial sodium-ion battery cathode materials.

[0004] The general formula of the current sodium ion layered transition metal oxide cathode material is Na x TMO2, along with Na + The change of NaO content forms different structures. Common structures include O3, P3, O'3 and P2 phases. The transition metal positions in layered oxides can be occupied by various metal ions (such as Li, Na, Mg, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Ir, Ru, etc.). The extranuclear electron configuration, oxidation state, and TM-O bond energy of these metal ions vary greatly, and with the change of NaO content, the transition metal positions in layered oxides can be occupied by various metal ions (such as Li, Na, Mg, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Ir, Ru, etc.). + Variations in the content form layered oxide cathode materials with different structures. O3-type high-nickel materials have high specific capacities, but when charged to higher voltages, they not only undergo multiphase transformations, leading to significant volume deformation, but also promote electrolyte decomposition and induce co-intercalation of solvent molecules, ultimately leading to severe structural deterioration and capacity decay during the charge-discharge process.

[0005] Summary of the Invention

[0006] In view of the technical problems existing in the background technology, the present invention provides a sodium ion layered metal oxide material, a preparation method thereof, a positive electrode material and a sodium ion battery, aiming to solve the technical problems of serious structural deterioration and capacity attenuation of the positive electrode material during the charge and discharge process.

[0007] In the first aspect, the present invention provides a sodium ion layered metal oxide material having the chemical formula shown in Formula I: Na x Ni a Mn b Ti (0.5-b) M (0.5-a) O (2-y) F y Formula I;

[0008] Wherein, 0.9≤x≤1.0, 0.3≤a<0.5, 0.3≤b≤0.4, 0.1≤1-ab≤0.35, 0≤y<0.1, and M includes at least one of Zn, Mg, Sn, Sb, Y and Cu.

[0009] In the embodiment of the present invention, the M element helps to improve the stability of the material. - Radius and O 2- The radius is similar, so it is feasible for F to replace O. By controlling the doping amount of F, it is possible to avoid excessive impurities in the finished product caused by F doping; the strong electronegativity of F can change the binding energy of oxygen elements in the lattice, thereby increasing the Na + The diffusion rate of Mn 3+ The Jahn-Teller effect of active ions causes lattice distortion, which improves the stability of the structure.

[0010] Preferably, the sodium ion layered metal oxide material is an O3 type manganese-based layered oxide material.

[0011] In a second aspect, the present invention provides a method for preparing the sodium ion layered metal oxide material as described above, comprising the following steps:

[0012] A) mixing a Na source, a Ni source, a Mn source, a Ti source, a M source, and a F source with a solvent in a stoichiometric ratio according to formula I and then coarsely grinding the mixture to obtain a first slurry;

[0013] B) grinding the first slurry to obtain a second slurry;

[0014] C) spray drying the second slurry to obtain a first powder;

[0015] D) calcining the powder according to the following procedure to obtain a second powder,

[0016] In an oxygen-containing atmosphere, heating the sample from room temperature to 110-130°C at a heating rate of 3-5°C / min, holding the temperature for 2-4 hours, then heating the sample to 440-460°C at a heating rate of 5-8°C / min, holding the temperature for 1-3 hours, then heating the sample to 850-950°C at a heating rate of 5-8°C / min, holding the temperature for 10-20 hours;

[0017] E) crushing, screening and removing iron from the second powder to obtain a sodium ion layered metal oxide material having a chemical formula of formula I; Na x Ni a Mn b Ti (0.5-b) M (0.5-a) O (2-y) F y Formula I;

[0018] Wherein, 0.9≤x≤1.0, 0.3≤a<0.5, 0.3≤b≤0.4, 0.1≤1-ab≤0.35, 0≤y<0.1, and M includes at least one of Zn, Mg, Sn, Sb, Y and Cu.

[0019] In an embodiment of the present invention, the second powder is calcined using a specific programmed temperature rise, which can reduce the occurrence of side reactions and the generation of impurities, while making the distribution of copper in the finished product more uniform, improving the uniformity of the material and the stability of the product, and further improving the electrochemical performance.

[0020] Preferably, the sodium ion layered metal oxide material is Na 0.95 Ni 0.45 Mn 0.3 Cu 0.05 Ti 0.2 O 1.9 5F 0.05 ,NaNi 0.48 Mn 0.4 Y 0.02 Ti 0.1 O 1.999 F 0.001 and Na 0.9 Ni 0.48 Mn 0.39 Cu 0.02 Mg 0.01 Ti 0.1 One or more of O2.

[0021] Preferably, the calcination procedure is specifically as follows:

[0022] In an oxygen-containing atmosphere, the temperature is increased from room temperature to 120-125°C at a heating rate of 4-5°C / min, kept warm for 2-3 hours, then increased to 450-455°C at a heating rate of 5-7°C / min, kept warm for 1-2 hours, then increased to 850-950°C at a heating rate of 5-8°C / min, and kept warm for 13-20 hours.

[0023] Preferably, the solvent used for the coarse grinding in step A) is water and / or alcohol, the solid content of the first slurry is 10-40%, and clogging of the coarse grinder, sand mill and connecting pipes is avoided while ensuring the output. The particle size of the first slurry is D100 <10 μm, and the particles in the slurry are prevented from clogging the sand mill filter.

[0024] Preferably, the particle size of the second slurry is D50 < 3 μm and D100 < 8 μm, so as to ensure that the particle size distribution of the first powder obtained after spray drying is more concentrated and avoid the appearance of large particles; the slurry is uniform, and the particle size of the second slurry is small, which does not allow sufficient contact between the particles, which is conducive to ensuring the uniformity of the cation distribution in the finished product.

[0025] In the embodiment of the present invention, grinding after coarse grinding can ensure that each insoluble particle in the slurry is fully ground, ensure the uniformity of the slurry, and improve the grinding efficiency.

[0026] Preferably, the particle size of the first powder is 2 μm<D50<15 μm, D100<40 μm, the moisture content is less than 1.5%, and BET>15 μm. 2 / g.

[0027] In an embodiment of the present invention, the first powder meets the above-mentioned indicators to ensure that less water vapor is generated during the sintering of the first powder, thereby avoiding sodium precipitation. The small particle size and large BET of the first powder ensure more complete contact between the particles during sintering, facilitating ion exchange and migration, thereby ensuring that the sintered material has higher crystallinity, more uniform cation distribution, and fewer impurities.

[0028] Preferably, during the calcination process, the oxygen content is 20-35%, the moisture content is less than 3%, and the carbon dioxide concentration is less than 1%.

[0029] In an embodiment of the present invention, the moisture, oxygen and carbon dioxide contents in the high-temperature furnace are detected online during the sintering process, and the gas supply amount, exhaust amount, and the ratio of oxygen and nitrogen in the supply gas are adjusted in a timely manner to control the moisture, oxygen and carbon dioxide contents in the high-temperature furnace within a control range, thereby avoiding excessive oxygen content and the formation of excessive impurities during the sintering process.

[0030] Preferably, rapid cooling is performed after calcination to obtain the second powder; the rapid cooling is a quenching treatment.

[0031] In the embodiment of the present invention, the cooling rate is accelerated during the cooling process after calcination, which helps to form a 3+ And the metastable phase with high sodium content between the layers improves the reversible capacity of the electrode material.

[0032] In a third aspect, the present invention provides a positive electrode plate, comprising the sodium ion layered metal oxide material described above or the sodium ion layered metal oxide material prepared by the preparation method described above.

[0033] In an embodiment of the present invention, the positive electrode plate includes the above-mentioned sodium ion layered metal oxide material, and thus has better structural stability, higher discharge specific capacity and higher capacity retention rate.

[0034] In a fourth aspect, the present invention provides a sodium ion battery comprising the positive electrode sheet described above.

[0035] In an embodiment of the present invention, the sodium ion battery includes the above-mentioned positive electrode plate, and thus has a higher discharge specific capacity and higher cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0037] FIG1 is a SEM image of the sodium ion layered metal oxide material in Example 1 of the present invention;

[0038] FIG2 is an XRD pattern of the sodium ion layered metal oxide material in Example 1 of the present invention;

[0039] FIG3 is a charge and discharge curve of the button battery in Example 1 of the present invention;

[0040] FIG4 is a charge and discharge curve of the button battery in Example 2 of the present invention;

[0041] FIG5 is a SEM image of the sodium ion layered metal oxide material in Example 2 of the present invention;

[0042] FIG6 is a charge and discharge curve of the button battery in Example 3 of the present invention;

[0043] FIG7 is a SEM image of the sodium ion layered metal oxide material in Example 3 of the present invention. DETAILED DESCRIPTION

[0044] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0046] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0047] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0048] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0049] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0050] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0051] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0052] Among the current structures of sodium ion layered transition metal oxide positive electrode materials, O3-type high-nickel materials have a higher specific capacity. However, when charged to a higher voltage, it not only causes multiphase transition and leads to a large volume deformation, but also promotes the decomposition of the electrolyte and induces the co-embedding of solvent molecules, ultimately leading to serious structural deterioration and capacity attenuation of the electrode material during the charge and discharge process.

[0053] In order to solve the above technical problems, the present invention provides a sodium ion layered metal oxide material, a preparation method thereof, a positive electrode sheet and a sodium ion battery, wherein the doping of F and M elements helps to improve the stability of the material, and the strong electronegativity of F can change the binding energy of oxygen elements in the lattice, thereby increasing the Na + The diffusion rate of Mn 3+ The Jahn-Teller effect of active ions causes lattice distortion, improving structural stability. Furthermore, by calcining the second powder using a specific programmed temperature increase, the present invention can reduce the occurrence of side reactions and the formation of impurities, while also making the copper distribution in the finished product more uniform, improving the material uniformity and product stability, and further enhancing electrochemical performance. As a result, the positive electrode sheet and sodium-ion battery using this sodium-ion layered metal oxide material have a higher discharge capacity and higher cycle performance.

[0054] In the first aspect, the present invention provides a sodium ion layered metal oxide material, which is an O3 type manganese-based layered oxide material having the chemical formula shown in Formula I: Na x Ni a Mnb Ti (0.5-b) M (0.5-a) O (2-y) F y Formula I;

[0055] Wherein, 0.9≤x≤1.0, 0.3≤a<0.5, 0.3≤b≤0.4, 0.1≤1-ab≤0.35, 0≤y<0.1, and M includes at least one of Zn, Mg, Sn, Sb, Y and Cu.

[0056] In one embodiment of the present invention, 0.9≤x≤1.0, preferably, 0.92≤x≤0.98, such as x is 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 1.0, preferably a range value with any of the above values ​​as the upper or lower limit.

[0057] In one embodiment of the present invention, 0.3≤a<0.5, preferably, 0.35≤a≤0.45, such as a is 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, preferably a range value with any of the above values ​​as the upper or lower limit.

[0058] In one embodiment of the present invention, 0<(0.5-a)≤0.2, preferably, 0.01≤(0.5-a)≤0.05. Within this range, it is possible to avoid excessive proportion of the M element. Since the M element has poor compatibility with oxides of elements such as Ni, Mn, and Ti during the sintering process, there are more impurities in the finished product, which in turn causes the energy density of the material to be too low.

[0059] In one embodiment of the present invention, 0.3≤b≤0.4, preferably, 0.32≤b≤0.38, such as b is 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, preferably a range value with any of the above values ​​as the upper or lower limit.

[0060] In one embodiment of the present invention, 0.1≤1-ab≤0.35, preferably, 0.2≤1-ab≤0.3.

[0061] In one embodiment of the present invention, 0≤y<0.1, preferably, 0.01≤y≤0.08, such as y is 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, or 0.09, preferably with any of the above values ​​as the upper or lower limit. When the value of y is within the above range, it is possible to avoid an excessively high proportion of the F element, which may result in a high amount of impurities (such as nickel oxide) in the finished product, resulting in a low energy density and poor structural stability of the material.

[0062] Specifically, in an embodiment of the present invention, the sodium ion layered metal oxide material is Na 0.95 Ni 0.45 Mn 0.3 Cu 0.05 Ti 0.2 O 1.95 F 0.05 ,NaNi 0.48 Mn 0.4 Y 0.02 Ti 0.1 O 1.999 F 0.001 and Na 0.9 Ni 0.48 Mn0. 39 Cu 0.02 Mg 0.01 Ti 0.1 One or more of O2.

[0063] After doping with F and M elements, the capacity retention rate of the material after 100 cycles of 1C is increased by 10% to 15%.

[0064] In a second aspect, the present invention further provides a method for preparing a sodium ion layered metal oxide material, comprising the following steps:

[0065] A) mixing a Na source, a Ni source, a Mn source, a Ti source, a M source, and a F source with a solvent in a stoichiometric ratio according to formula I and then coarsely grinding the mixture to obtain a first slurry;

[0066] B) grinding the first slurry to obtain a second slurry;

[0067] C) spray drying the second slurry to obtain a first powder;

[0068] D) calcining the powder according to the following procedure to obtain a second powder,

[0069] In an oxygen-containing atmosphere, heating the sample from room temperature to 110-130°C at a heating rate of 3-5°C / min, holding the temperature for 2-4 hours, then heating the sample to 440-460°C at a heating rate of 5-8°C / min, holding the temperature for 1-3 hours, then heating the sample to 850-950°C at a heating rate of 5-8°C / min, holding the temperature for 10-20 hours;

[0070] E) crushing, screening and removing iron from the second powder to obtain a sodium ion layered metal oxide material having a chemical formula of formula I; Na x Ni a Mn b Ti (0.5-b) M (0.5-a) O (2-y) F y Formula I.

[0071] In one embodiment of the present invention, the Na source is preferably one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium acetate, sodium oxalate and sodium citrate; the Ni source is preferably one or more of nickelous oxide (NiO), nickel oxide (Ni2O3), nickel hydroxide [Ni(OH)2], nickel hydroxide [Ni(OH)3], nickel carbonate and nickel oxalate; the Mn source is preferably one or more of manganese tetraoxide, manganese dioxide, manganese trioxide, manganese monoxide, manganese carbonate and manganese oxalate; the Ti source is preferably titanium dioxide and / or titanate (H2TiO3); the M source is preferably at least one of M oxide, M hydroxide, M carbonate, M oxalate and M citrate. When the M element is yttrium (Y), the M source is preferably Y oxide; the F source is preferably sodium fluoride. In the present invention, the Na source, Ni source, Mn source, Ti source, M source and F source are all weighed and mixed according to the molar number of the metal elements in the chemical formula shown in Formula I. This is a common technical means in the field and will not be repeated here in the present invention.

[0072] In one embodiment of the present invention, the solvent used for coarse grinding is preferably water and / or alcohol, more preferably deionized water and / or alcohol, the coarse grinding time is preferably 1 to 3 hours, more preferably 1 to 2 hours; the operating frequency of the coarse grinding is preferably 10 to 50 Hz, more preferably 20 to 40 Hz.

[0073] In one embodiment of the present invention, the solid content of the first slurry obtained after coarse grinding is preferably 10-40%, more preferably 20-30%, such as 10%, 15%, 20%, 25%, 30%, 35%, or 40%, preferably within a range with any of the above values ​​as the upper or lower limit; the particle size of the first slurry is preferably D100 < 10 μm, more preferably D100 < 5 μm.

[0074] After obtaining the first slurry, the present invention grinds the first slurry in a sand mill in an A / B tank circulation manner to obtain a second slurry.

[0075] In one embodiment of the present invention, the grinding time is preferably 2 to 5 hours, more preferably 3 to 4 hours, the rotation speed of the sand mill is preferably 200 to 1500 r / min, more preferably 500 to 1000 r / min, and the particle size of the second slurry is preferably D50 < 3 μm, D100 < 8 μm, preferably, D50 < 2 μm, D100 < 5 μm.

[0076] After obtaining the second slurry, the present invention spray-dries the second slurry to obtain a first powder.

[0077] In one embodiment of the present invention, the particle size of the first powder obtained by spray drying is preferably 2 μm<D50<15 μm, D100<40 μm, the moisture content is less than 1.5%, and BET>15 μm. 2 / g, more preferably, 5μm<D50<12μm, D100<30μm, moisture content less than 1.0%, BET>15m 2 / g.

[0078] After obtaining the first powder, the present invention calcines the powder, and the calcination is preferably performed according to the following procedure:

[0079] In an oxygen-containing atmosphere, the temperature is increased from room temperature to 110-130°C at a heating rate of 3-5°C / min, kept warm for 2-4 hours, then increased to 440-460°C at a heating rate of 5-8°C / min, kept warm for 1-3 hours, then increased to 890-910°C at a heating rate of 5-8°C / min, and kept warm for 10-20 hours.

[0080] In one embodiment of the present invention, the oxygen-containing atmosphere is preferably dry oxygen or dry air, or a mixture of dry oxygen and nitrogen, to prevent the material from coming into contact with water and carbon dioxide during the cooling process and causing deterioration. Preferably, the oxygen-containing atmosphere is a mixture of dry oxygen and nitrogen, wherein the volume fraction of oxygen is preferably 25-35%, more preferably 30%. While controlling the oxygen content in the high-temperature furnace, the adverse effects of water and carbon dioxide in the introduced gas on the finished product are avoided, which helps to reduce the free sodium content and pH of the finished product, and avoid excessively high free sodium content and pH of the material, which may lead to slurry gelation during battery production.

[0081] In one embodiment of the present invention, in the first stage, the temperature is first increased from room temperature to 110-130°C at a heating rate of 3-5°C / min and kept at this temperature for 2-4 hours. The purpose of this stage is mainly to reduce the water content of the first powder to avoid excessive moisture content in the high-temperature furnace atmosphere during the subsequent rapid heating process, which may cause side reactions and lead to excessively high impurities in the finished product.

[0082] During this stage, the heating rate is preferably 3-5°C / min, more preferably 3-4°C / min; the calcination temperature is preferably 110-130°C, more preferably 115-125°C, such as 110°C, 115°C, 120°C, 125°C, 130°C, preferably a range value with any of the above values ​​as the upper or lower limit; the insulation time is preferably 2-4 hours, more preferably 2-3 hours.

[0083] After the first stage of calcination, the temperature is raised to 440-460°C at a rate of 5-8°C / min and held at this temperature for 1-3 hours before the second stage of calcination. This stage is primarily intended to promote the decomposition and melting of the M element compound, improve the compatibility of the M element with other elements, and achieve a more uniform distribution of the M element in the finished product, thereby enhancing the uniformity of the material and ensuring product stability. Otherwise, the M element will be unevenly distributed in the finished product, resulting in inconsistent electrical properties when sampled at different points in the finished product and lower product stability. Alternatively, the compatibility of the M element with other elements will be poor, resulting in a high level of M element oxide impurities in the finished product, leading to poor electrical properties.

[0084] In one embodiment of the present invention, the heating rate of the second stage sintering is preferably 5-8°C / min, more preferably 6-7°C / min; the calcination temperature is preferably 440-460°C, more preferably 445-455°C, such as 440°C, 445°C, 450°C, 455°C, 460°C, preferably a range value with any of the above values ​​as the upper or lower limit; the holding time is preferably 1-3 hours, more preferably 1-2 hours.

[0085] After the second stage of calcination, the present invention heats the battery to 890-910°C at a heating rate of 5-8°C / min and holds the temperature for 10-20 hours before performing the third stage of calcination. This temperature and time helps avoid excessive impurities formed during the sintering process due to excessively high or low temperatures, thereby improving the crystallinity and purity of the finished product and thereby increasing the charge-discharge capacity.

[0086] In one embodiment of the present invention, the heating rate is preferably 5-8°C / min, more preferably 6-7°C / min; the calcination temperature is preferably 850-950°C, more preferably 860-940°C, such as 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, preferably with any of the above values ​​as the upper or lower limit of the range value, the holding time is preferably 10-20 hours, more preferably 15-16 hours.

[0087] Throughout the calcination process, the water content in the high-temperature furnace is controlled below 3%, the carbon dioxide concentration below 1%, and the oxygen content between 20% and 50%. This prevents excessive oxygen content, which can lead to excessive formation of impurities during sintering. The water, oxygen, and carbon dioxide levels in the high-temperature furnace are monitored online during sintering, and the gas flow rate, exhaust rate, and oxygen-nitrogen ratio are adjusted to maintain these levels within control ranges.

[0088] After calcination, the product is cooled to room temperature to obtain the second powder. It can be cooled naturally. In the present invention, it is preferred to quickly cool the calcined product to room temperature, such as quenching treatment, to accelerate the cooling rate, which helps to form a second powder containing more Mn. 3+ The metastable phase with a high sodium content between the layers is formed, thereby improving the reversible capacity of the electrode material. In the present invention, the quenching treatment is preferably performed by chilled water cooling or liquid nitrogen cooling.

[0089] After obtaining the second powder, the present invention performs crushing, screening and iron removal on the second powder to obtain a sodium ion layered metal oxide material. The humidity of the crushing and screening environment is controlled to be lower than 15%. The particle size range of the obtained sodium ion layered metal oxide material is: 0.5 μm < D50 < 12 μm, D100 < 40 μm, the content of magnetic foreign matter is lower than 150 ppm, the manganese dissolution is lower than 0.5 ppm, the free sodium is lower than 100 ppm, and the moisture is lower than 1000 ppm.

[0090] In one embodiment of the present invention, the pulverizing method is preferably a jet mill or a mechanical pulverizer; during screening, the material passes through at least two levels of screens, the mesh number of the first level screen is preferably 80-100 meshes, and the mesh number of the second level screen is preferably 120-320 meshes.

[0091] Crushing and screening can improve the uniformity of the finished product and prevent large particles in the finished product from having an adverse effect on electrical properties; controlling the humidity of the crushing and screening environment below 15% can prevent the sample from absorbing water and causing material deterioration, producing impurities, and reducing electrical properties.

[0092] In one embodiment of the present invention, the crushing, screening and iron removal processes of the second powder are continuous operations, which are connected by pipelines and transported under negative pressure. The finished product enters the crushing equipment after degassing. Dry nitrogen is introduced into the crushing, screening and iron removal processes for protection to prevent the material from contacting water and carbon dioxide and producing impurities.

[0093] In a third aspect, the present invention provides a positive electrode plate, comprising the sodium ion layered metal oxide material described above. The present invention does not specifically limit other materials used in the positive electrode plate, such as current collectors, conductive agents, adhesives, etc., and conventional raw materials for preparing positive electrode plates commonly used in this field can be used.

[0094] In a third aspect, the present invention provides a sodium ion battery comprising the aforementioned positive electrode sheet. The present invention does not impose any particular restrictions on other materials used in the sodium ion battery, such as the negative electrode and separator, and conventional raw materials commonly used in the preparation of sodium ion batteries in the art can be used.

[0095] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0096] Example 1

[0097] The chemical formula of sodium ion layered metal oxide material is: Na 0.95 Ni 0.45 Mn 0.3 Cu 0.05 Ti 0.2 O 1.95 F 0. 05,

[0098] Sodium carbonate, nickel oxide, manganese tetraoxide, titanium oxide, copper oxide, sodium fluoride, and deionized water were placed in a coarse grinder and mixed uniformly according to the molar ratio of the metal elements in the material chemical formula. The mixing time was 2 hours and the operating frequency was 30 Hz to obtain a first slurry (solid content of 25% and particle size: D100 <8.5 μm).

[0099] The first slurry was ground and mixed in a sand mill using an A / B tank cycle for 3 hours at a sand mill speed of 1000 r / min to obtain a second slurry (particle size: D50 < 3 μm, D100 < 8 μm).

[0100] The second slurry was spray dried to obtain a first powder (particle size: D50 < 10 μm, D100 < 35 μm, moisture content 0.5%, BET 30 μm). 2 / g);

[0101] The first powder was calcined in a high-temperature furnace. The calcination temperature curve was as follows: from room temperature to 120° C. at a rate of 5° C. / min, kept at that temperature for 2 hours, then to 450° C. at a rate of 5° C. / min, kept at that temperature for 2 hours, then to 900° C. at a rate of 5° C. / min, kept at that temperature for 13 hours. The atmosphere in the high-temperature furnace was a mixture of dry oxygen and nitrogen (with an oxygen ratio of 25%). The calcined powder was then rapidly cooled to room temperature using chilled water to obtain a second powder.

[0102] In this sintering process, the 120°C holding temperature for 2 hours is mainly to reduce the moisture content of the first powder and avoid excessive moisture content in the high-temperature furnace atmosphere during the subsequent rapid heating process, which would cause side reactions and lead to excessively high impurities in the finished product. The 450°C holding temperature for 2 hours is mainly to promote the decomposition and melting of copper oxide, improve the compatibility of copper with other elements, make the copper distribution in the finished product more uniform, improve the uniformity of the material, and ensure the stability of the product. Otherwise, the copper element in the finished product will be unevenly distributed, resulting in inconsistent electrical properties when sampled and tested at different points in the finished product, and low product stability; or the copper element has poor compatibility with other elements, resulting in high copper oxide impurities in the finished product, leading to poor electrical properties.

[0103] During the sintering process, the water content in the high-temperature furnace is controlled to be lower than 3%, the concentration of carbon dioxide is lower than 1%, and the oxygen content is controlled to be between 20% and 35%.

[0104] The second powder is crushed, screened, and iron-removed to obtain a sodium ion layered metal oxide material, wherein the humidity of the crushing and screening environment is controlled to be less than 15%. The obtained sodium ion layered metal oxide material has a particle size range of: D50 of 8.5 μm, D100 of 36 μm, a magnetic foreign matter content of less than 150 ppm, a manganese dissolution of less than 0.5 ppm, a free sodium of less than 100 ppm, and a moisture content of less than 1000 ppm.

[0105] The SEM of the sodium ion layered metal oxide material is shown in Figure 1. The sodium ion layered metal oxide exhibits a typical layered structure, with large particles formed by agglomeration of small particles, and the primary particle size is 0.7 to 7 μm.

[0106] The XRD of the sodium ion layered metal oxide material is shown in Figure 2;

[0107] A coin cell was prepared using a sodium-ion layered metal oxide material as the positive electrode. The charge-discharge curves in the 2-4.0V range are shown in Figure 3. The discharge capacity at 0.1C was 138 mAh / g. Before doping with Cu and F, the material retained approximately 80% of its capacity after 100 cycles at 1C. After doping with F and Cu, the discharge capacity at 0.1C remained essentially unchanged compared to the undoped material, but the material's capacity retention after 100 cycles at 1C was 91.2%, an increase of approximately 11%. This improvement was also approximately 5% compared to the 85.3% capacity retention after 100 cycles of the material doped with Cu alone. The introduction of the M element also improves the environmental stability of the layered metal oxide. Compared to the undoped material, the M-doped material exhibited a 5%-10% increase in discharge capacity after exposure to air for the same period of time.

[0108] Comparative Example 1

[0109] The sodium ion layered metal oxide material was prepared and assembled into a button cell according to the method in Example 1. The difference is that the chemical formula of the sodium ion layered metal oxide material is Na 0.95 Ni 0.5 Mn 0.3 Ti 0.2 O2.

[0110] A button cell was prepared according to the method in Example 1 and electrochemical performance tests were performed. The results showed that the discharge capacity at 0.1C was 135.5 mAh / g, and the capacity retention rate of the material after 100 cycles at 1C was approximately 80%.

[0111] Comparative Example 2

[0112] The sodium ion layered metal oxide material was prepared and assembled into a button cell according to the method in Example 1. The difference is that the chemical formula of the sodium ion layered metal oxide material is Na 0.95 Ni 0.45 Mn 0.3 Cu 0.05 Ti 0.2 O2.

[0113] A button cell was prepared according to the method in Example 1 and electrochemical performance tests were performed. The results showed that the discharge capacity at 0.1C was 137 mAh / g, and the capacity retention rate of the material after 100 cycles at 1C was approximately 85.3%.

[0114] Comparative Example 3

[0115] The sodium ion layered metal oxide material was prepared and assembled into a button cell according to the method in Example 1. The difference is that the chemical formula of the sodium ion layered metal oxide material is Na 0.95 Ni 0.5 Mn 0.3 Ti0.2 O 1.95 F 0.05 .

[0116] A button cell was prepared according to the method in Example 1 and electrochemical performance tests were performed. The results showed that the discharge capacity at 0.1C was 136 mAh / g, and the capacity retention rate of the material after 100 cycles at 1C was approximately 82.4%.

[0117] Comparative Example 4

[0118] A sodium ion layered metal oxide material was prepared and a button cell was assembled according to the method in Example 1, except that there was no first stage heating process. The temperature was directly raised to 450°C at 5°C / min and kept warm for 3 hours, and then raised to 900°C at 5°C / min and kept warm for 13 hours.

[0119] A button cell was prepared according to the method in Example 1 and electrochemical performance tests were performed. The results showed that the discharge specific capacity in the 2-4.0 V charge and discharge range was 125 mAh / g.

[0120] Comparative Example 5

[0121] A sodium ion layered metal oxide material was prepared and a button cell was assembled according to the method in Example 1. The difference was that there was no first stage heating process. The temperature was directly raised to 900°C at 5°C / min and kept warm for 13 hours. The discharge specific capacity in the 2-4.0V charge and discharge range was 121mAh / g.

[0122] Example 2

[0123] The chemical formula of sodium ion layered metal oxide material is: NaNi 0.48 Mn 0.4 Y 0.02 Ti 0.1 O 1.999 F 0.001 ,

[0124] Sodium bicarbonate, nickel oxide, manganese tetraoxide, titanium oxide, sodium fluoride, yttrium oxide and a certain amount of deionized water were placed in a coarse grinder and mixed uniformly according to the molar ratio of the metal elements in the material chemical formula. The mixing time was 2 hours and the operating frequency was 30 Hz to obtain a first slurry (solid content 30%, particle size: D100 <7 μm);

[0125] The first slurry was ground and mixed in a sand mill using an A / B tank cycle for 3 hours at a sand mill speed of 1000 r / min to obtain a second slurry (particle size: D50 < 2 μm, D100 < 7 μm).

[0126] The second slurry was spray dried to obtain the first powder (particle size: 3 μm < D50 < 10 μm, D100 < 30 μm, moisture less than 1%, BET of 30 μm). 2 / g);

[0127] The first powder is placed in a high-temperature furnace and calcined. The calcination temperature curve is as follows: from room temperature to 120°C at 4°C / min, kept at this temperature for 2 hours, then to 455°C at 6°C / min, kept at this temperature for 2 hours, then to 850°C at 7°C / min, kept at this temperature for 20 hours, and then the calcined material is rapidly cooled. The rapid cooling method can be liquid nitrogen cooling or chilled water cooling.

[0128] The sintering process is held at 120°C for 2 hours to reduce the moisture content of the first powder, preventing excessive moisture in the high-temperature furnace atmosphere during the subsequent rapid heating process, which could cause side reactions and result in excessively high impurities in the finished product. A maximum sintering temperature of 850°C improves the compatibility of Y with other elements, resulting in a more uniform distribution of Y in the finished product, improving material uniformity and ensuring product stability. Otherwise, the uneven distribution of Y in the finished product would lead to inconsistent electrical properties when sampled at different points in the finished product, resulting in poor consistency in the final product. Furthermore, a sintering temperature of 850°C prevents the finished product from having excessively large primary particles, which could reduce electrical properties.

[0129] During the sintering process, the water content in the high-temperature furnace is controlled to be lower than 2%, the concentration of carbon dioxide is lower than 1%, and the oxygen content is controlled to be between 20% and 50%.

[0130] The second powder is crushed, screened and iron-removed to obtain a sodium ion layered metal oxide material, and the humidity of the crushing and screening environment is controlled to be lower than 10%. The particle size range of the obtained sodium ion layered metal oxide material is: 2μm<D50<10μm, 25μm<D100<35μm, the content of magnetic foreign matter is less than 150ppm, the manganese dissolution is less than 0.5ppm, the free sodium is less than 100ppm, and the moisture is less than 1000ppm.

[0131] The SEM of the sodium ion layered metal oxide material is shown in FIG5 . The sodium ion layered metal oxide exhibits a typical layered structure, with large particles formed by agglomeration of small particles, and a primary particle size of 0.2 to 4.5 μm.

[0132] Using sodium ion layered metal oxide material as the positive electrode, a button cell was prepared. The charge and discharge curves in the range of 2-4.0V are shown in Figure 4. The discharge capacity at 0.1C is 135mAh / g, and the capacity retention rate after 100 cycles at 1C is about 85.2%. Before doping with Y and F (NaNi 0.5 Mn 0.4 Ti 0.1O2), the capacity retention rate of the material after 100 cycles of 1C is about 80%, and the discharge capacity at 0.1C is 135.5mAh / g. After doping with Y and F elements, the discharge capacity at 0.1C is slightly reduced compared to that of the undoped material, but the capacity retention rate of the material after 100 cycles of 1C is increased by about 5%. After Y doping, the layered metal oxide material has a strong YO bond, forming a stable structure, and the material is surrounded by a Y2O3 protective layer. The expanded Na layer also causes Na ions to be inserted not only into the surface, but also into the body. Therefore, the cycle performance of the material is improved after Y doping the material. In addition, yttrium oxide does not decompose or melt at 850°C, which is equivalent to introducing a small amount of impurity phase, but the amount of yttrium oxide added in this product is small and will not have a negative impact on the electrical properties.

[0133] Example 3

[0134] The chemical formula of sodium ion layered metal oxide material is: Na 0.9 Ni 0.48 Mn 0.39 Cu 0.02 Mg 0.01 Ti 0.1 O2,

[0135] Sodium carbonate, nickel hydroxide, manganese dioxide, titanium oxide, and alcohol were placed in a coarse grinder and mixed uniformly according to the molar ratio of the metal elements in the material chemical formula. The mixing time was 2 hours and the operating frequency was 30 Hz to obtain a first slurry (solid content of 20% and particle size: D100 <10 μm).

[0136] The first slurry was ground and mixed in a sand mill using an A / B tank cycle for 3 hours. The sand mill was turned to 1000 r / min to obtain a second slurry (particle size: D50 < 3 μm, D100 < 10 μm).

[0137] The second slurry was spray dried to obtain the first powder (particle size: 3 μm < D50 < 8 μm, D100 < 35 μm, moisture less than 1%, BET 30m 2 / g);

[0138] The first powder is placed in a high-temperature furnace and calcined. The calcination temperature curve is as follows: from room temperature to 120°C at 4°C / min, kept warm for 3 hours, then to 450°C at 7°C / min, kept warm for 1 hour, then to 950°C at 8°C / min, kept warm for 15 hours. The atmosphere in the high-temperature furnace is dry oxygen, and then rapidly cooled to room temperature to obtain a second powder. The rapid cooling method can be liquid nitrogen cooling or chilled water cooling.

[0139] In this sintering process, the 3-hour holding temperature at 120°C is primarily to reduce the moisture content of the first powder and prevent excessive moisture in the high-temperature furnace atmosphere during the subsequent rapid heating process, which could cause side reactions and result in excessively high impurities in the finished product. The 3-hour holding temperature at 450°C is primarily to promote the decomposition and melting of copper oxide, improve the compatibility of copper with other elements, and achieve a more uniform distribution of copper in the finished product, thereby enhancing the uniformity of the material and ensuring product stability. Otherwise, the uneven distribution of copper in the finished product would result in inconsistent electrical properties when sampled at different points in the finished product, resulting in lower product stability. Alternatively, the poor compatibility of copper with other elements could result in a higher level of copper oxide impurities in the finished product, leading to poor electrical properties.

[0140] During this sintering process, the water content in the high-temperature furnace is controlled to be less than 2%, and the carbon dioxide concentration is controlled to be less than 1%. The water and carbon dioxide contents in the high-temperature furnace are detected online during the sintering process, and the gas flow rate and exhaust rate are adjusted in a timely manner to keep the water and carbon dioxide contents in the high-temperature furnace within the control range.

[0141] The second powder is crushed, screened and iron-removed to obtain a sodium ion layered metal oxide material, and the humidity of the crushing and screening environment is controlled to be lower than 10%. The particle size range of the obtained sodium ion layered metal oxide material is: 3μm<D50<10μm, 25μm<D100<40μm, the content of magnetic foreign matter is lower than 150ppm, the manganese dissolution is lower than 0.5ppm, the free sodium is lower than 100ppm, and the moisture is lower than 1000ppm.

[0142] The SEM of the sodium ion layered metal oxide material is shown in FIG7 . The sodium ion layered metal oxide exhibits a typical layered structure, with large particles formed by agglomeration of small particles, and a primary particle size of 0.5-5 μm.

[0143] The chemical formula is Na 0.9 Ni 0.48 Mn 0.39 Cu 0.02 Mg 0.01 Ti 0.1O2 sodium ion layered metal oxide material as the positive electrode, the preparation of the button cell, the charge and discharge curve in the range of 2-4.0V is shown in Figure 6, the 0.1C discharge capacity is 129mAh / g, 1C cycle 100 weeks of capacity retention rate is 92.1%, while before doping with Cu and Mg (i.e. Na0.9Ni0.5Mn0.4Ti0.1O2), the material 1C cycle 100 weeks of capacity retention rate is about 80%, 0.1C discharge capacity is 135.5mAh / g. After doping with Cu and Mg elements, compared with the undoped, 0.1C discharge capacity is reduced, but the material 1C cycle 100 weeks of capacity retention rate increased by about 12%. Doping Mg on the basis of doping Cu is equivalent to using divalent magnesium ions to replace trivalent manganese ions, which can increase the interlayer spacing, thereby promoting the diffusion of sodium ions, and can also reduce the lattice strain caused by the sodium ion deintercalation process to enhance the stability of the layered structure. In addition, doping with divalent magnesium ions can reduce the structural deformation or volume change caused by the charge and discharge cycle of sodium ion batteries, inhibit irreversible phase change, and have an important impact on improving the reversible specific capacity of the material. In addition, Mg is non-electrochemically active in this material and does not participate in the redox reaction. However, the amount of magnesium oxide added in this product is small and will not have a negative impact on the electrical performance.

[0144] The above is only 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 within the scope of protection of the present invention.

Claims

1. A sodium ion layered metal oxide material, wherein the sodium ion layered metal oxide material is an O3 type manganese-based layered oxide material; the sodium ion layered metal oxide material is Na 0.95 Ni 0.45 Mn 0.3 Cu 0.05 Ti 0.2 O 1.95 F 0.05 ,NaNi 0.48 Mn 0.4 Y 0.02 Ti 0.1 O 1.999 F 0.001 and Na 0.9 Ni 0.48 Mn 0.39 Cu 0.02 Mg 0.01 Ti 0.1 One or more of O2; The method for preparing the sodium ion layered metal oxide material comprises the following steps: A) mixing a Na source, a Ni source, a Mn source, a Ti source, a M source and a F source with a solvent in a stoichiometric ratio in formula I and then coarsely grinding the mixture to obtain a first slurry; B) grinding the first slurry to obtain a second slurry; C) spray drying the second slurry to obtain a first powder; D) calcining the powder according to the following procedure to obtain a second powder, In an oxygen-containing atmosphere, the temperature is raised from room temperature to 110-130°C at a heating rate of 3-5°C / min, and kept at that temperature for 2-4 hours. The temperature is then raised to 440-460°C at a heating rate of 5-8°C / min, and kept at that temperature for 1-3 hours. The temperature is then raised to 850-950°C at a heating rate of 5-8°C / min, and kept at that temperature for 10-20 hours. E) crushing, screening and removing iron from the second powder to obtain a sodium ion layered metal oxide material having the chemical formula I.

2. The method for preparing the sodium ion layered metal oxide material according to claim 1, comprising the following steps: A) mixing a Na source, a Ni source, a Mn source, a Ti source, a M source and a F source with a solvent in a stoichiometric ratio in formula I and then coarsely grinding the mixture to obtain a first slurry; B) grinding the first slurry to obtain a second slurry; C) spray drying the second slurry to obtain a first powder; D) calcining the powder according to the following procedure to obtain a second powder, In an oxygen-containing atmosphere, the temperature is raised from room temperature to 110-130°C at a heating rate of 3-5°C / min, and kept at that temperature for 2-4 hours. The temperature is then raised to 440-460°C at a heating rate of 5-8°C / min, and kept at that temperature for 1-3 hours. The temperature is then raised to 850-950°C at a heating rate of 5-8°C / min, and kept at that temperature for 10-20 hours. E) crushing, screening and removing iron from the second powder to obtain a sodium ion layered metal oxide material.

3. The preparation method according to claim 2, characterized in that: The solvent used for the coarse grinding in step A) is water and / or alcohol, the solid content of the first slurry is 10-40%, and the particle size of the first slurry is D100<10 μm.

4. The preparation method according to claim 2, characterized in that: The calcination procedure is specifically as follows: In an oxygen-containing atmosphere, heat from room temperature to 120-125°C at a heating rate of 4-5°C / min, keep warm for 2-3 hours, then heat to 450-455°C at a heating rate of 5-7°C / min, keep warm for 1-2 hours, then heat to 850-950°C at a heating rate of 5-8°C / min, and keep warm for 13-20 hours.

5. The preparation method according to claim 2, characterized in that: During the calcination process, the oxygen content is 20-35%, the moisture content is lower than 3%, and the carbon dioxide concentration is lower than 1%.

6. The preparation method according to claim 2, characterized in that: After the calcination is completed, rapid cooling is performed to obtain a second powder; The rapid cooling is a quenching treatment.

7. A positive electrode sheet, characterized in that: The invention comprises the sodium ion layered metal oxide material according to claim 1 or the sodium ion layered metal oxide material prepared by the preparation method according to any one of claims 2 to 6.

8. A sodium ion battery, characterized in that: Including the positive electrode sheet as described in claim 7.

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