Sodium-ion battery positive electrode material and preparation method thereof

Abstract

The application provides a sodium ion battery positive electrode material and a preparation method thereof, the positive electrode material comprises a core body and a coating layer covering the core body, a doped layer is arranged between the core body and the coating layer, the core body is a layered metal oxide, the coating layer is a metal oxide, and metal ions in the coating layer penetrate into the core body to form the doped layer. In the application, the coating layer serves as a protection unit and does not participate in the redox reaction in the charging and discharging process, so that the volume change stress of the whole material in the cycle process can be reduced, the cycle stability and the capacity retention rate can be improved; meanwhile, in the high-temperature sintering process, the metal ions in the coating layer further diffuse and penetrate into the interior of the positive electrode material to realize doping and form the doped layer, so that the stability of the crystal in the cycle process and the structural stability thereof can be improved, the capacity retention rate of the positive electrode material in the cycle process can be improved, and the sodium ion battery positive electrode material has the advantages of high capacity, high cycle stability and air stability.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a sodium ion battery positive electrode material and a preparation method thereof. BACKGROUND

[0002] The rapid development of portable electronic devices, electric vehicles and renewable energy requires efficient and inexpensive energy storage technology. Although lithium ion batteries have a large market share in these fields, the high cost, serious safety problems and sustainability of raw materials still need to be addressed. Recently, sodium ion batteries are considered to be one of the effective complementary solutions for lithium ion battery application scenarios, especially in large-scale energy storage and low-speed electric vehicle application fields. Compared with lithium ion, the resources of sodium ion are more abundant and more uniform in the world, and most importantly, the positive electrode material and current collector of the sodium ion battery system are more inexpensive in theory.

[0003] Finding a suitable positive electrode material is the key to the development of sodium ion batteries. Researchers have reported various types of potential positive electrode materials, among which the most commonly studied sodium ion battery positive electrode materials include polyanion compounds, layered metal oxides and prussian blue analogues. The simple synthesis process and high theoretical capacity of the layered metal oxide have attracted widespread attention from researchers, and it is also considered to be the positive electrode material of the sodium ion battery that is most likely to achieve commercial application the fastest.

[0004] However, sodium-based layered oxides generally have a larger interlayer spacing than lithium, which accelerates the reaction of inserted sodium with air, and sodium-based layered oxides have strong reactivity when exposed to air. This ultimately results in high manufacturing, storage and electrode preparation costs for sodium ion batteries, greatly hindering the practical application of sodium ion batteries. At the same time, the layered metal oxide has a multiphase phase change during the cycle process, resulting in structural changes and poor cycle stability. Therefore, in order to promote the practical application of sodium ion batteries, it is of great significance to use low-cost process methods to solve the problems of poor air stability and poor cycle stability for the application and promotion of sodium ion batteries.

[0005] Chinese patent 107369826A discloses a lithium / sodium layered metal oxide positive electrode material doped and coated by double modification and a one-step synthesis method thereof. It coats ion compounds of lanthanide or actinide on the surface of the precursor by a sol method or a solid-phase ball milling method, and simultaneously performs metal or non-metal doping. The double modification significantly improves the electrochemical performance of the positive electrode material. However, the coating layer is rare earth elements such as lanthanide, which is expensive and difficult to obtain, and does not match the original intention of developing and designing sodium ion batteries as low-cost energy storage devices. At the same time, the sol method or the solid-phase ball milling method has problems such as low yield and poor process stability in large-scale production.

[0006] Chinese patent CN113937286A discloses a coated modified sodium ion battery positive electrode material and a preparation method thereof. First, an ion-doped positive electrode material is synthesized, and then a surface is coated with a manganese-rich shell. However, this method requires a two-step sintering process. The first step is to sinter the layered metal oxide, and the second step is to sinter the layered metal oxide with a coating structure. The two-step sintering process has high energy consumption. Moreover, since the coating layer also participates in the oxidation-reduction reaction during charging and discharging, there is a change in the crystal phase, resulting in poor cycle stability of the material. The capacity retention rate is only about 85% after 100 cycles.

[0007] Therefore, it is necessary to develop a sodium ion battery positive electrode material with low-cost and easily available structure, air stability and cycle stability, and to design a simple and large-scale application process for preparing the sodium ion battery positive electrode material. SUMMARY

[0008] In view of the above problems, one of the purposes of the present application is to provide a sodium ion battery positive electrode material. The sodium ion battery positive electrode material has the advantages of high capacity, high cycle stability and air stability.

[0009] To achieve the above-mentioned purpose, the first aspect of the present application provides a sodium ion battery positive electrode material, comprising a core and a coating layer coating the core, a doping layer between the core and the coating layer, the core being a layered metal oxide, the coating layer being a metal oxide, and the metal ions in the coating layer metal oxide penetrating into the core to form the doping layer.

[0010] The sodium ion battery positive electrode material of the present application forms a coating layer on the surface of the core, and has a doping layer between the core and the coating layer. The surface of the core is coated to achieve better air stability. In particular, the metal ions in the coating layer can diffuse and penetrate into the layered metal oxide core during sintering to form a doping layer. On the one hand, the doping element improves the crystal stability of the positive electrode material during the cycle process. On the other hand, the coating layer and the core have no obvious layer boundary, so that the combination between them is more compact, improving the structural stability. Therefore, the sodium ion battery positive electrode material of the present application has the advantages of high capacity, high cycle stability and air stability, and excellent electrochemical performance.

[0011] In some embodiments, the structure of the layered metal oxide is Na x M1 a M2 b M3 c O2, wherein M1, M2, M3 are transition metal elements, 0.2≤x≤1, a+b+c=1, 0≤a≤1, 0≤b≤1, 0≤c≤1.

[0012] In some embodiments, M1, M2, M3 each independently comprises at least one of Ni, Fe, Mn, Co, Cu, Cr, V.

[0013] In some embodiments, Na x M1 a M2 b M3 c O2 is an O3 phase, a P2 phase or an O3 / P2 mixed phase layered metal oxide.

[0014] In some embodiments, the metal oxide has a structural formula of M y O z wherein M comprises at least one of Ge, Rb, Cd, Zn, Zr, Mg, Al, Nb, Ti, Sn, Ca, Ru, Mo, Sb, Sr, Ag, 0

[0015] In some embodiments, the doping element of the doping layer is the metal M in the metal oxide M y O z .

[0016] In some embodiments, the thickness of the coating layer is 100 nm to 1 μm.

[0017] In some embodiments, the metal doping depth of the doping layer is 50 to 200 nm.

[0018] In some embodiments, the mass percentage of the coating layer material in the total mass of the core, the coating layer and the doping layer is 0.1 to 7 wt%.

[0019] The second object of the present application is to provide a preparation method of a sodium ion battery cathode material.

[0020] To achieve the above object, the second aspect of the present application provides a preparation method of a sodium ion battery cathode material, comprising the steps of:

[0021] (a) mixing a sodium source, a metal source and a first solvent to obtain a slurry, and then performing sand milling treatment and spray granulation on the slurry to obtain a precursor powder A;

[0022] (b) adding the precursor powder A into a second solvent and heating and stirring, then adding a solution containing a metal M, and removing the second solvent to obtain a precursor powder B;

[0023] (c) sintering the precursor powder B in an oxygen-containing atmosphere, and then cooling and milling to obtain the sodium-ion battery cathode material coated with the oxide of the metal M.

[0024] In the preparation method of the sodium-ion battery cathode material, the slurry is subjected to sand milling treatment and spray granulation to form a precursor powder A, a solution containing the metal M is added, the second solvent is removed to obtain a precursor powder B, and finally a sintering process is adopted to obtain the sodium-ion battery cathode material. The sand milling treatment can reduce the particle size of the raw material, improve the activity of the raw material, and make the raw material mixture more uniform. Without sand milling, directly using solid-phase mixing and sintering, the raw material particles are large, the activity is low, and the mixture is not uniform. Spray granulation can make the particles spherical, and the spherical particle precursor ensures that the particles have certain voids, which is beneficial to the discharge of gas and the contact of oxygen during the sintering process, and ensures that the reaction proceeds in the forward direction. If a conventional evaporation drying method is used, it is easy to cause crystallization and precipitation of sodium carbonate and difficult to ensure the uniformity of the appearance and particle size of the dried material. Therefore, the present application realizes the coating and doping modification effects by one-step method, and the process is stable and reliable, the product is uniform, and it is beneficial to large-scale production.

[0025] In some embodiments, the metal source includes at least one of an M1 metal source, an M2 metal source, and an M3 metal source, and each of the M1 metal source, the M2 metal source, and the M3 metal source is from a transition metal element.

[0026] In some embodiments, each of the M1 metal source, the M2 metal source, and the M3 metal source independently includes at least one of nickel oxide, iron oxide, manganese oxide, cobalt oxide, copper oxide, chromium oxide, and vanadium oxide.

[0027] In some embodiments, the sodium source includes at least one of sodium carbonate, sodium bicarbonate, sodium nitrate, and sodium hydroxide.

[0028] In some embodiments, the first solvent is selected from at least one of deionized water, ethanol, methanol, isopropanol, triethylene glycol, polyethylene glycol, acetone, and N-methyl pyrrolidone.

[0029] In some embodiments, the particle size of the slurry after sand milling treatment is controlled to be 50 nm≤D50≤1 μm and 200 nm≤D90≤2 μm.

[0030] In some embodiments, the particle size of the precursor powder A is 1 μm≤D50≤20 μm.

[0031] In some embodiments, in step (b), the second solvent is selected from at least one of deionized water, ethanol, methanol, isopropanol, triethylene glycol, polyethylene glycol, acetone, and N-methyl pyrrolidone.

[0032] In some embodiments, in step (b), the temperature of the heating stirring is 30-100℃.

[0033] In some embodiments, in step (b), the time of the heating stirring is 8-24h.

[0034] In some embodiments, in step (c), the temperature of the sintering is 600-1000℃.

[0035] In some embodiments, in step (c), the time of the sintering is 10-25h.

[0036] In some embodiments, in step (c), the oxygen content atmosphere is a gas with oxygen content of 20-80%.

[0037] In some embodiments, in step (c), the flow rate of the oxygen content atmosphere is 1-20L / min. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 Schematic diagram of the effect of the coating and doping double modification of the sodium ion battery cathode material of the present application.

[0039] Figure 2 SEM image of the sodium ion battery cathode material of Example 1 of the present application.

[0040] Figure 3 SEM image of the sodium ion battery cathode material of Comparative Example 1. DETAILED DESCRIPTION

[0041] The following is a preferred embodiment of the present application, it should be noted that for those skilled in the art, without departing from the principles of the present application, can make several improvements and refinements, these improvements and refinements are also considered within the scope of the present application.

[0042] Please refer to Figure 1 The sodium ion battery cathode material of an embodiment comprises a core and a coating layer coating the core, and a doping layer between the core and the coating layer, the core is a layered metal oxide, the coating layer is a metal oxide, and metal ions in the coating layer penetrate into the core to form the doping layer.

[0043] It can be understood that the sodium ion battery positive electrode material of the embodiment forms a coating layer on the surface of the core, and the coating layer and the core have a doped layer therebetween. The core surface is coated by the coating layer, which can achieve good air stability of the positive electrode material. In particular, the metal ions in the coating layer can simultaneously diffuse and penetrate into the layered metal oxide core during the sintering process to be doped, so that the metal ions in the coating layer metal oxide penetrate to form a doped layer. On the one hand, the metal doped element can improve the crystal stability during the cycle process of the positive electrode material, and on the other hand, the coating layer and the core have no obvious layer boundary, so that the combination between the two is more compact, and the structural stability is improved. Therefore, the sodium ion battery positive electrode material of the present application has the advantages of high capacity, high cycle stability and air stability, and excellent electrochemical performance.

[0044] In some embodiments, the layered metal oxide has a structural formula of Na x M1 a M2 b M3 c O2, wherein M1, M2, and M3 are all transition metal elements, 0.2≤x≤1, a+b+c=1, 0≤a≤1, 0≤b≤1, and 0≤c≤1. As an example, x can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 1.0, but is not limited to the listed values, and other values not listed in the above ranges are also applicable. In this embodiment, x is 1. As an example, a can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 1.0, but is not limited to the listed values, and other values not listed in the above ranges are also applicable. In this embodiment, a is 1 / 3, 1 / 6, etc. As an example, b can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 1.0, but is not limited to the listed values, and other values not listed in the above ranges are also applicable. In this embodiment, b is 1 / 3. As an example, c can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 1.0, but is not limited to the listed values, and other values not listed in the above ranges are also applicable. In this embodiment, c is 1 / 3, 1 / 2, etc. In some embodiments, the layered metal oxide contains only one transition metal element M1, a=1, b=c=0, i.e., the structural formula of the layered metal oxide is Na x M1O2; in some embodiments, the layered metal oxide contains only two transition metal elements M1 and M2, a+b=1, c=0, i.e., the structural formula of the layered metal oxide is Na x M1a M2 b O2, such as a = 1 / 2, b = 1 / 2, the structural formula of the layered metal oxide is Na x M1 1 / 2 M2 1 / 2 O2, but not limited to this. In some embodiments, the layered metal oxide contains three transition metal elements M1, M2 and M3, a = 0.5, b = 0.3, c = 0.2, that is, the structural formula of the layered metal oxide is Na x M1 0.5 M2 0.3 M3 0.2 O2, but not limited to this.

[0045] In some embodiments, the transition metal element includes at least one of Ni, Fe, Mn, Co, Cu, Cr, V, but not limited to this. The transition metal element has empty d, f orbit, which is conducive to accepting electrons, indirectly conducive to electron transfer, conducive to the conversion between electrical energy and chemical energy to realize energy storage and release. It can be understood that M1, M2 and M3 each independently includes at least one of Ni, Fe, Mn, Co, Cu, Cr, V. For example, M1 includes at least one of Ni, Fe, Mn, Co, Cu, Cr, V; M2 includes at least one of Ni, Fe, Mn, Co, Cu, Cr, V, and M3 includes at least one of Ni, Fe, Mn, Co, Cu, Cr, V. For example, the structural formula of the layered metal oxide can be Na x Ni a Fe b Mn c O2, Na x Cu a Fe b Mn c O2, Na x Cu a Co b Cr c O2, Na x Ni a V b Mn c O2, Na x Ni a Fe b O2, Na x Cu a Fe b O2, Na x Cu a O2, Na x Ni a O2, but not limited to this.

[0046] In some embodiments, Nax M1 a M2 b M3 c O2 is an O3 phase, a P2 phase or an O3 / P2 mixed phase layered metal oxide, as an example, Na x M1 a M2 b M3 c O2 is an O3 phase, and the O3 phase layered transition metal oxide has a high specific capacity.

[0047] In some embodiments, the metal oxide has a structural formula of M y O z wherein M includes at least one of Ge, Rb, Cd, Zn, Zr, Mg, Al, Nb, Ti, Sn, Ca, Ru, Mo, Sb, Sr, Ag, 0 < y < 3, and 0 < z < 5. As an example, y can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, but is not limited to the listed values, and other values not listed within the above ranges are also applicable. In this embodiment, y is 1, 2, etc. As an example, z can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, but is not limited to the listed values, and other values not listed within the above ranges are also applicable. In this embodiment, y is 1, 2, 3, 5, etc. Specifically, the metal oxide can be GeO2, Rb2O, CdO, ZnO, ZrO2, MgO, Al2O3, Nb2O5, TiO2, SnO2, CaO, RuO2, MoO2, Sb2O3, SrO, AgO, etc., but is not limited thereto.

[0048] In some embodiments, the doping element of the doping layer is a metal M in the metal oxide M y O z As an example, the doping element M includes at least one of Ge, Rb, Cd, Zn, Zr, Mg, Al, Nb, Ti, Sn, Ca, Ru, Mo, Sb, Sr, Ag. It should be understood that, during sintering, M in the metal oxide M y O z further diffuses into Na x M1 a M2 b M3 c O2 to form the doping layer, so that the metal of the coating layer and the metal of the doping layer are the same metal, and the coating layer and the core body have no obvious layer boundary, and the combination therebetween is more compact, thereby improving the structural stability.

[0049] In some embodiments, the thickness of the coating layer is 100 nm to 1 μm. For example, the thickness of the coating layer can be 100 nm, 140 nm, 180 nm, 220 nm, 250 nm, 280 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 800 nm, 850 nm, 950 nm, 1 μm, etc., but is not limited to the listed values, and other values not listed in the above ranges are also applicable.

[0050] In some embodiments, the metal doping depth of the doping layer is 50 to 200 nm. For example, the metal doping depth of the doping layer can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, or 200 nm, etc., but is not limited to the listed values, and other values not listed in the above ranges are also applicable.

[0051] In some embodiments, the mass percentage of the coating layer material in the total mass of the positive electrode material is 0.1 to 7 wt%. For example, the mass percentage of the coating layer material in the total mass of the core, the coating layer, and the doping layer can be 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, or 7 wt%, etc., but is not limited to the listed values, and other values not listed in the above ranges are also applicable. It can be understood that too low a content of the coating layer makes it difficult to uniformly coat, and thus cannot achieve a good coating effect; and too high a content of the coating layer results in a relatively small amount of active material, which affects the energy density.

[0052] A method for preparing a positive electrode material of a sodium ion battery according to an embodiment includes the following steps:

[0053] (a) mixing a sodium source, a metal source, and a first solvent to obtain a slurry, and then performing sand milling treatment and spray granulation on the slurry to obtain a precursor powder A;

[0054] (b) adding the precursor powder A into a second solvent and heating and stirring, then adding a solution containing metal M, and removing the second solvent to obtain a precursor powder B;

[0055] (c) sintering the precursor powder B in an atmosphere containing a certain amount of oxygen, and then cooling and milling to obtain an oxide of metal M coated metal M doped positive electrode material of a sodium ion battery.

[0056] The preparation method of the sodium ion battery cathode material in the embodiment can realize the coating and doping modification effects at the same time through a one-step sintering process to obtain a sodium ion battery cathode material with high capacity, high cycle stability and air stability, and the production process is simple, the production cost is reduced, and the production is easy to expand.

[0057] In some embodiments, the sodium source includes at least one of sodium carbonate, sodium bicarbonate, sodium nitrate, and sodium hydroxide. As an example, the sodium source can be selected from sodium carbonate, sodium bicarbonate, sodium nitrate, or sodium hydroxide alone, or a combination of sodium carbonate and sodium bicarbonate, a combination of sodium carbonate and sodium nitrate, a combination of sodium carbonate and sodium hydroxide, a combination of sodium bicarbonate and sodium nitrate, a combination of sodium bicarbonate and sodium hydroxide, a combination of sodium nitrate and sodium hydroxide, etc., or a combination of sodium carbonate, sodium bicarbonate, and sodium nitrate, etc., but is not limited thereto.

[0058] In some embodiments, the metal source includes at least one of an M1 metal source, an M2 metal source, and an M3 metal source, wherein each of the M1 metal source, the M2 metal source, and the M3 metal source is from a transition metal element. In some embodiments, the metal source contains only one transition metal element M1; in some other embodiments, the metal source contains only two transition metal elements M1 and M2; and in some other embodiments, the metal source contains three transition metal elements M1, M2, and M3.

[0059] In some embodiments, the transition metal element includes at least one of Ni, Fe, Mn, Co, Cu, Cr, and V. For example, each of the M1 metal source, the M2 metal source, and the M3 metal source is an oxide of a transition metal element M1, M2, and M3, respectively. It can be understood that each of the M1 metal source, the M2 metal source, and the M3 metal source independently includes at least one of nickel oxide, iron oxide, manganese oxide, cobalt oxide, copper oxide, chromium oxide, and vanadium oxide, but is not limited thereto. As an example, the M1 metal source includes at least one of nickel oxide, iron oxide, manganese oxide, cobalt oxide, copper oxide, chromium oxide, and vanadium oxide; the M2 metal source includes at least one of nickel oxide, iron oxide, manganese oxide, cobalt oxide, copper oxide, chromium oxide, and vanadium oxide; and the M3 metal source includes at least one of nickel oxide, iron oxide, manganese oxide, cobalt oxide, copper oxide, chromium oxide, and vanadium oxide. As an example, each of the M1 metal source, the M2 metal source, and the M3 metal source is selected from nickel oxide, iron oxide, and manganese oxide; and as another example, each of the M1 metal source, the M2 metal source, and the M3 metal source is selected from copper oxide, iron oxide, and manganese oxide, but is not limited thereto.

[0060] In some embodiments, the weight ratio of the sodium source to the metal source is 0.5 to 1. As an example, the weight ratio of the sodium source to the metal source can be, but is not limited to, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, but is not limited to the listed values, and other values not listed in the above range are also applicable.

[0061] In some embodiments, the first solvent is selected from at least one of deionized water, ethanol, methanol, isopropanol, triethylene glycol, polyethylene glycol, acetone, N-methylpyrrolidone, N-N dimethylformamide, acetone, acetonitrile and diethyl ether, and the suitable solvent can be selected according to the selected sodium source and metal source.

[0062] In some embodiments, the slurry after mixing the sodium source, the metal source and the first solvent is spray granulated to obtain the precursor powder A, that is, the first solvent can be removed during the spray granulation. As an example, the spray granulation can be achieved by a spray dryer, but is not limited thereto.

[0063] In some embodiments, sanding is performed before the spray granulation, that is, the suitable slurry particle size is obtained by the sanding process. As an example, the sanding process can be achieved by a sanding machine, but is not limited thereto. Further, the particle size of the slurry after sanding is controlled to be 50 nm≤D50≤1 μm. It can be understood that D50 refers to the particle size corresponding to 50% of the cumulative particle size distribution percentage of a sample. Further, the particle size of the slurry after sanding is controlled to be 200 nm≤D90≤2 μm. It can be understood that D90 refers to the particle size corresponding to 90% of the cumulative particle size distribution percentage of a sample. As an example, the value of D50 can be 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm or 1 μm, etc., but is not limited to the listed values, and other values not listed in the above ranges are also applicable. As an example, the value of D90 can be 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, etc., but is not limited to the listed values, and other values not listed in the above ranges are also applicable. In some embodiments, the particle size of the slurry after sanding is controlled to be 200 nm≤D50≤800 nm.

[0064] In some embodiments, the sanding time is 1 to 5 hours. As an example, the sanding time can be 1 h, 2 h, 3 h, 4 h or 5 h, but is not limited to the listed values, and other values not listed in the above ranges are also applicable.

[0065] In some embodiments, the particle size of the precursor powder A is 1 pm≤D50≤20 pm, for example, the particle size of the precursor powder A can be 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm, 7 pm, 8 pm, 9 pm, 10 pm, 11 pm, 12 pm, 13 pm, 14 pm, 15 pm, 16 pm, 17 pm, 18 pm, 19 pm, 20 pm, and the like, but not limited to the listed values, and other values not listed in the above ranges are also applicable.

[0066] In some embodiments, the second solvent is selected from at least one of de-ethanol, methanol, isopropyl alcohol, triethylene glycol, polyethylene glycol, acetone, N-methyl pyrrolidone, N-N dimethyl formamide, acetone, acetonitrile, and diethyl ether. Further, the second solvent is preferably ethanol.

[0067] In some embodiments, the temperature of the heating and stirring is 30 to 100°C, for example, the temperature of the heating and stirring can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, and the like, but not limited to the listed values, and other values not listed in the above ranges are also applicable.

[0068] In some embodiments, the time of the heating and stirring is 8 to 24 h, for example, the time of the heating and stirring can be 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h, and the like, but not limited to the listed values, and other values not listed in the above ranges are also applicable.

[0069] In some embodiments, the sintering temperature is 600 to 1000°C, for example, the sintering temperature can be 600°C, 700°C, 800°C, 900°C, or 1000°C, and the like, but not limited to the listed values, and other values not listed in the above ranges are also applicable. It can be understood that if the sintering temperature is too low, the raw materials are difficult to achieve sufficient fusion and reaction, the synthesis product deviates from the design value, the crystallinity is poor, and the electrochemical performance is poor; if the sintering temperature is too high, the product is prone to lose oxygen and the energy consumption is large, which affects the structure and stability of the product and the processing economy is poor.

[0070] In some embodiments, the sintering time is 10 to 25 hours, for example, the sintering time can be 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, or 25 hours, and the like, but not limited to the listed values, and other values not listed in the above ranges are also applicable.

[0071] In some embodiments, the oxygen content atmosphere is a gas with an oxygen content of 20 to 80%, for example, the oxygen content is 20%, 30%, 40%, 50%, 60%, 70%, or 80%, and the like, but not limited to the listed values, and other values not listed in the above ranges are also applicable.

[0072] In some embodiments, the flow rate of the oxygen content atmosphere is 1 L / min to 20 L / min, for example, the flow rate of the oxygen content atmosphere can be 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, 11 L / min, 12 L / min, 13 L / min, 14 L / min, 15 L / min, 16 L / min, 17 L / min, 18 L / min, 19 L / min, or 20 L / min, and the like, but not limited to the listed values, and other values not listed in the above ranges are also applicable.

[0073] The present application is inert oxide M y O z The shell is coated on Na x M1 a M2 b M3 c O2 core (nucleus) surface, on the one hand, effectively isolate Na x M1 a M2 b M3 c O2 and air contact, avoid moisture and carbon dioxide and the core of the side reaction, improve the air stability of the positive electrode material, on the other hand, the coating layer as a protection unit does not participate in the oxidation and reduction reaction in the charging and discharging process, can reduce the overall volume change stress of the material in the cycle process, improve the cycle stability and capacity retention rate; at the same time in the process of high temperature sintering, the metal ion M in the coating layer M y O z further to Na x M1 a M2 b M3 cThe O2 cathode material is doped by internal diffusion and permeation; that is, the coating and doping double modification is realized by one-step sintering method. x M1 a M2 b M3 c M in O2 can alleviate the change of Na x M1 a M2 b M3 c O crystal structure, improve the stability of the crystal in the cycle process, and on the other hand, due to this doping method, the coating layer and the core body have no obvious layer boundary, and the combination between them is more compact, which improves the structural stability and further improves the capacity retention rate of the cathode material in the cycle process. The preparation method of the sodium ion battery cathode material of the application adopts one-step sintering method, does not involve complex two-sintering process, simplifies the process flow, the coating and doping elements are relatively cheap and easy to obtain, reduces the production cost, and is suitable for large-scale production and application promotion.

[0074] In order to better illustrate the purpose, technical scheme and beneficial effects of the present application, the present application will be further described below in combination with specific examples. It should be noted that the following implementation method is a further explanation and description of the present application, and should not be regarded as a limitation of the present application.

[0075] Example 1

[0076] The sodium ion battery cathode material of the present embodiment comprises a core body and a coating layer coated on the core body, and has a doping layer between the core body and the coating layer. The core body is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, the coating layer is ZrO2, and the doping layer is Zr, which is called Zr-doped NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0077] The preparation method of the sodium ion battery cathode material of the present embodiment comprises the following steps:

[0078] (1) 74.7g of nickel oxide, 79.8g of iron oxide, 86.9g of manganese oxide and 158.9g of sodium carbonate are stirred and dispersed in 3000ml of deionized water to prepare a slurry;

[0079] (2) The slurry is pumped into a sand mill, and the particle size of the slurry is controlled to about D50=500nm and D90=1.2um by 1h sand milling treatment to obtain a precursor slurry;

[0080] (3) The precursor slurry is transported into the drying tower in the centrifugal spray dryer by peristaltic pump, and the solvent is evaporated instantaneously to obtain precursor powder A, and the particle size D50 of the precursor powder A is 10 μm;

[0081] (4) 100 g of the precursor powder A is dispersed by stirring in 100 ml of ethanol, then 30 ml of zirconium n-butyl alcohol solution is added, and stirring is continued at 60°C water bath for about 20 hours until the solvent is completely evaporated to obtain precursor powder B;

[0082] (5) The precursor powder B is placed in a corundum box, and the box is placed in a box furnace, sintered at 900°C for 25h in an air atmosphere, and naturally cooled. The obtained product is crushed and sieved to obtain ZrO2-coated Zr-doped NaNi 1 / 3 Fe 1 / 3Mn 1 / 3 O2.

[0083] Example 2

[0084] The sodium ion battery positive electrode material of the present embodiment comprises a core and a coating layer covering the core, and a doped layer between the core and the coating layer, the core is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, the coating layer is Al2O3, and the doped layer is Al, which is called Al2O3-coated Al-doped NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0085] The preparation method of the sodium ion battery positive electrode material of the present embodiment comprises the following steps:

[0086] (1) 74.7 g of nickel oxide, 79.8 g of iron oxide, 86.9 g of manganese oxide, and 158.9 g of sodium carbonate are dispersed by stirring in 3000 ml of deionized water to prepare a slurry;

[0087] (2) The slurry is pumped into a sand mill, and the particle size of the slurry is controlled at D50=400 nm and D90=1.0 um by sand milling for 1h to obtain a precursor slurry;

[0088] (3) The precursor slurry is transported into the drying tower in the centrifugal spray dryer by peristaltic pump, and the solvent is evaporated instantaneously to obtain precursor powder A, and the particle size D50 of the precursor powder A is 10 μm;

[0089] (4) 100 g of the precursor powder A is dispersed by stirring in 100 ml of ethanol, then 30 ml of zirconium n-butyl alcohol solution is added, and stirring is continued at 60°C water bath for about 20 hours until the solvent is completely evaporated to obtain precursor powder B;

[0090] (5) Put the precursor powder B into a corundum crucible, then put the crucible into a box furnace, sinter at 980°C for 28h in an air atmosphere, and naturally cool. The obtained product is crushed and sieved to obtain an Al-doped NaNi 1 / 3 Fe 1 / 3Mn 1 / 3 O2.

[0091] Example 3

[0092] The sodium ion battery cathode material of the present example comprises a core and a coating layer covering the core, and a doping layer between the core and the coating layer. The core is an Al-doped NaNi 2 / 9 Fe 1 / 3 Mn 1 / 3 Cu 1 / 9 O2, the coating layer is Nb2O5, and the doping layer is Nb, which is referred to as Nb2O5-coated Nb-doped NaNi 2 / 9 Fe 1 / 3 Mn 1 / 3 Cu 1 / 9 O2.

[0093] The preparation method of the sodium ion battery cathode material of the present example comprises the following steps:

[0094] (1) 38.2g of copper oxide, 115.5g of iron oxide, 136.3g of manganese oxide, 71.7g of nickel oxide, and 240.1g of sodium carbonate are stirred and dispersed in 3000ml of deionized water to prepare a slurry;

[0095] (2) The slurry is pumped into a sand mill for sanding treatment for 1h, and the particle size of the slurry is controlled at about D50=500nm and D90=900nm to obtain a precursor slurry;

[0096] (3) The precursor slurry is transported into a drying tower in a centrifugal spray dryer through a peristaltic pump, and the solvent is instantly evaporated to obtain a precursor powder A, and the particle size D50 of the precursor powder A is 12μm;

[0097] (4) 100g of the precursor powder A is stirred and dispersed in 100ml of ethanol, then 40ml of niobium oxalate solution is added, and the stirring is continued at 50°C water bath for about 20h until the solvent is completely evaporated to obtain a precursor powder B;

[0098] (5) Put the precursor powder B into a corundum crucible, then put the crucible into a box furnace, sinter at 980°C for 28h in an air atmosphere, and naturally cool. The obtained product is crushed and sieved to obtain an Al-doped NaNi 2 / 9 Fe 1 / 3Mn 1 / 3 Cu1 / 9 O2.

[0099] Example 4

[0100] The sodium ion battery positive electrode material of the embodiment comprises a core body and a coating layer coating the core body, and a doped layer between the core body and the coating layer, the core body is NaNi 1 / 3 Mn 2 / 3 O2, the coating layer is ZrO2, and the doped layer is Zr, which is called Zr-doped NaNi 1 / 3 Mn 2 / 3 O2.

[0101] The preparation method of the sodium ion battery positive electrode material of the embodiment comprises the following steps:

[0102] (1) 23.67g of nickel oxide, 57.96g of manganese oxide, 26.5g of sodium carbonate, and 42.5g of sodium nitrate are stirred and dispersed in 3000ml of ethanol to prepare a slurry;

[0103] (2) The slurry is pumped into a sand mill, and the slurry particle size is controlled at about D50=100nm and D90=300nm by sand milling for 1h to obtain a precursor slurry;

[0104] (3) The precursor slurry is transported into the drying tower of the centrifugal spray dryer through the peristaltic pump, and the solvent is evaporated instantaneously to obtain a precursor powder A, and the particle size D50 of the precursor powder A is 6μm;

[0105] (4) 100g of the precursor powder A is taken and dispersed in 100ml of isopropanol, then 30ml of zirconium carbonate solution is added, and the stirring is continued at 120℃ water bath for about 18 hours until the solvent is completely evaporated to obtain a precursor powder B;

[0106] (5) The precursor powder B is placed in a corundum box, and the box is placed in a box furnace, sintered at 800℃ for 22h in an air atmosphere, and naturally cooled, and the obtained product is crushed and sieved to obtain a ZrO2-coated Zr-doped NaNi 1 / 3 Mn 2 / 3 O2.

[0107] Example 5

[0108] The sodium ion battery positive electrode material of the embodiment comprises a core body and a coating layer coating the core body, and a doped layer between the core body and the coating layer, the core body is NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, the coating layer is CdO, and the doped layer is Cd, which is called CdO-coated Cd-doped NaNi 1 / 3 Co 1 / 3 Mn1 / 3 O2.

[0109] The preparation method of the sodium ion battery cathode material of the embodiment comprises the following steps:

[0110] (1) 74.7g of nickel oxide, 74.9g of cobalt oxide, 86.9g of manganese oxide, and 158.9g of sodium carbonate are stirred and dispersed in 3000ml of ethanol to prepare a slurry;

[0111] (2) The slurry is pumped into a sand mill, and the slurry particle size is controlled at D50 = about 300nm and D90 = about 700nm through 1h sand mill treatment to obtain a precursor slurry;

[0112] (3) The precursor slurry is transported into a drying tower in a centrifugal spray dryer through a peristaltic pump, and the solvent is instantly evaporated to obtain a precursor powder A, and the particle size D50 of the precursor powder A is 16μm;

[0113] (4) 100g of the precursor powder A is taken and stirred and dispersed in 100ml of isopropanol, then 30ml of dimethyl cadmium solution is added, and the stirring is continued at 80℃ water bath for about 18 hours until the solvent is completely evaporated to obtain a precursor powder B;

[0114] (5) The precursor powder B is placed in a corundum box, and the box is placed in a box furnace, sintered at 800℃ for 20h in an air atmosphere, and naturally cooled, and the obtained product is crushed and sieved to obtain a CdO coated Cd doped NaNi 1 / 3 Co 1 / 3Mn 1 / 3 O2.

[0115] Example 6

[0116] The sodium ion battery cathode material of the embodiment comprises a core body and a coating layer covering the core body, and a doped layer between the core body and the coating layer, the core body is NaNi 2 / 5 Fe 1 / 5 Mn 2 / 5 O2, the coating layer is MgO, and the doped layer is Mg, which is called MgO coated Mg doped NaNi 2 / 5 Fe 1 / 5 Mn 2 / 5 O2.

[0117] The preparation method of the sodium ion battery cathode material of the embodiment comprises the following steps:

[0118] (1) 29.7g of nickel oxide, 15.9g of iron oxide, 34.78g of manganese oxide, and 52.9g of sodium carbonate are stirred and dispersed in 2000ml of ethanol to prepare a slurry;

[0119] (2) Pump the slurry into the sand mill, and control the particle size of the slurry to be about D50=200 nm and about D50=500 nm by sand milling for 1 h to obtain a precursor slurry;

[0120] (3) The precursor slurry is transported into a drying tower in a centrifugal spray dryer by a peristaltic pump, and the solvent is evaporated instantaneously to obtain a precursor powder A, and the particle size D50 of the precursor powder A is 12 μm;

[0121] (4) 100 g of the precursor powder A is dispersed in 100 ml of N-methyl pyrrolidone by stirring, and then 30 ml of a magnesium citrate solution is added, and the stirring is continued at 90°C water bath for about 16 hours until the solvent is completely evaporated to obtain a precursor powder B;

[0122] (5) The precursor powder B is placed in a corundum box, and the box is placed in a box furnace, and sintered at 700°C for 24 h in an air atmosphere, and then naturally cooled, and the obtained product is crushed and sieved to obtain Mg-doped NaNi 2 / 5 Fe 1 / 5Mn 2 / 5 O2.

[0123] Example 7

[0124] The preparation method of this example is the same as that of Example 1, except that the zirconium n-butanol solution is added in step (4) of Example 1, and the dimethyl aluminum solution is added in step (4) of this example, and the rest is the same.

[0125] Example 8

[0126] The preparation method of this example is the same as that of Example 1, except that the zirconium n-butanol solution is added in step (4) of Example 1, and the niobium oxalate solution is added in step (4) of this example, and the rest is the same.

[0127] Example 9

[0128] The preparation method of this example is the same as that of Example 1, except that the zirconium n-butanol solution is added in step (4) of Example 1, and the titanium tetraisopropyl alcohol solution is added in step (4) of this example, and the rest is the same.

[0129] Comparative Example 1

[0130] The preparation method of the sodium ion battery positive electrode material of this comparative example comprises the following steps:

[0131] (1) 74.7 g of nickel oxide, 79.8 g of iron oxide, 86.9 g of manganese oxide, and 158.9 g of sodium carbonate are dispersed in 3000 ml of deionized water by stirring to prepare a slurry;

[0132] (2) Pump the slurry into a sand mill, and control the particle size of the slurry to be about D50=500 nm and D90=1.2 μm by sand milling for 1 h to obtain a precursor slurry;

[0133] (3) Deliver the precursor slurry into a drying tower in a centrifugal spray dryer by a peristaltic pump, and evaporate the solvent instantaneously to obtain a precursor powder A, wherein the particle size of the precursor powder A is D50=10 μm;

[0134] (4) Take 100 g of the precursor powder A, place it in a corundum box, and then place the box in a box furnace, and sinter the precursor powder A at 900 ℃ for 25 h in an air atmosphere, and then naturally cool the precursor powder A, and then crush and sieve the obtained product to obtain a layered metal oxide NaNi 1 / 3Fe 1 / 3 Mn 1 / 3 O2.

[0135] Comparative Example 2

[0136] This comparative example is basically the same as Example 1, except that in Example 1, the precursor slurry is delivered into a drying tower in a centrifugal spray dryer by a peristaltic pump, and the solvent is evaporated instantaneously to obtain a precursor powder A, wherein the particle size of the precursor powder A is D50=10 μm; while in Comparative Example 2, the precursor slurry is evaporated and dried to obtain a precursor powder A.

[0137] The positive electrode materials obtained in Example 1 and Comparative Example 1 are observed and analyzed by a scanning electron microscope, and the results are shown in FIGS. 1 and 2, respectively. Figure 2 and Figure 3 , Figure 2 is the morphology of the positive electrode material of Example 1 of the present application, Figure 3 is the morphology of the positive electrode material of Comparative Example 1, and Figure 2 and Figure 3 As can be seen from the comparison, the particles of the positive electrode material after coating are smoother and more complete, and have a higher sphericity.

[0138] The sodium-ion battery positive electrode materials obtained in Examples 1-3 and Comparative Example 1 are uniformly slurried with a binder (polyvinylidene fluoride PVDF dissolved in N-methyl pyrrolidone NMP, and the PVDF content is 3.5%) and a conductive agent (conductive carbon black SP) at a weight ratio of 8:1:1, and then coated on an aluminum foil current collector, and then subjected to drying, cutting and pressing to obtain positive electrode sheets. The assembled batteries are sealed by a sealing machine, and then subjected to electrochemical performance testing by using a new Wei battery test cabinet. The electrochemical data are shown in Table 1.

[0139] Electrochemical performance test of each example and comparative example in Table 1

[0140]

[0141] From the results of Table 1, it can be seen that the sodium-ion battery positive electrode material of Examples 1 to 3 has a first coulomb efficiency of more than 90% and a capacity retention rate of more than 90% after 500 cycles, while the sodium-ion battery positive electrode material of Comparative Example 1 is not modified by coating and doping, and its capacity retention rate after 500 cycles is only 75.1%. The main reason is that the coating layer acts as a protective unit and does not participate in the oxidation-reduction reaction in the charging and discharging process, which can reduce the volume change stress of the material as a whole during the cycle process, improve the cycle stability and capacity retention rate; at the same time, in the process of high-temperature sintering, the metal ions M in the coating layer M y O z further diffuse and penetrate into the Na x M1 a M2 b M3 c O2 positive electrode material; that is, the coating and doping double modification is realized at the same time by one-step sintering method, on the one hand, M in Na x M1 a M2 b M3 c O2 can alleviate the change of Na x M1 a M2 b M3 c O crystal structure during charging and discharging, improve the stability of the crystal during the cycle process, on the other hand, this doping method can make the coating layer and the core body have no obvious layer boundary, and the combination between them is more compact, which improves the structural stability and further improves the capacity retention rate of the positive electrode material during the cycle process.

[0142] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application, although the present application has been described in detail with reference to the preferred embodiments, but it is not limited to the examples listed in the embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalent, without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, The method comprises the following steps: (a) mixing a sodium source, a metal source and a first solvent to obtain a slurry, and then performing sand milling and spray granulation to obtain spherical particle precursor powder A; (b) adding the precursor powder A into a second solvent, heating and stirring, then adding a solution containing metal M, and removing the second solvent to obtain precursor powder B; (c) sintering the precursor powder B in an oxygen-containing atmosphere, and then cooling and grinding to obtain the metal M-doped sodium ion battery cathode material coated with the oxide of the metal M; The sodium ion battery positive electrode material comprises a core body and a coating layer covering the core body, a doped layer is arranged between the core body and the coating layer, the core body is a layered metal oxide, the coating layer is a metal oxide, metal ions in the coating layer penetrate into the core body to form the doped layer, the metal source comprises at least one of an M1 metal source, an M2 metal source and an M3 metal source, and a structural formula of the layered metal oxide is Na x M1 a M2 b M3 c O2, wherein M1, M2 and M3 are transition metal elements, 0.2≤x≤1, a+b+c=1, 0≤a≤1, 0≤b≤1, 0≤c≤1, M1, M2 and M3 each independently comprise at least one of Ni, Fe, Mn, Co, Cu, Cr and V, a structural formula of the metal oxide is M y O z , wherein M comprises at least one of Ge, Rb, Cd, Zn, Zr, Mg, Al, Nb, Ti, Sn, Ca, Ru, Mo, Sb, Sr and Ag, 0<y≤3, 0<z≤5.

2. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The method comprises at least one of the following features ① to ③: ① the thickness of the coating layer is 100 nm to 1 μm; ② the metal doping depth in the doping layer is 50 to 200 nm; ③ the mass percentage of the coating layer in the total mass of the core, the coating layer and the doping layer is 0.1 to 7 wt%.

3. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The M1 metal source, the M2 metal source and the M3 metal source each independently comprise at least one of nickel oxide, iron oxide, manganese oxide, cobalt oxide, copper oxide, chromium oxide and vanadium oxide.

4. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The method comprises at least one of the following features (1) to (12): (1) in step (a), the sodium source comprises at least one of sodium carbonate, sodium bicarbonate, sodium nitrate and sodium hydroxide; (2) in step (a), the first solvent is at least one selected from deionized water, ethanol, methanol, isopropanol, triethylene glycol, polyethylene glycol, acetone, N-methyl pyrrolidone, N,N-dimethylformamide, acetone, acetonitrile and diethyl ether; (3) the particle size of the slurry after the sand milling is controlled to be 50 nm≤D50≤1 μm and 200 nm≤D90≤2 μm; (4) the particle size of the precursor powder A is 1 μm≤D50≤20 μm; (5) in step (b), the second solvent is at least one selected from ethanol, methanol, isopropanol, triethylene glycol, polyethylene glycol, acetone, N-methyl pyrrolidone, N,N-dimethylformamide, acetone, acetonitrile and diethyl ether; (6) in step (b), the temperature of the heating and stirring is 30 to 100℃; (7) in step (b), the time of the heating and stirring is 8 to 24 h; (8) in step (c), the temperature of the sintering is 600 to 1000℃; (9) in step (c), the time of the sintering is 10 to 25 h; (10) in step (c), the oxygen-containing atmosphere is a gas with an oxygen content of 20 to 80%; (11) in step (c), the flow rate of the oxygen-containing atmosphere is 1 L / min to 20 L / min.

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