A positive electrode material, a preparation method thereof, and a sodium ion battery

Abstract

The application provides a positive electrode material and a preparation method thereof, and a sodium ion battery, so as to improve the initial coulomb efficiency of O3 phase sodium ion positive electrode material, and provide a sodium ion positive electrode material with high specific capacity and high initial coulomb efficiency. The positive electrode material comprises: a coating layer and an inner layer material coated by the coating layer, the coating layer is yCuO, and the inner layer material is Na x Ni a Fe b Mn c Cu d M e O 2‑β P β ;0

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly to a cathode material, a preparation method thereof, and a sodium-ion battery. Background Art

[0002] With the gradual depletion of lithium resources, sodium-ion batteries have attracted much attention due to the abundant sodium source reserves, capacity, and energy density advantages. Currently, among sodium-ion cathode materials such as sodium-rich layered oxides, sodium-rich polyanions, and aqueous Prussian blue, sodium-rich layered oxides have a two-dimensional insertion / extraction mode similar to that of lithium-rich layered oxides, making the corresponding sodium-ion batteries have a high power density similar to that of lithium-ion batteries. Moreover, the capacity and structural stability of sodium-rich layered oxides also have relatively prominent advantages; especially O3-phase layered oxides. Compared with P2-phase and O3 / P2 composite-phase layered oxides, O3-phase sodium-rich layered oxides have an extremely prominent gram capacity advantage due to their higher sodium ion molar content, and thus have also become a preferred cathode material type in actual production.

[0003] However, although O3-phase layered oxides have a high gram capacity, due to the difficulty of sodium ions to smoothly insert / extract during the charge-discharge process, they exhibit a low initial Coulomb efficiency. Summary of the Invention

[0004] The present invention provides a cathode material, a preparation method thereof, and a sodium-ion battery to improve the initial Coulomb efficiency of O3-phase sodium-ion cathode materials and provide a sodium-ion cathode material with high gram capacity and high initial Coulomb efficiency.

[0005] In a first aspect, an embodiment of the present application provides a cathode material, including:

[0006] A coating layer and an inner layer material coated by the coating layer, the coating layer is yCuO, and the inner layer material is Na x Ni a Fe b Mn c Cu d M e O 2-β P β ; 0 < y ≤ 0.10, 0.67 ≤ x ≤ 1, 0.11 ≤ a ≤ 0.44, 0.11 ≤ b ≤ 0.44, 0.11 ≤ c ≤ 0.55, 0.11 ≤ d ≤ 0.44, 0 ≤ e ≤ 0.44, 0 < β ≤ 0.5; M is a doping element, and M is selected from at least one of Li, Mg, Ca, Si, S, Sc, Ti, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Ta, Ir, and Bi; wherein,

[0007] In the X-ray diffraction pattern of the cathode material, the peak intensity of the CuO diffraction peak with a diffraction angle of 38°-39° is 50-800.

[0008] In the sodium-ion cathode material provided in this application embodiment, phosphorus (P) is doped into the O layer of the layered structure by anion anodes. This improves the system's disorder to address electron localization issues in the crystal structure, while simultaneously increasing the repulsive forces between phosphorus atoms in the P-Na-P layer, or between oxygen atoms in the P-Na-O layer, thus promoting the increase in the interlayer spacing of sodium ions and effectively enhancing the initial coulombic efficiency of the cathode material. Furthermore, since the cathode material's coating layer is CuO with a diffraction peak intensity of 50-800, the lattice mismatch between the coating layer and the internal material effectively promotes the extraction and insertion of sodium ions during charge-discharge, further enhancing the initial coulombic efficiency of the sodium-ion cathode material. Moreover, because sodium ion extraction and insertion can proceed more smoothly in this sodium-ion cathode material, its cycle stability is also improved. In addition, because CuO possesses relatively stable properties and is less prone to reacting with the electrolyte, side reactions between the active material and the electrolyte can be effectively avoided, further enhancing the cycle stability of the cathode material.

[0009] In one possible implementation, the sodium layer spacing in the unit cell of the positive electrode material is...

[0010] In one possible implementation, the cell density of the positive electrode material is 4.45-4.55 g / cm³. 3 .

[0011] In one possible implementation, the vacancy ratio in the cathode material is no greater than 0.5%.

[0012] In one possible implementation, the X-ray diffraction pattern of the cathode material contains diffraction peaks of the following crystal planes in the diffraction angle ranges of 16°-17°, 33°-34°, 35°-36°, 36°-37.5°, 41°-42.5°, 45°-46°, 53°-54.5°, 58°-59°, 62°-63.5°, and 65°-66°, respectively: (003), (006), (101), (012), (104), (015), (017), (018), (110), and (113).

[0013] In one possible implementation, the median particle size of the cathode material is 5.0-11.0 μm; the particle size distribution SPAN of the cathode material is 0.5-1.5.

[0014] In one possible implementation, the specific surface area of ​​the positive electrode material is 4.0-7.0 m².2 / g.

[0015] Secondly, embodiments of this application also provide a method for preparing the cathode material described in the first aspect and any possible implementation, comprising:

[0016] A first mixture containing a sodium source, a phosphorus source, and a precursor, and / or a second mixture containing a sodium source, a phosphorus source, a nickel source, an iron source, a manganese source, a copper source, and a dopant source are sintered N times to obtain a cathode material; wherein,

[0017] The precursor includes a transition metal hydroxyl oxide, where N is an integer not less than 2, and in the N sintering processes, the sintering temperature of the first sintering is 855-950℃, and the cooling rate of the first sintering is 50-100℃ / h.

[0018] In one possible implementation, the cooling rate of the first sintering is no greater than 75°C / h.

[0019] In one possible implementation, N=2, the N sintering consists of the first sintering and the second sintering, and the sintering temperature of the second sintering is 450-550℃.

[0020] In one possible implementation, the phosphorus source in the first mixture and the phosphorus source in the second mixture are each independently selected from at least one of: ammonium dihydrogen phosphate, sodium dihydrogen phosphate, sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and elemental phosphorus; and the transition metal hydroxyl oxide is Ni. f Fe g Mn h Cu l M m OOH; where,

[0021] 0.11≤f≤0.44, 0.11≤g≤0.44, 0.11≤h≤0.55, 0.11≤l≤0.44, 0≤m≤0.44; M is a dopant element, selected from at least one of the following: Li, Mg, Ca, Si, S, Sc, Ti, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Ta, Ir, and Bi.

[0022] In one possible implementation, the precursor further includes a transition metal oxide, which is obtained by pre-sintering the transition metal hydroxyl oxide at 300-400°C; wherein,

[0023] The transition metal oxide is Ni. f Fe g Mn h Cul M m O; 0.11≤f≤0.44, 0.11≤g≤0.44, 0.11≤h≤0.55, 0.11≤l≤0.44, 0≤m≤0.44; M is a dopant element, selected from at least one of: Li, Mg, Ca, Si, P, S, Sc, Ti, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Ta, Ir, and Bi.

[0024] Thirdly, embodiments of this application also provide a method for determining the vacancy ratio in the sodium-ion cathode material described in the first aspect and any possible implementation, comprising:

[0025] The vacancy ratio in the sodium ion cathode material is determined based on a preset formula; the preset formula is:

[0026] Wherein, ω is the vacancy ratio, ρ1 is the cell density of the reference material when there are no vacancies, and ρ2 is the cell density of the sodium ion cathode material. The reference material is Na. x Ni γ Fe η Mn ζ Zn θ O2; 0.67≤x≤1, |γ-a|≤0.2, |η-b|≤0.2, |ζ-c|≤0.2, |θ-d|≤0.2, |α-e|≤0.2.

[0027] One possible implementation is 0.11≤γ≤0.44, 0.11≤η≤0.44, 0.11≤ζ≤0.55, 0≤α≤0.44, 0≤θ≤0.44.

[0028] In one possible implementation, ρ1 = ρ0 / ω0; ρ0 is the cell density of the reference object, and ω0 is the vacancy ratio of the reference object.

[0029] One possible implementation is that the reference object is NaNi. 0.22 Fe 0.22 Mn 0.55 Zn 0.11 O2, then ρ1 = 4.508 g / cm³ 3 .

[0030] Fourthly, embodiments of this application also provide a sodium-ion battery, comprising:

[0031] The cathode material described in the first aspect and any possible implementation. Attached Figure Description

[0032] Figure 1 This is a comparison chart of the X-ray diffraction patterns of Example 1 and Comparative Example 1 provided by the embodiments of this application. Detailed implementation mode

[0033] Aiming at the problem of low initial Coulomb efficiency of O3-phase sodium-ion cathode materials in the prior art, the embodiments of this application provide a cathode material. The cathode material is a coating layer and an inner layer material coated by the coating layer. The coating layer is yCuO, and the inner layer material is Na x Ni a Fe b Mn c Cu d M e O 2-β P β ; 0 < y ≤ 0.10, 0.67 ≤ x ≤ 1, 0.11 ≤ a ≤ 0.44, 0.11 ≤ b ≤ 0.44, 0.11 ≤ c ≤ 0.55, 0.11 ≤ d ≤ 0.44, 0 ≤ e ≤ 0.44, 0 < β ≤ 0.5; M is a doping element, and M is selected from at least one of Li, Mg, Ca, Si, S, Sc, Ti, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Ta, Ir, and Bi.

[0034] In the X-ray diffraction pattern of this cathode material, the peak intensity of the CuO diffraction peak with a diffraction angle of 38° - 39° is 50 - 800.

[0035] On the one hand, in the above cathode material, since the P atomic radius of the anionic radical is much larger than that of the transition metal and is close to the atomic radius of the O atom, the P atoms in the above cathode material are mainly doped into the oxygen sites in the layered structure.

[0036] Secondly, sodium-ion cathode materials are ionic crystals, where there are no covalent bonds (electron pairs) between positive and negative ions. Instead, the crystal structure is formed by the attraction between the atomic nuclei of positive ions and the electron clouds of negative ions. Since the aforementioned cathode materials contain at least transition metal elements such as Na, Ni, Fe, Mn, and Cu, they exhibit high system disorder, effectively improving electron localization and promoting the extraction and insertion of electrons during the charge-discharge process, thus enhancing the initial coulombic efficiency. Furthermore, they avoid the problem of poor cycle stability caused by sodium ions being "stuck" at a certain site during extraction and insertion within the crystal structure. On this basis, after phosphorus (P) enters the layered structure, its electron cloud density is much greater than that of oxygen (O) due to its larger number of electrons. This increases the repulsive force between phosphorus and phosphorus or oxygen and oxygen in the P-Na-P or P-Na-O layers (electrons repel each other), thereby promoting an increase in the sodium interlayer spacing (O-Na-O), further enhancing the initial coulombic efficiency of the cathode material. Correspondingly, the rate performance is also improved with the increase in initial coulomb efficiency.

[0037] The aforementioned electron cloud is used to describe the probability distribution of the movement of electrons outside the nucleus.

[0038] Thirdly, this cathode material is actually a core-shell heterostructure. This is because the outer CuO and inner Na... x Ni a Fe b Mn c Cu d M e O 2-β P β The presence of lattice mismatch reduces the kinetic barrier for sodium ion insertion / extraction in the cathode material, thus promoting sodium ion extraction or insertion and further improving the initial coulombic efficiency of the cathode material. Furthermore, because the external CuO is relatively stable and does not react with the electrolyte, CuO can suppress side reactions between the electrolyte and the internal active material during charge-discharge, thereby improving the cycle stability of the cathode material.

[0039] Furthermore, the sodium layer spacing in the unit cell of the above-mentioned cathode material is... The unit cell density is 4.45-4.55 g / cm³. 3 The preferred value is 4.45-4.52 g / cm³. 3 .

[0040] Furthermore, although a higher vacancy rate in the cathode material is beneficial for sodium ion insertion / extraction and for improving the initial coulombic efficiency, an excessively high vacancy ratio can easily cause crystal structure distortion during sodium ion insertion / extraction, leading to deterioration in cycle stability. Therefore, in one embodiment of this application, the vacancy ratio in the cathode material is no greater than 0.5%; this vacancy ratio is obtained by the following formula: Where ω is the vacancy ratio, and ρ1 = 4.508 g / cm³ 3 ρ2 is the cell density of the aforementioned cathode material. The aforementioned vacancy ratio can be understood as the ratio of the number of vacancy sites in the crystal structure to the number of sites in the crystal structure without vacancies.

[0041] Furthermore, the X-ray diffraction (XRD) patterns of the above-mentioned cathode material contain the following diffraction peaks for each crystal plane in the diffraction angle ranges of 16°-17°, 33°-34°, 35°-36°, 36°-37.5°, 41°-42.5°, 45°-46°, 53°-54.5°, 58°-59°, 62°-63.5°, and 65°-66°: (003), (006), (101), (012), (104), (015), (017), (018), (110), and (113).

[0042] The median particle size of the above-mentioned cathode material is 5.0-11.0 μm; the particle size distribution SPAN of the cathode material is 0.5-1.5.

[0043] Furthermore, the specific surface area of ​​the aforementioned cathode material is 4.0-7.0 m². 2 The tap density of this cathode material is 1.5-2.5 g / cm³. 3 .

[0044] Based on the same inventive concept, this application provides a method for preparing the above-mentioned cathode material, which includes the following steps:

[0045] The cathode material is obtained by sintering a first mixture containing sodium source, phosphorus source and precursor, and / or a second mixture containing sodium source, phosphorus source, nickel source, iron source, manganese source, copper source and dopant source N times.

[0046] Wherein, N is an integer not less than 2, and in the N sintering processes, the sintering temperature of the first sintering is 855-950℃, and the cooling rate of the first sintering is 50-100℃ / h. The preferred first sintering temperature is 930℃, the preferred heating rate is 2℃ / min, and the preferred cooling rate is 74-76℃ / min.

[0047] It is worth noting that in the aforementioned multiple sintering processes, the temperature is first lowered to room temperature before being raised again. In this embodiment, the cooling rate of the high-temperature sintering (first sintering) is controlled to be 50-100℃ / h, preferably 50-75℃ / h, to achieve the purpose of dissolving Cu under slow cooling conditions. This allows Cu to uniformly adhere to the surface of the internal material, forming a coating layer and a core-shell heterostructure. This facilitates the efficient extraction and insertion of sodium ions through the core-shell heterostructure during the charging-discharging process of the final cathode material, thereby improving the initial coulombic efficiency, rate performance, and cycle stability of the cathode material. It also avoids the problem of uneven Cu precipitation in the saturated solid solution due to excessively high cooling rates, which would result in uneven vacancy distribution and uncontrollable numbers in the solid solution, ultimately compromising the reversibility of the cathode material.

[0048] The aforementioned precursors include transition metal hydroxyl oxides Ni f Fe g Mn h Cu l M m OOH. Wherein, 0.11≤f≤0.44, 0.11≤g≤0.44, 0.11≤h≤0.55, 0.11≤l≤0.44, 0≤m≤0.44. The dopant element M is selected from at least one of the following: Li, Mg, Ca, Si, S, Sc, Ti, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Ta, Ir, and Bi.

[0049] The sodium source in the first mixture and the sodium source in the second mixture are each independently selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, and sodium peroxide.

[0050] The phosphorus source in the first mixture and the phosphorus source in the second mixture are each independently selected from at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and elemental phosphorus.

[0051] The nickel source mentioned above is selected from at least one of nickel nitrate, nickel acetate, nickel sulfate, nickel chloride, and nickel oxide.

[0052] The iron source mentioned above is selected from at least one of the following: ferric nitrate, ferric acetate, ferric sulfate, ferric chloride, and iron(II,III) oxide.

[0053] The manganese source mentioned above is selected from at least one of manganese nitrate, manganese sulfate, manganese chloride, manganese carbonate, manganese acetate, manganese trioxide, and manganese tetroxide.

[0054] The copper source mentioned above is selected from at least one of copper sulfate, copper nitrate, copper chloride, and copper oxide.

[0055] When the aforementioned number of sintering cycles N=2, the N sintering cycles consist of the first sintering and the second sintering. The sintering temperature of the second sintering is 450-550℃, preferably 500℃; the heating rate is 1-5℃ / min, preferably 2℃ / min; and the sintering time is 4-7h, preferably 5h.

[0056] When the aforementioned number of sintering times N=3, the Nth sintering consists of the first sintering, the second sintering, and the third sintering. The sintering temperature of the second sintering can be 600-800℃, and the sintering temperature of the third sintering can be 450-550℃.

[0057] Furthermore, to improve preparation efficiency and increase the amount of reactants in the pot, the aforementioned precursor can be pre-sintered to remove some of the water of crystallization from the hydroxyl oxide. Therefore, in one embodiment of this application, the precursor may further include a transition metal oxide, which is obtained by pre-sintering a transition metal hydroxyl oxide at a heating rate of 1-5°C / min and a temperature of 300-400°C for 5-15 hours; thus, the precursor is a mixture of transition metal hydroxyl oxide and transition metal oxide.

[0058] The general molecular formula of this transition metal oxide is Ni. f Fe g Mn h Cu l M m O 1.5 ; 0.11≤f≤0.44, 0.11≤g≤0.44, 0.11≤h≤0.55, 0.11≤l≤0.44, 0≤m≤0.44; M is a dopant element, selected from at least one of: Li, Mg, Ca, Si, P, S, Sc, Ti, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Ta, Ir, and Bi.

[0059] The preferred heating rate for the pre-sintering is 2℃ / min, the preferred pre-sintering temperature is 350℃, and the preferred sintering time is 5h.

[0060] Based on the same inventive concept, this application also provides a method for determining the vacancy ratio in a sodium-ion cathode material, used to estimate the vacancy ratio in any of the aforementioned sodium-ion cathode materials. This method includes the following steps:

[0061] The vacancy ratio in the sodium-ion cathode material is determined based on a pre-defined formula. This pre-defined formula is:

[0062] Wherein, ω is the aforementioned vacancy ratio, ρ1 is the cell density of the reference material when there are no vacancies in the cell, and ρ2 is the cell density of the sodium ion cathode material.

[0063] Because Cu and Zn are adjacent in the periodic table, Cu has a molar mass of 63.546 and an atomic radius of [missing information]. The molar mass of Zn is 63.39, and its atomic radius is... Both possess similar physicochemical properties. Therefore, in this embodiment, Na is used as the reference. x Ni γ Fe η Mn ζ Zn θ M α O2. The X-ray diffraction pattern of this reference object shows no impurity peaks, indicating that it is suitable as a reference object as it contains no impurity phases.

[0064] Furthermore, to ensure that the crystal phase structure of the reference material is as close as possible to the crystal phase structure of the sodium-ion cathode material to be determined, the stoichiometry of Na in the reference material must be the same as that in the sodium-ion cathode material. The difference between the stoichiometry of other metal elements similar to Zn and Cu and their corresponding elements in the sodium-ion cathode material should not exceed 0.2. That is, 0.67≤x≤1, |γ-a|≤0.2, |η-b|≤0.2, |ζ-c|≤0.2, |θ-d|≤0.2, |α-e|≤0.2.

[0065] For example: 0.11≤γ≤0.44, 0.11≤η≤0.44, 0.11≤ζ≤0.55, 0≤θ≤0.44, 0≤e≤0.44.

[0066] The above ρ1 can be obtained by the following formula: ρ1=ρ0 / ω0; ρ0 is the cell density of the reference object, and ω0 is the vacancy ratio of the reference object.

[0067] For example, the reference is NaNi 0.22 Fe 0.22 Mn 0.55 Zn 0.11 O2, ρ1 = 4.508 g / cm³ 3 .

[0068] Because the sodium ion insertion / extraction efficiency increases with the increase of the vacancy ratio during charging and discharging of the cathode material, but when the vacancy ratio is too high, it will affect the stability of the cathode material. Therefore, this method can be used to screen or determine one or more cathode materials with high initial coulombic efficiency and high cycle stability.

[0069] When the vacancy ratio is between 0.1% and 0.5%, such as 0.2% or 0.4%, it can ensure that the sodium ion cathode material has high rate performance while also maintaining stability.

[0070] It should be noted that the reference objects in the embodiments of this application include, but are not limited to, NaNi. 0.22 Fe 0.22 Mn 0.55 Zn 0.11 Regarding O2, it should be noted that when determining the vacancy ratio of various sodium ion cathode materials, if it is necessary to compare various sodium ion cathodes, a reference object can be fixed to compare the impact of different elemental compositions in different sodium ion cathode materials, or the same elemental composition but different elemental contents, on the vacancy ratio in the cathode material.

[0071] The following examples and comparative figures illustrate the points.

[0072] Example 1

[0073] S1. Using a high-speed mixer, sodium carbonate, nickel oxide, iron tetroxide, manganese tetroxide, copper oxide, and ammonium dihydrogen phosphate are mixed in an elemental molar ratio of Na:Ni:Fe:Mn:Cu:P = 1:0.22:0.22:0.55:0.11:0.02 for 0.5 hours.

[0074] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0075] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.01CuO@NaNi. 0.22 Fe 0.22 Mn 0.55 Cu 0.10 O 1.98 P 0.02 .

[0076] The molar amount of copper oxide in this cathode material was determined by XRD analysis. External standard treatment was performed on copper oxide with diffraction peaks at 38°-39° in the XRD pattern and pure copper oxide, revealing a CuO stoichiometry of 0.01 in its external structure. The X-ray diffraction pattern of this cathode material is shown below. Figure 1 As shown.

[0077] Example 2

[0078] S1. Using a high-speed mixer, mix sodium carbonate, nickel oxide, iron tetroxide, manganese tetroxide, copper oxide, zinc oxide, and ammonium dihydrogen phosphate in an elemental molar ratio of Na:Ni:Fe:Mn:Cu:Zn:P = 1:0.22:0.22:0.44:0.11:0.11:0.02 for 0.5 h.

[0079] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0080] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.01CuO@NaNi. 0.22 Fe 0.22 Mn 0.44 Cu 0.1 Zn 0.11 O 1.98 P 0.02 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0081] Example 3

[0082] S1. Using a high-speed mixer, sodium carbonate, nickel oxide, iron tetroxide, manganese tetroxide, copper oxide, and ammonium dihydrogen phosphate are mixed in an elemental molar ratio of Na:Ni:Fe:Mn:Cu:P = 1:0.22:0.22:0.55:0.11:0.04 for 0.5 hours.

[0083] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0084] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.01CuO@NaNi. 0.22 Fe 0.22 Mn 0.55 Cu 0.1 O 1.96 P 0.04 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0085] Example 4

[0086] S1. Using a high-speed mixer, sodium carbonate, nickel oxide, iron tetroxide, manganese tetroxide, copper oxide, and ammonium dihydrogen phosphate are mixed in an elemental molar ratio of Na:Ni:Fe:Mn:Cu:P = 1:0.22:0.22:0.38:0.18:0.02 for 0.5 h.

[0087] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0088] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.013CuO@NaNi. 0.22 Fe 0.22 Mn 0.38 Cu 0.167 O 1.98 P 0.02 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0089] Example 5:

[0090] S1. Using a high-speed mixer, sodium carbonate, nickel oxide, iron tetroxide, manganese tetroxide, copper oxide, and ammonium dihydrogen phosphate are mixed in an elemental molar ratio of Na:Ni:Fe:Mn:Cu:P = 1:0.22:0.22:0.55:0.11:0.5 for 0.5 hours.

[0091] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0092] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.01CuO@NaNi. 0.22 Fe 0.22 Mn 0.55 Cu 0.1 O 1.5 P 0.5 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0093] Example 6

[0094] S1. Using a high-speed mixer, sodium carbonate, nickel oxide, iron tetroxide, manganese tetroxide, copper oxide, and ammonium dihydrogen phosphate are mixed in an elemental molar ratio of Na:Ni:Fe:Mn:Cu:P = 1:0.22:0.22:0.55:0.11:0.02 for 0.5 hours.

[0095] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 50℃ / h.

[0096] S3. Calcine at 500℃ for 5 hours at a heating rate of 2℃ / min, then cool to room temperature to obtain... 0.015 CuO@NaNi 0.2 2Fe 0.22 Mn 0.55Cu 0.095 O 1.98 P 0.02 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0097] Example 7

[0098] S1. Using a high-speed mixer, the transition metal precursor Ni... 0.22 Fe 0.22 Mn 0.55 Cu 0.11 Mix OOH with a mixture of sodium carbonate and ammonium dihydrogen phosphate for 0.5 h.

[0099] The ratio of the molar amount of sodium in sodium carbonate to the molar amount of metal in the transition metal precursor is 1; the ratio of the molar amount of phosphorus in ammonium dihydrogen phosphate to the molar amount of metal in the transition metal precursor is 0.02.

[0100] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0101] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.01CuO@NaNi. 0.22 Fe 0.22 Mn 0.55 Cu 0.1 O 1.98 P 0.02 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0102] Example 8

[0103] S1. Using a high-speed mixer, the transition metal precursor Ni... 0.22 Fe 0.22 Mn 0.44 Cu 0.11 Zn .11 Mix OOH with a mixture of sodium carbonate and ammonium dihydrogen phosphate for 0.5 h.

[0104] The ratio of the molar amount of sodium in sodium carbonate to the molar amount of metal in the transition metal precursor is 1; the ratio of the molar amount of phosphorus in ammonium dihydrogen phosphate to the molar amount of metal in the transition metal precursor is 0.02.

[0105] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0106] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.014CuO@NaNi.0.22 Fe 0.22 Mn 0.44 Cu 0.096 Zn 0.11 O 1.98 P 0.02 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0107] Example 9

[0108] S1. Using a high-speed mixer, the transition metal precursor Ni... 0.22 Fe 0.22 Mn 0.55 Cu 0.11 Mix OOH with a mixture of sodium carbonate and ammonium dihydrogen phosphate for 0.5 h.

[0109] The ratio of the molar amount of sodium in sodium carbonate to the molar amount of metal in the transition metal precursor is 1; the ratio of the molar amount of phosphorus in ammonium dihydrogen phosphate to the molar amount of metal in the transition metal precursor is 0.04.

[0110] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0111] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.01CuO@NaNi. 0.22 Fe 0.22 Mn 0.55 Cu 0.1 O 1.96 P 0.04 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0112] Example 10

[0113] S1. Using a high-speed mixer, the transition metal precursor Ni... 0.22 Fe 0.15 Mn 0.40 Cu 0.23 Mix OOH with a mixture of sodium carbonate and ammonium dihydrogen phosphate for 0.5 h.

[0114] The ratio of the molar amount of sodium in sodium carbonate to the molar amount of metal in the transition metal precursor is 1; the ratio of the molar amount of phosphorus in ammonium dihydrogen phosphate to the molar amount of metal in the transition metal precursor is 0.04.

[0115] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0116] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.025CuO@NaNi. 0.22 Fe 0.15 Mn 0.40 Cu 0.205 O 1.96 P 0.04 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0117] Example 11

[0118] S1. Using a high-speed mixer, the transition metal precursor Ni... 0.22 Fe 0.22 Mn 0.55 Cu 0.11 Mix OOH with a mixture of sodium carbonate and ammonium dihydrogen phosphate for 0.5 h.

[0119] The ratio of the molar amount of sodium in sodium carbonate to the molar amount of metal in the transition metal precursor is 1; the ratio of the molar amount of phosphorus in ammonium dihydrogen phosphate to the molar amount of metal in the transition metal precursor is 0.5.

[0120] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0121] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.01CuO@NaNi. 0.22 Fe 0.22 Mn 0.55 Cu 0.1 O 1.5 P 0.5 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0122] Example 12

[0123] S1. Using a high-speed mixer, the transition metal precursor Ni... 0.22 Fe 0.22 Mn 0.55 Cu 0.11 Mix OOH with a mixture of sodium carbonate and ammonium dihydrogen phosphate for 0.5 h.

[0124] The ratio of the molar amount of sodium in sodium carbonate to the molar amount of metal in the transition metal precursor is 1; the ratio of the molar amount of phosphorus in ammonium dihydrogen phosphate to the molar amount of metal in the transition metal precursor is 0.02.

[0125] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 50℃ / h.

[0126] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.015CuO@NaNi. 0.22 Fe 0.22 Mn 0.55 Cu 0.095 O 1.98 P 0.02 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0127] Comparative Example 1

[0128] S1. Using a high-speed mixer, mix sodium carbonate, nickel oxide, iron tetroxide, and manganese tetroxide in an elemental molar ratio of Na:Ni:Fe:Mn:Zn = 1:0.22:0.22:0.55:0.11 for 0.5 hours.

[0129] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0130] S3. Calcine at 500℃ for 5 hours at a heating rate of 2℃ / min, then cool to room temperature to obtain NaNi. 0.22 Fe 0.22 Mn 0.55 Zn 0.11 O2. The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0131] Comparative Example 2

[0132] S1. Using a high-speed mixer, the transition metal precursor Ni... 0.22 Fe 0.22 Mn 0.55 Zn 0.11 OOH was mixed with sodium carbonate for 0.5 h.

[0133] The ratio of the molar amount of sodium in sodium carbonate to the molar amount of metal in the transition metal precursor is 1.

[0134] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h.

[0135] S3. Calcine at 500℃ for 5 hours at a heating rate of 2℃ / min, then cool to room temperature to obtain NaNi. 0.22 Fe 0.22 Mn 0.55 Zn 0.11O2. The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0136] Comparative Example 3

[0137] S1. Using a high-speed mixer, sodium carbonate, nickel oxide, iron tetroxide, manganese tetroxide, copper oxide, and ammonium dihydrogen phosphate are mixed in an elemental molar ratio of Na:Ni:Fe:Mn:Cu:P = 1:0.22:0.22:0.55:0.11:0.02 for 0.5 hours.

[0138] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 105℃ / h.

[0139] S3. Calcine at 500℃ for 5 hours at a heating rate of 2℃ / min, then cool to room temperature to obtain... 0.007 CuO@NaNi 0.2 2Fe 0.22 Mn 0.55 Cu 0.103 O 1.98 P 0.02 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0140] Comparative Example 4

[0141] S1. Using a high-speed mixer, sodium carbonate, nickel oxide, iron tetroxide, manganese tetroxide, and ammonium dihydrogen phosphate are mixed in an elemental molar ratio of Na:Ni:Fe:Mn:P = 1:0.22:0.22:0.55:0.02 for 0.5 hours.

[0142] S2. The mixture was calcined at 930℃ for 12 h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h to obtain NaNi. 0.22 Fe 0.22 Mn 0.55 O 1.98 P 0.02 .

[0143] S3. Then, using a high-speed mixer, the semi-finished NaNi... 0.22 Fe 0.22 Mn 0.55 O 1.98 P 0.02 The mixture was prepared with copper oxide at a metal element molar ratio of 1:0.11 for 0.5 h, then calcined at 500 °C for 5 h at a heating rate of 2 °C / min, and finally cooled to room temperature to obtain 0.09CuO@NaNi. 0.22 Fe 0.22 Mn 0.55 Cu 0.02 O1.98 P 0.02 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0144] Comparative Example 5

[0145] S1. Using a high-speed mixer, the transition metal precursor Ni... 0.22 Fe 0.22 Mn 0.55 Cu 0.11 Mix OOH with a mixture of sodium carbonate and ammonium dihydrogen phosphate for 0.5 h.

[0146] The ratio of the molar amount of sodium in sodium carbonate to the molar amount of metal in the transition metal precursor is 1; the ratio of the molar amount of phosphorus in ammonium dihydrogen phosphate to the molar amount of metal in the transition metal precursor is 0.02.

[0147] S2. The mixture is calcined at 930℃ for 12h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 105℃ / h.

[0148] S3. Calcination was carried out at 500℃ for 5 hours at a heating rate of 2℃ / min, followed by cooling to room temperature to obtain 0.007CuO@NaNi. 0.22 Fe 0.22 Mn 0.55 Cu 0.103 O 1.98 P 0.02 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0149] Comparative Example 6

[0150] S1. Using a high-speed mixer, the transition metal precursor Ni... 0.22 Fe 0.22 Mn 0.55 OOH was mixed with sodium carbonate (sodium molar ratio 1) and ammonium dihydrogen phosphate (phosphorus molar ratio 0.02) for 0.5 h.

[0151] S2. The mixture was calcined at 930℃ for 12 h at a heating rate of 2℃ / min, and then cooled to room temperature at a cooling rate of 75℃ / h to obtain NaNi. 0.22 Fe 0.22 Mn 0.55 O 1.98 P 0.02 .

[0152] S3. Then, using a high-speed mixer, the semi-finished NaNi... 0.22 Fe 0.22 Mn 0.55 O 1.98 P 0.02The mixture was prepared with copper oxide at a metal element molar ratio of 1:0.11 for 0.5 h, then calcined at 500 °C for 5 h at a heating rate of 2 °C / min, and finally cooled to room temperature to obtain 0.09CuO@NaNi. 0.22 Fe 0.22 Mn 0.55 Cu 0.02 O 1.98 P 0.02 The molar amount of copper oxide in this cathode material was determined by XRD analysis.

[0153] The X-ray diffraction patterns of the test examples and comparative examples were used to determine the sodium interlayer spacing and cell density, respectively. The vacancy percentage in the crystal phase structure was determined according to the method provided in the embodiments of this application, with the cathode material in Comparative Example 1 as the reference; ρ1 = 4.508 g / cm³. 3 The sodium interlayer spacing, cell density, and vacancy ratio of each embodiment and comparative example are detailed in Table 1.

[0154] Further, the positive electrode powder, conductive agent Super-P, and binder PVDF were mixed in a mass ratio of 91:5:5, and an appropriate amount of NMP solution was added to form a slurry. This slurry was coated onto aluminum foil, dried, and then baked in a vacuum oven at 120°C for 12 hours. Afterwards, the battery was assembled in the drying room, using aluminum foil coated with hard carbon as the negative electrode and a 1 mol / L NaPF6 solution dissolved in a mixed organic solvent with a volume ratio of EC:EMC = 3:7 as the electrolyte, to form a pouch battery.

[0155] Using constant current charge and discharge mode, the first charge and discharge test was conducted at a current of 40mA within a voltage window of 1.5-4.3V, followed by a 600-cycle test at 400mAh. The test electrical performance results are shown in Table 2 below.

[0156] Table 1

[0157]

[0158]

[0159] Table 2

[0160]

[0161] Referring to Tables 1 and 2, compared with Comparative Examples 1-6, the embodiments have better capacity, cycle performance, and first efficiency (first coulomb efficiency).

[0162] In particular, the vacancy ratio in the comparative examples and in Comparative Examples 3 and 5 shows that when the cooling rate in step S1 is higher than 100℃ / h, the vacancy ratio in the crystal phase structure of Comparative Examples 3 and 5 will decrease significantly, that is, the vacancy content in the crystal phase structure will decrease, resulting in a decrease in the coulombic efficiency of Comparative Examples 3 and 5 for the first time.

[0163] Comparing the vacancy ratios in the comparative examples and in Comparative Examples 4 and 6, it can be seen that although Comparative Examples 4 and 6 can obtain vacancy ratios similar to those in the examples by adding copper oxide during the second calcination to form a coating layer, they cannot achieve the effect of uniform copper oxide precipitation in the core-shell heterostructure obtained by the method provided in the examples. Therefore, the vacancy distribution and content in Comparative Examples 4 and 6 show lower cycling stability.

[0164] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A positive electrode material, characterized in that, include: A coating layer and an inner layer material coated by the coating layer, the coating layer being yCuO and the inner layer material being Na x Ni a Fe b Mn c Cu d M e O 2-β P β ; 0 < y ≤ 0.10, 0.67 ≤ x ≤ 1, 0.11 ≤ a ≤ 0.44, 0.11 ≤ b ≤ 0.44, 0.11 ≤ c ≤ 0.55, 0.11 ≤ d ≤ 0.44, 0 ≤ e ≤ 0.44, 0 < β ≤ 0.5; M is a doping element, and M is selected from at least one of Li, Mg, Ca, Si, S, Sc, Ti, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Ta, Ir, and Bi; wherein, The cathode material is an O3 phase sodium ion cathode material; in the X-ray diffraction pattern of the cathode material, the peak intensity of the CuO diffraction peak with a diffraction angle of 38°-39° is 50-800.

2. The cathode material as described in claim 1, characterized in that, The cell density of the cathode material is 4.45-4.55 g / cm³. 3 .

3. The positive electrode material as described in claim 1, characterized in that, The sodium interlayer spacing in the cell of the cathode material is 3.2-3.4 Å.

4. The cathode material according to any one of claims 1-3, characterized in that, The vacancy rate in the cathode material is no greater than 0.5%.

5. The positive electrode material as described in claim 4, characterized in that, The X-ray diffraction pattern of the cathode material contains diffraction peaks of the following crystal planes in the diffraction angle ranges of 16°-17°, 33°-34°, 35°-36°, 36°-37.5°, 41°-42.5°, 45°-46°, 53°-54.5°, 58°-59°, 62°-63.5°, and 65°-66° respectively: (003), (006), (101), (012), (104), (015), (017), (018), (110), and (113).

6. The cathode material as described in claim 4, characterized in that, The median particle size of the cathode material is 5.0-11.0 μm; the particle size distribution SPAN of the cathode material is 0.5-1.

5.

7. The cathode material as described in claim 4, characterized in that, The specific surface area of ​​the cathode material is 4.0-7.0 m². 2 / g.

8. A method for preparing the cathode material according to any one of claims 1-7, characterized in that, include: A first mixture containing a sodium source, a phosphorus source, and a precursor, and / or a second mixture containing a sodium source, a phosphorus source, a nickel source, an iron source, a manganese source, a copper source, and a dopant source are sintered N times to obtain a cathode material; wherein, The precursor includes a transition metal hydroxyl oxide, where N is an integer not less than 2, and in the N sintering processes, the sintering temperature of the first sintering is 855-950℃, and the cooling rate of the first sintering is 50-100℃ / h.

9. The method as described in claim 8, characterized in that, The cooling rate of the first sintering is no greater than 75℃ / h.

10. The method as described in claim 8, characterized in that, N=2, the Nth sintering consists of the first sintering and the second sintering, and the sintering temperature of the second sintering is 450-550℃.

11. The method according to any one of claims 8-10, characterized in that, The phosphorus source in the first mixture and the phosphorus source in the second mixture are each independently selected from at least one of: ammonium dihydrogen phosphate, sodium dihydrogen phosphate, sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and elemental phosphorus; the transition metal hydroxyl oxide is Ni. f Fe g Mn h Cu l M m OOH; where, 0.11≤f≤0.44, 0.11≤g≤0.44, 0.11≤h≤0.55, 0.11≤l≤0.44, 0≤m≤0.44; M is a dopant element, selected from at least one of the following: Li, Mg, Ca, Si, S, Sc, Ti, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Ta, Ir, and Bi.

12. The method according to any one of claims 8-10, characterized in that, The precursor further includes a transition metal oxide, which is obtained by pre-sintering the transition metal hydroxyl oxide at 300-400°C; wherein... The transition metal oxide is Ni. f Fe g Mn h Cu l M m O 1.5 ; 0.11≤f≤0.44, 0.11≤g≤0.44, 0.11≤h≤0.55, 0.11≤l≤0.44, 0≤m≤0.44; M is a dopant element, selected from at least one of: Li, Mg, Ca, Si, P, S, Sc, Ti, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Ta, Ir, and Bi.

13. A method for determining the vacancy ratio in the cathode material according to any one of claims 1-7, characterized in that, include: The vacancy ratio in the sodium ion cathode material is determined based on a preset formula. The preset formula is: ω= ; Wherein, ω is the vacancy ratio, ρ1 is the cell density of the reference material when there are no vacancies, and ρ2 is the cell density of the sodium ion cathode material. The reference material is Na. x Ni γ Fe η Mn ζ Zn θ M α O2; 0.67≤x≤1, |γ-a|≤0.2, |η-b|≤0.2, |ζ-c|≤0.2, |θ-d|≤0.2, |α-e|≤0.

2.

14. The method as described in claim 13, characterized in that, ρ1 = ρ0 / ω0; ρ0 is the cell density of the reference object, and ω0 is the vacancy ratio of the reference object.

15. A sodium-ion battery, characterized in that, include: The cathode material according to any one of claims 1-7.

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