Positive electrode material and preparation method and application thereof

Abstract

The invention relates to a positive electrode material and a preparation method and application thereof. The chemical formula of the positive electrode material is NaHf < x > (AaNibMnc) < 1-x > O < 2 >, xlt; 0, 0, 0, 0; a < = 1, 0lt; b < = 1, 0lt; a is less than or equal to 1, b is less than or equal to 1, c is less than or equal to 1, a + b + c is equal to 1, A is selected from at least one of Fe, Cu and Co, the positive electrode material is of an O3-type crystal structure, and the Na-O interlayer spacing in the crystal structure is excellent in cycling stability and rate capability, so that the electrical performance of the sodium ion battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, in particular to a cathode material, its preparation method and application. Background Art

[0002] At present, there is still a large gap between the development and development of sodium-ion batteries and practical application and industrialization. The most important reason is that there are some problems with the cathode material during the use of sodium-ion batteries. Among them, layered transition metal oxides have the characteristics of high theoretical specific capacity, low cost, simple synthesis process, etc. as cathode materials, and are the primary choice for sodium-ion batteries.

[0003] The structures of layered transition metal oxides mainly include O3 type and P3 type. Among them, the layered transition metal oxides with O3 type structure mainly include Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (NaNFM), which can not only provide more sodium ion storage sites, but also has a higher specific capacity, so it is widely used in sodium-ion battery cathode materials. However, during the cycling process, due to the Jahn-teller effect of Mn 3+ , it will cause structural collapse, and the migration of Fe 3+ from the octahedral position of the transition metal layer to the tetrahedral position of the sodium layer will cause irreversible phase transformation, resulting in poor cycle stability. Summary of the Invention

[0004] Based on this, in view of the above problems, it is necessary to provide a cathode material, its preparation method and application; the cathode material has excellent cycle stability and rate performance, which is beneficial to improving the electrical performance of sodium-ion batteries.

[0005] A cathode material, the chemical formula of the cathode material is NaHf x (A a Ni b Mn c ) 1-x O2, where 0.02 < x < 0.2, 0 < a ≤ 1, 0 < b ≤ 1, 0 < c ≤ 1, a + b + c = 1, A is selected from at least one of Fe, Cu, Co, the cathode material is of O3 type crystal structure, and the Na-O layer spacing in the crystal structure is

[0006] In one embodiment, the unit cell parameters of the cathode material satisfy: 0.727 nm ≤ a = b ≤ 0.728 nm, 0.750 nm ≤ c ≤ 0.757 nm.

[0007] In one embodiment, in the X-ray diffraction pattern, under the same A element and the values of a, b, c, compared with NaAa Ni b Mn c Compared with O2, the diffraction peak of the (003) crystal plane in the positive electrode material shifts 0.1° - 0.2° towards a lower angle.

[0008] In one of the embodiments, in the X-ray diffraction pattern, with the same A element and the same values of a, b, and c, compared with NaA a Ni b Mn c O2, the diffraction peak of the (100) crystal plane in the positive electrode material shifts 0.08° - 0.18° towards a higher angle.

[0009] In one of the embodiments, the particle size of the positive electrode material is less than or equal to 10 μm.

[0010] A preparation method of a positive electrode material as described above, comprising the following steps:

[0011] Prepare a mixed metal salt solution according to the stoichiometric ratio of Hf x (A a Ni b Mn c ) 1-x O2, A is selected from at least one of Fe, Cu, and Co, 0.02 < x < 0.2, 0 < a ≤ 1, 0 < b ≤ 1, 0 < c ≤ 1, and a + b + c = 1;

[0012] Perform spray pyrolysis on the mixed metal salt solution to obtain an oxide precursor;

[0013] Mix the oxide precursor with sodium salt and then perform calcination to obtain the positive electrode material.

[0014] In one of the embodiments, the total concentration of metal ions in the mixed metal salt solution is 0.5 mol / L - 5 mol / L.

[0015] In one of the embodiments, the preparation conditions for performing spray pyrolysis on the mixed metal salt solution include: a flow rate of 5 L / min - 8 L / min and a temperature of 200°C - 1000°C.

[0016] In one of the embodiments, the preparation conditions for mixing the oxide precursor with sodium salt and then performing calcination include: heating to 600°C - 1000°C at a rate of 2°C / min - 10°C / min and performing calcination for 6 h - 20 h.

[0017] A positive electrode sheet, comprising a positive electrode current collector and a positive electrode material layer provided on the surface of the positive electrode current collector, wherein the positive electrode material layer comprises the positive electrode material as described above.

[0018] A sodium-ion battery, comprising a positive electrode as described above.

[0019] The cathode material described in this invention has a specific molar amount of Hf 4+ An ion-doped O3-type crystal structure, wherein the Na-O interlayer spacing in the crystal structure is [missing information]. This is beneficial for improving the extraction and insertion efficiency of sodium ions and reducing interlattice stress, thereby improving rate capability and cycle performance. Meanwhile, Hf 4+ Ion doping can not only increase the average valence state of manganese in the cathode material, but also make Mn 3+ The content of Mn decreases, thereby reducing the amount of Mn. 3+ The Jahn-Teller effect helps to further improve cycle stability and can also effectively suppress the phase transition caused by the transition metal jumping to the interlayer after sodium ions are released during charging and discharging, thereby further improving rate performance.

[0020] Therefore, the cathode material described in this invention has excellent cycle stability and rate performance, which is beneficial to improving the electrical performance of sodium-ion batteries. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The image shows a scanning electron microscope (SEM) image of the cathode material prepared in Example 1.

[0023] Figure 2 The image shows a comparison of X-ray diffraction peaks between Example 1 and Comparative Example 1, where A is the X-ray diffraction pattern of the cathode material prepared in Example 1, and B is the X-ray diffraction pattern of the cathode material prepared in Comparative Example 1.

[0024] Figure 3 The graph shows a comparison of the cycle performance of Example 1 and Comparative Example 1. In Example 1, A is the capacity retention rate curve of the coin cell assembled with the cathode material prepared in Example 1 during 50 cycles, and B is the capacity retention rate curve of the coin cell assembled with the cathode material prepared in Comparative Example 1 during 50 cycles.

[0025] Figure 4It is a comparison chart of the cycling performance between Example 2 and Comparative Example 1. Among them, C is the curve of the capacity retention rate during 50 cycles of the coin cell assembled with the cathode material prepared in Example 2, and D is the curve of the capacity retention rate during another 50 cycles of the coin cell assembled with the cathode material prepared in Comparative Example 1. Detailed implementation manners

[0026] To facilitate the understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments or examples and are not intended to limit the present invention.

[0028] The present invention provides a cathode material, and the chemical formula of the cathode material is NaHf x (A a Ni b Mn c ) 1-x O2, where 0.02 < x < 0.2, 0 < a ≤ 1, 0 < b ≤ 1, 0 < c ≤ 1, a + b + c = 1, A is selected from at least one of Fe, Cu, and Co. The cathode material has an O3-type crystal structure, and the Na-O layer spacing in the crystal structure is

[0029] The cathode material of the present invention has an O3-type crystal structure doped with Hf ions with a specific molar amount, and the Na-O layer spacing in the crystal structure is 4+ which is beneficial to improving the efficiency of sodium ion extraction and insertion and reducing the interlattice stress, thereby improving the rate and cycling performance. At the same time, the doping of Hf ions can not only increase the average valence state of manganese in the cathode material, reduce the content of Mn 4+ , thereby reducing the Jahn-teller effect of Mn 3+ , which is beneficial to further improving the cycling stability, but also can effectively inhibit the phase change caused by the transition of transition metals to the interlayer after sodium ion extraction during charge and discharge, thereby further improving the rate performance.

[0030] ​​In one embodiment, in the chemical formula of the positive electrode material, preferably 0.05 ≤ x ≤ 0.1, including but not limited to point values of any one of 0.05, 0.06, 0.075, 0.08, 0.09, 0.10 or range values between any two of them.

[0031] 0 < a ≤ 1, including but not limited to point values of any one of 0, 0.05, 0.10, 0.25, 0.33, 0.50, 0.60, 0.70, 0.80, 0.90, 1 or range values between any two of them.

[0032] 0 < b ≤ 1, including but not limited to point values of any one of 0, 0.05, 0.10, 0.25, 0.33, 0.50, 0.60, 0.70, 0.80, 0.90, 1 or range values between any two of them.

[0033] 0 < c ≤ 1, including but not limited to point values of any one of 0, 0.05, 0.10, 0.25, 0.33, 0.50, 0.60, 0.70, 0.80, 0.90, 1 or range values between any two of them.

[0034] Preferably, a:b:c satisfies 1:(1 - 18):(1 - 18), including but not limited to point values of any one of 1:1:1, 1:2:2, 1:2.5:1.5, 1:2:1 / 3, 1:8:1, 1:18:1 or range values between any two of them.

[0035] In one embodiment, in the crystal structure of the positive electrode material, the Na - O layer spacing includes but not limited to point values of any one of them or range values between any two of them.

[0036] In one embodiment, the unit cell parameters of the positive electrode material satisfy: 0.727 nm ≤ a = b ≤ 0.728 nm, including but not limited to point values of any one of 0.7270 nm, 0.7271 nm, 0.7272 nm, 0.7273 nm, 0.7274 nm, 0.7275 nm, 0.7276 nm, 0.7277 nm, 0.7278 nm, 0.7279 nm, 0.7280 nm or range values between any two of them.

[0037] 0.750 nm ≤ c ≤ 0.757 nm, including but not limited to point values of any one of 0.750 nm, 0.751 nm, 0.752 nm, 0.753 nm, 0.754 nm, 0.755 nm, 0.756 nm, 0.757 nm or range values between any two of them.

[0038] In one embodiment, in the X-ray diffraction pattern, with the same A element and the same values of a, b, and c, compared with NaA a Ni b Mn c O2, the diffraction peak of the (003) crystal plane in the positive electrode material is shifted to a lower angle by 0.1° - 0.2°, including but not limited to the point values of any one of 0.1°, 0.12°, 0.14°, 0.16°, 0.18°, 0.2 or the range values between any two of them.

[0039] In one embodiment, in the X-ray diffraction pattern, with the same A element and the same values of a, b, and c, compared with NaA a Ni b Mn c O2, the diffraction peak of the (100) crystal plane in the positive electrode material is shifted to a higher angle by 0.08° - 0.18°, including but not limited to the point values of any one of 0.08°, 0.11°, 0.12°, 0.13°, 0.14°, 0.15°, 0.16°, 0.17°, 0.18° or the range values between any two of them.

[0040] In one embodiment, the positive electrode material is a secondary particle polycrystalline structure composed of primary particles. Further preferably, the secondary particles include spherical shapes.

[0041] In one embodiment, the particle size of the positive electrode material is less than or equal to 10 μm, preferably 3 μm - 5 μm.

[0042] The present invention provides a method for preparing the positive electrode material as described above, comprising the following steps:

[0043] S1, prepare a mixed metal salt solution according to the stoichiometric ratio of Hf x (A a Ni b Mn c ) 1-x O2, where A is selected from at least one of Fe, Cu, and Co, 0.02 < x < 0.2, 0 < a ≤ 1, 0 < b ≤ 1, 0 < c ≤ 1, and a + b + c = 1;

[0044] S2, perform spray pyrolysis on the mixed metal salt solution to obtain an oxide precursor;

[0045] S3, mix the oxide precursor with a sodium salt and then perform calcination to obtain the positive electrode material.

[0046] In step S1, the total concentration of metal ions in the mixed metal salt solution is preferably 0.5 mol / L to 5 mol / L, including but not limited to any one of 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, and 5 mol / L, or a range between any two.

[0047] In one embodiment, the mixed metal salt solution includes at least a soluble nickel salt, a soluble manganese salt, a soluble hafnium salt, and a soluble salt containing element A. The soluble nickel salt is selected from at least one of nickel chloride, nickel sulfate, nickel nitrate, or nickel acetate; the soluble manganese salt is selected from at least one of manganese chloride, manganese sulfate, manganese nitrate, or manganese acetate; the soluble hafnium salt is selected from at least one of hafnium tetrachloride, hafnium sulfate, or hafnium nitrate; and the soluble salt containing element A is selected from at least one of ferrous chloride, ferrous sulfate, ferrous nitrate, ferric acetate, copper chloride, copper sulfate, copper nitrate, copper acetate, cobalt chloride, cobalt sulfate, cobalt nitrate, or cobalt acetate.

[0048] In one embodiment, it is preferable to stir the mixed metal salt solution at a temperature of 25°C-60°C to make it uniformly mixed.

[0049] In steps S2 to S3, the use of spray pyrolysis combined with solid-state method is beneficial to control the formation of regular spherical particle morphology of the obtained cathode material, increase the specific surface area, and enable the cathode material to fully contact the electrolyte, thereby improving the electrochemical performance of sodium-ion battery.

[0050] In one embodiment, the preparation conditions for spray pyrolysis of the mixed metal salt solution include: atomizing the mixed metal salt solution at a flow rate of 5 L / min-8 L / min with air or oxygen as the carrier gas, and pyrolyzing it at 200℃-1000℃.

[0051] The oxide precursor obtained by spray pyrolysis has a secondary particle polycrystalline structure composed of primary particles. More preferably, the secondary particles include spherical particles.

[0052] In one embodiment, the preparation conditions for calcining the oxide precursor with sodium salt include: heating to 600℃-1000℃ at a rate of 2℃ / min-10℃ / min and calcining for 6h-20h, wherein the sodium salt is selected from at least one of sodium hydroxide, sodium carbonate, sodium acetate, sodium nitrate, and sodium citrate.

[0053] This invention provides a positive electrode sheet, comprising a positive current collector and a positive electrode material layer disposed on the surface of the positive current collector, wherein the positive electrode material layer comprises the positive electrode material as described above. It is understood that the positive electrode material layer further comprises a conductive agent and a binder, but this invention does not limit the scope of the invention.

[0054] It should be noted that the positive electrode sheet can be prepared using existing processes, such as: mixing positive electrode material, conductive agent, binder and solvent in a specific ratio to form a slurry, coating the slurry onto the surface of the positive electrode current collector, and then drying it at 100℃-130℃ to obtain the positive electrode sheet. The conductive agent includes, but is not limited to, conductive carbon black; the binder includes, but is not limited to, polyvinylidene fluoride (PVDF); the solvent includes, but is not limited to, N-methylpyrrolidone (NMP); and the positive electrode current collector includes, but is not limited to, aluminum foil.

[0055] The present invention also provides a sodium-ion battery, including the positive electrode as described above. It is understood that the sodium-ion battery further includes a negative electrode, a separator, and an electrolyte; the present invention does not limit the negative electrode, separator, and electrolyte.

[0056] The following specific embodiments will further illustrate the cathode material, its preparation method, and its applications. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0057] Example 1

[0058] According to the molar ratio of Ni, Fe, and Mn being 1:1:1 and the ratio of the total molar amount of Ni, Fe, and Mn to the molar amount of Hf being 0.95:0.05, manganese chloride, ferrous chloride, nickel chloride, and hafnium tetrachloride were dissolved in water and stirred at 25°C for 2 hours to obtain a mixed metal salt solution, wherein the total concentration of metal ions in the mixed metal salt solution was 1 mol / L.

[0059] The mixed metal salt solution prepared above was atomized with air at a flow rate of 5 L / min and then sprayed into a gas pyrolysis furnace at a pyrolysis temperature of 700 °C. The powder collected at the bottom of the pyrolysis furnace is the oxide precursor Hf. 0.05 (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ) 0.95 O2.

[0060] The oxide precursor obtained above was mixed and ground with sodium carbonate at a ratio of 1:1.05 of total metal molar amount to sodium molar amount in the oxide precursor to obtain a mixed powder. The mixed powder was then placed in an alumina boat, which was then placed in a box-type atmosphere furnace and calcined at 750℃ for 11 hours in an air atmosphere at a heating rate of 2℃ / min. After natural cooling, the cathode material NaHf was obtained. 0.05 (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ) 0.95 O2.

[0061] The morphology of the cathode material prepared in Example 1 was examined using a scanning electron microscope (SEM, NEC 6700F). The results are as follows: Figure 1 As shown in the figure, the cathode material exhibits a spherical particle morphology with a diameter of less than 10 μm. XRD analysis of the cathode material prepared in Example 1 yielded the following results: Figure 2 As shown in Figure A, the cathode material exhibits a typical O3-type crystal structure.

[0062] Example 2

[0063] According to the molar ratio of Ni, Fe, and Mn being 1:1:1 and the ratio of the total molar amount of Ni, Fe, and Mn to the molar amount of Hf being 0.925:0.075, manganese chloride, ferrous chloride, nickel chloride, and hafnium tetrachloride were dissolved in water and stirred at 25°C for 2 hours to obtain a mixed metal salt solution, wherein the total concentration of metal ions in the mixed metal salt solution was 5 mol / L.

[0064] The mixed metal salt solution prepared above was atomized with air as the carrier gas at a flow rate of 8 L / min and then sprayed into a gas-jet pyrolysis furnace at a pyrolysis temperature of 750 °C. The powder collected at the bottom of the pyrolysis furnace is the oxide precursor Hf. 0.075 (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ) 0.925 O2.

[0065] The oxide precursor obtained above was mixed and ground with sodium carbonate at a ratio of 1:1.05 of total metal molar amount to sodium molar amount in the oxide precursor to obtain a mixed powder. The mixed powder was then placed in an alumina boat, which was then placed in a box-type atmosphere furnace and calcined at 800℃ for 10 hours in an oxygen atmosphere at a heating rate of 3℃ / min. After natural cooling, the cathode material NaHf was obtained. 0.075 (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ) 0.925 O2.

[0066] The morphology of the cathode material prepared in Example 2 was examined using a scanning electron microscope (SEM, NEC 6700F). The results are consistent with... Figure 1 Similarly, this cathode material also exhibits the morphological characteristics of spherical particles with a diameter of less than 10 μm.

[0067] Example 3

[0068] According to the molar ratio of Ni, Fe, and Mn being 1:1:1 and the ratio of the total molar amount of Ni, Fe, and Mn to the molar amount of Hf being 0.9:0.1, manganese chloride, ferrous chloride, nickel chloride, and hafnium tetrachloride were dissolved in water and stirred at 45°C for 2 hours to obtain a mixed metal salt solution, wherein the total concentration of metal ions in the mixed metal salt solution was 2.5 mol / L.

[0069] The mixed metal salt solution prepared above was atomized with air at a flow rate of 6 L / min and then spray-pyrolyzed in an air-jet atomization pyrolysis furnace at a pyrolysis temperature of 850 °C. The powder collected at the bottom of the pyrolysis furnace is the oxide precursor Hf. 0.1 (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ) 0.9 O2.

[0070] The oxide precursor obtained above was mixed and ground with sodium carbonate at a ratio of 1:1.05 of total metal molar amount to sodium molar amount in the oxide precursor to obtain a mixed powder. The mixed powder was then placed in an alumina boat, which was then placed in a box-type atmosphere furnace and calcined at 900℃ for 8 hours in an oxygen atmosphere at a heating rate of 5℃ / min. After natural cooling, the cathode material NaHf was obtained. 0.1 (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ) 0.9 O2.

[0071] Example 4

[0072] According to the molar ratio of Ni, Cu, and Mn of 4:2:4 and the ratio of the total molar amount of Ni, Cu, and Mn to the molar amount of Hf of 0.94:0.06, manganese chloride, copper chloride, nickel chloride, and hafnium tetrachloride were dissolved in water and stirred at 30°C for 2 hours to obtain a mixed metal salt solution, wherein the total concentration of metal ions in the mixed metal salt solution was 5.5 mol / L.

[0073] The mixed metal salt solution prepared above was atomized with air at a flow rate of 6 L / min and then sprayed at a pyrolysis temperature of 800 °C in an air-jet atomization pyrolysis furnace. The powder collected at the bottom of the pyrolysis furnace is the oxide precursor Hf. 0.06 (Ni 0.4 Cu 0.2 Mn 0.4 ) 0.94 O2.

[0074] The oxide precursor obtained above was mixed and ground with sodium carbonate at a ratio of 1:1.02 of total metal molar amount to sodium molar amount in the oxide precursor to obtain a mixed powder. The mixed powder was then placed in an alumina boat, which was then placed in a box-type atmosphere furnace and calcined at 800℃ for 15 hours in an oxygen atmosphere at a heating rate of 2℃ / min. After natural cooling, the positive electrode material NaHf was obtained. 0.06 (Ni 0.4 Cu 0.2 Mn 0.4 ) 0.94 O2.

[0075] Example 5

[0076] According to the molar ratio of Ni, Co, and Mn of 6:1:3 and the ratio of the total molar amount of Ni, Co, and Mn to the molar amount of Hf of 0.92:0.08, manganese chloride, cobalt nitrate, nickel chloride, and hafnium nitrate were dissolved in water and stirred at 30°C for 2 hours to obtain a mixed metal salt solution, wherein the total concentration of metal ions in the mixed metal salt solution was 2 mol / L.

[0077] The mixed metal salt solution prepared above was atomized with air at a flow rate of 7 L / min and then sprayed at a pyrolysis temperature of 850 °C in an air-jet atomizing pyrolysis furnace. The powder collected at the bottom of the pyrolysis furnace is the oxide precursor Hf. 0.08 (Ni 0.6 Co 0.1 Mn 0.3 ) 0.92 O2.

[0078] The oxide precursor obtained above was mixed and ground with sodium carbonate at a ratio of 1:1.05 of total metal molar amount to sodium molar amount in the oxide precursor to obtain a mixed powder. The mixed powder was then placed in an alumina boat, which was then placed in a box-type atmosphere furnace and calcined at 900℃ for 8 hours in an oxygen atmosphere at a heating rate of 5℃ / min. After natural cooling, the cathode material NaHf was obtained. 0.08 (Ni 0.6 Co 0.1 Mn 0.3 ) 0.92O2.

[0079] Example 6

[0080] According to the molar ratio of Ni, Fe, Co, and Mn of 2:2:1:1 and the ratio of the total molar amount of Ni, Fe, Co, and Mn to the molar amount of Hf of 0.91:0.09, manganese chloride, ferrous chloride, cobalt chloride, nickel chloride, and hafnium tetrachloride were dissolved in water and stirred at 30°C for 2 hours to obtain a mixed metal salt solution, wherein the total concentration of metal ions in the mixed metal salt solution was 0.5 mol / L.

[0081] The mixed metal salt solution prepared above was atomized with air as the carrier gas at a flow rate of 8 L / min and then sprayed into a gas-jet pyrolysis furnace at a pyrolysis temperature of 900 °C. The powder collected at the bottom of the pyrolysis furnace is the oxide precursor Hf. 0.09 (Ni 1 / 3 Fe 1 / 3 Co 1 / 6 Mn 1 / 6 ) 0.91 O2.

[0082] The oxide precursor obtained above was mixed and ground with sodium carbonate at a ratio of 1:1.02 of total metal molar amount to sodium molar amount in the oxide precursor to obtain a mixed powder. The mixed powder was then placed in an alumina boat, which was then placed in a box-type atmosphere furnace and calcined at 950°C for 6 hours in an oxygen atmosphere at a heating rate of 10°C / min. After natural cooling, the cathode material NaHf was obtained. 0.09 (Ni 1 / 3 Fe 1 / 3 Co 1 / 6 Mn 1 / 6 ) 0.91 O2.

[0083] Comparative Example 1

[0084] The difference between Comparative Example 1 and Example 1 is that the mixed metal salt solution was prepared according to a molar ratio of Ni:Fe:Mn = 1:1:1, and the resulting cathode material was NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0085] The cathode material prepared in Comparative Example 1 was subjected to XRD analysis, and the results are as follows: Figure 2 As shown in B.

[0086] Comparative Example 2

[0087] The difference between Comparative Example 2 and Example 1 is that a mixed metal salt solution was prepared with a total molar ratio of Ni, Fe, and Mn to Hf of 0.98:0.02, resulting in a positive electrode material of NaHf.0.02 (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ) 0.98 O2.

[0088] Comparative Example 3

[0089] The difference between Comparative Example 3 and Example 1 is that a mixed metal salt solution was prepared with a total molar ratio of Ni, Fe, and Mn to Hf of 0.8:0.2, resulting in a positive electrode material of NaHf. 0.2 (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ) 0.8 O2.

[0090] Comparative Example 4

[0091] The difference between Comparative Example 4 and Example 1 is that a mixed metal salt solution was prepared with a total molar ratio of Ni, Fe, and Mn to Ti of 0.95:0.05, resulting in a NaTi cathode material. 0.05 (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ) 0.95 O2.

[0092] Comparative Example 5

[0093] The difference between Comparative Example 5 and Example 1 is that a mixed metal salt solution was prepared with a total molar ratio of Ni, Fe, and Mn to Nb of 0.95:0.05, resulting in a positive electrode material of NaNb. 0.05 (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ) 0.95 O2.

[0094] The cathode materials prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to structural tests, and the results are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] The cathode materials prepared in Examples 1-6 and Comparative Examples 1-5 were assembled into sodium-ion batteries for performance testing. The specific preparation and testing methods are as follows:

[0099] 1. Electrode preparation

[0100] The positive electrode material, conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in a ratio of 8:1:1 to obtain a mixture. The mixed powder is then added to N-methylpyrrolidone (NMP) and stirred thoroughly to form a slurry. This slurry is coated onto the surface of aluminum foil and then vacuum dried in a vacuum drying oven at 120°C for 12 hours. After multiple rolling processes, the desired battery positive electrode sheet is obtained.

[0101] 2. Battery assembly

[0102] The test was conducted using the 2032 model button cell as a benchmark. The rolled battery electrode sheets were stamped into 14mm diameter discs, glass fiber was used as the separator, sodium metal sheet was used as the negative electrode, and NaClO4-based electrolyte was used. The assembly process was carried out in a glove box.

[0103] 3. Electrochemical performance testing

[0104] Electrochemical testing of the battery was conducted using a battery tester (Land2000) from Wuhan Landian Company. The battery was cycled 50 times at a temperature of 25℃, a voltage of 2V-4V, and a 1C rate. In addition, the battery was tested for rate performance at the same temperature and voltage at rates of 0.1C, 0.5C, 1C, 2C, 5C, and 0.1C. The test results are shown in Table 2.

[0105] Table 2

[0106]

[0107] Combination Figure 3 , Figure 4 As shown in Table 2, compared with Comparative Example 1, the rate capability and capacity retention of Examples 1-3 were improved, indicating that Hf ion doping can effectively weaken the Jahn-Teller effect and suppress complex phase transitions, which is beneficial to improving rate capability and structural stability.

[0108] The capacity retention rates of Comparative Examples 2 and 3 were both lower than those of Comparative Example 1, which was not doped with Hf ions. This indicates that neither too little nor too much Hf doping can reduce the Jahn-Teller effect or suppress complex phase transitions. Instead, it will affect the electrical performance.

[0109] Comparative Examples 4 and 5 were doped with Ti ions and Nb ions, respectively. However, the radius of Ti ions and Nb ions is smaller than that of Hf ions. After doping with Hf ions, the interlayer spacing of Na is larger. Therefore, the cycling performance after Ti ion doping and Nb ion doping is relatively weak.

[0110] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0111] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A positive electrode material, characterized in that, The chemical formula of the positive electrode material is NaHf x (A a Ni b Mn c ) 1-x O2, where 0.02 < x < 0.2, 0 < a ≤ 1, 0 < b ≤ 1, 0 < c ≤ 1, a + b + c = 1, A is selected from at least one of Fe, Cu, and Co, the positive electrode material has an O3-type crystal structure, and the Na-O layer spacing in the crystal structure is 2. The cathode material according to claim 1, characterized in that, The cell parameters of the cathode material satisfy: 0.727nm≤a=b≤0.728nm, 0.750nm≤c≤0.757nm.

3. The cathode material according to claim 1, characterized in that, In X-ray diffraction patterns, under the same A element and values ​​of a, b, and c, compared to NaA... a Ni b Mn c Compared to O2, the (003) crystal plane diffraction peak in the cathode material is shifted to a lower angle by 0.1°-0.2°.

4. The cathode material according to claim 1, characterized in that, In X-ray diffraction patterns, under the same A element and values ​​of a, b, and c, compared to NaA... a Ni b Mn c Compared to O2, the (100) crystal plane diffraction peak in the cathode material is shifted to a higher angle by 0.08°-0.18°.

5. The positive electrode material according to claim 1, characterized in that, The particle size of the positive electrode material is less than or equal to 10 μm.

6. A method for preparing a positive electrode material as described in any one of claims 1-5, characterized in that, Includes the following steps: According to Hf x (A a Ni b Mn c ) 1-x O₂, A is selected from at least one of Fe, Cu, and Co, 0.02 < x < 0.2, 0 < a ≤ 1, 0 < b ≤ 1, 0 < c ≤ 1, and a + b + c = 1 to prepare a mixed metal salt solution according to the stoichiometric ratio; The mixed metal salt solution was subjected to spray pyrolysis to obtain an oxide precursor; The oxide precursor is mixed with sodium salt and then calcined to obtain the cathode material.

7. The method for preparing the cathode material according to claim 6, characterized in that, The total concentration of metal ions in the mixed metal salt solution is 0.5 mol / L to 5 mol / L.

8. The method for preparing the cathode material according to claim 6, characterized in that, The preparation conditions for spray pyrolysis of the mixed metal salt solution include: a flow rate of 5 L / min-8 L / min and a temperature of 200℃-1000℃.

9. The method for preparing the cathode material according to claim 6, characterized in that, The preparation conditions for calcining the oxide precursor with sodium salt include: heating to 600℃-1000℃ at a rate of 2℃ / min-10℃ / min and calcining for 6h-20h.

10. A positive electrode plate, characterized in that, It includes a positive current collector and a positive electrode material layer disposed on the surface of the positive current collector, wherein the positive electrode material layer includes the positive electrode material as described in any one of claims 1-5.

11. A sodium-ion battery, characterized in that, Including the positive electrode as described in claim 10.

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