A sodium-ion battery layered oxide positive electrode material and a preparation method and application thereof

Abstract

The application relates to the technical field of sodium ion battery materials, and discloses a sodium ion battery layered oxide positive electrode material, characterized by a chemical formula of Na a Ni x Fe y Mn z M 1‑x‑y‑z O2, 0.8<=a<=1.1, 0<=x<=1, 0<=y<=1, 0<=z<=1, M=M1+M2, M1=at least one of Zn, Ca, Cu, Sb, Ba, Mg, Zr, Y, Cs, Mo, Sn, Ce, La, F, B, Ti, Zr and Li, and M2=at least one of B, Al, Zr, Ti, Ce, W and P; the metal or the salt thereof is pyrolyzed and sintered in a solvent system to obtain a finished product. The low-cost process provided by the application does not need to synthesize a precursor, but directly uses a one-step method to synthesize the sodium ion battery layered oxide positive electrode material. The method not only obviously improves the capacity, cycle and residual alkali of the sodium ion battery, but also is beneficial to large-scale promotion and application of the sodium ion battery.

Description

TECHNICAL FIELD

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

[0002] With the rapid development of new energy vehicles, new energy batteries are also in continuous research and innovation. From the classification, new energy batteries include lithium ion batteries, sodium ion batteries, lead-acid batteries, hydrogen fuel cells, etc. Among the foregoing, lithium ion batteries have gradually become the main part of modern new energy batteries due to their great advantages in battery capacity, service life, safety performance, charging and discharging speed, green environmental protection, etc., but other new energy batteries still have certain market prospects.

[0003] Sodium ion batteries mainly rely on the movement of sodium ions between the positive electrode and the negative electrode to work, which is similar to the working principle of lithium ion batteries, but sodium ion batteries have the advantages of excellent low temperature (-40℃) performance, high safety, zero voltage transportation and storage, fast charging and low cost. Therefore, the development of sodium ion batteries is a beneficial supplement and replacement for lithium ion batteries and ternary lithium ion batteries. Due to the inherent advantages of sodium ion batteries, they can be widely used in electric tools, small energy storage, large energy storage, passenger cars and other fields. In the future, with the continuous reduction of the cost of sodium ion batteries, it is an inevitable trend to replace lead-acid batteries used in two-wheeled vehicles and low-speed vehicles.

[0004] At present, due to the high cost of sodium ion battery layered oxide positive electrode materials, the cost of the battery cell is high, which causes the slow market promotion of sodium ion batteries. However, one way to solve the high cost of layered oxide positive electrode materials is to reduce the processing cost of the materials, because the processing cost accounts for about 50% of the cost of the positive electrode materials. Usually, the preparation of layered oxide positive electrode materials is to synthesize a hydroxide precursor first, then mix it with a sodium source and sinter, and then perform post-processing to obtain the final product. The synthesis of the hydroxide precursor not only has a long cycle, but also produces wastewater, waste gas and waste residue. In addition, the sodium ion battery layered oxide precursor will produce Fe 2+The pH range for the precipitation of ions as Fe(OH)2 in NaOH is 5.0-10.0, while the initial precipitation pH range of Ni(OH)2 and Mn(OH)2 is above 10.0, respectively. Therefore, during the synthesis of the nickel-iron-manganese layered oxide precursor, it is easy to cause the precipitation of iron ions prior to nickel and manganese ions, thereby causing the segregation of nickel, iron and manganese elements. Therefore, during the synthesis of the positive electrode material, the segregation of nickel, iron and manganese transition metal elements usually causes the mixing of sodium ions and transition metal elements, thereby causing the sodium ion battery positive electrode material to have high residual alkali, low capacity and poor cycle performance. Based on the foregoing, reducing the processing cost of the sodium ion battery layered oxide positive electrode material and improving the segregation phenomenon of elements is a key technical problem. SUMMARY

[0005] The technical problems solved by the present application are:

[0006] To solve the problems of high processing cost and element segregation of the existing sodium ion battery layered oxide positive electrode material.

[0007] The technical solutions adopted by the present application are:

[0008] In view of the above technical problems, the present application aims to provide a sodium ion battery layered oxide positive electrode material, a preparation method and application thereof.

[0009] In the present application, a one-step method is used to synthesize the sodium ion battery layered oxide positive electrode material, i.e., without synthesizing a precursor, but preparing a metal salt solution from metals or their salts and sodium salts, then obtaining solid powder particles through pyrolysis, and then obtaining an electrode material with uniform element distribution through sintering. In the foregoing, we further form a metal salt solution by adding nitric acid, ammonia and a chelating agent. The pyrolysis method uses spray pyrolysis, and after spray pyrolysis treatment, solid powder particles with uniform metal element distribution can be obtained. Although sol-gel method can synthesize gel-state substances by adding a chelating agent and controlling pH, it has the disadvantages of complex control conditions, unstable batch, long synthesis period and difficulty in industrial production. For example, the patent with publication number CN114520323A, during the process of heating the solvent to form a gel, it is easy to form upper and lower layers of the gel, thereby causing uneven heating, so that the element proportion in the upper and lower layers of the gel is not balanced and the elements are not uniform.

[0010] Based on this, the specific embodiments are:

[0011] The present application provides a sodium ion battery layered oxide positive electrode material, with a chemical formula of Na a Ni x Fe y Mn z M 1-x-y- zO2; wherein, 0.8≤a≤1.1, 0≤x≤1, 0≤y≤1, 0≤z≤1, M=M1+M2, M1=at least one of Zn, Ca, Cu, Sb, Ba, Mg, Zr, Y, Cs, Mo, Sn, Ce, La, F, B, Ti, Zr, Li, M2=at least one of B, Al, Zr, Ti, Ce, W, P; the metal or its salt is pyrolyzed in the solvent system, sintered to obtain the finished product.

[0012] Further, the M1 source is introduced in the solvent system, and the M2 source is introduced during sintering.

[0013] In the present application, the particle size D of the positive electrode material is 4-7 μm. 50

[0014] In the present application, the molar amount of the sodium source is A, the total molar amount of the nickel source, the iron source, the manganese source and the M source is B, and A:B=0.8-1.1:1.

[0015] The present application provides a preparation method of the aforementioned sodium ion battery layered oxide positive electrode material, comprising the following steps:

[0016] S1: placing the sodium source, the nickel source, the iron source, the manganese source and the M1 source in deionized water (solvent system), adding nitric acid, chelating agent and ammonia, adjusting the pH of the solution to 5-7, and then pyrolyzing by spraying to obtain an intermediate;

[0017] S2: sintering the intermediate in a rotary kiln, coating with the M2 source and sintering again to obtain the positive electrode material.

[0018] In the foregoing, the present application obtains a solid powder with uniform distribution of sodium, nickel, iron and manganese by pyrolysis, and since the mixture of the precursor and the sodium source is not sintered in the sagger, it can be treated in the rotary kiln. The existing track kiln sintering is suitable for the mixture of the precursor with a particle size of 3-15 μm and the sodium source with a particle size of 5-18 μm, which is sintered in the sagger. If the mixture is sintered in the rotary kiln, the precursor and the sodium source will be separated due to the centrifugal effect, causing segregation of sodium ions and nickel, iron and manganese, and ultimately leading to a decrease in the performance of the sodium ion battery positive electrode material.

[0019] In the present application, the mass ratio of nitric acid, chelating agent and ammonia is 0.1-1:0.015-0.5:1.5-2.5; the concentration of nitric acid is 2-5 M.

[0020] ​In the present application, the chelating agent is also called complexing agent, which refers to a complex containing two or more coordination atoms and having a ring structure formed by the coordination of metal atoms or ions. The chelating agent includes at least one of EDTA, DTPA, ATP, HEDP, EDTMPS, DTPMPA, citric acid, tartaric acid, oxalic acid, gluconic acid, polyacrylic acid, sodium gluconate and sodium citrate.

[0021] In the present application, the sodium source is a sodium salt, and the sodium salt is selected from at least one of sodium carbonate, sodium bicarbonate and sodium hydroxide.

[0022] In the present application, the first sintering is performed at a temperature of 800-980°C for 6-16h. Preferably, the temperature can be selected from 800°C, 850°C, 880°C, 900°C, 950°C, 980°C and the above-mentioned temperature ranges, and the time can be selected from 6h, 8h, 10h, 12h, 14h, 16h and the above-mentioned time ranges.

[0023] In the present application, the second sintering is performed at a temperature of 400-800°C for 5-10h. Preferably, the temperature can be selected from 400°C, 500°C, 650°C, 700°C, 750°C, 800°C and the above-mentioned temperature ranges, and the time can be selected from 5h, 6h, 7h, 8h, 9h, 10h and the above-mentioned time ranges.

[0024] In the present application, the sintering atmosphere in the first sintering and / or the second sintering is air, oxygen or a mixed gas with an oxygen concentration of more than 10%.

[0025] In the present application, the nickel source, the iron source, the manganese source and the M1 source are each independently selected from at least one of oxalate, acetate, nitrate, sulfate, chloride, oxide, hydroxide or metal powder.

[0026] In the present application, the M1 source includes the following features:

[0027] The M1 source includes at least one of zinc oxide, zinc hydroxide, calcium oxide, calcium hydroxide, copper oxide, tellurium oxide, barium oxide, barium hydroxide, magnesium oxide, magnesium hydroxide, zirconium oxide, zirconium hydroxide, yttrium oxide, cesium oxide, molybdenum oxide, ammonium molybdate, tin oxide, cerium oxide, lanthanum oxide, ammonium fluoride, sodium fluoride, boron oxide, boric acid, titanium oxide, zirconium oxide, zirconium hydroxide, lithium hydroxide and lithium carbonate.

[0028] In the present application, the M2 source includes the following features:

[0029] The M2 source includes at least one of boron oxide, boric acid, aluminum oxide, aluminum hydroxide, zirconium oxide, zirconium hydroxide, titanium oxide, cerium oxide, ammonium tungstate, monoammonium phosphate and diammonium phosphate.

[0030] The total element mass ratio of M2 in the coating agent is 0.1-0.8%;

[0031] The particle size D of the coating agent 50 <50nm.

[0032] Technical mechanism and beneficial effects adopted by the present application:

[0033] (1) The present application does not use the traditional precursor process method, but uses a one-step method to synthesize the sodium-ion battery layered oxide positive electrode material, which reduces the processing cost by more than 40% compared with the traditional process. For example, in the solution synthesis, sodium source, nickel source, iron source, manganese source, nitric acid, ammonia, chelating agent and dopant (M1 source) are added, and uniform distribution of sodium, nickel, iron, manganese elements and doping elements is obtained by spray pyrolysis, and low-energy consumption rotary kiln sintering is adopted, which is beneficial to the reduction of residual alkali of the positive electrode material, the improvement of discharge capacity and the improvement of cycle performance.

[0034] (2) The present application adds nitric acid, chelating agent and ammonia, uses nickel-iron-manganese metal powder or salt to react with nitric acid to form a nitrate solution, and the chelating agent can produce chelation with metal ions in the nitrate. Since the chelation effect of ammonia on iron ions is not good, it will cause the problem of uneven distribution of nickel-iron-manganese elements. Based on this, by adding other chelating agents with better chelation effect on iron ions, the purpose is to enhance the effect of uniform distribution of elements. Further, by optimizing the amount of chelating agent, pH value, temperature and other parameters in the solution, the metal elements in the powder particles after spray pyrolysis can be kept in uniform distribution, and then through rotary kiln sintering and back-end processing, a low-cost sodium-ion battery layered oxide positive electrode material with uniform element distribution is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 EDS diagram of the low-cost process sodium-ion battery layered oxide positive electrode material in Example 1;

[0036] Figure 2 EDS diagram of the traditional process sodium-ion battery layered oxide positive electrode material in Comparative Example 1;

[0037] Figure 3 Capacity curve diagram of the sodium-ion battery layered oxide positive electrode material in Example 1 and Comparative Example 1;

[0038] Figure 4 Cycle curve diagram of the sodium-ion battery layered oxide positive electrode material in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0039] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If specific conditions are not specified in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not specified, the conventional products that can be purchased in the market are adopted.

[0040] Embodiment 1

[0041] The embodiment provides a preparation method of a low-cost process sodium ion battery layered oxide cathode material, comprising the following steps:

[0042] (1) according to the molecular formula Na 0.8-1.1 Ni 0.225 Fe 0.315 Mn 0.36 Cu 0.055 Zn 0.02 Ca 0.015 B 0.005 Li 0.005 O2, Na2CO3 and Ni, Fe, Mn and Cu metal powder and ZnO, CaO, B2O3, Li2CO3 dopant are added into deionized water, and then 5M of 1% nitric acid (calculated by the total mass of the solvent), 2.5% of ammonia water (calculated by the total mass of the solvent) and 0.50% (calculated by the total mass of the solvent) (EDTA, DTPA, ATP, HEDP and sodium gluconate, the ratio of each component is 1:1:1:1:1) five kinds of chelating agents are added, the pH of the solution is adjusted to 7, and then a solid powder material is obtained by spray pyrolysis;

[0043] (2) the above-mentioned solid powder material is sintered in a rotary kiln in an air atmosphere at 880℃ for 16h, and then crushed and sieved, and then coated with 0.5% (Al+Zr+Ti) mass ratio of Al2O3, ZrO2 and TiO2 three kinds of coating agents in a coating machine, the size of the three kinds of coating agents is less than 50nm. Then, the second sintering is carried out in a rotary kiln at 600℃ for 8h, and then crushed and sieved, and finally the 4μm sodium ion battery layered oxide cathode material finished product is obtained.

[0044] Embodiment 2

[0045] The embodiment provides a preparation method of a low-cost process sodium ion battery layered oxide cathode material, comprising the following steps:

[0046] (1) according to the molecular formula Na 0.8-1.1 Fe 0.40 Mn 0.40 Zn 0.01 Ca 0.015 Mo 0.005 O 0.19 F0.01 NaOH, FeO, MnO, ZnO, CaO, MoO2, NH4F were added to deionized water, and then 0.1% nitric acid (calculated based on the total mass of the solvent) with a concentration of 4.5 M, 1.5% ammonia water (calculated based on the total mass of the solvent) with a mass fraction, and 0.015% (calculated based on the total mass of the solvent) (EDTMPS, DTPMPA, citric acid, tartaric acid and oxalic acid, the ratio of each component is 1:1:1:1:1) five chelating agents were added, the pH of the solution was adjusted to 5, and then a solid powder material was obtained by spray pyrolysis;

[0047] (2) The above solid powder material was sintered in a 980℃ rotary kiln with a mixed atmosphere containing 10% oxygen for 6h, crushed and sieved, and then coated with 0.8% (Zr+Ti+Ce+W) mass ratio of ZrO2, TiO2, CeO2 and WO3 four coating agents with a size less than 50nm in a coating machine. Then, the final product of 7μm sodium ion battery layered oxide positive electrode material was obtained after secondary sintering at 800℃ for 5h in a rotary kiln, crushing and sieving.

[0048] Example 3

[0049] The present embodiment provides a low-cost process for preparing a sodium ion battery layered oxide positive electrode material, comprising the following steps:

[0050] (1) According to the molecular formula Na 0.8-1.1 Ni 0.36 Fe 0.18 Mn 0.36 Sb 0.010 Mg 0.005 Zr 0.06 Y 0.005 Cs 0.02 O2, NaHCO3, Ni(OH)2, Fe(OH)2, Mn(OH)2, SbO, MgO, ZrO, Y2O3 and CsO2 were added to deionized water, and then 0.5% nitric acid (calculated based on the total mass of the solvent) with a concentration of 3M, 2% ammonia water (calculated based on the total mass of the solvent) with a mass fraction, and 0.20% (calculated based on the total mass of the solvent) (gluconic acid, polyacrylic acid, sodium gluconate and sodium citrate, the ratio of each component is 1:1:1:1) four chelating agents were added, the pH of the solution was adjusted to 5.5, and then a solid powder material was obtained by spray pyrolysis;

[0051] (2) The above solid powder material was sintered in a rotary kiln at 940℃ in a mixed atmosphere with an oxygen content of 10% for 10 hours. After crushing and sieving, it was coated with four coating agents (ZrO2, TiO2, CeO2, and NH4H2PO4) at a mass ratio of 0.1% (Zr+Ti+Ce+P) in a coating machine. The size of the four coating agents was less than 50 nm. Then, it was sintered again in a rotary kiln at 400℃ for 10 hours. After crushing and sieving, the 6 μm layered oxide cathode material for sodium-ion batteries was finally obtained.

[0052] Example 4

[0053] This embodiment provides a low-cost method for preparing layered oxide cathode materials for sodium-ion batteries, including the following steps:

[0054] (1) According to the molecular formula Na 0.8-1.1 Fe 0.70 Mn 0.26Mg0.005 Zr 0.005 Sn 0.005 Ti 0.005 O 0.19 F 0.01 O2, a mixture of NaHCO3H and NaHCO3, Fe(OH)2, Mn(OH)2, ZrO2, SnO, TiO2 and NH4F were added to deionized water, and then 0.8% nitric acid (based on the total mass of solvent) at a concentration of 2M, 2.5% ammonia (based on the total mass of solvent) and two chelating agents (gluconic acid and citric acid, with the above components in a 1:1 ratio) at a mass fraction of 0.40% (based on the total mass of solvent) were added. The pH of the solution was adjusted to 5.6, and then a solid powder was obtained by spray pyrolysis.

[0055] (2) The above solid powder material was sintered and held at a temperature of 20% oxygen in a rotary kiln at 900℃ for 10 hours. After being crushed and sieved, it was then coated with AlO at a mass ratio of 0.4% (Al+Zr+Ti+W) in a coating machine. 3、 ZrO2, TiO2 and (NH4)6W7O 24 Four coating agents, each with a size less than 50 nm, were used. The mixture was then sintered a second time at 650℃ in a rotary kiln for 5 hours. After crushing and sieving, a 5 μm layered oxide cathode material for sodium-ion batteries was finally obtained.

[0056] Example 5

[0057] This embodiment provides a low-cost method for preparing layered oxide cathode materials for sodium-ion batteries, comprising the following steps:

[0058] (1) According to the molecular formula Na 0.8-1.1 Ni 0.20Fe 0.35 Mn 0.35 Cu 0.055 Zn 0.02 Ca 0.015 La 0.005 Ti 0.005 O2, NaHCO3 mixture with NiO, FeO, MnO, CuO, ZnO, CaO, La2O3 and TiO2 added to deionized water, then 0.2% nitric acid (4M concentration, calculated by solvent mass), 1.8% ammonia (calculated by solvent mass), and 0.25% (calculated by solvent mass) of three chelating agents (DTMPS, DTPMPA and citric acid, the ratio of the above components is 1:1:1) were added to adjust the pH of the solution to 5.6, and then a solid powder was obtained by spray pyrolysis;

[0059] (2) The above solid powder material was sintered and held at 920℃ in an air atmosphere in a track kiln for 12 hours. After crushing and sieving, it was coated with a B2O3 coating agent with a mass ratio of 0.6% by weight in a coating machine. The size of the B2O3 was less than 50nm. Then, it was sintered again in a rotary kiln at 550℃ for 6 hours. After crushing and sieving, the final 5μm sodium-ion battery layered oxide cathode material was obtained.

[0060] Example 6

[0061] This embodiment provides a low-cost method for preparing layered oxide cathode materials for sodium-ion batteries, including the following steps:

[0062] (1) According to the molecular formula Na 0.8-1.1 Ni 0.25 Fe 0.35 Mn 0.30 Cu 0.050 Zn 0.025 Ca 0.015 B 0.005 Ce 0.005 O2, a mixture of Na2CO3 and NaOH, along with NiO, FeO, MnO, CuO, ZnO, CaO, B2O3 and CeO2, were added to deionized water. Then, 0.7% nitric acid (based on the total mass of solvent) at a concentration of 2M, 2.2% ammonia (based on the total mass of solvent), and four chelating agents (DTPA, ATP, sodium gluconate and sodium citrate, in a ratio of 1:1:1:1) at a mass fraction of 0.12% (based on the total mass of solvent) were added. The pH of the solution was adjusted to 5.9, and then a solid powder was obtained by spray pyrolysis.

[0063] (2) The above solid powder material was sintered in an oxygen atmosphere in a 940℃ orbital kiln for 16 hours. After crushing and sieving, it was coated with four coating agents (ZrO2, TiO2, CeO2, and WO3) at a mass ratio of 0.4% (Zr+Ti+Ce+W) in a coating machine. The size of the four coating agents was less than 50nm. Then, it was sintered again in a 700℃ rotary kiln for 5 hours. After crushing and sieving, the final 6μm sodium-ion battery layered oxide cathode material was obtained.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 1 is that the sodium cathode material is synthesized using a precursor process (sintering). The following is the precursor process synthesis process.

[0066] According to the molecular formula Na 0.8-1.1 Ni 0.225 Fe 0.315 Mn 0.36 Cu 0.055 Zn 0.02 Ca 0.015 B 0.005 Li 0.005 O2 was used to mix Na2CO3 with NiFeMnCu hydroxide precursor, ZnO, CaO, B2O3, and Li2CO3. The mixture was then sintered in an air atmosphere at 880℃ for 16 hours. After pulverization and sieving, it was coated with four coating agents (ZrO2, TiO2, CeO2, and WO3) at a mass ratio of 0.4% (Zr+Ti+Ce+W). The size of all four coating agents was less than 50 nm. A second sintering was then performed at 600℃ in a rotary kiln for 8 hours. After pulverization and sieving, a 4 μm layered oxide cathode material for sodium-ion batteries was finally obtained.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that no chelating agent was added.

[0069] Test case

[0070] Using the aforementioned embodiments and comparative examples as samples, performance tests were conducted on sodium ion layered oxide cathode material products.

[0071] 1. Free sodium or residual alkali test

[0072] The free sodium or residual alkali test was performed using an automatic potentiometric titrator, model: METTLER TOLEDO G20. 5g of sample solvent was weighed into 40mL of aqueous solution, sonicated for 30min, filtered, and diluted to a 100mL volumetric flask. After shaking and standing, the supernatant was used for testing. The results are shown in Table 1.

[0073] 2. Discharge capacity and cycle performance

[0074] The discharge capacity and cycle performance were tested using the following method: Sodium-ion battery positive electrode material was mixed with conductive carbon black and PVDF binder at a mass ratio of 80:10:10. NMP was added to form a uniform slurry, which was then coated onto aluminum foil. After drying and rolling, the slurry was cut into positive electrode sheets with a diameter of 14 mm. A sodium-ion battery was assembled using a CR2032 button cell. The separator was glass fiber, the electrolyte was a 1 mol / L NaPF6 solution with EC / PC / DEC solvent, and the negative electrode was a sodium sheet. The results are shown in Table 1 and... Figures 1-2 As shown (the materials obtained in Example 1 and Comparative Example 1 were used as samples for measurement).

[0075] 3. Sodium-ion battery test

[0076] Sodium-ion battery test conditions: temperature 25℃±1℃, charge / discharge cycle voltage range 2.0V-4.0V, current 0.1C (150mAh / g), cycle test conducted at 0.5C charge 1C discharge. Results are shown in Table 3.

[0077] Experimental results:

[0078] Figure 1 and Figure 2 The table shows the elemental EDS spectra of Ni, Fe, and Mn in the cross-sections of the sodium-ion battery cathode materials in Example 1 and Comparative Example 1. Table 1 (spectrums 24-30) and Table 2 (spectrums 31-37) show the molar ratios of Ni, Fe, and Mn in the cross-sections of the sodium-ion battery cathode materials in Example 1 and Comparative Example 1, respectively.

[0079] Table 1. Molar ratios of Ni, Fe, and Mn in Example 1

[0080] Molar ratio Design specification 24 25 26 27 28 29 30 Ni / mol% 22.50±1.50 22.32 23.37 23.52 21.49 22.91 21.83 22.37 Fe / mol% 31.50±1.50 30.79 31.72 30.93 32.04 32.06 31.63 32.14 Mn / mol% 36.00±1.50 36.89 34.91 35.55 36.47 35.03 36.54 35.49

[0081] Table 2 shows the molar ratios of Ni, Fe, and Mn in Comparative Example 1.

[0082] Molar ratio Design specification 31 32 33 34 35 36 37 Ni / mol% 22.50±1.50 23.18 21.72 22.31 21.82 20.93 22.73 20.71 Fe / mol% 31.50±1.50 33.28 34.04 32.63 30.81 34.11 32.34 33.46 Mn / mol% 36.00±1.50 33.54 34.24 35.06 37.37 34.96 34.93 35.83

[0083] According to the EDS spectra data in Tables 1 and 2, the Ni, Fe, and Mn elements in Example 1 are all within the design specifications, indicating a uniform element distribution without element segregation. However, the Ni, Fe, and Mn elements in Comparative Example 1 are not uniformly distributed; for example, the molar amounts of Fe and Mn in spectra 31 and 32 exceed the design specifications. This indicates that sodium cathode materials synthesized using traditional precursor processes are prone to uneven distribution of Ni, Fe, and Mn elements, which is caused by the uneven distribution of Ni, Fe, and Mn elements generated during precursor synthesis. Because a chelating agent capable of chelating Ni, Fe, and Mn, such as ethylenediaminetetraacetic acid (EDTA), is added during the solution preparation process in this invention, it effectively chelates with Ni, Fe, and Mn, thus reducing the likelihood of elemental unevenness during spray pyrolysis.

[0084] In addition, the sodium-ion battery cathode materials of Example 1 and Comparative Example 1 were subjected to capacity and cycle comparison tests, and the data results were compiled. Figure 3 and Figure 4 Table 3 summarizes the comparative data on capacity, cycling, free sodium, and pH for the examples and comparative examples.

[0085] Table 3. Physical and chemical test results

[0086]

[0087] As shown in Table 3, the sodium electrochemical positive materials prepared in Examples 1-6 have excellent discharge capacity, cycle life, free sodium content, and pH value. For example, the retention rate after 50 cycles is above 94%, and the free sodium content and pH value are below 0.9% and 12, respectively.

[0088] As can be seen from Table 3, the cathode material in Example 1 is: Na 0.8-1.1 Ni 0.225 Fe 0.315 Mn 0.36 Cu 0.055 Zn 0.02 Ca 0.015 B 0.005 Li 0.005The initial discharge capacity of O2 at 0.1C was 147 mAh / g, with a 50-cycle retention of 96.07%, residual alkali and pH of 0.367% and 11.76, respectively. In contrast, the initial discharge capacity of Comparative Example 1 at 0.1C was only 138 mAh / g, with a 50-cycle retention of 92.78%, residual alkali and pH of 4.742% and 12.43, respectively. These comparative data demonstrate that a uniform distribution of Ni, Fe, and Mn significantly improves the capacity and cycle life of sodium-ion battery cathodes. Since Ni, Fe, and Mn are typically located in the metal layer of sodium-ion battery cathodes, segregation can cause mixing of metal and sodium elements, increasing the resistance to sodium ion insertion / extraction and thus reducing the capacity and cycle performance of the sodium-ion battery cathode.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a layered oxide cathode material for sodium-ion batteries, characterized in that, The chemical formula of the layered oxide cathode material for the sodium-ion battery is Na. a Ni x Fe y Mn z M 1-x-y-z O2, 0.8≤a≤1.1, 0≤x≤1, 0≤y≤1, 0≤z≤1, M=M1+M2, M1=at least one of Zn, Ca, Cu, Sb, Ba, Mg, Zr, Y, Cs, Mo, Sn, Ce, La, F, B, Ti, Li, M2=at least one of B, Al, Zr, Ti, Ce, W, P; the metal or its salt is pyrolyzed and sintered in a solvent system to form the final product; The preparation method includes the following steps: S1: Sodium, nickel, iron, manganese, and M1 sources are placed in deionized water, and nitric acid, chelating agent, and ammonia are added. The pH of the solution is adjusted to 5-7, and the intermediate is obtained by spray pyrolysis. The mass ratio of nitric acid, chelating agent, and ammonia is 0.1~1:0.015~0.5:1.5~2.5; the concentration of nitric acid is 2~5M. S2 sinters the intermediate material in a rotary kiln once, then coat it with M2 source and sinter it a second time to obtain the cathode material; One-time sintering: temperature 800~980℃, time 6~16h; Secondary sintering: temperature 400~800℃, time 5~10h; In primary sintering and / or secondary sintering, the sintering atmosphere is air, oxygen, or a mixture of gases with an oxygen concentration of 10% or more. The chelating agent includes at least one of EDTA, DTPA, ATP, HEDP, EDTMPS, DTPMPA, citric acid, tartaric acid, oxalic acid, gluconic acid, polyacrylic acid, sodium gluconate, and sodium citrate. The molar amount of sodium source metal is A, and the total molar amount of nickel, iron, manganese and M sources metal is B, where A:B = 0.8~1.1:1; The particle size D of the positive electrode material 50 =4~7μm.

2. The preparation method according to claim 1, characterized in that, The sodium source is a sodium salt, which includes at least one of sodium carbonate, sodium bicarbonate, and sodium hydroxide. The nickel source, iron source, manganese source, and M1 source are each independently selected from at least one of oxalate, acetate, nitrate, sulfate, chloride, oxide, hydroxide, or metal powder.

3. The preparation method according to claim 1, characterized in that, The M2 source includes features (1-1) to (1-3): (1-1) The M2 source includes at least one of boron oxide, boric acid, aluminum oxide, aluminum hydroxide, zirconium oxide, zirconium hydroxide, titanium oxide, cerium oxide, ammonium tungstate, monoammonium phosphate, and diammonium phosphate; (1-2) The total elemental mass ratio in the M2 source is 0.1~0.8%; (1-3) Particle size D of M2 source 50 <50nm.

4. The preparation method according to claim 1, comprising the following steps: According to the molecular formula Na 0.8-1.1 Ni 0.225 Fe 0.315 Mn 0.36 Cu 0.055 Zn 0.02 Ca 0.015 B 0.005 Li 0.005 O2, Na2CO3, Ni, Fe, Mn and Cu metal powders, and ZnO, CaO, B2O3 and Li2CO3 dopants are added to deionized water, and then 1% nitric acid (5M concentration), 2.5% ammonia water (mass fraction) and five chelating agents (EDTA, DTPA, ATP, HEDP and sodium gluconate) (mass fraction 0.50%) are added. The ratio of EDTA, DTPA, ATP, HEDP and sodium gluconate is 1:1:1:1:

1. The pH of the solution is adjusted to 7, and then a solid powder substance is obtained by spray pyrolysis. The solid powder material was sintered and held at 880℃ in an air atmosphere for 16 hours. After crushing and sieving, it was coated with three coating agents, Al2O3, ZrO2 and TiO2, at a mass ratio of 0.5% in a coating machine. The size of the three coating agents was less than 50nm. Then, it was sintered again in a rotary kiln at 600℃ for 8 hours. After crushing and sieving, the final product of 4μm sodium-ion battery layered oxide cathode material was obtained. in, The total mass of 1% nitric acid, 2.5% ammonia, and 0.50% chelating agent is calculated based on the solvent.

5. The preparation method according to claim 1, comprising the following steps: According to the molecular formula Na 0.8-1.1 Fe 0.40 Mn 0.40 Zn 0.01 Ca 0.015 Mo 0.005 O 0.19 F 0.01 NaOH, FeO, MnO, ZnO, CaO, MoO2, and NH4F were added to deionized water. Then, 0.1% nitric acid (4.5M), 1.5% ammonia, and 0.015% chelating agents (EDTMPS, DTPMPA, citric acid, tartaric acid, and oxalic acid) were added in a ratio of 1:1:1:1:

1. The pH of the solution was adjusted to 5, and then a solid powder was obtained by spray pyrolysis. The solid powder material was sintered and held at a mixed atmosphere with 10% oxygen content in a rotary kiln at 980℃ for 6 hours. After crushing and sieving, it was coated with four coating agents, ZrO2, TiO2, CeO2 and WO3, at a mass ratio of 0.8% in a coating machine. The size of the four coating agents was less than 50nm. Then, it was sintered again in a rotary kiln at 800℃ for 5 hours. After crushing and sieving, the final product of 7μm sodium-ion battery layered oxide cathode material was obtained. in, The total mass of 0.1% nitric acid, 1.5% ammonia, and 0.015% chelating agent is calculated based on the solvent.

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