Method for preparing high-capacity and long-cycle sodium electric single-crystal positive electrode material under assistance of carbonate

Abstract

The invention discloses a method for preparing a high-capacity and long-cycle sodium electric single crystal positive electrode material under the assistance of carbonate, and relates to the technical field of battery materials. According to the invention, single crystallization is realized through simple component process optimization, growth of single crystal primary particles is promoted through surface action of large-radius cations in carbonate, and calcination temperature and excessive sodium are reduced; according to the invention, the content of carbonate is finely adjusted, so that the micron-sized single crystal with excellent electrochemical performance is obtained, and the single crystal particle has an ordered single crystal structure, a reasonable Na < + > migration path and relatively low interfacial activity; through the comprehensive effect of B element doping, the mechanical strength of the material is improved, and the redox behavior of lattice oxygen is inhibited, so that layered phase change is relieved, and the cycle performance of the battery is improved; the method is simple and easy to implement and low in cost, and can be widely applied to synthesis of other energy storage materials.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and specifically, to a method for preparing a sodium-ion single-crystal cathode material with high capacity and long cycle life by using carbonate assistance. Background Art

[0002] Sodium-ion batteries have been widely regarded as potential alternatives to lithium-ion batteries in large-scale power storage because of their good cost-effectiveness, abundant sodium resources in the earth, and embedding mechanism similar to that of lithium batteries. Among various oxide cathode materials, O3-NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is remarkable for its excellent reversible capacity and high Coulomb efficiency of the Na-rich O3-type layered oxide. However, due to irreversible phase transformation, the electrochemical performance, especially the cycle performance, still fails to meet expectations. At the same time, the existing methods for preparing O3-NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 single-crystal cathode materials (molten salt method and high-temperature sintering method with excess sodium) often have problems such as high cost, complex process, and unstable product performance.

[0003] For example, the patent application with the publication number CN117303460A discloses a carbonate precursor, a high-nickel single-crystal cathode material and a preparation method thereof. The preparation method of the high-nickel single-crystal cathode material includes the following steps: sintering the carbonate precursor and mixing it with lithium hydroxide and strontium carbonate; sintering the mixed material in a pure oxygen atmosphere and then naturally cooling it; then performing air flow pulverization to obtain an intermediate product; mixing it evenly with cobalt hydroxide, titanium dioxide and lithium hydroxide; and then sintering it in a pure oxygen atmosphere and naturally cooling it, and then naturally cooling it to obtain the product. This invention prepares a high-specific-surface-area precursor by the urea pyrolysis method, and then obtains a high-porosity precursor after pre-sintering, which can significantly reduce the high-temperature sintering temperature of the high-nickel single-crystal ternary material, effectively reduce the disproportionation reaction of trivalent nickel, and the prepared high-nickel single-crystal cathode material has the characteristics of large primary particles, smooth surface and high specific capacity. However, the synthesis process of the carbonate precursor in this invention has poor stability, low tap density, and it is difficult to control the particle morphology of the synthesized single-crystal cathode material.

[0004] For another example, the patent application with the publication number CN119170767A discloses a cathode material, a preparation method thereof, a cathode sheet and a sodium-ion battery. The cathode material includes a matrix material and a coating layer coated on the surface of the matrix material; the chemical formula of the matrix material is Na x A y Ni a Cu b Fe c Mn dO2, A includes Ca and / or Sr; the coating layer contains B and the mass ratio of B element to the mass ratio of the base material is 0.005-0.01. The invention can effectively improve the single crystal morphology of the positive electrode material sintered from the carbonate precursor by doping Ca and / or Sr to assist melting, obtain a single crystal morphology with rounded particles, and Sr / Ca enters the sodium layer to stabilize the structure, improve the compaction density of the material, and improve the rate performance and capacity; by setting a dense coating layer containing B elements, the specific surface area of ​​the positive electrode material can be reduced, the occurrence of side reactions can be reduced, the cycle performance can be improved, and the air stability of the material can be improved, and the slurry gel phenomenon can be reduced.

[0005] Therefore, developing a method for sodium-ion battery single crystal cathode material with high capacity and long cycle life is of great significance for promoting the development of sodium-ion batteries. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a high-capacity and long-cycle sodium-electric single crystal positive electrode material using carbonate as an aid. The method achieves high capacity and long-cycle performance of the sodium-electric single crystal positive electrode material by optimizing the selection and ratio of precursors, sodium sources, carbonates and boron-containing additives, as well as controlling the calcination conditions.

[0007] In order to achieve the above-mentioned purpose, the technical solution of the present invention is as follows:

[0008] The present invention provides a method for preparing a high-capacity and long-cycle sodium electric single crystal positive electrode material using carbonate as an auxiliary, comprising the following steps:

[0009] (1) fully mixing the precursor powder TM with the sodium source, the carbonate M and the boron-containing additive in a certain proportion to obtain a mixture;

[0010] The carbonate M is at least one of calcium carbonate, potassium carbonate, lithium carbonate, barium carbonate, zinc carbonate, magnesium carbonate, lanthanum carbonate and strontium carbonate;

[0011] (2) calcining the mixture obtained in step (1) in an air environment, and cooling naturally to room temperature to obtain the final product, i.e., the sodium electric single crystal positive electrode material Na 1-x M x TMO2;

[0012] The molar ratio of the metal element in the precursor powder TM to the sodium in the sodium source is 1:1-x, where x is 0.01-0.03 mol. Reducing the sodium ratio can reduce residual alkali and prevent slurry gelation.

[0013] In some embodiments of the present invention, in step (1), the precursor powder TM is Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, the precursor particle size D50 is 3 - 6 μm, and in the embodiments of the present invention, D 50 = 3.5 μm is taken as an example. The present invention uses a hydroxide precursor, which is the current industry mainstream and has better process stability and higher tap density.

[0014] In some embodiments of the present invention, in step (1), the sodium source is sodium carbonate or sodium bicarbonate.

[0015] In some embodiments of the present invention, in step (1), the boron-containing additive is at least one of boric acid, boron oxide, sodium borate, sodium metaborate, zinc borate, and copper borate.

[0016] Preferably, the doping amount of the boron-containing additive is 250 - 1000 ppm of the mass of the precursor.

[0017] The comprehensive effect of B element doping can improve the mechanical strength of the material, inhibit the redox behavior of lattice oxygen, and thus alleviate the layered phase transition.

[0018] Preferably, the carbonate M is a combination of calcium carbonate and potassium carbonate, strontium carbonate, or barium carbonate;

[0019] The molar ratio of the metal element in the precursor powder to calcium in calcium carbonate is 1:0.01 - 0.02, and the molar ratio of the metal element in the precursor powder to potassium in potassium carbonate, strontium in strontium carbonate, or barium in barium carbonate is 1:0.02.

[0020] The present invention first proposes to utilize the surface action of large-radius cations in carbonates to promote the growth of single-crystal primary particles. The large-radius cations promote single-crystal growth in the following ways:

[0021] Lowering the surface energy: The adsorption of large-radius cations may reduce the energy of the particle surface, making the particles more inclined to form a stable single-crystal structure rather than disordered polycrystals or aggregates.

[0022] Guiding the directional growth: The presence of large-radius cations may guide the particles to grow along specific crystallographic directions, thus forming an ordered single-crystal structure.

[0023] This mechanism not only reduces the calcination temperature but also reduces the excessive use of sodium. The large-radius cations play a "bridge" role during the sintering process, promoting the bonding and sintering between particles, thereby reducing the required calcination temperature. Stabilizing the crystal structure of the material and finely adjusting the content of carbonate also reduce the sodium excess.

[0024] Preferably, in step (2), the conditions for the segmented calcination are: in the first stage, first heat up to 550 °C and keep it warm for 5 h; in the second stage, then heat up to 850 - 1000 °C, and the calcination time is 10 - 20 h.

[0025] The present invention also provides a sodium - ion single - crystal cathode material prepared by the described method.

[0026] The present invention also provides a sodium - ion battery, including a cathode material, and the cathode material is the sodium - ion single - crystal cathode material described above. The sodium - ion battery further includes an anode, an electrolyte, and a separator. The electrolyte is 1M NaClO4 / (PC + 5% FEC), and the separator is Whatman glass fiber.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) Single - crystallization is achieved through simple compositional process optimization. The surface action of large - radius cations in carbonates is utilized to promote the growth of single - crystal primary particles, reducing the calcination temperature and sodium excess.

[0029] (2) By finely adjusting the carbonate content, micron - scale single - crystals with excellent electrochemical performance are obtained. Such single - crystal particles have an ordered single - crystal structure, a reasonable Na + migration path and low interfacial activity.

[0030] (3) Through the comprehensive effect of B - element doping, the mechanical strength of the material is improved, the redox behavior of lattice oxygen is inhibited, thereby alleviating the layer - like phase transition and improving the battery cycling performance.

[0031] (4) This method is simple and feasible, with low cost, and can be extended for use in the synthesis of other energy - storage materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the SEM image of the cathode material obtained in Example 2 of the present invention;

[0033] Figure 2 It is the SEM image of the cathode material obtained in Comparative Example 1 of the present invention;

[0034] Figure 3 It is the charge - discharge curve graph of the cathode material obtained in Example 2 of the present invention;

[0035] Figure 4 It is the 1C cycle 50 - turn retention rate graph of the cathode material obtained in Example 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] Example 1

[0037] Weigh the Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor powder (D 50Calcium carbonate (D = 3.5 μm) and Na2CO3 powder were weighed. Calcium carbonate was weighed according to a molar ratio of TM:Ca = 1:0.02, and potassium carbonate was weighed according to a molar ratio of TM:K = 1:0.02. Boric acid was weighed at a mass ratio of 500 ppm based on the mass of the precursor. The mixture was thoroughly mixed using an agate mortar, and then the mixture was heated in a box furnace (heating rate: 3 °C / min) to 550 °C and held for 5 h, and then heated (heating rate: 5 °C / min) to 900 °C and held for 15 h, and naturally cooled to room temperature to obtain the cathode material.

[0038] Example 2

[0039] Ni was weighed according to a molar ratio of TM:Na = 1:0.96 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor powder (D 50 =3.5μm) and Na2CO3 powder were weighed. Calcium carbonate was weighed according to a molar ratio of TM:Ca = 1:0.02, and strontium carbonate was weighed according to a molar ratio of TM:Sr = 1:0.02. Boric acid was weighed at a mass ratio of 500 ppm based on the mass of the precursor. The mixture was thoroughly mixed using an agate mortar, and then the mixture was heated in a box furnace (heating rate: 3 °C / min) to 550 °C and held for 5 h, and then heated (heating rate: 5 °C / min) to 900 °C and held for 15 h, and naturally cooled to room temperature to obtain the cathode material.

[0040] Example 3

[0041] Ni was weighed according to a molar ratio of TM:Na = 1:0.96 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor powder (D 50 =3.5μm) and Na2CO3 powder were weighed. Calcium carbonate was weighed according to a molar ratio of TM:Ca = 1:0.01, and barium carbonate was weighed according to a molar ratio of TM:Ba = 1:0.02. Boric acid was weighed at a mass ratio of 500 ppm based on the mass of the precursor. The mixture was thoroughly mixed using an agate mortar, and then the mixture was heated in a box furnace (heating rate: 3 °C / min) to 550 °C and held for 5 h, and then heated (heating rate: 5 °C / min) to 900 °C and held for 15 h, and naturally cooled to room temperature to obtain the cathode material.

[0042] Comparative Example 1

[0043] Ni was weighed according to a molar ratio of TM:Na = 1:0.96 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor powder (D 50=3.5 μm) and Na2CO3 powder, weigh boric acid according to the mass ratio of 500 ppm of the precursor mass, mix well using an agate mortar, then heat the mixture in a box furnace (heating rate 3 °C / min) to 550 °C and hold for 5 h, then heat (heating rate 5 °C / min) to 980 °C and hold for 15 h, and naturally cool to room temperature to obtain the cathode material.

[0044] Comparative Example 2

[0045] Weigh Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor powder (D 50 =3.5 μm) and Na2CO3 powder, weigh boric acid according to the mass ratio of 500 ppm of the precursor mass, mix well using an agate mortar, then heat the mixture in a box furnace (heating rate 3 °C / min) to 550 °C and hold for 5 h, then heat (heating rate 5 °C / min) to 950 °C and hold for 15 h, and naturally cool to room temperature to obtain the cathode material.

[0046] Comparative Example 3

[0047] Weigh Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor powder (D 50 =3.5 μm) and Na2CO3 powder, weigh calcium carbonate according to the molar ratio of TM:Ca = 1:0.02 and strontium carbonate according to the molar ratio of TM:Sr = 1:0.02, mix well using an agate mortar, then heat the mixture in a box furnace (heating rate 3 °C / min) to 550 °C and hold for 5 h, then heat (heating rate 5 °C / min) to 900 °C and hold for 15 h, and naturally cool to room temperature to obtain the cathode material.

[0048] Test Example 1

[0049] Preparation of battery electrode sheet: Weigh the active material, conductive agent (SP), and binder (PVDF) according to the mass ratio of 8:1:1. First, dissolve 40 mg of the weighed active material in a certain amount of NMP solvent and stir continuously until the active material is completely dissolved; then add PVDF to the active material solution; after PVDF is mixed with the active material, add the conductive agent, and then stir continuously. After the active material, SP, and PVDF are mixed evenly, use a coater to evenly coat the slurry on the aluminum foil. The coated copper foil is transferred to a vacuum drying oven and dried at 120 °C for 12 hours; finally, use a cutter to cut the dried electrode sheet into circular electrode sheets with a diameter of 14 mm, and weigh the cut electrode sheets.

[0050] Assembly of CR2032 button battery: In a glove box under an argon atmosphere, stack them in the order of the positive electrode case, negative electrode sheet, electrolyte, separator, electrolyte, sodium metal sheet, gasket, spring piece, and negative electrode case, and then use a sealing machine to press them into a button battery. After leaving it for 12 h for activation, perform tests. Among them, the positive and negative electrode cases, gaskets, and spring pieces are ultrasonically cleaned with absolute ethanol and vacuum dried, and then placed in the glove box for use; the electrolyte is 1 M NaClO4 / (PC + 5% FEC); the separator is Whatman glass fiber, and the battery test voltage window is set to 2.0 - 4.0 V.

[0051] The test results are shown in Table 1 (when testing the capacity of cycling 50 circles under the 1C current density of the present invention, first cycle one circle under the current densities of 0.1C, 0.2C, and 0.5C respectively, and then cycle 50 circles under the 1C current density).

[0052] Table 1 (unit: mAh / g)

[0053]

[0054] Figure 1 It is the electron microscopy image of Invention Example 2. It can be clearly seen that the single crystal morphology of the positive electrode material obtained by this method is excellent, the particles are dispersed, and the surface is smooth. The primary particle size is about 3 - 4 μm. Figure 2 It is the electron microscopy image of Comparative Example 1 of the invention. The single crystal morphology of this method is worse than that of Example 2, and there is a certain degree of agglomeration between them. From Table 1 and Figure 3 、 Figure 4 The results can prove that for the single crystal positive electrode materials prepared by Examples 1, 2, and 3 using this method compared with Comparative Examples 1 and 2 with traditional sintering (increasing the sintering temperature or increasing the sodium ratio) and Comparative Example 3 (without doping B), their discharge specific capacity and 50 - cycle retention rate are significantly improved. The 0.1C first - cycle discharge specific capacity of Example 2 reaches up to 139.65 mAh / g at a voltage of 2.0 - 4.0 V after using carbonate - assisted sintering with a reduced sintering temperature, and the retention rate after cycling 50 circles at 1C is 99.08%.

Claims

1. A method for preparing a sodium - ion single - crystal cathode material with high capacity and long cycle life by using carbonate assistance, characterized in that, The following steps are involved: (1) fully mixing the precursor powder TM with the sodium source, the carbonate M and the boron-containing additive in a certain proportion to obtain a mixture; The carbonate M is at least one of calcium carbonate, potassium carbonate, lithium carbonate, barium carbonate, zinc carbonate, magnesium carbonate, lanthanum carbonate and strontium carbonate; (2) calcining the mixture obtained in step (1) in an air environment, and cooling naturally to room temperature to obtain the final product, i.e., the sodium electric single crystal positive electrode material Na 1-x M x TMO2; The molar ratio of the metal element in the precursor powder TM to the sodium in the sodium source is 1:1-x; x is 0.01-0.04 mol.

2. The method for preparing a sodium-ion single-crystal cathode material with high capacity and long cycle life by using carbonate assistance according to claim 1, wherein In step (1), the precursor powder TM is Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, and the particle size D of the precursor 50 is 3 - 6 μm.

3. The method for preparing a sodium - ion single - crystal cathode material with high capacity and long cycle life by using carbonate assistance according to claim 1, wherein In step (1), the sodium source is sodium carbonate or sodium bicarbonate.

4. The method for preparing a sodium - ion single - crystal cathode material with high capacity and long cycle life by using carbonate assistance according to claim 1, wherein, In step (1), the boron-containing additive is at least one of boric acid, boric oxide, sodium borate, sodium metaborate, zinc borate and copper borate.

5. The method for preparing a sodium - ion single - crystal cathode material with high capacity and long cycle life by using carbonate assistance according to claim 4, wherein, The doping amount of the boron-containing additive is 250-1000 ppm of the precursor mass.

6. The method for preparing a sodium-ion single-crystal cathode material with high capacity and long cycle life by using carbonate assistance according to claim 1, wherein The carbonate M is a combination of calcium carbonate and potassium carbonate, strontium carbonate or barium carbonate; The molar ratio of the metal element in the precursor powder to calcium in calcium carbonate is 1:0.01-0.02, and the molar ratio of the metal element in the precursor powder to potassium in potassium carbonate, strontium in strontium carbonate or barium in barium carbonate is 1:0.

02.

7. The method for preparing a sodium - ion single - crystal cathode material with high capacity and long cycle life by using carbonate assistance according to claim 1, wherein In step (2), the conditions for the staged calcination are: the first stage is heated to 550°C and kept warm for 5 hours; the second stage is heated to 850-1000°C and the calcination time is 10-20 hours.

8. A sodium electric single crystal positive electrode material prepared according to the method of any one of claims 1-7.

9. A sodium-ion battery, comprising a positive electrode material, characterized in that, The positive electrode material is the sodium electric single crystal positive electrode material as described in claim 8.

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