LLZAO-coated sodium ion battery layered transition metal oxide positive electrode material

Abstract

The invention relates to the technical field of battery materials, in particular to an LLZAO-coated sodium ion battery layered transition metal oxide positive electrode material. The positive electrode material comprises a NaNi < 1 / 3 > Fe < 1 / 3 > Mn < 1 / 3 > O < 2 > inner core and a Li < 6.25 > La < 3 > Zr < 2 > Al < 0.25 > O < 2 > coating layer with the mass percent of 1%-10%. According to the invention, the lithium-rich characteristic of LLZAO is utilized, based on a dynamic compensation mechanism, the super-stable LLZAO-coated sodium ion battery layered transition metal oxide positive electrode material is provided, and the capacity and cycling stability of the layered oxide are improved. The preparation steps of the positive electrode material are simple to operate, and the positive electrode material is easy to prepare, is green and environment-friendly, can be suitable for a large-scale product production process, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly to a layered transition metal oxide cathode material for sodium-ion batteries coated with LLZAO. Background Art

[0002] In the current energy storage field, sodium-ion batteries have become a research hotspot due to their significant advantages in terms of cost, wide resource distribution, and environmental friendliness. Given the abundant reserves of sodium in the earth's crust and its low extraction cost, sodium-ion batteries are regarded as an energy storage technology with broad development prospects, especially in the field of large-scale energy storage system applications. In addition, compared with lithium-ion batteries, sodium-ion batteries exhibit better environmental compatibility in terms of material recycling and reuse.

[0003] Among many sodium-ion battery cathode materials, layered transition metal oxides have attracted much attention due to their unique structural characteristics and excellent electrochemical performance. Such materials usually exhibit a layered structure, and sodium ions can be rapidly inserted and extracted in the interlayer channels, thus supporting the charge and discharge processes of the battery. This structural feature of the layered transition metal oxide cathode material not only facilitates the rapid migration of sodium ions but also improves the charge and discharge efficiency and cycle stability of the battery, providing an important driving force for the progress of sodium-ion battery technology.

[0004] Although layered transition metal oxide cathode materials have shown great potential in sodium-ion battery applications, challenges including energy density, cycle stability, cost, and sodium ion transport efficiency still need to be overcome. Therefore, continuous scientific research and technological innovation are crucial for improving the performance of these materials. Summary of the Invention

[0005] In order to improve the energy storage performance of the layered transition metal oxide cathode material for sodium-ion batteries, including material capacity, cycle stability, etc., the present invention utilizes the lithium-rich characteristics of LLZAO and provides a super-stable LLZAO-coated layered transition metal oxide cathode material for sodium-ion batteries based on a dynamic compensation mechanism, including a NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 core and an LLZAO coating layer, where LLZAO represents Li 6.25 La3Zr2Al 0.25 O2; the mass percentage of the LLZAO coating layer in the cathode material is 1% - 10%.

[0006] The super-stable LLZAO-coated layered transition metal oxide cathode material for sodium-ion batteries of the present invention has the following advantages: (1) The components and ratios in the host layered transition metal oxide are retained, and the layered oxide structure remains unchanged after coating; (2) Since LLZAO has a lithium-rich property, it can supplement the sodium lost in the host layered oxide during the electrochemical cycling process and fix the lattice oxygen in the host material, thus effectively ensuring the structural integrity of the material and improving the material capacity and cycling stability.

[0007] Preferably, the mass percentage of the LLZAO coating layer in the cathode material is 1% - 5%.

[0008] More preferably, the mass percentage of the LLZAO coating layer in the cathode material is 2% - 4%.

[0009] Preferably, the particle size of the cathode material is 0.5 - 3 μm.

[0010] Furthermore, the present invention provides a method for preparing the cathode material, including: dissolving a lithium source, a lanthanum source, a zirconium source, and an aluminum source in a solvent, and then mixing with a NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 core solution, and calcining after evaporating the solvent.

[0011] Preferably, the lithium source is selected from at least one of lithium nitrate, lithium carbonate, lithium hydroxide, and lithium chloride; the lanthanum source is selected from at least one of lanthanum chloride, lanthanum nitrate, and lanthanum hydroxide; the zirconium source is selected from at least one of zirconium sulfate, zirconium acetate, zirconyl nitrate, and zirconium acetylacetonate; the aluminum source is selected from at least one of aluminum chloride and aluminum nitrate.

[0012] Preferably, the solvent is an alcohol solvent; and / or, the temperature for evaporating the solvent is 60°C - 90°C (more preferably 70°C - 90°C); and / or, the calcination temperature is 600°C - 900°C (more preferably 650°C - 850°C); and / or, the calcination time is 3 - 10 h (more preferably 4 - 7 h).

[0013] In a specific implementation process, the calcination temperature is independently selected from any value of 650°C, 700°C, 750°C, 800°C, 850°C or a range value between any two of the above.

[0014] In a specific implementation process, the calcination time is independently selected from any value of 4 h, 5 h, 6 h, 7 h or a range value between any two of the above.

[0015] Most preferably, after calcining at 750°C for 5 hours, the performance of the cathode material reaches the optimum.

[0016] Furthermore, the present invention provides a positive electrode paste for a sodium-ion battery, which contains the positive electrode material described above or the positive electrode material prepared by the preparation method described above.

[0017] Preferably, the positive electrode paste for the sodium-ion battery includes an active material, carbon nanotubes, and PVDF; the active material is the positive electrode material described above or the positive electrode material prepared by the preparation method described above.

[0018] Optionally, the mass ratio of the active material, carbon nanotubes, and PVDF is (7-9):(0.5-2):(0.5-1).

[0019] Preferably, the mass ratio of the active material, carbon nanotubes, and PVDF is (7-9):1:1.

[0020] Optionally, the carbon nanotubes are conductive carbon black.

[0021] Furthermore, the present invention provides the application of the positive electrode material described above or the positive electrode material prepared by the preparation method described above in the field of sodium-ion batteries.

[0022] Furthermore, the present invention provides a sodium-ion battery electrode sheet, which contains the positive electrode material described above or the positive electrode material prepared by the preparation method described above.

[0023] Furthermore, the present invention provides a sodium-ion battery, which contains the sodium-ion battery electrode sheet described above.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: By utilizing the lithium-rich characteristics of LLZAO and based on the dynamic compensation mechanism, the present invention provides a super-stable LLZAO-coated layered transition metal oxide positive electrode material for sodium-ion batteries, improving the capacity and cycle stability of the layered oxide. Moreover, the preparation steps of the positive electrode material of the present invention are simple, easy to prepare, green and environmentally friendly, and can be applied to the production process of large-scale products, having broad application prospects. Description of the Drawings

[0025] Figure 1 is the XRD pattern of NFM@3LLZAO.

[0026] Figure 2 is the TEM image of NFM@3LLZAO.

[0027] Figure 3 is the EDS spectrum of NFM@3LLZAO.

[0028] Figure 4 are the charge-discharge curves of NFM and NFM@3LLZAO at different rates.

[0029] Figure 5Charge and discharge curves of NFM and NFM@3LLZAO at 1C.

[0030] Figure 6 It is the EELS comparison diagram of NFM@3LLZAO before and after cycling.

[0031] Figure 7 It is the SXAS comparison diagram of NFM and NFM@3LLZAO before and after cycling; among them, A is before cycling and B is after cycling. Detailed implementation manners

[0032] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention. In the embodiments provided in this specification, for those without specific technologies or conditions indicated, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments without the manufacturer indicated, they are all conventional products that can be obtained through regular channels. The following embodiments use a Neware battery test system for constant current charge and discharge tests (cut-off voltage 2.0 - 4.0V, currents 0.1C, 0.2C, 0.5C, 1C, 2C and 5C, where 1C = 130 mAh g -1 ); use a JEF-2100 transmission electron microscope to observe the sample morphology; use a Bruker D8 in Germany to test the sample XRD. NFM in the following embodiments is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0033] Example 1

[0034] This example provides a layered transition metal oxide cathode material for sodium-ion batteries coated with LLZAO, with the chemical formula NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@xLLZAO, where x represents the mass percentage of the coated LLZAO, abbreviated as NFM@xLLZAO, and the preparation steps are as follows: Disperse 5 g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 in ethanol and ultrasonicate for 1 h to form solution A. According to the LLZAO component expression Li 6.25 La3Zr2Al 0.25Ingredient with O2, dissolve it in ethanol and stir for 2 h to form solution B. Taking the coating of 3% Li 6.25 La3Zr2Al 0.25 O2 as an example, dissolve 86.2 mg of LiNO3, 259.8 mg of La(NO3)3·6H2O, 196.7 mg of zirconium acetylacetonate, 18.8 mg of Al(NO3)3·9H2O and 630 mg of citric acid monohydrate in ethanol and stir for 2 h to form solution B.

[0035] Pour solution B into solution A, evaporate the ethanol solvent at 80 °C, then calcine in an oxygen furnace at 750 °C for 5 h. Immediately take out NFM@3LLZAO after the furnace temperature drops to 100 °C and store it in a glove box to prevent the oxide from absorbing water and affecting the performance.

[0036] Prepare NFM@1LLZAO, NFM@5LLZAO, NFM@8LLZAO, NFM@10LLZAO respectively according to the above preparation steps.

[0037] Figure 1 is the XRD pattern of NFM@3LLZAO. It can be seen from Figure 1 that NFM and NFM@3LLZAO have the typical structure of layered transition metal oxides, and metal doping does not affect the crystal structure of the material.

[0038] Figure 2 is the TEM image of NFM@3LLZAO. It can be seen from Figure 2 that NFM and NFM@3LLZAO have similar structural morphologies. Under the same preparation temperature and time, the coating does not affect the morphology of the material; but there is a layer of other substances shown on the outermost layer after coating. After scanning electron microscopy testing, the particle size of NFM@3LLZAO is about 2 μm.

[0039] Figure 3 is the EDS pattern of NFM@3LLZAO. It can be seen from Figure 3 that the elements are evenly distributed after coating, and the elements of the coating material are mainly distributed on the outermost layer, indicating that LLZAO is successfully coated.

[0040] Example 2

[0041] In this example, the sodium-ion battery layered transition metal oxide cathode material coated with LLZAO prepared in Example 1 is used as the active material to prepare the sodium-ion battery electrode sheet. The steps are as follows: (1)Weigh each substance according to the mass ratio of 400 mg of active substance: 50 mg of carbon nanotubes: 50 mg of PVDF = 8:1:1, grind them in a glove box, add 700 μL of NMP solvent after 30 minutes, continue grinding for 3 hours, and then use a 150-μm doctor blade to evenly coat the slurry on the aluminum foil.

[0042] (2)Transfer the aluminum foil coated with the slurry to a vacuum drying oven and dry it at 120 °C for 12 hours to obtain the sodium-ion battery electrode sheet.

[0043] Example 3

[0044] In this example, a button battery is assembled using the sodium-ion battery electrode sheet prepared in Example 2. The specific steps are as follows: Assemble in the order of the positive electrode case, positive electrode sheet (sodium-ion battery electrode sheet), separator, sodium sheet, gasket, spring piece, and negative electrode case, drop 100 μL of electrolyte (EC:PC solution of 1.0 M NaClO4 + 5% FEC), prepare the button battery, and after standing for 12 hours, cyclic charge-discharge tests (voltage window 2.0 - 4.0 V) can be carried out.

[0045] Figure 4 Figures for the charge-discharge curves of NFM and NFM@3LLZAO at different rates. Regardless of the current density, NFM@3LLZAO has the best electrochemical performance.

[0046] After cycling 350 times at 1C, the capacity retention rates of each battery are shown in Table 1.

[0047] Table 1 Capacity retention rate

[0048] Figure 5 Figure for the charge-discharge curve of NFM@3LLZAO at 1C. It can be seen that the cyclic stability of the NFM material after being coated with LLZAO is effectively enhanced, and the dynamic compensation effect of lithium plays a certain role.

[0049] Example 4 After performing constant current charge-discharge tests on a Neware system, disassemble the battery and then perform EELS and SXAS tests. The specific steps are as follows: Set the charge-discharge program as follows: stand for 30 s, charge at 0.1C, stand for 30 s, discharge at 0.1C. When the number of cycles is less than 50, return to the first step to complete the cyclic charge-discharge test of the battery. After cycling 60 times, disassemble the battery, obtain the positive electrode, scrape off the powder, and after drying, EELS and SXAS tests can be carried out.

[0050] Figure 6It is the EELS comparison diagram of NFM@3LLZAO before and after cycling. Before cycling, there is no obvious shift in the K-edge of Li in NFM@3LLZAO from the surface to the interior. However, after cycling, there is an obvious shift in the K-edge of Li from the surface to the interior, indicating that the coordination environment of Li in the material has changed, indicating that Li has entered the layered oxide interior and participated in the cycle, that is, the dynamic compensation mechanism in the present invention is verified.

[0051] Figure 7 It is the SXAS comparison diagram of NFM and NFM@3LLZAO before and after cycling. After cycling, the characteristic peak intensity of NFM decreases significantly, indicating that the material has experienced the loss of lattice oxygen during the redox process, which may lead to structural collapse and electrochemical performance degradation. While NFM@3LLZAO coated with LLZAO shows relatively stable oxygen K-edge peak intensity after cycling, indicating that the LLZAO coating reduces the release rate of lattice oxygen, improves the surface stability of the cathode material, and reduces surface side reactions.

[0052] Comparative Example 1 This comparative example provides a LLZAO-coated layered transition metal oxide cathode material for sodium-ion batteries. The only difference in the preparation steps from Example 1 is: Replace NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 with NaNi 0.4 Fe 0.2 Mn 0.4 O2; to obtain NFM(424)@3LLZAO.

[0053] The capacity retention rate was tested according to the test method of Example 3 and was 76%.

[0054] Comparative Example 2 This comparative example provides a LLZAO-coated layered transition metal oxide cathode material for sodium-ion batteries. The only difference in the preparation steps from Example 1 is: Replace the coating material Li 6.25 La3Zr2Al 0.25 O2 with LaAlO3; to obtain NFM@LAO.

[0055] The capacity retention rate was tested according to the test method of Example 3 and was 72%.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A LLZAO-coated layered transition metal oxide cathode material for sodium-ion batteries, characterized in that, including NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 core and an LLZAO coating layer, where LLZAO represents Li 6.25 La3Zr2Al 0.25 O2; the mass percentage of the LLZAO coating layer in the cathode material is 1% - 10%.

2. The cathode material according to claim 1, wherein The mass percentage of the LLZAO coating layer in the positive electrode material is 1% to 5%.

3. The cathode material according to claim 1, characterized in that, The particle size of the positive electrode material is 0.5 to 3 μm.

4. The preparation method of the cathode material according to any one of claims 1 to 3, characterized in that, Comprising: Dissolve a lithium source, a lanthanum source, a zirconium source, and an aluminum source in a solvent, and then mix it with a NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 core solution. After evaporating the solvent, calcine to obtain it.

5. The preparation method according to claim 4, characterized in that, The lithium source is selected from at least one of lithium nitrate, lithium carbonate, lithium hydroxide, and lithium chloride; the lanthanum source is selected from at least one of lanthanum chloride, lanthanum nitrate, and lanthanum hydroxide; the zirconium source is selected from at least one of zirconium sulfate, zirconium acetate, zirconyl nitrate, and zirconium acetylacetonate; the aluminum source is selected from at least one of aluminum chloride and aluminum nitrate.

6. The preparation method according to claim 4, characterized in that, The solvent is an alcohol solvent; and / or, the temperature at which the solvent evaporates is 60°C to 90°C; and / or, the calcination temperature is 600°C to 900°C; and / or, the calcination time is 3 to 10 h.

7. A cathode slurry for a sodium-ion battery, characterized in that, It contains the positive electrode material described in any one of claims 1 to 3 or the positive electrode material prepared by the preparation method described in any one of claims 4 to 6.

8. The positive electrode paste of the sodium ion battery according to claim 7, characterized in that, Comprising an active substance, carbon nanotubes, and PVDF; the active substance is the positive electrode material described in any one of claims 1 to 3 or the positive electrode material prepared by the preparation method described in any one of claims 4 to 6.

9. A sodium-ion battery electrode sheet, characterized in that, It contains the positive electrode material described in any one of claims 1 to 3 or the positive electrode material prepared by the preparation method described in any one of claims 4 to 6.

10. A sodium-ion battery, characterized in that, It contains the sodium-ion battery electrode sheet described in claim 9.

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