Sodium-ion layered cathode material, preparation method and cathode sheet

Abstract

The application discloses a sodium-ion layered positive electrode material, a preparation method and a positive electrode sheet. + , H + , F ‑ of a lithium-ion battery core recovery liquid; a sodium source and the lithium-ion battery core recovery liquid are prepared into a solution; (2) a sodium-ion layered positive electrode material is mixed into the solution to prepare a mixed slurry; (3) the mixed slurry is subjected to suction filtration and drying to obtain a precursor powder; and (4) the precursor powder is sintered to obtain the sodium-ion layered positive electrode material. The application overcomes the defects of poor cycle performance and unstable surface of the sodium-ion layered positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of cathode materials, specifically to a sodium ion layered cathode material, its preparation method, and a cathode sheet. Background Technology

[0002] Lithium-ion batteries are widely used in digital devices, new energy vehicles, and energy storage power stations. The global exploitability of lithium, nickel, and cobalt resources affects the price of raw materials for lithium-ion batteries, such as lithium carbonate, nickel sulfate, and cobalt sulfate. Secondly, as battery cells gradually reach the retirement standard of SOH ≤ 80%, the new energy industry faces a pressing issue: the cascade utilization of retired lithium-ion battery cells and the recycling of metal resources. Sodium-ion batteries, compared to lithium-ion batteries, offer advantages such as lower SOx levels (Na₂O₅). + With a wider distribution, lower mining difficulty, and greater cost advantage, it has attracted widespread attention from the new energy industry, such as polyanionic compounds, Prussian blue analogs, and layered oxides.

[0003] Based on different anionic groups, polyanionic compounds can be classified into the following categories: phosphates, pyrophosphates, sulfates, and silicates. Mixed-type polyanionic compounds have gained increasing attention due to their adjustable operating voltage and superior electrochemical performance. However, mixed-type polyanionic compounds suffer from problems such as low electronic conductivity, low specific capacity, low tap density, and low cycle life.

[0004] Prussian blue analogues are another promising cathode material. Based on defects, the content of water of crystallization and alkali metal ions, and the preparation conditions, sodium-based Prussian blue analogues can be classified into monoclinic, trigonal, cubic, and tetragonal structures. Defects in the preparation process of Prussian blue analogues are difficult to control, and bound water is difficult to remove, resulting in poor cycle performance and safety. Furthermore, they suffer from low tap density, leading to low volumetric energy density. Additionally, the release of cyanide at high temperatures poses a safety hazard. In conclusion, while Prussian blue analogues have promising applications, they still have a long way to go before practical commercialization.

[0005] Layered oxides (Na) x TMO2 (0≤x≤1, TM represents transition metal) is considered one of the most promising cathode materials due to its compact crystal structure, high specific capacity, high operating voltage, high energy density, tunable composition, ease of preparation, and large-scale production capability. It also features low Na+ content. + P-type Na with diffusion barrier x TMO2 exhibits relatively better cycling stability and rate performance, while the initial state contains more Na. + O type Na xTMO2 can provide higher theoretical capacity, but both types of sodium ion layered cathode materials have defects such as poor cycle performance and surface instability. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides a sodium-ion layered cathode material, a preparation method, and a cathode sheet, overcoming the defects of poor cycle performance and surface instability in sodium-ion layered cathode materials.

[0007] In a first aspect of the present invention, a method for preparing a sodium ion layered cathode material is provided, comprising the following steps:

[0008] (1) Provide Li + H + F - Lithium-ion battery cell recycling solution;

[0009] The sodium source and the lithium-ion battery cell recycling solution are prepared into a solution;

[0010] (2) The sodium-ion layered cathode material is mixed into the solution to prepare a mixed slurry;

[0011] (3) The mixed slurry is filtered and dried to obtain precursor powder;

[0012] (4) The precursor powder is sintered to obtain a sodium-ion layered cathode material. In a first aspect of the invention, lithium-ion battery cell recycling liquid is used as a raw material, which contains Li... + H + F - The acidic system, after being mixed with a sodium source, is combined with a sodium-based layered cathode material to form a slurry, enabling Li... + H + F - And Na + Attached to the sodium-ion battery layered cathode material, it is modified by doping during the subsequent sintering process. Specifically, H + To reduce the residual alkali content (NaOH, Na2CO3) on the surface of sodium ion layered cathode materials, one approach is to react with the residual alkali on the surface, thereby reducing it; another approach is to reduce the residual alkali content through cation exchange (H+). + / Li + with Na + Exchange, construct Na + Gradient structure; anion-modified F - Replace O 2- Simultaneously modulate the surface Li + / Na + The proportion improves structural stability, and part of F - Replace O 2-This causes some transition metal layer atoms to change from an ordered arrangement to a disordered arrangement, increasing the oxygen content in the material. 2- / O n- Stability and electrochemical activity, thereby improving capacity and capacity retention; while Li + Embedded in sodium ion layered cathode material to improve Na + Migration pathways enhance material stability and electrochemical performance.

[0013] According to an embodiment of the present invention, step (1), the sintering process includes: heating to 200℃~400℃ for a first-stage holding, then heating to 600℃~900℃ for a second-stage holding, followed by furnace cooling. This sintering process is carried out in two steps: ① the low-temperature sintering step mainly removes moisture to prepare for the next high-temperature sintering step; ② the high-temperature sintering step mainly promotes the migration of lithium ions to Na+. + Site, F - Replace O 2- Site.

[0014] According to an embodiment of the present invention, in step (1), the sintering atmosphere is compressed air. During the furnace cooling process, the compressed air is switched to an inert gas protective atmosphere to avoid the formation of alkali on the surface of the sodium ion layered cathode material during the cooling process. This prevents the surface of the sodium ion layered cathode material from contacting water and carbon dioxide in the air during the cooling process, thus avoiding an increase in surface alkali content.

[0015] According to an embodiment of the present invention, in step (4), the compressed air is switched to an inert gas protective atmosphere at a temperature below 200°C. This further reduces the residual alkali content on the surface of the cathode material.

[0016] Furthermore, in step (4), the inert gas protective atmosphere includes at least one of nitrogen and argon.

[0017] According to an embodiment of the present invention, in step (4), the heat preservation time of the first stage is 2h to 5h.

[0018] According to an embodiment of the present invention, the heat preservation time of the second stage is 5h to 8h.

[0019] According to an embodiment of the present invention, in step (1), the lithium-ion battery cell recycling solution further includes Na. + PO4 3- At least one of them.

[0020] According to an embodiment of the present invention, in step (1), the pH of the solution is 4 to 6. This provides sufficient H₂. + It participates in regulation to further reduce the residual alkali content on the surface of the cathode material.

[0021] According to an embodiment of the present invention, in step (2), the sodium-ion layered cathode material includes Na x TMO2, 0 < x ≤ 1. Wherein, TM is one or more of Ni, Fe, Mn, Cu, Mg, Zn, Sn, and Zr. Therefore, Li + The P2-O3 composite structure is constructed by embedding a TM layer and a Na layer of sodium ion-layered material, thereby improving the material's stability and electrochemical performance.

[0022] According to an embodiment of the present invention, in step (2), the solid content of the slurry is 50wt% to 80wt%. This further improves the production efficiency of sodium-ion layered cathode materials.

[0023] In a second aspect, the present invention provides a sodium-ion layered cathode material prepared according to the preparation method of the first aspect. Thus, the sodium-ion layered cathode material is doped with Li. + H + F - , specifically, H + To reduce the residual alkali content (NaOH, Na2CO3) on the surface of sodium ion layered cathode materials, F - Replace O 2- This causes some atoms in the transition metal layer to change from an ordered arrangement to a disordered arrangement, improving capacity and capacity retention; Li + Embedded in sodium-ion layered cathode materials, improving interlayer spacing and Na + While improving mobility, it also enhances material stability and electrochemical performance.

[0024] A third aspect of the present invention provides a positive electrode sheet comprising the sodium ion layered positive electrode material described in the second aspect. This results in good discharge capacity and capacity retention.

[0025] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0026] The following examples are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] In a first aspect of the present invention, a method for preparing a sodium ion layered cathode material is provided, comprising the following steps:

[0028] (1) Provide Li + H + F - Lithium-ion battery cell recycling solution;

[0029] Optionally, the lithium-ion battery cell recycling solution further includes Na. + PO4 3- At least one of them;

[0030] A solution is prepared by combining the sodium source and the lithium-ion battery cell recovery solution; thereby reducing the amount of sodium. + Excessive precipitation.

[0031] As an example, the sodium source includes at least one of sodium carbonate and sodium hydroxide.

[0032] Preferably, the pH of the prepared solution is 4–6. This provides sufficient H₂. + It participates in regulation to further reduce the residual alkali content on the surface of the cathode material.

[0033] (2) The sodium-ion layered cathode material is mixed into the solution to prepare a mixed slurry;

[0034] In some embodiments, the sodium-ion layered cathode material includes Na x TMO2, 0 < x ≤ 1. Wherein, TM is one or more of Ni, Fe, Mn, Cu, Mg, Zn, Sn, and Zr. Therefore, Li can be... + The P2-O3 composite structure is constructed by embedding a TM layer and a Na layer of sodium ion-layered material, thereby improving the material's stability and electrochemical performance.

[0035] In some embodiments, a slurry is prepared by stirring, for example, the stirring speed can be 600 rpm to 1000 rpm, and the stirring time can be 30 min to 60 min.

[0036] In some embodiments, the solid content of the slurry is 50 wt% to 80 wt%, for example, 50%, 60%, 70%, 80%, etc. This further improves the production efficiency of sodium-ion layered cathode materials.

[0037] (3) The mixed slurry is filtered and dried to obtain precursor powder;

[0038] In some embodiments, drying can be performed in a vacuum oven.

[0039] (4) The precursor powder is sintered to obtain a sodium ion layered cathode material;

[0040] In some embodiments, the sintering process includes: heating to 200°C to 400°C, for example, heating to 200°C, 300°C, 400°C, etc., for a first stage of heat preservation, then heating to 600°C to 900°C, for example, heating to 600°C, 700°C, 800°C, 900°C, etc., for a second stage of heat preservation, followed by furnace cooling;

[0041] The sintering atmosphere is compressed air. During furnace cooling, the compressed air is switched to an inert gas protective atmosphere to prevent the formation of alkali on the surface of the sodium ion layered cathode material during cooling. Further, the inert gas protective atmosphere includes at least one of nitrogen and argon.

[0042] It is understandable that compressed air simply pressurizes air, reducing its volume, without producing any liquid substances.

[0043] In some embodiments, the heat preservation time of the first stage is 2h to 5h, for example, 2h, 3h, 4h, 5h, etc.

[0044] In some embodiments, the insulation duration of the second stage is 5h to 8h, for example, 5h, 6h, 7h, 8h, etc.

[0045] In some embodiments, the compressed air is switched to an inert gas protective atmosphere below 200°C. This further reduces the residual alkali content on the surface of the cathode material. Preferably, the compressed air is switched to an inert gas protective atmosphere between 180°C and 100°C.

[0046] In a first aspect, the present invention utilizes lithium-ion battery cell recycling liquid as a raw material, which contains Li + H + F - The acidic system, after being mixed with a sodium source, is combined with a sodium-based layered cathode material to form a slurry, enabling Li... + H + F - And Na + It adheres to the sodium-ion battery layered cathode material, and during the subsequent sintering process, it is modified by doping into the sodium-ion battery layered cathode material. Specifically, H + Reduce the residual alkali content (NaOH, Na2CO3) on the surface of the sodium ion layered cathode material, while simultaneously regulating the surface Li + / Na + The proportion improves structural stability, and part of F - Replace O 2- This causes some transition metal layer atoms to change from an ordered arrangement to a disordered arrangement, increasing the oxygen content in the material. 2- / O n-2 Stability and electrochemical activity, thereby improving capacity and capacity retention; while Li + Embedded in sodium-ion layered cathode materials, it improves the interlayer spacing and Na... + While improving mobility, it also enhances material stability and electrochemical performance.

[0047] In a second aspect, the present invention provides a sodium-ion layered cathode material prepared according to the preparation method of the first aspect. Thus, the sodium-ion layered cathode material is doped with Li.+ H + F - , specifically, H + To reduce the residual alkali content (NaOH, Na2CO3) on the surface of sodium ion layered cathode materials, F - Replace O 2- This causes some atoms in the transition metal layer to change from an ordered arrangement to a disordered arrangement, improving capacity and capacity retention; Li + Embedded in sodium-ion layered cathode materials, improving interlayer spacing and Na + While improving mobility, it also enhances material stability and electrochemical performance.

[0048] A third aspect of the present invention provides a positive electrode sheet comprising the sodium ion layered positive electrode material described in the second aspect. This results in good discharge capacity and capacity retention.

[0049] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0050] Example 1

[0051] 1. Provide products containing Li + H + F - Lithium-ion battery cell recycling solution, in which Li + The concentration is 0.1 mol / L, H + The concentration is 0.5 mol / L, F - The lithium-ion battery cell recycling solution with a concentration of 0.05 mol / L was prepared into a sodium carbonate solution with a pH of 4 and a sodium carbonate concentration of 2 mol / L.

[0052] 2. Sodium-ion battery layered cathode material Na 0.5 NiO2 was added to the solution prepared in step 1 and stirred at 600 rpm for 30 min to obtain a mixed slurry with a solid content of 50%.

[0053] 3. The mixed slurry is filtered and vacuum dried to obtain precursor powder;

[0054] 4. The precursor powder was placed in a muffle furnace for sintering. The temperature was raised from room temperature to 200°C and held for 3 hours. Then the temperature was raised to 600°C and held for 5 hours. The furnace was then cooled. The sintering atmosphere was compressed air. When the furnace cooled to 200°C, the atmosphere inside the furnace was switched from compressed air to nitrogen. The furnace was then cooled to room temperature to obtain sodium ion layered cathode material.

[0055] Example 2

[0056] 1. Prepare a solution with a pH of 5 by mixing sodium carbonate with lithium-ion battery cell recycling liquid;

[0057] 2. Add the sodium-ion layered cathode material to the solution prepared in step 1, and stir at 800 rpm for 40 min to obtain a mixed slurry with a solid content of 60%.

[0058] 3. The mixed slurry is filtered and vacuum dried to obtain precursor powder;

[0059] 4. The precursor powder obtained in step 3 is placed in a muffle furnace for sintering. The temperature is raised from room temperature to 300°C and held for 5 hours. Then the temperature is raised to 700°C and held for 5 hours. The furnace is then cooled. The sintering atmosphere is compressed air. When the furnace is cooled to 200°C, the atmosphere inside the furnace is switched from compressed air to nitrogen. The furnace is then cooled to room temperature to obtain sodium ion layered cathode material.

[0060] Example 3

[0061] 1. Prepare a solution with a pH of 6 by mixing sodium carbonate with lithium-ion battery cell recycling solution containing anions and cations;

[0062] 2. Add the sodium-ion layered cathode material to the solution A3 prepared in step 1, and stir at 1000 rpm for 30 min to obtain a mixed slurry with a solid content of 80%.

[0063] 3. The above mixed slurry is filtered and vacuum dried to obtain precursor powder;

[0064] 4. The precursor powder was placed in a muffle furnace for sintering. The temperature was raised from room temperature to 300°C and held for 5 hours. Then the temperature was raised to 800°C and held for 5 hours. The furnace was then cooled. The sintering atmosphere was compressed air. When the furnace cooled to 200°C, the atmosphere inside the furnace was switched from compressed air to nitrogen. The furnace was then cooled to room temperature to obtain sodium ion layered cathode material.

[0065] Comparative Example 1

[0066] The sodium-ion layered cathode material from Example 1 was used directly as the product.

[0067] Comparative Example 2

[0068] The rest is the same as in Example 1, except that when the temperature is reduced to 200°C, the gas atmosphere inside the muffle furnace is kept as compressed air to obtain sodium ion layered cathode material.

[0069] Comparative Example 3

[0070] Using the sodium-ion layered cathode material from Example 1 as a precursor, and following steps 3 and 4 of Example 1, a sodium-ion layered cathode material was obtained.

[0071] The above embodiments and comparative examples were subjected to button cell testing and performance characterization:

[0072] The method for testing residual sodium in the cathode material is as follows: Weigh 10.000±0.050g of powder, disperse it in 100g of deionized water, stir thoroughly for 10min, and filter using filter paper to obtain a clear aqueous solution containing dissolved NaOH and Na2CO3; prepare a 0.1M HCl solution using concentrated hydrochloric acid. Use 0.1M HCl as the titrant, and MR and BTB as indicators, and perform titration on a potentiometric titrator. Determine the amount of HCl consumed based on the indicator or potential change, and record the corresponding volume. Calculate the content of NaOH and Na2CO3 based on the volume of HCl consumed.

[0073] The button cell test is as follows: Button cell assembly and testing include: mixing and grinding the prepared positive electrode material, conductive carbon black SP, and polyvinylidene fluoride (PVDF) in a 90:5:5 ratio until uniform, coating it onto aluminum foil as the positive electrode, using a sodium metal sheet as the negative electrode, a microporous polypropylene membrane as the separator, and a 1 mol / L sodium hexafluorophosphate solution as the electrolyte. The cells are assembled into a button cell in the following order: positive electrode shell, positive electrode, separator, negative electrode, and negative electrode shell. The test procedure is as follows: The discharge capacity at 0.1C was measured. The discharge capacity (mAh / g) at 0.1C, 0.5C, and 5C, as well as the capacity retention rate (%) after 100 cycles at 1C, were tested. The test results are shown in Table 1.

[0074] Table 1

[0075]

[0076] The results are shown in Table 1. As can be seen from the data in Table 1, compared with Comparative Examples 1-3, Examples 1-3, through Li... + F - PO4 3- Surface modification and heat treatment processes effectively improve the electrochemical performance and structural stability of sodium ion layered cathode materials. Specifically, the residual alkali (NaOH, Na2CO3) on the surface of the sodium ion layered cathode materials in Examples 1-3 is significantly reduced, and the discharge capacity (mAh / g) at 0.1C, 0.5C, and 5C, as well as the capacity retention rate after 100 cycles at 1C, are all improved to varying degrees compared with Comparative Examples 1-3.

[0077] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0078] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a sodium-ion layered cathode material, characterized in that, The method comprises the following steps: (1) providing a lithium ion cell recovery solution containing Li + , H + , F - ; a sodium source and the lithium-ion battery cell recovery liquid are prepared into a solution; (2) the sodium battery layered positive electrode material is mixed into the solution to prepare a mixed slurry; (3) the mixed slurry is subjected to suction filtration and drying to obtain a precursor powder; (4) the precursor powder is sintered to obtain a sodium-ion layered positive electrode material; In step (2), the sodium electro-layered cathode material comprises Na x TMO2, 0 < x < 1; wherein the TM is one or more of Ni, Fe, Mn, Cu, Mg, Zn, Sn, and Zr; the solid content of the slurry is 50wt%-80wt%; in step (4), the sintering comprises: heating to 200-400℃, performing first-stage heat preservation, then heating to 600-900℃, performing second-stage heat preservation, and then furnace cooling; the sintering atmosphere is compressed air, and during the furnace cooling process, the compressed air is switched to an inert gas protective atmosphere to avoid the generation of alkali on the surface of the sodium-ion layered positive electrode material during the cooling process; in step (4), the compressed air is switched to the inert gas protective atmosphere below 200℃.

2. The method of claim 1, wherein the sodium-ion layered cathode material is represented by the formula: NaM1M2O2, wherein M1 and M2 are transition metals. in step (4), the inert gas comprises at least one of nitrogen and argon.

3. The method of claim 1, wherein the sodium-ion layered cathode material is represented by the formula: NaM1M2O2, wherein M1 and M2 are transition metals. in step (4), the heat preservation time of the first-stage heat preservation is 2-5h; and / or, the heat preservation time of the second-stage heat preservation is 5-8h.

4. The method of claim 1, wherein the sodium-ion layered cathode material is represented by the formula: NaMnM'X2, wherein M and M' are transition metals, and X is a halogen element. In step (1), the lithium-ion battery cell recovery solution further comprises at least one of Na + , PO4 3- , and / or the pH of the solution is 4-6.

5. A sodium-ion layered cathode material, characterized in that, prepared according to any one of claims 1-4.

6. A positive electrode sheet characterized by comprising: the sodium-ion layered positive electrode material of claim 5.

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