Positive electrode material of sodium-ion battery, and preparation method therefor and use thereof

Abstract

A positive electrode material of a sodium-ion battery, and a preparation method therefor and the use thereof. The preparation method comprises the following steps: (1) mixing a modifier with a positive electrode precursor of a sodium-ion battery, and subjecting the resulting mixture to a first-step calcination treatment, so as to obtain a modified precursor; and (2) mixing the modified precursor with a sodium source, subjecting the resulting mixture to a second-step calcination treatment, so as to obtain a positive electrode material of a sodium-ion battery, wherein the modifier is decomposed in the first-step calcination treatment to generate an acidic gas. Residual alkali on a surface of a positive electrode material of a sodium battery can be reduced by using a simple, convenient and inexpensive method. During the calcination preparation process of the positive electrode material of a sodium battery, the residual alkali is directly reduced; therefore, the residual alkali on the surface of the material is reduced, the subsequent processes of washing, drying, regrinding and rescreening can be omitted, and the loss of sodium ions during the washing process is avoided.

Description

A sodium ion battery positive electrode material and its preparation method and application Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, for example, a sodium ion battery positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have been successfully commercialized. As the demand for batteries in electronic products increases, the demand for lithium resources has also increased accordingly. The growing demand for lithium and the scarcity of lithium resource reserves have caused people to worry about the sustainable application of lithium-ion batteries in the future. In contrast, sodium resources in nature are abundant and widely distributed. The battery cost is lower than that of lithium-ion batteries. They have a wider temperature operability and similar lithium intercalation chemical reactions. They have great potential for application in large-scale energy storage in the future. Sodium-ion batteries are generally considered to be the future alternative to lithium-ion batteries. At present, there is an urgent need to develop high-performance sodium cathode materials.

[0003] The residual alkali in sodium-ion battery cathode materials consists of Na₂CO₃ and NaOH, produced by side reactions with residual sodium sources during the calcination process. During subsequent use, excessive residual alkali can easily lead to a jelly-like slurry when the cathode material is homogenized, compromising homogenization and coating performance. In finished batteries, residual alkali can easily react with the electrolyte, shortening battery life. If residual alkali on the surface of the material is not controlled, the pH of the sodium-ion battery cathode material can reach around 13.

[0004] CN115995560A discloses a method and application for reducing residual alkali on the surface of a sodium ion battery positive electrode material. The sodium ion battery positive electrode material is prepared by a solid phase method or a liquid phase method; alcohols, acids and the sodium ion battery positive electrode material are uniformly mixed in a certain mass ratio, allowed to stand, and then filtered and dried.

[0005] CN108807969A discloses a method for reducing residual alkali on the surface of a layered positive electrode material for a lithium-ion battery, comprising the following steps: S1, adding pure water to a nickel-cobalt-manganese layered positive electrode material, stirring and washing, to obtain a wet material; S2, mixing the wet material with ethanol, stirring, filtering, and drying to obtain a powder; S3, mixing the powder with a nano-oxide, and then sintering the powder.

[0006] Although the washing process described in the above scheme can reduce residual alkali, direct washing of the sodium battery positive electrode material will cause sodium ions to dissolve and lose, causing damage to the crystal structure of the material and significantly reducing the discharge capacity of the material.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] This application provides a sodium-ion battery cathode material, its preparation method, and its application. This application utilizes a simple and inexpensive method to reduce residual alkali on the surface of the sodium-ion battery cathode material. By directly reducing the residual alkali on the surface of the material during the calcination preparation process of the sodium-ion battery cathode material, the subsequent washing, drying, re-grinding, and re-screening processes can be eliminated, thereby preventing the loss of sodium ions during the washing process.

[0010] In a first aspect, the present application provides a method for preparing a positive electrode material for a sodium ion battery, the preparation method comprising the following steps:

[0011] (1) mixing a modifier and a sodium ion battery cathode precursor, and performing a one-step calcination treatment to obtain a modified precursor;

[0012] (2) mixing the modified precursor and a sodium source, and performing a two-step calcination treatment to obtain the sodium ion battery positive electrode material;

[0013] The modifier decomposes to generate acidic gas during the one-step calcination process.

[0014] This application reduces residual alkali by mixing a modifier that can decompose to produce acidic gas, a sodium ion battery positive electrode material precursor, and a sodium source and calcining them at high temperature. These modifiers decompose to produce acidic gas during calcination, which partially etches the surface of the precursor. During the subsequent high-temperature calcination process, the sodium source can more easily enter the interior of the precursor through the etched points, achieving the purpose of a full fusion reaction, promoting the migration of the sodium source into the interior of the precursor, and thus reducing the residual sodium on the surface of the material.

[0015] In one embodiment, the mass ratio of the modifier in step (1) to the sodium ion battery positive electrode precursor is (1-5):100, for example: 1:100, 2:100, 3:100, 4:100 or 5:100, etc.

[0016] In one embodiment, the sodium ion battery cathode precursor includes Ni a Mn b A 1-a-b (OH)2, 0<a<1, 0<b<1, A includes any one of Co, Cu, Ti, Mo, Zr, Nb or Fe or a combination of at least two thereof.

[0017] In one embodiment, the modifier in step (1) includes any one of sodium sulfite, sodium nitrite, ammonium chloride or ethylenediaminetetraacetic acid, or a combination of at least two thereof.

[0018] In one embodiment, the atmosphere for the one-step calcination treatment in step (1) comprises air and / or oxygen.

[0019] In one embodiment, the temperature of the one-step calcination treatment in step (1) is 450-550°C, for example, 450°C, 480°C, 500°C, 520°C or 550°C.

[0020] In one embodiment, the one-step calcination treatment lasts for 2 to 5 hours, for example, 2 hours, 2.5 hours, 3 hours, 4 hours, or 5 hours.

[0021] In one embodiment, the sodium source in step (2) comprises sodium hydroxide and / or sodium carbonate.

[0022] In one embodiment, the molar ratio of the sodium element in the sodium source to the metal element in the modified precursor is (0.6-1):1, for example: 0.6:1, 0.7:1, 0.8:1, 0.9:1 or 1:1.

[0023] In one embodiment, the atmosphere of the two-step calcination treatment in step (2) includes air and / or oxygen.

[0024] In one embodiment, the temperature of the second-step calcination treatment in step (2) is 650-1000°C, for example, 650°C, 750°C, 800°C, 900°C or 1000°C.

[0025] The temperature of the two-step calcination described in the present application depends on the type of sodium source. When sodium carbonate is used as the sodium source, the temperature of the two-step calcination treatment needs to reach 800-1000°C. When sodium hydroxide is used as the sodium source, the temperature of the two-step calcination treatment is about 700°C. After the sodium source is melted, it can more easily enter the interior of the precursor particles through the etched position, so that the precursor and the sodium source are more evenly fused, and there are more reaction sites. After maintaining it at a further high temperature for several hours, the solid-state reaction can be fully carried out, thereby reducing the residual alkali.

[0026] In one embodiment, the two-step calcination treatment lasts for 8 to 15 hours, for example, 8 hours, 9 hours, 10 hours, 12 hours, or 15 hours.

[0027] In a second aspect, the present application provides a sodium ion battery positive electrode material, which is prepared by the method described in the first aspect.

[0028] In a third aspect, the present application provides a positive electrode plate, which comprises the sodium ion battery positive electrode material as described in the second aspect.

[0029] In a fourth aspect, the present application provides a sodium ion battery, which comprises the positive electrode sheet as described in the third aspect.

[0030] Compared with the related art, this application has the following beneficial effects:

[0031] (1) The method described in the present application can reduce the residual alkali on the surface of the positive electrode material of the sodium ion battery without water washing: salt modifiers such as sodium sulfite can decompose at high temperature to produce acidic gas. Under high temperature conditions, the acidic gas can pre-react with the hydroxide precursor and slightly etch the surface of the precursor, and the surface structure of the precursor after etching changes.

[0032] (2) After the modified precursor described in the present application is mixed with the sodium source, the sodium source can more easily enter the interior of the precursor particles through the etched position, so that the precursor and the sodium source are more evenly fused and there are more reaction sites. After further maintaining it at a high temperature for several hours, the solid-state reaction can be fully carried out, and ultimately the residual alkali amount is reduced.

[0033] (3) The residual alkali content of the sodium ion battery positive electrode material prepared by the method described in this application can reach less than 1.82%, and the capacity of the battery can reach more than 112.2 mAh / g after 100 cycles, and the capacity retention rate after 100 cycles can reach more than 90.7%.

[0034] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0035] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0036] The positive electrode precursors of the sodium ion batteries used in the examples and comparative examples of this application are all Ni 0.3 Mn 0.35 Fe 0.35 (OH)2.

[0037] Example 1

[0038] This embodiment provides a sodium ion battery positive electrode material, and the preparation method of the sodium ion battery positive electrode material is as follows:

[0039] (1) Sodium sulfite and a sodium ion battery cathode precursor were mixed in a mass ratio of 3:100, and calcined at 500°C for 4 hours in air to obtain a modified precursor;

[0040] (2) The modified precursor and sodium carbonate were mixed according to Na / M=0.8:1, and calcined at 900° C. for 10 h in air to obtain the sodium ion battery positive electrode material.

[0041] Example 2

[0042] This embodiment provides a sodium ion battery positive electrode material, and the preparation method of the sodium ion battery positive electrode material is as follows:

[0043] (1) Sodium nitrite and a sodium ion battery cathode precursor were mixed in a mass ratio of 5:100, and calcined at 450° C. for 5 h in air to obtain a modified precursor;

[0044] (2) The modified precursor and sodium hydroxide are mixed according to Na / M=1:1, and calcined at 700° C. for 8 h in air to obtain the sodium ion battery positive electrode material.

[0045] Example 3

[0046] This embodiment provides a sodium ion battery positive electrode material, and the preparation method of the sodium ion battery positive electrode material is as follows:

[0047] (1) ammonium chloride and a sodium ion battery cathode precursor were mixed in a mass ratio of 5:100, and calcined at 500°C for 4 hours in air to obtain a modified precursor;

[0048] (2) The modified precursor and sodium carbonate were mixed according to Na / M=0.6:1, and calcined at 920° C. for 10 h in air to obtain the sodium ion battery positive electrode material.

[0049] Example 4

[0050] This embodiment provides a sodium ion battery positive electrode material, and the preparation method of the sodium ion battery positive electrode material is as follows:

[0051] (1) Ethylenediaminetetraacetic acid and a sodium ion battery cathode precursor were mixed in a mass ratio of 1:100 and calcined at 550°C for 4 h in air to obtain a modified precursor;

[0052] (2) The modified precursor and sodium carbonate were mixed according to Na / M=0.8:1, and calcined at 900° C. for 10 h in air to obtain the sodium ion battery positive electrode material.

[0053] Example 5

[0054] This embodiment provides a sodium ion battery positive electrode material, and the preparation method of the sodium ion battery positive electrode material is as follows:

[0055] (1) Sodium sulfite and a sodium ion battery cathode precursor were mixed in a mass ratio of 0.5:100, and calcined at 500°C for 4 hours in air to obtain a modified precursor;

[0056] (2) The modified precursor and sodium carbonate were mixed according to Na / M=0.8:1, and calcined at 900° C. for 10 h in air to obtain the sodium ion battery positive electrode material.

[0057] Example 6

[0058] This embodiment provides a sodium ion battery positive electrode material, and the preparation method of the sodium ion battery positive electrode material is as follows:

[0059] (1) Sodium sulfite and a sodium ion battery cathode precursor were mixed in a mass ratio of 10:100, and calcined at 500°C for 4 hours in air to obtain a modified precursor;

[0060] (2) The modified precursor and sodium carbonate were mixed according to Na / M=0.8:1, and calcined at 900° C. for 10 h in air to obtain the sodium ion battery positive electrode material.

[0061] Example 7

[0062] This embodiment provides a sodium ion battery positive electrode material, and the preparation method of the sodium ion battery positive electrode material is as follows:

[0063] (1) Sodium sulfite and a sodium ion battery cathode precursor were mixed in a mass ratio of 3:100, and calcined at 400°C for 4 hours in air to obtain a modified precursor;

[0064] (2) The modified precursor and sodium carbonate were mixed according to Na / M=0.8:1, and calcined at 900° C. for 10 h in air to obtain the sodium ion battery positive electrode material.

[0065] Example 8

[0066] This embodiment provides a sodium ion battery positive electrode material, and the preparation method of the sodium ion battery positive electrode material is as follows:

[0067] (1) Sodium sulfite and a sodium ion battery cathode precursor were mixed in a mass ratio of 3:100, and calcined at 600°C for 4 hours in air to obtain a modified precursor;

[0068] (2) The modified precursor and sodium carbonate were mixed according to Na / M=0.8:1, and calcined at 900° C. for 10 h in air to obtain the sodium ion battery positive electrode material.

[0069] Comparative Example 1

[0070] The only difference between this comparative example and Example 1 is that sodium sulfite is not added, and other conditions and parameters are exactly the same as those in Example 1.

[0071] Comparative Example 2

[0072] The only difference between this comparative example and Example 1 is that sodium sulfite is replaced with sodium carbonate (releasing less acidic carbon dioxide), and other conditions and parameters are exactly the same as those in Example 1.

[0073] Performance testing:

[0074] Residual Alkali Test: Weigh the positive electrode materials prepared in the Examples and Comparative Examples and place them in an Erlenmeyer flask. Add 50 ml of CO2-free water and a rotor. Stir for 30 minutes using a stirrer. After stirring, pour the slurry into a funnel and vacuum filter. Rinse the remaining solids in the Erlenmeyer flask with 100 ml of CO2-free water in multiple batches. Pour the slurry into a funnel and filter to obtain a filtrate. Titrate the filtrate with HCl standard solution using an automatic titrator. Calculate the residual alkalinity value of the sample based on the hydrochloric acid consumption.

[0075] Electrochemical performance testing: Samples were weighed according to the layered cathode material ratio of SP:PVDF = 8:1:1. A mixed slurry was prepared using NMP as the solvent. The slurry was coated on aluminum foil, dried in an oven, and cut into positive electrode sheets. Coin-type cells were assembled using a sodium metal sheet as the negative electrode, glass fiber as the separator, and 1MNaPF6 (EC:DMC:EMC = 1:1:1 Vol%) as the electrolyte. Charge and discharge tests were conducted over a voltage range of 2.0-4.0V, with activation cycles at a 0.1C rate for two cycles and charge and discharge tests at a 0.5C rate for 100 cycles. The test results are shown in Table 1.

[0076] Table 1

[0077] As can be seen from Table 1, according to Examples 1-4, the residual alkali content of the sodium ion battery positive electrode material prepared by the method described in the present application can reach less than 1.82%, and the capacity of the battery can reach 112.2 mAh / g or more after 100 cycles (Example 3 has low sodium content and low capacity, but the cycle performance is still good. By appropriately adjusting the sodium content, the properties of the positive electrode material will be greatly improved), and the capacity retention rate after 100 cycles can reach more than 90.7%.

[0078] By comparison of Example 1 and Examples 5-6, it can be seen that during the preparation process of the sodium ion positive electrode material described in the present application, the amount of modifier added will affect its performance. The mass ratio of the modifier to the sodium ion battery positive electrode precursor is controlled at (1 to 5): 100, and the performance of the sodium ion positive electrode material obtained is better. If the amount of modifier added is too low, the amount of acidic gas generated by decomposition is insufficient to deeply etch the surface of the precursor. If the amount of modifier added is too high, there may be undecomposed additives that cover the surface of the precursor, resulting in a decrease in the miscibility of the subsequent precursor with the sodium source.

[0079] By comparing Example 1 with Examples 7-8, it can be seen that during the preparation process of the sodium ion positive electrode material described in the present application, the temperature of the one-step calcination affects its performance. When the temperature of the one-step calcination is controlled at 450-550°C, the performance of the prepared sodium ion positive electrode material is better. If the temperature of the one-step calcination is too low, the decomposition rate of the additive is slow or incomplete. If the temperature of the one-step calcination is too high, the decomposition rate of the additive is too fast, and the reaction time of the acidic gas and the precursor is shortened.

[0080] By comparing Example 1 and Comparative Example 1, it can be seen that the present application uses a modifier to modify the precursor, which can decompose at high temperature to produce acidic gas. Under high temperature conditions, the acidic gas can pre-react with the hydroxide precursor, slightly etching the surface of the precursor, and the surface structure of the precursor after etching changes. In the subsequent further calcination, the molten Na2CO3 can more easily enter the interior of the precursor particles through the etched position, making the fusion of the precursor and the sodium source more uniform, and there are more reaction sites. After further maintaining at high temperature for several hours, the solid-state reaction can be fully carried out, and ultimately the residual alkali is reduced.

[0081] From the comparison between Example 1 and Comparative Example 2, it can be seen that the selection of the modifier described in the present application is particularly important. If the acid gas generated by the decomposition of the modifier is not acidic enough, the precursor cannot be effectively etched, and thus the technical effect of the present application cannot be achieved.

[0082] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A method for preparing a positive electrode material for a sodium ion battery, comprising the following steps: (1) mixing a modifier and a sodium ion battery positive electrode precursor, and performing a one-step calcination treatment to obtain a modified precursor; (2) mixing the modified precursor and the sodium source, and subjecting the mixture to a two-step calcination treatment to obtain the sodium ion battery positive electrode material; The modifier is decomposed to generate acidic gas during the one-step calcination process.

2. The preparation method according to claim 1, wherein The mass ratio of the modifier and the sodium ion battery positive electrode precursor in step (1) is (1-5):

100.

3. The preparation method according to claim 1 or 2, wherein: The sodium ion battery positive electrode precursor includes Ni a Mn b A 1-a-b (OH)2, 0<a<1, 0<b<1, A includes any one of Co, Cu, Ti, Mo, Zr, Nb or Fe or a combination of at least two thereof.

4. The preparation method according to any one of claims 1 to 3, wherein The modifier in step (1) includes any one of sodium sulfite, sodium nitrite, ammonium chloride or ethylenediaminetetraacetic acid, or a combination of at least two thereof.

5. The preparation method according to any one of claims 1 to 4, wherein: The atmosphere for the one-step calcination treatment in step (1) includes air and / or oxygen.

6. The preparation method according to any one of claims 1 to 5, wherein: The temperature of the one-step calcination treatment is 450-550°C.

7. The preparation method according to any one of claims 1 to 6, wherein: The one-step calcination treatment takes 2 to 5 hours.

8. The preparation method according to any one of claims 1 to 7, wherein: The sodium source in step (2) includes sodium hydroxide and / or sodium carbonate.

9. The preparation method according to any one of claims 1 to 8, wherein: The molar ratio of the sodium element in the sodium source to the metal element in the modified precursor is (0.6-1):

1.

10. The preparation method according to any one of claims 1 to 9, wherein: The atmosphere of the two-step calcination treatment in step (2) includes air and / or oxygen.

11. The preparation method according to any one of claims 1 to 10, wherein: The temperature of the two-step calcination treatment in step (2) is 650-1000°C.

12. The preparation method according to any one of claims 1 to 11, wherein: The time of the two-step calcination treatment is 8 to 15 hours.

13. A sodium ion battery positive electrode material, wherein: The sodium ion battery positive electrode material is prepared by the method according to any one of claims 1 to 12.

14. A positive electrode sheet, wherein: The positive electrode sheet comprises the sodium ion battery positive electrode material as claimed in claim 13.

15. A sodium ion battery, wherein: The sodium ion battery comprises the positive electrode sheet as claimed in claim 14.

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