Sodium-ion battery positive electrode material, preparation method thereof and battery

Abstract

The invention discloses a sodium ion battery positive electrode material, a preparation method thereof and a battery, and belongs to the technical field of sodium ion batteries. The sodium ion battery positive electrode material provided by the invention comprises an inner layer and a coating layer, the inner layer is a layered oxide, the coating layer is a composite layer containing a material with an NASICON structure and carbon formed by in-situ carbonization, and the carbon formed by in-situ carbonization is derived from a complexing agent. Through the synergistic effect of the material with the NASICON structure and carbon formed by in-situ carbonization, charge transfer dynamics on the surface of the layered oxide is optimized, polarization is reduced, and the rate capability is improved. And the finally obtained sodium ion battery positive electrode material has good structural stability and excellent rate capability.

Description

Technical Field

[0001] This application belongs to the field of sodium-ion battery technology, and in particular relates to a sodium-ion battery cathode material, its preparation method, and the battery itself. Background Technology

[0002] Layered oxides possess high theoretical specific capacity, diverse compositions, and simple synthesis, making them advantageous as sodium storage materials. However, layered oxides also present some problems as cathode materials, particularly their poor electrochemical stability and the tendency for their structure to collapse. At high voltages, they exhibit significant issues such as the dissolution of transition metal ions and severe gas generation, severely impacting battery cycle life. Furthermore, safety concerns, such as those related to needle penetration, remain unavoidable challenges.

[0003] In recent years, with the continuous development of sodium-ion battery research, the industry has made many improvements to the performance of layered oxide cathode materials. Patent CN 119601638A uses layered oxide as the inner layer and sodium lanthanum zirconium oxide as the coating layer, preparing a sodium-ion battery cathode material through high-temperature sintering, which improves battery safety and cycle life; however, the coating layer reduces the material's rate performance. Patent CN119581537A fuses a mechanically fused layered oxide core material with a polyanion-based outer coating material, obtaining a cathode material with a core-shell structure of layered oxide and polyanion composites. However, mechanical fusion cannot guarantee effective bonding between the polyanion material and the layered oxide, posing a risk of polyanion detachment from the layered oxide material and failing to completely prevent side reactions between the layered oxide and the electrolyte.

[0004] Therefore, providing a sodium-ion battery cathode material that improves the structural stability and rate performance of sodium-ion batteries is of great research significance and application value. Summary of the Invention

[0005] To address the technical problem of existing coating-modified layered oxide technologies failing to simultaneously achieve structural stability and rate performance, the primary objective of this invention is to provide a sodium-ion battery cathode material. This material employs a composite layer comprising a material with a NASICON structure and carbon formed through in-situ carbonization as the coating layer, with a layered oxide as the inner layer, thereby obtaining a sodium-ion battery cathode material that improves both structural stability and rate performance.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned sodium-ion battery cathode material.

[0007] Another object of the present invention is to provide a sodium-ion battery comprising the above-described sodium-ion battery cathode material.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: This invention protects a sodium-ion battery cathode material, the sodium-ion battery cathode material comprising an inner layer and a coating layer, the inner layer being a layered oxide, and the coating layer being a composite layer comprising a material having a NASICON structure and carbon formed by in-situ carbonization; The carbon formed by the in-situ carbonization originates from the complexing agent.

[0009] Materials with a NASICON structure exhibit strong structural stability, delaying thermal runaway. Furthermore, by physically isolating and chemically bonding the surface, they prevent cracking and shedding of layered oxide crystal particles and dissolution of transition metals. This effectively avoids contact between the layered oxide cathode material and the electrolyte, reducing side reactions and thus improving the material's high-temperature stability. However, the high ionic conductivity of materials with a NASICON structure reduces their rate performance.

[0010] This invention innovatively achieves a tight bond between the NASICON-structured material and the layered oxide by forming in-situ carbonized carbon, preventing the coating layer from detaching due to weak adhesion. Simultaneously, the high ionic conductivity of the NASICON-structured material and the electronic conductivity of the carbon layer synergistically achieve a balance, optimizing the charge transport dynamics on the layered oxide surface, reducing polarization, and improving rate performance. This results in a sodium-ion battery cathode material that possesses both excellent structural stability and outstanding rate performance.

[0011] Preferably, the chemical formula of the material having the NASICON structure is Na. 1+x TM2(PO4)3, where 0≤x≤3, and TM is one or more of V, Ti, Al, Mn, Cr, Ni, Sn or Fe.

[0012] More specifically, the materials having a NASICON structure include, but are not limited to, Na3AlTi(PO4)3, NaTi2(PO4)3, Na3V2(PO4)3, Na3Al2(PO4)3, Na3Cr2(PO4)3, Na4MnV(PO4)3, and Na 2.5 Fe 1.5 Ti 0.5 (PO4)3, Na3V 1.5 Al 0.5 (PO4)3, Na3MnTi(PO4).

[0013] Preferably, the complexing agent includes one or more of polyvinylpyrrolidone, polydopamine, citric acid, or ethylenediaminetetraacetic acid.

[0014] Preferably, when the complexing agent is polyvinylpyrrolidone, the complexing agent also includes one or two of monosaccharides and / or disaccharides.

[0015] The monosaccharide may be glucose, fructose, etc., but more preferably glucose.

[0016] The disaccharide can be sucrose, maltose, etc., and more preferably sucrose.

[0017] More preferably, the monosaccharide and / or disaccharide and polyvinylpyrrolidone are mixed in a weight ratio of 1:0.5.

[0018] The preparation method of the above-mentioned sodium-ion battery cathode material includes the following steps: S1. The raw materials that form a material with a NASICON structure are mixed into a sol to obtain a precursor; a complexing agent is added, the pH is adjusted to 3-5, and the reaction is carried out to obtain a complex sol precursor; S2. The complex obtained in S1 is added to the layered oxide and reacted, and then annealed under an inert atmosphere to obtain the sodium-ion battery cathode material; The complexing agent is added at a rate of 0.05 to 0.5 times the mass of the material in the system that can form the NASICON structure.

[0019] Preferably, the layered oxide is added in an amount of 0.01 to 0.08 times the mass of the material in the system capable of forming the NASICON structure.

[0020] Preferably, in the sol of step S1, the total concentration of materials with the NASICON structure (i.e., the total concentration of Na+TM+PO4) is 0.2~1 mol / L.

[0021] Preferably, the pH-adjusting reagent is dilute nitric acid or ammonia.

[0022] Preferably, the annealing conditions in step S2 are to hold at 300~550℃ for 3~6 hours.

[0023] Preferably, the pH value of the reaction in step S2 involving the addition of layered oxides is 5-6.

[0024] Preferably, the solvent in step S2 is an aqueous ethanol solution.

[0025] Specifically, the solvent in step S2 is a mixture of ethanol and water in a volume ratio of 1:1.

[0026] Preferably, the inert atmosphere in step S2 is one or both of argon and nitrogen.

[0027] The chemical formula of the layered oxide is Na. y MO2, 0.5≤y≤1, M is selected from one or more of Mn, Fe, Cu, Ti, Ni, V, Co, Mg, Nb, Al or Zn.

[0028] The layered oxide was prepared according to existing technology.

[0029] Preferably, the method for preparing the layered oxide includes the following steps: A certain amount of sodium source is incorporated into the hydroxide precursor M(OH)2, and after uniform mixing, sintering is carried out. The sintered material is then crushed and sieved. M includes one or more of Mn, Fe, Cu, Ti, Ni, V, Co, Mg, Nb, Al, or Zn. The sodium source includes one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, or sodium acetate. The temperature range of the sintering process is 800℃~1200℃. The sintering time is 10~20 hours.

[0030] The present invention also protects a sodium-ion battery positive electrode, the positive electrode comprising the above-mentioned sodium-ion battery positive electrode material, a conductive agent, and a binder.

[0031] Specifically, the conductive agent and binder are selected according to existing technology.

[0032] Preferably, the conductive agent is Super-P.

[0033] Preferably, the adhesive is polyvinylidene fluoride (PVDF).

[0034] The present invention also protects a battery comprising the above-described sodium-ion battery positive electrode.

[0035] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a sodium-ion battery cathode material, comprising an inner layer and a coating layer. The inner layer is a layered oxide, and the coating layer is a composite layer of a material with a NASICON structure and carbon formed by in-situ carbonization. The carbon formed by in-situ carbonization is derived from a complexing agent. The material with a NASICON structure and the carbon formed by in-situ carbonization work synergistically to obtain a sodium-ion battery cathode material that improves the structural stability and rate performance of sodium-ion batteries. Attached Figure Description

[0036] Figure 1 This is a SEM image of Example 1; Figure 2 The EDS spectrum of Example 1; Figure 3 Cyclic test diagrams of batteries made from the cathode materials of Examples 1, 3 and Comparative Example 1. Detailed Implementation

[0037] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0038] Example 1 S1. Under magnetic stirring, sodium source, titanium source, aluminum source and phosphorus source were slowly added dropwise in a molar ratio of Na:Ti:Al:P = 3:1:1:3 and dissolved in deionized water to prepare a material precursor with a total concentration of 0.2 mol / L and a NASICON structure. Then, citric acid was added as a complexing agent at a mass ratio of 1:0.1 to the material with the NASICON structure Na3AlTi(PO4)3 and the complexing agent. The pH was adjusted to 3.0~5.0 and stirred for 1 hour to form a stable complex. S2. Take 10g of commercially available layered oxide NaNi with a particle size of 6μm. 0.2 Mn 0.4 Fe 0.3 Zn 0.1 O2 was dispersed in 500 mL of ethanol / water mixed solvent and sonicated for 30 minutes until uniformly suspended. Under stirring conditions, the complex was slowly added dropwise to the layered oxide suspension at a mass ratio of 0.02:1 for the material with the NASICON structure to the layered oxide. The pH was adjusted to 5-6, and the mixture was in a water bath at 80°C for 5 hours. Then, it was dried in an oven at 60°C for 10 hours to obtain powder, and finally annealed at 450°C for 4 hours under argon protection to obtain sodium ion cathode material.

[0039] The SEM and EDS images of the sodium-ion cathode material prepared in Example 1 are shown below. Figure 1 and Figure 2 .

[0040] Example 2 The experimental method is the same as in Example 1, except that the mass ratio of the material with the NASICON structure and the complexing agent citric acid in S1 is 1:0.5.

[0041] Example 3 The experimental method was the same as in Example 1, except that the mass ratio of the material with the NASICON structure to the layered oxide in S2 was 0.05:1.

[0042] Example 4 The experimental method is the same as in Example 1, except that the annealing temperature in S2 is 550℃.

[0043] Example 5 The experimental method is the same as in Example 1, except that in S1, polydopamine PDA is used instead of citric acid as the complexing agent.

[0044] Example 6 The experimental method is the same as in Example 1, except that the complexing agent in S1 is a mixture of glucose and polyvinylpyrrolidone in a weight ratio of 1:0.5.

[0045] Example 7 The experimental method is the same as in Example 1, except that the material with the NASICON structure is NaTi2(PO4)3.

[0046] Example 8 The experimental method is the same as in Example 1, except that the material with the NASICON structure is Na3V2(PO4)3.

[0047] Comparative Example 1 A commercially available layered oxide NaNi 0.2 Mn 0.4 Fe 0.3 Zn 0.1 O2, with a particle size of 6μm.

[0048] Comparative Example 2 S1. Under magnetic stirring, sodium source, titanium source, aluminum source and phosphorus source were slowly added dropwise in the molar ratio of Na:Ti:Al:P = 3:1:1:3 and dissolved in deionized water to prepare a material precursor with NASICON structure with a total concentration of 0.2 mol / L. S2. Disperse 10g of layered oxide in 500mL of ethanol / water mixed solvent and sonicate for 30 minutes until uniformly suspended. Under stirring conditions, slowly add the precursor of the material with the NASICON structure to the layered oxide suspension at a mass ratio of 0.02:1. Adjust the pH to 5-6, incubate in a water bath at 80℃ for 5 hours, then dry in an oven at 60℃ for 10 hours to obtain powder. Finally, anneal at 450℃ for 4 hours under argon protection to obtain a material with a layered oxide inner layer and a NASICON structure outer layer.

[0049] Comparative Example 3 The experimental method was the same as in Example 1, except that the mass ratio of the material with the NASICON structure and the complexing agent citric acid in S1 was 1:0.6.

[0050] Comparative Example 4 The experimental method was the same as in Example 1, except that the mass ratio of the material with the NASICON structure to the complexing agent citric acid in S1 was 1:0.02.

[0051] Performance test metrics for examples / comparative examples: The positive electrode materials prepared in the examples / comparative examples were used to prepare corresponding sodium-ion batteries. The preparation method is as follows: S1. The positive electrode material was mixed with NMP, binder and conductive agent to obtain a positive electrode slurry with a solid content of 58%. The slurry was coated, rolled and die-cut to obtain a positive electrode sheet; S2. The negative electrode material was mixed with water, conductive agent and binder to obtain a negative electrode slurry with a solid content of 45%. The slurry was coated, rolled and die-cut to obtain a negative electrode sheet; S3. The positive electrode sheet, negative electrode sheet and separator obtained in S1 and S2 were assembled, electrolyte was injected, and capacity separation and formation were performed to obtain the sodium-ion battery.

[0052] (1) Cycling performance: Cycle from 1.5V to 3.9V at 45℃ to obtain the number of cycles and discharge capacity data. SOH is the ratio of the current available capacity to the initial available capacity. Record the number of cycles when SOH drops to 80%.

[0053] (2) 15C rate performance: After the lithium-ion battery is fully charged at 0.2C constant current and constant voltage, it is discharged at 15C and its capacity retention rate is tested.

[0054] Performance test results of examples / comparative examples: Table 1 Test Results of Examples / Comparative Examples

[0055] The cycle performance of batteries assembled from the sodium-ion battery cathode materials prepared in Examples 1, 3, and 1 is shown in the figure. Figure 3 .

[0056] As can be seen from Table 1, after the sodium-ion battery cathode materials prepared in Examples 1 to 6 are assembled into batteries, the number of cycles is greater than 2300 before the battery health state drops to 80%, which shows excellent cycle stability and high structural stability of sodium-ion battery cathode materials; and at a high discharge rate of 15C, the capacity retention rate is ≥90%, showing excellent rate performance.

[0057] In Comparative Example 1, the layered oxide was not coated and was used directly as the positive electrode material. In Comparative Example 2, the coating layer of the sodium-ion battery positive electrode material was a material with a NASICON structure, but no complexing agent was added. In Comparative Example 3, the amount of complexing agent added to the coating layer of the sodium-ion positive electrode material was greater than the set range. In Comparative Example 4, the amount of complexing agent added to the coating layer of the sodium-ion positive electrode material was less than the set range. It can be seen from Comparative Examples 1 to 4 that the absence of coating, the absence of a complexing agent in the coating, or an inappropriate amount of complexing agent all lead to a decrease in the cycle performance of the battery.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A sodium-ion battery cathode material, characterized in that, The sodium-ion battery cathode material includes an inner layer and a coating layer. The inner layer is a layered oxide, and the coating layer is a composite layer containing a material with a NASICON structure and carbon formed by in-situ carbonization. The carbon formed by the in-situ carbonization originates from the complexing agent.

2. The sodium-ion battery cathode material according to claim 1, characterized in that, The chemical formula of the material having a NASICON structure is Na. 1+x TM2(PO4)3, where 0≤x≤3, and TM is one or more of V, Ti, Al, Mn, Cr, Ni, Sn or Fe.

3. The sodium-ion battery cathode material according to claim 1, characterized in that, The complexing agent includes one or more of polyvinylpyrrolidone, polydopamine, citric acid, or ethylenediaminetetraacetic acid.

4. The sodium-ion battery cathode material according to claim 3, characterized in that, When the complexing agent is polyvinylpyrrolidone, the complexing agent also includes one or two of monosaccharides and / or disaccharides.

5. A method for preparing the sodium-ion battery cathode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Mix the raw materials that form the NASICON structure into a sol to obtain a precursor; add a complexing agent, adjust the pH to 3-5, and react to obtain a complex sol precursor; S2. The complex obtained in S1 is added to the layered oxide and reacted, and then annealed under an inert atmosphere to obtain the sodium-ion battery cathode material; The complexing agent is added at a rate of 0.05 to 0.5 times the mass of the material in the system that can form the NASICON structure.

6. The preparation method according to claim 5, characterized in that, The layered oxide is added in an amount of 0.01 to 0.08 times the mass of the material in the system that can form the NASICON structure.

7. The preparation method according to claim 5, characterized in that, The pH value of the reaction in step S2 involving the addition of layered oxides is 5-6.

8. The preparation method according to claim 5, characterized in that, The annealing conditions described in step S2 are to hold at 300~550℃ for 3~6 hours.

9. A sodium-ion battery positive electrode, characterized in that, The positive electrode comprises the sodium-ion battery positive electrode material according to any one of claims 1 to 4, a conductive agent, and a binder.

10. A battery, characterized in that, The battery includes the sodium-ion battery positive electrode as described in claim 9.

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