A composite cathode material, its preparation method, cathode sheet, and sodium-ion battery

Abstract

This invention discloses a composite cathode material comprising a layered oxide and a coating layer, wherein the layered oxide has the general formula NaMe. 1‑ x Al x O2, wherein Me is one or more of nickel, iron, manganese, and cobalt, and x > 0; the coating layer covers the layered oxide and, from the inside out, includes a first coating layer, a second coating layer, and a third coating layer. The first coating layer is titanium aluminum carbide, the second coating layer is titanium nitride, and the third coating layer is nitrogen-doped polymeric porous carbon. The composite cathode material forms Al-N bonds. This invention also discloses a cathode sheet and a sodium-ion battery having this composite cathode material. This invention ensures good cycle performance while effectively controlling the cycle expansion rate.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a composite cathode material, preparation method, cathode sheet and sodium-ion battery. Background Technology

[0002] Layered oxides are commonly used cathode materials in sodium-ion batteries. However, they suffer from structural instability (sodium ions have a larger radius than lithium ions, making them prone to volume collapse during cycle insertion / extraction), poor conductivity, and high solubility in electrolytes. Therefore, current technologies often employ coating layers to improve their performance, such as nitrogen-doped carbon coating to enhance cycle stability, or multi-layer coating schemes. However, existing coating structures often suffer from insufficient interlayer bonding, resulting in cathode materials with insufficient ductility and high cycle expansion rates. Summary of the Invention

[0003] To address the shortcomings of the prior art, the present invention aims to provide a composite cathode material and its preparation method, solving the problems of insufficient interlayer bonding, insufficient ductility of the cathode material, and high cycle expansion rate. Another objective of the present invention is to provide a cathode sheet and a sodium-ion battery.

[0004] The technical solution of this invention is: a composite cathode material, comprising a layered oxide and a coating layer, wherein the layered oxide has the general formula NaMe. 1-x Al x O2, wherein Me is one or more of nickel, iron, manganese and cobalt, and x > 0; the coating layer covers the outside of the layered oxide, and the coating layer includes a first coating layer, a second coating layer and a third coating layer from the inside to the outside. The first coating layer is titanium aluminum carbide, the second coating layer is titanium nitride, and the third coating layer is nitrogen-doped polymeric porous carbon. The composite cathode material forms Al-N bonds.

[0005] Furthermore, the titanium aluminum carbide accounts for 1% to 3% of the mass of the layered oxide.

[0006] Furthermore, the titanium nitride accounts for 1% to 3% of the mass of the layered oxide.

[0007] Furthermore, the nitrogen-doped polymeric porous carbon accounts for 1% to 3% of the mass of the layered oxide.

[0008] Furthermore, the nitrogen-doped polymeric porous carbon is obtained by pre-oxidation and then carbonization of a nitrogen-containing organic polymer.

[0009] Another technical solution of the present invention is: a method for preparing a composite cathode material, comprising the following steps:

[0010] (1) Disperse titanium aluminum carbide in anhydrous ethanol, then add layered oxide and ultrasonically stir to obtain a mixed dispersion. The solid material after drying the mixed dispersion is heated to 450-550°C under a protective atmosphere.

[0011] (2) The titanium nitride and the product of step (1) are mixed, ball-milled, pressed into tablets and sintered. The sintered product is then ground and sieved.

[0012] (3) The product of step (2) is loaded into a fixed bed reactor, nitrogen is introduced and air is discharged, and then the reactor is heated to 110-120°C and purged with a mixture of nitrogen and hydrogen. Nitrogen-doped polymerized porous carbon is then loaded into the reaction via helium. After the reaction is completed, the carbon is washed, dried and calcined to obtain the composite cathode material.

[0013] Further, the nitrogen-doped polymeric porous carbon in step (3) is prepared by the following method: polypyrrole is pretreated by oxidation at 350-400°C in an air atmosphere, and then carbonized at 850-950°C in a nitrogen atmosphere.

[0014] Furthermore, the sintering temperature in step (2) is 750–900°C, and the calcination temperature in step (3) is 700–800°C.

[0015] Another technical solution of the present invention is: a positive electrode sheet, comprising a positive electrode current collector, wherein the surface of the positive electrode current collector is coated with a positive electrode slurry layer containing the aforementioned composite positive electrode material.

[0016] Another technical solution of the present invention is: a sodium-ion battery, comprising a negative electrode, an electrolyte, a separator, and the aforementioned positive electrode sheet.

[0017] Compared with the prior art, the present invention has the following significant advantages:

[0018] Using aluminum titanium carbide (ACH) as the first coating layer, ACH possesses a unique layered structure that combines the excellent properties of both metals and ceramics, including good conductivity, high hardness, and elastic modulus. The layered crystal structure of ACH (hexagonal crystal system, space group P63 / mmc) exhibits excellent lattice matching with layered oxides. After coating, it can limit volume changes in the cathode material through a "mechanical support" effect, suppressing phase transitions and thus improving cycle stability. ACH also combines the ductility of metals with the hardness of ceramics. Its weak van der Waals forces allow for interlayer slippage, effectively buffering the mechanical stress generated by volume changes during charging and discharging, reducing particle breakage and pulverization, and extending battery life. Furthermore, ACH has metallic conductivity, forming a continuous conductive network on the surface of the layered oxide particles after coating.

[0019] The third coating layer is nitrogen-doped polymeric porous carbon, which not only possesses high conductivity and chemical stability but also boasts low manufacturing cost and simple synthesis, and can smooth the surface structure of the material. Titanium nitride is used as the transitional second coating layer. The first and second coating layers contain the same element, titanium, while the second and third coating layers contain the same element, nitrogen. Utilizing the property that the presence of the same element increases the affinity between each reinforcing layer, interpenetration occurs between the layered oxide and the first coating layer, as well as among the other coating layers, further enhancing the bonding strength between layers and resulting in a tighter bond and better synergistic effect. Furthermore, the presence of Al-N bonds further strengthens the interfacial bonding, inhibits interlayer delamination, optimizes electron and ion transport channels, enhances the structural toughness of the coating layers, and improves the overall cycle performance of the cathode material. Attached Figure Description

[0020] Figure 1 This is a SEM image of the composite cathode material prepared in Example 1 of the present invention.

[0021] Figure 2 The image shows the XPS spectrum of the N1s of the composite cathode material prepared in Example 2 of this invention. Detailed Implementation

[0022] The present invention will be further described below with reference to the embodiments and accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. After reading this description, any modifications of this description in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0023] Example 1

[0024] The composite cathode material in this embodiment includes layered oxide NaNi. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2, layered oxide NaNi 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 is surrounded by titanium aluminum carbide, titanium nitride, and nitrogen-doped polymeric porous carbon, forming Al-N bonds in the composite cathode material. The mass ratio of titanium aluminum carbide, titanium nitride, and nitrogen-doped polymeric porous carbon in the layered oxide is 1%.

[0025] The preparation method of composite cathode material is as follows:

[0026] S1: First, prepare the core: Using the commonly used solid-state sintering method, combine sodium source (sodium carbonate), nickel source (nickel oxide), iron source (iron oxide), manganese source (manganese dioxide), and aluminum source (aluminum oxide) according to the NaNi... 0.5 Fe0.2 Mn 0.2 Al 0.1 O2 was stoichiometrically blended (molar ratio: 0.5:0.5:0.1:0.2:0.05), ball-milled under nitrogen for 10 h, and pressed into thin sheets with a diameter of 12 mm and a thickness of 2-3 mm at 10-15 MPa. The sheets were then solid-state sintered in air at 1000 °C with a heating rate of 5 °C / min for 10 h. After sintering, the sheets were crushed and screened to obtain layered oxide NaNi. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2.

[0027] 0.5Na2CO3+0.5NiO+0.1Fe2O3+0.2MnO2+0.05Al2O3+0.075O2→

[0028] NaNi 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 + 0.5CO2↑

[0029] S2: Add titanium aluminum carbide (CAS: 196506-01-1) to anhydrous ethanol, stir and sonicate for 2 hours to obtain a dispersion; add NaNi to the dispersion. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 was added, and the mixture was stirred and sonicated for 3 hours. Then, it was stirred and evaporated to dryness at 120°C, and dried in an oven at 150°C for 10 hours to obtain a solid. The solid was then heated to 500°C and held for 4 hours under a protective atmosphere to obtain the titanium aluminum carbide-coated cathode material. The titanium aluminum carbide contained NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 1% of O2.

[0030] S3: Titanium nitride (CAS: 25583-20-4) and the product of S2 were mixed and ball-milled with anhydrous ethanol as lubricant for 20 hours. The mixture was then compressed into tablets at 10 MPa and sintered at 800℃ for 7 hours. After cooling, grinding, and sieving, the double-layer coated material NaNi was obtained. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2@Ti3AlC2@TiN. The titanium nitride added is NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 1% of O2.

[0031] S4: Polypyrrole (CAS: 30604-81-0) was placed in a muffle furnace and pretreated with oxidation at 350°C for 3 hours in air atmosphere to obtain partially cross-linked polypyrrole precursors. The precursors were then transferred to a tube furnace and carbonized at 900°C (heating rate 2°C / min) for 6 hours in nitrogen atmosphere to obtain nitrogen-doped polymeric porous carbon.

[0032] S5: Apply the double-layer coating material NaNi obtained in step S3. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2@Ti3AlC2@TiN was loaded into a fixed-bed reactor, nitrogen was introduced to purge the air from the reactor, and the reactor was heated to 120°C. A mixture of nitrogen and hydrogen (nitrogen to hydrogen volume ratio 1:1) was then introduced at a flow rate of 50 mL / min for purging. The resulting solution was then prepared according to the NaNi... 0.5 Fe 0.2 Mn 0.2 Al 0.1 Nitrogen-doped polymeric porous carbon with an O2 mass ratio of 1% was introduced with helium gas and reacted for 60 minutes. After washing and demagnetization, the material was dried at 95°C for 1 hour. The dried material was then calcined at 700°C for 4 hours to obtain the final composite cathode material. The SEM image of the composite cathode material in this embodiment is shown below. Figure 1 As shown, the product has a smooth surface and is porous.

[0033] Example 2

[0034] The composite cathode material in this embodiment includes layered oxide NaNi. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2, layered oxide NaNi 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 is composed of titanium aluminum carbide, titanium nitride, and nitrogen-doped polymeric porous carbon in sequence, forming Al-N bonds in the composite cathode material. The mass ratio of titanium aluminum carbide, titanium nitride, and nitrogen-doped polymeric porous carbon in the layered oxide is 2%.

[0035] The preparation method of composite cathode material is as follows:

[0036] S1: First, prepare the core: layered oxide NaNi was prepared using the solid-state sintering method of Example 1. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2.

[0037] S2: Add titanium aluminum carbide (CAS: 196506-01-1) to anhydrous ethanol, stir and sonicate for 2 hours to obtain a dispersion; add NaNi to the dispersion. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 was added, and the mixture was stirred and sonicated for 3 hours. Then, it was stirred and evaporated to dryness at 120°C, and dried in an oven at 150°C for 10 hours to obtain a solid. The solid was then heated to 500°C and held for 4 hours under a protective atmosphere to obtain the titanium aluminum carbide-coated cathode material. The titanium aluminum carbide contained NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 2% of O2.

[0038] S3: Titanium nitride (CAS: 25583-20-4) and the product of S2 were mixed and ball-milled with anhydrous ethanol as lubricant for 20 hours. The mixture was then compressed into tablets at 10 MPa and sintered at 800℃ for 7 hours. After cooling, grinding, and sieving, the double-layer coated material NaNi was obtained. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2@Ti3AlC2@TiN. The titanium nitride added is NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 2% of O2.

[0039] S4: Polypyrrole (CAS: 30604-81-0) was placed in a muffle furnace and pretreated with oxidation at 350°C for 3 hours in air to obtain partially cross-linked polypyrrole precursors. The precursors were then transferred to a tube furnace and carbonized at 900°C (heating rate 2°C / min) for 6 hours in nitrogen atmosphere to obtain nitrogen-doped polymeric porous carbon.

[0040] S5: Apply the double-layer coating material NaNi obtained in step S3. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2@Ti3AlC2@TiN was loaded into a fixed-bed reactor, nitrogen was introduced to purge the air from the reactor, and the reactor was heated to 120°C. A mixture of nitrogen and hydrogen (nitrogen to hydrogen volume ratio 1:1) was then introduced at a flow rate of 50 mL / min for purging. The resulting solution was then prepared according to the NaNi... 0.5 Fe 0.2 Mn 0.2 Al 0.1Nitrogen-doped polymeric porous carbon with an O2 mass ratio of 2% was introduced with helium and reacted for 60 min. After washing and demagnetization, the material was dried at 95 °C for 1 h. The dried material was then calcined at 700 °C for 4 h to obtain the final composite cathode material.

[0041] Example 3

[0042] The composite cathode material in this embodiment includes layered oxide NaNi. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2, layered oxide NaNi 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 is surrounded by titanium aluminum carbide, titanium nitride, and nitrogen-doped polymeric porous carbon, forming Al-N bonds in the composite cathode material. The mass ratio of titanium aluminum carbide, titanium nitride, and nitrogen-doped polymeric porous carbon in the layered oxide is 3%.

[0043] The preparation method of composite cathode material is as follows:

[0044] S1: First, prepare the core: layered oxide NaNi was prepared using the solid-state sintering method of Example 1. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2.

[0045] S2: Add titanium aluminum carbide (CAS: 196506-01-1) to anhydrous ethanol, stir and sonicate for 2 hours to obtain a dispersion; add NaNi to the dispersion. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 was added, and the mixture was stirred and sonicated for 3 hours. Then, it was stirred and evaporated to dryness at 120°C, and dried in an oven at 150°C for 10 hours to obtain a solid. The solid was then heated to 500°C and held for 4 hours under a protective atmosphere to obtain the titanium aluminum carbide-coated cathode material. The titanium aluminum carbide contained NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 3% of O2.

[0046] S3: Titanium nitride (CAS: 25583-20-4) and the product of S2 were mixed and ball-milled with anhydrous ethanol as lubricant for 20 hours. The mixture was then compressed into tablets at 10 MPa and sintered at 800℃ for 7 hours. After cooling, grinding, sieving, and iron removal, a double-layer coated material NaNi was obtained. 0.5 Fe 0.2 Mn 0.2 Al0.1 O2@Ti3AlC2@TiN. The titanium nitride added is NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 3% of O2.

[0047] S4: Polypyrrole (CAS: 30604-81-0) was placed in a muffle furnace and pretreated with oxidation at 350°C for 3 hours in air to obtain partially cross-linked polypyrrole precursors. The precursors were then transferred to a tube furnace and carbonized at 900°C (heating rate 2°C / min) for 6 hours in nitrogen atmosphere to obtain nitrogen-doped polymeric porous carbon.

[0048] S5: Apply the double-layer coating material NaNi obtained in step S3. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2@Ti3AlC2@TiN was loaded into a fixed-bed reactor, nitrogen was introduced to purge the air from the reactor, and the reactor was heated to 120°C. A mixture of nitrogen and hydrogen (nitrogen to hydrogen volume ratio 1:1) was then introduced at a flow rate of 50 mL / min for purging. The resulting solution was then prepared according to the NaNi... 0.5 Fe 0.2 Mn 0.2 Al 0.1 Nitrogen-doped polymeric porous carbon with an O2 mass ratio of 3% was introduced with helium and reacted for 60 min. After washing and demagnetization, the material was dried at 95 °C for 1 h. The dried material was then calcined at 700 °C for 4 h to obtain the final composite cathode material.

[0049] Example 4

[0050] The composite cathode material in this embodiment includes layered oxide NaNi. 0.5 Co 0.2 Mn 0.2 Al 0.1 O2, layered oxide NaNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O2 is composed of titanium aluminum carbide, titanium nitride, and nitrogen-doped polymeric porous carbon in sequence, forming Al-N bonds in the composite cathode material. The mass ratio of titanium aluminum carbide, titanium nitride, and nitrogen-doped polymeric porous carbon in the layered oxide is 2%.

[0051] 0.5Na2CO3+0.5NiO+ 0.2CoCO3+ 0.2MnO2+ 0.05Al2O3+0.125O2 →

[0052] NaNi0.5 Co 0.2 Mn 0.2 Al 0.1 O2 + 0.7CO2↑

[0053] The preparation method of composite cathode material is as follows:

[0054] S1: First, prepare the core: Using the commonly used solid-state sintering method, combine sodium source (sodium carbonate), nickel source (nickel oxide), cobalt source (cobalt carbonate), manganese source (manganese dioxide), and aluminum source (aluminum oxide) according to the NaNi... 0.5 Co 0.2 Mn 0.2 Al 0.1 O2 was stoichiometrically blended (molar ratio: 0.5:0.5:0.2:0.2:0.05), ball-milled under nitrogen for 10 h, and pressed into thin sheets with a diameter of 12 mm and a thickness of 2-3 mm at 10-15 MPa. The sheets were then solid-state sintered under an oxidizing atmosphere at 1000 °C with a heating rate of 5 °C / min for 10 h. Afterwards, the sheets were crushed and screened to obtain layered oxide NaNi. 0.5 Co 0.2 Mn 0.2 Al 0.1 O2.

[0055] S2: Add titanium aluminum carbide (CAS: 196506-01-1) to anhydrous ethanol, stir and sonicate for 2 hours to obtain a dispersion; add NaNi to the dispersion. 0.5 Co 0.2 Mn 0.2 Al 0.1 O2 was added, and the mixture was stirred and sonicated for 3 hours. Then, it was stirred and evaporated to dryness at 120°C, and dried in an oven at 150°C for 10 hours to obtain a solid. The solid was then heated to 450°C and held for 4 hours under a protective atmosphere to obtain the titanium aluminum carbide-coated cathode material. The titanium aluminum carbide contained NaNi by mass. 0.5 Co 0.2 Mn 0.2 Al 0.1 2% of O2.

[0056] S3: Titanium nitride (CAS: 25583-20-4) and the product of S2 were mixed and ball-milled with anhydrous ethanol as lubricant for 20 hours. The mixture was then compressed into tablets at 10 MPa and sintered at 880℃ for 7 hours. After cooling, grinding, sieving, and iron removal, a double-layer coated material NaNi was obtained. 0.5 Co 0.2 Mn 0.2 Al 0.1 O2@Ti3AlC2@TiN. The titanium nitride added is NaNi by mass. 0.5 Co 0.2 Mn0.2 Al 0.1 2% of O2.

[0057] S4: Polypyrrole (CAS: 30604-81-0) was placed in a muffle furnace and pretreated with oxidation at 350°C for 3 hours in air atmosphere to obtain partially cross-linked polypyrrole precursors. The precursors were then transferred to a tube furnace and carbonized at 850°C (heating rate 2°C / min) for 7 hours in nitrogen atmosphere to obtain nitrogen-doped polymeric porous carbon.

[0058] S5: Apply the double-layer coating material NaNi obtained in step S3. 0.5 Co 0.2 Mn 0.2 Al 0.1 O2@Ti3AlC2@TiN was loaded into a fixed-bed reactor, nitrogen was introduced to purge the air from the reactor, and the reactor was heated to 150°C. A mixture of nitrogen and hydrogen (nitrogen to hydrogen volume ratio 1:1) was then introduced at a flow rate of 50 mL / min for purging. NaNi 0.5 Co 0.2 Mn 0.2 Al 0.1 Nitrogen-doped polymeric porous carbon with an O2 mass ratio of 2% was introduced with helium and reacted for 60 min. After washing and demagnetization, the material was dried at 95 °C for 1 h. The dried material was then calcined at 800 °C for 4 h to obtain the final composite cathode material.

[0059] Example 5

[0060] The composite cathode material in this embodiment includes layered oxide NaNi. 0.3 Fe 0.3 Mn 0.3 Al 0.1 O2, layered oxide NaNi 0.3 Fe 0.3 Mn 0.3 Al 0.1 O2 is surrounded by titanium aluminum carbide, titanium nitride, and nitrogen-doped polymeric porous carbon, forming Al-N bonds in the composite cathode material. The mass ratio of titanium aluminum carbide, titanium nitride, and nitrogen-doped polymeric porous carbon to Al-doped layered oxides is 2%.

[0061] The preparation method of composite cathode material is as follows:

[0062] S1: First, prepare the core: Using the commonly used solid-state sintering method, combine sodium source (sodium carbonate), nickel source (nickel oxide), iron source (iron oxide), manganese source (manganese dioxide), and aluminum source (aluminum oxide) according to the NaNi... 0.3 Fe 0.3 Mn 0.3 Al0.1 O2 was stoichiometrically blended (molar ratio: 0.5:0.3:0.15:0.3:0.05), ball-milled under nitrogen for 10 h, and pressed into thin sheets with a diameter of 12 mm and a thickness of 2-3 mm at 10-15 MPa. The sheets were then solid-state sintered at 1000 °C with a heating rate of 5 °C / min for 10 h. After sintering, the sheets were crushed and screened to obtain layered oxide NaNi. 0.3 Fe 0.3 Mn 0.3 Al 0.1 O2.

[0063] 0.5Na2CO3+0.3NiO+ 0.15Fe2O3+ 0.3MnO2+ 0.05Al2O3→

[0064] NaNi 0.3 Fe 0.3 Mn 0.3 Al 0.1 O2 + 0.5CO2↑

[0065] S2: Add titanium aluminum carbide (CAS: 196506-01-1) to anhydrous ethanol, stir and sonicate for 2 hours to obtain a dispersion; add NaNi to the dispersion. 0.3 Fe 0.3 Mn 0.3 Al 0.1 O2 was added, and the mixture was stirred and sonicated for 3 hours. Then, it was stirred and evaporated to dryness at 120°C, and dried in an oven at 150°C for 10 hours to obtain a solid. The solid was then heated to 550°C and held for 4 hours under a protective atmosphere to obtain the titanium aluminum carbide-coated cathode material. The titanium aluminum carbide contained NaNi by mass. 0.3 Fe 0.3 Mn 0.3 Al 0.1 2% of O2.

[0066] S3: Titanium nitride (CAS: 25583-20-4) and the product of S2 were mixed and ball-milled with anhydrous ethanol as lubricant for 20 hours. The mixture was then compressed into tablets at 10 MPa and sintered at 750℃ for 7 hours. After cooling, grinding, sieving, and iron removal, a double-layer coated material NaNi was obtained. 0.3 Fe 0.3 Mn 0.3 Al 0.1 O2@Ti3AlC2@TiN. The titanium nitride added is NaNi by mass. 0.3 Fe 0.3 Mn 0.3 Al 0.1 2% of O2.

[0067] S4: Polypyrrole (CAS: 30604-81-0) was placed in a muffle furnace and pretreated with oxidation at 400℃ for 3 hours in air atmosphere to obtain partially cross-linked polypyrrole precursors. The precursors were then transferred to a tube furnace and carbonized at 950℃ (heating rate 2℃ / min) for 6 hours in nitrogen atmosphere to obtain nitrogen-doped polymeric porous carbon.

[0068] S5: Apply the double-layer coating material NaNi obtained in step S3. 0.3 Fe 0.3 Mn 0.3 Al 0.1 O2@Ti3AlC2@TiN was loaded into a fixed-bed reactor, nitrogen was introduced to purge the air from the reactor, and the reactor was heated to 110°C. A mixture of nitrogen and hydrogen (nitrogen to hydrogen volume ratio 1:1) was then introduced at a flow rate of 50 mL / min for purging. The resulting solution was then processed according to the NaNi... 0.3 Fe 0.3 Mn 0.3 Al 0.1 Nitrogen-doped polymeric porous carbon with an O2 mass ratio of 2% was introduced with helium and reacted for 60 min. After washing and demagnetization, it was dried at 95 °C for 1 h. The dried material was then calcined at 750 °C for 4.5 h to obtain the final composite cathode material.

[0069] Comparative Example 1

[0070] The composite cathode material in this comparative example includes layered oxide NaNi. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2, layered oxide NaNi 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 is surrounded by titanium nitride and nitrogen-doped polymeric porous carbon, with titanium nitride and nitrogen-doped polymeric porous carbon each accounting for 2% of the mass of the layered oxide.

[0071] Its preparation process is as follows:

[0072] S1: First, prepare the core: layered oxide NaNi was prepared using the solid-state sintering method of Example 1. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2.

[0073] S2: Titanium nitride (CAS: 25583-20-4) and NaNi 0.5 Fe 0.2 Mn 0.2 Al 0.1O2 was mixed and ball-milled, with anhydrous ethanol added for lubrication, for 20 hours; the tableting pressure was 10 MPa; the sintering temperature was 800℃, and the sintering time was 7 hours. After cooling, grinding, sieving, and iron removal, titanium nitride-coated material was obtained. The mass of titanium nitride added was NaNi. 0.5 Fe 0.2 Mn 0.2 Al 0.1 2% of O2.

[0074] S3: Polypyrrole (CAS: 30604-81-0) was placed in a muffle furnace and pretreated with oxidation at 350°C for 3 hours in air to obtain partially cross-linked polypyrrole precursors. The precursors were then transferred to a tube furnace and carbonized at 900°C (heating rate 2°C / min) for 6 hours in nitrogen atmosphere to obtain nitrogen-doped polymeric porous carbon.

[0075] S4: The titanium nitride coating material prepared in step S2 is loaded into a fixed-bed reactor, nitrogen is introduced to purge the air from the reactor, and the reactor is heated to 120°C. A mixture of nitrogen and hydrogen (nitrogen to hydrogen volume ratio of 1:1) is introduced at a flow rate of 50 mL / min for purging. The titanium nitride coating material prepared in step S2 is then loaded into a fixed-bed reactor. 0.5 Fe 0.2 Mn 0.2 Al 0.1 Nitrogen-doped polymeric porous carbon with an O2 mass ratio of 2% was introduced with helium and reacted for 60 min. After washing and demagnetization, the material was dried at 95 °C for 1 h. The dried material was then calcined at 700 °C for 4 h to obtain the final product.

[0076] Comparative Example 2

[0077] The composite cathode material in this comparative example includes layered oxide NaNi. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2, layered oxide NaNi 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 is surrounded by titanium aluminum carbide and nitrogen-doped polymeric porous carbon, with titanium aluminum carbide and nitrogen-doped polymeric porous carbon each accounting for 2% of the mass of the layered oxide.

[0078] Its preparation process is as follows:

[0079] S1: First, prepare the core: layered oxide NaNi was prepared using the solid-state sintering method of Example 1. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2.

[0080] S2: Add titanium aluminum carbide (CAS: 196506-01-1) to anhydrous ethanol, stir and sonicate for 2 hours to obtain a dispersion; add NaNi to the dispersion. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 was added, and the mixture was stirred and sonicated for 3 hours. Then, it was stirred and evaporated to dryness at 120°C, and dried in an oven at 150°C for 10 hours to obtain a solid. The solid was then heated to 500°C and held for 4 hours under a protective atmosphere to obtain the titanium aluminum carbide-coated cathode material. The titanium aluminum carbide contained NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 2% of O2.

[0081] S3: Polypyrrole (CAS: 30604-81-0) was placed in a muffle furnace and pretreated with oxidation at 350°C for 3 hours in air to obtain partially cross-linked polypyrrole precursors. The precursors were then transferred to a tube furnace and carbonized at 900°C (heating rate 2°C / min) for 6 hours in nitrogen atmosphere to obtain nitrogen-doped polymeric porous carbon.

[0082] S4: The titanium-aluminum carbide coated cathode material prepared in step S2 is loaded into a fixed-bed reactor. Nitrogen gas is introduced to purge the air from the reactor. The reactor is heated to 120°C, and a mixture of nitrogen and hydrogen (nitrogen to hydrogen volume ratio of 1:1) is introduced at a flow rate of 50 mL / min for purging. The NaNi... 0.5 Fe 0.2 Mn 0.2 Al 0.1 Nitrogen-doped polymeric porous carbon with an O2 mass ratio of 2% was introduced with helium and reacted for 60 min. After washing and demagnetization, the material was dried at 95 °C for 1 h. The dried material was then calcined at 700 °C for 4 h to obtain the final product.

[0083] Comparative Example 3

[0084] The composite cathode material in this comparative example includes layered oxide NaNi. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2, layered oxide NaNi 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 is surrounded by titanium aluminum carbide and titanium nitride, with each of the two titanium aluminum carbide and titanium nitride accounting for 2% of the mass of the layered oxide.

[0085] Its preparation process is as follows:

[0086] S1: First, prepare the core: layered oxide NaNi was prepared using the solid-state sintering method of Example 1. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2.

[0087] S2: Add titanium aluminum carbide (CAS: 196506-01-1) to anhydrous ethanol, stir and sonicate for 2 hours to obtain a dispersion; add NaNi to the dispersion. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 was added, and the mixture was stirred and sonicated for 3 hours. Then, it was stirred and evaporated to dryness at 120°C, and dried in an oven at 150°C for 10 hours to obtain a solid. The solid was then heated to 500°C and held for 4 hours under a protective atmosphere to obtain the titanium aluminum carbide-coated cathode material. The titanium aluminum carbide contained NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 2% of O2.

[0088] S3: Titanium nitride (CAS: 25583-20-4) and titanium aluminum carbide-coated cathode material were mixed and ball-milled with anhydrous ethanol as lubricant for 20 hours; the pressing pressure was 10 MPa; the sintering temperature was 800℃ and the sintering time was 7 hours; after cooling, grinding, sieving, and iron removal, the final product was obtained. The mass of titanium nitride added was NaNi. 0.5 Fe 0.2 Mn 0.2 Al 0.1 2% of O2.

[0089] Comparative Example 4

[0090] The preparation method of composite cathode material is as follows:

[0091] S1: First, prepare the core: layered oxide NaNi was prepared using the solid-state sintering method of Example 1. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2.

[0092] S2: Add titanium aluminum carbide (CAS: 196506-01-1) to anhydrous ethanol, stir and sonicate for 2 hours to obtain a dispersion; add NaNi to the dispersion. 0.5 Fe 0.2 Mn 0.2 Al 0.1O2 was added, and the mixture was stirred and sonicated for 3 hours. Then, it was stirred and evaporated to dryness at 120°C, and dried in an oven at 150°C for 10 hours to obtain a solid. The solid was then heated to 500°C and held for 4 hours under a protective atmosphere to obtain the titanium aluminum carbide-coated cathode material. The titanium aluminum carbide contained NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 0.5% of O2.

[0093] S3: Titanium nitride (CAS: 25583-20-4) and the product of S2 were mixed and ball-milled with anhydrous ethanol as lubricant for 20 hours. The mixture was then compressed into tablets at 10 MPa and sintered at 800℃ for 7 hours. After cooling, grinding, sieving, and iron removal, a double-layer coated material NaNi was obtained. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2@Ti3AlC2@TiN. The titanium nitride added is NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 2% of O2.

[0094] S4: Polypyrrole (CAS: 30604-81-0) was placed in a muffle furnace and pretreated with oxidation at 350°C for 3 hours in air atmosphere to obtain partially cross-linked polypyrrole precursors. The precursors were then transferred to a tube furnace and carbonized at 900°C (heating rate 2°C / min) for 6 hours in nitrogen atmosphere to obtain nitrogen-doped polymeric porous carbon.

[0095] S5: Apply the double-layer coating material NaNi obtained in step S3. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2@Ti3AlC2@TiN was loaded into a fixed-bed reactor, nitrogen was introduced to purge the air from the reactor, and the reactor was heated to 120°C. A mixture of nitrogen and hydrogen (nitrogen to hydrogen volume ratio 1:1) was then introduced at a flow rate of 50 mL / min for purging. The resulting solution was then prepared according to the NaNi... 0.5 Fe 0.2 Mn 0.2 Al 0.1 Nitrogen-doped polymeric porous carbon with an O2 mass ratio of 0.5% was introduced with helium and reacted for 60 minutes. After washing and demagnetization, the material was dried at 95°C for 1 hour. The dried material was then calcined at 700°C for 4 hours to obtain the final composite cathode material.

[0096] Comparative Example 5

[0097] The preparation method of composite cathode material is as follows:

[0098] S1: First, prepare the core: layered oxide NaNi was prepared using the solid-state sintering method of Example 1. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2.

[0099] S2: Add titanium aluminum carbide (CAS: 196506-01-1) to anhydrous ethanol, stir and sonicate for 2 hours to obtain a dispersion; add NaNi to the dispersion. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2 was added, and the mixture was stirred and sonicated for 3 hours. Then, it was stirred and evaporated to dryness at 120°C, and dried in an oven at 150°C for 10 hours to obtain a solid. The solid was then heated to 500°C and held for 4 hours under a protective atmosphere to obtain the titanium aluminum carbide-coated cathode material. The titanium aluminum carbide contained NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 2% of O2.

[0100] S3: Titanium nitride (CAS: 25583-20-4) and the product of S2 were mixed and ball-milled with anhydrous ethanol as lubricant for 20 hours. The mixture was then compressed into tablets at 10 MPa and sintered at 800℃ for 7 hours. After cooling, grinding, sieving, and iron removal, a double-layer coated material NaNi was obtained. 0.5 Fe 0.2 Mn 0.2 Al 0.1 O2@Ti3AlC2@TiN. The titanium nitride added is NaNi by mass. 0.5 Fe 0.2 Mn 0.2 Al 0.1 0.5% of O2.

[0101] S4: Polypyrrole (CAS: 30604-81-0) was placed in a muffle furnace and pretreated with oxidation at 350°C for 3 hours in air atmosphere to obtain partially cross-linked polypyrrole precursors. The precursors were then transferred to a tube furnace and carbonized at 900°C (heating rate 2°C / min) for 6 hours in nitrogen atmosphere to obtain nitrogen-doped polymeric porous carbon.

[0102] S5: Apply the double-layer coating material NaNi obtained in step S3. 0.5 Fe 0.2 Mn 0.2 Al 0.1O2@Ti3AlC2@TiN was loaded into a fixed-bed reactor, nitrogen was introduced to purge the air from the reactor, and the reactor was heated to 120°C. A mixture of nitrogen and hydrogen (nitrogen to hydrogen volume ratio 1:1) was then introduced at a flow rate of 50 mL / min for purging. The resulting solution was then prepared according to the NaNi... 0.5 Fe 0.2 Mn 0.2 Al 0.1 Nitrogen-doped polymeric porous carbon with an O2 mass ratio of 0.5% was introduced with helium and reacted for 60 minutes. After washing and demagnetization, the material was dried at 95°C for 1 hour. The dried material was then calcined at 700°C for 4 hours to obtain the final composite cathode material.

[0103] The composite cathode materials obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to electronic conductivity tests using a conductivity meter. The composite cathode materials were fabricated into cathode sheets and their elongation was tested as follows: PVDF binder was added to NMP at a mass ratio of 1:8 and stirred to obtain a slurry. Then, the composite cathode material, conductive agent acetylene black, and slurry were mixed at a mass ratio of 97:1:2 and stirred under vacuum until the system was homogeneous, obtaining a cathode slurry. The cathode slurry was uniformly coated onto a cathode current collector, air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing, the cathode sheets were cut to the required specifications. The cathode sheets were cut into strips 15 mm wide and 100 mm long, fixed on a universal stretching machine, and stretched at a speed of 10 mm / s. The elongation of the cathode sheet was recorded when it broke. The results are shown in the table below.

[0104]

[0105] The results above show that:

[0106] In Comparative Example 1, without titanium aluminum carbide, the electronic conductivity and the elongation of the positive electrode decreased. The reason is that titanium aluminum carbide is a typical MAX phase material, and its conductivity exhibits metallic properties, which can significantly improve the conductivity of the material. The reason for the decrease in the elongation of the positive electrode is that titanium nitride has high hardness and wear resistance, but it is also brittle and easily cracks when subjected to impact. If the toughness of titanium aluminum carbide is lacking, the elongation of the electrode will decrease.

[0107] Comparative Example 2, without titanium nitride, showed little change in electronic conductivity and elongation.

[0108] In Comparative Example 3, without nitrogen-doped porous carbon, the electronic conductivity and elongation decreased. This is because nitrogen-doped porous carbon, being a carbon-based material, possesses excellent flexibility and a certain degree of plastic deformation capability (the interlayer or porous structure of carbon materials allows for a certain degree of stretching and bending without easily breaking). As the outermost coating layer, it acts like an "elastic buffer layer," adapting to deformation during electrode processing (such as rolling and cutting), dispersing external tensile stress, and preventing brittle fracture. The inner first coating layer (titanium aluminum carbide, a three-dimensional layered structure) and the second coating layer (titanium nitride) have mechanical properties more inclined towards "rigid support": while titanium aluminum carbide has a layered structure, it belongs to the MAX phase of ceramics, limiting its flexibility; titanium nitride (TiN) has high hardness and brittleness, with almost no plastic deformation capability. Without nitrogen-doped porous carbon, the overall flexibility of the coating layer decreases significantly, and the electrode lacks a "deformable buffer layer" during stretching, making it prone to rigid fracture and resulting in reduced elongation.

[0109] XPS analysis of nitrogen element was performed on the composite cathode material obtained in Example 2, such as... Figure 2 As shown, fitting revealed the formation of Al-N bonds. A possible reason is that when the various materials in the coating layer reach a certain content, some aluminum elements diffuse outwards during high-temperature sintering and combine with nitrogen elements in the third coating layer, forming Al-N bonds. This process also enhances interfacial stability and improves chemical stability. Furthermore, a battery was fabricated using the positive electrode sheet prepared in the aforementioned tests: The negative electrode active material graphite, conductive agent acetylene black, thickener CMC, and binder SBR were mixed in a mass ratio of 96.2:0.8:1.2:1.8. Deionized water was then added to the resulting mixture, and the mixture was stirred under vacuum until homogeneous, yielding a negative electrode slurry. This slurry was uniformly coated onto the negative electrode current collector, air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing, the slurry was cut to the required specifications to obtain negative electrode sheets. The positive electrode sheets, separator, and negative electrode sheets were stacked sequentially, and after assembly, a battery cell was obtained. The battery cell assembly is placed into the inner cavity of the battery casing. After drying, an electrolyte is injected into the inner cavity of the battery casing. The electrolyte solvent is ethylene carbonate, and the solute is sodium hexafluorophosphate (1 mol / L). After sealing, settling, formation, and capacity testing, a square sodium-ion battery is obtained. This square battery has a capacity of 20 Ah, a thickness of 15 mm, a width of 119 mm, and a height of 208 mm.

[0110] Sodium-ion batteries were charged at a constant current of 1C at room temperature (25℃), with a cutoff current of 0.05C, followed by a 10-minute rest period and a 0.7C discharge cycle, for a total of 1000 cycles. The capacity retention rate (%) and cycle expansion rate (%) after 1000 cycles were calculated. The upper limit of the charging voltage was 4.0V. The passing standard for the cycle performance test was: capacity retention rate ≥ 80% and cycle expansion thickness ≤ 10% after 1000 cycles. The test results are shown in the table below.

[0111]

[0112] In Comparative Example 1, without titanium aluminum carbide, the battery's capacity retention and cycle expansion rate decreased. This may be due to the lack of the conductivity and interlayer expansion buffering properties of titanium aluminum carbide.

[0113] In Comparative Example 2, without titanium nitride, the battery's capacity retention and cycle expansion rate decreased. Possible reasons include: 1. Titanium nitride serves as a transitional second coating layer. The first and second coating layers contain the same element, titanium, while the second and third coating layers contain the same element, nitrogen. The presence of the same element enhances the affinity between each reinforcing layer, allowing interpenetration between the layered oxide and the first coating layer, as well as between the coating layers themselves. This further improves the bonding strength between layers, resulting in a tighter bond and better synergistic effect. 2. Titanium nitride has excellent oxidation resistance, which can alleviate the structural collapse of the layered oxide under high voltage. Its combination with titanium aluminum carbide (Ti3AlC2) can reduce interfacial stress and promote element diffusion and bonding (such as Al-N bonds).

[0114] In Comparative Example 3, without nitrogen-doped porous carbon, the battery capacity retention rate decreased, possibly due to the lack of conductivity and structural smoothing effect of nitrogen-doped porous carbon.

[0115] In Comparative Example 4, the proportion of titanium aluminum carbide and nitrogen-doped polymeric porous carbon was too low, which affected the battery's capacity retention rate. The possible reasons are as described above.

[0116] In Comparative Example 5, if the proportion of titanium nitride and nitrogen-doped polymeric porous carbon is too low, it will affect the battery's capacity retention rate and cycle expansion rate, for possible reasons as mentioned above.

[0117] The applicant unexpectedly discovered that the capacity retention of the batteries prepared in Examples 2-5 was slightly improved compared to Example 1. Combined with XPS characterization, this may be because when the mass fraction of each coating layer is higher than 2%, Al-N bonds are formed in the composite cathode material. The formation of Al-N bonds further enhances the interfacial bonding strength, inhibits interlayer delamination, and thus improves the battery's capacity retention. The principle is as follows: the interfaces between titanium aluminum carbide (ceramic MAX phase) and TiN (rigid ceramic), and between TiN and nitrogen-doped carbon (carbon-based materials) may originally have weak bonding due to differences in chemical properties (such as polarity and lattice structure). Al-N bonds provide strong covalent bonds to the interfaces, significantly improving the interfacial bonding energy between the coating layers, reducing interlayer delamination caused by volume changes during charging and discharging (such as preventing voids between the first and second coating layers, and between the second and third coating layers when the core layer expands), thereby improving the structural integrity and cycle stability of the material, and thus improving the capacity retention.

Claims

1. A composite cathode material, comprising a layered oxide and a coating layer, characterized in that, The layered oxide has the general formula NaMe. 1-x Al x O2, wherein Me is one or more of nickel, iron, manganese, and cobalt, and x > 0; the coating layer covers the layered oxide, and the coating layer includes a first coating layer, a second coating layer, and a third coating layer from the inside to the outside. The first coating layer is titanium aluminum carbide, the second coating layer is titanium nitride, and the third coating layer is nitrogen-doped polymeric porous carbon. The composite cathode material forms Al-N bonds. The mass ratio of titanium aluminum carbide to the layered oxide is 1% to 3%, the mass ratio of titanium nitride to the layered oxide is 1% to 3%, and the mass ratio of nitrogen-doped polymeric porous carbon to the layered oxide is 1% to 3%.

2. The composite cathode material according to claim 1, characterized in that, The nitrogen-doped polymeric porous carbon is obtained by pre-oxidation and then carbonization of nitrogen-containing organic polymers.

3. A method for preparing the composite cathode material according to claim 1 or 2, characterized in that, Includes the following steps: (1) Disperse titanium aluminum carbide in anhydrous ethanol, then add layered oxide and ultrasonically stir to obtain a mixed dispersion. The solid material after drying the mixed dispersion is heated to 450-550°C under a protective atmosphere. (2) The titanium nitride and the product of step (1) are mixed, ball-milled, pressed into tablets and sintered. The sintered product is then ground and sieved. (3) The product of step (2) is loaded into a fixed bed reactor, nitrogen is introduced and air is discharged, and then the reactor is heated to 110-120°C and purged with a mixture of nitrogen and hydrogen. Nitrogen-doped polymerized porous carbon is then loaded into the reaction via helium. After the reaction is completed, the carbon is washed, dried and calcined to obtain the composite cathode material.

4. The method for preparing the composite cathode material according to claim 3, characterized in that, The nitrogen-doped polymeric porous carbon in step (3) is prepared by the following method: polypyrrole is pretreated by oxidation at 350-400°C in an air atmosphere, and then carbonized at 850-950°C in a nitrogen atmosphere.

5. The method for preparing the composite cathode material according to claim 3, characterized in that, The sintering temperature in step (2) is 750–900°C, and the calcination temperature in step (3) is 700–800°C.

6. A positive electrode plate, comprising a positive current collector, characterized in that, The surface of the positive electrode current collector is coated with a positive electrode slurry layer containing the composite positive electrode material as described in claim 1 or 2.

7. A sodium-ion battery, comprising a negative electrode, an electrolyte, a separator, and the positive electrode as described in claim 6.

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