Sodium-ion battery cathode material suitable for low-temperature environment and preparation method thereof

Abstract

The application discloses a sodium ion battery positive electrode material suitable for a low-temperature environment and a preparation method thereof, belongs to the technical field of electrode materials, and is used for solving the technical problem that the available capacity, electric conductivity and cycle stability of the sodium ion battery positive electrode material in the prior art are further improved in a low-temperature environment, and specifically comprises the following components in percentage by weight: 100 parts of a composite coating material, 3-5 parts of carbon black and 4-6 parts of modified graphite. The application is a multi-level structure synergistic design of precursor regulation, mesoporous carbon sphere construction, Sn-based composite coating and boron-doped modified graphite, which significantly improves the electric conductivity, capacity and low-temperature cycle stability of the sodium ion battery positive electrode material, so as to construct a positive electrode material system which has high efficient sodium storage capacity and excellent low-temperature performance.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, specifically to sodium-ion battery cathode materials suitable for low-temperature environments and their preparation methods. Background Technology

[0002] Sodium-ion batteries have shown great promise in large-scale energy storage and low-temperature applications due to their abundant resources, low cost, and excellent safety. However, traditional sodium-ion battery cathode materials still face many technical bottlenecks in practical applications, especially the performance degradation problem in low-temperature environments, which to some extent limits their applicability.

[0003] Currently, mainstream sodium-ion battery cathode materials suffer from problems such as insufficient stability of sodium storage sites and low ion and electron transport efficiency. Under low temperature conditions, the ion diffusion rate decreases significantly and the electrode interface impedance increases sharply, resulting in a significant decrease in battery discharge capacity, which cannot meet the requirements of low temperature scenarios. At the same time, the structural stability of the cathode material is poor. During long-term charge and discharge cycles, the active material is prone to agglomeration, dissolution or lattice distortion, which further aggravates capacity decay and shortens battery life.

[0004] Furthermore, the lack of synergistic design among the components makes it difficult to balance the sodium storage performance, conductivity, and structural stability of the material, thus failing to simultaneously meet the requirements of high initial charge-discharge efficiency, excellent room temperature and low temperature capacity, and long cycle stability.

[0005] Therefore, developing a sodium-ion battery cathode material that can synergistically optimize sodium storage sites, transport efficiency, and structural stability, and is suitable for low-temperature environments, has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a sodium-ion battery cathode material suitable for low-temperature environments and a method for preparing the same, in order to solve the technical problem of further improving the usable capacity, conductivity and cycle stability of sodium-ion battery cathode materials in low-temperature environments in the prior art.

[0007] The objective of this invention can be achieved through the following technical solution: a sodium-ion battery cathode material suitable for low-temperature environments, comprising the following components by weight: 100 parts of composite coating material, 3-5 parts of carbon black and 4-6 parts of modified graphite.

[0008] Furthermore, the preparation method of the composite coating material is as follows: sodium stannate hexahydrate and urea are added to a reaction vessel containing deionized water and anhydrous ethanol, and ultrasonically dispersed for 20-30 min. Then, precursor powder and hollow mesoporous carbon spheres are added, and ultrasonic dispersion is continued for 40-60 min. After that, the mixture is transferred to a high-pressure reaction vessel and reacted at 160-180℃ for 18-20 h. After the reaction is completed, the mixture is centrifuged, and the product is washed 3-4 times with deionized water and anhydrous ethanol, respectively. Then, it is transferred to a drying oven and dried at 60℃ for 6-8 h to obtain the composite coating material. The ratio of sodium stannate hexahydrate, urea, deionized water, anhydrous ethanol, precursor powder, and hollow mesoporous carbon spheres is 6-6.5 g: 11-12 g: 400 mL: 400 mL: 0.1-0.2 g: 1 g.

[0009] Reaction mechanism:

[0010] Sodium stannate hexahydrate and urea are ultrasonically dispersed in a deionized water-anhydrous ethanol mixed solvent to form a homogeneous solution. Simultaneously, the precursor powder and hollow mesoporous carbon spheres are fully dispersed. After being transferred to a high-pressure reactor, urea undergoes hydrolysis under hydrothermal conditions to generate ammonia, making the system alkaline. Sodium stannate hexahydrate hydrolyzes in the alkaline environment to generate a tin hydroxyl compound intermediate. This intermediate is further dehydrated and condensed to form SnO2 nanoparticles. The SnO2 nanoparticles and the precursor powder are combined through interfacial adsorption and are directionally deposited on the surface and within the mesoporous channels of the hollow mesoporous carbon spheres. After centrifugation and washing to remove unreacted urea, sodium stannate, and other impurities, and drying, a composite coating material with hollow mesoporous carbon spheres as the carrier and SnO2 and precursor powder as the composite coating layer is obtained.

[0011] Furthermore, the preparation method of the precursor powder is as follows: sodium acetate, nickel acetate tetrahydrate, and manganese acetate tetrahydrate are added to a reaction vessel containing an aqueous solution of ascorbic acid. After stirring at 20-30°C until the solid is completely dissolved, the temperature is raised to 60-80°C and stirred at a constant temperature for 22-24 hours. After standing at 60-80°C for 20-24 hours, the product is transferred to a drying oven and dried at 80-100°C for 20-24 hours. After grinding, the product is passed through a 400-mesh sieve. The ground fine powder is placed in a crucible and calcined at 400°C for 2-4 hours, then calcined at 700-800°C for 6-8 hours. After cooling to room temperature, the product is ground again and passed through a 500-mesh sieve to obtain the precursor powder.

[0012] Reaction mechanism:

[0013] Sodium acetate, nickel acetate tetrahydrate, and nickel acetate tetrahydrate dissociate into Na+ upon dissolving in ascorbic acid aqueous solution. + Ni 2+ Mn 2+ Ascorbic acid, through complexation with acetate ions, encapsulates metal ions and inhibits Ni. 2+ Mn2+ The metal ions are oxidized and then stirred under heating conditions to promote the slow hydrolysis of metal ions, generating metal hydroxide intermediates. These intermediates undergo dehydration condensation reactions to form colloidal particles, which gradually aggregate into a sol. Continuous stirring stabilizes the sol system. After standing at the same temperature, the colloidal particles further cross-link to form a three-dimensional network structure wet gel. The solvent in the wet gel is removed by drying. Then, it is calcined at 400°C to completely decompose the residual acetate and ascorbic acid in the dry gel into gases, generating amorphous Na, Ni, and Mn mixed oxides. Subsequently, the temperature is raised to 700-800°C for calcination, driving lattice rearrangement and atomic diffusion of the metal ions in the mixed oxides, ultimately forming a homogeneous amorphous Na. 0.5 Ni 0.25 Mn 0.75 O2 precursor powder.

[0014] Furthermore, the ratio of sodium acetate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, and ascorbic acid aqueous solution is 1.6g:2.5g:7.4g:110-120mL, and the mass fraction of the ascorbic acid aqueous solution is 1.5%.

[0015] Furthermore, the preparation method of the hollow mesoporous carbon spheres is as follows: tetraethyl orthosilicate is added to a reaction vessel containing anhydrous ethanol, deionized water and 25wt% ammonia water, and stirred at 20-30℃ for 10-20 min. Then, resorcinol and 37wt% formaldehyde aqueous solution are added, and the mixture is stirred for 20-24 h. After the reaction is completed, the mixture is centrifuged, and the product is washed 3-4 times with deionized water and anhydrous ethanol, respectively. The product is then transferred to a drying oven and dried at 60℃ for 24 h. After the product is transferred to a calcination furnace and calcined at 700-800℃ under a nitrogen atmosphere for 4-5 h, the product is transferred to a 3.85wt% sodium hydroxide aqueous solution and stirred for 6-8 h. After centrifugation, the product is transferred to a drying oven and dried at 60℃ for 24 h to obtain hollow mesoporous carbon spheres.

[0016] Reaction mechanism:

[0017] In a mixture of anhydrous ethanol and deionized water, tetraethyl orthosilicate undergoes hydrolysis with ammonia as a catalyst to generate a silicic acid intermediate. The intermediate is further dehydrated and condensed to form SiO2 sol microspheres. Subsequently, resorcinol and formaldehyde aqueous solution are added and undergo hydroxymethylation reaction in an alkaline environment to generate hydroxymethyl resorcinol. This hydroxymethyl resorcinol is then deposited on the surface of the SiO2 microspheres through a condensation reaction to form a phenolic resin coating layer. After centrifugation, washing, and drying, phenolic resin-coated SiO2 precursor powder is obtained. This precursor is calcined, and the phenolic resin undergoes a carbonization reaction to transform into an amorphous carbon shell. The SiO2 template remains stable, forming a carbon-coated SiO2 structure. Finally, the product is placed in an aqueous sodium hydroxide solution, where sodium hydroxide undergoes a metathesis reaction with the SiO2 template to generate soluble sodium silicate. After stirring to dissolve, centrifugation, and drying, the SiO2 template is removed, and finally, a carbon sphere material with a hollow mesoporous structure is obtained.

[0018] Furthermore, the ratio of the amounts of tetraethyl orthosilicate, anhydrous ethanol, deionized water, 25wt% ammonia, resorcinol, 37wt% formaldehyde aqueous solution, and 3.85wt% sodium hydroxide aqueous solution is 3.3-3.5mL:70mL:10mL:3mL:0.4g:0.5-0.6mL:80-100mL.

[0019] Furthermore, the modified graphite is prepared by the following steps:

[0020] A1. Add graphite to a reaction vessel containing concentrated sulfuric acid and concentrated nitric acid, stir at 60-70℃ for 2-3 hours. After the reaction is complete, filter, wash the filter cake with deionized water until the washing liquid is neutral, transfer it to a vacuum drying oven, and dry at 60℃ for 12 hours to obtain activated graphite.

[0021] A2. Add activated graphite to a reaction vessel containing deionized water and ultrasonically disperse for 20-30 minutes. Then add boric acid and stir for 2-3 hours. Transfer the mixture to a polytetrafluoroethylene-lined reaction vessel and react at 100-120°C for 4-6 hours. After the reaction is complete, cool to room temperature, filter, and wash the filter residue 3-4 times each with deionized water and ethanol. Then transfer the residue to a vacuum drying oven and dry at 60°C for 12 hours to obtain modified graphite.

[0022] Reaction mechanism:

[0023] In a mixed system of concentrated sulfuric acid and concentrated nitric acid, concentrated sulfuric acid acts as an intercalating agent, penetrating into the interlayer space of graphite to expand the interlayer spacing. Concentrated nitric acid acts as an oxidizing agent to oxidize and etch the graphite surface and edges, introducing oxygen-containing active functional groups such as hydroxyl, carboxyl, and epoxy groups. After washing and drying, surface-activated graphite is obtained. After ultrasonically dispersing the activated graphite in deionized water, boric acid is added as a Lewis acid. Under hydrothermal conditions, it undergoes coordination or dehydration condensation reactions with the oxygen-containing functional groups on the graphite surface to form stable COB covalent bonds, achieving chemical loading of boron on the graphite surface. After washing and vacuum drying, boron-modified graphite is obtained.

[0024] Furthermore, in step A1, the ratio of graphite, concentrated sulfuric acid, and concentrated nitric acid is 1g:12-18mL:4-6mL, the mass fraction of concentrated sulfuric acid is 98%, and the mass fraction of concentrated nitric acid is 65%; in step A2, the ratio of activated graphite, deionized water, and boric acid is 1g:100mL:0.5-0.8g.

[0025] This invention also proposes a method for preparing a sodium-ion battery cathode material suitable for low-temperature environments, which is prepared by the following steps:

[0026] S1. Add the composite coating material, carbon black, modified graphite and anhydrous ethanol to a ball mill and ball mill for 2-3 hours. Transfer to a forced-air drying oven and dry at 60-80℃ for 10-12 hours. Pass through a 300-400 mesh sieve to obtain a mixed powder.

[0027] S2. Transfer the mixed powder to a tube furnace, heat it to 400-500℃ at a rate of 2℃ / min and hold it for 2-3 hours. After cooling to room temperature, take it out, grind it, and pass it through a 400-500 mesh sieve to obtain sodium-ion battery cathode material.

[0028] The present invention has the following beneficial effects:

[0029] 1. The precursor powder of this invention is composed of a uniform amorphous layered structure of Na, Ni, Mn, and O elements, which provides stable lattice sites for reversible sodium storage and reduces irreversible reactions caused by structural distortion during ion insertion / extraction. The composite coating material uses hollow mesoporous carbon spheres as a carrier, and SnO2 nanoparticles and precursor powder are directionally deposited to form a composite coating layer. The synergistic effect of Sn, O, C and sodium storage elements isolates the active material from direct contact with the electrolyte, inhibits electrolyte decomposition and excessive oxidation of the active material surface. Modified graphite, after boron doping, forms COB covalent bonds, which not only improves its own electronic conductivity, but also synergistically constructs a uniform conductive network with carbon black, promotes uniform SEI film formation, and avoids the aggravation of local side reactions. The high specific surface area of ​​the hollow mesoporous carbon spheres further disperses the active components and conductive agents, reduces the increase in local impedance caused by agglomeration, and thus synergistically reduces the irreversible capacity loss during the first charge and discharge, significantly improving the first charge and discharge efficiency.

[0030] 2. The layered structure of Na, Ni, and Mn elements in the precursor powder of this invention is the core basis for reversible sodium storage, providing sufficient reversible sodium storage sites and laying the material foundation for high discharge capacity. The hollow structure and mesoporous channels of the hollow mesoporous carbon spheres, on the one hand, provide Na… + The material provides a fast channel for ion transport, reducing ion migration resistance at room temperature. On the other hand, it alleviates the problem of decreased ion diffusion rate in low-temperature environments, ensuring ion transport efficiency at low temperatures. The interfacial adsorption between SnO2 nanoparticles and precursors in the composite coating material enhances structural stability. The carrier function of hollow mesoporous carbon spheres effectively fixes the active components, inhibiting the dissolution, aggregation, and structural collapse of active substances during cycling. The three-dimensional conductive network formed by modified graphite and carbon black ensures efficient electron conduction at room temperature, low temperature, and during long-term cycling, preventing the active substances from being fully utilized due to blocked electron transport. The four substances work synergistically from multiple dimensions, including sodium storage site supply, ion / electron transport efficiency, and structural stability, enabling the material to have sufficient discharge capacity at room temperature, maintain good energy storage capacity at low temperatures, and effectively suppress capacity decay after long-term cycling.

[0031] 3. The modified graphite of this invention is oxidized and activated to introduce oxygen-containing functional groups and expand the interlayer spacing. Then, stable COB covalent bonds are formed through boron doping, which not only enhances its own electronic conductivity but also improves the interfacial bonding with other components, preventing the agglomeration of the conductive network. The hollow mesoporous carbon spheres are composed of C elements to form a highly conductive framework. Their mesoporous structure not only provides pathways for electronic conduction but also creates channels for ion transport, achieving synergistic matching of electron-ion conduction. In the composite coating material, SnO2 nanoparticles are uniformly dispersed on the surface and in the pores of the hollow mesoporous carbon, forming a conductive-sodium storage integrated structure with the precursor powder, reducing the resistance to electron transport between the active component and the conductive agent. The uniform amorphous structure of the precursor powder reduces the lattice resistance of ion insertion and extraction, and its tight bonding with the conductive network further optimizes the interfacial contact. The four substances form a synergistic effect in terms of electronic conduction efficiency, ion transport channels, and interfacial compatibility, significantly reducing the electronic and ion transport resistance inside the material and significantly improving the overall electrical conductivity performance. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In this application, the carbon black is selected from Tianjin Baochi Chemical Technology Co., Ltd., CAS No. 133-86-4, with a specific surface area of ​​70 m². 2 / g;

[0034] In this application, the graphite is selected from Lingshou County Yaoyang Mineral Products Processing Plant, with an expansion factor of 1.5 times and a moisture content of 0.1%.

[0035] Example 1

[0036] This embodiment provides a method for preparing a sodium-ion battery cathode material suitable for low-temperature environments, including the following steps:

[0037] S1. Preparation of precursor powder

[0038] Weigh out 16g of sodium acetate, 25g of nickel acetate tetrahydrate, and 74g of manganese acetate tetrahydrate and add them to a reaction vessel containing 1100mL of 1.5wt% ascorbic acid aqueous solution. Stir at 20℃ until the solid is completely dissolved, then heat to 60℃ and stir for 22h. Let stand at 60℃ for 20h, transfer the product to a drying oven, dry at 80℃ for 20h, grind, and pass through a 400-mesh sieve. Place the ground fine powder in a crucible, calcine at 400℃ for 2h, then calcine at 700℃ for 6h. After cooling to room temperature, grind again and pass through a 500-mesh sieve to obtain the precursor powder.

[0039] S2. Preparation of hollow mesoporous carbon spheres

[0040] Weigh 33 mL of tetraethyl orthosilicate and add it to a reaction vessel containing 700 mL of anhydrous ethanol, 100 mL of deionized water, and 30 mL of 25 wt% ammonia. Stir at 20 °C for 10 min. Then add 4 g of resorcinol and 5 mL of 37 wt% formaldehyde aqueous solution and stir for 20 h. After the reaction is complete, centrifuge and wash the product three times with deionized water and anhydrous ethanol, respectively. Transfer to a drying oven and dry at 60 °C for 24 h. Transfer to a calcination furnace and calcine at 700 °C under a nitrogen atmosphere for 4 h. After calcination, transfer to 800 mL of 3.85 wt% sodium hydroxide aqueous solution and stir for 6 h. Centrifuge and transfer the product to a drying oven and dry at 60 °C for 24 h to obtain hollow mesoporous carbon spheres.

[0041] S3. Preparation of composite coating materials

[0042] Weigh out 60g of sodium stannate hexahydrate and 110g of urea and add them to a reactor containing 4000mL of deionized water and 4000mL of anhydrous ethanol. Disperse the mixture by sonication for 20min. Then add 1g of precursor powder and 10g of hollow mesoporous carbon spheres and continue to disperse by sonication for 40min. Transfer the mixture to a high-pressure reactor and react at 160℃ for 18h. After the reaction is complete, centrifuge the mixture and wash the product three times with deionized water and anhydrous ethanol. Transfer the product to a drying oven and dry it at 60℃ for 6h to obtain the composite coating material.

[0043] S4. Preparation of modified graphite

[0044] Weigh 10g of graphite and add it to a reaction vessel containing 120mL of 98wt% concentrated sulfuric acid and 40mL of 65wt% concentrated nitric acid. Stir at 60℃ for 2h. After the reaction is complete, filter the mixture and wash the filter cake with deionized water until the washing liquid is neutral. Transfer the cake to a vacuum drying oven and dry at 60℃ for 12h to obtain activated graphite.

[0045] Weigh 10g of activated graphite and add it to a reaction vessel containing 1000mL of deionized water. Disperse the mixture ultrasonically for 20min. Then add 5g of boric acid and stir for 2h. Transfer the mixture to a polytetrafluoroethylene-lined reaction vessel and react at 100℃ for 4h. After the reaction is complete, cool to room temperature, filter, and wash the filter residue three times each with deionized water and ethanol. Then transfer the residue to a vacuum drying oven and dry at 60℃ for 12h to obtain modified graphite.

[0046] S5. Preparation of sodium-ion battery cathode materials

[0047] Weigh out 100 parts of composite coating material, 3 parts of carbon black, 4 parts of modified graphite and 140 parts of anhydrous ethanol by weight, add them to a ball mill and ball mill for 2 hours, transfer them to a forced-air drying oven and dry them at 60°C for 10 hours, and pass them through a 300-mesh sieve to obtain mixed powder.

[0048] The mixed powder was transferred to a tube furnace and heated to 400°C at a rate of 2°C / min. After holding at this temperature for 2 hours, the powder was cooled to room temperature, ground, and passed through a 400-mesh sieve to obtain the sodium-ion battery cathode material.

[0049] Example 2

[0050] This embodiment provides a method for preparing a sodium-ion battery cathode material suitable for low-temperature environments, including the following steps:

[0051] S1. Preparation of precursor powder

[0052] Weigh out 16g of sodium acetate, 25g of nickel acetate tetrahydrate, and 74g of manganese acetate tetrahydrate and add them to a reaction vessel containing 1150mL of 1.5wt% ascorbic acid aqueous solution. Stir at 25℃ until the solid is completely dissolved, then heat to 70℃ and stir for 23h. Let stand at 70℃ for 22h, transfer the product to a drying oven, dry at 90℃ for 22h, grind, and pass through a 400-mesh sieve. Place the ground fine powder in a crucible, calcine at 400℃ for 3h, then calcine at 750℃ for 7h. After cooling to room temperature, grind again and pass through a 500-mesh sieve to obtain the precursor powder.

[0053] S2. Preparation of hollow mesoporous carbon spheres

[0054] Weigh 34 mL of tetraethyl orthosilicate and add it to a reaction vessel containing 700 mL of anhydrous ethanol, 100 mL of deionized water, and 30 mL of 25 wt% ammonia. Stir at 25 °C for 15 min. Then add 4 g of resorcinol and 5.5 mL of 37 wt% formaldehyde aqueous solution and stir for 22 h. After the reaction is complete, centrifuge and wash the product three times with deionized water and anhydrous ethanol, respectively. Transfer to a drying oven and dry at 60 °C for 24 h. Transfer to a calcination furnace and calcine at 750 °C under a nitrogen atmosphere for 4.5 h. After calcination, transfer to 900 mL of 3.85 wt% sodium hydroxide aqueous solution and stir for 7 h. Centrifuge and transfer the product to a drying oven and dry at 60 °C for 24 h to obtain hollow mesoporous carbon spheres.

[0055] S3. Preparation of composite coating materials

[0056] Weigh out 62g of sodium stannate hexahydrate and 115g of urea and add them to a reactor containing 4000mL of deionized water and 4000mL of anhydrous ethanol. Disperse the mixture by sonication for 25min. Then add 1.5g of precursor powder and 10g of hollow mesoporous carbon spheres and continue to disperse by sonication for 50min. Transfer the mixture to a high-pressure reactor and react at 170℃ for 19h. After the reaction is complete, centrifuge the mixture and wash the product three times with deionized water and anhydrous ethanol. Then transfer the product to a drying oven and dry it at 60℃ for 7h to obtain the composite coating material.

[0057] S4. Preparation of modified graphite

[0058] Weigh 10g of graphite and add it to a reaction vessel containing 150mL of 98wt% concentrated sulfuric acid and 50mL of 65wt% concentrated nitric acid. Stir at 65℃ for 2.5h. After the reaction is complete, filter the mixture and wash the filter cake with deionized water until the washing liquid is neutral. Transfer the cake to a vacuum drying oven and dry at 60℃ for 12h to obtain activated graphite.

[0059] Weigh 10g of activated graphite and add it to a reactor containing 1000mL of deionized water. Disperse the mixture ultrasonically for 25min. Then add 6g of boric acid and stir for 2.5h. Transfer the mixture to a polytetrafluoroethylene-lined reactor and react at 110℃ for 5h. After the reaction is complete, cool to room temperature, filter, and wash the filter residue three times each with deionized water and ethanol. Then transfer the residue to a vacuum drying oven and dry at 60℃ for 12h to obtain modified graphite.

[0060] S5. Preparation of sodium-ion battery cathode materials

[0061] Weigh out 100 parts of composite coating material, 4 parts of carbon black, 5 parts of modified graphite and 145 parts of anhydrous ethanol by weight, add them to a ball mill and ball mill for 2.5 hours, transfer to a forced-air drying oven and dry at 70°C for 11 hours, and pass through a 300-mesh sieve to obtain a mixed powder.

[0062] The mixed powder was transferred to a tube furnace and heated to 450°C at a rate of 2°C / min, held at that temperature for 2.5 hours, cooled to room temperature, ground, and passed through a 400-mesh sieve to obtain sodium-ion battery cathode material.

[0063] Example 3

[0064] This embodiment provides a method for preparing a sodium-ion battery cathode material suitable for low-temperature environments, including the following steps:

[0065] S1. Preparation of precursor powder

[0066] Weigh out 16g of sodium acetate, 25g of nickel acetate tetrahydrate, and 74g of manganese acetate tetrahydrate and add them to a reaction vessel containing 1200mL of 1.5wt% ascorbic acid aqueous solution. Stir at 30℃ until the solid is completely dissolved, then heat to 80℃ and stir for 24h. Let stand at 80℃ for 24h, transfer the product to a drying oven, dry at 100℃ for 24h, grind, and pass through a 400-mesh sieve. Place the ground fine powder in a crucible, calcine at 400℃ for 4h, then calcine at 800℃ for 8h. After cooling to room temperature, grind again and pass through a 500-mesh sieve to obtain the precursor powder.

[0067] S2. Preparation of hollow mesoporous carbon spheres

[0068] Weigh 35 mL of tetraethyl orthosilicate and add it to a reaction vessel containing 700 mL of anhydrous ethanol, 100 mL of deionized water, and 30 mL of 25 wt% ammonia. Stir at 30 °C for 20 min. Then add 4 g of resorcinol and 6 mL of 37 wt% formaldehyde aqueous solution and stir for 24 h. After the reaction is complete, centrifuge and wash the product four times with deionized water and anhydrous ethanol, respectively. Transfer to a drying oven and dry at 60 °C for 24 h. Transfer to a calcination furnace and calcine at 800 °C under a nitrogen atmosphere for 5 h. After calcination, transfer to 1000 mL of 3.85 wt% sodium hydroxide aqueous solution and stir for 8 h. Centrifuge and transfer the product to a drying oven and dry at 60 °C for 24 h to obtain hollow mesoporous carbon spheres.

[0069] S3. Preparation of composite coating materials

[0070] Weigh out 65g of sodium stannate hexahydrate and 120g of urea and add them to a reaction vessel containing 4000mL of deionized water and 4000mL of anhydrous ethanol. Disperse the mixture by sonication for 30min. Then add 2g of precursor powder and 10g of hollow mesoporous carbon spheres and continue to disperse by sonication for 60min. Transfer the mixture to a high-pressure reaction vessel and react at 180℃ for 20h. After the reaction is complete, centrifuge the mixture and wash the product four times with deionized water and anhydrous ethanol. Transfer the product to a drying oven and dry it at 60℃ for 8h to obtain the composite coating material.

[0071] S4. Preparation of modified graphite

[0072] Weigh 10g of graphite and add it to a reaction vessel containing 180mL of 98wt% concentrated sulfuric acid and 60mL of 65wt% concentrated nitric acid. Stir at 70℃ for 3h. After the reaction is complete, filter the mixture and wash the filter cake with deionized water until the washing liquid is neutral. Transfer the cake to a vacuum drying oven and dry at 60℃ for 12h to obtain activated graphite.

[0073] Weigh 10g of activated graphite and add it to a reactor containing 1000mL of deionized water. Disperse the mixture by sonication for 30min. Then add 8g of boric acid and stir for 3h. Transfer the mixture to a polytetrafluoroethylene-lined reactor and react at 120℃ for 6h. After the reaction is complete, cool to room temperature, filter, and wash the filter residue 4 times each with deionized water and ethanol. Then transfer the residue to a vacuum drying oven and dry at 60℃ for 12h to obtain modified graphite.

[0074] S5. Preparation of sodium-ion battery cathode materials

[0075] Weigh out 100 parts of composite coating material, 5 parts of carbon black, 6 parts of modified graphite and 150 parts of anhydrous ethanol by weight, add them to a ball mill and ball mill for 3 hours, transfer them to a forced-air drying oven and dry at 80℃ for 12 hours, and pass them through a 400-mesh sieve to obtain mixed powder.

[0076] The mixed powder was transferred to a tube furnace and heated to 500°C at a rate of 2°C / min. After holding at that temperature for 3 hours, the powder was cooled to room temperature, ground, and passed through a 500-mesh sieve to obtain the sodium-ion battery cathode material.

[0077] Comparative Example 1

[0078] The difference between this comparative example and Example 3 is that step S1 is omitted and precursor powder is not added in step S3.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 3 is that steps S1 and S3 are omitted, and the hollow mesoporous carbon spheres prepared in step S2 are used to replace the composite coating material in step S5.

[0081] Comparative Example 3

[0082] The difference between this comparative example and Example 3 is that step S4 is omitted, and the modified graphite in step S5 is replaced with the graphite in step S4.

[0083] Performance testing:

[0084] The first charge-discharge efficiency of the sodium-ion battery cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 was determined according to Appendix C of GB / Z 155-2025 "General Rules for Cathode Materials of Sodium-ion Batteries".

[0085] The room temperature discharge capacity, low temperature discharge capacity at -20℃, and discharge capacity (i.e. capacity recovery ability) of the sodium-ion battery cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 were determined according to the standard T / CI 255-2023 "Performance Requirements and Test Methods for Sodium-ion Batteries".

[0086] The conductivity of the sodium-ion battery cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 was determined according to standard NB / T 10827-2021 "Test Method for Ion Conductivity of Power Battery Thin Films". The specific test results are shown in Table 1 below:

[0087] Table 1 - Performance Test Data of Samples

[0088]

[0089] Data Analysis:

[0090] Comparative analysis of the data in Table 1 above shows that the sodium-ion battery cathode material prepared by this invention has an initial charge-discharge efficiency of 93.2%, a room temperature discharge capacity of 135 mAh, a low temperature discharge capacity of 111 mAh at -20℃, a discharge capacity of 117 mAh after 500 cycles, and a conductivity of 70.2 S / m.

[0091] Compared with Example 1, the lack of the precursor, the main sodium storage component, significantly reduced the reversible sodium storage capacity of the material. Furthermore, the composite coating layer could not fully play its role in isolating the electrolyte and suppressing side reactions, ultimately leading to a significant degradation in various performance characteristics. The initial charge-discharge efficiency decreased from 93.2% in Example 3 to 80.6%; the room temperature discharge capacity decreased from 135mAh to 117mAh, a reduction of 18mAh; the -20℃ low temperature discharge capacity decreased from 111mAh to 97mAh, a reduction of 14mAh; the discharge capacity after 500 cycles decreased from 117mAh to 103mAh, a reduction of 14mAh; and the conductivity decreased slightly due to the lack of a low-conductivity precursor, from 70.2S / m to 64.8S / m, a decrease of 5.4S / m.

[0092] Comparative Example 2 lacks both a precursor to provide sufficient reversible sodium storage sites and a composite coating layer to inhibit the aggregation of active materials and electrolyte decomposition. Relying solely on the limited sodium storage capacity of hollow mesoporous carbon spheres, it ultimately suffers the greatest performance degradation. The initial charge-discharge efficiency drops from 93.2% to 75.9%, a decrease of 17.3 percentage points; the room temperature discharge capacity decreases from 135mAh to 109mAh, a reduction of 26mAh; the -20℃ low temperature discharge capacity decreases from 111mAh to 90mAh, a decrease of 21mAh; the discharge capacity after 500 cycles decreases from 117mAh to 94mAh, a reduction of 23mAh; and the conductivity, due to the lack of a composite-coated integrated conductive-sodium storage structure, decreases from 70.2S / m to 61.1S / m, a reduction of 9.1S / m.

[0093] In Comparative Example 3, the COB covalent bonds formed by boron doping of modified graphite enhance electron conductivity and dispersibility. However, ordinary graphite has poor conductivity and dispersibility, making it unable to form an efficient conductive system with carbon black and hollow mesoporous carbon spheres. This leads to increased electron transport resistance and uneven SEI film formation, ultimately resulting in a gradual decline in various performance characteristics. The initial charge-discharge efficiency decreased from 93.2% to 85.7%, a drop of 7.5 percentage points; the room temperature discharge capacity decreased from 135mAh to 124mAh, a reduction of 11mAh; the -20℃ low temperature discharge capacity decreased from 111mAh to 102mAh, a decrease of 9mAh; and the discharge capacity after 500 cycles decreased from 117mAh to 107mAh, a reduction of 10mAh. The conductivity was most significantly affected by the decrease in conductive network efficiency, decreasing from 70.2S / m to 57.2S / m, a drop of 13S / m, making it the most significantly degraded performance indicator in this comparative example.

[0094] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A sodium-ion battery cathode material suitable for low-temperature environments, characterized in that, Includes the following components by weight: 100 parts composite coating material, 3-5 parts carbon black and 4-6 parts modified graphite.

2. The sodium-ion battery cathode material suitable for low-temperature environments according to claim 1, characterized in that, The preparation method of the composite coating material is as follows: sodium stannate hexahydrate and urea are added to a reaction vessel containing deionized water and anhydrous ethanol, and ultrasonically dispersed for 20-30 min. Then, precursor powder and hollow mesoporous carbon spheres are added, and ultrasonic dispersion is continued for 40-60 min. After that, the mixture is transferred to a high-pressure reaction vessel and reacted at 160-180℃ for 18-20 h. After post-treatment, the composite coating material is obtained. The ratio of sodium stannate hexahydrate, urea, deionized water, anhydrous ethanol, precursor powder and hollow mesoporous carbon spheres is 6-6.5 g: 11-12 g: 400 mL: 400 mL: 0.1-0.2 g: 1 g.

3. The sodium-ion battery cathode material suitable for low-temperature environments according to claim 2, characterized in that, The precursor powder is prepared as follows: sodium acetate, nickel acetate tetrahydrate, and manganese acetate tetrahydrate are added to a reaction vessel containing an aqueous solution of ascorbic acid. The mixture is stirred at 20-30°C until the solid is completely dissolved. The temperature is then raised to 60-80°C and stirred for 22-24 hours. The mixture is then allowed to stand at 60-80°C for 20-24 hours. The product is then transferred to a drying oven and dried at 80-100°C for 20-24 hours. After drying, the product is ground and passed through a 400-mesh sieve. The ground fine powder is placed in a crucible and calcined at 400°C for 2-4 hours, then calcined at 700-800°C for 6-8 hours. After cooling to room temperature, the powder is ground again and passed through a 500-mesh sieve to obtain the precursor powder.

4. The sodium-ion battery cathode material suitable for low-temperature environments according to claim 3, characterized in that, The ratio of sodium acetate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, and ascorbic acid aqueous solution is 1.6g:2.5g:7.4g:110-120mL, and the mass fraction of the ascorbic acid aqueous solution is 1.5%.

5. The sodium-ion battery cathode material suitable for low-temperature environments according to claim 2, characterized in that, The method for preparing the hollow mesoporous carbon spheres is as follows: Tetraethyl orthosilicate is added to a reaction vessel containing anhydrous ethanol, deionized water, and 25 wt% ammonia. The mixture is stirred at 20-30°C for 10-20 min. Then, resorcinol and 37 wt% formaldehyde aqueous solution are added, and the mixture is stirred for 20-24 h. After the reaction is completed, the mixture is centrifuged, and the product is washed 3-4 times with deionized water and anhydrous ethanol, respectively. The product is then transferred to a drying oven and dried at 60°C for 24 h. After the product is transferred to a calcination furnace and calcined at 700-800°C under a nitrogen atmosphere for 4-5 h, the product is transferred to a 3.85 wt% sodium hydroxide aqueous solution and stirred for 6-8 h. The mixture is then centrifuged, and the product is transferred to a drying oven and dried at 60°C for 24 h to obtain hollow mesoporous carbon spheres.

6. The sodium-ion battery cathode material suitable for low-temperature environments according to claim 5, characterized in that, The ratio of tetraethyl orthosilicate, anhydrous ethanol, deionized water, 25wt% ammonia, resorcinol, 37wt% formaldehyde aqueous solution, and 3.85wt% sodium hydroxide aqueous solution is 3.3-3.5mL:70mL:10mL:3mL:0.4g:0.5-0.6mL:80-100mL.

7. The sodium-ion battery cathode material suitable for low-temperature environments according to claim 1, characterized in that, The modified graphite is prepared by the following steps: A1. Add graphite to a reaction vessel containing concentrated sulfuric acid and concentrated nitric acid, stir at 60-70℃ for 2-3 hours, and then perform post-treatment to obtain activated graphite. A2. Add activated graphite to a reactor containing deionized water and ultrasonically disperse for 20-30 minutes. Then add boric acid and stir for 2-3 hours. Transfer the mixture to a polytetrafluoroethylene-lined reactor and react at 100-120°C for 4-6 hours. After post-treatment, modified graphite is obtained.

8. The sodium-ion battery cathode material suitable for low-temperature environments according to claim 7, characterized in that, In step A1, the ratio of graphite, concentrated sulfuric acid, and concentrated nitric acid is 1g:12-18mL:4-6mL, the mass fraction of concentrated sulfuric acid is 98%, and the mass fraction of concentrated nitric acid is 65%. In step A2, the ratio of activated graphite, deionized water, and boric acid is 1g:100mL:0.5-0.8g.

9. The method for preparing a sodium-ion battery cathode material suitable for low-temperature environments according to any one of claims 1-8, characterized in that, The sodium-ion battery cathode material suitable for low-temperature environments is prepared by the following steps: S1. Add the composite coating material, carbon black, modified graphite and anhydrous ethanol to a ball mill and ball mill for 2-3 hours. Transfer to a forced-air drying oven and dry at 60-80℃ for 10-12 hours. Pass through a 300-400 mesh sieve to obtain a mixed powder. S2. Transfer the mixed powder to a tube furnace, heat it to 400-500℃ at a rate of 2℃ / min and hold it for 2-3 hours. After cooling to room temperature, take it out, grind it, and pass it through a 400-500 mesh sieve to obtain sodium-ion battery cathode material.

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