Ni-doped cobalt sulfide three-dimensional graphene negative electrode material for sodium ion batteries and preparation method thereof

Abstract

This invention relates to a Ni-doped cobalt sulfide three-dimensional graphene anode material for sodium-ion batteries and its preparation method, belonging to the field of electrochemical energy storage. A NiCoCN precursor is obtained by grinding and mixing nickel nitrate, cobalt nitrate, and urea uniformly, followed by air annealing. The precursor is then mixed with a commercial graphene oxide solution, stirred, centrifuged, washed, and dried to obtain a NiCoCN / graphene oxide precursor. High-temperature sulfidation using thiourea as a sulfur source via vapor deposition yields the NiCoSCN@three-dimensional graphene anode material. When this anode material is applied to sodium-ion battery anodes, nickel doping improves the rate performance and long-cycle stability of the material. (5 A g) ‑1 After 400 cycles, the capacity retention is ≥80% at 10 A g. ‑1 After 1000 cycles, the capacity retention rate can still reach over 65%. This method has a simple preparation process and broad application prospects in the energy field.

Description

[0001] Applicants: Jiangsu Jintianchen New Materials Co., Ltd., Jiangsu Jiangke Composite New Materials Co., Ltd., Jiangsu University Inventors: Song Qun, Xie Meng, Liu Ying, Xu Yuanguo, Li Yongming, Hu Chenchao, Liu Runxing, Xie Jimin, Dai Min Technical Field

[0002] This invention belongs to the field of novel secondary battery energy storage materials technology, and relates to a method for preparing a negative electrode material for sodium-ion batteries, using three-dimensional graphene as a conductive framework and Ni-doped cobalt sulfide composite three-dimensional graphene negative electrode material. Background Technology

[0003] Sodium-ion batteries have shown great potential for large-scale energy storage due to their advantages such as abundant sodium resources, low cost, and relatively high safety. However, the sodium ion radius (1.02 Å) is larger than that of lithium ions (0.76 Å), resulting in slow insertion / extraction kinetics in electrode materials and easily causing severe structural volume changes. This is a key bottleneck restricting the development of sodium-ion batteries. Developing anode materials with high specific capacity, excellent rate performance, and long cycle stability is currently a research hotspot.

[0004] Transition metal sulfides (such as NiS2 and CoS2) are considered promising anode materials for sodium-ion batteries due to their high theoretical specific capacity and abundant redox reactions. However, these materials typically experience significant volume expansion and contraction during charge and discharge, leading to pulverization of the active material and detachment from the current collector, resulting in rapid capacity decay. Furthermore, their poor intrinsic conductivity limits the improvement of rate performance.

[0005] Composite materials with carbon materials are an effective strategy for solving the aforementioned problems. Graphene, especially three-dimensional graphene, possesses high specific surface area, excellent conductivity, and good mechanical flexibility, providing a stable conductive network and physical space to buffer volume changes for active materials. Various graphene composite anode materials have been reported in existing technologies, such as nickel selenide / graphene, nickel-phosphorus-based / graphene, and flower-like Ni3S2 / three-dimensional graphene composites. However, these methods mostly employ hydrothermal or solvothermal methods, which suffer from complex processes, harsh reaction conditions, uneven distribution of active materials, or weak bonding with graphene. Vapor deposition can achieve uniform and robust loading of active materials on a carbon framework, but its application in preparing composites of nickel-cobalt bimetallic thiocyanate and three-dimensional graphene for use as anode materials in sodium-ion batteries has not yet been reported. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a NiCoSCN@3D graphene sodium-ion battery anode material and its preparation method that combine high specific capacity and long-term stability. This method utilizes a simple solid-phase grinding combined with a gas-phase sulfidation process to generate uniformly distributed NiCoSCN nanoparticles in situ on a 3D graphene framework. This effectively combines the high capacity advantage of bimetallic sulfides with the high conductivity and structural stability of the 3D graphene network. The material also exhibits excellent rate performance and long-term cycle stability, making it suitable for high-performance energy storage devices. The preparation process is simple, the conditions are controllable, and it is easy to scale up production.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a Ni-doped cobalt sulfide three-dimensional graphene sodium-ion battery anode material includes the following steps: 1. Preparation of NiCoCN precursor: Cobalt nitrate, nickel nitrate and urea are mixed and ground in a certain molar ratio, and then annealed in air atmosphere to obtain NiCoCN precursor powder.

[0008] 2. Preparation of NiCoCN / graphene oxide composite precursor: The NiCoCN precursor powder obtained in step 1 is mixed with graphene oxide dispersion, and after stirring, sonication, centrifugation, washing and drying, the NiCoCN / graphene oxide composite precursor is obtained.

[0009] 3. Preparation of NiCoSCN@3D graphene anode material by vapor-phase sulfidation: Using thiourea as the sulfur source, the NiCoCN / GO composite precursor obtained in step 2 was placed upstream and downstream of a tube furnace, respectively, for vapor-phase deposition under an inert atmosphere. During the reaction, the sulfur-containing gaseous species generated by the decomposition of thiourea sulfidated the NiCoCN precursor, while GO was thermally reduced to rGO, which further crosslinked with NiCoCN to form 3D graphene, ultimately yielding the NiCoSCN@3D graphene anode material.

[0010] 4. The obtained negative electrode material was mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 8:1:1, using N-methylpyrrolidone as a solvent, and stirred for 6 h to make the slurry uniform. The slurry was coated onto an aluminum foil current collector, vacuum dried, and then punched to obtain the negative electrode sheet. The negative electrode sheet was then assembled into a coin cell in a glove box for electrochemical testing.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Significant structural advantages: The three-dimensional graphene network provides a continuous pathway for the rapid transport of electrons and ions. Its porous structure can effectively buffer the volume expansion of NiCoSCN during the sodium ion insertion and extraction process, inhibit the agglomeration and pulverization of active materials, thereby significantly improving the cycling stability of the material.

[0012] 2. Prominent synergistic effect: The introduction of nickel-cobalt bimetal can regulate the electronic structure of the material through the synergistic effect between different metals, providing more redox active sites and helping to improve the reversible specific capacity of the material.

[0013] 3. Simple and efficient process: The chemical vapor deposition method enables in-situ and uniform growth of active materials on a three-dimensional graphene framework, resulting in a tight bond and low interfacial contact resistance. This method requires no complex templates or post-processing, has a simple process flow, good repeatability, and is suitable for large-scale production.

[0014] 4. Excellent electrochemical performance: When used as the anode of sodium-ion batteries, this composite material exhibits high reversible specific capacity, excellent rate performance and long cycle life, and has broad development prospects in the energy field. Attached Figure Description Figure 1 X-ray diffraction (XRD) patterns of the anode materials: (a) CoSCN@3D graphene; (b) NiCoSCN@3D graphene. The images clearly show a series of sharp and symmetrical characteristic diffraction peaks, with each peak position highly matching the standard crystal phase card. There are no obvious impurity peaks, indicating that the prepared NiCoSCN crystal has high crystallinity and excellent phase purity. The peak shift originates from nickel ions (Ni... 2+ The doping into the CoSCN lattice confirms the successful construction of the bimetallic Ni-Co sulfide system.

[0016] Figure 2 SEM images of the anode materials: (a) CoSCN@3D graphene; (b) NiCoSCN@3D graphene. The images clearly show that the NiCoSCN nanoparticles are more uniform in size, more densely distributed on the surface of the graphene oxide sheets, and exhibit excellent dispersion without local agglomeration. The graphene oxide sheets have more pronounced wrinkles, forming a three-dimensional interconnected porous network structure. The NiCoSCN particles are tightly anchored to the nodes and surfaces of the three-dimensional network, resulting in a larger interface contact area and stronger bonding. The overall material has higher porosity and better pore connectivity. Nickel doping effectively enhances the stability of the samples. The three-dimensional interconnected graphene network provides a continuous pathway for electron conduction, and the highly interconnected pores accelerate sodium ion migration, enhancing the material's rate performance while further strengthening structural stability.

[0017] Figure 3 The first three charge-discharge curves of the negative electrode material (0.1 A g) -1 (a) CoSCN@3D graphene; (b) NiCoSCN@3D graphene; Figure 3 (c) Comparison of the first 400 cycle performance tests of the anode materials CoSCN@3D graphene and NiCoSCN@3D graphene (5 A g) -1The charge-discharge curves show that the first discharge specific capacity is ≥ 600 mAh·g. -1 The first-cycle coulomb efficiency is ≥ 80%; the cycle performance diagram shows that at 5 A·g -1 After 400 cycles at high current density, the capacity retention rate still reaches over 80%. Undoped CoSCN@3D graphene material exhibits overcharge failure after 307 cycles at the same current density, confirming the excellent cycle stability of the NiCoSCN@3D graphene anode material. The second and third cycle charge-discharge curves almost completely overlap, with less voltage polarization and a more stable and wider redox plateau, indicating superior sodium ion insertion / extraction kinetics. The curves show no significant distortion, confirming the stability of the crystal structure during charge-discharge, without severe phase transitions or structural collapse. Nickel doping significantly improves the material's reversible specific capacity and optimizes sodium ion insertion / extraction kinetics; the highly overlapping cycle curves demonstrate the material's excellent electrochemical reversibility and interfacial stability.

[0018] Figure 4 The graph shows the first 1000 cycle performance test results (10 A g) of the NiCoSCN@3D graphene anode material. -1 The results showed that at 10 A·g -1 After cycling 1000 times at ultra-high current density, the reversible specific capacity still remains at 241 mAh·g. -1 The capacity retention rate reached 65%, which confirms that the NiCoSCN@3D graphene anode material has excellent rate performance. The 3D graphene framework effectively buffers the volume expansion of the active material, inhibits structural collapse and active material shedding, and the anode material has strong electrochemical reversibility and good structural stability. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Example 1:

[0020] The preparation method of NiCoSCN@3D graphene anode material includes the following steps: Step 1. Preparation of NiCoCN precursor: Accurately weigh nickel nitrate hexahydrate (Ni(NO3)2·6H2O) and cobalt nitrate hexahydrate (Ni(NO3)2·6H2O) to achieve a molar ratio of nickel ions to cobalt ions of 1:1. Weigh urea, ensuring its molar mass is four times the total molar mass of nickel and cobalt metal ions. Place the above raw materials in an agate mortar and grind continuously at room temperature for 40 minutes until the mixture becomes a uniform, viscous, pinkish-purple substance. Transfer the ground product to an alumina crucible and place it in a box-type muffle furnace. Under a static air atmosphere, heat to 400°C at a heating rate of 3°C / min and hold at this temperature for 3 hours. After the reaction is complete, allow it to cool naturally to room temperature to obtain NiCoCN precursor powder.

[0021] Step 2. Preparation of NiCoCN / graphene oxide precursor: A 3 mg / mL aqueous dispersion of graphene oxide (GO) was prepared. The Ni-CoCN precursor powder obtained in step 1 was weighed and slowly added to the GO dispersion at a NiCoCN to GO mass ratio of 8:1. The mixture was placed on a magnetic stirrer and stirred at 400 rpm at room temperature for 8 hours. Subsequently, the mixture was transferred to an ultrasonic homogenizer and sonicated at 300 W for 1.5 hours to obtain a uniformly dispersed black suspension. The suspension was centrifuged at 10,000 rpm for 3 minutes, and the supernatant was discarded. The precipitate was washed three times each with deionized water and anhydrous ethanol, alternating between the two methods. Finally, the precipitate was placed in a vacuum drying oven and dried at 60°C for 18 hours to obtain the Ni-CoCN / GO composite precursor.

[0022] Step 3. Preparation of NiCoSCN@3D graphene anode material by vapor-phase sulfidation: Thiourea (CH4N2S) was weighed as the sulfur source, with a mass five times that of the NiCoCN / GO composite precursor obtained in step 2, and placed in a ceramic boat. The NiCoCN / GO composite precursor powder obtained in step 2 was placed in another ceramic boat. The two ceramic boats were then placed sequentially into the quartz tube of a horizontal tube furnace, with the boat containing the thiourea positioned upstream of the gas flow and the boat containing the composite precursor positioned in the center of the isothermal zone. The distance between the two boats was approximately 15 cm. After sealing the quartz tube, high-purity argon was introduced as both a protective gas and a carrier gas, with a flow rate set to 100 sccm, for 30 minutes to fully replace the air inside the tube. Subsequently, under an argon atmosphere, the furnace temperature was raised to 500℃ at a heating rate of 5℃ / min and held at this temperature for 2 hours. During this process, the upstream thiourea decomposed thermally to produce sulfur-containing gases such as H2S, which were carried downstream by the argon gas to undergo a sulfidation reaction with NiCoCN to generate NiCoSCN. Simultaneously, GO was thermally reduced and self-assembled to form a three-dimensional graphene network. After the reaction is complete, heating is stopped, and argon gas is continuously purged for cooling to room temperature. The black, fluffy product in the downstream ceramic boat is then removed, yielding the final target product, NiCoSCN@3D graphene anode material.

[0023] Step 4. Assemble a battery using the NiCoSCN@3D graphene anode material and test it: The obtained negative electrode material was mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone was added as a solvent. The mixture was magnetically stirred for 2 h to form a uniform slurry. The slurry was coated onto an aluminum foil current collector and vacuum dried at 90 °C for 12 h. The resulting negative electrode sheet had a diameter of 12 mm. In an argon-filled glove box, a CR2032 coin cell was assembled using a sodium metal sheet as the counter electrode, glass fiber as the separator, and a 1 M NaPF6 solution in diethylene glycol dimethyl ether as the electrolyte for electrochemical testing.

[0024] Example 2: A method for preparing a Ni-doped cobalt sulfide three-dimensional graphene sodium-ion battery anode material, the specific steps of which are as follows: To investigate the effect of different GO addition amounts on electrochemical performance, the concentration of the GO solution in step 2 was changed, with the GO concentration controlled at 1 mg / L, 2 mg / L, 4 mg / L, and 5 mg / L, respectively. The remaining steps were the same as in Example 1. Example 3:

[0025] A method for preparing a Ni-doped cobalt sulfide three-dimensional graphene sodium-ion battery anode material, the specific steps of which are as follows: To investigate the effects of different vapor deposition temperatures on the material structure and properties, the deposition temperature in step 3 was changed to 400 °C, 450 °C, 550 °C, and 600 °C, respectively, while the remaining steps were the same as in Example 1. Attached Figure Description

[0026] Figure 1 This is the XRD pattern of the negative electrode material prepared in Example 1 of this invention. It can be clearly seen from the figure that a series of sharp and symmetrical characteristic diffraction peaks appear in the spectrum. The positions of each peak highly match those of the standard crystal phase card, and there are no obvious impurity peaks, indicating that the prepared NiCoSCN crystal has high crystallinity and excellent phase purity. The peak shift originates from nickel ions (Ni... 2+ The doping into the CoSCN lattice confirms the successful construction of the bimetallic Ni-Co sulfide system.

[0027] Figure 2 This is a SEM image of the negative electrode material prepared in Example 1 of this invention. The image clearly shows that the NiCoSCN nanoparticles are more uniform in size, more densely distributed on the surface of the graphene oxide sheets, and exhibit excellent dispersion with no local agglomeration. The graphene oxide sheets have more pronounced wrinkles, forming a three-dimensional interconnected porous network structure. The NiCoSCN particles are tightly anchored to the nodes and surfaces of the three-dimensional network, resulting in a larger interface contact area and stronger bonding. The overall material has higher porosity and better pore connectivity. Nickel doping effectively enhances the stability of the sample. The three-dimensional interconnected graphene network provides a continuous pathway for electron conduction, and the highly interconnected pores accelerate sodium ion migration, enhancing the material's rate performance and further strengthening structural stability.

[0028] Figure 3 The first three charge-discharge curves (0.1 A·g) of the negative electrode material prepared in Example 1 of this invention are shown. -1 ) and the first 400 laps cycle performance test (5 A·g) -1 The charge-discharge curve shows an initial discharge specific capacity of 600 mAh·g. -1 The first-cycle coulomb efficiency is ≥ 80%; the cycle performance diagram shows that at 5 A·g -1 After 400 cycles at high current density, the capacity retention rate still reaches over 80%. The charge-discharge curves of the second and third cycles almost completely overlap, with less voltage polarization and a more stable and wider redox plateau, indicating superior sodium ion insertion / extraction kinetics. The curves show no obvious distortion, confirming that the crystal structure of the material is stable during charge and discharge, without severe phase transitions or structural collapse. In contrast, undoped CoSCN@3D graphene exhibits overcharge and fails after 306 cycles. Nickel doping significantly improves the reversible specific capacity of the material and optimizes sodium ion insertion / extraction kinetics; the highly overlapping cycle curves demonstrate the material's excellent electrochemical reversibility and interfacial stability.

[0029] Figure 4 The first 1000 cycle performance tests (10 A·g) of the negative electrode material prepared in Example 1 of this invention. -1 The results showed that at 10 A·g-1 After cycling 1000 times at ultra-high current density, the reversible specific capacity still remains at 241 mAh·g. -1 The capacity retention rate reached 65%. This confirms that the NiCoSCN@3D graphene anode material has excellent long-term cycling stability and rate performance. The 3D graphene framework effectively buffers the volume expansion of the active material, inhibits structural collapse and active material shedding, and the anode material has strong electrochemical reversibility and good structural stability.

[0030] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A NiCoSCN@three-dimensional graphene sodium-ion battery anode material, characterized in that: Using three-dimensional graphene as a conductive framework, NiCoSCN nanoparticles in the negative electrode material are uniformly anchored on the surface and pores of the three-dimensional graphene sheets, forming a stable "point-surface" composite structure without obvious agglomeration. The three-dimensional graphene is a three-dimensional interconnected porous network formed by the thermal reduction self-assembly of graphene oxide, and the material as a whole exhibits a loose porous structure. The negative electrode material has a conductivity of 0.1 A g. -1 First-cycle discharge specific capacity ≥ 600 mAh g at current density -1 The first-round coulomb efficiency is ≥80%; in 5 Ag -1 After 400 cycles, the capacity retention is ≥80%; at 10 A g -1 After 1000 cycles, the capacity retention is ≥65%. The cycling curves show good overlap and no obvious distortion, demonstrating excellent electrochemical reversibility and interfacial stability.

2. A method for preparing a NiCoSCN@three-dimensional graphene sodium-ion battery anode material, characterized in that, Includes the following steps: (1) Preparation of NiCoCN precursor: Nickel nitrate, cobalt nitrate and urea are mixed and ground in proportion, and annealed in air atmosphere to obtain NiCoCN precursor powder; (2) Preparation of NiCoCN / graphene oxide composite precursor: The NiCoCN precursor powder obtained in step (1) is mixed with the graphene oxide aqueous dispersion, and then stirred, sonicated, centrifuged, washed and dried to obtain the NiCoCN / graphene oxide precursor. (3) Preparation of composite material by gas phase sulfidation: Using thiourea as sulfur source, thiourea and NiCoCN / graphene oxide precursor are placed upstream and downstream of the gas flow in a tube furnace, respectively. Under an inert atmosphere, the sulfur-containing gas phase species decomposed by thiourea sulfidate NiCoCN, while graphene oxide is thermally reduced to three-dimensional graphene, thus obtaining NiCoSCN@three-dimensional graphene sodium ion battery anode material.

3. The preparation method according to claim 2, characterized in that: In step (1), the nickel source is nickel nitrate hexahydrate, and the cobalt source is cobalt nitrate hexahydrate; the molar ratio of nickel ions to cobalt ions is 1:1, 2:1 or 1:2; the molar amount of urea is 4 times the total molar amount of nickel and cobalt metal ions.

4. The preparation method according to claim 2, characterized in that: In step (1), the grinding time is 30~50 min, the annealing heating rate is 2~4 ℃ / min, the annealing temperature is 380~420 ℃, and the holding time is 2.5~3.5 h.

5. The preparation method according to claim 2, characterized in that: In step (2), the concentration of the graphene oxide aqueous dispersion is 2~4 mg / mL; the mass ratio of NiCoCN precursor to graphene oxide is (7:1)~(9:1).

6. The preparation method according to claim 2, characterized in that: In step (2), the stirring speed is 300~500 rpm and the stirring time is 7~9 h; the ultrasonic power is 250~350 W and the ultrasonic time is 1~2 h; the centrifugation speed is 9000~11000 rpm and the centrifugation time is 2~4 min; the vacuum drying temperature is 50~70 ℃ and the drying time is 16~20 h.

7. The preparation method according to claim 2, characterized in that: In step (3), the mass of thiourea is 4 to 6 times the mass of the NiCoCN / GO composite precursor; the inert gas in the tube furnace is high-purity argon, the gas flow rate is 80 to 120 sccm, and the gas replacement time is 25 to 35 min.

8. The preparation method according to claim 2, characterized in that: In step (3), the vapor deposition heating rate is 4~6℃ / min, the reaction temperature is 450~600℃, and the holding time is 1.5~2.5 h; thiourea is placed upstream of the gas flow in the tube furnace, and the composite precursor is placed in the center of the constant temperature zone, with a distance of 10~20 cm between them.

9. The application of the NiCoSCN@3D graphene sodium-ion battery anode material according to claim 2 in sodium-ion batteries.

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