Synergistic composite layer hard carbon negative electrode material, preparation method thereof and sodium ion battery

Abstract

The invention is suitable for the technical field of materials, and provides a synergistic composite layer hard carbon negative electrode material and a preparation method thereof, and a sodium ion battery, the material has a layered composite structure of a current collector / a transition layer / a doped hard carbon layer / a protective layer, and the three layers have synergistic interaction in the aspects of electron conduction, ion diffusion and interface chemical compatibility. The transition layer is selected from at least one material of Ti, Cr, Al, Si, Mo, W and the like, and the thickness of the transition layer is 5-200nm; the doped hard carbon layer is amorphous carbon doped with at least one heteroatom of B, N, Si, Sn and the like, and the thickness of the doped hard carbon layer is 50-1000nm; and the protective layer is a carbon nitride, carbon oxide or hydrogenated carbon film, and the thickness is 5-50nm. Through the three-layer synergistic structure design and the magnetron sputtering preparation process, multiple synergistic interaction is achieved, the problems that a traditional hard carbon negative electrode and a current collector are poor in adhesion, an SEI film is unstable and interface impedance is high are effectively solved, and the material has excellent electrochemical performance and is suitable for the related energy storage field.

Description

Technical Field

[0001] This application belongs to the field of materials technology, and in particular relates to a synergistic composite layer hard carbon anode material and its preparation method, and a sodium-ion battery, which is suitable for high-performance energy storage applications in secondary battery systems such as sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries, as one of the ideal alternative technologies to lithium-ion batteries, have significant advantages such as abundant resources, low cost, and environmental friendliness, and have become a research hotspot and key industrialization direction in fields such as large-scale energy storage and low-speed electric vehicles. The performance of electrode materials directly determines the energy density, cycle life, and safety performance of sodium-ion batteries, among which the development of anode materials is a key factor restricting the commercialization process of sodium-ion batteries.

[0003] Currently reported sodium-ion battery anode materials include carbon-based, titanium-based, organic compounds, and alloys. Carbon-based materials are the most commercially promising anode material choice due to their high electrochemical activity, strong structural stability, low cost, and abundant resources. Traditional graphite materials suffer from low sodium storage capacity and poor cycle performance because of their narrow interlayer spacing (approximately 0.335 nm) and thermodynamic instability during sodium ion insertion / extraction. Hard carbon, as a difficult-to-graphitize amorphous carbon material, possesses a disordered structure composed of bent graphene nanosheets with a large interlayer spacing (0.37-0.40 nm) and abundant nanopores, providing ample diffusion channels and storage sites for sodium ions, and is considered the most promising anode material for sodium-ion batteries.

[0004] In particular, biomass-based hard carbon materials have shown unique advantages in cost control and green preparation, but there are still three major technical bottlenecks: First, the adhesion between hard carbon particles and current collectors is poor, and they are prone to falling off during long-term cycling, resulting in rapid capacity decay of the battery; Second, the initial coulombic efficiency is low (usually below 80%), mainly due to the uneven distribution of surface active sites, which leads to unstable formation of the solid electrolyte interphase (SEI) film and significant irreversible capacity loss; Third, the interfacial impedance is high, resulting in poor ion transport kinetics and affecting the rate performance of the battery.

[0005] To address the aforementioned issues, existing technologies employ surface modification methods such as chemical coating and liquid-phase coating to improve the surface structure of hard carbon. However, these methods suffer from drawbacks such as difficulty in precisely controlling thickness, poor film uniformity, and weak interfacial bonding. Magnetron sputtering, as a low-temperature, high-precision thin-film deposition technique, can form dense and uniform films on current collector surfaces. However, current technologies primarily focus on single-layer or simple bilayer film structure designs, failing to fully utilize the synergistic effects between multilayer interfaces and hindering the simultaneous optimization of electron transport, ion diffusion, and interfacial stability. Therefore, developing a multilayer synergistic composite structure that combines strong interfacial bonding, efficient charge transport, and SEI film stability is a key technological approach to overcoming the performance bottlenecks of traditional hard carbon anodes. Summary of the Invention

[0006] The purpose of this application is to provide a synergistic composite layer hard carbon anode material and its preparation method, as well as a sodium-ion battery. The aim is to achieve enhanced interface bonding, continuous charge transport, and optimized SEI stability through a three-layer synergistic design of transition layer / doped hard carbon layer / protective layer, thereby significantly improving the first coulombic efficiency, cycle stability, and sodium storage capacity of the hard carbon anode.

[0007] This application's embodiments are implemented as follows: a synergistic composite layered hard carbon anode material has a layered composite structure of current collector / transition layer / doped hard carbon layer / protective layer. The transition layer, doped hard carbon layer, and protective layer form a synergistic effect in terms of electron conduction, ion diffusion, and interfacial chemical compatibility. The transition layer material is selected from at least one of Ti, Cr, Al, Si, Mo, and W, and has a thickness of 5-200 nm. The doped hard carbon layer is an amorphous carbon structure doped with heteroatoms, wherein the heteroatoms are selected from at least one of B, N, Si, and Sn, and the layer thickness is 50-1000 nm. The protective layer is a carbon nitride, carbon oxide, or carbon hydrogen film with a thickness of 5-50 nm.

[0008] This application also provides a method for preparing the above-mentioned synergistic composite layer hard carbon anode material, including: S1: Place the cleaned current collector in a vacuum environment and deposit a transition layer on its surface using DC or RF magnetron sputtering process; S2: On the surface of the transition layer, a doped hard carbon layer is deposited in an inert or reactive atmosphere by using a carbon target and a doped target as sputtering sources, through single-target sputtering or dual-target co-sputtering. S3: Reactive magnetron sputtering is performed on the surface of the doped hard carbon layer, using a mixed gas containing N2, O2 or H2 as the deposition atmosphere to form a protective layer.

[0009] This application also provides a sodium-ion battery, wherein the negative electrode material of the sodium-ion battery is the aforementioned synergistic composite layer hard carbon negative electrode material.

[0010] This application embodiment achieves multiple synergistic effects of electronic conduction, interface compatibility, ion transport, and SEI film stability through a three-layer synergistic composite structure design of transition layer / doped hard carbon layer / protective layer and a precise magnetron sputtering fabrication process. This not only effectively solves the core bottlenecks of traditional hard carbon anodes, such as poor adhesion to the current collector, unstable SEI film, and high interface impedance, but also enables the material to exhibit excellent electrochemical performance, with a reversible specific capacity of up to 335.52 mAh / g, an initial coulombic efficiency of up to 93.53% (at least 20% higher than traditional hard carbon), and a capacity retention rate of up to 95.52% after 100 cycles (significantly better than the generally lower than 90% level of existing technologies). Simultaneously, this fabrication process has the advantages of controllable layer thickness and composition, scalability, and low production cost, making the synergistic composite hard carbon anode material widely applicable to sodium-ion batteries and other carbon-based energy storage devices. It provides high-performance anode solutions for large-scale energy storage, low-speed electric vehicles, and other fields, powerfully promoting the commercialization of sodium-ion batteries. Attached Figure Description

[0011] Figure 1 A schematic diagram of the overall structure of the synergistic composite layer hard carbon anode material provided in the embodiments of this application; Figure 2 A schematic diagram of the specific structure of the synergistic composite layer hard carbon anode material provided in Embodiment 1 of this application; Figure 3 This is a scanning electron microscope image of the synergistic composite layer hard carbon anode material provided in Embodiment 1 of this application; Figure 4 The constant current charge-discharge curves of the synergistic composite layer hard carbon anode material provided in Examples 1-5 of this application are shown. Figure 5 The 1C cycle performance diagram of the synergistic composite layer hard carbon anode material provided in Example 1 of this application; Figure 6 The 1C cycle performance diagram of the synergistic composite layer hard carbon anode material provided in Example 4 of this application; Figure 7 The constant current charge-discharge curves of the synergistic composite layer hard carbon anode material provided in Examples 6-9 of this application are shown. Figure 8 The 1C cycle performance diagram of the synergistic composite layer hard carbon anode material provided in Example 9 of this application; Figure 9 Constant current charge-discharge curves of the synergistic composite layer hard carbon anode materials provided in Comparative Examples 1-6 of this application; Figure 10The diagram shows the 1C cycle performance of the synergistic composite layer hard carbon anode material provided in Comparative Example 2 of this application. Figure 11 A scanning electron microscope image of the synergistic composite layer hard carbon anode material provided in Comparative Example 3 of this application; Figure 12 The diagram shows the 1C cycle performance of the synergistic composite layer hard carbon anode material provided in Comparative Example 3 of this application. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0013] This application provides a synergistic composite layer hard carbon anode material, such as... Figure 1 The structure shown has a layered composite structure of current collector / transition layer / doped hard carbon layer / protective layer. The transition layer, doped hard carbon layer, and protective layer have a synergistic effect in terms of electron conduction, ion diffusion, and interfacial chemical compatibility. The three layers are synergistically matched in terms of interfacial potential, chemical composition, and stress transfer to reduce interfacial impedance and stabilize the SEI film. Specifically, the transition layer reduces the electron barrier by adjusting the work function difference, and induces ordered nucleation of hard carbon to form a low-stress interface, which improves the electron transport efficiency between the current collector and the hard carbon layer, and enhances the bonding strength between the carbon layer and the current collector to avoid cycle shedding. The doped hard carbon layer, with its adjustable interlayer spacing and abundant active sites, constructs a low-impedance, highly stable ion transport channel, enhancing the ion-electron co-transport efficiency. The protective layer reacts with the hard carbon surface to form a N-rich or O-rich chemical film, effectively suppressing side reactions, homogenizing the SEI film formation process, and significantly reducing the first irreversible capacity loss. The three layers work together to form a comprehensive performance improvement synergistic effect.

[0014] The transition layer material is selected from at least one of Ti, Cr, Al, Si, Mo, and W, with a thickness of 5-200 nm; the doped hard carbon layer is an amorphous carbon structure doped with heteroatoms, the heteroatoms being selected from at least one of B, N, Si, and Sn, with a layer thickness of 50-1000 nm; the protective layer is a carbon nitride, carbon oxide, or carbon hydrogenation film with a thickness of 5-50 nm.

[0015] Preferably, the transition layer material is Mo, and the layer thickness is 50 nm.

[0016] Preferably, the heteroatom in the doped hard carbon layer is N, and the layer thickness is 500 nm.

[0017] Preferably, the protective layer is a carbon oxide film with a thickness of 20 nm.

[0018] This application also provides a method for preparing a hard carbon anode material with a synergistic composite layer structure constructed by magnetron sputtering, wherein the above-mentioned method for preparing the synergistic composite layer hard carbon anode material includes: S1: Place the cleaned current collector in a vacuum environment and deposit a transition layer on its surface using DC or RF magnetron sputtering process; S2: On the surface of the transition layer, using a carbon target and a doped target as sputtering sources, a doped hard carbon layer with adjustable interlayer spacing and active sites is deposited in an inert atmosphere or a reactive atmosphere by single-target sputtering or dual-target co-sputtering. S3: Reactive magnetron sputtering is performed on the surface of the doped hard carbon layer, using a mixed gas containing N2, O2 or H2 as the deposition atmosphere, to form a protective layer (carbon nitride, carbon oxide or carbon hydrogenation layer).

[0019] Preferably, the preparation method of the synergistic composite layer hard carbon anode material further includes: The material with the deposited multilayer structure is placed in an inert gas atmosphere and annealed at 500-800℃ to enhance the compactness of each film layer and the interlayer bonding force.

[0020] Preferably, in step S1, the working pressure of magnetron sputtering is 0.3-0.8 Pa, the sputtering power is 100-200 W, the deposition atmosphere is Ar gas, and the flow rate is 20-40 sccm.

[0021] Preferably, the inert atmosphere in step S2 is Ar gas, the reactive atmosphere is a mixture of Ar+N2 or Ar+H2 gas, the sputtering power is controlled at 150-300 W, and the deposition time is 30-120 min, so as to regulate the thickness of the doped hard carbon layer and the distribution of active sites.

[0022] Preferably, in step S3, the deposition atmosphere is a mixed gas of Ar:N2=3-5:1, Ar:O2=2-4:1 or Ar:H2=3-5:1, the sputtering power is 80-150 W, and the deposition time is 5-20 min, so as to ensure that the protective layer is dense and continuous and firmly bonded to the interface of the doped hard carbon layer.

[0023] This application also provides a sodium-ion battery, wherein the negative electrode material of the sodium-ion battery is the aforementioned synergistic composite layer hard carbon negative electrode material. Due to the excellent electrochemical performance of the negative electrode material, the sodium-ion battery has significantly improved in terms of energy density, cycle life and safety performance, and is suitable for large-scale energy storage, low-speed electric vehicles and other fields.

[0024] The following detailed embodiments illustrate the synergistic composite layer hard carbon anode material, its preparation method, and sodium-ion battery provided in this application. Unless otherwise specified, the experimental methods used in the embodiments are conventional methods; and the materials and reagents used are commercially available conventional products unless otherwise specified.

[0025] Example 1: S-Ti-B-CN-50 / 500 / 20 (1) Clean and dry a 10μm thick copper foil, place it in a vacuum chamber, and evacuate it to 5×10. -4 Pa; (2) A Ti transition layer with a thickness of about 50 nm was formed by DC magnetron sputtering of a Ti target at a power of 150 W, an Ar atmosphere (30 sccm), a working pressure of 0.5 Pa, and a deposition time of 5 min. (3) Then, the carbon target (200 W) and boron target (80 W) were switched to co-sputtering, Ar atmosphere (30 sccm), pressure 0.5 Pa, deposition for 60 min, to obtain a B-doped hard carbon layer with a thickness of about 500 nm; (4) Then, reactive sputtering was performed using a C target (120 W) in an Ar:N2=4:1 atmosphere for 10 min to form a carbon nitride protective layer of about 20 nm. (5) Annealing at 700℃ for 2 hours in an Ar atmosphere yields the final synergistic composite hard carbon anode material (Cu current collector / Ti transition layer / B-doped hard carbon layer / CN protective layer, structure as follows). Figure 2 (As shown).

[0026] Figure 3 The image shows an SEM image of the synergistic composite layer hard carbon anode material obtained in Example 1. It is clear from the image that the carbon layer surface is uniformly attached with a CN protective layer structure and the particles are uniform.

[0027] Cu foil with a synergistic composite layer of hard carbon anode material was cut into 12 mm circular anode sheets and transferred to a glove box for later use. 2016 coin cells were assembled in an Ar-filled MIKROUNA glove box, using the prepared carbon material anode as the anode, 1.0 mol / L NaPF6 / DME as the electrolyte, and a Na metal sheet as the counter electrode.

[0028] After the assembled button cells were left to stand for 8 hours, they were placed in a 30°C constant temperature testing system at 0.01-3 V (vs. Na). + Charge-discharge tests were conducted within the voltage range of / Na). The test results are as follows: Figure 4-5As shown, at a current density of 20 mA / g, the initial coulombic efficiency is 87.84%, and the initial charge capacity is 295.84 mAh / g; after 100 cycles at 1C, the capacity is 200.73 mAh / g, with a capacity retention rate of 84.99%.

[0029] Example 2: S-Al-B-CN-50 / 500 / 20 The preparation process of this embodiment is basically the same as that of Example 1, except that the transition layer is sputtered with an Al target, the DC magnetron sputtering power is 150 W, the thickness is 50 nm, and the other parameters are the same as those of Example 1.

[0030] The resulting composite layer structure is a Cu current collector / Al transition layer / B-doped hard carbon layer / CN protective layer. It was assembled into a coin cell and electrochemical tests were performed, with results as follows: Figure 4 As shown, at a current density of 20 mA / g, the initial coulombic efficiency is 89.12%, and the initial charge specific capacity is 308.27 mAh / g. This indicates that the Al transition layer is more beneficial than Ti in enhancing conductivity and improving the charge specific capacity and initial coulombic efficiency of the hard carbon material.

[0031] Example 3: S-Mo-B-CN-50 / 500 / 20 The preparation process of this embodiment is basically the same as that of Example 1, except that the transition layer is sputtered using a Mo target with a DC magnetron sputtering power of 150 W and a thickness of 50 nm. The other parameters are the same as those of Example 1.

[0032] The resulting composite layer structure is a Cu current collector / Mo transition layer / B-doped hard carbon layer / CN protective layer. It was assembled into a coin cell and electrochemical tests were performed, with results as follows: Figure 4 As shown, at a current density of 20 mA / g, the initial coulombic efficiency is 90.80%, and the initial charge specific capacity is 313.31 mAh / g. This indicates that the Mo transition layer is more conducive to promoting interfacial carbonization / wetting than Ti, simultaneously improving adhesion and reducing interfacial impedance, thereby enhancing the electrochemical performance of hard carbon materials.

[0033] Example 4: S-Ti-N-CN-50 / 500 / 20 The preparation process of this embodiment is basically the same as that of Example 1, except that the doped hard carbon layer is prepared by co-sputtering with a carbon target (200 W) and a nitrogen target (80 W) in an Ar atmosphere (30 sccm), a pressure of 0.5 Pa, and a deposition time of 60 min to obtain an N-doped hard carbon layer with a thickness of about 500 nm. The other parameters are the same as those in Example 1.

[0034] The resulting composite layer structure is a Cu current collector / Ti transition layer / N-doped hard carbon layer / CN protective layer. It was assembled into a coin cell and electrochemical tests were performed, with results as follows: Figure 4 , 6 As shown, at a current density of 20 mA / g, the initial coulombic efficiency is 91.55%, and the initial charge specific capacity is 323.14 mAh / g; after 100 cycles at 1C, the capacity is 270.67 mAh / g, with a capacity retention rate as high as 95.18%. This indicates that N doping significantly reduces interfacial impedance compared to B doping, promotes uniform SEI formation, and greatly improves the initial coulombic efficiency and cycle stability of hard carbon materials.

[0035] Example 5: S-Ti-B-CO-50 / 500 / 20 The preparation process of this embodiment is basically the same as that of Example 1, except that the protective layer is formed by reactive sputtering in an atmosphere of Ar:O2=3:1 for 10 min to form a carbon oxide protective layer of about 20 nm. The other parameters are the same as those of Example 1.

[0036] The resulting composite layer structure is a Cu current collector / Ti transition layer / B-doped hard carbon layer / CO protective layer. It was assembled into a coin cell and electrochemical tests were performed. The results are as follows: Figure 4 As shown, at a current density of 20 mA / g, the initial coulombic efficiency is 92.35%, and the initial charge specific capacity is 314.16 mAh / g. This indicates that the polarity of the CO-based protective layer is superior to that of CN, resulting in stronger electrolyte wettability, which promotes uniform SEI film formation and significantly improves the initial coulombic efficiency.

[0037] Example 6: S-Ti-B-CH-50 / 500 / 20 The preparation process of this embodiment is basically the same as that of Example 1, except that the protective layer is formed by reactive sputtering in an atmosphere of Ar:H2=4:1 for 10 min to form a 20 nm hydride protective layer. The other parameters are the same as those of Example 1.

[0038] The resulting composite layer structure is a Cu current collector / Ti transition layer / B-doped hard carbon layer / CH protective layer. It was assembled into a coin cell and electrochemical tests were performed, with results as follows: Figure 7 As shown, at a current density of 20 mA / g, the initial coulombic efficiency is 86.77%, and the initial charge specific capacity is 281.59 mAh / g. This indicates that the surface polarity of the CH-based protective layer is poor, leading to uneven local electric field distribution, inconsistent electrolyte decomposition, and the formation of an uneven SEI film. Therefore, the initial coulombic efficiency is lower than that of the embodiments using CN or CO protective layers.

[0039] Example 7: S-Al-N-CO-50 / 500 / 20 The preparation process of this embodiment is basically the same as that of Example 1, except that: the transition layer is sputtered with an Al target at 50 nm, the doped hard carbon layer is co-sputtered with CN, and the protective layer is a carbon oxide layer (Ar:O2=3:1). The other parameters are the same as those of Example 1.

[0040] The resulting composite layer structure is a Cu current collector / Al transition layer / N-doped hard carbon layer / CO protective layer. It was assembled into a coin cell and electrochemical tests were performed, with results as follows: Figure 7 As shown, at a current density of 20 mA / g, the initial coulombic efficiency is 93.02%, and the initial charge specific capacity is 329.65 mAh / g. This indicates that the synergistic optimization of the transition layer, dopant elements, and protective layer can further improve the electrochemical performance of the material.

[0041] Example 8: S-Mo-B-CO-50 / 500 / 20 The preparation process of this embodiment is basically the same as that of Example 1, except that: the transition layer is sputtered with a Mo target at 50 nm, the doped hard carbon layer is co-sputtered with CB, and the protective layer is a carbon oxide layer (Ar:O2=3:1). The other parameters are the same as those of Example 1.

[0042] The resulting composite layer structure is a Cu current collector / Mo transition layer / B-doped hard carbon layer / CO protective layer. It was assembled into a coin cell and electrochemical tests were performed. The results are as follows: Figure 7 As shown, at a current density of 20 mA / g, the initial coulombic efficiency is 90.77%, and the first-charge specific capacity is 324.44 mAh / g. This indicates that there is an interfacial synergy and performance enhancement effect between the Mo transition layer and the CO protective layer, which can effectively improve the electrochemical performance of hard carbon materials.

[0043] Example 9: S-Mo-N-CO-50 / 500 / 20 The preparation process of this embodiment is basically the same as that of Example 1, except that: the transition layer is sputtered with a Mo target at 50 nm, the doped hard carbon layer is co-sputtered with CN, and the protective layer is a carbon oxide layer (Ar:O2=3:1). The other parameters are the same as those of Example 1.

[0044] The resulting composite layer structure is a Cu current collector / Mo transition layer / N-doped hard carbon layer / CO protective layer. It was assembled into a coin cell and electrochemical tests were performed, with results as follows: Figure 7-8As shown, at a current density of 20 mA / g, the initial coulombic efficiency is 93.53%, and the initial charge specific capacity is 335.52 mAh / g; after 100 cycles at 1C, the capacity is 287.15 mAh / g, with a capacity retention rate as high as 95.52%. Experiments demonstrate that simultaneously optimizing the transition layer, the doped hard carbon layer, and the protective layer can achieve the best synergistic effect in electron / ion transport and interfacial chemical compatibility, thereby optimizing the material's reversible specific capacity, initial coulombic efficiency, and cycle stability.

[0045] Comparative Example 1: S-Mo-N-NoP-50 / 500 / 0 (1) Clean and dry a 10μm thick copper foil, place it in a vacuum chamber, and evacuate it to 5×10. -4 Pa; (2) Mo target DC magnetron sputtering was used with a power of 150 W, Ar atmosphere (30 sccm), working pressure of 0.5 Pa, and deposition time of 5 min to form a Mo transition layer with a thickness of about 50 nm; (3) Then, the carbon target (200 W) and nitrogen target (80 W) were switched to co-sputtering, Ar atmosphere (30 sccm), pressure 0.5 Pa, deposition for 60 min, and an N-doped hard carbon layer with a thickness of about 500 nm was obtained; (4) Annealing at 700℃ for 2 hours in an Ar atmosphere to obtain a composite layer structure (without a protective layer).

[0046] It was assembled into a coin cell and electrochemical tests were conducted, with the following results: Figure 9 As shown, at a current density of 20 mA / g, the initial coulombic efficiency was 79.07%, and the first-charge specific capacity was 270.43 mAh / g. Compared with Example 9, it was difficult to form a dense and uniform SEI film without a protective layer, resulting in more side reactions and greater reversible capacity loss. This indicates that the protective layer is crucial for stabilizing the SEI film and improving electrochemical performance.

[0047] Comparative Example 2: S-Mo-None-CO-50 / 500 / 20 The preparation process of this comparative example is basically the same as that of Example 9, except that the doped hard carbon layer is sputtered using a pure carbon target (200 W) without heteroatom doping, and the other parameters are the same as those of Example 9.

[0048] The resulting composite layer structure is a Cu current collector / Mo transition layer / pure hard carbon layer / CO protective layer. It was assembled into a coin cell and electrochemical tests were performed. The results are as follows: Figure 9-10As shown, at a current density of 20 mA / g, the initial coulombic efficiency was 82.00%, and the initial charge specific capacity was 265.63 mAh / g; after 100 cycles at 1C, the capacity was 186.37 mAh / g, with a capacity retention of 90.44%. Compared with Example 9, the absence of heteroatom doping resulted in insufficient active sites, increased interfacial impedance, and a significant decrease in both initial coulombic efficiency and cycle stability, indicating that heteroatom doping can effectively optimize the electrochemical performance of the hard carbon layer.

[0049] Comparative Example 3: S-Mo-None-NoP-50 / 500 / 0 The preparation process of this comparative example is basically the same as that of Example 9, except that the doped hard carbon layer is sputtered using a pure carbon target (200W) (without heteroatom doping) and there is no protective layer. The other parameters are the same as those of Example 9.

[0050] The resulting composite layer structure is Cu current collector / Mo transition layer / pure hard carbon layer (without protective layer). Figure 11 The SEM image shows that the carbon layer surface is rough and blocky, which contrasts sharply with the structure of the carbon layer with a uniform protective layer in Example 1. Electrochemical test results are as follows: Figure 9 , 12 As shown, at a current density of 20 mA / g, the initial coulombic efficiency was only 62.62%, and the first-charge specific capacity was 244.89 mAh / g; after 100 cycles at 1C, the capacity was 176 mAh / g, with a capacity retention of 85.55%. Compared with Example 9, without heteroatom doping and a protective layer, the structural stability, interfacial chemical compatibility, and electrochemical performance of the material all decreased significantly, fully demonstrating the necessity of the three-layer synergistic structure.

[0051] Comparative Example 4: S-Mo-N-CO-50 / 1500 / 20 The preparation process of this comparative example is basically the same as that of Example 9, except that the pressure during hard carbon layer sputtering is 0.7 Pa and the deposition time is 120 min, resulting in an N-doped hard carbon layer with a thickness of about 1500 nm. The other parameters are the same as those of Example 9.

[0052] It was assembled into a coin cell and electrochemical tests were conducted, with the following results: Figure 9 As shown, at a current density of 20 mA / g, the initial coulombic efficiency was 83.36%, and the first-charge specific capacity was 283.60 mAh / g. Compared with Example 9, the excessively thick hard carbon layer resulted in slower ion diffusion, longer electron transport paths, an overly dense carbon structure, and a reduction in sodium storage sites, leading to a decrease in capacity instead of an increase. This indicates that the thickness of the hard carbon layer needs to be controlled within a reasonable range (50-1000 nm).

[0053] Comparative Example 5: S-Mo-N-CO-250 / 500 / 20 The preparation process of this comparative example is basically the same as that of Example 9, except that the pressure during the sputtering of the transition layer is 0.9 Pa and the deposition time is 150 min, resulting in a Mo transition layer with a thickness of about 250 nm. The other parameters are the same as those of Example 9.

[0054] It was assembled into a coin cell and electrochemical tests were conducted, with the following results: Figure 9 As shown, at a current density of 20 mA / g, the initial coulombic efficiency is 82.20%, and the initial charge specific capacity is 274.21 mAh / g. Compared with Example 9, an excessively thick transition layer leads to poorer electronic conductivity and increased interfacial impedance, which is detrimental to the hard carbon film structure. This indicates that the thickness of the transition layer needs to be controlled within the range of 5-200 nm, and a thin and continuous transition layer has the best performance.

[0055] Comparative Example 6: S-Mo-N-CO-50 / 500 / 120 The preparation process of this comparative example is basically the same as that of Example 9, except that the pressure during sputtering of the protective layer is 0.7 Pa and the deposition time is 150 min, resulting in a carbon oxide protective layer with a thickness of about 120 nm. The other parameters are the same as those of Example 9.

[0056] It was assembled into a coin cell and electrochemical tests were conducted, with the following results: Figure 9 As shown, at a current density of 20 mA / g, the initial coulombic efficiency was 80.53%, and the first-charge specific capacity was 289.36 mAh / g. Compared with Example 9, the excessively thick protective layer hindered sodium ion transport, and the accumulation of internal stress led to film cracking and detachment, clogging of micropores and sodium storage structures, and inducing an unstable SEI. This indicates that the protective layer needs to maintain thin, dense, and continuous characteristics, with the thickness controlled within the range of 5-50 nm.

[0057] In summary, through the comparison of the above embodiments and comparative examples, it is evident that this application achieves multiple synergistic enhancements in electronic conduction, interface compatibility, ion transport, and SEI film stability through a three-layer synergistic structure design of transition layer-doped hard carbon layer-protective layer and a precise magnetron sputtering fabrication process. Among these, the Mo-N-CO system exhibits the best interfacial coupling and cycling performance. The prepared hard synergistic composite layer hard carbon anode material boasts a reversible specific capacity of up to 335.52 mAh / g, an initial coulombic efficiency ≥93%, and a capacity retention rate ≥95% after 100 cycles, significantly outperforming existing technologies. Furthermore, the fabrication process of this application offers advantages such as controllable layer thickness and composition, scalability, and low production costs, providing a high-performance anode solution for sodium-ion batteries and other carbon-based energy storage devices, demonstrating significant industrialization value and application prospects.

[0058] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0059] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A synergistic composite hard carbon anode material, characterized in that, The layered composite structure has a current collector / transition layer / doped hard carbon layer / protection layer, and the transition layer, doped hard carbon layer and protection layer form a synergistic effect in terms of electron conduction, ion diffusion and interface chemical compatibility. The transition layer material is selected from at least one of Ti, Cr, Al, Si, Mo and W, and the thickness is 5-200 nm. The doped hard carbon layer is an amorphous carbon structure doped with heteroatoms selected from at least one of B, N, Si and Sn, and the layer thickness is 50-1000 nm. The protection layer is a carbon nitride, carbon oxide or carbon hydride film, and the thickness is 5-50 nm.

2. The synergistic composite hard carbon anode material of claim 1, wherein, The transition layer material is Mo, and the layer thickness is 50 nm. 3.The synergistic composite hard carbon negative electrode material of claim 1, wherein, The heteroatoms in the doped hard carbon layer are N, and the layer thickness is 500 nm. 4.The synergic composite hard carbon negative electrode material of claim 1, wherein, The protection layer is a carbon oxide film, and the thickness is 20 nm.

5. A method for preparing the synergic composite hard carbon negative electrode material according to any one of claims 1-4, characterized in that, The method comprises the following steps: S1: placing the cleaned current collector in a vacuum environment, and depositing a transition layer on the surface of the current collector by a direct current or radio frequency magnetron sputtering process; S2: depositing a doped hard carbon layer on the surface of the transition layer by single-target sputtering or double-target co-sputtering in an inert atmosphere or a reactive atmosphere, with a carbon target and a doped target as the sputtering source; S3: forming a protection layer on the surface of the doped hard carbon layer by reactive magnetron sputtering in a mixed gas containing N2, O2 or H2 as the deposition atmosphere.

6. The method for preparing the synergic composite hard carbon negative electrode material according to claim 5, characterized in that, The method further comprises the following steps: After the deposition of the multi-layer structure is completed, the material is placed in an inert gas atmosphere and annealed at 500-800°C to enhance the density of each film layer and the interfacial bonding force.

7. The method of claim 5, wherein the method further comprises the step of: 5 heating the mixture to a temperature of 800-1200 °C for 1-10 hours in an inert atmosphere. 10 In step S1, the working pressure of the magnetron sputtering is 0.3-0.8 Pa, the sputtering power is 100-200 W, and the deposition atmosphere is Ar gas with a flow rate of 20-40 sccm.

8. The method of claim 5, wherein the method further comprises the step of: 8-1) mixing the compound of 8-1) with the compound of 8-2) to form the compound of 8-3). In step S2, the inert atmosphere is Ar gas, the reactive atmosphere is Ar+N2 or Ar+H2 mixed gas, the sputtering power is controlled at 150-300 W, and the deposition time is 30-120 min to control the thickness and active site distribution of the doped hard carbon layer.

9. The method of claim 5, wherein the method further comprises the step of: 9-1) mixing the compound of 8-1) with the compound of 8-2) to form the compound of 8-3). In step S3, the deposition atmosphere is a mixed gas with Ar:N2=3-5:1, Ar:O2=2-4:1 or Ar:H2=3-5:1, the sputtering power is 80-150 W, and the deposition time is 5-20 min to ensure that the protection layer is dense and continuous and has a firm interface bonding with the doped hard carbon layer.

10. A sodium-ion battery, characterized in that, The negative electrode material of the sodium ion battery is the synergistic composite layer hard carbon negative electrode material according to any one of claims 1-4.

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