Conductive agent and preparation method and application thereof

Abstract

The invention relates to a conductive agent and a preparation method and application thereof, in particular to the technical field of batteries. The conductive agent has a core-shell structure, and comprises: a metal core; the gradient titanium nitride layer is coated on the surface of the metal core; the alloy interface layer is formed between the metal core and the gradient titanium nitride layer; wherein the content of nitrogen in the gradient titanium nitride layer is gradually increased from inside to outside in a gradient manner. The conductive agent provided by the invention is used for solving the problems that a traditional carbon-based conductive agent for a sodium ion battery in related technologies limits high rate performance due to low intrinsic conductivity and is easy to oxidize and corrode in an alkaline electrolyte to cause poor cycle stability, and the effective conductivity is severely reduced due to introduction of high interface resistance in an existing surface coating technology.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a conductive agent and a preparation method and application thereof. BACKGROUND

[0002] Water-based sodium ion batteries have the advantages of high safety and low cost, but the performance bottleneck of the conductive agent limits the practical application. The current mainstream carbon-based conductive agent (such as acetylene black, carbon nanotube) has a low electrical conductivity (only 10 2 -10 3 S / m), and is easily oxidized and corroded in a high-concentration alkaline electrolyte, resulting in an increase in battery internal resistance and a reduction in cycle life. Although metal nanowires (such as copper and silver) have extremely high intrinsic electrical conductivity (>10 7 S / m), they are easily corroded and invalid in an alkaline environment; although the existing surface coating protection technology can inhibit corrosion, it will introduce high interfacial resistance, resulting in a loss of more than 90% of the effective electrical conductivity, and it is difficult to balance high conductivity and high stability.

[0003] Therefore, a new type of conductive agent is developed to improve the electrical conductivity, cycle performance and rate performance of sodium ion batteries. SUMMARY

[0004] The present application provides a conductive agent and a preparation method and application thereof, to solve the problems in the prior art that the traditional carbon-based conductive agent for sodium ion batteries has low intrinsic electrical conductivity, limits high rate performance, is easily oxidized and corroded in an alkaline electrolyte, resulting in poor cycle stability, and the existing surface coating technology introduces high interfacial resistance, resulting in a serious decrease in effective electrical conductivity.

[0005] The technical scheme provided by the present application is as follows: In a first aspect, the present application provides a conductive agent having a core-shell structure, comprising: a metal core; a gradient titanium nitride layer coated on the surface of the metal core; and an alloy interface layer formed between the metal core and the gradient titanium nitride layer; wherein the content of nitrogen element in the gradient titanium nitride layer increases from inside to outside.

[0006] In some embodiments, the metal core comprises copper nanowires.

[0007] In some embodiments, the diameter of the copper nanowires is 20-30 nm.

[0008] In some embodiments, the aspect ratio of the copper nanowires is >100.

[0009] In some embodiments, the thickness of the gradient titanium nitride layer is 2-3 nm.

[0010] In some embodiments, the gradient titanium nitride layer comprises an inner layer, an intermediate layer, and an outer layer from the inside out, wherein the atomic ratio of nitrogen to titanium in the inner layer is (0.75-0.85):1, the atomic ratio of nitrogen to titanium in the intermediate layer is (0.95-1.05):1, and the atomic ratio of nitrogen to titanium in the outer layer is (1.15-1.25):1.

[0011] In some embodiments, the thickness ratio of the inner layer, the intermediate layer and the outer layer is (0.01-1):(1-2):(2-3).

[0012] In some embodiments, the raw material components of the gradient titanium nitride layer include a nitrogen precursor and a titanium precursor.

[0013] In some embodiments, the nitrogen precursor includes NH3.

[0014] In some embodiments, the titanium precursor comprises TiCl4.

[0015] In some embodiments, the alloy interface layer comprises a Ti-Cu alloy layer.

[0016] In some embodiments, the titanium content in the Ti-Cu alloy layer is 10-15 at.

[0017] In some embodiments, the thickness of the Ti-Cu alloy layer is 0.5-1 nm.

[0018] Secondly, this application provides a method for preparing the conductive agent, comprising the following steps: Preparation of a metal core; A gradient titanium nitride layer is prepared on the surface of the metal core using atomic layer deposition (ALD) technology, and an alloy interface layer is formed between the metal core and the gradient titanium nitride layer. The nitrogen content in the gradient titanium nitride layer increases gradually from the inside to the outside.

[0019] In some embodiments, the atomic layer deposition temperature is 200-240°C.

[0020] In some embodiments, the pressure for atomic layer deposition is 0.1-0.5 Torr.

[0021] In some embodiments, the step of preparing the gradient titanium nitride layer includes: A first deposition cycle is performed on the surface of the metal core to obtain the inner layer; A second deposition cycle is performed on the side of the inner layer away from the surface of the metal core to obtain the intermediate layer; A third deposition cycle is performed on the side of the intermediate layer away from the inner layer to obtain the outer layer.

[0022] Thirdly, this application provides an electrode comprising an electrode active material, a binder, and a conductive agent, wherein the conductive agent comprises the conductive agent described above or a conductive agent prepared according to the method described above.

[0023] Fourthly, this application provides a sodium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an aqueous electrolyte, wherein the positive electrode and / or the negative electrode includes electrodes as described above.

[0024] Compared with existing technologies, the beneficial effects of this application are: 1. Achieving a synergistic breakthrough in conductivity and stability: By constructing a titanium nitride coating layer with a gradient nitrogen content on the surface of copper nanowires, the ultra-high intrinsic conductivity of the copper core (>10⁻⁶) is maintained. 5 While achieving a conductivity of S / m, its interfacial contact resistance is only 1 / 100 of that of a traditional uniform carbon-coated structure, which increases the effective conductivity of the conductive agent in alkaline electrolyte by more than two orders of magnitude.

[0025] 2. Excellent resistance to alkali corrosion: The nitrogen-rich phase in the outer layer of the gradient titanium nitride coating forms a dense passivation layer under alkaline conditions, suppressing the corrosion current density to 10. -8 A / cm 2 The following effectively blocks OH - The erosion of the copper core ensures that the conductive network maintains its structural integrity and functional stability during long-term cycling.

[0026] 3. It has significant cost and process advantages: By using inexpensive copper instead of precious silver as the conductive core, and combining it with atomic layer deposition technology, it is possible to achieve precise control of nanoscale thickness and composition. The cost of a single deposition is less than $0.1 / gram, which improves performance and provides a feasible industrialization path for large-scale preparation and application. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 Custom roll-to-roll ALD equipment provided for this application.

[0029] Figure 2 This is a schematic diagram of the conductive agent provided in Embodiment 1 of this application.

[0030] Figure 3 This is the XPS spectrum of the conductive agent in Example 1 of this application. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] The inventors' investigation revealed that one of the core bottlenecks facing aqueous sodium-ion batteries in practical applications lies in the lack of a highly efficient and stable conductive network. While traditional carbon-based conductive agents (such as acetylene black and carbon nanotubes) are relatively inexpensive, their intrinsic conductivity is only 10⁻⁶. 2 -10 3 The S / m ratio is insufficient to meet the demands of high-rate charge and discharge, and it is prone to electrochemical oxidation in strongly alkaline electrolytes, leading to continuous degradation of the conductive network and a sharp increase in battery internal resistance during cycling. Meanwhile, it possesses ultra-high conductivity (>10). 7 While high-strength metal nanowires (such as copper and silver) with a conductivity of S / m can significantly improve conductivity, they undergo severe corrosion reactions in alkaline environments. For example, copper can transform into insulating products such as Cu₂O and Cu(OH)₂, leading to the failure of the conductive structure. To address the corrosion problem, existing technologies typically employ uniform coatings (such as carbon layers) for protection. However, dense coatings introduce extremely high contact resistance at the metal-coating interface, causing the effective conductivity of the composite material to decrease by more than 90%, thus negating the high conductivity advantage of metallic materials. These research results indicate that developing a novel conductive agent that combines high conductivity, strong corrosion resistance, and low interfacial resistance in alkaline electrolytes is a key breakthrough for advancing the high performance and practical application of aqueous sodium-ion batteries.

[0033] In view of this, this application provides a conductive agent, its preparation method and application, to solve the problems in related technologies where traditional carbon-based conductive agents for sodium-ion batteries are limited by low intrinsic conductivity, resulting in poor high-rate performance, easy oxidation and corrosion in alkaline electrolytes leading to poor cycle stability, and existing surface coating technologies suffer from a severe decrease in effective conductivity due to the introduction of high interfacial resistance.

[0034] In a first aspect, this application provides a conductive agent having a core-shell structure, comprising: Metal core; A gradient titanium nitride layer covering the surface of the metal core; and, An alloy interface layer is formed between the metal core and the gradient titanium nitride layer; In the gradient titanium nitride layer, the nitrogen content increases gradually from the inside to the outside.

[0035] The conductive agent provided in this application has a core-shell structure, consisting of a metal core encapsulated within an inner core and a coating layer formed by a gradient titanium nitride layer. The metal core provides ultra-high intrinsic conductivity. The increasing nitrogen content from the inside out in the gradient titanium nitride layer creates a low-resistance alloy interface layer between the inner titanium-rich phase and the metal core, reducing the interfacial contact resistance to 1 / 100th that of traditional uniform carbon coating. Simultaneously, the outer nitrogen-rich phase forms a dense passivation layer in the alkaline electrolyte, suppressing the corrosion current density to below 10⁻⁶. -8 A / cm 2 The following effectively blocks OH - The conductive agent provided in this application can improve the rate performance and cycle stability of sodium-ion batteries by eroding the metal core.

[0036] In some embodiments provided in this application, the metal core comprises copper nanowires. Using copper nanowires as the metal core retains its extremely high intrinsic conductivity (>10). 7 Based on the S / m ratio, it can form a synergistic effect with the surface gradient titanium nitride coating: on the one hand, the gradient structure reduces the interfacial resistance to 1 / 100 of that of traditional carbon coating, allowing the conductive agent to maintain efficient charge transport capability in alkaline electrolytes; on the other hand, the nitrogen-rich surface layer forms a dense passivation layer, suppressing the corrosion current density to 10. -8 A / cm 2 The following effectively blocks OH - The process involves eroding the copper core and replacing the precious metal silver with inexpensive copper, combined with subsequent atomic layer deposition (ALD) processes to reduce the cost of a single deposition to less than $0.1 per gram.

[0037] In some embodiments provided in this application, the diameter of the copper nanowires is 20-30 nm. Limiting the diameter of the copper nanowires to this range ensures sufficient specific surface area for constructing a highly efficient conductive network while maintaining the mechanical strength of the nanowires themselves, preventing breakage during slurry dispersion and coating. If the diameter is too small (<20 nm), the nanowires are prone to agglomeration and have poor oxidation resistance; if the diameter is too large (>30 nm), the number of conductive nodes decreases for the same mass, making it difficult to form a dense percolation network.

[0038] It's important to clarify that the "diameter of a copper nanowire" refers to the widest distance (typically the outer diameter of a circular or near-circular cross-section) measured through its geometric center on a cross-section perpendicular to the nanowire's axis. It's a crucial one-dimensional structural parameter characterizing the nanowire's size, defining its nanoscale range (typically 1-100 nm), and determining its physicochemical properties (such as specific surface area, mechanical strength, and electrical transport behavior). The "aspect ratio" refers to the ratio (L / D) of the length (L) to the diameter (D) of nanowires, nanorods, or fibrous materials. It's a key geometric parameter characterizing the one-dimensional morphology of nanomaterials and predicting their macroscopic assembly behavior.

[0039] In some embodiments provided in this application, the aspect ratio of the copper nanowires is >100. Limiting the aspect ratio of the copper nanowires to the above range can significantly reduce the number of nodes in the conductive network, thereby reducing the contact resistance when electrons jump between particles and realizing long-range rapid electron transport; the higher the aspect ratio, the lower the percolation threshold required to form an effective conductive network, thereby reducing the amount of conductive agent added and increasing the proportion of active material.

[0040] In some embodiments provided in this application, the thickness of the gradient titanium nitride layer is 2-3 nm. Limiting the thickness of the gradient titanium nitride layer within this range achieves effective passivation and corrosion protection while minimizing the obstruction of electron transport by the inactive coating layer. If the thickness is less than 2 nm, it is difficult to form a continuous and dense protective film, and pinholes are prone to occur, leading to localized corrosion; if the thickness is greater than 3 nm, it will significantly increase the potential barrier for electron penetration, resulting in an increase in the overall resistivity of the conductive agent.

[0041] In some embodiments provided in this application, the gradient titanium nitride layer comprises, from the inside out, an inner layer, an intermediate layer, and an outer layer. The atomic ratio of nitrogen to titanium in the inner layer is (0.75-0.85):1, in the intermediate layer it is (0.95-1.05):1, and in the outer layer it is (1.15-1.25):1. This gradient titanium nitride layer, within the above parameter range, allows for a structural design where the nitrogen content increases from the inside out. The nitrogen-to-titanium ratio in the inner layer is close to that of metallic TiN, ensuring extremely low interfacial resistance with the metal core (only 1 / 100th that of traditional carbon coating). The intermediate layer is close to stoichiometric TiN, providing good conductive transition. The outer nitrogen-rich surface layer forms a dense passivation layer in the alkaline electrolyte, suppressing the corrosion current density to <10. -8 A / cm 2 This allows the metal core to maintain its ultra-high intrinsic electrical conductivity while also possessing excellent resistance to alkali corrosion.

[0042] In some embodiments provided in this application, the thickness ratio of the inner layer, the intermediate layer, and the outer layer is (0.01-1):(1-2):(2-3). Limiting the thickness ratio of the inner, intermediate, and outer layers within this range optimizes the balance between electron transport and corrosion resistance. The thinner inner layer (approaching metallic properties) ensures low contact resistance; the moderately thicker intermediate layer provides lattice transition and relieves stress; and the thicker outer layer (nitrogen-rich phase) provides a robust chemical inert barrier against alkaline electrolyte corrosion.

[0043] In some embodiments provided in this application, the raw material components of the gradient titanium nitride layer include a nitrogen precursor and a titanium precursor. As an example, the nitrogen precursor includes NH3; the titanium precursor includes TiCl4.

[0044] In some embodiments provided in this application, the alloy interface layer includes a Ti-Cu alloy layer. The Ti-Cu alloy interface layer constructed on the surface of the metal core effectively reduces the interface resistance between the gradient titanium nitride coating layer and the metal core by forming a gradient transition structure. Its interface resistance value is only 1 / 100 of that of a traditional carbon coating layer, thereby inhibiting the corrosion reaction of the metal core in alkaline electrolytes (such as 2Cu + 2OH⁻). - While achieving the effect of (+½O2→ Cu2O + H2O), it retains the core advantages of metal as an ultra-high conductivity metal, and achieves a synergistic improvement in conductivity, corrosion resistance and interface stability.

[0045] In some embodiments provided in this application, the titanium content in the Ti-Cu alloy layer is 10-15 at%. Limiting the titanium content in the Ti-Cu alloy layer to this range ensures the formation of stable metallic bonds at the interface, rather than high-resistance Schottky contacts. Within this range, the titanium content allows for good metallurgical bonding with copper, reducing interfacial energy; if the content is too low, the interfacial bonding is weak and easily peeled off; if the content is too high, it easily forms highly brittle intermetallic compounds, affecting flexibility.

[0046] In some embodiments provided in this application, the thickness of the Ti-Cu alloy layer is 0.5-1 nm. Limiting the thickness of the Ti-Cu alloy layer to this range enables electron tunneling transport using quantum size effects, adds almost no additional ohmic resistance, and is sufficient to anchor the subsequently grown titanium nitride layer, preventing interface oxidation.

[0047] Secondly, this application provides a method for preparing the conductive agent, comprising the following steps: Preparation of a metal core; A gradient titanium nitride layer is prepared on the surface of the metal core using atomic layer deposition (ALD) technology, and an alloy interface layer is formed between the metal core and the gradient titanium nitride layer. The nitrogen content in the gradient titanium nitride layer increases gradually from the inside to the outside.

[0048] The preparation method provided in this application sequentially constructs a Ti-Cu alloy interface layer and a gradient titanium nitride layer on the surface of a metal core using atomic layer deposition (ALD) technology, and can achieve a controllable increase in nitrogen content from the inside out, ultimately forming a nitrogen-rich surface layer. This structure can reduce the interface resistance to 1 / 100 of that of traditional carbon coating, while forming a dense passivation layer in an alkaline environment, resulting in a corrosion current density of less than 10. -8 A / cm², thus achieving high electrical conductivity and strong corrosion resistance in synergy, and the cost of a single deposition of atomic layer deposition process is less than US$0.1 / gram, which has significant cost and process advantages.

[0049] The preparation method of the metal core is not particularly limited, and those skilled in the art can choose flexibly as needed. In this application, the metal core is prepared by electrochemical deposition. Taking the preparation process of copper nanowires as an example, copper foil is immersed in a 0.1M CuSO4 + 0.05M H2SO4 electrolyte, and a voltage of -0.8V vs. Ag / AgCl is applied to grow copper nanowires in a porous anodic alumina (AAO) template; after removing the template, copper nanowire bundles are obtained.

[0050] In some embodiments provided in this application, the atomic layer deposition temperature is 200-240°C. Limiting the atomic layer deposition temperature to this range not only falls within the ALD window of the TiCl4 and NH3 reaction, ensuring the self-limiting growth and thickness uniformity of the deposited film, but also promotes the diffusion of Ti atoms from the interface into the shallow layer of the Cu lattice to form an alloy layer, while avoiding excessive temperature that could cause recrystallization, softening, or over-oxidation of the copper nanowires.

[0051] In some embodiments provided in this application, the pressure of the atomic layer deposition is 0.1-0.5 Torr. Limiting the pressure of the atomic layer deposition within the above range ensures that the precursor molecules have an appropriate mean free path, enabling them to fully penetrate into the deep interlayer gaps of the copper nanowire bundle, achieving 360-degree full coverage of the high aspect ratio nanomaterials, and avoiding coverage dead zones caused by the "shadow effect".

[0052] It should be noted that there are no specific limitations on the equipment used for atomic layer deposition, and those skilled in the art can choose flexibly according to their needs. In this application, a customized roll-to-roll atomic layer deposition apparatus with a spatially confined structure is used, such as... Figure 1As shown, the specific working principle is as follows: The equipment includes an unwinding unit, a reaction chamber unit, and a winding unit. Copper nanowires are loaded onto a flexible porous substrate and continuously transported into the reaction chamber by the unwinding unit. The reaction chamber employs either spatial isolation or time-pulse mode. As the substrate loaded with copper nanowires passes through the reaction zone, it is sequentially exposed to titanium precursor pulses, inert gas purging, nitrogen precursor pulses, and inert gas purging environments. By controlling the coupling between the substrate's travel speed (wind-to-wind speed) and the precursor pulse frequency, as well as a zoned heating temperature control system, precise layer-by-layer deposition of gradient components is achieved during dynamic transport. Finally, the winding unit collects the finished product, realizing the continuous and large-scale production of nanoscale coated conductive agents.

[0053] In some embodiments provided in this application, the steps for preparing the gradient titanium nitride layer include: A first deposition cycle is performed on the surface of the metal core to obtain the inner layer; A second deposition cycle is performed on the side of the inner layer away from the surface of the metal core to obtain the intermediate layer; A third deposition cycle is performed on the side of the intermediate layer away from the inner layer to obtain the outer layer.

[0054] Using a stepwise atomic layer deposition process, inner, middle, and outer layers of titanium nitride are sequentially deposited on the surface of a metal core. The nitrogen content distribution in each layer is controlled to ultimately form a gradient titanium nitride structure with gradually increasing nitrogen content from the inside out. The nitrogen-rich outer layer can form a dense passivation layer in an alkaline environment, effectively suppressing the corrosion current density to within 10. -8 With an A / cm² or less, the inner layer with a low nitrogen content close to the metal core forms a low-resistance contact with the alloy interface layer, reducing the overall interface resistance to 1 / 100 of that of traditional carbon coating, thereby achieving synergistic optimization of high conductivity and strong corrosion resistance.

[0055] Specifically, deposition was performed in sets of five ALD cycles. First, a titanium precursor (e.g., TiCl4) was pulsed into the reaction chamber containing the metal core for 50 ms, followed by purging with an inert gas to remove excess precursor and byproducts. Next, a nitrogen precursor (NH3) was pulsed in for 200 ms, maintaining the reaction temperature at 200°C for 300 ms to ensure sufficient chemical reaction of the precursor on the metal core surface. Purging was performed after each cycle. This process was repeated five times to form a low-nitrogen-content titanium nitride inner layer on the metal core surface.

[0056] A second set of 5 ALD cycles was then performed. The pulsed TiCl4 conditions (50 ms) were kept constant, while the pulsed NH3 time was shortened to 150 ms, the reaction temperature was increased to 220°C, and the reaction time per cycle was adjusted to 250 ms. Deposition was carried out under these conditions to form a titanium nitride intermediate layer with a moderate nitrogen content. This layer, located above the inner layer, serves as a transition between composition and structure.

[0057] Finally, a third set of 5 ALD cycles was performed. The TiCl4 pulse time remained at 50 ms, while the NH3 pulse time was further shortened to 100 ms, the reaction temperature was increased to 240°C, and the single-cycle reaction time was 200 ms. Under these conditions, a titanium nitride outer layer with the highest nitrogen content was deposited.

[0058] By successively shortening the NH3 pulse time and stepwise increasing the temperature, the nitrogen content in the coating layer was achieved to increase gradually from the inside to the outside, and XPS analysis verified that its N / Ti ratio met the design gradient.

[0059] Therefore, by using the preparation method provided in this application, and by precisely controlling the precursor pulse sequence and process parameters, a titanium nitride inner layer, a titanium nitride intermediate layer, and a titanium nitride outer layer with compositional gradients are sequentially constructed on the surface of the metal core.

[0060] Thirdly, this application provides an electrode comprising an electrode active material, a binder, and a conductive agent, wherein the conductive agent comprises the conductive agent described above or a conductive agent prepared according to the method described above.

[0061] Electrodes prepared using the conductive agent provided in this application exhibit an interface resistance that is only 1 / 100 that of traditional carbon-coated electrodes due to the core-shell structure of the conductive agent, which has a gradient titanium nitride layer covering the metal core. Furthermore, the nitrogen-rich titanium nitride outer layer on the surface can form a dense passivation layer, suppressing the corrosion current density to 10. -8 A / cm 2 Therefore, it is possible to construct a highly conductive and stable three-dimensional conductive network in a high-concentration alkaline electrolyte, which significantly improves the rate performance and cycle stability of the electrode.

[0062] There is no particular limitation on the type of electrode; those skilled in the art can choose flexibly as needed. The electrode provided in this application is a sodium ion electrode, including but not limited to at least one of a positive electrode and a negative electrode.

[0063] There are no specific limitations on the electrode active materials, and those skilled in the art can make flexible selections as needed. The electrode active materials provided in this application include, but are not limited to, sodium ion intercalation compounds (such as Na3V2(PO4)3 and NaMnO2).

[0064] The adhesive is not specifically limited, and those skilled in the art can choose flexibly as needed. The adhesives provided in this application include, but are not limited to, fluoropolymers (such as PVDF and PTFE).

[0065] In some embodiments provided in this application, the amount of conductive agent added is 1-5 wt% based on the total mass of the electrode. Limiting the amount of conductive agent allows for a precise balance between the electrode's conductivity and energy density. Since the conductive agent described in this application is based on a copper nanowire core, it possesses an extremely high aspect ratio and intrinsic conductivity, and its percolation threshold is far lower than that of traditional particulate carbon conductive agents. If the added amount is less than 1 wt%, the conductive network nodes are insufficient, making it difficult to form long-range continuous electron transport channels throughout the electrode, leading to increased internal resistance and limited rate performance. If the added amount is greater than 5 wt%, although conductivity is saturated, it significantly reduces the mass percentage of the active material in the electrode, thereby sacrificing the battery's volumetric and gravimetric energy density. Furthermore, excessive nanowires may lead to agglomeration, affecting the rheological properties and coating quality of the slurry.

[0066] Fourthly, this application provides a sodium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an aqueous electrolyte, wherein the positive electrode and / or the negative electrode includes electrodes as described above.

[0067] The sodium-ion battery provided in this application, by introducing the aforementioned metal core conductive agent with gradient titanium nitride coating into the positive and / or negative electrodes, can, on the one hand, improve the charge transport capability of the electrodes under high-rate conditions by utilizing its ultra-high intrinsic conductivity and extremely low interfacial resistance (only 1 / 100 of that of traditional carbon coating); on the other hand, by utilizing the passivation protection effect formed by the nitrogen-rich surface layer in the alkaline electrolyte (such as 6M NaOH), the corrosion current density is suppressed to 10. -8 A / cm 2 The following measures can prevent the conductive network from oxidizing and degrading during cycling, thereby synergistically achieving long-cycle stability and capacity retention of the battery under high power output.

[0068] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Example 1 1. Preparation of conductive agents (1) Preparation of the metal core: Copper nanowires were prepared by template electrochemical deposition. A pretreated porous anodic alumina template (AAO, pore size 25 nm) was used as the working electrode and immersed in an aqueous electrolyte consisting of 0.1 mol / L CuSO4 and 0.05 mol / L H2SO4. With an Ag / AgCl electrode as the reference electrode and a platinum sheet as the counter electrode, deposition was carried out at a constant potential of -0.8 V (relative to Ag / AgCl) for 30 minutes. After deposition, the AAO template was dissolved in 3 mol / L NaOH solution, and after repeated centrifugation and washing with deionized water, copper nanowires with a diameter of approximately 25±3 nm, a length of approximately 50±5 μm, and an aspect ratio of 110 were obtained and vacuum dried for later use.

[0069] (2) Spatial confinement ALD deposition of gradient titanium nitride layer: A custom roll-to-roll atomic layer deposition system was used to coat the surface of the copper nanowires obtained in step (1) with gradient titanium nitride: 1) Reaction conditions: The reaction chamber pressure is maintained at 0.3 Torr, and the substrate temperature is programmed according to the process steps.

[0070] 2) Precursors: TiCl4 is used as the titanium precursor, and NH3 is used as the nitrogen precursor and reducing agent.

[0071] 3) Gradient deposition process: The deposition process consists of three stages, totaling 15 ALD cycles. By progressively reducing the NH3 pulse time and increasing the deposition temperature, a gradient distribution of nitrogen content is achieved, gradually increasing from the inside out (N / Ti atomic ratio increases from approximately 0.8 to approximately 1.2). Specific process parameters are shown in Table 1 below. Table 1

[0072] 4) During the deposition process, high-purity nitrogen gas is introduced after each pulse step for thorough purging to prevent gaseous precursor reactions, ultimately obtaining a conductive agent with a structure of "copper nanowire core-Ti-Cu alloy interface layer-gradient titanium nitride layer" (see [link]). Figure 2 As shown in the figure, the thickness of the gradient titanium nitride layer is 1.5 nm, the thickness ratio of the inner layer, the middle layer and the outer layer in the gradient titanium nitride layer is 0.5:1.5:2.5, the titanium content in the Ti-Cu alloy layer is 12 at%, and the thickness of the Ti-Cu alloy layer is 0.8 nm.

[0073] in addition, Figure 3 XPS spectra of the conductive agent of Example 1 are shown. The results in the figure confirm that a titanium nitride coating layer was successfully prepared on the surface of copper nanowires.

[0074] 2. Preparation of sodium-ion batteries (1) Preparation of the positive electrode: Weigh the following by mass percentage: 3% of the titanium nitride gradient-coated copper nanowire conductive agent prepared in step 1, 92% of the Na3V2(PO4)3 positive electrode active material, and 5% of the polyvinylidene fluoride (PVDF) binder. Place the above materials together in N-methylpyrrolidone solvent and stir at 2000 rpm for 4 hours in a planetary mixer to obtain a uniform and stable positive electrode slurry. Use a doctor blade coating method to uniformly coat the above positive electrode slurry onto an aluminum foil current collector with a thickness of 20 μm. Then place the coated electrode in a vacuum oven at 120°C to dry for 12 hours, and then compact it by a roller press to control the compaction density of the electrode to be about 2.5 g / cm³. Finally, cut the electrode into a circular piece with a diameter of 12 mm, which is the positive electrode of the battery.

[0075] (2) Preparation of the negative electrode: Weigh the following materials by mass percentage: 92% hard carbon negative electrode active material, 3% conductive agent prepared in Example 1 above, 1.5% sodium carboxymethyl cellulose (CMC), and 3.5% styrene-butadiene rubber (SBR). Disperse the above materials in deionized water and stir evenly to prepare a negative electrode slurry. Coat the slurry evenly on a 10 μm thick copper foil current collector, dry it in a vacuum oven at 110℃ for 12 hours, roll it, and punch it into a negative electrode disc with a diameter of 12 mm.

[0076] (3) Battery assembly: Assembly was carried out in a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm). A CR2032 button cell battery case was used, with glass fiber filter paper (Whatman GF / D) as the separator and 1 mol / L Na2SO4 aqueous solution as the electrolyte. The battery was assembled in the order of "negative electrode case-negative electrode sheet-separator-electrolyte-positive electrode sheet-gasket-spring sheet-positive electrode case", and sealed with a sealing machine. After standing for 12 hours to allow the electrolyte to fully impregnate the battery, it was tested.

[0077] Example 2 Example 2 provides a conductive agent, differing from Example 1 only in the ALD process parameters: adjusting the number of cycles in the three stages. The first stage (inner layer) is cycled once, the second stage (middle layer) is cycled three times, and the third stage (outer layer) is cycled six times, for a total of 10 cycles. The resulting conductive agent with a "copper nanowire core-Ti-Cu alloy interface layer-gradient titanium nitride layer" structure has a gradient titanium nitride layer thickness of 2 nm, and the thickness ratio of the inner, middle, and outer layers in the gradient titanium nitride layer is 0.1:1:2. Everything else is the same as in Example 1.

[0078] Example 3 Example 3 provides a conductive agent, differing from Example 1 only in the ALD process parameters: adjusting the number of cycles in the three stages. The first stage (inner layer) is cycled 5 times, the second stage (middle layer) is cycled 10 times, and the third stage (outer layer) is cycled 15 times, for a total of 30 cycles. The resulting conductive agent with a "copper nanowire core-Ti-Cu alloy interface layer-gradient titanium nitride layer" structure has a gradient titanium nitride layer thickness of 3 nm, and the thickness ratio of the inner, middle, and outer layers in the gradient titanium nitride layer is 1:2:3. Everything else is the same as in Example 1.

[0079] Example 4 Example 4 provides a conductive agent, which differs from Example 1 in the control steps of the diameter and aspect ratio of the copper nanowires: In the metal core preparation step, an AAO template with a pore size of 20 nm is selected, and the electrodeposition time is adjusted to 35 minutes, so that the copper nanowires grow more densely and increase in length in the pores, resulting in copper nanowires with a diameter of 20 nm and an aspect ratio of 120. The rest is the same as in Example 1.

[0080] Example 5 Example 5 provides a conductive agent, which differs from Example 1 in the control steps of the diameter and aspect ratio of the copper nanowires: in the metal core preparation step, an AAO template with a pore size of 30 nm is selected, and the electrodeposition time is extended to 120 minutes to obtain nanowires with an ultra-large aspect ratio, resulting in copper nanowires with a diameter of 30 nm and an aspect ratio of 300. The rest is the same as in Example 1.

[0081] Example 6 Example 6 provides a conductive agent, which differs from Example 1 in the steps of controlling the titanium content and thickness in the Ti-Cu alloy layer: in the early stage of ALD deposition (the first 5 cycles), the deposition temperature is reduced to 190°C and the TiCl4 pulse time is shortened to 30ms to slow down the thermal diffusion rate and depth of Ti atoms into the Cu lattice. The resulting Ti-Cu alloy layer has a titanium content of 10at% and a thickness of 0.5nm, and the rest is the same as in Example 1.

[0082] Example 7 Example 7 provides a conductive agent, which differs from Example 1 in the steps of controlling the titanium content and thickness in the Ti-Cu alloy layer: In the early stage of ALD deposition (the first 5 cycles), the deposition temperature is increased to 250°C and the TiCl4 pulse time is extended to 80ms to enhance the thermal diffusion kinetics of Ti atoms. The resulting Ti-Cu alloy layer has a titanium content of 15at% and a thickness of 1.0nm. The rest is the same as in Example 1.

[0083] Comparative Example 1 Comparative Example 1 provides a conductive agent similar to that of Example 1, except that it does not contain a gradient titanium nitride layer.

[0084] Comparative Example 2 Comparative Example 2 provides a conductive agent similar to Example 1, except that the nitrogen element in the titanium nitride layer used for coating is uniformly distributed. Specifically, a uniform TiN (N / Ti≈1.0) coating layer is deposited on the surface of copper nanowires using a conventional ALD process with a constant NH3 pulse time (e.g., 150 ms) and a constant temperature (e.g., 220°C) throughout 15 cycles.

[0085] Comparative Example 3 Comparative Example 3 provides a conductive agent, which is a commercial acetylene black conductive agent purchased from Dongguan Kelude New Energy Technology Co., Ltd.

[0086] Performance testing The sodium-ion batteries obtained in Examples 1-8 and Comparative Examples 1-3 were subjected to performance tests, specifically testing their conductivity, rate performance, and cycle stability. The specific test steps are as follows: Conductivity test: The conductivity was measured using a powder resistivity tester (four-probe method). 0.5g of the conductive agent powder to be tested was accurately weighed, placed in a mold, and pressed into a cylindrical block under a pressure of 10 MPa. The thickness and diameter of the block were measured, and the resistance value was read using the four probes to calculate the conductivity (S / m).

[0087] Rate performance testing: Conducted on the LAND battery testing system. At 25°C, the voltage window was set to 0.0-2.0V (for full cells). First, activation was performed at 0.1C for 3 cycles, followed by constant current charge-discharge tests at 0.2C, 0.5C, 1C, 2C, and 5C rates, with 5 cycles at each rate. The discharge capacity at 5C rate was recorded.

[0088] Cyclic stability test: The battery is subjected to constant current charge-discharge cycle test at a high rate of 1C. The AC impedance (EIS) of the battery is measured before cycling, and the AC impedance is measured again after 100 cycles. The percentage increase in charge transfer resistance (Rct) is calculated to characterize the degree of corrosion and degradation of the conductive network; the capacity retention rate is also recorded during the cycling process.

[0089] The specific test results are shown in Table 2: Table 2

[0090] As shown in Table 2, compared with the test results of Comparative Examples 1-3, the sodium-ion batteries of Examples 1-7, using the conductive agent provided in this application, exhibit significant advantages in terms of conductivity, cycle stability, and rate performance.

[0091] Comparative Example 1, lacking a gradient titanium nitride layer, had its copper nanowires directly exposed to the alkaline electrolyte, resulting in severe corrosion. After cycling, the resistance increased by as much as 450%, and the nanowires almost failed at a high rate of 5C, with the capacity plummeting to 15 mAh / g. This indicates that the metal core without a protective layer cannot work stably in an alkaline environment.

[0092] Comparative Example 2, due to the use of a uniformly distributed titanium nitride layer, although corrosion was suppressed to some extent (resistance increase of 12%), its conductivity was only 4.5 × 10⁻⁶. 3 The S / m is much lower than that of the gradient structure embodiment, and the 5C capacity is only 85 mAh / g, indicating that the uniform coating layer introduces a high interface resistance, which limits the electron transport efficiency.

[0093] Comparative Example 3, due to the use of commercial acetylene black conductive agent, had the lowest initial conductivity (8.2 × 10⁻⁶). 2 The resistance increased by 320% after cycling (S / m), and the 5C capacity was only 62 mAh / g, indicating that traditional carbon-based conductive agents have low conductivity and are easily oxidized in alkaline environments, and cannot meet the requirements for high-rate long-cycle use.

[0094] The above results demonstrate that the conductive agent provided in this application, by constructing a gradient titanium nitride coating layer on the surface of copper nanowires, effectively solves the technical contradiction between the easy corrosion of metal nanowires in alkaline electrolytes and the coexistence of high interfacial resistance. Specifically, this gradient structure achieves ultra-high conductivity (>10). 5 The combination of S / m and excellent resistance to alkali corrosion. When applied to aqueous sodium-ion batteries, it can significantly suppress the impedance increase of the electrode during long-term cycling (resistance increase ≤15% after 500 cycles), and the raw material cost can be reduced by more than 50% thanks to the replacement of precious silver with inexpensive copper.

[0095] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0096] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified.

[0097] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A conductive agent, characterized in that, The conductive agent has a core-shell structure, comprising: Metal core; A gradient titanium nitride layer covering the surface of the metal core; and, An alloy interface layer is formed between the metal core and the gradient titanium nitride layer; In the gradient titanium nitride layer, the nitrogen content increases gradually from the inside to the outside.

2. The conductive agent as described in claim 1, characterized in that, The metallic core comprises copper nanowires; and / or, The copper nanowires have a diameter of 20-30 nm; and / or, The aspect ratio of the copper nanowires is >100.

3. The conductive agent as described in claim 1, characterized in that, The thickness of the gradient titanium nitride layer is 2-3 nm; and / or, The gradient titanium nitride layer comprises an inner layer, an intermediate layer, and an outer layer from the inside out. The atomic ratio of nitrogen to titanium in the inner layer is (0.75-0.85):1, the atomic ratio of nitrogen to titanium in the intermediate layer is (0.95-1.05):1, and the atomic ratio of nitrogen to titanium in the outer layer is (1.15-1.25):

1.

4. The conductive agent according to any one of claims 1-3, characterized in that, The thickness ratio of the inner layer, the intermediate layer, and the outer layer is (0.01-1):(1-2):(2-3); and / or, The raw material components of the gradient titanium nitride layer include a nitrogen precursor and a titanium precursor; and / or, The nitrogen precursor includes NH3; and / or, The titanium precursor includes TiCl4.

5. The conductive agent according to any one of claims 1-3, characterized in that, The alloy interface layer includes a Ti-Cu alloy layer; and / or, The thickness of the Ti-Cu alloy layer is 0.5-1 nm; and / or, The titanium content in the Ti-Cu alloy layer is 10-15 at.

6. A method for preparing the conductive agent according to any one of claims 1-5, characterized in that, include: Preparation of a metal core; A gradient titanium nitride layer is prepared on the surface of the metal core using atomic layer deposition (ALD) technology, and an alloy interface layer is formed between the metal core and the gradient titanium nitride layer. The nitrogen content in the gradient titanium nitride layer increases gradually from the inside to the outside.

7. The method as described in claim 6, characterized in that, The atomic layer deposition temperature is 200-240°C; and / or, The pressure for atomic layer deposition is 0.1-0.5 Torr.

8. The method as described in claim 6 or 7, characterized in that, The steps for preparing a gradient titanium nitride layer include: A first deposition cycle is performed on the surface of the metal core to obtain the inner layer; A second deposition cycle is performed on the side of the inner layer away from the surface of the metal core to obtain the intermediate layer; A third deposition cycle is performed on the side of the intermediate layer away from the inner layer to obtain the outer layer.

9. An electrode, characterized in that, It comprises an electrode active material, a binder, and a conductive agent, wherein the conductive agent comprises the conductive agent as described in any one of claims 1-5 or the conductive agent prepared by the method according to any one of claims 6-8.

10. A sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a membrane, and an aqueous electrolyte, wherein the positive electrode and / or the negative electrode includes the electrode as described in claim 9.

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