Battery current collector and preparation method, negative electrode-free sodium ion battery and preparation method

Abstract

The present invention provides a battery current collector and a preparation method, a negative electrode-free sodium ion battery and a preparation method, which relate to the technical field of sodium ion batteries, including: an aluminum foil substrate and a titanium-tungsten alloy coating coated on the surface of the aluminum foil substrate, wherein the titanium-tungsten alloy coating has a gradient component distribution and is prepared on the surface of the aluminum foil substrate by magnetron sputtering or plasma-enhanced chemical vapor deposition. The beneficial effect is that the synergistic effect of titanium and tungsten is used to regulate the electron distribution on the alloy surface, form a highly sodium-affinity active site, significantly reduce the sodium nucleation overpotential, and induce dense, dendrite-free sodium deposition behavior; solve the problem that the traditional aluminum foil current collector has low surface energy, resulting in uneven sodium ion deposition; the low-temperature deposition process can ensure the density and low defect density of the alloy coating while avoiding thermal deformation of the aluminum foil substrate; and can efficiently and stably prepare the titanium-tungsten alloy coating on the surface of the aluminum foil substrate to obtain a battery current collector suitable for negative electrode-free sodium ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a battery current collector and a preparation method thereof, and a negative electrode-free sodium ion battery and a preparation method thereof. Background Art

[0002] With the rapid development of the new energy industry, the safety, energy density, and resource sustainability of battery technology have become key factors driving industry upgrades. Traditional liquid lithium-ion batteries, due to their use of flammable organic electrolytes, have inherent drawbacks such as a high risk of thermal runaway and limited energy density. Furthermore, global lithium reserves are limited (approximately 0.0065% of lithium is found in the Earth's crust) and are unevenly distributed, resulting in a fragile supply chain and making it difficult to meet the urgent demand for high-performance batteries in sectors such as electric vehicles and energy storage.

[0003] As an emerging battery technology, anode-free sodium-ion batteries are considered an important path to overcome the bottleneck of sodium battery industrialization due to their advantages, such as not requiring a pre-loaded metallic sodium anode and simplifying the process. However, the core challenge of anode-free sodium-ion batteries lies in achieving efficient and uniform deposition of sodium metal on the current collector surface and stable cycling.

[0004] Currently, traditional aluminum foil current collectors have low surface energy, resulting in uneven sodium ion deposition, which can easily trigger dendrite growth, interfacial side reactions, and rapid capacity decay. To address these issues, researchers have proposed alloying modification strategies, such as aluminum-based alloy coatings, to reduce the sodium nucleation overpotential. However, these alloying coatings are accompanied by dramatic volume expansion during the alloying / de-alloying process (e.g., Na-Al alloying volume changes >200%), which can easily lead to pulverization of the current collector structure and repeated rupture of the solid electrolyte interface (SEI) film, severely limiting the battery's cycle life.

[0005] In addition, the high reactivity of metallic sodium makes conventional coating materials (such as copper and nickel) prone to chemical corrosion or phase change with sodium during long-term cycles, further exacerbating the increase in interfacial impedance and the degradation of electrochemical performance.

[0006] The existing technology for negative electrode current collectors of negative electrode-free sodium ion batteries has the following major disadvantages:

[0007] Uneven sodium deposition: The traditional aluminum foil current collector has low surface energy, which leads to uneven sodium ion deposition, easily inducing dendrite growth, affecting the safety and cycle life of the battery.

[0008] Significant volume expansion: Existing alloying modification strategies (such as aluminum-based alloy coatings) are accompanied by dramatic volume expansion during the alloying / de-alloying process, which can easily cause the current collector structure to become pulverized, seriously restricting the cycle life of the battery.

[0009] Poor chemical stability: The high reactivity of metallic sodium makes conventional coating materials susceptible to chemical corrosion or phase change with sodium during long-term circulation, resulting in increased interfacial impedance and degradation of electrochemical performance.

[0010] It is necessary to propose a solution to solve the shortcomings of the above-mentioned existing technologies and promote the leapfrog development of negative electrode-free sodium battery technology towards high energy density and long life. Summary of the Invention

[0011] In response to the problems existing in the prior art, the present invention provides a negative electrode-free sodium ion battery current collector based on a titanium-tungsten alloy gradient coating, comprising: an aluminum foil substrate, and a titanium-tungsten alloy coating coated on the surface of the aluminum foil substrate, wherein the titanium-tungsten alloy coating has a gradient component distribution.

[0012] Preferably, the titanium-tungsten alloy coating comprises a titanium-rich layer, a transition layer and a tungsten-rich layer stacked sequentially from the aluminum foil substrate outward; the ratio of titanium atoms to tungsten atoms in the titanium-rich layer, the transition layer and the tungsten-rich layer decreases sequentially to form the gradient component distribution.

[0013] Preferably, the transition layer includes multiple subdivided layers, and the ratio of the number of titanium atoms to tungsten atoms in the subdivided layers gradually changes from 3:1 to 1:1 in each layer.

[0014] Preferably, the ratio of the number of titanium atoms to the number of tungsten atoms in the titanium-tungsten alloy coating is in the range of 1:1 to 3:1.

[0015] Preferably, the ratio of the thickness of the titanium-rich layer to the thickness of the tungsten-rich layer is positively correlated with the overall number ratio of titanium atoms to tungsten atoms in the titanium-tungsten alloy coating.

[0016] Preferably, when the overall number ratio of titanium atoms to tungsten atoms in the titanium-tungsten alloy coating is 3:1, the thickness of the titanium-rich layer is greater than the thickness of the tungsten-rich layer; when the overall number ratio of titanium atoms to tungsten atoms in the titanium-tungsten alloy coating is 1:1, the thickness of the titanium-rich layer is less than the thickness of the tungsten-rich layer.

[0017] Preferably, the total thickness of the titanium-tungsten alloy coating is 50-500 nm.

[0018] The present invention also provides a method for preparing a negative electrode-free sodium ion battery current collector, which is used to prepare the negative electrode-free sodium ion battery current collector as described above, comprising: using a magnetron sputtering or plasma-enhanced chemical vapor deposition process to form a titanium-tungsten alloy coating with a gradient component distribution on the surface of an aluminum foil substrate.

[0019] The present invention also provides a negative electrode-free sodium ion battery, which uses the above-mentioned negative electrode-free sodium ion battery current collector as the negative electrode current collector.

[0020] The present invention also provides a method for preparing a negative electrode-free sodium ion battery, which is used to prepare the negative electrode-free sodium ion battery as described above, comprising: step S1, using an aluminum foil substrate coated with a titanium-tungsten alloy coating as a negative electrode current collector, and assembling it with a sodium metal positive electrode or a sodium compensation positive electrode and an electrolyte to form a negative electrode-free sodium ion battery; step S2, charging the negative electrode-free sodium ion battery. During the first charging, sodium ions are released from the positive electrode, preferentially nucleated on the surface of the titanium-tungsten alloy coating, and deposited as a dense metallic sodium layer, forming a negative electrode-free structure.

[0021] The above technical solution has the following advantages or beneficial effects:

[0022] 1. By applying a titanium-tungsten alloy coating with a gradient component distribution on the surface of an aluminum foil substrate, the synergistic effect of titanium and tungsten is utilized to regulate the electron distribution on the alloy surface, forming highly sodium-affinity active sites. This significantly reduces the sodium nucleation overpotential and induces dense, dendrite-free sodium deposition behavior. This solves the problem of uneven sodium ion deposition caused by the low surface energy of traditional aluminum foil current collectors.

[0023] 2. Using magnetron sputtering or plasma-enhanced chemical vapor deposition (PECVD) processes, a titanium-tungsten alloy coating is deposited on the surface of an aluminum foil substrate. This low-temperature deposition process prevents thermal deformation of the aluminum foil while ensuring the density and low defect density of the alloy coating. This allows for efficient and stable deposition of a titanium-tungsten alloy coating on the surface of an aluminum foil substrate, resulting in a battery current collector suitable for anode-free sodium-ion batteries.

[0024] 3. In the negative electrode-free sodium ion battery, aluminum foil with a titanium-tungsten alloy gradient coating is used as the negative electrode current collector. This coating solves the problems of sodium nucleation uniformity, volume stability and interface compatibility through its unique physicochemical properties (such as high sodium affinity, high modulus, low volume expansion rate and excellent chemical inertness), thereby improving the cycle life and safety of the negative electrode-free sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the structure of the titanium-tungsten alloy coating in a preferred embodiment of the present invention;

[0026] Figure 2 The present invention is a preferred embodiment of a process flow diagram of a method for preparing a negative electrode-free sodium ion battery. DETAILED DESCRIPTION

[0027] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment, and other embodiments may also fall within the scope of the present invention as long as they conform to the gist of the present invention.

[0028] In a preferred embodiment of the present invention, based on the above-mentioned problems existing in the prior art, a negative electrode-free sodium ion battery current collector based on a titanium-tungsten alloy gradient coating is provided, comprising: an aluminum foil substrate, and a titanium-tungsten alloy coating coated on the surface of the aluminum foil substrate, wherein the titanium-tungsten alloy coating has a gradient component distribution.

[0029] Specifically, this embodiment defines a core structure of a battery current collector, namely, a titanium-tungsten alloy gradient coating coated on the surface of an aluminum foil substrate, wherein the beneficial effects of the titanium-tungsten alloy and the gradient distribution are:

[0030] 1. Beneficial effects of coating

[0031] 1.1 High sodium affinity:

[0032] Technical principle: The weak adsorption of titanium (Ti) and sodium (Na) and the high electronic conductivity of tungsten (W) synergistically regulate the interfacial electron distribution.

[0033] Beneficial effects: This highly sodium-affinity active site can guide the uniform deposition of sodium ions and effectively inhibit dendrite growth, thereby improving the safety and cycle stability of the battery.

[0034] 1.2 Excellent mechanical stability:

[0035] Technical principle: Titanium tungsten alloy has high modulus (>200 GPa) and low thermal expansion coefficient (<6×10 -6 / K), which can withstand the mechanical stress during the sodium deposition / stripping process.

[0036] Beneficial effects: The coating volume change rate is <5% (much lower than the >200% of traditional Na-Al alloy), which avoids interface structure pulverization, maintains interface electrical contact stability, and significantly improves the cycle life of the battery.

[0037] 1.3 Good chemical stability:

[0038] Technical Principle: Titanium-tungsten alloy has excellent chemical inertness in a wide voltage range (0-5V vs. Na+ / Na), and can resist corrosion from sodium metal and electrolyte decomposition products.

[0039] Beneficial effects: Ensure the dynamic balance of interfacial impedance during long cycles, reduce interfacial side reactions, and improve the coulombic efficiency and cycle stability of the battery.

[0040] 1.4 Dynamic passivation layer protection:

[0041] Technical principle: The surface of titanium tungsten alloy spontaneously forms a dense TiO2-WO3 composite passivation layer during the cycle, which has high ionic conductivity (>10 -4 S / cm) and dynamic self-repairing ability effectively inhibit the decomposition of the electrolyte.

[0042] Beneficial effects: The passivation layer can block the corrosion of the interface by decomposition products of the electrolyte (such as Na2CO3), further improving the chemical stability and cycle life of the battery.

[0043] 2. Beneficial effects of gradient

[0044] 2.1 Enhance bonding strength:

[0045] Design principle: The coating forms a gradient component distribution from the bottom layer to the surface, and the bottom layer is a titanium-rich layer to enhance the bonding strength with the aluminum foil.

[0046] Beneficial effects: This gradient design ensures a close bond between the coating and the aluminum foil substrate, preventing the coating from falling off or powdering during cycling, and improving the reliability and durability of the battery.

[0047] 2.2 Improve electrical conductivity and chemical stability:

[0048] Design principle: The surface layer is a tungsten-rich layer to improve conductivity and chemical stability.

[0049] Beneficial effects: The high conductivity of the tungsten-rich layer can reduce the internal resistance of the battery and improve the battery's charge and discharge efficiency; at the same time, its excellent chemical stability can further protect the battery from electrolyte corrosion and extend the battery's service life.

[0050] In a preferred embodiment of the present invention, Figure 1 As shown, the titanium-tungsten alloy coating includes a titanium-rich layer 2, a transition layer 3 and a tungsten-rich layer 4 stacked in sequence from an aluminum foil substrate 1 outward; the ratio of titanium atoms to tungsten atoms in the titanium-rich layer, the transition layer and the tungsten-rich layer decreases in sequence, forming a gradient component distribution.

[0051] Specifically, the effects of providing the titanium-rich layer, the transition layer, and the tungsten-rich layer in this embodiment are as follows:

[0052] Titanium-rich layer: Directly in contact with the aluminum foil substrate, it has a high titanium (Ti) content (e.g., Ti:W ≈ 3:1). The high affinity between titanium and aluminum (low Al-Ti interface energy) is utilized to enhance the bonding between the coating and the aluminum foil, preventing peeling.

[0053] Transition layer: Located between the titanium-rich layer and the tungsten-rich layer, the composition changes continuously from titanium-rich to tungsten-rich (for example, the Ti:W ratio gradually transitions from 3:1 to 1:1). The composition gradient is achieved by dynamically controlling the target power or gas ratio in the magnetron sputtering process, ensuring a smooth transition between layers.

[0054] Tungsten-rich layer: The outermost layer has a high tungsten (W) content (e.g. Ti:W≈1:1). Utilizing the high electrical conductivity of tungsten (resistivity≈5.6×10 -8 Ω·m) and chemical inertness (resistant to sodium metal corrosion), optimizing the sodium ion deposition interface.

[0055] The titanium-rich layer, transition layer and tungsten-rich layer have the following beneficial effects:

[0056] 1. Enhanced bonding: The titanium-rich layer is in direct contact with the aluminum foil substrate. Due to the high affinity between titanium and aluminum, the bonding between the coating and the aluminum foil is significantly enhanced. This tight bond can effectively prevent the coating from peeling or powdering during battery cycling, improving the reliability and durability of the battery.

[0057] 2. Optimize conductivity and chemical stability: As the coating transitions from a titanium-rich layer to a tungsten-rich layer, the tungsten content gradually increases, and the conductivity of the coating also improves. The high conductivity of the tungsten-rich layer can significantly reduce the internal resistance of the battery and improve the battery's charge and discharge efficiency.

[0058] 3. Chemical stability: The high chemical inertness of the tungsten-rich layer enables it to resist sodium metal corrosion and erosion by electrolyte decomposition products, thereby protecting the battery from electrolyte damage and extending the battery life.

[0059] 4. Inducing uniform sodium deposition: Due to the weak adsorption of titanium and sodium and the high electronic conductivity of tungsten, the titanium-tungsten alloy coating can form active sites with low nucleation barriers, guiding the uniform deposition of sodium ions. This uniform sodium deposition behavior can effectively inhibit dendrite growth and improve battery safety and cycle stability.

[0060] 5. Suppressing Volume Expansion: Titanium-tungsten alloy has a high modulus and low volume expansion rate (<5%), which can withstand the mechanical stress during the sodium deposition / stripping process. This excellent mechanical stability can effectively suppress the volume expansion of the coating during the cycle, avoid interfacial structure powdering, and maintain interfacial electrical contact stability.

[0061] 6. Dynamic passivation layer protection: During the battery cycle, a dense TiO2-WO3 composite passivation layer spontaneously forms on the surface of the titanium-tungsten alloy. This passivation layer has high ionic conductivity and dynamic self-repairing capabilities, effectively inhibiting electrolyte decomposition and blocking the corrosion of electrolyte decomposition products on the interface, further improving the chemical stability and cycle life of the battery.

[0062] 7. Flexible Adjustment of Overall Performance: By adjusting the ratio and thickness of titanium and tungsten atoms in the titanium-rich layer, transition layer, and tungsten-rich layer, the overall performance of the coating can be flexibly controlled. For example, increasing the thickness of the titanium-rich layer can enhance bonding strength, while increasing the thickness of the tungsten-rich layer can improve conductivity and chemical stability. This flexible design allows the coating to be customized and optimized for different application scenarios.

[0063] In summary, the gradient component distribution of the titanium-tungsten alloy coating in the present invention achieves performance improvements in many aspects such as bonding strength, conductivity, chemical stability, sodium deposition uniformity, volume expansion inhibition, and dynamic passivation layer protection through the rational design of the titanium-rich layer, transition layer, and tungsten-rich layer, providing an efficient and reliable solution for the design of negative electrode-free sodium ion battery current collector.

[0064] In a preferred embodiment of the present invention, the titanium-rich layer contains titanium atoms and tungsten atoms in a first ratio.

[0065] In a preferred embodiment of the present invention, the tungsten-rich layer contains titanium atoms and tungsten atoms in a second ratio.

[0066] In a preferred embodiment of the present invention, the transition layer includes titanium atoms and tungsten atoms that change continuously and gradually from a first ratio to a second ratio.

[0067] Specifically, in this embodiment, the first ratio is preferably set to Ti:W=3:1, and the second ratio is preferably set to Ti:W=1:1; in a preferred embodiment of the present invention, the transition layer includes multiple subdivision layers, and the ratio of the number of titanium atoms and tungsten atoms in the subdivision layers gradually changes from 3:1 to 1:1 according to the level.

[0068] In a preferred embodiment of the present invention, the atomic number ratio of titanium atoms to tungsten atoms in the titanium-tungsten alloy coating is in a range of 1:1 to 3:1.

[0069] In a preferred embodiment of the present invention, the ratio of the thickness of the titanium-rich layer to the thickness of the tungsten-rich layer is positively correlated with the overall ratio of titanium atoms to tungsten atoms in the titanium-tungsten alloy coating.

[0070] In a preferred embodiment of the present invention, when the ratio of the number of titanium atoms to tungsten atoms in the titanium-tungsten alloy coating is 3:1, the thickness of the titanium-rich layer is greater than the thickness of the tungsten-rich layer.

[0071] Preferably, when the ratio of the number of titanium atoms to tungsten atoms in the titanium-tungsten alloy coating is 1:1, the thickness of the titanium-rich layer is less than the thickness of the tungsten-rich layer.

[0072] The atomic ratio range (1:1 to 3:1) is the average ratio of the entire coating. The atomic ratio of each layer in the gradient structure is designed differently according to functional requirements:

[0073] When the overall atomic ratio is 3:1 (Ti:W): the bottom layer accounts for a larger proportion (for example, the bottom layer accounts for 70% of the thickness, Ti:W=3:1; the surface layer accounts for 30%, Ti:W=1:1), and the overall average is 3:1.

[0074] When the overall atomic ratio is 1:1 (Ti:W): the bottom layer accounts for a smaller proportion (for example, the bottom layer accounts for 30% of the thickness, Ti:W=3:1; the surface layer accounts for 70%, Ti:W=1:1), and the overall average is 1:1.

[0075] Key point: The bottom layer of the gradient structure is always a titanium-rich layer (Ti:W≈3:1), and the surface layer is always a tungsten-rich layer (Ti:W≈1:1). The overall atomic ratio is adjusted only by the thickness ratio of each layer to ensure that the functional stratification remains unchanged.

[0076] In a preferred embodiment of the present invention, the total thickness of the titanium-tungsten alloy coating is 50-500 nm. The total coating thickness (50-500 nm) is achieved by adjusting the thickness ratio of each gradient layer, and the relationship between the atomic ratio and the layer distribution is as follows:

[0077] In one embodiment, the total thickness is 50 nm (very thin coating)

[0078] Bottom layer (Ti-rich layer): 20 nm, Ti:W=3:1

[0079] Intermediate transition layer: 15 nm, Ti:W from 3:1 to 1:1 (or a ratio close to 1:1)

[0080] Surface layer (tungsten-rich layer): 15 nm, Ti:W=1:1

[0081] The overall atomic ratio is ≈2:1 (the deposition rate of each layer is controlled by the sputtering time).

[0082] In another embodiment, the total thickness is 500 nm (thicker coating)

[0083] In this embodiment, the transition layer includes multiple subdivided layers, and the ratio of titanium atoms to tungsten atoms in the subdivided layers gradually changes from a first ratio to a second ratio in layers.

[0084] Bottom layer (Ti-rich layer): 200 nm, Ti:W=3:1

[0085] Intermediate transition layer: 200 nm, Ti:W from 3:1→1:1 (subdivided into 10 layers, each 20 nm, with gradual composition change)

[0086] Surface layer (tungsten-rich layer): 100 nm, Ti:W=1:1

[0087] The overall atomic ratio is ≈2:1 (fine gradient achieved through a multi-layer sputtering process).

[0088] Correspondence summary:

[0089] Atomic ratio control: The overall atomic ratio is adjusted by the thickness ratio of each layer, and the local ratio of titanium-rich bottom layer (Ti:W=3:1) and tungsten-rich surface layer (Ti:W=1:1) is fixed.

[0090] Thickness influence:

[0091] Thin coating (50 nm): has fewer gradient transition layers and steeper composition changes, suitable for high-magnification scenarios (reducing ion diffusion paths).

[0092] Thick coating (500 nm): The gradient transition is smoother and the components are subdivided into nano-level multilayers, which is suitable for long-cycle requirements (relieving mechanical stress).

[0093] In order to illustrate the beneficial effects of the titanium-tungsten alloy coating of the present invention, two additional comparative examples are added for comparison: Example 1 mentioned above: a titanium-tungsten alloy coating with a total thickness of 50 nm is coated on an aluminum foil substrate; Example 2 mentioned above: a titanium-tungsten alloy coating with a total thickness of 500 nm is coated on an aluminum foil substrate; Comparative Example 1: ordinary aluminum foil is used as a current collector for a battery without a negative electrode; aluminum foil specifications: aluminum foil thickness 12 nm; Comparative Example 2: carbon-coated aluminum foil is used as a current collector for a battery without a negative electrode; aluminum foil specifications: aluminum foil thickness 12 nm, carbon coating thickness 1 nm; Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are subjected to rate test, cycle capacity retention test, and coulombic efficiency test using the same test experimental process. The experimental results are shown in Table 1:

[0094] 1. Rate test plan:

[0095] 1.1. Charge at 0.5C current to the upper cut-off voltage; leave for 30 minutes;

[0096] 1.2, discharge at 0.2C current to the lower cut-off voltage, record the capacity C0; leave it for 30 minutes;

[0097] 1.3, Charge at 0.5C current to the upper cut-off voltage; leave for 30 minutes;

[0098] 1.4. Discharge at 1C current to the lower cut-off voltage and record the capacity C1;

[0099] 1.5. Calculate the rate retention rate: (C1 / C0*100%).

[0100] 2. Cyclic test plan:

[0101] 2.1. Charge at 1.0C current to the upper cut-off voltage; leave for 30 minutes;

[0102] 2.2, discharge at 1.0C current to the lower cut-off voltage; leave for 30 minutes;

[0103] 2.3. Repeat the above steps for 200 cycles; record the capacity of the first cycle C1, and the capacity of the 200th cycle C200;

[0104] 2.4. Calculate the cycle capacity retention rate: (C200 / C1*100%).

[0105] 3. Coulombic efficiency is obtained by calculating the ratio of discharge capacity to charge capacity in one cycle.

[0106] Table 1 Experimental results comparison table

[0107]

[0108] Table 2 200-cycle 1.0C / 1.0C cycle capacity retention test results

[0109]

[0110] For Example 1, the 50nm titanium-tungsten alloy coating had a coating thickness of 52nm after 200 charging cycles, and the coating thickness increased by 2nm, which is approximately equal to 4% (volume change rate <5%), which can solve the problem of severe volume expansion caused by alloying modification.

[0111] The following conclusions can be drawn from the comparison table of the above experimental results:

[0112] 1. Performance advantages of titanium-tungsten alloy coating vs. aluminum foil current collector

[0113] The battery current collector with titanium-tungsten alloy coating has high rate retention (>97%) and high capacity retention (>90%) and Coulombic efficiency >99.5%, while the existing ordinary aluminum foil current collector has low rate retention (<90%), low capacity retention (<55%), and Coulombic efficiency of only 94.0~99.0%.

[0114] Titanium-tungsten alloy coatings achieve the following through gradient atomic ratio design (Ti:W from 3:1→1:1):

[0115] High-magnification scene adaptation: The steep gradient of the thin coating (50 nm) shortens the ion diffusion path;

[0116] Long-cycle requirements are met: Gentle gradients of thick coatings (500 nm) disperse mechanical stresses.

[0117] 2. Effect of coating thickness on performance

[0118] Thin coating: By reducing the number of transition layers (e.g., only 3 layers in Example 1), the ion diffusion path is short, the rate retention rate is 99.02%, and fast charging and discharging are prioritized;

[0119] Thick coating: Subdivided into 10 layers to achieve nanoscale gradient, mechanical stress dispersion, and a capacity retention rate of 92.38%, taking into account both cycle life and capacity attenuation.

[0120] 3. Performance Difference Analysis of the Comparison Group

[0121] Comparative Example 1 (ordinary aluminum foil): Without coating protection, aluminum foil oxidation leads to increased interfacial impedance and rapid capacity decay (25.42%).

[0122] Comparative Example 2 (carbon-coated aluminum foil): The carbon coating (1 nm) partially alleviates oxidation, but the Coulombic efficiency (97.0-99.0%) is still lower than that of the titanium-tungsten coating.

[0123] Example 1 / 2: The corrosion resistance of the Ti-W alloy (especially the titanium-rich layer) significantly improves the interface stability, and the coulombic efficiency is >99.5%.

[0124] 4. Final Conclusion

[0125] The gradient atomic ratio design and optimized thickness of the titanium-tungsten alloy coating significantly improve the overall performance of batteries in high-rate scenarios and long cycle requirements. Comparative experiments have demonstrated that the coating outperforms traditional aluminum foil current collectors in rate retention, capacity retention, and coulombic efficiency, demonstrating its potential application value in next-generation battery technologies.

[0126] This invention utilizes a titanium-tungsten (Ti-W) alloy gradient coating design to address key challenges, including the dramatic volume expansion caused by alloying modification (reducing the volume change rate from >200% to <5%) and side reactions at the sodium metal-electrolyte interface (increasing Coulombic efficiency to >99.5%). Furthermore, the low-temperature deposition process prevents thermal deformation of the aluminum foil substrate, and the gradient structure enhances the coating's adhesion and corrosion resistance, making it compatible with liquid / solid systems and significantly improving battery cycle life (capacity retention >90% after 200 cycles) and safety.

[0127] The present invention also provides a method for preparing a negative electrode-free sodium ion battery current collector, which is used to prepare the above-mentioned negative electrode-free sodium ion battery current collector, comprising: using a magnetron sputtering or plasma-enhanced chemical vapor deposition process to form a titanium-tungsten alloy coating on the surface of an aluminum foil substrate.

[0128] Specifically, in this embodiment, a titanium-tungsten alloy coating is formed on the surface of an aluminum foil substrate by magnetron sputtering or plasma-enhanced chemical vapor deposition process, which is used to prepare a negative electrode-free sodium ion battery current collector, which has significant advantages.

[0129] Process advantages

[0130] High-quality coatings: Both magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD) techniques can produce dense, uniform, and highly adherent titanium-tungsten alloy coatings. These coatings exhibit excellent electrical conductivity and chemical stability, making them suitable as current collectors for anode-free sodium-ion batteries.

[0131] Low-temperature deposition: PECVD technology enables high-quality thin film deposition at lower temperatures, which helps protect the aluminum foil substrate from high-temperature damage while reducing energy consumption.

[0132] Strong controllability: By adjusting process parameters such as sputtering power, gas flow, deposition temperature, etc., the composition, structure and thickness of the coating can be precisely controlled to meet different application requirements.

[0133] Environmentally friendly and pollution-free: Both magnetron sputtering and PECVD technologies are dry processes that do not produce waste liquid, waste residue and other pollutants, and meet environmental protection requirements.

[0134] The following are two embodiments, one of which is specifically explained for a transition layer including multiple subdivision layers.

[0135] Example 1: Preparation of a titanium-tungsten alloy coating with 10 subdivided gradient transition layers by multi-layer sputtering process

[0136] In a preferred embodiment of the present invention, the titanium-tungsten alloy coating is designed as a three-layer structure, comprising a base layer, a transition layer, and a surface layer. The base layer is a titanium-rich layer, the surface layer is a tungsten-rich layer, and the transition layer comprises 10 subdivided layers, each 20 nm thick. The ratio of titanium atoms to tungsten atoms gradually transitions from 3:1 in the titanium-rich layer to 1:1 in the tungsten-rich layer. The total coating thickness is 500 nm.

[0137] The specific implementation steps included in this example are as follows:

[0138] Substrate pretreatment: Clean and dry the aluminum foil substrate to ensure that the surface is free of oil, oxides and other impurities.

[0139] Multilayer sputtering coating:

[0140] Bottom layer (titanium-rich layer): A titanium-rich layer with a thickness of 200 nm and an atomic ratio of Ti:W = 3:1 was deposited on the aluminum foil substrate using a magnetron sputtering process.

[0141] This layer serves as a base for the coating, providing good adhesion and initial conductivity.

[0142] Intermediate transition layer (10-layer subdivision structure): The transition layer is designed to have a 10-layer structure, with each layer having a thickness of 20 nm and a total thickness of 200 nm.

[0143] Layer 1 (close to the bottom layer): atomic ratio Ti:W=3:1, the same as the bottom layer.

[0144] The second layer: The atomic ratio begins to gradually decrease the proportion of titanium, such as Ti:W=2.8:1.

[0145] Layer 3: Continue to reduce the proportion of titanium, such as Ti:W=2.6:1.

[0146] And so on, the proportion of titanium in each layer gradually decreases until the 10th layer.

[0147] The 10th layer (near the surface): atomic ratio Ti:W=1:1, the same as the surface layer.

[0148] By precisely controlling the sputtering process parameters, a smooth transition of each layer's components can be achieved.

[0149] Surface layer (tungsten-rich layer): A tungsten-rich layer with a thickness of 100 nm and an atomic ratio of Ti:W=1:1 is deposited on the transition layer.

[0150] This layer provides excellent electrical conductivity and chemical stability as the final surface of the coating.

[0151] Specific examples:

[0152] The total thickness of the coating is 500 nm and consists of a base layer, 10 transition layers and a surface layer.

[0153] The bottom layer is a titanium-rich layer with a thickness of 200 nm and Ti:W=3:1.

[0154] The transition layer is a 10-layer subdivision structure, each layer is 20 nm, the total thickness is 200 nm, and the atomic ratio gradually transitions from Ti:W=3:1 to 1:1.

[0155] The surface layer is a tungsten-rich layer with a thickness of 100 nm and Ti:W=1:1.

[0156] Sputtering process control:

[0157] By precisely controlling parameters such as sputtering time, sputtering power and gas flow, precise control of the thickness of each layer and gradual change of the composition can be achieved.

[0158] Multi-layer sputtering equipment is used to ensure smooth transitions between layers and uniform changes in composition.

[0159] Post-treatment: The coated aluminum foil substrate is annealed to improve the crystallinity and overall performance of the coating.

[0160] Key point: The coating is designed as a three-layer structure, including a base layer, 10 subdivided transition layers and a surface layer.

[0161] The ratio of titanium atoms to tungsten atoms in the transition layer gradually changes from a titanium-rich layer to a tungsten-rich layer, thereby achieving a smooth transition of the components.

[0162] By precisely controlling the sputtering process parameters, optimized coating performance and customized design can be achieved.

[0163] In this embodiment, a titanium-tungsten alloy coating having 10 subdivided gradient transition layers is prepared by a multi-layer sputtering process, which meets the requirements of specific applications for coating performance and component gradient, and is suitable for the preparation of anode-free sodium ion battery current collector.

[0164] Example 2: Preparation method of negative electrode-free sodium ion battery current collector based on PECVD technology

[0165] This example describes an ultra-thin titanium-tungsten alloy coating with a total thickness of 50 nm. The coating is designed as a three-layer structure: a 20 nm bottom layer (titanium-rich layer) with a Ti:W ratio of 3:1; a 15 nm intermediate layer with a Ti:W ratio gradually varying from 3:1 to 1.5:1; and a 15 nm top layer (tungsten-rich layer) with a Ti:W ratio of 1:1. The overall coating atomic ratio is approximately 2:1, and the deposition rate of each layer is controlled by controlling the sputtering (here, PECVD deposition) time. This invention provides a method for depositing this titanium-tungsten alloy coating on an aluminum foil substrate using a plasma-enhanced chemical vapor deposition (PECVD) process, which can be used to prepare anode-free sodium-ion battery current collectors.

[0166] The specific implementation steps included in this example are as follows:

[0167] 1. Preparation of aluminum foil substrate:

[0168] Choose aluminum foil with a smooth surface, no oil stains, and no oxides as the substrate.

[0169] Clean and dry the aluminum foil to ensure the substrate surface is clean to improve the adhesion of the coating.

[0170] 2. PECVD equipment settings:

[0171] Check and confirm that the vacuum system, gas supply system, plasma generation system, etc. of the PECVD equipment are in good working condition.

[0172] Set the deposition chamber temperature to an appropriate range to ensure the stability of the deposition process and the quality of the coating.

[0173] 3. Titanium-tungsten alloy coating deposition:

[0174] 3.1 Bottom layer (Titanium-rich layer) deposition:

[0175] Precursor gases containing titanium and tungsten, such as titanium tetrachloride (TiCl4) and tungsten hexafluoride (WF6), and reaction gases (such as hydrogen H2 as a reducing gas and argon Ar as a carrier gas) are introduced.

[0176] The gas flow ratio was adjusted so that the atomic ratio of the deposited coating reached Ti:W=3:1.

[0177] Turn on the plasma generator to generate plasma to promote the chemical reaction and deposition of the precursor gas.

[0178] By precisely controlling the deposition time, the bottom layer thickness was ensured to be 20 nm.

[0179] 3.2 Intermediate transition layer deposition:

[0180] The flow ratio of the precursor gas was gradually adjusted so that the atomic ratio of the deposited coating gradually transitioned from Ti:W=3:1 to 1.5:1.

[0181] Use programmed control or manual step-by-step adjustment of gas flow ratio to achieve smooth transition of components.

[0182] Keep the plasma generator on to ensure stable deposition conditions.

[0183] By precisely controlling the deposition time, the thickness of the transition layer was ensured to be 15 nm.

[0184] 3.3 Surface layer (tungsten-rich layer) deposition:

[0185] The flow ratio of the precursor gas was adjusted so that the atomic ratio of the deposited coating reached Ti:W=1:1.

[0186] Keep the plasma generator on to ensure a stable deposition process.

[0187] By precisely controlling the deposition time, the surface layer thickness was ensured to be 15 nm.

[0188] 4. Post-coating treatment:

[0189] Turn off the plasma generator and stop the gas supply.

[0190] The deposition chamber was evacuated to a vacuum state and then cooled to room temperature.

[0191] Remove the coating sample and perform necessary cleaning and drying to remove any remaining deposits or reaction by-products.

[0192] Key Points:

[0193] A titanium-tungsten alloy coating with a total thickness of 50 nm was precisely prepared on the surface of an aluminum foil substrate using the PECVD process.

[0194] The coating is designed as a three-layer structure, and the thickness and composition of each layer meet the design requirements, achieving a smooth transition of components.

[0195] By precisely controlling the deposition time and gas flow ratio, precise control of the overall atomic ratio of the coating of approximately 2:1 was achieved.

[0196] The prepared negative electrode-free sodium ion battery current collector has excellent conductivity and sodium ion insertion / extraction performance, meeting the application requirements of sodium ion batteries.

[0197] This example successfully prepared a negative electrode-free sodium ion battery current collector with a titanium-tungsten alloy coating having a specific structure through the PECVD process, providing strong technical support for the research and development and application of sodium ion batteries.

[0198] The present invention also provides a negative electrode-free sodium ion battery, which adopts the negative electrode-free sodium ion battery current collector as the negative electrode current collector.

[0199] The present invention also provides a method for preparing a negative electrode-free sodium ion battery, which is used to prepare the negative electrode-free sodium ion battery as described above. Figure 2 As shown, it includes: step S1, using an aluminum foil substrate coated with a titanium-tungsten alloy coating as a negative electrode current collector, and assembling it with a sodium metal positive electrode or a sodium compensation positive electrode and an electrolyte to form a negative electrode-free sodium ion battery; step S2, charging the negative electrode-free sodium ion battery. During the first charging, sodium ions are released from the positive electrode, preferentially nucleate on the surface of the titanium-tungsten alloy coating, and deposited as a dense metallic sodium layer, forming a negative electrode-free structure.

[0200] Specifically, the negative electrode-free sodium ion battery uses the negative electrode-free sodium ion battery current collector as the negative electrode current collector, which has the following advantages:

[0201] In-situ dynamic protection of passivation layer: A dense TiO2-WO3 composite passivation layer is formed on the surface of titanium-tungsten alloy during the charging cycle, which blocks the corrosion of the interface by the decomposition products of the electrolyte (such as Na2CO3).

[0202] High mechanical robustness: The high modulus and low expansion properties of titanium-tungsten alloy ensure the integrity of the coating during the sodium deposition / stripping process, with no cracks in the coating after 100 cycles (verified by SEM). Charge and discharge cycles were performed at 0.5-3 C rates, monitoring sodium deposition morphology (SEM), interfacial impedance (EIS), and cycle life (capacity retention).

[0203] Full system adaptability: The coating is compatible with liquid and solid electrolyte systems, and exhibits stable performance under high-voltage positive electrodes (such as O3-type layered oxides) and a wide temperature range (-20~60°C).

[0204] The traditional aluminum foil current collector has a high sodium nucleation barrier (>100 mV) due to its low surface energy, and although existing alloying coatings (such as Al-Sn) can reduce the overpotential, the alloying reaction is accompanied by a violent volume expansion (>200%), which causes interface pulverization and capacity decay. The present invention regulates the atomic ratio of titanium and tungsten (1:1 to 3:1) and combines it with a magnetron sputtering low-temperature deposition process (150-300°C) to construct a gradient titanium-tungsten alloy coating on the surface of the aluminum foil (the bottom layer is rich in titanium to enhance bonding, and the surface layer is rich in tungsten to enhance conductivity), thereby simultaneously achieving near-zero volume expansion (<5%) and high chemical inertness. A nanoscale TiO2-WO3 composite passivation layer (5-10 nm thick) spontaneously forms on the surface of the titanium-tungsten alloy during the cycle, and its high ionic conductivity (>10 -4 S / cm) and dynamic self-healing ability effectively inhibit electrolyte decomposition (Coulomb efficiency>99.5%) and dendrite growth (deposition layer porosity<5%). In addition, the high modulus (>200 GPa) and low thermal expansion coefficient (<6×10 -6 The coating's excellent mechanical robustness, coupled with its high-temperature (>4 V) coating, is compatible with both liquid and solid electrolyte systems and maintains a stable interface (capacity retention >90% after 200 cycles) at high-voltage cathodes (>4 V) and over a wide temperature range (-20°C to 60°C). This technology, through collaborative innovation in material composition, process, and interface design, provides a highly compatible and long-life current collector solution for the industrialization of anode-free sodium batteries.

[0205] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of this specification and illustrations should be included in the protection scope of the present invention.

Claims

1. A battery current collector, characterized in that: include: An aluminum foil substrate, and a titanium-tungsten alloy coating coated on a surface of the aluminum foil substrate, wherein the titanium-tungsten alloy coating has a gradient component distribution; The titanium-tungsten alloy coating comprises a titanium-rich layer, a transition layer and a tungsten-rich layer stacked in sequence from the aluminum foil substrate outward; The ratio of the number of titanium atoms to tungsten atoms in the titanium-rich layer, the transition layer and the tungsten-rich layer decreases in sequence to form the gradient component distribution; The transition layer includes multiple subdivided layers, and the ratio of the number of titanium atoms to tungsten atoms in the subdivided layers gradually changes from 3:1 to 1:1 in each layer.

2. The battery current collector according to claim 1, characterized in that: The ratio of the number of titanium atoms to the number of tungsten atoms in the titanium-tungsten alloy coating is in the range of 1:1 to 3:

1.

3. The battery current collector according to claim 2, characterized in that: The ratio of the thickness of the titanium-rich layer to the thickness of the tungsten-rich layer is positively correlated with the overall number ratio of titanium atoms to tungsten atoms in the titanium-tungsten alloy coating.

4. The battery current collector according to claim 3, characterized in that: When the ratio of the number of titanium atoms to tungsten atoms in the titanium-tungsten alloy coating is 3:1, the thickness of the titanium-rich layer is greater than the thickness of the tungsten-rich layer; When the ratio of the number of titanium atoms to tungsten atoms in the titanium-tungsten alloy coating is 1:1, the thickness of the titanium-rich layer is less than the thickness of the tungsten-rich layer.

5. The battery current collector according to claim 1, wherein: The total thickness of the titanium-tungsten alloy coating is 50-500 nm.

6. A method for preparing a battery current collector, characterized in that: The method for preparing the battery current collector according to any one of claims 1 to 5 comprises: A titanium-tungsten alloy coating with a gradient component distribution is prepared on the surface of an aluminum foil substrate by adopting magnetron sputtering or plasma enhanced chemical vapor deposition process.

7. A negative electrode-free sodium ion battery, characterized in that: The battery current collector described in any one of 1-5 is used as the negative electrode current collector.

8. A method for preparing a negative electrode-free sodium ion battery, characterized in that: For preparing the negative electrode-free sodium ion battery as claimed in claim 7, comprising: Step S1, using the battery current collector obtained by coating the aluminum foil substrate with the titanium-tungsten alloy coating as the negative electrode current collector, and assembling it with a sodium metal positive electrode or a sodium compensation positive electrode and an electrolyte to form a negative electrode-free sodium ion battery; Step S2, charging the negative electrode-free sodium ion battery. During the first charging, sodium ions are released from the positive electrode, preferentially nucleated on the surface of the titanium-tungsten alloy coating, and deposited as a dense metallic sodium layer, forming a negative electrode-free structure.

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