Ag / Al composite ink with electrical conductivity, excellent printability and electrochemical activity and preparation method and application of Ag / Al composite ink

Abstract

The invention discloses Ag / Al composite ink with conductivity, excellent printability and electrochemical activity as well as a preparation method and application of the Ag / Al composite ink, and belongs to the technical field of printed electronic functional materials. The problem that existing conductive ink is inert metal and cannot directly participate in electrochemical reaction is solved. The preparation method comprises the following steps: preparing aluminum dispersion liquid; then mixing a resin binder, an organic alcohol ether solvent and a functional auxiliary agent to obtain an organic carrier; mixing the flake silver powder with an organic carrier to obtain a conductive silver substrate; and dropwise adding the aluminum dispersion liquid into a conductive silver substrate, and stirring to obtain the Ag / Al composite ink. The silver powder constructs a continuous three-dimensional conductive network, the aluminum powder serves as a discrete electrochemical activity center, and balance of electrochemical activity and conductivity is achieved. The ink disclosed by the invention is adaptive to air pressure extrusion type printing and silk-screen printing, and the asymmetric active electrode prepared by printing can be used for preparing an electrochemical device and has high sensitivity, quick response and excellent cycling stability.

Description

Technical Field

[0001] This invention belongs to the field of printed electronic functional materials technology, specifically relating to an Ag / Al composite ink that combines conductivity, excellent printability and electrochemical activity, as well as its preparation method and application. Background Technology

[0002] Printed electronics technology, as a core means of modern flexible electronics manufacturing, relies on traditional printing processes to deposit functional electronic materials on various substrates, enabling the fabrication of flexible, bendable, and conformal electronic devices. Currently, printed electronics technology is widely used in the manufacture of devices such as solar cells, antennas, transistors, capacitors, and various sensors. Conductive ink, as a key component of the printed electronics material system, directly determines the function and reliability of the final device. Currently, commercially available conductive inks are mainly based on chemically stable inert metals, such as silver, copper, and gold. These inks, after curing, can form highly conductive paths, perfectly meeting the manufacturing requirements of passive components such as interconnects and electrodes. Commonly used inert metal inks, represented by silver paste, have the advantages of forming highly conductive paths, low resistivity, and good stability, and have been widely used in the printing and fabrication of passive components such as interconnect lines and electrodes. However, as printed electronics technology develops towards functionalization, integration, and intelligence, functional devices based on asymmetric electrode structures (such as electrochemical sensors, metal-air batteries, and certain energy harvesting devices) are placing new demands on electrode materials. The working mechanism of asymmetric electrode structures requires that the electrode material not only conducts electrons but also participates in a continuous redox reaction as a reactant. Traditional inert metal inks, such as silver paste, have the drawback that the metals used are chemically stable and lack significant electrochemical activity. In functional devices requiring direct participation of the electrode material in redox reactions (such as electrochemical sensors, metal-air batteries, and certain energy harvesting devices), these inks can only act as electronic conductors and cannot provide a continuous current or voltage output as a reactant. Therefore, they cannot be used to construct the core of such devices—the active electrode. Based on the above requirements, the electrode material must be a metal with high electrochemical activity, such as aluminum or zinc. However, preparing such active metals into printable inks faces fundamental challenges: First, a dense insulating oxide layer will quickly form on the surface of the active metal particles, resulting in a significant increase in the resistance of the particles themselves. When these oxide-coated particles form a conductive film, the overall conductivity of the ink will deteriorate sharply, or even completely lose its conductive function. Second, the dispersion stability of active metal particles in the carrier is poor, and they are prone to agglomeration and sedimentation. Therefore, it is extremely difficult to prevent the oxidation of active metal particles in the ink system and maintain long-term electrochemical activity, resulting in rapid ink performance degradation, poor printing uniformity, and low batch consistency.

[0003] Therefore, there is an urgent need in this field to develop an ink material that combines good conductivity, excellent printability, and high electrochemical activity, and to use this ink to achieve the printing and preparation of asymmetric electrodes. Summary of the Invention

[0004] This invention addresses the problem that existing conductive inks are all inert metals and cannot directly participate in electrochemical reactions. It provides an Ag / Al composite ink that combines conductivity, excellent printability, and electrochemical activity, as well as its preparation method and applications.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: One objective of this invention is to provide a method for preparing an Ag / Al composite ink that combines conductivity, excellent printability, and electrochemical activity. This method includes the following steps: (1) Pre-dispersion of aluminum powder: Micron-sized spherical aluminum powder is mixed with organic alcohol ether solvent, and then stirred and sonicated to obtain an aluminum dispersion; (2) Preparation of organic carrier: The resin binder, organic alcohol ether solvent and functional additive are mixed and stirred to obtain the organic carrier; (3) Preparation of conductive silver substrate: Micron-sized flake silver powder is mixed with an organic carrier and stirred to obtain a conductive silver substrate; (4) Mixing and homogenization: Under stirring conditions, aluminum dispersion is added dropwise to conductive silver substrate to obtain mixed slurry. The mixed slurry is stirred and homogenized to obtain Ag / Al composite ink.

[0006] Further specifying, (1) the particle size of the micron-sized spherical aluminum powder is 5-20 μm.

[0007] Further specifying, (1) the mass-to-volume ratio of micron-sized spherical aluminum powder to organic alcohol ether solvent is 1 g: (1-10) mL.

[0008] Further specifying, the organic alcohol ether solvents in (1) and (2) are one or more of ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol butyl ether, propylene glycol methyl ether, diethylene glycol butyl ether, propylene glycol ethyl ether, and diethylene glycol dimethyl ether.

[0009] Further specifying, the resin binder in (2) is one or more of epoxy resin, acrylic resin, polyurethane resin, polyvinyl butyral (PVB), phenolic resin, polyester resin, and cellulose ester; different resins can be selected according to different application requirements to specifically adjust the final performance of Ag / Al composite ink: epoxy resin can provide extremely high adhesion and durability; polyurethane and PVB resins can provide excellent bending resistance for flexible substrate applications; acrylic resin and cellulose esters help to achieve good leveling and rapid film formation.

[0010] Further specifying, (2) the functional additives are used to adjust the viscosity and thixotropy of the ink.

[0011] Further specifying, the functional additive in (2) is a high-boiling-point solvent or a thixotropic agent.

[0012] Further specifying, the high-boiling-point solvent is one or more of the following: terpineol, butyl carbitol (diethylene glycol butyl ether), butyl carbitol acetate (diethylene glycol butyl ether acetate), triethylene glycol monobutyl ether, diethylene glycol dibutyl ether, tripropylene glycol monomethyl ether, dodecyl alcohol ester (dodecyl alcohol ester), hexadecyl alcohol ester (hexadecyl alcohol ester), benzyl benzoate, ethylene glycol butyl ether benzoate, dimethyl adipate, and tributyl citrate, with a mass ratio of high-boiling-point solvent to resin binder of (20-70):(30-80); the thixotropic agent is one or more of the following: fumed silica, organically modified montmorillonite, polyamide wax, hydrogenated castor oil, and polyethylene wax, with a mass ratio of thixotropic agent to resin binder of (1-15):(85-99).

[0013] Furthermore, when using thixotropic agents, the content of resin binder in the organic carrier is 25wt%-60wt%.

[0014] Further specifying, in (2), the mass ratio of resin binder to organic alcohol ether solvent is (10-30): (70-90).

[0015] Further, in (2), the stirring temperature is 50-70℃ and the time is 30-60 min.

[0016] Further specifying, the mass ratio of micron-sized spherical aluminum powder in (1) to conductive silver matrix in (3) is (20-60): (40-80).

[0017] Further specifying, the mass ratio of micron-sized spherical aluminum powder in (1) to conductive silver matrix in (3) is (9-50): (50-91).

[0018] Further specifying, (3) the diameter of the micron-sized flake silver powder is 1-10 μm.

[0019] Further specifying, (3) the mass ratio of micron-sized flake silver powder to organic carrier is (70-90): (10-30).

[0020] Further specifying, (3) the mass ratio of micron-sized flake silver powder to organic carrier is (75-85): (15-25).

[0021] Further specified, (3) the stirring speed is 500-2000 rpm and the time is 10-20 min.

[0022] Further specified, (4) the droplet acceleration of the aluminum dispersion is 0.1-1.0 mL / min.

[0023] Further, the stirring speed during the addition of aluminum dispersion in (4) is 200-800 rpm; the stirring speed during the homogenization process is 200-800 rpm, and the time is 6-12 h.

[0024] The second objective of this invention is to provide an Ag / Al composite ink prepared by the above-mentioned method that possesses conductivity, excellent printability, and electrochemical activity.

[0025] Further specifying, the ink includes conductive components, active metal components, organic carriers, and organic solvents.

[0026] Furthermore, the conductive component is micron-sized flake silver powder, the active metal component is micron-sized spherical aluminum powder, and the organic carrier is composed of resin binder, organic alcohol ether solvent and functional additives.

[0027] The third objective of this invention is to provide an application of the above-mentioned Ag / Al composite ink in pneumatic extrusion printing technology and screen printing technology.

[0028] Further specifying, the substrate used in pneumatic extrusion printing and screen printing technologies is polyethylene terephthalate (PET), polydimethylsiloxane (PDMS), polyimide (PI), or thermoplastic polyurethane (TPU).

[0029] Furthermore, when Ag / Al composite ink is used in pneumatic extrusion printing technology, the viscosity of Ag / Al composite ink is adjusted by a high-boiling-point solvent.

[0030] Furthermore, the viscosity of the Ag / Al composite ink at 25 ℃ after adjustment is 100~1000 cP.

[0031] Further specifying the parameters of the pneumatic extrusion printing technology are: heat treatment temperature 60-90 ℃, lower than the glass transition temperature or heat distortion temperature of the selected printing substrate, heat treatment time 10-50 min, printing 10-50 kPa, printing speed 1-5 mm / s, nozzle inner diameter 100-300 μm, and printing height 0.1-0.3 mm. This technology can achieve high-quality continuous pattern printing with controllable line width, clear edges, and no dripping, and can realize the printing preparation of active metal electrodes.

[0032] Furthermore, when Ag / Al composite ink is used in screen printing technology, the viscosity and thixotropy of Ag / Al composite ink are achieved by adjusting the solid content of the resin binder in the organic carrier and introducing a thixotropic agent.

[0033] The fourth objective of this invention is to provide an asymmetric active electrode obtained by pneumatic extrusion printing technology or screen printing technology in the above applications.

[0034] The fifth objective of this invention is to provide an application of the above-mentioned asymmetric active electrode in an electrochemical device.

[0035] Further defining the electrochemical device, it includes a pair of electrodes with different work functions, wherein the first electrode is an asymmetric active electrode formed by printing and curing the Ag / Al composite active metal ink, and the second electrode is a counter electrode formed by printing and curing an inert metal conductive paste.

[0036] The electrochemical devices composed of asymmetric active electrodes include, but are not limited to, electrochemical sensors, metal-air batteries, electrochemical catalytic devices, and energy harvesting devices.

[0037] The present invention has the following beneficial effects: The Ag / Al composite active metal ink of this invention overcomes the limitation of single inert metal inks, which can only exhibit conductivity, achieving a balance between conductivity and electrochemical activity. This ink, through the functional compounding of micron-sized flake silver powder and spherical aluminum powder, and the introduction of functional additives into an organic carrier for performance optimization, successfully solves the problems of easy oxidation, difficulty in dispersion, and difficulty in balancing conductivity and reactivity of active aluminum powder in printing ink systems. The Ag / Al composite ink of this invention can achieve controllable linewidth, clear edges, and strong adhesion of electrode patterns on flexible substrates such as polyethylene terephthalate (PET), polydimethylsiloxane (PDMS), polyimide (PI), and thermoplastic polyurethane (TPU) through pneumatic extrusion printing or screen printing processes, providing a key material foundation for the printed fabrication of high-performance asymmetric electrode structure devices. Compared with existing technologies, this invention also has the following advantages: (1) This invention achieves a balance between the conductivity and electrochemical activity of ink. Existing commercial conductive inks (such as silver paste and copper paste) have excellent conductivity, but because they are composed of inert metals, they cannot participate in continuous redox reactions as reactants, and therefore cannot be directly used to construct functional devices such as asymmetric electrodes. If active metals (such as aluminum) are used directly to prepare ink, a dense oxide layer will quickly form on the surface of the particles, leading to a sharp deterioration in the conductivity of the ink or even insulation, and it is difficult to store stably in the printing system. This invention constructs a continuous three-dimensional conductive network by using micron-sized flake silver powder to ensure efficient charge transfer; at the same time, micron-sized spherical aluminum powder is introduced as an electrochemical reaction active center. In an optimized organic carrier, the two materials undergo a special process of "preparing separately, then slowly adding and mixing, and finally homogenizing for a long time." This process physically separates and coats the aluminum powder with a silver powder network: the flake-like silver powder overlaps to form a continuous three-dimensional conductive network, which separates the micron-sized spherical aluminum powder particles, preventing direct, large-area contact between them, thus achieving physical separation. Simultaneously, during mixing, the surfaces of the flake-like silver powder and the micron-sized spherical aluminum powder adhere to the surfaces of the spherical particles, thus coating the aluminum powder particles with a layer of silver. This physical separation and coating effectively alleviates the problem of decreased ink conductivity caused by aluminum surface oxidation, giving the ink both the high conductivity of traditional silver paste and the high electrochemical activity of pure aluminum paste, while also providing long-term storage stability.

[0038] (2) The aluminum powder content is a key parameter determining the final performance of the ink. This invention achieves the composite of micron-sized flake silver powder and micron-sized spherical aluminum powder by adding aluminum dispersion droplets to a conductive silver substrate. The flake silver powder constructs a continuous three-dimensional conductive network to ensure basic conductivity, while the spherical aluminum powder serves as discrete electrochemical active centers. The mass ratio of micron-sized spherical aluminum powder to the conductive silver substrate in this invention needs to be precisely controlled between 0.2:1 and 1.5:1. Within this range, the Ag / Al composite ink can retain the high conductivity provided by the continuous three-dimensional network constructed by the silver powder, while also ensuring that the ink has sufficient electrochemical active sites. If the aluminum powder content is too low (causing the ink to approach pure silver paste), the electrochemical activity will be insufficient, resulting in incomplete electrochemical reactions and weak device output signals during subsequent applications; if the aluminum powder content is too high (causing the ink to approach pure aluminum paste), it will disrupt the continuity of the silver conductive network, causing the conductive network to break and resulting in a significant decrease in the overall conductivity of the ink. This invention ensures that the aluminum powder is effectively physically separated and coated by the silver-to-point network by precisely controlling the mass ratio of micron-sized spherical aluminum powder to conductive silver matrix. This significantly inhibits the collective oxidation of aluminum powder and the degradation of conductivity, while providing sufficient reaction sites, thus achieving a balance between electrochemical activity and conductivity, which is impossible for single-component inks.

[0039] (3) The ink of this invention is a tunable rheological system with wide applicability. By adjusting the type of resin, solid content, and amount of high-boiling-point solvent or thixotropic agent added to the organic carrier, the rheological properties of the ink can be controlled, making it suitable for both pneumatic extrusion printing (Ag / Al composite ink viscosity range 100-1000 cP, high-quality graphics obtained at 10-50 kPa air pressure, 1-5 mm / s printing speed, and 100-300 μm nozzle) and screen printing (by increasing the solid content of the resin binder in the organic carrier to 25wt%-60wt% and adding 1wt%-8wt% thixotropic agent, a high-viscosity, high-thixotropic paste is obtained, enabling flexible preparation from coarse wires to fine patterns). The Ag / Al composite ink of this invention can be cured at a temperature of 60-90 °C, which is lower than the glass transition temperature or heat distortion temperature of commonly used flexible substrates (such as PET, PI, TPU), avoiding thermal damage to the substrate during processing.

[0040] (4) This invention employs a stepwise preparation and homogenization process. The invention utilizes a unique process flow of "preparing separately first, then slowly adding and mixing, and finally homogenizing for a long time." Specifically: first, aluminum powder is pre-dispersed to form a uniform aluminum dispersion; then, a conductive silver matrix is ​​prepared; finally, the aluminum dispersion is added dropwise to the conductive silver matrix at a rate of 0.1-1.0 mL / min under stirring, followed by a long period (over 6 hours) of homogenization and stirring. This process effectively avoids rapid oxidation and agglomeration of aluminum powder, ensuring a uniform and stable distribution of aluminum powder in the silver conductive three-dimensional network. This process is not a simple mixing step, but a crucial step in ensuring the stability of the aluminum / silver powder composite structure and the reproducibility of ink performance, which is essential for achieving long-term storage stability and batch consistency of the ink.

[0041] (5) The Ag / Al composite ink of the present invention can be used as an active electrode in asymmetric devices and paired with an inert metal counter electrode (such as a pure silver electrode). When paired with an inert metal electrode (such as a silver electrode), it can form a high-performance electrochemical sensor, energy harvesting device, etc. The active electrode printed with the ink of the present invention can generate a significant and stable potential difference with the inert metal counter electrode, which is the direct reason for realizing sensing, power generation and other functions. Experiments have shown that the asymmetric electrode prepared by combining the Ag / Al active metal ink of the present invention with a humidity-sensitive material (such as graphene oxide) has excellent electrical output performance. The open-circuit voltage of a single device exceeds 600 mV, and the output voltage of the electrochemical humidity sensor formed by series connection can reach more than 2.5 V. It exhibits high sensitivity, fast response and excellent cycle stability in applications such as respiratory monitoring and non-contact sensing. Attached Figure Description

[0042] Figure 1The SEM microstructure and elemental distribution of the Ag / Al composite ink prepared in Example 1 are shown in (a) SEM image, (b) and (c) are the distribution diagrams of Al and Ag elements, respectively. Figure 2 This is a schematic diagram of the flexible printed moisture sensor of Example 1; Figure 3 This is a flowchart of the series integration of the electrochemical humidity sensor device in Example 1; Figure 4 Effect of different aluminum doping ratios on the voltage-time dynamic response curves of electrochemical humidity sensors: (a) 0.2:1; (b) 0.8:1; (c) 1.2:1; Figure 5 A photograph of the electrochemical humidity sensor prepared in Example 1 used in respiratory monitoring applications; Figure 6 The electrochemical performance test results are for the electrochemical humidity sensor prepared in Example 1. Figure 7 A photograph showing the electrochemical humidity sensor device prepared in Example 1 connected to an ESP 32 microcontroller. Figure 8 for Figure 7 The monitoring results of real-time acquisition and wireless transmission of dual-channel signals connected to the ESP 32 microcontroller are shown in (a) and (b), which are the real-time voltage monitoring curves of devices 1 and 2 when a finger approaches device 1; (c) and (d), which are the real-time voltage monitoring curves of devices 1 and 2 when a finger moves away from device 1; (e) and (f), which are the real-time voltage monitoring curves of devices 1 and 2 when a finger approaches device 2; and (g) and (h), which are the real-time voltage monitoring curves of devices 1 and 2 when a finger moves away from device 2. Device 1 is the device pointed to by the finger in (a) and (c), and device 2 is the device not pointed to by the finger in (a) and (c). Figure 9 The shape of the asymmetric electrode in Example 2. Detailed Implementation

[0043] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may also be implemented in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0044] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0045] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0046] Example 1 The preparation process of Ag / Al composite ink is as follows: (1) Pre-dispersion of aluminum powder: Weigh 6.0 g of spherical aluminum powder with a particle size of 10 μm and mix with 12 mL of ethylene glycol butyl ether solvent. Stir magnetically at 300 rpm for 15 min, and then sonicate for 20 min to fully disperse the aluminum powder and form a uniform and stable aluminum dispersion. (2) Preparation of organic carrier: 5 g of E-51 epoxy resin was mixed with 35 g of ethylene glycol butyl ether and 10 g of terpineol. The mixture was stirred at 60°C and 800 rpm for 40 min until the epoxy resin was completely dissolved, forming a uniform and transparent viscous liquid, which is the organic carrier. (3) Preparation of conductive silver substrate: Weigh 25 g of sheet-like silver powder with a thickness of 1 μm and mix it with 10 g of the organic carrier prepared in step (2). Stir at high speed at 800 rpm for 15 min to obtain a uniform conductive silver substrate. (4) Mixing and homogenization: At a stirring speed of 600 rpm, the aluminum dispersion obtained in step (1) was added dropwise to 5 g of the conductive silver matrix obtained in step (3) at a rate of 0.5 mL / min. After the addition was completed, the mixture was continuously magnetically stirred at a speed of 700 rpm for 8 hours to finally obtain Ag / Al composite ink with uniform composition and good stability. The mass ratio of aluminum powder to conductive silver matrix in the ink was 1.2:1.

[0047] The viscosity of the Ag / Al composite ink prepared in this embodiment was measured to be 450 cP at 25 °C. The microstructure and elemental distribution of the Ag / Al composite ink in this embodiment are as follows: Figure 1 As shown, Figure 1 The distribution of the active metal component Al in the composite ink and the construction of the Ag conductive network are explained. From Figure 1 (a) It can be seen that the Ag sheets are stacked and cover the spherical aluminum powder surface, and are interconnected with each other. Through Figure 1The EDS results in (b) and (c) show that Al is distributed throughout the mixed ink, resulting in a higher potential difference between the electrode made from this ink and a pure silver electrode. This manifests as a larger voltage signal output in the moisture sensor based on the electrochemical reaction. This indicates that the continuous distribution of Ag in the ink can form a conductive network, which is beneficial to improving the conductivity of the mixed slurry (ink).

[0048] The application of the Ag / Al composite ink prepared in this embodiment in pneumatic extrusion printing is as follows: Fabrication of asymmetric electrodes: A pneumatic extrusion printing system with a nozzle inner diameter of 250 μm was used. The printing pressure was set to 30 kPa, the printing speed to 2 mm / s, and the printing height to 0.2 mm. Conductive silver substrate was first printed on a PET substrate as an inert counter electrode (positive electrode material). Then, the Ag / Al composite ink was printed on the other side as an active electrode (negative electrode material), forming a planar asymmetric structure with an electrode spacing of 1 mm. The printed device was then heated at 70 °C for 30 min to cure the ink, resulting in an asymmetric electrode. This electrode can monitor humidity in this invention and is therefore also called a flexible printed humidity sensor.

[0049] The above-mentioned asymmetric electrode was used to prepare an electrochemical humidity sensor, and the specific process is as follows: 30 μL of a humidity-sensitive functional material (GO mixed solution, GO concentration of 5 mg / ml) was precisely drop-coated into the 1 mm electrode gap region of the asymmetric electrode and dried at 60 °C. The resulting device structure is shown below. Figure 2 As shown; By designing the printing nozzle path using CAD, it is possible to achieve, for example... Figure 3 The tandem integration shown ultimately yields an electrochemical humidity sensor.

[0050] like Figure 4 As shown in (c), the voltage output of a single device in the electrochemical humidity sensor can reach a maximum of 629.5 mV at 84% RH, and the output voltage of eight devices connected in series can reach 2.7 V. Figure 5 As shown, when the electrochemical humidity sensor is attached inside a breathing mask, waveforms can be successfully acquired, such as... Figure 6As shown, the respiration waveform is stable and exhibits periodic changes, demonstrating good repeatability and stability in continuous testing. The continuous testing method is as follows: based on the relative humidity of different saturated salt solutions at room temperature (RH=65% for NaBr, 75% for NaCl, and 84% for KCl), saturated salt solutions were prepared. A humidity testing platform was built, and nitrogen gas was introduced into the saturated salt solutions through a purging process to introduce gas with a certain relative humidity into the conical flask containing the device, thus controlling the relative humidity in the flask. Changing the saturated salt solution allows for the measurement of the sensor's voltage signal under different humidity levels. Simultaneously, a commercially available hygrometer was used to calibrate the relative humidity in the humidity testing flask in real time to obtain accurate and stable humidity levels, thereby improving the accuracy of the experiment. The electrical performance of the prepared non-contact sensor was tested using a Keysight digital multimeter, characterizing the device's open-circuit voltage, short-circuit current, and signal change rate. During the data acquisition process, the positive and negative wires of the meter are connected to the two electrodes of the device placed in humidity bottles of different saturated salt solutions. The output voltage of the device is monitored in real time using Keysight BenchVue software from Keysight Corporation on a computer to obtain the voltage-time curve.

[0051] like Figure 7 As shown, the electrochemical moisture sensor is connected to the ESP32 microcontroller to achieve real-time acquisition and wireless transmission of dual-channel signals. The monitoring results are as follows. Figure 8 As shown in Figures (a) and (b), this demonstrates that the sensor can achieve non-contact sensing applications. The voltage signal received from device 1 is defined as Channel 1, and the voltage signal received from device 2 is defined as Channel 2. As can be seen from Figures (a) and (b), when a finger approaches device 1, the signal of Channel 1 rises significantly and then remains at approximately 0.6 V. When the finger moves away from device 1, as shown in Figures (c) and (d), the voltage of Channel 1 begins to decrease, returning to near its initial value. During this process, Channel 2 remains in its initial state. Figures (e) and (f) show the real-time voltage monitoring curves of the two devices when a finger approaches device 2. It can be seen that when a finger approaches device 2, the signal of Channel 2 rises significantly and then remains at approximately 0.6 V. When the finger moves away from the device, as shown in Figures (g) and (h), the voltage of Channel 2 begins to decrease, returning to near its initial value. During this process, Channel 2 remains in its initial state. The monitoring results demonstrate that this device can achieve non-contact sensing applications.

[0052] Example 2 The preparation process of Ag / Al composite ink is as follows: (1) Pre-dispersion of aluminum powder: Weigh 3.0 g of spherical aluminum powder and mix with 6 mL of diethylene glycol butyl ether. Stir magnetically at 400 rpm for 15 min, and then sonicate for 20 min to fully disperse the aluminum powder and form a uniform and stable aluminum dispersion. (2) Preparation of organic carrier: 3 g of polyvinyl butyral (PVB) was dissolved in 4.2 g of diethylene glycol butyl ether, and 0.3 g of fumed silica was added as a thixotropic agent. The mixture was dispersed at high speed at 900 rpm to form a uniform, transparent, viscous liquid, i.e., 7.5 g of organic carrier. The content of resin binder in the organic carrier was 40 wt%. (3) Preparation of conductive silver substrate: Weigh 3.0 g of flake silver powder and mix with 0.75 g of organic carrier prepared in step (2). Stir at high speed for 15 min at 800 rpm to obtain a uniform conductive silver substrate, wherein the mass ratio of silver powder to organic carrier is 80:20. (4) Mixing and homogenization: Under a stirring speed of 600 rpm, the aluminum dispersion obtained in step (1) was added dropwise to 3.75 g of the conductive silver matrix obtained in step (3) at a rate of 0.3 mL / min. After the addition was completed, the mixture was continuously magnetically stirred at 600 rpm for 8 hours to finally obtain Ag / Al composite ink suitable for screen printing. The mass ratio of aluminum powder to conductive silver matrix in the ink was 0.8:1.

[0053] The application of the Ag / Al composite ink prepared in this embodiment in screen printing is as follows: Asymmetric electrode printing preparation: Using a 300-mesh screen, the above ink was printed onto a TPU substrate to form... Figure 9 The electrode pattern shown was printed and then heat-treated at 70 °C for 40 min to complete the curing process.

[0054] The electrode was subjected to bending cycle testing. After 500 bending cycles (bending radius 5 mm), the electrode resistance change rate was less than 5%, indicating that the electrode and the electrochemical device fabricated using it have excellent mechanical reliability in wearable applications.

[0055] 30 μL of humidity-sensitive functional material (GO mixed solution, GO concentration of 5 mg / ml) was precisely drop-coated into the 1 mm electrode gap region of the asymmetric electrode and dried at 60 °C. The preparation process and the structure of the resulting device are the same as those in Example 1. Figure 2 same.

[0056] The humidity sensing performance of the device was tested, and the results are as follows: Figure 4 As shown in (b), the sensor's dynamic response was tested under air humidity and 84% RH humidity, and its average voltage output was approximately 534.15 mV.

[0057] Comparative Example 1 (Comparison of Low Aluminum Content) The difference between this comparative example and Example 1 is that: (1) the spherical aluminum powder is 1.0 g and the ethylene glycol butyl ether solvent is 2.0 mL; (4) the mass ratio of aluminum powder to conductive silver matrix is ​​0.2:1, and the remaining process steps and parameter settings are the same as in Example 1.

[0058] The ink prepared in this comparative example still exhibits good printability. The processes for preparing the asymmetric electrode, individual device, and electrochemical humidity sensor in this comparative example are the same as in Example 1. Figure 4 (a) The results of dynamic response testing of a single device in a sensor manufactured using the same process at air humidity and 84% RH humidity. The average voltage output is approximately 119.51 mV, significantly lower than that of Example 1 (629.5 mV). This indicates that when the aluminum powder content is below the lower limit of the ratio range described in this invention, the electrochemical activity of the ink is insufficient, making it difficult to meet the requirements of high-output performance devices.

[0059] Comparative Example 2 (High Aluminum Content Comparison) The difference between this comparative example and Example 1 is that: (1) the spherical aluminum powder is 45.0 g, the ethylene glycol butyl ether solvent is 90 mL, and the ultrasonic treatment time is 40 min; (4) the conductive silver substrate is 25.0 g, the mass ratio of aluminum powder to conductive silver substrate is 1.8:1, and the remaining process steps and parameter settings are the same as in Example 1.

[0060] The ink prepared in this comparative example is significantly thick and difficult to disperse. The process for preparing the asymmetric electrode, individual device, and electrochemical humidity sensor in this comparative example is the same as in Example 1. The electrode formed after the ink in this comparative example is printed and cured has a resistance value as high as several MΩ (megaohms), and does not have effective conductivity. This is because the aluminum powder undergoes severe agglomeration at this time, which disrupts the continuity of the silver conductive network. Although the proportion of aluminum powder in the ink in this comparative example is relatively high, the individual device and the sensor itself in the prepared sensor have almost no voltage signal output. This indicates that when the aluminum powder content exceeds the proportion range described in this invention, the conductivity of the ink will be severely degraded, making it unsuitable for use as a functional electrode.

[0061] Comparative Example 3 (comparison of aluminum powder pre-dispersion process omitted) The difference between this comparative example and Example 1 is that the aluminum powder pre-dispersion treatment in step (1) is omitted, and 6.0 g of dry spherical aluminum powder is directly added to the 5.0 g conductive silver matrix obtained in step (3), and then homogenized by a mixer. The remaining process steps and parameter settings are the same as in Example 1.

[0062] The dried aluminum powder in this comparative example was difficult to disperse in the viscous conductive silver matrix, forming visible agglomerates. The process for preparing the asymmetric electrode in this comparative example was the same as in Example 1. The electrode obtained after ink printing and curing in this comparative example had a resistance value as high as several MΩ (megaohms), and did not have conductive function. This indicates that without the process of pre-dispersing the aluminum powder and then slowly adding and mixing it as described in this invention, it is impossible to obtain a composite ink with uniform aluminum powder distribution and both high conductivity and high electrochemical activity.

[0063] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an Ag / Al composite ink that combines conductivity, excellent printability, and electrochemical activity, characterized in that, The preparation method includes the following steps: (1) Pre-dispersion of aluminum powder: Micron-sized spherical aluminum powder is mixed with organic alcohol ether solvent, and then stirred and sonicated to obtain an aluminum dispersion; (2) Preparation of organic carrier: The resin binder, organic alcohol ether solvent and functional additive are mixed and stirred to obtain the organic carrier; (3) Preparation of conductive silver substrate: Micron-sized flake silver powder is mixed with an organic carrier and stirred to obtain a conductive silver substrate; (4) Mixing and homogenization: Under stirring conditions, aluminum dispersion is added dropwise to conductive silver substrate to obtain mixed slurry. The mixed slurry is stirred and homogenized to obtain Ag / Al composite ink.

2. The preparation method according to claim 1, characterized in that, (1) The particle size of the micron-sized spherical aluminum powder is 5-20 μm, and the mass-volume ratio of the micron-sized spherical aluminum powder to the organic alcohol ether solvent is 1 g: (1-10) mL. The organic alcohol ether solvents in (1) and (2) are one or more of ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol butyl ether, propylene glycol methyl ether, diethylene glycol butyl ether, propylene glycol ethyl ether, and diethylene glycol dimethyl ether.

3. The preparation method according to claim 1, characterized in that, (2) The resin binder is one or more of epoxy resin, acrylic resin, polyurethane resin, polyvinyl butyral, phenolic resin, polyester resin, and cellulose ester. The functional additive is a high-boiling-point solvent or thixotropic agent. The mass ratio of the resin binder to the organic alcohol ether solvent is (10-30): (70-90).

4. The preparation method according to claim 3, characterized in that, The high-boiling-point solvent is one or more of the following: terpineol, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, triethylene glycol monobutyl ether, diethylene glycol dibutyl ether, tripropylene glycol monomethyl ether, dodecyl alcohol ester, hexadecyl alcohol ester, benzyl benzoate, ethylene glycol butyl ether benzoate, dimethyl adipate, and tributyl citrate. The mass ratio of the high-boiling-point solvent to the resin binder is (20-70):(30-80). The thixotropic agent is one or more of the following: fumed silica, organically modified montmorillonite, polyamide wax, hydrogenated castor oil, and polyethylene wax. The mass ratio of the thixotropic agent to the resin binder is (1-15):(85-99).

5. The preparation method according to claim 1, characterized in that, (3) The diameter of the medium-micron flake silver powder is 1-10μm, and the mass ratio of the micron flake silver powder to the organic carrier is (70-90): (10-30). The mass ratio of the medium-micron spherical aluminum powder in (1) to the conductive silver matrix in (3) is (20-60): (40-80).

6. The preparation method according to claim 1, characterized in that, (4) The stirring speed when adding aluminum dispersion is 200-800 rpm; the stirring speed during the homogenization process is 200-800 rpm and the time is 6-12 h.

7. An Ag / Al composite ink with conductivity, excellent printability and electrochemical activity obtained by the preparation method according to any one of claims 1-6.

8. The application of the Ag / Al composite ink according to claim 7 in pneumatic extrusion printing technology and screen printing technology.

9. An asymmetric active electrode obtained by pneumatic extrusion printing or screen printing technology in the application of claim 8.

10. The application of the asymmetric active electrode of claim 9 in the fabrication of electrochemical devices.

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