CN119124408B - Flexible pressure sensor based on synergistic effect of double-layer capacitor and intrinsic pseudocapacitor - Google Patents
Flexible pressure sensor based on synergistic effect of double-layer capacitor and intrinsic pseudocapacitor Download PDFInfo
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Classifications
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- G—PHYSICS
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- G01L1/14—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators
- G01L1/142—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators using capacitors
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/13—Energy storage using capacitors
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Electric Double-Layer Capacitors Or The Like (AREA)
Abstract
本发明属于压力传感器领域，公开了基于双电层电容和本征赝电容协同作用的柔性压力传感器，其为层叠结构，从上至下依次为上电极层、粘接层、赝电容层、双电层电容层、赝电容层、粘接层和下电极层，在柔性压力传感器外整体包裹有封装层，其中：上电极层与所述下电极层为一对尺寸不同的圆形电极，且下电极层比上电极层的直径大；双电层电容层呈圆片形，直径与上电极层相同，在双电层电容层的上下表面对称设置有与双电层电容层同心的若干圆环形凸起；赝电容层均匀喷涂于双电层电容层上下表面。本发明制备的电容式柔性压力传感器具有超高灵敏度、高耐用性和优异的生物相容性和环境友好性。
The present invention belongs to the field of pressure sensors, and discloses a flexible pressure sensor based on the synergistic effect of double-layer capacitance and intrinsic pseudocapacitance, which is a stacked structure, which is an upper electrode layer, an adhesive layer, a pseudocapacitance layer, a double-layer capacitance layer, a pseudocapacitance layer, an adhesive layer and a lower electrode layer from top to bottom, and a packaging layer is wrapped around the flexible pressure sensor as a whole, wherein: the upper electrode layer and the lower electrode layer are a pair of circular electrodes of different sizes, and the lower electrode layer has a larger diameter than the upper electrode layer; the double-layer capacitance layer is in the shape of a disc, and the diameter is the same as that of the upper electrode layer, and a plurality of annular protrusions concentric with the double-layer capacitance layer are symmetrically arranged on the upper and lower surfaces of the double-layer capacitance layer; the pseudocapacitance layer is evenly sprayed on the upper and lower surfaces of the double-layer capacitance layer. The capacitive flexible pressure sensor prepared by the present invention has ultra-high sensitivity, high durability, excellent biocompatibility and environmental friendliness.
Description
Technical Field
The invention belongs to the field of sensors, and particularly relates to a flexible pressure sensor based on the synergistic effect of an electric double layer capacitor and an intrinsic pseudocapacitor.
Background
In the fields of human body wearable, man-machine interaction and the like, a flexible pressure sensor is paid attention to because the flexible pressure sensor has the advantages of light weight, softness, flexibility, strong stretchability, capability of accurately feeding back pressure signals and the like. The conductive ionic gel has good mechanical properties, excellent biocompatibility and strong self-healing capacity, and is an important material for preparing flexible pressure sensors. However, since the materials such as the electrode, the dielectric layer, the packaging layer and the like used in the sensor have a certain thickness, the sensor is limited by sensitivity of the sensor when being used in scenes such as small object grabbing and pulse wave monitoring, and the like, and the problems such as distortion and signal loss are easy to occur. Therefore, the capacitive pressure sensor with ultrahigh sensitivity has very wide application prospect.
Patent application CN110926663a proposes a method for preparing a wearable high-sensitivity pressure sensor capable of being washed by water, which uses spinning solution containing palladium and PAN for electrostatic spinning, chemical silver plating and film forming as upper and lower electrodes, and uses polymers such as plastics, nylon net and the like as dielectric layer materials to obtain the wearable sensor capable of being washed by water, high in sensitivity, light, thin and flexible.
Patent application CN110579296a proposes an electric double layer capacitor type flexible pressure sensor with reinforced inclined structure and a manufacturing method thereof, and an inclined microstructure electrode and an electrolyte layer formed by compounding polymer and ionic liquid are prepared, which have a wide measuring range and high sensitivity.
Patent application CN105865667A proposes a capacitive flexible pressure sensor based on a microstructured dielectric layer and a preparation method thereof, and the capacitive flexible pressure sensor with different sensitivity and test range is manufactured by designing different microstructured dielectric layers and adjusting the performance of the sensor through the shape, the size, the distribution and other condition changes of the microstructure of the dielectric layers.
Patent application CN111551290a proposes a wearable flexible capacitive pressure sensor and a preparation method thereof, a wire is attached to a polyimide substrate and is connected with an electrode, graphene aerogel with an internal microstructure is used as conductive filler and applied to a dielectric layer of the flexible capacitive pressure sensor, and sensitivity of the sensor is improved.
The jugs group discusses the pseudocapacitance mechanism of the CoAl-LDH and its derivatives in Journal of ENERGY CHEMISTRY, journal "The pseudocapacitance mechanism of graphene/CoAl LDH and its derivatives: Are all the modifications beneficial?", and compares the electrochemical performance differences of different derivatives after alkali etching, sulfonation and phosphorylation, making a great contribution to the application of the CoAl-LDH in supercapacitors.
The academic paper published by the journal of Chem, the Li subject group aims at "Ordered-Vacancy-Induced Cation Intercalation into Layered Double Hydroxides: A General Approach for High-Performance Supercapacitors" to electrochemically activate CoFe-LDH so as to improve the cation storage performance of the CoFe-LDH, and opens up a new way for developing promising and cost-effective electrochemical energy storage materials.
The academic paper "Printed and Flexible Capacitive Pressure Sensor with Carbon Nanotubes based Composite Dielectric Layer" published by Guo team journal Micromachines reports that the use of a mixture of Carbon Nanotubes (CNT) and Polydimethylsiloxane (PDMS) with different aspect ratios as a composite dielectric layer improves the sensitivity of a flexible pressure sensor, and the prepared sensor has both high sensitivity and high resolution.
The paper "Multilayer self-filled iontronic pressure sensor with ultrahigh sensitivity and broad sensing range" published by Marouen Zammali on the journal Sensors and Actuators A is a Physical, introduces a multilayer self-filling microstructure in the dielectric layer, thus not only greatly improving the sensitivity, but also widening the sensing range.
Although flexible pressure sensors based on ionic gels have made some progress in terms of improvement of sensitivity, the following disadvantages remain:
1. the existing capacitive flexible pressure sensor is usually only focused on the transmission of cations under the action of an external electric field and ignores the directional movement of anions when the dielectric layer hydrogel is designed, and an un-designed anion transmission channel is weaker than a cation transmission channel, so that anions move slowly under the action of the electric field, the conductivity of ionic gel is low, and the sensitivity of the sensor is further limited.
2. The existing capacitive flexible pressure sensor increases the sensitivity of the sensor by adding an ion source into a dielectric layer and forming an electric double layer between the dielectric layer and an electrode, however, the interface adsorption amount is limited due to the repulsion of the same charges when a single electric double layer capacitance mechanism is adsorbed, and the sensitivity of the sensor is limited.
3. When the existing capacitive flexible pressure sensor is designed on a dielectric layer, microstructures such as a cylinder, a cone and a pyramid are generally introduced into the surface, the initial capacitance is reduced and the sensitivity is increased by changing the contact area between the dielectric layer and an electrode under the action of pressure, and the sensor is difficult to have high sensitivity and high linearity due to the single microstructure design.
4. The existing capacitive flexible pressure sensor lacks an adhesive with high conductivity and high adhesiveness between an electrode and a dielectric layer, the too low conductivity of the adhesive can cause the too large time constant of the whole sensor to influence the high-frequency characteristic of the sensor, the insufficient adhesiveness of the adhesive can cause the sensor electrode and the dielectric layer to easily loose or fall off, and the reliability and the durability of the sensor are limited.
5. The existing capacitive flexible pressure sensor packaging layer generally adopts organic polymer films such as polyurethane and polyethylene, however, the organic polymer films can generate stimulation to human skin in the long-term use process due to poor air permeability, poor hygroscopicity, poor biocompatibility and the like, so that the application of the sensor on wearable equipment is limited.
6. The ionic gel and the packaging material of the existing capacitive flexible pressure sensor generally use organic polymer materials which are not easy to degrade, and the degradation treatment process of the ionic gel and the packaging material needs to be treated at high temperature or strong acid, strong alkali and strong oxidant are introduced, so that the degradation cost is high, harmful substances are easy to generate to damage the natural environment, and the wide application of the sensor is limited.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the flexible pressure sensor based on the synergistic effect of the double-layer capacitor and the intrinsic pseudocapacitance, and the sensitivity, the static and dynamic characteristics and the stability of the flexible pressure sensor are effectively improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention discloses a flexible pressure sensor based on the synergistic effect of an electric double layer capacitor and an intrinsic pseudocapacitor, which is of a laminated structure, and comprises an upper electrode layer, an adhesive layer, a pseudocapacitor layer, an electric double layer capacitor layer, a pseudocapacitor layer, an adhesive layer and a lower electrode layer from top to bottom in sequence, wherein the flexible pressure sensor is integrally wrapped with a packaging layer. The upper electrode layer and the lower electrode layer are a pair of circular electrodes with different sizes, and the diameter of the lower electrode layer is larger than that of the upper electrode layer. The double-layer capacitor layer is in a disc shape, the diameter of the double-layer capacitor layer is the same as that of the upper electrode layer, a plurality of annular protrusions concentric with the double-layer capacitor layer are symmetrically arranged on the upper surface and the lower surface of the double-layer capacitor layer, and the pseudo-capacitor layer is uniformly sprayed on the upper surface and the lower surface of the double-layer capacitor layer.
Further, the electric double layer capacitor layer is prepared from raw materials of polyvinyl alcohol (PEO), lithium sulfate (Li 2SO4), poly- [2- (methacryloyloxy) ethyl ] dimethyl- (3-sulfopropyl) ammonium hydroxide (PMAEDS), N-Methylenebisacrylamide (MBAA) and cellulose, wherein the raw materials comprise, by mass, 5% -20% of Li 2SO4, 5% -10% of PMAEDS, 5% -10% of MBAA, 10% -20% of PEO and the balance cellulose. Cellulose is highly crosslinked as a matrix material of the electric double layer capacitor layer, providing good mechanical properties to the electric double layer capacitor layer. The PEO constructs a transmission network of Li + in the double-layer capacitor layer, greatly improves the transfer speed of Li +, further reduces the response time of the sensor, and the cross-linked network formed by PMAEDS and MBAA forms a transmission channel for SO 4 2-, SO that the radius difference of anions and cations in Li 2SO4 is larger, the ion association pairing effect is weaker, li + is easy to dissociate, and the dissociated Li + and SO 4 2- can quickly and freely move in the double-layer capacitor layer along with the relaxation motion of cellulose chains and the formed ion channel.
Further, the total thickness (i.e., the height including the annular protrusions) of the electric double layer capacitor layer is 250-400 μm, the tensile strength is 10-30 MPa, the tensile fracture rate is not less than 50%, and the ionic conductivity is not more than 3×10 -2 S/cm under normal temperature conditions.
Further, the annular protrusions on the upper surface and the lower surface of the electric double layer capacitor layer are distributed at equal intervals, the cross section of each annular is isosceles trapezoid, the upper side length of the trapezoid of the cross section of each annular from inside to outside along the radius direction is increased by the same length difference, the lower side length is equal, and the heights of the annular protrusions are equal. Further, the radius of the double-layer capacitor layer is 2-5mm, the distance between the annular protrusions is 50-100 mu m, the radius of the inner circle of each annular is 200-1500 mu m, the side length of the lower side of the trapezoid of the cross section of each annular is 20-40 mu m, the side length of the upper side of the trapezoid of the cross section of each annular is 10-20 mu m, and the height of each annular is 10-20 mu m. By introducing the annular microstructure, the initial contact area of the double-electric-layer capacitor layer and the electrode layer is reduced, so that the initial capacitance is reduced, and the variation of an effective capacitance interface of the sensor under the action of external pressure is increased, so that the sensitivity of the sensor is improved. The circular rings with different widths enable the sensor to have consistent capacitance interface change under the pressure action of different ranges, so that the linearity of the sensor is improved.
Further, the pseudo-capacitance layer is made of CoAl layered double hydroxide (CoAl-LDH) subjected to electrochemical activation treatment, the thickness of the pseudo-capacitance layer is not more than 10-100 mu m, and the conductivity at normal temperature is not more than 5X 10 -2 S/cm. The CoAl-LDH has a two-dimensional lamellar structure, co 2+ and Al 3+ in the CoAl-LDH form a cationic layer, cl -、CO3 2-、NO3 - forms an anionic layer, on one hand, co 2+ in the cationic layer can lose electrons to oxidize to Co 3+ under high potential, reverse reaction Co 3+ is reduced to Co 2+ under low potential, oxidation-reduction reaction is carried out to cause capacitance change of a dielectric layer, and pseudocapacitance components are introduced into the sensor. On the other hand, the unique two-dimensional layered structure of the CoAl-LDH imparts an ultra-large surface area to the CoAl-LDH, providing a large number of adsorption sites. In the process of electric activation, part of metal ions of the cationic layer are separated from crystal lattices, and crystal lattice defects are introduced into the metal ions, so that the cationic layer can overcome electrostatic repulsive force to adsorb Li + in the double-layer capacitance layer under the action of an external electric field, and the sensitivity of the sensor is further improved by the synergistic effect of the double-layer capacitance and the pseudo-capacitance.
Further, the bonding layer is prepared from a mixture of epoxy resin serving as a viscous matrix, silver nano-particle decorated multiwall carbon nano-tube Ag-MWCNT serving as a conductive additive and an epoxy resin curing agent, wherein the mass percent of the epoxy resin in the mixture is 61.25-78%, the mass percent of the Ag-MWCNT is 5-15%, and the mass percent of the epoxy resin curing agent is 17-23.75%. The thickness of the bonding layer is 50-80 mu m, the tensile fracture rate is not lower than 40%, the tensile strength is 1.5-9.7 MPa, and the conductivity is 1500S/cm-8000S/cm at normal temperature. The multiwall carbon nanotubes modified with silver nanoparticles are added as a conductive aid to an adhesive epoxy resin for solving the defect of low conductivity of the epoxy resin.
Further, the upper electrode layer and the lower electrode layer are made of copper foil. The diameter of the upper electrode layer is 5-20 mm, and the diameter of the lower electrode layer is 0.5-1 mm larger than that of the upper electrode layer. The copper foil has high conductivity, good flexibility and ductility, and provides a good electrical basis for the application of the sensor to flexible wearable equipment.
Further, the packaging layer is formed by polymerizing cellulose and chitosan, the molecular weight of the chitosan is not lower than 30000, the viscosity is not lower than 400mPa/s, the granularity of the cellulose raw material is 300-400 meshes, and the viscosity is not lower than 80000mPa/s. The crosslinked network formed by cellulose and chitosan has a great number of micropore structures introduced on the surface, so that the crosslinked network has good air permeability, the network structure of the cellulose has enough strength, the service life of the sensor can be prolonged when the crosslinked network is used as an encapsulation layer, a great number of hydroxyl groups (-OH) and methoxy groups (-OCH 3) in cellulose molecules and chitosan molecules can form hydrogen bonds with water molecules, so that the crosslinked network has strong hygroscopicity, in addition, the cellulose and the chitosan have excellent biocompatibility, the crosslinked network can be used as the encapsulation layer, the sensor can be attached to the skin for a long time, the damage to the skin is avoided, and the cellulose and the chitosan can be naturally degraded as natural biological materials, so that the crosslinked network has excellent environment-friendly and sustainable properties.
The invention further provides a preparation method of the flexible pressure sensor based on the synergistic effect of the double-layer capacitor and the intrinsic pseudocapacitor, which comprises the following steps:
Step 1, preparation of an electric double layer capacitor layer
Adding PEO, PMAEDS, MBAA and cellulose into DMF, magnetically stirring at 60-80 ℃ for 2-3 hours until the solution is clear and transparent, then adding Li 2SO4 into the solution, continuously stirring for 2-3 hours until the solution is uniformly mixed to be in a white viscous state, and obtaining a flexible ionic gel material;
and injecting the flexible ionic gel material into a die of the electric double layer capacitor layer, and demolding after curing at 60-80 ℃ to obtain the electric double layer capacitor layer.
Step 2, preparing a pseudo-capacitor layer
Forming a three-electrode system by taking a CoAl-LDH as a working electrode, a calomel electrode as a reference electrode and a graphite electrode as a counter electrode, and circulating for 5 times at a speed of 50-200 mV/s in a KOH solution of 0.1-0.5 mol/L at 0-5V by using an electrochemical workstation to activate the CoAl-LDH to generate lattice defects so as to obtain an activated CoAl-LDH;
after grinding the activated CoAl-LDH, ultrasonically dispersing the activated CoAl-LDH in deionized water at a concentration of 0.05-0.2 g/mL to obtain a suspension;
And uniformly spraying the obtained suspension on the upper and lower surfaces of the double-layer capacitor layer respectively, drying at 50-80 ℃ to remove water, and repeating spraying and drying for 3-5 times to form pseudo-capacitor layers on the upper and lower surfaces of the double-layer capacitor layer.
Step 3, preparing an adhesive layer and an electrode layer
Adding a carboxylated multiwall carbon nanotube COOH-MWCNT into DMF, adding sodium dodecyl sulfate SDS to improve the dispersibility, heating to 50-80 ℃ after ultrasonic treatment for 1-3 hours, dropwise adding an AgNO 3 aqueous solution under stirring, continuing to keep the temperature and stir for 1-3 hours after the dropwise adding is finished, and then standing for 24-48 hours (without heating or stirring);
mixing Ag-MWCNT with epoxy resin for 0.5-1.5 h at a rotating speed of 1000-2000 rpm by using a high-speed mechanical mixer, and then carrying out ultrasonic treatment for 0.5-1.5 h to obtain an adhesive layer solution;
The adhesive layer solution is dried for 1-2 hours at the temperature of 80-120 ℃ to enable the solution to be sticky, adhesive layer ink is obtained, the adhesive layer ink and an epoxy resin curing agent are evenly mixed and then are respectively coated on copper foils serving as an upper electrode layer and a lower electrode layer to form an adhesive layer, and then the upper electrode layer and the lower electrode layer are fixed on the pseudo-capacitor layer through the adhesive layer.
Step 4, preparing the packaging layer
Adding cellulose powder into deionized water, heating and stirring at 70-90 ℃ until the cellulose powder is dissolved, adding chitosan with the same mass as the cellulose powder, adding hydrochloric acid with the mass concentration of 10% to adjust the pH value to 1-2, continuously heating and stirring for 2-4 hours, introducing the mixture into a flat plate die, drying at 70-100 ℃ for 1-3 hours to completely remove water and hydrochloric acid, washing the mixture with deionized water and ethanol in sequence, and air-drying the mixture to obtain an encapsulation film;
And uniformly coating a layer of mixture of epoxy resin and epoxy resin curing agent on the surfaces of the upper electrode layer and the lower electrode layer respectively by using a coating rod, then integrally adhering a packaging film on the outer side, and then applying pressure to the packaging film by a press machine until the packaging film is fully adhered to complete the packaging, thereby obtaining the flexible pressure sensor based on the synergistic effect of the double-layer capacitor and the intrinsic pseudocapacitor.
Compared with the prior art, the invention has the beneficial effects that:
1. The invention introduces cellulose as a basic skeleton into the electric double layer capacitance layer. On one hand, the long molecular chain of the high-polymerization-degree cellulose enables Li + and SO 4 2- to be transmitted in a matrix network by means of chain stretching movement of the long molecular chain, SO that the matrix of the electric double-layer capacitor layer has higher ion mobility, and the sensitivity of the sensor is improved. On the other hand, the crosslinked network formed by the cellulose provides excellent mechanical properties for the dielectric layer, so that the sensor has excellent repeatability.
2. According to the invention, PEO is introduced into the double-layer capacitor layer to construct a cation transmission channel, a C-O bond in PEO can be combined with Li + under the action of an external electric field and realize directional transportation of Li + along the direction of a polymer chain, and PEO constructs a transmission channel of Li + in ionic gel, so that Li + has a faster migration rate in the double-layer capacitor layer, the cation mobility of the double-layer capacitor layer is improved, cations are easier to migrate to the surface of an electrode under the action of the electric field, and the sensitivity of a sensor is improved.
3. According to the invention, PMAEDS is introduced into the electric double layer capacitor layer to construct an anion transmission channel, and a quaternary ammonium group with positive charges is arranged in PMAEDS, SO that the quaternary ammonium group can be combined with SO 4 2- and transmitted on a polymer chain, and a transmission channel of SO 4 2- is constructed, SO that SO 4 2- has a faster migration rate in the ionic gel, and the anion mobility of the dielectric layer is improved. In addition PMAEDS negatively charged sulfonate groups-SO 3 can bind to Li + and be transported on the polymer chains, further enhancing the mobility of Li + in the electric double layer capacitor layer. The synergistic effect of PEO and PMAEDS enables the electric double layer capacitor layer to have a larger dielectric constant compared with single Li + hydrogel, and further improves the sensitivity of the sensor.
4. The electrochemical activated CoAl-LDH is introduced on the surface of the electric double layer capacitor layer, and a pseudocapacitance component is introduced in a dielectric layer (the dielectric layer represents the combination of the electric double layer capacitor layer and the pseudocapacitance layer in the invention) by utilizing oxidation-reduction (Co 2+-Co3+) of metal ions and accompanying absorption and desorption of OH - of the CoAl-LDH under the additional voltage. Li 2SO4 is introduced into the electric double layer capacitor layer as a lithium ion source, and an electric double layer capacitor component is introduced into the dielectric layer. The lattice defect is introduced into the CoAl-LDH through electrochemical activation, so that Li + can be adsorbed and desorbed on the CoAl-LDH cationic layer in voltage circulation, the synergistic effect of the pseudo-capacitance component and the double-layer capacitance component is realized, the introduction of the pseudo-capacitance component and the synergistic effect of the two capacitance components enable the double-layer capacitance layer to have larger unit charge density relative to the pure ionic gel dielectric layer, the capacitance change of the sensor under the action of pressure is increased, and the sensitivity of the sensor is improved.
5. According to the invention, a casting process and a mold forming mode are adopted, circular ring-shaped bulge microstructures with different widths are introduced into the surface of the double-layer capacitor layer, on one hand, the introduction of the microstructures reduces the initial capacitance of the sensor, so that the sensor is more sensitive to the capacitance change of the dielectric layer, on the other hand, as the applied pressure is increased, the contact area between the electrode and the dielectric layer is increased, so that the interface capacitance between the electrode and the dielectric layer is gradually increased, and the introduction of the circular ring-shaped bulge microstructures increases the sensitivity of the sensor. The circular rings with different widths enable the sensor to have consistent capacitance interface change under the pressure action of different ranges, so that the linearity of the sensor is improved.
6. According to the invention, the multi-wall carbon nano tube Ag-MWCNT/epoxy resin adhesive decorated by the silver nano particles is arranged between the dielectric layer and the electrode, and a large number of oxygen atoms in the epoxy resin provide adsorption sites, so that the epoxy resin has a strong interface adsorption effect and strong adhesiveness, so that the desorption of the electrode and the dielectric layer is not easy to occur in long-term use of the sensor, and the consistency and stability of the sensor are improved. The introduction of the Ag-MWCNT forms a conductive network in the epoxy resin, so that the conductivity of the adhesive is greatly improved, the time constant of the sensor is further reduced, and the hysteresis characteristic of the sensor is optimized. The use of PEO in the electric double layer capacitor layer builds the Li + transport network so that Li + has a faster migration rate therein, thereby reducing the sensor delay and optimizing the hysteresis characteristics of the sensor.
7. The packaging layer is made of cellulose and chitosan, and the network structure of the cellulose enables the cellulose to have enough strength, so that the service life of the sensor can be prolonged when the packaging layer is used. The cellulose and the chitosan are biomass materials, have good biocompatibility, and the network formed by crosslinking the cellulose and the chitosan has good air permeability, and a large number of hydroxyl groups and methoxy groups on a molecular chain provide good hygroscopicity for the cellulose and the chitosan, so that the cellulose and the chitosan cannot stimulate human skin in the long-term use process, and the application range of the flexible pressure sensor is expanded.
8. The organic polymers such as PEO, PMAEDS, MBAA, cellulose and the like used in the invention can be naturally degraded or can be degraded in a simple way in a green way, substances harmful to the environment can not be generated, all reagents such as Li 2SO4 and CoAl-LDH are nontoxic and harmless to human bodies, and the whole sensor has strong environmental adaptability and durability.
Drawings
Fig. 1 is an overall structure diagram of a flexible pressure sensor based on the synergistic effect of an electric double layer capacitor and an intrinsic pseudocapacitor.
Fig. 2 is a schematic diagram of a mold for manufacturing an electric double layer capacitor layer and a microstructure of the manufactured electric double layer capacitor layer.
Fig. 3 is a schematic representation of the interaction of PEO formed conductive pathways with Li +.
Fig. 4 is a schematic illustration of interaction of conductive pathways formed by PMAEDS and MBAA with SO 4 2- and Li +.
FIG. 5 is a schematic structural diagram of a CoAl-LDH.
Fig. 6 is a schematic diagram of pseudocapacitive effects of a CoAl-LDH.
Fig. 7 is a schematic diagram of the principle of Li + adsorption and desorption in the activated CoAl-LDH lattice under the action of an electric field after the CoAl-LDH is electrically activated to generate lattice defects.
Fig. 8 is a stress-strain curve of a strip of Ag-MWCNT/epoxy conductive adhesive layer of the same cross-sectional area and the same length at different Ag-MWCNT concentrations.
FIG. 9 is a graph showing the resistance change of a strip of Ag-MWCNT/epoxy conductive adhesive layer of the same cross-sectional area and the same length at different concentrations of the Ag-MWCNT.
Fig. 10 is a graph showing stress-capacitance change rate curves under a stress range of 500KPa for the flexible pressure sensor (curve corresponding to S 1) and the pressure sensor without the pseudocapacitance layer (curve corresponding to S 2) based on the synergistic effect of the electric double layer capacitance and the intrinsic pseudocapacitance, which were manufactured in example 1.
Fig. 11 is a frequency characteristic curve of the flexible pressure sensor based on the synergy of the electric double layer capacitor and the intrinsic pseudocapacitance fabricated in example 1 at different frequencies.
Fig. 12 is a graph showing the repetitive characteristics of the flexible pressure sensor based on the synergistic effect of the electric double layer capacitor and the intrinsic pseudocapacitance fabricated in example 1.
Detailed Description
The following examples of the present invention will be described in detail with reference to the accompanying drawings, and are given by way of illustration of the detailed implementation and specific operation procedures of the present invention, but the scope of protection of the present invention is not limited to the following examples.
PEO used in the following examples was purchased from Shanghai Michelin Biochemical technologies Co., ltd (powder, mw: 100000).
PMAEDS used in the following examples was purchased from Shanghai Michelin Biochemical technologies Co., ltd (AR, 98.0%).
MBAA used in the following examples was purchased from Shanghai Michelin Biochemical technologies Co., ltd (AR, 99.0%).
Li 2SO4 used in the following examples was purchased from Shanghai Michelin Biochemical technology limited (AR, 98.0%).
The CoAl-LDH used in the following examples was purchased from Shanghai Alasdine Biotechnology Co., ltd.
DMF used in the following examples was purchased from Shanghai Michelin Biochemical technologies Co., ltd (AR, 99.5%).
Carboxylated multiwall carbon nanotubes (MWCNT-COOH) used in the following examples were purchased from Shanghai microphone Biochemical technology Co., ltd. (AR, 99.9%).
AgNO 3 used in the following examples was purchased from Shanghai Michelin Biochemical technologies Co., ltd (40 mg/mL).
The epoxy resins used in the following examples were purchased from Shanghai Michelin Biochemical technologies Co.
Sodium Dodecyl Sulfate (SDS) used in the following examples was purchased from Shanghai Michael Biochemical technologies Co., ltd (AR, 92.5-100.5%).
The epoxy curing agent 593 used in the following examples was purchased from zheng xiang da chemical industry.
The cellulose used in the following examples was purchased from Hebei Zhi Chengcellulose Limited (viscosity 100000 mPa/s).
The chitosan used in the following examples was purchased from Shanghai Alasdine Biochemical technologies Co., ltd (Mw-30000, viscosity >400 mPa/s).
Hydrochloric acid used in the following examples was purchased from Nanjing reagent (AR).
Example 1
As shown in fig. 1, the flexible pressure sensor based on the synergistic effect of the electric double layer capacitor and the intrinsic pseudocapacitance provided in this embodiment is a laminated structure, and includes, from top to bottom, an upper electrode layer 4a, an adhesive layer 3, a pseudocapacitance layer 2, an electric double layer capacitor layer 1, a pseudocapacitance layer 2, an adhesive layer 3 and a lower electrode layer 4b, and an encapsulation layer 5 is integrally wrapped outside the flexible pressure sensor.
The preparation of the flexible pressure sensor based on the synergistic effect of the electric double layer capacitor and the intrinsic pseudocapacitance in the embodiment comprises the following preparation steps:
Step 1, double electric layer capacitor layer
1G of PEO, 0.5g of MBAA, 0.5g PMAEDS g of cellulose and 20mL of DMF are added, the mixture is magnetically stirred at 80 ℃ for 2 hours until the solution is clear and transparent and no obvious particles are generated at the bottom of a beaker, then 1g of Li 2SO4 is added into the solution, and stirring is continued for 2 hours until the solution is uniformly mixed and is in a white viscous state, so that the flexible ionic gel material is obtained.
And (3) printing a mould containing a circular ring microstructure through 3D, casting the prepared flexible ionic gel material into the mould, drying and curing for 4 hours in a 70 ℃ incubator, and demoulding to obtain the electric double layer capacitor layer. The electric double layer capacitor layer obtained in this example was found to have a total thickness of 317. Mu.m, a tensile strength of 21.6MPa, a tensile breaking rate of 60.7% and an ionic conductivity of 1.3X10 -2 S/cm at room temperature.
Step 2, preparing a pseudo-capacitor layer
The method comprises the steps of forming a three-electrode system by taking a CoAl-LDH as a working electrode, a calomel electrode as a reference electrode and a graphite electrode as a counter electrode, circulating the CoAl-LDH at a speed of 100mV/s in a KOH solution of 0.1mol/L for 5 times at a speed of 0-5V to activate the CoAl-LDH to generate lattice defects to obtain activated CoAl-LDH, grinding 0.5g of activated CoAl-LDH, dispersing in 5mL of deionized water, and carrying out ultrasonic treatment for 30 minutes to obtain a stable suspension.
And uniformly spraying the obtained suspension on the upper and lower surfaces of the double-layer capacitor layer respectively, drying in an incubator at 80 ℃ to remove water, and repeating the spraying and drying for 3 times to form pseudo-capacitor layers on the upper and lower surfaces of the double-layer capacitor layer. The test shows that the ionic conductivity of the pseudo-capacitor layer obtained in the embodiment is 2.7X10 -2 S/cm under the normal temperature condition, and the thickness is 78 mu m.
Step 3, preparing an adhesive layer and an electrode layer
300Mg of COOH-MWCNT is mixed into 250mL of DMF, 100mg of SDS is added, ultrasonic treatment is carried out for 2 hours, heating is carried out to 60 ℃, 20mL of AgNO 3 water solution with the concentration of 20mg/mL is added dropwise under stirring, heat preservation and stirring are continued for 1 hour after the dripping is finished, then standing is carried out for 24 hours, finally, the reaction mixture is centrifuged, washed by deionized water and dried for 8 hours under the vacuum of 50 ℃ to obtain the Ag-MWCNT.
1G of Ag-MWCNT was mixed with 10g of epoxy resin using a high-speed mechanical mixer at 1500rpm for 30 minutes, and then sonicated for 1 hour to obtain an adhesive layer solution.
A piece of copper foil with the size of 5cm multiplied by 0.1mm is taken, the size of an upper electrode is set to be 4mm in radius, the size of a lower electrode is set to be 5mm in radius in a laser cutting machine, and the laser cutting machine is set to cut the copper foil at the cutting power of 80W, the cutting speed of 10mm/s and the focal length of 125 mm. After cutting, the surfaces of the two electrode layers are cleaned by deionized water and absolute ethyl alcohol at one time, and the upper electrode layer and the lower electrode layer are obtained after drying.
Drying the bonding layer solution at 100 ℃ for 1h to make the solution be obviously non-fluid viscous to obtain bonding layer ink, uniformly mixing the bonding layer ink with 2.5g of epoxy resin curing agent 593, respectively coating the bonding layer ink on copper foils serving as an upper electrode layer and a lower electrode layer to form bonding layers, and then fixing the upper electrode layer and the lower electrode layer on the pseudo-capacitor layer by using the bonding layers.
The adhesive layer obtained in this example was tested to have a thickness of 67. Mu.m, a tensile fracture rate of 68.2%, a tensile strength of 3.9MPa and an electrical conductivity of 6742S/cm at room temperature.
Step 4, preparing the packaging layer
Adding 5g of cellulose powder with granularity of 350 meshes and viscosity of 100000mPa/s into 20mL of deionized water, heating and stirring at 80 ℃ until the cellulose powder is dissolved, adding 5g of chitosan, adding hydrochloric acid with mass concentration of 10% to adjust pH to 1-2, continuously heating and stirring for 3 hours to enable the cellulose powder to react completely, introducing the cellulose powder into a flat plate die, drying at 80 ℃ for 2 hours to completely remove water and hydrochloric acid, washing with deionized water and ethanol in sequence, and air-drying to obtain the packaging film.
And uniformly coating a layer of mixture of epoxy resin and epoxy resin curing agent 593 on the surfaces of the upper electrode layer and the lower electrode layer respectively by using a coating rod, then integrally adhering a packaging film on the outer side, and then applying pressure to the packaging film by a press machine until the packaging film is fully adhered to complete packaging, so that a packaging layer wrapping the flexible pressure sensor is formed, and the flexible pressure sensor based on the synergistic effect of an electric double layer capacitor and an intrinsic pseudocapacitor is obtained.
Fig. 2 is a schematic diagram of a mold for manufacturing an electric double layer capacitor layer and a microstructure of the manufactured electric double layer capacitor layer. By introducing the regular annular bulge microstructure on the surface of the double-layer capacitor layer, on one hand, the change rate of the contact area of the double-layer capacitor layer and the electrode when the double-layer capacitor layer is stressed is increased, and the sensitivity and the response capability of the sensor are improved. On the other hand, the circular rings with different widths enable the sensor to have consistent capacitance interface change under the pressure action of different ranges, so that the linearity of the sensor is improved. Specifically, in this example, the radius of the electric double layer capacitor layer was 4mm, the spacing between the annular protrusions was 100 μm, the inner radius of each annular was 1000 μm, 1100 μm, 1200 μm in this order, the lower side length of the trapezoid of the cross section of each annular was 20 μm, the upper side length was 10 μm, and the height of each annular was 10 μm.
Fig. 3 is a schematic diagram showing interaction between a conductive channel formed by PEO and Li +, wherein rich O atoms on a PEO long chain provide adsorption sites for Li +, and Li + can move between different O atoms on a PEO chain and between PEO chains along with the telescopic movement and electric field action of the PEO chain, so that directional transmission of Li + on PEO is realized, and a transmission channel of Li + is constructed.
Fig. 4 is a schematic diagram of the interaction of PMAEDS with MBAA to form a conductive channel with SO 4 2- and Li +. The quaternary ammonium radical ion in PMAEDS is capable of binding to SO 4 2- and is transported on the cellulose chain by ion exchange between the relaxing movement of the cellulose chain and PMAEDS, creating a transport channel for SO 4 2-. Meanwhile, the sulfonate (SO 3 -) at the tail end of PMAEDS can adsorb and transmit Li +, and a high-speed transmission channel of Li + is constructed by cooperation of PEO. MBAA acts as a cross-linking agent, stabilizing the ion transport channel formed by PMAEDS.
FIG. 5 is a schematic structural diagram of a CoAl-LDH. The CoAl-LDH is of a two-dimensional layered structure, metal ions and hydroxyl (OH -) are approximately and densely stacked to form a cationic layer of the CoAl-LDH, carbonate (CO 3 2-) is filled between the two cationic layers to balance the charges of the cationic layers, and a certain space is reserved between the cationic layers and the occupation space of CO 3 2- due to electrostatic repulsion, so that CO 3 2- and Li + can enter and exit between the layers.
Fig. 6 is a schematic diagram of pseudocapacitance effects of a CoAl-LDH, where Co converts between +2 and +3 valences under the action of an applied electric field, with a small amount of OH - and Co 3 2- being desorbed, resulting in charge accumulation in the pseudocapacitance layer.
Fig. 7 is a schematic diagram of the principle of absorption and desorption of Li + in an activated CoAl-LDH lattice under the action of an electric field after the electric activation of CoAl-LDH to generate lattice defects, wherein the lattice defects are generated on the surface of the CoAl-LDH after the electrochemical treatment due to the desorption of H +, so that vacancies are provided for the intercalation of Li +, the absorption and desorption of Li + can be realized under the electric field by virtue of electrostatic action rather than chemical bond action between Li + and the activated CoAl-LDH, and the synergistic effect of an electric double layer capacitor and a pseudocapacitor is realized.
Fig. 8 and 9 are stress-strain curves and resistance change curves, respectively, for strips of Ag-MWCNT/epoxy conductive adhesive layers of the same length and the same cross-sectional area at different Ag-MWCNT concentrations. The total mass of the solution is controlled to be 10g unchanged when the conductive adhesive layer solution is prepared according to the step 3, and the amounts of the Ag-MWCNT added are regulated and controlled to be 0.5g, 0.8g, 1g, 1.2g and 1.5g respectively to form the conductive adhesive layer solution with mass fractions of 5%, 8%, 10%, 12% and 15%, and the conductive adhesive layer solution is cut into strips with mass fractions of 5mm multiplied by 1mm after being solidified for mechanical tensile test and resistance test. And (3) carrying out mechanical tensile test on the sensor by a drawing press ZQ990B, and carrying out resistance test by connecting a lead with an LCR resistance meter, and respectively drawing the obtained stress-strain curve and resistance change curve.
Fig. 8 is a stress-strain curve of the same length conductive adhesive layer strips of the same cross-sectional area at different Ag-MWCNT contents, showing that as the Ag-MWCNT content increases, the fracture stress gradually decreases, while the strain of the conductive adhesive layer strips gradually decreases at the same stress, indicating that the elasticity of the conductive adhesive layer strips gradually decreases as the Ag-MWCNT increases. The mass fraction of Ag-MWCNT is 8% -12% and the stress-strain curve is not much different. Fig. 9 is a graph showing the resistance change of the same length conductive adhesive layer strips of the same cross-sectional area at different Ag-MWCNT contents, showing that the resistance of the conductive adhesive layer strips gradually decreases as the Ag-MWCNT content increases. As can be obtained by combining fig. 8 and fig. 9, the conductive adhesive layer has relatively good adhesion and conductivity when the mass ratio of Ag-MWCNT is between 8% and 12%, so that an adhesive layer solution with a mass fraction of 10% is selected in the examples.
Fig. 10 is a graph showing stress-capacitance change rate curves of the flexible pressure sensor according to the present embodiment based on the synergistic effect of the electric double layer capacitance and the intrinsic pseudocapacitance, and the pressure sensor without the pseudocapacitance layer under a stress range of 500 KPa. The sensor of this embodiment has both high sensitivity of 9.47KPa -1 and high linearity of 0.814, and the sensitivity is improved by 42.4% compared to a pressure sensor without a pseudocapacitance layer (the sensitivity is 6.65 kPa -1), which indicates that the addition of the pseudocapacitance component effectively improves the sensitivity of the sensor.
Fig. 11 is a frequency characteristic curve of the flexible pressure sensor according to the present embodiment based on the cooperation of the electric double layer capacitor and the intrinsic pseudocapacitance at different frequencies. The curve shows that the sensor can obtain stable response under a wide range of loading frequency, and can still keep stable capacitance variation under the loading frequency of 10Hz, so that the sensor is suitable for application scenes of most flexible pressure sensors.
Fig. 12 is a graph showing the repetitive characteristics of the flexible pressure sensor based on the cooperation of the electric double layer capacitor and the intrinsic pseudocapacitance according to the present embodiment. The prepared sensor was subjected to 1000 stretching cycles and the capacitance change was recorded, and as can be seen from the graph, the sensor had good reproducibility even after undergoing multiple stretching.
The above description is illustrative of the invention and is not intended to be limiting, but is to be construed as being included within the spirit and scope of the invention.
Claims (10)
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| CN117968895A (en) * | 2024-02-01 | 2024-05-03 | 中国科学院苏州纳米技术与纳米仿生研究所 | MXene-based electrode and preparation method, capacitive pressure sensor and manufacturing method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114112119A (en) * | 2021-11-19 | 2022-03-01 | 河北工业大学 | Microstructured touch sensor based on pseudo-capacitance principle and preparation method thereof |
| CN117968895A (en) * | 2024-02-01 | 2024-05-03 | 中国科学院苏州纳米技术与纳米仿生研究所 | MXene-based electrode and preparation method, capacitive pressure sensor and manufacturing method |
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