A flexible all-solid-state N-type supercapacitor diode, a preparation method and application thereof

Abstract

The present application relates to a kind of flexible all-solid-state N type supercapacitor diode and its preparation method and application.The N type supercapacitor diode (N-CAPode) is characterized in that oxygen defect intercalation molybdenum oxide is used as working electrode, activated carbon is used as counter electrode, carbon nanotube film is used as current collector, polyvinyl alcohol / phosphoric acid (or perchloric acid, or sulfuric acid) hydrogel is used as electrolyte.Benefiting from the unique structure of molybdenum oxide and the charge double ion sieve effect, the prepared N-CAPode has the characteristics of storing charge in the negative bias direction, not only shows high specific capacitance, but also shows excellent diode rectification characteristics.In addition, the use of polymer gel electrolyte endows the N type supercapacitor diode with excellent electrochemical performance and rectification characteristics during repeated bending, even folding.Based on the all-solid-state N-CAPode, integrated device integrating energy storage and logic control is constructed.

Description

Technical Field

[0001] The present invention relates to the technical field of supercapacitors and ion diodes, and in particular to a flexible all-solid-state N-type supercapacitor diode and a preparation method and application thereof. Background Art

[0002] With the rapid development of flexible portable electronic devices such as smart sensors, human-computer interaction and brain-computer interfaces, there is an urgent need to develop highly integrated multifunctional devices. In most electronic devices, energy storage devices and diode-based logic circuits are indispensable, but they are usually independent of each other. Supercapacitors, as an important energy storage device, usually store electrical energy through electrostatic interactions between electrode interfaces and electrolyte ions or Faraday redox reactions. They have ultra-high power density and ultra-long cycle life and are widely used in high-power energy supply in electronic devices. At the same time, diodes allow current to pass in a specific direction and are indispensable building blocks for current rectification, switches, transistors, logic circuits, etc. Therefore, energy storage devices with diode characteristics, as units for building logic circuits, are of great significance to the integration and miniaturization of electronic devices.

[0003] In 2019, Kaskel [1] and colleagues first proposed a new type of supercapacitor diode (CAPode), which combines the unidirectional conduction characteristics of a diode and the energy storage characteristics of a supercapacitor. The first generation of CAPode was achieved by designing the pore sizes of microporous and mesoporous carbon materials as positive and negative electrodes, respectively. During the charging and discharging process, only anions smaller than the pore size of the microporous carbon can be absorbed into the microporous carbon, while cations of larger sizes are blocked. Therefore, the CAPode can only be charged unidirectionally in one polarization direction (the so-called open or chargeable direction, corresponding to the forward bias direction of a traditional diode), but can hardly store electrical energy in the reverse polarization (also called blocked or non-chargeable direction, corresponding to the reverse bias direction of the diode), thereby providing a current rectification function similar to a semiconductor diode. Accordingly, a CAPode that exhibits capacitive behavior in the positive potential range and no capacitive response in the negative potential region is defined as a P-CAPode. In contrast, an N-CAPode has high capacitance in the negative potential range and almost no capacitive response in the positive potential range. Recently, Yan [2] A new ion control strategy was reported to construct a CAPode with adjustable bias direction. Polyionic liquid was used as the electrolyte, and the blocking effect of electrode materials on large-sized polyanions or polycations was utilized to achieve the selective storage of cations or anions, and successfully constructed p-type and n-type CAPodes. Subsequently, Yan [3]The team also developed a pseudocapacitive diode based on the ion-selective surface redox reaction effect of ZnCo2O4 electrodes in alkaline electrolyte solutions, enriching the types of CAPodes. In addition, CAPodes based on the ion screening effect of pseudocapacitive materials (such as molybdenum oxide) have also been confirmed. It should be noted that almost all reported CAPodes are built based on liquid electrolyte systems, which have the risk of leakage during preparation and use, leading to performance degradation or even failure.

[0004] Therefore, in order to realize the practical application of CAPodes in various electronic devices, it is urgent to develop all-solid-state CAPodes with excellent flexibility.

[0005] The references are as follows:

[0006] [1] E. Zhang, N. Fulik, G.-P. Hao, H.-Y. Zhang, K. Kaneko, L. Borchardt, E. Brunner, S. Kaskel, An Asymmetric Supercapacitor–Diode (CAPode) for Unidirectional Energy Storage. Angew. Chem. Int. Ed. 2019, 58, 13060.

[0007] [2]JZFeng,Y.Wang,YTXu,HYMa,GWWang,P.Ma,Y.Tang,XBYan,Construction of Supercapacitor-Based Ionic Diodes with Adjustable BiasDirections by Using Poly(ionic liquid)Electrolytes.Adv.Mater.2021,33,2100887.

[0008] [3]P.Tang,W.Tan,F.Li,S.Xue,Y.Ma,P.Jing,Y.Liu,J.Zhu,X.Yan,APseudocapacitor Diode Based on Ion-Selective Surface RedoxEffect.Adv.Mater.2023,35,2209186. Summary of the Invention

[0009] The purpose of the present invention is to solve the problems and limitations of the above-mentioned existing supercapacitor diodes and provide a flexible all-solid-state N-type supercapacitor diode and its preparation method and application. The N-type supercapacitor diode (N-CAPode) is characterized by an oxygen defect intercalated molybdenum oxide (MoO x ) as the working electrode, activated carbon as the counter electrode, a carbon nanotube film as the current collector, and a polyvinyl alcohol / phosphoric acid (or perchloric acid, or sulfuric acid) hydrogel as the electrolyte. This N-type supercapacitor diode can be used in fields such as unidirectional energy storage and logic circuits. This N-type supercapacitor diode has negative bias direction energy storage, excellent rectification characteristics, good flexibility and stability, and can be used in fields such as unidirectional energy storage and logic circuits.

[0010] The purpose of the present invention can be achieved by the following technical solutions:

[0011] A flexible all-solid-state N-type supercapacitor diode, comprising a polyvinyl alcohol gel electrolyte layer, a current collector, a working electrode, and a counter electrode;

[0012] The working electrode is coated on the surface of the current collector to form a negative electrode sheet, and the counter electrode is coated on the surface of the current collector to form a positive electrode sheet;

[0013] The N-type supercapacitor diode is formed by stacking the positive electrode sheet, the polyvinyl alcohol gel electrolyte layer and the negative electrode sheet in this order.

[0014] Furthermore, the active material of the working electrode is oxygen-deficient intercalated molybdenum oxide (MoO x ), the active material of the counter electrode is activated carbon (AC), and the material of the current collector is a carbon nanotube film.

[0015] Furthermore, the mass loading of the molybdenum oxide on the carbon nanotube film is 1.0 to 10.0 mg cm –2 ;

[0016] The mass loading of the activated carbon on the carbon nanotube film is 1.0 to 10.0 mg cm –2 .

[0017] Furthermore, the polyvinyl alcohol gel electrolyte includes polyvinyl alcohol / phosphoric acid hydrogel electrolyte, polyvinyl alcohol / perchloric acid hydrogel electrolyte and polyvinyl alcohol / sulfuric acid hydrogel electrolyte.

[0018] Furthermore, the thickness of the negative electrode sheet is 25-50 microns.

[0019] The thickness of the positive electrode sheet is 75-150 microns.

[0020] The thickness of the polyvinyl alcohol gel electrolyte layer is 25-150 microns.

[0021] The present invention also provides a method for preparing a flexible all-solid-state N-type supercapacitor diode, and the specific preparation steps are as follows:

[0022] S1, preparation of molybdenum oxide nanobelts by a one-step hydrothermal method;

[0023] S2. Preparation of negative electrode molybdenum oxide / carbon nanotube composite electrode:

[0024] The molybdenum oxide nanobelts, carbon black (Super P), and binder prepared in step S1 are dispersed in a solvent to obtain a slurry, the slurry is coated on a carbon nanotube (CNT) film, and dried to obtain a negative electrode molybdenum oxide / carbon nanotube composite electrode;

[0025] S3. Preparation of positive activated carbon / carbon nanotube electrode:

[0026] Activated carbon powder, carbon black (Super P) and a binder are dispersed in a solvent to obtain a slurry, the slurry is coated on a carbon nanotube (CNT) film, and dried to obtain a positive activated carbon / carbon nanotube electrode;

[0027] S4. Preparation of polyvinyl alcohol gel electrolyte:

[0028] Adding polyvinyl alcohol (PVA) to deionized water, heating and stirring to form a polyvinyl alcohol aqueous solution, and then adding an acidic solution after cooling to obtain a polyvinyl alcohol gel electrolyte;

[0029] S5. Preparation of N-type supercapacitor diode:

[0030] The polyvinyl alcohol gel electrolyte obtained in step S4 is coated on the positive activated carbon / carbon nanotube electrode obtained in step S3, and after drying, a positive activated carbon / carbon nanotube electrode coated with polyvinyl alcohol gel electrolyte is obtained. The positive activated carbon / carbon nanotube electrode coated with polyvinyl alcohol gel electrolyte and the negative molybdenum oxide / carbon nanotube electrode are pressed together to assemble an N-type supercapacitor diode.

[0031] Furthermore, in step S1, the preparation method of the molybdenum oxide nanobelts is as follows:

[0032] S1-1, dissolving ammonium molybdate tetrahydrate and L(+)-tartaric acid in deionized water, stirring evenly, adding nitric acid, and continuing to stir to obtain a mixed solution;

[0033] S1-2. The mixed solution prepared in step S1-1 is subjected to a hydrothermal reaction. After the reaction is completed, a milky white precipitate is collected by centrifugation, washed multiple times, and then dried to obtain molybdenum oxide nanobelts.

[0034] Furthermore, in step S1-1, ammonium molybdate tetrahydrate: L(+)-tartaric acid: deionized water: nitric acid = 400-1000 mg: 200-500 mg: 20-100 mL: 0.5-5.0 mL;

[0035] The continued stirring time is 5 to 30 minutes.

[0036] Furthermore, in step S1-2, the hydrothermal reaction temperature is 100-200° C., and the hydrothermal reaction time is 12-24 hours;

[0037] The drying temperature is 50-100° C., and the drying time is 10-20 hours.

[0038] Furthermore, in step S2, the mass ratio of the molybdenum oxide powder, carbon black (Super P) and binder is 8:1:1.

[0039] Furthermore, in step S3, the mass ratio of the activated carbon powder, carbon black (Super P) and binder is 8:1:1.

[0040] Furthermore, in step S2 and step S3, the adhesive is polyvinylidene fluoride (PVDF), and the solvent is N-methyl-2-pyrrolidone (NMP);

[0041] The slurry is formed by stirring for 6 to 12 hours;

[0042] The drying temperature is 50-100° C., and the drying time is 10-20 hours.

[0043] Furthermore, in step S4, polyvinyl alcohol (PVA): deionized water: acidic solution = 0.5-5.0 g: 5-10 mL: 50-500 μL;

[0044] The stirring temperature is 50-100° C., and the stirring time is 1-12 hours;

[0045] The acidic solution includes phosphoric acid, perchloric acid and sulfuric acid.

[0046] Furthermore, in step S5, the amount of the polyvinyl alcohol gel electrolyte used on each positive activated carbon / carbon nanotube electrode is 30 to 100 μL.

[0047] In addition, the present invention also provides an application of a flexible all-solid-state N-type supercapacitor diode in unidirectional energy storage and logic circuits.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] (1) High rectification capability: The N-CAPode of the present invention has excellent rectification characteristics due to the unique structure of molybdenum oxide and the double ion screening effect of charge. The rectification ratio I(RR I ) up to 14.62, rectification ratio II (RR II ) as high as 96.18%. In the negative voltage range (–0.95 to 0V), small hydrogen ions can rapidly intercalate and deintercalate between the molybdenum oxide layers, generating a high redox current. In the positive voltage range (0 to +0.95V), however, due to the larger size of phosphate (sulfate, perchlorate, etc.) ions, they are difficult to adsorb on the molybdenum oxide electrode surface, resulting in a negligible response current, thus achieving a highly efficient rectification effect.

[0050] (2) Good electrochemical performance: The N-CAPode of the present invention has a good electrochemical performance at 0.5A g –1 At a current density of 1.5 GHz, the specific capacitance can reach 139.32 F g –1 Even at higher current densities (such as 7A g –1 ), it can still maintain a high specific capacitance (41.34F g-1), showing good rate performance.

[0051] (3) Excellent flexibility and stability: The electrochemical performance of the N-CAPode based on polyvinyl alcohol gel electrolyte remains almost unchanged at different bending angles; after 3000 consecutive bending cycles from 0° to 180°, the electrochemical and rectification performances do not change significantly, showing excellent flexibility and stability.

[0052] (4) Logic gate application: "AND" and "OR" logic gates were constructed. In the "AND" logic gate, when both N-CAPodes are negatively biased (-0.95V, denoted as "1"), the circuit is turned on and outputs a high current (denoted as "on"); when both N-CAPodes are positively biased (+0.95V, denoted as "0"), almost no current flows through the circuit (denoted as "off"). In the "OR" logic gate, as long as one of the N-CAPodes is negatively biased, the circuit is turned on, but the output current is lower than when both N-CAPodes are negatively biased. When both N-CAPodes are positively biased, almost no current flows through the circuit.

[0053] (5) The N-type supercapacitor diode (N-CAPode) of the present invention is characterized by the oxygen defect intercalation molybdenum oxide (MoO x ) as the working electrode, activated carbon as the counter electrode, carbon nanotube film as the current collector, and polyvinyl alcohol / phosphoric acid (or perchloric acid, or sulfuric acid) hydrogel as the electrolyte. Thanks to the unique structure and charge dual ion screening effect of molybdenum oxide, the prepared N-CAPode has the characteristic of storing charge in the negative bias direction, not only showing a high specific capacitance (139.32F g–1 ), showing excellent diode rectification characteristics (rectification ratio I is 14.62, rectification ratio II is 96.18%). In addition, the use of polymer gel electrolyte enables the N-type supercapacitor diode to maintain its excellent electrochemical properties and rectification characteristics during repeated bending and even folding (3000 times). Based on this all-solid-state N-CAPode, an integrated device integrating energy storage and logic control ("AND" and "OR") was constructed. The present invention provides an effective solution for the application of supercapacitor diodes in the fields of unidirectional energy storage and logic circuits, and is of great significance to the field of flexible and portable electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a scanning electron microscope photo of molybdenum oxide nanoribbons. The width of the nanoribbons is about 300nm and the length is about 10μm.

[0055] Figure 2 Transmission electron micrograph of MoO nanoribbons, showing mutually perpendicular lattice fringes, with lattice spacing corresponding to the (002) and (001) crystal planes of MoO nanoribbons, respectively.

[0056] Figure 3 This is the X-ray diffraction pattern of molybdenum oxide nanobelts, which has obvious diffraction peaks at the (020), (040), and (060) crystal planes, matching the molybdenum trioxide reference card (PDF#05–0508), confirming its monoclinic phase.

[0057] Figure 4 This is the Raman spectrum of molybdenum oxide nanoribbons. Typical fingerprint vibration modes appear at 291, 666, 819 and 996 cm-1, corresponding to the swing mode of the O=Mo=O double bond, the stretching mode of the triply coordinated oxygen (Mo-Os), the doubly coordinated oxygen (Mo-Oa) and the terminal oxygen (Mo=Ot), respectively.

[0058] Figure 5 This is the full X-ray photoelectron spectrum of molybdenum oxide nanobelts, showing typical peaks of Mo 3p, Mo 3d and O1s.

[0059] Figure 6 The O1s XPS spectrum of MoO nanoribbons indicates the presence of oxygen defects.

[0060] Figure 7 Mo 3d XPS spectrum of MoO nanoribbons, mainly composed of Mo 6+ ions (90.11%) and a small amount of Mo 5+ ions (9.89%).

[0061] Figure 8The cyclic voltammogram curves of N-CAPode at different scan rates show a typical asymmetric shape. There is a pseudocapacitive redox peak in the negative voltage range, while the response current is small in the positive voltage range. When the scan rate increases, the shape of the cyclic voltammogram curve remains basically unchanged, the peak current increases linearly, and the threshold voltage is stable at 0V.

[0062] Figure 9 The constant current charge and discharge curves of N-CAPode at different current densities are quasi-triangular and have unidirectional charging behavior. The charging and discharging time in the chargeable direction (negative voltage range) is much longer than that in the blocking direction (positive voltage range), and almost all the capacity is contributed by the potential range of –0.95 to 0V.

[0063] Figure 10 For N–CAPode at 2A g –1 The cycling stability under the current density is good, and it can maintain 83% of the initial capacity and almost 100% of the initial Coulombic efficiency after 2000 cycles.

[0064] Figure 11 The cyclic voltammetry curves of N-CAPode in different electrolytes (polyvinyl alcohol / phosphoric acid, polyvinyl alcohol / lithium chloride, polyvinyl alcohol / potassium hydroxide) show that polyvinyl alcohol / phosphoric acid electrolyte can provide higher response current and rectification performance than other commonly used gel electrolytes.

[0065] Figure 12 Schematic diagram of the structure of flexible N-CAPode based on polyvinyl alcohol / phosphoric acid hydrogel electrolyte.

[0066] Figure 13 These are optical photographs of flexible supercapacitors at different bending angles, showing that the device has no obvious structural delamination or damage during the bending process, proving its good flexibility.

[0067] Figure 14 The scanning rate of N-CAPode is 20 mV s when the bending angle is from 0° to 180°. –1 The CV curves of the electrodes are almost completely overlapped, indicating that bending has little effect on their electrochemical performance.

[0068] Figure 15 The GCD curves of N-CAPode with a current density of 1Ag-1 when the bending angle is from 0° to 180° are also almost identical, further illustrating its electrochemical stability in the bent state.

[0069] Figure 16 Figure 2 shows the electrochemical impedance spectroscopy (EIS) curves of N-CAPode at different bending angles. Its resistance and ion diffusion capacity remain almost unchanged, which explains the reason for its stable performance in the bent state from the perspective of electrochemical impedance.

[0070] Figure 17 Figure 3 shows the CV curve of N-CAPode after bending from 0° to 180° and undergoing multiple cycles. It remains similar to the initial state after 3000 consecutive bending cycles, reflecting its excellent cyclic bending stability.

[0071] Figure 18 The GCD curves of N-CAPode after bending to 180° and undergoing different cycle times are consistent with the CV curves, which once again proves the stability of its electrochemical performance during repeated bending.

[0072] Figure 19 The EIS curves of N-CAPode after being bent to 180° and undergoing different numbers of cycles further show that after multiple bending cycles, its electrochemical impedance characteristics remain basically unchanged and its internal structure is stable.

[0073] Figure 20 The chronoamperometric (CA) curves of the N-CAPode at a ±0.95V bias voltage show a high instantaneous current of 20.22mA at negative bias, but only 1.86mA at positive bias, demonstrating its excellent rectification performance. Furthermore, the current response decreases more rapidly at positive bias, which is attributed to ion surface adsorption rather than an intercalation / deintercalation mechanism.

[0074] Figure 21 Figure 3 is the curve of the N-CAPode rectification ratio changing with time. The rectification ratio reaches a maximum value of 33.6 at 2.2s, then gradually decays and stabilizes at 15.7. It is different from the rectification characteristics of semiconductor diodes and has its own unique change law.

[0075] Figure 22 Figure 3 is the current-time curve of N-CAPode under ±0.95V alternating voltage (applied for 1s each time). After multiple cycles, the final current under negative bias voltage is about four times that under positive bias voltage, further demonstrating its unidirectional charging capability.

[0076] Figure 23 The current-voltage (I-V) curve of the N-CAPode shows the on- and off-states of the device under different bias voltages. For example, at a negative bias of –0.95V, the charging current is –22.8mA, which is in the on-state (“on”); at a positive bias of +0.95V, the charging current is 1.9mA, which is in the off-state (“off”), indicating that it has excellent unidirectional charging capability.

[0077] Figure 24 This is a schematic diagram of the "AND" logic gate circuit, which consists of two N-CAPodes connected in series.

[0078] Figure 25The output signal diagram of the "AND" logic gate shows the actual output current under different input conditions, which is consistent with the truth table.

[0079] Figure 26 This is a schematic diagram of the "OR" logic gate circuit.

[0080] Figure 27 This is the output signal diagram of the "OR" logic gate. The experimental data shows the change of its output current under different inputs, which is consistent with the truth table.

[0081] Figure 28 Cycling stability of N-CAPode in different acidic electrolytes at a current density of 2Ag –1 After 2000 cycles, 71.49% of the initial capacity and almost 100% of the initial Coulombic efficiency were maintained in polyvinyl alcohol / sulfuric acid, and 62.28% of the initial capacity and almost 100% of the initial Coulombic efficiency were maintained in polyvinyl alcohol / perchloric acid. DETAILED DESCRIPTION

[0082] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0083] A method for preparing a flexible all-solid-state N-type supercapacitor diode, the specific preparation steps are as follows:

[0084] (1) MoO nanoribbons rich in oxygen vacancies were prepared by a one-step hydrothermal method, the specific steps being:

[0085] Dissolve 400-1000 mg of ammonium molybdate tetrahydrate and 200-500 mg of L(+)-tartaric acid in 20-100 mL of deionized water, stir thoroughly, then add 0.5-5.0 mL of nitric acid, and continue stirring for 5-30 minutes to obtain a mixed solution.

[0086] The mixed solution was then transferred to a Teflon-lined stainless steel autoclave and maintained at 100-200°C for 12-24 hours. The milky white precipitate was collected by centrifugation, washed three times with ethanol and deionized water, and dried overnight in a vacuum oven at 50-100°C to obtain molybdenum oxide nanobelts for later use.

[0087] (2) Preparation of negative electrode molybdenum oxide / carbon nanotube composite electrode:

[0088] The molybdenum oxide nanobelts, carbon black and polyvinylidene fluoride binder prepared in step (1) are dispersed in N-methyl-2-pyrrolidone in a mass ratio of 8:1:1, and stirred for 6 to 12 hours to form a uniform slurry.

[0089] The slurry was coated on the carbon nanotube film and dried in a vacuum oven at 50-100°C overnight to obtain a negative molybdenum oxide / carbon nanotube composite electrode. The mass loading of molybdenum oxide on the carbon nanotube film was 1.0-10.0 mg cm –2 .

[0090] (3) Preparation of positive activated carbon / carbon nanotube electrode:

[0091] Activated carbon powder, carbon black, and polyvinylidene fluoride binder were dispersed in N-methyl-2-pyrrolidone at a mass ratio of 8:1:1 and stirred for 6-12 hours to form a uniform slurry. The slurry was then doctor-coated on a carbon nanotube film and dried overnight in a vacuum oven at 50-100°C to obtain a positive activated carbon / carbon nanotube electrode. The mass loading of activated carbon on the carbon nanotube film was 1.0-10.0 mg cm –2 .

[0092] (4) Preparation of polyvinyl alcohol gel electrolyte:

[0093] Add 0.5-5.0 g of polyvinyl alcohol to 5-10 mL of deionized water, stir, and heat at 60-100°C for 1-12 hours to form a transparent polyvinyl alcohol aqueous solution. After the polyvinyl alcohol aqueous solution cools to room temperature, add 50-500 μL of phosphoric acid (or perchloric acid, or sulfuric acid) and stir to obtain a polyvinyl alcohol gel electrolyte (polyvinyl alcohol / phosphoric acid hydrogel electrolyte, polyvinyl alcohol / perchloric acid hydrogel electrolyte, or polyvinyl alcohol / sulfuric acid hydrogel electrolyte).

[0094] (5) Assembly of N-CAPode: 10–100 μL of polyvinyl alcohol gel electrolyte was coated on a positive activated carbon / carbon nanotube electrode, which was then placed in a vacuum oven to allow the electrolyte to fully permeate the electrode. The positive activated carbon / carbon nanotube electrode coated with polyvinyl alcohol gel electrolyte was pressed together with the negative molybdenum oxide / carbon nanotube electrode to assemble the N-CAPode.

[0095] The following describes some embodiments of the present invention in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0096] Example 1

[0097] See also Figure 12 This embodiment provides a method for preparing a flexible all-solid-state N-type supercapacitor diode. The specific preparation steps are as follows:

[0098] (1) Preparation of molybdenum oxide nanobelts:

[0099] 825 mg of ammonium molybdate tetrahydrate and 400 mg of L(+)-tartaric acid were weighed and placed in 50 mL of deionized water. The mixture was magnetically stirred for 30 min to fully dissolve the solute. Subsequently, 1 mL of nitric acid was added and stirring was continued for 10 min to obtain a mixed solution.

[0100] The mixed solution was transferred to a Teflon-lined stainless steel autoclave, which was sealed securely and then placed in an oven at 180°C for 24 hours. After the reaction was complete, the autoclave was removed and allowed to cool to room temperature. The resulting milky white precipitate was collected by centrifugation (8000 rpm). The precipitate was washed three times with ethanol and then deionized water to remove impurities. Finally, the precipitate was transferred to a vacuum oven and dried at 60°C for 24 hours to obtain molybdenum oxide nanobelts for later use.

[0101] (2) Preparation of negative electrode molybdenum oxide / carbon nanotube composite electrode:

[0102] The molybdenum oxide nanobelt powder, carbon black and polyvinylidene fluoride binder prepared in step (1) were weighed in a mass ratio of 8:1:1, dispersed in N-methyl-2-pyrrolidone, and magnetically stirred for 8 h to form a uniform slurry.

[0103] The slurry was evenly coated on the carbon nanotube film with a blade thickness of 100 μm. After the coating was completed, it was placed in a 60°C oven and dried for 12 hours to obtain a negative molybdenum oxide / carbon nanotube composite electrode, in which the mass loading of molybdenum oxide on the carbon nanotube film was 1.5 mg cm –2 .

[0104] (3) Preparation of positive activated carbon / carbon nanotube electrode:

[0105] Similarly, activated carbon powder, carbon black and polyvinylidene fluoride binder were weighed in a mass ratio of 8:1:1, placed in N-methyl-2-pyrrolidone and stirred for 8 h to form a uniform slurry.

[0106] The slurry was coated on the carbon nanotube film using a 300 μm thick doctor blade and then dried in an oven at 60 °C for 12 h to obtain a positive activated carbon / carbon nanotube electrode (AC / CNTs film electrode). The mass loading of AC in the AC / CNTs film was 4 mg cm –2 .

[0107] (4) Preparation of polyvinyl alcohol gel electrolyte:

[0108] Weigh 1g of polyvinyl alcohol solution and add it to 10mL of deionized water. Heat the mixture to 80°C with stirring for 2 hours until a transparent solution forms. After the solution cools to room temperature, accurately weigh 120μL of phosphoric acid and stir thoroughly with a magnetic stirrer to obtain a polyvinyl alcohol / phosphoric acid hydrogel electrolyte.

[0109] (5) Assembly of N-CAPode:

[0110] Take a prepared positive activated carbon / carbon nanotube electrode and evenly coat it with 60 μL of polyvinyl alcohol / phosphoric acid hydrogel electrolyte. Place the coated positive activated carbon / carbon nanotube electrode in a vacuum oven and maintain the vacuum for 10-30 minutes to allow the electrolyte to fully penetrate the electrode. Then, align and press the coated positive activated carbon / carbon nanotube electrode with the negative molybdenum oxide / carbon nanotube electrode to form an N-CAPode.

[0111] Performance Testing

[0112] The molybdenum oxide nanobelts prepared in step (1) of Example 1 were observed by scanning electron microscopy using a high-resolution field emission scanning electron microscope at an accelerating voltage of 5 kV to obtain their microscopic morphological characteristics, such as the width, length, surface morphology and other microstructural information of the molybdenum oxide nanobelts. Figure 1 This is a scanning electron microscope image of molybdenum oxide nanoribbons, showing its nanoribbon structure, with a width of about 300nm and a length of about 10μm.

[0113] The molybdenum oxide nanobelts prepared in step (1) of Example 1 were analyzed for their microstructure using a high-resolution transmission electron microscope. The crystal structure, interplanar spacing, and presence of defects were determined by observing lattice fringes and selected area electron diffraction patterns. Figure 2 Mutually perpendicular lattice fringes were observed, and the lattice spacing corresponded to the (002) and (001) crystal planes of the MoO nanoribbons, respectively.

[0114] The molybdenum oxide nanobelts prepared in step (1) of Example 1 were subjected to phase analysis using an X-ray diffractometer. Cu-Kα radiation was used as the light source, and the scanning range was 10°–60°. The crystal structure type was determined by comparing the position and intensity of the diffraction peaks with those of the standard card. Figure 3 The (020), (040) and (060) crystal planes have obvious diffraction peaks, which match the molybdenum trioxide reference card (PDF#05–0508), confirming its monoclinic phase. Raman spectrometer was used to test the molybdenum oxide nanobelts with a laser wavelength of 514 nm and a scanning range of 100-1200 cm-1. Figure 4The position and intensity of the Raman peaks in the sample were used to determine the vibration modes of the chemical bonds. For example, typical fingerprint vibration modes appeared at 291, 666, 819, and 996 cm-1, corresponding to the swing mode of the O=Mo=O double bond, the stretching mode of the triply coordinated oxygen (Mo-Os), the doubly coordinated oxygen (Mo-Oa), and the terminal oxygen (Mo=Ot), respectively. The elemental analysis and valence state of the molybdenum oxide nanoribbons were studied by X-ray photoelectron spectroscopy, and the types of elements contained were determined by analyzing the full spectrum. Figure 5 The typical peaks of Mo 3p, Mo 3d and O1s appeared in the sample. Further analysis of O1s( Figure 6 ) and Mo 3d ( Figure 7 ) to determine the valence state of Mo and the oxygen deficiency situation, such as the molybdenum oxide nanobelts are mainly composed of Mo 6+ ions (90.11%) and a small amount of Mo 5+ ions (9.89%), and the O 1s XPS spectrum showed the presence of oxygen defects.

[0115] Cyclic voltammetry test: Cyclic voltammetry test was performed on the N-CAPode prepared in Example 1 at different scan rates (e.g., 10–60 mV·s-1) using an electrochemical workstation. The scan voltage range was from –0.95 to +0.95 V ( Figure 8 ). By analyzing the shape of the cyclic voltammetry curve, the position of the redox peak and the current magnitude, its capacitance behavior and rectification characteristics are studied. For example, the cyclic voltammetry curve of N-CAPode shows a typical asymmetric shape, with a pseudocapacitive redox peak in the negative voltage range and a small response current in the positive voltage range. When the scan rate increases, the shape of the cyclic voltammetry curve remains basically unchanged, the peak current increases linearly, and the threshold voltage stabilizes at about 0V. According to the cyclic voltammetry curve, the rectification ratio I(RR I ) can be calculated by the following formula:

[0116]

[0117] Where ΔI1 and ΔI2 are the current difference between the redox peaks in the on-voltage region (i.e., –0.95–0 V) and the current difference in the blocking voltage region (i.e., the electrochemical double layer adsorption region, 0–0.95 V), respectively. –1 Time RR I Reaching a maximum value of 14.62 at 60mV s –1 It was still as high as 10.82.

[0118] Constant current charge and discharge test: at different current densities (such as 0.5–7.0 A g –1) was used to perform constant current charge and discharge tests on the N-CAPode prepared in Example 1, with a voltage range of -0.95 to +0.95 V ( Figure 9 ). According to the constant current charge and discharge curve, its specific capacitance, rectification ratio and other parameters are calculated, and its rate performance, energy storage capacity and rectification ability are analyzed. For example, the constant current charge and discharge curve of N-CAPode is quasi-triangular, with unidirectional charging behavior. The charging and discharging time in the rechargeable direction (negative voltage range) is much longer than that in the blocking direction (positive voltage range), and almost all the capacity is contributed by the potential range of -0.95 to 0V. According to the constant current charge and discharge curve, the mass specific capacity (C) and rectification ratio II (RR) of N-CAPode are II ) can be calculated by the following formula:

[0119]

[0120]

[0121] Where I, Δt, ΔU, m, C1 and C2 are discharge current, discharge time, voltage window, active material mass of the electrode, capacitance in the on-voltage region (i.e., redox region, i.e., –0.95 to 0 V) ​​and capacitance in the blocking voltage window (i.e., 0 to +0.95 V), respectively. –1 The specific capacitance is 139.32F g –1 , RR II As high as 96.18.

[0122] Electrochemical impedance spectroscopy (EIS) was performed on the N-CAPode prepared in Example 1 within a frequency range of 0.01 to 100 kHz. The charge transfer and ion diffusion processes were investigated by analyzing the semicircle diameter in the high-frequency region and the slope of the line in the low-frequency region of the EIS curve.

[0123] Flexibility test: The N-CAPode prepared in Example 1 was bent to different angles (such as 0°, 30°, 60°, 90°, 120°, 150°, and 180°), and cyclic voltammetry, constant current charge-discharge, and electrochemical impedance spectroscopy tests were performed to observe the changes in its electrochemical performance during the bending process. Figure 13 As shown in the figure, the optical photographs of the flexible supercapacitor at different bending angles show that the device has no obvious structural delamination or damage during the bending process, proving its good flexibility. For example, when the bending angle of N-CAPode is from 0° to 180°, the scan rate is 20mV s –1 The cyclic voltammetry curves of Figure 14 ), the current density is 1Ag -1 The constant current charge and discharge curves of Figure 15), indicating that bending has little effect on its electrochemical performance, and the electrochemical impedance spectroscopy curve shows that its electrochemical impedance characteristics remain basically unchanged ( Figure 16 ), proving its good flexibility.

[0124] Stability test: at 2A g –1 The N-CAPode prepared in Example 1 was subjected to 2000 charge-discharge cycle tests at a high current density of , and the changes in its capacity and coulombic efficiency were recorded to evaluate its cycle stability. Figure 10 After 2000 cycles, N-CAPode can still maintain 83% of its initial capacity and almost 100% of its initial Coulombic efficiency. Figure 17-19 After the N-CAPode was bent to 180° for 3000 consecutive bending cycles, it was subjected to cyclic voltammogram testing again to observe its performance changes. The results showed that there was no obvious change in its electrochemical and rectification performance, reflecting its excellent stability.

[0125] Rectification performance test: To evaluate the performance of MoO x The feasibility of the N-CAPode in electronic circuits and logic gates was investigated by standard electrochemical voltammetry to investigate its charge rectification capability. Figure 20 The chronoamperometric curve of N-CAPode under ±0.95V bias voltage is shown in Figure 2. At a negative bias voltage of -0.95V, the instantaneous current is as high as 20.22mA, while at a positive bias voltage of +0.95V, the instantaneous current is only 1.86mA, reflecting its good rectification characteristics. Moreover, under positive bias voltage, the positive bias current response decreases faster, which is due to its ion surface adsorption rather than insertion / deinsertion mechanism. Therefore, the rectification ratio between the response current of N-CAPode under negative bias and positive bias voltage reaches a maximum of 33.6 at 2.2s, and gradually decays and stabilizes at 15.7 after 600s. Figure 21 ), which is significantly different from the rectification characteristics of semiconductor diodes (which have a constant rectification ratio after applying a bias voltage). Figure 22 The current-time curve of N-CAPode under ±0.95V alternating voltage (applied for 1s each time) is shown. After multiple cycles, the final current under negative bias voltage is about four times that under positive bias, further demonstrating its unidirectional charging capability. Figure 23 The current-voltage (I-V) curve of N-CAPode shows its "ON" and "OFF" states under different bias voltages. For example, at a negative bias voltage of -0.95V, the charging current is -22.8mA, which is in the on state; at a positive bias voltage of +0.95V, the charging current is 1.9mA, which is in the blocking state, indicating that N-CAPode has excellent unidirectional conductivity.

[0126] Construct AND and OR logic gates: Follow Figure 24 and Figure 26 The circuit diagram shown uses two identical N-CAPodes to construct AND and OR logic gate circuits respectively, and connects wires and loads (such as LEDs).

[0127] Test logic operation: Apply different input voltage combinations to the logic gate circuit through the electrochemical workstation, record the output current or the working status of the load (such as the on and off of the LED), and compare and verify with the theoretical truth table.

[0128] like Figure 25 As shown in Table 1, in the AND logic gate, when negative bias is applied to both N-CAPodes, the circuit is turned on, high current is output, and the LED lights up; when positive voltage is applied to both N-CAPodes, almost no current flows through the circuit and the LED goes out.

[0129] like Figure 27 As shown in Table 2, in the OR logic gate, as long as one of the N-CAPodes is negatively biased, the circuit is turned on, but the output current is lower than when both N-CAPodes are negatively biased, and the LED lights up. When both N-CAPodes are positively biased, almost no current flows through the circuit and the LED turns off, thus verifying its logic gate function.

[0130] Table 1 Truth table of the AND logic gate

[0131]

[0132] Table 1 shows the output states for different input voltage combinations. When both N-CAPodes are negatively biased (–0.95V, denoted as “1”), the output current is high (“on”). When both N-CAPodes are positively biased (+0.95V, denoted as “0”), or one is positive and the other negative, the output current is low or almost no (“off”).

[0133] Table 2 Truth table of the "OR" logic gate

[0134]

[0135] Table 2 specifies the logical relationship between the input and output. As long as one of the N-CAPodes is negatively biased, the output is in the on state, but the current is lower than when both are negatively biased. When both are positively biased, the output is in the off state.

[0136] Comparative Example 1

[0137] This comparative example provides a method for preparing a capacitor diode. Except for using lithium chloride to prepare a polyvinyl alcohol / lithium chloride hydrogel electrolyte in step (4), the rest of the steps are the same as those in Example 1.

[0138] Comparative Example 2

[0139] This comparative example provides a method for preparing a capacitor diode. Except for using potassium hydroxide to prepare a polyvinyl alcohol / potassium hydroxide hydrogel electrolyte in step (4), the rest of the steps are the same as those in Example 1.

[0140] Performance Testing

[0141] like Figure 8 As shown, the cyclic voltammetry curves of the N-CAPode prepared in Example 1 and the capacitor diode prepared in Comparative Examples 1-2 in different electrolytes (polyvinyl alcohol / phosphoric acid, polyvinyl alcohol / lithium chloride, polyvinyl alcohol / potassium hydroxide) indicate that the polyvinyl alcohol / phosphoric acid electrolyte can provide higher response current and rectification performance than other commonly used gel electrolytes.

[0142] Example 2

[0143] This embodiment provides a method for preparing a flexible all-solid-state N-type supercapacitor diode. The specific preparation steps are as follows:

[0144] (1) Preparation of molybdenum oxide nanobelts:

[0145] The preparation steps of step (1) of Example 1 for preparing molybdenum oxide nanobelts were repeated to ensure the consistency and repeatability of the materials.

[0146] (2) Preparation of negative electrode molybdenum oxide / carbon nanotube composite electrode:

[0147] The negative electrode molybdenum oxide / carbon nanotube composite electrode was prepared according to the method of step (2) in Example 1, but the scraper thickness was changed to 150 μm to adjust the loading of molybdenum oxide on the carbon nanotubes to 2.0 mg cm –2 , the effects of different loading amounts on electrode performance were studied, with other conditions remaining unchanged.

[0148] (3) Preparation of positive activated carbon / carbon nanotube electrode:

[0149] The positive activated carbon / carbon nanotube electrode was prepared in the same manner as in step (3) of Example 1, except that the scraper thickness was changed to 400 μm to adjust the activated carbon mass loading to 5.0 mg cm –2 , the effect of the loading amount of active materials on the electrode performance was explored, and the other steps and conditions remained unchanged.

[0150] (4) Preparation of polyvinyl alcohol gel electrolyte:

[0151] The electrolyte was prepared by the method of step (4) in Example 1, but sulfuric acid was used instead of phosphoric acid to prepare polyvinyl alcohol / sulfuric acid hydrogel electrolyte to explore the effect of different electrolytes on electrode performance.

[0152] (5) Assembly of N-CAPode:

[0153] According to the assembly method of step (5) in Example 1, the prepared electrodes and electrolytes were assembled into N-CAPode for subsequent performance testing and analysis.

[0154] Example 3

[0155] This embodiment provides a method for preparing a flexible all-solid-state N-type supercapacitor diode. The specific preparation steps are as follows:

[0156] (1) Preparation of molybdenum oxide nanobelts:

[0157] The preparation steps of step (1) of Example 1 for preparing molybdenum oxide nanobelts were repeated to ensure the consistency and repeatability of the materials.

[0158] (2) Preparation of negative electrode molybdenum oxide / carbon nanotube composite electrode:

[0159] The negative electrode molybdenum oxide / carbon nanotube composite electrode was prepared according to the method of step (2) in Example 1, but the scraper thickness was changed to 150 μm to adjust the loading of molybdenum oxide on the carbon nanotubes to 2.0 mg cm –2 , the effects of different loading amounts on electrode performance were studied, with other conditions remaining unchanged.

[0160] (3) Preparation of positive activated carbon / carbon nanotube electrode:

[0161] The positive activated carbon / carbon nanotube electrode was prepared in the same manner as in step (3) of Example 1, except that the scraper thickness was changed to 400 μm to adjust the activated carbon mass loading to 5.0 mg cm –2 , the effect of the loading amount of active materials on the electrode performance was explored, and the other steps and conditions remained unchanged.

[0162] (4) Preparation of polyvinyl alcohol gel electrolyte:

[0163] The electrolyte was prepared by the method of step (4) in Example 1, but perchloric acid was used instead of phosphoric acid to prepare polyvinyl alcohol / perchloric acid hydrogel electrolyte to explore the effect of different electrolytes on electrode performance.

[0164] (5) Assembly of N-CAPode:

[0165] According to the assembly method of step (5) in Example 1, the prepared electrodes and electrolytes were assembled into N-CAPode for subsequent performance testing and analysis.

[0166] Performance testing and analysis

[0167] The N-CAPodes prepared in Examples 2 and 3 were subjected to the same structural characterization, electrochemical performance tests, flexibility and stability tests, and logic gate function tests as in Example 1. By comparing the performance data of N-CAPodes with different molybdenum oxide loadings, different activated carbon mass loadings, and different electrolytes, the influence of electrode structural parameters on device performance was analyzed. For example, Figure 28 After 2000 cycles, the N-CAPode retained 71.49% of its initial capacity and nearly 100% of its initial Coulombic efficiency in polyvinyl alcohol / sulfuric acid, and 62.28% of its initial capacity and nearly 100% of its initial Coulombic efficiency in polyvinyl alcohol / perchloric acid. However, as the acidity in the electrolyte increases, it may corrode the molybdenum oxide electrode material, resulting in low cycling stability. Based on these test results, the electrode preparation process parameters were further optimized to improve the performance of the N-CAPode.

[0168] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A flexible all-solid-state N-type supercapacitor diode, characterized in that: The N-type supercapacitor diode includes a polyvinyl alcohol gel electrolyte layer, a current collector, a working electrode and a counter electrode; The working electrode is coated on the surface of the current collector to form a negative electrode sheet, and the counter electrode is coated on the surface of the current collector to form a positive electrode sheet; An N-type supercapacitor diode is formed by stacking the positive electrode sheet, the polyvinyl alcohol gel electrolyte layer, and the negative electrode sheet in this order; The active material of the working electrode is oxygen-deficient intercalated molybdenum oxide, the active material of the counter electrode is activated carbon, and the material of the current collector is a carbon nanotube film; The polyvinyl alcohol gel electrolyte includes polyvinyl alcohol / phosphoric acid hydrogel electrolyte, polyvinyl alcohol / perchloric acid hydrogel electrolyte and polyvinyl alcohol / sulfuric acid hydrogel electrolyte.

2. The flexible all-solid-state N-type supercapacitor diode according to claim 1, characterized in that: The mass loading of molybdenum oxide on the carbon nanotube film is 1.0-10.0 mg cm –2 ; The mass loading of the activated carbon on the carbon nanotube film is 1.0-10.0 mg cm –2 .

3. The flexible all-solid-state N-type supercapacitor diode according to claim 1, characterized in that: The thickness of the negative electrode sheet is 25-50 microns. The thickness of the positive electrode sheet is 75-150 microns. The thickness of the polyvinyl alcohol gel electrolyte layer is 25-150 microns.

4. A method for preparing a flexible all-solid-state N-type supercapacitor diode according to any one of claims 1 to 3, characterized in that: The specific preparation steps are as follows: S1, preparation of molybdenum oxide nanobelts by a one-step hydrothermal method; S2. Preparation of negative electrode molybdenum oxide / carbon nanotube composite electrode: Dispersing the molybdenum oxide nanobelts, carbon black, and binder prepared in step S1 in a solvent to obtain a slurry, coating the slurry on the carbon nanotube film, and drying to obtain a negative electrode molybdenum oxide / carbon nanotube composite electrode; S3. Preparation of positive activated carbon / carbon nanotube electrode: Dispersing activated carbon powder, carbon black and a binder in a solvent to obtain a slurry, coating the slurry on a carbon nanotube film, and drying to obtain a positive activated carbon / carbon nanotube electrode; S4. Preparation of polyvinyl alcohol gel electrolyte: Adding polyvinyl alcohol to deionized water, heating and stirring to form a polyvinyl alcohol aqueous solution, and adding an acidic solution after cooling to obtain a polyvinyl alcohol gel electrolyte; S5. Preparation of N-type supercapacitor diode: The polyvinyl alcohol gel electrolyte obtained in step S4 is coated on the positive activated carbon / carbon nanotube electrode obtained in step S3, and after drying, a positive activated carbon / carbon nanotube electrode coated with polyvinyl alcohol gel electrolyte is obtained. The positive activated carbon / carbon nanotube electrode coated with polyvinyl alcohol gel electrolyte and the negative molybdenum oxide / carbon nanotube electrode are pressed together to assemble an N-type supercapacitor diode.

5. The method for preparing a flexible all-solid-state N-type supercapacitor diode according to claim 4, characterized in that: In step S1, the preparation method of the molybdenum oxide nanobelt is as follows: S1-1, dissolving ammonium molybdate tetrahydrate and L(+)-tartaric acid in deionized water, stirring evenly, adding nitric acid, and continuing stirring to obtain a mixed solution; S1-2. The mixed solution prepared in step S1-1 is subjected to a hydrothermal reaction. After the reaction is completed, a milky white precipitate is collected by centrifugation, washed multiple times, and then dried to obtain molybdenum oxide nanobelts.

6. The method for preparing a flexible all-solid-state N-type supercapacitor diode according to claim 5, characterized in that: In step S1-1, ammonium molybdate tetrahydrate: L(+)-tartaric acid: deionized water: nitric acid = 400-1000 mg: 200-500 mg: 20-100 mL: 0.5-5.0 mL.

7. The method for preparing a flexible all-solid-state N-type supercapacitor diode according to claim 4, characterized in that: In step S2, the mass ratio of the molybdenum oxide nanobelts, carbon black and binder is 8:1:1; In step S3, the mass ratio of the activated carbon powder, carbon black and binder is 8:1:1; In step S2 and step S3, the adhesive is polyvinylidene fluoride, and the solvent is N-methyl-2-pyrrolidone.

8. The method for preparing a flexible all-solid-state N-type supercapacitor diode according to claim 4, characterized in that: In step S4, polyvinyl alcohol: deionized water: acidic solution = 0.5-5.0 g: 5-10 mL: 50-500 μL; The acidic solution includes phosphoric acid, perchloric acid and sulfuric acid; In step S5, the amount of the polyvinyl alcohol gel electrolyte used on each positive activated carbon / carbon nanotube electrode is 30-100 μL.

9. Application of the flexible all-solid-state N-type supercapacitor diode according to any one of claims 1 to 3 in unidirectional energy storage and logic circuits.

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