CN106098395B - A kind of manganese dioxide fiber electrode and its preparation method and application - Google Patents

Abstract

The invention discloses a manganese dioxide fiber electrode, which comprises a current collector and a manganese dioxide fiber active layer attached to the current collector; the manganese dioxide fiber is a fiber with a large length/diameter ratio; The manganese dioxide fiber electrode does not contain binder. The preparation method of the manganese dioxide fiber electrode comprises: directly electrochemically depositing a weakly crystalline manganese dioxide deposition layer on the current collector, or performing anodic oxidation on the current collector to prepare manganese dioxide shaping the porous manganese dioxide layer; performing hydrothermal treatment on the manganese dioxide layer, so that the manganese dioxide layer on the surface of the current collector undergoes recrystallization and oriented growth, and obtains the manganese dioxide fiber electrode of the present invention. The manganese dioxide fiber electrode of the invention can be used to prepare an electrochemical supercapacitor, and has the advantages of high overall energy density, small environmental impact, easy process control, energy saving, and the like.

Description

A kind of manganese dioxide fiber electrode and its preparation method and application

technical field

The invention relates to the technical field of electrochemistry, and more specifically relates to a manganese dioxide fiber electrode and its preparation method and application.

Background technique

Electrochemical supercapacitors (ES), also known as electrochemical capacitors (EC), or simply supercapacitors (supercapacitors, ultracapacitors), are new energy storage devices that have attracted widespread attention in recent years. Because this type of capacitor mainly relies on the electrochemical process on the interface between the electrode and the solution to store energy, its capacity is 20 to 200 times that of traditional capacitors, reaching farads or even thousands of farads; its power density is dozens of times higher than that of batteries , which can meet the needs of high power output such as electric vehicle start-up acceleration. Electrochemical supercapacitors have the advantages of high power density of conventional capacitors and high energy density of rechargeable batteries, and are considered to be an efficient and practical new energy storage element.

Although supercapacitors have the advantages of high power output performance and long cycle life, their energy density is significantly lower compared with batteries. In order to improve the performance of supercapacitors, that is, to increase the specific energy while maintaining its advantages such as high specific power, research around transition metal oxide electrodes with electric double layer capacitance and faradaic pseudocapacitive behavior has attracted much attention. Although RuO2 can not only achieve high-power charging and discharging, but also has a relatively high mass-to-energy ratio, due to resource constraints, the key problem faced by this material is the high cost of materials, so it is difficult to obtain commercial promotion. In order to seek cheap supercapacitor electrode materials, research on the preparation and electrochemical performance of transition metal oxide materials such as NiO, Co3O4, V2O5, and MnO2 has been carried out. Among many transition metal oxides, MnO2 has attracted much attention because of its rich resources and high theoretical specific capacitance, but the actual prepared materials have low specific capacitance. More importantly, it is used as an electrode material for high-power devices in The capacity retention rate during high-rate charging and discharging needs to be improved.

The usual way to prepare manganese dioxide electrodes for supercapacitors is to prepare MnO2 powder materials first, then prepare them into slurry with binders, etc., and then coat them on the current collector to form the final electrode, which is easy to cause electrode active materials and Poor contact between current collectors affects the charging and discharging performance of the electrode. In addition, since the added binder and the like are non-electroactive substances, it will inevitably reduce the energy density of the entire electrode. It is mentioned in many literatures that manganese dioxide can be deposited on the surface of the current collector directly by anodic oxidation of manganese sulfate solution or cathodic reduction of permanganate ions, and a binder-free manganese dioxide electrode can be obtained. The layer is generally dense, the contact area between the electrode and the electrolyte is small, the crystallinity of the material is not good, the electronic conductivity itself is poor, and it is not conducive to the mass transfer of charged ions inside the material crystal. The specific capacitance and rate performance of charging and discharging are not ideal. In order to increase the contact area between the electrode active material and the electrolyte during the working process of the capacitor, the current research hotspot in this field is to grow various metals, carbon nanotube arrays or graphene on the metal current collector, and then grow various metals, carbon nanotube arrays or graphene on the metal, carbon nanotubes, etc. Manganese dioxide is electrodeposited on the surface of tubes or graphene and used as supercapacitor electrodes, but because these methods only change the morphology of the current collector without changing the morphology and crystallinity of the deposited manganese dioxide itself, when the deposited manganese dioxide layer When the thickness is relatively thick, an electrode with high specific capacitance and capacity retention cannot be obtained. In addition, the process of growing carbon nanotubes or graphene on the metal surface is relatively complicated, the cost is high, and it is difficult to realize industrial application.

Contents of the invention

(1) Technical problems to be solved

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, provide a manganese dioxide electrode with high overall energy density, good rate performance, and simple preparation process, and also provide the preparation method and application of the manganese dioxide electrode accordingly

(2) Technical solution

In order to solve the above technical problems, the present invention provides a manganese dioxide fiber electrode, the manganese dioxide fiber electrode includes a current collector and a manganese dioxide fiber active layer attached to the current collector; the manganese dioxide fiber is a long /diameter ratio fiber; no binder is contained in the manganese dioxide fiber electrode.

Preferably, the manganese dioxide fibers have a diameter of 5-50 nm and a length of 5-50 μm.

Preferably, the manganese dioxide fibers themselves grow on the current collector and interweave to form a stable active material layer.

Preferably, the manganese dioxide fiber active layer is a manganese dioxide deposition layer formed on the surface of the current collector by electrolyzing a soluble manganese salt solution or reducing permanganate by the cathode, or depositing a manganese coating on the surface of the current collector before performing the anode Oxidize the resulting manganese dioxide layer.

Preferably, the current collector is made of metal or nonmetal with good electrical conductivity and thermal stability, including stainless steel sheet, stainless steel mesh, nickel sheet, nickel foam and graphite sheet, carbon paper, and carbon cloth.

The present invention also provides the preparation method of described manganese dioxide fiber electrode, and this method comprises the following steps:

(1) Electrochemical deposition of weakly crystalline manganese dioxide deposition layer directly on the current collector, or cathode electrodeposition of metal manganese on the current collector followed by anodic oxidation to prepare an amorphous porous manganese dioxide layer.

(2) Put the manganese dioxide layer prepared in the above step (1) together with the current collector into the autoclave and seal it, then carry out hydrothermal treatment, so that the manganese dioxide layer on the surface of the current collector is recrystallized and oriented. After cooling, the electrode is taken out, washed, and dried to obtain a manganese dioxide fiber electrode.

Preferably, in step (2), an alkali metal sulfate aqueous solution with a concentration of 0.01-1 mol/L is injected into the autoclave before sealing and heating.

Preferably, in step (2), the temperature of hydrothermal treatment is 100-300°C.

Preferably, in step (2), the time of hydrothermal treatment is 8-48 hours.

The present invention also provides the application of the manganese dioxide fiber electrode in the preparation of electrochemical supercapacitor

(3) Beneficial effects

(1) The manganese dioxide fiber electrode prepared by the present invention mainly depends on the interweaving of fibers with large length/diameter ratio grown on the surface of the current collector to achieve the purpose of fixing and sufficient contact, without the need for non-electrically active electrodes such as binders. material, so the overall energy density of the electrode can be increased;

(2) In the manganese dioxide fiber electrode of the present invention, pores are formed between the manganese dioxide fibers, and the diameter of the fiber itself is small, which increases the contact area between the electrode active material and the electrolyte, and shortens the charge balance ion inside the active material. The diffusion path improves the utilization rate and rate performance of the electrode active material;

(3) In the manganese dioxide fiber electrode of the present invention, the manganese dioxide fiber has good crystallinity, good electronic conductivity, and a good internal tunnel structure is also conducive to the mass transfer of charged ions, further improving the specific capacitance and rate performance of the material ;

(4) During the preparation process of the manganese dioxide fiber electrode of the present invention, there is no need to prepare complex templates or perform special treatments such as surface nano-array growth on the current collector, and the preparation process is simple and clean, and the cost is low.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is the SEM figure of the manganese dioxide fiber electrode prepared by the present invention;

Fig. 2 is the cyclic voltammetry curve figure of the manganese dioxide electrode prepared by the present invention;

Fig. 3 is a graph of cyclic voltammetry of a manganese dioxide electrode prepared by a conventional electrodeposition method.

Detailed ways

Embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but should not be used to limit the scope of the present invention.

Compared with the existing preparation technology, the technical idea and process principle of the present invention have significant characteristics and technical advantages:

At present, the preparation of supercapacitor electrodes is mainly to prepare MnO2 powder materials first, and then prepare them into slurry with binders, etc., and then coat them on the current collector to form the final electrode, which will easily cause contact between the electrode active material and the current collector. Defective and affect the charge and discharge performance of the electrode. In addition, since the added binder and the like are non-electroactive substances, it will inevitably reduce the energy density of the entire electrode. It is mentioned in many literatures that manganese dioxide can be deposited on the surface of the current collector directly by anodic oxidation of manganese sulfate solution or cathodic reduction of permanganate ions, and a binder-free manganese dioxide electrode can be obtained. The layer is generally dense, the contact area between the electrode and the electrolyte is small, the crystallinity of the material is not good, the electronic conductivity itself is poor, and it is not conducive to the mass transfer of charged ions inside the material crystal, so the prepared electrode only contacts with the electrolyte. Part of the active material on the interface is utilized, and the active material inside the electrode is difficult to participate in the electrochemical reaction due to the limitation of mass transfer. Especially at high current density, the specific capacitance and rate performance of the material are not ideal. In order to increase the contact area between the electrode active material and the electrolyte in the working process of the capacitor, the current research hotspot in this field is to grow various metals, carbon nanotube arrays or graphene on the metal substrate, and then grow various metals, carbon nanotube arrays or graphene on these metals, carbon nanotubes, etc. Or electrodeposit manganese dioxide on the surface of graphene and use it as a supercapacitor electrode, but because these methods only change the morphology of the current collector without changing the morphology and crystallinity of the deposited manganese dioxide itself, when the thickness of the deposited manganese dioxide layer When it is relatively thick, the active material inside the deposition layer cannot be utilized, and the high-current charge-discharge capacity and rate performance of the material are still unsatisfactory. In addition, the process of growing carbon nanotubes or graphene on the metal surface is relatively complicated and costly, and it is difficult to realize industrial application.

In the present invention, the weakly crystalline or amorphous manganese dioxide deposition layer deposited on the current collector through electrochemical methods is subjected to hydrothermal treatment together with the current collector, so that the weakly crystalline or amorphous manganese dioxide can undergo hydrothermal treatment during the hydrothermal process. Carry out recrystallization and orientation growth, and transform into manganese dioxide fibers with large length/diameter ratio and more perfect crystallization, and these manganese dioxide fibers with large length/diameter ratio interweave and grow on the surface of the current collector, ensuring that the fibers are intertwined with each other There is no need to use adhesives for bonding between the space and the current collector to achieve sufficient and good contact. On the one hand, a large number of gaps are formed between the fibers inside the manganese dioxide layer, so as to facilitate the contact between the electrolyte and the manganese dioxide inside the electrode, and increase the electrode/electrolyte ratio. On the other hand, the diameter of the manganese dioxide fibers grown after hydrothermal treatment is only 5-50nm, which undoubtedly shortens the diffusion distance of the charged balance ions of the electrode active material during the charging and discharging process, that is, even if the thickness of the manganese dioxide layer on the electrode surface is relatively Large, but the diffusion distance of charge-balanced ions will not increase, which is conducive to improving the utilization rate of active materials and the rate retention rate of high-current charge and discharge. In addition, compared with the manganese dioxide deposition layer obtained by direct electrodeposition or anodic oxidation of metal manganese, the manganese dioxide fiber after hydrothermal treatment in the presence of alkali metal ions has better crystallinity, better electronic conductivity, and a tunnel structure inside the fiber. It is perfect, which is also conducive to the diffusion of charge-balanced ions inside it and improves the high-current charge-discharge rate retention rate of the material.

Unless otherwise defined, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The terminology used herein is only for the purpose of describing specific embodiments, and is not intended to limit the protection scope of the present invention.

Unless otherwise specified, the various reagents and raw materials used in the present invention are commercially available products or products that can be prepared by known methods.

The specific embodiment of the present invention is as follows:

A manganese dioxide fiber electrode comprises a current collector material and an active material attached to the current collector material, and the active material is mainly manganese dioxide fiber. The manganese dioxide fiber is a fiber with a large length/diameter ratio, the diameter of the fiber is 5-50nm, and the length is 5-50μm. The manganese dioxide fiber with a large length/diameter ratio grows on the current collector and interweaves with each other to form a stable active material layer. There is no need to use a binder to bond the active material and the current collector material, so there is no need to use a binder in the electrode. binder.

The preparation method of above-mentioned manganese dioxide fiber electrode comprises the following steps:

(1) Prepare a manganese dioxide deposition layer on the surface of the current collector.

The preparation of manganese dioxide deposition layer on the surface of the current collector can be done by conventional known methods, such as using the current collector as the anode to electrolyze the soluble manganese salt solution, using the current collector as the cathode to electrochemically reduce permanganate ions, or depositing on the surface of the current collector After metal manganese is anodized. The types of raw materials used, the electrodeposition parameters of solution concentration, etc. are not limited.

(2) Put the manganese dioxide electrode prepared in the above step (1) into an autoclave, inject pure water or a solution of lithium sulfate, sodium sulfate or potassium sulfate with a concentration not greater than 1mol/L, and seal it at 100-300°C The hydrothermal treatment is carried out at a temperature of 8 to 48 hours. After the internal temperature of the autoclave was cooled to room temperature, the electrode was taken out, rinsed with deionized water and dried to obtain the required manganese dioxide fiber electrode.

In order to facilitate the understanding of the present invention, the following will describe the present invention more fully and in detail with reference to the accompanying drawings and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

Fig. 1 is the SEM image of the manganese dioxide fiber electrode prepared by the present invention, it can be seen from the figure that the active material on the electrode is composed of a large number of intertwined manganese dioxide fibers with a large aspect ratio.

Fig. 2 adopts the cyclic voltammetry curve of the manganese dioxide electrode prepared by the present invention, as can be seen from the figure, the electrode prepared by the present invention is still substantially close to the shape of the curve at a scan rate of 500mV/s, and the capacity retention rate is good. The specific capacitance of manganese dioxide can be calculated according to the curve.

Fig. 3 is the cyclic voltammetry curve of the manganese dioxide electrode prepared by the conventional electrodeposition method. It can be seen from the figure that the electrode prepared by the conventional method obviously deviates from the shape of the curve at a scanning rate of 500mV/s, and the capacity retention rate is not high. Good, the specific capacitance of manganese dioxide can be calculated according to the curve.

Example 1:

A manganese dioxide fiber electrode comprises current collector material and active material manganese dioxide fiber attached to the current collector material. The diameter of the manganese dioxide fiber is 10-30nm and the length is 5-50μm. Manganese dioxide fibers grow on the current collector and interweave with each other without bonding with a binder.

The preparation method of above-mentioned manganese dioxide fiber electrode, comprises the steps:

(1) Dissolve a certain amount of MnSO ₄ ·H ₂ O and Na ₂ SO ₄ in deionized water to prepare a mixed solution containing 0.2 mol/L of manganese sulfate and 0.5 mol/L of sodium sulfate.

(2) The 304 stainless steel foil was cut into a stainless steel strip with an area of 4×1 cm ² as a current collector, and the current collector was ultrasonically washed with 10% sulfuric acid aqueous solution and acetone, and finally rinsed with water and dried. A 4×4cm ² titanium mesh is used as the cathode, the above-mentioned mixed solution containing manganese sulfate is used as the electrodeposition solution, and the current collector after surface cleaning is used as the anode (the working area is 1×2cm ² ), and the manganese sulfate solution is electrolyzed by constant current on stainless steel A manganese dioxide deposition layer is prepared on the current collector material, the anode current density is controlled at 4 mA/cm ² during constant current electrolysis, and the electrodeposition time is 4 minutes. Rinse the manganese dioxide electrode with deionized water after the electrodeposition is completed.

(3) Put the manganese dioxide electrode prepared by the above step (2) into a stainless steel autoclave lined with polytetrafluoroethylene, inject a concentration of 0.01mol/L lithium sulfate solution, seal and insulate at 150°C for 20 hours, After the autoclave was cooled to room temperature, the manganese dioxide electrode was taken out, rinsed with deionized water, and dried at 60° C. for 5 hours to obtain a manganese dioxide fiber electrode.

The morphology and size of the active material in the obtained manganese dioxide fiber electrode were analyzed by a field emission scanning electron microscope. The diameter of the manganese dioxide fiber was 10-30 nm and the length was 5-50 μm (see Figure 1). A 0.5mol/L lithium sulfate aqueous solution was used as the electrolyte, the manganese dioxide fiber electrode prepared above was used as the working electrode, and the platinum electrode with an area of 4× ^4cm2 was used as the auxiliary electrode to assemble a three-electrode system for cyclic voltammetry test. The potential range is -0.4～0.4V (relative to the saturated mercurous sulfate electrode), and when the scan rate is 5mV/s, the specific capacitance of the electrode active material is calculated according to the cyclic voltammetry curve to be 307.6F/g, and the scan rate is 500mV/s The cyclic voltammetry curve is still close to a rectangle (see Figure 2), the specific capacitance can reach 150.1F/g, and the capacity retention rate can reach 48.8%.

Example 2:

A manganese dioxide fiber electrode comprises current collector material and active material manganese dioxide fiber attached to the current collector material. The diameter of the manganese dioxide fiber is 30-50nm and the length is 5-50μm. Manganese dioxide fibers grow on the current collector and interweave with each other without bonding with a binder.

The preparation method of above-mentioned manganese dioxide fiber electrode, comprises the steps:

(1) Weigh a certain amount of KMnO ₄ and Na ₂ SO ₄ and dissolve them in deionized water to prepare a mixed solution containing 0.1 mol/L of potassium permanganate and 0.5 mol/L of sodium sulfate.

(2) The nickel sheet was cut into a stainless steel strip with an area of 4×1 cm ² as a current collector, and the current collector was ultrasonically washed with 10% sulfuric acid aqueous solution and acetone, and finally rinsed with water and dried. A 4×4cm ² titanium mesh is used as the anode, the above-mentioned potassium permanganate mixed solution is used as the electrodeposition solution, and the current collector after surface cleaning is used as the cathode (the working area is 1×2cm ² ), and the constant current cathode reduction method is used in the A manganese dioxide layer is prepared on the current collector material, and the manganese dioxide electrode is washed with deionized water after the electrolytic deposition is completed.

(3) Put the manganese dioxide electrode prepared by the above step (1) into a stainless steel autoclave lined with polytetrafluoroethylene, inject a concentration of 0.5mol/L potassium sulfate solution, seal and insulate at 150°C for 20 hours, After the autoclave was cooled to room temperature, the manganese dioxide electrode was taken out, rinsed with deionized water, and dried at 60° C. for 5 hours to obtain a manganese dioxide fiber electrode.

The morphology and size of the active material in the obtained manganese dioxide fiber electrode are analyzed by a field emission scanning electron microscope, and the diameter of the manganese dioxide fiber is 30-50 nm, and the length is 5-50 μm. A 0.5mol/L lithium sulfate aqueous solution was used as the electrolyte, the manganese dioxide fiber electrode prepared above was used as the working electrode, and the platinum electrode with an area of 4× ^4cm2 was used as the auxiliary electrode to assemble a three-electrode system for cyclic voltammetry test. The potential range is -0.4～0.4V (relative to the saturated mercurous sulfate electrode), and when the scan rate is 5mV/s, the specific capacitance of the electrode active material is calculated according to the cyclic voltammetry curve to be 291.3F/g, and the scan rate is 500mV/s The capacity retention rate reached 46.8%.

Example 3:

A manganese dioxide fiber electrode comprises current collector material and active material manganese dioxide fiber attached to the current collector material. The diameter of the manganese dioxide fiber is 5-20nm and the length is 7-50μm. Manganese dioxide fibers grow on the current collector and interweave with each other without bonding with a binder.

The preparation method of the above-mentioned manganese-containing transition metal composite oxide electrode comprises the following steps:

(1) Weigh a certain amount of MnSO ₄ ·H ₂ O, boric acid and (NH ₄ ) ₂ SO ₄ and dissolve them in deionized water to prepare 0.5 mol/L of manganese ions, 0.5 mol/L of boric acid, and 0.5 mol/L of sulfuric acid. The concentration of ammonium is a mixed solution of 1.5 mol/L, the pH value of the electroplating solution is adjusted to 4 with ammonia water and sulfuric acid, and it is set aside after stirring for 30 minutes.

(2) The carbon fiber paper is cut into a carbon paper current collector with an area of 4×1 cm ² , and the current collector is ultrasonically washed with acetone in turn, and finally rinsed with water and dried. Use a 4×4cm ² titanium mesh as the anode electrode, use the above mixed solution containing manganese and ammonium ions as the electroplating solution, and use the current collector after surface cleaning as the cathode (the working area is 1×2cm ² ), and use constant current electrodeposition The manganese coating was prepared on the current collector material by the method, the cathode current density was controlled at 150mA/cm ² during the constant current deposition, the electrodeposition time was 2 minutes, and the manganese coating electrode was obtained after the deposition was completed.

(3) The composite coating electrode prepared in the above step (2) is used as the anode, the stainless steel sheet (area 4×4cm ² ) is used as the cathode, and the saturated calomel electrode is used as the reference electrode. As the electrolyte, a constant-current anodic oxidation treatment was performed, and the anode current density was controlled at 1mA/cm ² during the anodic oxidation treatment. After the anode potential reached 0.8V, the oxidation was terminated, and the obtained manganese dioxide electrode was rinsed with deionized water.

(4) Put the manganese dioxide electrode prepared by the above step (3) into a stainless steel autoclave lined with polytetrafluoroethylene, inject a concentration of 1mol/L potassium sulfate solution, seal it and insulate it at 300°C for 48 hours, wait After the autoclave was cooled to room temperature, the manganese dioxide electrode was taken out, rinsed with deionized water, and then dried at 60° C. for 5 hours to obtain a manganese dioxide fiber electrode.

The morphology and size of the active material in the obtained manganese dioxide fiber electrode are analyzed by a field emission scanning electron microscope, and the diameter of the manganese dioxide fiber is 5-20 nm, and the length is 7-50 μm. A 0.5mol/L lithium sulfate aqueous solution was used as the electrolyte, the manganese dioxide fiber electrode prepared above was used as the working electrode, and the platinum electrode with an area of 4× ^4cm2 was used as the auxiliary electrode to assemble a three-electrode system for cyclic voltammetry test. The potential range is -0.4～0.4V (relative to the saturated mercurous sulfate electrode), and when the scan rate is 5mV/s, the specific capacitance of the electrode active material is calculated according to the cyclic voltammetry curve to be 301.2F/g, and the scan rate is 500mV/s , the capacity retention rate reached 51.2%.

Example 4:

A manganese dioxide fiber electrode comprises current collector material and active material manganese dioxide fiber attached to the current collector material. The diameter of the manganese dioxide fiber is 10-40nm and the length is 5-50μm. Manganese dioxide fibers grow on the current collector and interweave with each other without bonding with a binder.

The preparation method of above-mentioned manganese dioxide fiber electrode, comprises the steps:

(1) Dissolve a certain amount of MnSO ₄ ·H ₂ O and Na ₂ SO ₄ in deionized water to prepare a mixed solution containing 0.2 mol/L of manganese sulfate and 0.5 mol/L of sodium sulfate.

(2) The 304 stainless steel foil was cut into a stainless steel strip with an area of 4×1 cm ² as a current collector, and the current collector was ultrasonically washed with 10% sulfuric acid aqueous solution and acetone, and finally rinsed with water and dried. A 4×4cm ² titanium mesh is used as the cathode, the above-mentioned mixed solution containing manganese sulfate is used as the electrodeposition solution, and the current collector after surface cleaning is used as the anode (the working area is 1×2cm ² ), and the manganese sulfate solution is electrolyzed by constant current on stainless steel A manganese dioxide deposition layer is prepared on the current collector material, the anode current density is controlled at 4 mA/cm ² during constant current electrolysis, and the electrodeposition time is 4 minutes. Rinse the manganese dioxide electrode with deionized water after the electrodeposition is completed.

(3) Put the manganese dioxide electrode prepared by the above step (2) into a stainless steel autoclave lined with polytetrafluoroethylene, inject a concentration of 0.1mol/L sodium sulfate solution, seal and insulate at 100°C for 10 hours, After the autoclave was cooled to room temperature, the manganese dioxide electrode was taken out, rinsed with deionized water, and dried at 60° C. for 5 hours to obtain a manganese dioxide fiber electrode.

The morphology and size of the active material in the obtained manganese dioxide fiber electrode are analyzed by a field emission scanning electron microscope, and the diameter of the manganese dioxide fiber is 10-40 nm, and the length is 5-50 μm. A 0.5mol/L lithium sulfate aqueous solution was used as the electrolyte, the manganese dioxide fiber electrode prepared above was used as the working electrode, and the platinum electrode with an area of 4× ^4cm2 was used as the auxiliary electrode to assemble a three-electrode system for cyclic voltammetry test. The potential range is -0.4～0.4V (relative to the saturated mercurous sulfate electrode), and when the scan rate is 5mV/s, the specific capacitance of the electrode active material is calculated according to the cyclic voltammetry curve to be 304.1F/g, and the scan rate is 500mV/s , the capacity retention rate reached 49.5%.

Example 5:

A manganese dioxide fiber electrode comprises current collector material and active material manganese dioxide fiber attached to the current collector material. The diameter of the manganese dioxide fiber is 5-30nm and the length is 5-50μm. Manganese dioxide fibers grow on the current collector and interweave with each other without bonding with a binder.

The preparation method of above-mentioned manganese dioxide fiber electrode, comprises the steps:

(1) Dissolve a certain amount of MnSO ₄ ·H ₂ O and Na ₂ SO ₄ in deionized water to prepare a mixed solution containing 0.2 mol/L of manganese sulfate and 0.5 mol/L of sodium sulfate.

(2) The carbon fiber paper is cut into a carbon paper current collector with an area of 4×1 cm ² , and the current collector is ultrasonically washed with acetone in turn, and finally rinsed with water and dried. Use a 4×4cm ² titanium mesh as the anode electrode, use a 4×4cm ² titanium mesh as the cathode, use the above-mentioned mixed solution containing manganese sulfate as the electrodeposition solution, and use the current collector after surface cleaning as the anode (the working area is 1×2cm ² ), using constant current electrolysis of manganese sulfate solution to prepare a manganese dioxide deposition layer on the stainless steel current collector material, the anode current density during constant current electrolysis is controlled to 4mA/cm ² , and the electrodeposition time is 4 minutes. Rinse the manganese dioxide electrode with deionized water after the electrodeposition is completed.

(3) Put the manganese dioxide electrode prepared by the above step (2) into a stainless steel autoclave lined with polytetrafluoroethylene, inject a concentration of 0.5mol/L lithium sulfate solution, seal and insulate at 300°C for 30 hours, After cooling to room temperature with an autoclave, the manganese dioxide electrode was taken out, rinsed with deionized water, and dried at 60° C. for 5 hours to obtain a manganese dioxide fiber electrode.

The morphology and size of the active material in the obtained manganese dioxide fiber electrode are analyzed by a field emission scanning electron microscope, and the diameter of the manganese dioxide fiber is 5-30 nm, and the length is 5-50 μm. A 0.5mol/L lithium sulfate aqueous solution was used as the electrolyte, the manganese dioxide fiber electrode prepared above was used as the working electrode, and the platinum electrode with an area of 4× ^4cm2 was used as the auxiliary electrode to assemble a three-electrode system for cyclic voltammetry test. The potential range is -0.4～0.4V (relative to the saturated mercurous sulfate electrode), and when the scan rate is 5mV/s, the specific capacitance of the electrode active material is calculated according to the cyclic voltammetry curve to be 297.7F/g, and the scan rate is 500mV/s , the capacity retention rate reached 51.2%.

Comparative Example 1:

(1) Dissolve a certain amount of MnSO ₄ ·H ₂ O and Na ₂ SO ₄ in deionized water to prepare a mixed solution containing 0.2 mol/L of manganese sulfate and 0.5 mol/L of sodium sulfate.

(2) The 304 stainless steel foil was cut into a stainless steel strip with an area of 4×1 cm ² as a current collector, and the current collector was ultrasonically washed with 10% sulfuric acid aqueous solution and acetone, and finally rinsed with water and dried. A 4×4cm ² titanium mesh is used as the cathode, the above-mentioned mixed solution containing manganese sulfate is used as the electrodeposition solution, and the current collector after surface cleaning is used as the anode (the working area is 1×2cm ² ), and the manganese sulfate solution is electrolyzed by constant current on stainless steel A manganese dioxide deposition layer is prepared on the current collector material, the anode current density is controlled at 4 mA/cm ² during constant current electrolysis, and the electrodeposition time is 4 minutes. After the electrodeposition was completed, the manganese dioxide electrode was rinsed with deionized water and dried at 60° C. for 5 hours to obtain a comparative manganese dioxide electrode.

The morphology of the active material in the obtained comparative manganese dioxide electrode was analyzed by a field emission scanning electron microscope, and the obtained comparative manganese dioxide electrode was a dense deposition layer. A 0.5mol/L lithium sulfate aqueous solution was used as the electrolyte, the comparative manganese dioxide electrode prepared above was used as the working electrode, and a platinum electrode with an area of 4× ^4cm2 was used as the auxiliary electrode to assemble a three-electrode system for cyclic voltammetry test. The potential range is -0.4～0.4V (relative to the saturated mercurous sulfate electrode), and when the scan rate is 5mV/s, the specific capacitance of the electrode active material is calculated according to the cyclic voltammetry curve to be 270.0F/g; the scan rate is 500mV/s , the cyclic voltammetry curve obviously deviates from the rectangle (as shown in Figure 3), the specific capacitance is 72.2F/g, and the capacity retention rate is only 26.7%.

Conclusion: Compared with the manganese dioxide thin film electrode prepared by the conventional electrodeposition method, the manganese dioxide fiber electrode prepared by the present invention has higher specific capacitance and capacity retention rate.

The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications or equivalent replacements of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all should cover Within the scope of the claims of the present invention.

Claims (9)

1. A manganese dioxide fiber electrode is characterized in that the manganese dioxide fiber electrode comprises a current collector and a manganese dioxide fiber active layer attached to the current collector; the manganese dioxide fiber is a large length/diameter ratio fiber ; The manganese dioxide fiber electrode does not contain binder; Described manganese dioxide fiber electrode is made by following method: (1) Electrochemical deposition of weakly crystalline manganese dioxide deposition layer directly on the current collector, or anodic oxidation on the current collector to prepare an amorphous porous manganese dioxide layer after cathode electrodeposition of metal manganese; (2) Put the manganese dioxide layer prepared in the above step (1) together with the current collector into the autoclave and seal it, then carry out hydrothermal treatment, so that the manganese dioxide layer on the surface of the current collector is recrystallized and oriented. After cooling, the electrode is taken out, washed, and dried to obtain a manganese dioxide fiber electrode; The manganese dioxide fiber has a diameter of 5-50 nm and a length of 5-50 μm. 2. The manganese dioxide fiber electrode according to claim 1, characterized in that, the manganese dioxide fibers themselves grow on the current collector and interweave to form a stable active material layer. 3. manganese dioxide fiber electrode according to claim 1, is characterized in that, described manganese dioxide fiber active layer is the manganese dioxide formed on the current collector surface by electrolysis of soluble manganese salt solution or cathodic reduction of permanganate. The deposited layer, or the manganese dioxide layer obtained by depositing a manganese coating on the surface of the current collector and then performing anodic oxidation. 4. manganese dioxide fiber electrode according to claim 1, is characterized in that, described current collector material is the good metal or nonmetal of electrical conductivity and thermal stability, is specifically selected from stainless steel sheet, stainless steel mesh, nickel sheet, One of nickel foam, graphite sheet, carbon paper or carbon cloth. 5. the preparation method of the manganese dioxide fiber electrode described in any one of claim 1-4 is characterized in that, the method comprises the steps: (1) Electrochemical deposition of weakly crystalline manganese dioxide deposition layer directly on the current collector, or anodic oxidation on the current collector to prepare an amorphous porous manganese dioxide layer after cathode electrodeposition of metal manganese; (2) Put the manganese dioxide layer prepared in the above step (1) together with the current collector into the autoclave and seal it, then carry out hydrothermal treatment, so that the manganese dioxide layer on the surface of the current collector is recrystallized and oriented. After cooling, the electrode is taken out, washed, and dried to obtain a manganese dioxide fiber electrode. 6. the preparation method of manganese dioxide fiber electrode according to claim 5 is characterized in that, in step (2), in the autoclave before sealing heating, injection concentration is the alkali metal sulfate aqueous solution of 0.01～1mol/L , the alkali metal sulfate is lithium sulfate, sodium sulfate or potassium sulfate. 7. The method for preparing a manganese dioxide fiber electrode according to claim 5, characterized in that, in step (2), the temperature of the hydrothermal treatment is 100-300°C. 8. The method for preparing manganese dioxide fiber electrodes according to claim 5, characterized in that, in step (2), the hydrothermal treatment time is 8-48 hours. 9. The application of the manganese dioxide fiber electrode described in any one of claims 1-4 in the preparation of electrochemical supercapacitors.